No abstract

Hyper-cross-linked polystyrene sorbents with various degree of cross-linking ranging from 25% to over 100% were studied using positron annihilation lifetime (PAL) spectroscopy. Long-lived components of the lifetime distribution of positron annihilation, orthopositronium (o-Ps) lifetimes, give information on the effective size of elementary free volumes (unoccupied spaces), responsible for the properties of sorbents. Experiments were carried out in a vacuum, in air and also in oxygen and nitrogen. Narrow size distribution of elementary free volumes having radius of about 1.5 nm and concentration estimated as ∼10 19 cm -3 , were found in the samples with cross-linking higher than 40%. Some of the hyper-cross-linked samples gave positronium lifetime τ5 > 50 ns, which is among the highest values ever measured for organic polymer compounds. Positronium quenching (shortening of o-Ps lifetime) due to Ps exchange interaction with oxygen, dissolved in sorbents, gave information about the character of distribution of elementary free volumes in polymers.

We studied the equilibrium binding of two hydrophobic fluorescent dyes, ANS and bisANS, to four members of a family of intracellular lipid-binding proteins: IFABP, CRABP I, CRABP II, and ILBP. The spectral and binding parameters for the probes bound to the proteins were determined. Typically, there was a single binding site on each protein for the ligands. However, IFABP cooperatively bound a second bisANS molecule in the binding pocket. Comparative analysis of affinities and spectral characteristics for the two probes allowed us to examine the contributions of electrostatic and hydrophobic interactions to the binding process, and to address some aspects of the internal structure of the studied proteins.