十六烷基三甲基溴化铵水溶液热致相变的红外光谱研究

在280～320K的温度范围内考察了30％十六烷基三甲基溴化铵水溶液的红外光谱随温度的变化。结果表明该体系的凝聚胶-液晶相转变温度为300K。在300K以下的凝聚胶相,分子的极性头部基团处于高度“固定”的状态,分子的碳氢链以有序的相互平行方式排列,极性头与碳氢链之间有一定的倾斜角。在300K以上的液晶相,极性头内部CH_3-(N~+)基团以及整个极性头与碳氢链之间发生了旋转,碳氢链变为以六方亚晶胞填充形式存在,旦扭曲式构象异构体数量显著增多,极性头与碳氢链之间已不存在倾斜角,分子的亲水极性头和疏水碳氢链部分都处于“融化”状态。     

Analysis of Isomeric Alkylated Polycyclic Aromatic Hydrocarbons by Matrix Isolation Fourier Transform Infrared Spectroscopy

Abstract

Matrix isolation Fourier transform infrared spectra of isomeric methylnaphthalenes and methylbiphenyls, in N₂ matrices at 15 K, are compared with each other and with those of the respective parent hydrocarbons. The applicability of matrix isolation Fourier transform infrared spectroscopy to both identification and quantitative analysis of individual alkylated polycyclic aromatic hydrocarbon isomers in mixtures is demonstrated.     

The Benzylperoxyl Radical as a Source of Hydroxyl and Phenyl Radicals

The benzyl radical ( 1 ) is a key intermediate in the combustion and tropospheric oxidation of toluene. Because of its relevance, the reaction of 1 with molecular oxygen was investigated by matrix‐isolation IR and EPR spectroscopy as well as computational methods. The primary reaction product of 1 and O₂ is the benzylperoxyl radical ( 2 ), which exists in several conformers that can easily interconvert even at cryogenic temperatures. Photolysis of radical 2 at 365 nm results in a formal [1,3]‐H migration and subsequent cleavage of the O?O bond to produce a hydrogen‐bonded complex between the hydroxyl radical and benzaldehyde ( 4 ). Prolonged photolysis produces the benzoyl radical ( 5 ) and water, which finally yield the phenyl radical ( 7 ), CO, and H₂O. Thus, via a sequence of exothermic reactions 1 is transformed into radicals of even higher reactivity, such as OH and 7 . Our results have implications for the development of models for the highly complicated process of combustion of aromatic compounds.     

Water Adsorption on Platinum Dioxide and Dioxygen Complex: Matrix Isolation Infrared Spectroscopic and Theoretical Study of Three PtO2–H2O Complexes

The interactions of water molecule with platinum dioxygen complex and dioxide molecule are investigated by means of matrix isolation infrared spectroscopy and density functional calculations. The platinum atoms reacted with dioxygen to form the previously reported Pt(O₂) complex. The Pt(O₂) complex reacted with water molecule to give the Pt(O₂)–H₂O complex, which was characterized to involve hydrogen bonding between one O atom of Pt(O₂) and one H atom of H₂O (structure A ). Upon visible light irradiation, the hydrogen bonded Pt(O₂)???HOH complex rearranged to another Pt(O₂)–H₂O isomer (structure B ), which involves (O₂)Pt???OH₂ interaction. The Pt(O₂)–H₂O complex in structure B can be isomerized to the weakly bound platinum dioxide‐water complex (structure C ) under UV irradiation.     

Photochemistry and Reactivity of the Phenyl Radical–Water System: A Matrix Isolation and Computational Study

The reaction of the phenyl radical 1 with water has been investigated by using matrix isolation spectroscopy and quantum chemical calculations. The primary thermal product of the reaction between 1 and water is a weakly bound complex stabilized by an OH???π interaction. This complex is photolabile, and visible‐light irradiation (λ>420 nm) results in hydrogen atom transfer from water to radical 1 and the formation of a highly labile complex between benzene and the OH radical. This complex is stable under the conditions of matrix isolation, however, continuous irradiation with λ>420 nm light results in the complete destruction of the aromatic system and formation of an acylic unsaturated ketene. The mechanisms of all reaction steps are discussed in the light of ab initio and DFT calculations.     

