25 research outputs found
Theory of interlayer exchange interactions in magnetic multilayers
This paper presents a review of the phenomenon of interlayer exchange
coupling in magnetic multilayers. The emphasis is put on a pedagogical
presentation of the mechanism of the phenomenon, which has been successfully
explained in terms of a spin-dependent quantum confinement effect. The
theoretical predictions are discussed in connection with corresponding
experimental investigations.Comment: 18 pages, 4 PS figures, LaTeX with IOP package; v2: ref. added.
Further (p)reprints available from http://www.mpi-halle.de/~theory
Vacuum fluctuation forces between ultra-thin films
We have investigated the role of the quantum size effects in the evaluation
of the force caused by electromagnetic vacuum fluctuations between ultra-thin
films, using the dielectric tensor derived from the particle in a box model.
Comparison with the results obtained by adopting a continuum dielectric model
shows that, for film thicknesses of 1-10 nm, the electron confinement causes
changes in the force intensity with respect to the isotropic plasma model which
range from 40% to few percent depending upon the film electron density and the
film separation. The calculated force shows quantum size oscillations, which
can be significant for film separation distances of several nanometers. The
role of electron confinement in reducing the large distance Casimir force is
discussed
Thermal Stability of the Human Immunodeficiency Virus Type 1 (HIV-1) Receptors, CD4 and CXCR4, Reconstituted in Proteoliposomes
BACKGROUND: The entry of human immunodeficiency virus (HIV-1) into host cells involves the interaction of the viral exterior envelope glycoprotein, gp120, and receptors on the target cell. The HIV-1 receptors are CD4 and one of two chemokine receptors, CCR5 or CXCR4. METHODOLOGY/PRINCIPAL FINDINGS: We created proteoliposomes that contain CD4, the primary HIV-1 receptor, and one of the coreceptors, CXCR4. Antibodies against CD4 and CXCR4 specifically bound the proteoliposomes. CXCL12, the natural ligand for CXCR4, and the small-molecule CXCR4 antagonist, AMD3100, bound the proteoliposomes with affinities close to those associated with the binding of these molecules to cells expressing CXCR4 and CD4. The HIV-1 gp120 exterior envelope glycoprotein bound tightly to proteoliposomes expressing only CD4 and, in the presence of soluble CD4, bound weakly to proteoliposomes expressing only CXCR4. The thermal stability of CD4 and CXCR4 inserted into liposomes was examined. Thermal denaturation of CXCR4 followed second-order kinetics, with an activation energy (E(a)) of 269 kJ/mol (64.3 kcal/mol) and an inactivation temperature (T(i)) of 56°C. Thermal inactivation of CD4 exhibited a reaction order of 1.3, an E(a) of 278 kJ/mol (66.5 kcal/mol), and a T(i) of 52.2°C. The second-order denaturation kinetics of CXCR4 is unusual among G protein-coupled receptors, and may result from dimeric interactions between CXCR4 molecules. CONCLUSIONS/SIGNIFICANCE: Our studies with proteoliposomes containing the native HIV-1 receptors allowed an examination of the binding of biologically important ligands and revealed the higher-order denaturation kinetics of these receptors. CD4/CXCR4-proteoliposomes may be useful for the study of virus-target cell interactions and for the identification of inhibitors