水杨酰苯胺衍生物分子内电荷/质子转移荧光

将苯甲酰苯胺(BA)类电荷转移(CT)反应基团耦合到具有激发态分子内质子转移(ESIPT)反应通道的水杨酸(SA)分子中,设计合成了苯胺对/间位取代的水杨酰苯胺及其羟基甲基化衍生物邻甲氧基苯甲酰苯胺,考察了环己烷、乙醚、乙腈和甲醇中两类水杨酰苯胺衍生物吸收光谱和荧光光谱的溶剂效应和取代基效应.结果表明,水杨酰苯胺的荧光为SA-型质子转移(PT)荧光,对取代基的依赖性较小;当电子给体苯胺基的给电子能力提高时,如N-甲基水杨酰苯胺分子,其荧光为BA-型CT荧光.而羟基甲基化后的衍生物邻甲氧基苯甲酰苯胺则表现出与BA类似的荧光光谱特性,具有明显的取代基效应.认为水杨酰苯胺衍生物的激发态存在着相互竞争的BA-型CT和SA-型PT通道,二者可经苯胺基上取代基的电子效应调控.     

酞菁锌高效催化以二氧化碳、含氢硅烷和有机胺为原料合成甲酰胺类衍生物

目前为了有效地利用好CO2,主要策略有以下几种:(1)"水平途径"——无价态及能量变化,譬如生成尿素、环状碳酸酯、聚碳酸酯及噁唑烷酮类衍生物等;(2)"垂直途径"——有价态及能量变化,譬如直接加氢转化成碳一产品(甲酸、甲醛、甲醇、甲烷)等;(3)"对角线途径"——有价态及能量变化,即结合石油化工原料将CO2还原生成醇、醚、羧酸、亚胺、酰胺、酯等系列高附加值的精细有机化工产品.其中以二氧化碳和含氢硅烷为原料,通过有机胺的N-甲酰化反应合成甲酰胺类衍生物符合绿色化学和可持续发展的要求.基于仿生催化CO2分子活化的基本理论,我们借鉴强极性的有机溶剂可有效活化硅氢键的性质,创新性地将廉价易得的酞菁锌(ZnPc)作为类酶催化剂,并以化学计量的N,N'-二甲基甲酰胺(DMF)为添加剂,构成组分新颖并高效绿色的类酶协同催化体系,实现了在温和反应条件下高效高选择性地合成甲酰胺类衍生物.研究发现:以苯硅烷作为还原剂,当加入0.5 mol%ZnPc和2 mmol DMF,在25℃和0.5 MPa下仅需反应6 h,可得到收率为99%的N-甲基甲酰苯胺.更值得注意的是,当以更易得的聚甲基氢硅烷(PMHS)为还原剂时,加入5 mol%ZnPc和1 mL DMF,在80℃和1 MPa下反应8 h,N-甲基甲酰苯胺的收率也高达99%.实验结果表明:添加剂DMF可以通过溶剂化和强极性作用高效活化含氢硅烷中的Si?H键,然后具有亲电性的金属活性中心能够稳定氢负离子生成高活性锌氢中间体.即ZnPc/DMF之间的协同催化作用能够促进氢化物从含氢硅烷转移到CO2分子,进而有利于CO2分子的高效活化.综上所述,利用类酶催化剂反应专一性的特点,通过有机胺的N-甲酰化反应,实现了以CO2和含氢硅烷为原料在温和条件下甲酰胺类衍生物的绿色高效合成.这对于设计和开发更加高效的催化体系具有一定的指导作用和借鉴意义.     

