JK-1 Mol-1 Research Articles

New Sensitive Derivatization Methodology of Levofloxacin Antibiotic from its Dosage Formulations: Kinetic Spectrophotometric Methods for Determination

A modern validated kinetic spectrophotometric method with a novel coupling reagent has been described for the determination of levofloxacin (LEV) in pure and tablets. The method involves an oxidative-coupling reaction between LEV and 3-methyl-2-benzothiazolinone hydrazone hydrochloride monohydrate (MBTH), in the presence of Ce(IV) in H2SO4 medium at 25±1°C, to gives greenish-blue product. The reaction is followed spectrophotometrically by measuring the increase in absorbance with time at 629 nm and then is stable for more than 2 hrs. The initial rate, rate constant, fixed absorbance and fixed time methods have been tested for constructing the calibration graphs, and are linear. The most suitable analytical methods were the initial rate and fixed time (at 20 min) methods for determination of LEV in the concentration ranges of 2.0-35.0 μg mL-1 and 0.65-35.0 μg mL-1 with LOD is 0.422 and 0.074 μg mL-1, respectively. Molar absorptivity for the method was found to be 1.40×104 L mol-1 cm-1. The activation energy (E ), activation enthalpy (ΔH ‡), activation entropy (ΔS ‡) and Gibbs free energy (ΔG ‡) are estimated for the reaction and found to be 9.84 KJ mol-1, 7.40 KJ mol-1, 177.04 JK-1 mol-1 and -44.48 KJ mol-1, respectively. The kinetic proposed methods were further applied to the determination of LEV in tablet formulations with no interfere from the excipients.

Hydroxy-Substituted Polycyclic Aromatic Hydrocarbon Ions as Sources of CO and HCO in the Interstellar Medium.

Tandem mass spectrometry was used to explore the trends in the unimolecular fragmentation of the ionized hydroxy-substituted polycyclic aromatic hydrocarbons 1-naphthol, 9-hydroxyphenanthrene, and 1-hydroxypyrene. The main dissociation reactions across all ring systems were CO- and HCO-losses, with ionized 1-naphthol also losing H atoms. Both ionized 1-naphthol and 9-hydroxyphenanthrene displayed the sequential loss of C2H2 and C4H2 from the [M-HCO]+ ions, reminiscent of unsubstituted PAH ions. CO-loss is slightly favored for 1-naphthol and 9-hydroxyphenanthrene, at low collision energy, but less so for 1-hydroxypyrene. Reaction mechanisms for HCO- and CO-losses from 1-hydroxypyrene were derived from CCSD/6-31G(d)//B3-LYP/6-31G(d) calculations. The CO-loss mechanism is dominated by two transition states: TS-A governing a 1,3-H shift in the molecular ion and TS-C which governs a ring-closing step to form a five-member ring in the product ion. HCO-loss occurs over a much flatter potential energy surface with the intermediate being the product ion bound to the carbon atom of HCO. Imaging photoelectron photoion coincidence spectroscopy of 1-hydroxypyrene yielded threshold photon-energy resolved breakdown curves and time-of-flight distributions that were modeled with RRKM theory to give 0 K reaction energies for HCO- and CO-losses of 3.92 ± 0.05 and 2.91 ± 0.05 eV, respectively. The entropies of activation for the two channels were very different, 14 and 95 JK-1 mol-1, respectively, a result consistent with the calculated mechanisms. The threshold photoelectron spectrum yielded an IE value of 7.14 ± 0.01 eV for 1-hydroxypyrene.

Streptozocin; a GLUT2 binding drug, interacts with human serum albumin at loci h6DOM3-h7DOM3.

