Spectroscopic study of molecular associations between FMN and β-carbolines

The spectrophotometric and thermodynamic properties of molecular complexes of flavin mononucleotide (FMN) (riboflavin 5′-phosphate) with some β-carboline derivatives have been investigated in aqueous solution. The molecular associations have been examined by means of electronic absorption spectra, since in each a new charge-transfer band has been located, and also the variation of the fluorescence emission of FMN on the solutions has been observed. The formation constants for the molecular complexes were determined from absorption data using the Foster—Hammick—Wardley method. The quenching phenomenon observed in FMN fluorescence is related to the concentration of the β-carboline derivatives, allowing the calculation of the quenching constants for FMN-β-carboline complexes. Thermodynamic parameters have been determined from the values of association constants for the molecular complexes at various temperatures. The influence of substituents in the β-carboline molecule on the stability of the complexes formed was also investigated.     

Spectroscopic study of molecular associations between riboflavin and some (dihydro) β-carboline derivatives

The spectrophotometric and thermodynamic properties of molecular complexes of riboflavin (RFN) with some dihydro β-carboline derivatives have been investigated by using electronic absorption and fluorescence spectroscopic methods in aqueous solution. The molecular associations have been examined by means of eletronic absorption spectra, since in each, a new charge transfer-like band has been located, and also by observing the variation of the fluorescence emission of RFN on the solutions. The formation constants for the molecular complexes were determined from absorption data, using the Forster—Hammick—Wardley method. The quenching phenomenon observed in RFN fluorescence is related to the concentration of the dihydro β-carboline derivatives, allowing the calculation of the quenching constants for RFN—β-carboline complexes. Thermodynamic parameters have been determined from the values of association constants for the molecular complexes at various temperatures. The influence of substituents in the dihydro β-carboline molecule on the stability of the complexes formed was also investigated.     

Checking of mathematical calculation methods for the determination of kinetic parameters from non-isothermal measurements by test functions

The applied computing programs are checked by means of test values from theoretical models. First-order kinetics, the Avrami equation and the 2-dimensional diffusion equation have been calculated as theoretical values. The computer calculation was carried out both for the total reaction and for individual reaction intervals.For the calculation of kinetic parameters and the distinction between the various models, in principle, the integral method should be used. The calculation does not give any answer to the question whether there exists another equation not involved in the models selected, which describes the processes better. If there is no indication of the reaction, it should first be checked by the differential method. The correlation coefficient does not allow the individual model equations to be distinguished with statistical significance.     

Complex electrooptic research of nano-particle parameters in colloids

A research of some colloids has been carried out by means of dynamic light scattering, electrooptical and magnetooptical techniques. Intensity autocorrelation functions of scattered light have been compared to the relaxation curves of electrooptical effect for colloid particles of different shapes. The results of complex research confirm that the complicated character of light scattering by particles allows us to use the methods of birefringence and dichroism only formally when studying most colloid systems. Very thin nano-disperse structures are an exception to this rule. The investigation of polydispersity of some colloids was carried out by magnetooptical and two electrooptical techniques. Size distribution functions resulted from the different techniques agree. This justifies the suppositions about particle light scattering that are required for the use of the methods.     

有机试剂结构与性质的研究(X)——偶氮苯衍生物结构与吸收光谱的研究

本文应用PPP-SCF-CI法计算了偶氮苯衍生物的结构,发现偶氮苯衍生物波长最大的吸收峰(相应于电子从基态向第一激发态跃迁)是分子内荷移光谱,这些吸收峰的计算值与实验值完全一致.此外,还根据PPP计算结果研究了取代基对吸收光谱的影响.     

