Drug-metal interactions: copper(II) complex of the antidiabetic drug acetohexamide and pyridine

The preparation, spectral properties, and crystal structure of a copper(II) complex of 4-acetyl-N-[(cyclohexylamino)carbonyl]benzenesulfonamide, which is known as acetohexamide, and pyridine are reported. The complex Cu(AH)2(py)2, where AH = acetohexamide and py = pyridine, was prepared and characterized by X-ray and ESR. The complex is monoclinic, space group P2(1)/a, with a = 17.412(6), b = 9.039(2), c = 26.531(10) A, beta = 102.24(2) degrees, and Z = 4. The final refinement used 3892 unique reflections and gave an R value of 0.0646. The copper atom is surrounded by four nitrogen atoms in a square-planar arrangement, two from the acetohexamide ligands (Cu-N = 2.009 A) and two from the pyridine molecules (Cu-N = 2.016 A) in a trans geometry. The ESR data support a similar coordination behavior of the copper (g parallel greater than g perpendicular greater than ge) with the unpaired electron in the dx2-y2 orbital.     

Metal chelates of heterocyclic nitrogen-containing ketones. XIX. Some acetato- and nitrato-copper(II) complexes of phenyl-2 picolyl ketone hydrazone and phenyl-2-picolyl ketone phenyl hydrazone

Complexes of phenyl-2-picolyl ketone hydrazone and phenyl-2-picolyl ketone phenyl hydrazone, PPKhy and PPKPhy, respectively, with hydrated copper(II) acetate or hydrated copper(II) nitrate in mole ratio 1:1 or 1:2, metal:ligand, have been prepared. Various physical techniques including molar conductivity, spectral (IR, electronic, ESR and ¹H NMR) and magnetic measurements were used to study the nature and structure of the prepared complexes. The data showed that complexes [CuLX₂], X = OAc or ONO₂ and L = PPKhy or PPKPhy, are trigonal bipyramidal, [Cu(PPKPhy)₂] (NO₃)₂ is square planar and [Cu(PPKhy)₂](NO₃)₂ is tetrahedral. The acetate and nitrate groups in the mono- ligand complexes are found to be mono- and bidentate but in the ionized sphere in the bis-ligand complexes. The ligands are present in associated form in solution via intermolecular hydrogen bond and act as neutral bidentate coordinated to the copper(II) via the pyridine and azomethine nitrogen atoms.     

Electron spin echo envelope modulation spectroscopic study of iron-nitrogen interactions in myoglobin hydroxide and Fe(III) tetraphenylporphyrin models.

The electron-nuclear coupling in low-spin iron complexes including myoglobin hydroxide (MbOH) and two related model compounds, Fe(III) tetraphenylporphyrin(pyridine)(OR-) (R = H or CH3) and Fe(III) tetraphenylporphyrin(butylamine)(OR-) was investigated using electron spin echo envelope modulation (ESEEM) spectroscopy. The assignment of frequency components in ESEEM spectra was accomplished through the use of nitrogen isotopic substitution wherever necessary. For example, the proximal imidazole coupling in MbOH was investigated without interference from the contributions of porphyrin 14N nuclei after substitution of the heme in native Mb with 15N-labeled heme. Computer simulation of spectra using angle selected techniques enabled the assignment of parameters describing the hyperfine and quadrupole interactions for axially bound nitrogen of imidazole in MbOH, of axial pyridine and butylamine in the models, and for the porphyrin nitrogens of the heme in native MbOH. The isotropic component of axial nitrogen hyperfine interactions exhibits a trend from 5 to 4 MHz, with imidazole (MbOH) greater than pyridine greater than amine. The nuclear quadrupole interaction coupling constant e2Qq was near 2 MHz for all nitrogens in these complexes. The Qzz axis of the nuclear quadrupole interaction tensor for the proximal imidazole nitrogen in MbOH was found to be aligned near gz (gmax) in MbOH, suggesting that gz is near the heme normal. A crystal field analysis, that allows a calculation of rhombic and axial splittings for the d orbitals of the t2g set in a low-spin heme complex, based on the g tensor assignment gz greater than gy greater than gx, yielded results that are consistent with the poor pi-acceptor properties expected for the closed shell oxygen atom of the hydroxide ligand in MbOH. A discussion is presented of the unusual results reported in a linear electric field effect in EPR (LEFE) study of MbOH published previously [Mims, W. B., & Peisach, J. (1976) J. Chem. Phys. 64, 1074-1091].     

