Threshold-photoelectron spectroscopic study of methyl-substituted hydrazine compounds

The valence shell electronic structures of methylhydrazine (CH(3)NHNH(2)), 1,1-dimethylhydrazine ((CH(3))(2)NNH(2)) and tetramethylhydrazine ((CH(3))(4)N(2)) have been studied by recording threshold and conventional (kinetic energy resolved) photoelectron spectra. Ab initio calculations have been performed on ammonia and the three methyl substituted hydrazines, with the structures being optimized at the B3-LYP/6-31+G(d) level of theory. The ionization energies of the valence molecular orbitals were calculated using the Green's function method, allowing the photoelectron bands to be assigned to specific molecular orbitals. The ground-state adiabatic and vertical ionization energies, as determined from the threshold photoelectron spectra, were IE(a) = 8.02 +/- 0.16 eV and IE(v) = 9.36 +/- 0.02 eV for methylhydrazine, IE(a) = 7.78 +/- 0.16 eV and IE(v) = 8.86 +/- 0.01 eV for 1,1-dimethylhydrazine and IE(a) = 7.26 +/- 0.16 eV and IE(v) = 8.38 +/- 0.01 eV for tetramethylhydrazine. Due to the large geometry change that occurs upon ionization, these IE(a) values are all higher than the true thresholds. New features have been observed in the inner valence region and these have been compared with similar structure in the spectrum of hydrazine. The effect of resonant autoionization on the threshold photoelectron yield is discussed. New heats of formation (Delta(f)H) are proposed for the three hydrazines on the basis of G3 calculations: 107, 94, and 95 kJ/mol for methylhydrazine, 1,1-dimethyhydrazine and tetramethylhydrazine, respectively. The previously reported Delta(f)H for tetramethylhydrazine is shown to be erroneous.     

Mechanism-based cofactor derivatization of a copper amine oxidase by a branched primary amine recruits the oxidase activity of the enzyme to turn inactivator into substrate

The copper amine oxidases (CAOs) have evolved to catalyze oxidative deamination of unbranchedprimary amines to aldehydes. We report that a branched primary amine bearing an aromatization-prone moiety, ethyl 4-amino-4,5-dihydrothiophene-2-carboxylate (1), is recognized enantioselectively (S > R) by bovine plasma amine oxidase (BPAO) both as a temporary inactivator and as a substrate. Substrate activity results from an O(2)-dependent turnover of the covalently modified enzyme, with release of 4-aminothiophene-2-carboxylate (2) as ultimate product. Interaction of (S)-1 with BPAO occurs within the enzyme active site with a dissociation constant of 0.76 microM. Evidence from kinetic and spectroscopic studies, and HPLC analysis of stoichiometric reactions of BPAO with (S)-1, combined with a model study using a quinone cofactor mimic, establishes that the enzyme metabolizes 1 according to a transamination mechanism. Following the initial isomerization of substrate Schiff base to product Schiff base, a facile aromatization of the latter results in a metastable N-aryl derivative of the reduced cofactor aminoresorcinol, which is catalytically inactive. The latter derivative is then slowly oxidized by O(2), apparently facilitated partially by the active-site Cu(II), to form a quinonimine of the native cofactor that releases 2 upon hydrolysis or transimination with substrate amine. Preferential metabolism of (S)-1 is consistent with the preferential removal of the pro-Salpha-proton in metabolism of benzylamine by BPAO. This study represents the first report of product identification in metabolism of a branched primary amine by a copper amine oxidase and suggests a novel type of reversible mechanism-based (covalent) inhibition where inhibition lifetime can be fine-tuned independently of inhibition potency.     

Anodic oxidation of hydrazine and its methylderivatives on bare Pt and Pt electrode surfaces modified by underpotential metal adsorbates in acetonitrile

The electrooxidation of hydrazine and its methylderivatives (methylhydrazine and 1,1-dimethylhydrazine) on bare Pt and Pt electrode surfaces modified by underpotential metal adsorbates was studied in acetonitrile. On bare Pt, one-third of the molecules of the substances under examination undergo a two-electron oxidation to the corresponding diimides, while the remaining number of molecules act as the required proton acceptors in neutral acetonitrile. In alkaline solutions, hydrazine undergoes a quantitative four-electron oxidation process, while its methyl derivatives are oxidized quantitatively to the corresponding diimides in the same media. The pronounced inhibition effects on hydrazine oxidation caused by underpotential T1 and Pb adsorbates were interpreted in terms of a change in the chemical interaction of hydrazine molecules and the electrode surface modified by the underpotential metal adsorbates.     

