Biomedical subjects

M M Harding

Publications and source records attributed to M M Harding.

At least 19 recordsLinked to original sources

PubMed2001

Hydrophobic analogues of the winter flounder 'antifreeze' protein.

The synthesis, solution conformation and ice-growth inhibition properties of four new analogues of the type I 37-residue winter flounder 'antifreeze' protein are reported. All four analogues contain two extra salt bridges to facilitate comparison of results with previously published data. In two analogues, all four threonine residues in the native polypeptide were mutated to 2-amino butyric acid (an unnatural amino acid) and isoleucine, respectively. The butyric acid analogue was approximately 85% helical at 3 degrees C, modified the shape of ice growth, and exhibited reduced hysteresis compared to the native protein (9% at 4 mM). These results show that the gamma-methyl group of threonine, which is present in the sidechain of 2-amino butyric acid, is not sufficient for activity. The isoleucine analogue, in which the threonine hydroxyl group is replaced by an ethyl group, was 100% helical at 3 degrees C, showed no hysteresis but was able to modify the shape of ice crystal growth. In the third and fourth analogues, mutations of the aspartic acids 1 and 5 to alanine, and asparagines 16 and 27 to leucine in the threonine- and valine-substituted analogues did not affect the helicity of the polypeptides, but removed the ability to inhibit ice growth.

Alanine↗

PubMed2001

Inhibition of human topoisomerase II by the antitumor metallocenes.

The ability of antitumor active metallocenes Cp2MCl2, (M=Ti, V, Mo, Nb) and the biologically inactive derivative (MeCp)2TiCl2, to inhibit the relaxation of supercoiled plasmid DNA pBR322 by human topoisomerase II has been studied by gel electrophoresis. All metallocenes inhibit the enzyme with maximum inhibition observed at 2.0 mM (Cp2TiCl2), 3.0 mM (Cp2MoCl2), 0.2 mM (Cp2NbCl2), 0.25 mM (Cp2VCl2) and 2.0 mM (MeCpTiCl2). The implications for the mechanism of antitumor activity of the metallocene dihalides are discussed.

Antineoplastic Agents↗

PubMed2001

A (1)H NMR study of the interaction of antitumor metallocenes with glutathione.

The interaction of the antitumor active metallocene dihalides Cp(2)MCl(2) (M=Ti, Nb, Mo) and 1 equiv. of glutathione was studied by (1)H NMR spectroscopy at pD 2-7 in 4 mM NaCl solutions. No interaction between glutathione and titanocene dichloride was detected at pD 2, while at pD 5-7 competitive hydrolysis of the cyclopentadienyl ligands occurred. With niobocene dichloride formation of approximately 20% of an adduct was observed at pD 2 and 5, but hydrolysis of the Cp ligands in the adduct occurred over 24 h. Molybdocene dichloride formed two stable adducts at pD 6 which were tentatively assigned as a Cp(2)Mo-glutathione chelate involving coordination of the cysteine thiol and glycine carboxylate to the metal centre, and a thiol centred 1:2 Cp(2)Mo-glutathione complex. The implications for the mechanism of antitumor action of the metallocene dihalides is discussed.

Antineoplastic Agents↗

PubMed2001

Geometry of metal-ligand interactions in proteins.

The geometry of metal-ligand interactions in proteins is examined and compared with information for small-molecule complexes from the Cambridge Structural Database (CSD). The paper deals with the metals Ca, Mg, Mn, Fe, Cu, Zn and with metal-donor atom distances, coordination numbers and extent of distortion from ideal geometry (octahedral, tetrahedral etc.). It assesses the agreement between geometry found in all metalloprotein structures in the Protein Data Bank (PDB) determined at resolution < or = 1.6 A with that predicted from the CSD for ligands which are analogues of amino-acid side chains in proteins [Harding (1999), Acta Cryst. D55, 1432-1443; Harding (2000), Acta Cryst. D56, 857-867]. The agreement is reasonably good for these structures but poorer for many determined at lower resolution (examined to 2.8 A resolution). For metal-donor distances, the predictions from the CSD, with minor adjustments, provide good targets either for validation or for restraints in refinement of structures where only poorer resolution data is available. These target distances are tabulated and the use of restraints is recommended. Validation of angles or the use in refinement of restraints on angles at the metal atom is more difficult because of the inherent flexibility of these angles. A much simplified set of parameters for angle restraints with quite large standard deviations is provided. (Despite the flexibility of the angles, acceptable and preferred coordination numbers and shapes are well established and a summary table is provided.) An unusual and perhaps biochemically important feature of Zn coordination with carboxylate seen in the CSD examples is also clearly present in metalloprotein structures. With metals like Ca, carboxylate coordination is monodentate or bidentate (two M-O bonds of nearly equal length). In Zn carboxylates a continuous range between monodentate and bidentate coordination is found, with one Zn-O bond of normal length and another of any length between this and a van der Waals contact.

