氧弹燃烧灰化法测定有机物中磷

用氧弹燃烧法灰化有机物进行元素测定，操作简便，快速，无污染，该方法用于有机物中磷的分析，结果可靠。     

Role of surface crossings in the photochemistry of nitromethane

The photodissociation dynamics of nitromethane (CH(3)NO(2)) starting at the S(3) excited state has been studied at the complete active space self-consistent field level of theory in conjunction with atomic natural orbital type basis sets. In addition, the energies of all the critical points and the energy profiles connecting them have been recomputed with the multiconfigurational second-order perturbation method. It is found that the key step in the reaction mechanism is a radiationless decay through an S(3)S(2) conical intersection. The branching space spanned by the gradient difference and nonadiabatic coupling vectors of this crossing point comprises dissociation into excited nitromethane plus singlet atomic oxygen [CH(3)NO(1A")+O((1)D)] and S(3)-->S(2) deactivation, respectively. Furthermore, deactivated nitromethane S(n (n<3)) can decompose in subsequent steps into CH(3)+NO(2), where NO(2) is generated at least in two different electronic states (1 (2)B(2) and 1 (2)A(1)). It is shown that formation of excited nitric oxide NO(A (2)Sigma) arises from CH(3)NO(1A") generated in the previous step. In addition, four crossings between singlet and triplet states are localized; however, no evidence is found for a relevant role of such crossings in the photochemistry of CH(3)NO(2) initiated at S(3) state in the gas phase.     

Solid state coordination chemistry of copper(II)/α-hydroxycarboxylato/2,2′-bipyridine systems

Four new two-ligand complexes of copper(II) with 2,2′-bipyridine and one of three different α-hydroxycarboxylic acids (lactic, H₂LACO; 2-methyllactic, H₂MLACO; and mandelic, H₂MANO) were prepared. Complexes 1–3 of general formula [Cu(HL)₂(bipy)]·nH₂O (HL=monodeprotonated acid), were characterized by elemental analysis, IR, electronic and EPR spectroscopy, magnetic measurements and thermogravimetric analysis. Complexes 1 (HL=HLACO, n=2), 2 (HL=HMLACO, n=1) and 3a (the result of attempted recrystallization of 3, of formula [Cu(HMANO)(bipy)₂](HMANO)·H₂MANO·CH₃CN were studied by X-ray diffractometry. The copper atom is in an elongated, tetragonally distorted octahedral environment in 1 and 2 and in 3a has a coordination polyhedron intermediate between a square pyramid and a trigonal bipyramid, as evaluated in terms of the parameter τ. In 1 and 2 the α-hydroxycarboxylato ligand is bidentate and monoanionic but in 3a there are three forms: a monodentate monoanion, a monoanionic counterion, and a neutral molecule.     

Two New Sesquiterpenes from Eupatorium lindleyanum

Various germacrane sesquiterpenes have been isolated from many species of the Eupatorium.In recent years these compounds have been increasing interest due to their insecticidal,cytotoxic,antitumor-promoting and insect-antifeedant activities1.In our present study,we have investigated the chemical constituents of Eupatorium lindleyanum DC.,which is a geo-authentic medicine of Jiangsu province.It is used as a antipyretic drug.Two novel germacrane sesquiterpenes(Figure1)were found by us from th…     

Optimisation of stir bar sorptive extraction for the analysis of volatile phenols in wines

An easy, fast and reliable analytical method is proposed for the determination of the concentration of volatile phenols (ethyl- and vinylphenols) in wines. The novel stir bar sorptive extraction (SBSE) technique is employed, following a simple and fast procedure that allows 15 samples to be extracted simultaneously using very small sample volume. Extracts are desorbed in a thermodesorption system (TDS) coupled on-line to a gas chromatograph-mass spectrometry system. The SBSE offers better recovery and linear regression coefficient (r2) for the four volatile phenols than solid-phase extraction (SPE). The mass spectrometric detection in selected ion monitoring mode contributes to the lower detection limit and good sensibility obtained with this method.     

Diastereoselective synthesis of 3,4-disubstituted 5-(p-tolylsulfinyl)-5,6-dehydropiperidin-2-ones: chirality transfer in the enantioselective synthesis of ethyl (+)-(3S,4aS,7aS)-1-oxo-octahydro-1H-cyclopenta[c]pyridine-3-carboxylate

The base-mediated reaction of enantiomerically pure -sulfinylketimine (+)-1 with (E)-,β-disubstituted propenoate esters afforded 3,4-disubstituted-5-(p-tolylsulfinyl)-5,6-dehydropiperidin-2-ones 9-13 and 14 with high or complete diastereoselectivity. A sole diastereomer of the four possible ones, with regard to the nature of ester, was isolated, which revealed the stereocontrol of the chiral sulfinyl group in the Michael reaction and transenolization steps. In addition, the enantioselective synthesis of ethyl (+)-(3S,4aS,7aS)-1-oxo-octahydro-1H-cyclopenta[c]pyridine-3-carboxylates (+)-17 is described (five steps; 47% yield; ee 97%). The absolute configuration of stereocentres introduced in (+)-17 was assigned on the basis of ¹H NMR data.     

