Effect of the amount of lignin on tensile properties of single wood fibers
大学英语3 期末考试题 ,阅读题题库急加DA AN!
第一次Why do smokers tend to weigh less than nonsmokers and gain weight when they give up the habitContrary to “common knowledge”, nonsmokers do not generally eat more than smokers, nor do they exercise less, studies find. Research performed on smokers at rest indicates that nicotine (尼古丁) itself can increase basal metabolic (新陈代谢的) rates, meaning smokers burn more energy than nonsmokers during periods of inactivity. But surveys suggest most smokers smoke not while completely at rest, but while performing light activities such as desk work that can increase metabolic rates by two or three times. Unless nicotine’s metabolic effects increase proportionally with metabolic rates, its influence on weight might be insignificant.Now a study shows that nicotine’s e ffects on body-fuel consumption indeed increase proportionally with increases in activity. “These results indicate that the metabolic effect of nicotine may play a greater part in accounting for body-weight differences between smokers and nonsmokers than w as previously believed,” says Kenneth A. Perkins and his colleagues at the University of Pittsburgh School of Medicine.The researchers gave a nicotine nose spray to individuals performing light work — in this case riding an exercise bicycle modified to allow easy riding while subjects remain seated in a comfortable armchair. The activity raised resting metabolic rates two to three times.By analyzing air breathed out, the researchers calculated energy consumption in the armchair bicyclists before and after giving the nose spray and compared the relative changes with subjects in the control group given placebo (（试验药物用的）无效对照剂) nose sprays. Relative to their baseline bicycle expenditures, individuals in the nicotine group expended considerably more energy than did those in control group while doing the same amount of work. With nicotine, Perkins says, “It’s as if the body is becoming much less efficient in using its stored energy.”While the results may seem discouraging to smokers who’d like to quit without gaining weight, Perkins notes that walking an extra mile a day should make up for the difference in metabolic efficiency. And he says smokers would have to gain “well more than 50 pounds” to counterbalance the health risks of continued smoking.1. What might “common knowledge” say about smokers and nonsmokersA) ?Smokers eat more and exercise more than nonsmokers.B) ?Smokers eat less and exercise less than nonsmokers.C) ?Smokers eat less and exercise more than nonsmokers.√D) ?Smokers eat more and exercise less than nonsmokers.答案：C2. When might nicotine influence smokers’ weight significantlyA) ?When Nicotine’s metabolic effects and metabolic ratesincrease at the same rate. √B) ?While smokers are exercising.C) ?While smokers are at rest.D) ?When Nicotine’s metabolic effects increaseproportionally with the amount of light activities.答案：A3. The word “subjects” in the fourth paragraph means .A) ?people under medical treatmentB) ?researchersC) ?people undergoing an experiment √D) ?addicted smokers答案：C4. What have the researchers found out in their studyA) ?People in the armchair expended more energy than peopledoing desk work.B) ?People in the control group breathed out more air.C) ?People without nicotine nose spray are becoming muchless efficient in using energy.D) ?People in the nicotine group consumed more energy. √答案：D5. Why do the study results seem discouraging to some smokers according to the passageA) ?Because they want to gain weight to tackle the healthrisks of continued smoking.B) ?Because they want to quit smoking and still keep fit.√C) ?Because they want to walking an extra mile a day tolose some weight.D) ?Because they want to keep fit without having to quitsmoking.答案：BA certain amount of controversy has been caused by the publication of a new report by a team of educationalists headed by Pro. B. J. Smith. The report claims to havestatistical evidence that children who attend a number of different schools through their parents having to move around the country are more than normally vulnerable to a vicious cycle of low academic achievement. There are also indications, says Professor Smith, of an unusually high rate of psychological dismay among such children.The professor, who has long suspected that the effect on children whose parents travel to different parts of the country in search of work has not been sufficiently researched, stresses that this is not merely an expression of prejudice. “We are not dealing here with opinions,” he says, “It’s true, my personal feeling is that for children’s well-being, they should stay in one school. However, our findings are based on research and not on any personal attitudes that I or my colleagues may have on the subject.”Capt. Thomas Muller, an Army lecturer for the past 20 years and himself a father of two, said, “I’ve never heard such rubbish. As far as I’m concerned, absolutely no harm is done to the education of children who change schools regularly — as long as they keep to the same system as in our Army school. In my experience —and I’ve known quite a few of them — Army children are as well-adjusted as any others, if not more so. What the Professor doesn’t appear to appreciate is the fact that in such situations children will adapt much bett er than adults.”?When this was put to Professor Smith, he said that at no time had his team suggested that all such children were backward or dismayed in some way, but simply that in their experience there was a clear tendency.?“Our findings indicate t hat while the extremely bright child can cope with regular emotional turbulence without harming his or her general academic progress, the majority of children suffer from constantly having to enter a new learning environment.”6. What does Professor Smith’s report suggestA) ?Children shouldn’t change schools too often. √B) ?Children who have to move around the country are betterat academic achievement.C) ?Children attending many schools have caused a certainamount of controversy.D) ?Children who attend different schools are morevulnerable to vicious diseases.答案：A7. What does Professor Smith think of the findings of the researchA) ?They are proved by the research. √B) ?They are just based on his personal feeling.C) ?They may merely be an expression of prejudice.D) ?They are based on personal attitudes.答案：A8. What does Capt. Thomas Muller think of children who change schools regularlyA) ?They can actually deal with the new environment betterthan adults. √B) ?They do no harm to the education.C) ?They find it difficult to keep to the same system.D) ?They are generally ill-adjusted.答案：A9. How does Professor Smith defend himself again Capt. Thomas MullerA) ?He suggests that children having regular emotionalturbulence do not harm their academic progress.B) ?He argues that only a few children will suffer fromchanging schools regularly.C) ?He stresses that the majority of children tend tosuffer from constantly adapting to a new learningenvironment. √D) ?He believes that extremely bright child likes to entera new learning environment.答案：C10. What does the passage mainly talk aboutA) ?How army children get used to a new learningenvironment.B) ?Whether children would be affected by changing schoolsregularly. √C) ?The procedure Professor Smith followed to conduct astudy.D) ?The opinions people have about children who oftenchange schools.答案：BRecently there has been a tendency to sympathize with thieves whose operations have been carried out on a grand scale, and no attempt whatever has been made tohold them responsible. Some of the most thievish (像窃贼的) transactions have flourished and are still flourishing. Their success and their wealth are the only things recognized. They are honored as financiers and men of affairs, looked up to and respected.?In reality they are nothing more and nothing less than a lot of merciless and heartless thieves. Fraud is fraud and cheating is cheating despite the artistic manner in which it is committed or the size of the scale upon which it is operated.?It is time these men were classed properly and placed where they rightly belong, for they are no better than the miserable sneak-thief who steals a penny from a blind man’s dog.?For the past two or three years working people who have made sacrifices to save a few pennies have been cheated most unmercifully. Their hard-earned savings have been stolen from them by every possible scheme from the obvious looting (打劫) of a bank to the higher and more artistic method of legalized high risk, complex financial products. Men high up in the financial world have lent their names to some of the most shady and notorious schemes that ever dishonored a community or a people. Because of this the most diligent and economical (节俭的) American people have been induced to place their hard-earned and carefully guarded savings in what they were led to believe was a safe investment, only to find out when too late that they had fallen into the hands of a gang of extremely respectable cheats. They cannot recover what they have lost.?The thief is too powerful to be affected by the law while the victim is too weak to put its machinery in motion. It may be that the law is defective, or it may be that those having its machinery in charge are influenced by the wealth of the transgressors (违犯者). Whatever or whichever it is that is responsible ought to be investigated and the evil remedied.11. What does the tendency mentioned in the first paragraph reflectA) ?People encourage some of the most thievishtransactions to flourish.B) ?People only respect success and wealth without anymoral judgment. √C) ?People prefer to carry out operations on a grand scale.D) ?People have made attempt to hold thieves responsible.