Evolution of ferromagnetism from a frustrated state in LixNi(2-x)O2 (0.67 < x < 0.98)

Two-dimensional triangular-lattice antiferromagnetic systems continue to be an interesting area in condensed matter physics and LiNiO2 is one such among them. Here we present a detailed experimental magnetic study of the quasi-stoichiometric LixNi2-xO2 system (0.67deficiency in a controlled manner, an increase in the ordering temperature is observed. Most strikingly, with the Li deficiency the nature of the magnetic ground state is changed from spin glass to ferromagnetic, with two intermediate states-namely cluster glass and re-entrant spin glass. The critical behaviour of the re-entrant spin glass is also studied here. The critical exponents (beta, gamma and delta) are extracted from the modified Arrot plot, Kouvel-Fisher method, and critical isotherm analysis. The critical exponents match with the long-range mean-field model. The values of the critical exponents are confirmed by the Widom scaling law: delta = 1 + gamma beta(-1). Furthermore, the universality class of the scaling relations is verified, where the scaled m and scaled h collapse into two branches. Finally, based on our observations, a phase diagram is constructed.

Classification of Myopathies on Molecular basis in Drosophila using Raman spectroscopy

Myopathies are muscular diseases in which muscle fibers degenerate due to many factors such as nutrient deficiency, infection and mutations in myofibrillar etc. The objective of this study is to identify the bio-markers to distinguish various muscle mutants in Drosophila (fruit fly) using Raman Spectroscopy. Principal Components based Linear Discriminant Analysis (PC-LDA) classification model yielding >95% accuracy was developed to classify such different mutants representing various myopathies according to their physiopathology.

Molecular flexibility of Mycobacterium tuberculosis ribosome recycling factor and its functional consequences: An exploration involving mutants

Internal mobility of the two domain molecule of ribosome recycling factor (RRF) is known to be important for its action. Mycobacterium tuberculosis RRF does not complement E. coli for its deficiency of RRF (in the presence of E. coli EF-G alone). Crystal structure had revealed higher rigidity of the M. tuberculosis RRF due to the presence of additional salt bridges between domains. Two inter-domain salt bridges and one between the linker region and the domain containing C-terminal residues were disrupted by appropriate mutations. Except for a C-terminal deletion mutant, all mutants showed RRF activity in E. coli when M. tuberculosis EF-G was also co-expressed. The crystal structures of the point mutants, that of the C-terminal deletion mutant and that of the protein grown in the presence of a detergent, were determined. The increased mobility resulting from the disruption of the salt bridge involving the hinge region allows the appropriate mutant to weakly complement E. coli for its deficiency of RRF even in the absence of simultaneous expression of the mycobacterial EF-G. The loss of activity of the C-terminal deletion mutant appears to be partly due to the rigidification of the molecule consequent to changes in the hinge region.

Hypersensitivity of hypoxia grown Mycobacterium smegmatis to DNA damaging agents: Implications of the DNA repair deficiencies in attenuation of mycobacteria

Mycobacteria are an important group of pathogenic bacteria. We generated a series of DNA repair deficient strains of Mycobacterium smegmatis, a model organism, to understand the importance of various DNA repair proteins (UvrB, Ung, UdgB, MutY and Fpg) in survival of the pathogenic strains. Here, we compared tolerance of the M. smegmatis strains to genotoxic stress (ROS and RNI) under aerobic, hypoxic and recovery conditions of growth by monitoring their survival. We show an increased susceptibility of mycobacteria to genotoxic stress under hypoxia. UvrB deficiency led to high susceptibility of M. smegmatis to the DNA damaging agents. Ung was second in importance in strains with single deficiencies. Interestingly, we observed that while deficiency of UdgB had only a minor impact on the strain's susceptibility, its combination with Ung deficiency resulted in severe consequences on the strain's survival under genotoxic stress suggesting a strong interdependence of different DNA repair pathways in safeguarding genomic integrity. Our observations reinforce the possibility of targeting DNA repair processes in mycobacteria for therapeutic intervention during active growth and latency phase of the pathogen. High susceptibility of the UvrB, or the Ung/UdgB deficient strains to genotoxic stress may be exploited in generation of attenuated strains of mycobacteria. (C) 2013 Elsevier Ireland Ltd. All rights reserved.

