Guided ion beam and theoretical studies of sequential bond energies of water to sodium cysteine cation

Journal ArticleAbsolute bond dissociation energies of water to sodium cysteine (Cys) cations and cysteine to hydrated sodium cations are determined experimentally by collision-induced dissociation of Na+Cys(H2O)x, where x = 1 - 4, complexes with xenon in a guided ion beam mass spectrometer. Experimental results show that the binding energies of water and cysteine to the complexes decrease monotonically with increasing number of water molecules. Quantum chemical calculations at three different levels show reasonable agreement with the experimental bond energies. The calculations indicate that the primary binding site for Na+ changes from charge-solvated tridentate chelation at the amino nitrogen, carbonyl oxygen, and sulfur sidechain for x = 0 and 1 to the C terminus of zwitterionic cysteine for x = 4, whereas different levels of theory provide conflicting predictions for x = 2 and 3. The first solvent shell of Na+Cys is found to be complete at four waters. This is fewer than needed for the aliphatic amino acid glycine, because the functionalized side-chain of Cys provides an internal solvation site, a binding motif that probably applies for most other functionalized amino acids

Magnons in Ferromagnetic Metallic Manganites

Ferromagnetic (FM) manganites, a group of likely half-metallic oxides, are of special interest not only because they are a testing ground of the classical doubleexchange interaction mechanism for the colossal magnetoresistance, but also because they exhibit an extraordinary arena of emergent phenomena. These emergent phenomena are related to the complexity associated with strong interplay between charge, spin, orbital, and lattice. In this review, we focus on the use of inelastic neutron scattering to study the spin dynamics, mainly the magnon excitations in this class of FM metallic materials. In particular, we discussed the unusual magnon softening and damping near the Brillouin zone boundary in relatively narrow band compounds with strong Jahn-Teller lattice distortion and charge/orbital correlations. The anomalous behaviors of magnons in these compounds indicate the likelihood of cooperative excitations involving spin, lattice, as well as orbital degrees of freedom.Comment: published in J. Phys.: Cond. Matt. 20 figure

Molecular Characterization of Spiroplasma Viruses and the Mechanism of Resistance of Spiroplasma Citri Lines to Infection by the Virus SVTS2

