Diheteroarylmethanes. 6.(1) Probing the Electron-Withdrawing Rank of Heteroaryl Groups by Conformational Studies of Push-Pull Ethylenes. Isolation of NH-Enamine Tautomers of alpha,alpha-Diheteroarylacetaldehydes (Heteroaryl = 2-Benzoxazolyl, 2-Benzothiazolyl)

Enamines and enol ethers substituted in the beta position by the 2-benzoxazolyl and 2-benzothiazolyl group have been obtained by condensing dimethylformamide dimethyl acetal and ethyl orthoformate, respectively, with bis(2-benzoxazolyl)methane and bis(2-benzothiazolyl)methane. A dynamic NMR and semiempirical (PM3) investigation on rotational energy barriers has been carried out in order to rank the electron-withdrawing capacity of the heterocyclic rings. The NMR-based evaluation of the energy barriers corresponding to the rotation along the enaminic double bond has shown that the pi-electron-withdrawing power of benzothiazole is larger than that of benzoxazole, in full accord with previously obtained charge demand values based on (13)C and (15)N pi-charge/shift relationships. The NMR and the computational approaches have led to consistent results. The X-ray crystal structure of alpha,alpha-bis(2-benzothiazolyl)-beta-(dimethylamino)ethene shows that only one heteroaryl ring is coplanar with the enaminic double bond, while the second one is twisted by 73 degrees relative to such a plane. Moreover, in this case calculations closely reproduce the experimental results. In the calculated transition states corresponding to the rotational process along the enamine double bond, the two heteroaryl groups become coplanar and conjugation develops between the enaminic nitrogen electron pool and both heterocycles. The lower rotational barrier observed in the case of the 2-benzothiazolyl derivatives, with respect to the 2-benzoxazolyl derivatives, is therefore a direct consequence of the higher electron-withdrawing power of the former group. Furthermore, a stabilizing intramolecular nonbonded S.S interaction in the rotational transition state of the benzothiazolyl derivatives is evidenced by the calculations. An unprecedented isolation of the NH-enamine tautomer involving the benzoxazolyl and benzothiazolyl ring in alpha,alpha-diheteroacetaldehydes has been performed, confirming these heterocycles as strong electron-withdrawing substituents.     

硅表面嫁接有机单分子膜的研究近况

由于在微电子、化学 /生物化学传感器、纳米技术及太阳能等领域具有潜在的应用价值 ,通过 Si— C键在硅表面上直接嫁接有机单分子膜 ,已成为近几年新开展的研究热点 .对这一研究领域进行了概要综述     

Study of the polymer latex coalescence by dielectric measurements at microwave frequency—feasibility of the method

The measurement of the complex dielectric constant ( ^*=–j) in the dipolar absorption domain of the free water molecule (microwave region) permits us to follow quasi-specifically and precisely the water circulation during the coalescence process of a latex. Weight losses and dielectric constants variations have been simultaneously recorded upon latex drying, in a resonant cavity at 5 and 9 GHz and under controlled atmosphere and temperature. Two different latexes were studied (polybutylacrylate (PBuA) and polystyrene (PS)) from which the glass transition temperature effect was investigated. It is found that the harder the polymer particles, the more clearly evidenced the flocculation and packing points are. This method appears to be quite reliable for discriminating the various steps in the film formation process of latexes.     

Oxidation of methionine residues in aqueous solutions: free methionine and methionine in granulocyte colony-stimulating factor

The free energy barriers and a mechanism of the oxidation of the amino acid methionine in water and in granulocyte colony-stimulating factor (G-CSF) are analyzed via combined quantum mechanical and molecular mechanical (QM/MM) methods, constrained molecular dynamics, and committor probability calculations. The computed free energy barrier of free methionine amino acid is very close to the measured value (14.7 +/- 1.2 versus 15.5 +/- 0.02 kcal/mol). The reaction coordinate was found to be the difference between the O-O bond of H2O2 and the S-O bond, where the S is the sulfur atom of the methionine residue. It was confirmed by computing the committor probability distribution and the distribution of constrained forces that this coordinate is not coupled to the activation of other degrees of freedom. The computed free energies of the oxidation of methionine residues in G-CSF indicate that the protein environment has insignificant effects on the reaction barriers of oxidation. This result further validates our proposal that the access of solvent to methionine sites, as measured by the two-shell water coordination number, governs the kinetics of the oxidation reaction of methionine groups in a protein molecule. We also found that the number of hydrogen bonds between the distal oxygen of H2O2 and the water molecules near the methionine increases along the reaction coordinate as oxidation progresses, indicating that the charge separation developed during the oxidation by H2O2 is stabilized by specific interactions with water molecules, such as hydrogen bonding.     