答案：B12. How did working people lose their hard-earned savingsA) ?They lent their money to men high up in the financialworld.B) ?They were cheated by the bank. √C) ?They were unlucky in investment.D) ?They were robbed by the thieves nearby.答案：B13. When the writer says “a gang of extremely respectable cheats” in Paragraph Four, it is implied that .A) ?they are well-educated but ill-behaved √B) ?they are respectable in artistic cheatingC) ?they are cheats with respectable goalsD) ?they are not well-educated but respected答案：A14. What could be a possible reason for the thieves to escape from law according to the passageA) ?They are powerful enough to ignore the law.B) ?There are defects in the law. √C) ?They are wealthy enough to compensate the victims.D) ?The victim is too weak to investigate them.答案：B15. It can be inferred from the passage that .A) ?there are too many thieves and robbersB) ?industrious and honest people should be highly paidC) ?moral standards are always upheldD) ?any thief should b e punished √答案：D??? People often ask which is the most difficult language to learn, and it is not easy to answer because there are many factors to take into consideration. Firstly, in a first language the differences are unimportant as people learn their mother tongue naturally, so the question of how hard a language is to learn is only relevant when learning a second language.???? A native speaker of Spanish, for example, will find Portuguese much easier to learn than a native speaker of Chinese, for example, because Portuguese is very similar to Spanish, while Chinese is very different, so first language can affect learning a second language. The greater the differences between the second language and our first, the harder it will be for most people to learn. Many people answer that Chinese is the hardest language to learn, possibly influenced by the thought of learning the Chinese writing system, and the pronunciation of Chinese does appear to be very difficult for many foreign learners. However, for Japanese speakers, who already use Chinese characters in their own language, learning writing will be less difficult than for speakers of languages using the Roman alphabet.???? Some people seem to learn languages readily, while others find it very difficult. Teachers and the circumstances in which the language is learned also play an important role, as well as each learner's motivation for learning. If people learn a language because they need to use it professionally, they often learn it faster than people studying a language that has no direct use in their day to day life.???? Apparently, British diplomats and other embassy staff have found that the second hardest language is Japanese, which will probably come as no surprise to many, but the language that they have found to be the most problematic is Hungarian. This does not mean that Hungarian is the hardest language to learn for everyone, but it causes British diplomatic personnel, who are generally used to learning languages, the most difficulties.???? Different cultures and individuals from those cultures will find different languages more difficult. In the case of Hungarian for British learners, it is not a question of the writing system, which uses a similar alphabet, but the grammatical complexity, though native speakers of related languages may find it easier, while struggling with languages that the British find relatively easy.16. Why is it hard to say which language is the most difficult to learnA) ?Because it is only relevant when learning a secondlanguage.B) ?Because differences between languages areunimportant.C) ?Because people learn their mother tongue naturally.D) ?Because many factors have to be considered. √答案：D17. Who will find Portuguese much easier to learnA) ?A native speaker of JapaneseB) ?A native speaker of HungarianC) ?A native speaker of Spanish √D) ?A native speaker of Chinese答案：C18. What is the most problematic language to British diplomats and other embassy staffA) ?Japanese B) ?Spanish C) ?Hungarian√D) ?Chinese答案：C19. Why do many people think Chinese is the hardest language to learnA) ?Because the pronunciation of Chinese is difficult. √B) ?Because the grammar of Chinese is complex.C) ?Because Chinese is not directly used in their life.D) ?Because Chinese uses the Roman alphabet.答案：A20. What factors cannot affect learning a second language according to the passageA) ?each learner's motivation for learningB) ?neighboring countries √C) ?teachers and the circumstancesD) ?first language答案：B??? In 1976, Winkler wrote a My Turn about the overwhelming reaction to the character he played on the popular television sitcom (情景喜剧), “Happy Days”. The show was at its peak, and Fonzie was its superstar. In fact, Americans related so strongly to the character that Winkler became apparently permanently part of the country’s broad, extended family. Three decades later, fans still greet the actor with Fonzie’s signature thumbs-up sign and a long, drawn out “Aaay!”???? “All these years later, the warmth I am treated with is unbelievable, and it’s all over the world,” Winkler says. He no longer receives the 50,000 fan letters a year that he got during “Happy Days”’s original run, but they still come by the hundreds. And on the stre et, folks tend to have a common reaction. “They thank me for makingthem laugh for so long. They say, ‘I grew up with you,’ or ‘my children grew up with you,’ or, ‘we sat and watched it together’,” he says.???? Winkler says his Fonzie days came back to him vividly as he read over his old My Turn. Cast on his 28th birthday, the Yale-trained performer had been a struggling actor, dreaming of fame. The dream turned real very quickly. “We were hardly on the air when this thing started to snowball, going from zero to 60 in about three seconds,” Winkler recalls.???? Today, Winkler gives speeches to college students about living their dreams, focusing on how to become a successful actor. “If you are determined, have a sense of humor and never take your eye off what it is you want, you can actually have it,” he says.???? Winkler is also at work on his first children’s book, co-authoring with Lin Oliver. He was recently named executive producer of “Hollywood Squares” and produces the show “Intuition” on the Game Show Network. His next movie, “Holes”, based on a children’s book, is scheduled for release this winter. In October 2000, Winkler made his Broadway debut costarring with John Ritter in the show “The Dinner Party.”???? But through it all, Winkler remains Fonzie. “I think he is the architect of my home, of my professional life, and of my good fortune in the world,” Winkler says. “He literally is the foundation for everything that was to come.”21. Which of the following is NOT mentioned as fans’ reaction t o FonzieA) ?Fans write lots of letters to Winkler for many years.B) ?Fans thank Winkler when they meet him on the street.C) ?Fans greet Winkler by imitating Fonzie’s signature.D) ?Fans sit and watch the sitcom together with Winkler.√答案：D22. Which of the following influences him most according to the authorA) ?The television sitcom “Happy Days”. √B) ?The show “The Dinner Party”.C) ?The movie “Holes”.D) ?The show “Intuition”.答案：A23. Which of the following can be inferred from the passageA) ?Winkler spent long time struggling to make his dreamcome true.B) ?successful actor must have a sense of humor.C) ?Fans like Winkler as a superstar only for a few years.D) ?Fonzie usually utters a long, drawn out “Aaay!” in“Happy Days”. √答案：D24. What does the word “snowball” in Paragraph three most probably mean.A) ?throw at B) ?a ball made of snowC) ?grow rapidly √D) ?melt easily答案：C25. Which of the following is the author primarily concerned with in this passageA) ?Winkler’s article My TurnB) ?Fans’ reaction to Fonzie played by WinklerC) ?Winkler’s life as an actorD) ?Winkler and his sitcom “Happy Days” √答案：D第二次We all laugh. We all hurt. We all make mistakes. We all dream, that’s life. It’s a journey. Please follow these rules to make the journey of your life a journey of joy! Staying positive through the cold season could be your best defense against getting ill, new study findings suggest.?In an experiment that exposed healthy volunteers to a cold or flu virus, researchers found that people with a generally sunny disposition (性格) were less likely to fall ill. The findings, published in the journal Psychosomatic Medicine, build on evidence that a “positive emotional style” can help ward off the common cold and other illnesses.?Researchers believe the reasons may be both objective as in happiness boosting immune function and subjective as in happy people being less troubled by a scratchy throat or runny nose. “People with a positive emotional style ma y have different immune response to the virus,” explained lead study author Dr Sheldon Cohen of Carnegie Mellon University in Pittsburgh. “And when they do get a cold, they may interpret their illness as being less severe.”Cohen and his colleagues had found in a previous study that happier people seemed less likely to catch a cold, but some questions remained as to whether the emotional trait itself had the effect.?For the new study, the researchers had 193 healthy adults with complete standard measures of personality traits, self-perceived health and emotional “style”. Those who tended to be happy, energetic and easy-going were judged as having a positive emotional style, while those who were often unhappy, tense and hostile had a negative style. The researchers gave them nose drops containing either a cold virus or a particular flu virus. Over the next six days, the volunteers reported on any aches, pains, or sneezing (打喷嚏) they had, while the researchers collected objective data. Cohen and his colleagues found that based on objective measures of nasal woes (鼻部的不适), happy people were less likely to develop a cold.1. The new study findings in the experiment suggest that _________.A) ?Having a good disposition is more likely to get ill.B) ?Being optimistic is more probable to keep healthy. √C) ?Having a negative emotion is harmful to the character.D) ?Staying positive is more likely to catch cold.