Linear Arrhenius Plot Research Articles

Results Comparison of Alkali-Reactivity Tests for Same Aggregates, Using a Kinetic Model

A kinetic based comparison between expansion tests for alkali-aggregate reactivity was carried out deriving critical rates from test criteria, in an earlier paper. The present paper checks the assumptions and models of that earlier comparison against results with real aggregates varying in alkali reactivity. Using the same approach, for each aggregate, expansion rates for three expansion tests were estimated, corrected for alkalinity and depicted as an Arrhenius plot. The relationship used data from NF P18-590, ASTM C 1260 and ASTM C 227 expansion test-methods and shows linear Arrhenius plots for several aggregates, aligned almost parallel to the line obtained for test criteria. Aspects related to the different experimental conditions on test-methods and their effects are discussed. The proposed conclusion is that both standards and aggregate results, in the given conditions, are not inconsistent from the kinetic point of view. Some suggestions are made for improving the accuracy of the relationship obtained.

Structural, conductivity and dielectric properties of Li2SO4

Li2SO4 have been synthesized from lithium sulphate monohydrate by melting at 880C and slow cooling. The XRD results indicates that the melt cooled Li2SO4 is crystallized to monoclinic structure. The AC conductivity (σac) and dielectric relaxation (Tan δ) have been measured within the temperature range 170-250C and frequency range 100 Hz -120 kHz, respectively. The DC conductivities are conveniently extracted from σac (typical values ~2 x 10 and ~2 x10 S/cm at 200 and 250C, respectively) and are fitted to linear Arrhenius plot. The slope of this linear plot leads to an activation energy of 1.10 eV. It is found that the conduction in Li2SO4 is mainly through Li+. Further, we carried out first principles calculations and obtained the structural and bonding properties of Li2SO4. From band structure, Li2SO4 is found to be a wide band gap insulator with a band gap of 6.1eV. The partial density of states reveals the finite states of Li+ near to Fermi level, which limits its use of full capacity. This indicates a kinetic barrier for Li ions and electrons ambipolar diffusion.

Characterization of Thermotoga maritima glycerol dehydrogenase for the enzymatic production of dihydroxyacetone

NAD-dependent Thermotoga maritima glycerol dehydrogenase (TmGlyDH) converts glycerol into dihydroxyacetone (DHA), a valuable synthetic precursor and sunless tanning agent. In this work, recombinant TmGlyDH was characterized to determine if it can be used to catalyze DHA production. The pH optima for glycerol oxidation and DHA reduction at 50°C were 7.9 and 6.0, respectively. Under the conditions tested, TmGlyDH had a linear Arrhenius plot up to 80°C. TmGlyDH was more thermostable than other glycerol dehydrogenases, remaining over 50% active after 7h at 50°C. TmGlyDH was active on racemic 1,2-propanediol and produced (R)-1,2-propanediol from hydroxyacetone with an enantiomeric excess above 99%, suggesting that TmGlyDH can also be used for chiral synthesis. (R)-1,2-propanediol production from hydroxyacetone was demonstrated for the first time in a one-enzyme cycling reaction using glycerol as the second substrate. Negative cooperativity was observed with glycerol and DHA, but not with the cofactor. Apparent kinetic parameters for glycerol, DHA, and NAD(H) were determined over a broad pH range. TmGlyDH showed little activity with N(6)-carboxymethyl-NAD(+) (N(6)-CM-NAD), an NAD(+) analog modified for easy immobilization to amino groups, but the double mutation V44A/K157G increased catalytic efficiency with N(6)-CM-NAD(+) ten-fold. Finally, we showed for the first time that a GlyDH is active with immobilized N(6)-CM-NAD(+), suggesting that N(6)-CM-NAD(+) can be immobilized on an electrode to allow TmGlyDH activity in a system that reoxidizes the cofactor electrocatalytically.

Study on degradation kinetics of sulforaphane in broccoli extract

The objective of this study was to investigate the thermal degradation kinetics of sulforaphane (SF) in broccoli extract at selected temperatures (60, 75, 82 and 100°C) and pH values (2.2, 3.0, 4.0, 5.0 and 6.0). The results indicated that SF is unstable at high temperatures, but is more heat-stable when present in acidic food products. The degradation rate constants of SF in broccoli extract were lower than those obtained in purified SF. The thermal degradation of SF followed first-order reaction kinetics, and the rate constant increased with increase of temperature and pH values. The rate constant vs temperature relationships, which yield linear Arrhenius plots, were described by a simpler exponential equation, and a mathematical model was developed, using the steady-state kinetic parameters obtained to predict the retentions of SF at various pH values, heating times and temperatures.

