Complex formation between nickel(II) and some pentamine (substituted salicylato)cobalt(III) ions

The kinetics of reversible complexation of NiII with pentamine(substituted salicylato)cobalt(III) ions, [Co(N5){O2CC6H3(X)OH}]2+[N5= 5NH3, (en)2(NH3)(cis isomer, en = ethane-1,2-diamine) or tetren (tetraethylenepentamine), X = 3-NO2; N5= 5NH3, X = 5-NO2], was investigated by the stopped-flow technique at 15–35 °C, pH 5.70–6.90 and I= 0.30 mol dm−3(ClO4−). The formation of [(Co(N5){O2CC6H3(X)O}Ni]3+ occurs via the reaction of [Ni(OH2)6]2+ with the phenoxide form of the cobalt(III) substrates. The rate and activation parameters have been determined for the formation and dissociation of the binuclear species in which nickel(II) is chelated by the salicylate moiety. The data are consistent with and Id mechanism. The rate constant for spontaneous dissociation of the binuclear species to the reacting partners is sensitive to the nature of the pentamine moiety and decreases in the sequence tetren > (en)2(NH3)− 5NH3. The acid-catalysed dissociation of cis-[(en)2(NH3)Co{O2CC6H3(NO2−3)O}Ni]3+ conforms to a two-step process

Antimicrobial efficacy of n-[3- chloro-(substituted aryl)-4-oxoazetidin- 1-yl] pyridine-4- carboxamides against resistant bacterial strains obtained from clinical isolates

Abstract Background: The treatment of infectious diseases is still an important and challenging problem due to emerging infectious diseases and increasing number of multi-drug resistant microbial pathogens which cause a variety of illnesses ranging from hospital-acquired pneumonia, bloodstream infections, urinary tract infections from catheters, abdominal infections and even meningitis. Methods: The main objective of the present study was to evaluate the antimicrobial efficacy and β-lactamase inhibitory activity of the synthesized 2-azetidinones against resistant bacterial strains obtained from clinical isolates. Results: The tested 2-azetidinones exhibited antimicrobial efficacy comparable to the standard drugs Ampicillin and Griseofelvin. Among the tested compounds, N-[3-chloro-2-(2,5-dimethoxyphenyl)-4-oxoazetidin-1-yl]pyridine-4-carboxamide(5o) exhibited the highest activity with MIC of 6.25 µg/mL (Gram +ve and Gram –ve bacteria),1.56 µg/mL (A. niger) and 3.12 µg/mL(A. terrus and P. chrysogenum) respectively. Also all the screened compounds (5d, 5f, 5h,5j,5o) exhibited more pronounced activity (MIC: 125 µg/mL) against resistant K. pneumonia obtained from clinical isolates compared to standard antibiotic Amoxycillin. The compounds when tested as admixtures with the standard antibiotic amoxicillin (1:2) exhibited similar antibacterial spectra in comparison to the most widely employed clinical combination Augmentin. The 2-azetidinonescan prove to be a cheaper alternative with similar potential β-lactamase inhibitory activity thereby proving their utility and benefit towards the development of anti-infectives for the treatment of infections caused by drug resistant microorganisms

Kinetics of Acid, Iron{III) & Aluminium(III) Catalysed Aquation of trans-Bis(Hmalonato)bis(ethylenediamine)cobalt(III) Ion

The H+, Fe3+ and AI3+ catalysed aquation of trans-bis(Hmalonato)-bis(ethylenediamine )cobalt(III) yields cis-(aquo)(Hmalonato)bis(ethylenediamine)cobalt(III) as the major cobalt(III) product. The binuclear complexes, trans-[(en)2Co(malH)malM](n+1)+ (M = Fe3+, Al3+) are the reactive species. The equilibrium constant for formation of binuclear species and the rate constant of its aquation are reported. For the acid catalysed aquation in the range of [H+] = 0.1-0.8 mol dm-3 (I = 1.0 mol dm-3), kobs versus [H+] plot is linear indicating that the complex does not undergo significant protonation under the condition of acidity employed. The activation parameters (DH1 and DS1) for the metal ion and H+ catalysed paths are comparable to those for the trans ->cis isomerisation of trans- [Co(en)2(OH2)malH]2+. This is consistent with the fact that trans ->cis isomerisation in the present situation actually occurs during substitution reaction

Kinetics and mechanism of formation of binuclear complexes of iron(III) with malonatopentaaminecobalt(lll) and <i>trans-</i>bis(Hmalonato)bis-(ethylenediamine)cobalt(III) ions in aqueous solution