Metal complexes of anti-inflammatory drugs. Part III. Nictindole complexes of copper(II) halides

The preparation and properties of the copper(II) halide complexes CuX₂(NIDOL)₂ (where X = Cl, Br) are reported for the anti-inflammatory drug nictindole (NIDOL). The diffuse reflectance spectra, magnetic moments and electron spin resonance spectra are consistent with a tetragonally distorted pseudo-octahedral environment around the copper(II) ions. The infrared spectra indicate monodentate coordination of the neutral drug to the central metal ion via the nitrogen atom of the pyridine ring.     

Evaluation of antiproliferative activities and apoptosis induction caused by copper(II)–benzothiazolesulfonamide complexes in Jurkat T lymphocytes and Caco-2 cells

Two copper(II) complexes with a benzothiazolesulfonamide ligand, [Cu(L)₂(py)₂] (1) and [Cu(en)₂(L)₂] (2) [HL is N-2-(4-methylbenzothiazole)toluenesulfonamide, py is pyridine, en is ethylenediamine], were prepared and then characterized with the aid of X-ray crystallography and spectroscopy. Whereas the copper(II) ion in 1 presents a square-planar geometry, in 2 it has a distorted octahedral environment. In addition, although the ligand is monodentate in both complexes, it exhibits different coordination behavior in each, interacting through the benzothiazole nitrogen atom in 1 and through the sulfonamide nitrogen atom in 2. The propensity for binding of 1 and 2 to calf thymus DNA was studied by thermal denaturation, viscosimetry, and cyclic voltammetry. The ability of the complexes to cleave DNA was studied in vitro through ascorbate activation and was tested by monitoring the expression of the yEGFP gene containing the RAD54 reporter. Moreover, their antiproliferative activity was verified in two cellular models: yeast and human tumor cells in culture. While 1 was found to be the more active cleaving agent in vitro, 2 showed a higher propensity for inflicting DNA damage at the cellular level. The biological studies carried out with human tumor cells, namely, colon adenocarcinoma Caco-2 cells (HTB-37) and leukemia Jurkat T lymphocytes (TIB-152), confirmed that both compounds inhibit the growth of these cell lines, although 2 is more effective. This difference is associated with the latter compound’s greater ability to induce cell death by apoptosis. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Monomeric and dimeric mixed-ligand copper(II) complexes of 2,2′-bipyridine/1,10-phenanthroline and 1-methylimidazole with imidazoles as catalysts for superoxide dismutation

Monomeric complexes [Cu(LL)(L′)(NO₃)₂] (where LL is 2,2′-bipyridine or 1,10-phenanthroline and L′ is 1-methylimidazole) and dimeric complexes [Cu₂(LL)₂(L″)]NO₃ (where L″ is an anion of imidazole or 2-methylimidazole) have been synthesized. These complexes show a d-d transition in the range of 600 to 710 nm. The infrared spectra of monomeric complexes show that the NO₃⁻ is coordinated to copper as a monodentate ligand through an oxygen atom. The ESR spectra of monomeric complexes indicate that the ligands are bonded in axial environment around copper (square pyramidal geometry) with three nitrogen donors occupying an equatorial plane. The ESR spectra of dimeric complexes show a broad signal at about G = 2 with an additional weak signal at about G = 4. This suggests that two copper atoms are in close proximity of < 7 Å. The ESR studies reveal that the formation of imidazolate-bridged binuclear copper(II) complexes from [Cu(LL)(L′)(NO₃)₂] and imidazole is pH dependent with apparent pK_a values of 8.25 to 8.30. The superoxide dismutase activity of ICu(phen)(L′)(NO₃)₂], [Cu(bipy)(L′)(NO₃)₂], and [Cu₂(bipy)₂(L′)₂(L″)]NO₃ has been measured and the latter two complexes show better activity than the former complex.     

