Role of the countercation in diastereoselective alkylations of pyramidalized bicyclic serine enolates. An easy approach to alpha-benzylserine

The use of a chiral serine equivalent as an excellent chiral building block has been demonstrated in the synthesis of alpha-benzylserine through a diastereoselective lithium enolate alkylation reaction and subsequent acid hydrolysis. The role of a coordinating countercation (lithium) in the alkylation reaction has been investigated. Theoretical studies have been performed in order to elucidate the stereochemical outcome of the alkylation process, which occurs with total retention of configuration.     

Observation of three behaviors in confined liquid water within a nanopool hosting proton-transfer reactions

In this contribution, we report on studies of rotational and diffusional dynamics of 7-hydroxyquinoline (7HQ) within a reverse micelle (RM) containing different amounts of water. Analyzed in terms of the wobbling-in-a-cone model, the data reveal structural and dynamical properties of the nanopool. We clearly observed three regions in the behavior of confined water molecules within the RM hosting a double proton-transfer reaction between the probe and water. This observation remarkably reproduces the change of calculated water density within this life-mimicking medium. The number of water molecules per AOT head in the transition regions changes from 2 to 5, the latter being very near to the full solvation number (6) of the RM heads. Moreover, the H-bonds breaking and making within the RM to give new structures of the probe strongly affect the environment fluidization in different extents, reflected in different relaxation times of these structures; however, they are of similar sizes. We discuss the role of RM confinement and the proton-transfer dynamics on the behavior of water and their relationships to the packing of water molecules in the studied range of concentrations.     

Inflation,quantum fields,and CMB anisotropies

Inflationary cosmology has proved to be the most successful at predicting the properties of the anisotropies observed in the cosmic microwave background (CMB). In this essay we show that quantum field renormalization significantly influences the generation of primordial perturbations and hence the expected measurable imprint of cosmological inflation on the CMB. However, the new predictions remain in agreement with observation, and in fact favor the simplest forms of inflation. In the near future, observations of the influence of gravitational waves from the early universe on the CMB will test our new predictions.     

In‐capillary microextraction using monolithic polymers: Application to preconcentration of carbamate pesticides prior to their separation by MEKC

In the present work we report a novel procedure for in‐capillary microextraction using a monolithic polymeric sorbent. In the proposed methodology, sample treatment takes place in the CE instrument but in a different capillary from that used for the electrophoretic separation. Polymers based on butyl methacrylate and divinylbenzene formed in situ inside a capillary column were assayed. The best results were found with the divinylbenzene‐based polymers. The usefulness of the proposed procedure was checked for the determination of carbamate pesticides (Methomyl, Asulam, Carbendazim, Aldicarb, Carbetamide, Propoxur, Pirimicarb, Carbaryl, Carbofuran and Methiocarb) and three of their degradation compounds (Aldicarb sulphoxide, 2‐isopropoxyphenol and α‐naphthol) using MEKC. The optimization of the MEKC is reported, a good separation of the 13 analytes being obtained in less than 6 min. The analytical method using in‐capillary microextraction was validated in terms of linearity, repeatability, precision (RSD≤18% for 50 μg/L), and LODs (1–16 μg/L), and it revealed the usefulness of this in‐capillary preconcentration procedure for the determination of analytes of intermediate polarity.     

Electrochemical synthesis of PEDOT derivatives bearing imidazolium‐ionic liquid moieties

Novel poly(3,4‐ethylenedioxythiophene) (PEDOT) polymers bearing imidazolium‐ionic liquid moieties were synthesized by electrochemical polymerizations. For this purpose, new functional monomers were synthesized having an 3,4‐ethylenedioxythiophene (EDOT) unit and an imidazolium‐ionic liquid with different anions such as tetrafluoroborate (BF), bis(trifluoromethane)sulfonimide ((CF₃SO₂)₂N^?), and hexafluorophosphate (PF). Next, polymer films were obtained by electrochemical synthesis in dicholoromethane solutions. Obtained polymers were characterized, revealing the characteristics of PEDOT in terms of electrochemical and spectroelectrochemical properties, FTIR, ¹H NMR, and AFM microscopy. Interestingly, the hydrophobic character of electropolymerized films could be modified depending on the anion type. The hydrophobicity followed the trend PF > (CF₃SO₂)₂N^? > BF > pure PEDOT as determined by water contact angle measurements. Furthermore, the polymers could be dissolved in a range of polar organic solvents such as dimethylformamide, propylene carbonate, and dimethyl sulfoxide making these polymers interesting candidates for wet processing methods. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3010–3021, 2009     

New insights into alpha-GalNAc-Ser motif: influence of hydrogen bonding versus solvent interactions on the preferred conformation

The structural features of the mucin-type simplest model, namely, the glycopeptide alpha-O-GalNAc-l-Ser diamide, have been investigated by combining NMR spectroscopy, molecular dynamics simulations, and DFT calculations. In contrast to previous reports, the study reveals that intramolecular hydrogen bonds between sugar and peptide residues are very weak and, as a consequence, not strong enough to maintain the well-defined conformation of this type of molecule. In fact, the observed conformation of this model glycopeptide can be satisfactorily explained by the presence of water pockets/bridges between the sugar and the peptide moieties. Additionally, DFT calculations reveal that not only the bridging water molecules but also the surrounding water molecules in the first hydration shell are essential to keep the existing conformation.     

Models of spherical shells as sources of Majumdar–Papapetrou type spacetimes

By starting with a seed Newtonian potential–density pair we construct relativistic thick spherical shell models for a Majumdar–Papapetrou type conformastatic spacetime. As a simple example, we considerer a family of Plummer–Hernquist type relativistic spherical shells. As a second application, these structures are then used to model a system composite by a dust disk and a halo of matter. We study the equatorial circular motion of test particles around such configurations. Also the stability of the orbits is analyzed for radial perturbation using an extension of the Rayleigh criterion. The models considered satisfying all the energy conditions.     

Newtonian Dynamics from the Principle of Maximum Caliber

The foundations of Statistical Mechanics can be recovered almost in their entirety from the principle of maximum entropy. In this work we show that its non-equilibrium generalization, the principle of maximum caliber (Jaynes, Phys Rev 106:620–630, 1957), when applied to the unknown trajectory followed by a particle, leads to Newton’s second law under two quite intuitive assumptions (both the expected square displacement in one step and the spatial probability distribution of the particle are known at all times). Our derivation explicitly highlights the role of mass as an emergent measure of the fluctuations in velocity (inertia) and the origin of potential energy as a manifestation of spatial correlations. According to our findings, the application of Newton’s equations is not limited to mechanical systems, and therefore could be used in modelling ecological, financial and biological systems, among others.     

Rapid access to ketones related to oleanolic and ursolic acids

We describe in this article a process with which to obtain different ketones related to oleanolic and ursolic acids from a natural source, Salvia canariensis L., with minimal use of chromatography columns. Amongst the isolated compounds was 12α-bromo-3-oxo-olean-13, 28-olide (3), which was fully characterised, including a characterisation of its molecular configuration by X-ray crystallographic analysis by 1 and 2-dimensional NMR techniques.     

Bidirectional Redox Molecular Switches: Electron-induced Cyclization and Cycloreversion Processes in Metacyclophanes

A reversible bidirectional ring-opening and ring-closing system triggered by electricity has been prepared by using metacyclophan-1-enes, a known thermo-photochromic molecular switch system.