Conformations of the amino terminal tetrapeptide of emerimicins and antiamoebin in solution and in the solid state

The conformations of Boc-l-Phe-(AiB)3-OH (1) and Boc-l-Phe-(Aib)3-OMe (2) which correspond to the amino terminal sequence of the emerimicins and antiamoebins have been studied in solution using 270 MHz 1H n.m.r. In dimethyl sulphoxide solution both peptides show the presence of two strongly solvent shielded Aib NH groups, consistent with a consecutive β-turn conformation, involving the Aib(3) and Aib(4) NH groups in intramolecular 4 → I hydrogen bonds. This folded conformation is maintained for 2 in chloroform solution. Nuclear Overhauser effect studies provide evidence for a Type II Phe-Aib β-turn. An X-ray diffraction study of Boc-(d,l)-Phe-(Aib)3-OH establishes a single type III(III′) β-turn conformation with Aib(2)-Aib(3) as the corner residues. A single intramolecular 4 → I hydrogen bond between Phe(I) CO and Aib(4) NH groups is observed in the crystal. The solution conformation may incorporate a consecutive type II-III′ structure for the Phe(1)-Aib(2)-Aib(3) segment, with the initial type II β-turn being destabilized by intermolecular interactions in the solid state.

Activity–Composition Relations in the Nickel Oxide–Magnesium Oxide System at 1300 K by the Solid-State Galvanic Cell Technique

The activity of NiO in NiO-MgO rock salt solid solution has been measured at 1300 K by employing a solid-state galvanic cell: Pt,Ni+ NiO||(CaO)ZrO2||Ni + (Nix,Mgl-x)O, Pt. A high-density tube of Zr02-15 mol% CaO has been used as the solid electrolyte for the emf measurements. The activities of the component oxides in the rock salt solid solution exhibit negative deviation from ideality at the temperature of investigation. The solid solution obeys regular solution behavior at 1300 K. The value of the regular solution parameter is found to be -12000 ((l000) J mol-1. The composition dependence of ΔGEx obtained in this study agrees reasonably well with the calorimetric data reported in the literature for NiO-MgO solid solution.

Photochromism of alkylisophthalaldehydes in the solid state: structure–reactivity correlations

The crystal and molecular structures of the photochromic compounds 2,5-dimethylisophthalaldehyde (I) and 5-isopropyl-2-methylisophthalaldehyde (II) have been determined by single crystal X-ray analyses. The intramolecular gamma-hydrogen abstraction process involved in the photoenolisation of I and II in the solid state has been rationalised in the light of relevant geometrical parameters.

A furnace for in situ synchrotron Laue diffraction and its application to studies of solid-state phase transformations

The design of a new microfurnace for use for Laue diffraction studies of solid-state transformations is described. The furnace operates in the temperature range 298-573 K with a thermal stability of about ± 0.1 K. The potential of the synchrotron-radiation Laue diffraction technique for studies of structural phase transitions is demonstrated. Experimental data on phase transitions in caesium periodate, potassium tetrachlorozincate and pentaerythritol are presented.

Solid State Electrochemical Sensors in Process Control

The basic principles of operation of gas sensors based on solid-state galvanic cells are described. The polarisation of the electrodes can be minimised by the use of point electrodes made of the solid electrolyte, the use of a reference system with chemical potential close to that of the sample system and the use of graded condensed phase reference electrodes. Factors affecting the speed of response of galvanic sensors in equilibrium and non-equilibrium gas mixtures are considered with reference to products of combustion of fossil fuels. An expression for the emf of non-isothermal galvanic sensors and the criterion for the design of temperature compensated reference electrodes for non-isothermal galvanic sensors are briefly outlined. Non-isothermal sensors are useful for the continuous monitoring of concentrations or chemical potentials in reactive systems at high temperatures. Sensors for oxygen, carbon, and alloying elements (Zn and Si) in liquid metals and alloys are discussed. The use of auxiliary electrodes permits the detection of chemical species in the gas phase which are not mobile in the solid electrolyte. Finally, the cause of common errors in galvanic measurements, and tests for correct functioning of galvanic sensors are given. 60 ref.--AA

Four decades of research in solid state chemistry

Solid state chemistry was in its infancy when the author got interested in the subject. In this article, the author outlines the manner in which the subject has grown over the last four decades, citing representative examples from his own contributions to the different facets of the subject. The various aspects covered include synthesis, structure, defects, phase transitions, transition metal oxides, catalysts, superconductors, metal clusters and fullerenes. In an effort to demonstrate the breadth and vitality of the subject, the author shares his own experiences and aspirations and gives expression to the agony and ecstacy in carrying out experimental research in such a frontier area in India.