Size Control and Magnetic Property Trends in Cobalt Ferrite Nanoparticles Synthesized Using an Aqueous Chemical Route

Cobalt ferrite (CoFe2O4) is an engineering material which is used for applications such as magnetic cores, magnetic switches, hyperthermia based tumor treatment, and as contrast agents for magnetic resonance imaging. Utility of ferrites nanoparticles hinges on its size, dispersibility in solutions, and synthetic control over its coercivity. In this work, we establish correlations between room temperature co-precipitation conditions, and these crucial materials parameters. Furthermore, post-synthesis annealing conditions are correlated with morphology, changes in crystal structure and magnetic properties. We disclose the synthesis and process conditions helpful in obtaining easily sinterable CoFe2O4 nanoparticles with coercive magnetic flux density (H-c) in the range 5.5-31.9 kA/m and M-s in the range 47.9-84.9 A.m(2)Kg(-1). At a grain size of similar to 54 +/- 2 nm (corresponding to 1073 K sintering temperature), multi-domain behavior sets in, which is indicated by a decrease in H-c. In addition, we observe an increase in lattice constant with respect to grain size, which is the inverse of what is expected of in ferrites. Our results suggest that oxygen deficiency plays a crucial role in explaining this inverse trend. We expect the method disclosed here to be a viable and scalable alternative to thermal decomposition based CoFe2O4 synthesis. The magnetic trends reported will aid in the optimization of functional CoFe2O4 nanoparticles

The Presence of Multiple Cellular Defects Associated with a Novel G50E Iron-Sulfur Cluster Scaffold Protein ( ISCU) Mutation Leads to Development of Mitochondrial Myopathy

Background: Muscle-specific deficiency of iron-sulfur (Fe-S) cluster scaffold protein (ISCU) leads to myopathy. Results: Cells carrying the myopathy-associated G50E ISCU mutation demonstrate impaired Fe-S cluster biogenesis and mitochondrial dysfunction. Conclusion: Reduced mitochondrial respiration as a result of diminished Fe-S cluster synthesis results in muscle weakness in myopathy patients. Significance: The molecular mechanism behind disease progression should provide invaluable information to combat ISCU myopathy. Iron-sulfur (Fe-S) clusters are versatile cofactors involved in regulating multiple physiological activities, including energy generation through cellular respiration. Initially, the Fe-S clusters are assembled on a conserved scaffold protein, iron-sulfur cluster scaffold protein (ISCU), in coordination with iron and sulfur donor proteins in human mitochondria. Loss of ISCU function leads to myopathy, characterized by muscle wasting and cardiac hypertrophy. In addition to the homozygous ISCU mutation (g.7044GC), compound heterozygous patients with severe myopathy have been identified to carry the c.149GA missense mutation converting the glycine 50 residue to glutamate. However, the physiological defects and molecular mechanism associated with G50E mutation have not been elucidated. In this report, we uncover mechanistic insights concerning how the G50E ISCU mutation in humans leads to the development of severe ISCU myopathy, using a human cell line and yeast as the model systems. The biochemical results highlight that the G50E mutation results in compromised interaction with the sulfur donor NFS1 and the J-protein HSCB, thus impairing the rate of Fe-S cluster synthesis. As a result, electron transport chain complexes show significant reduction in their redox properties, leading to loss of cellular respiration. Furthermore, the G50E mutant mitochondria display enhancement in iron level and reactive oxygen species, thereby causing oxidative stress leading to impairment in the mitochondrial functions. Thus, our findings provide compelling evidence that the respiration defect due to impaired biogenesis of Fe-S clusters in myopathy patients leads to manifestation of complex clinical symptoms.

Estimation of the 2.0(5) helix type i -> i hydrogen bond energy at Aib*-Oxa motif: an isodesmic approach

Bending at the valence angle N-C-alpha-C' (tau) is a known control feature for attenuating the stability of the rare intramolecular hydrogen bonded pseudo five-membered ring C-5 structures, the so called 2.0(5) helices, at Aib. The competitive 3(10)-helical structures still predominate over the C5 structures at Aib for most values of tau. However at Aib*, a mimic of Aib where the carbonyl 0 of Aib is replaced with an imidate N (in 5,6-dihydro-4H-1,3-oxazine = Oxa), in the peptidomimic Piv-Pro-Aib*-Oxa (1), the C(5)i structure is persistent in both crystals and in solution. Here we show that the i -> i hydrogen bond energy is a more determinant control for the relative stability of the C5 structure and estimate its value to be 18.5 +/- 0.7 kJ/mol at Aib* in 1, through the computational isodesmic reaction approach, using two independent sets of theoretical isodesmic reactions. (C) 2014 Elsevier Ltd. All rights reserved.

