Molecular orbital treatments of hydrogen bonded systems. 2. Dimers of water and HCN

Calculations were performed to investigate the reliabilities of the CNDO/2, PRDDO, and MNDO approximate molecular orbital methods. Systems selected for study included the linear, cyclic, and bifurcated dimers of water as well as the linear and cyclic dimers of HCN. The PRDDO method was found to provide the most consistently accurate reproduction of ab initio and experimental data. CNDO/2 performed fairly well in a number of cases but yielded extremely poor results for the cyclic dimers of both H₂O and HCN. Hydrogen bond strengths were consistently underestimated by MNDO which also furnished erroneously large intermolecular separations. In addition, MNDO calculations indicate the bifurcated water dimer to be most stable in contrast to other quantum mechanical and experimental information.See Ref. [1] for Paper 1 of this series.     

Reaction of carboxamide with Cu2Oisonitrile complex; formation of a new chelated copper(I) complex

Reaction of carboxamides with Cu₂O in the presence of t-butyl isocyanide gave new chelated copper(I) complexes, which probably are formed by the insertion of t-butyl isocyanide into the coppernitrogen bond of copper(I) amide isonitrile complexes, which were initially produced from the carboxamides and Cu₂Ot-butyl isocyanide complex. The same chelated copper(I) complexes were prepared more readily by the reaction of the corresponding N-trimethylsilyl-carboxamides with Cu₂Ot-butyl isocyanide complex. Reactions of the copper(I) complexes thus obtained with alkylating agents, such as alkyl halides, alkyl tosylates and triethyloxonium tetrafluoroborate, also were described.     

Theoretical Study of Weakly Bound Dimers between Hydrogen Fluoride and Some Polar Molecules

Weakly bound linear and bent dimers, FH—X (where X = CO, OC, CNH, NCH, N₂O and ON₂), are investigated using the DFT B3LYP and ab initio MP2 methods with the same basis sets (6–311++G(3df,2pd)). The strengths of the H—C or H—N H‐bonds in dimers FH—CO, FH—CNH, and FH—N₂O are compared with those of the H—O or H—N H‐bonds in dimers FH—OC, FH—NCH, and FH—ON₂. The results obtained for the H‐bond distances, the elongation effect of the HF bond, the red shift of the HF stretching frequency, and the energy difference between the dimer and the charge transfer reveal that the H‐bonds of the first group of dimers are stronger than those of the second. The Gibbs energies calculated for the six dimer formations indicate that the weakly bound dimers are unstable at room temperature (T = 298 K) (FH—X's → FH + X's, ΔG < 0).     

Synthesis and Visible Spectral Behaviour of Some New N‐Bridgehead Heterocyclic Cyanine Dyes Incorporating Pyrazolo (4,5‐b) Indolizine (Benzoindolizine)

The new unsymmetrical N‐bridgehead, apo (zeromethine), mono‐methine, dimethine, meso substituted tetramethine and styryl cyanine dyes incorporating pyrazolo (4,5‐b) indolizine (benzoindolizine) nuclei were prepared. Structural confirmation was carried out by elemental analyses, IR, H‐NMR, mass spectra and ¹³C‐NMR with the aid of carbon DEPT spectral data. The visible absorption spectra for the newly synthesized cyanines were examined in 95% ethanol.     

Synthesis and Structure Determination of Some New N‐Glycosides of 4,5‐Disubstituted‐1,2,4‐Triazole‐3‐Thiones

Some new N‐glycosides of 4‐(2‐phenylethyl)‐5‐pyridyl‐1,2,4‐triazole‐3‐thiones were synthesised by the coupling reaction of halo sugar with 4,5‐disubstituted 3H‐1,2,4‐triazole‐3‐thiones in the presence of mercuric cyanide and dry nitromethane as solvent, followed by deprotection using dry ammonia in methanol. All of the above compounds were fully characterized by means of infrared, ¹H NMR spectroscopy, mass spectroscopy and elemental analysis.     

Comparison between ab Initio and Modified INDO-MO Calculations of N20

Both STO-3G ab initio and s-p separation-type-modified INDO semiempirical methods were applied to molecular-orbital calculation of the N₂₀ molecule. From these two methods, the optimized bond distances between the nearest N atoms (d_n-n) and the most calculated thermodynamic data are close to each other. The positive values of ΔH_a° and ΔG_a° for the atomization reaction in this work prove that N₂₀ is stable. In contrast to conventional INDO and MINDO/3, but similar to former AMI and MNDO calculations, both ΔH_r° and ΔG_r° are positive in the formation reaction, which indicates that N₂₀ belongs to the category of high-energy molecules.     

