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At least 1,315 records · Page 73Linked to original sources
PubMed1995

Measurement of maximal oxygen consumption of thoroughbred horses at an altitude of 1250m using open-circuit flow-through calorimetry.

This study determined the maximal O2 uptake (VO2max) of Thoroughbred horses acclimatised to mild hypobaric conditions using a standard exercise test on a treadmill inclined at a 7% slope. The O2 uptake (VO2) versus speed relationship was linear below the exercise intensity required to attain VO2max. The VO2max of individual horses ranged from 143.5 to 172.6 ml/kg/min. The proportion of total variance for the VO2 versus speed relationship was greater than 0.992, and the coefficients of variation in repeated tests in individual horses ranged between 0.07 and 1.54%. The VO2 versus speed relationship attained a plateau at speeds above the VO2max, which ranged from 9.3 to 12.0 m/s. When work intensity was increased above that of the VO2max, there was no further increase in VO2, thus showing that a maximum had been attained.

Acclimatization↗
PubMed1996

Differential scanning calorimetry study of the influence of phospholipid analogs with a carbonyl-terminated sn-2 chain on the interdigitated phases formed by 1-stearoyl-2-capryl-sn-glycero-3-phosphatidylcholine (C18:C10-PC).

Synthetic glycerophosphocholines with highly asymmetric chain lengths form interdigitated bilayers in the gel phase. In nature, phospholipids with one hydrocarbon chain approximately twice as long as the other can arise from the autooxidation of unsaturated linkages in the acyl chain, and thus the oxidation products would contain a carbonyl group at the chain terminus. In this study, we have investigated the thermotropic behavior of bilayers prepared from mixtures of the well-studied, mixed-chain phospholipid, 1-stearoyl-2-capryl-sn-glycero-3-phosphocholine (C18:C10-PC, 1), with synthetic 1-stearoyl-2-acyl-sn-glycero-3-phosphocholines in which the sn-2 chain is approximately one-half the length of the sn-1 chain and contains a C==O group near the omega terminus. Phase diagrams of binary mixtures of 1 with a chain-terminal ketone-PC analog (2) or with a chain-terminal ester-PC analog (3) in excess water exhibited gel-phase immiscibility over a wide compositional range, but miscibility in the liquid-crystalline phase. However, 1 was completely miscible with C18:C10:1 delta 10-PC (compound 4), which bears a chain-terminal carbon-carbon double bond, in both the gel and liquid-crystalline phases. The calorimetric data suggest that phosphatidylcholines (PC) with carbonyl-terminated chains, which can be produced by autooxidation of naturally abundant 1-saturated-2-unsaturated phospholipids such as 1-stearoyl-2-oleoyl-PC, may not form the normal triple-chain mixed interdigitated structure characteristic of hydrocarbon-terminated PCs in gel-phase bilayers.

Calorimetry, Differential Scanning↗
PubMed1977

Calorimetry of cholinesterase activity in serum.

Cholinesterase activity in human serum was measured calorimetrically and compared to values obtained with the spectrophotometric method of Rappaport et al. [Clin. Chim. Acta 4, 227 (1959)]. The response of the calorimeter upon mixing serum with acetylcholine corresponded to the cholinesterase activity of the serum, the thermogram peak height being linearly related to enzyme activity at serum dilution volumes at which interference heat was negligible. The interference heat contributed by the dilution mixing characteristics of serum, studied separately, was found to be similar for heat-denatured, aged, or lyophilized samples. In all cases, heat of mixing was negligible when 1 ml of serum in buffer (2/3 by vol) was mixed with 1 ml of buffer. When this amount of serum was assayed with acetylcholine, cholinesterase activities of 2 and 3 kU/liter were recorded as thermograms with peak heights of 2.3 and 3.5 cm, respectively.

Acetylcholine↗
PubMedDate not supplied

[Effect of radiation on the structure of model and natural biomembranes using differential scanning calorimetry].

A novel method of DSC studies of biomembranes has been proposed, making it possible to investigate the influence of ionizing radiations upon the structure of water dispersions of phospholipids and phospholipid-based systems of natural origin, e.g., rat liver homogenates and erythrocyte ghosts. It is shown that in certain concentration range of the bonded water thermograms obtained are reproducible during heating and cooling cycles and can give information about phase state, supramolecular ordering and radiation sensitivity of the systems under consideration.

Animals↗
PubMedDate not supplied

[Formation and melting of ordered structures in denatured myoglobin with differing water content: differential scanning calorimetry method].

The possibility of superstructure formation in denatured globular proteins has been studied through the temperature dependence of the absolute values of heat capacity in the myoglobin-water system with water content from 80 to 25% in the temperature range 20-160 degrees C. For all the composition range studied it is found that after the denaturation of myoglobin the new regular structures with reversible melting are formed. These structures are similar in properties to the thermotropic gels in concentrated myoglobin solutions. Decrease of the water content influences the formation of these non-native ordered structures in denatured protein and increases the dispersion of its formation and melting temperatures.

