甲壳素类液晶高分子的研究V.取代基个数及长度对羟乙基壳聚糖液晶性的综合影响

采用碱壳聚糖的方法合成了一系列具有不同摩尔醚化度 (DME)的新的液晶性壳聚糖衍生物羟乙基壳聚糖 (HECS) .用酸氧化蚀刻的方法 ,在扫描电子显微镜 (SEM )下证实了其胆甾型的液晶织构 .以甲酸为溶剂 ,研究了摩尔醚化度对羟乙基壳聚糖溶致液晶性的影响 .结果表明 ,在该体系中 ,摩尔醚化度能综合取代基个数及长度两个结构因素的影响 ,当DME较低时 (<～ 2 0 ) ,这种影响关系类似于取代基个数 (即取代度 )的影响 ,当DME较高时 (>～ 2 0 ) ,则类似于取代基长度的影响 .前者对液晶临界浓度的影响很小 ,而后者却有显著影响 .此外还观察到当DME >～ 2 0时出现水溶性 ,HECS的水溶液也呈现典型的胆甾指纹状织构     

两亲性羧甲基壳聚糖衍生物的表面活性研究

将羧甲基壳聚糖与烷基缩水甘油醚在碱性条件下反应,合成了一系列新型的两亲性化合物(2-羟基-3-烷氧基)丙基-羧甲基壳聚糖,对其表面性质的研究结果表明,对同一衍生物,在所研究范围内,取代度越高,降低表面张力的能力及效率越高;对同一取代度的不同衍生物,疏水链越长,降低表面张力的能力越强;对链较短和取代度较大的衍生物,如(2-羟基-3-丁氧基)丙基羧甲基壳聚糖(HBP-CMCHS),在外加电解质存在时溶液的表面张力曲线出现2个转折点,表明可能有分子内胶束形成;而对链较长的衍生物,如(2-羟基-3-十二烷氧基)丙基羧甲基壳聚糖(HDP-CMCHS),则无明显的临界胶束浓度,有外加电解质时表面张力曲线也未出现2个转折点.     

甲壳素类液晶高分子的研究：Ⅱ.侧基长度和取代度对羧酰化壳聚糖的？…

五种羧酰化壳聚糖即乙酰化、丙酰化、丁酰化、己酰化和庚酰化壳聚糖在二氯乙酸溶液中均呈现胆甾型致液晶相。临界浓度随侧基长度的增加而增加，但取代度（从０．２１变化到０．９４）对临界浓度没有影响。在两相共存浓度区内，均呈现典型的滴状织构。从两相共存到完全液晶相的转变浓度也随侧基长度的增加而增加。     

两亲性壳聚糖衍生物的合成及其自聚集现象

以壳聚糖为主链, 聚乙二醇单甲醚为亲水性链段, 癸二酸为疏水链段, 合成了一系列两亲性壳聚糖衍生物. 通过FTIR, 1H NMR和X射线粉末衍射等手段对壳聚糖衍生物进行了结构表征, 由元素分析方法计算出衍生物的取代度. 采用直接溶解法制备了壳聚糖衍生物的空白胶束, 通过透射电子显微镜(TEM)观察了胶束的形态. 由动态光散射(DLS)测定了胶束的粒径及分布, 并以芘为分子探针, 通过荧光光谱法测定了壳聚糖衍生物的临界聚集浓度(CAC). 研究结果表明, 壳聚糖主链上疏水链段的取代度越大, 其衍生物的临界聚集浓度越低, 相同浓度下的胶束的粒径也越小.     

甲壳素类液晶高分子的研究Ⅱ-侧基长度和取代度对羧酰化壳聚糖的液晶性的影响

五种羧酰化壳聚糖即乙酰化、丙酰化、丁酰化、己酰化和庚酰化壳聚糖在二氯乙酸溶液中均呈现胆甾型溶致液晶相．临界浓度随侧基长度的增加而增加,但取代度（ 从０－２１ 变化到０－９４） 对临界浓度没有影响．在两相共存浓度区内,均呈现典型的滴状织构．从两相共存到完全液晶相的转变浓度也随侧基长度的增加而增加．     

甲壳素类液晶高分子的研究Ⅵ.邻苯二甲酰化壳聚糖中酰胺酸取代度对液晶性的影响

通过控制不同反应时间和邻苯二甲酸酐 壳聚糖的摩尔比制备不同取代度的邻苯二甲酰化壳聚糖(PHCS) .用FTIR研究了反应机理和产物结构 ,观察到PHCS含两类取代即酰胺酸取代和酰亚胺取代 .反应时间较短时主要为前者 ,取代度表示为DS1 ;反应时间较长时主要为后者 ,取代度表示为DS2 .对PHCS在二氯乙酸 (DCA)中的液晶行为观察 ,结果表明 ,PHCS的临界浓度随DS1 的增加而显著增加 .DS1 对PHCS临界浓度的影响明显大于DS2 的影响 .基本上为酰胺酸取代的PHCS的临界浓度高于溶解度 ,以至于观察不到     

