Trimethylsilylethynyl ketones as surrogates for ethynyl ketones in the double Michael reaction

Trimethylsilylethynyl ketones can be desilylated in the presence of a tethered carbon diacid and induced to undergo a double Michael reaction in situ. The trimethylsilylethynyl ketones can serve as surrogates of ethynyl ketones that are difficult to prepare or isolate.     

The bicyclic n,n'-diacylaminal: a new motif for molecular self-assembly

A cage-shaped N,N'-diacylaminal crystallizes from some aromatic solvents as "supramolecular chair cyclohexanes", squat cylindrical hexamers with approximate D3d symmetry containing two arene molecules, and from other aromatic and nonaromatic solvents as infinite tapes. A homologous diacylaminal crystallizes only as an infinite tape. The hexamers represent the first examples of cyclic hexamers held together by %@mt;sys@%%@bold@%R%@rsf@%%@sx@%2%@be@%2%@sxx@%%@fn;(;vis;full;auto@%8%@fnx;);vis;full@%-type%@mx@% hydrogen bonds in which the hydrogen-bonded atoms are not coplanar. The diacylaminal represents a new supramolecular synthon, one perhaps more suited to the design of three-dimensional architectures.     

Surface chemistry of silicon nanoclusters

We employ density functional and quantum Monte Carlo calculations to show that significant changes occur in the gap of fully hydrogenated nanoclusters when the surface contains passivants other than hydrogen, in particular atomic oxygen. In the case of oxygen, the gap reduction computed as a function of the nanocluster size provides a consistent interpretation of several recent experiments. Furthermore, we predict that other double bonded groups also significantly affect the optical gap, while single bonded groups have a minimal influence.     

Optical properties of passivated silicon nanoclusters: the role of synthesis

The effect of preparation conditions on the structural and optical properties of silicon nanoparticles is investigated. Nanoscale reconstructions, unique to curved nanosurfaces, are presented for silicon nanocrystals and shown to have lower energy and larger optical gaps than bulk-derived structures. We find that high-temperature synthesis processes can produce metastable noncrystalline nanostructures with different core structures than bulk-derived crystalline clusters. The type of core structure that forms from a given synthesis process may depend on the passivation mechanism and time scale. The effect of oxygen on the optical of different types of silicon structures is calculated. In contrast to the behavior of bulklike nanostructures, for noncrystalline and reconstructed crystalline structures surface oxygen atoms do not decrease the gap. In some cases, the presence of oxygen atoms at the nanocluster surface can significantly increase the optical absorption gap, due to decreased angular distortion of the silicon bonds. The relationship between strain and the optical gap in silicon nanoclusters is discussed.     

A new synthetic approach to the polycyclic polyprenylated acylphloroglucinols

[reaction: see text] The three-carbon alpha,alpha'-annulation of a sterically hindered cyclic beta-keto ester can be achieved by alkynylation with 3,3-diethoxypropyne, syn reduction of the alkyne with Co(2)(CO)(8) and Et(3)SiH, and an intramolecular aldol reaction. The method is potentially useful for the synthesis of nemorosone, hyperforin, and other polycyclic polyprenylated acylphloroglucinols.     

In situ device for salinity measurements (chloride detection) of ocean surface

Microbend sodium chloride sensors based on polymer swelling are the latest approach to fiberoptic sodium chloride sensors. We have designed, constructed, and tested a compact microbend fiberoptic sodium chloride sensor that utilizes microbend and polymer swelling effects through the use of modified polymer beads. The design of this sensor is an improvement over previously reported microbend sensors. This sodium chloride sensor has shown feasibility as a practical, stable, inexpensive device with excellent performance and most of the desirable sensor properties including reversibility. Further optimization of the sensor is possible for the various applications we envision.     

A simple method for controlled immobilization of proteins on modified SAMs

This paper describes a method for modifying self-assembled monolayers (SAMs) with the nitrilotriacetic acid (NTA) group for subsequent immobilization of hexahistidine tagged proteins. The method has two important improvements over previous ones; firstly it avoids the need to carry out a complex synthesis of the chelator alkanethiols prior to deposition because the reactions are performed in situ on a preassembled SAM. This in situ approach also avoids phase segregation of alkanethiols with different functional groups, especially bulky ones such as NTA and tri(ethylene glycol), since a simple SAM is employed as the starting material. The approach reported here uses mercaptohexadecanoic acid to form a well-ordered homogeneous carboxyl-terminated SAM on a gold surface. The carboxyl group was then condensed with an NTA derivative containing an amino group to form a peptide bond. The product is a surface that, after chelating Ni(2+) ions, binds histidine tagged proteins. The loading of NTA groups can be controlled by choice of reaction conditions thereby removing the need for a second alkanethiol to dilute the surface density of chelator groups and prevent molecular crowding. Both factors allow rapid attainment of optimal protein loading. Fluorescence imaging demonstrated that (His)(6) enhanced green fluorescent protein was reversibly immobilized and importantly, was functional on the surface. Furthermore, data from surface plasmon resonance, cyclic voltammetry and fluorescence spectrometry provided additional information on the specific and reversible immobilization of (His)(6) proteins on the NTA-modified SAM surface.     

Zero energy solutions of the Dirac equation in an N-pseudoparticle field

Zero-energy solutions of the Dirac equation are found for a fermion in the field of a Euclidean Yang-Mills pseudoparticle configuration with Pontryagin number N. In this field we find N non-singular normalizable zero-energy solutions.     

Rheological relationships for concentrated polymer solutions

Using a network model for concentrated polymer solutions, an expression is calculated for the stress tensor, defined in terms of the moments of the distribution function and the kinetic equation for these moments. In the limiting case the results obtained coincide with known results for normal Newtonian liquids.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 126–132, March–April, 1976.