Nanoscale Assembly of Paramagnetic Organic Radicals on Au(111) Single Crystals

The successful thin‐film deposition of a pyrene‐substituted nitronyl nitroxide radical under controlled conditions has been demonstrated. The electronic properties, chemical environment at the interface, and morphology of the thin films have been investigated by a multitechnique approach. Spectroscopic and morphological analyses indicate a Stranski–Krastanov growth mode and weak physisorption of molecules onto the metallic surface. Electron spin resonance (ESR) spectroscopy shows that evaporation processes and deposition do not affect the paramagnetic character of the molecules. Useful concepts for the engineering of new, purely organic‐based magnets, which may open the way to fruitful exploitation of organic molecular‐beam deposition for assembly on solid surfaces in view of future technological applications, are presented.     

Oxidative halogenation of substituted pyrroles with Cu(II). Part IV. Bromination of 2-(2′-hydroxybenzoyl)pyrrole. A new synthesis of bioactive analogs of monodeoxypyoluteorin

The selective bromination with copper(II) bromide of the pyrrole ring in 2-(2′-hydroxybenzoyl)pyrrole II in the heterogeneous phase is described giving in almost quantitative yield the 4,5-dibromo derivative VI. The subsequent introduction of halogen into the phenol moiety was observed when the reaction was performed in the homogeneous phase with an excess of halogenating agent. The pentabromo derivative IX , a compound very active against Staphylococcus aureus (mic = 17 nmoles per dm^?3), was obtained by exhaustive bromination of the title compound. Poor yields of chloro derivatives of II were obtained by reaction of the parent compound with copper(II) chloride.     

STRSCNE: A Scaled Trust-Region Solver for Constrained Nonlinear Equations

In this paper a Matlab solver for constrained nonlinear equations is presented. The code, called STRSCNE, is based on the affine scaling trust-region method STRN, recently proposed by the authors. The approach taken in implementing the key steps of the method is discussed. The structure and the usage of STRSCNE are described and its features and capabilities are illustrated by numerical experiments. The results of a comparison with high quality codes for nonlinear optimization are shown.     

Photosynthetic light-harvesting is tuned by the heterogeneous polarizable environment of the protein

In photosynthesis, special antenna proteins that contain multiple light-absorbing molecules (chromophores) are able to capture sunlight and transfer the excitation energy to reaction centers with almost 100% quantum efficiencies. The critical role of the protein scaffold in holding the appropriate arrangement of the chromophores is well established and can be intuitively understood given the need to keep optimal dipole-dipole interactions between the energy-transferring chromophores, as described by Fo?rster theory more than 60 years ago. However, the question whether the protein structure can also play an active role by tuning such dipole-dipole interactions has not been answered so far, its effect being rather crudely described by simple screening factors related to the refractive index properties of the system. Here, we present a combined quantum chemical/molecular mechanical approach to compute electronic couplings that accounts for the heterogeneous dielectric nature of the protein-solvent environment in atomic detail. We apply the method to study the effect of dielectric heterogeneity in the energy migration properties of the PE545 principal light-harvesting antenna of the cryptomonad Rhodomonas CS24. We find that dielectric heterogeneity can profoundly tune by a factor up to ～4 the energy migration rates between chromophore sites compared to the average continuum dielectric view that has historically been assumed. Our results indicate that engineering of the local dielectric environment can potentially be used to optimize artificial light-harvesting antenna systems.     

Development of a capillary electrophoresis method for the assay of ramipril and its impurities: an issue of cis-trans isomerization

The development of a rapid and selective capillary electrophoresis method for the quantitation of ramipril and its eight main impurities in pharmaceutical dosage form is described. Ramipril and three of its impurities contain a proline-similar moiety which causes in solution the presence of interconverting cis-trans isomers with respect to the amide bond. The interplay between electrophoretic migration and isomerization may yield the presence of an undesired interconversion zone between the two isomer peaks in the electropherogram, depending on the experimental conditions. Different capillary electrophoresis operative modes and pseudostationary phases were evaluated, both in normal and reverse polarity, in order to find the essential analytical parameters which could make it possible to overcome this issue and thus accurately quantify the analytes. The best results were obtained by using microemulsion electrokinetic chromatography in reverse polarity, where all the compounds which undergo cis-trans interconversion migrate as a single narrow peak. Experimental design led to identification of the following optimised conditions: background electrolyte, microemulsion made by 88.95% of 90 mM phosphate pH 2.5, 1.05% of n-heptane and 10.00% of SDS/n-butanol in 1:2 ratio; voltage, -26 kV; temperature, 17°C. Applying these conditions, the baseline separation of the analytes was obtained in about 10 min. Validation of the method following ICH guidelines was carried out and the procedure was applied to a real sample of ramipril tablets.     

Computational experience with numerical methods for nonnegative least‐squares problems

We discuss the solution of large‐scale box‐constrained linear least‐squares problems by two recent affine‐scaling methods: a cyclic Barzilai–Borwein strategy and an Inexact Newton‐like method where a preconditioning technique allows for an efficient computation of the steps. A robust globally and fast locally convergent method based on the combination of the two procedures is presented along with extensive numerical results. Copyright © 2010 John Wiley & Sons, Ltd.     

Stability of radical-functionalized gold surfaces by self-assembly and on-surface chemistry

We have investigated the radical functionalization of gold surfaces with a derivative of the perchlorotriphenylmethyl (PTM) radical using two methods: by chemisorption from the radical solution and by on-surface chemical derivation from a precursor. We have investigated the obtained self-assembled monolayers by photon-energy dependent X-ray photoelectron spectroscopy. Our results show that the molecules were successfully anchored on the surfaces. We have used a robust method that can be applied to a variety of materials to assess the stability of the functionalized interface. The monolayers are characterized by air and X-ray beam stability unprecedented for films of organic radicals. Over very long X-ray beam exposure we observed a dynamic nature of the radical–Au complex. The results clearly indicate that (mono)layers of PTM radical derivatives have the necessary stability to withstand device applications.

We have investigated the radical functionalization of gold with a derivative of the perchlorotriphenylmethyl radical using two methods: by chemisorption from the radical solution and by on surface chemical derivation from a precursor.     

Quasi-Newton methods for constrained nonlinear systems: complexity analysis and applications

We address the solution of constrained nonlinear systems by new linesearch quasi-Newton methods. These methods are based on a proper use of the projection map onto the convex constraint set and on a derivative-free and nonmonotone linesearch strategy. The convergence properties of the proposed methods are presented along with a worst-case iteration complexity bound. Several implementations of the proposed scheme are discussed and validated on bound-constrained problems including gas distribution network models. The results reported show that the new methods are very efficient and competitive with an existing affine-scaling procedure.     

A reduced Newton method for constrained linear least-squares problems

We propose an iterative method that solves constrained linear least-squares problems by formulating them as nonlinear systems of equations and applying the Newton scheme. The method reduces the size of the linear system to be solved at each iteration by considering only a subset of the unknown variables. Hence the linear system can be solved more efficiently. We prove that the method is locally quadratic convergent. Applications to image deblurring problems show that our method gives better restored images than those obtained by projecting or scaling the solution into the dynamic range.