Calculation of NMR lanthanide-induced chemical shifts. The paradox of the pseudocontact model for europium reagents with coordination at the pyridine nitrogen atom

1981 ◽  
Vol 22 (3) ◽  
pp. 332-337 ◽  
Author(s):  
I. Kordova ◽  
A. A. Fomichev ◽  
V. P. Zvolinskii ◽  
A. N. Gusarov ◽  
V. G. Pleshakov ◽  
...  
Keyword(s):  
Nitrogen Atom ◽  
Chemical Shifts ◽  
Pyridine Nitrogen Atom ◽  
Pyridine Nitrogen

Crystal structures of 7-azaindole, an unusual hydrogen-bonded tetramer, and of two of its methylmercury(II) complexes

1990 ◽  
Vol 68 (1) ◽  
pp. 193-201 ◽  
Author(s):  
Pascal Dufour ◽  
Yves Dartiguenave ◽  
Michèle Dartiguenave ◽  
Nathalie Dufour ◽  
Anne-Marie Lebuis ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Nitrogen Atom ◽  
Hydrogen Bonds ◽  
Crystal Structures ◽  
Membered Ring ◽  
Pyridine Nitrogen Atom ◽  
Nitrate Ions ◽  
Pyridine Nitrogen ◽  
Independent Molecules ◽  
Hydrogen Bonded

Crystals of 7-azaindole ([Formula: see text], a = 11.312(4), b = 14.960(6), c = 15.509(5) Å, α = 102.86(3), β = 108.78(3), γ = 90.71(3)°, Z = 16, R = 0.052) contain tetrameric units of approximate S4 symmetry, in which the molecules are associated by means of four complementary N—H … N hydrogen bonds. [CH3Hg(7-azaindole)]NO3 ([Formula: see text], a = 7.818(3), b = 7.884(3), c = 9.135(4) Å, α = 97.89(3), β = 109.13(3), γ = 103.28(3)°, Z = 2, R = 0.039) contains well-separated nitrate ions and complex cations in which the methylmercury group is linearly bonded to the pyridine nitrogen atom, whereas the five-membered ring remains protonated. In the neutral [CH3Hg(azaindolate)] complex ([Formula: see text], a = 10.926(10), b = 11.333(8), c = 11.647(10) Å, α = 92.13(8), β = 104.83(9), γ = 111.86(7)°, Z = 6, R = 0.048), methylmercury groups have substituted the N—H proton in the five-membered ring for the three symmetry-independent molecules. Intermolecular secondary Hg … N bonds are found with pyridine nitrogens. Keywords: azaindole, methylmercury, crystal structure.

scholarly journals Study of the hydrolysis and ionization constants of Schiff base from pyridoxal 5′-phosphate and n-hexylamine in partially aqueous solvents. An application to phosphorylase b

1986 ◽  
Vol 238 (1) ◽  
pp. 137-144 ◽  
Author(s):  
J Donoso ◽  
F Muñoz ◽  
A García Del Vado ◽  
G Echevarría ◽  
F García Blanco
Keyword(s):  
Schiff Base ◽  
Nitrogen Atom ◽  
Ph Value ◽  
Equilibrium Constants ◽  
Solvent Polarity ◽  
Hydrolysis Rate ◽  
Ionization Constants ◽  
Pyridine Nitrogen Atom ◽  
Pyridine Nitrogen ◽  
Pka Value

Formation and hydrolysis rate constants as well as equilibrium constants of the Schiff base derived from pyridoxal 5′-phosphate and n-hexylamine were determined between pH 3.5 and 7.5 in ethanol/water mixtures (3:17, v/v, and 49:1, v/v). The results indicate that solvent polarity scarcely alters the values of these constants but that they are dependent on the pH. Spectrophotometric titration of this Schiff base was also carried out. We found that a pKa value of 6.1, attributed in high-polarity media to protonation of the pyridine nitrogen atom, is independent of solvent polarity, whereas the pKa of the monoprotonated form of the imine falls from 12.5 in ethanol/water (3:17) to 11.3 in ethanol/water (49:1). Fitting of the experimental results for the hydrolysis to a theoretical model indicates the existence of a group with a pKa value of 6.1 that is crucial in the variation of kinetic constant of hydrolysis with pH. Studies of the reactivity of the coenzyme (pyridoxal 5′-phosphate) of glycogen phosphorylase b with hydroxylamine show that this reaction only occurs when the pH value of solution is below 6.5 and the hydrolysis of imine bond has started. We propose that the decrease in activity of phosphorylase b when the pH value is less than 6.2 must be caused by the cleavage of enzyme-coenzyme binding and that this may be related with protonation of the pyridine nitrogen atom of pyridoxal 5′-phosphate.