Streptozocin (STZ) is a broad range antibiotic, highly genotoxic, antineoplastic and hyperglycemic. HSA is the most abundant protein in physiology and it binds to almost all exogenic and endogenic ligands, including drugs. STZ-induced fluorescence quenching of HSA has been done at pH 7.4, pH 3.5 and at pH 7.4 with 4.5 M urea at temperatures 286 K, 291 K, and 306 K. Ksv found to be 103 M-1, binding constant 1.5X103M-1 and binding sites ~1. But, Ksv for HSA and glucopyranose interaction was found lesser than that of HSA-STZ binding. Binding of STZ/glucopyranose on HSA seems to result in complex formation as calculated Kq > 1010 M-1 s-1. The number of binding sites, binding constants, and binding energies were increased with temperature. The ΔG0, ΔH0, and ΔS0 for HSA-STZ interaction were found to be -17.7 × 103 J·mol-1; 2.34 × 105 J·mol-1 and 841 JK-1 mol-1 respectively at pH 7.4 and 291 K. The comparative bindings of N, F and I states of HSA with STZ and their molecular docking analyses indicate that IIIA-B junction (i.e., inter-helix h6DOM3-h7DOM3) is the probable binding site, a locus close to fatty acid binding site-5. These results could be useful for therapeutic and analytical exploitation of STZ, as albumin used as the vehicle for drug delivery.

Investigation of New Ionic Plastic Crystals in Tetraalkylammonium Tetrabuthylborate

New plastic crystals of NEt3PrBBu4 and NEt2Pr2BBu4 were formed in a new region of ionic plastic crystal. In this area, globular cations and anions are assembled by weak interactions. Differential scanning calorimeter (DSC) measurements of these salts showed a low entropy change of 19:6 and 14:0 JK-1 mol-1 at each melting point, respectively. On the basis of solid-state 1H and 13C nuclear magnetic resonance (NMR) spectra and electrical conductivity measurements, isotropic reorientation and ion transfer of globular cations and anions were detected in these crystals. The other compounds of NEt x Me(4-x)BBu4 (x = 1 - 3) showed tumbling motions and low activation energies of self-diffusion in crystals

Permanganate Oxidation of Sulfadiazine: Analytical Method Development and Kinetic Study

A multi-disciplinary approach has been made in this article where, the oxidation reaction of permanganate and sulfadiazine has been used to develop analytical method to quantitate the drug and the second part is the kinetic study of the oxidation reaction. The estimation of the drug is made at 602 nm. The developed method has been validated as per the international conference on harmonization (ICH) guidelines. The regression treatment of the linearity data yielded the linear regression equation A=0.00786+0.0184 C. Limit of detection and limit of quantitation was found to be 2.33 and 7.065, respectively. Since, the reaction proceeded such that the absorbance increased with increase in time, kinetic study of the reaction was performed. The kinetic parameters were performed at 602 nm. The reaction obeyed pseudo first-order kinetics in [alkaline KMnO4] and fractional order in [sulfadiazine]. The oxidation reaction was carried out at varied temperatures viz. 25, 30, 35, 40 and 45 (±0.1°C). On the basis of the observed results, mechanism of the reaction has been proposed. Activation parameters such as energy of activation, enthalpy, entropy and Gibbs free energy were determined and found to be 8.73 (kJ mol-1), 77.57 (kJ mol-1), 173 (JK-1 mol-1), 25.99 (kJ mol-1) respectively.

Removal of C.I. Basic Red 46 (BR 46) from contaminated water by adsorption onto hardened paste of Portland cement: Equilibrium isotherms and thermodynamic parameters study

The present study was carried out to investigate the potential of hardened paste of Portland cement (HPPC) as a low-cost adsorbent for the removal of Basic Red 46 (BR 46) from contaminated water by using batch adsorption studies. In this work, HPPC has been selected as adsorbent because of the main advantages such as high efficiency, simple separation of sludge, abundant availability and low-cost material. The removal of dye in aqueous medium through the process of adsorption with HPPC under a set of variables (contact time, adsorbent dosage, pH, temperature and adsorbent particles size) has been investigated. Results showed that removal of BR 46 increased over 80% with increasing adsorbent dosage, temperature, contact time, pH and adsorbent particle size decreasing.Also the equilibrium adsorption data were fitted well for Temkin isotherm. The adsorption of BR 46 was endothermic and spontaneous with ∆Hâ—¦ values of +5.452 kJ mol−1 and ∆Sâ—¦ values of 0.035 JK-1 mol-1. The free energy changes ∆Gâ—¦ was evaluated with temperature increasing. From the experimental results, it may be concluded that HPPC was an efficient and economical adsorbent for BR 46 removal. Key words: Adsorption, Basic Red 46 removal, hardened paste of Portland cement, kinetics, equilibrium isotherm, thermodynamic.

