Citrinal A,a novel tricyclic derivative of citrinin,from an algicolous fungus Penicillium sp.i-1-1

Citrinal A(1),a novel tricyclic compound with a rare tetrahydro-2H-benzofuro[7-b][1,4]dioxin-9(3H)-one skeleton,along with two known related compounds,citrinin(2) and 2,3,4-trimethyl-5,7-dihydroxy-2,3-dihydrobenzofuran(3) were isolated from an algicolous fungus Penicillium sp.i-1-1.The structure and stereochemistry of 1 were determined by comprehensive spectral and biogenic analysis.Its cytotoxic effects on the A-549 and HL-60 cell lines were evaluated.     

Electronic structure of the polydiacetylenes: effect of bond length variations in a model system

SCF Xα calculations are reported for a cyclic molecule whose bonding sequence is a model for the backbone bonding sequence in the polydiacetylenes. The electronic structure of the model molecule, with particular emphasis on the two lowest energy optical transitions, is determined in conjunction with a systematic variation in bonding sequence. Transition energies are in fair agreement with experiment for polydiacetylenes with the acetylene linkage,

, and for the model molecule in solution. The same analysis predicts a substantial red shift on going to the butatriene linkage,

, whereas a small blue-shift is observed experimentally. This qualitative disagreement between theory and experiment is attributed to the inability of the present scheme to represent excitonic excitations and/or the neglect of interchain interactions. The transition energies from the SCF Xα treatment can be satisfactorily represented in a simple Hückel model with the following resonance integral-bond length relationship:β_ij = 67.28 exp (-d_ij/0.424) eV.     

Schisanlactone G,a new 3,4-seco-lanostane triterpenoid from Schisandra sphenanthera

A new 3,4-seco-lanostane triterpenoid,schisanlactone G (1),was isolated from the fruits of Schisandra sphenanthera.Its structure was established on the basis of extensive spectroscopic analysis.2009 Rong Tao Li.Published by Elsevier B.V.on behalf of Chinese Chemical Society.All fights reserved.     

FeCl_3 catalyzed diarylmethanes formations

Under mild condition,using FeCl3 as catalyst,a series of functionalized diarylmethanes were prepared efficiently from the reactions of arenes with paraformaldehyde.This catalytic system is not sensitive to air and moisture.     

Selectively colorimetric detection of cysteine with triangular silver nanoprisms

Triangular silver nanoprisms were prepared and applied to make colorimetric detection of cysteine based on our findings that cysteine could lead to the blue shift of the dipole plasmon resonance absorption,but other 19 kinds of natural amino acids could not.Cysteine with a concentration 160 nmol/L can result in a color change that can be discerned with naked eyes.     

Ultraviolet photoelectron spectroscopy of Pd-Si glasses

In order to determine systematic changes in the density of states with alloy composition, photoelectron spectra at hv=21.2 eV were measured for several amorphous alloys based on the well-known Pd-Si glass system. Three binary alloys with 15, 20, and 25 at. % Si, two ternaries, Pd₈₀ Si₁₇ Cu₃ and Pd₈₀ Si₁₄ Cu₆, and polycrystalline Pd were analyzed. Compared to Pd, both the density of states at the Fermi energy and the d-band width are reduced in the glasses. The d-bands display an overall shift of 0.4 eV over the range of alloy compositions studied. Partial agreement with recent density of states calculations was obtained.     

Electronic structure of poly-diacetylene: Calculations on a model system

Calculations of electronic structure have been performed for a molecule that models poly-diacetylene. The self-consistent field, X_α method was used. It is concluded that poly-diacetylene has a nearly-free-electron-like valence band and is best described as a wide band gap semiconductor. The π → π^* transition of the model molecule is in numerical agreement with the size of the band gap observed in most poly-diacetylene systems.     

Effect of three-body forces on the lattice dynamics of noble metals

A simple method to generate an effective electron-ion interaction pseudopotential from the energy wave number characteristic obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the experimental and theoretical phonon dispersion curves.     

An ultra-low hydrolysis sol-gel route for titanosilicate xerogels and their characterization

In this work TiO₂-SiO₂ xerogels were prepared through an ultra low hydrolysis method using titanium and silicon alkoxide. The samples were heat treated to 500°C. The xerogels were characterized using TGA/DTA, FTIR, XRD and TEM. The samples showed the formation of Si–O–Ti bridges by its characteristic vibration within 925–960 cm⁻¹ range. Si–O–Si bond angles were calculated using the central force network model. The TiO₂ in all the samples crystallized on heat treatment to 500°C. The crystallite size calculated using the Scherer formula from the XRD was verified from the Transmission Electron Micrograph. Samples heat treated to 350°C remained amorphous and hence could be used as hosts for biomaterials and organic optical materials.