Reliable radical stabilization energies from diffusion Monte Carlo calculations

We assess the performance of variational (VMC) and diffusion (DMC) quantum Monte Carlo methods for calculating the radical stabilization energies of a set of 43 carbon-centered radical species. Even using simple single-determinant trial wavefunctions, both methods perform exceptionally well, with mean absolute deviations from reference values well under the chemical accuracy standard of 1 kcal/mol. In addition, the use of DMC results in a highly concentrated spread of errors, with all 43 results within chemical accuracy at the 95% confidence level. These results indicate that DMC is an extremely reliable method for calculating radical stabilization energies and could be used as a benchmark method for larger systems in future.     

Improving the Switching Capacity of Glyco-Self-Assembled Monolayers on Au(111)

Self-assembled monolayers (SAMs) decorated with photoisomerizable azobenzene glycosides are useful tools for investigating the effect of ligand orientation on carbohydrate recognition. However, photoswitching of SAMs between two specific states is characterized by a limited capacity. The goal of this study is the improvement of photoswitchable azobenzene glyco-SAMs. Different concepts, in particular self-dilution and rigid biaryl backbones, have been investigated. The required SH-functionalized azobenzene glycoconjugates were synthesized through a modular approach, and the respective glyco-SAMs were fabricated on Au(111). Their photoswitching properties have been extensively investigated by applying a powerful set of methods (IRRAS, XPS, and NEXAFS). Indeed, the combination of tailor-made biaryl-azobenzene glycosides and suitable diluent molecules led to photoswitchable glyco-SAMs with a significantly enhanced and unprecedented switching capacity.     

Engineered-membranes: A novel concept for clustering of native lipid bilayers

A strategy for clustering of native lipid membranes is presented. It relies on the formation of complexes between hydrophobic chelators embedded within the lipid bilayer and metal cations in the aqueous phase, capable of binding two (or more) chelators simultaneously Fig. 1. We used this approach with purple membranes containing the light driven proton pump protein bacteriorhodopsin (bR) and showed that patches of purple membranes cluster into mm sized aggregates and that these are stable for months when incubated at 19 °C in the dark. The strategy may be general since four different hydrophobic chelators (1,10-phenanthroline, bathophenanthroline, Phen-C10, and 8-hydroxyquinoline) and various divalent cations (Ni²⁺, Zn²⁺, Cd²⁺, Mn²⁺, and Cu²⁺) induced formation of membrane clusters. Moreover, the absolute requirement for a hydrophobic chelator and the appropriate metal cations was demonstrated with light and atomic force microscopy (AFM); the presence of the metal does not appear to affect the functional state of the protein. The potential utility of the approach as an alternative to assembled lipid bilayers is suggested.     

Chemo-, regio-, and enantioselective Pd-catalyzed allylic alkylation of indolocarbazole pro-aglycons

[reaction: see text] Monosubstituted isomerically pure indolopyrrolocarbazole precursors have been prepared via palladium-catalyzed asymmetric allylic alkylation methodology, employing both achiral cyclopentenyl electrophiles and chiral glycal derivatives. Chemoselective allylation of (bis)indole lactam pro-aglycon 3 allows access to N-distally substituted indolopyrrolocarbazole derivatives; glyoxamide precursor 14 provides entry into N-proximally substituted derivatives.     

Noetherian down-up algebras

Down-up algebras were introduced by G. Benkart and T. Roby to better understand the structure of certain posets. In this paper, we prove that is equivalent to being right (or left) Noetherian, and also to being a domain. Furthermore, when this occurs, we show that is Auslander-regular and has global dimension 3.

     

Application of dn/dc data for the determination of partial specific volumes of dissolved macromolecules. II. Partial specific volume of ovalbumin in aqueous solution

The theory of an interferometric method for determining partial specific volumes of macromolecules is briefly reviewed. The experimental technique developed in this laboratory is described. Detailed results are given on the partial specific volume of ovalbumin in aqueous solution and its dependence on pH and KCl concentration. The results are compared, as far as possible, with dilatometric results obtained in another laboratory. The contribution of a change in partial specific volume of the macromolecules and in the partial specific volume of the water associated with them to the results is analyzed, and the scope of a possible complication due to changes in molecular polarizability is pointed out.     

Interferometric technique for measuring broadband ultrashort pulses at the sampling limit

We present a new technique for measuring ultrashort optical pulses by use of spectral phase interferometry for direct electric-field reconstruction that is suitable for large bandwidth pulses. The method does not require generation of a replica of the pulse to be measured and encodes the spectral phase information in a spatial interference pattern. A major advantage of this method is that the spectral sampling saturates the Whittaker-Shannon bound. Moreover, the technique allows for the characterization of some types of space-time coupling. An experimental demonstration of the technique is presented.     

Surface crystallization of amorphous solid water

We demonstrate that the crystallization of thin, supported amorphous solid water layers is initiated at the water surface. This is concluded from the observation of sequential crystallization of amorphous water at the surface, in the bulk, and at the water-support interface. A surface nucleation model quantitatively reproduces the observed transformation kinetics at the three sites.