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At least 829 records · Page 46Linked to original sources
PubMed2006

Chemical glycosylation: new insights on the interrelation between protein structural mobility, thermodynamic stability, and catalysis.

Chemical protein glycosylation was employed to sequentially modulate the structural dynamics of the serine protease alpha-chymotrypsin as evidenced from amide H/D exchange kinetics. The reduction in alpha-CT's structural dynamics at increasing glycan molar contents statistically correlated with the increased thermodynamic stability (T(m)) and reduced rate of enzyme catalysis (k(cat)) exhibited by the enzyme upon chemical glycosylation. Temperature-dependent experiments revealed that native-like structural dynamics and function could be restored for the glycosylated conjugates at temperature values close to their thermodynamic stability suggesting that the concept of "corresponding states" can be extended to glycoproteins. These results demonstrate the value of chemical glycosylation as a tool for studying the role of protein structural dynamics on protein biophysical properties; e.g. enzyme stability and function.

Animals↗
PubMed2006

Studying thermodynamic aspects of sublimation, solubility and solvation processes and crystal structure analysis of some sulfonamides.

Crystal structures of N-(2-chlorophenyl)-benzene-sulfonamide (I), N-(2,3-dichlorophenyl)-benzene-sulfonamide (II), N-(4-chlorophenyl)-benzene-sulfonamide (III) were solved by X-ray diffraction method. Temperature dependencies of saturated vapor pressure and thermodynamic functions of sublimation process were calculated (I: DeltaG(sub)(298)=50.4kJmol(-1); DeltaH(sub)(298)=114+/-1kJmol(-1); DeltaS(sub)(298)=213+/-3Jmol(-1)K(-1); II: DeltaG(sub)(298)=54.1kJmol(-1); DeltaH(sub)(298)=124.9+/-1.6kJmol(-1); DeltaS(sub)(298)=237+/-5Jmol(-1)K(-1); III: DeltaG(sub)(298)=49.9kJmol(-1); DeltaH(sub)(298)=98.6+/-1.9kJmol(-1); DeltaS(sub)(298)=163+/-5Jmol(-1)K(-1)). Thermochemical parameters of fusion process for the compounds were obtained. Enthalpies of evaporation were estimated from enthalpies of sublimation and fusion. Temperature dependencies of the solubility in water, n-octanol and n-hexane were measured. The thermodynamic functions of solubility and solvation processes were deduced. Specific and non-specific solvation terms were distinguished using the transfer from the "inert"n-hexane to the other solvents. The transfer processes of the molecules from water to n-octanol were analyzed and main driven forces were established.

1-Octanol↗
PubMed2006

Thermodynamic stability and formation of aggregates of human immunoglobulin G characterised by differential scanning calorimetry and dynamic light scattering.

The final process step of polyclonal human immunoglobulin G is formulation with agents such as sugars, polyols, amino acid and salts. Often the most stable formulations were empirically identified. Physicochemical methods, such as differential scanning calorimetry and dynamic light scattering, provide a deeper insight on the biophysical properties of such a protein solution. The combination of these methods proved to be sensitive enough to detect fine differences in the properties relevant for the development of stable protein solutions. The influence of additives, such as maltose and glycine in combination with water or low concentrations of salts, on human immunoglobulin preparations was analysed. Differential scanning calorimetry illustrated that 0.2 M glycine had better stabilising effects compared to 10% maltose. Dynamic light scattering and differential scanning calorimetry revealed that solutions preventing aggregation were not optimal in terms of thermodynamic stability. Aggregation was minimised with increasing ionic strength, shown by dynamic light scattering, whereas thermodynamic stability for heat sensitive parts of human immunoglobulin G, analysed with differential scanning calorimetry, was decreased.

Biophysical Phenomena↗
PubMed2005

Huperzine A--human serum albumin association: chromatographic and thermodynamic approach.

