Field studies on the environmental factors in controlling microcystin production in the subtropical shallow lakes of the Yangtze River

Microcystin (MC) problem made more and more care about in China, intercellular MC (Int-MC) and cellular MC (Cel-MC) were important contents to reflect the producing-MC ability by cyanobacteria and by lakes. To study the correlations between Int-MC, Cel-MC concentration and biological and environmental factors, eight cyanobacterial blooming lakes were studied in the middle and lower reaches of the Yangtze River. Microcystin-RR (MC-RR) and Microcystin-LR (MC-LR) were the primary toxin variants in our data. From the linear correlations between MC and environmental factors, cellular-YR had significant correlation with most of chemical factors except total nitrogen (TN) and the ratio of total nitrogen and total phosphorus (TN/TP), most intracellular MC analogues had significant correlations with total dissolved nitrogen (TDN), ammonium (NH4+), nitrite (NO2-), TP, total dissolved phosphorus (TDP), Microcystis. From the canonal correspondence analysis, Int-MC concentrations were closely related with the chemical and biological factors, such as TP, total organic carbon (TOC), chlorophyll a (Chl a), Microcystis biomass, et al. While Cel-MC contents, especially Cel-RR and Cel-LR, were closely related with light environmental in the lakes such as water depth and transparence.

Microstructure studies of PdGe/Ge ohmic contacts to n-type GaAs formed by rapid thermal annealing

A low resistance and shallow ohmic contact to n-GaAs is performed by using Ge/Pd/GaAs trilayer structure and rapid thermal annealing process. The dependence of specific contact resistivity on the temperature of rapid thermal annealing is investigated. A good ohmic contact is formed after annealing at 400-500 degrees C for 60 s. The best specific contact resistivity is 1.4 x 10(-6) Omega cm(2). Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS) and scanning electron microscopy (SEM) are used to analyze the interfacial microstructure. A strong correlation between the contact resistance and the film microstructure is observed.

Loess magnetic properties in the Ili Basin and their correlation with the Chinese Loess Plateau

     Over the past two decades, magnetoclimatological studies of loess-paleosol sequences in the Chinese Loess Plateau (CLP) have made outstanding achievements, which greatly promote the understanding of East Asian paleomonsoon evolution, inland aridification of Asia, and past global climate changes. Loess magnetic properties of the CLP have been well studied. In contrast, loess magnetic properties from outside the CLP in China have not been fully understood. We have little knowledge about the magnetic properties of loess in the Ili Basin, an intermontane depression of the Tianshan (or Tien Shan) Mountains. Here, we present the results of rock magnetic measurements of the Ili loess including mass magnetic susceptibility (χ) and anhysteretic remanent magnetization (ARM), high/low temperature dependence of susceptibility (TDS) and hysteresis, as well as X-ray diffraction (XRD) for mineral analysis. Based on the comparison with loess-paleosol sequences in the CLP (hereafter referred to as the Chinese loess), we discuss the possible magnetic susceptibility enhancement mechanism of the Ili loess. The results show that 1) the total magnetic mineral concentration of the Ili loess is far lower than that of the Chinese loess, though they have similar magnetic mineral compositions. The ferrimagnetic minerals in the Ili loess are magnetite and maghemite, and the antiferromagnetic mineral is hematite; XRD analysis also identifies the presence of ilmenite. The ratio of maghemite is lower in the Ili loess than in the Chinese loess, but the ratios of magnetite and hematite are higher in the Ili loess than in the Chinese loess. 2) The granularity of magnetic minerals in the Ili loess, dominated by pseudo-single domain (PSD) and multi-domain (MD) grains, is generally much coarser than that of the Chinese loess. Ultrafine pedogenically-produced magnetic grains have a very limited contribution to the susceptibility enhancement. Rather, PSD and MD particles of magnetite and maghemite are the main contributors to the enhancement of susceptibility in the Ili loess. 3) The susceptibility enhancement mechanism for the Ili loess is complicated and superimposes both a wind velocity/vigor model (Alaskan or Siberian model) and the in situ ultrafine grain pedogenic model; the former might play an important role in the Ili loess. 4) Magnetic susceptibility enhancements of the Ili loess are related not only to the eolian input of the source area, but also to the local climate, landform, and geological background. Therefore, great care should be taken when reconstructing paleoclimate using magnetic susceptibility data from the Ili loess.

Correlation between initial chromatid damage and survival of various cell lines exposed to heavy charged particles

The biophysical characteristics of heavy ions make them a rational source of radiation for use in radiotherapy of malignant tumours. Prior to radiotherapy treatment, a therapeutic regimen must be precisely defined, and during this stage information on individual patient radiosensitivity would be of very great medical value. There are various methods to predict radiosensitivity, but some shortfalls are difficult to avoid. The present study investigated the induction of chromatid breaks in five different cell lines, including one normal liver cell line (L02), exposed to carbon ions accelerated by the heavy ion research facility in Lanzhou (HIRFL), using chemically induced premature chromosome condensation (PCC). Previous studies have reported the number of chromatid breaks to be linearly related to the radiation dose, but the relationship between cell survival and chromatid breaks is not clear. The major result of the present study is that cellular radiosensitivity, as measured by D-0, is linearly correlated with the frequency of chromatid breaks per Gy in these five cell lines. We propose that PCC may be applied to predict radiosensitivity of tumour cells exposed to heavy ions.

