Determination of the piezoelectric constant d14 of trigonal selenium crystals

Using the gain-bandwidth method, the piezoelectric constant d₁₄ of trigonal selenium has been deduced from measurements of the admittance and the electromechanical resonance frequencies of appropriately cut bars. The value was found to be |d₁₄| = (2.54 ± 0.2) × 10^?2C/N.     

Immobilisierte Leucin-Aminopeptidase. Anwendungen in der Proteinchemie

Ohne Zusammenfassung     

Synthesis ofo-thiatelluraphenylenezirconocenes. X-ray crystal structure of

o-Thiatelluraphenylenezirconocene complexes were obtained in good yield by reaction of dilithiumo-benzenthiatelluride with zirconocene dichlorides. These compounds represent the first examples of heterodichalcogenaphenylene bent metallocences. They were characterized by spectroscopic methods and the effect on the n.m.r. results of stepwise substitution of one and two Te atoms for S is discussed. X-ray crystal structure analysis was performed for one representative complex. The structure is very similar to that previously reported for a diselenaphenylene complex, but the disorder observed for chalcogen atoms prevents an accurate comparison of the geometrical parameters with other related compounds.     

Réactions induites par ies halogénures de pyridinium. XXVII. Sur la formation d'ethers cycliques par action du chlorure ou du bromure de pyridinium sur l'hexanediol-2,5

It has been shown that cyclodehydration of 2,5-hexanediols into 2,5-dimethyltetrahydrofurans can be effected with pyridinium chloride or bromide as well as with any other reagent formerly used for the purpose. The various secondary reactions accompanying this cyclodehydration have been determined, and plausible mechanisms for the ring closure are outlined.     

Nichtlineares Relaxationsverhalten von PMMA unterhalb der Einfriertemperatur

Zusammenfassung Das nichtlineare viskoelastische Relaxationsverhalten von Polymethylmethacrylsäureester (PMMA) wird an Hand von dynamischen Untersuchungen im Frequenzbereich von 10^–3 bis 10^–1 Hz, sowie durch Zug- bzw. Druckversuche bei verschiedenen Dehngeschwindigkeiten ( ) im Temperaturbereich von –80 °C bis + 80 °C unterhalb der Einfriertemperatur untersucht. Insbesondere wird die oft in der Literatur zitierte BeziehungE(t) =f(t)g (), d. h. auch im nichtlinearen Bereich bleibt bei jeweils auf konstante Dehnung bezogenen Dispersionskurven das Relaxationsspektrum unverändert, auf ihre Gültigkeit für PMMA geprüft. Dabei wurden bereits bei Dehnungsamplituden von 1 % Abweichungen von dieser Formel festgestellt, die mit zunehmender Dehnungsamplitude größer wurden.Mit 11 Abbildungen     

Processus de diffusion associe a certains modeles d'Ising a spins continus

Sans résumé     

Locating the vertices of a steiner tree in an arbitrary metric space

Given a tree each of whose terminal vertices is associated with a given point in a compact metric space, the problem is to optimally associate a point in this space to each nonterminal vertex of the tree. The optimality criterion is the minimization of the sum of the lengths, in the metric space, over all edges of the tree. This note shows how a dynamic programming solution to this problem generalizes a number of previously published algorithms in diverse metric spaces, each of which has direct and significant applications to biological systematics or evolutionary theory.     

The reaction of 2,4-diamino-6-piperidinopyrimidine 3-oxide with acid anhydrides

2,4-Diamino-6-piperidinopyrimidine 3-oxide reacts preferentially with acid anhydrides at the 4-amino group. The structures of amide products are readily assigned by the position of the 5-H.     

Chlorofluoroiodomethane as a potential candidate for parity violation measurements

CHFClI is among the more favorable molecules for parity violation (PV) measurements in molecules. Despite the fact that calculated PV effects are two orders of magnitude smaller than in some organometallic compounds, CHFClI displays interesting features which could make possible a new experimental PV test on this molecule. Indeed, ultrahigh resolution spectroscopy using an ultrastable CO(2) laser is favored by several intrinsic properties of this molecule. For example, the high vapor pressure of CHFClI allows investigation by supersonic beam spectroscopy. Indeed, the spectroscopic constants have been accurately determined by microwave and millimetre wave spectroscopy. This is important for the subsequent selection of an appropriate absorption band of CHFClI that could be brought to co?ncide with the absorption of CO(2). Partially resolved (+)- and (-)-CHFClI enantiomers with respectively 63.3 and 20.5% ee's have been recently prepared and analyzed by molecular recognition using chiral hosts called cryptophanes. Finally, the S-(+)/R-(-) absolute configuration was ascertained by vibrational circular dichro?sm (VCD) in the gas phase.     

Vibrational spectrum of katoite Ca3Al2[(OH)4]3: a periodic ab initio study

The vibrational spectrum of the Si-free katoite hydrogarnet (116 atoms in the unit cell) has been calculated at the periodic ab initio quantum mechanical level with the CRYSTAL program, by using a Gaussian type basis set and the hybrid B3LYP Hamiltonian. The harmonic frequencies at the Gamma point have been obtained by diagonalizing the mass-weighted Hessian matrix, that is evaluated by numerical differentiation of the analytical first derivatives of the energy with respect to the atomic Cartesian coordinates. The parameters controlling the numerical differentiation, as well as the numerical integration of the exchange-correlation functional for the self-consistent field (SCF) calculation, are shown to affect the obtained frequencies by less than 3 cm-1. Before diagonalization, the dynamical matrix is transformed to a block diagonal form according to the irreducible representations of the point group, so that the 345 vibrational modes are automatically classified by symmetry. Various tools are adopted (graphical representation, isotopic substitution, "freezing" part of the unit cell) that permit a complete classification of normal modes and, in particular, an analysis of the modes in terms of simple models (octahedra modes, Ca modes, H stretching, bending, rotations). The harmonic OH stretching band (48 modes) is quite narrow (20 cm-1), indicating that the interaction among OH groups is very weak. As the OH stretching modes are known to be totally separable from the other modes and strongly anharmonic, the one-dimensional Schroedinger equation for the anharmonic oscillator is solved numerically for the two extreme situations, corresponding to the vibration of one decoupled OH and of all 48 OH groups moving in phase. The anharmonic frequencies are 3682 and 3673 cm-1, respectively, in good agreement with IR experiments (a single band at 3661 cm-1 with a width at half band height of 33 cm-1) and confirming that the interaction between OH groups is extremely weak.