Photochromic Dihetarylethenes: XX. Synthesis and Photochromic Properties of Dithienylethenes with a Fixed Conformation

>A procedure was developed for the synthesis of bis(2,5-dimethyl-3-thienyl)ethenes with partially fixed molecular conformation, and their photochromic properties in solution were studied. The structure of photochromic 1-(2,5-dimethyl-3-thienyl)-7,9-dimethyl-5,6-dihydrothieno[3',4' : 3,4]pyrido[1,2-c][1,3]oxazol-3-one, as well as of 1-(2,5-dimethyl-3-thienyl)-7,9-dimethylthieno[3',4' : 3,4]pyrido[1,2-c][1,3]oxazol-3-one possessing no photochromic properties, was determined by X-ray analysis.     

Fundamental Change in the Nature of Chemical Bonding by Isotopic Substitution

Isotope effects are important in the making and breaking of chemical bonds in chemical reactivity. Here we report on a new discovery, that isotopic substitution can fundamentally alter the nature of chemical bonding. This is established by systematic, rigorous quantum chemistry calculations of the isotopomers BrLBr, where L is an isotope of hydrogen. All the heavier isotopomers of BrHBr, BrDBr, BrTBr, and Br⁴HBr, the latter indicating the muonic He atom, the heaviest isotope of H, can only be stabilized as van der Waals bound states. In contrast, the lightest isotopomer, BrMuBr, with Mu the muonium atom, alone exhibits vibrational bonding, in accord with its possible observation in a recent experiment on the Mu+Br₂ reaction. Accordingly, BrMuBr is stabilized at the saddle point of the potential energy surface due to a net decrease in vibrational zero point energy that overcompensates the increase in potential energy.     

一种逆向光致变色螺吡喃化合物的光消色关环反应机理研究

研究了逆向光致变色化合物１′－十八烷基－３′，３′－二甲基－６，８二硝基螺［２Ｈ－１－苯并吡喃－２，２′－吲哚啉］的可见光消色机理。通过吸收光谱测定其在不同溶剂及含不同添加剂时，可见光照射后有色体［ＭＣ］关环的光量子产率。结果表明Ｏ２、三苯基胺等三线态猝灭剂对关环反应光量子产率几乎没有影响。据此提出关环反应主要是通过单线态的途径进行的结论。     

Energy Surface and Conformation Dynamics of Molecules

The topology of energy surfaces and the dynamics of conformationally-labile molecules are discussed. A base model is introduced for an ideal lattice on a multidimensional torus for the energy level surfaces of rotational-isomeric chains. Specific features of the dynamics of molecules of various types are discussed, together with the problems of the formation of a three-dimensional structure and the link between the conformational mobility and the chemical act of reactions.     

Ultrafast Dynamics of the Transoid-cis Isomer Formed in Photochromic Reaction from 3H-Naphthopyran

Recent efforts in designing new 3H-naphthopyran derivatives have been focused on efficient coloration process with a short fading time of the colored transoid-cis TC isomer. It is desirable to avoid photoisomerization of TC leading to transoid-trans TT isomers in the photoreaction. Long lifetime of TT can hamper fast applications such as dynamic holographic materials and molecular actuators, the residual color is one of the serious issues for photochromic lenses. Herein we characterize the photophysical and photochemical channels of TC excited state deactivation competing with the unwanted TC → TT isomerization process. Transient absorption spectroscopy reveals a very short lifetime of the singlet excited TC (≈0.8 ps) and its deactivation channels as S₁→S₀ internal conversion (major), intersystem crossing S₁→T₁, pyran ring formation, photoenolization and TC → TT isomerization. Computations support the S₁→S₀ and T₁→S₀ channels as responsible for photostabilization of the TC form.     

碱性溶液中甲醇分子诱导的肌血球素构象变化

考察了不同pH值的碱性溶液中甲醇分子对诱导肌血球素构象变化的影响. 电喷雾电离质谱(ESI-MS)测量结果表明, 当pH分别为11.0, 11.4, 12.0时, 不同体积分数的甲醇(30%, 50%, 70%及90%)和水混合溶液将诱导肌血球素的构象变化. 当pH=11.0时, 肌血球素在溶液中均以hMb为主要形态存在(即血红素稳定存在于肌红蛋白中); 当pH=11.4时, 30%甲醇中的肌血球素仍以hMb为主, 但升高甲醇比例会导致hMb上的辅基脱落生成aMb(蛋白质分子); 当pH=12.0时, 溶液中的肌血球素均以aMb为主. 但当应用负离子质谱测量模式时, 检测出的肌血球素负离子均以aMb构象为主. 同时采用圆二色谱(CD)及紫外-可见(UV-Vis)光谱等研究发现, pH值和甲醇含量分别决定蛋白质分子的二级和三级结构的变化.     

Cyclization Dynamics and Competitive Processes of Photochromic Perfluorocyclopentene Dithienylethylene in Solution

Time-resolved absorption spectroscopy measurements were performed to study the dynamics of photochromic 1,2-Bis(2,4-dimethylthiophene-3-yl)perfluoro-cyclopentene (DMTPF) in chloroform, including antiparallel conformer ring-closure reaction and parallel conformer photophysics. All characteristic times are given, discussed and compared to a previous publication concerning the close molecule substituted with phenyl rings. (Hamdi et al., PCCP, 2016). Apart from the expected photocyclization process, condensed ring by-product formation is observed and hypotheses concerning the origin of this by-product are presented.     

