Two Novel Hexadepsipeptides with Several Modified Amino Acid Residues Isolated from the Fungus

Two new cyclohexadepsipeptides have been isolated from the fungus Isaria. Fungal growth in solid media yielded hyphal strands from which peptide fractions were readily isolable by organic-solvent extraction. Two novel cyclodepsipeptides, isaridin A and isaridin B, have been isolated by reverse-phase HPLC, and characterized by ESI-MS and 1H-NMR. Single crystals of both peptides have been obtained, and their 3D structures were elucidated by X-ray diffraction. The isaridins contain several unusual amino acid residues. The sequences are cyclo(β-Gly-HyLeu-Pro-Phe-NMeVal-NMePhe) and cyclo(β-Gly-HyLeu-β-MePro-Phe-NMeVal-NMePhe), where NMeVal is N-methylvaline, NMePhe N-methylphenylalanine, and HyLeu hydroxyleucine (=2-hydroxy-4-methylpentanoic acid). The two peptides differ from one another at residue 3, isaridin A having an (S)-proline at this position, while β-methyl-(S)-proline (=(2S,3S)-2,3,4,5-tetrahydro-3-methyl-1H-pyrrole-2-carboxylic acid) is found in isaridin B. The solid-state conformations of both cyclic depsipeptides are characterized by the presence of two cis peptide bonds at HyLeu(2)-Pro(3)/HyLeu(2)-β-MePro(3) and NMeVal(5)-NMePhe(6), respectively. In isaridin A, a strong intramolecular H-bond is observed between Phe(4)CO⋅⋅⋅HNβ-Gly(1), and a similar, but weaker, interaction is observed between β-Gly(1)CO⋅⋅⋅HNPhe(4). In contrast, in isaridin B, only a single intramolecular H-bond is observed between β-Gly(1)CO⋅⋅⋅HNPhe(4

Laser-fused refractory oxides for optical coatings

Laser sintering was carried out using a high power continuous-wave CO2 laser to prepare pellets of zirconia (ZrO2), hafnia (HfO2) and yttria (Y2O3) mixed oxides as starting materials in the deposition of optical coatings. Hardened recrystallized pellets appeared to have been formed during laser treatment. X-ray diffraction analysis revealed a monoclinic-to-tetragonal phase transformation in the binary system while the ternary system was found to have a mixture of two crystalline phases. Cross-sectional scanning electron microscopy showed two isothermal crystalline regions in the ternary system. The optical inhomogeneity was low in the films deposited from the laser-fused pellets, but the absorption at a wavelength of 351 nm increased with increasing HfO2 content. The films deposited from laser-fused pellets were analysed by electron spectroscopy for chemical analysis and found to be stoichiometric and homogeneous.

Measurement of the corrosion rate of aluminium in sodium hydroxide using holographic interferometry

The application of holographic interferometry to the measurement of the corrosion rate of aluminium in sodium hydroxide is investigated. Details of the fabrication of the corrosion cell and the experimental procedure are given. Thickness loss of aluminium was found for different dissolution times and compared with the conventional weight-loss method using a microbalance.

Perturbation of critical solution temperatures by impurity doping

An expression is developed for the variation of the critical solution temperature of a binary liquid system when a third component (dopant) is added, using an extension of the regular solution theory. The model can be used for UCST, LCST and for closed loop systems and has the correct features in the limiting cases.

A New Liquid Level Sensor for Process-Control Applications

Many process-control systems are air-operated. In such an environment, it would be desirable and economical to use pneumatic sensors. Bubble-back pressure sensors perform quite satisfactorily, but in case of viscous inflammable and slurry-like liquids with a tendency to froth, this level sensor is inadequate. The method suggested in this paper utilizes a pneumatic capacitor, one boundary of which is formed by the liquid level, to modulate a fluid amplifier feedback oscillator. The absence of moving parts and economy obtained makes this method attractive for process-control applications. The system has been mathematically modeled and simulated on an IBM 360/44 digital computer. Experimental values compare fairly well with the theoretical results. For the range tested, the sensor is found to have a linear frequency variation with the liquid level Extended running in the laboratory shows that the system is very reliable. This system has been found insensitive to temperature variations of up to 15ðC.