Simultaneous Determination of Hydrazine,Methylhydrazine and 1,1-Dimethylhydrazine in Waters by HPLC with Spectrophotometric Detection Using Catalysis to Obtain Derivatives

Journal of Analytical Chemistry - A simple, rapid, and sensitive method is developed for the simultaneous determination of hydrazine, methylhydrazine, and 1,1-dimethylhydrazine in waters based on...     

Spectrophotometric determination of hydrazine,methylhydrazine, and 1,1-dimethylhydrazine with preliminary derivatization by 5-nitro-2-furaldehyde

5-Nitro-2-furaldehyde, a new derivatizing agent for the spectrophotometric determination of hydrazine, methylhydrazine, and 1,1-dimethylhydrazine is proposed. It is characterized by high solubility in water and by a substantial difference in the positions of absorption bands of the formed colored derivatives. The kinetics of the reaction of analyte derivatization is studied, and reaction conditions (pH 5, concentration of derivatizing agent 2 mM, 60° C, duration 40 min) are optimized. The limits of detection are 5, 3, and 1.5 μg/L for hydrazine, methylhydrazine, and 1,1-dimetlhydrazine, respectively. A possibility of the spectrophotometric determination of analytes in their simultaneous presence using the Firordt method is shown. The developed approach is successfully applied to the analysis of polluted peat bog soil selected at a place of impact of the first step of a carrier rocket.     

Catalytic turnover of benzylamine by a model for the lysine tyrosylquinone (LTQ) cofactor of lysyl oxidase

Lysyl oxidase differs from other copper amine oxidases in that its active quinone cofactor reflects cross-linking of a lysyl residue into the tyrosine-derived quinone nucleus found in the plasma and other copper amine oxidases. A model for the lysyl oxidase cofactor (LTQ), 3,3-dimethyl-2,3-dihydroindole-5,6-quinone (4), was synthesized and found to be stable to both hydrolysis and oxidation events that prevent simpler models from functioning as turnover catalysts. We show that 4 catalyzes the aerobic oxidative deamination of benzylamine, though turnover eventually ceases on account of oxidation of the dihydrobenzoxazole tautomer of the "product Schiff base" to form a benzoxazole, a reaction that may be physiologically relevant. The mechanism of the overall reaction profile was elucidated by a combination of optical and NMR spectroscopy and O(2) uptake studies.     

Electrochemical determination of hydrazine and methyl- and 1,1-dimethylhydrazine in air

An electrochemical cell capable of detecting levels of hydrazine, methylhydrazine (MMH) and 1,1-dimethylhydrazine (UDMH) in air is described. It is coupled with a dynamic air-sampling system and electronic control and amplification circuitry to provide a direct-reading portable analyser. The characteristics of this monitoring instrument are discussed. While most of the reported data are specifically for MMH vapour analysis, qualitatively similar results can be obtained when using this instrument for hydrazine or UDMH measurements.     

Simultaneous Determination of Hydrazine,Methylhydrazine, and 1,1-Dimethylhydrazine by High-Performance Liquid Chromatography with Pre- and Post-Column Derivatization by 5-Nitro-2-Furaldehyde

Approaches to the chromatographic determination of 1,1-dimethylhydrazine and two main products of its degradation (hydrazine and methylhydrazine) on their simultaneous presence are proposed using derivatization by 5-nitro-2-furaldehyde and multi-wavelength spectrophotometric detection of the formed derivatives in the visible spectral region. A combination of preliminary derivatization with separation in the reversed-phase HPLC mode and also ion-chromatographic separation with post-column derivatization allowed us to reach the limits of detection for analytes lower than 1 μg/L and to determine 1,1-dimethylhydrazine at the level of the maximum permissible concentration without preconcentration. The developed approaches were tested on an acid extract of a sample of peat bog soil collected at the place of impact of the first stage of a carrier rocket. The identity of the results obtained by different methods and the high level of soil pollution by hydrazines are shown.     

Nucleophilic Substitution of Chlorine with Hydrazine,Methylhydrazine, and 1,1-Dimethylhydrazine in 5-Aryl-2-chloromethyl-1,3,4-oxadiazoles

The reactions of 1,1-dimethylhydrazine, methylhydrazine, and hydrazine hydrate with 5-aryl-2-chloromethyl-1,3,4-oxadiazoles were studied. The structures and compositions of the final products were confirmed by ¹H NMR spectroscopy and elemental analysis.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 3, 2005, pp. 470–473.Original Russian Text Copyright © 2005 by Baranov, Tsypin, Malin, Laskin.     