Spiroplasma citri M200H is a triply cloned isolate derived from citri Maroc R8A2. Plaques are formed on agar lawns of M200H infected by spiroplasma virus SVTS2, which was isolated from melliferum TS2. Two virus- resistant citri lines, MR2 and MR3, were derived from colonies growing within cleared plaques on lawns of M200H inoculated at a high MOI with SVTS2. The resistant lines did not produce plaques when inoculated with SVTS2 virions. Protein profiles of the resistant lines were compared with each other and. with those of the parent strain using 1- and 2-D polyacrylamide gel electrophoresis. There were no significant differences among the 1-D SDS-PAGE protein profiles. In 2-D gels, three proteins, Pl, P2 and P3, seen in the parent strain M200H, were missing or significantly reduced in both resistant lines. Pl and P2 were membrane-associated proteins. By using antiserum against a membrane protein preparation from citri, 7 additional membrane-associated proteins were identified in 2-D gels of proteins from M200H, MR2 and MR3. Genomic DNA fingerprints of M200H, MR2 and MR3 were similar. Electron microscopy i I showed SVTS2 particles bound to M200H cell surfaces. Pre~ incubation of.ÃÆâ⠡‰ ¾Ã‚¢ÃƒÆ’ĉ⠡¬Â ÃƒÂ¢Ã¢â€šÂ¬Ã¢â€žÂ¢ÃƒÆ’ƒÂà ¡Ãƒâ€šÃ‚¢ÃƒÆ’Æ’Ã ¡Ãƒâ€šÃ‚¢ÃƒÆ’¢â‚¬Å¡Ã‚à ¡Ãƒâ€šÃ‚¬ÃƒÆ’ĉ⠡¬Â¦Ãƒâ€šÃ ¡Ãƒâ€šÃ‚¡ÃƒÆ’ƒÆ’Æâ⠡‰ ¾Ã‚¢ÃƒÆ’Æ’Ã ¡Ãƒâ€šÃ‚¢ÃƒÆ’¢â⠡¡Ã ¡Ãƒâ€šÃ‚¬ÃƒÆ’…à ¡Ãƒâ€šÃ‚¡ÃƒÆ’ƒÆ’‚Ãâ⠡¡Ãƒâ€šÃ ¡Ãƒâ€šÃ‚§.. citri M200H with antiserum against total membrane protein of.ÃÆâ⠡‰ ¾Ã‚¢ÃƒÆ’ĉ⠡¬Â ÃƒÂ¢Ã¢â€šÂ¬Ã¢â€žÂ¢ÃƒÆ’ƒÂà ¡Ãƒâ€šÃ‚¢ÃƒÆ’Æ’Ã ¡Ãƒâ€šÃ‚¢ÃƒÆ’¢â‚¬Å¡Ã‚à ¡Ãƒâ€šÃ‚¬ÃƒÆ’ĉ⠡¬Â¦Ãƒâ€šÃ ¡Ãƒâ€šÃ‚¡ÃƒÆ’ƒÆ’Æâ⠡‰ ¾Ã‚¢ÃƒÆ’Æ’Ã ¡Ãƒâ€šÃ‚¢ÃƒÆ’¢â⠡¡Ã ¡Ãƒâ€šÃ‚¬ÃƒÆ’…à ¡Ãƒâ€šÃ‚¡ÃƒÆ’ƒÆ’‚Ãâ⠡¡Ãƒâ€šÃ ¡Ãƒâ€šÃ‚§.. citri significantly reduced the number of plaques produced on subsequent inoculation with SVTS2, but pre-incubation with antisera specific for individual membrane proteins of 55 kd, 77 kd and 89 kd did not. Thus, these membrane proteins probably are not involved in virus attachment or invasion.Spiroplasmavirus SVTS2, isolated from Spiroplasma melliferum TS2, produces plaques when inoculated onto lawns of citri M200H.citri lines MR2 and MR3, originally selected as colonies growing within plaque boundaries on a lawn of M200H inoculated with SVTS2, were resistant to SVTS2. Electroporation of SVTS2 DNA into M200H produced 1.5 X 105 transfectants/ug SVTS2 DNA. No transfection occurred in the M200H-derived lines MR2 or MR3. Native viruses isolated from M200H, MR2 and MR3 were designated SVM200H, SVMR2 and SVMR3. Restriction enzyme digestion patterns of the RF DNA of SVM200H, SVMR2, and SVMR3 were similar. RF DNAs of all the native viruses shared some homology with the SVTS2 DNA probe. Three bands {1.3 kb, 2.1 kb and 5.1 kb) not present in SVM200H hybridized strongly in SVMR2, and two of these bands {1.3 kb and 2.1 kb) also hybridized in SVMR3, indicated that a fragment of SVTS2 DNA was present in native virus RF DNA {extrachromosomal ds DNA) in MR2 and MR3, but not in M200H. Four weak hybridization bands (4.3, 6.5, 8.4 and 10.8 kb) were detected in the genomes of all three lines when probed with the SVTS2 DNA probe. There was also strong hybridization to 13.6 kb and 19.2 kb EcoRI fragments of the chromosomes of MR2 and MR3, but not to the chromosome of M200H. This indicated that SVTS2 DNA integrated into the genome of MR2 and MR3, but not M200H. When native virus SVMR3 RF, which contained a 2.1 kb SVTS2 DNA fragment, was transfected into M200H, the transformed spiroplasma was resistant to SVTS2. These results are consistant with the interpretation that SVTS2 fragments, inserted into the spiroplasma chromosome or extrachromosomal DNA, may function as a viral incompatibility element and provide immunity to superinfection by SVTS2.Virus SVTS2, isolated from the honeybee spiroplasma, Spiroplasma melliferum TS2, can infect the phytopathogen citri. SVTS2 was found to infect floricola and all except two citri strains tested. SVTS2 was determined by Western blotting to have five proteins (60, 107, 140, 153 and 181 kd). A restriction map of SVTS2 RF indicated one EcoRI, one HpaII, two BstyI/ Sau3AI, four