答案：B2. The phrase “ward off” in Paragraph 2 most probably means“_________”.A) ?shrug off B) ?give in C) ?keep away√D) ?set aside答案：C3. It can be inferred from Dr. Sheldon Cohen’s interpretation that ______________.A) ?people with a positive emotion are more likely tointerpret their illness objectively.B) ?people with a negative emotion are more likely to boostimmune function to the virus.C) ?people with a negative emotion are more likely tointerpret their illness subjectively.D) ?people with a positive emotion are more likely toregard their illness as less serious. √答案：D4. It can be learnt from the passage that the benefits of having a positive emotional style are _____________.A) ?to be further studiedB) ?still dubiousC) ?self-evidentD) ?proven by scientific research √答案：D5. Which of the following would be the best TITLE for the passageA) ?A Happy Journey Full of JoyB) ?Scientific Evidence of Staying HealthyC) ?The Secrets of Staying PositiveD) ?The Health Benefits of Staying Positive √答案：DHow is it that despite our amazing powers of production there are still hundreds of millions of people all over the earth in continuous want and poverty, and dangerously near the brink of starvation What are the causes of poverty Everyone is forced to realize and recognize its existence and no one has yet found a cure for it.?Every thinking man has realized that poverty and starvation are not inevitable in the scheme of things. On the contrary, the fruitful earth yields enough for every one of the human beings inhabiting its surface without the twisted distrib ution of nature’s generosity (慷慨). This twisting is caused by our crude and ill developed ideas of distribution and the improper ordering of human services. In the first place, these services can be hindered at their source, and among the factors that operate in this direction may be war, crime, lack of healthy supervision, insufficient attention to rising generations, monopolies (垄断) and various private ownerships that limit the usefulness of property, and neglected and wasteful destruction of property.?In the second place, the great cause of poverty is unproductive consumption. Services become unproductive when they are devoted to supplying luxuries or an excessive quantity of necessaries, which may be summed up in a single word: waste. These are the primary causes of poverty; they are responsible for the presence of starvation.?Is there a remedy?The elimination of waste through perfect production and distribution is a problem that is slowly but surely being solved by the great combinations of capital that have destroyed competition. These monopolies, selfish in the extreme and with no thought beyond profit at any price, are rendering us useful service by teaching us the importance of cooperation and cooperative methods. When these great industrial combinations, these wonderfully smooth running great business machines become the property of all the people and cease to be operated for private gain, a great step will have been taken in the direction of the solution of the starvation problem. When everyone will produce according to his ability and consume according to his needs, then, and not until then will poverty and starvation depart entirely and forever from the minds of men.6. According to the passage, starvation _____.A) ?is due to excessive consumption by human beingsB) ?is inevitable in whatever conditionC) ?is owing to the improper distribution of nature’sgenerosity √D) ?is the result of insufficient production答案：C7. Which of the following can hinder human services at their sourceA) ?Crime and lack of wealthy supervision.B) ?Private ownerships and unproductive consumption.C) ?War and destruction of property. √D) ?Luxuries and an excessive quantity of necessaries.答案：C8. Why does unproductive consumption is considered as the great cause of poverty in Paragraph ThreeA) ?Because people stop producing but only consume.B) ?Because people who don’t produce are responsible forthe presence of starvation.C) ?Because people devote too much to luxuries and don’tproduce anything.D) ?Because people are supplied with excessive quantityof necessaries and waste a lot. √答案：D9. How to eliminate waste through production and distribution according to the passageA) ?By seeking profit at any price and being selfish.B) ?By cooperating and making the industrial combinationspublic property. √C) ?By creating more monopolies to make more profits.D) ?By privatizing business machines and teaching theimportance of cooperation.答案：B10. When can the starvation problem be solved according to the passageA) ?When the great industrial combinations cease to beoperated for private gain.B) ?When private monopolies become public property and theelement of profit is eliminated.C) ?When production is organized based on personalcapa bilities and distribution on individual needs. √D) ?When efficiency of production has been greatlyenhanced.答案：C??? MY NEIGHBOR HAS A GUN. In fact, not having the good fortune to live in the last house on a dead-end street, I am surrounded by neighbors with guns. My situation is hardly novel, since most American households own at least one weapon. We now have enough privately owned guns to arm nearly every man, woman and child in the country. And some of those children are not just imaginary gun users, as recent statistics indicate.???? My neighbors’ guns make me nervous; I’m afraid that they might go off at the wrong time, pointed in the wrong direction. I’ve asked why such dangerous items are allowed to clutter up the house. I’ve gotten seve ral answers, from constitutional rights to the innocent sport of blasting birds out of the skies. I’d like to focus on just one of these reasons.???? My neighbor tells me that curling up at night with his gun nearby makes him feel safer. Safer from what A madman out to better the going entry in the “Guinness Book of World Records” for bloody brutality My neighbor faces far less danger from the mentally ill killer, who fortunately is extremely rare, than he does from my other neighbor who also has a gun. Contrary to the public myth, mental patients have crime rates far below those of my neighbor or me; for all categories of crime and for homicide in particular. One of the few safe places left to live in this gun-packing country is on the grounds of your local mental hospital, where the residents are far less aggressive than my neighbor and guns are checked in at the gate.???? Safer from some intruder (侵入者) in the night seeking to deprive his wife of her virtue or him of his new color television According to best available estimates, my neighbor’s odds of doing himself in accidentally with his own gun are about five times higher than his odds of being done in by some intruder. As a gun owner, my neighbor would be better advised to invest his money in locks and a loud dog. Actually, the intruder in the night accounts for fewer than three percent of our gun deaths. The bulk comes from perfectly law-abiding (守法的) but gun-toting (持枪的) people like my neighbors, who kill each other, themselves, or me.11. Which of the following can be inferred from the first paragraphA) ?Some American children have used gun to kill people.√B) ?Every person in this country knows how to use guns.C) ?Each American household owns at least one weapon.D) ?The author lives in the last house on a dead-end street.答案：A12. Which of the following may be NOT the reason why neighbors’ guns make the author nervousA) ?Their arms might kill me by accident.B) ?Dislike the sport of blasting birds out of the skies.√C) ?Their guns might point in the wrong direction.D) ?Their guns might go off at the wrong time.答案：B13. What does the author imply in the passageA) ?madman kills people to enter “Guinness Book of WorldRecords”.。
人教版高中英语必修二Unit5Music重点归纳笔记(带答案)
人教版高中英语必修二Unit5Music重点归纳笔记单选题1、After breakfast, I packed up and______ again.A．set outB．set upC．set downD．set in答案：A考查动词短语词义辨析。
句意：早餐后，我收拾好行李，再次出发。
A. set out出发；B. set up建立；C. set down记下；D. set in开始；到来。
由上文“After breakfast, I packed up”可知，早餐后，“我”收拾好行李后，再次出发，故选A。
2、_______of danger in the street at night, she had to go home, with a friend_______her.A．Reminding, followingB．Having reminded, followingC．Having been reminded, followingD．Reminded, followed答案：C考查非谓语动词。
句意：想到（被提醒到）晚上在街上有危险，她不得不让一个朋友跟着她回家。
分析可知，空格处均为非谓语，动词remind和主语she之间是被动关系，且remind这一动作先于谓语动词“had to go home”，故用其过去分词或者现在分词的完成被动式作状语，表原因；介词with后接复合宾语，动词follow和宾语a friend之间是主动关系，故用其现在分词作宾语补足语。
故选C项。
3、DX Sports Watch is only _________online, so go to our website and place your order. A．ordinaryB．availableC．typicalD．appealing答案：B考查形容词词义辨析。
句意：DX Sports Watch仅在网上可以购买，因此请访问我们的网站并下订单。
专业英语
Definition of polymers A simple understanding of polymers can be gained by imaging them to be like a chain or, perhaps, a string of pearls, where the individual pearl represent small molecules that are chemically bonded together. Therefore, a polymer is a molecule made up of smaller molecules that are joined together by chemical bonds. The word polymer means „many parts or units.‟ The parts or units are the small molecules that combine. The result of the combination is, of course, a chainlike molecule (polymer). Usually the polymer chains are long, often consisting of hundreds of units, but polymers consisting of only a few units linked together are also known and can be commercially valuable.
