Na-montmorillonite hydrates under ethane rich reservoirs: NPzzT and muPzzT simulations

Na-montmorillonite hydrates in presence of ethane molecules are studied by means of hybrid Monte Carlo simulations in the NP(zz)T and muP(zz)T ensembles. The NP(zz)T ensemble allows us to study the interlaminar distance as a function of water and ethane content. These data show clear plateaus for lower ethane contents and mainly for water contents consistent with the formation of a single water layer. In addition, from this ensemble the structure for some of these interlaminar compositions were analyzed. For systems containing few ethane molecules and water enough to complete a single layer, it was observed that ethane mainly situates close to the interlayer midplane and adopts a nearly parallel arrangement to the clay surface. On the other hand, the muP(zz)T ensemble allows us to determine the interlaminar distance and water-ethane content for any specific reservoir. Here, some important findings are the following: the partial exchange of water by ethane molecules that enhances for decreasing the water vapor pressure; the obtention of a practically constant interlaminar space distance as a function of the water vapor pressure; the conservation of ion solvation shells; the enhancement of the water-ethane exchange for burial conditions; and finally, the incapability for a dehydrated clay mineral to swell in a dry and rich ethane atmosphere.     

Tandem mass spectrum of a farnesyl transferase inhibitor--gas-phase rearrangements involving imidazole

Compound 1 (1-(3-chlorophenyl)-4-[1-(4-cyanobenzyl)imidazolylmethyl]-2-piperazinone hydrochloride) is a farnesyl transferase inhibitor intended for treatment of cancer. A detailed analysis of the electrospray ionization mass spectrometry and tandem mass spectrometry data of protonated 1 shows that in the gas phase, upon collision-induced dissociation, this ion undergoes complicated rearrangement and fragmentation. These processes include a novel two-step rearrangement. The first step involves a gas-phase intramolecular S(N)2 reaction that forms an intermediate. The second step consists of three competitive rearrangement/fragmentation pathways of the intermediate, giving rise to protonated 2, protonated methylene-imidazole, and a distonic methylimidazole radical cation. Deuterated 1 was studied under the same experimental conditions, and the results strongly support the proposed two-step rearrangement process. It is noted that the unique structure of 1, especially the imidazole ring of 1, plays a critical role in the rearrangement of protonated 1.     

Constrained phosphite ester complexes of π-cyclopentadienylmolybdenum tricarbonyl halides

The synthesis of complexes of the type π-C₅H₅Mo(CO)₂LX and π-C₅H₅Mo(CO)L₂X, where XCl, Br, or I and LP(OCH₂)₃CR (RCH₃, C₂H₅, or C₃H₇), is reported. Infrared and conductance data verified that all compounds existed as covalent species in solution. Each of the three π-C₅H₅Mo(CO)₂LCl complexes was isolated as an inseparable mixture of cis and trans isomeric forms. Only the trans forms of the remaining π-C₅H₅Mo(CO)₂LX complexes were observed in solution, as indicated by infrared and PMR spectra. All of the π-C₅H₅Mo(CO)L₂X compounds apparently exist in primarily one isomeric form in solution; their PMR spectra, which exhibited a sharp triplet resonance for the ?OCH₂? protons of the phosphite ligands and a single sharp π-C₅H₅ proton signal, indicated a predominantly trans arrangement of the phosphite ligands at room temperature.     

Plant tissue-based bioselective membrane electrode for glutamate

A novel potentiometric membrane electrode with selective response to L-glutamate over the 2 × 10^-4–1.3 × 10^-2 M concentration range is constructed by immobilizing slices of yellow squash tissue at a CO₂ gas sensor. This system represents the first successful use of intact plant materials as biocatalysts in the construction of bioselective potentiometric membrane electrodes; as a result, the range of future possibilities may be greatly extended. The glutamate-sensing electrode combines excellent selectivity characteristics over some 25 possible interferences tested, good reproducibility, and a useful lifetime of 7 days in aqueous samples.     

Nonlinear plasma response

The decomposition method (G. Adomian, “Stochastic Systems,” Academic Press, New York/London, 1983; G. Adomian, “Stochastic Systems II,” in press) (and earlier work of Adomian referenced therein) allows solution without linearization of problems normally requiring the self-consistent field technique. The latter technique can provide a sufficiently accurate approximation in weakly coupled plasma, but the decomposition method of Adomian provides a superior and physically preferable methodology for the general case.     

Counterexamples in optimal quadrature

It is widely believed that order of exactness is a good measure of the quality of an algorithm for numerical quadrature. We show that this is not the case, by exhibiting a situation in which the optimal algorithm does not even integrate constants exactly. We also show that there are situations in which the penalty for using equidistant nodes is unbounded. Finally, we show that the complexity of obtaining an -approximation can be an arbitrary function of , i.e., there is no hardest quadrature problem.     

A New Setting for Polynomial Continuous-Time Systems, and a Realization Theorem

The paper deals with polynomial continuous time systems on algebraicmanifolds. The main result states that a nonlinear system maybe regularly immersed into a polynomial algebraically observablesystem ifi its observation algebra is finitely generated andregular. We also indicate some perspectives for future workin this direction.     

Single and double passage AFP NMR/ON studies of54MnNi

High resolution conventional AFP NMR/ON studies provide evidence for very small efg's of predominantly negative sign at the nucleus of the nominal S-state ion⁵⁴Mn in single crystal nickel when the applied field is paralled to the 111 direction. The form of the mid passage signals for opposing sweep directions indicates a unique efg super-imposed upon a random component of comparable magnitude. The advantages of a second analyzing sweep performed during spin lattice relaxation of a conventional post-passage AFP NMR/ON sweep are demonstrated.     

Reaction of o-aminophenyldiphenylmethanol with α-acetylenic ketone

Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, p. 1432, October, 1993.