南京地区12种常绿阔叶树种冬季抗寒性动态变化

选取南京地区露地引种的12种常绿阔叶树种,借助电导法对其抗寒性进行研究,结果表明:12种常绿树种在2003年与2005年冬季期间,抗寒能力高低排序具有很好的一致性与重复性.12种常绿树种在2005年10月至2006年3月期间随冬季低温诱导进行其抗寒能力呈逐渐增强趋势,其中在1月中旬树种抗寒能力均达到最强,而通常在10月份或3月份期间树种抗寒能力最弱.比较而言,12种常绿阔叶树种对冬季低温条件响应的快慢程度各有差异,其中樟科的香樟(Cinnamomum camphora)、浙江樟(Cinnamomum japonicum)属于低温快速响应型,而冬青科的冬青(Ilex purpurea)、大叶冬青(Ilex latifolia)属于低温滞缓响应型,其余树种为正常响应型.12种常绿阔叶树种试验所得抗寒能力结果与引种地冬季观察结果具有很好的对应性.研究结果可为常绿阔叶树种进一步向较高纬度地区的引种与栽培管理工作提供重要的参考.     

Optical studies of a conformational change in DNA before melting

The circular dichroism of double-stranded DNA is temperature dependent prior to its melting. As the temperature is increased the spectrum becomes more nonconservative. This is certainly due to a conformational change within the framework of the double helix. To ascertain the nature of the conformational change, a series of synthetic and natural DNA's from a variety of sources was investigated. The same qualitative changes were seen for all the DNA samples, independent of base composition. However, there were definite quantitative differences, with poly [d(A-T)] manifesting the largest effect. Oligomers of the form [d(A-T)]_n with n = 10 to 21 behaved in a manner similar to the polymer. There is no observed chain-length dependence. The breadth of the pre-melt transition indicates a low ΔH (less than 5 kcal./mole); the lack of dependence on chain length indicates that the co-operative unit is smaller than eight base pairs.     

Hen egg white lysozyme fibrillation: a deep‐UV resonance Raman spectroscopic study

Amyloid fibrils are associated with numerous degenerative diseases. The molecular mechanism of the structural transformation of native protein to the highly ordered cross‐β structure, the key feature of amyloid fibrils, is under active investigation. Conventional biophysical methods have limited application in addressing the problem because of the heterogeneous nature of the system. In this study, we demonstrated that deep‐UV resonance Raman (DUVRR) spectroscopy in combination with circular dichroism (CD) and intrinsic tryptophan fluorescence allowed for quantitative characterization of protein structural evolution at all stages of hen egg white lysozyme fibrillation in vitro. DUVRR spectroscopy was found to be complimentary to the far‐UV CD because it is (i) more sensitive to β ‐sheet than to α ‐helix, and (ii) capable of characterizing quantitatively inhomogeneous and highly light‐scattering samples. In addition, phenylalanine, a natural DUVRR spectroscopic biomarker of protein structural rearrangements, exhibited substantial changes in the Raman cross section of the 1000‐cm^–1 band at various stages of fibrillation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies on the possible biological effects of 50 Hz electric and/or magnetic fields: Evaluation of some glycolytic enzymes,glycolytic flux,energy and oxido-reductive potentials in human erythrocytes exposed in vitro to power frequency fields

An attempt has been made to understand whether 50 Hz electric and magnetic fields (EMFs) are involved in producing bioeffects by exposing human erythrocytes in vitro. The study evaluated some key glycolytic enzymes, glucose consumption, lactate production, energy charge, 2,3-diphosphoglycerate, and reduced glutathione levels. all of which are biochemical parameters significant to erythrocyte function. Cells exposed to individual or superimposed EMFs have not shown any significant difference compared with the controls. © 1993 Wiley-Liss. Inc.     

Kinetic,isotherm and thermodynamic investigations on adsorption of trace elements and pigments from soybean oil using high voltage electric field-assisted bleaching: A comparative study

In this study, the amounts of trace elements (Fe (II) and Cu (II)) and pigments (chlorophyll and carotenoid) in soybean oil were evaluated under high voltage electric field (HVEF) bleaching method at different voltage (10 and 20 kV), temperature (35–65 °C), time (0−30 min) and clay percentage (0.5–2 %) and then were compared to the industrial bleaching method (IBM). The kinetic data of ions and pigments adsorbed on activated bentonite clay under IBM and HVEF at two voltages of 10 and 20 kV followed the mechanism of the pseudo-first-order model (PFOM). The carotenoid and chlorophyll equilibrium data followed a Freundlich isotherm type model, which demonstrated multilayer adsorption under HVEF. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°) displayed that the adsorption of trace metal ions and pigments on bentonite clay under IBM and HVEF were feasible, endothermic and spontaneous between 35 and 65 °C. The results indicated that the HVEF, especially at higher voltage, has a high remarkable capability to remove metal ions and pigments from soybean oil than the IBM. The highest removal capacity for metal and pigments of soybean oil bleaching were obtained in the order of HVEF-20 kV > HVEF-10 kV > IBM.     