Kinetics and mechanism of electron transfer to pyridinium chlorochromate (VI) from sulfur containing amino acid, L-cysteine in aqueous and micellar media

Kinetics and mechanism of electron transfer to pyridinium chlorochromate (VI) from sulfur containing amino acid, L-cysteine in aqueous and micellar media The electron transfer reaction of L-cysteine (RSH) with pyridinium chlorochromate (PCC) has been studied spectrophotometrically over the range 2.0 ≤ 103 [RSH] ≤ 6.0; 0.01 ≤ [H+] ≤ 0.2; 298 ≤ T ≤ 318 K and I = 0.3 mol dm-3 (NaClO4). The electron transfer reaction has also been carried out in the presence of anionic, cationic and neutral micelle. The reaction in acid medium is strongly catalyzed by changing [SDS]T (sodium dodecyl sulfate) up to 3 × 10-2 mol dm-3, beyond this concentration of SDS, the rate is retarded. The cationic and neutral micelle has a small effect on the rate. ΔH≠ (kJ mol-1) and ΔS≠ (JK-1 mol-1) values for the k1 and k2 paths are 30.20 ± 0.25, -159.65 ± 0.83 and 29.60 ± 0.62, -127.09 ± 2.17, respectively. The negative activation entropy is indicative of the ordered transition state for the electron transfer reaction. Formation of 2-amino-3-(2-amino-2-carboxy-ethyl) disulfanyl-propanoic acid as product is strongly supported by IR spectra.

KINETICS AND MECHANISM OF OXIDATION OF P-ANISIDINE BY FE(III) SOLUTION IN ACIDIC MEDIUM

Kinetics of oxidation of p-anisidine by Fe(III) ion was studied spectrophotometry in acidic medium. The rate constant was found to increase with increasing p-anisidine and hydrogen ion concentrations. The order of reaction was found to be first order with respect to both Fe(III) ion and p-anisidine concentration. The suggested mechanism involves the interaction of the reactive species of the reactants to form the activated complex which decompose in a rate determining step to products. The rate law was derived and activation parameters are calculated to be H* = 47 kJ mol-1 and S* = -148.6 JK-1 mol-1

KINETICS AND MECHANISM OF OXIDATION OF L-ASCORBIC ACID BY CHROMIUM (VI)

The kinetics of oxidation of L-ascorbic acid by potassium chromate was studied as a function of pH, L-ascorbic acid concentration and temperature using the spectrophotometric technique. The rate of reaction is first order with respect to the concentration of each reactant and increases as [H+] increases. The kinetic data indicate involvement of the monoprotonated ascorbate species (HA-) in the redox process. A mechanism involving the formation of chromium (VI)- ascorbate intermediate is a rate-determining step followed by a redox step was suggested. The activation enthalpy and activation entropy changes for the reaction have been calculated to be ΔH*= 69 kJmol-1 and ΔS*= -209 JK-1 mol-1, respectively.

Synthesis, Properties and X-ray Crystal Structures of Nickel(II) Complexes of a Hexaazamacrotetracyclic Ligand

The complexes [N2(L2)2(H2O)4]Cl4(1) and [Ni(L2)](ClO4)2 ⋅2H2O (2) (L = 1,3,10,12,16,19-hexaazatetracyclo [17,3,1,1 12.16,04.9]tetracosane) have been synthesized and structurally characterized by X-ray crystallography, spectroscopic and cyclic voltammetry. The crystal structure of 1 has a distorted octahedral geometry with two secondary and two tertiary amines of the macrocycle and two water molecules. In 2, the coordination geometry around the nickel atom is square-planar with four nitrogen atoms of the macrocycle. The equilibrium [Ni(L2)]2+ + 2H2O &rlhar2; [Ni(L2)(H2O)2]2+ has been studied in aqueous solution over a temperature range, yielding Δ H° = -19.0 ± 0.2 kJ mol-1 and Δ S° = - 56.0 ± 0.4 JK-1 mol-1. Cyclic voltammetry of the complexes give two one-electron waves corresponding to Ni(II)/Ni(III) and Ni(II)/Ni(I) processes. The electronic spectra and redox potentials of the complexes are influenced significantly by the geometry.