Figure 1.1 Diagram illustrating the definition of plastics.
As Figure 1.1 shows, all materials can be classified as gases, simple liquids, or solids, with the understanding that most materials can be converted from one state to another through heating or cooling. If only materials that are structural solids at normal temperatures are examined, three major types of materials are encountered: metals, polymers, and ceramics. The polymer materials can be further divided into synthetic polymers and natural polymers. Most synthetic polymers are those that do not occur naturally and are represented by materials such as nylon, polyethylene, and polyester. Some synthetic polymers could be manufactured copies of naturally occurring materials (such as
血药浓度和药效的关系英文作文
血药浓度和药效的关系英文作文The relationship between blood concentration and drug effectiveness is a crucial aspect of pharmacology and therapeutics. Blood concentration, often referred to as plasma concentration or serum concentration, refers to the amount of a drug present in the bloodstream at a given time. This concentration is directly linked to the drug's effectiveness, as it determines how much of the drugreaches its target site and how potent its therapeuticaction will be.Drug absorption, distribution, metabolism, andexcretion (ADME) are the four primary factors thatinfluence blood concentration. The rate and extent of drug absorption from the site of administration determine how quickly the drug enters the bloodstream. Distributionrefers to how the drug spreads throughout the body,reaching its target tissues and organs. Metabolism, the chemical transformation of the drug within the body, can either increase or decrease its blood concentration, depending on whether the metabolism leads to inactivationor activation of the drug. Excretion, the elimination ofthe drug from the body, is the final step in the ADME process, and it also affects blood concentration.Blood concentration is typically measured in micrograms per milliliter (μg/mL) or nanomoles per liter (nmol/L), depending on the drug and its properties. The optimal blood concentration for a drug is typically determined through clinical trials and pharmacokinetic studies, which aim to establish the dose-response relationship and identify the minimal effective concentration (MEC) and the maximal tolerable concentration (MTC).Drug effectiveness is influenced by both the blood concentration and the pharmacokinetic properties of the drug. A drug with a high affinity for its target site and a low clearance rate from the body is likely to be more effective at lower blood concentrations. Conversely, a drug with low affinity and high clearance may require higher blood concentrations to achieve the desired therapeutic effect.In addition to blood concentration, other factors such as the duration of drug exposure, the route of administration, and the patient's physiological status canalso affect drug effectiveness. For example, drugs administered intravenously typically achieve higher and faster blood concentrations than those administered orally. Similarly, patients with liver or kidney dysfunction may experience altered drug metabolism and excretion, leadingto changes in blood concentration and effectiveness.In summary, the relationship between bloodconcentration and drug effectiveness is complex and multifaceted. Understanding this relationship is crucialfor optimizing drug dosing, achieving desired therapeutic effects, and minimizing adverse effects. Future research in the field of pharmacology and therapeutics will continue to elucidate the intricacies of this relationship, leading to improved patient outcomes and more effective drug therapies. **血药浓度与药效的关系**血药浓度与药效之间的关系是药理学和治疗学中的关键方面。
恩格列净联合利格列汀治疗2型糖尿病的临床疗效研讨
·药物与临床·糖尿病新世界 2023年11月恩格列净联合利格列汀治疗2型糖尿病的临床疗效研讨郑伟坤，陈文娜，薛笑楠，陈琳，官雯娟鹰潭市人民医院内分泌科，江西鹰潭335000[摘要]目的探讨对2型糖尿病患者采用恩格列净+利格列汀药物展开疾病治疗后获得临床效果。
方法选取2022年9月—2023年9月鹰潭市人民医院收治的60例2型糖尿病患者为研究对象，依据为投掷硬币法分为参照组和研究组，各30例。
参照组采用利格列汀治疗；研究组在参照组基础上加用恩格列净治疗。
对比两组2型糖尿病患者的药物治疗总有效率、炎症因子水平、血糖以及胰岛素指标水平、生存质量评分以及不良反应发生率。
结果研究组药物治疗总有效率、炎症因子水平、血糖以及胰岛素指标水平、生存质量评分优于参照组，差异有统计学意义（P<0.05）；两组不良反应（恶心呕吐、头晕头痛、腹痛腹泻、过敏）总发生率比较，差异无统计学意义（P>0.05）。
结论临床对2型糖尿病患者采用恩格列净+利格列汀药物治疗，提高患者用药疗效，改善炎症因子水平，降低血糖以及胰岛素指标水平，提高生存质量，可以获得显著效果。
[关键词] 恩格列净；利格列汀；2型糖尿病；炎症因子；血糖；胰岛素水平；生存质量；不良反应[中图分类号] R59 [文献标识码] A [文章编号] 1672-4062（2023）11（b）-0121-04Study on the Clinical Efficacy of Empagliflozin Combined with Linagliptin in the Treatment of Type 2 Diabetes MellitusZHENG Weikun, CHEN Wenna, XUE Xiaonan, CHEN Lin, GUAN WenjuanDepartment of Endocrinology, Yingtan People's Hospital, Yingtan, Jiangxi Province, 335000 China[Abstract] Objective To explore the clinical effect of empagliflozin + linagliptin in type 2 diabetes mellitus.Methods 60 cases of type 2 diabetes mellitus patients in Yingtan People's Hospital from September 2022 to Septem⁃ber 2023 were selected, they were divided into reference group and study group according to the coin toss method, with 30 cases in each group. The reference group was treated with linagliptin, the study group added emaglipzin to the reference group. The total effective rate, inflammatory factor level, blood glucose and insulin index level, quality of life score and incidence of adverse reactions were compared between the two groups of patients with type 2 diabetes.Results The total response rate, inflammatory factor level, blood glucose, insulin index level and quality of survival score in the study group were better than the reference group, and the differences were statistically significant (P< 0.05); and the total incidence of adverse effects (nausea, vomiting, dizziness, headache, abdominal pain, diarrhea, al⁃lergy) of the two groups, the difference was not statistically significant (P>0.05). Conclusion Clinical treatment with empagliflozin + linagliptin in patients with type 2 diabetes can improve the efficacy of medication, improve the level of inflammatory factors, reduce blood glucose and insulin indicators, and improve the quality of life, which can achieve significant effects.[Key words] Empagliflozin; Linagliptin; Type 2 diabetes mellitus; Inflammatory factor; Blood glucose; Insulin level; Survival quality; Adverse reaction2型糖尿病属于全身代谢性疾病一种，其以胰岛素抵抗作为主要表现。
氢键的应用
how the standard perception of halogen substituents, which assumes an isotropic negative electron density around the halogen, was replaced by a description that takes the σ-hole into account. Halogen bonds have been found to occur in a multitude of inorganic, organic, and biological systems.4,5 In an early study from the 1950s, Hassel and Hvoslef solved the crystal structure of the equimolar Br2:dioxane adduct and found Br···O contacts featuring distances substantially below the sum of the van der Waals radii of both atoms, indicating a strong attractive interaction between both atoms.6,7 In 1984, a search of the Cambridge crystallographic data files for short iodine···N/O/S contacts revealed that these interactions are also formed in biologically relevant systems, being employed by nature for the molecular recognition of thyroid hormones at their target proteins such as transthyretin.8 In protein−ligand environments, halogen bonds can be formed between a halogenated ligand and any accessible Lewis base in the binding pocket.9 Probably because of its presence in every amino acid, the backbone carbonyl oxygen function is the most prominent Lewis base involved in halogen bonds in protein binding sites, as found from an analysis of the Protein Data Bank (PDB).10,11 Additionally, halogen bonds can be formed involving side chain groups, such as hydroxyls in serine, threonine, and tyrosine, carboxylate groups in aspartate and glutamate, sulfurs in cysteine and methionine, nitrogens in histidine, and the π surfaces of phenylalanine, tyrosine, histidine, and tryptophan. Several examples for these contacts are given in Figure 2.
