Organometallic derivatives of peptides: Application to peptide receptor analysis

Complexation of 2-amino-4-hexynoic acid (Aha) with transition metal carbonyl derivatives and Aha-containing peptides was achieved with fair to good yields. This should permit the detection of peptide-receptor interaction by FT-IR instead of radiolabeling.     

Vinylsilyl Grignard reagents as aryne traps. A new route to (arylalkenyl)silanes.

A general method for preparing (arylalkenyl)silanes via nucleophilic capture of arynes with vinyltrimethylsilyl Grignard reagents is described.     

The Odyssey of Entropy: Cryptography

After being introduced by Shannon as a measure of disorder and unavailable information, the notion of entropy has found its applications in a broad range of scientific disciplines. In this paper, we present a systematic review on the applications of entropy and related information-theoretical concepts in the design, implementation and evaluation of cryptographic schemes, algorithms, devices and systems. Moreover, we study existing trends, and establish a roadmap for future research in these areas.     

Signless Laplacians of finite graphs

We survey properties of spectra of signless Laplacians of graphs and discuss possibilities for developing a spectral theory of graphs based on this matrix. For regular graphs the whole existing theory of spectra of the adjacency matrix and of the Laplacian matrix transfers directly to the signless Laplacian, and so we consider arbitrary graphs with special emphasis on the non-regular case. The results which we survey (old and new) are of two types: (a) results obtained by applying to the signless Laplacian the same reasoning as for corresponding results concerning the adjacency matrix, (b) results obtained indirectly via line graphs. Among other things, we present eigenvalue bounds for several graph invariants, an interpretation of the coefficients of the characteristic polynomial, a theorem on powers of the signless Laplacian and some remarks on star complements.     

High temperature x-ray powder diffractometric studies of the superconducting compound YBa2Cu3O7-x from room temperature to 1300 K in air

At room temperature, the compound YBa₂Cu₃O_7-x is orthorhombic, distorted perovskite, deficient in oxygen. X-ray powder diffractograms obtained for this compound over a range of temperatures between room temperature (298 K) and 1300 K in air reveal no change in X-ray diffraction pattern up to 1200 K except for slight shift in peak positions and variations in peak intensities because of thermal expansion and stoichiometry changes in oxygen or metal ion sub-lattices. At temperatures above ∼ 1250 K, the compund undergoes an irreversible transition to a new phase analogous to Y₂BaCuO₅ green phase which is an insulator. Temperature variation of lattice parameters shows an anisotropic expansion. Expansion along c-axis being maximum. Coefficients of linear thermal expansion along a and b axes are almost the same (δ_a≈δ_b≈7×10⁻⁶.K⁻¹) while along c-axis it is double (δ_c≈15×10^-6. K⁻¹) than that of a or b. Coefficient of volume thermal expansion of the unit cell (δ_v≈29×10⁻⁶.K⁻¹) obeys the relation δ_v≈δ_a+δ_b+δ_c for an orthorhombic symmetry in the range 298–1200K in air.     

High temperature superconductivity in Y-Ba-Cu-O and Y-Ba-Sr-Cu-O systems

Mixed metal oxides Y-Ba-Cu-O and Y-Ba-Sr-Cu-O have been prepared in varying compositions and by changing process parameters. Superconductivity with critical temperatures in the range of 70 to 100 K is reported.     

Core polarization effects in the Hartree-Fock-random phase approximation schemes

Core polarization effects in odd nuclei are investigated in the framework of the Hartree-Fock and random phase approximation schemes. The results of the particle vibration coupling model are recovered by linearizing the equations of motion in the interaction Hamiltonian between the external and the core particles. The formalism is used to study the renormalization of diagonal and off-diagonal M1 matrix elements. It is found that M1 polarization effects exhibit a very strong dependence on the range of the force.     

Positron annihilation in the vicinity of the critical solution point of methanol-cyclohexane mixtures

The positron annihilation method was used to investigate critical phenomena in liquid mixtures of methanol and cyclohexane. Anomalies in the annihilation parameters near the critical solution temperature were found.     

Preparation and study of a lithium phthalocyanine radical: optical and magnetic properties

A metallophthalocyanine radical, PcLi, was prepared by electrochemical oxidation of the corresponding dianion. The redox properties in solution show that PcLi is both easily reduced and easily oxidized (ΔE = E^red_1/2-E_1/2^ox = 0.83 V). This property is of the utmost importance for obtaining intrinsic molecular semiconductors. The optical properties are similar to those for oxidized phthalocyanines and involve two low-lying π-π transitions at 430 and 810 nm. Despite the tendency to aggregation, the ESR spectrum of the isolated PcLi molecule has been obtained. It is consistent with an unpaired electron delocalized over the whole phthalocyanine ring.     

FTIR spectroscopic studies of the CH3S + NO2 reaction under atmospheric conditions

Product studies using FTIR absorption spectrometry have been performed in a 420 xxx reaction chamber on the 254 nm photolysis of mixtures containing CH₃SSCH₃ and NO₂ at ppm concentrations in 760 Torr of O₂/N₂ diluent. The results indicate that the CH₃S radicals formed by photolysis of CH₃SSCH₃ react primarily with NO₂, forming CH₃SO and NO. In the presence of O₂ an unstable intermediate whose IR absorption spectrum resembles a peroxynitrate compound is observed. The intermediate has been tentatively assigned to methyl sulfinyl peroxynitrate, CH₃S(O)OONO₂. Other products include SO₂, CH₃SNO, CH₃SNO₂, CH₃NO₃, CH₃SO₃H, and HCHO.