Ruthenium complexes of substituted hydrazine: new solution- and solid-state binding modes

The methylhydrazine complex [Ru(NH(2)NHMe)(PyP)(2)]Cl(BPh(4)) (PyP=1-[2-(diphenylphosphino)ethyl]pyrazole) was synthesised by addition of methylhydrazine to the bimetallic complex [Ru(mu-Cl)(PyP)(2)](2)(BPh(4))(2). The methylhydrazine ligand of the ruthenium complex has two different binding modes: side-on (eta(2)-) when the complex is in the solid state and end-on (eta(1)-) when the complex is in solution. The solid-state structure of [Ru(PyP)(2)(NH(2)NHMe)]Cl(BPh(4)) was determined by X-ray crystallography. 2D NMR spectroscopic experiments with (15)N at natural abundance confirmed that in solution the methylhydrazine is bound to the metal centre by only the -NH(2) group and the ruthenium complex retains an octahedral conformation. Hydrazine complexes [RuCl(PyP)(2)(eta(1)-NH(2)NRR')]OSO(2)CF(3) (in which R=H, R'=Ph, R=R'=Me and NRR'=NC(5)H(10)) were formed in situ by the addition of phenylhydrazine, 1,1-dimethylhydrazine and N-aminopiperidine, respectively, to a solution of the bimetallic complex [Ru(mu-Cl)(PyP)(2)](2)(OSO(2)CF(3))(2) in dichloromethane. These substituted hydrazine complexes of ruthenium were shown to exist in an equilibrium mixture with the bimetallic starting material.     

Reactions of copper(II)-phenol systems with O2: models for TPQ biosynthesis in copper amine oxidases

Copper(II) complexes supported by a series of phenol-containing bis(pyridin-2-ylmethyl)amine N(3) ligands (denoted as L(o)H, L(m)H, and L(p)H) have been synthesized, and their O(2) reactivity has been examined in detail to gain mechanistic insights into the biosynthesis of the TPQ cofactor (2,4,5-trihydroxyphenylalaninequinone, TOPA quinone) in copper-containing amine oxidases. The copper(II) complex of L(o)H (ortho-phenol derivative) involves a direct phenolate to copper(II) coordination and exhibits almost no reactivity toward O(2) at 60 °C in CH(3)OH. On the other hand, the copper(II) complex of L(m)H (meta-phenol derivative), which does not involve direct coordinative interaction between the phenol moiety and the copper(II) ion, reacts with O(2) in the presence of triethylamine as a base to give a methoxy-substituted para-quinone derivative under the same conditions. The product structure has been established by detailed nuclear magnetic resonance (NMR), infrared (IR) spectroscopy, and electrospray ionization-mass spectroscopy (ESI-MS) (including (18)O-labeling experiment) analyses. Density functional theory predicts that the reaction involves (i) intramolecular electron transfer from the deprotonated phenol (phenolate) to copper(II) to generate a copper(I)-phenoxyl radical; (ii) the addition of O(2) to this intermediate, resulting in an end-on copper(II) superoxide; (iii) electrophilic substitution of the phenolic radical to give a copper(II)-alkylperoxo intermediate; (iv) O-O bond cleavage concomitant with a proton migration, giving a para-quinone derivative; and (v) Michael addition of methoxide from copper(II) to the para-quinone ring and subsequent O(2) oxidation. This reaction sequence is similar to that proposed for the biosynthetic pathway leading to the TPQ cofactor in the enzymatic system. The generated para-quinone derivative can act as a turnover catalyst for aerobic oxidation of benzylamine to N-benzylidene benzylamine. Another type of copper(II)-phenol complex with an L(p)H ligand (para-phenol derivative) also reacts with O(2) under the same experimental conditions. However, the product of this reaction is a keto-alcohol derivative, the structure of which is qualitatively different from that of the cofactor. These results unambiguously demonstrate that the steric relationship between the phenol moiety and the supported copper(II) ion is decisive in the conversion of active-site tyrosine residues to the TPQ cofactor.     

Rotational isomerism as studied by nuclear quadrupole coupling.: Theoretical and experimental 14NX tensors for hydrazine,methylhydrazine, and 1,2-dimethylhydrazine

The nuclear quadrupole coupling constants of the ¹⁴N nuclei for hydrazine, the inner and outer conformers of methylhydrazine, and the inner-outer and the outer-outer conformers of 1,2-dimethylhydrazine are calculated by an ab initio SCF method, and also by a CI calculation for hydrazine. The results are compared with available experimental values. Characteristic dependence of the X tensors on the conformational structure is demonstrated. An application of theoretical hyperfine structures to a spectral analysis is discussed.     