邻苯二甲酰化壳聚糖的合成与溶致液晶表征

从全脱乙酰化壳聚糖出发,在室温下合成了一系列不同取代度的邻苯二甲酰化壳聚糖(PhCS),由于反应条件温和,产物未发生进一步的酰亚胺化.X射线电子能谱(XPS)被用来测定PhCS的取代度.测定结果表明在N上和O上均发生取代,N上反应的取代度随酸酐用量的增加基本保持不变(0.26±0.03),而O上的取代度却不断变大(0.01～1.54),合成产物的总取代度为0.26～1.81.邻苯二甲酰化壳聚糖可溶解于普通的有机溶剂,如DMSO、二氯乙酸和甲酸,并形成溶致液晶.测定了PhCS在这些溶剂中的临界浓度(c*),结果表明c基本上不受取代度变化的影响.     

邻苯二甲酰化壳聚糖的合成与溶致液晶表征

从全脱乙酰化壳聚糖出发,在室温下合成了一系列不同取代度的邻苯二甲酰化壳聚糖(PhCS),由于反应条件温和,产物未发生进一步的酰亚胺化.X射线电子能谱(XPS)被用来测定PhCS的取代度.测定结果表明在N上和O上均发生取代,N上反应的取代度随酸酐用量的增加基本保持不变(0.26±0.03),而O上的取代度却不断变大(0.01～1.54),合成产物的总取代度为0.26～1.81.邻苯二甲酰化壳聚糖可溶解于普通的有机溶剂,如DMSO、二氯乙酸和甲酸,并形成溶致液晶.测定了PhCS在这些溶剂中的临界浓度(c),结果表明c基本上不受取代度变化的影响.     

甲壳素类液晶高分子的研究Ⅳ.脱乙酰度对壳聚糖液晶性的影响

通过壳聚糖乙酰化法制备了不同脱乙酰度的壳聚糖 ,并研究了脱乙酰度这一结构因素对壳聚糖溶致液晶性的影响 .观察到脱乙酰度为 5 0 %左右时 ,壳聚糖在水中和二氯乙酸中的溶致液晶临界浓度最高 .壳聚糖在水中的溶致液晶临界浓度远低于在二氯乙酸中的临界浓度 .     

氰乙基羟丙基壳聚糖的溶致和热致液晶性研究

从壳聚糖出发先羟丙基化再氰乙基化,合成了氰乙基羟丙基壳聚糖(羟丙基的摩尔取代度为3.2,氰乙基的取代度为1.0).氰乙基羟丙基壳聚糖(CNHPCS)和羟丙基壳聚糖(HPCS)两者都有胆甾型溶致液晶性,浓溶液呈现指纹状织构.在二氯乙酸中,前者的临界浓度(29%,质量分数,下同)高于后者(17%).这一结果可以用引入氰乙基增加了分子间作用力从而使得链刚性增加来解释.CNHPCS在熔点193℃和分解温度220℃之间很窄的温区内观察到有热致液晶胆甾相.CNHPCS固体膜的胆甾相螺距采用激光小角光散射法测定,结果与偏光显微镜测得的数值一致.     

Studies on Lyotropic Liquid‐Crystalline N‐Alkyl Chitosans in Formic Acid

A series of derivatives of chitosan – N‐alkyl(methyl, ethyl, propyl and butyl) chitosans – were synthesized from completely deacetylated chitosan. The degree of substitution (from 0.15 to 0.81) of the N‐ethyl chitosan were obtained by controlling the molar ratio of the reactants. All the products showed lyotropic liquid‐crystalline properties regardless of the length of the side chains and the degree of substitution. The critical concentration (C*) of the samples were measured by both microscopy and refractometry. C* seemed not to vary with the degree of substitution (ds) in the case of a given subsitituent chain, but rose dramatically depending on the length of the substituent group as this was varied from methyl to butyl. The results were explained according to Flory's classical theory as well as experimental of X‐ray diffraction measurements.     