Photophysics of indole-2-carboxylic acid (I2C) and indole-5-carboxylic acid (I5C): Heavy atom effect

In this study the effect of carboxylic group substitution in the 2 and 5 position of indole ring on the photophysics of the parent indole chromophore has been studied. The photophysical parameters crucial in triplet state decay mechanism of aqueous indole-2-carboxylic acid (I2C) and indole-5-carboxylic acid (I5C) have been determined applying our previously proposed methodology based on the heavy atom effect and fluorescence and phosphorescence decay kinetics [Kowalska-Baron et al., 2012]. The determined time-resolved phosphorescence spectra of I2C and I5C are red-shifted as compared to that of the parent indole. This red-shift was especially evident in the case of I2C and may indicate the possibility of hydrogen bonded complex formation incorporating carbonyl CO, the NH group of I2C and, possibly, surrounding water molecules. The possibility of the excited state charge transfer process and the subsequent electronic charge redistribution in such a hydrogen bonded complex may also be postulated. The resulting stabilization of the I2C triplet state is manifested by its relatively long phosphorescence lifetime in aqueous solution (912μs). The relatively short phosphorescence lifetime of I5C (56μs) may be the consequence of more effective ground-state quenching of I5C triplet state. This hypothesis may be strengthened by the significantly larger value of the determined rate constant of I5C triplet state quenching by its ground-state (4.4×108M−1s−1) as compared to that for indole (6.8×107M−1s−1) and I2C (2.3×107M−1s−1). The determined bimolecular rate constant for triplet state quenching by iodide kqT1 is equal to 1×104M−1s−1; 6×103M−1s−1 and 2.7×104M−1s−1 for indole, I2C and I5C, respectively. In order to obtain a better insight into iodide quenching of I2C and I5C triplet states in aqueous solution, the temperature dependence of the bimolecular rate constants for iodide quenching of the triplet states has been expressed in Arrhenius form. The linearity of the obtained Arrhenius plots clearly indicated the existence of one temperature-dependent non-radiative process for the de-excitation of I2C and I5C triplet state in the presence of iodide. This process may be attributed to the solute-quenching by iodide and, most probably, proceeds via reversibly formed exciplex. The activation energies obtained from linear Arrhenius plots (1.89kcal/mol for I5C; 2.55kcal/mol for I2C) are smaller as compared to that for diffusion controlled reactions in aqueous solution (about 4kcal/mol), which may indicate the great importance of the electrostatic interactions between solute and iodide ions in lowering the energy barrier needed for the formation of the triplet-quencher complex. Based on the theoretical predictions (at the DFT(CAM-B3LYP)/6-31+G(d,p) level of theory) and careful analysis of the obtained FTIR spectra it may be concluded that in the solid state I2C and I5C molecules form associates by intermolecular NH⋯OC and OH⋯OC hydrogen bonding interactions, whereas the existence of intramolecular NH⋯OC interactions in the solid state of I2C and I5C is highly unlikely.

TK1656, a thermostable l-asparaginase from Thermococcus kodakaraensis, exhibiting highest ever reported enzyme activity

Two L-asparaginase homologs, TK1656 and TK2246, have been found in the genome of Thermococcus kodakaraensis. The gene encoding TK1656 consists of 984 nucleotides corresponding to a polypeptide of 328 amino acids. To examine the properties of TK1656, the structural gene was cloned, expressed in Escherichia coli and the purified gene product was characterized. TK1656 exhibited high asparaginase activity (2350 U mg⁻¹) but no glutaminase activity. The enzyme also displayed the D-asparaginase activity but 50% to that of L-asparaginase. The highest activity was observed at 85°C and pH 9.5. TK1656 catalyzed the conversion of L-asparagine to L-aspartatic acid and ammonia following Michaelise-Menten kinetics with a K(m) and V(max) values of 5.5 mM and 3300 mmol min⁻¹ mg⁻¹, respectively. The activation energy from the linear Arrhenius plot was found to be 58 kJ mol⁻¹. Unfolding studies suggested that urea could not induce complete unfolding and inactivation of TK1656 even at a concentration 8 M; however, in the presence of 4 M guanidine hydrochloride enzyme structure was unfolded with complete loss of enzyme activity.