Amino Acids↗

PubMed2000

Detection of DNA via an ion channel switch biosensor.

Detection of DNA by an ion channel switch biosensor has been demonstrated in a model system, using single-stranded oligonucleotide sequences of 52-84 bases in length. Two different biotinylated probes are bound, via streptavidin, either to the outer region of a gramicidin ion channel dimer or to an immobilized membrane component. The ion channels are switched off upon detection of DNA containing complementary epitopes to these probes, separated by a nonbinding region, at nanomolar levels. The DNA cross-links the ion channel to the immobilized species, preventing ions passing through the channel. Addition of DNase I after the target DNA has been added switches the ion channels on. The DNA response is dependent on the rate of hybridization of the individual probes to their complementary epitopes, as shown by using a single probe against DNA containing a repeat of the complementary epitope. These results were correlated with hybridization rates determined using surface plasmon resonance (BIAcore 2000), and with free energies of dimer formation for the probes.

Anti-Bacterial Agents↗

PubMed2000

Synthesis of functionalized chiral carbocyclic cleft molecules complementary to Tröger's base derivatives.

The synthesis of optically pure functionalized cleft molecules derived from dibenzobicyclo[b,f][3.3.1]nona-5a,6a-diene-6,12-dione is reported. These clefts are reminiscent of Tröger's base but contain clefts with different dimensions and additional carbonyl (or alcohol) groups that may be utilized in molecular recognition studies. The 2,8-dimethyl and 2,8-dibromo derivatives were synthesized via an intramolecular Friedel-Crafts acylation and were resolved by chiral HPLC. The 2,8-dinitro derivative was prepared by regiospecific nitration of dibenzobicyclo[b,f][3.3.1]nona-5a, 6a-diene-6,12-dione. The dibromo and dinitro derivatives allow direct access to a range of functionalized molecular clefts. Palladium-catalyzed coupling of the dibromo derivative afforded the disubstituted phenyl, anisole, and acetylene derivatives, while reduction of the dinitro derivative and acetylation provided amino-dione and amide-hydroxyl derivatives. X-ray crystal structures of the dimethyl 12, dibromo 13, di(p-methoxyphenyl) 16, dinitro 18, and dimethyl dinitro 22 derivatives show cleft angles between the planes between the aromatic rings of 84-104 degrees. The synthetic route, structural features, and potential for molecular recognition studies of this class of clefts are compared with those of the more widely studied Tröger's base cleft molecules.

Bridged-Ring Compounds↗

PubMed2000

The geometry of metal-ligand interactions relevant to proteins. II. Angles at the metal atom, additional weak metal-donor interactions.

Geometrical data which could be of relevance in the structure determination, structure refinement, assessment or understanding of metalloproteins have been extracted from the Cambridge Structural Database (CSD). The CSD contains crystallographic data from 'small-molecule' structures determined by X-ray or neutron diffraction to an accuracy and precision much better than that of most current protein structure determinations. Structures of Mg, Mn, Fe, Cu and Zn complexes with ligands whose donor atoms may be only N, O, S or Cl have been selected and analysed in terms of the geometry of the metal coordination group - octahedral, tetrahedral, tetragonal pyramidal etc. The r.m.s. deviation of all the interbond angles around the metal atom provides a measure, delta, of the deviation from ideal geometry. Average values of delta are tabulated for the different metals in each type of complex. For simple non-chelated complexes of Mn, Fe and Zn, distortions of up to 5 degrees in octahedral complexes and 10 degrees in tetrahedral complexes are found to be normal and seem likely to be a consequence of packing effects, ligand bulk or intramolecular effects. Substantially larger distortions are found for some other metals and geometries and are common for chelated complexes. Brief comments on six-, seven- and eight-coordinate Ca complexes are included. Tables are also presented showing that for four- and five-coordinate complexes of Zn and Cu it is quite common to find additional weakly coordinated ligands, usually with N or O donor atoms and with M.N,O distances longer than a normal bond length but shorter than a van der Waals contact, e.g. in the range 2.4-3.0 A for Zn and 2.6-3.0 A for Cu. Although the contributions to bond valency or bonding energy of such interactions may not be great, their effect on geometry can be considerable; they can, for example, cause much larger distortions of tetrahedral Zn complexes than indicated above.