Correlation between the characteristics and catalytic performance of Ni-V-O catalysts in oxidative dehydrogenation of propane

Ni - V - O series catalysts for the oxidative dehydrogenation (ODH) of propane were prepared and characterized by BET, XRD, H-2- TPR, O-2-TPD-MS and electrical conductivity. At 425 degreesC a C3H6 selectivity of 49.9% was observed on Ni0.9V0.1OY at a C3H8 conversion of 19.4%, and the obtained selectivity is almost two times higher than that over NiO at the roughly same conversion of C3H8. The mobile oxygen species created by the interaction of NiO and V2O5 has been found in the composite catalysts by O-2-TPD-MS and electrical conductivity studies, which seems to be responsible for the enhanced selectivity of the propane oxidative dehydrogenation.

Carbon monoxide adsorption on molybdenum phosphides: Fourier transform infrared spectroscopic and density functional theory studies

Molybdenum phosphide (MoP) and supported molybdenum phosphide (MoP/gamma-Al2O3) have been prepared by the temperature-programmed reduction method. The surface sites of the MoP/gamma-Al2O3 catalyst were characterized by carbon monoxide (CO) adsorption with in situ Fourier transform infrared (FT-IR) spectroscopy. A characteristic IR band at 2037 cm(-1) was observed on the MoP/gamma-Al2O3 that was reduced at 973 K. This band is attributed to linearly adsorbed CO on Mo atoms of the MoP surface and is similar to IR bands at 2040-2060 cm(-1), which correspond to CO that has been adsorbed on some noble metals, such as platinum, palladium, and rhodium. Density functional calculations of the structure of molybdenum phosphides, as well as CO chemisorption on the MoP(001) surface, have also been studied on periodic surface models, using the generalized gradient approximation (GGA) for the exchange-correlation functional. The results show that the chemisorption of CO on MoP occurred mainly on top of molybdenum, because the bonding of CO requires a localized mininum potential energy. The adsorption energy obtained is DeltaH(ads) approximate to -2.18 eV, and the vibrational frequency of CO is 2047 cm-1, which is in good agreement with the IR result of CO chernisorption on MoP/gamma-Al2O3.

Studies of the intermolecular DNA triplexes of C+center dot GC and T center dot AT triplets by electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry

Formation and stabilities of four 14-mer intermolecular DNA triplexes, consisting of third strands with repeating sequence CTCT, CCTT, CTT, or TTT, were studied by electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) in the gas phase. The gas-phase stabilities of the triplexes were compared with their CD spectra and melting behaviors in solution, and parallel correlation between two phases were obtained. In the presence of 20 mm NH4+ (pH 5.5), the formation of the TTT triplex was not detected in both solution and the gas phase.

Peripheries of molecular projection in three-dimensional space and studies of quantitative structure-activity relationships

A new index, i.e., the periphery representation of the projection of a molecule from 3D space to a 2D plane is described. The results, correlation with toxicity of substituted nitrobenzenes, obtained by using periphery descriptors are much better than that obtained by using the areas (i.e., shadows) of projections of the compounds. Even better results were achieved by using the combination of periphery descriptors and the projections areas as well as the indicated variable K reflecting the action of group NO position on the benzene ring.

Studies on the non-covalent complexes between oleanolic acid and cyclodextrins using electrospray ionization tandem mass spectrometry

Non-covalent inclusion complexes formed between an anti-inflammatory drug, oleanolic acid (OA), and alpha-, beta- and gamma-cyclodextrins (CDs) were investigated by means of solubility studies and electrospray ionization tandem mass spectrometry (ESI-MSn). The order of calculated association constants (K-1:1) of complexes between OA and different CDs in solution is in good agreement with the order of their relative peak intensities and the relative CID energies of the complexes under the same ESI-MSn conditions. These results indicate a direct correlation between the behaviors of solution- and gas-phase complexes. ESI-MS can thus be used to evaluate solution-phase non-covalent complexes successfully. The experimental results show that the most stable 1:1 inclusion complexes between three CDs and OA can be formed, but 2:1 CD-OA complexes can be formed with beta- and gamma-CDs. Multi-component complexes of alpha-CD-OA-beta-CD (1:1:1), alpha-CD-OA-gamma-CD (1:1:1) and beta-CD-OA-gamma-CD (1:1:1) were found in equimolar CD mixtures with excess OA. The formation of 2:1 and multi-component 1:1:1 non-covalent CD-OA complexes indicates that beta- and gamma-CD are able to form sandwich-type inclusion non-covalent complexes with OA. The above results can be partly supported by the relative sizes of OA and CD cavities by molecular modeling calculations.