Co-ordination compounds derived from dimethylhydrazones of cyclohexane-1,2-dione, 2-acetyl- and 2-benzoylpyridines and 4-bezoylpyridine

The 1,1-dimethylhydrazones of cyclohexane-1,2-dione (CDDMH), 2-acetylpyridine (APDMH) and 2-benzoylpyridine (2BPDMH) from tetrahedral complexes MX₂L (M = Co(II), Zn(II); X = Cl, Br) in which the ligand is chelating through the methylene nitrogen atoms (CDDMH) or one methylene and one pyridine nitrogen atom (APDMH, 2BPMDH). Octahedral complexes CoX₂L₂ (X = Cl, NCS; L = APDMH, 2BPDMH) have also been isolated but no tris-ligand complexes. The ligand 4-benzoylpyridine-dimethylhydrazone (4BPDMH) does not chelate but forms tetrahedral complexes MX₂(4BPDMH)₂ in which the unidentate ligand co-ordinates through the pyridine nitrogen atom.     

Synthesis and structural analysis of the copper(II) complexes of N2-(2-pyridylmethyl)-2-pyridinecarboxamide

Previous investigations of the potential of metal-organic compounds as inhibitors of human immunodeficiency virus type I protease (HIV-1 PR) showed that the copper(II) complex diaqua [bis(2-pyridylcarbonyl)amido] copper(II) nitrate dihydrate and the complex bis[N2-(2,3,6-trimethoxybenzyl)-4-2-pyridinecarboxamide] copper(II) behaved as inhibitors of HIV-1 PR. In a search for similar readily accessible ligands, we synthesised and studied the structural properties of N2-(2-pyridylmethyl)-2-pyridinecarboxamide (L) copper(II) complexes. Three different crystal structures were obtained. Two were found to contain ligand L simultaneously in a tridentate and bidentate conformation [Cu(L(tri)L(bi))]. The other contained two symmetry-related ligands, coordinated through the pyridine nitrogen and the amide oxygen atoms [Cu(L(bi))(2)]. A search of the Cambridge Structural Database indicated that L(tri) resulting from nitrogen bound amide hydrogen metal substitution is favoured over chelation through the amide oxygen atom. In our case, we calculated that the conformation of L(tri) is 11 kcal/mol more favourable than that of L(bi). ESI-MS experiments showed that the Cu(L(bi))(2) structure could not be observed in solution, while Cu(L(tri)L(bi))-related complexes were indeed present. The lack of protease inhibition of the pyridine carboxamide copper(II) complexes was explained by the fact that the Cu(L(bi)L(tri)) complex could not fit into the HIV-1 active site.     

Synthesis and characterization of 1:2 metal complexes of the biheteroaromatic ligand 2-(2′-pyridyl)quinoxaline (L) and the X-ray structure of [CuL2](PF6)

The first 1:2 metal complexes of 2-(2′-pyridyl)quinoxaline (L) have been isolated. The physical and spectroscopic characteristics of the compounds [MCl₂L₂] (M = Ni, Cu, Cd) and [Cu^IL₂](PF₆) are described. The structure of the copper(I) complex has been determined by X-ray diffraction methods. Crystals are orthorhombic, space group P_cnb with A = 11.014(2), B = 12.886(2), C = 17.806(4) Å, V = 2527.1(9) ų and Z = 4. Refinement of the structure gave a final R factor of 0.046 (R_w = 0.041) for 814 unique reflections having I > 2.0σ(I). The ligand L acts as a bidentate chelate, the ligated atoms being the pyridine nitrogen and the nearest quinoxaline nitrogen. The structure of [CuL₂]⁺ consists of a distorted tetrahedral arrangement around the copper(I) atom with Cu---N bond lengths of 2.023(6) and 2.059(5) Å and the N---Cu---N angle of the chelating ligand equal to 80.6(2)°. A monomeric trans pseudo-octahedral stereochemistry is assigned for the [MCl₂L₂] complexes.     