酞菁锌高效催化以二氧化碳、含氢硅烷和有机胺为原料合成甲酰胺类衍生物（英文）

目前为了有效地利用好CO_2,主要策略有以下几种:(1)"水平途径"——无价态及能量变化,譬如生成尿素、环状碳酸酯、聚碳酸酯及噁唑烷酮类衍生物等;(2)"垂直途径"——有价态及能量变化,譬如直接加氢转化成碳一产品(甲酸、甲醛、甲醇、甲烷)等;(3)"对角线途径"——有价态及能量变化,即结合石油化工原料将CO_2还原生成醇、醚、羧酸、亚胺、酰胺、酯等系列高附加值的精细有机化工产品.其中以二氧化碳和含氢硅烷为原料,通过有机胺的N-甲酰化反应合成甲酰胺类衍生物符合绿色化学和可持续发展的要求.基于仿生催化CO_2分子活化的基本理论,我们借鉴强极性的有机溶剂可有效活化硅氢键的性质,创新性地将廉价易得的酞菁锌(Zn Pc)作为类酶催化剂,并以化学计量的N,N’-二甲基甲酰胺(DMF)为添加剂,构成组分新颖并高效绿色的类酶协同催化体系,实现了在温和反应条件下高效高选择性地合成甲酰胺类衍生物.研究发现:以苯硅烷作为还原剂,当加入0.5mol%Zn Pc和2 mmol DMF,在25 ℃和0.5 MPa下仅需反应6 h,可得到收率为99%的N-甲基甲酰苯胺.更值得注意的是,当以更易得的聚甲基氢硅烷(PMHS)为还原剂时,加入5 mol%Zn Pc和1 mL DMF,在80 ℃和1 MPa下反应8 h,N-甲基甲酰苯胺的收率也高达99%.实验结果表明:添加剂DMF可以通过溶剂化和强极性作用高效活化含氢硅烷中的Si-H键,然后具有亲电性的金属活性中心能够稳定氢负离子生成高活性锌氢中间体.即Zn Pc/DMF之间的协同催化作用能够促进氢化物从含氢硅烷转移到CO_2分子,进而有利于CO_2分子的高效活化.综上所述,利用类酶催化剂反应专一性的特点,通过有机胺的N-甲酰化反应,实现了以CO_2和含氢硅烷为原料在温和条件下甲酰胺类衍生物的绿色高效合成.这对于设计和开发更加高效的催化体系具有一定的指导作用和借鉴意义.     

溶剂对聚酰胺-胺树形分子模板法原位制备CdS量子点的影响

为了研究非配位型溶剂对聚酰胺-胺(PAMAM)树形分子的模板法制备CdS量子点的影响, 分别以水、甲醇及二者的混合物( ∶ ＝2∶1)为溶剂, 以4.5代PAMAM树形分子为模板制备了CdS量子点. 结果表明, 相同条件下, 以甲醇为溶剂时制备的CdS量子点为单晶, 平均直径2.7 nm, 尺寸分布窄, 发光强度高; 以水为溶剂制备的CdS量子点为多晶, 平均直径为5.7 nm, 尺寸分布宽, 发光强度低; 在甲醇与水的混合溶剂中制备的CdS量子点为单晶和多晶共存, 平均直径为4.1 nm, 尺寸分布及发光强度都居中. 这主要是由于树形分子的模板作用不同造成的. 树形分子在甲醇中能充分伸展, 起到内模板作用; 树形分子与水之间由双氢键作用而产生交联, 不利于Cd^2＋与树形分子内部基团的配位, 主要起到外模板作用; 在甲醇与水的混合溶剂中, 树形分子则同时起到了内模板和外模板作用.     

甲醇和氨对腺嘌呤水解脱氨机理的影响(英文)

用密度泛函理论在B3LYP/6-311G(d,p)水平上研究了甲醇和氨辅助的腺嘌呤水解脱氨机理,结果表明该反应首先是在水的亲核进攻下形成一个四面体结构中间体,然后该中间体通过构象变化得到两个不同构象,从而找到两条不同反应路径.在路径a中,辅助分子参与了过渡态的形成,起到转移氢原子的作用;而在路径b中,辅助分子仅作为介质,没有参与过渡态的形成.在氨辅助的情况下,腺嘌呤在亲核反应前发生了胺-亚胺异构化,而在甲醇辅助机理中则未发生该异构化.能量结果表明甲醇辅助腺嘌呤脱氨反应具有与水辅助类似的势垒,而氨辅助反应的势垒则比水辅助的高.     

N-(末端三丁基锡取代基)酰亚胺的光诱导单电子转移成环反应

合成了两种新的分子内给受电子体系N-[2-(2-三丁基锡甲硫基)乙基]邻苯二甲酰亚胺(1a)和N-(3-三丁基锡丙基)马来酰亚胺(1b),并在甲醇、乙腈-30%水、乙腈中进行了光诱导单电子转移反应.化合物1a在光诱导下发生分子内单电子转移反应,以很高的产率和区域选择性生成环胺醇2.化合物1b在光诱导下发生分子内单电子转移反应生成环胺醇3,同时有[2+2]环加成副反应产物4生成.以上所有新化合物的结构经质谱和核磁共振谱验证.     

