16-脱氢孕烯醇酮醋酸酯的环境友好合成法

Instead of environmentally toxic chromium oxidant, singlet oxygen generated photcchemically was used as environmentally friendly and benign oxidizing agent to accomplish the transformation of pseudodiosgenin diacetate to diosone efficiently in a low toxic and less expensive solvent acetone. Accordingly 16-dehydropregnenolone acetate(16-DPA), an important intermediate for preparation of steroidal drugs, was prepared in good yield (75%) when photoreaction was run in acetone/acetic anhydride/pyridine system. The mild reaction condition as well as simple and environmentally friendly process made the method commercially viable and important for production of 16-DPA in industrial scale.     

Synthesis of Some New Heterobicyclic Nitrogen Systems Bearing 7H‐1,2,4‐Triazolo[1,5‐d]tetrazol‐6‐yl Moiety for Biological Interest

Reaction of 6‐mercapto‐7H‐1,2,4‐triazolo[1,5‐d]tetrazole ( 1 ) wtih 1,2‐phenylenediamine afforded N‐{7H‐1,2,4‐triazolo[1,5‐d]tetrazol‐6‐yl}‐1,2‐phenylenediamine which was cyclized to benzimidazolyl‐1,2,4‐triazolo[1,5‐d]tetrazoles using various one‐carbon cyclizing agents. Also, the treatment of 1 with maleic anhydride or phthalic anhydride gave the corresponding thio derivatives followed by hydrazinolysis to afford the thio heterobicyclic systems. Former structures of the products have been established upon elemental and spectral analyses.     

[1‐Allylpyridinium][Cu2Cl3]: Synthesis,X‐ray Structure and the Regularity of Crystal Architecture of 1‐Allyl/(amino)‐pyridinium Copper(I) Chloride π‐Complexes

By alternating‐current electrochemical technique crystals of copper(I) π‐complex with 1‐allylpyridinium chloride of [C₅H₅N(C₃H₅)][Cu₂Cl₃] ( 1 ) composition have been obtained and structurally investigated. Compound 1 crystallizes in monoclinic system, space group C2/c a = 24.035(1) Å, b = 11.4870(9) Å, c = 7.8170(5) Å, β = 95.010(5)°, V = 2150.0(2) ų (at 100 K), Z = 8, R = 0.028, for 4836 independent reflections. In the structure 1 trigonal‐pyramidal environment of π‐coordinated copper(I) atom is formed by a lengthened to 1.376(2) Å C=C bond of allyl group and by three chlorine atoms. Other two copper atoms are tetrahedrally surrounded by chlorine atoms only. The coordination polyhedra are combined into an original infinite (Cu₄Cl₆^2—)_n fragment. Structural comparison of 1 and the recently studied copper(I) chloride π‐complexes with 3‐amino‐, 2‐amino‐, 4‐amino‐1‐allylpyridinium chlorides of respective [LCu₂Cl₃] ( 2 ), [L₂Cu₂Cl₄] ( 3 ), and [LCuCl₂] ( 4 ) compositions allowed us to reveal the trend of the inorganic fragment complication which depends on pKa (base) value of the corresponding initial heterocycle.     