Spectrophotometric determination of hydrazine and 1,1-dimethylhydrazine,separately or in admixture

A rapid, sensitive spectrophotometric method for the determination of hydrazine and 1,1-dimethylhydrazine, separately or in mixtures of varying proportions, is described. The analysis is based on the well-known reaction of these compounds with salicylaldehyde to form, in the case of hydrazine, a symmetrical azine, or with 1,l-dimethylhydrazine, a hydrazone. Absorbance measurements were made in the ultraviolet at wavelengths characteristic of the derivatives and of salicylaldehyde; the results were calculated by means of simultaneous equations. The procedure is sensitive to concentrations of hydrazine as low as 0.3 μg/ml and of 1,1-dimethylhydrazine as low as 0.25 μg/ml. This corresponds to initial sample solutions having a concentration of 3.0 mg of hydrazine and 1.25 mg of 1,1-dimethyl hydrazine per ml.     

Enantiomer-specific binding of ruthenium(II) molecular wires by the amine oxidase of Arthrobacter globiformis

The copper amine oxidase from Arthrobacter globiformis (AGAO) is reversibly inhibited by molecular wires comprising a Ru(II) complex head group and an aromatic tail group joined by an alkane linker. The crystal structures of a series of Ru(II)-wire-AGAO complexes differing with respect to the length of the alkane linker have been determined. All wires lie in the AGAO active-site channel, with their aromatic tail group in contact with the trihydroxyphenylalanine quinone (TPQ) cofactor of the enzyme. The TPQ cofactor is consistently in its active ("off-Cu") conformation, and the side chain of the so-called "gate" residue Tyr296 is consistently in the "gate-open" conformation. Among the wires tested, the most stable complex is produced when the wire has a -(CH2)4- linker. In this complex, the Ru(II)(phen)(bpy)2 head group is level with the protein molecular surface. Crystal structures of AGAO in complex with optically pure forms of the C4 wire show that the linker and head group in the two enantiomers occupy slightly different positions in the active-site channel. Both the Lambda and Delta isomers are effective competitive inhibitors of amine oxidation. Remarkably, inhibition by the C4 wire shows a high degree of selectivity for AGAO in comparison with other copper-containing amine oxidases.     

Sorption-chromatographic determination of hydrazine and its substituted derivatives in air

Working conditions were found for the chemisorption preconcentration of hydrazine, phenylhydrazine, and 1,1-dimethylhydrazine from air with tubes containing silica gel with immobilized 4-chloro-5,7-dinitrobenzofurazan and the subsequent determination by high-performance liquid chromatography with diode array detection. A recovery of 98% (hydrazine), 90% (phenylhydrazine), and 97% (1,1-dimethylhydrazine) is attained at a thickness of the sorbent layer of 2 cm, an aspiration rate of 0.2–0.8 L/min, and a volume of aspirated air of 10 L. Silica gel with a particle size of 0.1–0.3 mm impregnated with 4-chloro-5,7-dinitrobenzofurazan (2 wt %) was used as the sorbent. The detection limits of compounds without regard for preconcentration after their desorption are 0.01 (hydrazine), 0.017 (1,1-dimethylhydrazine), and 0.015 mg/m³ (phenylhydrazine).     

Determination of hydrazine and 1,1-dimethylhydrazine as salicyldehyde derivates by liquid chromatography with electrochemical detection

Summary Determination of hydrazine and 1,1-dimethylhydrazine after derivatization with salicylaldehyde was done using high-performance liquid chromatography with electrochemical detection. The oxidation of the phenolic group of salicylaldazine (S-HY) and salicylaldehyde-1,1-dimethylhydrazone (S-UDMH) was optimized with respect to ionic strength, pH, and applied potential. Less than 5 ng of S-HY and S-UDMH could be detected. The detection limits for hydrazine and 1,1-dimethylhydrazine solutions were estimated to be 0.025 and 0.20 ppm, respectively.     

