Rotating crystal ESR cavity for angular variation studies at room temperature

We describe an X-band ESR cavity for angular variation studies on single crystals at room temperature. The cavity was found to have a high Q over wide rotation angles. Review of Scientific Instruments is copyrighted by The American Institute of Physics.

Singlet emission studies on porphyrins appended with heterocyclic bases

Porphyrins appended in the meso positions with 1,2-diazole, indole and quinoline are shown to exhibit enhanced fluorescence quantum yields relative to meso tetraphenyl porphyrin. The singlet emission yields decrease with the number of appended heterocyclic bases. An intramolecular charge transfer resonance mechanism has been advanced to interpret these results.

High-Pressure Low-Temperature Locknut Cell For Both Electron-Paramagnetic-Res And Nmr-Studies To 10 Kilobars And 77-K

A locked high-pressure cell with working pressure range up to 10 kbars suitable for low-temperature studies to 77 K has been described. It can be used for both EPR and NMR studies of single crystals (and other solid samples). The high-pressure seal and all other aspects of the cell remain the same for either application. Only a change of the bottom plug is required for a switch from a nuclear-magnetic-resonance (NMR) to an electron-paramagnetic-resonance (EPR) experiment. Details of the procedure for the calibration of pressure inside the cell at various temperatures are discussed. The performance of the cell in EPR (Cr3+ion) and NMR (27Al nucleus) studies is reported.

Conformational analysis of small disulfide loops. Spectroscopic and theoretical studies on a synthetic cyclic tetrapeptide containing cystine

The conformational analysis of the synthetic peptide Boc-Cys-Pro-Val-Cys-NHMe has been carried out, as a model for small disulfide loops, in biologically active polypeptides. 'H NMR studies (270 MHz) establish that the Val(3) and Cys(4) NH groups are solvent shielded, while 13C studies establish an all-trans peptide backbone. Circular dichroism and Raman spectroscopy provide evidence for a right-handed twist of the disulfide bond. Analysis of the vicinal (JaB)c oupling constants for the two Cys residues establishes that XI - *60° for Cys(4), while some flexibility is suggested at Cys( 1). Conformational energy calculations, imposing intramolecular hydrogen bonding constraints, favor a P-turn (type I) structure with Pro(2)-Va1(3) as the corner residues. Theoretical and spectroscopic results are consistent with the presence of a transannular 4 - 1 hydrogen bond between Cys( 1) CO and Cys(4) NH groups, with the Val NH being sterically shielded from the solvent environment.

Low-temperature and high-pressure Raman and x-ray studies of pyrochlore Tb2Ti2O7: Phonon anomalies and possible phase transition

We have carried out temperature- and pressure-dependent Raman and x-ray measurements on single crystals of Tb2Ti2O7. We attribute the observed anomalous temperature dependence of phonons to phonon-phonon anharmonic interactions. The quasiharmonic and anharmonic contributions to the temperature-dependent changes in phonon frequencies are estimated quantitatively using mode Grüneisen parameters derived from pressure-dependent Raman experiments and bulk modulus from high-pressure x-ray measurements. Further, our Raman and x-ray data suggest a subtle structural deformation of the pyrochlore lattice at ~9 GPa. We discuss possible implications of our results on the spin-liquid behavior of Tb2Ti2O7.

Assessment of prey overlap between a native (Polistes humilis) and an introduced (Vespula germanica) social wasp using morphology and phylogenetic analyses of 16S rDNA

In newly invaded communities, interspecific competition is thought to play an important role in determining the success of the invader and its impact on the native community. In southern Australia, the native Polistes humilis was the predominant social wasp prior to the arrival of the exotic Vespula germanica (Hymenoptera: Vespidae). Both species forage for similar resources (water, pulp, carbohydrate and protein prey), and concerns have arisen about potential competition between them. The aim of this study was to identify the protein foods that these wasps feed on. As many prey items are masticated by these wasps to the degree that they cannot be identified using conventional means, morphological identification was complemented by sequencing fragments of the mitochondrial 16S rRNA gene. GenBank searches using blast and phylogenetic analyses were used to identify prey items to at least order level. The results were used to construct complete prey inventories for the two species. These indicate that while P. humilis is restricted to feeding on lepidopteran larvae, V. germanica collects a variety of prey of invertebrate and vertebrate origin. Calculated values of prey overlap between the two species are used to discuss the implications of V. germanica impacting on P. humilis. Results obtained are compared to those gained by solely 'conventional' methods, and the advantages of using DNA-based taxonomy in ecological studies are emphasized.

Studies On Thermal-Decomposition Of Double-Base Propellants

The scanning thermogram of a block sample of a double-base propellant shows a shoulder around 200°C which is not observed in a powder sample of the sample propellant. The heat of decomposition was also found to be different In the two cases. Product analysis and activation energy calculations show that nitroglycerine un dergoes decomposition in the block sample, whereas it vaporizes in the powder sample.

