Imino Hydrogen Research Articles

N,O versus O,O′ co-ordination in β-iminodiketonato complexes: a reinvestigation

The solid-state structures of the iminodiketonato complexes obtained in the reaction of cyanogen with [M(acac)2](M = Ni or Cu, acac = acetylacetonate) and [Cu(bzacen)](bzacen = Schiff base anion formed between ethane-1,2-diamine and benzoylacetone) have been reinvestigated. The X-ray data have been recollected, under improved conditions, for one form of [Ni(acac·C2N2)2](labelled β) and the structure determined according to an N,O co-ordination mode. This model gives a better crystallographic R factor compared with the previous one based on an O,O′ atom ligating set (0.029 vs. 0.047) and, in addition, clearly indicates the presence of the imino hydrogen. The structure of the analogous copper derivative and of [Cu(bzacen·2C2N2)] have been recalculated from the reported data and, also in these cases, the hypothesis of N,O co-ordination improves the refinement of the data (R= 0.055 vs. 0.062 and 0.060 vs. 0.081, respectively). An accurate Fourier-transform IR study, including 13C labelling, of the two forms (α and β) in which [Ni(acac·C2N2)2] can be isolated indicates that this co-ordination mode is also adopted by the α form, which is thus a ligand conformation isomer of the β form.

Palladium(II) Complexes of Tridentate Ligands. The Crystal Structure of Chloro[2,6-di(2-imidazolin-2-yl)pyridine]palladium(II) Chloride

Mono(ligand) palladium(II) complexes of 2,6-di-(thiazol-2-yl)pyridine (1a), 2,6-di(4-methylthia-zol-2-yl)pyridine (1b), 2,6-di(thiazol-4-yl)pyridine (2a), 2,6-di(imidazolin-2-yl]pyridine (3) and 2,6-di(benzimidazol-2-yl)pyridine (4a) of the general formula [ PdLCl ] Cl have been prepared. Stoichiometries have been confirmed by C, H, N and Pd analyses; the presence of solvate molecules has been confirmed by thermogravimetry . The crystal structure of [ PdLCl ]Cl.H2O, L = (3), has been determined by single-crystal X-ray diffractometry. The compound crystallizes in an orthorhombic space group, Pna21, a 7.427(2), b 21.932(3), c 8.935(1)Ǻ. The geometry of the complex cation is approximately square planar. The imidazolinyl rings closely approach planarity which is imposed by the delocalization of π-density in the NCN moiety. A hydrogen-bonding scheme involving the imino hydrogens of the ligand, chloride ions and the water molecule is present. The structure was refined by least-squares methods to a residual of 0.018 for 1273 reflections.

NMR studies of nucleic acids. Deuterium isotope effects on carbon-13 chemical shifts in hydrogen-bonded complexes of pyrimidines and purines

{sup 13}C NMR spectra were recorded for chloroform solutions of 2',3'-O-isopropylidene-5'-O-acetyladenosine (1), 2',3',5'-O-tribenzoyluridine (2), 2',3'-O-isopropylidene-5'-O-acetyluridine (2a), 2',3'-O-isopropylidene-5'-O-(tert-butyldimethylsilyl)guanosine (3), and 2',3'-O-isopropylidene-5'-O-(tert-butyldimethylsilyl)cytidine (4) in which the imino hydrogens were partially exchanged with deuterium. Upfield two-bond deuterium isotope effects (DIE) on {sup 13}C chemical shifts were detected under conditions of slow exchange as multiple peaks for the appropriate resonances and ranged in magnitude from 40 ppB for the amino interaction with C2 in guanosine to 217 ppB for the imino interaction with C4 in the uridine self-association dimer. {sup 13}C chemical shifts and DIEs for 2 were measured at 12 different concentrations from 219 to 231 K. The data were used in an iterative procedure to estimate chemical shifts at C2 and C4 for monomeric and dimeric forms of 2, equilibrium constants and enthalpies for self-association, and the distribution of isomeric self-association dimers. Enthalpies for formation of hydrogen bonds to C2 and C4 in 2 were similar, {Delta}H = {minus}1.8 kcal/mol. DIEs at C2 and C4 increased upon formation of a hydrogen bond to the carbonyl oxygens. The maximal increase for each center was estimated to be 90 ppB. Small increases were also observed in DIEs when nucleosides 1-4 were mixed with theirmore » complementary bases. 38 refs., 3 figs., 7 tabs.« less

