Ron Catterall

Recombination kinetics following nanosecond laser photolysis of carbonmonoxyhaemoglobin

The kinetics of the ultrafast ligand recombination following 347 nm laser photolysis of aqueous solutions of carbonmonoxyhaemogloblin have been investigated. The process is biphasic and the rate constants for the two processes as functions of temperature have been used to give activation energies of 6 +/- 3.9 kJ . mol-1 for the fast process and 31 +/- 4.8 kJ . mol-1 for the slow process. Frequency factors have also been calculated. The two processes are discussed in relation to both low-temperature studies and model calculations on the rate of entry of carbon monoxide into haem proteins.

Electron spin resonance spectra of solvated alkali metal atoms in frozen solutions of sodium, potassium, rubidium, and caesium in hexamethylphosphoramide

Abstract Low temperature glasses formed by rapid freezing of potassium-, rubidium-, and caesium-hexamethylphosphoramide (HMPA) solutions gave electron spin resonance (ESR) spectra which consisted of a central singlet (Gaussian) resonance and a multiplet of lines characteristic of hyperfine coupling to a single metal nucleus. The species giving rise to the resolved metal hyperfine coupling have been identified as solvated alkali metal atoms with metal n s orbital occupation in the range 60–70% of the free-atom value. The species responsible for the central singlet have been identified as large Bohr radius states with associated low (≲ 1% of the free-atom value) unpaired electron spin density at the metal nucleus. In sodium-HMPA glasses, a strong absorption from collodial sodium metal effectively obscured the resonance from the low atomic character state, but signals attributed to spin transitions of the solvated sodium atom were observed. An estimate of matrix pertubations in A iso in terms of an atomic-like interaction potential for lithium, potassium and caesium atoms trapped in a HMPA matrix predicts shifts in A iso (from the free-atom value) an order-of-magnitude below those observed experimentally. The observed deviations in A iso and g e from free atom values have been interpreted in terms of a molecular orbital picture originally proposed to explain the magnetic properties of silver atoms in various polar matrices. A comparison of magnetic parameters ( A iso, g e) for the states identified in frozen M-HMPA solutions with those for fluid solutions of the alkali metals in amines and ethers show strong similarities between results for the two phases. Our results are used to distinguish between current models for the fluid solutions. It is proposed that the observed hyperfine splitting in fluid amine solutions arises from a dynamic interconversion between two (or more) paramagnetic species, one with a very low (≲ 1%) occupancy of the metal n s orbital and one with approximately 60–70% occupancy.

Magnetic properties of intermediate impurity states in frozen solutions of alkali metals in hexamethylphosphoramide

Abstract Electron spin resonance spectra at 77 K show the existence of several, discrete, intermediate impurity states which differ markedly in the percent occupation of the metal outer n s orbital. It is proposed that an amorphous matrix allows impurity states to assume only certain discrete eigenstates within the bandgap.

Electron spin relaxation studies of spin—phonon interactions in sodium and potassium metals

Abstract Conduction electron spin resonance (CESR) spectra are reported for colloidal alkali metal particles in frozen solutions of sodium and potassium in hexa Electron spin—lattice relaxation rates are governed primarily by spin—orbit coupling during spin—phonon scattering of high velocity electrons, an resistivity. A novel method of isolating the spin—orbit contribution to spin relaxation at 1.3 K is described: there is no evidence for freezing in of Umklapp pro

Density of states in the gap of a disordered material using E.S.R./optical correlations

Abstract Electron-spin-resonance studies of rapidly frozen solutions of alkali metals in anhydrous hexamethylphosphoramide (HMPA) indicate the presence of several, distinct localized electron states. Optical studies of similar species in a variety of fluid solutions reveal a simple correlation between the optical transition energy and the degree of occupation of the alkali-metal ns orbital. From this information we evaluate a distribution function for the various (localized) paramagnetic states present in the low-temperature disordered system. The localized states assume only a few, discrete eigenstates within the host (HMPA) bandgap. We speculate on the possible origin of these states; particular emphasis is placed upon the influence of lone-pair electrons and steric effects in determining the molecular configurations of the host matrix around the alkali atom during the quenching process. We point out the striking similarities between the eigenfunctions/eigenstates of matrix-bound states and the excited ...

Ion-pairing and electron spin resonance spectra of solutions of alkali metals in polar solvents

Abstract Electron spin resonance (ESR) spectra of solutions of potassium in mixtures of ethylamine and ethylenediamine are reported. It is shown that a simple ion-pairing treatment is quantitatively capable of predicting the form of the ESR spectra in this system and in a wide variety of other metal-solvent systems.

Observation of the rubidium-85, -87 solid-state hyperfine structure anomaly by electron spin resonance spectroscopy

The rubidium-85, -87 hyperfine structure anomaly for rubidium ‘atomiclike’ impurity states in a host matrix (hexamethylphosphoramide) has been measured by electron spin resonance spectroscopy. The average value [(1·672 ± 0·8) × 10-3] for an impurity state with approximately 70 per cent rubidium-5s atomic character is in overall agreement with the experimental value [(3·515 ± 0·004) × 10-3] for gas-phase rubidium atoms with 100 per cent occupancy of the 5s orbital. It is emphasized that, disregarding any enhanced mixing of higher angular momentum (L > 0) states in the matrix-bound state, the behaviour of the unpaired electron at (or inside) the nucleus is the same irrespective of whether the atom is in the gas phase or embedded in a host matrix. The slight decrease in the measured hyperfine structure anomaly for the solid-state species, as compared with its gas-phase counterpart, is reconciled with an appreciable admixture of rubidium 5p character into the impurity atom ground state wavefunction.

Ammonia diffusion and proton shifts in the alkaline earth hexaammines

Abstract Ammonia diffusion and proton shifts in Ca(NH 3 ) 6 , Sr(NH 3 ) 6 , and Ba(NH 3 ) 6 have been studied by high-resolution proton magnetic resonance. Ammonia diffuses rapidly in these compounds above ≈ 100 K by a hopping mechanism. Proton shifts are negative and very small and are interpreted in the light of recent ab initio calculations on metal—ammonia complexes.

Experimental observation of Wannier-Mott impurity ground states in an amorphous medium

Abstract The experimental observation of Wannier-Mott impurity ground states in an amorphous material is reported.

Eosin Y–macromolecule complexes. Part 1.—Application of exciton theory to the study of the arrangement of eosin Y molecules in polycation-induced eosin Y dimers

Evidence is presented for the formation of eosin Y dimers as the highest aggregates of complexes between eosin Y and poly-L-lysine, poly(p-xylyl viologen) or cetyl pyridinium. The absorption spectra of these complexes have been obtained free from contamination by eosin Y monomer spectrum and have been fitted with Gaussian band models using a non-linear least-squares fitting computer program. Using such models, simple excition theory had been employed to calculate parameters such as the orientations and molecular separations of the components of the eosin Y dimer. Where appropriate these parameters have been compared with the dimensions of the repeating unit and the possible conformations of the polymer.