Copper (II) complexes of sterically hindered o-diphenol derivatives: synthesis, characterization and microbiological studies

Cu (II) complexes with the sterically hindered diphenol derivatives 3,5-di(tert-butyl)-1,2-benzenediol (I), 4,6-di(tert-butyl)-1,2,3-benzenetriol (II) and the sulfur-containing 4,6-di(tert-butyl)-3-(2-hydroxyethylsulfanyl)-1,2-benzenediol (III) and 2-[4,6-di(tert-butyl)-2,3-dihydroxyphenylsulfanyl]acetic acid (IV) have been synthesized and characterized by elemental analysis, TG/DTA, FT-IR, ESR, XPS, XPD and conductivity measurements. Compounds I–III can coordinate in their singly deprotonated forms and act as bidentate ligands. These compounds yield Cu (II) complexes of the stoichiometry Cu(L)₂, which have square planar geometry (g_| > g_⊥ > g_e). Unlike them, compound IV behaves as a terdentate ligand, and its complex Cu(L^IV)₂ has distorted octahedral geometry. According to ESR data, only the Cu(L^II)₂ complex contains a very small amount of phenoxyl radicals. Antimicrobial activities of these ligands and their respective Cu (II) complexes have been determined with respect to Gram-positive and Gram-negative bacteria, as well as on yeasts. Their phytotoxic properties against Chlorella vulgaris 157 were also examined.     

Direct detection of renal function markers using microchip CE with pulsed electrochemical detection

Creatinine, creatine, and uric acid are three important compounds that are measured in a variety of clinical assays, most notably for renal function. Traditional clinical assays for these compounds have focused on the use of enzymes or chemical reactions. Electrophoretic microchips have the potential to integrate separation power of capillary electrophoresis with devices that are small, portable, and have the speed of conventional sensors. The development of a microchip CE system for the direct detection of creatinine, creatine, and uric acid is presented. The device uses pulsed amperometric detection (PAD) to detect the nitrogen-containing compounds as well as the easily oxidizable uric acid. Baseline separation of creatinine, creatine and uric acid was achieved using 30 mM borate buffer (pH = 9.4) in less than 200 s. Linear calibration curves were obtained with limits of detection of 80 microM, 250 microM and 270 microM for creatinine, creatine and uric acid respectively. An optimization of the separation conditions and a comparison of PAD with other amperometric detection modes is also shown. Finally, analysis of a real urine sample is presented with validation of creatinine concentrations using a clinical assay kit based on the Jaffé reaction.     

Syntheses and photophysical properties of some 5(2)-aryl-2(5)-(4-pyridyl)oxazoles and related oxadiazoles and furans

A number of 5-aryl-2-(4-pyridyl)oxazoles, a 2-aryl-5-(4-pyridyl)oxazole, the related oxadiazole and furan, several 2-(4-pyridyl)cycloalkano[d]oxazoles, and many of their quaternary salts were prepared. No single standard synthesis was effective for preparation of more than a few of the 25 free bases described; methods often unique to a base were employed. Minor variations in structure sometimes produced large differences in absorption and emission wavelengths, as well as in the magnitude of the extinction coefficient. The salts are of interest as laser dyes, scintillation fluors, biological stains, and shifters for luminescent solar concentrators.     

Heterotricyclodecane XXI 2-Aza-7-thia-twistane (bzw. 2-Thia-7-aza-twistane)

2-Aza-7-thia-twistanes (or 2-thia-7-aza-twistanes, respectively) The suitably substituted 9-thiabicylo[3.3.1]nonanes 7–9 and 17 were synthesized and subsequently cyclized to the 2-aza-7-thia-twistanes 21–23 and 19 , respectivelly, from which several other twistane derivatives ( 20 and 24–29 ) were prepared.     

Information Entropy and Uncertainty Relations

Information entropy is introduced as a measure of quantum mechanical uncertainty. An uncertainty relation based on information entropy is obtained as an alternative to the Heisenberg inequality. In two typical examples, the entropic uncertainty relation is shown to be bounded in situations where the Heisenberg inequality diverges or grows too large to be useful.