Reduction of derived Hochschild functors over commutative algebras and schemes

We study functors underlying derived Hochschild cohomology, also called Shukla cohomology, of a commutative algebra S essentially of finite type and of finite flat dimension over a commutative noetherian ring K. We construct a complex of S-modules D, and natural reduction isomorphisms for all complexes of S-modules N and all complexes M of finite flat dimension over K whose homology H(M) is finitely generated over S; such isomorphisms determine D up to derived isomorphism. Using Grothendieck duality theory we establish analogous isomorphisms for any essentially finite-type flat map of noetherian schemes, with f^!OY in place of D.     

Mass spectral study of alkali-cationized Boc-carbo-beta3-peptides by electrospray tandem mass spectrometry

Electrospray tandem mass spectrometry was used to study the dissociation reactions of [M+Cat]+ (Cat = Na+ and Li+) of Boc-carbo-beta3-peptides. The collision-induced dissociation (CID) spectra of [M+Cat-Boc]+ of these peptides are found to be significantly different from those of [M+H-Boc]+ ions. The spectra are more informative and display both C- and N-terminus metallated ions in addition to characteristic fragment ions of the carbohydrate moiety. Based on the fragmentations observed in the CID spectra of the [M+Cat-Boc]+ ions, it is suggested that the dissociation involves complexes in which the metal ion is coordinated in a multidentate arrangement involving the carbonyl oxygen atoms. The CID spectra of [M+Cat-Boc]+ ions of the peptide acids show an abundant N-terminal rearrangement ion [b(n)+17+Cat]+ which is absent for esters. Further, two pairs of positionally isomeric Boc-carbo-beta3-peptide acids, Boc-NH-Caa(S)-beta-hGly-OH (11) and Boc-NH-beta-hGly-Caa(S)-OH (12), and [Boc-NH-Caa(S)-beta-hGly-Caa(S)-beta-hGly-OH] (13) and [Boc-NH-beta-hGly-Caa(S)-beta-hGly-Caa(S)-OH] (14), were differentiated by the CID of [M+Cat-Boc]+ ions. The CID spectra of compounds 11 and 13 are significantly different from those of 12 and 14, respectively. The abundance of [b(n)+17+Cat]+ ions is higher for peptide acids 12 and 14 with a sugar group at the C-terminus when compared to 11 and 13 which contain a sugar moiety at the N-terminus. The observed differences between the CID spectra of these isomeric peptides are attributed to the difference in the preferential site of metal ion binding and also on the structure of the cyclic intermediate involved in the formation of the rearrangement ion.     

Potential of mean force between hydrophobic solutes in the Jagla model of water and implications for cold denaturation of proteins

Using the Jagla model potential we calculate the potential of mean force (PMF) between hard sphere solutes immersed in a liquid displaying water-like properties. Consistent estimates of the PMF are obtained by (a) umbrella sampling, (b) calculating the work done by the mean force acting on the hard spheres as a function of their separation, and (c) determining the position dependent chemical potential after calculating the void space in the liquid. We calculate the PMF for an isobar along which cold denaturation of a model protein has previously been reported. We find that the PMF at contact varies non-monotonically, which is consistent with the observed cold denaturation. The Henry constant also varies non-monotonically with temperature. We find, on the other hand, that a second (solvent separated) minimum of the PMF becomes deeper as temperature decreases. We calculate the solvent-solvent pair correlation functions for solvents near the solute and in the bulk, and show that, as temperature decreases, the two pair correlation functions become indistinguishable, suggesting that the perturbation of solvent structure by the solute diminishes as temperature decreases. The solvent-solute pair correlation function at contact grows as the temperature decreases. We calculate the cavity correlation function and show the development of a solvent-separated peak upon decrease of temperature. These observations together suggest that cold denaturation occurs when the solvent penetrates between hydrophobic solutes in configurations with favorable free energy. Our results thus suggest that cold denatured proteins are structured and that cold denaturation arises from strong solvent-solute interactions, rather than from entropic considerations as in heat denaturation.     

Isolation,structural assignment and synthesis of (SE)-2-methyloctyl 3-(4-methoxyphenyl) propenoate from the marine soft coral Sarcophyton ehrenbergi

A new metabolite 1 has been isolated from the marine soft coral Sarcophyton ehrenbergi along with two known diterpenoids 2 and 3 and cholesterol 4. The structure of 1 was determined by means of detailed spectroscopic analysis and unambiguously confirmed to have the S configuration by the synthesis of both enantiomers using 4-benzyl-2-oxazolidinone auxiliaries. (S)- and (R)-1, 3 and some of the synthetic intermediates were evaluated for cytotoxic activity against human lung cancer (A549), prostate cancer (DU145), cervical cancer (HeLa) and breast cancer (MCF-7) cell lines in an in vitro bioassay.     

