Liquid crystalline dendrimers containing photoactive cinnamate units

Cinnamate‐containing dendrimers have been prepared by peripheral functionalization of the amine groups of a poly(propyleneimine) dendrimer with 4‐methoxycinnamate‐ or 4‐(N,N‐dimethylamino)cinnamate‐derived units and/or 4‐cyanobiphenyl units in different proportions. The synthesis, full characterization in solution, thermal properties and optical properties of the novel monomers, homodendrimers and codendrimers are reported. The composition of the molecular structure of the codendrimers has been elucidated by matrix assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). These liquid crystalline dendrimers display lamellar SmA mesophases. The codendrimers have been tailored in such a way that the photoactive units and the liquid crystal units absorb in different regions in order to allow better control over the processes induced by light. Linearly polarized UV light irradiation studies performed on thin films of the cinnamate codendrimers show that they are photoresponsive. A photoinduced anisotropy is generated with increasing exposure time, but in‐plane amplification of anisotropy by thermal annealing in the mesophase was not observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

The MM2QM tool for combining docking,molecular dynamics,molecular mechanics,and quantum mechanics†

The use of the MM2QM tool in a combined docking + molecular dynamics (MD) + molecular mechanics (MM) + quantum mechanical (QM) binding affinity prediction study is presented, and the tool itself is discussed. The system of interest is Mycobacterium tuberculosis (MTB) pantothenate synthetase in complexes with three highly similar sulfonamide inhibitors, for which crystal structures are available. Starting from the structure of MTB pantothenate synthetase in the “open” conformation and following the combined docking + MD + MM + QM procedure, we were able to capture the closing of the enzyme binding pocket and to reproduce the position of the ligands with an average root mean square deviation of 1.6 Å. Protein–ligand interaction energies were reproduced with an average error lower than 10%. The discussion on the MD part and a protein flexibility importance is carried out. The presented approach may be useful especially for finding analog inhibitors or improving drug candidates. © 2012 Wiley Periodicals, Inc.     

Profiles analysis of proanthocyanidins in the argun nut (Medemia argun—an ancient Egyptian palm) by LC–ESI–MS/MS

Medemia argun is an ancient palm rich in proanthocyanidins (PACs). These polyphenolic compounds are widely distributed in plants and are an integral part of the human diet. A sensitive high‐performance liquid chromatography and electrospray ionization mass spectrometry (HPLC–ESI–MS) method in the negative ion mode for sequencing these ubiquitous and highly beneficial antioxidants is described in order to profile different PACs in M. argun nuts. The analytical protocol based on tandem mass spectrometry was used to sequence dimers, trimers, tetramers and pentamers with different A‐type, B‐type and A/B‐type linkages. Diagnostic ions resulting from heterocyclic ring fission and retro‐Diels–Alder reaction of flavan‐3‐ol provided information on the hydroxylation pattern and the type of interflavan bond. The sequences were discovered through ions derived from quinone methide cleavage of the interflavan bond. The identification of PACs linkages through LC–MSⁿ eliminates a number of tedious separation steps. The method was successfully applied to give a view of PAC profile in M. argun nuts. M. argun nuts contained 636.88 mg/g PACs (as equivalent of (þ)‐catechin). The data obtained in our research show that M. argun is a rich source of hydrolyzable PACs. Copyright © 2014 John Wiley & Sons, Ltd.     

Efficient Preparation and X-Ray Structure Analyses of (2R)-N-pyruvoyl- and (2R)-N-(phenylglyoxyloyl)bornane-10,2-sultam

An efficient synthesis of the two title compounds is reported, as well as their X-ray crystal-structure analyses. A discussion based on stereoelectronic considerations rationalizes the first example of a crystalline SO₂/C(O) syn-periplanar conformer of a N-acylbornane-10,2-sultam.     

Temperature controller for thermal ionization mass spectrometry.

We describe the use of a simple voltage stabilizer that controls the filament temperature (T(f)) in the ion source of a thermal ionization mass spectrometer. The filament voltage (V(f)) is measured by means of a separate pair of wires connected inside of the ion source in parallel to the wires supplying power. It has been demonstrated that V(f) is directly proportional to T(f) in a wide range of filament temperature. The T(f) value is solely controlled by the reference voltage (V(r)) that can be manually selected from a voltage divider or by means of a computer. Digital signals from the computer in the form of a series of pulses are transmitted opto-electronically and subsequently converted to analog signals. The temperature controller described here was successfully applied for analysis of potassium concentration by the isotope dilution method.     

Surface charge microscopy: novel technique for mapping charge-mosaic surfaces in electrolyte solutions

The effective surface potential, called the zeta potential, is commonly determined from electrophoretic mobility measurements for particles moving in a solution in response to an electric field applied between two electrodes. The situation can be reversed, with the solution being forced to flow through a plug of packed particles, and the streaming potential of the particles can be calculated. A significant limitation of these electrokinetic measurements is that only an average value of the zeta potential/streaming potential is measured--regardless of whether the surface charge distribution is homogeneous or otherwise. However, in real-world situations, nearly all solids (and liquids) of technological significance exhibit surface heterogeneities. To detect heterogeneities in surface charge, analytical tools which provide accurate and spatially resolved information about the material surface potential--particularly at microscopic and submicroscopic resolutions--are needed. In this study, atomic force microscopy (AFM) was used to measure the surface interaction forces between a silicon nitride AFM cantilever and a multiphase volcanic rock. The experiments were conducted in electrolyte solutions with different ionic strengths and pH values. The colloidal force measurements were carried out stepwise across the boundary between adjacent phases. At each location, the force-distance curves were recorded. Surface charge densities were then calculated by fitting the experimental data with a DLVO theoretical model. Significant differences between the surface charge densities of the two phases and gradual transitions in the surface charge density at the interface were observed. It is demonstrated that this novel technique can be applied to examine one- and two-dimensional distributions of the surface potential.     

Origin of adhesion in humid air

The origin of adhesion in humid air is investigated by pull-off force measurements between nanoscale contacts using atomic force microscopes in controlled environments from ultrahigh vacuum through various humidity conditions to water. An equivalent work of adhesion (WOA) model with a simplified interface stress distribution is developed, combining the effects of screened van der Waals and meniscus forces, which describes adhesion in humid air and which self-consistently treats the contact stress and deformation. Although the pull-off force is found to vary significantly with humidity, the equivalent WOA is found to be invariant. Increasing humidity alters the nature of the surface adhesion from a compliant contact with a localized, intense meniscus force to a stiff contact with an extended, weak meniscus force.