Synthesis of Morin–Zinc(II) Complex and its Interaction with Serum Albumin

A morin–zinc(II) complex (MZ) was synthesized and its interaction with bovine serum albumin (BSA) were studied by molecular spectroscopy including fluorescence emission spectra, UV-visible spectra, circular dichroism (CD) spectra, three-dimensional fluorescence spectra, and synchronous fluorescence spectra. The interaction mechanism of BSA and MZ was discussed by fluorescence quenching method and Förster non-radiation energy transfer theory. The thermodynamic parameters ΔH ^θ, ΔG ^θ, ΔS ^θ at different temperatures were calculated and the results indicate the interaction is an exothermic as well as entropy-driven process. Hydrogen bond forces played the most important role in the reaction. The fluorescence probe experiment showed that the binding site of MZ is in subdomain IIA of BSA and the distance between BSA and MZ is 3.17 nm at normal body temperature. The conformation changes of BSA in presence of MZ were investigated by CD spectra and three-dimensional fluorescence spectra.     

Fluorometric probing on the binding of hematoxylin to serum albumin

The binding of a cell nucleus stain, hematoxylin (HTL), to bovine serum albumin (BSA) was studied by spectroscopy including fluorescence spectra, UV–Visible absorption, circular dichroism (CD) spectra, synchronous and three-dimensional fluorescence spectra. The results indicated that the binding had led to static fluorescence quenching, with non-radiation energy transfer happening within single molecule. The observed binding constant was calculated to be 10^5.588 l mol^?1 at 311 K and one binding site had formed. The thermodynamic parameters of the interaction complied with ΔG ^θ < 0, ΔH ^θ < 0, ΔS ^θ < 0 and the results indicate that hydrogen bonds played major role in the reaction. The distance r between donor (BSA) and acceptor (HTL) was obtained according to the Förster theory of non-radiation energy transfer. The structural change of BSA molecules with addition of HTL was analyzed and the optimized geometry of HTL–BSA was investigated by fluorescence probe method.     

Synthesis of an octupolar compound and its biological effects on serum albumin

A special rigid planar structural octupolar molecule titled 2,4,6-tris(p-methylstyryl)-s-triazine (TMT) was synthesized and its interaction with bovine serum albumin (BSA) were studied by molecular spectroscopy. The quenching mechanism of fluorescence of BSA by TMT was discussed. The thermodynamic parameters ΔH ^θ, ΔG ^θ, ΔS ^θ at different temperatures were calculated and the results indicate hydrogen bond forces played major role in the reaction and the reaction was mainly enthalpy-driven. The distance r between donor (BSA) and acceptor (TMT) was obtained according to Förster theory of non-radiation energy transfer. Circular dichroism (CD) spectra, synchronous and three-dimensional fluorescence spectra were used to investigate the structural change of BSA molecules with addition of TMT, the result indicates that the α-helical structures of BSA molecules reduced in the presence of TMT. Sketch map of the interaction process was analyzed at molecular level.     

Studies on the interaction between benzidine and bovine serum albumin by spectroscopic methods

The interaction between bovine serum albumin (BSA) and benzidine (BD) in aqueous solution was investigated by fluorescence spectroscopy, circular dichroism (CD) spectra and UV–Vis spectroscopy, as well as resonance light scattering spectroscopy (RLS). It was proved from fluorescence spectra that the fluorescence quenching of BSA by BD was a result of the formation of BD–BSA complex, and the binding constants (K _a) were determined according to the modified Stern–Volmer equation. The enthalpy change (ΔH) and entropy change (ΔS) were calculated to be ?34.11 kJ mol^?1 and ?25.89 J mol^?1 K^?1, respectively, which implied that van der Waals force and hydrogen bond played predominant roles in the binding process. The addition of increasing BD to BSA solution caused the gradual enhancement in RLS intensity, exhibiting the forming of the aggregate. Moreover, the competitive experiments of site markers suggested that the binding site of BD to BSA was located in the region of subdomain IIA (sudlow site I). The distance (r) between the donor (BSA) and the acceptor (BD) was 4.44 nm based on the Förster theory of non–radioactive energy transfer. The results of synchronous fluorescence and CD spectra demonstrated the microenvironment and the secondary conformation of BSA were changed.     

