EPR observation of phase transitions in calcium cadmium acetate hexahydrate: Using Mn2+ and Cu2+ ions as probe

Results of temperature dependence of EPR spectra of Mn2+ and Cu2+ ions doped calcium cadmium acetate hexahydrate (CaCd(CH3COO)4•6H2O) have been reported. The investigation has been carried out in the temperature range between room temperature ( 300 K) and liquid nitrogen temperature. A I-order phase transition at 146 ± 0.5 K has been confirmed. In addition a new II-order phase transition at 128 ± 1 K has been detected for the first time. There is evidence of large amplitude hindered rotations of CH3 groups which become frozen at 128 K. The incorporation of Cu2+ and Mn2+ probes at Ca2+ and Cd2+ sites respectively provide evidence that the phase transitions are caused by the molecular rearrangements of the common coordinating acetate groups between Ca2+ and Cd2+ sites. In contradiction to the previous reports of a change of symmetry from tetragonal to orthorhombic below 140 K, the symmetry of the host is concluded to remain tetragonal in all the three observed phases between room temperature and liquid nitrogen temperature.

Estimation of cosmological parameters from neutral hydrogen observations of the post-reionization epoch

The emission from neutral hydrogen (HI) clouds in the post-reionization era (z <= 6), too faint to be individually detected, is present as a diffuse background in all low frequency radio observations below 1420MHz. The angular and frequency fluctuations of this radiation (similar to 1 mK) are an important future probe of the large-scale structures in the Universe. We show that such observations are a very effective probe of the background cosmological model and the perturbed Universe. In our study we focus on the possibility of determining the redshift-space distortion parameter beta, coordinate distance r(nu), and its derivative with redshift r(nu)('). Using reasonable estimates for the observational uncertainties and configurations representative of the ongoing and upcoming radio interferometers, we predict parameter estimation at a precision comparable with supernova Ia observations and galaxy redshift surveys, across a wide range in redshift that is only partially accessed by other probes. Future HI observations of the post-reionization era present a new technique, complementing several existing ones, to probe the expansion history and to elucidate the nature of the dark energy.

Regional differentiationnext term in previous termbull sperm plasma membranesnext term

previous termBull spermnext term heads and tails have been separated by proteolytic digestion (trypsin) and previous termplasma membranesnext term have been isolated, using discontinuous sucrose density gradient centrifugation. previous termPlasma membranenext term bound Ca2+-ATPase is shown to be associated mostly with the tail previous termmembranes.next term Pyrene excimer fluorescence and diphenylhexatriene fluorescence polarization experiments indicate a more fluid lipid phase in the tail region. Differences in surface charge distribution have been found, using 1-anilinonaphthalene-8-sulfonate and Tb3+ as fluorescent probes.

Kinetics of interaction of Cotton Leaf Curl Kokhran Virus-Dabawali (CLCuKV-Dab) coat protein and its mutants with ssDNA

Gemini viral assembly and transport of viral DNA into nucleus for replication, ssentially involve DNA-coat protein interactions. The kinetics of interaction of Cotton LeafCtirl Kokhran Virus-Dabawali recombinant coat protein (rCP) with DNA was studied by electrophoretic mobility shift assay (EMSA) and Surface plasmon resonance (SPR). The rCP interacted with ssDNA with a K-A, of 2.6 +/- 0.29 x 10(8) M-1 in a sequence non-specific manner. The CP has a conserved C2H2 type zinc finger motif composed of residues C68, C72, H81 and H85. Mutation of these residues to alanine resulted in reduced binding to DNA probes. The H85A mutant rCP showed the least binding with approximately 756 fold loss in the association rate and a three order magnitude decrease in the binding affinity as compared to rCP. The CP-DNA interactions via the zinc finger motif could play a Crucial role ill Virus assembly and in nuclear transport. (C) 2009 Elsevier Inc.

