Global expression analysis of CESA and CSL genes in Arabidopsis

We have used Affymetrix gene chips to measure the expression of 10 CESA and 29 CSL genes of Arabidopsis in different developmental stages or organs. These measurements reveal that many of the genes exhibit different levels of expression in the various organs. While several CESA genes are highly expressed in all the tissues examined, very few CSL genes approach such high levels of expression. This suggests that the CSL genes either encode enzymes for the synthesis of minor components of cell walls or are expressed only in specific cell types. The expression data also highlights the potential importance of the CESA genes for primary and secondary cell wall formation during different developmental stages and in the different organs examined.     

Light scattering by aggregates of magnetite nanoparticles in a magnetic field

The effect of variation of the scattered light intensity in a magnetic fluid with aggregates of magnetite particles several microns in size under the action of a magnetic field is studied. The effect relaxation times are determined when the magnetic field is turned on and off. This effect is found to be caused by the orientation of anisotropically magnetized aggregates. Experimental data are used to calculate the average anisotropy of the magnetic susceptibility of the aggregate and estimate its magnetic permeability.     

Electric dipole moments of magnetite colloidal particles in liquid dielectrics

The effects of alternating and pulsed fields on the electric birefringence in a colloided system of magnetite particles suspended in kerosene are studied. The permanent dipole moment is found to substantially influence the orientation of magnetite particles in alternating fields with frequencies of higher than 15 Hz. The mechanism for the generation of the permanent dipole moments in magnetite colloidal particles suspended in low-conductivity liquids is discussed.     

Polymerization of diacetylenes by hydrogen bond templated adlayer formation

Adlayers were formed on self-assembled monolayers (SAMs) formed by alkanethiols on gold. Base SAMs exposing amide functional groups at the SAM surface were formed with 12-mercaptododecanamide. Adlayers of diacetylene-containing monomers were then formed via amide hydrogen bonding in decalin and decalin/toluene mixtures. Grazing angle FTIR, contact angle measurements, and ellipsometry suggest that these adlayer films exhibit ordering and packing similar to that of SAMs on gold. Resonance Raman spectroscopy showed that these diacetylene adlayers could be readily polymerized by exposure to UV light.     

Chiral imides as potential chiroptical switches: synthesis and optical properties

A series of chiral aromatic imides and diimides were synthesized and their electrochemical, absorption, fluorescent, and chiroptical properties were examined for their potential application as molecular chiroptical switches. These compounds exhibit strong UV-vis absorptions, and can be electrochemically reduced to radical anions that absorb in the near infrared (NIR) region. Further reduction to the dianionic states results in new absorptions in the visible region. The changes in circular dichroism upon redox switching were apparent in the UV-vis region but were absent in the NIR region.     

A post-Hartree-Fock model of intermolecular interactions

Intermolecular interactions are of great importance in chemistry but are difficult to model accurately with computational methods. In particular, Hartree-Fock and standard density-functional approximations do not include the physics necessary to properly describe dispersion. These methods are sometimes corrected to account for dispersion by adding a pairwise C6R6 term, with C6 dispersion coefficients dependent on the atoms involved. We present a post-Hartree-Fock model in which C6 coefficients are generated by the instantaneous dipole moment of the exchange hole. This model relies on occupied orbitals only, and involves only one, universal, empirical parameter to limit the dispersion energy at small interatomic separations. The model is extensively tested on isotropic C6 coefficients of 178 intermolecular pairs. It is also applied to the calculation of the geometries and binding energies of 20 intermolecular complexes involving dispersion, dipole-induced dipole, dipole-dipole, and hydrogen-bonding interactions, with remarkably good results.     

Identification of inhibitors for UDP-galactopyranose mutase

The flavoenzyme uridine 5'-diphosphate (UDP)-galactopyranose mutase (UGM) plays a key role in the cell wall biosynthesis of many pathogens, including Mycobacterium tuberculosis. Using a synthetic fluorescent ligand, we screened 16 000 compounds in a fluorescence polarization assay. Effective inhibitors of UGM were identified.     

Asymmetric allylic alkylation of ketone enolates: an asymmetric Claisen surrogate

[reaction: see text] The combination of catalytic palladium(0) and Trost ligand provides an effective catalyst for the rearrangement of allyl beta-ketoesters. The mechanism of the transformation involves formation of pi-allyl palladium intermediates which undergo enantioselective attack by ketone enolates. Decarboxylation of beta-ketocarboxylates allows regiospecific generation of enolates under extremely mild conditions.     

Measurement of five dipolar couplings from a single 3D NMR multiplet applied to the study of RNA dynamics

A new three-dimensional NMR experiment is described that yields five scalar or dipolar couplings from a single cross-peak between three spins. The method is based on the E.COSY principle and is demonstrated for the H1'-C1'-C2' fragment of ribose sugars in a uniformly 13C-enriched 24-nucleotide RNA stem-loop structure, for which a complete set of couplings was obtained for all nonmodified nucleotides. The values of the isotropic J couplings and the 13C1' and 13C2' chemical shifts define the sugar pucker. Once the sugar pucker is known, the five dipolar couplings between C1'-H1', C2'-H2', H1'-H2', C1'-H2', and C2'-H1', together with C1'-C2', C3'-H3', and C4'-H4' available from standard experiments, can be used to derive the five unknowns that define the local alignment tensor, thereby simultaneously providing information on relative orientation and dynamics of the ribose units. Data indicate rather uniform alignment for all stem nucleotides in the 24-nt stem-loop structure, with only a modest reduction in order for the terminal basepair, but significantly increased mobility in part of the loop region. The method is applicable to proteins, nucleic acids, and carbohydrates, provided 13C enrichment is available.     

Microchannel wall coatings for protein separations by capillary and chip electrophoresis

The necessity for microchannel wall coatings in capillary and chip-based electrophoretic analysis of biomolecules is well understood. The regulation or elimination of EOF and the prevention of analyte adsorption is essential for the rapid, efficient separation of proteins and DNA within microchannels. Microchannel wall coatings and other wall modifications are especially critical for protein separations, both in fused-silica capillaries, and in glass or polymeric microfluidic devices. In this review, we present a discussion of recent advances in microchannel wall coatings of three major classes--covalently linked polymeric coatings, physically adsorbed polymeric coatings, and small molecule additives. We also briefly review modifications useful for polymeric microfluidic devices. Within each category of wall coatings, we discuss those used to eliminate EOF, to tune EOF, to prevent analyte adsorption, or to perform multiple functions. The knowledgeable application of the most promising recent developments in this area will allow for the separation of complex protein mixtures and for the development of novel microchannel wall modifications.