Asymmetric synthesis of beta-hydroxy amino acids via aldol reactions catalyzed by chiral ammonium salts

The Cinchona alkaloid derived chiral ammonium salt developed by Park and Jew functions as an effective catalyst for the synthesis of beta-hydroxy alpha-amino acids via asymmetric aldol reactions under homogeneous conditions. The syn diastereomers are obtained in good ee, and aryl-substituted aliphatic aldehydes are the best substrates for the reaction. These results represent the highest ee's obtained to date in direct aldol reactions of glycine equivalents catalyzed by inexpensive, readily prepared chiral ammonium salts.     

Synthesis of the core structure of acutumine

[reaction: see text] The tricyclic core of the bioactive natural product acutumine has been synthesized. Key steps include an oxidative phenolic coupling to form a masked o-benzoquinone, an anionic oxy-Cope rearrangement to construct an all-carbon quaternary center, and a Michael-type cyclization to form an amine-bearing quaternary carbon. The target compound exists in solution as an enol, in contrast to related compounds that are ketones. A model explaining these observations is presented.     

Synthesis of beta-substituted alpha-amino acids via Lewis acid promoted radical conjugate additions to alpha,beta-unsaturated alpha-nitro esters and amides

[reaction: see text] Beta-substituted alpha,beta-unsaturated alpha-nitro esters and amides undergo radical conjugate additions when treated with an appropriate Lewis acid. Deuterium studies revealed that the acidic alpha-stereocenter of the alpha-nitro ester products does not racemize under strictly controlled workup conditions. The alpha-nitro amides did racemize significantly during chromatography, but this could be greatly minimized by subjecting the crude adducts to subsequent transformations. The conjugate addition products can be elaborated into beta-substituted alpha-amino acids in two simple steps.     

Role of electronic structure of ruthenium polypyridyl dyes in the photoconversion efficiency of dye‐sensitized solar cells: Semiempirical investigation

ZINDO/S calculations on cis‐Ru(4,4′‐dicarboxy‐2,2′‐bipyridine)₂(X)₂ and cis‐Ru(5,5′‐dicarboxy‐2,2′‐bipyridine)₂(X)₂ complexes where X = Cl^?, CN^?, and NCS^? reveal that the highest occupied molecular orbital (HOMO) of these complexes has a large amplitude on both the nonchromophoric ligand X and the central ruthenium atom. The lowest‐energy metal to ligand charge transfer (MLCT) transition in these complexes involves electron transfer from ruthenium as well as the halide/pseudohalide ligand to the polypyridyl ligand. The contribution of the halide/pseudohalide ligand(X) to the HOMO affects the total amount of charge transferred to the polypyridyl ligand and hence the photoconversion efficiency. The virtual orbitals involved in the second MLCT transition in 4,4′‐dicarboxy‐2,2′‐bipyridine complexes have higher electron density on the ? COOH group compared to the lowest unoccupied molecular orbital and hence a stronger electronic coupling with the TiO₂ surface and higher injection efficiency at shorter wavelengths. In comparison, the virtual orbitals involved in the second MLCT transition in 5,5′‐dicarboxy‐2,2′‐bipyridine complexes have lesser electron density on the ? COOH group, leading to a weaker electronic coupling with the TiO₂ surface and therefore lower efficiency for electron injection at shorter wavelengths for these complexes. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Porous silicon templates for electrodeposition of nanostructures

We report the fabrication and characterization of porous silicon templates for electrodeposition of high aspect ratio one-dimensional metallic nanostructures (nanowires/nanoparticles) in them. Even though nanostructures/nanowires in the past have been fabricated in alumina, polymer or silica templates, the advantages of this approach are the possibility for seamless integration of nanostructures with other silicon components, and silicon based sensors because of better physical and electrical interconnection between the nanostructure and the silicon substrate. In this work, fabrication and characterization of nanowires/nanostructures such as single-segment Ni–Fe and Au and two-segment Ni–Fe/Au electrodeposited in the porous silicon template are presented. The templates with ordered and controlled nanometer-sized pores, 40 nm and 290 nm in diameter, were created through porous Si etching. The morphology, composition and structural characteristics of the template and of the single-segment Ni–Fe and Au and two-segment Ni–Fe/Au nanostructures of diameter 275±25 nm, length up to 100 μm and pitch of 1 μm were analyzed using scanning electron microscopy and X-ray diffraction techniques. The micrographs confirm that the plating parameters have a strong influence on morphology and composition of the structures. Further, the Ni–Fe images show the formation of both vertical and branched nanowires along with nanoparticles, from breakage/discontinuous growth of nanowires. Ni–Fe nanostructures were further analyzed for temperature-dependent magnetization and magnetization vs. magnetic field measurements using a commercial physical property measurement system. They reveal no magnetic anisotropy of the nanostructures probably due to a balance between ‘reduced’ shape anisotropy from branched and rough pore surfaces and magnetocrystalline anisotropy. PACS 61.46.+w; 75.75.+a; 81.07.-b; 81.16.Be