Metal complexes of the schiff bases 2-pyridinylhydrazine and 2-quinolinyl-hydrazine with 2-pyridinecarboxaldehyde N-oxide,including some N-oxide-bridged antiferromagnetic complexes of cobalt(II) and nickel(II)

Metal complexes of 2-pyridine carboxaldehyde 2′-pyridinylhydrazone 1-oxide (poph) and 2-pyridinecarboxaldehyde 2′-quinolinylhydrazone 1-oxide (poqh) are reported with copper(II), nickel(II), cobalt(II), iron(II) and manganese(II). Each ligand appears to function as an ONN donor, via the pyridine N-oxide oxygen, the imine nitrogen, and a pyridine or quinoline nitrogen. The complexes have been characterised by magnetic susceptibility measurements to liquid nitrogen temperature, and also by electronic, infrared, X-ray powder diffraction, and Mössbauer spectra. No magnetic interaction was detected with the copper(II) complexes. All the complexes of metal nitrates appear to be monomers.The complexes of poph with the halides and thiocyanates of nickel(II) and cobalt(II) appear to be six-coordinate and N-oxide-bridged; they exhibit varying degress of antiferromagnetic interaction and the magnetic data for the nickel(II) complexes have been fitted to various models. In contrast, the bulky ligand poqh produces halide-bridged six-coordinate nickel(II) complexes and monomeric five-coordinate cobalt(II) complexes.This behaviour by poqh resembles that of the related NNN ligands paphy and paqhy, which are the Schiff bases of 2-pyridinecarboxaldehyde with 2-pyridinylhydrazine and 2-quinolinylhydrazine, respectively.     

Copper(II) complexation by pituitary adenylate cyclase activating polypeptide fragments.

Results are reported from potentiometric and spectroscopic (UV-Vis, CD, and ESR) studies of the protonation constants and Cu2+ complex stability constants of pituitary adenylate cyclase activating polypeptide fragments (HSDGI-NH2, TDSYS-NH2, RKQMAVKKYLAAVL-NH2). With HSDGI-NH2, the formation of a dimeric complex Cu2H-2L2 was found in the pH range 5-8, in which the coordination of copper(II) is glycylglycine-like, while the fourth coordination site is occupied by the imidazole N3 nitrogen atom, forming a bridge between two copper(II) ions. The formation of dimeric species does not prevent the deprotonation and coordination of the amide nitrogen, and in pH above 8 the CuH-2L complex is formed. Aspartic acid in the third position of peptide sequence stabilizes the CuH-2L species and prevents the coordination of a fourth nitrogen donor. Aspartic acid residue in the second position of TDSYS-NH2 stabilizes the CuL (2N) complex but does not prevent deprotonation and binding of the second and third peptide nitrogens to give 3N and 4N complexes at higher pH. The tetradecapeptide amide forms with copper(II) ions unusually stable 3N and 4N complexes compared to pentaalanine amide.     

Synthesis and characterization of polypyridineruthenium(II) complexes containing a linear ambidentate ligand, NCO or NCS, and reaction of isocyanato complexes under acidic conditions

Isocyanato and isothiocyanatopolypyridineruthenium complexes, [Ru(NCX)Y(bpy)(py)₂]ⁿ⁺ (bpy=2,2′-bipyridine, PY=pyridine; X=O, Y=NO₂ for n=0, and Y=py for n=1; X=S, Y=NO₂ for n=0, Y=NO for n=2, and Y=py for n=1), were synthesized by the reaction of polypyridineruthenium complexes with potassium cyanate or sodium thiocyanate salt. Isocyanatoruthenium(II) complexes, [Ru(NCO)(NO₂)(bpy)(py)₂] and [Ru(NCO)(bpy)(py)₃]⁺, react under acidic conditions to form the corresponding ammineruthenium complexes, [Ru(NO)(NH₃)(bpy)(py)₂]³⁺. The molecular structures of [Ru(NCO)(bpy)(py)₃]ClO₄, [Ru(NCS)(NO)(bpy)(py)₂](PF₆)₂ and [Ru(NO)(NH₃)(bpy)(py)₂](PF₆)₃ were determined by X-ray crystallography.     