曙红与卟啉分子间和分子内的光致相互作用

合成了以半刚性链(一CH_2phCH_2—)和柔性链(—(CH_2)_4—)连接的曙红-卟啉二元化合物及其模型化合物.通过吸收光谱、荧光光谱、激发光谱及荧光寿命研究了模型化合物分子间的相互作用和二元化合物分子内的光致电子转移和能量传递.结果表明:二元化合物的模型化合物曙红乙酯和卟啉易形成基态复合物 在二元化合物分子内激发曙红时,曙红能将其单重态能量传递给卟啉,并能引发分子内的电子转移;激发卟啉时,能发生曙红向卟啉的电子转移.分析了分子构型和溶剂极性对2种过程的影响.     

PNIPA和PDEA在水-甲醇混合溶剂中性质的研究

分别研究了聚N-异丙基丙烯酰胺（PNIPA）和聚N,N-二乙基丙烯酰胺（PDEA）在水-甲醇混合溶剂中的溶液性质.结果表明,在PDEA和PNIPA体系中均存在水和甲醇分子之间的复合.由于PDEA比PNIPA的亲脂性强,在水-甲醇混合溶剂中,水与甲醇分子形成的复合物对PDEA和PNIPA的溶剂化作用不同,导致随着体系中甲醇体积分数（φ）的增大,PNIPA体系的低临界溶解温度（TLCS）发生了再进入相转变,而PDEA体系的TLCS则逐渐升高.     

苝醌/富勒烯C60超分子与电子给体的电子转移作用

利用紫外-可见吸收光谱、瞬态吸收光谱及X射线衍射等方法研究了苝醌染料竹红菌素镁离子配合物(Mg2+-HA)与富勒烯C60的相互作用. 结果表明, Mg2+-HA与C60在溶液和固体状态下都能够形成稳定的超分子. Mg2+-HA存在条件下, C60能够溶于多种极性溶剂, 在二甲基亚砜(DMSO)中的溶解度能够达到1×10^-4 mol·L^-1. 作为超分子体系中的光捕获分子, Mg2+-HA能显著地提高C60与N,N-二甲基苯胺(DMA)的光诱导电子转移反应效率, 生成的C60负离子自由基的电子自旋共振光谱(ESR)信号强度比未加入Mg2+-HA时增强了9倍左右.     

溶剂效应和取代基效应对2-(2-氨基苯基)苯并噻唑光谱性质及激发态分子内质子转移的影响

合成了多种2-(2-氨基苯基)苯并噻唑(APBT)氨基氢原子被供电子及吸电子基团取代的衍生物, 并用紫外光谱﹑荧光光谱等方法和密度泛函理论(DFT)计算研究了溶剂效应和取代基效应对衍生物的光谱性质及激发态分子内质子转移(ESIPT)的影响规律. 结果表明, 相比于非极性溶剂环己烷, 随溶剂极性的增加及APBT-溶剂分子间氢键的形成, APBT的紫外-可见最大吸收峰和荧光最大发射峰均发生了一定程度的红移, 并对APBT的ESIPT产生了影响. 在APBT分子的氨基氮原子上引入不同的吸电子或斥电子取代基, 对氮原子的电荷性质有较大的影响. 在环己烷溶剂中, 甲基取代后的APBT仅有单重荧光发射峰, 体系未发生ESIPT过程; 而COCH₂Cl等吸电子基团能促进APBT的ESIPT, 其荧光发射光谱出现了明显的双重峰, 表明体系发生了激发态分子内质子转移反应. 量子化学的理论计算较好地验证了光谱实验结果.     

On the relative strengths of amide…amide and amide…water hydrogen bonds

We have performed Hayes—Stone intermolecular perturbation theory (IMPT) calculations on amide…water and amide…amide complexes in order to estimate the change ΔW in intermolecular interaction energy associated with the hydrogen bond exchange process amide(NH)…water+water…(OC)amideamide(NH)…(OC)amide+water…water. ΔW is found to be small and varies by almost 5 kJ/mol and in sign for the amides formamide, acetamide, N-methyl formamide and N-methyl acetamide. The main variations in the amide hydrogen bond energies occur in the electrostatic and exchange-repulsion contributions. This reflects the variation in the charge distributions of the hydrogen bonding groups between the different amides. Thus, we cannot quantify an isolated hydrogen bond strength with any great accuracy, and care must be used in extrapolating model potentials based on small model systems to peptides and proteins.     

