Isolation,reactions and x-ray structure of tetraethylammonium dihydridotetracarbonylrhenate

The isolation and characterization of the novel hydridic compound [Net₄][H₂Re(CO)₄], obtained from the reaction of Re₂(CO)₁₀ with methanolic KOH, are described. Its reactions with I₂, strong acids, and ethanol are reported. The salt gives triclinic crystals, investigated by X-ray analysis, with cell constants a = 14.493(6), b = 7.564(3), c = 7.930(3) Å, α = 72.97(4)°, β = 81,73(4)°, γ = 96.63(4)°; space group P$\text{1}$. The structure was solved by conventional Patterson and Fourier methods and refined by least-squares up to a final R values of 0.071, for 1586 independent counter data. The anion exhibits a distorted octahedral geometry, with the two hydrido ligands in cis position between themselves. The mean values of the ReC and CO distances are 1.89 and 1.21 Å. The carbonyl groups are significantly bent towards the hydrido ligands.     

The penrose transform and the topology of certain algebraic varieties

We study the multivaluedness of functions obtained via the Penrose transform. We show that the monodromy group of the Penrose transform of a meromorphic function with an irreducible pole variety is the full symmetric group.Research supported by CNR.     

Dynamics of chain molecules. Intramolecular diffusion controlled reactions for a pair of terminal reactive groups

The first order intramolecular rate constant for the reaction between the terminal groups of flexible macromolecules is calculated in the partial draining case, following the theory formulated by Wilemski and Fixman for diffusion controlled reactions. Substantial differences with respect to the nondraining and free-draining limits are evidenced, and it is shown that the rate constant in the partial-draining case has relevant contributions from all the modes of the bead-spring chain. The effects of chain flexibility and hydrodynamic interaction in macromolecules of increasing molecular weight are examined. The effective diffusion constant of the end groups increases with both the flexibility and the length of the chain. Numerical results for polystyrene (PS) and polydimethylsiloxane (PDMS) are presented and employed to calculate the relative quantum yield for fluorescence quenching. For highly flexible chains, like PDMS, quenching effects are expected in a range of molecular weight well above the limit of validity of the bead-spring model. On the contrary, for more rigid polymers, like PS, the quenching can be observed only at molecular weights lower than this limit. The calculated behavior is compared with some experimental results recently obtained by the authors.     

APPLICATIONS OF ELECTRONIC ENERGY TRANSFER IN SOLUTION*,†

Abstract— lntermolecular transfer of electronic energy is a powerful tool for obtaining information about excited molecules in solution. Proper application of excitation transfer requires giving careful attention to the spectroscopic properties of the donor and acceptor and accounting for all possible donor-acceptor interactions of consequence. Water presents no particular difficulties so that electronic energy transfer methods can be applied to the photochemistry of biologically important molecules in aqueous solvents.     

Time-reversal invariance and thermodynamics of electromagnetic fields in materials with memory

Summary In this work we consider thermal and electric conduction in rigid materials with memory. The implications due to the invariance of the entropy production under time-reversal are examined in detail. Some interesting conditions on the relaxation functions of the heat flux, the electric current and the internal energy density are discussed.

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Sunto In questo lavoro gli Autori studiano la conduzione termica ed elettrica in un materiale rigido con memoria. Vengono esaminate in dettaglio le conseguenze, dovute alla invarianza della produzione entropica per inversione temporale, sulle funzioni di rilassamento per il flusso di calore, la densità di corrente elettrica e la densità di energia interna.

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This work was supported by the ? Gruppo Nazionale per la Fisica Matematica ? of C.N.R.

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Entrata in Redazione il I^o ottobre 1973.     

PHOTOOXIDATIVE AND SPECTRAL STUDIES ON CYTOCHROME c. CONFORMATIONAL CHANGES INDUCED BY BINDING OF CARDIOLIPIN

Abstract— Binding of cardiolipin to ferrocytochrome c , to form a 4:1 molar complex, results in an approximately sixfold increase of the tryptophan fluorescence emission. Furthermore, appreciable perturbations of the circular dichroism spectrum occur in the Soret and in the far-ultraviolet regions. The irradiation of the ferrocytochrome–cardiolipin complex at pH 8·8 with visible light leads to the photooxidative modification of histidine-18, tyrosine-48 and methionine-80. Comparison of the above findings with those concerning unbound ferrocytochrome c suggests that the interaction between cardiolipin and ferrocytochrome c provokes a perturbation of the protein conformation, which possibly involves the disruption of the hydrogen bonds linking the aromatic rings of tryptophan-59 and tyrosine-48 with one propionic side chain of the heme.     

Ovals in a plane coordinatised by a regular nearfield of dimension 2 over its centre

We give a characterisation of the Rosati oval in the regular nearfield plane of dimension 2 over its centre.