HinfI, and four Tag! sites. This map differs from those of viruses SpVl-78 and SpVl-aa, both isolated from citri. Clones of the complete SVTS2 RF DNA (6.5 kb) and a fragment (3.2 kb) were obtained. Partial DNA sequencing showed that the 3.2 kb fragment was identical to that of a segment of the 6.5 kb DNA. Methylation of one of the Sau3AI sites of SVTS2 RF DNA in citri M200H was observed. DNA hybridization showed that five EcoRI fragments of the genome of melliferum TS2 hybridized to the SVTS2 DNA probe, indicating that SVTS2 DNA was integrated into the genome of melliferum TS2 in at least three sites. DNA sequence analysis showed that SVTS2 had 56% identity to SpVlA virus designated SVBR3, isolated from Spiroplasma citri BR3-3X (one strain of the spiroplasma which causes horseradish brittle root disease), is rod-shaped and 6-8 X 198-215 nm. Purified SVBR3 had a density of 1.26 g/cm3 in CsCl. Virus DNA sensitivity to mung bean nuclease indicated a single-stranded form. These features are consistent with those of group I spiroplasma viruses (SpVl). The replicative form of SVBR3 is approximately 8.6 Kb. The virus infected most strains ofÃÆâ⠡‰ ¾Ã‚¢ÃƒÆ’ĉ⠡¬Â ÃƒÂ¢Ã¢â€šÂ¬Ã¢â€žÂ¢ÃƒÆ’ƒÂà ¡Ãƒâ€šÃ‚¢ÃƒÆ’Æ’Ã ¡Ãƒâ€šÃ‚¢ÃƒÆ’¢â‚¬Å¡Ã‚à ¡Ãƒâ€šÃ‚¬ÃƒÆ’ĉ⠡¬Â¦Ãƒâ€šÃ ¡Ãƒâ€šÃ‚¡ÃƒÆ’ƒÆ’Æâ⠡‰ ¾Ã‚¢ÃƒÆ’Æ’Ã ¡Ãƒâ€šÃ‚¢ÃƒÆ’¢â⠡¡Ã ¡Ãƒâ€šÃ‚¬ÃƒÆ’…à ¡Ãƒâ€šÃ‚¡ÃƒÆ’ƒÆ’‚Ãâ⠡¡Ãƒâ€šÃ ¡Ãƒâ€šÃ‚§. citri tested, but not other spiroplasma species. Many restriction enzymes specific for G + C rich DNA did not digest SVBR3 RF DNA, suggesting a low G + C content. SVBR3 RF DNA restriction digestion patterns differed from those of another SpVl-type virus, SVTS2 (isolated fromÃÆâ⠡‰ ¾Ã‚¢ÃƒÆ’ĉ⠡¬Â ÃƒÂ¢Ã¢â€šÂ¬Ã¢â€žÂ¢ÃƒÆ’ƒÂà ¡Ãƒâ€šÃ‚¢ÃƒÆ’Æ’Ã ¡Ãƒâ€šÃ‚¢ÃƒÆ’¢â‚¬Å¡Ã‚à ¡Ãƒâ€šÃ‚¬ÃƒÆ’ĉ⠡¬Â¦Ãƒâ€šÃ ¡Ãƒâ€šÃ‚¡ÃƒÆ’ƒÆ’Æâ⠡‰ ¾Ã‚¢ÃƒÆ’Æ’Ã ¡Ãƒâ€šÃ‚¢ÃƒÆ’¢â⠡¡Ã ¡Ãƒâ€šÃ‚¬ÃƒÆ’…à ¡Ãƒâ€šÃ‚¡ÃƒÆ’ƒÆ’‚Ãâ⠡¡Ãƒâ€šÃ ¡Ãƒâ€šÃ‚§. melliferum). Western blotting using anti-SVTS2 serum showed that SVBR3 had two polypeptides in common with SVTS2. Hybridization of Southern blots showed that SVBR3 had no detectable DNA sequence relatedness to SVTS2. The viral DNA was cloned in E- coli DH5a. Partial DNA sequencing indicated that SVBR3 had 51% residue identity with DNA of SpV1-R8A2 and 37% identity to SpV4 (two previously characterized spiroplasmaviruses). DNA hybridization showed that viral DNA integrated into the genome of citri BR3-3X at nine or more sites. Different viral DNA integration patterns in citri lines of the BR group and those of the R8A2 group may be useful genetic markers for spiroplasma classification.Genomic DNA fingerprint analysis was used to compare three lines of Spiroplasma citri. BR3-T is insect transmissible and pathogenic; BR3-G is insect nontransmissible, but pathogenic; BR3-P is either insect nontransmissible or nonpathogenic. All three lines were derived from strain BR3- 3X by different maintenance conditions during the past 10 years. Although the genomic DNA fingerprints of all three lines were similar, when compared to the transmissible line (BR3-T), BR3-G lacked three EcoRI fragments (0.4 kb, 0.5 kb, and o.a kb), while BR3-P lacked one EcoRI fragment (0.5 kb). BR3-P contains one EcoRI fragment (0.9 kb) not seen in either BR3-T or BR3-G. The genomes of these citri lines were digested with EcoRI and probed with a DNA probe of virus SVBR3, which naturally infects citri BR3. Viral DNA hybridized to the genome of all test lines indicating viral DNA integrated into the genome of all three lines at 6-9 sites. Viral DNA hybridization bands of 3.1 kb and 25.4 kb occurred in BR3-T, but not in BR3-G and BR3-P. However, a band of 7.1 kb occurred in BR3-G and BR3-P, but not in BR3- T. These results indicated that the viral DNA integrates at different sites in insect transmissible and nontransmissible lines. In these limited tests, the presence of 3.1 kb and 25.4 kb fragments correlate with insect transmissibility and the presence of a 7.1 kb fragment correlates with non-transmissibility. Viral DNA integration in the spiroplasma genome may cause disruption or rearrangement of a gene or genes required for spiroplasma insect transmission.Plant Patholog