Migration of antimony from PET trays into food simulant and food: determination of Arrhenius parameters and comparison of predicted and measured migration data

Migration experiments with small sheets cut out from ovenable PET trays were performed in two-sided contact with 3% acetic acid as food simulant at various temperatures. The fraction of diffusible antimony (Sb) was estimated to be 62% in the PET sample under study. Apparent diffusion coefficients of Sb in PET trays were determined experimentally. Measurement of migration between 20 and 150°C yielded a linear Arrhenius plot over a wide temperature range from which the activation energy (E a) of 188 ± 36 kJ mol−1 and the pre-exponential factor (D 0) of 3.6 × 1014 cm2 s−1 were determined for diffusing Sb species. E a was similar to previously reported values for PET bottles obtained with a different experimental approach. E a and D 0 were applied as model parameters in migration modelling software for predicting the Sb transfer in real food. Ready meals intended for preparation in a baking oven were heated in the PET trays under study and the actual Sb migration into the food phase was measured by isotope dilution ICP-MS. It was shown that the predictive modelling reproduces correctly experimental data.

The Arrhenius Equation Revisited

The Arrhenius equation has been widely used as a model of the temperature effect on the rate of chemical reactions and biological processes in foods. Since the model requires that the rate increase monotonically with temperature, its applicability to enzymatic reactions and microbial growth, which have optimal temperature, is obviously limited. This is also true for microbial inactivation and chemical reactions that only start at an elevated temperature, and for complex processes and reactions that do not follow fixed order kinetics, that is, where the isothermal rate constant, however defined, is a function of both temperature and time. The linearity of the Arrhenius plot, that is, Ln[k(T)] vs. 1/T where T is in °K has been traditionally considered evidence of the model's validity. Consequently, the slope of the plot has been used to calculate the reaction or processes’ “energy of activation,” usually without independent verification. Many experimental and simulated rate constant vs. temperature relationships that yield linear Arrhenius plots can also be described by the simpler exponential model Ln[k(T)/k(Treference)] = c(T-Treference). The use of the exponential model or similar empirical alternative would eliminate the confusing temperature axis inversion, the unnecessary compression of the temperature scale, and the need for kinetic assumptions that are hard to affirm in food systems. It would also eliminate the reference to the Universal gas constant in systems where a “mole” cannot be clearly identified. Unless proven otherwise by independent experiments, one cannot dismiss the notion that the apparent linearity of the Arrhenius plot in many food systems is due to a mathematical property of the model's equation rather than to the existence of a temperature independent “energy of activation.” If T+273.16°C in the Arrhenius model's equation is replaced by T+b, where the numerical value of the arbitrary constant b is substantially larger than T and Treference, the plot of Ln k(T) vs. 1/(T+b) will always appear almost perfectly linear. Both the modified Arrhenius model version having the arbitrary constant b, Ln[k(T)/k(Treference) = a[1/ (Treference+b)-1/ (T+b)], and the exponential model can faithfully describe temperature dependencies traditionally described by the Arrhenius equation without the assumption of a temperature independent “energy of activation.” This is demonstrated mathematically and with computer simulations, and with reprocessed classical kinetic data and published food results.

Kinetics of Oxidation of Propranolol by Sodium – N – Chloro – pToluene Sulphonamide in NaOH medium. A Mechanistic Study

Propranolol is used for treating high blood pressure, heart pain, abnormal rhythms of the heart and some neurologic conditions. Kinetics and oxidation of Propranolol (PPL) ((RS)-1-(1-methylethylamino)-3-(1-naphthyloxy)propan-2-ol) by sodium -Nchloro – p-toluenesulphonamide (Chloramine – T or CAT) in NaOH medium at 298K have been studied. The rate was first order in [CAT]o, fractional order in [PPL] and zero order in [OH ]. Addition of p-toluenesulphonamide, NaCl and NaBr did not affect the rate of the reaction. Variation in ionic strength did not affect the rate of the reaction indicating that non – ionic species are involved in the rate limiting step. Dielectric effect of the medium showed positive effect. Rate increased with increase in temperature from 288K to 318K. From the linear Arrhenius plot, activation parameters were computed. Addition of reaction mixture to aqueous acrylonitrile solution did not initiate polymerization, showing the absence of free radicals species. Oxidation products were identified. TsNClNa, the reactive species oxidizes the substrate. Based on kinetic results, reaction stoichiometry and oxidation products, a suitable mechanism have been proposed.