125-129The kinetics of formation of binuclear complexes between iron (III) and malonatopentaaminecobalt(lll) and trans-bis(Hmalonato)bis(ethylenediamine)cobalt(III) have been studied using stopped-flow technique in the concentration ranges [H+]=0.050-0.30, [Fe(Ill)]=0.005-0.03, and I= 0.5 mol dm-3 and over the temperature range 15.0 to 30.0°C. A general mechanism is proposed which accounts for the available data on the formation of binuclear species involving mainly the reactions of Fe3+ and FeOH2+ with the undissociated form of the cobalt(III) substrates. The rate data for the various paths for transbis(Hmalonato)bis(ethylenediamine)cobalt(III) are slightly higher than those for the corresponding pen-taamine analogues. The activation parameters for the various paths are also reported

Metal ion interaction with dimethyl phosphate anion a model system to study the conformational changes at the phosphate site of nucleic acids

The influence of metal ions on the conformation of dimethyl phosphate anion around its O-P bonds, has been studied theoretically. The perturbation caused due to metal ions like Na+ and Mg2+ seems to affect the free dimethyl phosphate anion conformation to a considerable extent. In particular, the fully extended conformation becomes much more favourable in the metal ion dimethyl phosphate complex

Spatial configuration of single-stranded polynucleotides. Calculations of average dimensions and nmr coupling constants

The probability distributions of the torsional angles (&#934;', &#969;', &#969;, &#934;, and &#968;), which fix the structure of nucleotide backbone, have been calculated using the results of energy calculations based on extended Huckel theory (EHT), complete neglect of differential overlap (CNDO), perturbative configuration interaction using localized orbitals (PCILO), and classical potential functions (CPF) methods. Statistical average values of the vicinal 1H1H, 1H31P, and 13C31P nmr coupling constants J have been calculated from the generalized Karplus relations using the probability distribution in the &#934;', &#934;, and &#968; space. Experimental J values for polyribouridylic acid (polyU) support the theoretical predictions for these torsional angles. Using Monte Carlo technique, random coils of single-stranded polynucleotides have been simulated and the mean-square end-to-end distance r2 has been calculated. Molecular orbital methods (EHT, CNDO, and PCILO) suggest considerable flexibility around OP bonds, leading to fairly small values for the characteristic ratio (C&#8734;~4). Observed values of the unperturbed characteristic ratio for polynucleotides are quite large (C&#8734;~18) suggesting a relatively rigid nucleotide backbone. The results based on molecular orbital calculations can be reconciled with the experimental values by introducing an additional stabilization of ~2 kcal mol-1 for the predicted minimum energy ragion (&#934;' ~240&#176;, &#969;' ~290&#176;, &#969; 290&#176;, &#934; 180&#176;, and &#968; 60&#176;). Such a stabilization may arise from the association of water molecules and metal ions with the phosphate group and (or) Coulomb interaction between neighboring phosphate groups. The calculations provide a semiquantitative estimate of torsional rigidity in the nucleotide backbone

Kinetics and mechanism of complex formation between (histidinato)- pentaamminecobalt(III) and Ni(II) in aqueous medium

1001-1004The kinetics of reversible formation of binuclear complex between histidinatopentaarnminecobalttlll) and Ni(ll) has been investigated at 20-40°C, I = 0.3 mol dm-3,[Ni(II)]= 0.01-0.05 mol dm-3 and pH= 5.65 to 6.84. The formation of the binuclear species occurs via [H+] independent and [H+]-1 dependent paths, the latter arising out of protonation preequilibrium of the pendant amine function of the histidine moiety bound to cobalt(III) by the carboxylate group. The dissociation of the binuclear species is pH independent in the range studied. The rate and activation parameters for the formation and dissociation of the binuclear species are reported. The rate limiting step in the formation of the binuclear species is the rate of water dissociation from Ni(OH2). The results are consistent with chelation of Ni(ll) by the tertiary nitrogen and primary amine group of histidine moiety

Kinetics and mechanism of base hydrolysis of trans-bis(Hmalonato)bis(ethylenediamine)cobalt(III) ion

The kinetics of the first step of base hydrolysis oftrans-bis(Hmalonato)bis(ethylenediamine)cobalt(III) [malH-=HO2CCH2CO2-] has been investigated in the 15-35&#176; C range, I=0.3 mol dm-3 (NaClO4) and [OH-]=0.015-0.29 mol dm-3. The rate law is given by -d In[complex]T/dt=k1[OH-] and at 30&#176; C, k1=8.5&#215;10-3 dm3 mol-1s-1, &#916;H&#8800;=117.0&#177;7.0 kJ mol&#8722;1 and S=99.0&#177;24.0 JK-1mol-1. The activation parameters data are consistent with the SN1cb mechanism

Solvent Effect on Stabilities of Binuclear Complexes of Oxalatopentaamminecobalt(III) with Fe(III), Al(III) & Ni(II)

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