右美托咪定对心脏不停跳冠状动脉搭桥术麻醉诱导及术后转归的影响
第28卷 第31期 中国现代医学杂志 Vol. 28 No.31 2018年11月 China Journal of Modern Medicine Nov. 2018收稿日期：2018-03-09[通信作者] 陈立建，E-mail ：chenlijian77@DOI: 10.3969/j.issn.1005-8982.2018.31.016文章编号： 1005-8982（2018）31-0082-05右美托咪定对心脏不停跳冠状动脉搭桥术麻醉诱导及术后转归的影响耿兴强，陈立建，林慕雅，赵庆，程新琦，张雷，顾尔伟（安徽医科大学第一附属医院 麻醉科，安徽 合肥 230022）摘要：目的 观察右美托咪定对不停跳冠状动脉搭桥术麻醉诱导及术后转归的影响。
方法 选取择期心脏不停跳冠状动脉搭桥手术患者61例，随机分为对照组（C 组，n =30）和右美托咪定组（D 组，n =31）。
D 组于诱导前15 min 给予右美托咪定0.6μg/kg，继之0.4μg/（kg·h）持续输注至手术结束；C 组给予等体积生理盐水输注。
麻醉诱导采用咪达唑仑0.02 mg/kg、初始丙泊酚靶控输注（TCI）浓度1.0μg/ml，每隔1 min 增加0.3μg/ml，至意识消失，给予舒芬太尼0.8～1.0μg/kg、罗库溴铵0.6～0.9 mg/kg，肌松满意进行插管。
记录入室（T 0）、给予负荷量15 min（T 1）、意识消失时（T 2）、插管前（T 3）、插管1 min（T 4）、插管3 min （T 5）、插管5 min （T 6）的心率（HR）、平均动脉压（MAP）、每搏量（SV）、心输出量（CO）、心脏指数（CI）、脑电双频谱指数（BIS），以及T 2、T 3、T 6及手术结束时丙泊酚TCI 效应室浓度、总剂量及血管活性药的使用量。
记录术后苏醒时间、拔管时间、ICU 驻留时间及出院时间。
结果 与C 组比较，D 组在T 2、T 3、T 6及手术结束时丙泊酚TCI 效应室浓度、丙泊酚用量和血管活性药用量均降低（P <0.05），在C 组中，与T 3比较，T 4时刻血流动力学指标升高（P <0.05）。
Comparative study of organosolv lignins from wheat straw
Industrial Crops and Products23(2006)180–193Comparative study of organosolv lignins from wheat strawFeng Xu a,Jin-Xia Sun b,c,RunCang Sun c,a,∗,Paul Fowler c,Mark S.Baird da State Key Laboratory of Pulp&Paper Engineering,South China University of Technology,Guangzhou510641,Chinab College of Forestry,The North-Western University of Agricultural and Forest Sciences and Technology,Yangling712100,Chinac The BioComposites Centre,University of Wales,Bangor LL572UW,UKd Department of Chemistry,University of Wales,Bangor LL572UW,UKReceived10March2004;accepted19May2005AbstractDewaxed wheat straw was treated with acetic acid–H2O(65/35,v/v),acetic acid–H2O(80/20,v/v),acetic acid–H2O(90/10, v/v),formic acid–acetic acid–H2O(20/60/20,v/v/v),formic acid–acetic acid–H2O(30/60/10,v/v/v),methanol–H2O(60/40, v/v)and ethanol–H2O(60/40,v/v)using0.1%HCl as a catalyst at85◦C for4h,in which78.2,80.0,88.2,89.4,94.1,23.5 and37.4%of the original lignin,and42.4,58.7,70.0,65.1,76.5,14.2and22.2%of the original hemicelluloses was released, respectively.Lignins obtained were characterized by their content of hemicelluloses,composition of phenolic acids and aldehydes, molecular weight,thermal stability and by UV,Fourier transform infrared(FT-IR),1H and13C nuclear magnetic resonance(NMR) spectroscopy.The results showed that aqueous organic acid was more effective than aqueous organic alcohol for extensive delignification and selective fractionation of cellulose,lignin and hemicelluloses from the straw.In particular,the addition of formic acid gave a significant effect on the dissolution of lignin.All the acid-insoluble lignin fractions contained small amounts of contaminated hemicelluloses as shown by their content of neutral sugars,0.9–4.3%,and had weight-average molecular weight between3960and4340g mol−1.An increase in concentration of acetic acid or formic acid in organosolv resulted in an increment in release of guaiacyl units and in lignin condensation.However,the lignin preparations released during the treatment with aqueous organic alcohol without organic acid contained almost equal amounts of non-condensed guaiacyl and syringyl units with fewer p-hydroxyphenyl units.The-O-4ether bonds together with-,-5and5-5 carbon–carbon linkages were identified to be present in lignin substructures.©2005Elsevier B.V.All rights reserved.Keywords:Wheat straw;Lignin;Organic acids;Phenolics;FT-IR;13C NMR∗Corresponding author.Tel.:+441248370588; fax:+441248370594.E-mail address:bcs00a@(R.Sun).1.IntroductionLarge amounts of lignin are produced every year by the pulping processes as a by-product of wood and non-wood delignification.However,the availability of0926-6690/$–see front matter©2005Elsevier B.V.All rights reserved. doi:10.1016/j.indcrop.2005.05.008F.Xu et al./Industrial Crops and Products23(2006)180–193181lignin is not as high as could be expected from this fact (Oliet et al.,2001).The commercial pulping processes (kraft and sulphite technologies)lead to high quality pulps,but fractions such as lignin and hemicelluloses (accounting for50–55%of the dry weight of wood and straw)are employed in low added value applications such as producing process energy(Vila et al.,2003). Organosolv pulping,based on the utilization of organic solvents as delignification agents,provides an interest-ing alternative to the current commercial technologies, since they lead to a solid phase enriched in cellulose and to liquors containing hemicellulose-degradation products and lignin-degradation products free from sulphur.In organosolv pulping,a mixture of organic solvent and water is used as cooking liquor.The solvent primar-ily acts on the promotion of vegetal tissue impregnation and the solubilization of the lignin fragments so pro-duced(Balogh et al.,1992;Gilarranz et al.,2000). In non-catalyzed pulping(autocatalyzed),the cook-ing liquor becomes acidified due to the acetic acid released from the wood.However,in catalyzed pulping the liquor can be acidic,neutral or alkaline depend-ing on the nature of the additives employed(Aziz and Sarkanen,1989).During organosolv acid delignifica-tion,the Acetosolv process(based on the utilization of HCl-catalyzed acetic acid media)and Formacell pro-cess(formic acid-catalyzed media)have proved to be promising process to achieve complete utilization of lignocellulosics without impact to environment.Both processes have ability to cause extensive removal of both lignin and hemicelluloses under mild conditions, with no significant cellulose degradation.By either of these processes(Nimz and Casten,1986;Sano et al., 1990;Pan and Sano,2000),wood and non-wood can be simply fractionated to pulp,lignin and monosaccha-rides or hemicellulosic-degradation products,which makes it easy to utilize them for more valuable prod-ucts.The pulp can be used for either paper or cellu-lose derivatives,such as carboxymethylcellulose,cel-lophane,viscose or cellulose acetate.The lignin can be converted to valuable products,such as carbonfibre (Uraki et al.,1995),activated carbonfibres(Uraki et al., 1997)and adhesives(Pan and Sano,1998).From the monosaccharides or hemicellulosic-degradation prod-ucts,sugars or other chemicals,sweetening materials, food additives,fuel and polymers can be obtained (Fengel and Wegener,1984).Lignin is an extremely complex three-dimensionalpolymer(typically found in vascular plants)formed by dehydrogenative polymerization of p-hydroxycinnamyl,coniferyl and sinapyl alcohols.These three lignin precursors(‘monolignols’)giverise to the so-called p-hydroxyphenyl(H),guaiacyl(G)and syringyl(S)phenylpropanoid units,whichshow different abundances in lignins from differentgroups of vascular plants,as well as in different planttissues and cell-wall layers.During polymerizationof the above p-hydroxycinnamyl alcohols involved,the formation of aryl ether(involving C4)interunitlinkages is strongly favoured.In addition,a smallproportion of lignin units remains as phenolic,beinglinked only by C–C bonds,such as-5,-1,-5,-and␣-linkages.Although this phenolic moiety represents a low(and variable)fraction of the totallignin,it can strongly affect the reactivity of thepolymer(Camarero et al.,1999).During organosolvacid delignification,lignin is dissolved essentially byacid-catalyzed cleavage of such bonds as␣-aryl etherand arylglycerol--aryl ether in the lignin macro-molecule(Sarkanen,1990).However,the cleavage of -aryl ether bonds occurs at lower extent(Goyal et al., 1992).The cleavage of ether bonds gives rise to new phenolic hydroxyl groups in lignin,which affect some