Pyridine Ring Nitrogen Research Articles

Nicotinic acid complexes with uranyl salts

The potentially bidentate ligand, nicotinic acid, forms 2 : 1 complexes with uranyl chloride, sulphate, nitrate and acetate which have been characterized by i.r. spectral measurements down to 200 cm−1 in the solid state. These studies indicate conclusively that nicotinic acid coordinates onlyvia its pyridine ring nitrogen in all cases. The uranyl chloride arid sulphate complexes are monomeric hexacoordinated structures, while the nitrate and acetate complexes are octacoordinate around uranium.

Mixed Ligand Complexes Derived from the Reactions of Diaquabis-(3-hydroxy-2-methyl-4-pyronato)-cobalt(II), -nickel(II), and -zinc(II) with Pyridine and 4-Substituted Pyridines

Abstract The pyridine(py), 4-methylpyridine(4-Me-py) and 4-cyanopyridine(4-CN-py) adducts of bis(3-hydroxy-2-methyl-4-pyronato) complexes (ML2) of cobalt(II), nickel(II), and zinc(II) have been synthesized: CoL2(py)n (where n=2 or 3), NiL2(py)3, ZnL2(py), ML2(4-Me-py)2 (where M=Co(II), Ni(II), and Zn(II)), ML2(4-CN-py) (where M=Co(II) and Zn(II)), and NiL2(4-CN-py)2. Based on the magnetic, spectral, and thermogravimetric data, three of these complexes, ZnL2(py) and ML2(4-CN-py) (where M=Co(II) and Zn(II)), are presumed to have a five-coordinate structure, while the other complexes are presumed to be octahedral. In the case of the 4-cyanopyridine complexes, the infrared spectra show that the pyridine-ring nitrogen is linked to the metal ion and that the nitrogen atom of the nitrile group is not coordinated.

Some Three-coordinate Complexes of Mercury(II)

Abstract Nicotinic acid, nicotinamide and N-methylnicotinamide – pyridine derivatives with a carboxyl or amido group in the β-position in the ring – possess two potential donor sites, (i) pyridine ring nitrogen, and (ii) carbonyl oxygen in the case of nicotinamide and N-methylnicotinamide or carboxyl oxygen in nicotinic acid. As monodentate ligands bonding may occur through any one of these sites. One cannot rule out the possibility of the two coordination sites bonding to different metal ions (bidentate bridging ligand) resulting in polymeric structures. It should be possible to distinguish between the likely modes of metal–ligand bonding by i.r. spectroscopy. Except for the complexes of mercury(II) chloride and bromide with nicotinamide1 there is no report on those of mercury(II) halides and pseudohalides with these ligands. The present communication describes the coordination compounds formed by the interaction of mercury(II) chloride, bromide, cyanide and thiocyanate with nicotinic acid, nicotinamide and N-methylnicotinamide. The complexes isolated have been characterized by molecular conductance, molecular weight and infrared spectral measurements down to 200 cm−1 to elucidate the mode of metal–ligand bonding and the tentative stereochemistries of the complexes. Most of the complexes isolated have 1:1 stoichiometry (metal:ligand) and are considered to have monomeric, three-coordinated structures in the solid state.

Crystal and molecular structure of [Cu(NO3)2(C8H12N2O2)2]H2O, a structure containing an unusual zwitterion of pyridoxamine and a symmetric nitrate–oxygen bridge

A single crystal structure determination of [Cu(NO3)2(pm)2]H2O has established that copper is chelated to two pyridoxamine (pm) zwitterions through the amino groups and phenolate oxygen atoms, that the protons lost from the phenolic groups have been used to protonate the pyridine ring nitrogen atoms, and that the Cu(pm)2 units are bridged by a single oxygen atom from one of the nitrate groups.

Cyclization‐elimination reactions in the mass spectra of aminopyridine derivatives II‐aryl sulfonamides of 2‐aminopyridine and related compounds

AbstractThe mass spectra of aryl sulfonamides of some 2‐aminopyridines and 2‐aminopyrimidine show abundant peaks corresponding tothe loss of SO2 and HSO2 from the molecular ion. Evidence in favour of a cyclization‐elimination reaction involving bond formation between the pyridine ring nitrogen and the ortho position of the benzene ring is presented.

Vitamin B-6-catalyzed beta-elimination of serine and O-phosphoserine. Qualitative and quantitative aspects of catalytic influences at the rate-limiting step, a comparison with the rate of enzymatic beta-elimination.