Kinetics and Mechanism of Oxidation of Diethyl Ether by Chloramine-T in Acidic Medium

The kinetics of oxidation of diethyl ether (DE) with sodium N-chloro-p-toluenesulphonamide (CAT) in hydrochloric acid solution has been studied at (313°K).The reaction rate show a first order dependence on [CAT] and fractional order dependence on each [DE] and [H+] .The variation of ionic strength of the medium has no significant effect on the reaction rate , addition of p-toluenesulphonamide (p-TSA) affects the reaction rate marginally the rate increased with decreasing dielectric constant of the medium , the stochiometry of the reaction was found to be 1:2 and oxidation products were identified , A Michaelis – Menten type mechanism has been suggested to explain the results.The equilibrium and the decomposition constants of CAT – diethyl ether complex have been evaluated. Thermodynamic parameters were computed by studying reaction at temperatures range ( 308 – 323°K) for the rate limiting step and for the observed first order constants by the linear Arrhenius plot. The mechanism proposed and the derived rate law are consistent with observed kinetics.

Simultaneous catalytic removal of NOx and soot particulates over CuMgAl hydrotalcites derived mixed metal oxides

A series of CuMgAl hydrotalcites derived oxides were prepared by co-precipitation and calcination methods and tested for the simultaneous catalytic removal of NOx and soot. The obtained samples were characterized by XRD, N 2 adsorption-desorption, H 2-TPR and ICP-AES techniques. The crystal phases, porous structures and redox properties of the catalysts were strongly influenced by Cu substitution contents and calcination temperatures. The CuMgAl mixed oxides with mesoporous properties exhibit high activity for the simultaneous NOx-soot removal. Among the tested catalysts, 3.0Cu-800 sample shows the best performance with the ignition temperature of soot = 260 °C and the total amounts of N 2 = 6.0 × 10 − 5 mol. Based on the experimental work, a primitive kinetics analysis was carried out from the non-steady (dynamic) TPR measurements. Linear Arrhenius plots of rates of CO 2, N 2 and N 2O formation were observed around the onset of formation curves where the substantial amount of the soot still remains in the soot/catalyst mixture and the effective area of the soot/catalyst contact can be regarded as constant. Finally, a compensation effect was found for the formation of CO 2, N 2 and N 2O over CuMgAl mixed oxides with CuO as the predominant phase.

Oxidation of d-glucose by N-bromophthalimide in the presence of chlorocomplex of iridium(III): a kinetic and mechanistic study

The kinetics of Iridium (III) catalyzed oxidation of d-glucose [d-glu] has been studied by N-bromophthalimide [NBP] in the acidic medium (pH 1.3) at 303 K. The reaction followed first-order kinetics with respect to [NBP] from 0.5 × 10−4 to 4.0 × 10−4 mol dm−3. The results indicate the first-order kinetics in [iridium(III)] chloride at lower concentrations from 0.75 × 10−6 to 5.8 × 10−6 mol dm−3 tends towards a zero order at its higher concentrations (up to 13.36 × 10−6 mol dm−3). Zero-order kinetics with respect to [d-glu] from 2.0 × 10−3 to 20.0 × 10−3 mol dm−3 was observed throughout its variation. A positive effect on the oxidation rate was observed for [Cl−] from 0.2 × 10−5 to 2.4 × 10−5 mol dm−3 and the rate of reaction decreased with increase in dielectric constant (decreasing acetic acid from 35 to 15%) of the medium. A negative effect was observed on the reaction rate for [H+] from 1.5 × 10−2 to 12.0 × 10−2 mol dm−3. Addition of reduced product of oxidant, i.e., phthalimide from 1.0 × 10−4 to 8.0 × 10−4 mol dm−3 did not show a significant effect on the oxidation velocity. Rate of reaction increased with increase in ionic strength from 0.2 × 10−1 to 4.0 × 10−1 mol dm−3 of the medium, i.e., increase in [KNO3]; the rate of reaction was increased. From the linear Arrhenius plot of log k 1 versus 1/T, the activation energy (Ea = 50.91 kJ mol−1) was calculated. With the help of the energy of activation, parameters such as enthalpy of activation (ΔH # = 48.39 kJ mol−1), entropy of activation (ΔS # = −321.63 JK mol−1), Gibbs free energy of activation (ΔG # = 145.84 kJ mol−1) and frequency factor (Log A = −3.97) were also calculated. A suitable mechanism in conformity with kinetic observations was proposed to explain reaction stoichiometry and product analysis.

