松香活性基团的改性及应用研究进展

本文主要介绍了松香的活性基团即:-C=C-双键(共轭和非共轭)和-COOH羧基官能团,并对这两种活性基团展开主要的反应研究。分别阐述了松香这两种活性基团改性后在造纸工业、黏合剂工业、表面活性剂工业及医学方面的应用进展。     

紫胶树脂改性研究进展

本文概述了紫胶树脂的特点和应用范围,并且分析和阐述了其化学改性和物理改性的方法和原理,在化学方面,利用各种化学试剂对紫胶树脂上的羧基、羟基、醛基等活性基团进行改性;在物理方面,对紫胶树脂的成膜性质和相态进行改进。展望了紫胶树脂作为未来绿色材料的发展前景和方向。     

柠檬渣微波改性及吸附pb~(2+)的性能研究

为了研究柠檬渣微波改性后的吸附性能,测量了改性柠檬渣对pb~(2+)的吸附率、柠檬渣的比表面积(BET)、灰分、碘吸附值和孔结构;并利用红外光谱(IR)、紫外光谱(UV)、差热分析(TG-DTA)、扫描电镜(SEM)和能谱(EDS)对柠檬渣进行了表征。微波改性的柠檬渣对pb~(2+)吸附率比化学改性和预处理后的柠檬渣都有明显增加。与化学改性相比,柠檬渣经微波改性后比表面积有所减小,灰分率增大近5倍,碘吸附值增大近1.5倍;产生羧基和内酯基的量相对较多,酚羟基产生的量相对较少。改性柠檬渣吸附pb~(2+)后,总体骨架没有改变。微波改性柠檬渣在206 nm左右处有最大紫外吸收峰,吸附pb~(2+)后在192 nm左右处出现最大吸收峰。微波改性的柠檬渣和吸附pb~(2+)后的柠檬渣都有三个失重过程,主要由碳组成,pb~(2+)能被改性柠檬渣有效吸附,但pb~(2+)的重量和原子百分比都不高。改性后的柠檬渣表面变得疏松,孔数量明显增加。     

多糖的氧化改性及在生物医药领域的应用

氧化是多糖化学改性中最为简单和广泛应用的方法之一,它将多糖的大量羟基转变为醛基或羧基,并赋予多糖许多理想的性能。氧化多糖已被广泛应用于食品、医药和化工等领域。本文中,笔者介绍了以高碘酸盐、次氯酸钠和过氧化氢为氧化剂制备氧化多糖的机制与条件,探讨了氧化对多糖分子结构和物化性能的影响。最后,对氧化多糖在蛋白基生物材料交联剂、包合物制备和新型抗菌剂等生物医药领域的应用进行了介绍。     

低能铁离子束辐照氨基酸衍生物的红外光谱结构表征

利用傅里叶变换红外光谱（FTIR）技术研究了能量为110keV的Fe^ 离子束辐照L（ ）-半胱氨酸盐酸盐单晶水合物固态样品的结构变化情况。对辐照样品的两次红外光谱分析结果有所不同,表明固态样品不同部位受低能铁离子束作用后可发生不同的分子改性;但二者又具有一定的相似性,都反映了原分子中氨基、羧基和巯基等基团的受损及硝基和酰胺基团等的生成。     

冬油菜和春油菜在冷驯过程中膜脂分子的变化

研究了冬油菜和春油菜两种油菜品种在4℃冷驯3天后11类151种膜脂分子的变化,计算了其中膜脂的相对含量、双键指数和碳链长度值。结果发现油菜膜脂的膜脂分子组成模式及其冷驯诱导的膜脂分子组成变化与前期实验中的拟南芥情况非常相似,冷驯3天诱导的膜脂分子组成变化较小,但是膜脂的双键指数略有升高,春油菜双键指数和冷驯积累的脯氨酸含量都比冬油菜多。上述结果说明,油菜的冷驯需要更多的时间,春油菜对冷驯比较敏感。     

细胞色素C引起心磷脂的还原

本工作采用FT-IR和NMR技术,研究了心磷脂(CL)与还原态细胞色素C作用后其脂肪酸链中双键数目的变化。发现伴随细胞色素C的氧化,CL双键被部分还原为单键,提示CL可能直接参与吸呼链的电子传递。     

