5746-18-9Relevant articles and documents
Hydrogen bonds and conformational analysis of bis(1-methylisonicotinate) hydrochloride monohydrate by X-ray diffraction, vibrational spectra and B3LYP calculations
Szafran,Katrusiak,Dega-Szafran
, p. 46 - 53 (2006)
In the crystal structure of bis(1-methylisonicotinate) hydrochloride monohydrate, (MIN)2H·Cl·H2O, 1-methylisonicotinate betaines are hemiprotonated and form a homoconjugated cation through a short asymmetric O·H·O hydrogen bond of length 2.456(3) A?. Water molecules and Cl- anions are linked alternatively by hydrogen bonds of lengths 3.202(3) and 3.282(2) A? into planar zigzag chains along the [c] direction. The Cl- anion additionally interacts electrostatically with two positively charged nitrogen atoms of the neighboring MIN molecules. The most stable conformers of (MIN)2H·Cl·H2O, (MIN)2H·Cl, (MIN)2H·H2O and (MIN)2H have been analyzed by the B3LYP/6-31G(d,p) calculations in order to determine the influence of the anion and water molecule on the hydrogen bond in the homoconjugated MIN·H·MIN unit. The FTIR spectrum of (MIN)2H·Cl·H2O shows a broad and intense absorption in the 1500-400 cm-1 region, typical for short hydrogen bonds. The bands at 3416 and 3378 cm-1 confirm the presence of medium-strong hydrogen bonds between water molecules and Cl- anions.
Degradation of three related bis(pyridinium)aldoximes in aqueous solutions at high concentrations: Examples of unexpectedly rapid amide group hydrolysis
Korte,Shih
, p. 782 - 786 (1993)
The principal initial degradation products of two bis(pyridinium)aldoxime organophosphate-inhibited acetylcholinesterase reactivators, 1 (HI-6) and 3 (HS-6), in concentrated nonbuffered aqueous solutions approximating potential therapeutic dosage concentrations were found to be the carboxylic acid derivatives 2 and 4 formed from the hydrolysis of the amide functional group. Compounds 2 and 4 were prepared by heating 1 and 3 in the presence of high concentrations of hydroxylamine hydrochloride and characterized by 1H and 13C NMR, IR, and UV analyses. Estimates of the rates of hydrolysis of the amide groups in 1 and 3 and in model compounds 5, 7, and 8 under similar conditions were determined. The unexpectedly rapid hydrolysis of the amide groups in 1 and 3 was attributed to both the hydrogen ion catalysis of the concentrated aqueous solutions of the unusually acidic bis(pyridinium)aldoximes 1 and 3 and general acid catalysis by the aldoxime group.
X-ray and ab initio studies of the structure and vibrational spectra of 4-carboxy-1-methylpyridinium chloride
Szafran,Koput,Dega-Szafran,Katrusiak
, p. 66 - 81 (2006)
The effects of hydrogen bonding, inter- and intramolecular electrostatic interactions on the structure of 4-carboxy-1-methylpyridinium chloride (1-Me-isonicotinic acid chloride, 1-methyl-isonicotinium chloride), MINH·Cl, in the crystal and isolated molecule have been studied by X-ray diffraction, FTIR, Raman, 1H and 13C NMR spectra, B3LYP, MP2 and MP3 theoretical methods. In the crystal, the complex structure is stabilized by the O-H?Cl- hydrogen bond of 2.940(3) A?, and N+?Cl- interionic electrostatic interactions. In the isolated molecule, according to the B3LYP, MP2 and MP3 calculations, the Cl- anion is engaged in a shorter O-H?Cl- hydrogen bond of 2.931, 2.856 and 2.880 A?, respectively, and forms one distinct intramolecular electrostatic contact. The calculated bond lengths and bond angles are in good agreement with the X-ray data, except for the conformation of the COOH group, which is cis (syn) in the crystal and trans (anti) in the isolated molecule. The experimental solid-state vibrational spectra of MINH·Cl and MIND·Cl have been tentatively assigned on the basis of the MP2/ccpVDZ calculated frequencies and intensities. Analysis of the effects of quaternization of isonicotinic acid on the chemical shifts of the ring carbons and protons revealed correlations between the experimental carbon-13 and proton chemical shifts and the computed magnetic isotropic screening tensors.
One-electron-reduction potentials of pyrimidine bases, nucleosides, and nucleotides in aqueous solution. Consequences for DNA redox chemistry
Steenken,Telo,Novais,Candeias
, p. 4701 - 4709 (2007/10/02)
The reduction potentials in aqueous solution of the pyrimidine bases, nucleosides, and nucleotides of uracil (U) and thymine (T) were determined using the technique of pulse radiolysis with time-resolved spectrophotometric detection. The electron adducts of U and T were found to undergo reversible electron exchange with a series of ring-substituted N-methylpyridinium cations with known reduction potential. From the concentrations of the pyrimidine electron adducts and the reduced N-methylpyridinium compounds at electron-transfer equilibrium, the thermodynamical equilibrium constants were obtained and from these the reduction potentials. The results show U and T and their nucleosides and nucleotides to have very similar reduction potentials, ～ -1.1 V/NHE at pH 8, i.e., the effect of methylation at C5, C6, or of substitution at N1 is small, ≤0.1 V. In the case of cytosine (C) the electron adduct is protonated (probably at N3), even up to pH 13. The protonated adduct (C(H)?) undergoes a reversible electron transfer with the N-methylpyridinium cations. This is accompanied in one direction by transfer of a proton but by that of a water molecule in the other direction. As a result of the protonation of the electron adduct, the effective ease of reduction of C in aqueous solution is similar to that of U and T. It is suggested that in DNA the tendency for C?- to be protonated (by its complementary base G) is larger by ≥10 orders of magnitude than that for protonation of T?- by its complementary base A. This results in C and not T being the most easily reduced base in DNA. A further consequence is that lack of neutralization by intrapair proton transfer of T?- enables the irreversible extra-pair protonation on C6 of the radical anion to take place.