Cellulosic polyelectrolytes: synthetic pathways to regioselectively substituted ammonium and phosphonium derivatives

Cationic polysaccharide polyelectrolytes are important synthetic targets for drug and gene delivery, especially by encapsulation of nucleic acids and proteins through electrostatic interactions. They also have potential as paracellular permeability enhancers that may increase transport across the gastrointestinal (GI) epithelium, especially for therapeutic hydrophilic macromolecules. Semisynthetic chitosan has been more heavily investigated as a cationic polysaccharide polyelectrolyte. This study explores the synthetic conditions needed to produce ammonio and phosphonio cellulose derivatives regioselectively by halogen displacement at C-6 while maximizing the degree of substitution (DS) of cationic substituent. Regioselective substitution was successful, however there were found to be some limitations to the DS and solubility of ammonium derivatives prepared in this way (highest DS 0.43); conversely, water-soluble 6-phosphonio-6-deoxycellulose derivatives were produced with DS > 0.5, with highest DS of 0.73. The repulsion between accumulating positive charges was confirmed as a likely source of DS limitation since high DS (0.9) of 6-triethylamino cellulose was synthesized under comparable conditions. Further reaction of 6-ammonio-co-6-bromo derivatives with a thiol produced 6-ammonio-co-6-thiolated products with improved aqueous solubility. The thiol DS of 0.68 determined by elemental analysis confirmed substitution of residual bromide from low DS (0.30) ammonium products to give essentially complete substitution at C-6.     

NMR Characterization of Substituted Aromatic Poly (Ether Sulofone)s

Abstract

The synthesis of a variety of substituted bisphenol A polysulfones, including nitro, amino, aminomethyl, ethyl, and methyl derivatives, is described. Nuclear magnetic resonance (NMR) (both proton and carbon, and several 2-D experiments) data confirm conclusions on the substitution site based on arguments on inductive effects in the phenyl rings. The proton ortho to the oxygen in the bisphenol A (BPA) residue is replaced in electrophilic substitution reactions. The degree of substitution was also calculated from the NMR results. The ethyl and methyl derivatives were expected, from the starting reactants, to each have a BPA ring substituted. The NMR data showed that, on the average, this is true. The nitro derivative also has substitution in every BPA ring, while the amino and aminomethyl derivatives have only intermittent BPA rings substituted. Measured degrees of substitution (DS) varied from 0.11 to 2.25.     

Enthalpies of formation of monoderivatives of hydrocarbons: Interaction of polar groups with an alkyl group

Energies of hydrocarbon monoderivatives CH(3)X, C(2)H(5)X, n-C(4)H(9)X, and n-C(5)H(11)X with 16 different substituents X were calculated at the levels B3LYP/6-311+G(d,p) and B3LYP/AUG-cc-pVTZ//B3LYP/6-311+G(d,p). The results were used to test the validity of the additive rule that has served commonly for estimating the enthalpies of formation Delta(f)H(T). The exact additivity corresponds to zero reaction energy DeltaE of the isodesmic reaction, in which the substituent X is transferred from one alkyl group R to another. Additivity is approximately fulfilled for butyl and pentyl derivatives with the differences less than 0.3 kJ mol(-1) (except charged groups X). Methyl derivatives deviated from the additive rule up to 22 kJ mol(-1) for dipolar groups X and 45 kJ mol(-1) for charged group, in agreement with the available experiments and with the anticipation of all suggested empirical schemes. In addition, smaller deviations of ethyl derivatives (3 or 20 kJ mol(-1), respectively) were observed here for the first time. There is no correlation between the deviations of methyl and ethyl derivatives; they are also not related to steric effects, and only partly to polarization. Deviations of methyl derivatives are proportional to the electronegativity of the first atom of the substituent; even when the definition of electronegativity is somewhat questionable, one can say in any case that it is controlled by the first atom.     

Synthesis and Characterization of a Novel Liquid Crystalline Chitin — Quaternary Ammonium Chitosan Salt

N-Butyl chitosan(NBCS) derivatives were prepared by introducing butyl groups into the amine groups of chitosan via Schiff base intermediates. The quaternization of NBCS was carried out by using ethyl iodide to produce water-soluble cationic polyelectrolytes. The degree of the substitution of the products was measured by means of the electron spectroscopy for a successful chemical analysis. The quaternary ammonium chitosan salt(QACS) was proved to be a novel cholesteric liquid crystalline chitin, by means of the polarized optical microscopy and the circular dichroism spectropolarimetry. The critical mass fraction of the QACS/formic acid solution forming a lyotropic liquid crystal phase was 50%, which was almost the same as that of the NBCS/formic acid solution, but much hiuher than that of the chitosan in the same solvent.     