Calorimetry, Differential Scanning↗
PubMed2000

A New Interpretation of Contact Angle Variations in View of a Recent Analysis of Immersion Calorimetry.

The values of the contact angles of different liquids on the same solid are classically interpreted by theories assuming that the vapor adsorption is negligible on solids presenting contact angles. This implies that the solid may be defined by a certain tension, called "critical tension", which is not clearly thermodynamically defined. These assumptions are in disagreement with modern theories of vapor adsorption science. In this paper, it is shown that it is possible to understand the contact angle values using a rigorous derivation of the Young equation, which links the contact angle, the liquid-vapor surface tension of the drop, and the surface tension of the solid in equilibrium with its own vapor. Numerical approximations allow the contact angle variation to be predicted, without use of ad hoc definitions. It is then possible to link vapor adsorption results and contact angle experiments. It is also possible to deduce the surface tension of solids simply and to compute contact angles on powders without using the Washburn method. Copyright 2000 Academic Press.

Journal Article↗
PubMed2003

The reactivity of ethylene oxide in contact with iron oxide fines as measured by adiabatic calorimetry.

Samples of various iron oxides suspended above ethylene oxide in an adiabatic calorimeter exhibit exothermic activity at temperatures as low as room temperature. A gamma-Fe(2)O(3) sample was found to show the highest reactivity with ethylene oxide. Ethylene oxide in combination with most of the iron oxide fines tested displayed exothermic activity below 100 degrees C. Self-heat rates near 2000 degrees C/min were observed for the gamma-Fe(2)O(3) fines while rates in excess of 100 degrees C/min were found for other fines (alpha-Fe(2)O(3) and hydrated alpha-Fe(2)O(3)). In two cases (alpha-Fe(3)O(4) and alpha-Fe(2)O(3)), pressurization rates above 1000 psi/min took place. No reactivity was observed for ethylene oxide with the FeO. Thermal inertia effects in commercial operation, such as heat uptake by the equipment to which fines are attached, are presumed to be a factor in limiting the occurrence of related exotherms in ethylene oxide manufacturing facilities.

Disinfectants↗
PubMed1997

Analysis of differential scanning calorimetry data for proteins. Criteria of validity of one-step mechanism of irreversible protein denaturation.

We consider in this work the analysis of the excess heat capacity C(p)(ex) versus temperature profiles in terms of a model of thermal protein denaturation involving one irreversible step. It is shown that the dependences of ln C(p)(ex) on 1 T (T is the absolute temperature) obtained at various temperature scanning rates have the same form. Several new methods for estimation of parameters of the Arrhenius equation are explored. These new methods are based on the fitting of theoretical equations to the experimental heat capacity data, as well as on the analysis of the dependence d(ln C (p)(ex)) d ( 1 T ) on 1 T . We have applied the proposed methods to calorimetric data corresponding to the irreversible thermal denaturation of Torpedo californica acetylcholinesterase, cellulase from Streptomyces halstedii JM8, and lentil lectin. Criteria of validity for the one-step irreversible denaturation model are discussed.

Journal Article↗
PubMed2004

Thermochemistry of aqueous hydroxyl radical from advances in photoacoustic calorimetry and ab initio continuum solvation theory.

Photoacoustic signals from dilute ( approximately 30 mM) solutions of H2O2 were measured over the temperature range from 10 to 45 degrees C to obtain the reaction enthalpy and volume change for H2O2(aq) --> 2 OH(aq) from which we ultimately determined DeltafG degrees , DeltafH degrees and partial molal volume, v degrees , of OH (aq). We find DeltarH = 46.8 +/- 1.4 kcal/mol, which is 4 kcal/mol smaller than the gas-phase bond energy, and DeltaVr = 6.5 +/- 0.4 mL/mol. The v degrees for OH in water is 14.4 +/- 0.4 mL/ml: smaller than the v degrees of water. Using ab intio continuum theory, the hydration free energy is calculated to be -3.9 +/- 0.3 kcal/mol (for standard states in number density concentration units) by a novel approach devised to capture in the definition of the solute cavity the strength and specific interactions of the solute with a water solvent molecule. The shape of the cavity is defined by "rolling" a three-dimensional electron density isocontour of water on the ab initio water-OH minimum interaction surface. The value of the contour is selected to reproduce the volume of OH in water. We obtain for OH(aq): DeltafH degrees = -0.2 +/- 1.4 and DeltafG degrees = 5.8 +/- 0.4 kcal/mol that are in agreement with literature values. The results provide confidence in the pulsed PAC technique for measuring aqueous thermochemistry of radicals and open the way to obtaining thermochemistry for most radicals that can be formed by reaction of OH with aqueous substrates while advancing the field of continuum solvation theory toward ab initio-defined solute cavities.

Journal Article↗