Growth of Orthorhombic SnS Nanobox Structures on Seeded Substrates

Tin sulfide (SnS) nanostructures have been synthesized using a simple and low temperature chemical solution method on seeded substrates, and their structural and optical properties have been investigated. The as-grown SnS nanostructures with well-defined facets exhibited good stoichiometry between constituent elements. These nanobox structures are preferentially oriented along the 010] direction by having 100] and 001] orientations as surrounding facets and exhibited Two distinguishable optical band gaps of 1.36 and 1.9 eV. The effect of solution concentration as well as seed layer on the morphology or SnS structures has also been studied, and finally, the growth mechanism of the regular SnS nanobox structures is proposed.

Optical properties of activated reactive evaporated TiO2 films

This paper discusses the optical properties of single-layer TiO2 films deposited using an activated reactive evaporation process. The combined effects of substrate temperature (in the range 70–200 °C) and discharge currents (0–400 mA) on refractive index, extinction coefficient and packing density of these films are investigated. Significant changes in refractive index values have been observed with increases in substrate temperature and discharge current. The change in refractive index is correlated with the variation in packing density. The variation in extinction coefficient was reduced using the combined effects of substrate temperature and discharge currents. A comparison with films deposited in neutral oxygen has also been made.

Channel Volatiles Of South Indian Cordierites As Indicators Of Metamorphic Fluid Composition

The channel volatiles in cordierites of the Precambrian high-grade metapelites from southern and eastern Karnataka northern Tamil Nadu and southern Kerala were analyzed in an attempt to use them as metamorphic fluid fugacity indicators. Infrared powder absorption spectra, used to characterize the channel volatiles, showed that all the 21 analyzed cordierites have H2O and CO2 as the channel volatiles, indicating the predominantly H2O-CO2 composition of the metamorphic fluids. The H2O fraction in the metamorphic fluid was computed using a published thermodynamic method in conjunction with gravimetrically determined cordierite channel H2O content, available P - T estimates and an appropriate equation of state for the H2O - CO2 fluids. The IR data and these calculated X(H2O) values indicate an overall correlation between the variation in the relative proportion of H2O and CO2 in the fluids and the metamorphic grade. The average computed X(H2O) values are: 0.78 for the amphibolite facies eastern Karnataka pelites, 0.36 for the amphibolite facies southern Karnataka pelites, 0.19 for the southern Karnataka transitional zone rocks and 0.13 for the northern Tamil Nadu granulites. Consistently low X(H2O) values, at about 0.2, were obtained for the orthopyroxene-bearing assemblages.

Compositional dependence of crystallization of As-Te glasses

Thermal crystallization studies have been carried out on bulk, semiconducting AsxTe100−x glasses of different compositions using Differential Scanning Caloritmery. AsxTe100−x glasses with x < 40, are found to exhibit one glass transition and one crystallization. On the other hand, glasses with composition 40 less-than-or-equals, slantxless-than-or-equals, slant 50 show one glass transition and two crystallization reactions. It has been found that in glasses with x greater-or-equal, slanted 40, the two crystallization reactions progressively merge with an increase in arsenic concentration. Consequently AsxTe100−x glasses with x greater-or-equal, slanted 50 show only one crystallization. The composition dependence of crystallization temperatures and activation energies for crystallization estimated by Kissinger's method, show marked deviations at a composition x = 40. These observations can be explained in terms of the changes in the local structure of the material with composition.