The determination of hydrazine and 1,1-dimethylhydrazine,separately or in mixtures,by high-pressure liquid chromatography

A rapid, sensitive liquid chromatographic method for the determination of hydrazine and 1,1-dimethylhydrazine, separately or in mixtures of varying proportions, is described. The procedure involves salicylaldehyde derivative formation followed by chromatography on a reversed phase (octadecylsilane) column with acetonitrile (52%)—0.14 M potassium dihydrogenphosphate (48%) as a mobile phase and u.v. (254 nm) detection. This system is sensitive to 2 μg ml^-1 of hydrazine and 5 μg ml^-1 of 1,1-dimethylhydrazine and has a relative standard deviation of less than 1%. Monomethylhydrazine forms an unstable salicylaldehyde hydrazone; although it cannot be determined, it can be detected (sensitivity 5 μg ml^-1 ) and does not interfere with quantitative measurement of either hydrazine or 1,1-dimethylhydrazine.     

Trapping of a dopaquinone intermediate in the TPQ cofactor biogenesis in a copper-containing amine oxidase from Arthrobacter globiformis

The biogenesis of the topaquinone (TPQ) cofactor of copper amine oxidase (CAO) is self-catalyzed and requires copper and molecular oxygen. A dopaquinone intermediate has been proposed to undergo 1,4-addition of a copper-associated water molecule to form the reduced form of TPQ (TPQ(red)), followed by facile oxidation by O(2) to yield the mature TPQ (TPQ(ox)). In this study, we have incorporated a lysine residue in the active site of Arthrobacter globiformis CAO (AGAO) by site-directed mutagenesis to produce D298K-AGAO. The X-ray crystal structure of D298K-AGAO at 1.7-A resolution revealed that a covalent linkage formed between the epsilon-amino side chain of Lys298 and the C2 position of a dopaquinone derived from Tyr382, a precursor to TPQ(ox). We assigned the species as an iminoquinone tautomer (LTI) of lysine tyrosylquinone (LTQ), the organic cofactor of lysyl oxidase (LOX). The time course of the formation of LTI at pH 6.8 was followed by UV/vis and resonance Raman spectroscopies. In the early phase of the reaction, an LTQ-like intermediate was observed. This intermediate then slowly converted to LTI in an isosbestic manner. Not only is the presence of a dopaquinone intermediate in the TPQ biogenesis confirmed, but it also provides strong support for the proposed intermediacy of a dopaquinone in the biogenesis of LTQ in LOX. Further, this study indicates that the dopaquinone intermediate in AGAO is mobile and can swing from the copper site into the active-site wedge to react with Lys298.     

Co—MgO催化剂上NO—程序升温表面反应和NO—CH4反应

ＮＯ，程序升温表面反应（ＴＰＳＲ），ＮＯ－ＣＨ４反应，Ｃｏ－ＭｇＯ     

A dopaquinone model that mimics the water addition step of cofactor biogenesis in copper amine oxidases

The consensus mechanism for biogenesis of the 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor in copper amine oxidases involves a key water addition to the dopaquinone intermediate. Although hydration of o-quinones seems straightforward and was implicated previously in aqueous autoxidation of catechols to give ultimately hydroxyquinones, a recent study (Mandal, S.; Lee, Y.; Purdy, M. M.; Sayre, L. M. J. Am. Chem. Soc. 2000, 122, 3574-3584) showed that the observed hydroxyquinones arise not from hydration, but from addition to the o-quinones of H(2)O(2) generated during autoxidation of the catechols. In the enzyme case, hydration of dopaquinone is proposed to be mediated by the active site Cu(II). To establish precedent for this mechanism, we engineered a catechol tethered to a Cu(II)-coordinating unit, such that the corresponding o-quinone could be generated in situ by oxidation with periodate (to avoid generation of H(2)O(2)). Thus, coordination of 4-((2-(bis(2-pyridylmethyl)amino)ethylamino)methyl)-1,2-benzenediol (1) to Cu(II) and subsequent addition of periodate resulted in rapid formation of the TPQ-like corresponding hydroxyquinone. Hydroxyquinone formation was seen also using Zn(II) and Ni(II), but not in the absence of M(II). Under the same conditions, periodate oxidation of the simple catechol 4-tert-butylcatechol does not give hydroxyquinone in the presence or absence of Cu(II). M(II)OH(2) pK(a) data for the Cu(II), Zn(II), and Ni(II) complexes with the pendant tetradentate ligand in the masked (dimethyl ether) catechol form, and kinetic pH-rate profiles of the metal-dependent hydroxyquinone formation from periodate oxidation of catechol 1, suggested a rate-limiting addition step of the ligand-coordinated M(II)OH to the o-quinone intermediate. This study represents the first chemical demonstration of a true o-quinone hydration, which occurs in cofactor biogenesis in copper amine oxidases.