Activation Parameters Derived From a Temperature Dependent Large Amplitude ac Voltammetric Study of the Electrode Kinetics of the Cp2M0/+ Redox Couples (M = Fe, Co) at a Glassy Carbon Electrode

Heterogeneous charge transfer rate constants (k°) for the oxidation of ferrocene, Fc (k° = 0.21 cm s(-1) at 20 °C), and the reduction of the cobaltocenium cation, Cc(+) (k° = 0.12 cm s(-1) at 18 °C), in CH(2)Cl(2) (0.5 M Bu(4)NPF(6)) at a glassy carbon (GC) electrode were determined as a function of temperature using the higher harmonic components available in Fourier transformed large amplitude ac voltammetry. The measured k° values lie at the upper end of the analytically useful range available for the acquisition of meaningful kinetic data for these very fast (i.e., close to reversible) processes. Measurements of the kinetics are facilitated by the ac technique because contributions resulting from uncompensated resistance and slow electrode kinetics, both of which also vary with temperature, can be distinguished via their different contributions to individual harmonics. Values of k° measured over the temperature range of -18 to +20 °C for the Fc(0/+) and Cc(+/0) processes gave linear Arrhenius plots yielding free energies of activation (ΔG(‡)) estimates of 17.0 and 18.0 kJ mol(-1), respectively, in excellent agreement with theoretical values derived from Marcus theory. An analogous temperature dependence is indicated in a study of the Fc(0/+) process in acetonitrile (0.1 M Bu(4)NPF(6)), but the greater k° value evident makes the temperature dependence of these parameters more difficult to quantify as departures from reversibility are minimal, even in the higher harmonics.

A Comprehensive Examination of the Contributions to Binding and Activation Entropies

The elucidation of the role of entropic effects in enzyme catalysis and binding free energy is a problem of practical and fundamental interest. In order to address this problem it is essential to develop simulation methods capable of evaluating the entropic contribution to the overall free energy. Such an evaluation is useful for assessing temperature effects and exploring specialized options in enzyme design. In fact, the general ability to evaluate activation entropies of chemical reactions in solution has long been a challenge to computational chemists. Here we present what is probably the first microscopic evaluation of all of the relevant components to the relevant entropy, namely, configurational, polar solvation and hydrophobic entropies. All of these contributions are evaluated by the restraint release (RR) approach. In the case of binding entropies we found out major compensation effects in both the solvation and hydrophobic effect, and despite some overestimate, can provide very useful insight. Furthermore, exciting current use of our approach lead to the elucidation of the origin of the puzzling strong temperature dependence of the activation entropy in ADH. It is found that this effect does not reflect any dynamical factor, but rather the change in the polarization of the protein polar groups (plus water molecules) upon moving from the ground state to the transition state. This helps to resolve the long-standing question about the origin of the observed non linear Arrhenius plot.

Mechanism of the Swern Oxidation: Significant Deviations from Transition State Theory