Complexes of Formaldehyde and α-Dicarbonyls with Hydroxylamine: FTIR Matrix Isolation and Theoretical Study

The interactions of formaldehyde (FA), glyoxal (Gly) and methylglyoxal (MGly) with hydroxylamine (HA) isolated in solid argon and nitrogen were studied using FTIR spectroscopy and ab initio methods. The spectra analysis indicates the formation of two types of hydrogen-bonded complexes between carbonyl and hydroxylamine in the studied matrices. The cyclic planar complexes are stabilized by O–H⋯O(C), and C–H⋯N interactions and the nonplanar complexes are stabilized by O–H⋯O(C) bond. Formaldehyde was found to form with hydroxylamine, the cyclic planar complex and methylglyoxal, the nonplanar one in both argon and nitrogen matrices. In turn, glyoxal forms with hydroxylamine the most stable nonplanar complex in solid argon, whereas in solid nitrogen, both types of the complex are formed.     

Infrared spectra of two sexithiophenes in neutral and doped states: a theoretical and spectroscopic study

The FT-infrared spectra of two sexithiophenes having their end ,′-positions substituted by n-hexyl or -thiohexyl groups, in neutral and doped states, are studied with the main aim of deriving information about the π-electrons delocalization and about the electronic structure of the charged defects created upon doping with iodine. The analysis of the experimental data is aided by Density Functional Theory calculations. The modifications in the electronic structure of the sexithiophene backbone induced by the n-thiohexyl encapsulation are discussed from the point of view of single molecule interactions in thiol-terminated π-conjugated oligomers bound to metallic or cluster electrodes.     

聚 (4-乙烯基吡啶硝酸盐)、硅硫酸和溴化铵催化氧化硫化物生成亚砜

 A new catalytic procedure for the chemoselective oxidation of sulfides to sulfoxides was studied. A variety of aliphatic and aromatic sulfides were subjected to sulfoxidation by combining poly(4-vinyl pyridinium nitrate), silica sulfuric acid (SiO₂-OSO₃H), and catalytic amounts of ammonium bromide in CH₂Cl₂ in the presence of a few drops of water at room temperature. Excellent yields were obtained.     

Conflicting Observations Resolved by a Far IR and UV/Vis Study of the NO3 Radical

Codeposition of NO and O ₂ diluted in Ne at 6 K yield a ON???OO complex that exhibit strong UV absorption. This complex is converted into NO₃ radicals by UV irradiation, and is regenerated by radiation of visible light (see spectra).

     

Determination of Total Selenium in Human Urine and Serum by Graphite-Furnace Atomic-Absorption Spectrophotometry with Palladium-Nickel-Ammonium Nitrates as a Matrix Modifier

After human urine or serum was diluted (1 + 9) with HNO₃ (0.2%, v/v) and standard additions of Se solution (100 μ L^?1), the diluted sample (10 μL) was introduced into the graphite cuvette. The matrix modifier [10μL, containing Pd (0.6 μg) + Ni (25 μg) + NH₄NO₃ (80 μg) in HNO₃ (0.2%, v/v) for urine, or Pd (0.3 μg) + Ni (30 μg) + NH₄NO₃ (80 μg) + Triton X-100 (0.04%) in HNO₃ (0.2%, v/v) for serum, respectively] was added and the mixture was heated according to a temperature program. The matrix modifier containing NH₄NO₃ in a suitable amount and a small amount of Pd enhanced the sensitivity for Se. The method detection limits (3σ) after dilution were about 4.9 ± 0.8 and 2.36 ± 0.18 μg L^?1 for urine and serum, respectively. The accuracy of this method was tested with SRM #2670 human urine Se and Seronorm Trace Elements #116 human serum Se, respectively, and the results of 97.6 – 101% and 100 – 104% were obtained with precision ± 0.3% and ± 2%, respectively. This method can be applied easily and accurately to the determination of concentration of total Se in human urine and serum.     

