trans-4-Hydroxy-l-proline: a novel starting material for N-alkylpyrroles synthesis

The reaction of aldehydes with trans-4-hydroxy-l-proline was studied for the first time, resulting in the formation of N-alkylpyrroles in good to excellent yields, via decarboxylation followed by redox isomerization under neutral conditions. The neutral conditions allow access to efficient synthesis of N-alkyl pyrroles with high functional group tolerance.     

Modifying metal nanoparticle placement on carbon supports using an aerosol-based process, with application to the environmental remediation of chlorinated hydrocarbons

A facile aerosol-based process (ABP) is developed to vary the placement of iron nanoparticles on the external surface of carbon microspheres or within the interior. This is accomplished through the competitive mechanisms of sucrose carbonization and the precipitation of soluble iron salts, in an aerosol droplet passing through a high temperature heating zone. At lower aerosolization temperatures, carbonization occurs first leading to iron salt precipitation on the external surface, while at higher temperatures interior placement occurs through concurrent iron salt precipitation and sucrose carbonization. The resulting composites are highly conducive to the reductive dechlorination of compounds such as trichloroethylene (TCE) as the carbon support is a strong adsorbent, and zerovalent iron effectively reduces TCE to innocuous gases such as ethane. Since both iron and carbon are widely used catalysts and catalyst supports, the simple process of modifying iron placement has significant potential applications in heterogeneous catalysis.     

Detection and identification of alkylphosphonic acids by positive electrospray ionization tandem mass spectrometry using a tricationic reagent

The retrospective detection and identification of degradation products of chemical warfare agents are of immense importance in order to prove their spillage and use. A highly sensitive liquid chromatography/electrospray ionization tandem mass spectrometric (LC/ESI-MS/MS) method--using an imidazolium-based tricationic reagent--was developed for the detection and identification of the anionic degradation products of nerve agents. A commercially available solution of 1,3-imidazolium-bis-(1-hexylbenzylimidazolium) trifluoride (IBHBI) formed adducts with alkylphosphonic acids (APAs), allowing detection of the APAs by positive mode ESI-MS. Tandem mass spectrometry was used for the unambiguous identification of the APAs. Parameters influencing the formation and stability of these adduct during mass spectrometric analysis, such as solvent composition, concentration of IBHBI, effect of pH and interferences by salts, were optimized. The absolute limits of detection (0.1 ng) for achieved for the APAs were better than those previously reported, and linear dynamic ranges of 10-2000 ng mL(-1) were achieved. The method was repeatable with a relative standard deviation ≤7.3%. APAs present in aqueous samples provided by the Organization for the Prohibition of Chemical Weapons during the 22(nd) and 24(th) Official Proficiency tests were detected and identified as IBHBI adducts. The added advantage of this method is that low-mass analytes are detected at higher mass, thus obviating the problem with background noise at low mass.     

CsF mediated rapid condensation of 1,3-cyclohexadione with aromatic aldehydes:Comparative study of conventional heating vs.ambient temperature

A mild,efficient and high yielding protocol for the synthesis of 2,2'-arylmethelene dicyclohexane-1,3-dione derivatives at room temperature and 9-aryl-l,8-dihydrooctahydroxanthene at conventional heating using cesium fluoride as a catalyst is reported.The major advantages of this reaction are excellent yield,very short reaction time and use of inexpensive catalyst.     

New geometry-inspired relaxations and algorithms for the metric Steiner tree problem

Determining the integrality gap of the bidirected cut relaxation for the metric Steiner tree problem, and exploiting it algorithmically, is a long-standing open problem. We use geometry to define an LP whose dual is equivalent to this relaxation. This opens up the possibility of using the primal-dual schema in a geometric setting for designing an algorithm for this problem. Using this approach, we obtain a 4/3 factor algorithm and integrality gap bound for the case of quasi-bipartite graphs; the previous best integrality gap upper bound being 3/2 (Rajagopalan and Vazirani in On the bidirected cut relaxation for the metric Steiner tree problem, 1999). We also obtain a factor \({\sqrt{2}}\) strongly polynomial algorithm for this class of graphs. A key difficulty experienced by researchers in working with the bidirected cut relaxation was that any reasonable dual growth procedure produces extremely unwieldy dual solutions. A new algorithmic idea helps finesse this difficulty—that of reducing the cost of certain edges and constructing the dual in this altered instance—and this idea can be extracted into a new technique for running the primal-dual schema in the setting of approximation algorithms.     