Liquid structures of water, methanol, and hydrogen fluoride at ambient conditions from first principles molecular dynamics simulations with a dispersion corrected density functional

Using first principles molecular dynamics simulations in the isobaric-isothermal ensemble (T = 300 K, p = 1 atm) with the Becke-Lee-Yang-Parr exchange/correlation functional and a dispersion correction due to Grimme, the hydrogen bonding networks of pure liquid water, methanol, and hydrogen fluoride are probed. Although an accurate density is found for water with this level of electronic structure theory, the average liquid densities for both hydrogen fluoride and methanol are overpredicted by 50 and 25%, respectively. The radial distribution functions indicate somewhat overstructured liquid phases for all three compounds. The number of hydrogen bonds per molecule in water is about twice as high as for methanol and hydrogen fluoride, though the ratio of cohesive energy over number of hydrogen bonds is lower for water. An analysis of the hydrogen-bonded aggregates revealed the presence of mostly linear chains in both hydrogen fluoride and methanol, with a few stable rings and chains spanning the simulation box in the case of hydrogen fluoride. Only an extremely small fraction of smaller clusters was found for water, indicating that its hydrogen bond network is significantly more extensive. A special form of water with on average about two hydrogen bonds per molecule yields a hydrogen-bonding environment significantly different from the other two compounds.     

Variation of atomic charges during proton transfer in hydrogen bonds

The point atomic charges in a number of ionic H-bonded systems are studied by ab initio calculations as functions of the proton transfer coordinate. In the proton-bound complexes of water–water, ammonia–ammonia, formamide–water, formamide–ammonia, and dimethylether–ammonia, the net atomic charges were obtained using Mulliken population analysis and from the diagonal elements of the atomic polar tensors calculated at the HF/4–31G and MP2/6–31 + G** levels. The dependence of the atomic charges upon the coordinate of the transferring proton was found to be close (within an error of 0.02 e) to a linear function for intermolecular distances in the 2.5–2.8 Å range. The obtained charge and charge flux dependencies highlight the electron redistribution during the proton transfer process and provide insights into the source of the high infrared (IR) intensities of stretching modes of N? H and O? H bonds undergoing hydrogen bonding. © 1994 by John Wiley & Sons, Inc.     

丙烯环氧化反应中TS-1催化剂失活研究

采用丙烯气相进料,在预混段中先与双氧水的甲醇溶液混合后进入固定床反应器,考察了进料液中pH值、丙二醇单甲醚、乙硫醇以及铁锈等对丙烯环氧化连续反应中TS-1分子筛催化剂性能的影响。结果表明,进料液体pH值对催化剂的催化性能有影响,适宜的进料液体pH值在7左右;副产物丙二醇单甲醚含量的增加不会对催化剂性能产生影响;乙硫醇量的增加使环氧丙烷选择性下降,但不会引起催化剂的失活;而进料液体中铁锈的引入会导致催化剂中部分孔堵塞,使催化剂部分失活。当进料液中的pH值用0.1mol/L的氨水调节为7左右,在反应温度55℃,反应压力0.7MPa,TS-1催化剂具有较好的稳定性,经130h的连续试验考察,双氧水的转化率和环氧丙烷的选择性约为90%。     

Laser spark formamide decomposition studied by FT-IR spectroscopy

High-resolution FT-IR spectroscopy was used for the analysis of the products of formamide dissociation using a high-energy Asterix laser. In the experiment, the detected products of the formamide LIDB dissociation were hydrogen cyanide, ammonia, carbon monoxide, carbon dioxide, nitrous oxide, hydroxylamine, and methanol. The molecular dynamics of the process was simulated with the use of a chemical model. The chemistry shared by formamide and the products of its dissociation is discussed with the respect to the formation of biomolecules.     

Interactions of polar hydrogen bond donor solvents with ions: a theoretical study

Structural Chemistry - Intermolecular interactions between molecules of protic solvents (water, methanol, formic acid, formamide, methylamine and ammonia) and monatomic ions (Li+, Na+, K+,...     

