Determination of the mode of interaction of Mn2+ and Cu2+ with cis-inositol by 13C NMR spectroscopy

Natural abundance ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) was used to study the mode of binding of Mn²⁺ and Cu²⁺ to the cyclitol, cis-inositol. Resonance linewidths and the electron nuclear relaxation rates [(T₁^e)^?1 values] were used to establish that a unique binding site exists for these metal-ions on this cyclitol involving only the three axial hydroxyl groups. This work may aid in the development of new organometallic complexes used as paramagnetic relaxation agents in magnetic resonance imaging research.     

NMR studies on UO22+ complexes with pyridoxal

The interaction of pyridoxal with dioxouranium(VI) acetate was studied by ¹H and ¹³C NMR measurements in D₂O and CD₃OD.The results indicate that the preferred bonding site is the C-3O^? donor, and the major species obtained under the experimental conditions used is the equimolar complex.     

Stereochemistry of Gd3+ and Mn2+ interactions with D-gluconamide derivatives by 13C NMR spectroscopy

Natural abundance ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) was used to study the mode of binding of Gd³⁺ and Mn²⁺ to the polyol portion of several synthetic D-gluconamides. The results indicate that Gd³⁺ forms a single, unique binding structure requiring three oxygen atoms. The binding of Mn²⁺ to the polyol portion of these compounds appears to be nonspecific. The carbohydrate containing model compounds studied may be used to design new metal-ion chelating agents.     

The crystal and molecular structure of [Co(NH3)5PO4]·3H2O,a Na+-K+ ATPase probe

The title compound, Co(NH₃)₅PO₄, prepared by a modified literature procedure, was used to study the inhibition of Na⁺-K⁺ ATPase and to serve as a structural model for ML₄(nucleotide) complexes. The structure was determined by single crystal X-ray diffraction techniques. The crystals are monoclinic, space group P2₁/n, a = 8.638(3), b = 14.517(2), c = 9.145(2) Å, and β = 112.71(2)°. The structure, solved by the heavy atom method to an R value of 3.3% for 1924 reflections, consists of a slightly distorted octahedron with the cobalt bound to the five amines and a monodentate phosphate. Solution structural data is taken from ³¹P NMR measurements. From comparison with other metal phosphate complexes it is concluded that multiple monodentate coordination of a di- or triphosphate closely resembles the coordination of a monophosphate This is based on the similarity of the MO bond angle which is 129.6° in the present example.     

Metal ion-tetracycline interactions in biological fluids. Part 4. Potential influence of ca2+ and mg2+ ions on the bioavailability of chlortetracycline and demethylchlortetracycline,as expected from their computer-simulated distributions in blood plasma

Coordination of tetracydines with calcium and magnesium was previously shown to exert a determining effect on the distribution of these antibiotics in blood plasma. In particular, it was clearly established by computer simulation that the free fraction of the drug is quite negligible with respect to its metal-bound fraction. The bioavailabiity of a tetracycline in blood plasma is thus expected to depend directly on the electrical charge of its predominant metal complexes in the biofluid. On account of the metal to ligand ratio corresponding to the usual therapeutic levels, bioavailability is critically sensitive to the property of the antibiotic to give rise to electrically charged binuclear species. The blocking of one of the two potential binding sites of the tetracycline molecule should thus result in a larger percentage of neutral complexes, hence in a better tissue penetration by the drug.The present work is devoted to the investigation of the coordination of 7-chlortetracycline (CTC) and 6-demethyl-7-chlortetracycline (DMC) with calcium and magnesium in blood plasma. The influence of the chloro substituent is discussed with respect to the objective defined above.     

Solution and solid state behavior of Co2+, Ni2+ and Zn2+ tosylaminoacidate systems: Crystal and molecular structure of bis(N-tosylglycinato)tetraaquocobalt(II) and bis(N-tosyl-β-alaninato)tetraaquozinc(II) complexes

The interactions between N-tosylamino acids and cobalt(II), nickel(II) and zinc(II) ions in aqueous solution and in the solid state have been investigated. From concentrated aqueous solutions, compounds of general formula [M(II)(N-tosylaminoacidato)₂(H₂O)₄](M = Co(II), Ni(II) and N-tosylaminoacidato = N-tosylglycinate (Tsgly^?), N-tosyl-α- and -β-alaninate (Ts-α- and Ts-β-ala^?); M = Zn(II) and N-tosylaminoacidate = Tsgly^?, Ts-β-ala^?) and [Zn(II)(N- tosylaminoacidato)₂(H₂O)₂] were isolated and characterized by means of thermogravimetric, electronic and infrared spectra. For two of them: [Co(Tsgly)₂(H₂O)₄](I) and [Zn(Ts-β-ala)₂(H₂O)₄](II) the crystal and molecular structures were also determined. Both compounds crystallize in the monoclinic space group P2₁/c, with two formula units in a cell of dimensions: a = 13.007(6), b = 5.036(2), c = 18.925(7) Å, β = 102.33(3)° for (I) and a = 14.173(6), b = 5.469(2), c = 17.701(7) Å, β = 106.63(3)° for (II). The structures were solved by the heavy-atom method and refined by least-squares calculations to R = 0.031 and 0.064 for (I) and (II) respectively. The cobalt and zinc atoms lie in the centers of symmetry, each bonded to two amino- acid molecules through a carboxylic oxygen atom and four water molecules in a slightly tetragonally distorted octahedral geometry. The second carboxylic oxygen atom is not involved in metal coordination. Electronic and X ray-powder spectra suggest that the tetrahydrate complexes of Co²⁺, Ni²⁺ and Zn²⁺ ions of the same amino acids are isomorphous and isostructural. No coordinative interactions between ligand and metal ions were found in aqueous solution on varying the pH values before hydroxide precipitation.     