Configuration of benzoylpyridineoximes studied by 1H and 13C NMR. Effect of protonation of the pyridine nitrogen atom

1990 ◽  
Vol 26 (8) ◽  
pp. 898-902
Author(s):  
V. P. Lezina ◽  
S. G. Rozenberg ◽  
O. M. Glozman ◽  
L. A. Zhmurenko ◽  
V. A. Zagorevskii
Keyword(s):  
Nitrogen Atom ◽  
13C Nmr ◽  
Pyridine Nitrogen Atom ◽  
1H And 13C Nmr ◽  
Pyridine Nitrogen

scholarly journals The metabolic origin of trigonelline in the rat

1981 ◽  
Vol 200 (3) ◽  
pp. 495-500 ◽  
Author(s):  
J S Sandhu ◽  
D R Fraser
Keyword(s):  
Nitrogen Atom ◽  
Nicotinic Acid ◽  
Intestinal Mucosa ◽  
Pyridine Nitrogen Atom ◽  
Pyridine Nitrogen ◽  
Oral Doses

A hypothesis of Mason & Kodicek [(1970) Biochem. J. 120, 515-521] that esterified nicotinic acid in niacytin from cereals is a precursor for trigonelline was investigated in rats. Single oral doses of niacytin resulted in the excretion of trigonelline in urine but only in rats that were niacin-deficient and were fed a cereal diet. These animals were found to have an abnormally permeable intestine, which allowed the uptake of molecules not usually absorbed. Orally administered synthetic [14C]nicotinoyl[3H]methylcellulose was shown to be absorbed by niacin-deficient rats on a cereal diet and [14C]trigonelline was excreted in urine. These data indicate that dietary cereal induces a permeability defect in the intestinal mucosa of niacin-deficient rats, which allows the uptake of macromolecular niacytin. The nicotinoyl pyridine nitrogen atom is then methylated and slow hydrolysis releases trigonelline from the macromolecule.

scholarly journals Indolizines and pyrrolo[1,2-c]pyrimidines decorated with a pyrimidine and a pyridine unit respectively

2015 ◽  
Vol 11 ◽  
pp. 1079-1088 ◽  
Author(s):  
Marcel Mirel Popa ◽  
Emilian Georgescu ◽  
Mino R Caira ◽  
Florentina Georgescu ◽  
Constantin Draghici ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Nitrogen Atom ◽  
Steric Hindrance ◽  
Cycloaddition Reaction ◽  
Dipolar Cycloaddition ◽  
Pyridine Nitrogen Atom ◽  
Structural Isomers ◽  
X Ray ◽  
Pyridine Nitrogen

The three possible structural isomers of 4-(pyridyl)pyrimidine were employed for the synthesis of new pyrrolo[1,2-c]pyrimidines and new indolizines, by 1,3-dipolar cycloaddition reaction of their corresponding N-ylides generated in situ from their corresponding cycloimmonium bromides. In the case of 4-(3-pyridyl)pyrimidine and 4-(4-pyridyl)pyrimidine the quaternization reactions occur as expected at the pyridine nitrogen atom leading to pyridinium bromides and consequently to new indolizines via the corresponding pyridinium N-ylides. However, in the case of 4-(2-pyridyl)pyrimidine the steric hindrance directs the reaction to the pyrimidinium N-ylides and, subsequently, to the formation of the pyrrolo[1,2-c]pyrimidines. The new pyrrolo[1,2-c]pyrimidines and the new indolizines were structurally characterized through NMR spectroscopy. The X-ray structures of two of the starting materials, 4-(2-pyridyl)pyrimidine and 4-(4-pyridyl)pyrimidine, are also reported.

scholarly journals Nucleophilic Attack at the Pyridine Nitrogen Atom in a Bis(imino)pyridine System: The Local Hard and Soft Acids and Bases Principle Perspective

2017 ◽  
Vol 56 (3) ◽  
Author(s):  
Arlette Richaud ◽  
Francisco Méndez
Keyword(s):  
Nitrogen Atom ◽  
Nucleophilic Attack ◽  
Pyridine Nitrogen Atom ◽  
Pyridine Nitrogen ◽  
Acids And Bases

Motivated by the unprecedented nucleophilic attack at the pyridine nitrogen atom in bis(imino)pyridines, observed by Gambarotta <em>et al.</em> and Gibson <em>et al.</em>, and the fact that normally pyridine undergoes reactions with electrophiles at its nitrogen atom, we applied the local hard and soft acids and bases principle to assert that nucleophilic attack at pyridine nitrogen atom depends fundamentally on stereoelectronic factors.

