Structural elucidation of a compound extracted from Streptomyces Sp.NLKB45.

A Streptomyces Sp. NLKB45 was isolated from the Nellore coastal region. After checking antimicrobial and antifungal activity the strain was subjected to fermentation in starch casein broth medium. HPLC was used to purify the culture filtrate after it had been extracted with ethyl acetate. The extract showed antibacterial and anticancer properties. The extract was processed and the compound isolated was further analyzed using FTIR, mass spectroscopic method and one- and two-dimensional NMR techniques. Based on the data gathered the compound was identified as 7-((5-methylpyridin-2-ylamino) (phenyl) methyl) quinolin-8-ol with a weight-average molecular weight of about 341 Da.

Weak ferromagnetism and magnetoelectric coupling through the spin-lattice coupling in (1-x)Pb(Fe2/3W1/3)O3-(x)BiFeO3 (x = 0.1 and 0.4) solid solution.

We report on the structure, spin-lattice and magneto-electric coupling in (1-x)Pb(Fe2/3W1/3)O3-(x)BiFeO3(where x = 0.1 and 0.4) (PBFW) solid solution synthesized through two-step solid-state reaction method. The room temperature (RT) crystallographic studies were carried out using x-ray diffraction and neutron diffraction measurements which show a single-phase Pseudocubic crystal system with Pm-3m space group. Rietveld refinement was carried out to obtain the structural parameters using Fullprof software and the observed structural parameters are in good agreement with the previous reports. Temperature-dependent neutron diffraction measurements reveal the presence of commensurate G-type antiferromagnetic structure. The magnetic structure was analyzed using the propagation wave vector k ∼ (½ ½ ½) for both the solid solutions. The obtained lattice constants increase linearly and the magnetic moment decrease with temperature, which shows a remarkable anomaly around the magnetic (T N ∼ 405 K for x = 0.1 and 531 K for x = 0.4) transition temperatures. This anomaly clearly indicates the existence of spin-lattice and magnetoelectric coupling. The magnetic susceptibility (ZFC and FC at 500 Oe) and M-H hysteresis loop measurements show spontaneous magnetic moment due to the Fe3+-O2--Fe3+ superexchange interaction coexisting with the weak ferromagnetism. Bifurcation of ZFC and FC curve reveals the strong anisotropic nature. Astonishingly, magnetic measurements show the non-zero magnetic moment above T N and broadening of the magnetic transition indicates the presence of short-range uncompensated sublattice weak ferromagnetic clusters in the paramagnetic region. The Mossbauer spectroscopy and electron paramagnetic resonance studies exhibit the RT magnetically ordered system and confirm the +3 state of Fe along with the fraction of Fe2+ ions.

Phonon and magnetoelastic coupling in Al0.5Ga0.5FeO3: Raman, magnetization and neutron diffraction studies.

The intriguing coupling phenomena among spin, phonon, and charge degrees of freedom in materials having magnetic, ferroelectric and/or ferroelastic order have been of research interest for the fundamental understanding and technological relevance. We report a detailed study on structure and phonons of Al0.5Ga0.5FeO3 (ALGF), a lead-free magnetoelectric material, carried out using variable temperature dependent powder neutron diffraction and Raman spectroscopy. Neutron diffraction studies suggest that Al3+ ions are distributed in one tetrahedrally (BO4) and three octahedrally (BO6) coordinated sites of the orthorhombic (Pc21n) structure and there is no structural transition in the temperature range of 7-800 K. Temperature dependent field-cooled and zero-field-cooled magnetization studies indicate ferrimagnetic ordering below 225 K (TN), and that is reflected in the low temperature powder neutron diffraction data. An antiferromagnetic type arrangement of Fe3+ ions with net magnetic moment of 0.13 µB/Fe3+ was observed from powder neutron diffraction analysis and it corroborates the findings from magnetization studies. At the magnetic transition temperature, no drastic change in lattice strain was observed, while significant changes in phonons were observed in the Raman spectra. The deviation of several mode frequencies from the standard anharmonicity model in the ferrimagnetic phase (below 240 K) is attributed to coupling effect between spin and phonon. Spin-phonon coupling effect is discernable from Raman bands located at 270, 425, 582, 695, 738, and 841 cm-1. Their coupling strengths (λ) have been estimated using our phonon spectra and magnetization results. BOn (n = 4, 6) libration (restricted rotation) mode at 270 cm-1 has the largest coupling constant (λ∼ 2.3), while the stretching vibrations located at 695 and 738 cm-1 have the lowest coupling constant (λ∼ 0.5). In addition to the libration mode, several internal stretching and bending modes of polyhedral units are strongly affected by spin ordering.