FT-IR and 1H NMR spectroscopic evidence of sugar ring conformational change in NH4GpG on complexation to form cis-[Pt(NH3)2(GpG)]+

The conformational change of the ribose ring in NH₄GpG and cis-[Pt(NH₃)₂(GpG)]⁺ was confirmed by FT-IR spectroscopic evidence as being C2′-endo, C3′-endo, anti, gg sugar ring pucker in the solid state. These results were compared with ¹H NMR spectral data in aqueous solution. The FT-IR spectrum of NH₄GpG shows marker bands at 802 cm^?1 and 797 cm^?1 which are assigned to the C3′-endo, anti, gg sugar-phosphate vibrations of ribose (?pG) and ribose (Gp?), respectively. The FT-IR spectrum of cis-[Pt(NH₃)₂(GpG)]⁺ (with N7N7 chelation in the GpG sequence) shows a marker band at 800 cm^?1 which is assigned to the C3′-endo, and a new shoulder band at 820 cm^?1 related to a C2′-endo ring pucker. The ribose conformation of (?pG) moiety in NH₄-GpG, C3′-endo, anti, gg changes into C2′-endo, anti, gg when a platinum atom is chelated to N7N7 in the GpG sequence.     

Effects of phenoxide ligation: Synthesis and characterization of the [Mo2Fe6S8(SEt)3(OPh)6]3− ion

Reaction of phenol with an alkylthiolate-ligated double cubane complex effects phenolate substitution at the terminal positions; the product can be isolated as its benzyltriethylammonium salt. The phenolate cluster possesses unaltered magnetic properties and blue shifted optical spectra, and undergoes ligand exchange reactions with electrophiles as expected for terminal phenolate substitution. Increased isotropic proton NMR shifts and large negative shifts in corresponding first and second reduction potentials are consistent with increased donation of electron density to the [MoFe₃S₄]³⁺ cores for phenolate versus thiophenolate terminal ligands to iron. Similar behavior has been observed for Fe₄S₄, Fe₂S₂ and MoS₂Fe systems.     

Reactions of copper(II) and nickel(II) compounds of 6-methyl-2-picolylamine with acetone,including and x-ray structural analysis of [Ni(C20H28N4)(NO3)]NO3

The reaction with acetone of nickel(II) and copper(II) bis-chelated compounds of 6-methyl-2-pyridylmethylamine gives compounds of the quadridentate [N₄] ligand 2,6-diaza-1,7-bis-(6′-methyl-2′-pyridyl)-3,5,5-trimethyl-hept-2-ene(Q). In the nickel series also, a bis-chelated perchlorate of the terdentate ligand 2-aza-1-(6′-methyl-2′-pyridyl)-3-methyl-hex-2-ene-5-one was obtained. In the copper series, five-coordinate species [Cu(Q)X]X (X = Br, I, NCS) and [Cu(QX]ClO₄ (X = Cl) were isolated. If left in acetone, these undergo further reaction, with increasing ease in the order Cl < Br < I. An intermediate formation of a transient brown colour suggests the possible involvement of a copper(I) intermediate. The nature of the products was established by an X-ray analysis of the structure of [Ni(Q)NO₃]NO₃. Crystals are orthorhombic, a = 20.36(2), b = 13.38(1), c = 8.226(5) Å, space group Pna2₁. Using two-circle diffractometer data (1598 reflections), the structure was solved by Patterson and Fourier methods, and refined by block diagonal least-squares methods to a final R of 0.030. The expected quadridentate ligand was found in the cis-β configuration about the metal, with coordination sphere completed by a bidentate nitrate. Bond-lengths and angles within the molecular cation were unexceptionable considering the small ‘bite’ of the chelated nitrato group of only 59°.     