Characterization of coprecipitated ferroelectric Bi2 VO5·5

Fine powders of orthorhombic bismuth vandate (Bi2VO5.5) have been synthesized by coprecipitation method. Powder X-ray diffraction and electron microscopic techniques have been used to characterize these samples. The formation of the monophasic Bi2VO5.5 was confirmed. The compacted powders sintered at 1070 K have been characterized for their dielectric properties as a function of both temperature (300-900 K) and frequency (100 Hz-10 MHz) and found to be superior to those obtained by the conventional solid-state reaction route.

Solid state physics through the years: Need for new initiatives

Solid state physics developed in India later than elsewhere in the world. What is particularly disconcerting is the poor state of experimental solid state physics today. A new thrust and better funding are essential if this field has to thrive in the country.

Whither solid state physics

The physics of the solid state has grown into that of condensed matter and is now expanding into the study of a bewildering variety of complex systems. After a brief survey of this progression, I enquire into the health of solid state physics; many signs of vitality and growth are found. The Indian scene in this field is briefly sketched, and some suggestions are offered on how to make it more lively,

Determination of the Gibbs energy of diamond using a solid state cell

he chemical potential of carbon in diamond, relative to its value in graphite, has been directly determined using a solid state electrochemical cell incorporating single crystal CaF2 as the solid electrolyte. The cell can be represented as Pt, C(graphite) + CaC2 + CaF2double vertical barCaF2double vertical barCaF2 + CaC2 + C(diamond), Pt The reversible emf of this cell is directly related by the Nernst equation to the Gibbs free energy change for the conversion of diamond to graphite. The difference in the chemical potential of carbon in the two crystal structures varies linearly with temperature in the range 940 to 1260 K ?C(diamond) ? ?C(graphite) = 1100 + 4.64T (±50) J mol?1 On the average, the values given by the equation are 320 J mol?1 less positive than the currently accepted ones based on calorimetric studies. The difference is primarily in the enthalpy term.

Studies in crystal engineering: Effect of fluorine substitution in crystal packing and topological photodimerization of styryl coumarins in the solid state

Styryl coumarins generally yield centrosymmetric (alpha-mode, anti-HT) photodimers when subjected to irradiation in the solid state, However, the substitution of fluorine dramatically alters the packing mode and steers the molecules 4-(4-fluorostyryl)coumarin 1 and 4-(2-fluorostyryl)coumarin 2 to form a stereospecific photodimer, beta-mode, syn-HH across the styrenic double bond (yield 78-85%). The stereochemistry of the photodimer 2a has been established by X-ray crystallography. There is no evidence for the presence of C-H ... F interactions. The true nature of the weak atom-atom interactions called into play when fluorine is substituted is not clear, It is observed that the fluoro substituted compounds have greater crystal density than the corresponding unsubstituted ones.

Solid state amorphization in binary Ti---Ni, Ti---Cu and ternary Ti---Ni---Cu system by mechanical alloying

An amorphous phase has been synthesized by mechanical alloying in a planetary mill over a nickel content range of 10�70 at.% in the Ti---Ni system and a copper content range of 10�50 at.% in the Ti---Cu system. In the case of ternary Ti---Ni---Cu alloys the glass-forming composition range has been found to be given by x = 10�20 for Ti60Ni40 ? xCux, x = 10 � 30 for Ti50Ni50 ? xCux and x = 10 � 40 for Ti40Ni60 ? xCux alloys. The difficulty in the amorphization of copper-rich compositions is explained in the light of enthalpy composition diagrams calculated for the ternary solid solution and the amorphous phase.

Solid-state photobehaviour and crystal packing of o-chlorobenzylidene-DL-piperitone: influence of molecular topology on photobehaviour

C17H19ClO, M(r) = 274.7, triclinic, P1BAR, a = 11.154 (3), b = 12.685 (2), c = 12.713 (2) angstrom, alpha = 100.68 (1), beta = 113.58 (1), gamma = 104.50 (2)-degrees, V = 1511.1 (6) angstrom3, Z = 4, D(m) = 1.22, D(x) = 1.215 Mg m-3, Cu K-alpha, lambda = 1.5418 angstrom, mu = 2.16 mm-1, F(000) = 584, T = 293 K, R = 0.057 for 3481 observed reflections. The title compound is photostable in the crystalline state and lattice-energy calculations have been employed to rationalize the photobehaviour. The well-known beta-steering ability of the chloro group is not operative in this system as there are no Cl...Cl interactions in the crystal lattice. All five benzylidene-DL-piperitone structures so far studied are alpha-packed and the molecular topology appears to be a deciding factor even in the presence of steering groups.