High-pressure differential scanning microcalorimeter.

A differential scanning microcalorimeter for studying thermotropic conformational transitions of biopolymers at high pressure has been designed. The calorimeter allows taking measurements of partial heat capacity of biopolymer solutions vs. temperature at pressures up to 3000 atm. The principles of operation of the device, methods of its calibration, as well as possible applications are discussed.

Polar Phase of Superfluid (3)He in Anisotropic Aerogel.

We report the first observation of the polar phase of superfluid (3)He. This phase appears in (3)He confined in a new type of aerogel with a nearly parallel arrangement of strands which play the role of ordered impurities. Our experiments qualitatively agree with theoretical predictions and suggest that in other systems with unconventional Cooper pairing (e.g., in unconventional superconductors) similar phenomena may be found in the presence of anisotropic impurities.

High pressure stabilization of collagen structure.

Scanning microcalorimetry has been used to study heat denaturation of small es, Cyrillicollagen at high pressure. It has been demonstrated that an increase of the pressure by 200 MPa enlarges the structure stability by 6.8 degrees C. The pressure increase does not affect the cooperativity of transition and only slightly decreases its enthalpy. The changes of the partial specific volume of collagen as well as its isothermal compressibility and thermal expansibility during transition have been estimated. In contrast to denaturation of most globular proteins, denaturation of collagen proceeds with an increase of the partial specific volume at ambient pressure. Moreover, the absolute value of the collagen volume increment is distinctly greater than this in most globular proteins. The volume increment diminishes when the pressure increases due to the difference in the compressibility for folded and unfolded states. This effect is compensated to some extent by the differences in heat expansion. The volume increment alters its sign when the pressure reaches about 324+/-20 MPa and the temperature of denaturation grows to 49.7 degrees C. Further pressure growing destabilizes the collagen structure.

High pressure effect on the main transition from the ripple gel P'beta phase to the liquid crystal (Lalpha) phase in dipalmitoylphosphatidylcholine. Microcalorimetric study.

Scanning microcalorimetry has been used to study the high pressure effect on the main transition from the ripple gel P'(beta) phase to the liquid crystal (L(alpha)) phase in DPPC (dipalmitoylphosphatidylcholine). It has been demonstrated that an increase of the pressure by 200 MPa shifts the transition to higher temperatures by 36.4 degrees. The pressure increase does not affect the cooperativity of transition but reduces noticeably its enthalpy. The changes of the molar partial volume, isothermal compressibility as well as volume thermal expansibility during transition in DPPC suspension have been estimated. It has been shown that monovalent ions (Na(+), Cl(-)) in solution slightly affect the main thermodynamic parameters of the transition. Calcium ions significantly decrease distinction in compressibility and thermal expansibility between liquid-crystal and ripple gel phases of lipid suspension, which in its turn reflects less difference in their volume fluctuations.

Many-body dipole-dipole interactions between excited Rb atoms probed by wave packets and parametric four-wave mixing.

Dipole-dipole interactions between excited Rb atoms at long range (approximately 300a0-2150a0) have been observed with molecular wave packets and a coherent nonlinear optical process. Fourier analysis of the parametric four-wave mixing (PFWM) signal wave intensity produced in femtosecond pump-probe experiments demonstrates the appearance of sidebands associated with the Rb 7s-5d(5/2) quantum beating frequency of approximately 18.3 THz. Calculations show that the observed sideband splittings and Fourier domain profiles result from multiple atom, dipole-dipole interactions, and ensembles comprising five or fewer Rb (7s, 6p) atoms account for virtually all of the data.