酚类抑制剂抗5-脂氧合酶的分子对接研究

目的:研究抗5-脂氧合酶酚类抑制剂的结构活性关系及作用机制。方法:构建7个抗5-脂氧合酶阳性酚类抑制剂分子库,利用Autodock 4.2和iGEMDOCK 2.1软件包对受体与抑制剂进行模拟对接研究并计算结合自由能。结果:用Autodock 4.2、iGEMDOCK 2.1计算得到的结合自由能与抑制剂的抑制活性之间都存在良好的相关性,它们的决定系数(R2)依次为0.856 64和0.784 41,标准误差(SD)分别为0.430 92和5.323 35,P值分别为0.002 79和0.007 98;配体与受体之间形成的氢键在决定配体在受体活性部位的构象及定位中起重要作用,但两者结合的主要驱动力为范德华作用力;具有碳氧双键及与该双键共轭的碳碳双键的多环酚类化合物有较强的抗5-脂氧合酶活性。结论:Autodock 4.2比iGEMDOCK 2.1预测抗5-脂氧合酶酚类抑制剂的能力强;具有碳氧双键及与该双键共轭的碳碳双键的多环酚类化合物有较强的抗5-脂氧合酶活性。     

粘土改性技术用于絮凝除藻的研究进展

当前, 藻类水花及其带来的藻毒素污染愈演愈烈, 治理藻害成为改善水环境的当务之急。受安全、技术及成本的限制, 人们试图通过改性粘土实现更加高效、安全的藻害去除效果。基于已有的研究成果, 对改性粘土的除藻机理、改性方法及絮凝效果的影响因素进行了归纳总结。目前, 改性粘土去除藻害的研究和应用大多局限于海水水体, 很多淡水除藻的研究和实践尚未取得理想效果。今后可以考虑通过有机-无机改性结合的方法或开发新型改性剂拓展改性粘土技术絮凝除藻的应用范围。总之, 开发相对安全、可防止蓝藻泛起、藻毒素释放及底泥营养盐二次污染等问题的改性粘土来絮凝沉降藻类, 是未来利用改性粘土治理藻害需要解决的问题和重点研究方向。     

多不饱和脂肪酸对人体的作用

多不饱和脂肪酸又叫多烯酸,是指分子结构中含有２个或２个以上不饱和双键的脂肪酸。双键愈多,不饱和程度愈高,营养价值也愈高［１］。随着科学的发展,某些多不饱和脂肪酸对人体的作用进一步被认识,特别是以廿二碳六烯酸、廿碳五烯酸和一般植物油中的亚油酸（常与亚麻...     

4-Amino-6-methylhept-2-enoic acid: a leucine analogue and potential probe for localizing sites of proteolytic control in the hepatocyte.

A recent analysis of leucine analogues has suggested that the carboxyl group is not required for mediating low concentration proteolytic inhibition in liver cells. In designing a probe to localize the regulatory site(s), we tested this hypothesis by synthesizing an analogue with a 2-carbon insert between the carboxyl and alpha-carbon. The Wittig product, a trans olefin, was fully active. Surprisingly, low concentration activity was lost when the double bond was eliminated by hydrogenation although some inhibitory effectiveness at high concentrations was evident. Since the double bond extends the carboxyl group away from the alpha-carbon, the results support the above hypothesis as well as the feasibility of adding functional groups to the carboxyl end of leucine.     

Endoplasmic oleoyl-PC desaturase references the second double bond

The regiospecificity for the gene product of fad2,(1) the microsomal oleoyl-PC desaturase from higher plants, differs from some previous suggestions. Rather than only referencing the carboxyl group (a Delta(12) desaturase) or the methyl terminus (an omega-6 desaturase), this desaturase locates the second double bond in its substrates by first referencing the existing double bond. This specificity was demonstrated for the oleoyl-PC desaturase cDNA from the developing seeds of peanut (Arachis hypogaea L) expressed in yeast (Saccharomyces cerevisae). The expressed enzyme was capable of desaturating monounsaturated fatty acyl groups in membrane lipids. Endogenous palmitoleate was desaturated to cis, cis 9,12 hexadecadienoate (9(Z)12(Z)C16:2), endogenous oleate to linoleate (9(Z)12(Z) octadecadienoate), and cis 10-nonadecenoate (provided as a supplement in the growth medium) to 10(Z)13(Z)C19:2. The rule, Delta(x+3) where x=9 is the double bond location in the substrate, best describes the consistent placement of the second double bond in the above monounsaturated substrates for the oleoyl-PC desaturase of higher plants.     

