The effect of dipole-dipole interaction on zero-THz frequency polarisation

The effect of intramolecular dipole-dipole interaction on polarisation at frequencies from 0 – 10¹² Hz in dipolar media is investigated using a numerical solution of the Sturm-Liouville eigenvalue problem to which the governing Smoluchowski equation reduces. The results of Budó for the long-wavelength limit are extended to all frequencies up to the far infrared, where the predominant inertial effects are treated using a preliminary first-order correction. The numerical method of Pryce may be used to investigate much more realistic interaction potentials than the simple harmonic and cosine form considered by Budó. These simple forms are, however, sufficient to indicate that the integrated absorption intensity per molecule in the far infrared is very sensitive to dipole-dipole interaction and relative hydrodynamic drag on both interacting groups. Applications of the theory to the disordered solid and nematic phases are considered.     

A mass spectrometric study of the pyrolysis of gibberellic acid

The behaviour of gibberellic acid (GA₃) under electron impact and chemical ionization conditions has been examined. The tendency of GA₃ to undergo pyrolysis by the loss of the elements of water and carbon dioxide has been identified. Two methods of sample introduction can be used to minimize the occurrence of this pyrolysis. Accurate mass measurement allows the composition of the pyrolysis product to be determined and metastable techniques confirm the structure of this product to be epi-allogibberic acid rather than its isomer allogibberic acid. This result corrects a misconception in the literature and illustrates the advantage of metastable methods compared with accurate mass measurements, for the determination of small structural differences within a molecule.     

Plant hormones. X. The constitution of phaseic acid; a relative of abscisic acid from Phaseolus multiflorus. An interpretation of the mass spectrum of phaseic acid and a probable structure

After a detailed examination and interpretation of the MS of phaseic acid and methyl phaseate structure (I) is preferred for this putative relative of abscisic acid from Phaseolus multiflorus. Two facts, more difficult to reconcile with this structure are an abnormally large long-range coupling and the apparent inability of phaseic acid to undergo an alkali-induced β-elimination of the epoxide oxygen to the γ- hydroxy-β-unsaturated ketone. Attempted one step conversion of methyl phaseate into methyl abscisate produced a complex but apparently identical reaction mixture to that obtained from methyl abscisate when treated under the same conditions.     

The diffraction of radio waves by the curvature of the earth

This paper gives a simplified approximate derivation of the field at moderate heights and distances due to an oscillating electric dipole at moderate height above the earth, taking into account the curvature and electrical constants of the earth. The method applies to both vertically and horizontally polarized waves. It is closely connected with treating the earth as flat, the propagation of the waves being curved upwards. In this way the expansions in Legendre functions can be replaced by Fourier integrals, which are simpler to handle. The results of previous workers are reproduced, but are obtained more directly in a form suitable for easy computation.     

C-terminal processing of yeast Spt7 occurs in the absence of functional SAGA complex

Background  

Spt7 is an integral component of the multi-subunit SAGA complex that is required for the expression of ~10% of yeast genes. Two forms of Spt7 have been identified, the second of which is truncated at its C-terminus and found in the SAGA-like (SLIK) complex.     

Reinvestigating 2,5-di(pyridin-2-yl)pyrazine ruthenium complexes: selective deuteration and Raman spectroscopy as tools to probe ground and excited-state electronic structure in homo- and heterobimetallic complexes

The mono- (1) and dinuclear (2) ruthenium(II) bis(2,2'-bipyridine) complexes of 2,5-di(pyridin-2-yl)pyrazine (2,5-dpp), for which the UV/Vis absorption and emission as well as electrochemical properties have been described earlier, are reinvestigated here by resonance, surface enhanced and transient resonance Raman spectroscopy together with selective deuteration to determine the location of the lowest lying excited metal to ligand charge transfer ((3)MLCT) states. The ground state absorption spectrum of both the mono- and dinuclear complexes are characterised by resonance Raman spectroscopy. The effect of deuteration on emission lifetimes together with the absence of characteristic bipy anion radical modes in the transient Raman spectra for both the mono- and dinuclear complexes bridged by the 2,5-dpp ligand confirms that the excited state is 2,5-dpp based; however DFT calculations and the effect of deuteration on emission lifetimes indicate that the bipy based MLCT states contribute to excited state deactivation. Resonance Raman and surface enhanced Raman spectroscopic (SERS) data for 1 and 2 are compared with that of the heterobimetallic complexes [Ru(bipy)(2)(2,5-dpp)PdCl(2)](2+)3 and [Ru(bipy)(2)(2,5-dpp)PtCl(2)](2+)4. The SERS data for 1 indicates that a heterobimetallic Ru-Au complex forms in situ upon addition of 1 to a gold colloid.     

Efficient implementation of Jacobi's diagonalization method on the DAP

Summary The DAP architecture brings into consideration the Jacobi method where several non-interacting rotations can be performed in parallel. However the design of the algorithm is crucial in a parallel environment. In this paper we shall consider two techniques specifically designed to reduce the organisation and the arithmetic components of the parallel Jacobi method.     

Plant hormones. IX. Phaseic acid, a relative of abscisic acid from seed of Phaseolus multiflorus. Possible structures

IR, UV, NMR and MS have been used to investigate the structure of phaseic acid, a C₁₅-acid isolated from immature seed of Phaseolus multiflorus. Of the seven structures considered, the spectroscopic data is best interpreted in terms of the epoxide (I) or the oxetane (XV). Phaseic acid appears to be a close structural relative of the natural plant growth inhibitor, (S)-(+)-abscisic acid     

Redox control of meso-zinc(II) ferrocenylporphyrin based fluorescence switches

The efficient on/off switching of fluorescence from thienyl- and phenyl-substituted porphyrin-ferrocene dyads is achieved through redox control of excited-state electron-transfer quenching.     

Thienyl—Appended porphyrins: Synthesis,photophysical and electrochemical properties,and their applications

This review focuses on the synthesis, photophysical and electrochemical properties of thienyl porphyrins where processes such as electron transfer, energy transfer and electropolymerisation are discussed. The purpose of this review is to examine the influence of the thienyl ring, whether it be directly connected (via meso and β positions) or indirectly connected (via a covalent linker or axial coordination) on the ground and excited state electronic properties of the porphyrin macrocycle. Additionally, the importance of the electronic properties of a bridging oligothiophene between the porphyrin and another centre in supramolecular systems is discussed. Also included are applications of thienyl porphyrins in such areas as catalysis, therapeutics, (opto)electronics and electron-transfer/light-harvesting systems.