Study on the Interaction between Florasulam and Bovine Serum Albumin

In this paper, the interaction between florasulam (FU, 2′,6′,8-trifluoro-5-methoxy [Kragh-Hansen U, Molecular aspects of ligand binding to serum albumin. Pharmacol Rev 33(1):17–53 1981; Carter DC and Ho JX, Structure of serum albumin. Adv Protein Chem 45:153–203 1994; He XM, and Carter DC, Atomic structure and chemistry of human serum albumin. Nature 358(6383):209–215 1992] triazolo [1,5-c]pyrimidine-2-sulfonanilide) and bovine serum albumin (BSA) was investigated by fluorescence, ultraviolet absorption (UV) and Far-UV circular dichroism (CD) spectrometries. A strong fluorescence quenching was observed and the quenching mechanism was considered as static quenching. The binding constant of FU with BSA at 299 and 309 K were obtained as 1.5?×?10⁴ and 7.1?×?10³ l mol^?1, respectively. There was one binding site between FU and BSA. The thermodynamic parameters enthalpy change (ΔH) and entropy change (ΔS) were calculated as ?57.89 kJ mol^?1 and ?113.6 J mol^?1 K^?1, respectively, which indicated that the acting force between FU and BSA was mainly hydrogen bond and Van der Waals force. According to the Förster non-radiation energy transfer theory, the average binding distance between donor (BSA) and acceptor (FU) was obtained (r?=?1.59 nm). The investigations of the UV/Vis and CD spectra of the system showed that the conformation of BSA was changed in presence of FU.     

Nitroaniline Isomers Interaction with Bovine Serum Albumin and Toxicological Implications

The interactions of 2-nitroaniline (2-NA), 3-nitroaniline (3-NA) and 4-nitroaniline (4-NA) with bovine serum albumin (BSA) have been investigated by means of fluorescence spectrometry, synchronous fluorescence spectrometry and UV absorption spectrometry under the simulative physiological conditions. Association constants (K _A ) were estimated by the remarkable static quenching effect of 2-NA, 3-NA and 4-NA to the intrinsic fluorescence of BSA, and thermodynamic parameters such as enthalpy change (ΔH) and entropy change (ΔS) were calculated according to van’t Hoff equation. The results show that hydrophobic force plays a main role in the interaction of nitroanilines to BSA, nitroanilines have high affinity to BSA and the affinity order is as follows: 4-NA?>?2-NA?>?3-NA. On the basis of this study, it is found that percents of the binding of nitroanilines to BSA are almost no relative to the concentrations of nitroanilines, and correlation between K _A and logK _ow is disclosed. In the meantime, relationships between the combination of nitroanilines with BSA and toxicological implications were also discussed. In addition, synchronous fluorescence method was used to study the interaction mechanisms between nitroanilines and BSA, and energy transfer distances from BSA to nitroanilines were estimated based on the Förster’s non-radiation energy transfer theory. The results suggest that the binding site for nitroanilines on BSA is close to the sub-domain IIA where Trp 214 is located.     

Collisional depolarization of fluorescence of polyatomic molecules in the gas phase by excited state quenchers

A new method of extracting information on the efficiencies of quenching of an excited state and collisional reorientation from the data on the fluorescence depolarization of molecular vapors by quenchers of the excited state is proposed. The method does not involve collisional cross sections and fluorescence lifetimes. From the experimental data on the depolarization of polarized luminescence of para-quaterphenyl and 2-(4′-dimethylamine) phenyl-5-phenyloxydiazole by oxygen and nitrogen, the ratios of the constants of the excitedstate quenching and orientation randomization (fluorescence depolarization) by oxygen are obtained. For these molecules, the probabilities of the excited-state quenching q and orientation randomization s per collision with oxygen molecules are determined (q=0.25±0.04 and s=0.13±0.04 for para-quaterphenyl and q=0.2±0.04 and s=0.21±0.04 for 2-(4′-dimethylamine)phenyl-5-phenyloxydiazole). The self-quenching of fluorescence of perylene vapors, with the probability 0.28 per collision, is found.     