The synthesis of six new huperzine analogues was reported. Each product presents an amidification of the free amine on huperzine A. The synthesis strategy of these new huperzine A derivatives is based on a condensation with an acyl anhydride. The binding on HSA of two molecule series (huperzine and benzodiazepine, respectively) was investigated with high performance liquid affinity chromatography (HPLAC) using an HSA column. A thermodynamic approach showed that binding huperzine A on HSA involved hydrophobic and Van der Waals interactions. A comparative thermodynamic study with benzodiazepine molecules was carried out to determine the potential binding site of huperzine derivatives on HSA.

Alkaloids↗
PubMed2004

Kinetics and thermodynamics of the adsorption of some dyestuffs and p-nitrophenol by chitosan and MCM-chitosan from aqueous solution.

The effect of initial concentration, temperature, and shaking rate on the adsorption of three dyestuffs [orange II (O-II), crystal violet (CV), and reactive blue 5 (RB5)] and an ideal adsorbate, p-nitrophenol (PNP), by chitosan (Sigma C-3646) and the effect of temperature on the adsorption of O-II and CV by monocarboxymethylated chitosan (MCM-chitosan) were investigated. Kinetic data obtained for the adsorption of each dyestuff and PNP by chitosan and of O-II and CV by MCM-chitosan at different temperatures were applied to the Lagergren equation, and adsorption rate constants (k(ads)) at these temperatures were determined. These rate constants related to the adsorption of O-II and RB5 by chitosan and of O-II by MCM-chitosan were applied to the Arrhenius equation, and activation energies (E(a)) were determined. In addition, the isotherms for adsorption, at different temperatures, of each dyestuff and PNP by chitosan and of O-II and CV by MCM-chitosan were also determined. These isothermal data were applied to linear forms of isotherm equations that they fit, and isotherm constants were calculated. Because the isotherm curves obtained for the adsorption of O-II and CV by chitosan and of CV by MCM-chitosan fit the Langmuir adsorption isotherm, b constants were applied to thermodynamic equations, and thermodynamic parameters (delta G, delta H, and delta S) were calculated. Lastly, chitosan and MCM-chitosan were compared with respect to the ability to take up the dyestuffs and PNP.

Adsorption↗
PubMed2004

Uranyl sorption by smectites: spectroscopic assessment of thermodynamic modeling.

Batch sorption experiments and thermodynamic modeling of the interaction of UO2(2+) and its hydrolysis products with two smectitic clay minerals, the reference material SWy-1 [McKinley et al., Clays Clay Miner. 43 (1995) 586] and the soil isolate LK-1 [Turner et al., Geochim. Cosmochim. Acta 30 (1996) 3399], have established a conceptual framework for uranyl/smectite surface complexation based on general reactions between aqueous uranyl species and the reactive sites on the mineral surfaces. In this report, we have formulated and spectroscopically tested a set of hypotheses based on this conceptual framework using samples prepared under similar or identical conditions to evaluate the agreement between surface complexation/speciation as enumerated by spectroscopic characterization and that elaborated by the surface complexation model. Both steady-state and time-resolved optical emission spectral data are presented for uranyl on both smectite minerals as well as on the analogue phases SiO2 and Al(OH)3 spanning the pH range from approximately 4 to 8 and the background electrolyte concentrations from approximately 0.001 to 0.1 M. The spectral data enable the explicit identification of an outer-sphere exchange-site population of the hydrated cation [UO2(OH2)5(2+) ] in SWy-1. Spectral data also clearly establish the existence of inner-sphere surface complexes on the analogue phases and on the amphoteric clay crystallite edge sites [aluminol (>Al-OH) and silanol (>Si-OH)]. Based on the spectral characteristics of these uranyl edge-site populations, it is possible to readily infer for the SiO2, Al(OH)3, and SWy-1 samples the evolution in surface speciation with increasing pH to more hydrolyzed uranyl-surface complexes consistent with the conceptual model. The spectral domain characteristics of the edge-site populations on LK-1 with increasing pH suggest that there is no change in the hydrolysis of the uranyl-surface species. However, emission lifetime data are interpreted as indicating a shift in the surface speciation of the same uranyl-surface species from aluminol sites to silanol sites with pH increase. This observation is also consistent with the conceptual framework of the model. Data are also reported for Eu3+/smectite samples to provide additional insight into the exchange site populations. The emission spectra for Eu3+ in the basal-plane exchange sites differs significantly between SWy-1 and LK-1 samples reflecting a difference in the basal plane spacing between these two minerals, but the emission lifetime data suggest that the Eu3+ cation remains fully hydrated in both systems. The overall general description of surface speciation of uranyl on these mineral phases as enumerated by spectroscopy is in good accord with that derived from the conceptual thermodynamic model, lending added confidence to our understanding and descriptions of surface complexation behavior in this complex geochemical system.

