Fmoc-FF二肽分子自组装过程的分子动力学研究

采用分子动力学方法模拟研究了Fmoc-FF二肽分子在溶液中的自组装过程,探究了自组装过程中的驱动力及水桥结构对聚集体稳定性的影响.结果表明,Fmoc-FF二肽分子可以在水溶液中自组装形成结构规整的圆柱形纳米棒;根据Fmoc环间的径向分布函数,通过比较二肽分子之间及二肽分子与水分子间的相互作用,推测二肽分子间的π-π相互作用是自组装过程的主要驱动力;另外的驱动作用体现在二肽分子与水分子之间形成的氢键,其中水分子以水桥结构连接不同的二肽分子,这种水桥结构对自组装结构具有稳定作用.     

Fmoc和Boc双取代赖氨酸环二肽的合成及其凝胶化性能研究

以Boc-Lys(Cbz)-OH为原料首先合成出赖氨酸环二肽, 进而再分别与Fmoc-OSu和(Boc)₂O反应得到Fmoc和Boc双取代赖氨酸环二肽. 发现这两种赖氨酸环二肽衍生物在常见醇类、甲苯和氯代溶剂中能形成稳定的热可逆凝胶, 最低凝胶化浓度(MGC)范围为1%～5% (w). 凝胶的储存模量均高于损耗模量, 并且复合粘度在频率扫描范围内呈线性降低趋势. 电镜分析表明, 凝胶因子在不同溶剂中可自组装成微纳米纤维网络结构, 纤维直径越细, 凝胶透明度越高. 红外和荧光光谱分析表明在自组装的过程中氢键主要在甲苯和氯代溶剂中发挥驱动力的作用, π-π堆积主要在醇类溶剂中起作用. 核磁氢谱测试表明来自凝胶因子骨架上酰胺和侧链上氨酯基中的氢键共同参与了凝胶化过程.     

基于横向分子间氢键的棒-线型分子自组装研究进展

棒-线(Rod-Coil)型分子的合成及其自组装行为研究是当前超分子材料研究领域的重要研究方向. 与传统的柔性(Coil-Coil)型嵌段聚合物和Rod-Coil型嵌段聚合物相比, Rod-Coil型分子表现出不同的相行为、自组织特性和微结构, 可以自组装形成多种纳米结构. 研究结果显示, 横向分子间氢键是Rod-Coil型分子自组装形成液晶相和(或)有机凝胶等自组装体的主要驱动力. 主要介绍目前文献报道的横向分子间氢键驱动下的Rod-Coil型分子自组装.     

由自组装构筑蛋白酶响应性近红外/磁共振双显影微球

由分子侧链上修饰近红外荧光分子的聚赖氨酸及表面聚丙烯酸修饰的磁共振显影磁性纳米颗粒为组装单元,采用自组装法构筑了在近红外、磁共振双重显影中均具有蛋白酶响应性的纳米尺度自组装微球.微球形成的组装驱动力为聚赖氨酸侧链氨基与磁性纳米颗粒表面羧基在水相中的静电相互作用,两类组装前驱体在静电力作用下组装为纳米尺度团聚体,再通过戊二醛对氨基的适度交联来构筑胰蛋白酶响应的双显影复合微球.该复合微球处于自组装聚集状态时,微球内近红外荧光分子间的距离减小从而发生荧光共振能量转移,导致荧光分子的自淬灭;而在胰蛋白酶活化后的解组装状态,微球内聚赖氨酸重复单元间的酰胺键被胰蛋白酶切断,荧光分子间距扩大,共振能量转移现象消失,从而导致复合微球在胰蛋白酶存在下释放荧光,荧光释放强度/淬灭强度的比值最高可达18.此外,自组装微球的磁共振显影同样具有胰蛋白酶敏感性,这与组装—解组装过程导致微球内磁性纳米颗粒的局部浓度及聚集状态发生变化有关.细胞和动物实验研究表明,复合微球呈现低细胞毒性,并可特异性地对胰蛋白酶阳性的细胞和组织进行近红外/磁共振双显影,在胰蛋白酶的生物影像学检测中具有潜在的应用前景.     

环芳酰胺的合成及自组装行为

本文主要综述了近年来由三中心氢键和远程位阻效应促进的环芳酰胺合成,以及利用该类化合物进行自组装行为的研究进展. 在研究一步高效成环的基础上,对合成不同孔径刚性大环的方法进行了探讨. 改变大环周边侧链的性质可以调控这类大环分子的自组装行为. 最后对环芳酰胺的应用进行了简单介绍     

用于氢键组装的星形光电材料的合成与表征

合成了一系列具有光电活性的星状共轭分子, 并在端基上引入了不同个数或不同类型的氢键基团. 包括端基上分别带有1, 2和3个羧酸基团的星状芴分子, 以及结构更为刚性的3个端基均为2,4-二胺基三嗪环的三聚茚分子, 以此形成一个系列的分子结构, 便于进行系统性研究. 同时我们对这些星状分子进行了紫外和荧光光谱的表征, 发现星状核和长烷基侧链能有效地阻止分子间π-π堆积和增大固态薄膜的无定形态. 最终这些功能性分子将有望由氢键诱导在石墨或者金属表面形成有序的自组装结构.     

