Novel Deep Cavity Calix[4]pyrroles Derived from Steroidal Ketones

Novel steroidal calix[4]pyrroles were prepared in excellent yields from commercially available cholic acid derivatives using an efficient synthetic sequence. Once in hand, it was found that these calix[4]pyrroles exist in the form of four different configurational isomers. Separation of these isomers was achieved readily using normal phase HPLC techniques. Once purified, the steroidal calix[4]pyrroles were screened via -FABMS analyses to judge their utility in effecting the enantioselective recognition of appropriate organic anions. Results that provided support for antipodal R > S selectivity were obtained in the case of both tartaric acid and mandelic acid. Direct extraction studies were then carried out and these confirmed the pattern of R > S selectivity observed by -FABMS.     

Application of magnetically perturbed time-dependent density functional theory to magnetic circular dichroism: calculation of B terms

Magnetically perturbed time-dependent density functional theory is applied to the calculation of the magnetic circular dichroism (MCD) B terms of closed shell molecules. Two approaches to evaluating B term parameters are described: a sum-over-states-type approach and an approach based on the direct solution of the matrix equations. The advantages and disadvantages and technical challenges of each approach are described. The interpretation of the parameters in terms of ground and excited state perturbations are discussed. Several applications of the methodology are described. Calculations of the MCD of ethene are used to compare the sum-over-states and direct solution approaches and to illustrate the potential for analysis. The other applications involving azabenzes, sulfur-nitrogen heterocycles and quinone molecules are compared with experiment and other theoretical calculations. For the most part, all important features of the observed spectra are reproduced.     

Large Deviations for Diffusions Interacting Through Their Ranks

We prove a large deviations principle (LDP) for systems of diffusions (particles) interacting through their ranks when the number of particles tends to infinity. We show that the limiting particle density is given by the unique solution of the appropriate McKean‐Vlasov equation and that the corresponding cumulative distribution function evolves according to a nondegenerate generalized porous medium equation with convection. The large deviations rate function is provided in explicit form. This is the first instance of an LDP for interacting diffusions where the interaction occurs both through the drift and the diffusion coefficients and where the rate function can be given explicitly. In the course of the proof, we obtain new regularity results for tilted versions of such a generalized porous medium equation.© 2016 Wiley Periodicals, Inc.     

Finding electromagnetic and chemical enhancement factors of surface-enhanced Raman scattering

The authors report two methods to determine electromagnetic and chemical enhancement factors in surface-enhanced Raman scattering (SERS), which are based on saturation property and decay dynamics of photoluminescence and concurrent measurements of photoluminescence and resonance Raman scattering intensities. Considerations for experimental implementation are discussed. This study is expected to facilitate the understanding of SERS mechanisms and the advancement of the usage of SERS in chemical and biological sensor applications.     

Novel,Monomeric Cyanine Dyes as Reporters for DNA Helicase Activity

The dimeric cyanine dyes, YOYO-1 and TOTO-1, are widely used as DNA probes because of their excellent fluorescent properties. They have a higher fluorescence quantum yield than ethidium homodimer, DAPI and Hoechst dyes and bind to double-stranded DNA with high affinity. However, these dyes are limited by heterogeneous staining at high dye loading, photocleavage of DNA under extended illumination, nicking of DNA, and inhibition of the activity of DNA binding enzymes. To overcome these limitations, seven novel cyanine dyes (Cyan-2, DC-21, DM, DM-1, DMB-2OH, SH-0367, SH1015-OH) were synthesized and tested for fluorescence emission, resistance to displacement by Mg²⁺, and the ability to function as reporters for DNA unwinding. Results show that Cyan-2, DM-1, SH-0367 and SH1015-OH formed highly fluorescent complexes with dsDNA. Of these, only Cyan-2 and DM-1 exhibited a large fluorescence enhancement in buffers, and were resistant to displacement by Mg²⁺. The potential of these two dyes to function as reporter molecules was evaluated using continuous fluorescence, DNA helicase assays. The rate of DNA unwinding was not significantly affected by either of these two dyes. Therefore, Cyan-2 and DM-1 form the basis for the synthesis of novel cyanine dyes with the potential to overcome the limitations of YOYO-1 and TOTO-1.     

Force dependence of transition rates in atomic friction

The lateral forces during stick-slip motion of an atomic force microscope cantilever on highly oriented pyrolytic graphite are measured and analyzed. We identify the regimes where thermally activated interstitial hopping of the cantilever tip proceeds according to a single-step reaction scheme and extract the corresponding force-dependent transition rates directly from the experimental data. We find that such a single-step reaction scenario is valid only at relatively high velocities, while at slower pulling speeds, a more complicated hopping mechanism must be at work. We suggest formation of multiple bonds of the tip-sample contact as a possible candidate for this mechanism.     

1-Aryl-1-chloro-2,2,2-trifluoroethylisocyanates—convenient reagents for synthesis of 2-aryl-2-trifluoromethyl-2,3-dihydro-4H-benzo[e][1,3]oxazin-4-ones

1-Aryl-1-chloro-2,2,2-trifluoroethylisocyanates react with 3-alkoxyphenols to form N-(1-aryl-2,2,2-trifluoroethylidene)-O-(3-alkoxyphenyl)urethanes, which undergo intramolecular thermal cyclization into derivatives of 2-aryl-2-trifluoromethyl-2,3-dihydro-4H-benzo[e][1,3]oxazin-4-ones.     

Steroid-porphyrin conjugate for saccharide sensing in protic media

A new saccharide receptor in protic media has been designed and synthesized. The receptor combines advantages of steroids, which are responsible for saccharide binding, and of the porphyrin moiety acting as a signalling component of the molecule due to changes in UV-vis electronic spectra. The synthesis is based on condensation of steroid aldehyde with pyrrole to form the porphyrin unit with four protected steroid moieties. After deprotection, meso-substituted porphyrin contains 12-hydroxy groups on the steroidal part. The receptor is soluble in aqueous solutions and exhibits high complexation affinity towards saccharides. Because the receptor extensively aggregates in water, most of the experiments were performed in 50% aqueous 2-propanol where aggregation is significantly eliminated. Binding is evidenced by spectral changes in the Soret region of the receptor in UV-vis absorption spectra allowing the evaluation of the binding constants. Additional confirmation of binding is obtained using 1H NMR, Raman and IR spectroscopies and the surface plasmon resonance technique. The receptor exhibits higher selectivity for oligosaccharides over monosaccharide. The results point to the importance of a combination of multiple binding via H-bonding and hydrophobic interactions.     

Chemoselective aminomethylation of harmol

Chemistry of Heterocyclic Compounds - Aminomethylation of harmol (7-hydroxy-1-methyl-β-carboline) was investigated. It was shown that the reaction proceeds chemoselectively to form...