Infrared and electron paramagnetic resonance study of nitrosyl(protoporphyrin IX dimethyl ester)iron(II) and its complexes with nitrogenous bases as model systems for nitrosylhemoproteins: effect of solvent polarity

Infrared and electron paramagnetic resonance spectra of nitrosyl(protoporphyrin IX dimethyl ester)iron(II)(Fe(PPDME)(NO)) and its complexes with nitrogenous bases (N bases) such as imidazoles, pyridines, aliphatic amines, and anilines have been measured in various solvents. At room temperature, giso, Aiso, and nu NO values of five-coordinate Fe(PPDME)(NO) decreased with an increase in solvent polarity parameter ET, indicating the interaction between the solvent and the vacant axial coordination position. It has been found that the nu NO value of six-coordinate species is very sensitive to the solvent polarity, while the giso value is less sensitive. The solvent effect on the equilibrium constants, which are evaluated from the intensity change of the NO stretching band for five- and six-coordinate species, is discussed.     

Interactions between polynucleotides and platinum (II) complexes

Reaction of either $\text{cis}$ or $\text{trans}$ Pt(NH₃)₂Cl₂ with poly(A) in dilute aqueous solution leads to quantitative precipitation of the polymer at Pt/nucleotide ratios above 0.5. It is proposed that at ratios less than this, intramolecular binding of one Pt to two bases is favored; at higher ratios, intermolecular cross-linking becomes important and precipitation results. The absence of isomer selectivity in precipitation implies that the biological specificity of the $\text{cis}$ form results from a process other than cross-linking of polynucleotide strands. Other observations suggest that the coordinated ammonia of nucleotide-platinum(II) ammine complexes may be unusually labile.     

Structures of two N(1)-bound platinum(II)-6-oxopurine complexes. Comparisons with complexes derived from platinum (II) anti-tumor agents

The preparation and molecular structure of [(diethylenetriamine) (7,9-dimethylhypoxanthine) platinum(II)] (PF₆)₂·1.5H₂O and [(ethylenediamine) (7,9-dimethylhypoxanthine)₂platinum(II)] (PF₆)₂, are reported. These complexes represent the first structurally characterized N(1)-bound Pt(II) 6-oxopurine complexes. In each case, the Pt(II)N(1) bond length [2.051(6)A in the diethylenetriamine complex and 2.021(8)A in the ethylenediamine complex] indicates a strong metal-to-base binding. Both complexes contain interligand hydrogen bonds, with the ammine ligand acting as the donor and the O(6) atom of the base acting as the acceptor. These N(1)-bound complexes are compared with N(7)-bound 6-oxopurine and N(3)-bound cytosine complexes of Pt(II) anti-tumor agents.     

Manganese(II), iron(II) and nickel(II) chloride complexes with monodeprotonated anionic guanine

Upon refluxing 2:1 mixtures of guanine (guH) and MnCl₂, FeCl₂ or NiCl₂ in a 7:3 (v/v) mixture of ethanol and triethyl orthoformate for 1–2 weeks, partial substitution of gu^? for Cl^? groups occurs, and solid complexes of the M(gu)Cl·2ROH (R = C₂H₅ for M = Mn; R = H for M = Fe, Ni) type are obtained. The new complexes are pentacoordinated and appear to be linear chainlike polymeric species, involving a single-bridged

_n backbone. Coordination number five is attained by the presence of one terminal chloro and two terminal ROH ligands per metal ion. Most probable binding sites of bidentate bridging gu^? are the N(7) and N(9) imidazole ring nitrogens. IR evidence rules out the possibility of coordination of gu^? through any of the exocyclic potential ligand sites (O(6) oxygen or N(2) nitrogen) [1].     

Nuclear magnetic resonance spectroscopy of cobalt (II) porphyrin-quinone complexes

Weak intermolecular complexes of cobalt(II) and nickel(II) mesoporphyrin dimethyl ester with 1,4-naphthoquinone, vitamin K-3, vitamin K-1 and ubiquinone 30 have been detected by ¹H-NMR spectroscopy in chloroform solutions. The relative orientation of the components of complexes is discussed.     

