Dissociation of sulfur dioxide by ultraviolet multiphoton absorption between 224 and 232 nm

Multiphoton excitation and dissociation of SO(2) have been investigated in the wavelength range from 224 to 232 nm. Strong evidence is found for two-photon excitation to the H Rydberg state, followed by dissociation to SO + O and ionization of the SO product by absorption of a third photon. The two-photon excitation is resonantly enhanced via the C (1)B(2) intermediate state, and the two-photon yield spectrum thus bears a strong resemblance to the spectrum of this intermediate. Imaging of the O((3)P(2)), S((1)D(2)), and SO products suggests that, following dissociation of SO(2) from the H state, SO is produced in the A and B electronic states. S((1)D(2)) is produced both from two-photon dissociation of SO(2) to give S((1)D(2)) + O(2) and by single-photon dissociation of SO(+). In the former process, the O(2) is likely formed in all of its lowest three electronic states.     

Quantum chemical calculations and mutational analysis suggest heat shock protein 90 catalyzes trans-cis isomerization of geldanamycin

The affinity of geldanamycin (GA) for binding to heat shock protein 90 (HSP90) is 50- to 100-fold weaker than is the affinity of the structurally distinct natural product radicicol. X-ray crystallography shows that although radicicol maintains its free conformation when bound to HSP90, the conformation of GA is dramatically altered from an extended conformation with a trans amide bond to a kinked shape in which the amide group in the ansa ring has the cis configuration. We have performed ab initio quantum chemical calculations to demonstrate that the trans-cis isomeriztion of GA in solution is both kinetically and thermodynamically unfavorable. Thus, we propose that HSP90 catalyzes the isomerization of GA. We identify Ser113, a conserved residue outside the ATP binding pocket, as essential for the isomerization of GA. In support of this model, we show that radicicol binds equally well to both wild-type HSP90 and the Ser113 mutant, whereas the binding of GA to the Ser113 mutant is decreased significantly from its binding to wild-type HSP90. Based on this finding, a mechanism of keto-enol tautomerization of GA catalyzed by HSP90 is proposed. The added requirement of isomerization prior to tight binding may explain the enhanced binding affinity of GA for HSP90 in a cell extract versus in a purified form.     

Oxygen binding to sulfur in nitrosylated iron--thiolate complexes: relevance to the Fe-containing nitrile hydratases

Iron-nitrosyl complex containing S-bonded monosulfinate [PPN][(NO)Fe(S,SO2-C6H4)(S,S-C6H4)] (3) has been isolated from sulfur oxygenation of complex [PPN][(NO)Fe(S,S-C6H4)2] (2) which is obtained from addition of NO molecule to [PPN][(C4H8O)Fe(S,S-C6H4)2] (1) in organic solvents. This result reveals that binding of NO to the iron center promotes sulfur oxygenation of iron dithiolates by dioxygen and stabilizes the S-bonded sulfinate iron species. Analysis of the bond angles for complexes 2 and 3 reveals that iron is best described as existing in a distorted trigonal bipyramidal coordination environment surrounded by one NO, three thiolates, and one sulfinate in complex 3, whereas the distorted square pyramidal geometry is adopted in complex 2. Complex 3 further reacts in organic solvents with molecular oxygen in the presence of [PPN][NO2] to produce the dinuclear bis(sulfinate) complex [PPN]2[(NO)Fe(SO2,SO2-C6H4)(S,S-C6H4)]2 (4). Complex 3 showed reaction with PPh3 in THF/CH2Cl2 to yield complex 2 and Ph3PO. Upon photolysis of CH2Cl2 solution of complex 3 under N2 purge at ambient temperature, the UV-vis and IR spectra consistent with the formation of complex 2 demonstrate that complex 2 and 3 are photochemically interconvertible. Obviously, complex 3 is thermally quite stable but is photochemically active toward [O] release. Also described are the X-ray crystal structures of 3 and 4.     

Solventless synthesis of monodisperse Cu2S nanorods, nanodisks, and nanoplatelets

Cu(2)S nanocrystals with disklike morphologies were synthesized by the solventless thermolysis of a copper alkylthiolate molecular precursor. The nanodisks ranged from circular to hexagonal prisms from 3 to 150 nm in diameter and 3 to 12 nm in thickness depending on the growth conditions. High resolution transmission electron microscopy (HRTEM) revealed the high chalcocite (hexagonal) crystal structure oriented with the c-axis ([001] direction) orthogonal to the favored growth direction. This disk morphology is thermodynamically favored as it allows the extension of the higher energy [100] and [110] surfaces with respect to the [001] planes. The hexagonal prism morphology also appears to relate to increased C-S bond cleavage of adsorbed dodecanethiol along the more energetic [100] facets relative to [001] facets. Monodisperse Cu(2)S nanodisks self-assemble into ribbons of stacked platelets. This solventless approach provides a new technique to synthesize anisotropic metal chalcogenide nanostructures with shapes that depend on both the face-sensitive thermodynamic surface energy and the surface reactivity.     