Adsorption↗
PubMed2004

Thermodynamic and functional properties of legumin (11S globulin from Vicia faba) in the presence of small-molecule surfactants: effect of temperature and pH.

We report on the effect of a set of water-dispersible small-molecule surfactants (the main and the longest-hydrocarbon components of which are a citric acid ester of monostearate, a sodium salt of stearol-lactoyl lactic acid, and a polyglycerol ester of stearic acid) on molecular, thermodynamic, and functional properties of the major storage protein of broad beans (Vicia faba) legumin in different molecular states (native, heated, and acid-denatured). The interaction between legumin and the surfactants has been characterized by a combination of thermodynamic methods, namely, mixing calorimetry and multiangle laser static and dynamic light scattering. It was found that hydrogen bonds, electrostatic interactions, and hydrophobic contacts provided a basis for the interactions between the surfactants and both the native and the denatured protein in aqueous medium. Intensive association of the protein molecules in a bulk aqueous medium in the presence of the surfactants was revealed by static and dynamic laser light scattering. In consequence of this, both the surface activity and the gel-forming ability of legumin increased markedly, which has been shown by tensiometry, estimation of protein foaming capacity, and steady-state viscometry. A likely molecular mechanism underlying the effects of small-molecule surfactants on legumin structure-forming properties at the interface and in a bulk aqueous medium is discussed.

Acids↗
PubMed2005

The influence of chitosans with defined degrees of acetylation on the thermodynamic data for copper coordination.

The interaction of copper with three different chitosans having degrees of deacetylation of 77.5, 81.5, and 86.1%, named C, A, and F, respectively, was followed by the batch method at 298+/-1 K and the values obtained were fitted to a modified Langmuir equation. These interactions were also obtained by calorimetric titration. Experimentally, 50.0 mg of each chitosan was suspended in doubly distilled water at 298.15+/-0.02 K under mechanical turbine stirring. The titration was performed by adding increments of 10 microl of a 0.10 mol dm3 Cu(NO3)2 aqueous solution and the calorimetric isotherms obtained were adjusted to a modified Langmuir equation. From the net thermal effects K and DeltaH values were calculated, also permitting the acquisition of other thermodynamic data for the chitosan-copper interaction at the solid/liquid interface. The exothermic enthalpic values of -45.65+/-1.97, -49.91+/-1.57, and -48.64+/-0.82 kJ mol(-1), for chitosans C, A, and F, respectively, reflect the degree of deacetylation. The spontaneity of the systems is shown by the negative DeltaG values, -36.1+/-0.2, 36.8+/-0.1, and -38.1+/-0.3 kJ mol(-1) for the same sequence of chitosans. The negative entropic values, -34, -44, and -35 J mol(-1) K(-1), are in agreement with an ordering of solvent as the complexation occurred. The intensity of the thermal effects and the thermodynamic data obtained from the copper/chitosan interactions can be associated with the ability of these biopolymers to extract copper from aqueous solutions.

Acetylation↗
PubMed2005

Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewater with low-cost adsorbents.

This note revisits the literature evaluating the thermodynamic parameters of adsorption equilibrium uptakes of heavy metals and dyes from water and wastewater streams using low-cost adsorbents derived from agricultural waste, industrial wastes, inorganic particulates, or some natural products. We highlighted the possible flaws in some adsorption studies when their thermodynamic parameters were assessed, since compensation effects during enthalpy and entropy evaluation were possibly overlooked.