Ultramicro analysis of bioactive substances: an approach based on the development of highly selective fluorogenic reagents

Highly sensitive methods established in our laboratories are outlined for the determination of bioactive substances including oligopeptides and related enzyme activities (i.e. aromatic aldehydes, their precursors and related amine-metabolizing enzymes, α-keto acids, sialic acids, catecholamines, their metabolites and biosynthetic enzymes, biogenic guanidines, arginine- and tyrosine-containing peptides, reducing sugars, fatty acids involving prostaglandines, nucleosides and nucleic acid bases with active imino hydrogen and biogenic alcoholic compounds) in biological materials, by means of conventional fluorometry and mostly pre- and postcolumn fluorescence derivatization high performance liquid chromatography. A series of mono- and bifunctional fluorogenic reagents has been developed for the selective derivatization of such bioactive substances and as enzyme substrates. Their use in the methods is briefly referred in the text.

The rotation-inversion spectrum of ketenimine, H2CCNH

Abstract High-resolution measurements of μc-type transitions of ketenimine in the 4- to 7-GHz region revealed a splitting of each line caused by the inversion motion of the imino hydrogen. The inversion splitting amounts to 66 kHz. Data from ab initio molecular orbital calculations for the changes of the geometrical parameters during the inversion motion have been used to carry out semirigid bender calculations. A barrier height of 4700 ± 200 cm−1 and an equilibrium HNC angle of 115.4 ± 0.6° have been derived. In addition, the microwave spectrum of the N-deuterated species has been assigned. The inversion splitting could not be resolved but the quadrupole coupling of the deuterium nucleus has been observed. Attempts to detect the inversion splitting in methanimine, H2CNH, have been unsuccessful, suggesting a higher barrier than in ketenimine.

Geometrical Isomerism of Phenylhydrazones of α-Keto Esters. II. p-Substituted Phenylhydrazones of Ethyl Pyruvate and 2,4-Dinitrophenylhydrazones of Some α-Keto Esters

Abstract Each geometrical isomer of various substituted phenylhydrazones of ethyl pyruvate and 2,4-dinitrophenylhydrazones of some α-keto esters was isolated in a pure state. Partial isomerizations of the E-isomers of the former hydrazones to the Z-isomers took place by keeping solutions of the hydrazones in organic solvents containing C, H, and Cl in the dark. An E- or Z-structure was assigned to each molecule on the basis of IR and 1H NMR spectra. In all cases, isomers with higher Rf-values on a silica gel TLC (using benzene as a developing solvent) involved an intramolecular hydrogen bonding between the imino hydrogen and the ester carbonyl oxygen. Thus, the Z-structure was assigned. An E-structure was assigned to other isomers with lower Rf-values. The present assignment is, thus, entirely the same as that proposed in a previous investigation.

Gas Chromatography–Mass Spectrometry of Trimethylsilylated Imino Derivatives of Alanine

