Conformational Volume Changes Research Articles

Theoretical analysis of high-pressure effects on conformational equilibria

Along with temperature, pressure is the most important physical parameter determining the thermodynamic properties and reactivity of chemical systems. In this work, we discuss the effects of high pressure on conformational properties of organic molecules and propose an approach toward calculation of conformational volume changes based on molecular dynamics simulations. The results agree well with the experimental data. Furthermore, we demonstrate that pressure can be used as an instrument for fine-tuning of molecular conformations and to propel a properly constructed molecular rotor possessing a suitable combination of energy and volume profiles.

Influence of HbCO Structure of the Bar-Headed Goose on Photolysis Thermodynamics as Studied by the Nanosecond Laser-Ultrasonic Technique

The bar-headed goose, a specialized high-altitude species, has a capacity for high oxygen uptake from a hypoxic environment. It thus has a higher oxygen affinity than other bird species of lower-altitude environments. Oxygen affinity is determined by molecular structures and genetic mutations of hemoglobin (Hb), which can also influence the coordinating structures and dynamics of oxygen-Hb. To explore the structural differences in Hbs as between high and low altitude species, photolysis dynamic parameters, including quantum yield, enthalpy, and conformational volume changes in carboxy-Hbs (HbCO) for the bar-headed goose and low altitude counterparts (the Chinese goose and chicken) were investigated by the laser pumping-probing technique and photoacoustic calorimetry. Comparing the photolysis results for HbCO of the three species, the enthalpy and conformational volume changes of the bar-headed goose were much smaller than those of the others, although the quantum yields of all three species are similar. To explain the possible mechanisms of these differences, modifications of salt bridges and key residue mutations at the α β subunit interfaces of the proteins are described and discussed briefly.

Photolyses of mammalian carboxy-hemoglobin studied by photoacoustic calorimetry

The enthalpy and conformational volume changes in the photolyses of carboxy-hemoglobin (HbCO) of human, bovine, pig, horse and rabbit are investigated by photoacoustic calorimetry. Considering the time scales of the exciting laser pulse and the receiving ultrasound transducers (PVDF films and PZT ceramics), as well as the reaction lifetimes in the photolysis processes of HbCO, the measured results are related to the geminate recombination and tertiary relaxation in photolyses of HbCO. Moreover, the quantum yields of the five mammals are also measured by laser pump-probe technique. The results show that the dynamic parameters, such as enthalpy and conformational volume changes, differ between the processes of the geminate recombination and tertiary relaxation. Also, the dynamic parameters differ among the five mammals although some of them may be consistent with each other.

Photolyses of carboxy-hemoglobin of bar-headed goose studied by photoacoustic calorimetry

As a specialized species native to high altitude, bar-headed goose can fly annually over an altitude of 9000m, which means that its hemoglobin has a higher oxygen affinity than its lowland relatives, such as goose and chicken. To study the mechanism of the phenomena, laser ultrasonic calorimetry is used to study dynamic processes associated with photolyses of carboxy hemoglobin (HbCO), including the enthalpy and conformational volume changes, of bar-headed goose and its lowland relatives. Considering the time scales of the reaction lifetimes in the photolyses processes of HbCO, two kinds of piezoelectric transducers, a PVDF film and a PZT ceramic, are used as acoustic signal detectors. For evaluating the relative enthalpy change and the relative conformational volume change in the process, the quantum yield of the photolysis must be taken into account, which has been measured by pump-probe technique. The results show that the enthalpy and conformational volume changes of bar-headed goose are obviously sma...

Geminate recombinations in photolysis of carboxy-hemoglobin studied by photoacoustic calorimetry

Enthalpy and conformational volume changes in photo-dissociation of carboxy-hemoglobin of human, bovine, pig, horse and rabbit are investigated by photoacoustic calorimetry (PAC). Considering the time scale of the experimental system, the results should be related to geminate recombinations in photolysis dynamics. The results show that the enthalpy and conformational volume changes for different species are different, and can be correlated with the protein structures.

Photolyses of mammalian oxy-hemoglobin studied by nanosecond photoacoustic calorimetry

Enthalpy and conformational volume changes in photolyses of oxy-hemoglobin (HbO 2) of human, bovine, pig, horse and rabbit are investigated by photoacoustic calorimetry. In the experiment, a pulsed Nd:YAG laser is used as an exciting source, and a PVDF film transducer and a PZT transducer are used to detect the photoacoustic signals. Based on the time scales of the excitation and detection systems as well as the photolysis processes of HbO 2, it can be indicated that the measured enthalpy and conformational volume changes are related to slow geminate recombination and tertiary relaxation in photolyses of HbO 2, which are with the time scale of 30–40 ns and 100–150 ns, respectively. The results show that the enthalpy and conformational volume changes are different for both photolysis processes of HbO 2 and also for various mammals. The different results among the five mammals are analyzed and discussed briefly.

