Favorable pendant-amino metal chelation in VX nerve agent model systems

We have performed DFT computational studies [B3LYP, 6-31+G] to obtain metal ion coordination isomers of VX-Me [MeP(O)(OMe)(SCH2CH2NMe2)], a model of two of the most lethal nerve agents: VX [MeP(O)(OEt)(SCH2CH2N(iPr)2)] and Russian-VX [MeP(O)(OCH2CHMe2)(SCH2CH2N(Et)2)]. Our calculations involved geometry optimizations of the neutral VX-Me model as well as complexes with H+, Li+, Na+, K+, Be2+, Mg2+, and Ca2+ that yielded 2-8 different stable chelation modes for each ion that involved mainly mono- and bidentate binding. Importantly, our studies revealed that the [O(P),N] bidentate binding mode, long thought to be the active mode in differentiating the hydrolytic path of VX from other nerve agents, was the most stable for all ions studied here. Binding energy depended mainly on ionic size as well as charge, with binding energies ranging from 364 kcal mol(-1) for Be2+ to 33 kcal mol(-1) for K+. Furthermore, calculated NMR shifts for VX-Me correlate to experimental values of VX.     

Catalytic degradation of the nerve agent VX by water-swelled polystyrene-supported ammonium fluorides

The catalytic degradation of the nerve agent VX (O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate) by water-swelled polymer-supported ammonium fluorides is described. VX (0.06-0.53 mol/mol F(-)) is rapidly degraded (t(1/2) ～ 10-30 min) to form the "G-analogue" (O-ethyl methylphosphonofluoridate), which hydrolyzes (t(1/2) ～ 1-1.5 h) to the nontoxic EMPA (ethyl methylphosphonic acid). The toxic desethyl-VX is not formed. The catalytic effect of fluoride is maintained even when 6 equiv of VX are loaded. GB (O-isopropyl methylphosphonofluoridate) and desethyl-VX agents are also degraded under these conditions.     

Analysis of VX nerve agent hydrolysis products in wastewater effluents by ion chromatography with amperometric and conductivity detection

An analytical method, based on the use of ion chromatography, was developed to monitor the levels of three regulated VX hydrolysis products in the effluent from a biological wastewater treatment process--ethylmethylphosphonic acid, methylphosphonic acid and 2-(diisopropyl)aminoethanethiol. Previous methods have not been applied to wastewater matrices or 2-(diisopropyl)aminoethanethiol. Despite the specificity and sensitivity constraints of this method, it was possible to measure the compounds in bioreactor effluents down to a level substantially below the US Army discharge limit of 0.1% (w/v). Analytical data was confirmed by liquid chromatography-mass spectrometry (LC-MS) at an independent laboratory.     

Absolute proton affinity for acetaldehyde

Dissociative photoionization mass spectrometry has been used to measure appearance energies for the 1-hydroxyethyl cation (CH(3)CH=OH(+)) formed from ethanol and 2-propanol. Molecular orbital calculations for these two unimolecular fragmentation reactions suggest that only methyl loss from ionized 2-propanol does not involve excess energy at the threshold. The experimental appearance energy of 10.31 +/- 0.01 eV for this latter process results in a 298 K heat of formation of 593.1 +/- 1.2 kJ mol(-1) for CH(3)CH=OH(+) and a corresponding absolute proton affinity for acetaldehyde of 770.9 +/- 1.3 kJ mol(-1). This value is supported by both high-level ab initio calculations and a proposed upward revision of the absolute isobutene proton affinity to 803.3 +/- 0.9 kJ mol(-1). A 298 K heat of formation of 52.2 +/- 1.9 kJ mol(-1) is derived for the tert-butyl radical.     

On the proton affinity of pteridine

All-valence-electron and perturbation calculations suggest that pteridine may preferably be protonated at the pyrazine moiety. Correlation between these results and some experimental data is presented.     

