Plasma Destruction of Ozone Depleting Substances

The literature on the plasma destruction of ozone depleting substances (ODS) such as CCl₂F₂ and CBrF₃ is reviewed, and compared with more recent work on the decomposition of CCl₂F₂ and CBrClF₂ in oxygen and steam. A comprehensive kinetic scheme for the decomposition of CBrClF₂, which includes the decomposition of CCl₂F₂ and CBrF₃, is presented. Simulations performed with this scheme, and experimental results, demonstrate the importance of allowing for the interconversion of ODS in the assessment of plasma destruction devices.Both experimental and modeling results show that the efficiency of operation of a practical plasma ODS destruction device can be quantified in terms of a throughput parameter, the feed to plasma power ratio (units mol (kWh)^-1), or in terms of the thermochemical mixing temperature, T_m, of the plasma, ODS and oxidant. At low throughputs and high T_m, essentially complete destruction may be achieved, with below-ppm quantities of ODS remaining in the plasma exhaust gases. As throughput rises and Tm falls, a threshold is reached above which the ODS residual rises steeply towards the practical working limit set for ODS destruction by the Montreal Protocol (a destruction level of 99.99%). The assessment of this limit must include all ODS in the exhaust gases, weighted for ozone depleting potential. The use of steam, rather than oxygen, as the oxidizing gas gives superior destruction performance.     

Large-scale purification of antisense oligonucleotides by high-performance membrane adsorber chromatography

Very high flux ion-exchange membranes were utilized for a novel purification of antisense oligonucleotides (20-mer). Strong anion-exchange membranes were produced by attaching polymeric ligands onto a microporous cellulosic matrix. The oligonucleotides purified were therapeutic single-stranded phosphorothioates deoxyribonucleotides. Although small-scale membrane devices (15 cm2) had similar resolution to traditional chromatographic columns; their throughputs were superior. Greater than a 1300-fold scale-up produced very similar purity and yields of the phosphorothionate product. Scale-up experiments were conducted with a 2 m2 surface area membrane module. These modules were easily capable of very high throughputs of 0.5 to 2 l/min. High purity and yields were achieved by both step and linear gradient elution.     

Development of carbohydrate-based scaffolds for restricted presentation of recognition groups. Extension to divalent ligands and implications for the structure of dimerized receptors

The solution structure of glycosyl amides has been studied by using NMR. A strong preference is displayed by tertiary aromatic glycosyl amides for E-anti structures in contrast with secondary aromatic glycosyl amides where Z-anti structures predominate. The structural diversity displayed by these classes of molecules would seem to be important as the directional properties of the aromatic ring, or groups attached to the aromatic ring, would be determined by choosing to have either a secondary or tertiary amide at the anomeric center and could be considered when designing bioactive molecules with carbohydrate scaffolds. The structural analysis was also carried out for related divalent secondary and tertiary glycosyl amides and these compounds display preferences similar to that of the monovalent compounds. The constrained divalent compounds have potential for promoting formation of clusters that will have restricted structure and thus have potential for novel studies of mechanisms of action of multivalent ligands. Possible applications of such compounds would be as scaffolds for the design and synthesis of ligands that will facilitate protein-protein or other receptor-receptor interactions. The affinity of restricted divalent (or higher order) ligands, designed to bind to proteins that recognize carbohydrates which would facilitate clustering and concomitantly promote protein-protein interactions, may be significantly higher than monovalent counterparts or multivalent ligands without these properties. This may be useful as a new approach in the development of therapeutics based on carbohydrates.     

Deposition of CTAB-terminated nanorods on bacteria to form highly conducting hybrid systems

Gold nanorods and nanospheres capped with positively charged CTAB are deposited on the surface of gram-positive bacterium having negatively charged teichoic acid brushes. The deposition rate is more than an order of magnitude faster than that for peptide and nucleic acid capped nanoparticles. For the nanorods, never been reported before, the strong electrostatic attraction causes the rods to bend conformally over the curved bacterium surface in random orientations. This leads to formation of an efficient percolating cluster (i.e., low contact resistance and high radius of gyration) with 104-fold higher current at 3-fold lower coverage compared to a monolayer from nanospheres. The high monolayer conductivity at only approximately 10% coverage for nanorods has potential for fabricating a novel class of bioelectronic devices by coupling electronic "nanocircuitry" at the surface to the biological function of microorganisms.     