Optimal use of data in parallel tempering simulations for the construction of discrete-state Markov models of biomolecular dynamics

Parallel tempering (PT) molecular dynamics simulations have been extensively investigated as a means of efficient sampling of the configurations of biomolecular systems. Recent work has demonstrated how the short physical trajectories generated in PT simulations of biomolecules can be used to construct the Markov models describing biomolecular dynamics at each simulated temperature. While this approach describes the temperature-dependent kinetics, it does not make optimal use of all available PT data, instead estimating the rates at a given temperature using only data from that temperature. This can be problematic, as some relevant transitions or states may not be sufficiently sampled at the temperature of interest, but might be readily sampled at nearby temperatures. Further, the comparison of temperature-dependent properties can suffer from the false assumption that data collected from different temperatures are uncorrelated. We propose here a strategy in which, by a simple modification of the PT protocol, the harvested trajectories can be reweighted, permitting data from all temperatures to contribute to the estimated kinetic model. The method reduces the statistical uncertainty in the kinetic model relative to the single temperature approach and provides estimates of transition probabilities even for transitions not observed at the temperature of interest. Further, the method allows the kinetics to be estimated at temperatures other than those at which simulations were run. We illustrate this method by applying it to the generation of a Markov model of the conformational dynamics of the solvated terminally blocked alanine peptide.     

Gas chromatography-electron ionization-mass spectrometry analysis of O,O'- dialkyl methylphosphonites for verification analysis of the Chemical Weapons Convention

Gas chromatography-mass spectrometry (GC-MS) analysis of O,O'-dialkyl methylphosphonites (DAMPs) was carried out with a view to developing a database and understanding the mechanism of fragmentation. DAMPs are included in the list of schedule 2B4 chemicals of the Chemical Weapons Convention. GC-MS analysis of DAMPs and their deuterated analogs revealed that their fragmentations were dominated by α-cleavages, alkenyl radical loss and hydrogen rearrangements. Based on fragment ions of deuterated analogs and density functional theory calculations, the fragmentation routes were rationalized.     

Differentiation of diasteromeric α-sulfanyl-β-amino acid derivatives by electrospray ionization tandem mass spectrometry

A set of diastereomeric α-sulfanyl-β-amino acid derivatives, which are important building blocks for pharmaceuticals with potent biological activity, are studied by electrospray ionization tandem mass spectrometry. The collision induced dissociation (CID) spectra of [M+H](+), [M+NH(4)](+), [M+Na](+) and [M+Li](+) of the diastereomers were studied, among them the CID of [M+Na](+) and [M+Li](+) showed consistent differences in the relative abundance of characteristic ions that enabled distinction of the anti isomers from syn isomers. The decomposition pathways for the diagnostic ions were arrived at based on high-resolution mass spectrometry data, multiple mass spectrometry data, deuterium labeling experiments and the mass shift in accordance with the substituents located at different places. Loss of (R(1)-C(6)H(4)-CH=NH) and (Cat-NH-SO(2)R(2)) from [M+Cat](+), where Cat=Na and Li, and the product ions as a results of McLafferty rearrangement involving either >S=O or >C=O group were found to be diagnostic. The McLafferty rearrangement product ions involving >S=O group were more abundant in syn isomers while those involving >C=O group were more abundant in anti isomer. The selectivity observed in the decomposition of [M+Li](+) ions was found to be similar to that of [M+Na](+) ions, but in few cases the differences are marginal in the decomposition [M+Li](+) ions.