Absolute proton affinity of some polyguanides

The problem of the absolute proton affinity (APA) of some polyguanides is addressed by the MP2(fc)/6-311+G//HF/6-31G theoretical model. It is shown that the linear chain polyguanides exhibit increased basicity as a function of the number of guanide subunits. However, the saturation effect yields an asymptotic APA value of 254 kcal/mol. Branched polyguanides on the other hand have higher APAs than their linear counterparts. The largest proton affinity is found in a doubly bifurcated heptaguanide, being as high as 285 kcal/mol, thus potentially representing one of the strongest organic bases. Finally, it is found that all polyguanides protonate at imino nitrogen atoms, since they are apparently susceptible the most to the proton attack. The origin of their very high intrinsic basicity is traced down to a dramatic increase in the resonance interaction of the corresponding conjugate bases. For instance, the increase in the resonance energy in the protonated guanidine is estimated to be in a range of 24-27 kcal/mol, which is higher than the aromatic stabilization in benzene. The proton affinity of some polycyclic guanides including Schwesinger proton sponge and porphine is briefly discussed.     

Determination of trace amounts of Russian toxic agent VX

Method was developed for detection of residual amounts of Russian toxic agent RVX on metallic surface. The method is based on RVX conversion into O-isobutyl ester of methylphosphonic acid fluoride on a filter impregnated with silver fluoride, followed by detection of the formed derivative using a flame photometer. The method sensitivity has been enhanced by application of a large volume injection (0.20 mL). The method allows determination of RVX levels corresponding to the sanitary regulations and is intended for control measures at the toxic agents elimination establishments and for determination of the Danger grade of metallic waste.     

Enamines I. Vinyl Amine,a Theoretical Study of its Structure,electrostatic potential,and proton affinity

The structure of vinyl amine and its reactivity towards a proton is studied by the PRDDO SCF MO method. The equilibrium structure is found to be non-planar and barriers to inversion- and rotation-dominated processes are calculated. Proton addition to vinyl amine, as a model of enamine protonation, is examined by means of electrostatic molecular potentials and C- versus N-proton affinities.     

Dissociation of proton-bound complexes and proton affinity of benzamides

Proton-bound heterodimers of substituted benzamides 1–15 and N,N-dimethyl benzamides 16–30, respectively, with a series of reference bases were generated under chemical ionization conditions. Their dissociation into the protonated amide AH⁺ and protonated reference base BH⁺ was studied by metastable ion techniques and by collision-induced dissociation (CID) to examine substituent effects on the proton affinity (PA) of the benzarnides and to elucidate some aspects of the dissociation dynamics of proton-bound clusters. The PAs of the substituted benzarnides were determined by bracketing the amide by a pair of reference bases to give rise to more and less abundant signals of the protonated base in the mass-analyzed ion kinetic energy (MIKE) spectra of the proton-bound heterodimers. The substituent effects observed agree with O-protonation in both the primary and the tertiary benzamides. However, the susceptibility of the benzamide to polar substituent effects is remarkably small, which indicates a “resonance saturation”), of the amide group. The relative abundances of AH⁺ and BH⁺ in the MIKE and collisional activation (CA) mass spectra depend strongly on the pressure of the collision gas during CID, and in certain cases a reversal of the relative abundances with increasing pressure that favors the formation of BH+ from a less basic reference base is observed. Although this effect underlines the limited possibilities of the “kinetic method” for PA determination by CID of proton-bound heterodimers, it uncovers important kinetic effects during the dissociation of proton-bound heterodimers and of proton transfer reactions in the gas phase.. In the case of the protonated amide clusters, the observed intensity effects in the CA mass spectra are explained by a double-well potential energy surface caused by solvation of the protonated base by the polar amide in the protonated heterodimer.     

SiH+5 and the proton affinity of monosilane

Tandem mass spectrometric studies show that SiH⁺₅ is formed in bimolecular reactions of SiH₄ and NH⁺₂, C₂H⁺₃, C₂H⁺₆ and C₃H⁺₈ ions. The dependence of the reaction cross sections on ion energy indicates the formation of SiH⁺₅ from NH⁺₂, C₂H⁺₃, and C₂H⁺₆ to be exothermic reactions, while formation from C₃H⁺₈ is endothermic. Using known thermochemical data, these facts permit the assignment of 150 and 156 kcal/mole to the lower and upper limits of the proton affinity of monosilane.     

