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PubMed1990

A thermodynamic model of hemoglobin suitable for physiological applications.

We propose a quantitative model of the thermodynamics of hemoglobin in contact with its five major ligands (O2, CO2, Cl-, 2,3-bisphosphoglycerate, and H+). Our model incorporates the two-state formalism of J. Monod, J. Wyman, and J.P. Changeux (J. Mol. Biol. 12: 88-118, 1965) for treatment of quanternary transitions and also the mean field formalism of K. Linderstrom-Lang (C. R. Trav. Lab. Carlsberg Ser. Chim. 15: 1-30, 1924) for treatment of electrostatic interactions. On the basis of this approach, we develop an algorithm for the efficient computation of observable quantities, such as the occupancy of various ligand binding sites, and an objective statistical procedure for determining both maximum likelihood values and confidence limits of all the intrinsic thermodynamic parameters of hemoglobin. Finally, we show that the predictions of our theory are in good agreement with independent experimental observations.

Carbon Dioxide↗

PubMed1987

Solvent flow in osmosis and hydraulics: network thermodynamics and representation by bond graphs.

A tutorial introduction to network thermodynamics and bond graphs as a modeling technique for any physiochemical system is presented with a particular emphasis on reaction diffusion systems. It combines the generality of nonequilibrium thermodynamics with the advantages of a graph theory. It is applied to the representation of osmotic and hydraulic flows across a semipermeable membrane on the basis of the solvent diffusion theory of osmosis. This theory allows for an easy derivation of the van't Hoff law of osmotic pressure from the Fick law of diffusion. Molar flows and volume flows are transformed into one another by transducers, the modulus of which is the partial molar volume of water, in such a way that power is conserved by a reciprocal transformation between the chemical potential and the pressure. Osmotic and hydraulic resistances are calculated, and their dependence on pore size is estimated.

Diffusion↗

PubMed1982

Effect of furosemide on the thermodynamic parameters of frog skin.

The formalism of nonequilibrium thermodynamics (NET) was used to analyze the effect of diuretic furosemide on the transport mechanism of frog skin. Mucosal furosemide increased the active conductance of Na+ across the mucosal membrane of the cells, producing an increased transport of Na+ (short-circuit current). Furosemide also increased both the thermodynamic affinity of the metabolic reaction supplying energy to the sodium pump and the degree of coupling between transport and metabolism. It changed the phenomenological cross-coefficient of the NET description as well as the stoichiometric ratio, indicating that its effect cannot be explained simply on the basis of a change in Na+ conductance. The effect on the NET parameters was independent of the presence of either chloride or sulfate as the principal anion in the solutions, and was qualitatively similar to the effect produced by mucosal application of triphenylmethylphosphonium ion.

Animals↗

PubMed1992

Human red-cell acid phosphatase (ACP1): kinetic and thermodynamic characterization of the KUK variant.

The Km constant and the sensitivity to inhibitors were determined for the rare variant KUK of red cell acid phosphatase. At the same time, the thermodynamic energies of activation and of inactivation were measured. The kinetic parameters were not very different from those of the usual ACP1 C alloenzymes. However, they differed in their thermodynamic energies: the conformational structure of the ACP1 KUK protein being less stable.

Acid Phosphatase↗

PubMed2004

Thermodynamics and phase equilibria involving nano phases in the Cu-Ag system.

The surface tensions of the Cu-Ag system have been evaluated using Butler's equations. Since the evaluation is dependent on the thermodynamic properties of the surface phases, they are calculated based on the first and second order differentials of the surface tension at infinite dilution. The present study establishes significant differences in the properties between the surface phase and bulk phases of the system. The study of the adsorption behaviour finds silver to be surface active relative to copper, which results in the preferential adsorption of silver in the alloys. Furthermore, in view of the differences in terms of fundamental thermodynamic properties between the two phases coupled with the volume-to-radius ratio as depicted by the Thomson-Freundlich concept, the nano phases of the system exhibit a pronounced increase in the adsorption behaviour relative to that of the planar interface of the system. As expected based on the above combined effect of the surface properties, present research shows a considerable decrease in the melting points of the metals, solid-solid, solid-liquid transition and eutectic temperature with a consequent increase in the solubilities of the terminal phases of the system.

Adsorption↗

PubMedDate not supplied

Treatment of hypothermia in trauma victims: thermodynamic considerations.

