Diproline Templates as Folding Nuclei in Designed Peptides. Conformational Analysis of Synthetic Peptide Helices Containing Amino Terminal Pro-Pro Segments

The effect of N-terminal diproline segments in nucleating helical folding in designed peptides has been studied in two model sequences Piv-Pro-Pro-Aib-Leu-Aib-Phe-OMe (1) and Boc-Aib-Pro-Pro-Aib-Val-Ala-Phe-OMe (2). The structure of 1 in crystals, determined by X-ray diffraction, reveals a helical (RR) conformation for the segment residues 2 to 5, stabilized by one 4 -> 1 hydrogen bond and two 5 -> 1 interactions. The N-terminus residue, Pro(1) adopts a polyproline II (P-II) conformation. NMR studies in three different solvent systems support a conformation similar to that observed in crystals. In the apolar solvent CDCl3, NOE data favor the population of both completely helical and partially unfolded structures. In the former, the Pro-Pro segment adopts an alpha(R)-alpha(R) conformation, whereas in the latter, a P-II-alpha(R) structure is established. The conformational equilibrium shifts in favor of the P-II-alpha(R) structure in solvents like methanol and DMSO. A significant population of the Pro(1)- Pro(2) cis conformer is also observed. The NMR results are consistent with the population of at least three conformational states about Pro- Pro segment: trans alpha(R)-alpha(R), trans P-II-alpha(R) and cis P-II-alpha(R). Of these, the two trans conformers are in rapid dynamic exchange on the NMR time scale, whereas the interconversion between cis and trans form is slow. Similar results are obtained with peptide 2. Analysis of 462 diproline segments in protein crystal structures reveals 25 examples of the alpha(R)-alpha(R) conformation followed by a helix. Modeling and energy minimization studies suggest that both P-II-alpha(R) and alpha(R)-alpha(R) conformations have very similar energies in the model hexapeptide 1

A Multi frequency study of Radio Intensity Variations For Active Galactic Nuclei of Different Optical Classes

A study of radio intensity variations at seven frequencies in the range 0.3 to 90 GHz for compact extragalactic radio sources classified as BL Lacs and high- and low-optical polarization quasars (HPQs and LPQs) is presented. This include the results of flux-density monitoring of 33 compact sources for three years at 327 MHz with the Ooty Synthesis Radio Telescope. The degrees of 'short-term' (tau less than about 1 yr) variability for the three optical types are found to be indistinguishable at low frequencies (less than 1 GHz), pointing to an extrinsic origin for the low-frequency variability. At high frequencies, a distinct dependence on optical type is present, the variability increasing from LPQs, through HPQs to BL Lacs. This trend persists even when only sources with ultra-flat radio spectra (alpha greater than -0.2) are considered. Implications of this for the phenomenon of high-frequency variability and the proposed unification schemes for different optical types of active galactic nuclei are discussed.

Engineering behavior of uplifted Smectite-rich Cochin and Mangalore marine clays

The present study aims to assess whether the smectite-rich Cochin and Mangalore clays, which were deposited in a marine medium and subsequently uplifted, exhibit consistency limits response typical of expanding lattice or nonexpanding (fixed) lattice-type clays on artificially changing the chemical environment. The chemical and engineering behaviors of Cochin and Mangalore marine clays are also compared with those of the smectite-rich Ariake Bay marine clay from Japan. Although Cochin, Mangalore, and Ariake clays contain comparable amounts of smectite (32-45%), Ariake clay exhibits lower consistency limits and much higher ranges of liquidity indices than the Indian marine clays. The lower consistency limits of the Ariake clay are attributed to the absence of well-developed, long-range, interparticle forces associated with the clay. Also, Ariake clay exhibits a significantly large (48-714 times) decrease in undrained strength on remolding in comparison to Cochin and Mangalore clays (sensitivity ranges between 1 and 4). A preponderance of long-range, interparticle forces reflected in the high consistency limits of Cochin and Mangalore clays (wL range from 75 to 180%) combined with low natural water contents yield low liquidity indices (typically <1) and high, remolded, undrained strengths and are considered to be responsible for the low sensitivity of the Indian marine clays.

Effect of Substrate and Annealing Temperatures on Mechanical Properties of Ti-rich NiTi Films

The effect of substrate and annealing temperatures on mechanical properties of Ti-rich NiTi films deposited on Si (100) substrates by DC magnetron sputtering was studied by nanoindentation. NiTi films were deposited at two substrate temperatures viz. 300 and 400 degrees C. NiTi films deposited at 300 degrees C were annealed for 4 h at four different temperatures, i.e. 300, 400, 500 and 600 degrees C whereas films deposited at 400 degrees C were annealed for 4 h at three different temperatures, i.e. 400, 500 and 600 degrees C. The elastic modulus and hardness of the films were found to be the same in the as-deposited as well as annealed conditions for both substrate temperatures. For a given substrate temperature, the hardness and elastic modulus were found to remain unchanged as long as the films were amorphous. However, both elastic modulus and hardness showed an increase with increasing annealing temperature as the films become crystalline. The results were explained on the basis of the change in microstructure of the film with change in annealing temperature.