Exocyclic Substitution of Five-Membered Ring Chlorophosphates: A Reexamination of the rule For Nucleophilic Substitution at Phosphorus

Abstract

Opposite to the SN²(P) reactions taking place with inversion, which are highly dependent upon the nature of the nucleophile, exocyclic substitutions of five-membered ring chlorophosphates with retention show a marked kinetic levelling effect, emphasing silicon-type argumentations.     

Synthesis of Aromatic Polythioethers Containing 1,3,5-Triazine Ring by Aromatic Nucleophilic Substitution Polymerization

Abstract

Reaction of 2,4-dichloro-6-phenyl-1,3,5-triazines with bis(4-mercaptophenyl) sulfide in the presence of a base in THF afforded the corresponding condensation polymer as a whole aromatic polythioether in moderate yield. The polymerization of several 2,4-dichloro-1,3,5-triazine derivatives with this dithiols also proceeded in the o-dichlorobenzene-water two-phase system by using phase transfer catalysts. The resulting polymers consisted of THF-soluble and -insoluble fractions. The x-ray diffraction pattern indicated that these THF-insoluble polymers have a highly crystalline nature. Further, the polymers obtained here showed high thermal stability.     

Conformation Control of Conjugated Polymers

In the past few decades, conjugated polymers have aroused extensive interest in organic electronic applications. The electrical performance of conjugated polymers has a close relationship with their backbone conformation. The conformation of the polymer backbone strongly affects the πelectron delocalization along polymer chains, the energy band gap, interchain interactions, and further affects charge transport properties. To realize a rigid coplanar backbone that usually possesses efficient intrachain charge transport properties and enhanced π–π stackings, such conformation control becomes a useful strategy to achieve high-performance (semi)conducting polymers. This minireview summarizes the most important polymer structures through conformation control at the molecular level, and then divides these rigid coplanar conjugated polymers into three categories: 1) noncovalent interactions locked conjugated polymers; 2) double-bond linked conjugated polymers; 3) ladder conjugated polymers. The effect of the conformation control on physical nature, optoelectronic properties, and their device performance is also discussed, as well as the challenges of chemical synthesis and structural characterization.     

酶联免疫分析法探测Cry1Ab蛋白在不同介质中的构象变化

采用酶联免疫分析（ELISA）方法,根据构象变化后的蛋白与抗体结合能力下降从而导致ELISA测定值降低的原理,探测了转cry1Ab基因水稻表达的Cry1Ab蛋白在不同溶液介质中的热致构象变化行为,以及不同有机溶剂及溶液pH值对该蛋白构象变化的影响程度。实验表明,Cry1Ab蛋白在不同条件下的构象变化程度可以灵敏地通过ELISA方法检测。在不同的介质中,CrylAb蛋白的热致构象变化程度不同。在Na2SO4介质中,该蛋白具有较高的热稳定性;SDS的存在,可以促进该蛋白的构象变化。常温下,25％（V／V）的有机溶剂乙腈、异丙醇、甲醇、乙醇均能使该蛋白的构象发生转变,其中以乙腈最为显著。醇类溶剂对Cry1Ab蛋白的构象影响程度随疏水性增大而增大;溶液pH值也对该蛋白的构象变化产生影响。pH在8-10之间,该蛋白构象能保持稳定;酸或过碱性的溶液均能使蛋白构象偏离原始状态,从而引起ELISA测定值的降低。另外,腐殖酸能在一定时间内保持Cry1Ab蛋白构象的稳定性。     

单嘧磺隆晶体-活性构象转换的分子动力学模拟

应用分子动力学模拟方法对单嘧磺隆在水、正辛醇和正辛烷3种不同溶剂中的构象行为、单嘧磺隆与3种溶剂之间的相互作用能及氢键相互作用进行了计算研究. 计算结果表明, 在3种不同的溶剂中, 单嘧磺隆的优势构象不同; 其构象转换过程, 特别是转换成活性构象的过程主要发生在水溶液中; 与溶剂分子间的相互作用是分子构象行为的决定因素; 单嘧磺隆的脲桥部分可以和含氢键接受体的溶剂形成氢键, 分子间与分子内氢键的竞争可能是从晶体构象转换成活性构象的主要驱动力.     

可改变DNA构象的非离子糖基表面活性剂

通过Zeta电位及粒径分析考察发现随着体系中辛基葡萄糖多苷表面活性剂质量 农度的增加，DNA分子在溶液中的构趋于缩拢。通过DNA-C_8APG复合物的UV吸收及 CD谱图进一步考察了DNA二级结构变化。随后的扫描电子显微镜（SEM）照片也证实 DNA分子在水溶液中的构象缩拢。通过表面张力UV图谱分析，推测非离子糖基表面 活性剂与DNA分子复合物结合的可能结构是表面活性剂与DNA之间的疏水作用及 多羟基的糖类的亲水头基结构与DNA带负电的核酸磷酸骨架以氢健的方式结合。     

压力诱导溶液中蛋白质构象变化的谱学研究

高压诱导蛋白质发生构象变化,引起蛋白质去折叠,并在某种条件下发生聚集,其结果是蛋白质原有的构造被破坏、发生变性。这些过程与蛋白质本身的结构密切相关。同时,折叠中间体结构的揭示对于研究蛋白质去折叠过程也具有重要意义。本文综述了高压诱导下多种谱学方法用于蛋白质构象变化的研究进展,主要包括高压红外光谱、高压荧光光谱及高压小角X射线扫描等多种技术手段在研究中蛋白质构象变化方面所能提供的重要信息,并对相关领域存在的问题及今后的发展作出展望。