Improved protocol for asymmetric, intramolecular heteroatom Michael addition using organocatalysis: enantioselective syntheses of homoproline, pelletierine, and homopipecolic acid

An improved protocol for the construction of enantioenriched pyrrolidine, indoline, and piperidine rings using an organocatalyzed, intramolecular heteroatom Michael addition is described. Application to the enantioselective synthesis of homoproline, homopipecolic acid, and pelletierine has been accomplished.     

Analysis of odour compounds from scented consumer products using gas chromatography-mass spectrometry and gas chromatography-olfactometry

Scented consumer products are being bought in increasing amounts and gaining more popularity. There is, however, relatively little information available about their ingredients, emissions and allergenic potential. Frequently, a mixture of different fragrance substances and not solely an individual substance contributes to the overall desired smell. The aim of this study was to investigate the odorous volatile organic compounds (OVOCs) in consumer products containing fragrances. Over 44 products were selected: various scented candles, printing products with different scent types and other products types particularly meant to be used indoors. Measurements were carried out in a desiccator. Air samples were collected on thermal desorption tubes to determine the released fragrance substances by means of gas chromatography-mass spectrometry (GC-MS). Moreover, gas chromatography-olfactometry (GC-O) was used to obtain sensory data and to ensure no important odorant was overlooked. Using both methods it was possible to distinguish between odour active and inactive compounds and subsequently to identify almost 300 different odorants across all scented products. Besides the advantage of differentiation, as the human nose is a very sensitive detector, GC-O was found to be a useful tool for detecting traces and chosen target compounds. One focus in this study lay on the 26 EU-regulated fragrance allergens to prove their relevance in scented consumer goods. In total, 18 of them were identified, with at least one substance being present in almost every product. Benzyl alcohol, cinnamaldehyde, citronellol, eugenol, linalool and limonene were the prevalently detected allergens. Particularly linalool and limonene were observed in over 50% of the products. In addition, eugenol appeared to be one of the most frequently detected compounds in trace-level concentrations in the candle emissions.     

Nanostructured silica thin films self-assembled with electron donors and acceptors to measure electron tunneling

Surfactant-templated, mesostructured thin films are synthesized such that photoelectron donors and electron acceptors are separated spatially in the different regions of the thin film. A photoelectron donor is placed within the silica framework by using a silylated derivative of the well-known tris(bipyridine)ruthenium(II) cation. Selective placement of the electron acceptor is achieved by using a surfactant derivative of methyl viologen. Luminescence decay traces and luminescence spectra are collected for the electron donor in the presence of varying amounts of the electron acceptor. Because of the spatial separation of the donor and acceptor noncontact electron transfer occurs and the electron-transfer rate decreases exponentially with the distance separating the donor and acceptor. Luminescence decay traces are calculated and fit to the experimental data in order to extract a value for the contact quenching rate, k0 (s(-1)), as well as the exponential decay constant beta (A(-1)) which governs how fast the electron-transfer rate decreases as a function of the donor-acceptor distance. The value beta = 2.5 +/- 0.4 A(-1) shows that the mesostructured material is an excellent insulator, better than frozen organic glasses or proteins and approaching that of vacuum. Combining deliberate placement methods, spectroscopy, and calculations has made possible the first measurement of beta for the silica region of mesoporous thin films.     

Evaluation of sample fractionation using micro-scale liquid-phase isoelectric focusing on mass spectrometric identification and quantitation of proteins in a SILAC experiment

Mass spectrometric methods based on stable isotopes have shown great promise for identification and quantitation of complex mixtures. Stable isotope labelling by amino acids in cell culture (SILAC) is a straightforward and accurate procedure for quantitation of proteins from cell lines, that are cultured in media containing the natural amino acid or its isotopically labelled analogue, giving rise to either 'light' or 'heavy' proteins. The two cell populations are pooled and treated as a single sample, which allows the use of various protein purification methods without introducing errors into the quantitative analysis. The quantitation of the proteins is based on the intensities of the light and heavy peptides. The increased number of peptides in a quantitative experiment arising from peptide pairs implies that prefractionation is critical prior to liquid chromatography/mass spectrometric (LC/MS) analysis to minimise signal suppression effects and errors in measurements of the intensity ratios. In this study, the effect of a prefractionation step on identification and quantitation of proteins in a SILAC experiment was evaluated. We show that micro-scale liquid-phase isoelectric focusing in the Micro Rotofor separates proteins into well-defined fractions and reduces the sample complexity. Furthermore, the fractionation enhanced the number of identified proteins and improved their quantitation.     

Effect of low intensity laser interaction with human skin fibroblast cells using fiber-optic nano-probes

Over the past forty years, many efforts have been devoted to study low power laser light interactions with biological systems. Some of the investigations were performed in-vitro, on bulk cell populations. Our present work was undertaken to apply specially engineered fiber-optic based nano-probes for the precise delivery of laser light on to a single cell and to observe production of low power laser light induced reactive oxygen species (ROS). A normal human skin fibroblast (NHF) cell line was utilized in this investigation and the cells were irradiated under two different schemes of exposure: (1) an entire NHF cell population within a Petri dish using a fan beam methodology, and (2) through the precise delivery of laser energy on to a single NHF cell using fiber-optic nano-probe. Photobiostimulative studies were conducted through variation of laser intensity, exposure time, and the energy dose of exposure. Laser irradiation induced enhancement in the rate of cell proliferation was observed to be dependent on laser exposure parameters and the method of laser delivery. The total energy dose (fluence) had a greater influence on the enhancement in the rate of cellular proliferation than compared to laser intensity. The enhancement in the growth rate was observed to have a finite life-time of several days after the initial laser exposure. Fluorescent life-time imaging of ROS was performed during the nano-based single cell exposure method. The kinetics of ROS generation was found to depend strongly on the laser fluence and not on the laser intensity.     