The relatively high specific heat of the human body makes hypothermia very difficult to treat. Although there are many treatment methods available, most evaluations of rewarming techniques are based on clinically observed rewarming rates, and they do not take into account initial core temperature, ambient temperature, the patient's own heat production, the effects of anesthesia, paralytic agents, and other variables. A heat transfer model is proposed that simulates the flow of heat through the body of a hypothermic patient. The model uses first principles involved in heat transfer and thermodynamics to describe the effects of currently available rewarming techniques. A commercially available routine is used to solve the equations, which also include any heat exchange between the patient's body and the environment, as well as metabolic heat generation as a function of time and core temperature. This thermodynamic analysis of rewarming, based on computer modeling of heat transfer, provides a scientific basis on which to establish guidelines for appropriate selection of treatment strategies for hypothermia, and it indicates that direct blood warming or infusion of warm intravenous fluids are the most effective rewarming techniques.

Body Temperature Regulation↗

PubMed1989

Phosphocreatine represents a thermodynamic and functional improvement over other muscle phosphagens.

In vertebrate tissues, the only phosphagen is phosphocreatine (PC), and the corresponding phosphotransferase is creatine phosphokinase (CPK). Among invertebrates, a variety of phosphotransferase reactions are found in addition to CPK, including arginine phosphokinase (APK), glycocyamine phosphokinase (GPK), taurocyamine phosphokinase (TPK) and lombricine phosphokinase (LPK). Although there is some uncertainty about the exact value, the apparent equilibrium constant for the CPK reaction (K'cpk = [creatine][ATP]/[PC][ADP]), under physiological conditions similar to those of vertebrate muscle, ranges from 100 to 160. The corresponding K' value for the APK reaction is somewhat controversial, and K' values for the GPK. TPK and LPK reactions are not known. In this study, conventional and 31P-NMR methods were used to evaluate the equilibrium constants for the APK, GPK, TPK and LPK reactions relative to that of CPK. The corresponding K' values for the APK, GPK, TPK and LPK reactions, expressed as a percentage of K'cpk, are 13, 29, 29 and 32%, respectively. The exclusively invertebrate phosphagens exist as a cohort of thermodynamically more stable compounds. Thus, PC constitutes a thermodynamic (and functional) improvement, in that the CPK reaction is able to buffer ATP at much higher ATP/ADP ratios than are other phosphagens. However, possession of a phosphagen system with a lower K' value may be advantageous under certain specific physiological conditions such as intracellular acidosis.

Adenine Nucleotides↗

PubMed1988

Thermodynamic study on enhancement of percutaneous penetration of drugs by Azone.

The mechanism whereby Azone (AZ, 1-dodecylazacycloheptan-2-one) enhances drug penetration through the hairless rat abdominal skin was investigated thermodynamically. Three kinds of drugs, indomethacin, ibuprofen and sulfanilamide which have similar solubilities in a mixed organic solvent (ethanol-diethylcarbitol, 40:60 v/v), were selected to evaluate the drug penetration with or without 5% AZ. Transdermal delivery rates were determined at 27 and 37 degrees C by using an in vitro diffusion cell procedure and the abdominal full-thickness skin of hairless rat. The solubility of each of the three drugs in the solvent with AZ was similar to that without AZ. Ethanol in the vehicle penetrated through the skin prior to the drugs. Activation energies for the skin penetration of the three drugs in the presence of AZ were decreased compared to those in its absence. For all drugs the partition coefficients between the skin and vehicle with AZ were 2-80 times higher than those without it. The activity coefficients of drugs in the presence of AZ in the skin were 2-90 times lower than those without the enhancer. These results suggested that the enhancing effect of AZ was not due to changing the solubility of the drugs in solvents but to increasing the thermodynamic activities and the affinities of the drugs to skin.

Administration, Cutaneous↗

PubMed1997

Thermodynamics of partitioning of the antimalarial drug mefloquine in phospholipid bilayers and bulk solvents.

The antimalarial drug mefloquine binds avidly to phospholipids in biomembranes. The thermodynamics of the partitioning process in dimyristoylphosphatidylcholine (DMPC) bilayers was investigated to give some insight into the drug-phospholipid interaction. Thermodynamic parameters for the partition equilibria were evaluated from the equilibrium partition coefficients measured as a function of temperature. Negative values of delta H and delta S were obtained for the transfer of mefloquine from the aqueous to the gel phase of the phospholipid. The partitioning is enthalpy controlled which suggests that mefloquine interacts strongly with the phospholipid phase. In contrast, the partitioning of mefloquine into the liquid crystalline phase of DMPC is entropy controlled which is typical of a hydrophobic interaction between mefloquine and the aqueous phase. The partitioning of mefloquine into the bulk solvents octanol and hexane were found to be enthalpy and entropy controlled, respectively. The enthalpy dominated partitioning of mefloquine into gel phase DMPC and octanol is attributed to the occurrence of hydrogen bonding and van der Waals interactions between solute and solvent. The flat shape of mefloquine may further aid its interaction with the orderly domains of the lipidic/organic phase. This is apparent from a comparison of the partitioning characteristics of another structurally related but conformationally different molecule, quinine into DMPC and octanol.

