Binding Interaction of Captopril with Metal Ions: A Fluorescence Quenching Study

The binding interaction of captopril (CPL) with biologically active metal ions Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ was investigated in an aqueous acidic medium by fluorescence spectroscopy. The experimental results showed that the metal ions quenched the intrinsic fluorescence of CPL by forming CPL‐metal complexes. It was found that static quenching was the main reason for the fluorescence quenching. The quenching constant in the case of Cu²⁺ was highest among all quenchers, perhaps due to its high nuclear charge and small size. Quenching of CPL by metal ions follows the order Cu²⁺>Ni²⁺>Co²⁺>Ca²⁺>Zn²⁺>Mn²⁺>Mg²⁺. The quenching constant K_sv, bimolecular quenching constant K_q, binding constant K and the binding sites "n" were determined together with their thermodynamic parameters at 27 and 37°C. The positive entropy change indicated the gain in configurational entropy as a result of chelation. The process of interaction was spontaneous and mainly ΔS‐driven.     

Synthesis,characterization, antimicrobial and diuretic study of Mg(II), Mn(II), Fe(II) and VO(II) complexes of chemotherapeutic importance

The synthesis, characterization and diuretic activity of four new biologically active complexes of Mg(II) and VO(II) with bidentate Schiff base ligand acetazolamide–salicylaldimine (L) obtained from the inserted condensation of 5-acetamido-1,3,4-thiadiazole-2-sulphonamide (acetazolamide) with salicylaldehyde in a 1:1 molar ratio have been reported. Using this bidentate ligand complexes of Mg(II), Mn(II), Fe(II) and VO(II) with general formula ML₂ have been synthesized. The synthesized complexes were characterized by several techniques using elemental analysis, FT-IR, electronic spectra, TGA, mass, particle size analysis and molar conductance measurements. The elemental analysis data suggest the stoichiometry to be 1:2 [M:L]. The molar conductance measurements suggest non-electrolytic nature of the complexes. Infrared spectral data agreed with the coordination to the central metal ion through deprotonated phenolic oxygen and azomethine nitrogen atoms. On the basis of spectral studies, octahedral geometry is suggested for Mg(II), Mn(II), Fe(II) and square pyramidal geometry is suggested for VO(II) complexes. The pure drug, synthesized ligand and metal(II) complexes were screened for their antimicrobial activities against Eschericia coli, Bacillus subtilis, Aspergillus niger and Aspergillus flavous. The results show that the metal complexes were more active than the ligand and pure drug against these microbial species as expected. The ligand and its Mg(II) complexes was screened for their diuretic activity also.     

A general thiol assay based on the suppression of fluorescence resonance energy transfer in magnetic-resin core-shell nanospheres coated with gold nanoparticles

A simple, rapid and sensitive fluorescence resonance energy transfer (FRET) method is presented for the determination of thiols. It is based on the thiol-induced enhancement effect of the surfactant sodium dodecyl sulfate (SDS) on the efficiency of fluorescence resonance energy transfer (FRET) in nanospheres consisting of a magnetic (Fe₃O₄) core and a phenol-formaldehyde resin (PFR) shell containing gold nanoparticles (AuNPs). The luminescence of the core-shell nanospheres at excitation/emission wavelengths of 390/445 nm, respectively, is quenched by the AuNPs which act as energy acceptors. The interaction of AuNPs with thiol compounds in the presence of SDS suppresses FRET and gives rise to a fluorescent signal whose intensity is proportional to the thiol concentration. The analytical features of seven thiols (homocysteine, thioglycolic acid, glutathione, dodecanethiol, cysteamine, cysteine and N-acetylcysteine) were studied. Detection limits are in the range from 0.14 to 0.49 μmol L⁻¹. The precision of the method, expressed as the relative standard deviation, ranges from 0.4 to 4.9 %. The method was applied to the determination of total thiols in water samples with recovery values between 88.7 and 104.6 %.

The fluorescence resonance energy transfer in magnetic-resin core-shell nanospheres coated with gold nanoparticles is inhibited by thiol compounds in the presence of sodium dodecyl sulfate. This gives rise to a fluorescent signal whose intensity is proportional to the thiol concentration.

     

Synthesis and structure of azole-fused indeno[2,1-c]quinolines and their anti-mycobacterial properties

Prompted by our discovery of a new class of conformationally-locked indeno[2,1-c]quinolines as anti-mycobacterials, compounds 2a and 3a (Fig. 1; MIC < 0.39 μg mL(-1) and 0.78 μg mL(-1), respectively)(14) with a freely rotating C2-imidazolo substituent, we herein describe the synthesis of pentacyclic azole-fused quinoline derivatives 4 and 5, in which we have restricted the rotation of the C2-imidazolo moiety by fusing it to the adjacent quinoline-nitrogen to give a five-membered fused azole heterocycle. The idea of locking the flexibility of the system by conformational constraint was simply to reduce its entropy, thereby reducing the overall free-energy of its binding to the target receptor. Out of 22 different azole-fused indeno[2,1-c]quinoline derivatives, seven structurally distinct compounds, 9, 15, 17, 25, 27, 28 and 29, have shown 79-99% growth inhibition of Mycobacterium tuberculosis H37Rv at a fixed dose of 6.25 μg mL(-1). The efficacies of these compounds were evaluated in vitro for 8/9 consecutive days using the BACTEC radiometric assay upon administration of single dose on day one. Of these, two compounds, 9 and 28, inhibited growth of M. tuberculosis very effectively at MIC < 0.39 μg mL(-1) (0.89 μM and 1 μM, respectively). These active compounds 9, 15, 17, 25, 27, 28 and 29 were screened for their cytotoxic effect on mammalian cells (human monocytic cell line U937), which showed that the human cell survival is almost unperturbed (100% survival), except for compound 25, hence these new compounds with new scaffolds have been identified as potent anti-mycobacterials, virtually with no toxicity. Thus these "hit" molecules constitute our important "leads" for further optimization by structure-activity relationship against TB.     