Influence of grain-refiner addition on the morphology of fe-bearing intermetallics in a semi-solid processed Al-Mg-Si alloy

© The Minerals, Metals & Materials Society and ASM International 2013The three-dimensional morphologies of the Fe-bearing intermetallics in a semisolid-processed Al-Mg-Si alloy were examined after extracting the intermetallics. α -AlFeSi and β-AlFeSi are the major Fe-bearing intermetallics. Addition of Al-Ti-B grain refiner typically promotes β-AlFeSi formation. β-AlFeSi was observed with a flat, plate-like morphology with angular edges in the alloy with and without grain refiner, whereas α -AlFeSi was observed as "flower"-like morphology in the alloy with grain refiner. © 2013 The Minerals, Metals & Materials Society and ASM International

A Frequency-Independent Method for Computing the Physical Optics-Based Electromagnetic Fields Scattered From a Hyperbolic Surface

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Evolution of spin-wave excitations in ferromagnetic metallic manganites

Neutron scattering results are presented for spin-wave excitations of three ferromagnetic metallic $A_{1-x}A^{\prime}_{x}$MnO$_3$ manganites (where $A$ and $A^\prime$ are rare- and alkaline-earth ions), which when combined with previous work elucidate systematics of the interactions as a function of carrier concentration $x$, on-site disorder, and strength of the lattice distortion. The long wavelength spin dynamics show only a very weak dependence across the series. The ratio of fourth to first neighbor exchange ($J_4/J_1$) that controls the zone boundary magnon softening changes systematically with $x$, but does not depend on the other parameters. None of the prevailing models can account for these behaviors.Comment: Submitted to Phys. Rev. Let

Signature of Magnetic Phase Separation in the Ground State of Pr1-xCaxMnO3

Neutron scattering has been used to investigate the evolution of the long- and short-range charge-ordered (CO), ferromagnetic (FM), and antiferromagnetic (AF) correlations in single crystals of Pr1-xCaxMnO3. The existence and population of spin clusters as refected by short-range correlations are found to drastically depend on the doping (x) and temperature (T). Concentrated spin clusters coexist with long-range canted AF order in a wide temperature range in x = 0.3 while clusters do not appear in x = 0.4 crystal. In contrast, both CO and AF order parameters in the x = 0.35 crystal show a precipitous decrease below ~ 35 K where spin clusters form. These results provide direct evidence of magnetic phase separation and indicate that there is a critical doping x_c (close to x = 0.35) that divides the phase-separated site-centered from the homogeneous bond-centered or charge-disproportionated CO ground state.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Letter