Studying reactions that proceed from highest excited states of molecules using fluorescence quenching

The steady-state monochromatic excitation of a luminophore that has fluorescing products is considered. The effect of dynamic quenching of highest excited states on the fluorescence of singlet states under its excitation via singlet S ₁ and S _n (n ≥ 2) states is discussed. It is shown that the use of the method of fluorescence dynamic quenching by foreign impurities opens new possibilities for studying photoreactions that proceed via S _n singlet states. A large number of primary photoprocesses are considered which include the electron density redistribution (the internal electron transfer) in the excited state, protolytic reactions, intramolecular proton transfer (phototautomerization), hydrogen bonding, and formation of excimers and exciplexes. It is shown that, upon dynamic quenching, the bimolecular quenching constant of an excited level depends on the amount of thermal energy released in the luminophore before the occurrence of the light emission event. Based on the experimental measurements of the fluorescence spectra at different quencher contents, the calculation of the Stern-Volmer constant for reaction products is considered in detail. It is shown that this constant can be most reliably determined from the dependence of the fluorescence intensity ratio of the initial reagents and the quencher product rather than from the dependence of the fluorescence intensity of the products on the concentration of the quencher. The relations determined are used in analysis of the experimental fluorescence spectra of solutions of 3-hydroxyflavone excited by radiation with different wavelengths lying in the range of the S ₁ and S ₂ absorption bands. The temperature behavior of the Stern-Volmer constant for different fluorescence bands of 3-hydroxyflavone is considered. It is shown that, if these constants for the normal and tautomeric forms are correctly determined, their temperature dependences are similar.     

Mandelstam-Brillouin scattering spectra of aqueous solutions of γ-picoline and manifestation of a phase transition of the structural type in these spectra at low concentrations of γ-picoline

The frequency shift Δv of the Mandelstam-Brillouin components in an solution of γ-picoline is studied in relation to the temperature t of the solution (in the range 10–80°C) and the concentration x of γ-picoline (x < 0.1 ppm). The following specific features of the behavior of the quantity Δv are observed: (i) an inversion of the sign of the temperature coefficient of the dependence Δv(t) with a change in the concentration of the solution and (ii) the occurrence of two maxima on the isotherms of the dependence Δv(x), which behave significantly differently with the solution temperature and concentration. These experimental results are discussed from the viewpoint of the manifestation of a phase transition of the structural type in these spectra at small concentrations of γ-picoline in water.     

Kramers–Kronig Relations in Representation of Modulation Polarimetry by an Example of the Transmission Spectra of GaAs Crystal

The increments of the real and imaginary components of the complex refractive index ΔN = Δn–iΔk of a lightly doped GaAs crystal with a donor concentration of ~10¹⁶ cm^–3 have been measured using modulation polarimetry. It is shown that, within this representation, the birefringence and dichroism spectra (Δn(ω) and Δk(ω), respectively) obtained in the transparency window of a sample subjected to probe strain are derivatives of the corresponding functions: Δn(ω) ≈ dn/dω and Δk(ω) ≈ dk/dω. The experimental characteristics and primary dependences n(ω) and k(ω) derived from them by graphical integration are in agreement with the results of other researchers and measurements carried out by independent methods. The results obtained are compared (taking into account the integral (Kramers–Kronig) relations) with the resonance parameters: amplitude and phase in the Drude–Lorenz model. Agreement between the experimental characteristics and theoretical model predictions can be obtained by choosing an appropriate value of resonance damping parameter.     

Calibration procedure of the Δ<Emphasis Type="Italic">E</Emphasis>–<Emphasis Type="Italic">E</Emphasis> detectors for <Emphasis Type="Italic">dp</Emphasis> breakup investigation at nuclotron

Calibration procedure of ΔE ? E detectors used in dp breakup reaction measurement in the framework of DSS project is discussed. Time information from all PMTs along with amplitude information and known energy values of pp quasi elastic reaction are used to find calibration coefficients for ΔE and E detectors. Calibration coefficients are used to recover deposited particle energies. ΔE vs. E plots, energies and missing mass spectra are compared with geant4 Monte Carlo simulation. Missing mass for particular physical configuration is calculated as a test of the calibration procedure quality.     

Fluorescence of the <Emphasis Type="Italic">cis</Emphasis>-dimers of porphyrins containing ethylene bridges

The absorption and fluorescence spectra of solutions of the porphyrin dimers containing ethylene bridges, binding two Zn(II)octaethylporphyrin molecules or one Zn(II)octaethylporphyrin and one octaethylporphyrin molecule into cis conformation, were studied. For both studied cis-dimers, structureless absorption spectra were observed, only in general resembling the spectra of initial molecules, as well as weak fluorescence with a wide bell-shaped spectrum with a maximum at 680–700 nm and a quantum yield of about Φ_f≈3×10^?5, which is three orders of magnitude lower as compared to the fluorescence of initial monomeric porphyrins. A strong dependence of the fluorescence yield on a medium viscosity was revealed. In addition, low-yield irreversible cis-trans photoisomerization of cis-dimers was detected. A mechanism responsible for the strong intramolecular quenching of fluorescence of the porphyrin dimers containing ethylene bridges is suggested to be a conformation transformation in the region of the ethylene bridge, leading the molecular system to the region of “conic crossing” of the energy surfaces of excited and ground electron states.     

