INTRAMOLECULAR EXCIPLEX FORMATION IN Nα-ACETYL-1-PYRENYLALANYL-1-METHYLTRYPTOPHAN METHYLESTER

Abstract— The synthesis, absorption and emission properties of erythro (e) and threo (t) Na-acetyl-1-pyrenylalanyl-1-methyltryptophan methylester (APTE) are reported. From the dependency of the exciplex emission maximum on the solvent polarity, the exciplex dipole moment of erythro and threo APTE were calculated. The evolution of the ratio of the quantum yield of exciplex emission and the quantum yield of emission from the locally excited state is correlated with solvent polarity and with the tendency of the solvent to interact with the peptide chain through hydrogen bonding. It is shown that solvents, inert towards the peptide function, shift the equilibrium between the two ground state conformations towards C₇, in which an exciplex geometry can be reached. Hydrogen accepting solvents shift the conformational equilibrium towards C₅, which cannot form an exciplex directly within the lifetime of excited pyrene.     

Gmelin handbook of inorganic chemistry, 8th edit., S — Sulfur-Nitrogen Compounds,Part 2: Compounds with Sulfur of Oxidation Number IV: Springer-Verlag,Berlin, Heidelberg,New York,Tokyo, 1985, xiv + 333 pages,DM 1144, ISBN 3-540-93512-6

A close examination of the ESR spectrum of a paramagnetic complex formed from bis(ethoxythiocarbonyl)sulfide and dimanganese decacarbonyl has revealed, for the first in this type of radical adduct, ₁₃C hyperfine coupling in natural abundance from the carbonyl ligands.     

Ta4P4S29: A new tunnel structure with inserted polymeric sulfur

Ta₄P₄S₂₉ was prepared from the elements heated together in stoichiometric proportions in an evacuated Pyrex tube for 10 days at 500°C. The crystal symmetry is tetragonal, space group P4₃2₁2, with the cell parameters: a = b = 15.5711(7) Å, c = 13.6516(8) Å, V = 3309.9(5) ų, and Z = 4. The structure calculations were conducted from 2335 reflections and 146 variables, leading to R = 0.033. The structure basic framework, corresponding to the chemical composition [TaPS₆], is made of biprismatic bicapped [Ta₂S₁₂] units (average d_TaS = 2.539 Å), including sulfur pairs (average d_SS = 2.039 Å), bonded to each other through [PS₄] tetrahedral groups (average d_PS = 2.044 Å) sharing sulfurs. This framework leaves large tunnels running along the c axis of the cell and in which (S₁₀)_∞ sulfur chains are found to be inserted (average d_SS = 2.052 Å and SSS = 105.75°). Diamagnetic and semiconducting Ta₄P₄S₂₉ can be formulated: Ta^V₄P^V₄(S^?II)₁₆(S^?II₂)₄(S⁰₅).     

Über Perrhenate. 1. Zur Kenntnis von LiReO4

About Perrhenates. 1. On LiReO₄ For the very first time anhydrous LiReO₄ was prepared in transparent, colourless single crystals from Li₂O₂ and Re₂O₇ (closed Au-pipe; 350°C; 14 d). The crystal structure, P1 , with a = 9.652(1), b = 8.455(1), c = 6.928(1) Å, α = 101,53° (1), β = 106.55° (1), γ = 97.22° (1), Z = 6, d_x = 4.92 g/cm³, d_pyk = 4,81 g/cm³ was solved (four-circle-diffractometer data PW 1100, 2151 I₀ (hkl), AgKα; R = 0.073, R_w = 0.076). There are three kinds of functionally different Li⁺. The Madelung Part of the Lattice Energy, MAPLE, was calculated.     

The polymorphic transformations of cobalt molybdate

Polymorphic transformations of CoMoO₄ were studied by means of high temperature X-ray measurements within the temperature range 25–1200°C. On heating phase a obtained from low temperature modification b a new modification a′ was discovered. Phase a obtained by thermal decomposition of solvated α-CoMoO₄ shows different behaviour. At 700–930°C depending on the conditions of preparation it transforms irreversibly into still another modification a″. On cooling, a mixture of phases a + a″ is obtained, the presence of a″ being responsible for the explosionwise transition into b, observed around the room temperature.     

Rearrangement thermique des α-ceto, α-cyano epoxydes en dioxoles : Etude du mecanisme de la reaction

The thermolysis of α-cyano α-keto epoxides to give dioxoles is a new rearrangement. The reactivity of the epoxides is dependent upon the nature of the substituents on the epoxide ring, and solvent polarity. When the reaction is carried in the presence of benzaldehyde, a 1,3 cycloadduct is obtained. These results are in good agreement with a carbonyl ylide intermediate.     

Nitro compounds as alkylating reagents in friedel-crafts conditions : Reaction of 2-nitropropane with benzene

Friedel-Crafts reaction of benzylic or tertiary nitro compounds with benzene gave normal alkylation products. Similarly, 2-nitropropane (2-NP) gave cumene (1) which underwent further transformation affording a mixture whose behaviour with time was investigated : results were consistent with oxidative formation of the cumyl carbonium ion (7').     

Reaction of β-amino-α,β-unsaturated esters and amides with aryl diazonium salts : Synthesis of cinnoline derivatives

Conjugated esters and amides react with aryldiazonium salts at room temperature (MeCN) to form the corresponding iminium hydrazone derivatives, which can be thermally cyclized to cinnoline-3-esters and cinnoline-3-amides. In general the intermediate iminium salts derived from the enamine amides cyclize faster than those from the enamine esters. Furthermore, the ease of cyclization depends upon the structure of the base-component of the enamine ester or the amide and the substituent in the aryl moiety of the diazonium salt. The configurational structure of the iminium hydrazones, studied by NMR spectroscopy, has been shown to involve H-bonding of the hydrazonyl N-H with the ester or the amide CO group.