Chelating Agents↗

PubMed2000

Antitumour metallocenes: structure-activity studies and interactions with biomolecules.

The metallocene dihalides are a relatively new class of small, hydrophobic organometallic anticancer agents that exhibit antitumour properties against numerous cell lines including leukemias P388 and L1210, colon 38 and Lewis lung carcinomas, B16 melanoma, solid and fluid Ehrlich ascites tumours and several human colon and lung carcinomas transplanted into athymic mice. Titanocene dichloride 1 has been the most widely studied metallocene and the drug is currently in phase II clinical trials. Formation of metallocene-DNA complexes has been implicated in the mechanism of antitumour properties of the metallocenes, as both titanocene dichloride 1 and vanadocene dichloride 2 inhibit DNA and RNA synthesis, and titanium and vanadium accumulate in nucleic acid-rich regions of tumour cells. However, in contrast to the well characterized platinum-based anticancer drugs, the active species responsible for antitumour activity in vivo has not been identified and the mechanism whereby irreparable DNA damage and/or structural modification of DNA or other cellular targets occurs is poorly understood. This review will focus on recent studies that have been carried out in order to identify the biologically active species and more fully understand the molecular level mechanism of action of the metallocene dihalides. Studies with nucleotides, oligonucleotides, DNA and proteins including topoisomerases, protein kinase C and transferrin have provided important insight into potential cellular transport mechanisms and the interaction of metallocenes with biomolecular targets. New structure activity studies including the design of hydrolytically stable metallocenes and the preparation of highly water soluble amino acid analogues have not led to improved anticancer activity of titanocene dichloride 1. The vastly different chemical and hydrolytic stability of each of the metallocenes points to a unique mechanism of action of each metallocene in vivo.

Animals↗

PubMed1999

Type I 'antifreeze' proteins. Structure-activity studies and mechanisms of ice growth inhibition.

The type I 'antifreeze' proteins, found in the body fluids of fish inhabiting polar oceans, are alanine-rich alpha-helical proteins that are able to inhibit the growth of ice. Within this class there are two distinct subclasses of proteins: those related to the winter flounder sequence HPLC6 and which contain 11-residue repeat units commencing with threonine; and those from the sculpins that are unique in the N-terminal region that contains established helix breakers and lacks the 11-residue repeat structure present in the rest of the protein. Although 14 type I proteins have been isolated, almost all research has focused on HPLC6, the 37-residue protein from the winter flounder Pseudopleuronectes americanus. This protein modifies both the rate and shape (or 'habit') of ice crystal growth, displays hysteresis and accumulates specifically at the {2 0 2; 1} ice plane. Until very recently, all models to explain the mechanism for this specific interaction have relied on the interaction of the four threonine hydroxyls, which are spaced equally apart on one face of the helix, with the ice lattice. In contrast, proteins belonging to the sculpin family accumulate specifically at the {2 1; 1; 0} plane. The molecular origin of this difference in specificity between the flounder and sculpin proteins is not understood. This review will summarize the structure-activity and molecular modelling and dynamics studies on HPLC6, with an emphasis on recent studies in which the threonine residues have been mutated. These studies have identified important hydrophobic contributions to the ice growth inhibition mechanism. Some 50 mutants of HPLC6 have been reported and the data is consistent with the following requirements for ice growth inhibition: (a) a minimum length of approx. 25 residues; (b) an alanine-rich sequence in order to induce a highly helical conformation; (c) a hydrophobic face; (d) a number of charged/polar residues which are involved in solubility and/or interaction with the ice surface. The emerging picture, that requires further dynamics studies including accurate modelling of the ice/water interface, suggests that a hydrophobic interaction between the surface of the protein and ice is the key to explaining accumulation at specific ice planes, and thus the molecular level mechanism for ice growth inhibition.

Amino Acid Sequence↗

PubMed1999

The geometry of metal-ligand interactions relevant to proteins.