Orientational and motional properties of copper (II) complexes of dibenzotetraaza [14]annulenes in lipid bilayers: an ESR study.

ESR studies of two copper(II) complexes of substituted dibenzotetraaza [14]annulenes, CuL and CuLA, in dimyristoylphosphatidylcholine (DMPC) and egg yolk phosphatidylcholine (EYPC) are reported. Our data show that both complexes partition into the membranes and that the rotational motion of CuL is faster than CuLA. Analysis of the ESR spectra of these complexes in DMPC vesicles indicate that the Cu-motion parameter, which is a measure of the degree of resolution of the nitrogen hyperfine structure, changes abruptly at the main phase transition. At 1 mole %, both complexes lowered the fluid/gel phase transition temperature by 2 degrees C as measured by the Cu-motion parameter. A gradual change of the Cu-motion parameter is observed in EYPC liposomes over the same temperature range. ESR spectra of both CuL and CuLA in oriented membranes reveal that both complexes are well oriented with the plane of the complex perpendicular to the bilayer surface.     

Direct evidence of nitrogen coupling in the copper(II) complex of bovine serum albumin by S-band electron spin resonance technique

ESR spectra of the tight binding Cu(II) complex of bovine serum albumin (BSA) has been studied using S-band. At physiological pH, only one form of copper binding to BSA was detected from the ESR spectra. From previous X-band ESR spectra, nitrogen superhyperfine splittings were observable in the g perpendicular region; however, the resolution of the g parallel region was not sufficient to confirm the exact donor atoms of the complex. Using low-frequency ESR (2-4 GHz) at 77 K, we have resolved the nitrogen superhyperfine structure in the g parallel region. A computer simulation method has been developed for distinguishing between three and four nitrogen donor atoms. The Hyde-Froncisz theory of g and A strain broadening has been modified to use a field-swept calculation for the line shape. The observed intensity pattern and the computer simulation of such spectra positively confirm the structure of Cu(II) ion coordinated to four in-plane nitrogen atoms in frozen aqueous solutions of Cu(II)-BSA complexes at physiological pH. This is the first time that this binding site has been confirmed on the protein instead of a protein fragment or model compound. This work is another example of the usefulness of the S-band ESR technique for characterizing the metal-protein interactions when random variation in g factors cause line broadening in conventional X-band ESR spectra.     

Electrochemical synthesis and crystal structure of (3-trimethylsilylpyridine-2-thiolato) copper(I), [Cu4(3-Me3Sipyt)4]

(3-Trimethylsilyl-pyridine-2-thiolato-S,N)copper(I), [Cu(3-Me₃Sipyt)], was obtained by electrochemical oxidation of copper metal in an acetonitrile solution of the neutral ligand. The compound is tetrameric and the four copper atoms are arranged with distorted tetrahedral geometry, each copper atom being trigonally coordinated to one nitrogen and two sulfur atoms of three different ligands. Crystal data: 14₁/a, a=14.608(2), C=19.366(4) Å, V=4133(2), Å, Z=4, D_calc=1.581 g cm⁻³, R=0.0397 for 848 reflections.     

Tuning electronic structure and photophysical properties of [Ir(ppy)2(py)2]+ by substituents binding in pyridyl ligand: a computational study

Iridium (III) 2-phenylpyridine (ppy) complexes with two suitable monodentate L ligands [Ir(ppy)(2)(L)(2)](+) (ppy = 2-phenylpyridine, py = pyridine, L = 4-pyCN 1, 4-pyCHO 2, 4-pyCl 3, py 4, 4-pyNH(2) 5) were studied by density functional theory (DFT) and time-dependent DFT methods. The influences of ligands L on the electronic structure and photophysical properties were investigated in detail. The compositions and energy levels of the lowest unoccupied molecular orbital (LUMO) are changed more significantly than those of the highest occupied molecular (HOMO) by tuning L ligands. With the electronegativity decrease of L ligands 4-pyCN > 4-pyCHO > 4-pyCl > py > 4-pyNH(2), the LUMO distributing changes from py to ppy, and the absorptions have an obvious red shift. The calculated results showed that the transition character of the absorption and emission can be changed by adjusting the electronegativity of the L ligands. In addition, no solvent effect was observed in the absorptions and emissions.     