Abstract Trimethylsilylation of seven imino derivatives of alanine with N,O-bis(trimethylsilyl)trifluoroacetamide in acetonitrile was studied. The imino derivatives include 2,2′-iminodipropionitrile (1), 2,2′-iminodipropionamide (2), 2,2′-iminodipropionic acid (3), 2-(1-cyanoethylamino)propionamide (4), 2-(1-cyanoethylamino)propionic acid (5), 2-(1-carbamoylethylamino)propionic acid (6), and 3,5-dimethyl-2,6-piperazinedione (7). The reaction products were identified by gas chromatography–mass spectrometry. Under the present reaction conditions (at 100 °C for 30 min), hydrogen atoms of carboxyl and carbamoyl groups and an imide hydrogen were readily replaced by the trimethylsilyl (TMS) group, but imino hydrogens were not replaced because of the steric hindrance of N-substituent group. For the carbamoyl group, only one hydrogen was replaced. Consequently, 1 was not trimethylsilylated. Furthermore, no definite trimethylsilylation products were obtained for 4. Upon electron impact at 70 eV, 2, 3, and 5–7 gave rather simple spectra with molecular (M+) and M −15 (loss of CH3) ions characteristic of TMS derivatives. A fragment, M −117 (loss of COOTMS) or M −116 (loss of CONHTMS), was very prominent for 2, 3, 5, and 6. Other important ions such as m/z 70 were noted. Preparations and properties of some of the imino derivatives are also described.

Isotope effects on radiationless transitions from the lowest excited singlet state of tetraphenylporphin

The deuterium isotope effect on the radiationless transition from the lowest excited singlet state of tetraphenylporphin has been investigated. Deuteration of the center imino hydrogen atoms of the porphin ring gives rise to large isotope effects, lengthening the flourescence lifetimes and increasing the flourescence and triplet quantum yields. These results indicate that NH vibrations of the center of the porphin ring play an important role in internal conversion.

The microwave spectrum of pyrrolidine

The rotational spectra of the normal and N-D isotopic species of pyrrolidine have been measured. The molecule exists in an envelope conformation, with the nitrogen atom out of the plane containing the carbon atoms and with the imino hydrogen in the axial position. The analysis of the rotational spectra of two and three vibrationally excited states for the normal and N-D isotopic species, respectively, indicates that both barriers to pseudorotation and to the imino hydrogen inversion are relatively high. Additionally, the N(14) quadrupole coupling constants have been determined.

Correlation of lac operator DNA imino proton exchange kinetics with its function.

The kinetics for imino hydrogen exchange, at individual base pairs in the DNA sequence corresponding to the lactose operon operator of Escherichia coli, has been examined by NMR saturation recovery measurements as a function of temperature. Three 17-base-pair subsections of the lac operator DNA were chemically synthesized for these studies. The results support our previous observations in the 36-base-pair complete lac operator DNA fragment that has been used in our previous NMR studies. The results indicate faster opening kinetics at a GTG/CAC that is also the site of operator mutations leading to the highest level of constitutive beta-galactosidase synthesis. The GTG/CAC sequence occurs frequently and often symmetrically in prokaryotic and eukaryotic DNA sites where one anticipates specific protein interaction for gene regulation or recombination.

Detection of the imino hydrogen bond in GC pairs by 1H and 15N nuclear magnetic resonance spectroscopy

“Limiting” 1H and 15N chemical shifts for the imino moiety of G in the G base pair were evaluated in model studies using chloroform soluble 2′,3′-O-iderivatives and were found to be significantly downfield from previously reported shifts measured in dimethylsulfoxide.

Proton NMR studies of 15N-labeled Escherichia coli tRNAfMet. An unambiguous assignment for the G-U pair and detection of a uridine resonance at 11.4 ppm

Results form /sup 1/H NMR studies of /sup 15/N-labeled Escherichia coli tRNA/sub f//sup Met/ indicated an unambiguous assignment for the G-U pair and detection of a uridine resonance at 11.4 ppm. Results indicated that signals for only 24-25 imino protons are clearly seen for E. coli tRNA/sub f//sup Met/ at 35/sup 0/C. Since 21 imino hydrogens participate in presumably more stable secondary interactions, only 3 or perhaps 4 peaks for tertiary hydrogen bonds are visible. Our results with /sup 15/N-labeled material indicate that uridine imino hydrogens in s/sup 4/U8-A14, rT54-A58, and G18-psi55-P58 (or U60) account for three of these tertiary signals.

