Inorganic Biochemistry Volume 3

A Review of the Literature Published Up to 1980

By H. A. O. Hill

The Royal Society of Chemistry

Copyright © 1982 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85186-565-2

Contents

Chapter 1 Inorganic Analogues of Biological Molecules By C. A. McAuliffe, 1,
Chapter 2 Storage, Transport, and Function of the Cations of Groups IA and IIA By M. N. Hughes, 33,
Chapter 3 Transport and Storage of Transition Metals By R. R. Crichton and J.-C. Mareschal, 78,
Chapter 4 Oxygen-Transport Proteins By M. Brunori, B. Giardina, and H. A. Kuiper, 126,
Chapter 5 Oxidases and Reductases By A. E. G. Cass, 183,
Chapter 6 Zinc Metalloenzymes By A. Galdes, 268,
Chapter 7 Manganese Metalloproteins and Manganese-Activated Enzymes By A. R. McEuen, 314,
Chapter 8 Trace Elements in Animal Nutrition By J. R. Arthur, I. Bremner, and J. K. Chesters, 344,
Chapter 9 Inorganic Elements in Biology and Medicine By N. J. Birch and P. J. Sadler, 372,

CHAPTER 1

Inorganic Analogues of Biological Molecules

C. A. McAULIFFE

1 Complexes of Amino-Acids and Peptides

Simple Amino-Acids and Peptides. — The structural characteristics of the binding of calcium ion to the aminocarboxylates EDTA and NTA (nitrilotriacetate) are shown in Ca[Ca(EDTA)]·7H2O and Na[Ca(NTA)]. In the former, the Ca2+ has eight-fold co-ordination with a sexidentate EDTA ligand and in the latter the Ca2+ has seven-fold co-ordination with a quadridentate NTA ligand. Infrared band assignments have been made for cadmium glycinate monohydrate.

The compound [Mo2(gly)4Cl2]·xH2O (gly = glycine) has been obtained in two different crystalline forms; form 1 (x = 3) contains two equivalent [Mo2(gly)4]4+ ions per unit cell, with d/(Mo — Mo) = 2.112 Å and weak axial co-ordination of Cl- [d/(Mo ··· Cl) = 2.882 Å]. For form 2 (x = 2.61) there are three crystallo-graphically independent molecules, each residing on a crystallographic inversion centre. When solutions of [Mo2{O2CCH(NH3)R}4]4+ and KNCS are mixed,red to red-purple complexes [Mo2{O2CCH(NH3)R}2(NCS)4]·nH2O are obtained.For the glycinate (R = H, n = 1) and L-isoleucinate (R = CHMeEt, n = 4.5) there are cisoid arrangements of the amino-acid groups, and the four N-bonded NCS ions, together with the molybdenum atoms, form a sawhorse arrangement; the Mo–Mo distances are in the range 2.132 — 2.154 Å. The solution structure and equilibria of vanadium(V), molybdenum(VI), and tungsten(VI) complexes formed by H4EDTA, ethylenediamine-TVTV-diacetic (H2EDDA), H3NTA, and iminodiacetic (H2IDA) acids show that formation constants of the 1:1 complexes increase with the number of chelate rings, as expected, and decrease from V to Mo and W for a given ligand.