Studies on intramolecular hydrogen bonding between the pyridine nitrogen and the amide hydrogen of the peptide: synthesis and conformational analysis of tripeptides containing novel amino acids with a pyridine ring.

For the first time tripeptides, Z-AA(1)-Xaa-AA(3)-OMe (AA(1) and AA(3) = Gly or Aib, Xaa = 2Pmg and 2Pyg) were prepared containing alpha-methyl-alpha-(2-pyridyl)glycine (2Pmg) and alpha-(2-pyridyl)glycine (2Pyg) by solid-phase Ugi reaction. These results clearly indicate that for the preparation of tripeptides containing an amino acid with a pyridine ring, the solid-phase Ugi reaction is very useful.NMR analysis clarified that 2Pmg-containing tripeptides adopt a unique conformation with an intramolecular hydrogen bond between 2Pmg-NH and the pyridine nitrogen. However, in the case of Z-Gly-2Pyg-Gly-OMe, the intramolecular hydrogen bonding between 2Pyg-NH and the pyridine nitrogen was not observed, whereas Z-Aib-2Pyg-Aib-OMe adopts a unique conformation with an intramolecular hydrogen bond between 2Pyg-NH and a pyridine nitrogen. Conformational analysis of the tripeptides, Z-AA(1)-Xaa-AA(3)-OMe (AA(1), AA(3) = Gly or Aib, Xaa = alpha,alpha-di(2-pyridyl)glycine (2Dpy), alpha-phenyl-alpha-(2-pyridyl)glycine (2Ppg), 2Pmg and 2Pyg), clarified that when an alpha,alpha-disubstituted glycine with a 2-pyridyl group at an alpha-carbon atom is introduced into any peptide, an intramolecular hydrogen bond between a pyridine nitrogen and an amide proton is formed and conformational mobility of the peptide backbone is restricted.     

Platinum(II) and palladium(II) complexes with dithiocarbamates and amines: synthesis, characterization and cell assay

The [M(ESDT)Cl]n (M = Pd or Pt; ESDT = EtO2CCH2(CH3)NCS2, methylamino-acetic acid ethyl ester-dithiocarboxylate) species have been reacted with various amines (py, pyridine; PrNH2, n-propylamine; c-BuNH2, cyclobutylamine; en, ethylenediamine) in dichloromethane or chloroform with the aim to obtain mixed ligand complexes. The neutral complexes [M(ESDT)(L)Cl] (L = py, PrNH2 or c-BuNH2) and the ionic species ([M(ESDT)(L)2]Cl and [M(ESDT)(En)]Cl) have been isolated, and characterized by IR and proton NMR spectroscopies. The crystal structure of [Pd(ESDT)(PrNH2)Cl] has been determined by X-ray crystallography. The behaviour of the complexes in various solvents was described on the basis of the proton NMR spectra. The complexes and the dithiocarbamato intermediates have been tested for in vitro cytostatic activity against human leukemic HL-60 and HeLa cells.     

Spontaneous resolution of binary copper(II) complexes with racemic dipeptides: crystal structures of glycyl-L-alpha-amino-n-butyrato copper(II) monohydrate, glycyl-D-valinato copper(II) hemihydrate, and glycyl-L-valinato copper(II) hemihydrate