Aggregation effects on evaporation and the air/water interface of dodecyltrimethylammonium hydroxide solutions

 The system dodecyltrimethylammonium hydroxide (DTAOH)–water was studied by surface tension, ion-selective electrodes and evaporation in an electrobalance. Results confirmed earlier conclusions about a stepwise aggregation mechanism in DTAOH solutions. The aggregation process started at a total concentration C _T=(2.51±0.10)×10^-4 mol dm^-3) which probably corresponds to the formation of dimers. At C _T= (1.300±0.041)×10^-3 mol dm^-3 there was a change in the surface and evaporation behavior, corresponding to the formation of small, fully ionized aggregates which grew with increasing concentration. At C _T= (1.108±0.010)×10^-2 mol dm^-3 the formation of true micelles with hydroxide counterions in the Stern layer did not change significantly the evaporation and adsorption behavior. This means that between this concentration and C _T=(3.02±0.28)× M28.8n10^-2 mol dm^-3, the changes in structure were gradual. At the latter concentration there was a sudden change in the monolayer state at the air/water interface, with a strong surfactant desorption, and a major change in evaporation behavior. The changes are compatible with the formation of few, large aggregates reducing the total concentration of kinetically independent solute units, which in turn increased the activity of the solvent. This phenomenon is in agreement with literature information. The reduction in the evaporation rate of water was mainly due to the reduction of the water activity, caused by colligative effects. The reduction of the effective area available for evaporation had only a slight effect in water evaporation. Received: 9 January 1997 Accepted: 19 October 1997     

Simultaneous quantitative measurement of a new platelet activating factor antagonist (BN 50730) and its two main metabolites in human plasma and urine by LC-MS

Summary A simple and sensitive assay has been developed for the quantitative measurement of a new platelet activating factor antagonist (BN50730), and its two main metabolites (BN50727 and BN50922), at the picomole level in human plasma and urine. The three compounds of interest and the internal standard (BN50765) were measured by combined LC-negative chemical ionization MS. A simple solid-liquid extraction procedure was used to isolate the parent drug and the two metabolites. The MS was tuned to monitor the intense ionm/z 333 generated in the ion source by a dissociative capture process. The assay was on 1 ml plasma or 0.1 ml urine and the quantitation limit was calculated as 1 ng·ml^–1. The very low relative standard deviations and mean percentages of error calculated for within-day or between-day repeatability assays demonstrate the ruggedness of the technique for routine determination in biological fluids. Some preliminary results on the pharmacokinetics of the parent drug and its two main metabolites illustrate the applicability of this method.     

Li2Br(NH2): Das erste ternäre Alkalimetallamidhalogenid

Li₂Br(NH₂): The First Ternary Alkali Metal Amide Halide The pseudobinary system LiNH₂/LiBr was investigated by X-ray methods. The crystal structure of the compound Li₂Br(NH₂) was solved by single crystal data: Li₂Br(NH₂): Pnma, Z = 8, a = 12.484(2) Å, b = 7.959(1) Å, c = 6.385(1) Å, Z(F_o) with (F_o)² ≧ 3σ(F_o)² = 348, Z (parameter) = 51, R/R_w = 0.019/0.021 Li₂Br(NH₂) crystallizes in a new type of structure. To one another isolated chains of [Li₂Li_4/2(NH₂)₂²⁺] show the motif of closest rod packing. They are connected via bromide ions in a distorted cubic primitive arrangement.     

Synthesis and characterization of MCM-48 tubular membranes

MCM-48 membranes have been prepared on alumina supports of different pore sizes. A battery of characterization techniques has been used to study the physical properties and the quality of the membranes prepared. The highest quality membranes were prepared on supports with pore size of up to 60 nm. The MCM-48 membranes were tested in the separation of gas phase mixtures and a cyclohexane/O₂ selectivity higher than 270 was obtained. The selective separation of organic compounds from inert components is a result of the cooperative effects of capillary condensation in MCM-48 pores and of the specific interactions of the permeating compounds and the membrane material.