Sequences that adopt non-B-DNA conformation in form V DNA as probed by enzymic methylation

pBR322 form V DNA is a highly torsionally strained molecule with a linking number of zero. We have used sequence- specific DNA methylases as probes for B-DNA in this molecule, exploiting the inability of methylases to methylate single-stranded DNA and Z-DNA, both of which are known to occur in form V DNA. Some sequences in form V DNA were shown to be totally in the B-form, others were totally in an altered, unmethylatable conformation, while still other sites appeared to exist partly in altered and partly in normal B-conformation. Some potential Z-forming sequences (alternating pyrimidine/purine) of less than seven base-pairs were not in the Z conformation in form V DNA, whereas others did adopt an altered structure, indicating a modulating influence of flanking sequences. Furthermore, regions of imperfect alternating pyrimidine/purine structure were sometimes capable of adopting an altered structure. In addition, some regions of altered structure had no apparent Z-forming sequences, nor were they in polypurine stretches, which have also been proposed to form left-handed DNA. These non-B-DNA conformations may represent novel left-handed helical structures or sequences that become single stranded under torsional strain. Long regions of either altered (unmethylatable) DNA or B-DNA were not always observed. In fact, one region showed three transitions between B-like DNA and altered structure within 26 base-pairs.

Electroconductance in single-wall carbon nanotubes

A comparative study of the electric-field induced hopping transport probes the effective dimensionality (D) in bulk and ultrathin films of single-wall carbon nanotubes (SWNTs). The values of the scaling function exponents for the electroconductance are found to be consistent with that in three-dimensional and two-dimensional systems. The significant difference in threshold voltage in these two types of SWNTs is a consequence of the variation in the number of energetically favorable sites available for charge carriers to hop by using the energy from the field. Furthermore, a modification to the magnetotransport is observed under high electric-fields.

Regional differentiation in bull sperm plasma-membranes

Bull sperm heads and tails have been separated by proteolytic digestion (trypsin) and plasma membranes have been isolated, using discontinuous sucrose density gradient centrifugation. Plasma membrane bound Ca2+-ATPase is shown to be associated mostly with the tail membranes. Pyrene excimer fluorescence and diphenylhexatriene fluorescence polarization experiments indicate a more fluid lipid phase in the tail region. Differences in surface charge distribution have been found, using 1-anilinonaphthalene-8-sulfonate and Tb3+ as fluorescent probes.

Fluorescent probe and NMR studies of the aggregation of bile salts in aqueous solution

The binding of the fluorescent probes 1-anilino-8-naphthalene sulfonate and dansyl cadaverine to the sodium salts of cholic, deoxycholic and dehydrocholic acids has been investigated. Enhanced probe solubilisation accompanies aggregation. Monitoring of fluorescence intensities as a function of bile salt concentration permits the detection of primary micelle formation, as well as secondary association. The transition concentrations obtained by fluorescence are in good agreement with values determined for the critical micelle concentrations, by other methods. Differences in the behaviour of cholate and deoxycholate have been noted. Fluorescence polarisation studies of 1,6-diphenyl-1,3,5-hexatriene solubilised in bile salt micelles suggest a higher microviscosity for the interior of the deoxycholate micelle as compared to cholate. 1H NMR studies of deoxycholate over the range 1–100 mg/ml suggest that micelle formation leads to a greater immobilisation of the C18 and C19 methyl groups as compared to the C21 methyl group. Well resolved 13C resonances are observed for all three steroids even at high concentration. Both fluorescence and NMR studies confirm that dehydrocholate does not aggregate.

Use of transverse beam polarization to probe anomalous V V H interactions at a Linear Collider

We investigate use of transverse beam polarization in probing anomalous coupling of a Higgs boson to a pair of vector bosons, at the International Linear Collider (ILC). We consider the most general form of V V H (V = W/Z) vertex consistent with Lorentz invariance and investigate its effects on the process e(+)e(-) -> f (f) over barH, f being a light fermion. Constructing observables with definite C P and naive time reversal ((T) over tilde) transformation properties, we find that transverse beam polarization helps us to improve on the sensitivity of one part of the anomalous Z Z H Coupling that is odd under C P. Even more importantly it provides the possibility of discriminating from each other, two terms in the general Z Z H vertex, both of which are even under C P and (T) over bar. Use of transversebeam polarization when combined with information from unpolarized and linearly polarized beams therefore, allows one to have completely independent probes of all the different parts of a general ZZH vertex.

Mapping of assembled epitopic regions of human chorionic gonadotropin reveals proximity of CTP alpha to the determinant loop beta 93-100

Three overlapping assembled epitopes of beta hCG have been mapped using MAb probes and a single step solid phase radioimmunoassay. These epitopes have been shown to be at receptor binding region comprising of the loop region beta Cys93-Cys100. Importance of disulphide bonds in maintaining integrity of these epitopes is assessed. Two MAbs (INN 58 and INN 22) interact with the beta region as well as the alpha C-terminal peptide, while the other MAb INN 24 interacts with only the beta region. Cross-reactivity pattern with beta hCG and hLH as web as the reported crystal structure of hCG substantiates the epitope identification. The results demonstrate utility of MAbs as probes in investigations on three-dimensional structure of gonadatropins.