Identification of compounds and specific functional groups in the wavelength region 168-330 nm using gas chromatography with UV detection

A GC-UV instrumental set up with two different GC units has been used for determination of specific functional groups and compounds in complex mixtures. Separations have been made using a micro gas chromatograph built into a gas flow cell and by means of an external capillary gas chromatograph linked to the same gas flow cell. Four various applications (cigarette smoke, petroleum, dust, flavour) have been performed in order to demonstrate the potential of the GC-UV method. Gas phase UV spectra have been recorded in the region of 168-330 nm. Based on a gas phase spectrum reference library the identification of unknowns as well as the determination of specific functional groups have been achieved. A table showing the spectral shapes and positions of the absorption bands for 50 specific functional groups is presented. The advantage of using derivative spectra in order to amplify spectral details and improve selectivity is discussed. Regarding sensitivity, it has been found that identifications can be made in the mid-pg range and limit of detection for naphthalenes are at a level of 0.5-3 pg/s.     

Calculations of XPS spectra for oxyanions and related compounds by the discrete variational-Xα method

Calculations of molecular-orbital energies and x-ray photoelectron spectra have been carried out for the third-row oxyanions, transition-metal oxyanions, SiO₂ and TiO₂, by the discrete variational-Xα cluster method. The calculated orbital energies are consistent with those determined from the XPS experiments. Theoretical XPS line shapes with Gaussian are generally in good agreement with the observed spectra. However, underestimation has been found for the photopeak intensities in the low-binding-energy region of TiO₂. The discrepancy is partially attributed to the use of inaccurate photoionization cross-section for the Ti3d orbital.     

PICOSECOND LASER PHOTOLYSIS STUDIES OF FLUORESCENCE QUENCHING MECHANISMS OF FLAVIN: A DIRECT OBSERVATION OF INDOLE-FLAVIN SINGLET CHARGE TRANSFER STATE FORMATION IN SOLUTIONS and FLAVOENZYMES

Formation of singlet charge transfer (heteroexcimer) states in the course of the fluorescence quenching of lumiflavin and riboflavin tetrabutyrate by indole and N-methylindole have been directly observed by means of time-resolved absorption spectral measurements using a picosecond laser photolysis method. Similar transient spectra have been observed also in the case of a flavoenzyme, D-amino acid oxidase.     

The binding properties of photosensitizer methylene blue to herring sperm DNA: a spectroscopic study

Methylene blue (MB) is a phenothiazinium photosensitizer with promising applications in the photodynamic therapy (PDT) for anticancer treatment. The binding properties of MB to herring sperm DNA have been investigated by the measurements of absorption spectra, quenching experiments and the elucidation of the photobleaching processes. Remarkable hypochromic and bathochromic effects of MB in the presence of increasing amounts of DNA have been observed in the absorption spectra. The quenching of MB by the DNA bases obeys the Stern-Volmer equation and ferrocyanide quenching of MB in the absence and presence of DNA is also measured as extended experiments. Results from the above spectral measurements are all consistent with the intercalative binding mode of MB to DNA with the Kb value of 1.89 x 10(4) M(-1). The photobleaching processes of MB and its DNA complex have also been studies, which indicate that the photobleaching of MB and its DNA complex proceeds with different mechanisms and the reactive oxygen species are responsible for the self-sensitized photooxidation of MB.     

Electron transfer interaction of dihydroxyquinones with amine quenchers: dependence of the quenching kinetics on the aliphatic and aromatic nature of the amine donors

Studies on the electron transfer (ET) interaction of 1,4-dihydroxy-9,10-anthraquinone and 6,11-dihydroxy-5,12-naphthacenequinone with aliphatic and aromatic amine (AlA and ArA, respectively) donors have been investigated in acetonitrile solutions. Steady-state (SS) measurements show quenching of the quinone fluorescence by amines, without indicating any change in the shape of the fluorescence spectra. No significant change in the absorption spectra of the quinones is also observed in the presence of the amines. For all the quinone-amine pairs, the bimolecular quenching constants (kq) estimated from SS and time-resolved measurements are found to be similar. Variation in the kq values with the oxidation potentials of the amines indicates the involvement of the ET mechanism for the quenching process. A reasonably good correlation between the kq values and the free energy changes (deltaG0) for the ET reactions following Marcus' outer-sphere ET theory also supports this mechanism. It is seen that for both the quinone-ArA and quinone-AlA systems, the kq values initially increase and then get saturated at some diffusion-controlled limiting values (kqDC) as deltaG0 values gradually become more negative. Interestingly, however, it is seen that the kqDC value for the quinone-AlA systems is substantially lower than that for quinone-ArA systems. Such a large difference in the kqDC values between quinone-AlA and quinone-ArA systems is quite unusual. Present results have been rationalized based on the assumption that an orientational restriction is imposed for the encounter complexes in quinone-AlA systems to undergo ET reactions, which arises because of the localized (at amino nitrogen) shapes of the highest-occupied molecular orbitals (HOMO) of AlA in comparison to the pi-like HOMO of the ArA.     