Reversed-phase HPLC enantioseparation of pantoprazole using a teicoplanin aglycone stationary phase—Determination of the enantiomer elution order using HPLC-CD analyses

A direct HPLC method was developed for the enantioseparation of pantoprazole using macrocyclic glycopeptide-based chiral stationary phases, along with various methods to determine the elution order without isolation of the individual enantiomers. In the preliminary screening, four macrocyclic glycopeptide-based chiral stationary phases containing vancomycin (Chirobiotic V), ristocetin A (Chirobiotic R), teicoplanin (Chirobiotic T), and teicoplanin-aglycone (Chirobiotic TAG) were screened in polar organic and reversed-phase mode. Best results were achieved by using Chirobiotic TAG column and a methanol-water mixture as mobile phase. Further method optimization was performed using a face-centered central composite design to achieve the highest chiral resolution. Optimized parameters, offering baseline separation (resolution = 1.91 ± 0.03) were as follows: Chirobiotic TAG stationary phase, thermostated at 10°C, mobile phase consisting of methanol/20mM ammonium acetate 60:40 v/v, and 0.6 mL/min flow rate. Enantiomer elution order was determined using HPLC hyphenated with circular dichroism (CD) spectroscopy detection. The online CD signals of the separated pantoprazole enantiomers at selected wavelengths were compared with the structurally analogous esomeprazole enantiomer. For further verification, the inline rapid, multiscan CD signals were compared with the quantum chemically calculated CD spectra. Furthermore, docking calculations were used to investigate the enantiorecognition at molecular level. The molecular docking shows that the R-enantiomer binds stronger to the chiral selector than its antipode, which is in accordance with the determined elution order on the column—S- followed by the R-isomer. Thus, combined methods, HPLC-CD and theoretical calculations, are highly efficient in predicting the elution order of enantiomers.     

Axial chirality in biaryl N,N-dialkylaminopyridine derivatives bearing an internal carboxy group

Axial chirality in N,N-dimethylaminopyridines as well as N,N-dipropylaminopyridines bearing an internal carboxy group were evaluated based on their racemization barriers and circular dichroism spectra. The half-life of racemization of N,N-dipropylaminopyridine derivative 2 was estimated to be 19.7 days at 20°C. Its enantiomers isolated as optically active forms showed positive-negative and negative-positive Cotton effects for (+)- 2 and (−)- 2 , respectively, from 310 to 210 nm. Furthermore, (−)- 2 was applied as a chiral nucleophilic catalyst and exhibited asymmetric induction in acylative kinetic resolution of 1-(1-naphthyl)ethane-1-ol.     

Hysteresis in poly‐2′‐deoxycytidine i‐motif folding is impacted by the method of analysis as well as loop and stem lengths

In DNA, i‐motif (iM) folds occur under slightly acidic conditions when sequences rich in 2′‐deoxycytidine (dC) nucleotides adopt consecutive dC self base pairs. The pH stability of an iM is defined by the midpoint in the pH transition (pH_T) between the folded and unfolded states. Two different experiments to determine pH_T values via circular dichroism (CD) spectroscopy were performed on poly‐dC iMs of length 15, 19, or 23 nucleotides. These experiments demonstrate two points: (1) pH_T values were dependent on the titration experiment performed, and (2) pH‐induced denaturing or annealing processes produced isothermal hysteresis in the pH_T values. These results in tandem with model iMs with judicious mutations of dC to thymidine to favor particular folds found the hysteresis was maximal for the shorter poly‐dC iMs and those with an even number of base pairs, while the hysteresis was minimal for longer poly‐dC iMs and those with an odd number of base pairs. Experiments to follow the iM folding via thermal changes identified thermal hysteresis between the denaturing and annealing cycles. Similar trends were found to those observed in the CD experiments. The results demonstrate that the method of iM analysis can impact the pH_T parameter measured, and hysteresis was observed in the pH_T and T_m values.     

The inhibitory effect of benzenethiol on the cresolase and catecholase activities of mushroom tyrosinase

The inhibitory effect of benzenethiol on the cresolase and catecholase activities of mushroom tyrosinase (MT) have been investigated at two temperatures of 20 and 30°C in 10 mM phosphate buffer solution, pHs 5.3 and 6.8. The results show that benzenethiol can inhibit both activities of mushroom tyrosinase competitively. The inhibitory effect of benzenethiol on the cresolase activity is more than the catecholase activity of MT. The inhibition constant (K_i) value at pH 5.3 is smaller than that at pH 6.8 for both enzyme activities. However, the K_i value increases in cresolase activity and decreases in catecholase activity due to the increase of temperature from 20 to 30°C at both pHs. Moreover, the effect of temperature on K_i value is more at pH 6.8 for both cresolase and catecholase activities. The type of binding process is different in the two types of MT activities. The binding process for catecholase inhibition is only entropy driven, which means that the predominant interaction in the active site of the enzyme is hydrophobic, meanwhile the electrostatic interaction can be important for cresolase inhibition due to the enthalpy driven binding process. Fluorescence and circular studies also show a minor change in the tertiary structure, without any change in the secondary structure, of the enzyme due to the electrostatic interaction in cresolase inhibition by benzenethiol at acidic pH.