Insights on the Pseudo-Enantiomeric Properties of Bifunctional Cinchona Alkaloid Squaramide-Derived Organocatalyst

The use of pseudo enantiomers is a well-known method of achieving products of complementary stereochemistry. Only rarely can different enantiomers of a product be accessed without modulation of the catalyst. Recently, a system was reported wherein two different enantiomers of spirocycles were obtained by a cascade reaction of unsaturated pyrrolin-4-ones with mercaptoacetaldehyde catalyzed by a single optimized cinchona alkaloid squaramide-derived organocatalyst. It was originally proposed that the E/Z geometry of the unsaturated pyrrolin-4-one dictated the stereochemistry of the spirocycle product, but this was not investigated further. In the present work, we have investigated the nature of a pseudo-enantiomeric organocatalyst conformation applying density functional theory calculations for investigating the transition states for the reaction. Furthermore, the influence of the double-bond geometry of the pyrrolin-4-one has been studied beyond what is possible to test experimentally. The results provide a greater understanding for this class of reactions that may be applicable in future methodology development.     

Uniform algebras on the sphere invariant under group actions

It is shown under certain conditions that a uniform algebra on the unit sphere S in C ² that is invariant under the action of the 2-torus must be C(S). Contrasting with this, an example is presented showing that the statement becomes false when 2 is replaced by n > 2. It is also shown that C(M) is the only uniform algebra on a smooth manifold M that is invariant under a transitive Lie group action on its maximal ideal space. The results presented answer a question raised by Ronald Douglas in connection with a conjecture of William Arveson.     

A Peak Point Theorem for Uniform Algebras Generated by Smooth Functions on Two-Manifolds

We establish the peak point conjecture for uniform algebrasgenerated by smooth functions on two-manifolds: if A is a uniformalgebra generated by smooth functions on a compact smooth two-manifoldM, such that the maximal ideal space of A is M, and every pointof M is a peak point for A, then A = C(M). We also give an alternativeproof in the case when the algebra A is the uniform closureP(M) of the polynomials on a polynomially convex smooth two-manifoldM lying in a strictly pseudoconvex hypersurface in Cⁿ.     

Polynomial approximation on three-dimensional real-analytic submanifolds of

It was once conjectured that if is a uniform algebra on its maximal ideal space and if each point of is a peak point for , then . This peak point conjecture was disproved by Brian Cole in 1968. However, it was recently shown by Anderson and Izzo that the peak point conjecture does hold for uniform algebras generated by smooth functions on smooth two-manifolds with boundary. Although the corresponding assertion for smooth three-manifolds is false, we establish a peak point theorem for real-analytic three-manifolds with boundary.

     

Light-induced modulation of Porphyromonas gingivalis growth

The bacterium Porphyromonas gingivalis is a clinically significant agent in periodontitis, a disease for which there is no definitive cure. Several groups have attempted to kill this bacterium using low levels of light in the absence of a photosensitizer, with conflicting results. We hypothesize that it is not possible to kill P. gingivalis by targeting endogenous porphyrins for a photochemical reaction. We demonstrated that irradiation of P. gingivalis with 455 or 625 nm light emitting diodes did not induce a photochemical killing of the cultures. Controlled temperature experiments indicate that irradiation at either wavelength did not significantly impact the growth of P. gingivalis cultures, as compared to non-irradiated controls. Rather, the irradiation caused a temperature increase in the growth medium, which altered the growth of the cultures. These results indicate that heat-induced killing of P. gingivalis could be the mechanism behind successful irradiation experiments with this bacterium.     

Multiple voltage-gradient gel electrophoresis system

A new device, based on the principle of voltage-gradient gel electrophoresis, was developed in order to enhance differentiation of the distance across the range of molecular masses in the electrophoretic fractionation of nucleic acids in an agarose matrix. The apparatus has a series of modular parallel plates, placed slantwise to allow reiteration of the voltage gradient effect along the gel. This subjects DNA fragments of variable length to differential runnings according to their original position in the gel. Both the number of slantwise plates and the distance between them can be changed to modify operating performance. Our system allows better fractionations as compared to conventional electrophoresis, since it forms gel areas in which distancing between the ranges of molecular masses is enhanced.     

Polynomial approximation on real-analytic varieties in

We prove: Let be a compact real-analytic variety in . Assume (i) is polynomially convex and (ii) every point of is a peak point for . Then . This generalizes a previous result of the authors on polynomial approximation on three-dimensional real-analytic submanifolds of .

     

Modulation of ionization and structural properties of weak polyelectrolytes due to 1D, 2D,and 3D confinement

What is the impact of reducing the space available to molecules onto their properties is a fundamental question for capillary systems, molecular biology and transport, protein and material sciences. Possibly influenced by space restriction, ionization degree has rarely been studied for confined polyelectrolytes; Monte Carlo titrations and coarse‐grained models are thus used to investigate structural and ionization changes induced on a single polyelectrolyte chain by confinement into slit (1D), cylindrical (2D), or spherical (3D) cavities. Four polyelectrolyte models differing in chain stiffness and the possible formation of charged hydrogen bonds (c? H? bonds) are studied. Low pH effective ionization constants (pK_a ) of confined chains are lower than for the free species if c? H? bonds can be formed. This is especially evident for 3D‐confined stiff chains, a finding rationalized by the impact of global compression onto chain conformations. If no c? H? bonds are allowed, chain ionization is largely unaffected by 1D or 2D confinement, while it is depressed by 3D. Chain confinement Helmholtz energy (ΔA _conf) was computed as a function of both pH and confining width (W) to gauge the impact of ionization‐induced stiffening onto ΔA _conf versus W behavior, the partition coefficient governing absorption, and the average number of c? H? bond formed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1088–1102