industrial uses of lignins and lignocellulosic materials, since they increase lignin solubility(favouring its alkaline extraction during paper or pulp manufacture), and modifies the reactivity of technical lignins to be used as raw material for manufacture of lignin-based adhesives and other applications(Camarero et al., 1999).The aim of this work was to study the influence ofvarious organosolvs on physico-chemical properties oflignins dissolved from wheat straw at atmospheric pres-sure.Two favourable organic acids were chosen to beused,formic acid and acetic acid.In comparison,aque-ous methanol and ethanol were also used as cookingsolvents.In order to get more information on chemicalstructures and relationship between physical proper-ties and chemical structures,the lignins were chem-ically characterized in this paper by their fractionalyield,sugar composition,content of phenolic acids andaldehydes,and molecular weights.Other techniquessuch as Fourier transform infrared(FT-IR)and1H and 13C nuclear magnetic resonance(NMR)spectroscopy were also used to investigate the changes occurring182F.Xu et al./Industrial Crops and Products23(2006)180–193in lignin structure during the organosolv treatment processes.2.Materials and methods2.1.MaterialsWheat straw(Variety Riband)was kindly supplied by B Lloyd Co.,Llangefni.The composition(%,w/w) of the straw is cellulose39.0%,hemicelluloses38.7%, lignin17.0%,ash1.8%and wax1.9%on a dry weight basis.The deviations of these contents from their respective means were all less than8%.After being dried at60◦C in an oven for16h,the straw was ground to pass through a0.7mm screen and then extracted with toluene–ethanol(2/1,v/v)in a Soxhlet extractor for6h. The dewaxed straw was further dried at60◦C for12h. All chemicals used were of analytical or reagent grade.anosolv treatmentOrganosolv treatment was carried out in a500ml glass reactor at atmospheric pressure.The extractive free powder(10.0g)was treated under seven differ-ent organosolv systems(Table1)using0.1%HCl as a catalyst at85◦C for4h with a liquor to solid ratio of 20:1(ml/g)under stirring,respectively.After the reac-tor was loaded with wheat straw and the cooking liquor, it was heated to the operating temperature,which was then maintained throughout the experiment.After treat-ment,the residue enriching in cellulose wasfiltrated on a nylon cloth,then washed with hot acid–water mixture andfinally,washed with hot distilled water.The hemicelluloses(hemicellulosic degradation prod-ucts)were isolated from the concentrated hydrolysates by precipitation with three volumes of95%ethanol (22◦C,12h).The solubilized lignins were obtained from the corresponding supernatants by reprecipita-tion after evaporation of all the organic solvents.The acid-insoluble lignin fractions were then washed with acidified water and freeze-dried.Note that the treat-ments with acetic acid–H2O(65/35,v/v)was for lignin preparation L1,acetic acid–H2O(80/20,v/v)for L2, acetic acid–H2O(90/10,v/v)for L3,formic acid–acetic acid–H2O(20/60/20,v/v/v)for L4,formic acid–acetic acid–H2O(30/60/10,v/v/v)for L5,methanol–H2O (60/40,v/v)for L6and ethanol–H2O(60/40,v/v)for L7,respectively.The scheme for organosolv treatment and the isolation of lignin is illustrated in Fig.1.All experiments were performed at least in duplicate.Yield of lignin is given on a dry weight basis related to the starting material.2.3.Characterization of the lignin preparationsThe neutral sugar composition of the contami-nated hemicelluloses in lignins was determined as their alditol-acetate derivatives by gas chromatography(GC) after hydrolysis with2M trifluoroacetic acid for2h at 120◦C(Blakeney et al.,1983).The chemical compo-sition of phenolics liberated from alkaline nitroben-zene oxidation of the lignins(175◦C, 2.5h)was determined on a Hichrom H5ODS HPLC column of dimensions250mm×4.6mm(Phenomenex Co.,Bei-jing).The identification of the individual compounds was detected at280nm by computer comparison of the retention times and peak areas with the authenticTable1Extraction conditions of organosolv-soluble ligninsExperiment anosolv system Catalyst Temperature(◦C)Liquor to solidratio(ml/g)Reaction time(h)W1Acetic acid–H2O(65/35,v/v)0.1%HCl8520:14W2Acetic acid–H2O(80/20,v/v)0.1%HCl8520:14W3Acetic acid–H2O(90/10,v/v)0.1%HCl8520:14W4Formic acid–acetic acid–H2O(20/60/20,v/v/v)0.1%HCl8520:14W5Formic acid–acetic acid–H2O(30/60/10,v/v/v)0.1%HCl8520:14W6Methanol–H2O(60/40,v/v)0.1%HCl8520:14W7Ethanol–H2O(60/40,v/v)0.1%HCl8520:14F.Xu et al./Industrial Crops and Products23(2006)180–193183Fig.1.Scheme for isolation of acid-insoluble lignin preparations obtained by treatment of dewaxed wheat straw with organosolv under acidic conditions.phenolics.Methods of UV spectra recording,measure-ment of the molecular-average weights and thermal analysis of lignin samples have been described in pre-vious papers(Sun et al.,1999,2003).All nitroben-zene oxidation results represent the mean of at least triplicate samples and each oxidation mixture was chromatographed twice.Other experiments were per-formed in duplicate.The standard errors or deviations were observed to be lower than6.5%except for the variation among the triplicate nitrobenzene oxidation (7.0–16.8%).FT-IR spectra were obtained on an FT-IR spec-trophotometer(Nicolet750)using a KBr disc contain-ing1%finely ground samples.The solution-state1H and13C NMR spectra were obtained on a Bruker MSL-300spectrometer at300and74.5MHz,respectively. 1H NMR spectrum was recorded at25◦C from25mg of sample dissolved in1.0ml DMSO-d6.For each sam-ple,16scans were collected.The13C NMR spectrum was recorded at25◦C from250mg of sample dissolved in1.0ml DMSO-d6after30,000scans.A70◦pulseflip-ping angle,a10s pulse width and a15s delay time between scans were used.3.Results and discussion3.1.Fractional yield and purity of ligninIn comparison to other organosolv processes under neutral and alkaline conditions,the recovery of Aceto-solv lignin in this study does not need a previous step of reduction,and consequently the further neutraliza-tion of liquors is also avoided.The acid-insoluble lignin fractions were therefore obtained from the supernatants by reprecipitation in water solution after evaporation of all the organic solvents.Table2gives the fractional yields of the lignins dissolved in various organosolvs. Obviously,the results indicated that the higher yield of lignin was obtained when the treatment was per-formed using organic acid as a solvent between lignin preparations L1and L5;in this case,the yield of lignin was13.3–16.0%,corresponding to78.2–94.1%on total lignin of straw.Interestingly,an increase in acetic acid concentration from65to80%and to90%resulted in an increment in lignin yield from13.3%(in L1)to13.6% (in L2)and to15.0%(in L3),respectively.The current results were consistent with the studies on acetic acidTable2The yield(%dry matter)of the lignin preparationsLignin fraction Lignin preparation aL1L2L3L4L5L6L7 Total solubilized lignins13.313.615.015.216.0 4.0 6.4 Acid-insoluble lignins b9.09.111.611.712.5 3.0 4.8 Acid-soluble lignins c3.83.72.42.52.00.8 1.4 Lignin associated in solubilized hemicelluloses0.50.81.01.01.50.20.2a L1,L2,L3,L4,L5,L6and L7represent the lignin preparations obtained by treatment of the dewaxed wheat straw with acetic acid–H2O (65/35,v/v),acetic acid–H2O(80/20,v/v),acetic acid–H2O(90/10,v/v),formic acid–acetic acid–H2O(20/60/20,v/v/v),formic acid–acetic acid–H2O(30/60/10,v/v/v),methanol–H2O(60/40,v/v)and ethanol–H2O(60/40,v/v)and0.1%HCl as a catalyst at85◦C for4h,respectively.b Represent the lignin fractions obtained by precipitation of the supernatant solution at pH1.5after isolation of the solubilized hemicelluloses.c Represent the lignin fractions which are still solubilized in the pH1.5supernatant after precipitation of the acid-insoluble lignin fractions and obtained by difference(total solubilized lignin–acid-insoluble lignin–lignin associated in the solubilized hemicelluloses).184F.Xu et al./Industrial Crops and Products23(2006)180–193pulping of wheat straw under atmospheric pressure by Pan and Sano(1999).The authors stated that acetic acid had been proved to be an effective organosolv for both extensive delignification of wood or non-wood and selective fractionation of cellulose,lignin and hemicel-luloses.Similar results have been reported by Nimz and Casten(1986)and Davis et al.