Photochemical studies on the binding of an organic fluoride to bovine serum albumin

The interaction of fipronil (FPN), a pesticide containing fluorine, to bovine serum albumin (BSA) was studied by spectroscopy including fluorescence spectra, UV–Visible absorption, scattering spectra, circular dichroism (CD) spectra, synchronous and three-dimensional fluorescence spectra. The number of binding sites n and observed binding constant Kb was measured by fluorescence quenching method. The thermodynamic parameters ΔH, ΔG, ΔS at different temperatures were calculated and the results indicate that hydrophobic forces played major role in the reaction. The distance r between donor (BSA) and acceptor (FPN) was obtained according to the Förster theory of non-radiation energy transfer. The structural change of BSA molecules with addition of FPN was analyzed and the results may be helpful to biologists, chemists and therapeutists.     

Study on the interaction of chromate with bovine serum albumin by spectroscopic method

The interaction between two chromates [sodium chromate (Na₂CrO₄) and potassium chromate K₂CrO₄)] and bovine serum albumin (BSA) in physiological buffer (pH 7.4) was investigated by the fluorescence quenching technique. The results of fluorescence titration revealed that two chromates could strongly quench the intrinsic fluorescence of BSA through a static quenching procedure. The apparent binding constants K and number of binding sites n of chromate with BSA were obtained by the fluorescence quenching method. The thermodynamic parameters enthalpy change (ΔH), entropy change (ΔS) were negative, indicating that the interaction of two chromates with BSA was driven mainly by van der Waals forces and hydrogen bonds. The process of binding was a spontaneous process in which Gibbs free energy change was negative. The distance r between donor (BSA) and acceptor (chromate) was calculated based on Forster’s non-radiative energy transfer theory. The results of UV–Vis absorption, synchronous fluorescence, three-dimensional fluorescence and circular dichroism (CD) spectra showed that two chromates induced conformational changes of BSA.     

The investigation of the interaction between ribavirin and bovine serum albumin by spectroscopic methods

The interaction between ribavirin (RIB) with bovine serum albumin (BSA) has been investigated by fluorescence quenching technique in combination with UV–vis absorption and circular dichroism (CD) spectroscopies under the simulative physiological conditions. The quenching of BSA fluorescence by RIB was found to be a result of the formation of RIB–BSA complex. The binding constants and the number of binding sites were calculated at three different temperatures. The values of thermodynamic parameters ?H, ?S, ?G at different temperatures indicate that hydrophobic and hydrogen bonds played important roles for RIB–BSA association. The binding distance r was obtained according to the theory of FÖrster’s non–radiation energy transfer. The displacement experiments was performed for identifying the location of the binding site of RIB on BSA. The effects of common ions on the binding constant of RIB and BSA were also examined. Finally, the conformational changes of BSA in the presence of RIB were also analyzed by CD spectra and Synchronous fluorescence spectra.     

Spectroscopic Investigation of the Interaction Between Copper (II) 2-oxo-propionic Acid Salicyloyl Hydrazone Complex and Bovine Serum Albumin

The interaction between copper (II) 2-oxo-propionic acid salicyloyl hydrazone (Cu^IIL) and bovine serum albumin (BSA) under physiological conditions was investigated by the methods of fluorescence spectroscopy, UV-Vis absorption, and circular dichroism spectroscopy. Fluorescence data showed that the fluorescence quenching of BSA by Cu^IIL was the result of the formation of the BSA–Cu^IIL complex. The apparent binding constants (K _a) between Cu^IIL and BSA at four different temperatures were obtained according to the modified Stern–Volmer equation. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS), for the reaction were calculated to be ?80.79 kJ mol^?1 and ?175.48 J mol^?1 K^?1 according to van’t Hoff equation. The results indicated that van der Waals force and hydrogen bonds were the dominant intermolecular force in stabilizing the complex. The binding distance (r) between Cu^IIL and the tryptophan residue of BSA was obtained to be 4.1 nm according to Förster’s nonradioactive energy transfer theory. The conformational investigation showed that the application of Cu^IIL increased the hydrophobicity of amino acid residues and decreased the α-helical content of BSA (from 62.71% to 37.31%), which confirmed some microenvironmental and conformational changes of BSA molecules.     

Binding of 1-substituted carbazolyl-3,4-dihydro-β-carbolines with DNA: Molecular dynamics simulation and MM-GBSA analysis

Molecular Mechanics-Generalized Born-Solvent Accessibility free energy calculations were used to analyse DNA binding affinity of 1-substituted carbazolyl-3,4-dihydro-β-carboline molecules. In this study, DNA structure with sequence of d(CGATCG)2 was used for simulations. 15 ns molecular dynamics simulations of the studied complexes were performed. The calculated free energy was compared with experimental antitumor activity (IC₅₀). The predicted free energies decreased with the increase of IC₅₀ values. It was shown that molecules 1–6 bind to DNA via intercalation mode, while molecules 7–9 bind through groove binding mode. Also, it was found that the vdW energy term (ΔE_vdW) and the non-polar desolvation energy (ΔG_SA) are the favorable terms for binding energy, whereas net electrostatic energies (ΔE_ele + ΔG_GB) and conformational entropy energy (TΔS) are unfavorable ones.     

