Investigation of human hair fibers using lateral force microscopy.

Atomic force microscopy (AFM) and lateral force microscopy (LFM) were used to investigate the morphologic and surface changes associated with various surface modifications to human hair. These included extraction with a series of solvents, bleaching, and treatment with a cationic copolymer. The study assessed the ability of these techniques to distinguish the changes in surface properties, including morphology and friction coefficient, as manifested in changes brought about by the indicated surface modifications. While topographic morphology can easily be investigated with contact AFM. LFM offers an additional tool for probing the surface distribution of oils and waxes. The removal of surface lipids from the fiber surface was accomplished using soxhlet extraction with t-butanol and n-hexane, while the free internal lipids (within the fiber structure) were removed by extraction with a mixture of chloroform and methanol (70:30, v/v). In addition, the surface of hair was modified with the cationic polymer, co(vinyl pyrrolidone-methacrylamidopropyl trimethylammonium chloride [PVP/MAPTAC]), and its distribution on the surface was monitored. Ambient AFM and LFM studies of surface modified and native fibers clearly indicate that when investigated as a function of tip loading force, the different modifications result in changes of the friction coefficient, which increase in this order: native, bleached, solvent extracted, and polymer-treated hair. Friction images show surface variations that are interpreted as areas of varying lipid film coverage. In addition, topographic images of the fibers show the presence of small pores, which become increasingly prevalent upon solvent extraction.

A stable, multi-subunit complex of beta2glycoprotein I.

Beta2glycoprotein I (beta2GPI) is a 54-kDa plasma protein which is recognized as an autoantigen for antibodies from patients with antiphospholipid syndrome (APS). SDS-PAGE (under reducing conditions) of beta2GPI from three sources indicates that the 54-kDa beta2GPI band is accompanied by a band corresponding to an 8-kDa protein. In the absence of detergent and reducing agents (native PAGE), beta2GPI demonstrated a large complex (molecular mass approximately 320 kDa) which is dissociable by boiling in 6-8 M urea, yielding several lower molecular mass bands, one of which corresponds to the 8-kDa protein observed in SDS-PAGE. Sera from five healthy adults demonstrated native beta2GPI migration equivalent to the commercially purified protein. Atomic force microscopy (AFM) images of native beta2GPI show aggregrates of particles each having a diameter of 30-35 nm. This is consistent with a globular unit the size of which would be substantially larger than that expected for a 54-kDa protein. These experiments suggest that the 54-kDa beta2GPI monomer subunits exist as a multimeric complex with the 8-kDa protein.

(RbxK1-x)3C60 Superconductors: Formation of a Continuous Series of Solid Solutions.

By means of an approach that employs alkali-metal alloys, bulk single-phase (RbxK1-x)(3)C(6O) superconductors have been prepared for all x between 0 and 1. For x = 1 it is shown that the maximum superconducting fraction, which approaches 100% in sintered pellets, occurs at a Rb to C(60) ratio of 3:1. More importantly, single-phase superconductors are formed at all intermediate values of x, and it is shown that the transition temperature (T(c)) increases linearly with x in this series of materials. The formation of a continuous range of solid solutions demonstrates that the rubidium- and potassium-doped C(60) superconducting phases must be isostructural, and furthermore, suggests that the linear increase in T(c) with x results from a chemical pressure effect.