(1986)during the delig-nification of lignocellulosics using acetic acid–water mixture.More importantly,as the data shown in Table2, the highest yield of lignin was obtained when formic acid was added into acetic acid.Treatment with formic acid–acetic acid–H2O(20/60/20and30/60/10,v/v/v) led to a release of88.2%(in L4)and94.1%(in L5) of the original lignin from the straw,respectively.This indicated that the addition of formic acid showed a sig-nificant effect on the dissolution of lignin.In this case, the yield of lignin increased by1.9and2.7%when formic acid increased from0to20%and to30%.Based on atmospheric acetic acid pulping of wood,Nimz and Schoene,1993concluded that when5–10%of formic acid was added into acetic acid,the pulps could be obtained with improved qualities and kappa number below5.In other words,these processes achieved a ‘fractionation’of the lignocellulosic raw materials into separate streams containing hemicellulose-degradation products,lignin-degradation products and cellulose,all of them being utilizable for different end-product appli-cations.It should be noted that the yield of lignin obtained by using methanol–H2O(60/40,v/v)and ethanol–H2O (60/40,v/v)together with0.1%HCl as a catalyst at 85◦C for4h,was less than half the yield of organic acid isolated lignin,4.0%in L6and6.4%in L7.This confirmed again that organic acid,e.g.formic acid and acetic acid,is more powerful solvent for delignification than aqueous alcohol,such as methanol/ethanol–water mixtures.The fairly low lignin yields of L6and L7can partially be explained by the relatively low hydrox-onium ion concentration in aqueous alcohol system, since lignin dissolution is expected to be proceeded by the acid-catalyzed cleavage of␣-aryl and-aryl ether linkages in the lignin macromolecule and the rate of delignification is highly pH-dependent.This effective role of organic acid at high concentration is probably due to rapid hydrolysis of hemicelluloses, resulting in increased porosity and accessibility of the solvent to lignin,since significant amounts of hemi-celluloses(42.4,58.7,70.0,65.1and76.5%of the original hemicelluloses obtained by treatment with acetic acid–H2O(65/35,v/v),acetic acid–H2O(80/20, v/v),acetic acid–H2O(90/10,v/v),formic acid–acetic acid–H2O(20/60/20,v/v/v)and formic acid–acetic acid–H2O(30/60/10,v/v/v),respectively,data not shown)were released or degraded during the treat-ments using organic acids,while only small quantities of them(14.2and22.2%of the original hemicelluloses, data not shown)dissolved during the treatments with aqueous methanol and ethanol,respectively.Further-more,as expected,the acid-insoluble lignin fraction in Table2was the major fraction,comprising67.7–78.1% of the total solubilized lignins,while the lignin frac-tion associated in the solubilized hemicelluloses,was accounted only3.1–9.4%of the released lignins.This result suggested that treatment with various organo-solvs under the acidic conditions given substantially cleaved the ether bonds between lignin and hemicellu-loses from the cell walls of wheat straw.In this study,UV–vis absorption measurements of the seven acid-insoluble lignin fractions were per-formed using a dioxane–water mixture,which ver-ify the purity of lignins atλ=250–380nm.Spectra of acid-insoluble lignin fractions L2(spectrum L2), L3(spectrum L3),L4(spectrum L4)and L6(spec-trum L6)solubilized during the treatment with acetic acid–H2O(80/20,v/v),acetic acid–H2O(90/10,v/v), formic acid–acetic acid–H2O(20/60/20,v/v/v)and methanol–H2O(60/40,v/v),respectively,are illus-trated in Fig.2.The maximum absorption at280nm originates from non-conjugated phenolic groups in the lignin.The presence of a second characteristic region of lignin absorption around318nm can be assigned to the presence of both ferulic and p-coumaric acids (Scalbert et al.,1986).Interestingly,as shown in the spectra,a highest absorption coefficient occurred in L6 fraction,suggesting that the most pure lignin prepara-tion can be obtained when aqueous alcohol was used as an organosolv.On the other hand,the lowest absorption coefficient of L4fraction,released during the treatment with formic acid–acetic acid–H2O(20/60/20,v/v/v), was undoubtedly due to the highest amounts of bound hemicelluloses and other non-lignin materials.It can be seen that the purity of the lignin decreased in the order: aqueous alcohol-soluble lignin,acetic acid–water-soluble lignin,formic acid–acetic acid–water-soluble lignin.F.Xu et al./Industrial Crops and Products23(2006)180–193185Fig.2.UV spectra of acid-insoluble lignin preparations isolated with acetic acid–H2O(80/20,v/v,sample L2,spectrum L2),acetic acid–H2O (90/10,v/v,sample L3,spectrum L3),formic acid–acetic acid–H2O(20/60/20,v/v/v,sample L4,spectrum L4)and methanol–H2O(60/40,v/v, sample L6,spectrum L6)combining with0.1%HCl as a catalyst at85◦C for4h from dewaxed wheat straw.Organosolv treatment under the acidic condi-tions used resulted in intensive hydrolysis of lignin–hemicellulose bonds and,accordingly,in low hemicel-lulose content in the isolated lignins.Table3shows the content of sugars determined after acid hydroly-sis of acid-insoluble lignin fractions.Even under mild organic alcohol reaction conditions,the total hemi-cellulose content never exceeded5%.The relatively high amount of xylose and arabinose suggested that the main hemicelluloses bonded to lignin were arabinoxy-lans.Glucose and galactose could also be found in all lignin samples.Trace amount of mannose was present in some cases.No clear effect of treatment conditions on the amount of hemicelluloses in lignin prepara-tions was observed except for the lignin preparation L4,which had a noticeable amount of hemicelluloses as determined by the sugar content,4.3%.This high-est content of hemicelluloses in L4preparation implied that there were more chemical linkages between lignin and polysaccharides in L4than in other lignin prepara-tions,which were stable to aqueous formic acid–acetic acid hydrolysis.p-Coumaric and ferulic acids present in wheat straw lignin might be favourable to this kind of linkages.In particular,ferulic acid might form cross-links between lignin by ether bonds through its pheno-lic oxygen in the cell walls of wheat straw and hemicel-luloses by simultaneous esterification of their carboxyl group to the C-5position of arabinose substituents of arabinoglucuronoxylans(Himmelsbach and Barton, 1980).The presence of linkages between hemicellu-loses and lignin makes it difficult to prepare wheat straw lignin free from polysaccharides.Similar results were reported for purification of wheat straw lignins by Ben-Ghedalia and Yosef(1994).Table3The content of