First-row transition-metal(II) complexes of N-acetyl-DL-valine of the type [M(AcValO-)]·xH2O (M = Co or Ni, x = 2; M = Zn, x = 0) (AcValO- = N-acetyl-DL-valinate) and their amine adducts of the type [M(AcValO-)2]·B2(B = pyridine, 3- or 4-methylpyridine, or 1,10-phenanthroline) have been isolated; the CoII and NiII compounds have MO6 and MO4N2 chromophores. In [Co(dien){(S)-glutamato-2}]+ the (S)-glutamic acid behaves as a bidentate ligand with a dangling — (CH2)2COO- group. 1:1 Complexes between bivalent Co, Ni, and Cu and tetrapeptides containing tyrosine and glycine residues are formed in solution over a wide pH range; protons are ionized from terminal groups as well as from peptidic nitrogen atoms. Resulting from the intramolecular addition of cobalt(III)-bound H2O and OH- to glycinamide, glycylglycine isopropyl ester and glycylglycine also co-ordinated to cobalt(III) in the cis– [Co(en)2(OH2/OH)(GlyNHR)]3+/2+ ions (R = H, CH2CO2C3H7, or CH2CO-). Both the aquo- and the hydroxo-species form [Co(en)2(GlyO)]2+ for the dipeptide complex (R = CH2CO2C3H7), but loss of hydroxide also occurs, resulting in the chelated amide [Co(en)2(GlyNHR)]3+. The c.d. spectra of complexes of the type [Co(amOH)(N)2(O)2], where amOH = 2-aminoethanol or (S)-2-aminopropan-1-ol and (N)2(O)2 = (gly)2, (β-ala)2, (ox)(en), or (ox)(NH3)2, have been measured. The kinetics and steric course of basic hydrolysis (displacement of X-) of the species trans-[Co(en)2X{O2CCH(R)NH2}]+ show that, for the DL-alanine and DL-aminobutyric acid complexes, 65±5% of trans– and 35±5% of cis– [Co(en)2-OH{O2CCH(R)NH2}]+ are formed. The quadridentate ligand (2S,2‘S)-1,1′-(ethane-l,2-diyl)bis(pyrrolidine-2-carboxylic acid) dihydrochloride (H2pren·2-HCl) has been derived from (5′)-proline, and cis-α geometrical isomers have been obtained, viz Na[Co(pren)(CO3)]·3H2O, [Co(pren)(H2O)2]ClO4·2H2O, and [Co(pren)(H2O)Cl]·1½H2O. The differential reactivity of the α-methylene protons of bis(pyridoxylideneglycinato)cobalt(III) may have inferences for reactions that are catalysed by vitamin B6. The X-ray crystal structure of fac(N)-Δ-tris-(L-asparaginato)cobalt(III) trihydrate shows that the amide groups of the two side-chains approach the central metal atom, and the oxygen atoms are connected through intramolecular hydrogen-bonds. The separation of the meridional isomers of [Co(α1-α2)2]- (Hα1- Hα2 is a dipeptide, H2NCHR1-CONHCHR2CO2H, ranging from Gly-Gly to L-Phe-L-Phe) has been achieved by Gillard and co-workers. Detailed comparison of the 1H n.m.r. spectrum of the pairs of diastereoisomers enabled determination of their absolute configuration unambiguously for [Co(L-Phe-GlyO)2]- and [Co(Gly-L-PheO)2]-. The Hg2+-catalysed removal of Br- from cis-[Co(en)2Br(GlyNHR)]2+ results in the immediate formation of [Co(en)2(GlyNHR)]3+ containing the chelated amide or dipeptide; full retention of configuration about the CoIII centre obtains, and no intermediate aqua-complex is formed. An effective t.l.c. technique has been developed for the separation of cobalt(III) geometrical isomers and diastereoisomers and various derivatized amino-acid and peptide ligands.

Single-crystal X-ray structures of the hippurates [M(hipp)2(H2O)3]·2H2O (M = Ni or Cu) show the compounds to be isostructural and to crystallize as linear chains with canted metal octrahedra. Mixed ligand complexes [MHAL] and [MAL] (A=histamine, 1,10-phenanthroline, or α, α’-bipyridyl; L = O-phospho-DL-serine; M = Cu, Ni, Co, or Zn) contain terdentate O-phosphoserine in MAL for Ni, Co, or Zn but bidentate for Cu. Owing to the planar configuration in the Cu complex, the phosphate moiety is not bound.