Optical properties of Cu(II) complexes with heparin and related glycosaminoglycans.

Absorption and circular dichroism measurements have been carried out to obtain information regarding the stability and the nature of complexes between Cu(II) and heparin, and between Cu(II) and related glycosaminoglycans. In the presence of Cu(II), all glycosaminoglycans, except keratan sulfate, show a characteristic absorption band near 237 nm, which we assign to charge-transfer bands involving ligands to metal ion. From the absorbance values, the formation constants of Cu(II)-heparin and Cu(II)-(itN)-desulfated heparin have been determined to be approximately 1 × 10⁴ and 2 × 10² mol^?1, respectively. The large difference in the stability constant values is attributed to the difference in the charge density of the polymers, and to involvement of more than one ligand in the case of heparin. The CD characteristics of the Cu(II)-heparin complex suggest that both carboxyl and sulfamino groups are involved as ligands. The appearance of extrinsic CD bands in heparin, heparan sulfate, dermatan sulfate, and N-desulfated heparin at pH > 5 is ascribed to asymmetry of chelate rings. Absence of CD change in chondroitin sulfate and N-desulfated heparin (pH < 5) in the presence of Cu(II) suggests that only the carboxyl group is involved in those complexes. The differences either in iduronic acid conformation (C-1 vs. 1-C) or in intersaccharide linkages between dermatan sulfate and heparin (or heparan sulfate) are revealed in the difference CD spectra between the complexes and the polymers. The change in the intrinsic Cotton effect on complex formation is accounted for as a change in spatial orientation of the ligand groups rather than as a major conformational change of the polymers.     

Free metal ion depletion by "Good's" buffers. III. N-(2-acetamido)iminodiacetic acid, 2:1 complexes with zinc(II), cobalt(II), nickel(II), and copper(II); amide deprotonation by Zn(II), Co(II), and Cu(II)

Potentiometric, visible, infrared, electron spin, and nuclear magnetic resonance studies of the complexation of N-(2-acetamido)iminodiacetic acid (H2ADA) by Ca(II), Mg(II), Mn(II), Zn(II), Co(II), Ni(II), and Cu(II) are reported. Ca(II) and Mg(II) were found not to form 2:1 ADA2- to M(II) complexes, while Mn(II), Cu(II), Ni(II), Zn(II), and Co(II) did form 2:1 metal chelates at or below physiological pH values. Co(II) and Zn(II), but not Cu(II), were found to induce stepwise deprotonation of the amide groups to form [M(H-1ADA)4-(2)]. Formation (affinity) constants for the various metal complexes are reported, and the probable structures of the various metal chelates in solution are discussed on the basis of various spectral data.     

The interaction of cyanocobalamin and some of its analogs with manganese(II) and gadolinium(III)

The influence of the paramagnetic ions Mn²⁺ and Gd³⁺ on the proton-decoupled ¹³C nuclear magnetic resonance spectra of three cyanocobalamin-monocarboxylic acids has been observed. The paramagnetic ions bind preferentially to the free carboxylate groups and cause the broadening of specific carbon resonances adjacent to these groups. These specific line-broadening effects have been used to assign the carbonyl carbons of the a-, f-, and g-acetamide side chains and have allowed us to confirm and/or correct the assignments of several carbon resonances that were assigned tentatively before.     

X-ray crystal and molecular structures of the Ni(II) and Co(II) complexes of 2'-deoxyguanosine-5'-monophosphate.

The structures of [Ni(5′-dGMP)(H₂O)₅] and [Co(5′-dGMP)(H₂O)₅] have been solved by single-crystal x-ray diffraction techniques. Their common geometry consists of a metal ion octahedrally coordinated to the N₇ atom of guanine and five water ligands. The phosphate group of the nucleotide is hydrogenbonded to two of the coordinated water molecules.     