1-Octanol↗

PubMed2004

Thermodynamic consideration of the charge transfer interaction of the donor: acceptor type between chloranilic acid and haloperidol.

The thermodynamic parameters of the charge transfer complex between chloranilic acid and haloperidol were studied. Haloperidol in pure form and in dosage form was assayed in this study. The method was based on charge transfer complex formation between the drug, which acted as an n-donor, and chloranilic acid, which acted as a pi acceptor in a non aqueous solvent. The complex stoichiometry was found to be 1:2 (haloperidol: chloranilic acid) with the maximum absorption band at a wavelength of 576 nm. The complex obeyed Beer's law. The thermodynamic parameters investigated included stability constant, molar absorptivity, free energy change, enthalpy, and entropy. The method was successfully applied in the analysis of commercially available haloperidol tablets without interference from its excipients, with good precision and reproducibility, compared with the official assay method (non aqueous titration) described for haloperidol in the compendium.

Benzoquinones↗

PubMed2006

Synthesis, thermodynamics stability constant and relaxation properties of neutral Gd(III) complex with derivative from diethylene triamine pentaacetic acid and p-hydroxybenzoyl hydrazine.

A novel ligand, diethylenetriamine-N,N''-bis(acetyl-p-hydroxybenzoyl hydrazine)-N,N',N''-triacetic acid (H3L) was synthesized and characterized on the basis of elemental analysis, molar conductivity, 1H-NMR spectrum, FAB-MS, TG-DTA analysis and IR spectrum. Its complex of Gd(III) holding promise of magnetic resonance imaging (MRI) was synthesized, and relaxivity (R1) of complex and Gd(DTPA)2- used as a control was determined in water solution, respectively. The relaxivity of GdL (R1 = 6.39 l.mmol(-1).s(-1)) was larger than that of Gd(DTPA)2- (R1 = 4.34 l.mmol(-1).s(-1)). The relaxivity of GdL has also been investigated in human serum albumin (HSA) solution, the relaxivity of GdL was enhanced from 6.39 l.mmol(-1).s(-1) in water solution to 7.69 l.mmol(-1).s(-1) in HSA solution. In addition, thermodynamics stability constant of GdL was determined. The results showed that complex of GdL is a prospective MRI contrast agent, although the thermodynamic stability constant of GdL complex (K(GdL) = 10(19.56)) was a little less than that of Gd(DTPA)2- (K(Gd-DTPA) = 10(20.73)).

Contrast Media↗

PubMed2003

Thermodynamic determination of plasma and leukocyte beta-hexosaminidase isoenzymes in homozygote and heterozygote carriers for the GM2 gangliosidosis B1 variant.

In the GM2 gangliosidosis B1 variant, the mutated isoenzyme A of beta-hexosaminidase (Hex) is incapable of hydrolyzing ganglioside GM2 and negatively charged substrates. Biochemical characterization of this lysosomal disease is carried out using synthetic alpha-subunit-specific sulfated substrates, as heat-inactivation assays are not applicable. The apparent enzyme activation energy of Hex using the chromogenic substrate 3,3'-dichlorophenolsulfonphthaleinyl N-acetyl-beta-D-glucosaminide is related directly to the relative proportions of Hex A and Hex B isoenzymes. This thermodynamic variable was used for the study of Hex enzyme heterogeneity in 3 patients with the GM2 gangliosidosis B1 variant and 6 heterozygote carriers. Hex activity was determined at 25 degrees C, 30 degrees C, 35 degrees C, and 37 degrees C in a Cobas Bio analyzer (Roche Diagnostics, Basel, Switzerland), and Arrhenius plot slopes and apparent activation energies were calculated in plasma samples and mononuclear and polymorphonuclear leukocyte lysates. The determination of the Hex isoenzymes in plasma presented a high discrimination power for B1 variant patients but not for heterozygote carriers, in whom false-negative results may be obtained. However, thermodynamic evaluation of the isoenzyme composition of Hex in leukocyte lysates permits the biochemical identification of patients with the GM2 gangliosidosis B1 variant and of heterozygote carriers.