Line shapes of saturated absorption spectra in hollow cathode discharges

The saturated absorption line shapes of sputtered uranium atoms in hollow cathode discharges have been investigated using a single axial mode tunable CW laser. The spectral profiles observed under specific experimental conditions exhibit a marked deviation from the usual saturated absorption line shape function. These new features appear under the low velocity changing collision rate, high quenching rate and in the regime of strong pump saturation. A generalized line shape function based on population dynamics along with quenching mechanisms is derived and used to discuss the observed spectra. Our results suggest that the additional features in the observed spectra may be attributed to coherent effects which are manifested under suitable experimental conditions.     

Quantitative Auger electron spectroscopic analysis of carbides,nitrides and carbonitrides

A novel method for the quantitative evaluation of Auger electron spectra based on peak areas is presented. Sample and reference spectra in integral mode are filtered by an area conserving digital filter. This transforms the peak shapes influenced by chemical effects into standard peak shapes. After filtering a linear combination of reference spectra, differentiated spectra accounting for peak shifts and some low order polynomials to account for variations in the background is fitted to the sample spectrum by a least squares method. The need to approximate the spectrum of the secondary electron background explicitly for direct calculation of peak areas is thus eliminated. Filters of different widths are applied to reduce errors by chemical effects. The composition of the sample is computed from the composition of the reference samples and the coefficients obtained from the fit.To demonstrate the validity of this technique it has been applied to both, Gaussian model peaks and spectra of titanium carbonitrides. A further test on an alloy series is under investigation. The results show that the method works as predicted and gives accurate quantification.     

<Emphasis Type="Italic">ABCD</Emphasis>-<Emphasis Type="Italic">Tool</Emphasis>, a software suite for the analysis of α/β spectra from liquid scintillation counting

This paper presents the alpha/beta complete deconvolution tool (ABCD-Tool), a C++ application for the analysis of spectra from liquid scintillation counting (LSC) measurements. In addition to the basic algorithms for standard gross alpha/beta analysis and the determination of the counting efficiency, the software implements a recent unfolding technique based on Fourier transforms, which gives precise and reliable results even in the case of complex, strongly overlapping spectra. The application is designed to be used with alpha/beta spectra generated from Perkin Elmer Wallac Quantulus 1220. However, future upgrades are scheduled in order to extend the compatibility to spectra from other LSC instruments in commerce.     

Effect of halogenated compounds on the photophysics of C70 and a monoadduct of C70: Some implications on optical limiting behaviour

The fluorescence spectra, quantum yields and lifetimes of C₇₀ and a pseudo-dihydro derivative (C₇₀R) have been measured in a wide range of solvents at room temperature. This information is important for the development of reverse saturable absorbers. Phosphorescence spectra and phosphorescence lifetimes were also measured at low temperature. The fluorescence is subject to quenching by halogenated compounds. The efficiency of quenching follows the order I>Br≫Cl. The nature of the quenching is shown to vary, with chlorinated compounds exhibiting static quenching of fullerene fluorescence, owing to nonfluorescent complex formation, whilst those compounds containing bromine and iodine exhibit dynamic quenching due to the external heavy-atom effect, that increases the intersystem crossing rate constant in the fluorophore–perturber complex. This constant is evaluated by an original method from the bimolecular quenching rate constants. The phosphorescence quantum yield of both fullerenes at 77 K slightly increases in the presence of iodobenzene, in spite of a strong decrease in phosphorescence lifetime. The marked increase of the intersystem crossing rate constant in concentrated solutions owing to the external heavy-atom effect is of interest for the application of fullerenes as fast-responding optical limiters (reverse saturable absorbers) of intense laser pulses, even in cases where the triplet quantum yield is of the order of unity.     