Geometrical data which could be of relevance in the structure determination, structure refinement, assessment or understanding of metalloproteins have been extracted from the Cambridge Structural Database (CSD). The CSD contains crystallographic data from 'small-molecule' structures determined by X-ray or neutron diffraction to an accuracy much better than that of most current protein structure determinations. The structures selected have a crystallographic R factor </= 0.065 and contain Ca, Mg, Mn, Fe, Cu or Zn interacting with ligands which are analogues of the amino-acid side chains commonly found in proteins; they include carboxylate groups, alcohols, phenolates, thiolates, imidazole groups and also water molecules. For each pair, the mean metal-donor-atom distance, the sample standard deviation and the range of observed values are tabulated, using approximately 4500 observations in all. Where practicable, subsets with different coordination numbers and/or oxidation states are given. Also included are inter-bond angles at the ligand donor atom, the orientation of carboxylate and imidazole groups with respect to the metal-donor-atom bond and some other aspects of ligand geometry. Thus, for example, target distances and their standard deviations could be easily looked up for the validation of a metalloprotein structure or for use in restrained refinement with low-resolution data.

Carboxylic Acids↗

PubMed1998

Valine substituted winter flounder 'antifreeze': preservation of ice growth hysteresis.

Three mutant polypeptides of the type I 37-residue winter flounder 'antifreeze' protein have been synthesized. All four threonine residues in the native peptide were been mutated to serine, valine and glycine respectively and two additional salt bridges were incorporated into the sequences in order to improve aqueous solubility. The peptides were analyzed by nanoliter osmometry, the 'ice hemisphere' test, the 'crystal habit' test, measurement of ice growth hysteresis and CD spectroscopy. While the valine and serine mutants retain the alpha-helical structure, only the valine mutant retains 'antifreeze' activity similar to that of the native protein. These data show that the threonine hydroxyl groups do not play a crucial role in the accumulation of the native 'antifreeze' protein at the ice/water interface and the inhibition of ice growth below the equilibrium melting temperature.

Amino Acid Substitution↗

PubMed1997

DNA-binding studies of XSPTSPSZ, derivatives of the intercalating heptad repeat of RNA polymerase II.

The synthesis, solution conformation, and interaction with DNA of three 8-residue peptides structurally related to the heptad repeat unit found at the C-terminus of RNA polymerase II are reported. Peptides QQ, XQ, and PQ are derived from the parent sequence YSPTSPSY (peptide YY), which was reported to bind to DNA by bisintercalation [M. Suzuki (1990) Nature, Vol. 344, pp. 562-565], and contain either a 2-quinolyl (Q), 2-quinoxolyl (X), or 5-phenanthrolyl (P) group in place of the aromatic side chains of the N- and C-terminal tyrosine residues present in the parent sequence. The combined results of linear dichroism and induced CD measurements of peptides QQ, XQ, and PQ with calf thymus DNA are consistent with weak binding of the peptides to DNA in a preferred orientation in which the chromophores are intercalated. Small increases in the melting temperatures of poly[d(A-T)2] are also consistent with the peptides interacting with DNA. While enzymatic footprinting with DNase I showed no protection from cleavage by the enzyme, chemical footprinting with fotemustine showed that the peptides modify the reactivity of the major groove, presumably via minor groove binding. Peptide QQ inhibited fotemustine alkylation significantly more than either XQ or PQ, and slightly more than YY. In aqueous solution, nmr experiments on QQ, XQ, and PQ show a significant population of a conformation in which Ser2-Pro3-Thr4-Ser5 form both type I and type II beta-turn conformations in equilibrium with open chain conformations. Nuclear magnetic resonance titration experiments of PQ with (GCGTACGC)2 showed small changes in chemical shifts, consistent with the formation of a weak nonspecific complex. Analogous experiments, using peptides QQ and XQ with (GCGTACGC)2, and peptide YY with (CGTACG)2, showed no evidence for the interaction of the peptides with these oligonucleotides. These results show that peptides of general structure XSPTSPSZ are weak nonspecific DNA binders that differ significantly from previously characterized S(T)PXX DNA-binding motifs that are generally AT-selective minor groove binders.

Amino Acid Sequence↗

PubMed1997

Interaction of the antitumour antibiotic streptonigrin with DNA and oligonucleotides.

