Spin fluctuations with two-dimensional XY behavior in a frustrated S = 1/2 square-lattice ferromagnet

The spin dynamics of the layered square-lattice vanadate Pb2VO(PO4)2 is investigated by electron spin resonance at various magnetic fields and at temperatures above magnetic ordering. The linewidth divergence towards low temperatures seems to agree with isotropic Heisenberg-type spin exchange suggesting that the spin relaxation in this quasi-two dimensional compound is governed by low-dimensional quantum fluctuations. However, a weak easy- plane anisotropy of the g factor points to the presence of a planar XY type of exchange. Indeed, we found that the linewidth divergence is described best by XY-like spin fluctuations which requires a single parameter only. Therefore, ESR-probed spin dynamics could establish Pb2VO(PO4)2 as the first frustrated square lattice system with XY-inherent spin topological fluctuations.Comment: 5 pages, 3 figure

Mol. Cell. Proteomics

Chemical cross-linking in combination with mass spectrometric analysis offers the potential to obtain low-resolution structural information from proteins and protein complexes. Identification of peptides connected by a cross-link provides direct evidence for the physical interaction of amino acid side chains, information that can be used for computational modeling purposes. Despite impressive advances that were made in recent years, the number of experimentally observed cross-links still falls below the number of possible contacts of cross-linkable side chains within the span of the cross-linker. Here, we propose two complementary experimental strategies to expand cross-linking data sets. First, enrichment of cross-linked peptides by size exclusion chromatography selects cross-linked peptides based on their higher molecular mass, thereby depleting the majority of unmodified peptides present in proteolytic digests of cross-linked samples. Second, we demonstrate that the use of proteases in addition to trypsin, such as Asp-N, can additionally boost the number of observable cross-linking sites. The benefits of both SEC enrichment and multiprotease digests are demonstrated on a set of model proteins and the improved workflow is applied to the characterization of the 20S proteasome from rabbit and Schizosaccharomyces pombe

Towards an experimentally feasible controlled-phase gate on two blockaded Rydberg atoms

We investigate the implementation of a controlled-Z gate on a pair of Rydberg atoms in spatially separated dipole traps where the joint excitation of both atoms into the Rydberg level is strongly suppressed (the Rydberg blockade). We follow the adiabatic gate scheme of Jaksch et al. [1], where the pair of atoms are coherently excited using lasers, and apply it to the experimental setup outlined in Ga\"etan et al. [2]. We apply optimisation to the experimental parameters to improve gate fidelity, and consider the impact of several experimental constraints on the gate success.Comment: 10 pages, 14 figure

Evolution of DIMBOA-Glc o-methyltransferases from flavonoid o-methyltransferases in the grasses

O-Methylated benzoxazinoids (BXs) and flavonoids are widespread defenses against herbivores and pathogens in the grasses (Poaceae). Recently, two flavonoid O-methyltransferases (FOMTs), ZmFOMT2 and ZmFOMT3, have been reported to produce phytoalexins in maize (Zea mays). ZmFOMT2 and ZmFOMT3 are closely related to the BX O-methyltransferases (OMTs) ZmBX10-12 and ZmBX14, suggesting a common evolutionary origin in the Poaceae. Here, we studied the evolution and enzymatic requirements of flavonoid and BX O-methylation activities in more detail. Using BLAST searches and phylogenetic analyses, we identified enzymes homologous to ZmFOMT2 and ZmFOMT3, ZmBX10-12, and ZmBX14 in several grasses, with the most closely related candidates found almost exclusively in species of the Panicoideae subfamily. Biochemical characterization of candidate enzymes from sorghum (Sorghum bicolor), sugar cane (Saccharum spp.), and teosinte (Zea nicaraguensis) revealed either flavonoid 5-O-methylation activity or DIMBOA-Glc 4-O-methylation activity. However, DIMBOA-Glc 4-OMTs from maize and teosinte also accepted flavonols as substrates and converted them to 3-O-methylated derivatives, suggesting an evolutionary relationship between these two activities. Homology modeling, sequence comparisons, and site-directed mutagenesis led to the identification of active site residues crucial for FOMT and BX OMT activity. However, the full conversion of ZmFOMT2 activity into BX OMT activity by switching these residues was not successful. Only trace O-methylation of BXs was observed, indicating that amino acids outside the active site cavity are also involved in determining the different substrate specificities. Altogether, the results of our study suggest that BX OMTs have evolved from the ubiquitous FOMTs in the PACMAD clade of the grasses through a complex series of amino acid changes

Mechanisms of membrane processes, electric gene transfer and cell fusion Report on the workshop held at the Zentrum für Interdisziplinäre Forschung in Bielefeld on 3–4 April 1986

Dorfmüller T, Förster W, Neumann E. Mechanisms of membrane processes, electric gene transfer and cell fusion Report on the workshop held at the Zentrum für Interdisziplinäre Forschung in Bielefeld on 3–4 April 1986. Bioelectrochemistry and Bioenergetics. 1987;17(1):7-8