Ionization energy reductions in small 2,5-dihydroxybenzoic acid-proline clusters

The photoionization of (pro)(n)DHB (pro = proline, DHB = 2,5-dihydroxybenzoic acid, n = 0, 1, 2 or 4) clusters was studied both experimentally and computationally. Experimentally the (pro)(n)DHB clusters are generated in the gas phase by laser desorption and supersonic jet entrainment. The photoionization thresholds are then determined by the mass-selective measurement of both one- and two-color photoionization efficiency curves. These experiments demonstrate that the ionization energies (IEs) of the (pro)(n)DHB clusters are substantially reduced in comparison with the IE of free DHB. Computational studies of the (pro)(n)DHB clusters provide insights into the mechanism of IE reduction. For the (pro)DHB system the IE reduction results from spin delocalization in the ion state of the cluster. In contrast, for the (pro)(2)DHB and (pro)(4)DHB clusters the IE reduction results from an inductive delocalization of electron density from pro to DHB in the ground state of the cluster. This latter effect, which is a result of the specific hydrogen-bonding interactions occurring in the mixed clusters, leads to IE reductions of >1 eV. Finally, determination of the energetics of the (pro)(2)DHB radical cation demonstrate that the DHB-to-proline proton transfer reaction is a barrierless, exoergic process in the ion state and that energetic demands for cluster dissociation to protonated (pro)(2) plus a deprotonated DHB radical are substantially lower than those for cluster dissociation to (pro)(2) plus DHB(+*). Cumulatively, these studies provide new energetic and mechanistic insights into both primary and secondary MALDI ionization processes.     

An ab initio theoretical study of electronic structure and properties of 2'-deoxyguanosine in gas phase and aqueous media

Molecular geometries of two structural forms of 2'-deoxyguanosine (keto-N9R and keto-N7R, R = the sugar moiety) considering both the C2'-endo and C3'-endo conformations of the sugar ring and those of the complexes of these species with two water molecules each were optimized employing the ab initio RHF procedure. A mixed basis set consisting of the 6-311+G* basis set for the nitrogen atom of the amino group and the 4-31G basis set for all the other atoms was used. The RHF calculations were followed by correlation correction of the total energy at the MP2 level. Both the structural forms of 2'-deoxyguanosine were solvated using the polarized continuum model (PCM) of the self-consistent reaction field (SCRF) theory and the corresponding RHF optimized geometries at the RHF and MP2 levels. Geometry optimization was also performed in aqueous media using the Onsager model at the RHF level using the above-mentioned mixed basis set, and subsequently, using the reoptimized geometries, single-point MP2 calculations were performed. It is found that both the keto-N9R and keto-N7R forms of 2'-deoxyguanosine as well as their complexes with two water molecules each would occur, particularly at the water-air interface. Though the normal Watson-Crick-type base pairing would not be possible with the keto-N7R form of 2'-deoxyguanosine(G*), two other (G*-C and G*-T) base pairing schemes may occur with this form of the nucleoside, which may cause mutation. The present calculated geometry of the keto-N9R form of the anti-conformation of 2'-deoxyguanosine including the dihedral angle chi(CN) agree satisfactorily with the available crystallographic results. The present results also agree satisfactorily with those obtained by other authors earlier for the keto-N9R form of 2'-deoxyguanosine using B3LYP and MP2 methods employing the 6-31G* basis set. Using transition state calculations, it is shown that tautomerism of guanine and other similar molecules where the tautomers would coexist would be facilitated by the occurrence of the H(+) and OH(-) fragments of water molecules. Further, this coexistence of the two tautomers appears to make the C8 carbon atom located between the N7 and N9 nitrogen atoms susceptible to attack by the OH(-) group. Thus, an explanation is obtained for the efficient formation of the reaction product 8-hydroxy-2'-deoxyguanosine, which serves as a biomarker for oxidative damage to DNA in biological systems.     

On the calculation of arbitrary multielectron molecular integrals over Slater‐type orbitals using recurrence relations for overlap integrals. III. Auxiliary functions \documentclass{article}\pagestyle{empty}\begin{document}$Q_{nn'}^{q}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$G_{-nn'}^{q}$\end{document}

The auxiliary functions $Q_{nn'}^{q}(p,pt)$ and $G_{-nn'}^{q}(p_{a},p,pt)$ which are used in our previous paper [Guseinov, I. I.; Mamedov, B. A. Int J Quantum Chem 2001, 81, 117] for the computation of multicenter electron‐repulsion integrals over Slater‐type orbitals (STOs) are discussed in detail, and the method is given for their numerical computation. The present method is suitable for all values of the parameters p_a, p, and pt. Three‐ and four‐center electron‐repulsion integrals are calculated for extremely large quantum numbers using relations for auxiliary functions obtained in this paper. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Superconductivity in copper, silver, and gold compounds