Multiple forms of soluble invertases in sugarcane juice: Kinetic and thermodynamic analysis

Soluble invertases were partially purified from storage tissue of an early maturing and high sucrose accumulating genotype Co89003 using ammonium sulphate fractionation and DEAE-cellulose column chromatography. The three different acid invertase isoforms named as A-I, A-II and A-III were identified at late grand growth stage of cane development, whereas only one neutral invertase isoform was detected at maturity stage of cane growth. The final purification achieved for A-I, A-II, A-III and neutral invertase isoform was 37, 45, 7 and 17-fold, respectively. The optimum pH values for A-I, A-II, A-III and neutral isoform were observed to be 5.0, 4.5, 4.5 and 7.0, respectively. Apparent Michaelis constant i.e. Km of different acidic isoforms at its optimum pH and temperature varied from 50.0 to 83.3 mM. For neutral invertase isoform, Km value was 44.0mM at its optimum pH and temperature. The highest Vmax/Km value of A-I isoform indicates the maximum kinetic perfection of this isoform and it may be the major vacuolar enzyme involved in sucrose hydrolysis. From the study of effect of temperature on Km and Vmax values of neutral invertase isoform, the enthalpy change, entropy change and energy of activation were observed to be -21.1 kJ mol-1,-40.5 JK-1 mol-1, and 42.5 kJmol-1, respectively. Among the different metal ions tested, manganese chloride strongly inhibited the activity of all soluble acid invertase isoforms and thus, may be utilized to induce early maturity and controlling sucrose inversion in sugarcane thereby increasing sugar recovery.

1H NMR Study of Aqueous Molybdomethylarsonates

The aqueous molybdomethylarsonate system was studied by 1H NMR, and it was found that a significant amount of [(CH3As)2Mo5O21]4- was formed in solution together with [(CH3As)2Mo6O24(OH2)]4-. The 1H NMR measurements also established that the [(CH3As)2Mo6O24(OH2)]4- species undergoes an exchange reaction with the free arsonate ion in solution, while the [(CH3As)2Mo5O21]4- species does not. The activation parameters for the exchange process were determined to be ΔH⧧ = 63 ± 4 kJ mol-1 and ΔS⧧ = −19 ± 14 JK-1 mol-1.

Influence of sample pH on the conformational backbone dynamics of a pseudotripeptide (H‐Tyr‐TicΨ[CH2‐NH] Phe‐OH) incorporating a reduced peptide bond: An NMR investigation

In the present paper we investigate the influence of sample pH on the conformational and dynamical properties of the pseudotripeptide H-Tyr-Tic psi [CH2-NH]Phe-OH (TIP[psi]; Tic: 1,2,3,4,-tetrahydroisoquinoline-3-carboxylic acid) using various one- and two-dimensional nmr techniques in conjunction with molecular modeling. Studies were conducted at three different pH levels corresponding to the zwitterionic peptide containing a formal positive charge (pH 3.1), the deprotonated molecule (pH 9.1), and a situation at neutral pH (pH 7.2) involving both protonated and deprotonated states of the reduced peptide bond. Analysis of the one-dimensional1H-nmr spectra reveals that in solution TIP[psi] is in slow dynamic exchange between conformations containing cis and trans configurations of the Tyr-Tic bond. An nmr pH dependence study of the cis:trans ratio indicated that the exchange process was governed by the protonation state of the reduced bone amine. From the nmr data, reduced peptide bond pK alpha values of 6.5 and 7.5 were determined for the cis and trans conformers, respectively. It was concluded that conformations containing a trans Tyr-Tic bond are stabilized at low pH by an intramolecular hydrogen bond between the Tyr carbonyl and the reduced peptide bond protonated amine. This observation was corroborated by molecular mechanics investigations that revealed low energy trans structures compatible with nmr structural data, and furthermore, were consistently characterized by the existence of a strong N+ H ... O = C interaction closing a seven-membered cycle. The dynamics of cis-trans isomerization about the Tyr-Tic peptide bond were probed by nmr exchange experiments. The selective presaturation of exchanging resonances carried out at several temperatures between 50 and 70 degrees C allowed the determination of isomerization rate constants as well as thermodynamic activation parameters. delta G not equal to values were in close agreement with the cis-->trans energy barrier found in X-Pro peptide fragments (approximately 83 kJ/mol). A large entropic barrier determined for the trans-->cis conversion of TIP[psi] (5.7 JK-1 mol-1 at pH 3.1;6.5 J K-1 mol-1 at pH 9.1) is discussed in terms of decreased solvent molecular ordering around the conformers possessing a trans Tyr-Tic bond. Evidence that the neutral form of the reduced peptide bond gains rigidity upon protonation was obtained from relaxation measurements in the rotating frame. T1 rho measurements of several protons in the vicinity of the reduced peptide bond were made as a function of spin-lock field.(ABSTRACT TRUNCATED AT 400 WORDS)

