Pressure broadening study at low temperature: application to methane

We studied the R(0) line profile in the CH4 v4 band from room temperature to 188 K with N2 as a perturber, to 100 K with O2 as perturber, and from room temperature to 15 K using He as a perturber. The N2 and O2 measurements were performed over a total pressure range of 15-110 mbar, and for the He measurements the maximum sample pressure at 15 K was 1.10 mbar. Broadening parameters were determined, taking into account the confinement narrowing (Dicke effect), and narrowing parameters, deduced from the soft or hard collision model, are compared with the dynamic friction coefficient calculated values. We also obtained preliminary values for the temperature dependence of the N2, O2 and He line broadening parameters for this transition.     

Chirospecific Syntheses of Conformationally Constrained 7-Azabicycloheptane Amino Acids by Transannular Alkylation

A new method is reported for the chirospecific preparation of optically pure 1-carboxy-7-azabicycloheptane amino acids for the generation of peptidomimetics as conformational probes. The method allows for the multigram preparation of these amino acid analogues through use of a thiolactam sulfide contraction and a transannular alkylation sequence as the key C-C bond-forming steps, starting from L-glutamic acid. The route provides access to two common intermediates, 7-(benzyloxycarbonyl)-1-carboxy-7-azabicyclo[2.2.1]-3-heptane and (1S,4R)-7-(benzyloxycarbonyl)-1-carboxy-7-azabicyclo[2.2.1]-3-heptanone tert-butyl ester, for elaboration to symmetrical and chiral amino acid homologues, respectively. Decarboxylation of the C-1 carboxy unit of the latter intermediate also demonstrated the applicability of the method for a short, chirospecific preparation of a (+)-epibatidine intermediate, (1S,4R)-7-(tert-butyloxycarbonyl)-1-carboxy-7-azabicyclo[2.2.1]-3-heptanone.     

Use of Silicon Substituents in the Syntheses of Natural and Non-natural Molecules

Trimethylsilyl groups have been used in our research as a director as well as a bulky and lipophilic group in our quest for natural and non-natural molecules.     

Acid digestion of geological and environmental samples using open-vessel focused microwave digestion

The application of open vessel focused microwave acid digestion is described for the preparation of geological and environmental samples for analysis using inductively coupled plasma-mass spectrometry (ICP-MS). The method is compared to conventional closed-vessel high pressure methods which are limited in the use of HF to break down silicates. Open-vessel acid digestion more conveniently enables the use of HF to remove Si from geological and plant samples as volatile SiF4, as well as evaporation-to-dryness and sequential acid addition during the procedure. Rock reference materials (G-2 granite, MRG-1 gabbros, SY-2 syenite, JA-1 andesite, and JB-2 and SRM-688 basalts) and plant reference materials (BCR and IAEA lichens, peach leaves, apple leaves, Durham wheat flour, and pine needles) were digested with results comparable to conventional hotplate digestion. The microwave digestion method gave poor results for granitic samples containing refractory minerals, however fusion was the preferred method of preparation for these samples. Sample preparation time was reduced from several days, using conventional hotplate digestion method, to one hour per sample using our microwave method.     

The effect of substituents on the extraction behavior of hydroxamic acids

The extraction behavior of several alkyl-substituted hydroxamic acids in chloroform solution with several metal ions is described. Among the N-phenylacylhydroxamic acids used, those with o-alkyl substituents on either the phenyl or acyl ring generally do not extract metals, apparently because of steric problems at the O=CNO^? chelation site. An improved synthesis of substituted hydroxamic acids is reported.     

Genotoxic properties of 2-dodecylcyclobutanone, a compound formed on irradiation of food containing fat

When food containing fat is treated by ionizing radiation, a group of 2-alkylcyclobutanones is formed. These components contain the same number of carbon atoms as their precursor fatty acids and the alkyl group is located in ring position 2. Thus, from palmitic acid 2-dodecylcyclobutanone is derived. To date, there is no evidence that the cyclobutanones occur in unirradiated food. Therefore, these components cannot be considered inherent to food, and for questions pertaining to risk assessment of irradiated food it would be advisable to determine the genotoxic and toxic potentials of cyclobutanones. Measurements of DNA damage in cells exposed to 2-dodecylcyclobutanone, employing the single cell microgel electrophoresis technique, have been carried out. In vitro experiments using rat and human colon cells indicate that 2-docylcyclobutanone in the concentration range of about 0.30 – 1.25 mg/ml induces DNA strand breaks in the cells. Simultaneously, a concentration related cytotoxic effect is observed as was determined by trypan blue exclusion. To which extent these in vitro findings are of relevancy for the in vivo human exposure situation needs to be investigated in further studies. In vivo tests in rats are in progress.     