Synthesis and characterization of a series of new mixed ligand complexes of manganese(III), iron(III), nickel(II), copper(II) and zinc(II) with schiff bases of N,N-diethylamino-dithiocarbamate as ligands

Twenty new bioactive complexes of Mn(III), Fe(III), Ni(II), Cu(II) and Zn(II) have been prepared containing Schiff bases of N,N-diethylaminodithio- carbamate as ligands. These complexes have been characterized by elemental analyses, IR and UV-Vis spectroscopy as well as by magnetic susceptibility measurements. The spectra of the complexes suggest that the ligands are coordinated to the metal ions via the sulfur atoms of the dithiocarbamato group.     

Solution chemistry and Mössbauer study of iron(II) and iron(III) complexes from gallocyanine

The iron solution chemistry of the FeCl₃-gallocyanine system has been investigated by pH titration, UV visible spectroscopy and Mössbauer spectroscopy. Iron reduction was found in the pH range 2–5 and photo-reduction of the iron(III) present was also noted. Due to the instability of the species present in solution, the use of gallocyanine as a spectrophotometric indicator in iron systems is not encouraged. The iron-gallocyanine system was proposed as a potential model of the photosensitive anti-cancer drug, Bleomycin.     

The preparation and characterisation of some complexes of iron(II) with amino acids

The following complexes of iron(II) with the amino acids glycine, alanine, phenylglycine, phenylalanine, leucine, serine, aspartic acid, glutamic acid, glutamine, tryptophan, histidine, methionine, S-methylcysteine, cystine, and glycylglycine have been isolated: Fe(Gly)₂, Fe(Ala)₂, Fe(Phegly)₂, Fe(Phe)₂·2H₂0, Fe(Leu)₂·2H₂0, Fe(Ser)₂, Fe(Asp)·2H₂0, Fe(Glu)·2H₂0, Fe(Gln)₂, Fe(Trp)₂, Fe(His)₂·H₂0 and 2H₂0, Fe(Met)₂, Fe(MeCys)₂, Fe(CysCys) and Fe(GlyGly)₂. Their magnetic behaviour, reflectance spectra, and Mössbauer parameters are consistent with high spin, hexacoordinate iron(II), and imply extended structures involving carboxylate bridges.     

Immunological and circular dichroism studies of maleylated f-1 (A) histone and complexes with DNA

Complexes of calf thymus f-1 (A) histone and homologous DNA were examined by circular dichroism. The maleylation of f-1 (A) produces a polypeptide with decreased ability to modify the circular dichroism spectrum of f-1 (A)-DNA complexes. By the introduction of two to three maleyl groups per f-1 (A) molecule, the alteration of the DNA CD spectrum is reduced by nearly half compared to that induced by the native nonmaleylated f-1 (A). Similarly maleylation reduces the serological reactivity of the histone, i.e., the reaction of the maleylated f-1 (A) with specific complement fixing f-1 (A) antibodies. On the other hand, moderate maleylation of f-1 (A) improves the cross-inhibition of the f-2b-anti-f-2b reaction by native f-1 (A) while extensively maleylated f-1 (A) is inert with respect to the same reaction. These results are interpreted in terms of possible conformational changes induced in f-1 (A) by maleylation, partially due to decreasing the histone net charge and perhaps as well as removal of specific site charges necessary for correct binding and interaction. Such an interpretation is consistent with the altered CD spectrum of maleylated f-1 (A) (i.e., a decreased and slightly red-shifted [θ]₁₉₈) and moreover explains why maleylation of two to three lysines per f-1 (A) molecule hinders simultaneously the very different DNA-histone and histone-complement fixing antibody interactions.     

Synthesis and characterization of tertiary phosphine Pd(0) complexes

The synthesis of PdL_n complexes (L = tertiary phosphine; n = 2,3,4) is reported. The coordination number results to be a function of the steric hindrance of the phosphine. Two-coordinate, 14-electron complexes, have been isolated with bulky phosphines (PPrⁱ₃, P (cyclohexyl)₃, PBu^t₂Ph). The behaviour in solution of the PdL_n complexes has been studied by ¹³C NMR spectroscopy.     

