One-Third Magnetization Plateau with a Preceding Novel Phase in Volborthite.

We have synthesized high-quality single crystals of volborthite, a seemingly distorted kagome antiferromagnet, and carried out high-field magnetization measurements up to 74 T and ^{51}V NMR measurements up to 30 T. An extremely wide 1/3 magnetization plateau appears above 28 T and continues over 74 T at 1.4 K, which has not been observed in previous studies using polycrystalline samples. NMR spectra reveal an incommensurate order (most likely a spin-density wave order) below 22 T and a simple spin structure in the plateau phase. Moreover, a novel intermediate phase is found between 23 and 26 T, where the magnetization varies linearly with magnetic field and the NMR spectra indicate an inhomogeneous distribution of the internal magnetic field. This sequence of phases in volborthite bears a striking similarity to those of frustrated spin chains with a ferromagnetic nearest-neighbor coupling J_{1} competing with an antiferromagnetic next-nearest-neighbor coupling J_{2}.

Magnetic control of transverse electric polarization in BiFeO3.

Numerous attempts have been made to realize crossed coupling between ferroelectricity and magnetism in multiferroic materials at room temperature. BiFeO3 is the most extensively studied multiferroic material that shows multiferroicity at temperatures significantly above room temperature. Here we present high-field experiments on high-quality mono-domain BiFeO3 crystals reveal substantial electric polarization orthogonal to the widely recognized one along the trigonal c axis. This novel polarization appears to couple with the domains of the cycloidal spin order and, hence, can be controlled using magnetic fields. The transverse polarization shows the non-volatile memory effect at least up to 300 K.

Surface charge of Plasmodium falciparum merozoites as revealed by atomic force microscopy with surface potential spectroscopy.

Electric charges on the surface of Plasmodium falciparum merozoites and erythrocytes were investigated by atomic force microscopy with surface potential spectroscopy. The apical end of merozoites was positively charged, while the entire erythrocyte surface was negatively charged. Transmission electron microscopy also demonstrated that negatively charged nanogold particles attached to the apical end of merozoites, and cationized ferritin particles attached to the entire surface of the erythrocyte. This indicates that the surface charge at the apical end of the merozoite may play an important role in invasion of the erythrocyte.

CR1 density polymorphism on erythrocytes of falciparum malaria patients in Thailand.

Complement receptor type 1 (CR1) on erythrocytes shows an inherited numerical polymorphism which correlates with a HindIII-RFLP (restriction fragment length polymorphism) of the CR1 gene in various populations. To investigate the relationship between CR1 density polymorphism and disease severity, we typed 185 Thai patients with acute falciparum malaria (55 severe and 130 uncomplicated) for their genotypes of this polymorphism. The level of expression of erythrocyte CR1 from 42 randomly selected patients was measured by enzyme-linked immunosorbent assay (ELISA). We observed a significantly higher frequency of homozygotes of the CR1 low density allele (LL) among the severe group as compared to the uncomplicated group (P = 0.005). CR1 expression on erythrocytes from patients with the LL genotype was significantly lower than homozygotes with the high density allele (HH) (P < 0.0001) and heterozygotes (HL) (P = 0.013). The results suggest that a genetically-determined low CR1 density on erythrocytes may be a risk factor for developing a more severe form of malaria in Thai subjects.

Invasive forms of Toxoplasma gondii, Leishmania amazonensis and Trypanosoma cruzi have a positive charge at their contact site with host cells.

We examined the surface charges of invasive forms of Toxoplasma gondii, Leishmania amazonensis, and Trypanosoma cruzi by atomic force microscopy and surface potential spectroscopy. We found that the specific part of the protozoan which makes initial contact with the host cell is positively charged. This indicates that the positive charge at the site of contact facilitates binding of the invasive protozoan to negatively charged host cells.

Attachment of Moraxella catarrhalis occurs to the positively charged domains of pharyngeal epithelial cells.

Attachment of bacteria to host cells is the initial step in the pathogenesis of infection. Several factors, such as hydrophobicity, surface electric charge, and van der Waals force, are considered to be responsible for the attachment step. However, it is not clear why bacteria and epithelial cells, both of which possess a negative surface charge, do not repel one another. In the present study, we used Moraxella catarrhalis and pharyngeal epithelial cells to study the surface charges of structures involved in the attachment. By atomic force microscopy (AFM) equipped with surface potential spectroscopy, it was found that the cell surface microplicae have a positive charge of 30.1+/-3.6 mV (mean+/-SE). The depressions between the microplicae have a negative surface charge of 43.5+/-4.0 mV. Using cationic ferritin and electron microscopy (EM) we confirmed that the depressions between the microplicae have a negative charge. By AFM and by using cationic ferritin with EM, it was found that the net surface charge of the bacterial cells is negative. By both AFM and EM, it was found that the bacterial cells attach to the microplicae of the pharyngeal epithelial cell. Our work confirmed the general belief that both kinds of cells do have a net negative charge. We conclude that there are positively and negatively charged domains on the surface of human pharyngeal epithelial cells. M. catarrhalis evidently attaches to the positively charged domain (i.e. microplicae) of pharyngeal epithelial cells.