Metal-penicillamine interactions. Part 1. Preparation and crystal structure of a 1:1 complex of mercuric chloride with d-penicillamine, 2[μ3-Cl){HgSC(CH3)2CH(NH3)COO}3·3(μ2-Cl)· 2(H3O)·(H2O·Cl)3

A 1:1 complex of mercuric chloride with D-peniccillamine has been isolated and characterised as 2[(μ₃-Cl){HgSC(CH₃)₂CH(NH₃)COO}3]·3(μ₂-Cl)·2(H₃O)·(H₂O·Cl)₃. The compound crystallises in cubic space group P4₁32, with a = 18.679(5) Å and Z = 4. The structure, refined to R_F = 0.086 for 443 observed Mo-Kα diffractometer data, features a triply bridging chloride ion linking three equivalent [HgSC(CH₃)₂CH(NH₃)COO]⁺ units [Hg-Cl = 2.37(1) Å, Hg-Cl-Hg′ = 98.5(9)°]. The carboxylate groups of a pair of adjacent penicillamine ligands are strongly linked via a symmetrical O?H?O hydrogen bond of length 2.24(8) Å, and neighboring pyramidal trinuclear [μ₃-Cl){HgSC(CH₃)₂CH(NH₃)-COO}₃]²⁺ moieties are further connected by symmetrical chloride bridges [Hg-Cl = 3.06(2) Å; HgClHg′' = 79.6(7)°] to form a three-dimensional network. The voids in the lattice are filled by hydronium ions and novel planar cyclic hydrogen-bonded (H₂O·Cl^?)₃ rings of edge O-H?Cl = 2.46(4) Å.     

Affinity labeling of spinach ferredoxin-NADP+ oxidoreductase with periodate-oxidized NADP+

Periodate-oxidized NADP⁺ (dialdehyde-NADP⁺) inactivated soluble ferredoxin-NADP⁺ oxidoreductase and combined covalently to the enzyme. This inactivation was first order with respect to dialdehyde-NADP⁺ and followed saturation kinetics, indicating that the enzyme initially forms a reversible complex with the inactivator. NADP⁺ afforded complete protection against inactivation, while spinach ferredoxin was uneffective. In the presence of exogenous ferredoxin and illuminated thylakoids, the nucleotide analog functioned as a coenzyme for the reductase, although with rather lower efficiency than NADP⁺. It also acted as a competitive inhibitor with respect to NADPH in diaphorase activity. Incorporation of radioactivity from periodate-oxidized [³H]NADP⁺ gave a stoichiometry of 0.85 mol of reagent/mol of reductase, indicating that the modification of a single residue in the flavoprotein is responsible for the loss of enzymatic activity.     

Interaction of Ca2+ with (Na+ + K+)-ATPase: Properties of the Ca2+-stimulated phosphatase activity

Ca²⁺ inhibited the Mg²⁺-dependent and K⁺-stimulated p-nitrophenylphosphatase activity of a highly purified preparation of dog kidney (Na⁺ + K⁺)-ATPase. In the absence of K⁺, however, a Mg²⁺-dependent and Ca²⁺-stimulated phosphatase was observed, the maximal velocity of which, at pH 7.2, was about 20% of that of the K⁺-stimulated phosphatase. The Ca²⁺-stimulated phosphatase, like the K⁺-stimulated activity, was inhibited by either ouabain or Na⁺ or ATP. Ouabain sensitivity was decreased with increase in Ca²⁺, but the K_0.5 values of the inhibitory effects of Na⁺ and ATP were independent of Ca²⁺ concentration. Optimal pH was 7.0 for Ca²⁺-stimulated activity, and 7.8–8.2 for the K⁺-stimulated activity. The ratio of the two activities was the same in several enzyme preparations in different states of purity. The data indicate that (a) Ca²⁺-stimulated phosphatase is catalyzed by (Na⁺ + K⁺)-ATPase; (b) there is a site of Ca²⁺ action different from the site at which Ca²⁺ inhibits in competition with Mg²⁺; and (c) Ca²⁺ stimulation can not be explained easily by the action of Ca²⁺ at either the Na⁺ site or the K⁺ site.     

Synthesis and characterization of uranyl(VI) and thorium(IV) complexes with phosphine oxides. The crystal structure of UO2(NO3)2(NO2-C6H4Ph2PO)2

Uranyl(VI) and thorium(IV) complexes of the type UO₂(NO₃)₂(L¹)₂, UO₂(NO₃)₂(L²)₂, UO₂(CH₃COO)₂L¹, UO₂(CH₃COO)₂L², Th(NO₃)₄(L¹)₂ and Th(NO₃)₄(L²)₂ (L¹ = (2-nitro)phenyl-bis-phenyl phosphine oxide, L² = triferrocenylphosphine oxide) are reported, together with their physico-chemical properties.The crystal structure of UO₂(NO₃)₂(L¹)₂ is also reported. The crystals are monoclinic, space group P2₁/n with a = 17.78(1), b = 13.88(1), c = 17.37(1) Å, β = 114.8(1)° for Z = 4. The uranium atom is 8-coordinated, the uranyl(VI) group being equatorially surrounded by an irregular hexagon of six oxygen atoms from two trans neutral ligands and two nitrato groups.