Hydrolysis study of organic acid anhydrides by differential thermal analysis--II. Maleic anhydride and trimellitic anhydride

Differential thermal analysis has been used to follow the hydrolysis of maleic anhydride (MA) and trimellitic anhydride (TMA). On exposure of MA to an atmosphere of 96 % relative humidity, maleic acid is produced, hydrolysis being complete in 21 hr at 22 degrees, but no hydrolysis occurs at a relative humidity of 50%. When exposed to an atmosphere of 96% relative humidity, TMA is quite stable for short periods, but hydrolyses slowly, the production of trimellitic acid being complete in 113 hr at 22 degrees.     

Photochemical production and release of gaseous NO2 from nitrate-doped water ice

Temperature-programmed NO2 emissions from frozen aqueous NaNO3 solutions irradiated at 313 nm were monitored as function of nitrate concentration and heating rate, H, above -30 degrees C. Emissions increase nonmonotonically with temperature, displaying transitions suggestive of underlying metamorphic transformations. Thus, NO2 emissions surge at ca. -8 degrees C in frozen [NO3-] > 200 microM samples warmed at H = 0.70 degrees C min(-1) under continuous irradiation, and also in the dark from samples that had been photolyzed at -30 degrees C. The amounts of NO2 released in individual thermograms, SigmaN, increase less than linearly with [NO3-] or the duration of experiments, revealing the significant loss of photogenerated NO2. The actual SigmaN proportional, variant [NO3-]1/2 dependence (at constant H) is consistent with NO2 hydrolysis: 2NO2 + H2O --> NO3- + NO2- + 2H+, overtaking NO2 desorption, even below the eutectic point (-18 degrees C for aqueous NaNO3). The increasingly larger NO2 losses detected in longer experiments (at constant [NO3-]) are ascribed to secondary photolysis of trapped NO2. The relevance of present results to the interpretation of polar NO2 measurements is briefly analyzed.     

Fast atom bombardment and collision-induced dissociation of prostaglandins and thromboxanes: Some examples of charge remote fragmentation

The mass spectra of products found by collisional activation of selected prostaglandins and thromboxanes were studied by tandem mass spectrometry as barium carboxylate salts and as carboxylate anions. Collision-induced dissociation (CID) of these closed shell ions generated by fast atom bombardment mass spectrometry reveals a wealth of structural information for these hydroxy acids. Decomposition reactions were found to be dependent upon the eicosanoid ring structure and the type of ion being studied, either positive or negative ion. The bariated carboxylate salts undergo reactions by processes that are similar to those previously characterized as charge remote mechanisms in which neutral species are lost as in thermal and photolytic decompositions. The most abundant ion is formed by loss of water from each of the hydroxyl groups present on the prostaglandin or thromboxane structure. For these multifunctionalized eicosanoids, typical patterns of decomposition emerge as characteristic of the oxygen substituents present along the carbon chain of the eicosanoid structure. The structural information obtained from the barium salts along with those from the carboxylate anions is substantially different, yet the structural information from each process is complementary. The CIDs of positive ions (metalated salts) provide structural information concerning the substituents between the carboxyl group and C₁₂ of the eicosanoid structure, whereas the decompositions of the carboxylate anions (negative ion mode) provide data concerning structure alterations of the eicosanoid structure between C₁₅ and C₂₀     

Synthesis of 7-substituted imidazo[1,2-a]pyrimidin-5(1H)-ones

The synthesis of 7-substituted imidazo[1,2-a]pyrimidin-5(1H)-ones by either of 2 methods is reported.