Copper(II) complexes with glycyl-DL-alpha-amino-n-butyric acid (H2gly-DL-but), glycyl-DL-valine (H2gly-DL-val), glycyl-DL-norleucine (H2gly-DL-norleu), glycyl-DL-threonine (H2gly-DL-thr), glycyl-DL-serine (H2gly-DL-ser), glycyl-DL-phenylalanine (H2gly-DL-phe), and glycyl-L-valine (H2gly-L-val), have been prepared and characterized by IR, powder diffuse reflection, CD and ORD spectra, and magnetic susceptibility measurements, and by single-crystal X-ray diffraction. The crystal structures of the copper complex with H2gly-DL-but, the copper complex with H2gly-DL-val, and [Cu(gly-L-val)]n.0.5nH2O have been determined by a single-crystal X-ray diffraction method. As for the structure of the copper complex with H2gly-DL-but, the configuration around the asymmetric carbon atom is similar to that of [Cu(gly-L-val)]n.0.5nH2O. Therefore it is concluded that the copper complex with H2gly-DL-but is [Cu(gly-L-but)]n.nH2O. On the contrary, as for the structure of the copper complex with H2gly-DL-val, the configuration around the asymmetric carbon atom is different from that of [Cu(gly-L-val)]n.0.5nH2O. Therefore it is concluded that the copper complex with H2gly-dl-val is [Cu(gly-D-val)]n.0.5nH2O. So during the crystallization of the copper(II) complexes with H2gly-DL-but and H2gly-DL-val, spontaneous resolution has been observed; the four complexes have separated as [Cu(gly-D-but)]n.nH2O, [Cu(gly-L-but)]n.nH2O, [Cu(gly-D-val)]n.0.5nH2O, and [Cu(gly-L-val)]n.0.5nH2O, respectively. [Cu(gly-L-but)]n.nH2O is orthorhombic with the space group P2(1)2(1)2(1). [Cu(gly-D-val)]n.0.5nH2O and [Cu(gly-L-val)]n.0.5nH2O are monoclinic with the space group C2. In these complexes, the copper atom is in a square-pyramidal geometry, ligated by a peptide nitrogen atom, an amino nitrogen atom, a carboxyl oxygen atom, and a carboxyl oxygen atom and a peptide oxygen atom from neighboring molecules. So these complexes consist of a two-dimensional polymer chain bridged by a carboxyl oxygen atom and a peptide oxygen atom from neighboring molecules. The axial oxygen atom is located above the basal plane and the side chain of an amino acid is located below it. These polymer chains consist of only one or the other type of optical isomers; no racemic dipeptides are found. Therefore, spontaneous resolution has been observed in the crystallization of copper(II) complexes with H2gly-DL-but and H2gly-DL-val. The crystal structure of [Cu(gly-D-val)]n.0.5nH2O agrees almost completely with that of [Cu(gly-L-val)]n.0.5nH2O, except for the configuration around the asymmetric carbon atom.     

Synthesis, spectroscopic and structural characterization of some novel adducts of copper(II) salts with unidentate nitrogen bases

Syntheses, spectroscopic characterization and single crystal X-ray studies are reported for a number of complexes of copper(II) salts with simple monodentate nitrogen bases. The 1:4 adduct of copper(II) sulfate with 3,5-dimethylpyridine (m₂py) CuSO₄·4m₂py, takes the form [(O₃SO)Cu(m₂py)₄], the Cu-O vector of the square-pyramidal coordination environment being disposed on the 4-axis in tetragonal space group P4/n. The complex CuCO₃·Cu(NCS)₂·4py is a linear polymer, taking the form ?O·Cu(py)₂·O·C{O·Cu(py)₂(NCS)₂}·O·Cu(py)₂? (etc.), all atoms lying in the mirror plane of space group Pnma, excepting the pair of ‘py’ (pyridine) ligands disposed to either side. In Cu(OH)I·3/4I₂·2py·1/2MeCN ≡ [{(py)₂Cu(OH)}₄](I₃)₃I·2MeCN a novel cubanoid tetranuclear cation is found (2-symmetry). The EPR spectra of the above compounds show a trend in the anisotropy of the g-values that correlates well with the crystal structures. Obtained only in small quantities but supported by single crystal X-ray studies are the adduct of Cu(OH)Cl with pyrrolidine (pyrr), Cu(OH)Cl:pyrr (1:3), which takes the centrosymmetric binuclear form [(pyrr)₃Cu(μ-OH)₂Cu(pyrr)₃]Cl₂, the copper atom being disposed in a distorted trigonal bipyramidal array, and the adduct 3CuCl₂·CuO·4quin, [Cu₄Cl₆O(quin)₄]Cl₂, which contains the familiar Cu₄Cl₆O core with monodentate quinuclidine (quin) attached to the copper atoms; this compound crystallizes in the cubic space group .