Enthalpy and conformational volume changes of mammalian oxy-hemoglobins investigated by pulsed photoacoustic calorimetry

Enthalpy and conformational volume changes induced by laser photo-dissociation reactions of mammalian oxy-hemoglobin, such as human, bovine, pig, horse and rabbit oxy-hemoglobins, are investigated by pulsed photoacoustic calorimetry. Generally, the response time of the photoacoustic calorimetry is restricted by the width of the laser pulse and the bandwidth of the acoustic detector. Considering the time window of the experimental system, the enthalpy and conformational volume changes detected should be caused by the tertiary relaxation of the heme proteins. In order to calculate the enthalpy and conformational volume changes, the quantum yields of the photo-dissociation products of oxy-hemoglobins must be measured and taken into account. Finally, the enthalpy and conformational volume changes of the oxy-hemoglobins connected with the tertiary relaxation are obtained, which show that for all measured mammalian oxy-hemoglobins the values of enthalpy changes are in the range of 30.0–46.8 kcal/mol and volume changes are of 2.3–7.8 ml/mol although the quantum yields for the different species may have much bigger differences. A possible explanation of the results is presented.

Laser-induced dissociation of bovine oxy-hemoglobin studied by a pulsed photoacoustic method

The kinetics and thermodynamics of enthalpy and conformational volume changes related to photo-dissociations of bovine oxide-hemoglobins has been investigated by ns pulsed photoacoustic method. The enthalpy and volume changes associated with the photo-dissociation are obtained as 35.7′3 Kcal/mol and 4.8′1 mL/mol respectively. The results are close to those of oxide-hemoglobins of human, but quite different with the values of carbon-monoxide-hemoglobins of human, and some discussions are given.

Determination of Reaction Enthalpy and Conformational Volume Changes by Photoacoustic Spectroscopy

The reaction enthalpy and conformational volume changes can be qualitatively estimated by means of the temperature-dependent pulsed photoacoustic spectroscopy. The curves for heat-releasing fraction and conformational volume changes with different temperatures are presented. The simultaneous equations for determination of the enthalpy and volume changes are established based on temperature-dependent measurements, and applied to study the photolysis of coenzyme system.

High pressure study on molecular conformational equilibria of n-pentane

The n-pentane molecule has the basic conformations, TT, TG, and GG. It is important for understanding the conformational behavior of chain molecules. We have studied the effect of pressure on the conformations of n-pentane in the condensed phase by using high pressure infrared spectroscopy with a diamond anvil cell up to 28.9 kbar. Compression of liquid n-pentane increases the concentration of the more globular conformers, while the TT conformer only exists as a high pressure solid. The volume changes for TT to TG, TG to GG, and TT to GG forms are −1.0±0.2, −1.1±0.3, and −2.1±0.3 cm3/mol, at 20 °C, respectively. The conformational volume changes in liquid n-alkanes are discussed in terms of the solvent-excluded volume.

Conformational enthalpy and volume changes in bromocyclohoexane determined by Raman spectroscopy

Raman spectra of bromocyclohexane have been recorded as a function of temperature between 22 and 135°C and as a function of pressure from 1 bar to 7.0 kbar. The integrated intensities of the bands at 657 and 687 cm −1 have been used to monitor the relative populations of the axialand equatorial forms respectively. From these data, enthalpy and volume differences of 1.1 ± 0.3 kJ mol −1 and −2.2 ± 0.3 cm 3 mol −1 respectively were determined for the equatorial—axial equilibrium.

Conformational enthalpy and volume changes in chlorocyclohexane determined by Raman spectroscopy

AbstractThe Raman spectrum of chlorocyclohexane has been recorded as a function of temperature from −40 to +110 °C and the conformational enthalpy for the equatorial to axial equilibrium was determined as 1.10±0.13 kJ mol−1 for ΔH. Changes in the Raman spectrum as a function of pressure up to 5.6 kbar have been interpreted in terms of a shift in the conformational equilibrium to favour the axial form at high pressure. The associated conformational volume change has been calculated as 2.33±0.27 cm3 mol−1.

Determination of conformational volume changes in liquid 1-bromoalkanes at high pressure by Raman spectroscopy

An increase of pressure induces a shift of conformational equilibrium from PC to PH conformers in liquid 1-bromoalkanes, and is accompanied by a measurable change in molar volume.