Triplet-triplet transfer of electronic excitation energy in vapors of organic molecules

The rate constants of the triplet-triplet (T-T) transfer of energy of the electronic excitation obtained in the gas phase for two sets of donor-acceptor pairs with various spectral characteristics are compared with those predicted by the theories of nonradiative transitions. The rate constants K _TT and efficiencies β_DA of the T-T transfer are estimated from quenching of the phosphorescence of biacetyl by aromatic hydrocarbons (anthracene, 9-methylanthracene, 9,10-dimethylanthracene, 9-phenylanthracene, pyrene, and chrysene) and from quenching of the delayed fluorescence of benzophenone, 4-phenylbenzophenone, anthraquinone, carbazole, and naphthalene by biacetyl, as well as from the sensitization of phosphorescence of biacetyl by these compounds. The causes of the broad variations of β_DA in the gas phase from 0.35 (biacetyl-anthracene) to 10^?4 (biacetyl-chrysene) are discussed for the studied donor-acceptor pairs, which differ in the exothermicity of the process and in the configuration of the lowest triplet levels of the molecules participating in the transfer. The dependences of the transfer rate constants K _TT on the free energy change ΔG (the range from 0.4 to ?1.7 eV) are analyzed. It is shown that, in gas-phase systems, K _TT increase with the exothermicity of the transfer, attain a highest value, and then decrease in the range of negative ?ΔG. The observed differences in the experimental values of β_DA are discussed in terms of changes in the free energy ΔG of the process, in the energy of rearrangement of the nuclear configuration of the molecules during the transfer, and in the matrix elements of the interaction.     

Photoluminescence in germanium with a quasi-equilibrium dislocation structure

The dislocation-related photoluminescence of n-Ge single crystals with a quasi-equilibrium structure of 60° dislocations is investigated at a temperature of 4.2 K. It is shown that the dislocation-related photoluminescence spectra are described by a set involving from 8 to 13 Gaussian lines with a width of less than 15 meV. With due regard for the data available in the literature, the Gaussian lines with maxima at energies in the range 0.47 < E _m ≤ 0.55 eV are assigned to the emission of 90° Shockley partial dislocations involved in quasiequilibrium segments of 60° dislocations with different values of the stacking fault width Δ (Δ = Δ₀, Δ < Δ₀, and Δ > Δ₀). It is revealed that the d8 line at the energy E _m = 0.513 eV, which corresponds to the emission of straight segments with the equilibrium stacking fault width Δ₀, dominates in the photoluminescence spectra only at dislocation densities N _D < 10⁶ cm^?2. As the dislocation density N _D increases, the intensity of the d8 line decreases with the d7 line (E _m ≈ 0.507 eV) initially and the d7 and d6 lines (E _m ≈ 0.501 eV) then becoming dominant in the photoluminescence spectrum. The d7 and d6 lines are attributed to the emission of segments with stacking fault widths Δ < Δ₀. Possible factors responsible for the formation of stacking faults with particular widths Δ ≠ Δ₀ for quasi-equilibrium dislocations are discussed.     

A Fluorescence Study of New Angular Polycyclic Blue Light-Emitting pyrazolo[3,4-<Emphasis Type="Italic">h</Emphasis>][1,6]naphthyridine and their Interaction with Bovine Serum Albumin (BSA)

The blue light-emitting pyrazolo[3,4-h][1,6]naphthyridines has been synthesized by Friedländer condensation of 4-amino-3-(4-phenyl)-1-phenyl-1H-pyrazolo[3,4-b]pyridine-5-carbaldehyde (o-aminoaldehyde) 1 with different cyclic ketones and 1,3-diketones. The synthesized angular polycyclic naphthyridine derivatives were studied for Semi-empirical, thermal, UV–vis and fluorescence spectroscopic properties on binding with bovin serum albumin (BSA). These fluorescence properties together with the neutral, hydrophobic nature of these compounds make these fluorophores good fluorescence probe for studying the micropolarity of proteins like BSA and in general the ligand-protein interactions. All of them displays bright absorption at 394 nm &; emission in visible region (491 nm). Quantum yields of all synthesized compounds were calculated.     

