Spectrofluorimetric determination of cysteine by 5-maleimidyl-2-(m-methylphenyl)benzoxazole

A new thiol weak-fluorescence probe, 5-maleimidyl-2-(m-methylphenyl)benzoxazole (MMPB), gives a highly fluorescence product in the presence of Cys. In this paper, MMPB has been developed for the fluorimetric determination of cysteine (Cys). At lambda(ex)/lambda(em) = 305.6/425.6 nm, the linear range is from 0 to 3.3 x 10(-7) mol l(-1) and the detection limit (sigma = 3) of 6.2 x 10(-10) mol l(-1). The main advantage of this method lies in the relative high selectivity compared with the methods using other N-substituted maleimide type of thiol reagents, in which 0.15-fold (molar ratio) of GSH is allowed and most of other amino acids at 100-fold (molar ratio) level had no obvious effect on the results. The proposed method has been applied to the determination of Cys in real samples.     

Calculations on the octupolar molecules with enhanced two-photon absorption cross sections based on the Zn (II) and Cu (I) as centers

The equilibrium geometries, electronic structures, as well as one- and two-photon absorption cross sections of a series of octupolar chromophores with Zn(2+) or Cu(+) as coordinate centers and 4,4'-bis(dibutylaminostyryl)-[2,2']-bis(bipyridyl) as ligands have been determined by using B3LYP/6-31G and ZINDO methods. These molecules are designed by controlled combination of two or three bipyridyl ligands with the metal centers. The results show that Zn(2+) is an effective template for the design of octupolar structures which enable it to form tetrahedral and octahedral coordinated complexes; while Cu(+) only exists in a tetrahedral coordinated complex, comparing the tetrahedral complex with Zn(2+) as the center with that of Cu(+) as the center, it is found that the complex with the Cu(+) center is a better two-photon absorption material than the former as far as the transparency/nonlinearity is concerned. Furthermore, for the same metal center of Zn(2+), both one- and two-photon absorptions of the tetrahedral complex are redshifted relative to those of the octahedral complex, is attributed to the spiroconjugation effect in the tetrahedral complex. Our theoretical findings are consistent with recent experimental observations and provide an important foundation for the design of improved transparency-nonlinearity two-photon absorption materials.     

过氧化氢与N—甲基苯胺盐酸盐引发体系的研究

在水介质中,研究了新型的过氧化氢/N-甲基苯胺盐酸盐引发体系对 AM 与 PVA 的接枝共聚。产物经紫外光谱、红外光谱和 ~1H-核磁共振进行表征,并提出了引发机理。     

Effect of particle size in preparative reversed-phase high-performance liquid chromatography on the isolation of epigallocatechin gallate from Korean green tea

To isolate epigallocatechin gallate (EGCG) of catechin compounds from Korean green tea (Bosung, Chonnam), a C18 reversed-phase preparative column (250x22 mm) packed with packings of three different sizes (15, 40-63, and 150 microm) was used. The sample extracted with water was partitioned with chloroform and ethyl acetate to remove the impurities including caffeine. The mobile phases in this experiment were composed of 0.1% acetic acid in water, acetonitrile, methanol and ethyl acetate. The injection volume was fixed at 400 microl and the flow rate was increased as the particle size becomes larger. The isolation of EGCG with particle size was compared at a preparative scale and the feasibility of separation of EGCG at larger particle sizes was confirmed. The optimum mobile phase composition for separating EGCG was experimentally obtained at the particle sizes of 15 and 40-63 microm in the isocratic mode, but EGCG was not purely separated at the particle size of 150 microm.     

DOPING LEVEL INCREASE OF POLY(3-METHYLTHIOPHENE)FILM DURING ELECTROCHEMICAL POLYMERIZATION PROCESS

The Raman spectra of poly(3-methylthiophene) (PMeT) films with different thicknesses, which have beenelectrochemically deposited on a flat stainless steel electrode surface by direct oxidation of 3-methylthiophene in borontrifluoride diethyl etherate (BFEE) at a constant applied potential of 1.38 V (versus SCE), have been investigated byexcitation with a 633-nm laser beam. The spectroscopic results demonstrated that the doping level of PMeT film wasincreasing during film growth. This finding was also confirmed by electrochemical examination. Moreover, the Raman bandsassigned to radical cations and dications in doped PMeT films were found approximately at 1420 and 1400 cm~(-1),respectively. Radical cations and dications coexist on the backbone of PMeT as conductive species and their concentrationsincrease with the increase of doping level. Successive cyclic voltammetry was proved to be an effective approach toimproving the doping level of as-grown thin compact PMeT film.     