Interaction of point defects with twin boundaries in Au： A molecular dynamics study

The molecular dynamics simulation technique with many-body and semi-empirical potentials （based on the embedded atom method potentials） has been used to calculate the interactions of point defects with （1 1 1）, （1 1 3）, and （1 2 0） twin boundaries in Au at different temperatures. The interactions of single-, di-, and tri-vacancies （at on- and off-mirror sites） with the twin interfaces at 300 K are calculated. All vacancy clusters are favorable at the on-mirror arrangement near the （1 1 3） twin boundary. Single- and di-vacancies are more favorable at the on-mirror sites near the （1 1 l） twin boundary, while they are favorable at the oft-mirror sites near the （1 2 0） twin boundary. Almost all vacancy clusters energetically prefer to lie in planes closest to the interface rather than away from it, except for tri-vacancies near the （1 2 0） interface at the off-mirror site and for 3.3 and 3.4 vacancy clusters at both sites near the （1 1 1） interface, which are favorable away from the interface. The interaction energy is high at high temperatures.     

Weak real integral characterizations for exponential stability of semigroups in reflexive spaces

Let (t _n ) be a sequence of nonnegative real numbers tending to ∞, such that 1≤t _n+1?t _n ≤α for all natural numbers n and some positive α. We prove that a strongly continuous semigroup {T(t)} _t≥0, acting on a Hilbert space H, is uniformly exponentially stable if $$\sum_{n=0}^\infty\varphi\bigl(\bigl|\bigl\langle T(t_n)x, y\bigr\rangle\bigr|\bigr)<\infty, $$ for all unit vectors x, y in H. We obtain the same conclusion under the assumption that the inequality $$\sum_{n=0}^\infty\varphi\bigl(\bigl|\bigl\langle T(t_n)x, x^\ast\bigr\rangle\bigr|\bigr)<\infty, $$ is fulfilled for all unit vectors x∈X and x ^?∈X ^?, X being a reflexive Banach space. These results are stated for functions φ belonging to a special class of functions, such as defined in the second section of this paper. We conclude our paper with a Rolewicz’s type result in the continuous case on Hilbert spaces.     

Transition metal complexes of potassium dihydridobis-, hydridotris- and tetrakis-(thiophenolyl)borate anions

Summary The three new potential chelating ligands dihydridobis-, hydridotris- and tetrakis-(thiophenolyl)borate anions, and their chelates with first row transition metals have been synthesised. The divalent and trivalent metal ions form complexes in 12 and 13 (metal:ligand) ratios respectively. The number of ligands coordinated correspond to the number of anions replaced in the metal salis. The compounds were characterized by elemental analysis, i.r. spectra, magnetic susceptibility measurements and electronic spectral studies. The Cr^III and Fe^III complexes of dihydridobis- and hydridotris-(thiophenolyl)borates appear to be octahedral, and those of Cu^II are proposed to be square planar. Tetrahedral geometry is suggested for the Mn^II, Co^II and Ni^II complexes. The tetrakis-(thiophenolyl)borate yielded octahedral complexes with all the metal ions except for Cu^II which is square planar. The ligand field parameters 10Dq, B and have also been calculated wherever possible. The ligands may be placed in the vicinity of EDTA in the nephelauxetic series.     

HOW HYDROGEN BONDING OF CARBAZOLE TO ETHANOL AFFECTS ITS FLUORESCENCE QUENCHING RATE BY ELECTRON ACCEPTOR QUENCHER MOLECULES

Abstract— Absorption spectra and fluorescence quenching of carbazole (C) and N-ethyl carbazole (EC) by some aliphatic halocarbons have been studied in 3-methylpentane (3MP) and ethanol (EtOH). Both steady-state and transient kinetic measurements were used to determine the quenching rate constants ( k _q). These rate constants were found to be sensitive to the polarity and also to the hydrogen bonding ability of the solvents used. Endothermic electron transfer reactions were shown to take place in these systems. When the electron donor C is involved in hydrogen bonding with EtOH, the net effect is a decrease in k _q. This is explained by taking into account the red-shifted (0,0) transition energy (E_s) of the ¹ L _b absorption band when the reaction is nearly diffusion controlled. For reaction far from diffusion controlled, the E _s value correction to k_q is not enough to explain the low k _qvalue observed.     

New heterotrinuclear complexes containing copper(II) and a group IV metal

Summary Heterotrinuclear complexes of the type [Cu₂(TETA)₂Cl₄M] (M = Si, Ge, Sn, Ti and Zr; TETA = triethylene tetramine) have been prepared by direct reaction of [Cu[TETA)]Cl₂ with MCl₄ in a 21 ratio in MeOH. The compounds have been characterized by elemental analyses, e.s.r., electronic and i.r. spectra, magnetic susceptibility and conductivity measurements. The results indicate that [Cu(TETA)]Cl₂ is square planar and ionic, while its heterotrinuclear complexes, [Cu₂(TETA)₂Cl₄M], are covalent with an octahedral environment around the copper(II) ion.