UV光引发表面接枝两性离子水凝胶层的制备及抗细菌黏附性能

采用聚合和交联的SiO₂有机/无机杂化溶胶作为基材, 通过与两性离子单体层之间的过渡层, 在紫外光作用下引发杂化溶胶和两性离子单体溶液中的双键反应, 使生成的杂化层在基材和表面的两性离子聚合物之间形成辅助性黏接作用, 从而在基材表面构筑两性离子水凝胶层. 通过傅里叶红外光谱(FTIR)、 原子力显微镜(AFM)和接触角测试等方法对所制备的两性离子水凝胶层和杂化层的表面进行了表征. 以空白玻璃片为对照样品, 以金黄色葡萄球菌和大肠杆菌为试验菌, 研究了用两性离子凝胶层修饰的玻璃表面的抗细菌黏附性能. 结果表明, 在SiO₂杂化过渡层中引入线型-Si-(CH₂)₂-O-链段可有效提高杂化过渡层对基材的附着力, 并改善其柔韧性. 与对照样品相比, 用两性离子凝胶层修饰的玻璃表面具有优异的抗菌黏附性能.     

Synthesis of N-confused phlorins via an addition/cyclization pathway

The syntheses of N-confused phlorins are provided by reactions of N-confused porphyrins with nitrilimines and with dialkyl acetylenedicarboxylate. Both reactions involve zwitterionic intermediates and proceed through an addition/cyclization pathway.     

Alkylation of carbonyl compounds in water: formation of C-C and C-O bonds in the presence of surfactants

The formation of C-C and C-O bonds by the reaction of enolate intermediates with electrophilic substrates commonly requires strong bases, aprotic solvents and very low temperatures. A way of performing the same reactions with sodium hydroxide at moderate temperatures in aqueous surfactant solutions is presented. Different halides, ketones and surfactants (cationic, zwitterionic and anionic) have been used. The results obtained show that the amount of ketone alkylation is much higher and that the reactions are faster in the presence than in the absence of surfactant aggregates. The hydrolysis of the halide is minimised in the presence of cationic or zwitterionic surfactants.     

Structural relationships in small molecule interactions governing gas-phase enantioselectivity and zwitterionic formation

Gas-phase zwitterionic amino acids were formed in complexes of underivatized beta-cyclodextrin through reactions with a neutral base, n-propylamine. The reaction was performed in the analyzer cell of an electrospray ionization-Fourier transform mass spectrometer. Most of the natural amino acids were studied with three cyclodextrin hosts including alpha-, beta-, and gamma-cyclodextrin to understand better the structural features that lead to the stabilization of the zwitterionic complexes. Molecular dynamics calculations were performed to provide insight into the structural features of the complexes. The rate constants of the reactions were obtained through kinetic plots. Examination of both L- and D-enantiomers of the amino acid showed that the reaction was enantioselective. The reaction was then employed to analyze mixtures of Glu enantiomers naturally occurring in the bacteria Bacillus licheniformis.     

Tracking reactive intermediates in phosphine-promoted reactions with ambiphilic phosphino-boranes

The ambiphilic phosphino-borane i-Pr2P(o-C6H4)BMes2 affords stable versions of key zwitterionic intermediates by reactions with diethyl azodicarboxylate or PhNCO.     

Photoredox Reaction of Naphthoquinone C-Glycoside Revisited: Insight into Stereochemical Aspect

Insights into the naphthoquinone photoredox reactions have been gained from the reactions of a C-glycosyl naphthoquinone. The retentiveness comes from the balance of the lifetime of intermediary zwitterionic species relative to the conformational change to bring about the stereo-mutating C−C bond rotation.     

Zwitterionic intermediates in enamine-singlet oxygen reactions. configuration-interaction studies on the indole-singlet oxygen reactions

The theoretical calculations using INDO-RHF CI method have demonstrated that the reaction of singlet oxygen with 1,2,3-trimethylindoles proceeds via a zwitterionic peroxide intermediate. The calculations provide important predictions for the mechanism of enamine-singlet oxygen reactions.     

Preparation of zwitterionic electron acceptors and donors

The reactions of 4, 4'-bipyridine and nicotinamide with 1, 3-propane sultone yields zwitterionic electron acceptors. Reaction of dimethylaminoethyl ferrocene with 1, 3-propane sultone yields a zwitterionic ferrocene electron donor. The electron acceptors and donor are reduced and oxidized to the respective radical anions and ferrocenyl cation. Dipropyl-4, 4'-bipyridinium disulfonate and the ferrocene derivative quench the excited Ru(bipy)₃²⁺.     

Mechanistic implications in the Morita-Baylis-Hillman alkylation: isolation and characterization of an intermediate

An intermediate phosphonium salt has never been isolated from the Morita-Baylis-Hillman (MBH) reaction. Due to the weakly basic counterion produced in the MBH alkylation and allylation reactions, the reaction can be stopped after electrophilic attack on the zwitterionic enolate and an intermediate isolated. Upon analysis of the crystal structure, a trans geometry is observed, suggesting that there is no electrostatic interaction between phosphorus and oxygen in the zwitterionic enolate that undergoes alkylation, thus giving new mechanistic insight into the MBH reaction.     

