Additive NMR chemical shift parameters for deshielded methine protons

The use of additive parameters for the prediction of NMR chemical shifts is widely practised. However, no correlations are available for highly deshielded methine protons. In this work, methine chemical shifts have been studied using both multiple linear regression analysis and Simplex function minimization in an effort to determine under what limiting circumstances the additivity of shift parameters can be expected to apply. As expected, it was not possible to explain satisfactorily all methine shifts with a single set of substituent parameters. However, if only the deshielded cases were considered (H—CXYZ, where at least two of the three groups X, Y, and Z are electron-withdrawing), a much better set of parameters could be determined. Using a data set of 440 of these deshielded methine shifts, involving 31 different substituents, a standard error of estimate of 0.20 ppm is found for protons spread between 3.0 and 7.5 ppm.     

A new environment-sensitive fluorescent amino acid for Fmoc-based solid phase peptide synthesis

A new 4-(N,N-dimethylamino) phthalimide-based environment-sensitive fluorescent building block for solid phase peptide synthesis, has been synthesized and incorporated into peptides. Peptides incorporating this residue show great potential for biological applications in sensing protein/protein interactions.     

General method for the synthesis of caged phosphopeptides: tools for the exploration of signal transduction pathways

[reaction: see text] An interassembly approach for the synthesis of peptides containing 1-(2-nitrophenyl)ethyl-caged phosphoserine, -threonine, and -tyrosine has been developed. Photochemical uncaging of these peptides releases the 2-nitrophenylethyl protecting group to afford the corresponding phosphopeptide. The peptides described herein are based on phosphorylation sites of kinases involved in cell movement or cell cycle regulation and demonstrate the versatility of the method and compatibility with the synthesis of polypeptides, including a variety of encoded amino acids.     

Polypyrrole Nanospheres with Magnetic and Cell‐Targeting Capabilities

The preparation of polypyrrole/Fe₃O₄ nanospheres by a facile mini‐emulsion polymerization method is investigated using poly(ethylene glycol), poly(ethylene oxide), poly(vinyl alcohol), and hyaluronic acid as surfactants. Hyaluronic acid is deemed the most suitable surfactant since it results in well‐dispersed nanospheres of 80–100 nm, and offers the advantages of biocompatibility, cell adhesive property, and the availability of functional groups for attachment of other molecules. These polypyrrole/Fe₃O₄ nanospheres are magnetic and can be further functionalized with a cancer antibody, herceptin. Our results show that this combination of hyaluronic acid and herceptin results in high specific uptake of the nanospheres by cancer cells.

     

Electronic and vibrational transition moment directions in 7-dimethylamino-3-methyl-N-methyl-d3-4-phenylethynylcarbostyril

We report the synthesis and photophysical characterization of 7-dimethylamino-3-methyl-N-methyl-d(3)-4-phenylethynylcarbostyril, a chromophore of interest as a rotator in surface-mounted molecular rotors. Measurement of UV-vis absorption and fluorescence spectra, steady state fluorescence and excitation anisotropy, and linear dichroism in the IR and UV-vis permitted a determination of absolute vibrational and electronic transition moment directions in this previously unreported chromophore. The first singlet-singlet absorption and fluorescence are polarized perpendicular to the axle of the rotator. Density functional theory calculations of electronic excitation and vibrational frequencies gave results in very good agreement with those observed. Calculated IR transition moment directions showed rather poor agreement with experiment.     

PLUXter: rapid discovery of metal-organic framework structures using PCA and HCA of high throughput synchrotron powder diffraction data

This paper reports on a systematic method--called PLUXter--developed for screening and data mining of large numbers of potential metal-organic framework compounds that have been synthesized then subsequently analyzed with high throughput synchrotron radiation X-ray powder diffraction. The first part of the method utilizes principal components analysis (PCA), which allows materials to be ranked in order of crystallinity so that undesirable amorphous materials may be identified and eliminated. The second part allows structural grouping within and between samples to be observed using hierarchical cluster analysis (HCA). Classification using a single linkage distance produced unsatisfactory clusters however the dendrogram's structural relationships were used to establish and guide the boundaries of groups. The resultant grouping identities allowed further structure-property studies to be undertaken on representative structures from the clusters, significantly reducing time and the use of resources.