Theoretical studies of nonlinear optical properties of compounds K(4)Ln(2)(CO3)(3)F-4 (Ln=Pr, Nd, Sm, Eu, Gd)

K(4)Ln(2)(CO3)(3)F-4 (Ln=Pr, Nd, Sm, Eu, Gd) is a special type of frequency doubling compound, whose crystal structure exhibits a scarcity of fluorine ions. This leads to two different coordination polyhedrons in the general position of K(2) atoms: [K(2)O6F(1)(2)F(2)] and [K(21)O6F(1)(2)] in a 2/1 ratio. The chemical bonding structures of all constituent atoms of the compound K4Gd2(CO3)(3)F-4 (KGCOF) are comprehensively studied; moreover, the relationship between the chemical bonding structure and the nonlinear optical (NLO) properties is investigated from the chemical bond viewpoint. The theoretical prediction of the NLO tensor coefficient d(11) of KGCOF is in agreement with experimental observation. Theoretical analyses show that the nonlinearity of this crystal type mainly originates from K-O bonds. In addition, the correlation between the NLO tensor d(11) and the refractive index n(0) of KGCOF is discussed. (C) 2000 American Institute of Physics. [S0021-8979(00)07506-X].

NMR studies of Gd(DTPA-BIN) in human serum albumin solution

Stable gadolinium complexes, such as Gd(DTPA) and Gd(DOTA), are usually used as the contrast agents for magnetic resonance imaging(MRI). Reported here are the enhanced relaxation properties of a novel gadolinium complex, diethylene-triaminopentaacetate Lis (isoniazid) [Gd(DTPA-BIN)], in aqueous and in human serum albumin(HSA) solution, which indicates that (1) two Gd(DTPA-BIN) can integrate non-covalently with one HSA with an equilibrium constant of 0. 02 mmol(-2) . L-2 ; (2) the relaxivities are 3. 28 and 4. 92 mmol(-1) . L . s(-1) for the free Gd(DTPA-BIN) and the [Gd(DTPA-BIN)](2), HSA conjugator, respectively; (3) the rotational correlation time of protein conjugator is notably higher than that of the free complex, The above results may imply that Gd(DTPA-BIN) has a higher tissue selectivity than that of its parent Gd(DTPA).

Studies on quantitative structure-activity relationship between the structures of derivatives of benzamide and their antiallergic activities

Molecular connectivity index and comparative molecular field analysis (CoMFA) have been applied to the studies of the correlation of the derivatives of benzamide and their antiallergic activities. The results achieved by using CoMFA based on 3D factors are much better than that obtained by using multiple regression analysis based on majorly 2D structural information. The CoMFA results show that the dominant factor which affects activity is steric, whereas electrostatic effect only plays an unimportant role.

Studies on three-dimensional quantitative structure-activity relationships between the structures of N-nitroso compounds and their carcinogenic activities

Comparative molecular fiels analysis (CoMFA) has been applied to the studies of the correlation of the N-nitroso compounds and their carcinogenic activities, The comparison of CoMFA results with different lattice spacing and different atom probes was investigated, CoMFA resulted in a quantitative description of the major steric and electrostatic field effects and gave significant new insights to factors governing potency.

Studies on polyepichlorohydrin-based polyurethane/poly(MMA-co-St) IPNs

Interpenetrating polymer networks of polyepichlorohydrin-based polyurethane/poly(MMA-co-St) have been prepared with simultaneous mettled by changing the weight fraction of MMA(W-MMA) in copolymer of MMA with styrene. The IPNs have been studied by DSC, TEM and dynamic mechanical spectroscopy(DMS). The results show that the IPNs have only one T-g, when W-MMA is greater than 0. 6. But when W-MMA IMA is less than 0. 4, the IPNs have two T(g)s, and phase separation is observed on TEM. The phenomenon is explained according to the solubility parameters(delta) and the fraction of hydrogen bond(delta(h)) of P (MMA-co-St). The study reveals that there is a close correlation among the delta, domain size and mechanical properties of PU (PECH)/P(MMA-co-St) IPN.

Predicting protein interaction interfaces from protein sequences: Case studies of subtilisin and phycocyanin

Identification of protein interaction interfaces is very important for understanding the molecular mechanisms underlying biological phenomena. Here, we present a novel method for predicting protein interaction interfaces from sequences by using PAM matrix (PIFPAM). Sequence alignments for interacting proteins were constructed and parsed into segments using sliding windows. By calculating distance matrix for each segment, the correlation coefficients between segments were estimated. The interaction interfaces were predicted by extracting highly correlated segment pairs from the correlation map. The predictions achieved an accuracy 0.41-0.71 for eight intraprotein interaction examples, and 0.07-0.60 for four interprotein interaction examples. Compared with three previously published methods, PIFPAM predicted more contacting site pairs for 11 out of the 12 example proteins, and predicted at least 34% more contacting site pairs for eight proteins of them. The factors affecting the predictions were also analyzed. Since PIFPAM uses only the alignments of the two interacting proteins as input, it is especially useful when no three-dimensional protein structure data are available.