Self-catalytic mechanism of prebiotic reactions: From formamide to purine bases

Complete reaction pathway of prebiotic reactions for formation of the purine nucleobases adenine, hypoxanthine, guanine, isoguanine, 2,6-diaminopurine, and xanthine from pure formamide are presented. All reactants (hydrogen cyanide, ammonia, water, formic acid, urea) and catalysts (formamide and formimidic acid) needed in the self-catalyzed reactions are available from a starting compound, formamide. The required raw materials are obtained by partial decomposition of formamide.     

On a possible invariance of a transition structure to the effects produced by ancillary H-bonding molecules: Modeling the effects of Ser-48 in the hydride-transfer step of liver alcohol dehydrogenase

The influence of a hydroxyl group simulating Ser-48 in the hydride-transfer step characteristic of liver alcohol dehydrogenase is studied on the hydride-transfer reaction as modeled by a methanolate anion interacting with a cyclo propenyl cation. It is shown first that this is an adequate model by comparing it to the methanolate-pyrydinium cation model transition structure, (TS ). The side-chain effect is modeled first by adding water and then with methanol located at the position that Ser-48 occupies in the enzyme; a supermolecule approach is used. It is found that (i) the normalized advance coordinate (NAC ) for the exchanged hydrogen has an invariant value at the TS and the reactant, while for the product, the NAC depends upon the external perturbation introduced by the ancillary molecule (the TS is reactant-like); (ii) the products are strongly destabilized, so the (activation) barrier with respect to the TS diminishes; (iii) the energy gap between reactants and products is sensibly diminished by the presence of methanol; (iv) the alcoholate moiety in the hydride transfer complex is not spontaneously protonated; and (v) there is a negligible charge transfer between the hydride-transfer system and models of Ser-48. In the present simplified model, methanol appears to have a catalytic effect via hydrogen bonding. © 1996 John Wiley & Sons, Inc.     

Catalytic chain transfer for molecular weight control in the emulsion homo- and copolymerizations of methyl methacrylate and butyl methacrylate

The behavior of catalytic chain transfer in semi-batch emulsion polymerization has been studied for two monomers, viz, methyl and n-butyl methacrylate. Two different catalytic chain transfer reagents were used with different water solubilities: cobaloxime boron fluoride (COBF), which was found to partition approximately equally between organic and aqueous phases, and tetra-phenyl cobaloxime boron fluoride (COPhBF), which was found to reside predominantly in the organic phase. The difference in hydrophilicity between the two transfer agents was found to affect the polymerization mechanism. COBF exhibited superior transfer behavior in all cases, whereas the restricted mobility of the COPhBF had a deleterious effect on the efficiency of the transfer mechanism. The best results were achieved under monomer flooded conditions using COBF. MALDI-TOF mass spectrometry analysis shows catalytic chain transfer to be the dominant mechanism initiating and stopping chain growth as none of the chains appear to have initiator fragment end groups. Analysis of copolymers by MALDI-TOF mass spectrometry reveals both molecular weight and composition data. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 859–878, 1997     

The Modification of Hydroxyl Surfaces of Formamide-Intercalated Kaolinites Synthesized by Controlled Rate Thermal Analysis

Controlled rate thermal analysis (CRTA) technology made possible the separation of adsorbed formamide from intercalated formamide in formamide-intercalated kaolinites. X-ray diffraction shows that the CRTA-treated formamide-intercalated kaolinites remain expanded after CRTA treatment. The Raman spectra of the CRTA-treated formamide-intercalated kaolinites are significantly different from those of the intercalated kaolinites with both intercalated and adsorbed formamide. An intense band is observed at 3629 cm(-1), attributed to the inner surface hydroxyls hydrogen bonded to the formamide. Broad bands are observed at 3600 and 3639 cm(-1) and are attributed to the inner surface hydroxyls, which are hydrogen bonded to the adsorbed water molecules. The hydroxyl stretching band of the inner hydroxyl is readily observed at 3621 cm(-1) in the Raman spectra of the CRTA-treated formamide-intercalated kaolinites. The results of thermal analysis show that the amount of intercalated formamide between the kaolinite layers is independent of the presence of water. The Raman bands of the formamide in the CRTA-treated intercalated kaolinites are readily observed. Copyright 2001 Academic Press.