The fluoride ion affinity of tungsten pentafluoride and the electron affinity of tungsten hexafluoride.

Enthalpies of oxidative alkaline hydrolysis of the salts LiWF₆ and NaWF₆ are −549 and −519 kj mol^-1 respectively. From these results and earlier thermochemical results for KWF₆, RbWF₆, and from crystal structure data for these salts, it has proved possible to assess the charge distribution within the WF₆^- anion in these salts, and to estimate the fluoride ion affinity of WF₅ and the electron affinity of WF₆.     

Estimation of proton donor ability of surface hydroxy groups in terms of proton affinity

A method to estimate the proton donor ability of hydroxy groups in terms of proton affinity (PA) is suggested. The PA of hydroxy groups of aerosil and of decationated zeolite type Y have been determined.

---

(PA). PA .

     

Work function and negative electron affinity of ultrathin barium fluoride films

Thin films of barium fluorides with different thicknesses were deposited on GaAs substrate by electron beam evaporation. The aim of the work was to identify the best growth conditions for the production of coatings with a low work function suitable for the anode of hybrid thermionic-photovoltaic (TIPV) devices. The chemical composition and work function φ of the films with different thicknesses were investigated by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The lowest value of φ = 2.1 eV was obtained for the film with a thickness of ~2 nm. In the valence band spectra of the films at low kinetic energy, near the cutoff, a characteristic peak of negative electron affinity was present. This effect contributed to a further reduction of the film's work function.     

The proton affinity and the structure of protonated species of methylsilane

An ab initio LCAO-MO-SCF calculation was made on the proton affinity (PA ) of methylsilane (CH₃SiH₃) by using STO -3G, MIDI -1, and MIDI -1* basis sets. Three types of protonated methylsilane are taken into account, and their geometrical parameters are optimized. The calculated PA of CH₃SiH₃ is 160.5 kcal/mol, which exceeds that of SiH₄ by 11.5 kcal/mol. The protonated species (I) which refers to Si—C bond protonation is shown to be most favorable, and to be a weak σ-complex between CH₄ and SiH. Other two species are also σ-complexes between H₂ molecule and SiH₃CH or CH₃SiH, and similar to CH, SiH, GeH, and C₂H.     

MNDO study of the proton affinity of fluorinated formaldehydes and acetones

The MNDO molecular orbital method is employed to calculate the proton affinities of fluorinated formaldehydes and acetones. Agreement with experimentally reported proton affinities is good. In the acetone series a decrease in proton affinity is calculated for each successive fluorine substituent. The calculated strength of the intramolecular hydrogen bond in the protonated fluoro-formaldehydes and acetones is 0.6—2.7 kcal mol⁻¹, in good agreement with the experimental value of 2—3 kcal mol⁻¹ in the protonated fluoroacetones. Examination of the calculated charge distribution shows that the trends in proton affinity can be understood qualitatively both in terms of initial-state and final-state effects caused by the fluorine substituents. Protonation at the fluorine atom is less stable by about 25 kcal mol⁻¹ than protonation at the oxygen atom for monofluoroacetone.     

Density functional computations of proton affinity and gas-phase basicity of proline

The proton affinity and gas-phase basicity of proline were evaluated by using density functional theory coupling the B3-LYP hybrid functional with the extended 6--311++G** basis set. Cis and trans conformations of the carboxyl moiety for both exo and endo ring structures were considered for the neutral proline. The results show that the most stable structure of proline has the endo ring conformation with the carboxyl group in the cis position. The structure at the global minimum is stabilized by an intramolecular hydrogen bond. The nitrogen of the ring in the exo form is the preferred protonation site. The calculated proton affinity (924.3 kJ mol(-1)) and gas-phase basicity (894.4 kJ mol(-1)) are in very good agreement with the experimental counterparts.