Analysis of the interaction of gallic acid and myoglobin by UV-vis absorption spectroscopy

UV-vis absorption spectroscopy has been used to analyze the interaction of myoglobin (Мb) and gallic acid (GA). The binding constants (4.38 × 10⁴ M^–1 at 298.15 K and 0.42 × 10⁴ М^–1 at 308.15K), the number of binding sites (h = 1.0), and the thermodynamic parameters of binding (ΔH, ΔS, and ΔG) have been determined. Hydrogen bonds have been shown to play a major role in the stabilization of the GA–Мb complexes. GA binding led to slight changes in the electronic state of the heme ring of the protein.     

Multi-spectroscopic studies on the interaction between traditional Chinese herb,helicid with pepsin

Study on the binding properties of helicid by pepsin systematically using multi-spectroscopic techniques and molecular docking method, and these interactions comprise biological recognition at molecular level and backbone of biological significance in medicine concerned with the uses, effects, and modes of action of drugs. We investigated the mechanism of interaction between helicid and pepsin by using various spectroscopic techniques viz., fluorescence spectra, UV–Vis absorption spectra, circular dichroism (CD), 3D spectra, synchronous fluorescence spectra and molecular docking methods. The quenching mechanism associated with the helicid–pepsin interaction was determined by performing fluorescence measurements at different temperatures. From the experimental results show that helicid quenched the fluorescence intensity of pepsin via a combination of static and dynamic quenching process. The binding constants (K_a) at three temperatures (288, 298, and 308 K) were 7.940?×?10⁷, 2.082?×?10⁵ and 3.199?×?10⁵ L mol^?1, respectively, and the number of binding sites (n) were 1.44, 1.14, and 1.18, respectively. The n value is close to unity, which means that there is only one independent class of binding site on pepsin for helicid. Thermodynamic parameters at 298 K were calculated as follows: ΔH^o (??83.85 kJ mol^?1), ΔG^o (??33.279 kJ mol^?1), and ΔS^o (??169.72 J K^?1 mol^?1). Based on thermodynamic analysis, the interaction of helicid with pepsin is driven by enthalpy, and Van der Waals’ forces and hydrogen bonds are the main forces between helicid and pepsin. A molecular docking study further confirmed the binding mode obtained by the experimental studies. The conformational changes in the structure of pepsin was confirmed by 3D fluorescence spectra and circular dichroism.     

Theoretical Aspects of Differential Scanning Calorimetry as a Tool for the Studies of Equilibrium Thermodynamics in Pharmaceutical Solid Phase Transitions

Although differential scanning calorimetry (DSC) is a non-equilibrium technique, it has been used to gain energetic information that involves phase equilibria. DSC has been widely used to characterize the equilibrium melting parameters of small organic pharmaceutical compounds. An understanding of how DSC measures an equilibrium event could make for a better interpretation of the results. The aim of this mini-review was to provide a theoretical insight into the DSC measurement to obtain the equilibrium thermodynamics of a phase transition especially the melting process. It was demonstrated that the heat quantity obtained from the DSC thermogram (ΔH) was related to the thermodynamic enthalpy of the phase transition (ΔH ^P ) via: ΔH?=?ΔH ^P /(1?+?K ^??1) where K was the equilibrium constant. In melting, the solid and liquefied phases presumably coexist resulting in a null Gibbs free energy that produces an infinitely larger K. Thus, ΔH could be interpreted as ΔH ^P. Issues of DSC investigations on melting behavior of crystalline solids including polymorphism, degradation impurity due to heating in situ, and eutectic melting were discussed. In addition, DSC has been a tool for determination of the impurity based on an ideal solution of the melt that is one of the official methods used to establish the reference standard.     

Distinctive Fluorescence of Quinacrine-labelled Human <Emphasis Type="Italic">G</Emphasis> Group Chromosomes

HUMAN chromosomes can be identified by their distinctive quinacrine fluorescence pattern¹. We have used this technique to study abnormalities in the G group. Since this report was first submitted, two other reports on the fluorescence of G group chromosomes have been published^2,3.     