Farago and Mullen have examined the copper complex of a ninhydrinpositive ligand in the water extract from the roots of the copper-tolerant strain of Armeria maritima; this may be a copper–proline species. An increasing number of Schiff-base amino-acid ligands are being complexed to copper(II). Thus, the glycine residue in N-salicylideneglycyl-L-valinatocopper(II) reacts with formaldehyde in aqueous solution at pH 8.5, and the resulting complex gives seryl-L-valine that contains optically active serine. The copper complexes obtained from the reactions of Cu2+ with Schiff bases derived from histamine and salicylaldehyde or pyridine-2-carbaldehyde in acidic solutions are mononuclear, whilst tetranuclear complexes are obtained in basic solutions. In µ-(N-salicylidene-L-valinato-O)-N-salicylidene-L-valinatodiaquadicopper(II) there is one square-pyramidal and one planar co-ordination of copper. The A-salicylidene-L-valinato-group occupies three positions of the basal plane around Cu-1 and a co-ordinated water molecule occupies the fourth position. An oxygen atom of the adjacent carboxylate group occupies the axial position. The basal plane of Cu-2 contains three atoms of the ligand and a water molecule. Copper(II) complexes with terdentate Schiff-bases derived from the condensation of (+)-(hydroxymethylene)camphor or (-f)-(hydroxymethylene)menthone with a series of (S)- and (R)-amino-acids have been isolated; little interaction between the various chiral centres has been found, and the conformation of the chelate rings depends mainly on the configuration of the α-carbon atom of the amino-acid. The crystalline trans-isomer of bis(glycinato)copper(II) is, contrary to many reports, a monohydrate. The dehydration of the solid cis-monohydrate at sufficiently high temperatures leads to the mainly anhydrous trans-complex, which readily re-hydrates to give the trans-monohydrate; this is a useful preparative technique. The reaction of a methanolic suspension of CuCOCl with histamine (hm) at 0°C gives a solution from which [Cu(hm)(CO)]BPh4 is recovered, whilst a methanolic suspension of CuI in the presence of histamine reversibly absorbs carbon monoxide (1 molecule of CO per Cu atom), giving [Cu2(hm)3(CO)2]2+. An X-ray analysis of the BPh2- salt shows the presence of a dimeric cation, with one histamine molecule chelated to each copper and the other one bridging the two metal atoms. Crystal structures of bis-(L-leucinato)and bis-(D,L-2-aminobutyrato)-copper(n) show both to contain tetragonally co-ordinated copper ions, arranged in isolated sheets. Equatorial N2O2 ligation is provided by the trans co-ordination of two amino-acids, whilst axialCu — O ligation by two neighbouring amino-acids completes the co-ordination of the metal and links the CuL2 units to form carboxylate-bridged sheets of CuII ions. The lines in the n.m.r. spectra of a single crystal of trans-[Cu(DL-Ala)2]·H2O are shifted by both the electron–nuclei dipole–dipole and the Fermi-contact interactions; analysis of the spectra can yield both Cu–proton distances and isotropic coupling constants of protons. A dependence of the paramagnetic line-broadening of n.m.r. spectra on pH has been observed for histidine- (e.g. Gly-Gly-His) and glycine-containing (e.g. Gly, Gly-Gly, Gly-Gly-Gly, and Gly-Gly-Gly-Gly) peptide-copper(II) systems. A cyanogen complex CuC3N3H3O gives glycine on hydrolysis. Potentiometry of the system of copper(II)and L-3-(3,4-dihydroxyphenyl)-2-methylalanine (methyldopa) in aqueous solution, using a glass electrode, shows that both mononuclear and oligonuclear complexes occur, the former including a series of successively deprotonated species at higher ligand:metal ratios. An equilibrium study of the mixed-ligand complexes of copper(II) and amino-acids and 2,2′-bipyridyl with thiodicarboxylic and pyridinedicarboxylic acids has been reported. Margerum and co-workers have continued their work on copper(III)–peptide complexes, and report electron-transfer reactions of these species with hexachloroiridate(III), the oxidative decarboxylation of glyoxalate ion by a deprotonated-amine copper(III)–peptide complex, and the electron-transfer reactions of copper(III)–peptide complexes with [Co(phen)3]2+.

