Organocatalyzed Tsuji-Trost reaction: a new method for the closure of five- and six-membered rings

A combination of organotransition metal catalysis and organocatalysis allows for Tsuji-Trost 5-exo- and 6-exo-cyclizations of aldehydes. This transformation can also be accomplished as a catalytic asymmetric reaction, which affords vinylcyclopentane derivatives with up to 98%ee.     

Field Effect and Local Gating in Nitrogen-Terminated Nanopores (NtNP) and Nanogaps (NtNG) in Graphene

Functionalization of electrodes is a wide-used strategy in various applications ranging from single-molecule sensing and protein sequencing, to ion trapping, to desalination. We demonstrate, employing non-equilibrium Green′s function formalism combined with density functional theory, that single-species (N, H, S, Cl, F) termination of graphene nanogap electrodes results in a strong in-gap electrostatic field, induced by species-dependent dipoles formed at the electrode ends. Consequently, the field increases or decreases electronic transport through a molecule (benzene) placed in the nanogap by shifting molecular levels by almost 2 eV in respect to the electrode Fermi level via a field effect akin to the one used for field-effect transistors. We also observed the local gating in graphene nanopores terminated with different single-species atoms. Nitrogen-terminated nanogaps (NtNGs) and nanopores (NtNPs) show the strongest effect. The in-gap potential can be transformed from a plateau-like to a saddle-like shape by tailoring NtNG and NtNP size and termination type. In particular, the saddle-like potential is applicable in single-ion trapping and desalination devices.     

THE EFFECT OF NORFLURAZON ON PHOTOTROPIC REACTION IN Phaseolus aureus Roxb. SEEDLINGS

Abstract. The phototropic response of norflurazon-treated mung bean seedlings has been studied to evaluate the possible role of carotenoids, carotenoid-derived growth substances, or other factors in the perception/reaction system. Phototropism was slowed significantly in plants grown in white and blue light in the presence of norflurazon. This effect was evident in norflurazon-bleached seedlings, as well as in those whose pigment system was not affected, due to a shorter period of herbicide action. The possible modes of norflurazon action are discussed.     

Polypyrrole-coated capillaries for capillary zone electrophoresis

Fused-silica capillaries are permanently coated by silanization with 3-{[3-(N-pyrrole)-2-hydroxypropyl]amino}propyltriethoxysilane followed by oxidative polymerization of the pyrrole moieties with iron (III) or peroxodisulfate in the presence of chloride, perchlorate, or dextransulfate as anions. This approach allows to modulate the EOF in its magnitude as well as in its direction. With the small anions chloride and perchlorate, the EOF is reversed below pH 5 while with the large dextransulfate polyanions (DS) the EOF is relatively constant over the pH range from 2.5 to 9.4. This can be of advantage at low pH, at which the EOF of uncoated capillaries is close to zero. Application for separation of some herbicides is shown. The lifetime of PP-modified capillaries is satisfactory: the decrease in EOF is less than 3% during 80 analyses (160 min) and less than 5% over three months of storage. The reproducibility of capillary modification is about 5% (RSD of EOF).     

Synthesis, biology, and modeling of a C-4 carbonyl C,D-seco-taxoid

A C,D-seco-paclitaxel derivative 26 was prepared from taxine and tested for biological activity. Chemical reactivity of the seco-compounds proved to be substantially modified, with respects to taxoids. The corresponding C,D-seco-taxoid does not show tubulin stabilizing activity or cytotoxicity. Explanation of these observations based on molecular modeling is provided.     

A convenient procedure for the preparation of Garner’s aldehyde

The palladium/silane reduction of a serine thioester derivative allows for the preparation of enantiomerically pure Garner’s aldehyde from serine, in gram quantities within 24 h.     

New Insights into the Mechanism of Reduction of Tertiary Phosphine Oxides by Means of Phenylsilane

The mechanism of the reduction of phosphine oxides by PhSiH₃ was established on the basis of kinetic measurements and Density Functional Theory (DFT) calculations. In particular, it has been proved that the model reaction between tri‐n‐butylphosphine oxide and phenylsilane occurs via a nonpolar mechanism. The data presented herein allow prediction and verification of the applicability of the new reduction reagents and conditions for industrially attractive processes.     

Fully atomistic molecular‐mechanical model of liquid alkane oils: Computational validation

Fully atomistic molecular dynamics simulations were performed on liquid n‐pentane, n‐hexane, and n‐heptane to derive an atomistic model for middle‐chain‐length alkanes. All simulations were based on existing molecular‐mechanical parameters for alkanes. The computational protocol was optimized, for example, in terms of thermo‐ and barostat, to reproduce properly the properties of the liquids. The model was validated by comparison of thermal, structural, and dynamic properties of the normal alkane liquids to experimental data. Two different combinations of temperature and pressure coupling algorithms were tested. A simple differential approach was applied to evaluate fluctuation‐related properties with sufficient accuracy. Analysis of the data reveals a satisfactory representation of the hydrophobic systems behavior. Thermodynamic parameters are close to the experimental values and exhibit correct temperature dependence. The observed intramolecular geometry corresponds to extended conformations domination, whereas the intermolecular structure demonstrates all characteristics of liquid systems. Cavity size distribution function was calculated from coordinates analysis and was applied to study the solubility of gases in hexane and heptane oils. This study provides a platform for further in‐depth research on hydrophobic solutions and multicomponent systems. © 2014 Wiley Periodicals, Inc.     

Near‐Infrared‐III‐Absorbing and ‐Emitting Dyes: Energy‐Gap Engineering of Expanded Porphyrinoids via Metallation

The synthesis of organometallic complexes of modified 26π‐conjugated hexaphyrins with absorption and emission capabilities in the third near‐infrared region (NIR‐III) is described. Symmetry alteration of the frontier molecular orbitals (MOs) of bis‐Pd^II and bis‐Pt^II complexes of hexaphyrin via N‐confusion modification led to substantial metal d_π–p_π interactions. This MO mixing, in turn, resulted in a significantly narrower HOMO–LUMO energy gap. A remarkable long‐wavelength shift of the lowest S₀→S₁ absorption beyond 1700 nm was achieved with the bis‐Pt^II complex, t ‐Pt₂‐3 . The emergence of photoacoustic (PA) signals maximized at 1700 nm makes t ‐Pt₂‐3 potentially useful as a NIR‐III PA contrast agent. The rigid bis‐Pd^II complexes, t ‐Pd₂‐3 and c ‐Pd₂‐3 , are rare examples of NIR emitters beyond 1500 nm. The current study provides new insight into the design of stable, expanded porphyrinic dyes possessing NIR‐III‐emissive and photoacoustic‐response capabilities.