Compressive tidal heating of a disk galaxy in a rich cluster

The restricted three-body method is used to model the effect of the mean tidal field of a cluster of galaxies on the internal dynamics of a disk galaxy falling into the cluster for the first time. In the model adopted the galaxy experiences a tidal field that is compressive within the core of the cluster. The planar random velocities of all components in the disk increase after the galaxy passes through the core of the cluster. The low-velocity dispersion gas clouds experience a relatively larger increase in random velocity than the hotter stellar components. The increase in planar velocities results in a strong anisotropy between the planar and vertical velocity dispersions. It is argued that this will make the disk unstable to the 'fire-hose instability' which leads to bending modes in the disk and which will thicken the disk slightly. The mean tidal fields in rich clusters were probably stronger during the epoch of cluster formation and relaxation than they are in present-day relaxed clusters.

Cloning and sequence of a cDNA encoding a novel hybrid prolme-rich protein associated with cytokinin-induced haustoria formation in Cuscuta reflexa

A complete cDNA encoding a novel hybrid Pro-rich protein (HyPRP) was identified by differentially screening 3x10(4) recombinant plaques of a Cuscuta reflexa cytokinin-induced haustorial cDNA library constructed in lambda gt10. The nucleotide (nt) sequence consists of: (i) a 424-bp 5'-non coding region having five start codons (ATGs) and three upstream open reading frames (uORFs); (ii) an ORF of 987 bp with coding potential for a 329-amino-acid (aa) protein of M(r), 35203 with a hydrophobic N-terminal region including a stretch of nine consecutive Phe followed by a Pro-rich sequence and a Cys-rich hydrophobic C terminus; and (iii) a 178-bp 3'-UTR (untranslated region). Comparison of the predicted aa sequence with the NBRF and SWISSPROT databases and with a recent report of an embryo-specific protein of maize [Jose-Estanyol et al., Plant Cell 4 (1992) 413-423] showed it to be similar to the class of HyPRPs encoded by genes preferentially expressed in young tomato fruits, maize embryos and in vitro-cultured carrot embryos. Northern analysis revealed an approx. 1.8-kb mRNA of this gene expressed in the subapical region of the C. reflexa vine which exhibited maximum sensitivity to cytokinin in haustorial induction.

DNA Condensation by the Rat Spermatidal Protein TP2 Shows GC-Rich Sequence Preference and Is Zinc Dependent

Transition protein-2 (TP2), isolated from rat testes, was recently shown to be a zinc metalloprotein. We have now carried out a detailed analysis of the DNA condensing properties of TP2 with various polynucleotides using circular dichroism spectroscopy. The condensation of the alternating copolymers by TP2 (incubated with 10 mu M ZnSO4), namely, poly(dG-dC). poly(dG-dC) and poly(dA-dT). poly(dA-dT), was severalfold higher than condensation of either of the homoduplexes poly(dG). poly-(dC) and poly(dA). poly(dT) or rat oligonucleosomal DNA. Between the two alternating copolymers, poly(dG-dC). poly(dG-dC) was condensed 3.2-fold more effectively than poly(dA-dT). poly(dA-dT). Preincubation of TP2 with 5 mM EDTA significantly reduced its DNA-condensing property. Interestingly, condensation of the alternating copolymer poly(dI-dC). poly(dI-dC) by TP2 was much less as compared to that of poly(dG-dC). poly(dG-dC). The V8 protease-derived N-terminal fragment (88 aa) condensed poly(dA-dT). poly(dA-dT) to a very small extent but did not have any effect on poly(dG-dC). poly-(dG-dC). The C-terminal fragment (28 aa) was able to condense poly(dA-dT) . poly(dA-dT) more effectively than poly(dG-dC). poly(dG-dC). These results suggest that TP2 in its zinc-coordinated form condenses GC-rich polynucleotides much more effectively than other types of polynucleotides. Neither the N-terminal two-thirds of TP2 which is the zinc-binding domain nor the C-terminal basic domain are as effective as intact TP2 in bringing about condensation of DNA.

