MASS SPECTRAL STUDIES ON SYNTHETIC ANALOGUES OF ORGANOPHOSPHORUS TOXIN ISOLATED FROM PTYCHODISCUS BREVIS

Abstract

A series of structurally related organophosphorus oximes analogous to O,O-dipropyl-(E)-2-(1-methyl-2-oxopropylidene)phosphorahydrazidothioate-(E)-oxime, isolated from Ptychodiscus brevis, have been synthesised and subjected to electron impact (EI) mass spectral studies. These studies, though aimed at total identification of these compounds, resulted in certain interesting observations and hence are being reported. In order to confirm the observations under electron impact and to support the mechanism of fragmentation we have also performed tandem mass spectrometry experiments in some cases.     

Chemical Ionization Mass Spectrometry of Steroids

Abstract

The chemical ionization mass spectra of a group of commonly occuring steroids are discussed. Intense signals (base peak) are observed in the molecular ion region for hydrocarbons and ketones. Functional group elimination is observed with sterols and especially their methyl and TMSi ethers, with the result that base peaks for these compounds are found at m/e values well below the expected molecular ion region. These observations are compared with those from the corresponding electron impact spectra.     

Synthesis and thermal characterization of copper and calcium mixed phosphates

A series of compounds with composition of Ca_1–xCu_xHPO₄, where x varied from 0.05 to 0.5 were synthesized by precipitation method. The compounds were characterized by elemental analysis, X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and thermogravimetry. The chemical stabilities of solids were investigated at several pH. Elemental analysis of copper, calcium and phosphorus are in agreement with the proposed composition. The formation of lamellar phosphates was evidenced. The stability of the set of compounds was better for samples with high copper content.     

Crystal structure and properties of the new vanadyl(IV)phosphates Na2MVO(PO4)2, M=Ca and Sr

Two new complex vanadyl(IV)phosphates Na₂MVO(PO₄)₂ (M=Ca, Sr) were synthesized in evacuated quartz ampoules and investigated by means of X-ray diffraction, electron microscopy, DTA, ESR and magnetic susceptibility measurements. The crystal structure of Na₂SrVO(PO₄)₂ was solved ab initio from X-ray powder diffraction data. Both compounds are isostructural: a=10.5233(3) Å, b=6.5578(2) Å, c=10.0536(3) Å and a=10.6476(3) Å, b=6.6224(2) Å, c=10.2537(3) Å for Ca and Sr, respectively; S.G. Pnma, Z=4. The compounds have a three-dimensional structure consisting of V⁴⁺O₆ octahedra connected by PO₄ tetrahedra via five of the six vertexes forming a framework with cross-like channels. The strontium and sodium atoms are located in the channels in an ordered manner. Electron diffraction as well as high-resolution electron microscopy confirmed the structure solution. The new vanadylphosphates are Curie-Weiss paramagnets in a wide temperature range down to 2 K with θ=12 and 5 K for Ca and Sr phases, respectively.     

THE MASS SPECTRA OF PHOSPHONYL COMPOUNDS PART 31. DIMETHYL AND DIETHYL ALKANE- AND SUBSTITUTED-METHANE PHOSPHONATES

Abstract

The electron impact mass spectra of 28 related phosphonates have been determined. Ethyl, iso-propyl and tert-butyl groups which are bound directly to phosphorus, fragment to the corresponding alkenes; similar iso-propyl and tert-butyl groups in the dimethyl esters also fragment to ethylene and propene respectively, i.e. the P-alkyl group rearranges with transfer of the elements of a methyl group to the phosphorus ion. The diethyl alkenephosphonates undergo double hydrogen rearrangements of an ethoxy group to give dihydroxyphosphonium ions. The di- and trihydroxyphosphonium ions have a characteristic fragmentation which involves loss of water. This characteristic has been used as evidence for the rearrangement of a phosphacylium ion to a dihydroxyphosphonium ion. Some other unusual rearrangements involving the combination of the groups bound to phosphorus and oxygen have been observed.     

Electron ionization mass spectra of organophosphorus compounds Part V: Mass fragmentation modes of some azolyl,azinyl, and azepinyl phosphonates as cyclic α-aminophosphonates

Mass fragmentation pathways of eight synthetic organophosphorus compounds, belonging to azolyl, azinyl, and azepinyl phosphonates as cyclic α-aminophosphonates 1a,b–4a,b were investigated by electron impact mass spectrometry with the aim of obtaining a better understanding of their fragmentation processes. The intensity of the recorded molecular ion peaks showed moderate values. Compounds 1a,b–3a,b have almost identical fragmentation routes via easy elimination of phosphonate groups which can be fragmented into the cation PO₂ as base peaks. On the contrary, compounds 4a,b started their fragmentation via removal of 4-chlorophenyl moieties.     