Crystal structure of CmlI,the arylamine oxygenase from the chloramphenicol biosynthetic pathway

The diiron cluster-containing oxygenase CmlI catalyzes the conversion of the aromatic amine precursor of chloramphenicol to the nitroaromatic moiety of the active antibiotic. The X-ray crystal structures of the fully active, N-terminally truncated CmlIΔ33 in the chemically reduced Fe²⁺/Fe²⁺ state and a cis μ-1,2(η ¹:η ¹)-peroxo complex are presented. These structures allow comparison with the homologous arylamine oxygenase AurF as well as other types of diiron cluster-containing oxygenases. The structural model of CmlIΔ33 crystallized at pH 6.8 lacks the oxo-bridge apparent from the enzyme optical spectrum in solution at higher pH. In its place, residue E236 forms a μ-1,3(η ¹:η ²) bridge between the irons in both models. This orientation of E236 stabilizes a helical region near the cluster which closes the active site to substrate binding in contrast to the open site found for AurF. A very similar closed structure was observed for the inactive dimanganese form of AurF. The observation of this same structure in different arylamine oxygenases may indicate that there are two structural states that are involved in regulation of the catalytic cycle. Both the structural studies and single crystal optical spectra indicate that the observed cis μ-1,2(η ¹:η ¹)-peroxo complex differs from the μ-η ¹:η ²-peroxo proposed from spectroscopic studies of a reactive intermediate formed in solution by addition of O₂ to diferrous CmlI. It is proposed that the structural changes required to open the active site also drive conversion of the µ-1,2-peroxo species to the reactive form.     

Decreased formation of branched-chain short fatty acids in <Emphasis Type="Italic">Bacillus amyloliquefaciens</Emphasis> by metabolic engineering

Objectives

To reduce the unpleasant odor during 1-deoxynojirimycin (DNJ) production, the genes of leucine dehydrogenase (bcd) and phosphate butryltransferase (ptb) were deleted from Bacillus amyloliquefaciens HZ-12, and the concentrations of branched-chain short fatty acids (BCFAs) and DNJ were compared.

Results

By knockout of the ptb gene, 1.01 g BCFAs kg^?1 was produced from fermented soybean by HZ-12Δptb. This was a 56% decrease compared with that of HZ-12 (2.27 g BCFAs kg^?1). Moreover, no significant difference was found in the DNJ concentration (0.7 g kg^?1). After further deletion of the bcd gene from HZ-12Δptb, no BCFAs was detected in fermented soybeans with HZ-12ΔptbΔbcd, while the DNJ yield decreased by 26% compared with HZ-12.

Conclusions

HZ-12Δptb had decreased BCFAs formation but also maintained the stable DNJ yield, which contributed to producing DNJ-rich products with decreased unpleasant smell.

     

Deleterious mutations in various <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> strains carrying meiotic mutation <Emphasis Type="Italic">c(3)G</Emphasis>

In the absence of meiotic recombination, deleterious mutations, decreasing the viability, are accumulated and fixed in small Drosophila populations. Study of the viability of hybrid progenies of three laboratory Drosophila melanogaster strains carrying meiotic mutation c(3)G ¹⁷ has suggested that the deleterious mutations are negatively synergistic in their interaction. The deleterious mutations localized to the pericentromeric region of chromosome 3 are threefold more efficient as compared with the mutations located in distal regions. Substitution of a new chromosome for the balancer chromosome in a strain with meiotic mutation c(3)G ¹⁷ partially restores (by ～20%) the viability of homozygotes c(3)G ¹⁷ /c(3)G ¹⁷ over the first 20–30 generations. Further cultivation for 30 generations with the same balancer again decreases the viability to the initial level. An epigenetic nature of deleterious mutations is discussed.     

Modulation of proline metabolic gene expression in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> under water-stressed conditions by a drought-mitigating <Emphasis Type="Italic">Pseudomonas putida</Emphasis> strain

Although amelioration of drought stress in plants by plant growth promoting rhizobacteria (PGPR) is a well reported phenomenon, the molecular mechanisms governing it are not well understood. We have investigated the role of a drought ameliorating PGPR strain, Pseudomonas putida GAP-P45 on the regulation of proline metabolic gene expression in Arabidopsis thaliana under water-stressed conditions. Indeed, we found that Pseudomonas putida GAP-P45 alleviates the effects of water-stress in A. thaliana by drastic changes in proline metabolic gene expression profile at different time points post stress induction. Quantitative real-time expression analysis of proline metabolic genes in inoculated plants under water-stressed conditions showed a delayed but prolonged up-regulation of the expression of genes involved in proline biosynthesis, i.e., ornithine-Δ-aminotransferase (OAT), Δ ¹ -pyrroline-5-carboxylate synthetase1 (P5CS1), Δ ¹ -pyrroline-5-carboxylate reductase (P5CR), as well as proline catabolism, i.e., proline dehydrogenase1 (PDH1) and Δ ¹ -pyrroline-5-carboxylate dehydrogenase (P5CDH). These observations were positively correlated with morpho-physiological evidences of water-stress mitigation in the plants inoculated with Pseudomonas putida GAP-P45 that showed better growth, increased fresh weight, enhanced plant water content, reduction in primary root length, enhanced chlorophyll content in leaves, and increased accumulation of endogenous proline. Our observations point towards PGPR-mediated enhanced proline turnover rate in A. thaliana under dehydration conditions.     