Adsorption↗
PubMed2006

Kinetics and thermodynamics of bromophenol blue adsorption by a mesoporous hybrid gel derived from tetraethoxysilane and bis(trimethoxysilyl)hexane.

A mesoporous hybrid gel is prepared with tetraethoxysilane (TEOS) and bis(trimethoxysilyl)hexane (TSH) as precursors without using any templating agent. Nitrogen sorption, TG-DTA, FTIR, and point of zero charge (PZC) measurement are used to characterize the gel. The gel has a specific surface area of 695 m(2) g(-1) with a pore size of 3.5 nm, a pore volume of 0.564 cm(3) g(-1), and a point of zero charge (PZC) of 6.2. The kinetics and thermodynamics of bromophenol blue (BPB) adsorption by the gel in aqueous solution are investigated comprehensively. The effects of initial BPB concentration, pH, ionic strength, and temperature on the adsorption are investigated. Kinetic studies show that the kinetic data are well described by the pseudo-second-order kinetic model. Initial adsorption rate increases with the increase in initial BPB concentration and temperature. Adsorption activation energy is found to be 62.5-67.5 kJ mol(-1) depending on the initial BPB concentration. Internal diffusion appears to be the rate-limiting step for the adsorption process. The equilibrium adsorption amount increases with the increase in the initial BPB concentration, solution acidity, and ionic strength, but decreases with the increase in temperature. The thermodynamic analysis indicates that the adsorption is spontaneous and exothermic. The adsorption isotherms can be well described with Freundlich equation indicating the heterogeneity of the hybrid gel surface. Electrostatic and hydrophobic interactions are suggested to be the dominant mechanism for adsorption.

Adsorption↗
PubMed2006

Adsorption of cyanuric acid on activated carbon from aqueous solution: effect of carbon surface modification and thermodynamic characteristics.

The performance of a conventional and two surface-modified activated carbon samples was investigated for the sorption of cyanuric acid from aqueous solution by varying the process parameters such as initial concentration, pH, temperature, dose of adsorbents, and agitation time. The modified carbon samples obtained by acid and ammonia treatment of the conventional sample had a higher BET surface area (989 and 1010 m2 g-1, respectively) and higher specific mesopore surface area (27.36 and 33.21 m2 g-1, respectively) compared to the untreated material (820 and 18.25 m2 g-1). The solute removal was found to be favored at lower solute concentration, increased agitation time, increased adsorbent dose, and lower temperature. The modified adsorbents outperformed the conventional activated carbon for sorption of cyanuric acid especially at higher pH (>7.5) and with increasing temperature. The Freundlich model appears to fit the isotherm data better than the Langmuir model. The thermodynamic parameters (DeltaG degrees ads, DeltaH degrees, and DeltaS degrees) were evaluated showing that the sorption process was thermodynamically favorable, spontaneous, and exothermic. The findings can be used for predictive modeling for analysis and design adsorption systems for removal of cyanuric acid and other polar atrazine degradation products from environmental aqueous samples.

Adsorption↗
PubMed2006

Investigations into the kinetics and thermodynamics of Sb(III) adsorption on goethite (alpha-FeOOH).

This study reports thermodynamic and kinetic data of Sb(III) adsorption from single metal solutions onto synthetic aqueous goethite (alpha-FeOOH). Batch equilibrium sorption experiments were carried out at 25 degrees C over a Sb:Fe molar range of 0.005-0.05 and using a goethite concentration of 0.44 g Fe/L. Experimental data were successfully modelled using Langmuir (R2 > or = 0.891) and Freundlich (R2 > or = 0.990) isotherms and the following parameters were derived from triplicate experiments: Kf = 1.903 +/- 0.030 mg/g and 1/n = 0.728 +/- 0.019 for the Freundlich model and b = 0.021 +/- 0.003 L/mg and Qmax = 61 +/- 8 mg/g for the Langmuir model. The thermodynamic parameters determined were the equilibrium constant, Keq =1.323 +/- 0.045, and the Gibb's free energy, DeltaG0 = -0.692 +/- 0.083 kJ/mol. The sorption process is very fast. At a Sb:Fe molar ratio of 0.05, 40-50% of the added Sb is adsorbed within 15 min and a steady state is achieved. The experimental data also suggest that desorption can occur within 24 h of reaction due to the oxidation of Sb(III) on the goethite surface. Finally, calculated pH of the aqueous solution using MINTEQ2 agrees well with the measured pH (3.9 +/- 0.7; n = 30). At pH 4, the dominant Sb species in solution are Sb(OH)3 and HSbO2 which both likely adsorb as inner sphere complexes to the positively charged goethite surface.