Multi‐Electron Reactions Enabled by Anion‐Based Redox Chemistry for High‐Energy Multivalent Rechargeable Batteries

The development of multivalent metal (such as Mg and Ca) based battery systems is hindered by lack of suitable cathode chemistry that shows reversible multi‐electron redox reactions. Cationic redox centres in the classical cathodes can only afford stepwise single‐electron transfer, which are not ideal for multivalent‐ion storage. The charge imbalance during multivalent ion insertion might lead to an additional kinetic barrier for ion mobility. Therefore, multivalent battery cathodes only exhibit slope‐like voltage profiles with insertion/extraction redox of less than one electron. Taking VS₄ as a model material, reversible two‐electron redox with cationic–anionic contributions is verified in both rechargeable Mg batteries (RMBs) and rechargeable Ca batteries (RCBs). The corresponding cells exhibit high capacities of >300 mAh g^?1 at a current density of 100 mA g^?1 in both RMBs and RCBs, resulting in a high energy density of >300 Wh kg^?1 for RMBs and >500 Wh kg^?1 for RCBs. Mechanistic studies reveal a unique redox activity mainly at anionic sulfides moieties and fast Mg²⁺ ion diffusion kinetics enabled by the soft structure and flexible electron configuration of VS₄.     

Electron Impact Mass Spectra of Some Substituted C-Phenyl N-tert-Butyl Nitrones (PBN's)

Abstract

The electron impact mass spectra of fifteen 4-substituted PBN's and PBN itself have been obtained using the probe method. Strong molecular ion peaks were observed in most cases. Fragmentation follows two major pathways depending on the polarity of the substitutent: the tert-butyl bond breaks to produce either the tert-butyl cation or isobutylene. The latter route is analogous to the well known McLafferty rearrangement. Fragmentation to produce the tert-butyl radical is a minor route. Electron-donating polar substituents appear to enhance fragmentation to isobutylene.     

Mass Spectrometric Distinction of Free Phenoxy Fatty Acids from Phenols Part I: Application of El-Mass Spectrometry

Abstract

By comparison of electron impact mass spectra of 16 phenoxy fatty acids with their corresponding phenols, it becomes obvious that the major parts of both spectra are identical.

The dominating signal is the phenol ion. It corresponds to the molecule ion for free phenols and to that fragment for the phenoxy fatty acids which is formed by the loss of the acid moiety under proton migration. As the signals of higher masses than the phenol ions are small in most cases, and as these substances have comparable chromatographic properties, correct identification in mixtures is difficult to achieve. The spectra of both classes of compounds are given to allow the selection of specific signals for the differentiation of fatty acids versus phenols, when this is possible.     

Electron impact fragmentation mechanisms of 2,4,6-trinitrotoluene derived from metastable transitions and isotopic labeling

Precursors of the major ions in the electron impact spectrum of 2,4,6-trinitrotoluene have been determined by observations of metastable peaks and isotope shifts. In 2,4,6-trinitrotoluene with adjacent CH₃ and NO₂ groups, the facile transfer of a methyl hydrogen to oxygen followed by loss of an OH group gives rise to the m/z 210 ion which plays a key role in the six important fragmentation sequences that have been identified. A similarity of the reactions in the mass spectrometer to the decomposition pathways induced by other stimuli has been observed.     

金属氧化物掺杂改善LiFePO4电化学性能

采用氧化物前驱体对磷酸铁锂(LiFePO₄)进行少量金属离子掺杂，并用XRD，SEM和恒电流充放电对掺杂的LiFePO₄进行了研究。结果表明，少量的掺杂离子在很大程度上提高了LiFePO₄的电化学性能，特别是大电流放电性能。1.0 mol%的Nb⁵⁺掺杂LiFePO₄的0.1 C放电容量约150 mAh·g^-1；即使在3 C倍率下放电，也有117 mAh·g^-1的容量。掺杂的效果与掺杂离子的半径、价态密切相关，半径小、价态高的离子对提高LiFePO₄的电化学性能有利。在掺杂量较小时(<2.0 mol%)，掺杂效果与掺杂离子的浓度关系不大。     

Biological applications of amide and amino acid containing synthetic macrocycles

ABSTRACT

Amino acid derived macrocycles with elaborate well-defined stereochemistry are a unique class of compounds that have been isolated from natural sources. Macrocycles like cyclosporine, octreotide, and valinomycin have been used in multiple applications, like drugs or ion sensors. Chemists have long been fascinated by the unique molecular recognition capabilities of these macrocycles and tried to design synthetic analogs with similar functions. This article is focused on reviewing current research on amide and amino acid containing macrocycles that have been developed in research laboratories for biological recognition, specifically for anion sensing, ion transport, carbohydrate sensing, and peptide sensing.     