Statistical techniques in activation analysis

Technical methods involved in activation analysis have received widespread publicity during recent years. Even more recently, various statistical techniques have been employed in conjunction with such technical methods in order to provide a better means of estimating the amounts of various pure chemical elements contained in an unknown mixture. In particular, the method of “least squares” has been employed extensively. However, for the most part, usual least squares applications in activation analysis have utilized the ordinary matrix model Y = Xβ +ρ, under the “error” assumptions (a) zero means, (b) variances proportional to Y and (c) zero covariances. In addition to the fact that assumptions (b) and (c) may lead to erroneous results, previous applications allow only point estimation, with no provision for confidence intervals and tests for model goodness of fit. The present paper is concerned with a feasible iterative estimation procedure which eliminates the necessity for assumptions (b) and (c), and which allows construction of confidence intervals and a test for model goodness of fit. A numerical example of the application of the technique is included. Further, an indication is given of how the technique can be extended to apply in the case of “restricted” least squares (quadratic programming).     

Polymer crystallinity and its effect on the non-linear bending creep rate for a polyphenylene sulphide thermoplastic composite

Recent developments have led to the introduction of advanced thermoplastic composites such as Polyphenylene Sulphide (PPS), which can be used structurally at higher temperatures. Because of its thermoplastic nature, it can also be hot worked by bringing the working temperature considerably above the glass transition temperature. However, such annealing processes also affect its degree of crystallinity, which in turn affect the properties of the material. This paper reports on the effect of matrix crystallinity on the rate of creep deformation in three point bending of some reinforced PPS composites. This work was based on a non-linear approach based on a Power law creep model creep deformation analysis. The effect of annealing on the non-linear creep deformation of the PPS composite specimens has been analysed using a Power Law creep model. Results indicate that the creep deformation for both 20 and 40% reinforced samples were relatively similar despite the difference in the amount of fibre reinforcement. In contrast, the value of the creep component decreased exponentially with the % crystallinity. for both 20 and 40%, reinforced samples.     

Molecular structure of meso-tetraphenylporphyrinatothallium(III) cyanide: Tl(tpp) (CN)

meso-Tetraphenylporphyrinatothallium(III) cyanide, Tl(tpp)(CN), was previously assumed to be monomeric and has been confirmed by X-ray analysis to exist as two independent molecules in one asymmetric unit. This unit displays two square-pyramidal coordination geometries for the thallium atoms with the cyano ligand coordinated to both Tl atoms. It crystallizes in the triclinic space group P , with a 10.003(3), b 16.231(7), c 21.277(8) Å, 89.98(3), β 90.57(3), γ 90.31(3)°' and z = 4. The structure was solved by direct methods. A total of 7995 unique reflections having I > 3σ(I) was measured with an automated diffractometer and used to refine the crystal structure to a conventional R factor of 6.05 %. The thallium-cyanide distances are 2.140(14) Å (for thallium(I)) and 2.277(14) Å (for thallium(2)) respectively, with thallium(1) situated 0.908 Å above the porphyrin ring and thallium(2) located 1.027 Å below the ring. IR and NMR spectroscopy p rovide complementary methods for investigation of the CN ligand. The characteristic band observed at 2160 cm⁻¹ in the FTIR spectrum is assigned to the CN stretching in the Tl(tpp)(CN) complex. The ¹³C resonance of axial cyano ligand is observed with a pulse delay of 3.5 s at 24°C at 139.2 ppm (with ¹J(²⁰⁵Tl-¹³C) 5394 and ¹J(²⁰³Tl-¹³C) 5344 Hz). This observation disagrees with the conclusion, drawn from previous work, in that an exchange process involving the apical ligand explains the invisibility due to line broadening at 35°C of the ¹³C signal.     

Computer Handling of Chemical and Biological Data of Traditional Chinese Medicines

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Ketalizations of aryl ω-(2-imidazolyl)alkyl ketones by glycerol and 3-mercapto-1,2-propanediol. synthesis and characterization of cis- and trans-{2-aryl-2-[ω-(2-imidazolyl)alkyl](1,3-dioxolan-4-yl and 1,3-oxathiolan-5-yl)}methanols

Aryl 2-[(2-imidazolyl)ethyl or 3-(2-imidazolyl)propyl]ketones were ketalized by glycerol or 3-mercapto-1,2-propanediol in boiling benzene in the presence of 4-toluenesulfonic acid to provide the title compounds. The aryl substituents are 4-chloro-, 4-bromo-, 4-fluoro-, or 2,4-dichlorophenyl. While aryl (2-imidazolyl)methyl ketones condensed with glycerol to form cis- and trans-{2-aryl-2-[(2-imidazolyl)methyl]-4-(hydroxymethyl)}-1,3-dioxolanes, related condensations with 3-mercapto-1,2-propanediol, under similar, or even more stringent reaction conditions, produced no 1,3-oxathiolane analogs, with the starting ketones being recovered. Separation and structure determination of these racemic cis and trans isomeric products are described. The structure of these stereoisomers was established by means of ¹H and ¹³C nmr correlation and nOe experiments. Selective methylation of the N-unsubstituted 2-imidazolyl alcohols with one equivalent sodium hydride and methyl iodide provided the corresponding N-methyl alcohols in excellent yields. With excess benzoyl chloride, N-unsubstituted 2-imidazolyl alcohols were initially converted to O, N-dibenzoates from which the N-benzoyl group was easily cleaved by ammonium hydroxide in ethanol to provide benzoate esters.     

Condensed as-triazines. Synthesis of 7-aryl-8H-[1,4]thiazino[2,3-e]-1,2,4-triazin-3(2H)-one

Ring closure of 6-amino-3-oxo-as-triazine-5-thione with α-haloketones provides the thiazino[2,3-e]-1,2,4-triazines which dehydrate via an unusual pathway to give 7-aryl-8H[1,4]thiazino[2,3-e]-1,2,4-triazin-3(2H)-ones.