金纳米棒自组装的研究进展

金纳米棒具有独特的光电性能,其自组装形成的功能组装体能够展现出更加优异的整体协同性能,在纳米材料科学和生物医学领域中有广泛而重要的应用前景.本文从诱导自组装各种驱动作用力的角度,综述了金纳米棒自组装的最新研究进展,具体内容包括:表面张力引发的自组装、化学作用驱动如静电作用或氢键作用等引发的自组装以及生物分子识别作用引发的自组装.     

二元组装体集群时的高选择性杂化重组行为

多样性自组装体在混合时,通常表现出互不干扰的自分类性,能高度选择性地自分类堆积.但结构极为相似的组装子在相互混合时,会发生交互作用并表现出重组现象.文中合成和观测了具有芳香环边墙和不同酰胺侧链的C型甘脲分子夹为组装单元的混合组装行为.研究发现,此类分子在各自以单一态物质溶解于CDCl3时,能通过π-π相互作用和氢键形成二聚自组装体;若将两种具有不同酰胺侧链的C型甘脲分子夹两两混合,从理论上推测应有三种二聚自组装堆积态存在：A·A、B·B、A·B.但经1HNMR分析发现了一个有趣的现象,即当酰胺侧链上的取代基R′分别为具有C-H结构（如1和2）与PhF5基（5）的组装体两两混合时,二聚组装主要呈现出高度选择性杂化重组的A·B结构态.这种取代基控制的高选择性重组行为可能是基于π-π相互作用、N—H…O氢键,以及C—H…π等三重作用力的协同结果.     

固相合成法制备组氨酸-苯丙二肽及其自组装研究

本文以组装性能良好的苯丙氨酸二肽(FF)为母体分子,用组氨酸对其进行化学修饰,通过多肽固相合成法合成了组氨酸-苯丙二肽(HisFF)凝胶因子。合成的HisFF分子通过质谱(MS)、核磁共振(NMR)和液相色谱(HPLC)方法测试确定精确的结构和纯度。HisFF聚集体的形貌结构通过透射电子显微镜(TEM)和扫描电子显微镜(SEM)观察。HisFF分子在甲苯、氯仿和乙酸乙酯溶剂中形成凝胶强度不同,TEM实验结果表明纤维强度和聚集形态影响其凝胶的强度。组氨酸-苯丙二肽在多种溶剂中,通过不同组装方法可以组装成各种各样的纳米结构。例如,HisFF在丙酮、甲醇和乙酸乙酯溶剂中可组装成纳米颗粒、纳米管和螺旋状纳米纤维;组氨酸-苯丙二肽先经HFIP溶解再通过溶剂稀释后,可得到不同直径的纳米纤维。但是在四氢呋喃、乙醇和乙腈溶剂中,两种方法组装的形貌几乎无变化。     

碱基腺嘌呤与多肽酰胺间氢键作用的最佳位点

正确理解核酸碱基和蛋白质多肽间的作用机制有助于人们利用这些生物分子有效地进行分子设计,进而制备具有特殊纳米结构和功能的生物分子材料.本文优化得到了碱基腺嘌呤与N-甲基乙酰胺、甘氨酸二肽、丙氨酸二肽形成的20个氢键复合物的结构并计算了结合能,探讨了腺嘌呤与多肽酰胺间氢键作用的最佳位点.研究发现:腺嘌呤可以使用两个不同位点(A1位点和A2位点)与N-甲基乙酰胺形成N―H…N型或者N―H…O=C型氢键复合物,腺嘌呤使用A1位点与N-甲基乙酰胺形成的N―H…N型氢键复合物更稳定;二肽分子可以使用主链上两个不同位点(丙氨酸的Ala7位点和Ala5位点或者甘氨酸的Gly7位点和Gly5位点)与腺嘌呤形成含有N―H…N和N―H…O=C两条氢键的复合物,二肽分子使用Ala7或Gly7位点与腺嘌呤形成的氢键复合物更稳定;腺嘌呤与多肽间的氢键作用强于其与N-甲基乙酰胺的作用.基于分子中的原子理论与自然键轨道计算结果分析了氢键作用的本质.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Synthesis of pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles by Curtius reaction in Morita-Baylis-Hillman derivatives

Synthesis of substituted pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles from the Morita-Baylis-Hillman derivatives of acrylates via saponification followed by Curtius reaction is described.     

正丁胺对激光染料荧光谱影响的研究

用正丁胺作为碳源,采用射频辉光放电制备碳膜,选用激光染料R6G和聚乙二醇混合液作为蒸气源,采用单源热蒸发,在蒸发室与染料同时沉积得到混合膜,用拉曼光谱和红外光谱分析了碳膜的结构和键合方式,分析表明:碳膜中存在胺基团和氢原子.混合膜的荧光谱测量结果表明,认为正丁胺对染料荧光谱的影响是因为胺基和氢原子的存在.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.