Adsorption↗
PubMed2006

Thermodynamics of aqueous solutions of dodecyldimethylethylammonium bromide.

The thermodynamic properties of the aqueous solutions of dodecyldimethylethylammonium bromide (DEDAB) were determined as a function of concentration by means of direct methods. Dilution enthalpies at 298 and 313 K, densities and sound velocities at 298 K were measured, allowing the determination of apparent and partial molar enthalpies, volumes, heat capacities and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudo-phase transition approach. These data allow for the determination of the effect of the -CH2- group, when added to the polar head of alkyltrimethylammonium bromides. The properties mainly affected by this addition are the enthalpies and, as a consequence, the entropies. The lowering of the charge density on the quaternary nitrogen due to the inductive effect of the ethyl group, greater than that of the methyl one, raises the plateau value of apparent and molar enthalpy by a quantity similar to that due to the removing of a methylene group from the hydrophobic chain. This effect does not play a great role in the value of the cmc (i.e. on the free energy of micelle formation), since the small decrease in cmc of DEDAB compared to DTAB reflects the increase in the overall hydrophobicity of the molecule. Volumes of DEDAB are greater than those of DTAB by about 15 cm3 mol(-1), both at infinite dilution and at micellar phase, a value in agreement with that generally accepted for a methylene group. The trends of apparent molar heat capacities and compressibilities vs m are the same as for DTAB: in fact, these quantities are related to the number of water molecules involved in the hydrophobic processes in solution, not very greatly affected by the substitution of a methyl group by an ethyl one on the polar head. In summary, this substitution affects to a significant extent the first derivatives of the free energy, but does not affect the second derivatives.

Adsorption↗
PubMed2006

Thermodynamics of ions and water transport in porous media.

The thermodynamic framework of Prigogine, de Groot, and Mazur is extended to study the transport of ions and water in thermoporoelastic materials assuming infinitesimal deformations. New expressions are developed for the first and second principles of nonequilibrium thermodynamics of multicomponent systems and a generalized power balance equation is derived. For porous materials, all the components cannot be treated on a symmetric basis. A Lagrangian framework associated with deformation of the solid phase is introduced and, in this framework, Curie's principle is used to set up the form of the linear constitutive equations describing the transport of ions, water, and heat through the pore network. The material properties entering these equations were recently obtained by Revil and Linde [J. Colloid Interface Science 302 (2006) 682-694] using a volume-averaging approach based in the Nernst-Planck and Stokes equations. This provides a way to relate the material properties entering the constitutive equations to two textural parameters characterizing the topology of the pore space of the material (namely the tortuosity of the pore space and the permeability). The generalized power balance equation is used to derive the linear poroelastic constitutive equations (including the osmotic pressure) to describe the reversible contribution of deformation of the medium in response to ions and water transport through the connected porosity.

Elasticity↗
PubMed2004

Computer simulation for prediction of performance and thermodynamic parameters of high energy materials.