ChemInform Abstract: THE MICROWAVE SPECTRUM OF PIPERIDINE: EQUATORIAL AND AXIAL GROUND STATES

Abstract The microwave spectra of piperidine and N-deuterated piperidine were investigated between 8 and 40 GHz. The ground states of both equatorial and axial conformers have been identified by both type-A and type-C transitions, and the substitution coordinates of the imino hydrogen have been determined for both conformers. Dipole-moment components for the equatorial conformer are μa = 0.178 D, μc = 0.80 D, μ = 0.82 D, and for the axial conformer are μa = 1.07 D, μc = 0.521 D, μ = 1.19 D. The quadrupole coupling constants for the axial conformer are: χaa = −3.80 MHz, χbb = 2.91 MHz, χcc = 0.83 MHz and for the equatorial conformer χcc = −4.83 MHz. The rotational constants indicate a significant flattening of the ring in axial piperidine compared with equatorial piperidine. The equatorial conformer is the more abundant; intensity measurements on several sets of lines indicate the excess energy of the axial conformer to be 3.1 ± 0.3 kJ mole−1. This represents a significant change from our earlier reported value and is now more in line with measurements obtained by other methods.

The microwave spectrum of piperidine: Equatorial and axial ground states

The microwave spectra of piperidine and N-deuterated piperidine were investigated between 8 and 40 GHz. The ground states of both equatorial and axial conformers have been identified by both type- A and type- C transitions, and the substitution coordinates of the imino hydrogen have been determined for both conformers. Dipole-moment components for the equatorial conformer are μ a = 0.178 D, μ c = 0.80 D, μ = 0.82 D, and for the axial conformer are μ a = 1.07 D, μ c = 0.521 D, μ = 1.19 D. The quadrupole coupling constants for the axial conformer are: χ aa = −3.80 MHz, χ bb = 2.91 MHz, χ cc = 0.83 MHz and for the equatorial conformer χ cc = −4.83 MHz. The rotational constants indicate a significant flattening of the ring in axial piperidine compared with equatorial piperidine. The equatorial conformer is the more abundant; intensity measurements on several sets of lines indicate the excess energy of the axial conformer to be 3.1 ± 0.3 kJ mole −1. This represents a significant change from our earlier reported value and is now more in line with measurements obtained by other methods.

The fragmentation behaviour of some spirobenzthiazoles under electron impact

AbstractThe electron impact induced fragmentations of ten spiro‐benzthiazoles have been studied. The principal decomposition reactions have been elucidated by metastable studies, exact mass measurements, and by deuterium exchange of the imino hydrogen. The primary fragmentation step is an α‐cleavage reaction, which leads to ring opening of the ring fused to the benzthiazole moiety of the molecule. The subsequent decompositions resemble those of cyclohexylamines. They follow a general pattern, the details of which are discussed with respect to the nature and position of the heteroatom in the saturated ring.

Synthesis, spectral and structural studies, and an evaluation of the hydrogen bonding of some phenylhydrazones

A series of 46 phenylhydrazones, some novel, containing a variety of structural types has been synthesised. These have been studied by 1H n.m.r. and i.r. spectroscopy with respect to potential inter- and intra-molecular hydrogen bonding. ortho-Nitro or -carbonyl groups form strong hydrogen bonds to the imino-group which are readily observed by 1H n.m.r. but not by i.r. spectroscopy. ‘Terminal’ carbonyl groups also form strong hydrogen bonds to the imino-group and these can be detected by both i.r. and 1H n.m.r. spectroscopy. When both ortho-nitro- or -carbonyl groups and ‘terminal’ carbonyl groups are present the imino hydrogen atom is doubly hydrogen bonded and this is apparent in the 1H n.m.r. spectrum. The formation of an intramolecular hydrogen bond in the phenylhydrazone prevents the formation of an intermolecular hydrogen bond between the phenylhydrazone and a polar solvent.