The interaction of the aminoquinone antitumour antibiotic streptonigrin with plasmid DNA, calf thymus DNA and oligonucleotides, in the presence and absence of metal ions, has been studied using circular dichroism, NMR spectroscopy and gel electrophoresis experiments. In the absence of metal ions, streptonigrin does not interact with DNA. Incubation of the two enantiomers of streptonigrin with calf thymus DNA, in the presence of excess zinc(II), showed no evidence of selective interaction of the natural enantiomer, (R)-streptonigrin, with the DNA by circular dichroism. The interaction of streptonigrin with the hexanucleotide d(GCATGC)2 was studied by 1H- and 31P-NMR spectroscopy. In the presence of four equivalents of zinc(II) nitrate and one equivalent of streptonigrin, small changes in chemical shifts of the proton resonances associated with T4 and G5 were detected as well as P4 and P5, consistent with a weak interaction of the zinc(II)-streptonigrin complex with the most accessible binding sites, involving the phosphate groups and guanine N7, at either end of the duplex. In contrast, no significant interaction between the metal complex and d(ATGCAT)2 was detected. Gel electrophoresis experiments were carried out to probe the sequence specificity of the interaction of the non-covalent streptonigrin-metal complexes with DNA, the DNA cleavage reaction of supercoiled DNA, and the specificity of the cleavage reaction. DNase I footprinting showed no sequence specific interactions. Zinc(II), copper(II) and manganese(II) enhanced the cleavage of supercoiled DNA into nicked and linear forms of DNA, while magnesium showed no cleavage reactions under identical conditions. The DNA cleavage reaction of streptonigrin and NADH in the presence and absence of metal ions was studied. Overall, little sequence specificity was observed, but slightly different cleavage patterns suggest that the DNA cleavage can be influenced by the nature of the metal ions.

Animals↗

PubMed1996

Organometallic anticancer agents. 2. Aqueous chemistry and interaction of niobocene dichloride with nucleic acid constituents and amino acids.

The solution chemistry and interactions of niobocene dichloride, Cp2NbCl2, with nucleosides, nucleotides, and amino acids has been studied by 1H and 31P NMR spectroscopy. The 1H NMR spectrum of Cp2NbCl2 in 10% DMSO-d6/D2O contains two sharp singlets consistent with hydrolysis of the halide ligands and oxidation of the paramagnetic Nb(IV) complex to a diamagnetic Nb(V) complex. Cp2NbCl2 does not dissolve in the absence of oxygen, and Cp2NbCl2(OH) and Cp2NbCl2 when dissolved in 10% DMSO/D2O have identical 1H NMR spectra, consistent with formation of a Nb(V) complex as the antitumor active species in solution. With all nucleosides and nucleotides, except adenosine-5'-monophosphate (dAMP), no evidence of binding was detected on addition of up to 2.0 equiv of niobocene dichloride. In the case of dAMP, a minor complex (10%) was detected with 0.5 equiv of Cp2NbCl2 (pH 5.2). No evidence for interaction of aqueous solutions of Cp2NbCl2 with glutamic acid, serine, or histidine was found. The lack of interaction of niobocene dichloride with nucleic acid constituents and amino acids is markedly different from the chemistry exhibited by antitumor active metallocenes Cp2MCl2 (M = Ti, Mo, V) and suggests that the mechanism of antitumor action of Cp2NbCl2 is significantly different from other metallocene dihalides.

Amino Acids↗

PubMed1996

Recording diffraction data for structure determination for very small crystals.

An account is given of experiences in recording diffraction data with synchrotron radiation to determine structures for very small crystals, too small for use with conventional X-ray sources and diffractometers. The effect of crystal composition as well as size on the relative intensity of diffraction patterns of different crystals is noted. Crystal mounting is briefly described. Experimental methods are outlined including detectors and other instrumentation, and a range of examples is given; these include the use of both monochromatic area-detector systems for intensity measurement and of the white-beam Laue method. Choice of the shortest wavelength available with adequate intensity is recommended. The examples include organic, organometallic and aluminophosphate compounds; in all cases structure determination was important in relation to chemical research projects - they were not chosen as ;test' crystals. Comparison is made of the quality of the structure refinements achieved with those from synchrotron radiation powder diffraction - the alternative method when good-sized crystals are not available. Commonly it is found that when good-quality large crystals of a substance cannot be grown, the small crystals are poor in quality with substantial mosaic spread; the relationship between mosaic spread, structure, morphology and crystal growth is explored.