Metamorphic-metasomatic fluids and Al, Si order/disorder of K-rich alkali feldspars from southern Indian high grade terrain

The structural state of K-feldspars in the quartzofeldspathic gneisses, charnockites, metapelites and pegmatites from the southern Kamataka, northern Tamil Nadu and southern Kerala high-grade regions of southern India has been characterized using petrographic and powder X-ray diffraction methods. The observed distribution pattern of structural state with a preponderance of disordered K-feldspar polymorphs in granulites compared to the ordered microclines in the amphibolite facies rocks is interpreted to reflect principally the varying H2O contents in the metamorphic-metasomatic fluids across metamorphic grade. The K-feldspars in the pegmatites of granitic derivation and in a pegmatite of inferred metamorphic origin also point to the important role of aqueous fluids in their structural state.

Fluorescence and visual sensing of nitroaromatic explosives using electron rich discrete fluorophores

Several pi-electron rich fluorescent aromatic compounds containing trimethylsilylethynyl functionality have been synthesized by employing Sonogashira coupling reaction and they were characterized fully by NMR (H-1, C-13)/IR spectroscopy. Incorporation of bulky trimethylsilylethynyl groups on the peripheral of the fluorophores prevents self-quenching of the initial intensity through pi-pi interaction and thereby maintains the spectroscopic stability in solution. These compounds showed fluorescence behavior in chloroform solution and were used as selective fluorescence sensors for the detection of electron deficient nitroaromatics. All these fluorophores showed the largest quenching response with high selectivity for nitroaromatics among the various electron deficient aromatic compounds tested. Quantitative analysis of the fluorescence titration profile of 9,10-bis(trimethylsilylethynyl) anthracene with picric acid provided evidence that this particular fluorophore detects picric acid even at ppb level. A sharp visual detection of 2,4,6-trinitrotoluene was observed upon subjecting 1,3,6,8-tetrakis (trimethylsilylethynyl) pyrene fluorophore to increasing quantities of 2,4,6-trinitrotoluene in chloroform. Furthermore, thin film of the fluorophores was made by spin coating of a solution of 1.0 x 10(-3) M in chloroform or dichloromethane on a quartz plate and was used for the detection of vapors of nitroaromatics at room temperature. The vapor-phase sensing experiments suggested that the sensing process is reproducible and quite selective for nitroaromatic compounds. Selective fluorescence quenching response including a sharp visual color change for nitroaromatics makes these fluorophores as promising fluorescence sensory materials for nitroaromatic compounds (NAC) with a detection limit of even ppb level as judged with picric acid.

The production of AlN-rich matrix composites by the reactive infiltration of Al alloys in nitrogen

Aluminium nitride (AlN)-Al matrices reinforced with Al2O3 particulate have been fabricated by reactive infiltration of Al-2% Mg alloy into Al2O3 preforms in N-2 in the temperature range of 900-1075 degreesC. The growth of composites of useful thickness was facilitated by the presence of a Mg-rich external getter, in the absence of which composite growth is self-limiting and terminates prematurely. Successful growth of composites has been attributed to the reduction in residual oxygen partial pressure brought about by the reaction with oxygen of highly volatile Mg in the getter alloy. The microstructure of the matrix consists of AlN-rich regions contiguous with the particulate with metal-rich channels in-between, thereby suggesting that nitridation initiates by preferential wicking of alloy along the particle surfaces. The increase in nitride content of the matrix with temperature is consistent with hardness values that vary between similar to3 and 10 GPa. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Stress Evolution With Temperature in Titanium-Rich NiTi Shape Memory Alloy Films

The effect of deposition temperature on residual stress evolution with temperature in Ti-rich NiTi films deposited on silicon substrates was studied. Ti-rich NiTi films were deposited on 3? Si (100) substrates by DC magnetron sputtering at three deposition temperatures (300, 350 and 400 degrees C) with subsequent annealing in vacuum at their respective deposition temperatures for 4 h. The initial value of residual stress was found to be the highest for the film deposited and annealed at 400 degrees C and the lowest for the film deposited and annealed at 300 degrees C. All the three films were found to be amorphous in the as-deposited and annealed conditions. The nature of the stress response with temperature on heating in the first cycle (room temperature to 450 degrees C) was similar for all three films although the spike in tensile stress, which occurs at similar to 330 degrees C, was significantly higher in the film deposited and annealed at 300 degrees C. All the films were also found to undergo partial crystallisation on heating up to 450 degrees C and this resulted in decrease in the stress values around 5560 degrees C in the cooling cycle. The stress response with temperature in the second thermal cycle (room temperature to 450 degrees C and back), which is reflective of the intrinsic film behaviour, was found to be similar in all cases and the elastic modulus determined from the stress response was also more or less identical. The three deposition temperatures were also not found to have a significant effect on the transformation characteristics of these films such as transformation start and finish temperatures, recovery stress and hysteresis.