Spin phonon coupling in Mn doped HoFeO3 compounds exhibiting spin reorientation behaviour.

An investigation has been carried out on the spin phonon coupling in a series of isostructural polycrystalline orthorhombic (Space group Pnma) compounds HoFe1-X Mn X O3 (x ⩽ 0.6) exhibiting spin reorientation below Néel temperature (T N), using magnetization, neutron diffraction, and Raman scattering techniques. Mn doping leads to an anomalous increase in the spin reorientation temperature (T SR), shifting it close to room temperature from T SR ~ 60 K for x = 0 sample, and concomitant lowering of T N. The T SR is absent in samples for x ⩾ 0.5. The magnetic structure undergoes a transition at T SR from Γ4 → Γ1 in the Mn doped compounds as against Γ4 → Γ2 observed in HoFeO3 sample. In the region T < T N an anomalous softening of Raman phonon modes viz., B 2g(5) and B 3g(3), identified with the stretching motion and breathing mode, respectively, of Fe/Mn-O6 octahedra, is observed in compounds exhibiting spin-reorientation behaviour, indicating a spin-phonon coupling in these compounds. A quadratic correlation between the deviation of phonon frequency and variation of antiferromagnetic moment (Δω [Formula: see text] M 2) is observed in these compounds. The temperature evolution of the M2+ mode obtained from the analysis of neutron diffraction data based on symmetry adapted mode decomposition of the Pnma structure further corroborates the mode softening observation.

Screening and identification of novel isolate Streptomyces sp., NLKPB45 from Nellore costal region for its biomedical applications.

Actinobacteria, which are the prolific producers of antibiotics and significant suppliers to the pharmaceutical industry, can produce a wide variety of bioactive metabolites. An actinomycete strain designated NLKPB45 was isolated from mangrove soils samples of Nellore coastal regions Andhra Pradesh and assessed for antibiotic production and activity against pathogenic bacteria. From a total of 9 mangrove soil samples, 143 acinomycetes were isolated. Among the isolated them 6 actinomycetes strains showed potential antibacterial activity against at two tested pathogens gram positive and gram negative bacteria E. coli and S. aureus. The potent strain NLKPB45 was identified by 16S gene isolation and sequencing to the Streptomyces genus. The ethyl acetate extracts also as shown excellent antimicrobial activity against Salmonella sp., staphylococcus aureus, E. coli, and B. subtilus were detected in both the supernatant extract samples from fermentations of culture NLKPB45. The anticancer activity of extracts in the HeLa with IC50 value of 37.1924 µg/ml, MCF-7 IC50 value of 40.9177 µg/ml and HT 29 IC50 value of 43.3758 µg/ml.

High Pressure Phases and Amorphization of a Negative Thermal Expansion Compound TaVO5.

Negative thermal expansion material TaVO5 is recently reported to have pressure induced structural phase transition and irreversible amorphization at 0.2 and above 8 GPa, respectively. Here, we have investigated the high pressure phase of TaVO5 using in situ neutron diffraction studies. The first high pressure phase is identified to be monoclinic P21/ c phase, same as the low temperature phase of TaVO5. On heating, amorphous TaVO5 transformed to a new crystalline phase, which showed signatures of higher coordination of vanadium indicating pressure induced amorphization (PIA). PIA observed in TaVO5 might be due to the kinetic hindrance of pressure induced decomposition (PID) into a compound with higher coordination of vanadium. Mechanism of PIA observed in TaVO5 is investigated by carrying out ex situ Raman, XRD, XPS, and XAS measurements. We have also proposed a pressure-temperature phase diagram of TaVO5 qualitatively delineating the phase boundaries between the ambient orthorhombic, monoclinic, and amorphous phases.

Nonmonotonic particle-size-dependence of magnetoelectric coupling in strained nanosized particles of BiFeO3.