Micelle Effects of Functionalized Surfactants, 1-Cetyl-3-(2-hydroxyiminopropyl)imidazolium Halides,in Reactions with p-Nitrophenyl p-Toluenesulfonate,Diethyl p-Nitrophenyl Phosphate,and Ethyl p-Nitrophenyl Ethylphosphonate

1-Cetyl-3-(2-hydroxyiminopropyl)imidazolium chloride and bromide were synthesized for the first time. These compounds are functionalized zwitterionic surfactants which give rise to micelle formation in aqueous solution. Kinetic and thermodynamic analysis of nucleophilic cleavage of p-nitrophenyl p-toluenesulfonate, diethyl p-nitrophenyl phosphate, and ethyl p-nitrophenyl ethylphosphonate in the presence of 1-cetyl-3-(2-hydroxyiminopropyl)imidazolium halide micelles showed that the latter are powerful nucleophilic reagents whose kinetic behavior can be described in terms of a simple pseudophase distribution model. The efficiency of substrate solubilization with zwitterionic surfactant micelles and the reactivity of the oximate fragment in the micelle phase were estimated on a quantitative level. The observed acceleration of S_N2 reactions with the examined p-nitrophenyl esters relative to analogous reactions of zwitterionic 1-methyl-3-(2-hydroxyiminopropyl)imidazolium halides is, respectively, 12800, 550, and 900 times; it is explained mainly by increased concentration of the reactants in micelles.     

Nucleophile‐Initiated Catalytic and Multicomponent Reactions

A number of well‐known reactions, proceed through the intermediacy of dipolar/zwitterionic species generated via the addition of a neutral nucleophile with an unsaturated electrophile. A mechanistic understanding of these reactions was made possible by seminal contributions of Huisgen. The design of novel reactions based on such dipolar species was, however, not pursued in detail for a long time. Our efforts to exploit various reactivity profiles available for the zwitterionic/dipolar intermediates have resulted in the discovery of a large number of novel, convenient protocols to access a wide variety of products. The nucleophilic initiators may participate in the reaction or play a mediating role depending upon the nature of nucleophile, its quantity and the reaction conditions. In a majority of these transformations two electrophilic components, that would normally be inert towards each other, are combined by the intermediacy of a nucelophile. A brief summary of such nucleophile‐initiated novel reactions that were developed in our research group are described. Reactions involving a variety of nucleophiles such as phosphines, pyridine, quinoline, isoquinoline, isocyanides, dimethoxycarbene and N‐heterocyclic carbenes (NHCs) are discussed.     

New methodology for functionalization of the imidazole ring by alkynes

A new methodology for functionalization of the imidazole ring via the zwitterionic intermediates and their carbene tautomers generated by nucleophilic addition of 1-substituted imidazoles to electron-deficient acetylenes followed by reactions with the appropriate electrophiles is discussed.     

An Mo-theoretical characterization of organic reaction mechanisms—IV : Thermal (2+2) reactions

Various types of thermal (2+2) reactions are mechanistically differentiated in terms of the phase continuity plus the triplet stability of the restricted Hartree-Fock molecular orbitals relevant to the entire reaction systems. The former criterion allows to discriminate between the symmetry-allowed and -forbidden reactions while the latter permits distinction between biradical and nonradical reactions. It follows that the two-step cycloaddition involving a zwitterionic intermediate, for instance, should be characterized as a symmetry-forbidden nonradical process. The mechanistic features theoretically inferred for several known examples of reactions are all found to be compatible with observation.     

Applications of phthalimide photochemistry to macrocyclic polyether, polythioether, and polyamide synthesis.

Irradiation of phthalimides which contain N-linked omega-trimethylsilylmethyl-substituted polyether, polythioether, and polysulfonamide chains results in efficient production of the corresponding macrocyclic polyether, polythioether, and polysulfonamide products. These photocyclization reactions follow sequential single electron transfer (SET)-desilylation pathways. Only in the cases of phthalimides, bearing mixed ether-thioether N-substituents, do these excited-state cyclization reactions proceed with lower degrees of regioselectivity. This is a result of competitive desilylation and alpha-to-sulfur deprotonation reactions of the zwitterionic diradical intermediates formed by initial SET.     

2-苯基吲哚单重态氧反应机理

本文比较了在甲醇介质下, 2-苯基吲哚(1)单重态氧反应中的捕捉反应以及2-苯基-3H-吲哚-3-酮(4)的亲核加成反应特征。结果显示, 在1的单重态氧反应中, 捕捉反应主要发生于两性离子(2)阶段, 而4并非导致捕捉产物的重要中间体。根据上述事实, 结合有关反应溶剂极性效应的研究结果, 对反应机理进行了探讨。     