Triplet repeat polymorphism & fragile X syndrome in the Indian context

Mental retardation due to fragile X syndrome is one of the genetic disorders caused by tripler repeat expansion, CGG repeat involved in this disease is known to exhibit polymorphism even among normal individuals. Here we describe the development of suitable probes for detection of polymorphism in CGG repeat at FMR1 locus as well as the diagnosis of fragile X syndrome. Using these methods polymorphism at the FMR1 locus has been examined in 161 individuals. Ninety eight patients with unclassified mental retardation were examined, of whom 7 were found to have the expanded (CGG) allele at the FMR1 locus, The hybridization pattern for two patients has been presented as representative data.

A fluctuation-based characterization of athermal phase transitions:Application to shape memory alloys

We employ a fluctuation-based technique to investigate the athermal component associated with martensite phase transition, which is a prototype of temperature-driven structural transformation. Statistically, when the phase transition is purely athermal, we find that the temporal sequence of avalanches under constant drive is insensitive to the drive rate. We have used fluctuations in electrical resistivity or noise in nickel titanium shape memory alloys in three different forms: a thin film exhibiting well-defined transition temperatures,a highly disordered film, and a bulk wire of rectangular cross-section. Noise is studied in the realm of dynamic transition,viz.while the temperature is being ramped, which probes into the kinetics of the transformation at real time scales,and could probably stand out as a promising tool for material testing in various other systems, including nanoscale devices.

W physics at the ILC with polarized beams as a probe of the Littlest Higgs model

We study the possibility of using W pair production and leptonic decay of one of the W's at the ILC with polarized beams as a probe of the Littlest Higgs Model. We consider cross-sections, polarization fractions of the W's, leptonic decay energy and angular distributions, and left-right polarization asymmetry as probes of the model. With parameter values allowed by present experimental constraints detectable effects on these observables at typical ILC energies of 500 GeV and 800 GeV will be present. Beam polarization is further found to enhance the sensitivity.

Variations in the Levels of Chloroplast tRNAs and Aminoacyl-tRNA Synthetases in Senescing Leaves of Phaseolus vulgaris

The relative amounts of chloroplast tRNAs(Leu), tRNA(Glu), tRNA(Phe), tRNAs(Thr), and tRNA(Tyr) and of chloroplastic and cytoplasmic aminoacyl-tRNA synthetases were compared in green leaves, yellowing senescing leaves, and N(6)-benzyladenine-treated senescing leaves from bean (Phaseolus vulgaris, var Contender). Aminoacylation of the tRNAs using Escherichia coli aminoacyl-tRNA synthetases indicated that in senescing leaves the relative amount of chloroplast tRNA(Phe) was significantly lower than in green leaves. Senescing leaves treated with N(6)-benzyladenine contained higher levels of this tRNA than untreated senescing leaves. No significant change in the relative amounts of chloroplast tRNAs(Leu), tRNAs(Thr), and tRNA(Tyr) was detected in green, yellow senescing, or N(6)-benzyladine-treated senescing leaves. Relative levels of chloroplast tRNAs were also estimated by hybridization of tRNAs to DNA blots of gene specific probes. These experiments confirmed the results obtained by aminoacylation and revealed in addition that the relative level of chloroplast tRNA(Glu) is higher in senescing leaves than in green leaves. Transcription run-on assays indicated that these changes in tRNA levels are likely to be due to a differential rate of degradation rather than to a differential rate of transcription of the tRNA genes. Chloroplastic and cytoplasmic leucyl-, phenylalanyl-, and tyrosyl-tRNA synthetase activities were greatly reduced in senescing leaves as compared to green leaves, whereas N(6)-benzyladenine-treated senescing leaves contained higher enzyme activities than untreated senescing leaves. These results suggest that during senescence, as well as during senescence-retardation by cytokinins, changes in enzyme activities, such as aminoacyl-tRNA synthetases, rather than reduced levels of tRNAs, affect the translational capacity of chloroplasts.

Fluorescent probe studies of biomembranes and model systems. The design and use of anionic site reporters

The fluorescence properties of a homologous series of fluorescent alkylamines are described. The binding of the probes to crythrocyte membranes increases with the length of the alkyl chain. The probes are shown to interact more strongly with membranes than with protein and lipid model systems. The binding of the probes to the membrane is sensitive to the cation concentration of the medium.