Deprotonation of the alkoxysulfonium intermediate has been shown to be rate-determining in the Swern oxidation of benzyl alcohol. Directly following this rate-determining step is the intramolecular syn-β-elimination of the ylide. In the present study, intramolecular (2)H kinetic isotope effects (KIEs) are used to gain insight into this syn-β-elimination step. As a result of the stereogenic sulfur center in the ylide intermediate, two diastereomeric transition states (endo-TS1 and exo-TS1) must be assumed to contribute to the intramolecular KIE. The intramolecular (2)H KIE determined at -78 °C is 2.82 ± 0.06. Attempts to reproduce this measurement computationally using transition state theory and a Bell tunneling correction yielded a value (1.58) far below that determined experimentally. Computational analysis is complicated by the existence of two distinct transition structures owing to the stereogenic center. Two extremes of Curtin-Hammett kinetics are explored using energies, vibrational frequencies, and moments of inertia from computed transition structures. Neither Curtin-Hammett scenario can reproduce the observed KIE to any acceptable degree of fidelity. Evidence based upon previous kinetics measurements and calculations upon a model system suggests that the stereogenic sulfur center is not likely to undergo inversion to a significant degree at the temperatures at which the Swern oxidation is performed here. Proceeding under the assumption of no stereoinversion at the sulfur center, calculations predict a nearly linear Arrhenius plot for the KIE--even with the inclusion of a one-dimensional tunneling correction. By contrast, the experimentally determined temperature dependence shows a significant concave upward curvature indicative of the influence of tunneling. Notably, KIEs measured in CCl(4), CHCl(3), CH(2)Cl(2), dichloroethane, and chlorobenzene at -23 °C showed little variance. This finding discounted the possible influence from dynamical effects due to incomplete vibrational relaxation. An ad hoc amplification of the imaginary frequencies corresponding to the first-order saddle points corresponding to endo-TS1 and exo-TS1 allowed us to reproduce the experimental temperature dependence of the KIE using only two adjustable parameters applied to a kinetic scenario that involves four isotopomeric transition states. The cumulative data and computational modeling strongly suggest that, even though the intramolecular (2)H KIE observed in these experiments is small, this reaction requires a multidimensional description of the tunneling phenomenon to accurately reproduce experimental trends.

Linalool Dehydratase-Isomerase, a Bifunctional Enzyme in the Anaerobic Degradation of Monoterpenes

Castellaniella (ex Alcaligenes) defragrans strain 65Phen mineralizes monoterpenes in the absence of oxygen. Soluble cell extracts anaerobically catalyzed the isomerization of geraniol to linalool and the dehydration of linalool to myrcene. The linalool dehydratase was present in cells grown on monoterpenes, but not if grown on acetate. We purified the novel enzyme ∼1800-fold to complete homogeneity. The native enzyme had a molecular mass of 160 kDa. Denaturing gel electrophoresis revealed one single protein band with a molecular mass of 40 kDa, which indicated a homotetramer as native conformation. The aerobically purified enzyme was anaerobically activated in the presence of 2 mm DTT. The linalool dehydratase catalyzed in vitro two reactions in both directions depending on the thermodynamic driving forces: a water secession from the tertiary alcohol linalool to the corresponding acyclic monoterpene myrcene and an isomerization of the primary allylalcohol geraniol in its stereoisomer linalool. The specific activities (V(max)) were 140 nanokatals mg(-1) for the linalool dehydratase and 410 nanokatals mg(-1) for the geraniol isomerase, with apparent K(m) values of 750 μm and 500 μm, respectively. The corresponding open reading frame was identified and revealed a precursor protein with a signal peptide for a periplasmatic location. The amino acid sequence did not affiliate with any described enzymes. We suggest naming the enzyme linalool dehydratase-isomerase according to its bifunctionality and placing it as a member of a new protein family within the hydrolyases (EC 4.2.1.X).

Application of a validated stability-indicating chromatographic method to evaluate the reproducibility between batches of small peptides in solution

A stability-indicating reversed-phase high-performance liquid chromatographic method was developed and validated as per the International Conference on Harmonization (ICH) guidelines to evaluate the reproducibility of batches of synthetic peptides included in a stability program, in particular cholecystokinin (CCK-4) peptide. Both isothermal and nonisothermal approaches were used to determine stability under experimental conditions and the resulting degradation products were identified by liquid chromatography–mass spectrometry (LC–MS). The principal degradation product was the cyclic dimer, although another two products derived from it were also detected, due to the loss of one or two Phe-NH 2 residues. The dimerization follows first-order kinetics, whereas the hydrolytic cleavage implies both consecutive and in-parallel processes. The linear Arrhenius plot indicates that the degradation mechanism and kinetics do not change with temperature or the batch, but the degradation rate does depend on the batch, for example, the shelf-life at 25 °C was 2.54 days for batch 3, which is 13-times lower than batch 2. This variability is caused by a change in the synthesis process introduced by the manufacturer. The combination of these two elements: the analytical and stability-evaluating methods provide enough data to establish a stability-indicating profile, as required by the guideline ICH-Q6B for biotechnological/biological products.

