Chemistry in low-temperature matrices

Abstract

the Progress of Chemistry, Section C. The report is divided into sections: weak adducts and conformational isomers; reactions of atoms; high-temperature molecules; photochemistry; biological molecules; astrochemistry. The last two sections reflect the fact that matrix isolation now extends into areas outside the traditional mainstream disciplines of chemistry. There are a number of areas where substantial progress has been made during the period of this report. First, the routine use of laser-ablation to generate atoms and to initiate atomic reactions in matrices has increased the scope of matrix isolation to synthesise many new molecular species in inorganic chemistry. Laser-ablation allows ground state atoms to be more easily studied than is the case when atoms are produced by thermal methods. Moreover, this procedure allows atoms to be generated from materials where thermal production is difficult. Secondly, the manufacture of more efficient closed-cycle helium refrigerators allows hydrogen matrices to be deposited readily. A significant body of work therefore has focussed upon metal hydrides, dihydrogen complexes and other hydrogen species in matrices. Underpinning all of this experimental work are theoretical calculations, without which the correct identification of most matrix isolation molecules would remain dangerously ambiguous. Infrared spectroscopy remains-as it has for the past 50 years-the workhorse of matrix isolation studies. It does seem that this situation will not change-it is impossible to conceive of another spectroscopic method that combines the necessary sensitivity to study molecules at very low dilution with the structural information required to make a reasonably certain identification.

FTIR matrix isolation and theoretical studies of glycolic acid dimers

“…In this paper we present results of experimental and theoretical studies of glycolic acid dimers. Matrix isolation (MI) coupled with FTIR spectroscopy was applied which is an established technique for studying small hydrogen bonded systems [27][28][29]. When supported with computational methods the isolated hydrogen bonded complex structures are well resolved and distinguishable.…”

The application of synchrotron radiation and in particular X-ray absorption spectroscopy to matrix isolated species

“…Matrix isolation is an experimental method for stabilising otherwise intractable, unstable and highly reactive species long enough for them to be spectroscopically characterised. The use of solid noble gases was originally pioneered by George Pimentel in the 1950s [1] and has now developed into a mature technique that has been used to study a wide selection of species [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. In essence, it is similar to preparing a KBr disc for IR spectroscopy, except that the KBr is replaced by a cryogenic matrix such as solid neon, argon or nitrogen, and true atomic or molecular dilution is achieved.…”

Cryoradiolysis as a Method for Mechanistic Studies in Inorganic Biochemistry

“…All primary products formed at low temperatures are assigned as unprotonated peroxo-ferric complexes ([Fe--O 2 ] À in author's notation) with significant spin density on both oxygen atoms of peroxide confirmed by 17 Bartlett and Symons reported an unusual EPR spectrum from cryoreduced monomeric oxy-hemoglobin from Glycera dibranchiate. Radiolysis was performed at several temperatures between 77and 4.2K with g-rays and X-rays.…”

“…Traditional experimental methods for studies of chemical kinetics are based on time-resolved methods monitoring relaxation of the system after fast perturbation via rapid change of composition (mixing of the reagents), rapid changes of conditions, for example, temperature jump or pressure jump, photolysis, and so on. 17 Trapping methods to study unstable intermediates in protein crystals have been reviewed by Schlichting. Both approaches require sufficient buildup of the reaction intermediates, and can detect only those transient species that are accumulated up to certain levels during the reaction.…”