Using high resolution powder x-ray and neutron diffraction experiments, we determined the off-centered displacement of the ions within a unit cell and magnetoelectric coupling in nanoscale BiFeO3 (≈20-200 nm). We found that both the off-centered displacement of the ions and magnetoelectric coupling exhibit nonmonotonic variation with particle size. They increase as the particle size reduces from bulk and reach maximum around 30 nm. With further decrease in particle size, they decrease precipitously. The magnetoelectric coupling is determined by the anomaly in off-centering of ions around the magnetic transition temperature (T N ). The ions, in fact, exhibit large anomalous displacement around the T N which is analyzed using group theoretical approach. It underlies the nonmonotonic particle-size-dependence of off-centre displacement of ions and magnetoelectric coupling. The nonmonotonic variation of magnetoelectric coupling with particle size is further verified by direct electrical measurement of remanent ferroelectric hysteresis loops at room temperature under zero and ∼20 kOe magnetic field. Competition between enhanced lattice strain and compressive pressure appears to be causing the nonmonotonic particle-size-dependence of off-centre displacement while coupling between piezo and magnetostriction leads to nonmonotonicity in the variation of magnetoelectric coupling.

Revealing magnetic ordering and spin-phonon coupling in Y1-x Tb x MnO3 (0.1 ⩽ x ⩽ 0.3) compounds.

The structural and magnetic properties of the Y1-x Tb x MnO3 (0.1 ⩽ x ⩽ 0.3) compounds were investigated. Neutron diffraction patterns for all three samples, recorded at room temperature (RT), were fitted to the nuclear structure confirming the paramagnetic nature of the compounds. At 2.8 K, for the x = 0.1 sample magnetic moments of the Tb3+ ionic as well as Mn3+ ionic were ordered. At 5 K for the x = 0.2 sample only the Mn3+ ionic magnetic moments were ordered. There were six sites for Mn atoms. Three on the z = 0 plane and three on the z = 0.5 plane (where z corresponds to +c axis).The Mn3+ionic moments were confined to the a-b plane with a net magnitude of 2.78(3) µ B, and 2.90(3) µ B for the x = 0.1 and the x = 0.2 samples. The Tb3+ionic moments had a magnitude of 1.36(4) µ B at 2.8 K and were aligned antiferromagnetically along the crystallographic c-axis for the x = 0.1 sample. The low moment in comparison with Mn3+ free ions has been attributed to crystalline electric fields similar to that found in the parent compound YMnO3 and also in another rare earth manganite viz HoMnO3. The x = 0.3 sample was found to be a canonical spin glass. To investigate the role of the above spin ordering in Y1-x Tb x MnO3 in governing the phonon dynamics, temperature dependent Raman measurements were carried out. We observed the deviation of the phonon frequency near 685 cm-1 and its line-width from the expected anharmonic behaviour around magnetic ordering temperature for Tb substituted compounds with x = 0.1 and 0.2. This was attributed to the spin-phonon coupling in these systems. The anomalous behaviour of this phonon mode in the canonical spin glass compound with x = 0.3, indicated that the coupling sustained even in the presence of only local magnetic ordering.

Structural manipulation and tailoring of dielectric properties in SrTi1-xFexTaxO3 perovskites: Design of new lead free relaxors.

We report composition dependent structure evolution from SrTiO3 to SrFe0.5Ta0.5O3 by powder X-ray and neutron diffraction studies of SrTi1-2xFexTaxO3 (0.00 ≤ × ≤ 0.50) compositions. Structural studies reveal cubic (Pm3m) perovskite-type structure of the parent SrTiO3 for x up to 0.075 and cation disordered orthorhombic (Pbnm) perovskite-type structure for x ≥ 0.33. A biphasic region consisting of a mixture of cubic and orthorhombic structures is found in the range for 0.10 ≤ × ≤ 0.25. Dielectric studies reveal transformation from a normal dielectric to relaxor like properties with increasing Fe(3+) and Ta(5+) concentration. Dielectric response is maximum at x = 0.33 in the series. The results establish a protocol for designing new lead-free relaxor materials based on the co-substitution of Fe(3+) and Ta(5+) for Ti(4+) in SrTiO3. A complex interplay of strain effects arising from distribution of cations at the octahedral sites of the perovskite structure controls the dielectric properties.

Experimental and theoretical investigations on the polymorphism and metastability of BiPO4.