scholarly journals Fabrication of PEBA/Cu2O mixed-matrix membranes and their application in pyridine recovery from aqueous solution

RSC Advances ◽  
2017 ◽  
Vol 7 (37) ◽  
pp. 22936-22945 ◽  
Author(s):  
Jian Hua Chen ◽  
Zhen Bo Su ◽  
Jing Ping Xu ◽  
Li Jing Lin ◽  
Xin Fei Dong ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Nitrogen Atom ◽  
Metal Ions ◽  
Lone Pair ◽  
Mixed Matrix Membranes ◽  
Pyridine Nitrogen Atom ◽  
Mixed Matrix ◽  
Pyridine Nitrogen ◽  
Matrix Membranes

The lone pair of electrons of the pyridine nitrogen atom can form a complex with some metal ions such as Cu+, Ag+, etc.

Palladium(II) and Platinum(II) Complexes of N-3-Pyridinylmethanesulfonamide

2001 ◽  
Vol 56 (11) ◽  
pp. 1217-1226
Author(s):  
Nicolay I. Dodoff
Keyword(s):  
Nitrogen Atom ◽  
Ir Spectra ◽  
Electric Conductivity ◽  
Elemental Analysis ◽  
Nmr Spectra ◽  
Pyridine Nitrogen Atom ◽  
Normal Coordinate ◽  
H Nmr ◽  
Pyridine Nitrogen ◽  
Square Planar

The complexes cis-[Pd(PMSA)2Cl2] cis-[Pt(PMSA)2X2], trans-[Pt(PMSA)2I2] and [Pt(PMSA)4]Cl2 (PMSA = N-3-pyridinylmethanesulfonamide; X = Cl, Br, I) have been synthesized and characterized by elemental analysis, molar electric conductivity, IR and 1H NMR spectra. A detailed assignment of the IR spectra (4000-150 cm-1) of the complexes, supported by an approximate normal coordinate analysis, has been performed. The complexes are of square-planar type and the PMSA ligand is coordinated via the pyridine nitrogen atom.

scholarly journals Diaquabis{μ-1,5-bis[(pyridin-2-yl)methylidene]carbonohydrazide(1–)}di-μ-chlorido-tetrachloridotetrazinc(II)

2020 ◽  
Vol 76 (8) ◽  
pp. 1349-1352
Author(s):  
Thierno Moussa Seck ◽  
Papa Aly Gaye ◽  
Cheikh Ndoye ◽  
Ibrahima Elhadji Thiam ◽  
Ousmane Diouf ◽  
...  
Keyword(s):  
Nitrogen Atom ◽  
Hydrogen Bonds ◽  
Oxygen Atom ◽  
Basal Plane ◽  
Chloride Anion ◽  
Methanol Solution ◽  
Pyridine Nitrogen Atom ◽  
Imino Nitrogen ◽  
Pyridine Nitrogen ◽  
Dinuclear Unit

A tetranuclear ZnII complex, [Zn4(C13H11N6O)2Cl6(H2O)2] or {[Zn2(HL)(H2O)(Cl2)](μCl)2[Zn2(HL)(H2O)(Cl)]}2, was synthesized by mixing an equimolar amount of a methanol solution containing ZnCl2 and a methanol solution containing the ligand H2 L [1,5-bis(pyridin-2-ylmethylene)carbonohydrazide]. In the tetranuclear complex, each of the two ligand molecules forms a dinuclear unit that is connected to another dinuclear unit by two bridging chloride anions. In each dinuclear unit, one ZnII cation is pentacoordinated in a N2OCl2 in a distorted square-pyramidal geometry, while the other ZnII cation is hexacoordinated in a N3OCl2 environment with a distorted octahedral geometry. The basal plane around the pentacoordinated ZnII cation is formed by one chloride anion, one oxygen atom, one imino nitrogen atom and one pyridine nitrogen atom with the apical position occupied by a chloride anion. The basal plane of the hexacoordinated ZnII cation is formed by one chloride anion, one hydrazinyl nitrogen atom, one imino nitrogen atom and one pyridine nitrogen atom with the apical positions occupied by a water oxygen atom and a bridged chloro anion from another dinuclear unit, leading to a tetranuclear complex. A series of intramolecular C—H...Cl hydrogen bonds is observed in each tetranuclear unit. In the crystal, the tetranuclear units are connected by intermolecular C—H...Cl, C—H...O and N—H...O hydrogen bonds, forming a planar two-dimensional structure in the ac plane.

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