(Dimethylamino)borylene and Related Complexes of Electron-Rich Metal Fragments: Generation of Nucleophile-Resistant Cations by Spontaneous Halide Ejection

Spontaneous halide ejection from a three-coordinate Lewis acid has been shown to offer a remarkable new route to cationic metal complexes featuring a linear, multiply bonded boron-donor Ligand. The exploitation of electron-rich [CpM(PR3)(2)] fragments within boryl systems of the type LnMB(hal)NR2 leads to the spontaneous formation in polar solvents of chemically robust borylene complexes, [LnM(BNR2)](+), with exceptionally low electrophilicity and short M-B bonds. This is reflected by M-B distances (ca. 1.80 angstrom for FeB systems) which are more akin to alkyl-/aryl-substituted borylene complexes and, perhaps most strikingly, by the very low exothermicity associated with the binding of pyridine to the two-coordinate boron center (Delta H = -7.4 kcal mol(-1), cf. -40.7 kcal mol(-1) for BCl3). Despite the strong pi electron release from the metal fragment implied by this suppressed reactivity and by such short M-B bonds, the barrier to rotation about the Fe=B bond in the unsymmetrical variant [CpFe(dmpe)(BN{C6H4OMe-4}Me)](+) is found to be very small (ca. 2.9 kcal mol(-1)). This apparent contradiction is rationalized by the orthogonal orientations of the HOMO and HOMO-2 orbitals of the [CpML2](+) fragment, which mean that the M-B pi interaction does not fall to zero even in the highest energy conformation.

Interrelation of grain boundary microstructure and texture in a hot rolled Ni-rich NiTi alloy

This investigation deals with the evolution of grain boundary microstructure and crystallographic texture during hot rolling of a Ni-rich NiTi alloy. Electron backscattered diffraction studies revealed the occurrence of several coincidence site lattice (CSL) boundaries. The origin of these boundaries has been identified. The crystallographic texture of the deformed sample consists mainly of (1 1 1)parallel to normal direction fiber. The texture components on the fiber exhibit some correlation with the type of CSL boundary. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Peraluminous sapphirine-cordierite pods in Mg-rich orthopyroxene granulite from southern India: Implications for lower crustal processes

Sapphirine-cordierite intergrowths occur as pods within garnet-absent, high-Mg orthopyroxene-granulite xenoliths in the Kambam valley, Madurai Block, southern India. Whereas the cores of the pods are composed of sapphirine (X-Mg = 0.871-0.897) - cordierite (X-Mg = 0.892-0.931) intergrowth along with rutile, zircon and monazite, the rims are characterized by cordierite, apatite, plagioclase, K-feldspar, quartz and minor calcite. The surrounding matrix comprises orthopyroxene (maximum Al2O3 4.1 wt.%, X-Mg 0.848-0.850), plagioclase, biotite and quartz, similar to the assemblage in the surrounding charnockites. Sapphirine in the Kambam rocks is characterized by high Al contents with an end-member composition in the range of 7:9:3 and 3:5:1. The occurrence of peraluminous sapphirine in association with cordierite and in the absence of phases such as sillimanite and garnet is distinct from ultrahigh-temperature assemblages in other localities within the Madurai Block. The peraluminous composition of the pods suggests that these domains could represent cryptic pathways through which aluminous melts migrated. The reaction of such peraluminous melts with Mg-rich orthopyroxene in the host granulite at temperatures of 1025 degrees C and pressures around 8 kbar as computed from phase equilibria modeling followed by an isobaric cooling is inferred to have generated the sapphirine-cordierite pods. The unusual high-Mg orthopyroxene granulite suggests interaction of supracrustal rocks with mafic magmas, which probably acted as the heat source for the partial melting of lower crust and UHT metamorphism.

Caryophyllene-Rich Essential Oil of Didymocarpus tomentosa: Chemical Composition and Cytotoxic Activity

The essential oil from the leaves of Didymocarpus tomentosa was extracted by hydrodistillation and analyzed by GC/FID and GC/MS. Twenty five constituents amounting to 81.6% of the oil were identified. The leaf oil contained 78.7% sesquiterpenes and 2.9% monoterpenes. The leaf essential oil of D. tomentosa is a unique caryophyllene-rich natural source containing beta-caryophyllene, caryophyllene oxide, alpha-humulene and humulene oxide. The cytotoxic activity of the oil was determined by the BSLT using shrimp larva and the MTT assay using HeLa tumor cell line. The oil showed significant cytotoxic activity with LC50 and IC50 values of 12.26 and 11.4 mu g/mL, respectively. This is the first report on the chemical composition and cytotoxic activity of the essential oil of D. tomentosa.