In this work we report the metastability and the energetics of the phase transitions of three different polymorphs of BiPO4, namely trigonal (Phase-I, space group P3(1)21), monoclinic monazite-type (Phase-II, space group P2(1)/n) and SbPO4-type monoclinic (Phase-III, space group P2(1)/m) from ambient and non-ambient temperature powder XRD and neutron diffraction studies as well as ab initio density functional theory (DFT) calculations. The symmetry ambiguity between P2(1) and P2(1)/m of the high temperature polymorph of BiPO4 has been resolved by a neutron diffraction study. The structure and vibrational properties of these polymorphs of the three polymorphs have also been reported in detail. Total energy calculations have been used to understand the experimentally observed metastable behavior of trigonal and monazite-type BiPO4. Interestingly, all of the three phases were found to coexist after heating a single phasic trigonal BiPO4 to 773 K. The irreversible nature of these phase transitions has been explained by the concepts of the interplay of the structural distortion, molar volume and total energy.

Nanostructures of Sr2+ doped BiFeO3 multifunctional ceramics with tunable photoluminescence and magnetic properties.

Careful tuning of formation (calcination) temperature of Sr(2+) doped BiFeO(3) multiferroic ceramics results in tailorable particle morphologies ranging from spherical to pillar-like. Based on the minimization of Gibb's free energy approach, the dominant homogeneous mechanism for particle growth is suggested. The chemical substitution of a trivalent ion (Bi(3+)) by a divalent ion (Sr(2+)) causes the transformation of certain fraction of Fe(3+) to Fe(4+) and/or the appearance of oxygen vacancies. This has been respectively proved by the analysis of XPS and refinement of neutron diffraction data. Although significant modification in the particle morphology is observed, the crystal unit cell remains rhombohedral with a R3c space group but interesting variations in physical properties are achieved. O-vacancies induced strong and sharp photoluminescence activity in the IR region, similar to ZnO, is reported for the first time. This observation opens up a new application for multiferroic ceramics. SQUID M-H data confirms the straightening of the canted spin structure of BiFeO(3), which in turn results in magnetism similar to ferromagnetic materials. Findings of the magneto-dielectric effect are also discussed to claim the multiferroic nature of the sample.

Composition and temperature-induced structural changes in lead-tellurite glasses on different length scales.

Processes occurring at macroscopic and microscopic length scales across the glass transition (T(g)) in lead-tellurite glass (PbO)(x)(TeO(2))(1-x) (x = 0.1-0.3) are investigated using Brillouin and Raman spectroscopy, respectively. For all the samples, the temperature dependence of the longitudinal acoustic (LA) mode is found to exhibit a universal scaling below T(g) and a rapid softening above T(g). The lower value of elastic modulus at a higher concentration of network modifier PbO, estimated from Brillouin data, arises due to loss of network rigidity. From quantitative analysis of the reduced Raman spectra, several modes are found to exhibit anomalous changes across T(g). Instead of the expected anharmonic behaviour, several modes exhibit hardening, suggesting stiffening of the stretching force constants with temperature, the effect being more pronounced in glasses with higher x. In addition, incorporation of PbO in the glass is also found to narrow down the bond-length distribution, as evident from the sharpening of the Raman bands. The stiffening of the force constants of molecular units at a microscopic length scale and the decrease of elastic constant attributed to loss of network rigidity on a macroscopic length scale appear to be opposite. These different behaviours at two length scales are understood on the basis of a microscopic model involving TeO(n) and PbO units in the structure.

A growth walk model for estimating the canonical partition function of interacting self-avoiding walk.

We have explained in detail why the canonical partition function of interacting self-avoiding walk (ISAW) is exactly equivalent to the configurational average of the weights associated with growth walks, such as the interacting growth walk (IGW), if the average is taken over the entire genealogical tree of the walk. In this context, we have shown that it is not always possible to factor the density of states out of the canonical partition function if the local growth rule is temperature dependent. We have presented Monte Carlo results for IGWs on a diamond lattice in order to demonstrate that the actual set of IGW configurations available for study is temperature dependent even though the weighted averages lead to the expected thermodynamic behavior of ISAW.

Coil-globule transition of a single short polymer chain: an exact enumeration study.

The authors present an exact enumeration study of short self-avoiding walks in two as well as in three dimensions that addresses the question, "what is the shortest walk for which the existence of all the three scaling regimes--coil, globule, and the theta--could be demonstrated." Even though they could easily demonstrate the coil and the globule phase from free energy considerations, they could demonstrate the existence of a theta temperature only by using a scaling form for the distribution of gyration radius. That even such short walks have a scaling behavior is an unexpected result of this work.