High-temperature superconductivity exists in layered, square-planar cuprates, but is almost absent in most other Cu(II) compounds and in most Ag(II) and Au(II) compounds. Valence state II is quite unusual in silver and gold and often disproportionates to valence states I and III ("negative-U compounds"). The two-electron difference in oxidation state is suggestive of electron pairing, a prerequisite for superconductivity. In the present paper the connection between disproportionation and geometrical structure on one hand and superconductivity on the other is discussed by using the accepted theory for mixed valence complexes. It is concluded that absence of superconductivity in gold and silver compounds can be connected to the instability of oxidation state II and the large difference in equilibrium geometry between oxidation states I and III.     

Immunosensors Based on Layer‐by‐Layer Self‐Assembled Au Colloidal Electrode for the Electrochemical Detection of Antigen

Colloidal Au particles have been deposited on the gold electrode through layer‐by‐layer self‐assembly using cysteamine as cross‐linkers. Self‐assembly of colloidal Au on the gold electrode resulted in an easier attachment of antibody, larger electrode surface and ideal electrode behavior. The redox reactions of [Fe(CN)₆]^4?/[Fe(CN)₆]^3? on the gold surface were blocked due to antibody immobilization, which were investigated by cyclic voltammetry and impedance spectroscopy. The interaction of antigen with grafted antibody recognition layers was carried out by soaking the modified electrode into a phosphate buffer at pH 7.0 with various concentrations of antigen at 37 °C for 30 min. Further, an amplification strategy to use biotin conjugated antibody was introduced for improving the sensitivity of impedance measurements. Thus, the sensor based on this immobilization method exhibits a large linear dynamic range, from 5–400 μg/L for detection of Human IgG. The detection limit is about 0.5 μg/L.     

Sensitive Voltammetric Response of p‐Nitroaniline on Single‐Wall Carbon Nanotube‐Ionic Liquid Gel Modified Glassy Carbon Electrodes

An ionic liquid (i.e., 1‐butyl‐3‐methylimidazolium hexafluorophosphate, BMIMPF₆)‐single‐walled carbon nanotube (SWNT) gel modified glassy carbon electrode (BMIMPF₆‐SWNT/GCE) is fabricated. At it the voltammetric behavior and determination of p‐nitroaniline (PNA) is explored. PNA can exhibit a sensitive cathodic peak at ?0.70 V (vs. SCE) in pH 7.0 phosphate buffer solution on the electrode, resulting from the irreversible reduction of PNA. Under the optimized conditions, the peak current is linear to PNA concentration over the range of 1.0×10^?8–7.0×10^?6 M, and the detection limit is 8.0×10^?9 M. The electrode can be regenerated by successive potential scan in a blank solution for about 5 times and exhibits good reproducibility. Meanwhile, the feasibility to determine other nitroaromatic compounds (NACs) with the modified electrode is also tested. It is found that the NACs studied (i.e., p‐nitroaniline, p‐nitrophenol, o‐nitrophenol, m‐nitrophenol, p‐nitrobenzoic acid, and nitrobenzene) can all cause sensitive cathodic peaks under the conditions, but their peak potentials and peak currents are different to some extent. Their peak currents and concentrations show linear relationships in concentration ranges with about 3 orders of magnitude. The detection limits are 8.0×10^?9 M for p‐nitroaniline, 2.0×10^?9 M for p‐nitrophenol, 5.0×10^?9 M for o‐nitrophenol, 5.0×10^?9 M for m‐nitrophenol, 2.0×10^?8 M for p‐nitrobenzoic acid and 8.0×10^?9 M for nitrobenzene respectively. The BMIMPF₆‐SWNT/GCE is applied to the determination of NACs in lake water.