A series of trimethylplatinum(IV) complexes [PtMe3(AA)2]- and [PtMe3 (AA)L] (HAA = alanine, valine, phenylalanine, or α-aminoisobutyric acid) have been isolated; mixtures of diastereoisomers are formed when the amino-acid also contains an asymmetric carbon atom. The solution and solid-state c.d. spectra of the amino-acid [(S)-serine, (S)-valine, and (S)-proline] complexes of bivalent Pd and Pt show a fairly consistent pattern, which is opposite to that shown by the dipeptide [Gly-(S)-Ala and (S)-Ala-Gly] complexes. The c.d. spectra of bivalent Pd, Ni, and Cu complexes of NN’-bis-(L-alanyl)-l,3-propanediaminate anion, ML, are discussed in comparison with those of cis– and trans-bis(amino-carboximidato) -complexes. The nature of diastereoisomeric discrimination in the series of platinum(II) complexes trans(N/olefin)-chloro[N-methyl-(S)-prolinato] (olefin)platinum has been investigated by 1H, 13C, and 195Pt n.m.r. methods.

Dimethylgold(III) complexes with the anions of glycine, alanine, valine, cysteine, histidine, and imidazole, i.e. [Me2AuL], have been the subject of an infrared spectroscopic study. The kinetics and mechanism of formation of pentammine(glycine)rhodium(III) ion from pentammineaquarhodium(III) ion and glycine in weakly acidic media have been reported.

Sulphur-containing Amino-Acids. — The three possible donor sites in methionine have attracted interest for some time. To the [Cu(met)2] complex that was originally prepared has recently been added the copper(m) complex of L-methionine methyl ester. The L-methionylglycinato-group acts as a quinquedentate ligand (involving amino-nitrogen; ionized amide-nitrogen, one carboxylato-, and one bridged carboxylato-group) towards copper(II). cyclo-L-Methionyl-L-methionine has been shown to co-ordinate as a neutral species to palladium(II), gold(III), and copper(II).

Organotin chlorides have been shown to bind to L-cysteine, DL-penicillamine, L-cysteine ethyl ester, N-acetyl-L-cysteine, L-cysteic acid, and glutathione. The mononuclear molybdenum(V) complexes of cysteinyl peptide are suggested to resemble those of the molybdenum centres in nitrate reductase and other molybdo-enzymes. Some reactions of triorganotin(IV) compounds with L-cysteine, L-cysteine ethyl ester, N-acetyl-L-cysteine, and glutathione have also been reported. The X-ray crystal structure of (2-aminothiazoline)cobalt(III) shows N5O co-ordination around the cobalt, with the cysteinyl sulphur unbound. Four kinds of [Co(N)2(O)3(S)] mixed complexes [(L- or D-aspartato, or L-methioninato) have been prepared.

D-Penicillamine forms species MA and MA2 (M = Ni) that contain N,S coordination in aqueous solution. Copper and zinc complexes of Schiff-base ligands that contain penicillamine have been prepared.

The fourth N-terminal amino-acid in the peptide chain of corticotropin is methionine. The electron-pair-donor ability of the thioether sulphur atom in the macromolecule has been elucidated on the basis of its ability to co-ordinate to silver(I)ion.

Amino-Acids that contain Heterocyclic N-Donors. The six isomers of the [Co(L- or D-Asp)(L-His)] complex have been prepared and the isomerization in the absence of any catalyst has been studied. The equilibrium mole fractions of these isomers in water have been found for L-transO5cisN5, L-cisO5transN5, and L-fac, to be 0.53, 0.06, and 0.41, respectively. The X-ray crystal structure of trans-amine-bis-(L-histidinato)cobalt(III) perchlorate dihydrate shows octahedral co-ordination with the amino-nitrogen, the imidazole nitrogen, and a carboxylate oxygen atom of each histidinate. The two imidazole groups, as well as the two carboxylate groups, are ligated cis to one another; the amines are trans. Some linear and circular dichroism spectra in the visible range for two isomers of the bis(histidinato)cobalt(III) complex in the crystal phase, i.e. all-cis– and trans-amine, have been reported. The anion D-H2NCH(CH2C5H4N)-CO2-, a terdentate analogue of histidinate, complexes with cobalt(III) to form [Co(D-PyAla)2]NO3·½H2O; the most stable form of this is that in which the carboxylate groups of the two ligands are mutually trans. The hydrolysis of cis-[CoCl(en)2(imH)]2+ (imH = imidazole) by base has been studied over the pH range 8.26 — 9.74.

(Continues…)Excerpted from Inorganic Biochemistry Volume 3 by H. A. O. Hill. Copyright © 1982 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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