A new code viz., Linear Output Thermodynamic User-friendly Software for Energetic Systems (LOTUSES) developed during this work predicts the theoretical performance parameters such as density, detonation factor, velocity of detonation, detonation pressure and thermodynamic properties such as heat of detonation, heat of explosion, volume of explosion gaseous products. The same code also assists in the prediction of possible explosive decomposition products after explosion and power index. The developed code has been validated by calculating the parameters of standard explosives such as TNT, PETN, RDX, and HMX. Theoretically predicated parameters are accurate to the order of +/-5% deviation. To the best of our knowledge, no such code is reported in literature which can predict a wide range of characteristics of known/unknown explosives with minimum input parameters. The code can be used to obtain thermochemical and performance parameters of high energy materials (HEMs) with reasonable accuracy. The code has been developed in Visual Basic having enhanced windows environment, and thereby advantages over the conventional codes, written in Fortran. The theoretically predicted HEMs performance can be directly printed as well as stored in text (.txt) or HTML (.htm) or Microsoft Word (.doc) or Adobe Acrobat (.pdf) format in the hard disk. The output can also be copied into the Random Access Memory as clipboard text which can be imported/pasted in other software as in the case of other codes.

Chemistry, Physical↗
PubMed2006

Adsorption thermodynamic and kinetic studies of trihalomethanes on multiwalled carbon nanotubes.

Multiwalled carbon nanotubes (MWCNTs) were purified by mixed HNO3/H2SO4 solution and were employed as adsorbents to study adsorption kinetics and thermodynamics of trihalomethanes (THMs) from chlorinated drinking water. The amount of THMs adsorbed onto CNTs decreased with a rise in temperature and high adsorption capacities were found at 5 and 15 degrees C. Under the same conditions, the purified CNTs possess two to three times more adsorption capacities of CHCl3, which accounts for a major portion of THMs in the chlorinated drinking water, than the commercially available PAC suggesting that CNTs are efficient adsorbents. The thermodynamic analysis revealed that the adsorption of THMs onto CNTs is exothermic and spontaneous.

Adsorption↗
PubMed2003

The relationship between conservation, thermodynamic stability, and function in the SH3 domain hydrophobic core.

To investigate the relationships between sequence conservation, protein stability, and protein function, we have measured the thermodynamic stability, folding kinetics, and in vitro peptide-binding activity of a large number of single-site substitutions in the hydrophobic core of the Fyn SH3 domain. Comparison of these data to that derived from an analysis of a large alignment of SH3 domain sequences revealed a very good correlation between the distinct pattern of conservation observed at each core position and the thermodynamic stability of mutants. Conservation was also found to correlate well with the unfolding rates of mutants, but not to the folding rates, suggesting that evolution selects more strongly for optimal native state packing interactions than for maximal folding rates. Structural analysis suggests that residue-residue core packing interactions are very similar in all SH3 domains, which provides an explanation for the correlation between conservation and mutant stability effects studied in a single SH3 domain. We also demonstrate a correlation between stability and the in vivo activity of mutants, and between conservation and activity. However, the relationship between conservation and activity was very strong only for the three most conserved hydrophobic core positions. The weaker correlation between activity and conservation seen at the other seven core positions indicates that maintenance of protein stability is the dominant selective pressure at these positions. In general, the pattern of conservation at hydrophobic core positions appears to arise from conserved packing constraints, and can be effectively utilized to predict the destabilizing effects of amino acid substitutions.

Amino Acid Sequence↗
PubMed2003

Structural characterization of the 69 nucleotide potato spindle tuber viroid left-terminal domain by NMR and thermodynamic analysis.

The 69 nucleotide left-terminal domain (T(L)) of the potato spindle tuber RNA viroid (PSTVd) constitutes one of its five structural elements. Due to a twofold complementary sequence repeat, two possible conformations are proposed for the T(L) secondary structure; an elongated-rod and a bifurcated form. In the present study, two T(L) mutants were designed that remove the symmetry of the sequence repeats and ensure that either the bifurcated or the elongated-rod conformation is thermodynamically favored. Imino 1H and 15N resonances were assigned for both mutants and the native T(L) domain based on 1H-1H NOESY and heteronuclear 1H-15N HSQC high-resolution NMR spectra. The NMR secondary structure analysis of all constructs establishes unambiguously the elongated-rod form as the secondary structure of the native T(L) domain. Temperature-gradient gel electrophoresis and UV melting experiments corroborate these results. A combined secondary structure and sequence analysis of T(L) domains of other Pospiviroidae family members indicates that the elongated-rod form is thermodynamically favored for the vast majority of these viroids.

Base Sequence↗