Converged quantum calculations of HO2 bound states and resonances for J=6 and 10

Bound and resonance states of HO(2) are calculated quantum mechanically using both the Lanczos homogeneous filter diagonalization method and the real Chebyshev filter diagonalization method for nonzero total angular momentum J=6 and 10, using a parallel computing strategy. For bound states, agreement between the two methods is quite satisfactory; for resonances, while the energies are in good agreement, the widths are in general agreement. The quantum nonzero-J specific unimolecular dissociation rates for HO(2) are also calculated.     

Heavy metal phosphate nanophases in silica: influence of radiolysis probed via f-electron state properties

We have assessed the feasibility of carrying out time- and wavelength-resolved laser-induced fluorescence measurements of radiation damage in glassy silica. The consequences of alpha decay of Es-253 in LaPO₄ nanophases embedded in silica were probed based on excitation of 5f states of Cm³⁺, Bk³⁺, and Es³⁺ ions. The recorded emission spectra and luminescence decays showed that alpha decay of Es-253 ejected Bk-249 decay daughter ions into the surrounding silica and created radiation damage within the LaPO₄ nanophases. This conclusion is consistent with predictions of an ion transport code commonly used to model ion implantation. Luminescence from the ⁶D_7/2 state of Cm³⁺was used as an internal standard. Ion-ion energy transfer dominated the dynamics of the observed emitting 5f states and strongly influenced the intensity of observed spectra. In appropriate sample materials, laser-induced fluorescence provides a powerful method for fundamental investigation of alpha-induced radiation damage in silica.     

Synthesis and Characterization of Ag2S Nanocrystals in Hyperbranched Polyurethane at Room Temperature

Ag₂S nanoparticles in hyperbranched polyurethane matrix were prepared through the in situ reaction with thioacetamide as the sulfur source at room temperature. Transmission electron microscopic analysis revealed a uniform spherical shape for Ag₂S nanoparticles, with an average size of about 4-10 nm and a narrow size distribution. X-ray powder diffraction and UV-vis spectroscopy were also used to characterize the obtained nanoparticles     

Near-infrared fluorimetric determination of nucleic acids by shifting the ion-association equilibrium between heptamethylene cyanine and Alcian blue 8GX

A new method based on near-infrared (near-IR) fluorescence recovery, employing a two-reagent system which is composed of an anionic heptamethylene cyanine (HMC) and a polycationic phthalocyanine dye, Alcian blue 8GX, is presented for the determination of nucleic acids. With a maximum excitation wavelength at 766 nm and a maximum emission wavelength at 796 nm, the fluorescence recovery is linear with the concentration of nucleic acids added. Factors including the acidity of the medium, the reaction time, the optimal ratio of the two reagents, as well as the influence of foreign substance were all investigated. Meanwhile, the mechanism of fluorescence recovery was also studied. Under the optimal conditions, the linear ranges of the calibration curves were 10-250 ng ml⁻¹ for calf thymus DNA (CT DNA) and 10-200 ng ml⁻¹ for yeast RNA. The detection limits were 6.8 ng ml⁻¹ for CT DNA and 6.3 ng ml⁻¹ for yeast RNA, respectively. The method has been applied to the analysis of practical samples and the recovery results were satisfactory.     

Theoretical Study of Weakly Bound Dimers between Hydrogen Fluoride and Some Polar Molecules

Weakly bound linear and bent dimers, FH—X (where X = CO, OC, CNH, NCH, N₂O and ON₂), are investigated using the DFT B3LYP and ab initio MP2 methods with the same basis sets (6–311++G(3df,2pd)). The strengths of the H—C or H—N H‐bonds in dimers FH—CO, FH—CNH, and FH—N₂O are compared with those of the H—O or H—N H‐bonds in dimers FH—OC, FH—NCH, and FH—ON₂. The results obtained for the H‐bond distances, the elongation effect of the HF bond, the red shift of the HF stretching frequency, and the energy difference between the dimer and the charge transfer reveal that the H‐bonds of the first group of dimers are stronger than those of the second. The Gibbs energies calculated for the six dimer formations indicate that the weakly bound dimers are unstable at room temperature (T = 298 K) (FH—X's → FH + X's, ΔG < 0).