First-Principles Study of Structure, Vibrational, and Elastic Properties of Stoichiometric and Calcium-Deficient Hydroxyapatite

Hydroxyapatite (HAp), a primary constituent of human bone, is usually nonstoichiometric with varying Ca/P molar ratios, with the well-known fact that Ca deficiency can cause marked reductions in its mechanical properties. To gain insights into the mechanism of this degradation, we employ first-principles calculations based on density functional theory and determine the effects of Ca deficiency on structure, vibrational, and elastic properties of HAp. Our simulation results confirm a considerable reduction in the elastic constants of HAp due to Ca deficiency, which was experimentally reported earlier. Stress-induced transformation of the Ca-deficient defected structure into a metastable state upon the application of stress could be a reason for this. Local structural stability of HAp and Ca-deficient HAp structures is assessed with full phonon dispersion studies. Further, specific signatures in the computed vibrational spectra for Ca deficiency in HAp can be utilized in experimental characterization of different types of defected HAp.

Targeting Mycobacterium tuberculosis nucleoid-associated protein HU with structure-based inhibitors

The nucleoid-associated protein HU plays an important role in maintenance of chromosomal architecture and in global regulation of DNA transactions in bacteria. Although HU is essential for growth in Mycobacterium tuberculosis (Mtb), there have been no reported attempts to perturb HU function with small molecules. Here we report the crystal structure of the N-terminal domain of HU from Mtb. We identify a core region within the HU-DNA interface that can be targeted using stilbene derivatives. These small molecules specifically inhibit HU-DNA binding, disrupt nucleoid architecture and reduce Mtb growth. The stilbene inhibitors induce gene expression changes in Mtb that resemble those induced by HU deficiency. Our results indicate that HU is a potential target for the development of therapies against tuberculosis.

beta gamma-fused turn structures in sugar amino acid (SAA) containing cyclic tetrapeptides with alpha 3 delta architecture

The current manuscript describes conformational analysis of 15-membered cyclic tetrapeptides (CTPs), with alpha 3 delta architecture, containing sugar amino acids (SAA) having variation in the stereocenter at C5 carbon. Conformational analyses of both the series, in protected and deprotected forms, were carried out in DMSO-d(6) using various NMR techniques, supported by restrained MD calculations. It was intriguing to notice that the alpha 3 delta macrocycles got stabilized by both 10-membered beta-turn as well as a seven-membered gamma-turn, fused within the same macrocycle. The presence of fused sub-structures within a 15-membered macrocycle is rare to see. Also, the stereocenter variation at C5 did not affect the fused turn structures and exhibited similar conformations in both the series. The design becomes highly advantageous as fused reverse turn structures are occurring in the cyclic structure with minimalistic size macrocycle and this can be applied to develop suitable pharmacophores in the drug development process. (C) 2014 Elsevier Ltd. All rights reserved.

Multicomponent Assembly of Fluorescent-Tag Functionalized Ligands in Metal-Organic Frameworks for Sensing Explosives

Detection of trace amounts of explosive materials is significantly important for security concerns and pollution control. Four multicomponent metal organic frameworks (MOFs-12, 13, 23, and 123) have been synthesized by employing ligands embedded with fluorescent tags. The multicomponent assembly of the ligands was utilized to acquire a diverse electronic behavior of the MOFs and the fluorescent tags were strategically chosen to enhance the electron density in the MOFs. The phase purity of the MOFs was established by PXRD, NMR spectroscopy, and finally by singlecrystal XRD. Single-crystal structures of the MOFs-12 and 13 showed the formation of three-dimensional porous networks with the aromatic tags projecting inwardly into the pores. These electron-rich MOFs were utilized for detection of ex- plosive nitroaromatic compounds (NACs) through fluorescence quenching with high selectivity and sensitivity. The rate of fluorescence quenching for all the MOFs follows the order of electron deficiency of the NACs. We also showed the detection of picric acid (PA) by luminescent MOFs is not always reliable and can be misleading. This attracts our attention to explore these MOFs for sensing picryl chloride (PC), which is as explosive as picric acid and used widely to prepare more stable explosives like 2,4,6-trinitroaniline from PA. Moreover, the recyclability and sensitivity studies indicated that these MOFs can be reused several times with parts per billion (ppb) levels of sensitivity towards PC and 2,4,6-trinitrotoluene (TNT).

