Vibrational Properties and DFT Calculations of Perovskite-Type Methylhydrazinium Manganese Hypophosphite.

Recently discovered hybrid perovskites based on hypophosphite ligands are a promising class of compounds exhibiting unusual structural properties and providing opportunities for construction of novel functional materials. Here, we report for the first time the detailed studies of phonon properties of manganese hypophosphite templated with methylhydrazinium cations ([CH3NH2NH2][Mn(H2PO2)3]). Its room temperature vibrational spectra were recorded for both polycrystalline sample and a single crystal. The proposed assignment based on Density Functional Theory (DFT) calculations of the observed vibrational modes is also presented. It is worth noting this is first report on polarized Raman measurements in this class of hybrid perovskites.

Mechanistic insights into the ANRORC-like rearrangement between methylhydrazine and 1,2,4-oxadiazole derivatives.

We herein present the first in-depth theoretical study devoted to elucidate the mechanism of the reaction between 1,2,4-oxadiazole derivatives and methylhydrazine. For this purpose, the reaction between methylhydrazine and some polyfluoroaryl-1,2,4-oxadiazoles has been employed as a model reaction. The analysis of the potential energy surface (PES) indicates that the most favorable path involves an initial amine attack at the C(2') site of the aryl moiety to yield an aryl-hydrazine intermediate whose thermodynamic stability appears as the main determinant of the favored reaction path. Next, the cyclization step leading to a spiro intermediate through a favored 5-exo-trig process appears as the rate determining step. Additionally, this study highlights the relevance of the torsional strain effects on the favored ANRORC pathway. Finally, both the origins of the substituent effects on the regioselectivity patterns as well as the need of using a large excess of nucleophile to afford the favored ANRORC pathway are discussed.

Pervaporation performance of PPO membranes in dehydration of highly hazardous mmh and udmh liquid propellants.

Polyphenylene oxide (PPO) membranes synthesized from 2,6-dimethyl phenol monomer were subjected to pervaporation-based dehydration of the highly hazardous and hypergolic monomethyl hydrazine (MMH) and unsymmetrical dimethyl hydrazine (UDMH) liquid propellants. Membranes were characterized by TGA, DSC and SEM to study the effect of temperature besides morphologies of surface and cross-section of the films, respectively. Molecular dynamics (MD) simulation was used to study the diffusion behavior of solutions within the membrane. CFD method was employed to solve the governing mass transfer equations by considering the flux coupling. The modeling results were highlighted by the experimental data and were in good agreement. High separation factors (35-70) and reasonable water fluxes (0.1-0.2 kg/m(2)h) were observed for separation of the aqueous azeotropes of MMH (35 wt%) and UDMH (20 wt%) and their further enrichment to >90% purity. Effect of feed composition, membrane thickness and permeate pressure on separation performance of PPO membranes were investigated to determine optimum operating conditions.

Discovery of S-adenosyl-L-homocysteine hydrolase inhibitors based on non-adenosine analogs.

High throughput screening using Automated Ligand Identification System (ALIS) resulted in the discovery of a new series of S-adenosyl-L-homocysteine hydrolase inhibitors based on non-adenosine analogs. The optimization campaign led to very potent and competitive compound 39 with a Ki value of 1.5 nM. Compound 39 could be a promising lead compound for research to reduce elevated homocysteine levels.

Developing a trace level GC-MS method for detecting methylhydrazine in an experimental drug substance.

Methylhydrazine (NH(2)NHCH(3), CAS 60-34-4) is a highly reactive reducing agent used as an intermediate for synthesizing an experimental drug substance. Methylhydrazine is a known mutagen, an animal carcinogen, and a suspected human carcinogen. A gas chromatography-mass spectrometry method was developed as a limit test method for analyzing trace levels of methylhydrazine in the experimental drug substance. The method utilizes acetone as a dissolving solvent for the drug substance and a derivatizing agent for methylhydrazine in the meantime, thus eliminating the need for post-derivatization sample clean-up prior to analysis. The gas chromatographic (direct injection) conditions provide good separation for the acetone-methylhydrazine derivative (acetone methylhydrazone) from matrix interference, and mass spectrometric detection (selected ion monitoring mode, m/z 86) allows sufficient sensitivity for detecting 1 part per million methylhydrazine relative to the drug substance.

CH3NHNH2 + OH reaction: mechanism and dynamics studies.