The rate of spontaneous cleavage of the glycosidic bond of adenosine

Previous estimates of the rate of spontaneous cleavage of the glycosidic bond of adenosine were determined by extrapolating the rates of the acid- and base-catalyzed reactions to neutral pH. Here we show that cleavage also proceeds through a pH-independent mechanism. Rate constants were determined as a function of temperature at pH 7 and a linear Arrhenius plot was constructed. Uncatalyzed cleavage occurs with a rate constant of 3.7 × 10 −12 s −1 at 25 °C, and the rate enhancement generated by the corresponding glycoside hydrolase is ∼5 × 10 12-fold.

Non-Steroidal Anti-Inflammatory Drug Induced Membrane Fusion: Concentration and Temperature Effects

Membrane fusion is a critical step in many biological events. The fusion process is always induced by different fusogenic agents of which proteins and peptides form the largest group. The mechanistic details of the fusion process vary depending on the nature of the fusogenic agents. However, membrane fusion induced by small drug molecules at physiologically relevant concentration has not been observed. Only recently our group has shown that three painkillers, namely, meloxicam, piroxicam, and tenoxicam, belonging to the oxicam group of non-steroidal anti-inflammatory drugs (NSAIDs) share this property. In this work, we present the effect of drug concentration and temperature on the kinetics of the fusion process. Small unilameller vesicles (SUVs) formed by dimyristoylphosphatidylcholine (DMPC) with an average diameter of 50-60 nm were used as model membranes. Fluorescence assays were used to probe the time dependence of lipid mixing, content mixing, and leakage whereas transmission electron microscopy (TEM) was used to image the fusion process and to calculate the average diameter of the vesicles. The results show that, in this fusion process, lipid mixing and content mixing are two sequential events and can occur even at a very low drug to lipid ratio (D/L) of 0.018. For a D/L ratio greater than 0.045, leakage of the vesicles leading to rupture compete with the fusion thereby inhibiting it. Temperature variation in the presence of drugs gives linear Arrhenius plots and is used to calculate the activation energies for the lipid mixing and content mixing, which are less compared to that seen in SUVs with a smaller diameter of 45 nm. Thermodynamic parameters of the transition state are calculated. The fusogenic property of the drugs has been interpreted in terms of the ability of the drugs to introduce membrane perturbation even at such low D/L ratios as studied here.

Effect of substrate temperature on structural, optical and electrical properties of pulsed laser ablated nanostructured indium oxide films

Nanocrystalline indium oxide (INO) films are deposited in a back ground oxygen pressure at 0.02 mbar on quartz substrates at different substrate temperatures ( T s) ranging from 300 to 573 K using pulsed laser deposition technique. The films are characterized using GIXRD, XPS, AFM and UV–visible spectroscopy to study the effect of substrate temperature on the structural and optical properties of films. The XRD patterns suggest that the films deposited at room temperature are amorphous in nature and the crystalline nature of the films increases with increase in substrate temperature. Films prepared at T s ≥ 473 K are polycrystalline in nature (cubic phase). Crystalline grain size calculation based on Debye Scherrer formula indicates that the particle size enhances with the increase in substrate temperature. Lattice constant of the films are calculated from the XRD data. XPS studies suggest that all the INO films consist of both crystalline and amorphous phases. XPS results show an increase in oxygen content with increase in substrate temperature and reveals that the films deposited at higher substrate temperatures exhibit better stoichiometry. The thickness measurements using interferometric techniques show that the film thickness decreases with increase in substrate temperature. Analysis of the optical transmittance data of the films shows a blue shift in the values of optical band gap energy for the films compared to that of the bulk material owing to the quantum confinement effect due to the presence of quantum dots in the films. Refractive index and porosity of the films are also investigated. Room temperature DC electrical measurements shows that the INO films investigated are having relatively high electrical resistivity in the range of 0.80–1.90 Ωm. Low temperature electrical conductivity measurements in the temperature range of 50–300 K for the film deposited at 300 K give a linear Arrhenius plot suggesting thermally activated conduction. Surface morphology studies of the films using AFM reveal the formation of nanostructured indium oxide thin films.