Synthesis and Crystallochromy of 1,4,7,10‐Tetraalkyltetracenes: Tuning of Solid‐State Optical Properties of Tetracenes by Alkyl Side‐Chain Length

We synthesized a series of 1,4,7,10‐tetraalkyltetracenes using a new 2,6‐naphthodiyne precursor and 2,5‐dialkylfurans as starting materials (alkyl=methyl to hexyl). Surprisingly, the solid‐state color of the tetracenes ranges through yellow, orange, and red. Both yellow and red solids are obtained for the butyl derivative. Optical properties in solution show no marked differences; however, those in the solid state show characteristics that vary with alkyl side‐chain length: methyl, propyl, and pentyl derivatives are orange; ethyl and butyl derivatives are yellow; and another butyl and hexyl derivative are red. X‐ray analyses reveal that the molecular structures are planar, semi‐chair, or chair forms; the chair form takes a herringbone‐like arrangement and the other forms take slipped parallel arrangements. The mechanism of crystallochromy is discussed in terms of molecular structure, crystal packing, and calculations that take account of exciton coupling.     

Preparation and properties of a new type of comb-shaped, amphiphilic cellulose derivative

Comb-shaped, amphiphilic O-(2- hydroxy-3-butoxypropyl) cellulose (HBPC) was prepared by a homogeneous reaction of cellulose with butyl glycidyl ether (BGE) in a 10% (w/w) LiCl--DMAc solution. It was found that: (a) the molar substitution (MS) of water-soluble HBPC ranges from 0.4 to 1.0, and is nearly equal to its degree of substitution (DS), indicating that the HBPC derivatives obtained are comb-shaped polymers; (b) the water-soluble HBPC shows a thermally reversible sol-gel transition in aqueous solution; and (c) the derivative having a DS of 0.6 shows surface activity with critical micelle concentration (cmc) in the order of 0.8 g/l and surface tension of 31.5 dyn/cm     

Modified amylose biodegradability by α-amylases

The site-selective syntheses of water-soluble (O-2/O-3)-substituted amylose derivatives containing butyl ester, carboxymethyl, succinyl or quaternary ammonium side groups was carried out. In addition, routine chemical methods which did not employ protection-deprotection steps provided water soluble (O-2/O-3/O-6)-substituted products. The biodegradation of these products as a function of site-of-substitution and degrees of substitution (ds) was studied by the α-amylases from Aspergillus oryzae and Bacillus subtilis. Consistent with the results reported previously for acetyl amylose (Ref. 1), the O-2/O-3 substituted butyl amylose derivatives degraded faster and to higher percentages than the corresponding O-2/O-3/O-6 substituted derivatives. Also, the overall rates and percentages of degradation for butyl amylose were much lower than acetyl amylose derivatives of comparable degree and site of substitution. Therefore, for the two enzymes studied, the introduction of longer chain length acyl side groups greatly reduced substrate degradability. For the charged derivatives, the rate and percentage of degradation decreased in the order carboxymethyl > succinyl > quaternary ammonium at comparable degree and site of substitution. We concluded that, as the length of the charged side chain substituent increased, the rate and extent of biodegradation decreased. Furthermore, in contrast to the results for neutral acetyl and butyl side groups, there was no significant difference in the rate and %-degradation for charged side chain substituent groups when comparing O-2/O-3 and O-2/O-3/O-6-substituted derivatives. Finally, the introduction of anionic or cationic side chain groups resulted in decreased susceptibility to α-amylase catalyzed chain cleavage when compared to similarly substituted acetyl and butyl amylose derivatives.     

Radical copolymerization of alkyl 2‐norbornene‐2‐carboxylate with alkyl acrylates: Facile incorporation of norbornane framework into poly(alkyl acrylate)s

Radical copolymerization of alkyl 2‐norbornene‐2‐carboxylates (alkyl = Me 1a , nBu 1b ) with alkyl acrylates (alkyl = ethyl, methyl, and n‐butyl) was investigated. Copolymerization of 1a,b with the alkyl acrylates initiated by 1,1′‐azobis (cyclohexane‐1‐carbonitrile) at 85 °C proceeded to give random copolymers, although the homopolymerization of 1a,b did not proceed efficiently under the same conditions. Typically, bulk copolymerization of 1a with ethyl acrylate in a feed ratio of 1:3 ([ 1a ]:[EA]) afforded a copolymer with M_n = 33,300 containing 19.4 mol % of 1a unit in the composition. An increase of T_g derived from the incorporation of the rigid norbornane framework was observed, although the extent of the temperature rise was rather moderate. The ternary radical copolymerization of 1a,b /alkyl acrylate/N‐phenylmaleimide proceeded to give copolymers with the three repeating units in the main chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4597–4605, 2007