Influence of a magnetic two-phase state on the magnetocaloric effect in the La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>x</Subscript>MnO<Subscript>3</Subscript> manganites

The magnetocaloric effect ΔT_ex and the magnetization in La_1?xSr_xMnO₃ single crystals (x=0.1, 0.125, 0.175, 0.3) have been experimentally studied. The magnetic entropy and the magnetocaloric effect ΔT_th were computed from magnetization curves. All the samples exhibited a maximum in the ΔT_th(T) curve at T=T _max ^′ . A step was observed on the ΔT_ex(T) curve in the region of T _max ^′ , with the value of ΔT_ex on this step being substantially smaller than ΔT_th. The step on the ΔT_ex(T) curve was followed by a maximum, which appeared at a temperature 20–40 K above T _max ^′ . This anomalous behavior of ΔT_ex and ΔT_th is assigned to the coexistence of two magnetic (ferro-and antiferromagnetic) phases in the crystal. The calculated value of ΔT_th is determined primarily by the ferromagnetic part of the crystal and disregards the negative contribution from the antiferromagnetic part of the crystal to ΔT_ex.     

The Coherence Time of Infinite Quantum Well

The relationship among the Coherence time (CT) τ, the Variation frequency λ, the energy separation ΔE and coupling constant α in quantum well was investigated using Pekar type variational method. The results indicated that the Coherence time τ is positively proportional to the Variation frequency λ, but the energy separation ΔE and coupling constant α are negatively correlated with the Coherence time τ. When ΔE is more than 10ev, and when α is more than 5, τ decreases sharply.     

Special features of the structure of the beta-stability line for nuclei

The mass-number (A) dependence Z _β(A) for nuclei lying on the beta-stability line (BSL) is calculated for A and Z values in the ranges of A = 2–258 and Z = 1–100, respectively. The calculated values are compared with experimental data. The deviations ΔZ = Z _expt ? Z _β are analyzed. This analysis of ΔZ reveals that there are three regions of A values in which the A dependence of ΔZ is parabolic. The possible forms of the A dependence of ΔZ are analyzed, and it is shown that the majority of nuclei belong to several parabolas simultaneously.     

Low-temperature contribution to the resonant tunneling conductance of a disordered N–I–N junction

A formula for the contribution ΔG ^res(T) to the resonant tunneling conductance of the N–I–N junction (where N is a normal metal and I is an insulator) with a weak (low impurity concentrations) structural disorder in the I layer from the low-temperature “smearing” electron Fermi surfaces in its N shores is obtained. It is shown that the temperature dependence ΔG ^res(T) in such a “dirty” junction qualitatively differs from the corresponding dependence ΔG ₀(T) in a “pure” (without resonant impurities in the I layer) junction: ΔG ^res(T) < 0, d(ΔG ^res)/dT < 0; ΔG ₀(T) > 0, d(ΔG ₀)/dT > 0, which can serve as an experimental test of the presence of impurity tunneling resonances in the disordered I layer.     

A theoretical investigation of the effect of water on the structure and fluorescence spectra of L-tryptophan

Fluorescence spectra of two long-wavelength electron transitions S₀ ← ¹L_b and S₀ ← ¹L_a in uncharged and zwitterionic forms of L-tryptophan (Trp) in aqueous solution and in the complex of Trp with water molecule were calculated using the Frank–Condon approximation. Geometric parameters of Trp in electronically excited states were determined, and the vibrational structure of vibronic spectra was analyzed. It was shown that the relative position of structural fragments of alanine (R-Ala) and indole (R-In) could have a determining effect on the fluorescence and formation of the vibrational structure of electronic spectra. The increase of the rotation angle between the R-Ala and R-In, which depends on the Trp environment, results in the Trp fluorescence originating only from the singlet excited state ¹L_a.     