Properties of KSCN-rich Molten NaSCN-KSCN Mixtures

Abstract For molten (Na, K)SCN mixtures with more than 50 mol% KSCN the molar volume Vm,electrical conductivity, χ, refractive index n, surface tension γ and heat capacity CP were measured in dependence of composition and temperature, γ exhibited the minimum at ca. 70 mol% KSCN and Cp was 148 JK-1 mol-1 in the range of 413 to 471 K. The electronic polarizabilities of the ions in the molten state were estimated by the semiclassical Clausius-Mossotti equation

Large delta H not equal to and delta S not equal to values obtained in hydrolysis of alpha-chymotrypsin or catalase with alpha-chymotrypsin.

α-Chymotryptic hydrolyses of globular proteins, α-chymotrypsin (Chym) and catalase (Cata), were examined kinetically at pH 7.8 and temperatures between 30 and 50°C. In both cases, the reactions followed second-order rate equations; -d[Chym]/dt=k(chy-chy)[Chym]2 for the autolysis of Chym and -d[Cata]/dt=k(chy-cat)[Chym] [Cata] for the chymotryptic hydrolysis of Cata. From the Arrhenius plots, ΔH≠/kJ mol-1 and ΔS≠/JK-1 mol-1 were obtained as follows : for k(chy-chy)/dm3 mol-1 s-1, 270 and 681 at 30-44°C, and for k(chy-cat)/dm3 mol-1 s-1, 72.0 and 2.32 at 30-42°C, respectively. At higher temperatures than 45°C, the Arrhenius plots showed upward-concave curvatures in both cases. These extremely large activation parameters obtained for Chym autolysis and moderately large activation parameters obtained for Cata proteolysis are discussed in terms of deformation of the three-dimensional structures and the sites of proteolysis in the globular structures of the two enzymes.

Pantolactone as a plastic crystal.

D-Pantolactone crystals showed anomalous thermal behavior, that is, two endothermic peaks (62.0 and 91.6°C) were observed in the differential scanning calorimetry curves. The entropy change of the first transition was calculated as 44.4 JK-1 mol-1 and that of the second transition was 9.20 JK-1 mol-1. The powder X-ray diffraction patterns of D-pantolactone differed significantly before and after the transition (62.0°C) and only one sharp peak at 2θ=17.4° was observed at 75°C. At 75°C, carbon-13 nuclear magnetic resonance chemical shifts of D-pantolactone were clearly observed by the pulse Fourier-transform technique.It was concluded that D- and L-pantolactone showed a stable plastic crystal phase between 62.0 and 91.6°C, and that DL-pantolactone is in a plastic crystal phase at room temperature.

Solvent Exchange on (N,N-Diethylformamide)-[2,2',2'-Tri(Dimethylamino)Triethyl-Amine]Nickel (II)

A 1H n.m.r . study yields kex(298.2K) = 944�42s-1, ΔH‡ = 23.1�0.7 kJ mol-1 and ΔS‡ = -111�2 JK-1 mol-1 for N,N- diethylformamide exchange [Ni(N(CH2CH2NMe2)3)-(OCHNEt2)]2+. These data are compared with those of related species.

The theory of holes and the activation energy of viscosity in some nitrate melts at low temperatures