Geometrical Isomerism of 2,4-Dinitrophenylhydrazones of Some Pyruvic Esters

Abstract Visible, IR, and PMR spectra of 2,4-dinitrophenylhydrazones (DNPH) of some pyruvic esters were studied. It is suggested that each α-isomer with a higher Rf-value involves an intramolecular hydrogen bond between the imino hydrogen and the ester carbonyl group, to which the Z-structure is assigned. The E-structure is assigned to each β-isomer with a lower Rf-value.

Synthetic studies with carbonates. Part 6. Syntheses of 2-hydroxyethyl derivatives by reactions of ethylene carbonate with carboxylic acids or heterocycles in the presence of tetraethylammonium halides or under autocatalytic conditions

Reactions of ethylene carbonate (1a) with a variety of carboxylic acids catalysed by tetraethylammonium halides gave the corresponding 2-hydroxyethyl esters along with the diesters arising from disproportionation of the former products induced by the quaternary ammonium halides. Formation of the disproportionation products could be minimized by use of a short reaction time. The autocatalytic reactions of (1a) with strongly acidic carboxylic acids at elevated temperature gave ethylene glycol diesters selectively. Reaction mechanisms are discussed. Reactions of cyclic carbonates such as (1a) and propylene carbonate(1b) with acid anhydrides or active acyl compounds such as p-nitrophenyl acetate in the presence of tetraethylammonium iodide gave alkylene glycol diesters or 2-acyloxyalkyl aryl ethers in high yields. An attempt to extend this reaction to cyclohexane-1,2-diyl carbonate was unsuccessful, but a reaction with 1,2-epoxycyclohexane succeeded; this enabled us to examine the stereochemistry of the reaction. Finally, N-2-hydroxyethylation of a series of heterocyclic compounds having acidic imino hydrogen atoms was performed, both with tetraethylammonium iodide as catalyst and without a catalyst.

Simultaneous determination of N-unsubstituted and N-substituted nitroazoles and criteria for their identification—III : Chromatographic separation and polarographic determination of halo-nitroimidazoles

Methods for identifying and determining halo-nitroimidazoles appearing together during synthetic processes, regardless of the preparation methods, are proposed. Polarographic determination can be used in all synthetic processes when halo-nitroimidazoles have been obtained by nitration of the halo-imidazoles. When the halo-nitroimidazoles have been obtained from 5(4)-halo-4(5)-nitroimidazoles by substitution of the imino hydrogen atom, and when only one N-substituted derivative has been obtained in a reaction mixture, simultaneous polarographic determination of both compounds is possible, but only when an alkaline medium is used as supporting electrolyte. In some cases, simultaneous polarographic determination of all three compounds present in a reaction mixture during N-substitution processes [one 5(4)-halo-4(5)-nitroimidazole and two N-substituted isomers] is also possible with alkaline supporting electrolyte. Explanations are given of the phenomena on which the simultaneous polarographic determination is based. When simultaneous polarographic determination cannot be used to determine the amount of each polarographically-active compound present in a reaction mixture, the compounds can be separated chromatographically and then determined individually by polarography.

Photoxidation retardants—I. Spectra-structure correlation of some anilino substituted salicylanilides

The electronic absorption spectra of salicylanilide and eight of its derivatives (with substituents o-OCH 3, o-Cl (a), m-OH, m-OCH 3, p-Cl, p-OH, p-OCH 3 and p-CH 3) have been determined in various solvents and in buffers. It was found that the structure is dominated by the formation of intramolecular hydrogen bonding between the hydroxyl and the carbonyl groups rather than that between the hydroxyl and imino groups. For (a). an additional hydrogen bond occurs between the imino hydrogen and the chlorine in the 2′-position. Intramolecular charge transfer occurs through the non-bonding electrons on the imino group as donor, rather than through the aniline group, and the carbonyl group as acceptor. In strongly polar solvents, the enol structure occurs.