EPR study of the spin dynamics of the (La<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>Pr<Subscript>y</Subscript>)<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> system

The EPR of Mn ions in the (La_1?yPr_y)_0.7Ca_0.3MnO₃ system has been studied within a broad range of temperatures (4<T<600 K) and Pr concentrations (0≤y≤1), as well as under isotope substitution of ¹⁸O for ¹⁶O. All compositions were shown to undergo transitions to a magnetically ordered state with decreasing temperature. Magnetic phase diagrams were constructed for systems with different oxygen isotopes. The diagrams include paramagnetic, ferromagnetic, and antiferromagnetic regions. In the paramagnetic region, at temperatures not too close to the phase transition points, the Mn ion linewidth ΔH _pp (T) is related to the magnetic susceptibility χ(T) through the relation ΔH _pp (T) = [χ₀/χ(T)]ΔH _pp (∞) + ΔH₀, where ΔH _pp (∞) is the width of the exchange-narrowed line in the high-temperature approximation, χ₀ ∝ 1/T is the susceptibility of noninteracting ions, and ΔH₀ is the residual width originating from the sample porosity and resonance-field scatter in unoriented grains of a powder sample. An analysis of the data on ΔH _pp (∞), ΔH₀, and χ(T) made it possible to estimate the symmetric and antisymmetric exchange interaction of Mn ions and of the noncubic crystal-field component of the oxygen ions. These parameters were found to be independent of the oxygen isotope species to within experimental error.     

Aggregation and microenvironmental properties of gemini and conventional mixed surfactants systems: A fluorometric study

Aggregation behavior of cationic gemini (hexanediyl-1,5-bis(dimethylcettylammonium bromide) (16-5-16)) surfactant with conventional single chain surfactants cetyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB) were studied with the help of fluorescence measurements. Fluorescence probe is a proficient technique for examining the surfactant-surfactant interaction and aggregation. The micelle aggregation number (N _agg) was measured using steady-state fluorescence quenching method. The micelle aggregation numbers of binary combinations fall between those of constituent surfactants. The micropolarity (I ₁/I ₃), binding constant (K _sv) and dielectric constant (D _exp) of mixed systems were determined from the ratio of peaks intensity in the pyrene fluorescence spectrum. The I ₁/I ₃ values were found to be more than >1, showing more polar environment around pyrene in the mixed micelle as compared to the pure micelles.     

Interaction of dirac particle AMM with Coulomb field of a superheavy nucleus: Perturbative and nonperturbative aspects

The interaction ΔU_AMM of the Dirac particle anomalous magnetic moment (AMM) with the Coulomb field of a nucleus and its effect on the low-lying atomic levels are studied for Zα > 1 using both perturbative and essentially nonperturbative approaches. The Zα dependence of particle wavefunctions (WFs) is fully taken into account from the beginning. In deriving the ΔU_AMM contribution, the nucleus is viewed either as a uniformly charged extended Coulomb source or as a distributed system formed by pointlike u and d quarks. When estimated nonperturbatively, the ΔU_AMM-induced effects in the Dirac equation framework prove to be identical for these two cases. At the same time, the ΔU_AMM-induced effect is specific in that its perturbative and nonperturbative estimates are very different for Δg ? const and practically identical as soon as the dynamical screening of AMM at short distances is taken into account in the Dirac equation.     

Fluorescence quenching of vaporous polycyclic aromatic hydrocarbons by oxygen

The fluorescence quenching by oxygen of vapors of nine polycyclic aromatic hydrocarbons with strongly different oxidation potentials 0.44 eV < E _ox < 1.61 eV (anthracene, 9-methylanthracene, 2-aminoanthracene, 9,10-dibromanthracene, pyrene, chrysene, phenanthrene, fluoranthene, and carbazole) is studied. From the dependences of the fluorescence decay rates and intensities on the oxygen pressure P _O2, the quenching rate constants k _S ^O2 for the excited singlet states S ₁ and the fraction f _S ^O2 of the S ₁ states quenched by oxygen are estimated. At P _O2 = 5 Torr, the k _S ^O2 constants vary from 1.2 × 10⁷ to 3.0 × 10⁵ s^?1 Torr^?1, while the fraction of the quenched excited singlet states changes from 0.1 (fluoranthene) to 0.7 (chrysene) and 0.8 (pyrene). The dependences of k _S ^O2 on the photophysical and electron-donor characteristics of the fluorescing compounds are analyzed. It is shown that, in the gas phase of anthracene and its derivatives, the magnitudes of k _S ^O2 are limited by the rate constants of gas-kinetic collisions k _gk and do not depend on the electron-donor characteristics of fluorophores, while the fraction of quenched states f _S ^O2 changes with the oxidation potential. For compounds with k _S ^O2 < k gk, both the rate constants k _S ^O2 and the fraction of quenched states f _S ^O2 depend on the E _ox of sensitizers, which demonstrates an important role played by the charge-transfer interactions in quenching of the S ₁ states. The dependence of the rate constants k _S ^O2 on the free energy of electron transfer ΔG _et is considered.