Female↗

PubMed2005

Innovative kinetic and thermodynamic analysis of a purified superactive xylanase from Scopulariopsis sp.

Two isoenzymes of endo-1,4-beta-xylanase (EC 3.2.1.8) from Scopulariopsis sp. were purified by a combination of ammonium sulfate precipitation, hydrophobic interaction, and anion-exchange and gel filtration chromatography. The native mol wts of the least acidic xylanase (LAX) and the highly acidic xylanase (HAX) were 25 and 144 kDa and the subunit mol wts were 25 and 36 kDa, respectively. The kcat values of LAX and HAX for oat-spelt xylan at 40 degrees C, pH 6.5, were 95,000 and 9900 min-1 and the Km values of LAX and HAX were 30 and 3.3 mg/mL. The thermodynamic activation parameters of xylan hydrolysis showed that the high activity of LAX when compared with HAX was not owing to a reduction in DeltaH# but was entropically driven. High-performance liquid chromatography analysis of the degradation products showed that LAX formed both xylotrioses and xylobioses, but HAX predominantly formed xylotrioses. The half-lives of LAX and HAX at 50 degrees C in 50 mM 2-N-morpholino ethanesulfonic acid (MES), pH 6.5 buffer were 267 and 69 min, respectively. Thermodynamic analysis showed that at lower temperatures, the increased thermostability of LAX (DeltaH#=306 kJ/mol) compared with HAX (DeltaH#=264 kJ/mol) was owing to more noncovalent surface interactions. At higher temperatures, LAX (DeltaS*=-232 J/[mol.K]) was more thermostable than HAX (DeltaS*=490 J/[mol.K]) owing to a more ordered transition-state conformation. An energy-activity diagram was introduced showing that kcat/Km does not successfully explain the true kinetic behavior of both xylanase isoenzymes. The simultaneously thermostable and highly active LAX could be utilized in biotechnological processes involving xylan hydrolysis.

Ascomycota↗

PubMed1990

Binding of the bovine basic pancreatic trypsin inhibitor (Kunitz inhibitor) to human and bovine factor Xa. A thermodynamic study.

The effect of pH and temperature on the apparent association equilibrium constant (Ka) for the binding of the bovine basic pancreatic trypsin inhibitor (BPTI, Kunitz inhibitor) to human and bovine factor Xa (Stuart-Prower factor; EC 3.4.21.6) has been investigated. Under all the experimental conditions, values of Ka for BPTI binding to human and bovine factor Xa are identical. On lowering the pH from 9.5 to 4.5, values of Ka (at 21.0 degrees C) for BPTI binding to human and bovine factor Xa decrease, thus reflecting the acidic pK shift of the His57 catalytic residue from 7.1, in the free enzyme, to 5.2, in the proteinase-inhibitor complex. At pH 8.0, values of the apparent thermodynamic parameters for BPTI binding to human and bovine factor Xa are: Ka = 2.1 x 10(5)M-1 (at 21.0 degrees C), delta G degree = -29.7 kJ/mol (at 21.0 degrees C), delta S degree = +161 entropy units (at 21.0 degrees C), and delta H degree = +17.6 kJ/mol (temperature-independent over the explored range, from 5.0 degrees C to 45.0 degrees C). Thermodynamics of BPTI binding to human and bovine factor Xa have been analysed in parallel with those of related serine (pro)enzyme/Kazal- and /Kunitz-type inhibitor systems. Considering the known molecular models, the observed binding behaviour of BPTI to human and bovine factor Xa was related to the inferred stereochemistry of the proteinase/inhibitor contact region.

Animals↗

PubMedDate not supplied

Thermodynamic and magnetic resonance studies on the hydration of polymers: II. Protein-water interactions in powered ribonuclease.

ESR studies on spin-labeled amorphous RNase A as a function of varying concentrations of sorbed H2O and D2O will be presented. A relaxation analysis of saturation transfer (ST-)ESR spectra of 14N(1H) nitroxide spin-label molecules essentially fixed at amino acid residue His-105 will be given. A characteristic correlation has been observed between the microdynamic behavior--expressed by the rotational correlation times of the paramagnetic label--and the macroscopic thermodynamic entropy for the sorption process of H2O and D2O at RNase. This correlation is particularly pronounced at low water concentrations, vis., nH2O/nprotein less than or equal to 100. A significant difference in this concentration range exists between the two systems "RNase-H2O" and "RNase-D2O", which is manifested not only by the thermodynamic data but also by the microdynamic behavior extracted from the corresponding non-linear ESR absorption line shapes.