Asymmetric Multicomponent Reactions Based on Trapping of Active Intermediates

Metal carbenes derived from transition metal‐catalyzed decomposition of diazo compounds react with nucleophiles with heteroatoms, such as alcohols and amines, to generate highly active oxonium/ammonium ylides intermediates. These intermediates can be trapped by appropriate electrophiles to provide three‐component products. Based on this novel trapping process, we have developed novel multicomponent reactions (MCRs) of diazo compounds, alcohols/anilines, and electrophiles. The nucleophiles were also extended to electron‐rich heterocycles (indoles and pyrroles)/arenes, in which the resulting zwitterionic intermediates were also trapped by electrophiles. By employing efficient catalysis strategy, the reactions were realized with excellent stereocontrol and wide substrate scope. In this personal account, we introduce our breakthroughs in the development of novel asymmetric MCRs via trapping of the active ylides and zwitterionic intermediates with a number of electrophiles, such as imines, aldehyde, and Michael acceptors, under asymmetric catalysis. Transition metal/chiral Lewis acid catalysis, transition metal/Brønsted acid catalysis, and chiral transition‐metal catalysis, enable excellent stereocontrolled outcomes. The methodologies not only provide experimental evidence to support the existence of protic onium ylides intermediates/zwitterionic intermediates and the stepwise pathways of carbene‐induced O?H, N?H and C?H insertions, but also offer a novel approach for the efficient construction of chiral polyfunctional molecules.     

Reinvestigation of aminomethyltrifluoroborates and their application in Suzuki-Miyaura cross-coupling reactions

A reinvestigation into the chemical composition of potassium aminomethyltrifluoroborates is reported. These trifluoroborato salts have been reassigned as zwitterionic ammoniomethyltrifluoroborates. Minor adjustments to the previously disclosed reaction conditions are reported that permit a similar level of activity as nucleophiles in Suzuki-Miyaura cross-coupling reactions.     

Development of a new carbon-carbon bond forming reaction. new organic chemistry of sulfur dioxide. Asymmetric four-component synthesis of polyfunctional sulfones.

At low temperature 1-alkoxy-1,3-dienes add to sulfur dioxide activated by a Lewis or Br?nstedt acid and generate zwitterionic intermediates that can be quenched by enoxysilanes. The resulting beta,gamma-unsaturated silyl sulfinates can be desilylated and reacted with methyl iodide to provide polyfunctional sulfones. Exploratory studies of this four-component synthesis of sulfones are reported. Enantiomerically pure derivatives containing up to three new stereogenic centers can be obtained using enantiomerically pure (E,E)-1-alkoxy-2-methylpenta-1,3-dienes derived from alpha-methyl benzyl alcohols, including the Greene's chiral auxiliary. The stereochemistry of the reactions is consistent with a mechanism involving the suprafacial hetero-Diels-Alder addition of sulfur dioxide to the 1-alkoxy-1,3-dienes that are rapidly ionized into zwitterionic intermediates.     

Rearrangement of 1,3-dipolar cycloadducts derived from bis(phenylazo)stilbene: a DFT level mechanistic investigation

The 1,3-dipolar cycloaddition of bis(phenylazo)stilbene with activated ethene and ethyne derivatives and the subsequent rearrangement of the cycloadducts have been studied using model compounds at the B3LYP/6-31G(d) level of density functional theory (DFT). From the structural and electronic features, a five-membered zwitterionic ring system 9 (1,2,3-triazolium-1-imide system) formed from bis(phenylazo)ethylene is confirmed as the active 1,3-dipole species in the reaction. Formation of the 1,3-dipolar cycloadduct from the alkyne derivative is found to be 26.0 kcal/mol exergonic, and it requires an activation free energy of 19.4 kcal/mol. The 1,3-cycloadduct formed in the reaction undergoes a very facile migration of a nitrogen-bearing fragment, passing through a zwitterionic transition state. A small activation free energy of 8.2 kcal/mol is observed for this step of the reaction, and it is 19.6 kcal/mol exergonic. Further activation of the newly formed rearranged product is possible under elevated temperatures, again passing through a zwitterionic transition state and resulting in the formation of 2,5-dihydro-1,2,3-triazine derivatives. Such derivatives have been recently reported by Butler et al. (J. Org. Chem. 2006, 71, 5679). The charge separation in 9 and the zwitterionic transition states are stabilized through the pi-system of the phenyl rings and the carbonyl groups. Similar structural, electronic, and mechanistic features are obtained for the reaction of 9 with the ethylenic dipolarophile acrylonitrile. Molecular electrostatic potential analyses of the 1,3-dipole and the zwitterionic transitions states are found to be very useful for characterizing their electron delocalization features. The solvation effects can enhance the feasibility of these reactions as they stabilize the zwitterionic transition states to a great extent.     

Polymers by the reaction of bis(pyrylium salts) with diamines: A novel approach to ionene polymers

The following reactions of pyrylium salts with amines are described: (1)bis(pyrylium salts) with amines; (2) diamines with pyrylium salts; and (3) bis(pyrylium salts) with diamines. Both (1) and (2) give bis(pyridinium salts) in high yields, and (3) gives the corresponding polymers which are isolated and characterized. This procedure was applied to cationic bis(pyrylium salts) to give cationic dimers and polymers, and further to zwitterionic bis(pyrylium salts) to yield the corresponding zwitterionic dimers and polymers.