Effect of acyl chain unsaturation on the conformation of model diacylglycerols: a computer modeling study.

In a previous modeling study we identified an angle iron-shaped conformation of docosahexaenoic acid and showed that an sn-1-stearoyl diacylglycerol (DG) that contained an sn-2-docosahexaenoyl group in this conformation could adopt a highly regular shape. In the present study we compared the properties of this DG with those of sn-1-stearoyl DGs that contained other unsaturated fatty acyl groups in the sn-2 position. The major findings were that: 1) sn-1-stearoyl DGs that contain polyenoic fatty acids in the sn-2 position can assume regular shapes, and 2) these shapes differ depending on the location of the double bonds. sn-2-Polyenoic fatty acyl groups with a double bond sequence that begins close to the carboxyl ester bond are associated with one type of regular shape, while sn-2-polyenoic fatty acyl groups with a double bond sequence that begins toward the middle of the chain are associated with another. Such shapes would not have been predicted by current ideas relating membrane fluidity to unsaturation. In contrast, another finding of the present study, that sn-1-stearoyl-2-oleoyl DG can adopt, at best, only a highly irregular shape is in good agreement with the results of previous investigators.     

Preparation of well-defined protein conjugates using enzyme-assisted reverse proteolysis

A two-step approach to the production of well-defined protein conjugates is described. In the first step, a linker group, carbohydrazide, having unique reactivity (a hydrazide group) is attached specifically to the carboxyl terminus by using enzyme-catalyzed reverse proteolysis. Since the hydrazide group exists nowhere else on the protein, specificity is assured in a subsequent chemical reaction (formation of a hydrazone bond) of the modified protein with a molecule (chelator, drug, or polypeptide) carrying an aldehyde or keto group. The product is sufficiently stable at neutral pH, no reduction of the hydrazone bond being necessary for the hydrazones described. Protein modification is thus restricted to the carboxyl terminus and a homogeneous product results. With insulin as a model, conditions are described for producing such well-defined conjugates in good yields. The use of other linker groups besides carbohydrazide, and applications of these techniques to antibody fragments, are discussed.     

Comparison of vasodilatory properties of 14,15-EET analogs: structural requirements for dilation

Epoxyeicosatrienoic acids (EETs) are endothelium-derived eicosanoids that activate potassium channels, hyperpolarize the membrane, and cause relaxation. We tested 19 analogs of 14,15-EET on vascular tone to determine the structural features required for activity. 14,15-EET relaxed bovine coronary arterial rings in a concentration-related manner (ED(50) = 10(-6) M). Changing the carboxyl to an alcohol eliminated dilator activity, whereas 14,15-EET-methyl ester and 14,15-EET-methylsulfonimide retained full activity. Shortening the distance between the carboxyl and epoxy groups reduced the agonist potency and activity. Removal of all three double bonds decreased potency. An analog with a Delta8 double bond had full activity and potency. However, the analogs with only a Delta5 or Delta11 double bond had reduced potency. Conversion of the epoxy oxygen to a sulfur or nitrogen resulted in loss of activity. 14(S),15(R)-EET was more potent than 14(R),15(S)-EET, and 14,15-(cis)-EET was more potent than 14,15-(trans)-EET. These studies indicate that the structural features of 14,15-EET required for relaxation of the bovine coronary artery include a carbon-1 acidic group, a Delta8 double bond, and a 14(S),15(R)-(cis)-epoxy group.     

1H NMR spectroscopic evidence of interaction between ibuprofen and lipoproteins in human blood plasma

Recent studies have suggested that ibuprofen inhibits low-density lipoprotein oxidation in a high dose-dependent manner and is a promising drug for treatment of the conditions associated with atherosclerosis. In this article, we present the NMR spectroscopic evidence for the interaction between ibuprofen and phospholipids in lipoprotein particles in intact human plasma. Ibuprofen caused chemical shift upfield drifts for the protons of -N(+)(CH(3))(3) moieties of phosphatidylcholine and sphingomyelin, olefinic chains (-CH[double bond]CH[bond], [bond]CH[triple bond]CHCH(2)CH[triple bond]CH[bond], [bond](CH(2))(n)CH(2)CH[double bond]), and (CH(2))(n) and CH(3) groups, from unsaturated lipids in lipoprotein particles. The ibuprofen may interact directly with the above-mentioned groups of phospholipids or induce structural changes in the lipoproteins. This may shed light on the mechanism by which the drug protects against oxidative modification of lipoproteins.     