NaBH3CN and other systems as substitutes of tin and silicon hydrides in the light or heat-initiated reduction of halosugars: a tunable access to either 2-deoxy sugars or 1,5-anhydro-itols

UV light-promoted reduction of acetobromoglucose by NaBH₃CN in t-BuOH afforded 1,3,4,6-tetra-O-acetyl-2-deoxy-α-d-arabino-hexopyranose in high yield and purity, via a Surzur–Tanner rearrangement, while, with 10 mol % thiophenol added, acetylated 1,5-anhydro-d-glucitol was cleanly obtained. Such tin-free and mild reductions, presumed to proceed via radical pathways, were more efficient with NaBH₃CN compared to NaBH₄ or NaBD₄, and do not occur with acetochloroglucose. Similar reductions to 1,3,4,6-tetra-O-acetyl-2-deoxy-α-d-arabino-hexopyranose were achieved upon heating to 80 °C t-BuOH or CH₃CN solutions of NaBH₃CN and AIBN, but with a lower selectivity due to competing ionic reactions. With other pyranosyl bromides, reductions by NaBH₃CN could be tuned similarly (d-galacto), but some (d-manno, 5-thio-d-xylo) gave mainly or exclusively 1,5-anhydro-itols. Other conditions, or reagents promoting SET process, afforded also reduced products, but with lower rates or selectivities. Primary iodides were reduced readily with NaBH₃CN under UV light.     

S‐endo‐2‐Norbornyl‐N‐n‐butylcarbamate as a Potential Pseudomonas Lipase Inhibitor to Probe the Enantioselectivity of the Enzyme by Kinetic and Molecular Docking Evaluation

Obesity is a complex health issue and it can cause many health and social problems. Previous studies reported that lipase is a main target for obesity treatment. We synthesized R‐exo‐2‐norbornyl‐N‐n‐butylcarbamate and S‐exo‐2‐norbornyl‐N‐n‐butylcarbamate as potential pseudomonas lipase inhibitors to probe the enantioselectivity of the enzyme and demonstrated that R‐exo‐2‐norbornyl‐N‐n‐butylcarbamate had better enzyme enantioselectivity, ki and the docking model with Pseudomonas species lipase in our previous studies. In this article, we reported the property of the Pseudomonas species lipase inhibitors, R‐and S‐endo‐2‐norbornyl‐N‐n‐butylcarbamate and compared the docking models of these two compounds with R‐ and S‐exo‐2‐norbornyl‐N‐n‐butylcarbamates by AutoDock. We found that S‐endo‐2‐norbornyl‐N‐n‐butylcarbamate has the best enantioselectivity, ki and docking model and this study could provide useful information about enzyme enantioselectivity for the development of Pseudomonas species lipase inhibitors for obesity treatment.     

[ReIII(thiourea-S)6]Cl3 · 4 H2O and [ReIII(N-methylthiourea-S)6]Cl3 as Precursors to other ReIII Complexes: a Kinetic Study in Aqueous Media. Crystal Structure of [ReIII(N-methylthiourea-S)6](PF6)3 · H2O

Capability of [Re^III(tu-S)₆]Cl₃, where tu = thiourea, as a precursor to other Re^III complexes by ligand substitution in aqueous medium is studied. For the decomposition of [Re(tu-S)₆]Cl₃, experiments suggest pseudo first order kinetics and observed rate constants vary from 1.3 × 10^–2 to 9.6 × 10^–2 min^–1 in the pH range 2.80–5.04. Experiments in presence of incoming ligand (ethylendiaminetetraacetic acid or diethylentriaminepentaacetic acid) show that ligand substitution is significantly slower than decomposition of the precursor, even when pH and temperature are modified. Similar results were obtained working with [Re^III(Metu-S)₆]Cl₃, where Metu = N-methylthiourea. Molecular structure of [Re^III(Metu-S)₆](PF₆)₃ · H₂O was determined by single crystal X-ray diffractometry. The coordination polyhedron around the Re ion is a distorted octahedron. The six methylthiourea ligands are bonded to the metal through the sulfur atoms [bond lengths range from 2.409(2) to 2.451(2) Å].