Journal Article↗

PubMed1996

Enzymatic and chemical footprinting of anthracycline antitumor antibiotics and related saccharide side chains.

DNase I and three DNA chemical footprinting agents were used to compare the DNA binding properties of the anthracycline antitumor antibiotics daunomycin, aclacinomycin A, and ditrisarubicin B. These anthracyclines contain a tetracyclic chromophore which intercalates into DNA and a monosaccharide, trisaccharide, and two trisaccharide side chains, respectively. These side chains consist of between one and three 2,6-dideoxy, 1,4-diaxially linked sugars. Three chemical probes, fotemustine, dimethyl sulfate, 4-(2'-bromoethyl)phenol, and the enzymic probe DNase I were used in the footprinting experiments. The chemical probes provided a clear picture of the binding pattern at 37 degrees C and more detailed information than that obtained using the standard DNase I footprinting assay. All three anthracyclines showed preferred binding to 5'-GT-3' sequences in both the chemical and enzymatic footprinting. DNase I footprinting showed that the number of base pairs of DNA protected from cleavage increased with the number of saccharide groups present at particular sites and is consistent with DNA binding of the saccharide side chains. Alkylation of runs of guanine by fotemustine was inhibited by all three anthracyclines, while alkylation by dimethyl sulfate was enhanced for most guanines. The probe 4-(2'-bromoethyl)phenol showed that all three anthracyclines completely protected all of the adenines in the minor groove from alkylation, and enhanced major groove guanine alkylation was observed with aclacinomycin A, daunomycin, and, to a much lesser extent, ditrisarubicin B. These results are consistent with intercalation of the aglycone ring and binding of the rigid, hydrophobic saccharide side chains in the minor groove. Footprinting of four methyl glycosides related to the anthracyclines showed no evidence of DNA binding with any of the agents studied.

Aclarubicin↗

PubMed1995

Synchrotron radiation laue diffraction for the time-resolved study of a transformation in crystals of p(4)n(4)cl(8).

Experiments are described to show some of the potential of the synchrotron radiation Laue method for the study of structural change within single crystals. In the metastable tetragonal crystals of P(4)N(4)Cl(8) the eight-membered P(4)N(4) ring is in a boat conformation, with symmetry {\bar 4}. On heating to ca 340 K the crystals transform, slowly to a second tetragonal form in which the ring conformation is a chair, its symmetry {\bar 1}. Both structures are known [Hazekamp, Migchelsen & Vos (1962). Acta Cryst. 15, 539-543; Wagner & Vos (1968). Acta Cryst. B24, 707-713]. In the transformation the molecular packing, unit-cell dimensions and crystal quality remain almost unchanged. To study this transformation, series of Laue diffraction patterns were recorded at 2-3 min intervals over a period of 30-40 min, while the temperature was raised to 373 K. For two series, reflection intensities were measured and they allowed determination and refinement of the fraction of boat and chair molecules present in a mixed boat/chair model of the structure. No significant change in the crystal occurs below ca 340 K; at or above 340 K, 40-50% of the molecules are converted from boat to chair conformations within 5 min, but the remainder of the conversion is much slower, even when the temperature is raised towards 370 K.

Journal Article↗

PubMed1995

Application of synchrotron radiation laue diffraction to small single crystals of a mineral - structure determination and identification.

The potential of synchrotron radiation Lane diffraction Patterns for structure determination and for identification of small single crystallites is illustrated. Diffraction Patterns were recorded for several crystallites, </=20 mum in all dimensions, with the intention of determining an unknown mineral structure. They were the largest particles in the sample. They appeared to represent at least two different phases, but eventually it became clear that neither corresponded to the unknown phase. However, it has been possible to show that both identification and structure determination are practicable from Laue diffraction patterns of crystallites of this size. For one crystallite the diffraction patterns were used to derive unit-cell dimensions and from these the crystallite could be identified as either PbCO(3), cerussite, or SrCO(3), strontianite. Using intensity measurements it could be shown to be PbCO(3). Identification could be similarly achieved for many other small single crystallites, and the procedure is described. For another crystallite, a complete structure determination was carded out and it was then recognized as malachite, Cu(2)(OH)(2)CO(3). The structure found is in very good agreement with that previously determined by Zigan, Joswig, Schuster & Mason [Z. Kristallogr. (1977), 145, 412-416].

Journal Article↗