neutral sugars(%lignin sample,w/w)in the acid-insoluble lignin preparationsNeutral sugars/uronic acids Lignin preparation aL1L2L3L4L5L6L7 Arabinose0.60.40.40.90.60.30.3 Xylose 1.00.80.8 2.1 1.10.30.4 Mannose Tr b Tr Tr Tr Tr Tr Tr Galactose0.20.20.30.60.40.10.1 Glucose0.20.40.40.70.60.20.2Total 2.0 1.8 1.9 4.3 2.80.9 1.0 a Corresponding to the lignin preparations in Table2.186F.Xu et al./Industrial Crops and Products23(2006)180–193position of phenolic acids and aldehydesThe results of alkaline nitrobenzene oxidation of seven organosolv lignin preparations are listed in Table4.As can be seen,all the lignin preparations gave vanillin and syringaldehyde as main products accompa-nied with their corresponding aromatic acids in minor quantity,suggesting that the organosolv lignins mainly resulted from guaiacyl–syringyl units.The presence of fewer p-hydroxybenaldehyde and p-hydroxybenzoic acid was considered most probably to the indicative of non-condensed p-hydroxyphenyl units,indicating the incorporation of p-hydroxycinnamoyl alcohol in wheat straw organosolv lignin.The occurrence of significant amounts of non-condensed guaiacyl and syringyl units with relatively fewer p-hydroxyphenyl units revealed that the seven organosolv lignins could be justified as GSH-lignin such as grass type lignin.The rela-tive molar ratios of G(the relative total moles of vanillin,vanillic acid and acetovanillin)to S(the rel-ative total moles of syringaldehyde,syringic acid and acetosyringone)and to H(the relative total moles of p-hydroxybenzaldehyde and p-hydroxybenzoic acid) were found to be4:3:1in L1and L2,7:4:1in L3, 4:4:1in L4,5:4:1in L5,4:4:1in L6and6:6:1in L7. Apparently,an increase in acetic acid or formic acid concentration in a mixture of organosolv resulted in an increment in release of guaiacyl units.This means that the fraction with more guaiacyl units were much easier to extract than that with more syringyl units during the preparation of organosolv lignins with relatively high concentration of acetic acid or formic acid,or that gua-iacyl units were less condensed or cross-linked than syringyl units in the cell walls of wheat straw.On the other hand,these data also suggested that syringyl units were condensed to a great extent during the treatment with the concentration(90%)of aqueous acetic acid and formic acid–acetic acid–water mixture than other units.The total yield of oxidation products decreased from38.69%(L2)to24.68%(L3)with an increase in acetic acid concentration from80to90%and reduced from23.89%(L4)to17.97%(L5)when the formic acid increased from20to30%in the treating mix-ture of formic acid–acetic acid–water,implying that condensation degree of the lignins increased as the concentration of acetic acid or formic acid raised.In other words,the lignin preparations extracted with a relatively high concentration of acetic acid or formic acid were highly condensed and difficult to oxidize while the lignin preparation dissolved during the treat-ment with60%aqueous methanol(L6)was least con-densed and easiest to oxidize,due to its highest yield of nitrobenzene oxidation products(50.68%).These different degrees of lignin condensation demonstratedTable4The composition(%lignin sample,w/w)of phenolic acids and aldehydes from nitrobenzene oxidation of the acid-insoluble lignin preparations Phenolic acids and aldehydes Lignin preparation aL1L2L3L4L5L6L7p-Hydroxybenzoic acid 1.49 1.500.250.770.57 1.340.40 p-Hydroxybenzaldehyde 1.68 2.36 1.03 1.340.78 2.72 1.58 Vanillic acid 1.36 2.810.68 1.020.72 2.52 2.02 Vanillin12.8615.899.689.207.2217.1811.78 Syringic acid0.63 1.270.320.890.460.82 1.22 Syringaldehyde11.3811.379.658.937.1721.4614.26 Acetovanillin0.530.540.380.360.23 1.650.80 Acetosyringone 1.00 1.880.690.720.40 1.600.76 p-Coumaric acid0.380.400.350.240.180.720.56 Ferulic acid0.470.640.330.300.160.580.28 Cinnamic acid0.0300.0260.0410.120.0780.0920.080 Total31.8138.6924.6823.8917.9750.6833.74 Molar ratio(G:S:H)b4:3:14:3:17:4:14:4:15:4:14:4:16:6:1a Corresponding to the lignin fractions in Table2.b G represents the sum of total moles of vanillin,vanillic acid and acetovanillin;S represents the sum of total moles of syringaldehyde,syringic acid and acetosyringone;H represents the sum of total moles of p-hydroxybenzaldehyde and p-hydroxybenzoic acid.F.Xu et al./Industrial Crops and Products23(2006)180–193187the different behaviour of lignins during the various organosolv treatments.In addition,the low yields of L3,L4and L5could also be explained either as the removal of p-coumaric and ferulic acids ester and/or ether-linked to protolignin,which exist in a remark-able amount in gramineae lignin(Sun et al.,2000),or as the occurrence of condensation between the units of the lignin during the concentration(90%)of aqueous acetic acid and formic acid–acetic acid–water mixture in the atmospheric organic acid treatment with0.1% HCl as a catalyst.3.3.Molecular weightWeight-average(¯M w)and number-average(¯M n) molecular weights and polydispersity(¯M w/¯M n)of the seven acid-insoluble lignin preparations from wheat straw are summarized in Table5.Clearly,the seven lignin fractions showed no significant difference in their molecular-average weights,which ranged¯M w from3960to4340g mol−1.These data indicated that the organosolv under the conditions given had no sub-stantial influences on the¯M w of the lignins from wheat straw.In other words,aqueous organic acids and aque-ous alcohols appeared to have equal effect on the degra-dation of lignin into small segments by cleavage of ␣-aryl and-aryl ether linkages when0.1%HCl was used as a catalyst.In addition,the seven lignin fractions also gave a fairly analogous polydispersity,ranging between1.56and1.71.3.4.FT-IR spectraAmong the analysis techniques described in the lit-erature,FT-IR spectroscopy shows interesting charac-teristics such as high sensitivity and selectivity,high signal-to-noise ratio,accuracy,data handling facil-ity,mechanical simplicity and short time andsmall Fig.3.FT-IR spectra of acid-insoluble lignin preparations isolated with acetic acid–H2O(80/20,v/v,sample L2,spectrum1),acetic acid–H2O(90/10,v/v,sample L3,spectrum2)and formic acid–acetic acid–H2O(20/60/20,v/v/v,sample L4,spectrum3)combining with 0.1%HCl as a catalyst at85◦C for4h from dewaxed wheat straw. amount of sample required for the analysis(Hortling et al.,1997).In addition,the spectrum of a lignin sample gives an overall view of its chemical structure (Gilarranz et al.,2001).Fig.3shows FT-IR spectra of acid-insoluble lignin preparations isolated with acetic acid–H2O(80/20,v/v,sample L2,spectrum1),acetic acid–H2O(90/10,v/v,sample L3,spectrum2)and formic acid–acetic acid–H2O(20/60/20,v/v/v,sam-ple L4,spectrum3)combining with0.1%HCl as a catalyst at85◦C for4h from dewaxed wheat straw. The spectral profiles and the relative intensities of the bands were rather similar in three spectra,which confirmed that the‘core’of lignin structure did not change significantly during the aqueous organic acid treatment.Table6gives the assignments of FT-IR absorp-tion bands of the lignins,aromatic skeleton vibrations occur at1606,1507and1434cm−1,in which the aromatic semicircle vibration(a vibration involvingTable5Weight-average(¯M w)and number-average(¯M n)molecular weights and polydispersity(¯M w/¯M n)of the acid-insoluble lignin preparations Lignin preparation aL1L2L3L4L5L6L7¯M w4130433039604140417043404280¯M n2530276023302650266026302500¯M w/¯M n1.631.571.701.561.571.651.71 a Corresponding to the lignin fractions in Table2.。