A Synthetic Strategy for Cofacial Porphyrin-Based Homo- and Heterobimetallic Complexes

We present a straightforward and generally applicable synthesis route for cofacially linked homo- and heterobimetallic porphyrin complexes. The protocol allows the synthesis of unsymmetrical aryl-based meso-meso as well as β-meso-linked porphyrins. Our method significantly increases the overall yield for the published compound known as o-phenylene-bisporphyrin (OBBP) by a factor of 6.8. Besides the synthesis of 16 novel homobimetallic complexes containing Mn^III, Fe^III, Ni^II, Cu^II, Zn^II, and Pd^II, we achieved the first single-crystal X-ray structure of an unsymmetrical cofacial benzene-linked porphyrin dimer containing both planar-chiral enantiomers of a Ni^II₂ complex. Additionally, this new methodology allows access to heterobimetallic complexes such as the Fe^III-Ni^II containing carbon monoxide dehydrogenase active site analogue. The isolated species were investigated by various techniques, including ion mobility spectrometry, DFT calculations, and UV/Vis spectroscopy. This allowed us to probe the influence of interplane distance on Soret band splitting.     

Constructions of categories of setoids from proof-irrelevant families

When formalizing mathematics in constructive type theories, or more practically in proof assistants such as Coq or Agda, one is often using setoids (types with explicit equivalence relations). In this note we consider two categories of setoids with equality on objects and show, within intensional Martin-Löf type theory, that they are isomorphic. Both categories are constructed from a fixed proof-irrelevant family F of setoids. The objects of the categories form the index setoid I of the family, whereas the definition of arrows differs. The first category has for arrows triples \((a,b,f:F(a)\,\rightarrow \,F(b))\) where f is an extensional function. Two such arrows are identified if appropriate composition with transportation maps (given by F) makes them equal. In the second category the arrows are triples \((a,b,R \hookrightarrow \Sigma (I,F)^2)\) where R is a total functional relation between the subobjects \(F(a), F(b) \hookrightarrow \Sigma (I,F)\) of the setoid sum of the family. This category is simpler to use as the transportation maps disappear. Moreover we also show that the full image of a category along an E-functor into an E-category is a category.     

Determination of exciton-phonon coupling elements in single-walled carbon nanotubes by Raman overtone analysis

Raman excitation profiles are obtained and compared for carbon nanotube radial breathing mode (RBM) fundamental and overtone vibrations for 5 specific chiralities. Fitting of the Raman excitation data is performed using Raman transform theory. The Huang-Rhys factors obtained from the modeling are directly related to the magnitude of the RBM exciton-phonon coupling element, which is shown to be in a weak coupling limit. The values of exciton-phonon coupling strengths and the possible role of revealed non-Condon effects are in agreement with quantum-chemical modeling.     

Evaporation of femtoliter sessile droplets monitored with nanomechanical mass sensors

We present a time-resolved study of the evaporation in air of minuscule sessile droplets deposited by nanodispensing techniques. Highly sensitive nanomechanical resonators are designed to monitor in time the mass variation of evaporating liquid droplets. The precision of the measurement setup enables the study of droplets with diameters in the 1 mum range, which correspond to volumes of femtoliters and smaller, 9 orders of magnitude smaller than most of presently published data. Experimental data are compared with macroscopic models.     

Coarse-grained molecular dynamics modeling of strongly associating fluids: thermodynamics, liquid structure, and dynamics of symmetric binary mixture fluids

Symmetric binary mixtures capable of strong association via a highly directional and saturable specific interaction between unlike molecules are investigated by canonical molecular dynamics simulations. The specific interaction of the molecules is defined in a new coarse-grained pair potential that can be applied in continuous molecular dynamics as well as in Monte Carlo simulations. The thermodynamic, structural, and dynamic properties of the associating mixture fluids are investigated as a function of density, temperature, and association strength of the specific interaction. Detailed analysis of the simulation data confirms a two-stage mechanism in the formation of specific bonds with increasing interaction strength, including a fast dimerization process and a subsequent stage of perfecting the bonds. A large heat capacity peak is found during the formation or breaking of the bonds, reflecting the large energy fluctuation introduced by the strong association. The fractions of nonbonded molecules obtained from the simulations as a function of density, temperature, and interaction strength are in excellent agreement with the predictions of Wertheim's thermodynamic perturbation theory. The translational and rotational dynamics of the Tmer mixture are effectively retarded with increasing association strength and are analyzed in terms of autocorrelation functions and a non-Gaussian parameter for the translational dynamics. The lifetimes of molecules in bonded and nonbonded states provide detailed information about the transformation of molecules between the bonded state and the nonbonded state. Finally, simulation sampling problems inherent to strongly interacting systems are easily overcome using the parallel tempering simulation technique. This latter result confirms that with the new continuous coarse-grained simulation potential we have a versatile and flexible interaction potential that can be used with many available molecular dynamics and Monte Carlo algorithms under various ensembles.