Electron Impact and Chemical Ionization Mass Spectral Analysis of a Volatile Uranyl Derivative

Abstract

Quadrupole mass spectral analysis of the volatile uranium ligand complex bis (1,1,1,5,5,5-hexafluoro-2,4 pentanedionato) dioxouranium-di-n-butyl sulfoxide is described utilizing electron impact (EI) and methane chemical ionization (CI) ion sources. All major ions are tentatively identified and the potential usefulness of this complex for determining uranium isotope 235_U/238_U abundance is demonstrated.     

Comparative photophysical behaviour of naphthalene-linked crown ethers and aza crown ethers of varying cavity dimensions

A comparative time-resolved emission studies of several naphtho-crown ethers I–V, where metal ions can be complexed in a predetermined orientation with respect to the naphthalene (Naph) π-plane and naphthalene-linked aza crown ethers (L1 and L2) have been presented. In both the systems, crown ethers and aza crown ethers, naphthalene fluorescence gets quenched. In the systems I to V, the quenching is mainly due to efficient spin-orbit coupling (SOC) leading to greater population of the lowest triplet state of naphthalene. This SOC depends on the orientation of the crown ring with respect to the Naph-π-plane. However, in the systems L1 and L2, the quenching is due to photoinduced electron transfer (PET) from nitrogen lone pair of the aza crown ring to naphthalene moiety and consequent exciplex formation. The results have been interpreted using the time-resolved emission studies of all the compounds in various solvents, their alkali metal ion complexes, and protonated ligands.     

Separation Américium—Curium: Constantes de Dissociation des Complexes Avec L'Acide Hydroxéthylénediaminetriacétique

Abstract

The complex equilibria between hydroxyethyLenediamine-triacetic acid and americium and curium are investigated employing an ion exchange resin technique. The dissociation constants of the complexes of the two metals as their trivalent ions are reported to be 10^4.58 and 10^4.54, respectively [μ = 0.15 (HC1 + KC1)].     

Ion association in calcium phosphate solutions at 37°C

Ion association in the system Ca(OH)₂–H₃PO₄–KCl–H₂O at 37°C has been studied potentiometrically over a range of pH from 3 to 9. The experimental conditions were optimized for the accurate determination of the association constants for the formation of the ion pairs CaH₂PO ₄ ⁺ , CaHPO₄ and CaPO ₄ ^– which were found to be 27.9±0.1, 591±2, and (1.35±0.02)×10⁶ L-mol^–1, respectively.     

The elimination of carbon monoxide from molecular ions of phenol and other [C6H6O]+˙ isomers

Phenol and five acyclic isomeric compounds have been investigated using electron impact and field ionization techniques, mass analysed ion kinetic energy spectrometry and collision induced dissociation mass analysed ion kinetic energy spectrometry. The kinetic energy release data corresponding to the elimination of carbon monoxide from the molecular ions show that at least two structures of the reactant ion are involved. The electron impact and field ionization collision induced dissociation mass analysed ion kinetic energy spectra indicate that under electron impact conditions, the phenol ion partially isomerizes to another ion structure. An isomerization of about 40% to the structure of cis-2-hexen-4-yn-1-al is in good accordance with the spectral data.     

Loss of hydroxyl radical from cis- and trans-1-cyclohexyl 2-phenyl-3-benzoylaziridines: A unique eight-centered rearrangement elimination

Following electron impact ionization of the title compounds, a rapid electrocyclic ring opening of the [M]⁺˙ of both isomers occurs. A subsequent fragmentation of each is loss of hydroxyl which occurs by rearrangement to the carbonyl function. Properties of [M? OH]⁺ are in accord with a stable structure for this ion and therefore it is assigned as the 4-phenylisoquinium ion. The proposed mechanism and ion structures are supported by deuterium labeling and defocused metastable ion studies.     

The Analysis of Fluoride in the Acetic Acid Leach Solution of Fluorspar with an Ion-Selective Electrode

Abstract

An analytical procedure for the determination of fluoride ion left in the acetic acid leach solution of the U. S. Customs method for fluorspar is presented. The technique described employs an Orion fluoride ion-selective electrode. A semilogarithmic plot of fluoride ion concentration versus millivolt response yields a linear calibration curve. The new procedure s shown to compare favorably with the Customs method in economy analysis time, accuracy and precision.