The overall reaction rates for the beta-elimination of serine and O-phosphoserine, catalyzed by various vitamin B-6 analogs (pyridoxal 5'-phosphate, 5'-deoxypyridoxal and N-methylpyridoxal 5'-phosphate) in the presence or absence of Cu2+ ions, are determined. The comparison of the pH-dependence of the molar activities of the three vitamin B-6 aldehydes in beta-elimination of serine enables the characterization of the different active Schiff base species and the single catalytic events. The Schiff base which has a positive charge on the pyridine ring nitrogen and a fully ionized phosphate group shows the highest molar activity. The phosphate group acts as an intramolecular general base catalyst, most probably at the alpha-carbon proton of the amino acid. Furthermore general acid catalysis by buffer species occurs at the beta-hydroxy group serine. These facts together provide a kinetically unambiguous description of the mechanism of the reaction: the removal of the proton at the alpha-carbon atom of serine is the rate-limiting step and is followed by the more rapid elimination of the b-hydroxy group of serine. The forward rate constant of the rate-limiting step is calculated for each of the reactions mentioned. The rate constants are compared with respect to the effectiveness of the individual catalytic components in the vitamin B-6-dependent beta-elimination. For optimal conditions the reaction of O-phosphoserine is faster by a factor of 10(4) in the velocity of the beta-elimination than the corresponding acid-catalyzed beta-elimination of serine. For the eliminations at the alpha- and beta-carbon atoms of O-phosphoserine in vitamin B-6-catalysed reactions a common transition state is discussed. From a comparison of the fastest vitamin beta-6-dependent model reaction with the rate of an enzymatic beta-elimination it is suggested that for those beta-elininating enzymes where the rate-limiting step is the same as in the model, the catalytic components mentioned could suffice to explain the velocity of the rate-limiting step.

Imidazole and nicotinamide adducts of cobalt(II) and nickel(II) dithiophosphinates

Visible, magnetic (81–302°K), and IR studies on nicotinamide and imidazole adducts of Co( X) 2 and Ni( X) 2 ( X = diphenyldithiophosphinate and its p-tolyl analogue) indicate the formation of penta- and hexa-coordinate compounds. It is found that pentacoordinate adducts have the CoS 4N chromophore, while octahedral complexes have both MS 4N 2 and MN 6 (M  Co(II), Ni(II)) chromosomes depending on the base molecule. From an examination of IR spectra it is concluded that the pyridine ring nitrogen of nicotinamide acts as the donor atom.

Complexes of esters of pyridine carboxylic acids. Part I. complexes with Ni(II) and Co(II) thiocyanates

The syntheses of Nickel(II) and Cobalt(II) thio- cyanate complexes of type ML n(NCS) 2 where M = Co or Ni and n = 2 for L = methyl picolinate (MP), ethyl picolinate (EP), isopropyl picolinate (IP) and n = 4 for L = ethyl nicotinate (EN) and ethyl isonicotinate (EIN), are described. The complexes have been characterised by elemental analyses, molar conductance, magnetic susceptibility, thermogravimetric, electronic and infrared spectral data. The complexes are non-electrolytes in nitrobenzene and have high spin distorted octahedral structure with N-bonded thiocyanate groups in trans-position. MP, EP and IP act as bidentate ligands coordinating through pyridine ring nitrogen and carbonyl oxygen while EN and EIN act as unidentate ligands and coordinate through ring nitrogen only. The values of splitting energy (10 Dq), Racah parameter (B) and nephelauxetic ratio (β) have been evaluated for the nickel complexes.

The Crystal and Molecular Structure of Vitamin B6 Derivatives. I. Pyridoxal Phosphate Hydrate and Pyridoxal Phosphate Methyl Hemiacetal

Abstract Pyridoxal phosphate hydrate (PLPHYD) was crystallized from an aqueous solution in the form of monoclinic needles; space group P21⁄c with a=10.503, b=13.608, c=7.488 Å, β=93.71° and four molecules in the unit cell. Prism-shaped crystal of pyridoxal phosphate methyl hemiacetal (PLPMHA) was obtained by dissolving the pyridoxal phosphate hydrate crystals into 90% methanol; space group P\barl, with cell dimensions, a=9.42, b=10.61, c=6.20 Å, α=105.6°, β=95.7°, and γ=99.7°, and two molecules per cell. Intensity data were collected on an automated diffractometer for PLPHYD and photographically for PLPMHA. Crystal structures have been determined by the symbolic addition method. Refinements were done by the block-diagonal least-squares procedures, the final R value being 0.093 for PLPHYD and 0.112 for PLPMHA. The free aldehyde group of pyridoxal phosphate interacts with water molecule to form gem-diol in the crystalline state of PLPHYD and the gem-diol group of PLPHYD with methanol to form methyl hemiacetal. One of the two hydrogen atoms on a phosphate group is liberated and protonated to the pyridine ring nitrogen atom, resulting in the zwitterionic structure for both PLPHYD and PLPMHA molecules. All hydrogen bonds in PLPHYD are intermolecular ones, but in PLPMHA there is one OH–O intramolecular hydrogen bond.