A predictive approach to CVD of crystalline layers of TMDs: the case of MoS2

Layered transition metal dichalcogenides (TMDs), such as MoS2, are candidate materials for next generation 2-D electronic and optoelectronic devices. The ability to grow uniform, crystalline, atomic layers over large areas is the key to developing such technology. We report a chemical vapor deposition (CVD) technique which yields n-layered MoS2 on a variety of substrates. A generic approach suitable to all TMDs, involving thermodynamic modeling to identify the appropriate CVD process window, and quantitative control of the vapor phase supersaturation, is demonstrated. All reactant sources in our method are outside the growth chamber, a significant improvement over vapor-based methods for atomic layers reported to date. The as-deposited layers are p-type, due to Mo deficiency, with field effect and Hall hole mobilities of up to 2.4 cm(2) V-1 s(-1) and 44 cm(2) V-1 s(-1) respectively. These are among the best reported yet for CVD MoS2.

Contrasting Electronic Requirements for C-H Binding and C-H Activation in d(6) Half-Sandwich Complexes of Rhenium and Tungsten

A computational study of the interaction half-sandwich metal fragments (metal=Re/W, electron count=d(6)), containing linear nitrosyl (NO+), carbon monoxide (CO), trifluorophosphine (PF3), N-heterocyclic carbene (NHC) ligands with alkanes are conducted using density functional theory employing the hybrid meta-GGA functional (M06). Electron deficiency on the metal increases with the ligand in the order NHC < CO < PF3 < NO+. Electron-withdrawing ligands like NO+ lead to more stable alkane complexes than NHC, a strong electron donor. Energy decomposition analysis shows that stabilization is due to orbital interaction involving charge transfer from the alkane to the metal. Reactivity and dynamics of the alkane fragment are facilitated by electron donors on the metal. These results match most of the experimental results known for CO and PF3 complexes. The study suggests activation of alkane in metal complexes to be facile with strong donor ligands like NHC. (C) 2015 Wiley Periodicals, Inc.

Rab9A is required for delivery of cargo from recycling endosomes to melanosomes

Melanosomes are a type of lysosome-related organelle that is commonly defective in Hermansky-Pudlak syndrome. Biogenesis of melanosomes is regulated by BLOC-1, -2, -3, or AP-1, -3 complexes, which mediate cargo transport from recycling endosomes to melanosomes. Although several Rab GTPases have been shown to regulate these trafficking steps, the precise role of Rab9A remains unknown. Here, we found that a cohort of Rab9A associates with the melanosomes and its knockdown in melanocytes results in hypopigmented melanosomes due to mistargeting of melanosomal proteins to lysosomes. In addition, the Rab9A-depletion phenotype resembles Rab38/ 32-inactivated or BLOC-3-deficient melanocytes, suggesting that Rab9A works in line with BLOC-3 and Rab38/ 32 during melanosome cargo transport. Furthermore, silencing of Rab9A, Rab38/ 32 or its effector VARP, or BLOC-3-deficiency in melanocytes decreased the length of STX13-positive recycling endosomal tubules and targeted the SNARE to lysosomes. This result indicates a defect in directing recycling endosomal tubules to melanosomes. Thus, Rab9A and its co-regulatory GTPases control STX13-mediated cargo delivery to maturing melanosomes.

Virulent Salmonella enterica infections can be exacerbated by concomitant infection of the host with a live attenuated S. enterica vaccine via Toll-like receptor 4-dependent interleukin-10 production with the involvement of both TRIF and MyD88.

During systemic disease in mice, Salmonella enterica grows intracellularly within discrete foci of infection in the spleen and liver. In concomitant infections, foci containing different S. enterica strains are spatially separated. We have investigated whether functional interactions between bacterial populations within the same host can occur despite the known spatial separation of the foci and independence of growth of salmonellae residing in different foci. In this study we have demonstrated that bacterial numbers of virulent S. enterica serovar Typhimurium C5 strain in mouse tissues can be increased by the presence of the attenuated aroA S. Typhimurium SL3261 vaccine strain in the same tissue. Disease exacerbation does not require simultaneous coinjection of the attenuated bacteria. SL3261 can be administered up to 48 hr after or 24 hr before the administration of C5 and still determine higher tissue numbers of the virulent bacteria. This indicates that intravenous administration of a S. enterica vaccine strain could potentially exacerbate an established infection with wild-type bacteria. These data also suggest that the severity of an infection with a virulent S. enterica strain can be increased by the prior administration of a live attenuated vaccine strain if infection occurs within 48 hr of vaccination. Exacerbation of the growth of C5 requires Toll-like receptor 4-dependent interleukin-10 production with the involvement of both Toll/interleukin-1 receptor-domain-containing adaptor inducing interferon-beta and myeloid differentiation factor 88.