Quambalaria species associated with plantation and native eucalypts in Australia

This study aimed to determine which species of Quambalaria are associated with shoot blight symptoms on Corymbia spp. An additional aim was to determine the presence and impact of quambalaria shoot blight on Eucalyptus species used in plantation development in subtropical and tropical regions of eastern Australia. Surveys identified three Quambalaria spp. -Q. pitereka, Q. eucalypti and Q. cyanescens - from native and plantation eucalypts, as well as amenity plantings, including the first confirmed report of Q. eucalypti from Eucalyptus plantations in Australia. Symptom descriptions and morphological studies were coupled with phylogenetic studies using ITS rDNA sequence data. Quambalaria pitereka was the causal agent of blight symptoms on species and hybrids in the Corymbia complex. Quambalaria eucalypti was identified from Eucalyptus species and a single Corymbia hybrid. Quambalaria cyanescens was detected from native and plantation Corymbia spp.

The suitability of non-target native mangroves for the survival and development of the lantana bug Aconophora compressa, an introduced weed biological control agent

Aconophora compressa (Hemiptera: Membracidae), a biological control agent introduced against the weed Lantana camara (Verbenaceae) in Australia, has since been observed on several non-target plant species, including native mangrove Avicennia marina (Acanthaceae). In this study we evaluated the suitability of two native mangroves, A. marina and Aegiceras corniculatum (Myrsinaceae), for the survival and development of A. compressa through no-choice field cage studies. The longevity of females was significantly higher on L. camara (57.7 ± 3.8 days) than on A. marina (43.3 ± 3.3 days) and A. corniculatum (45.7 ± 3.8 days). The proportion of females laying eggs was highest on L. camara (72%) followed by A. marina (36%) and A. corniculatum (17%). More egg batches per female were laid on L. camara than on A. marina and A. corniculatum. Though more nymphs per shoot emerged on L. camara (29.9 ± 2.8) than on A. marina (13 ± 4.8) and A. corniculatum (10 ± 5.3), the number of nymphs that developed through to adults was not significantly different. The duration of nymphal development was longer on A. marina (67 ± 5.8 days) than on L. camara (48 ± 4 days) and A. corniculatum (43 ± 4.6 days). The results, which are in contrast to those from previous glasshouse and quarantine trials, provide evidence that A. compressa adults can survive, lay eggs and complete nymphal development on the two non-target native mangroves in the field under no-choice condition.

At a Crossroad: Immigration Reform and American Unionism

"Since the founding days of the Republic, the relationship between American unionism and mass immigration has been contentious. No issue has caused the labor movement more agony and irony. It is no surprise, therefore, that throughout its history the American labor movement has sought to influence U.S. immigration policy."

Studies on tryptophan residues of Abrus agglutinin Stopped-flow kinetics of modification and fluorescence-quenching studies

The presence of two essential tryptophan residues/molecule was implicated in the binding site of Abrus agglutinin [Patanjali, Swamy, Anantharam, Khan & Surolia (1984) Biochem. J. 217, 773-781]. A detailed study of the stopped-flow kinetics of the oxidation of tryptophan residues revealed three classes of tryptophan residues in the native protein. A discrete reorganization of tryptophan residues into two phases was observed upon ligand binding. The heterogeneity of tryptophan exposure was substantiated by quenching studies with acrylamide, succinimide and Cs+. Our study revealed the microenvironment of tryptophan residues to be hydrophobic, and also the presence of acidic amino acid residues in the vicinity of surface-localized tryptophan residues.

Circular dichroism and nuclear magnetic resonance studies on the complexation of valinomycin with calcium

Complexation of valinomycin (VM) with the divalent cation Ca2+ in a lipophilic solvent, acetonitrile (CH3-CN), has been studied by using circular dichroism and proton and carbon- 13 nuclear magnetic resonance (‘H NMR and I3C NMR). From analyses of the spectral data, it is concluded that VM forms a 2:l (peptideion-peptide) sandwich complex with Ca2+, at low concentration of VM. At moderate conocentrations of the salt, in addition to the sandwich complex, an equimolar (1:l) complex different from those observed for potassium and sodium is also observed. At very large concentrations of the calcium salt, the data suggested a complex with a conformation similar to that of the free VM in polar solvents. Possible conformations for the sandwich and the equimolar VM-calcium complexes are proposed.

beta.-Turn conformation of N-acetyl-L-prolylglycyl-L-phenylalanine. Crystal structure and solution studies

Pro-Gly segments in peptides and proteins are prone to adopt the 0-turn conformation. This paper reports experimental data for the presence of this conformation in a linear tripeptide N-acetyl-L-prolylglycyl-L-phenylalanineb oth in the solid state and in solution. X-ray diffraction data on the tripeptide crystal show that it exists in the type I1 0-turn conformation. CD and proton NMR data show that this conformation persists in trifluoroethanol and methanol solutions in equilibrium with the nonhydrogen-bonded structures. Isomerization around the acetyl-prolyl bond is seen to take place in dimethyl sulfoxide solutions of the tripeptide.