A comparative study on the photochemistry of two bipyridyl derivatives: [2,2'-bipyridyl]-3,3'-diamine and [2,2'-bipyridyl]-3,3'-diol.

The two isoelectronic bipyridyl derivatives, [2,2'-bipyridyl]-3,3'-diamine and [2,2'-bipyridyl]-3,3'-diol, are experimentally known to undergo very different excited-state double-proton-transfer processes, which result in fluorescence quantum yields that differ by four orders of magnitude. Herein, density functional theory (DFT), time-dependent DFT (TDDFT), and complete active space self-consistent field (CASSCF) calculations are used to study the double-proton-transfer processes in the ground and first singlet pi-->pi* excited state. The quantum-chemistry calculations indicate 1) the existence of only one energy minimum in the ground electronic state corresponding to reactants (thus avoiding the possibility of a fast fluorescent relaxation process from the photoproducts region), 2) an endoergic process of the complete double proton transfer, and 3) the presence of a conical intersection in the excited intermediate region of [2,2'-bipyridyl]-3,3'-diamine. These facts explain the very low fluorescence quantum yield in [2,2'-bipyridyl]-3,3'-diamine compared to [2,2'-bipyridyl]-3,3'-diol.     

Quantifying the relative contribution of hydrogen bonding and hydrophobic environments, and coordinating groups, in the zinc(II)-water acidity by synthetic modelling chemistry

Ligands derived from the tripodal N4 ligand tris(pyridylmethyl)amine ((pyCH2)3N, tpa) of general formula (6-RNHpyCH2)nN(CH2py)(3-n)(R = H, n= 1-3 L(1-3); R = neopentyl, n= 1-3 L'(1-3)) were used to elucidate and quantify the magnitude of the effects exerted by hydrogen bonding and hydrophobic environments in the zinc-water acidity of their complexes. The pKa of the zinc-bound water molecule of [(L(1-3))Zn(OH2)]2+ and [(L'(1-3))Zn(OH2)]2+ 1'-3' was determined by potentiometric pH titrations in water (1-3) or water-ethanol (1:1) (1'-3'). The zinc(II) water acidity gradually increases as the number of -NH2 hydrogen bonding groups adjacent to the water molecule increases. Thus, the zinc-bound water of [(L3)Zn(OH2)]2+ and [(tpa)Zn(OH2)]2+ deprotonate with pKa values of 6.0 and 8.0, respectively. The pKa of the water molecule, however, is only raised from 8.0 in [(tpa)Zn(OH2)]2+ to 9.1 in [(bpg)Zn(OH2)]+ (bpa =(pyCH2)2N(CH2COO-)). Moreover, the acidity of the zinc-bound water of several of the five-coordinate zinc(II) complexes with the hydrogen bonding groups is greater than that of four-coordinate [((12)aneN3)Zn(OH2)]2+ (pKa = 7.0). This result shows that the magnitude of the effect exerted by the hydrogen bonding groups can be larger than that induced by changing one neutral by one anionic ligand, and/or even by changing the coordination number of the zinc(II) centre. The X-ray structure of [(L'2)Zn(OH)]ClO4 2' and [(L'3)Zn(OH)]ClO4.CH3CN 3'.CH3CN is reported, and show the neopentylamino groups forming N-H...O hydrogen bonds with the zinc-bound hydroxide. Although, which have hydrogen bonding and hydrophobic groups, have a zinc-bound water more acidic than [(tpa)Zn(OH2)]2+, their pKa is not always lower than that of 1-3. This result suggests that a hydrogen bonding microenvironment may be more effective than a hydrophobic one to increase the zinc-water acidity.     

S0 ring-puckering potential energy function for coumaran

With the aid of a reported inversion splitting value, the far-infrared spectrum resulting from the ring-puckering vibration of coumaran has been reassigned and the one-dimensional potential energy function has been determined. The barrier to planarity is 155 +/- 4 cm(-1) and the dihedral angle is 25 degrees . These results agree well with the millimeter wave spectra values of 152 cm(-1) and 23 degrees , which utilized different data and a different type of potential function for the calculations. The MP2/cc-pvtz ab initio values of 238 cm(-1) and 26.5 degrees agree more poorly. If the benzene ring is assumed to remain rigid, the calculated barrier drops to 204 cm(-1). The puckering potential functions for the ring-flapping and ring-twisting vibrationally excited states were also determined and the barriers were found to be 149 and 156 cm(-1), respectively.     

Controlling the size of nanostructures in thin films via blending of block copolymers and homopolymers

The effects of molecular weight and concentration of poly (methyl methacrylate) (PMMA) homopolymer or symmetric short polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymer on the size of the nanostructures of its blends with symmetric long PS-b-PMMA diblock copolymer have been investigated by atomic force microscopy. By careful controlling of the film thickness, solvent selectivity, and annealing time, PMMA cylindrical microdomains oriented normal to the film surface were obtained in all thin films. With the addition of both low- and high-molecular-weight PMMA homopolymers, the cylindrical domain sizes increased although it was less obvious for the lower molecular weight homopolymer. In contrast to the homopolymer, adding the short chain diblock copolymer resulted in a decrease in the cylindrical domain size, which was ascribed to the reduction of the interfacial tension and increase in the stretching energy.