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.     

Linked functions in allosteric proteins: Extension of the concerted (MWC) model for ligand-linked subunit assembly and its application to human hemoglobins

The allosteric model of Monod et al. (1965) (MWC) has been extended to take into account the effects of subunit dissociation. The problem is formulated theoretically in terms of a general model for two allosteric species (dimers and tetramers) linked by a polymerization reaction. Relationships are presented for interpreting the dimer-tetramer association constants in terms of allosteric model parameters.Sub-cases of the general model were tested against recent experimental data on the oxygenation-linked dimer-tetramer equilibria in normal human hemoglobin and in the variant hemoglobin Kansas (β₁₀₂, Asp → Thr). The objectives of these analyses were: (1) to find the simplest models capable of describing the linked dimer-tetramer equilibria in the two hemoglobin systems, and (2) to evaluate the corresponding model parameters so that allosteric properties of the two hemoglobins may be compared.In the simplest version of the model, the dimer is half of an R-state tetramer. This model was found to be excluded unequivocally by the data for both normal hemoglobin and hemoglobin Kansas when the α and β chains have equal binding affinities. When this two-state model was modified to permit non-equivalent affinities for the chains, the model could be fitted to hemoglobin Kansas, but not to hemoglobin A. A model, in which the dimers are allowed to exist in a state different from the tetramer R state, was found to be consistent with the data for hemoglobin A, with equivalent binding by the α and β chains. For hemoglobin A, the unliganded R-state tetramers have a different subunit dissociation energy from that of fully liganded R-state tetramers. The simplest model capable of describing both hemoglobin A and hemoglobin Kansas was obtained by extending this three-state model to permit (but not require) functional non-equivalence of the α and β chains. For these MWC models, unique estimates were obtained for the model parameters.The allosteric constants for tetrameric hemoglobins A and Kansas are approximately equal. The value obtained from hemoglobin A is similar to previous estimates, whereas the value for hemoglobin Kansas is lower than previously estimated (Edelstein, 1971) by approximately two orders of magnitude. The low affinity of hemoglobin Kansas tetramer does not arise from an unusually high allosteric constant favoring the T-state species. It is largely the consequence of a greatly reduced oxygen affinity of β chains in the T state, and reduced values for the ratio between affinities in the R and T states.     

Electronic structure and magnetic coupling of two dinuclear trigonal bipyramidal cobalt(II) complexes

The EPR spectra of zinc-doped (bis(N-methylsalicylaldiminato)cobalt(II), (Zn, Co) SALMe, which was found to be dinuclear, and of zinc-doped bis(N,N-bis(2-(diethylamino)ethyl)-2-hydroxyethylamino-O)dicobalt(II)diperchlorate, (Zn, Co)n₃o, were recorded at liquid helium temperature and X-band frequency.The polycrystalline powder spectra of (Zn, Co)SALMe were interpreted within an effective S = 1/2 spin hamiltonian formalism with g₁ = 1.8, g₂ = 2.7, g₃ = 6.2, while those of (Zn, Co)n₃o showed only one band at G= 6.9. The single crystal spectra for the latter yielded g₁ = 0.31(4), g₂ = 0.84(4), g₃ = 6.86(2). The electronic structure of the complexes was calculated using the AOM, and the lowest Kramers doublet for CoSALMe was found to be ±1/2 while a ±3/2 doublet was found for Con₃o. The temperature dependence of the magnetic susceptibility of CoSALMe was measured between 295 and 4.2 K. The data were fitted with two different methods which either took into account or neglected the zero-field splitting of single ions. The coupling was found to be antiferromagnetic with J = 9.8(2) cm^-1 (J is defined through the hamiltonian = JS₁·S₂). The extent of the magnetic interaction between the metal ions for both the complexes was discussed on the basis of a structural analysis.