The molar activation energy for viscous flow of some solutions of fused nitrates, in the temperature range 360-400 K, for solute mole fractions XM [math] 0.1, has been found to conform to the following equation :E* = X5 [math] + XM [math]where,[math] : activation energy of the solvent[math] : contribution of the solute to the activation energy of the solution.A good order of magnitude of the molar contribution of one component to the activation energy is obtained by assuming that this contribution is close to the energy of formation of the smallest hole, or vacant site, which gives the following equation :[math]with n = 1 for a monovalent nitrate and n = 2 for a divalent nitrateE* : contribution of the component to the activation energyTm : melting point of the componentΔSi : entropy contribution to the entropy of fusion which is involved in the process of incorporation of holes or empty sites at the melting pointθi : ratio of the number of empty sites to the total number of sites in the liquid phase at the melting point.θi and ∆Si are solutions of the following system of equations :[math]R : gas constantThe above two equations stem from a physical interpretation which considers the entropy variation associated with the incorporation of holes, or vacant sites, to be equivalent to the entropy of mixing of these vacant sites with the regular occupied sites. Simultaneously, the requirements is set that this entropy variation be a linear function of the volume variation originating from the vacant sites. Such a requirement being imposed on a function which has no linear part except in the vicinity of an inflection point, the coordinates of this point yield the values of θi and ∆Si needed to estimate E* :θi = 0.17 ∆Si = 23 JK-1 mol-1* whence the equation :E* = 56 n Tm n = 1 or 2E* in Jmol-1

Anation and solvent exchange on (N,N-Dimethylformamide)[2,2',2''-tri(N,N-dimethylamino) triethylamine]nickel(II) and solvent exchange on Bis(N,N-dimethylformamide)-[2,2',2''-triaminotriethylamine]nickel(II)

Anation of [Ni{N(CH2CH2NMe2)3}(OCHNMe2)]2+ by Br-, N3 - and NCS- is characterized by rate laws consistent with the operation of an interchange mechanism (1) and the small variation of k1 characterizing these processes suggest that the activation mode is probably dissociative (d). Typically for anation by NCS- ki(298.2K) = 170 � 6 s-1, ∆H‡ = 44.0 � 2.1 kJ mol-1 and ∆S‡ =-54.7 � 7.2 JK-1 mol-1. The exchange of OCHNMe2 on [Ni{N(CH2CH2Nme2}3)-(OCHNMe2)]2+ is characterized by kex(298.2 K)=203 � 20s-1, ∆H‡ = 42.6 � 2.0 kJ mol-1 and ∆S‡ = -58 � 8 JK-1 mol-1(if it is assumed that this is the only nickel(II) species undergoing exchange) but the derivation of these parameters is complicated by the presence of a minor species believed to be [Ni{N(CH2CH2NMe2)3}(0CHNMe2)2]2+. Nevertheless the similarity of kex and ki observed for Br-, N3- and NCS- are consistent with both OCHNMe2 exchange and anation on [Ni {N(CH2CH2Nme2)3}(OCHNMe2)]2+ proceeding predominantly through an Id mechanism. For comparative purposes 0CHNMe2 exchange on [Ni{N(CH2CH2NHz)3}(OCHNMe2)2]2+, which is characterized by kex(298.2 K) = (1.4 � 0.2) × 105 and (1.9 � 0.9) × 107 s-1 for the non-equivalent OCHNMe2 sites, has also been studied.

A structural, solvent exchange and spin equilibrium study of (N,N-dimethylformamide)(R,S,R,S)-(1,4,8,11-tetramethyl-l,4,8,11- tetraazacyclotetradecane)nickel(II)

The molecular structure of R,S,R,S-[Ni {(-N(Me)(CH2)2N(Me)(CH2)3-)2} (OCHNMe2)](SO3CF3)2 has been determined in the solid state by X-ray diffraction methods. The geometry about nickel(11) is midway between square based pyramidal and trigonal bipyramidal with OCHNMe2 occupying the axial or an equatorial site in these geometries respectively. The nickel(II) is displaced 0.29 � from the least-squares tetraaza plane on the same side as the four methyl groups and OCHNMe2. In OCHNMe2 solution the formation of this five-coordinate high-spin species by coordination of OCHNMe2 by its four-coordinate low-spin precursor is characterized by K(298.2 K) = 10 � 2, ∆H = -12.8 � 2.7 kJ mol-1 and ∆S = -24.1 � 9.O JK-l mol-1 as determined by spectrophotometry. 1H (300 MHz) n.m.r. studies show that kwx(298.2 K) = (1.6 � 0.2) × 107 s-1, ∆H‡ = 27.8 � 0.4 kJ mol-1 and ∆S‡ = -13.O � 2.0 JK-1 mol-1 characterize the exchange of OCHNMe2 on R,S,R,S-[Ni {(-N(Me)(CH2)2N(Me)(CH2)3-)2 }(OCHNMe2)]2+.