Short-term effects of crop rotation,residue management,and soil water on carbon mineralization in a tropical cropping system

The purpose of this study was to investigate the short-term effects of maize (Zea mays)-fallow rotation, residue management, and soil water on carbon mineralization in a tropical cropping system in Ghana. After 15 months of the trial, maize–legume rotation treatments had significantly (P?C ₀ (μg CO₂–C g^?1) than maize–elephant grass (Pennisetum purpureum) rotations. The C ₀ for maize–grass rotation treatments was significantly related to the biomass input (r?=?0.95; P?=?0.05), but that for the maize–legume rotation was not. The soil carbon mineralization rate constant, k (per day), was also significantly related to the rotation treatments (P?k values for maize–grass and maize–legume rotation treatments were 0.025 and 0.036 day^?1 respectively. The initial carbon mineralization rate, m ₀ (μg CO₂–C g^?1 day ^?1), was significantly (P?θ. The m ₀ ranged from 3.88 to 18.67 and from 2.30 to 15.35 μg CO₂–C g^?1 day^?1 for maize–legume and maize–grass rotation treatments, respectively, when the soil water varied from 28% to 95% field capacity (FC). A simple soil water content (θ)-based factor, f _w, formulated as: \(f_{\text{w}} = \left[ {\frac{{\theta - \theta _{\text{d}} }}{{\theta _{{\text{FC}}} - \theta _{\text{d}} }}} \right]\), where θ _d and θ _FC were the air-dry and field capacity soil water content, respectively, adequately described the variation of the m ₀ with respect to soil water (R ²?=?0.91; RMSE?=?1.6). Such a simple relationship could be useful for SOC modeling under variable soil water conditions.     

Interactions of human serum albumin with bioactive 3<Emphasis Type="Italic">H</Emphasis>-imidazo[4,5-<Emphasis Type="Italic">a</Emphasis>]acridines: Insights from fluorescence spectroscopic studies

Several 3H-imidazo[4,5-a]acridine derivatives were conveniently synthesized by the reaction of imidazo[4,5-a]acridones in boiling POCl3. The imidazoacridones were obtained by rearrangement of 3H-imidazo[4',5':3,4]benzo[c]isoxazoles in concentrated sulfuric acid containing nitrous acid at room temperature. The structures of all newly synthesized compounds were confirmed by IR, ¹H NMR, and mass spectral data. The interactions of 3H-imidazo[4,5-a]acridines with human serum albumin (HSA) were studied by fluorescence spectroscopy. The binding of 3H-imidazo[4,5-a]acridines quenches the HSA fluorescence, revealing a 1: 1 interaction with a binding constant of about 2.34 × 10⁵–3.16 × 10⁶ M^–1. A decrease in fluorescence intensity at 339 nm, when excited at 280 nm, is attributed to changes in the environment of the protein fluorophores caused by the presence of the ligand. The differences in interactions of 3H-imidazo[4,5-a]acridines with HSA were observed using spectrofluorimetry technique.     

Microbial transformations of steroids

The preparation ofΔ ^{1, 4} , 17-dione fromΔ ⁴ , 17-dione with the aid ofFusarium lateritium 403 is described, the yield being 80%, referred to the original steroid. The undesirable 1-dehydrotestololactone is formed under the given conditions only in traces. If progesterone was used as the starting steroid the yield of the undesirable 1-dehydrotestololactone is 40%, referred to the progesterone used. Dehydroepiandrosterone was not transformed by theFusarium lateritium strain to steroid metabolites. During the preparation of 1-dehydrotestosterone fromΔ ⁴ -androstene-3, 17-dione, using two successive microbial procedures (dehydrogenation of the A ring in position 1–2 and reduction of the keto group at C₁₇ giving rise to the corresponding 17β-hydroxy derivative), the isolation yield was 55–60%, referred to the starting steroid.