Structural study of La(0.75)Sr(0.25)CrO(3) at high temperatures.

A high-temperature neutron diffraction study has been carried out on La(0.75)Sr(0.25)CrO(3) compound in the temperature range 300-1400 K. On doping the parent compound LaCrO(3) with Sr at the La site, the orthorhombic (Pbnm) to rhombohedral ([Formula: see text]) structural transition shifts to lower temperatures. From quantitative Rietveld analysis it is found unequivocally that there is a two-phase coexistence (orthorhombic and rhombohedral phases with ∼89 and 11 weight%, respectively) in the temperature range 300-470 K and a three-phase coexistence (with a new cubic phase with space group Pm3m) in the temperature range 480-1400 K. The weight percentages of the orthorhombic, rhombohedral and cubic phases were found to be ∼49%, 37% and 14%, respectively, in the temperature range 480-1300 K, while over 1350-1400 K, the average weight percentages of orthorhombic, rhombohedral and cubic phases were found to be ∼41%, 41% and 18%, respectively. The coefficients of volume thermal expansion and linear thermal expansion have been determined for all three phases. The importance of the present study has been discussed for practical applications of the studied compound in solid oxide fuel cells.

Interacting growth walk: a model for hyperquenched homopolymer glass?

We show that the compact self-avoiding walk configurations, kinetically generated by the recently introduced interacting growth walk (IGW) model, can be considered as members of a canonical ensemble if they are assigned random values of energy. Such a mapping is necessary for studying the thermodynamic behavior of this system. We have presented the specific heat data for the IGW, obtained from extensive simulations on a square lattice; we observe a broad hump in the specific heat above the theta point, contrary to expectation.

Biosynthesis of rifamycin SV by Amycolatopsis mediterranei MTCC17 in solid cultures.

Studies were performed on the production of rifamycin SV, an ansamycin compound, extensively used for curing tuberculosis, leprosy and several other mycobacterial infections, using a strain of Amycolatopsis mediterranei MTCC17 in solid cultures. Wheat bran was employed as a solid substrate. The culture produced 4 g of rifamycin SV/kg of substrate. Pre-treatment of the substrate with dilute HCl was found to increase the yield of rifamycin SV by 300% (from 4 to 12 g x kg of substrate(-1)). Various process parameters were tested to establish the best conditions for the maximum production of the compound and a initial moisture level of 80%, inoculum size of 40%, initial substrate pH of 7.0, incubation temperature of 26 degrees C and a 7 day fermentation period were found to be optimal. Different solvents were used for the extraction of rifamycin SV from the fermented matter and methanol was found to be most suitable. Under optimized conditions, the yield of rifamycin SV further increased from 12 to 32 g x kg of substrate(-1), showing an 8-fold increase from the initial value.

Interacting growth walk: a model for generating compact self-avoiding walks.

We propose an algorithm based on local growth rules for kinetically generating self-avoiding walk configurations at any given temperature. This algorithm, called the interacting growth walk (IGW) model, does not suffer from attrition on a square lattice at zero temperature, in contrast to the existing algorithms. More importantly, the IGW model facilitates growing compact configurations at lower temperatures--a feature that makes it attractive for studying a variety of processes such as the folding of proteins. We demonstrate that our model correctly describes the collapse transition of a homopolymer in two dimensions.

Sticky spheres, entropy barriers, and nonequilibrium phase transitions.

A sticky spheres model to describe slow dynamics of a nonequilibrium system is proposed. The dynamical slowing down is due to the presence of entropy barriers. An exact steady state analysis of the representative mean field equations, in the case when the clusters are chosen with the same a priori probability, demonstrates a nonequilibrium phase transition from an exponential cluster size distribution to a power law.

Effect of uracil on rifamycin SV production by Amycolatopsis mediterranei MV35R.

The effect of different organic nitrogen compounds on the production of rifamycin SV by Amycolatopsis mediterranei MV35R and their optimum concentrations have been described. Results obtained indicate that rifamycin SV production increased from 4020 mg l-1 to 4575 mg l-1 when organic nitrogen compound uracil was added at 0.2% (w/v) concentration to the fermentation medium by A. mediterranei MV35R. The rifamycin SV yield was enhanced by 505 mg l-1 using uracil (2 g l-1) when compared with barbital.