Nicotinic Acid as a Ligand Affecting Leghemoglobin Structure and Oxygen Reactivity

A small molecule, hitherto called X, which is present in legume root nodules and ligates reversibly to the monomeric protein, leghemoglobin, with formation of a hemochrome structure, is identified as nicotinic acid. The binding constants at pH 5.3 are K = 7.3 x 10(5) M(-1) and K = 3.0 x 10(4) M(-1) for combination of nicotinic acid with ferric and ferrous leghemoglobin, respectively. This high affinity binding of ligand requires an unsubstituted pyridine ring nitrogen atom and an ionized carboxyl group in the 3-position of the ring. Binding of nicotinic acid is favored at acid pH and is reflected by diminished apparent affinity of leghemoglobin for oxygen.

Chelates of cupric salts with diethyl pyridine- and 4-methylpyridine-2-phosphonates

Synthetic and characterization studies of copper (II) perchlorate, nitrate and tetrafluoroborate complexes with diethyl pyridine-2-phosphonate (DEPP) and diethyl 4-methylpyridine-2-phosphonate (DEMPP) are reported. Complexes with the stoicheiometry Cu L 2 X 2 were generally obtained. DEPP and DEMPP act invariably as bidentate O,N-ligands in these complexes, coordinating through both the PO oxygen and the pyridine ring nitrogen. The Cu L 2 X 2 ( X  ClO 4, BF 4) chelates involve exclusively ionic ClO 4 or BF 4 groups and were formulated as [Cu L 2] X 2 with a square planar CuO 2N 2 moiety. The Cu(NO 3) 2 complexes are square pyramindal involving coordination of one monodentate nitrato group at the axial position: [Cu L 2(ONO 2)](NO 3). Electronic and i.r. spectral evidence suggests that DEMPP is a stronger ligand than DEPP.

Interaction of Pyridoxal Analogues with Glutamate Apodecarboxylase and Aspartate Apoaminotransferase

The interaction of a variety of pyridoxal analogues with glutamate decarboxylase and aspartate aminotransferase has been studied. Pyridoxal phosphate N-oxide, N-methylpyridoxal phosphate, 3-O-methylpyridoxal phosphate, 4-de-(formyl)-4-vinyl pyridoxal phosphate, and pyridoxal analogues which contain modified substituents in position 5 (CH2CH2OPO3H2, CH(CH3)OPO3H2, CH2PO3H2, and CH2-CH2COOH) are bound at the pyridoxal phosphate binding site of the enzymes. The reaction of the analogues with the apoenzymes prevented activation with pyridoxal phosphate. Pyridoxal phosphate, pyridoxal phosphate N-oxide, O-methylpyridoxal phosphate, and the homologue of pyridoxal phosphate bind to apodecarboxylase to give absorption spectra characteristic of protonated Schiff bases. The rates of binding, the coenzyme constants, and the activation of the enzymes were determined for the analogues with aspartate apoaminotransferase and glutamate apodecarboxylase. The phosphate group of the coenzyme plays an important role in binding to the enzymes and in maintaining the enzymes and coenzymes in the proper conformation for catalysis. There are more stringent structural requirements for interaction of pyridoxal phosphate with the decarboxylase than with the transaminase. The free phenolic hydroxyl group and the free pyridine ring nitrogen are of importance in the interaction of pyridoxal phosphate with glutamate apodecarboxylase, but not as much as with aspartate apoaminotransferase. However, the phenolic hydroxyl group and the pyridine ring nitrogen are very important in the activation of the transminase. The addition of pyridoxal phosphate N-oxide to apodecarboxylase yields enzyme which is 29% as active as the native holoenzyme. The decarboxylase-N-oxide complex and the native glutamate decarboxylase have similar Km values for glutamate and Ki values for glutarate.

Qualitative Applications of the NMR Spectra of Alkylpyridines: Part I. Chemical Shifts of the Ring Protons

Spectroscopic identification of pyridine compounds isolated from complex substances such as shale oil is greatly aided by NMR chemical-shift data on the pyridine-ring protons. Chemical shifts of the ring protons in CCl4 and C6H6 solution and the differential shift of the protons in these two solvents are reported. A paramagnetic shift is observed in the directional character of the proton alpha to the nitrogen in the pyridine ring. These data are used to determine structural information from the spectrum of a mixture of pyridine homologs.

Polyfluoro-heterocyclic compounds. Part VI. Nucleophilic substitution in tetrafluoro-4-nitropyridine

Reaction of tetrafluoro-4-nitropyridine with ammonia and sodium methoxide leads to considerable replacement of the nitro-group, unlike 2,3,5,6-tetrafluoro-4-nitrobenzene which gives exclusive replacement of fluorine ortho to the nitro-group. The pyridine-ring nitrogen is the greatest single factor in determining the orientation of nucleophilic attack. Competition experiments show relative reactivities to be in the order: pentafluoropyridine ≈ pentafluoronitrobenzene > tetrafluoro-4-nitropyridine. Fluorine-19 n.m.r. spectra of derivatives of pentafluoropyridine have been examined but the effect of substituent methoxyl and amino-groups on chemical shifts was not consistent, especially in the presence of a nitro-group.