Effect of substrate temperature on the properties of ZrO2 films prepared by d.c. reactive magnetron sputtering

Studies of ZrO2 films prepared by d.c. reactive magnetron sputtering are described. The effects of substrate temperature on the packing density, refractive index, extinction coefficient and crystallinity phase have been investigated in the temperature range 25–450 °C. The refractive index varied from 1.84 to 1.95 and extinction coefficient from 2 × 10−3 to 9.6 × 10−3. This was explained on the basis of an increase in packing density from 0.686 to 0.813. The change in packing density has been attributed to a decrease in the oxygen condensation at higher temperatures. Annealing results in a decrease in refractive index and increase in extinction coefficient. The films deposited at 150 °C showed a monoclinic phase which transforms to a tetragonal phase at higher substrate temperatures.

Effects of thermal annealing on the properties of zirconia films prepared by ion-assisted deposition

The effect of thermal annealing in the range 300–800 °C on the properties of zirconia films prepared by ion assisted deposition was studied. It was found that at low temperature the cubic phase is formed. This phase is stable up to 700 °C. All the films exhibit a monophasic monoclinic structure at 800 °C. The stress, estimated from X-ray patterns, shows a transition from tensile to compressive with increasing ion fluence. The refractive index and extinction coefficient do not seem to change appreciably up to 700 °C, showing a marked degradation thereafter. Single step annealing to the highest temperature was found to result in better stability than multistep annealing.

Electrical Contact Resistance in Thin (<= 0.5 mu m) Gold Plated Contacts: Effect of Gold Plating Thickness

This paper describes the electrical contact resistance (ECR) measurements made on thin gold plated (gold plating of <= 0.5 mu m with a Ni underlayer of similar to 2 mu m) oxygen free high conductivity (OFHC) Cu contacts in vacuum environment. ECR in gold plated OFHC Cu contacts is found to be slightly higher than that in bare OFHC Cu contacts. Even though gold is a softer material than copper, the relatively high ECR values observed in gold plated contacts are mainly due to the higher hardness and electrical resistivity of the underlying Ni layer. It is well known that ECR is directly related to plating factor, which increases with increasing coating thickness when the electrical resistivity of coating material is more than that of substrate. Surprisingly, in the present case it is found that the ECR decreases with increasing gold layer thickness on OFHC Cu substrate (gold has higher electrical resistivity than OFHC Cu). It is analytically demonstrated from the topography and microhardness measurements results that this peculiar behavior is associated with thin gold platings, where the changes in surface roughness and microhardness with increasing layer thickness overshadow the effect of plating factor on ECR.

Processing map for hot working of as cast magnesium

The constitutive flow behaviour in hot working of as cast magnesium has been studied with the help of a processing map developed in the temperature range 300-550°C and strain rate range 0·001-100 s−1. The map, interpreted using the dynamic materials model, revealed that the material undergoes dynamic recrystallisation at 425°C and 0·3 s−1, which are the optimum parameters for hot working. Ai temperatures higher than 450°C and strain rates lower than about 0·1 s−1, wedge cracking occurs in as cast magnesium. The wedge cracking domain has a high efficiency of power dissipation (60%), whereas the dynamic recrystallisation domain has a value of 34%. At temperatures below 450°C and strain rates above 10 s−1, the material exhibits flow instability in the form of mechanical twinning. At higher temperatures and strain rates, instability is manifested by flow localisation.

Properties of ion assisted deposited titania films

Thin films of titanium dioxide have been deposited using ion assisted deposition with oxygen ions in the energy range 100�500 eV and current densities up to 100 ?A/cm2. It has been observed that the refractive index of the films increases up to 300 eV and the extinction coefficient increased only nominally up to 300 eV. Optical band gap calculations have shown a strong dependence of the gap on the energy of incident ions. Beyond a critical energy and current density of the ions the refractive index and extinction coefficient of the films start deteriorating. It has also been found that beyond the critical values the optical band gap value decreases. The maximum refractive index obtained was 2.49 at an energy of 300 eV and 50 ?A/cm2 current density. Post?deposition annealing of the films at 500?°C resulted in a slight increase in refractive index without affecting the extinction coefficient. X?ray diffraction studies revealed a monophasic anatase structure in these films. ?