Rotational Spectroscopy and Conformational Flexibility of 2-Phenylethanethiol: The Dominant S-H⋅⋅⋅π Intramolecular Hydrogen Bond.

We present a rotational-computational investigation of the aromatic mercaptan 2-phenylethanethiol, addressing its potential energy surface, conformational equilibrium, internal dynamics and intramolecular interactions. The experiment used broadband chirped-pulse Fourier transform microwave spectroscopy in a supersonic jet expansion, recording the rotational spectrum in the 2-8 GHz frequency region. Two different conformers were detected in the spectrum.

Hydrogen Bonding in the Dimer and Monohydrate of 2-Adamantanol: A Test Case for Dispersion-Corrected Density Functional Methods.

Weakly-bound intermolecular clusters constitute reductionist physical models for non-covalent interactions. Here we report the observation of the monomer, the dimer and the monohydrate of 2-adamantanol, a secondary alcohol with a bulky ten-carbon aliphatic skeleton. The molecular species were generated in a supersonic jet expansion and characterized using broadband chirped-pulse microwave spectroscopy in the 2-8 GHz frequency region.

Torsional chirality and molecular recognition: the homo and heterochiral dimers of thenyl and furfuryl alcohol.

Furfuryl alcohol and thenyl alcohol contain a labile torsional chiral center, producing transiently chiral enantiomers interconverting in the nanosecond time-scale. We explored chiral molecular recognition using the weakly-bound intermolecular dimers of both alcohols, freezing stereomutation. Supersonic jet broadband microwave spectroscopy revealed homo and heterochiral diastereoisomers for each alcohol dimer and the structural characteristics of the clusters.

Molecular Rotation Spectrum of Tetracyclic Quinolizidines: Observation of -Matrine and the Elusive -Matrine.

We characterized the bis-quinolizidine tetracyclic alkaloid (5, 6, 7, 11)-matrine in a supersonic jet expansion, using chirped-pulsed broadband microwave spectroscopy. Previous crystal diffraction analyses suggested 16 diastereoisomers associated with matrine's four carbon stereocenters but were inconclusive whether the lactamic nitrogen atom would additionally produce separated -/- diastereoisomers or if both species may interconvert through low potential barriers. Our experiment simultaneously detected - and -matrine through their rotational spectrum, confirming the possibility of conformational rearrangement in matrine alkaloids.

A Concise Route for the Synthesis of Tetracyclic Meroterpenoids: (±)-Aureol Preparation and Mechanistic Interpretation.

A new concise general methodology for the synthesis of different tetracyclic meroterpenoids is reported: (±)-aureol (), the key intermediate of this general route. The synthesis of (±)-aureol () was achieved in seven steps (28% overall yield) from (±)-albicanol. The key steps of this route include a C-C bond-forming reaction between (±)-albicanal and a lithiated arene unit and a rearrangement involving 1,2-hydride and 1,2-methyl shifts promoted by BF•EtO as activator and water as initiator.

Mimicking Halimane Synthases: Monitoring a Cascade of Cyclizations and Rearrangements from Epoxypolyprenes.

We have developed and rationalized a biomimetic transformation mimicking halimane synthases based on a Lewis acid-catalyzed cascade of cyclizations and rearrangements of epoxypolyprenes. Two rings, three stereogenic centers, and a new double bond were generated in a single chemical operation. Based on this cascade transformation, we achieved a unified strategy toward the stereoselective total syntheses of halimene-type terpenoids and analogues as a proof-of-concept study.

Rotational Spectrum, Tunneling Motions, and Intramolecular Potential Barriers in Benzyl Mercaptan.

The rotational spectrum of benzyl mercaptan (parent and four isotopologues) has been assigned in a supersonic jet expansion using chirped-pulse Fourier transform microwave spectroscopy. The spectrum is characterized by torsional tunneling doublings, strongly perturbed by Coriolis interactions. The experimental rotational constants reveal that the sulfur atom is located above the ring plane in a conformation.

Sulfur Hydrogen Bonding in Isolated Monohydrates: Furfuryl Mercaptan versus Furfuryl Alcohol.

The hydrogen bonds involving sulfur in the furfuryl mercaptan monohydrate are compared with the interactions originating from the hydroxyl group in furfuryl alcohol. The dimers with water were created in a supersonic jet expansion and characterized using microwave spectroscopy and supporting molecular orbital calculations. In furfuryl alcohol-water, a single isomer is observed, in which the water molecule forms an insertion complex with two simultaneous hydrogen bonds to the alcohol (O-H⋅⋅⋅O ) and the ring oxygen (O -H⋅⋅⋅O ).

Rotational spectra of tetracyclic quinolizidine alkaloids: does a water molecule flip sparteine?

Sparteine is a quinolizidine alkaloid used as a chiral auxiliary in asymmetric synthesis. We examine whether hydration by a single molecule can flip sparteine from the most stable trans conformation to the bidentate cis arrangement observed in catalytic complexation to a metal center. Sparteine and the sparteine-water dimer were generated in a supersonic jet expansion with HO and HO, and characterized by broadband chirped-pulse microwave spectroscopy.

A DFT-Based Computational-Experimental Methodology for Synthetic Chemistry: Example of Application to the Catalytic Opening of Epoxides by Titanocene.

A novel DFT-based Reaction Kinetics (DFT-RK) simulation approach, employed in combination with real-time data from reaction monitoring instrumentation (like UV-vis, FTIR, Raman, and 2D NMR benchtop spectrometers), is shown to provide a detailed methodology for the analysis and design of complex synthetic chemistry schemes. As an example, it is applied to the opening of epoxides by titanocene in THF, a catalytic system with abundant experimental data available. Through a DFT-RK analysis of real-time IR data, we have developed a comprehensive mechanistic model that opens new perspectives to understand previous experiments.

A research capacity strengthening project for infectious diseases in Honduras: experience and lessons learned.

Background: In Honduras, research capacity strengthening (RCS) has not received sufficient attention, but an increase in research competencies would enable local scientists to advance knowledge and contribute to national priorities, including the Millennium Development Goals (MDGs).

Objective: This project aimed at strengthening research capacity in infectious diseases in Honduras, focusing on the School of Microbiology of the National Autonomous University of Honduras (UNAH). The primary objective was the creation of a research-based graduate program for the continued training of researchers.

Newly diagnosed versus relapsed idiopathic thrombotic thrombocytopenic purpura: a comparison of presenting clinical characteristics and response to treatment.

The remission rate with plasma exchange (PE) in thrombotic thrombocytopenic purpura (TTP) exceeds 80%, but the disease relapses in up to 20-30% of the cases. Clinical characteristics and response to treatment of relapsed TTP are not well defined. The objective of the present study was to compare the clinical and biological characteristics at presentation and the response to treatment between de novo and relapsed TTP.

Microscopic description of the irradiation-induced amorphization in silicon.

We have investigated the atomistic mechanism behind the irradiation-induced amorphization in Si using molecular dynamics simulation techniques. The microscopic description of the process is based on the defect known as bond defect or IV pair. IV pairs recombine very fast when isolated, but if they interact to each other they survive longer times and thus accumulate giving rise to amorphization.