Computer Simulation↗

PubMedDate not supplied

Thermodynamic and spectroscopic characterization of the berenil and pentamidine complexes with the dodecanucleotide d(CGCGATATCGCG)2.

The dodecanucleotide d(CGCGATATCGCG)2 was characterized by thermodynamic and UV-spectrophotometric measurements. A van't Hoff enthalpy of delta H(uv)v.H. approximately -190 kJ/mol was determined for the thermal transition using UV spectroscopy. This value was confirmed by differential scanning calorimetry (DSC). In addition we obtained the thermodynamic data delta HDSC = -405.1 kJ/mol, delta SDSC = -1290 J/mol.K and delta GDSC = -53.2 kJ/mol for the helix to coil transition of the dodecanucleotide. The association of berenil and the oligonucleotide was accompanied with a stabilization of the host duplex (increase in Tm) and an increase in the van't Hoff enthalpy. The berenil binding parameters (delta delta HDSC = -32.6 kJ/mol, delta delta SDSC = -72 J/mol.K and delta delta GDSC = -11.1 kJ/mol) revealed significant differences compared to those of the pentamidine aggregation (delta delta HDSC = -23.7 kJ/mol, delta delta SDSC = -53 J/mol.K and delta delta GDSC = -7.8 kJ/mol). The transition of the pure oligonucleotide was characterized by a substantial amount of intermediate states (sigma DSC = 0.43) which decreased significantly upon binding of the drugs (sigma DSC approximately 0.80). The structural features of the complexes were analyzed by FT-IR spectroscopy. From these experiments we conclude that the configurations in the berenil and pentamidine complexes are different.

Antiprotozoal Agents↗

PubMed2005

Thermodynamic and kinetic aspects of RNA pulling experiments.

Recent single-molecule pulling experiments have shown how it is possible to manipulate RNA molecules using laser tweezers. In this article we investigate a minimal model for the experimental setup which includes an RNA molecule connected to two polymers (handles) and a bead trapped in the optical potential and attached to one of the handles. We start by considering the case of small single-domain RNA molecules, which unfold in a cooperative way. The model qualitatively reproduces the experimental results and allows us to investigate the influence of the bead and handles on the unfolding reaction. A main ingredient of the model is to consider the appropriate statistical ensemble and the corresponding thermodynamic potential describing thermal fluctuations in the system. We then investigate several questions relevant to extract thermodynamic information from experimental data. The kinetics of unfolding is also studied by introducing a dynamical model. Finally, we apply the model to the more general problem of a multidomain RNA molecule with Mg(2+) tertiary contacts that unfolds in a sequential way.

Biophysics↗

PubMed2004

Kinetics and thermodynamics of lipid amphiphile exchange between lipoproteins and albumin in serum.

We have examined the kinetics and thermodynamics of the exchange of a fluorescent amphiphile derived from a phospholipid, NBD-DMPE, between serum albumin and the serum lipoproteins of high density (HDL2 and HDL3), LDL, and VLDL. Binding of the fluorescent lipid amphiphile to bovine serum albumin is characterized, at 35 degrees C, by an equilibrium binding constant of approximately 3 x 10(6) M(-1) and a characteristic time < or = 0.1 s. Association of NBD-DMPE with the lipoprotein particles, if considered as a partitioning of amphiphile monomers between the aqueous phase and the lipoprotein particles, is characterized by an equilibrium partition coefficient between 10(5) and 10(6), being highest for LDL and lowest for HDL. The association of NBD-DMPE monomers with lipoprotein particles can be described by insertion rate constants on the order of 10(5) M(-1) s(-1) for VLDL and LDL and 10(4) M(-1) s(-1) for HDL. The desorption rate constants are on the order of 10(-5) s(-1) for all particles. The study was performed as a function of temperature between 15 and 35 degrees C. This permitted the calculation of the equilibrium thermodynamic parameters (deltaG(o), deltaH(o), and deltaS(o)) as well as the activation parameters (deltaG++(o), deltaH++(o), and deltaS++(o)) for the insertion and desorption processes. The association equilibrium is dominated by the entropic contribution to the free energy in all cases. The results are discussed in relation to phospholipid and amphiphile exchange phenomena involving the lipoproteins.

Adult↗