A direct dynamics study was carried out for the multichannel reaction of CH(3)NHNH(2) with OH radical. Two stable Conformers (I, II) of CH(3)NHNH(2) are identified by the rotation of the -CH(3) group. For each conformer, five hydrogen-abstraction channels are found. The reaction mechanisms of product radicals (CH(3)NNH(2) and CH(3)NHNH) with OH radical are also investigated theoretically. The electronic structure information on the potential energy surface is obtained at the B3LYP/6-311G(d,p) level and the energetics along the reaction path is refined by the BMC-CCSD method. Hydrogen-bonded complexes are presented at both the reactant and product sides of the five channels, indicating that the reaction may proceed via an indirect mechanism. The influence of the basis set superposition error (BSSE) on the energies of all the complexes is discussed by means of the CBS-QB3 method. The rate constants of CH(3)NHNH(2) + OH are calculated using canonical variational transition-state theory with the small-curvature tunneling correction (CVT/SCT) in the temperature range of 200-1000 K. Slightly negative temperature dependence of rate constant is found in the temperature range from 200 to 345 K. The agreement between the theoretical and experimental results is good. It is shown that for Conformer I, hydrogen-abstraction from -NH- position is the primary pathway at low temperature; the hydrogen-abstraction from -NH(2) is a competitive pathway as the temperature increases. A similar case can be concluded for Conformer II. The overall rate constant is evaluated by considering the weight factors of each conformer from the Boltzmann distribution function, and the three-term Arrhenius expressions are fitted to be k(T) = 1.6 x 10(-24)T(4.03)exp (1411.5/T) cm(3) molecule(-1) s(-1) between 200-1000 K.

Formation and decay of tetrazane derivatives--a Car-Parrinello molecular dynamics study.

The complications during flight 510 of the Ariane Project were ascribed to problems in the upper stage engine that employs the bipropellant monomethylhydrazine (MMH) and nitrogen tetroxide (NTO). This has led to the question what conditions or reactions possibly cause an uncontrolled behaviour in the combustion process of MMH/NTO. We use first-principles molecular dynamics to investigate the reactions of the hypergolic mixture in different chemical situations. It was possible to observe the ultrafast redox reaction between the reactants on the timescale of an unconstrained simulation. We show that electrostatic attraction is crucial for the understanding of this reaction. Besides a cold reaction preceding the ignition, a reaction path leading to the highly reactive compound dimethyltetrazane could be identified.

Gas chromatography-mass spectrometry determination of the pentafluorobenzoyl derivative of methylhydrazine in false morel (Gyromitra esculenta) as a monitor for the content of the toxin gyromitrin.

The main toxic compound found in false morel (Gyromitra esculenta) is acetaldehyde-N-methyl-N-formylhydrazone (gyromitrin). This paper describes a method of determining the total hydrazones content based on acid hydrolysis of gyromitrin and other related hydrazones in air-dried false morel followed by derivatisation of methylhydrazine with pentafluorobenzoyl chloride. The derivative, tris-pentafluorobenzoyl methylhydrazine (tris-PFB-MH) is analyzed by gas chromatography-mass spectrometry. The overall precision of the method is better than 10% (relative standard deviation) for 0.5 ng/microl methylhydrazine in solution. The minimum detectable concentration of methylhydrazine (tris-PFB-MH) by this method is estimated to be approximately 12 pg/microl, which is equal to 0.3 microg/g dry matter (DM) of false morel.

Active-site structure of the soluble quinoprotein glucose dehydrogenase complexed with methylhydrazine: a covalent cofactor-inhibitor complex.

Soluble glucose dehydrogenase (s-GDH) from the bacterium Acinetobacter calcoaceticus is a classical quinoprotein. It requires the cofactor pyrroloquinoline quinone (PQQ) to catalyze the oxidation of glucose to gluconolactone. The precise catalytic role of PQQ in s-GDH and several other PQQ-dependent enzymes has remained controversial because of the absence of comprehensive structural data. We have determined the crystal structure of a ternary complex of s-GDH with PQQ and methylhydrazine, a competitive inhibitor of the enzyme. This complex, refined at 1.5-A resolution to an R factor of 16.7%, affords a detailed view of a cofactor-binding site of s-GDH. Moreover, it presents the first direct observation of covalent PQQ adduct in the active-site of a PQQ-dependent enzyme, thereby confirming previous evidence that the C5 carbonyl group of the cofactor is the most reactive moiety of PQQ.

Ion mobility spectrometry of hydrazine, monomethylhydrazine, and ammonia in air with 5-nonanone reagent gas.

Hydrazine (HZ) and monomethylhydrazine (MMH) in air were monitored continuously using a hand-held ion mobility spectrometer equipped with membrane inlet, 63Ni ion source, acetone reagent gas, and ambient temperature drift tube. Response characteristics included detection limit, 6 ppb; linear range, 10-600 ppb; saturated response, >2 ppm; and stable response after 15-30 min. Ammonia interfered in hydrazines detection through a product ion with the same drift time as that for MMH and HZ. Acetone reagent gas was replaced with 5-nonanone to alter drift times of product ions and separate ammonia from MMH and HZ. Patterns in mobility spectra, ion identifications from mass spectra, and fragmentation cross-sections from collisional-induced dissociations suggest that drift times are governed by ion-cluster equilibria in the drift region of the mobility spectrometer. Practical aspects including calibration, stability, and reproducibility are reported from the use of a hand-held mobility spectrometer on the space shuttle Atlantis during mission STS-37.