¹⁴N nuclear quadrupole resonance study of polymorphism in famotidine.

(14)N nuclear quadrupole resonance (NQR) in two known polymorphs of famotidine was measured. At room temperature, seven quadrupolar sets of transition frequencies (ν(+), ν(-), and ν(0)) corresponding to seven different nitrogen sites in the crystal structure of each of the two polymorphs were found. This confirms the expected ability of NQR to distinguish polymorph B from its analog A.

Mass spectrometric investigations of alpha- and beta-cyclodextrin complexes with ortho-, meta- and para-coumaric acids by negative mode electrospray ionization.

The mass spectrometric characterization of aqueous solutions of alpha- and beta-cyclodextrins (CDs) and o-, m- and p-coumaric acids (CAs) by negative ion electrospray ionization (ESI) indicates that the [CD+CA](-) ions were sourced from the inclusion complex present in solution and from the anion attached to CD molecules formed in the spray processes. The anion adducts formed in the spray process contribute significantly to the signal intensity of an ionized inclusion complex thus overestimating the calculated stability constant (K) of solution-phase complexes by one to two orders of magnitude. The relative intensities of anion adducts in mass spectra depend on the concentration ratio of the anion and the CD in spray droplets, while the relative intensity of the ionized inclusion complex depends on CD and CA concentrations in solutions and the value of K.

Low-frequency velocity correlation spectrum of fluid in a porous media by modulated gradient spin echo.

In addition to the fast correlation for local stochastic motion, the molecular velocity correlation function in a fluid enclosed within the pore boundaries features a slow long time-tail decay. Here we present its study by the NMR modulated gradient spin-echo method (MGSE) [1] on a system of water trapped in the space between the closely packed polystyrene beads. With MGSE pulse sequence, a repetitive train of RF pulses with interspersed gradient pulses periodically modulates the spin phase.

Effect of pH on red blood cell deformability.

The effect of pH on the red blood cell (RBC) deformability, which is a consequence of a change of cell membrane elastic properties is studied experimentally. With the intention to reduce the effects on deformability of cell geometry and cytoplasmic viscosity, we measured the deformability of the cells with the same volume at various pH of cell suspension from 6.2 to 8.

Influence of equinatoxin II on coronary smooth muscle membrane fluidity.

Equinatoxin II forms pores in artificial as well as in natural phospholipid bylayers. As it also reduces the perfusion through the coronary arteries it seemed reasonable to investigate the interaction of this protein with the plasmalemma of the vascular smooth muscle cells more directly with the patch-clamp method and with EPR using the spin probe methyl ester of 5-doxylpalmitate. In the EPR spectra at least three regions in the membranes were identified with different membrane fluidity.

Intermediates in denaturation of a small globular protein, recombinant human stefin B.

Guanidinium HCl (GdmHCl), pH, and heat denaturation of the recombinant human stefin B, a low molecular weight protein inhibitor of cysteine proteinases, has been followed by circular dichroism. From the noncoincidence of the transitions in the near and far UV, the existence of stable intermediate states possessing few persistent tertiary interactions but most of the native-like secondary structure, was inferred. These intermediate states exist at equilibrium under various conditions, namely, state G at 1.