13C nuclear magnetic resonance spectra of 1,2-dioctadec-cis-enoyl-sn-glycero-3-phosphorylcholines.

The 13C NMR spectra of all sixteen 1,2-dioctade-cis-enoyl-sn-glycero-3-phosphorylcholines have been obtained. Resonance lines of the olefinic, methylene, methyl and carboxyl carbon nuclei are sufficiently characteristic to permit unequivocal designation of double bond position for each isomer. Two resonances of the sn-glycero-3-phosphorylcholine structure have been reassigned.     

A method of mapping protein sumoylation sites by mass spectrometry using a modified small ubiquitin-like modifier 1 (SUMO-1) and a computational program

Post-translational modification by small ubiquitin-like modifier 1 (SUMO-1) is a highly conserved process from yeast to humans and plays important regulatory roles in many cellular processes. Sumoylation occurs at certain internal lysine residues of target proteins via an isopeptide bond linkage. Unlike ubiquitin whose carboxyl-terminal sequence is RGG, the tripeptide at the carboxyl terminus of SUMO is TGG. The presence of the arginine residue at the carboxyl terminus of ubiquitin allows tryptic digestion of ubiquitin conjugates to yield a signature peptide containing a diglycine remnant attached to the target lysine residue and rapid identification of the ubiquitination site by mass spectrometry. The absence of lysine or arginine residues in the carboxyl terminus of mammalian SUMO makes it difficult to apply this approach to mapping sumoylation sites. We performed Arg scanning mutagenesis by systematically substituting amino acid residues surrounding the diglycine motif and found that a SUMO variant terminated with RGG can be conjugated efficiently to its target protein under normal sumoylation conditions. We developed a Programmed Data Acquisition (PDA) mass spectrometric approach to map target sumoylation sites using this SUMO variant. A web-based computational program designed for efficient identification of the modified peptides is described.     

Modification of a carboxyl group that appears to cross the permeability barrier in the red blood cell anion transporter

A recently developed method for converting protein carboxyl groups to alcohols has been used to examine the functional role of carboxyl groups in the red blood cell inorganic anion-transport protein (band 3). A major goal of the work was to investigate the carboxyl group that is protonated during the proton-sulfate cotransport that takes place during net chloride-sulfate exchange. Three kinds of evidence indicate that the chemical modification (Woodward's reagent K followed by borohydride) converts this carboxyl to an alcohol. First, monovalent anion exchange is inhibited irreversibly. Second, the modification stimulates sulfate influx into chloride-loaded cells and nearly eliminates the extracellular pH dependence of the sulfate influx. (The stimulated sulfate influx in the modified cells is inhibitable by stilbenedisulfonate.) Third, the proton influx normally associated with chloride-sulfate exchange is inhibited by the modification. These results would all be expected if the titratable carboxyl group were converted into the untitratable, neutral alcohol. In addition to altering the extracellular pH dependence of sulfate influx, the chemical modification removes the intracellular pH dependence of sulfate efflux. The modification is performed under conditions in which the reagent does not cross the permeability barrier. The large effect on the intracellular pH dependence of sulfate transport suggests that a single carboxyl group can at different times be in contact with the aqueous medium on each side of the permeability barrier.     

Mature collagen crosslinks

During incubation with physiological buffers at 37°, as well as during $\text{in vivo}$ maturation, native collagen fibers display a progressive increase in tensile strength and insolubility. This is paralleled by a progressive loss of reducible, intermolecular crosslinks. The experiments described in this paper indicate that nucleophilic addition of lysine and/or hydroxylysine residues to the electrophilic double bond of the reducible crosslinks transforms them into more stable, non-reducible crosslinks. Indeed, modification of lysine/hydroxylysine residues completely blocks this transformation, while modification of his, arg, glu and asp is without effect. On the basis of these and other experiments, tentative structures are proposed for the stable crosslinks.