Advances in experimental and computational methodologies have led to a recent renewed interest in the Hofmeister series and its molecular origins. New results are surveyed and assessed. Insights into the underlying mechanisms have been gained, although deeper molecular understanding still seems to be elusive. The principal reason appears to be that the Hofmeister series emerges from a combination of a general effect of cosolutes (salts, etc.) on solvent structure, and of specific interactions between the cosolutes and the solute (protein or other biopolymer). Hence every system needs to be studied individually in detail, a state of affairs which is likely to continue for some time. A deeper understanding of the Hofmeister series can be an extraordinarily valuable guide to designing experiments, including not only those probing the series per se, but also those designed to elucidate the adsorption, aggregation and stabilization phenomena which underlie so many biological events. The aim of this review is to provide an up-to-date framework to guide such understanding, consolidating recent advances in the many fields on which the Hofmeister series impinges.

The Hofmeister series: salt and solvent effects on interfacial phenomena

Kraitchman has shown that a single isotopic substitution on an atom is sufficient to determine directly the coordinates of that atom with respect to the principal axes of the original molecule. Kraitchman's formulas represent exact solutions of the equations for the equilibrium moments of inertia. However, the effects of the zero‐point vibrations are such that the coordinates obtained by substitution from the ground state moments of inertia I0 are systematically less than r0. These coordinates have here been called r (substitution) or rs, and it is found that rs≃(r0+re)/2, and Is= ∑ imirsi2≃(I0+Ie)/2.In the usual method of solution, the coordinate of one atom is determined from the equation for I0, and therefore the difference I0—Is must be made up by this one coordinate. This introduces a large error in the structures normally determined from ground state constants, and results in variations of 0.01 A in structures determined from different sets of isotopic species. If instead, we obtain the structure on...

A new criterion for the determination of molecular structures from ground state rotational constants

Mixed sequence DNA can exist in two right-handed and one left-handed double helical conformations--A, B and Z. Under conditions of high water activity the B conformation prevails. If the water activity is reduced on addition of salt or organic solvents, transformation occurs to A-DNA or, in DNAs with alternating purine-pyrimidine sequences, to the left-handed Z-DNA. In crystal structure analyses of oligonucleotides, the free oxygen atoms of adjacent phosphate groups along the polynucleotide chain in B-DNA are found at least 6.6 A apart and individually hydrated whereas they are as close as 5.3 A in A-DNA and 4.4 A in Z-DNA, and bridged by water molecules. We suggest that this more economical hydration in A- and Z-DNA compared with B-DNA is the underlying cause of B----A and B----Z transitions.

DNA conformation is determined by economics in the hydration of phosphate groups

Information pertaining to the stereochemistry of metalloporphyrins and other tetrapyrroles continues to expand. The present article reviews important developments of this structural chemistry. Detailed updates on the relationship of the structure and physical properties of iron derivatives are given. Metalloporphyrins with unusually high or low oxidation states are reviewed. Surveys of recent work on π-cation radical complexes, bound O2 species, tetrapyrroles with N-substituents, the stereochemistry of ring-reduced tetrapyrroles and a variety of novel species are given. Newly developed data concerning experimental electron density studies are summarized. Detailed reviews of porphyrin-porphyrin (π-π) interactions in the solid state are given. A variety of important conformational aspects of metalloporphyrins and their consequent results on physical properties are presented. Finally, a number of isomorphous series and crystal packing effects in tetrapyrroles have been detailed.

Recent advances in the stereochemistry of metallotetrapyrroles

Cytochrome P450s (P450s) are subject to inhibition/inactivation by various chemically diverse agents, which may interact directly or indirectly with either the P450 prosthetic heme or the protein moiety or with both moieties. This inhibition is clinically relevant, as it can block physiological pathways as well as result in therapeutically significant beneficial or adverse effects and clinically relevant drug–drug interactions. Herein, we discuss the various chemical agents and their chemical mechanisms that lead to such reversible, quasi-irreversible, or irreversible inhibition of these enzymes. We note that such inhibition targeted at P450-dependent physiological and/or pathological processes has been ingeniously and effectively harnessed not only in the design and development of clinically relevant therapeutic agents but also of fungicides, insecticides, and herbicides.

Inhibition of Cytochrome P450 Enzymes

Dichlorocarbene Complexes of Iron(II)‐Porphyrins–Crystal and Molecular Structure of Fe(TPP)(CCl2)(H2O)

Solvation of the left-handed hexamer d(5BrC-G-5BrC-G-5BrC-G) in crystals grown at two temperatures

An iron(iii)-porphyrin complex with a vinylidene group inserted into an iron-nitrogen bond: relevance to the structure of the active oxygen complex of catalase

Addition compounds of Lewis acids MXn and acyl halides RCOX occur as intermediates in Friedel-Crafts acylations. IR and NMR studies on these intermediates have indicated the probable existence of structural isomers. In X-ray structural analysis, it is possible to distinguish two forms, i.e. the molecular form, in which the compounds are present as donor-acceptor complexes RCXO→MXn, and the ionic form, in which they can be formulated as oxocarbenium salts [RCO]+[MXn+1]−. The compounds of the donor-acceptor type RCXO→MXn are characterized by the formation of a coordinate oxygen-metal bond; the transfer of electrons from the oxygen to the metal of the acceptor is always due to a weak donor-acceptor interaction. The positive charge of the aryloxocarbenium ions is partly delocalized over the aromatic nucleus. The positive charge in alkyloxocarbenium ions, on the other hand, is essentially localized on the carbon atom of the carbonyl group, as is confirmed by electron density distribution calculations.

Structures of the Intermediate Complexes in Friedel‐Crafts Acylations

Molybdenum(IV)-porphyrin derivatives: the oxo(5,10,15,20-tetra-p-tolylporphyrinato)molybdenum(IV), MoO(TTP), and the dichloro(5,10,15,20-tetra-p-tolylporphyrinato)molybdenum(IV), Mo(Cl)21(TTP). Syntheses and structures

Bernard Chevrier

Papers

Dichlorocarbene Complexes of Iron(II)‐Porphyrins–Crystal and Molecular Structure of Fe(TPP)(CCl2)(H2O)

Solvation of the left-handed hexamer d(5BrC-G-5BrC-G-5BrC-G) in crystals grown at two temperatures

An iron(iii)-porphyrin complex with a vinylidene group inserted into an iron-nitrogen bond: relevance to the structure of the active oxygen complex of catalase

Structures of the Intermediate Complexes in Friedel‐Crafts Acylations

Molybdenum(IV)-porphyrin derivatives: the oxo(5,10,15,20-tetra-p-tolylporphyrinato)molybdenum(IV), MoO(TTP), and the dichloro(5,10,15,20-tetra-p-tolylporphyrinato)molybdenum(IV), Mo(Cl)21(TTP). Syntheses and structures