Oxovanadium complex as potential nucleic acid binder

DNA binding study of a vanadium(V) complex, Oxo-chloro-bis-N-phenylbenzohydroxamto-vanadium(V), derived from N-phenylbenzohydroxamic acid(PBHA) form a violet color complex with vanadium (V) in presence of hydrochloric acid is performed using absorption, fluorescence and viscometric techniques. The binding parameters of the PBHA-V(V) complex using calf thymus DNA (ct-DNA) and torula yeast RNA (t-RNA) have been determined. The complex shows the ability of cooperatively minor groove binding with ct-DNA as indicated by remarkable hyperchromicity and a blue shift of the absorption spectra. Quenching of metal complex calculation was carried out with Stern-Volmer equation and K_sv was found to be 2.32 ± 0.18 × 10⁴ M^?1, while in the case of t-RNA, enhancement is observed and that means the compound was not able to displace the Ethidium Bromide(EB)-t-RNA complex. Molecular docking was also applied to predict the mode of interaction of the hydroxamic acid with ct-DNA and t-RNA. DNA binding results of the complex are compared with those of the parent ligand.     

水解钛醇盐制备TiO2膜及其光敏染料的相互作用

A method of preparation of stable, homogeneous and controlled thickness TiO2 film through hydrolysis of Ti(OC4H9)4 is introduced in detail. The structure and property of the film have been investigated by means of SEM and FT-IR techniques. The strong quenching effect between sensitizing dyes and TiO2 film is observed in their fluorescence spectra.     

On the dynamics of the H+ +D2(v=0,j=0)-->HD+D + reaction: a comparison between theory and experiment

The H+ +D2(v=0,j=0)-->HD+D + reaction has been theoretically investigated by means of a time independent exact quantum mechanical approach, a quantum wave packet calculation within an adiabatic centrifugal sudden approximation, a statistical quantum model, and a quasiclassical trajectory calculation. Besides reaction probabilities as a function of collision energy at different values of the total angular momentum, J, special emphasis has been made at two specific collision energies, 0.1 and 0.524 eV. The occurrence of distinctive dynamical behavior at these two energies is analyzed in some detail. An extensive comparison with previous experimental measurements on the Rydberg H atom with D2 molecules has been carried out at the higher collision energy. In particular, the present theoretical results have been employed to perform simulations of the experimental kinetic energy spectra.     

在线性壳聚糖膜内原位还原制备银纳米粒子及银单晶体

采用光还原方法，在线性壳聚糖膜内原位还原获得球形银粒子(粒径10～30 nm)和外观呈三角形、六边形的银单晶体(边长200～2000 nm)；采用电化学方法，在壳聚糖膜内制备了球形银纳米粒子，粒径为5～8 nm.用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、红外光谱(IR)和X射线衍射(XRD)等测试技术对壳聚糖/银复合物进行了表征，对光还原过程中银晶体结构由多晶到单晶的转变原因进行了初步的分析和探讨.     

Qualitative Analyses of Coins by Using a Si(Li) Detector and An Xrf-Exciter System

X-ray fluorescence spectra of many coins are studied using a Si(Li) detector and an XRF-exciter system. Some qualitative and semiquantitative analyses have been carried out. It is demonstrated that this method can be a very powerful means to study the archaeology of metal objects, especially the copper alloys, such as coins and bronze vessels.     

Characterization of the malate-aluminum(III) complex using 1H and 27Al NMR spectroscopy

Structural elucidation of a malate-aluminum(III) complex has been carried out using 1H and 27Al NMR spectroscopy. The 1H chemical shift perturbation clearly indicated the interaction between malate and Al(III) ion. The measurements of 27Al NMR and 1H-13C HSQC spectra demonstrated that the major form of a complex comprised two equivalent malate ions and two unequivalent Al(III) ions. With this constraint, an equilibrium geometry of the complex was proposed by a semi-empirical molecular orbital calculation.