Synthesis of trans-1,2-diphenyl-3,4-bis[4-(2,6-diphenyl-4H- pyranylidenyl)]cyclobutane: correction and structure proof

The reaction of phenyl lithium acetylide ($\text{2}$) with 2,6-diphenylpyrylium perchlorate ($\text{1}$) is solvent dependent. With diethyl ether as solvent, the isolated product differed from that previously reported and is reassingned as 2,6-diphenyl-4-phenylacetylenyl-4$\text{H}$-pyran ($\text{5}$). On the other hand, in THF the title compound ($\text{6}$) was obtained; its structure confirmed by single-crystal x-ray crystallography.     

Some difficulties in the application of the concept of density of states

The problem of defining N(E), the density of states, for molecular systems is discussed. It is shown that a numeric evaluation of N(E) is often only approximate, even for continuous data, and is not well defined for quantized systems. The application of the concept of density of states is discussed, particularly with regard to the RRKM theory of unimolecular reactions. The sum of states, W(E), and density of states curves are evaluated for several harmonic and anharmonic model systems and the results discussed in order to illustrate the foregoing considerations.     

The evolution of poly(lactic acid) degradability by dielectric spectroscopy measurements

Dielectric spectroscopy is a powerful method that allows the study of the dynamics of polymers in a wide frequency range. The different regimes of the dielectric spectra can be observed and the dynamics of the primary and secondary relaxations can be found.In this work, the systems investigated included industrial and purified poly(lactic acid), PLA. This is an aliphatic polyester, one of the most important biocompatible and biodegradable material that has received increasing attention in the last 10 years.Thermal analyses indicated that the glass transition temperature of the polymer was about 320 K.The β relaxation was observed between −150 °C and −30 °C, depending on the measurement frequency (1 Hz-100 kHz), and was assigned to the secondary relaxation in the glassy state. We studied the changes that are connected with the water penetration in the polymer, and directly affect that relaxation process. Water molecules confined by polymer chains and in the polymer networks play an important role in the degradation of the matrix, and then we can observe the evolution of that degradation during some weeks, in a controlled humidity environment. It is accepted that water preferentially enters in the amorphous zones, but also affects the crystalline regions. It is observed a clear evolution of the relaxation activation energy during the degradation of the polymer.The dielectric relaxation results are complemented with molar mass measurements during the degradation process with time.     

Synthesis,renal vasodilator and dopamine-sensitive adenylate cyclase activities of O-Methyl derivatives of 6-chloro-2,3,4,5-tetr ahydro-1-(4-hydroxyphenyl)-1H-3-benzazepin-7,8-diol (SK&F 82526)

The three possible mono-O-methyl derivatives of 6-chloro-2,3,4,5-tetrahydro-1-(4-hydroxyphenyl)-1H-3-benzazepin-7,8-diol (SK&F 82526) ( 1 ) have been synthesized to facilitate the isolation and characterization of metabolites of this compound and for biological testing. The syntheses generally involved preparation of appropriately substituted benzaldehydes, conversion of these to phenylacetic acids and use of these to N-acylate arylethanolamines. The phenylacetamides thus formed were reduced to amines and these were deprotected and cyclized to the desired final products. In one case deprotection followed cyclization. These compounds were tested as activators of dopamine-sensitive adenylate cyclase (a measure of DA-1 agonist activity) and as renal vasodilators. All three O-methyl derivatives were much less potent than 1 in cyclase activation and as renal vasodilators. Weak inhibition of adenyl cyclase was also observed for all three compounds and one showed weak renal vasoconstrictor activity. Preliminary investigation of the metabolism of 1 disclosed that two of the three monomethoxy compounds were formed in trace amounts in the rat and the dog. In a related investigation, the trimethoxy derivative of 1 was subjected to acid-catalyzed hydrolysis conditions. The relative ease of cleavage of methoxy groups was 7 > > 4′ > 8.