Ultraviolet resonance Raman spectroscopy of folded and unfolded states of an integral membrane protein

The vibrational structure of native anchoring tryptophan (Trp) and tyrosine residues in an integral membrane protein, bacterial outer membrane protein A (OmpA), have been investigated using UV resonance Raman (UVRR) spectroscopy for the first time. Spectra of native OmpA, a single-Trp mutant, and a Trp-less mutant were recorded in folded and unfolded states, and reveal significant changes in tryptophan structure and local environment. Salient alterations upon folding include loss of hydrogen-bonding character of indole N1H, evidenced by a shift in W17 frequency from 874 and 878 cm(-1), and growth in hydrophobicity of the local tryptophan environment, supported by increase in the ratio I1361/I1340. In addition to these site-specific changes in a single tryptophan residue, modification of the vibrational structure of the remaining native tryptophan and tyrosine amino acids is also evident. Finally, the UVRR data presented here indicate that the structures of OmpA folded in vesicle and folded in detergent may differ, and provide important foundations for ongoing studies of membrane protein folding.     

Synthesis of 3,5-difluorotyrosine-containing peptides: application in substrate profiling of protein tyrosine phosphatases

Fully protected 3,5-difluorotyrosine (F2Y), Fmoc-F2Y(tBu)-OH, is efficiently prepared by a chemoenzymatic process and incorporated into individual peptides and combinatorial peptide libraries. The F2Y-containing peptides display kinetic properties toward protein tyrosine phosphatases (PTPs) similar to their corresponding tyrosine-containing counterparts but are resistant to tyrosinase action. These properties make F2Y a useful tyrosine surrogate during peptide library screening for optimal PTP substrates.     

Cellular internalization and targeting of semiconductor quantum dots

Peptide-mediated internalization and organelle targeting of quantum dots.     

MULTIPLE CHROMOPHORE SPECIES IN PHYTOCHROME*,†,‡

Abstract— Buffered aqueous solutions of pure phytochrome, when irradiated at 730 nm, had a main absorption band at about 660 nm and a shoulder or secondary band at 580–600 nm. When irradiated at 660 nm, these absorption bands bleached and a pair of bands at 670 and 725–730 nm appeared. When 660 nm irradiated samples were placed in the dark the 730 nm absorption slowly bleached and the 670 nm absorption band shifted to 660 nm. The kinetics of the bleaching indicated that two populations of P_FR existed initially. These two populations decayed by first order kinetics with k's of 4.8 × 10^-4 sec^-1 and 3.1 × 10^--⁵ sec^-1at 25°. While the bleaching of P_FR was occumng, the appearance of the 660 nm and 580–600 nm absorption bands characteristic of P_R took place. The kinetics of the increase in the 580 and 660 nm absorption bands indicated that it was arising from two populations of reactants by two first order reactions with k's of 6.4 × 10^-4 sec^-1 and 3.1 × 10^-5sec^-1 at 25°. When the sodium chloride concentration of the solvent was changed the proportions of the kinetically different populations were altered. In some conditions, especially in the presence of air. reversible but non-reciprocal changes in the four absorption bands were observed. These effects were evident after the lapse of many hours in the dark. When native phytochrome was treated with sodium dodecyl sulfate all absorption bands but the 580–600 nm absorption band were bleached and photoreversibility was lost. When native phytochrome was treated with glutaraldehyde, the 730 nm absorption band was bleached but photoreversibility was retained. It was concluded that at least four species of chromophore exist in phytochrome with absorption maxima at 580, 660 , 670 and 730 nm. Each chromophore is capable of being bleached by appropriate irradiation or in the dark by chemical reactions rather than photochemical reactions. The reactions are probably coupled redox reactions between the 580–660 nm pair and the 670–730 pair of chromophores. Discrepancies observed in the reciprocity of the absorption changes in these paired bands are probably due to various degrees of uncoupling and secondarily to the redox potential of the solvent when such uncoupling occurs.     

Achieving flame retardancy and mechanical integrity via phosphites in bio-based resins

Bio-based flame retardant (FR) resins typically exhibit diminished mechanical properties compared with their petroleum-based counterparts. Recent experiments identified a promising FR phosphorus-bearing vanillin-based epoxy resin, EP2, that exhibited superior thermomechanical properties compared to that of petroleum-based diglycidyl ether of bisphenol A. However, the structure/property relationships of such phosphorus-containing bio-based resins are relatively under-explored and cannot be resolved via experiments alone. Here, molecular simulations are used to explore these relationships for a resin comprising EP2 cured with 4,4-diaminodiphenylmethane. The predicted thermomechanical properties are consistent with experimental observations, and critically, the structural analysis reveals the importance of the pendant phosphite group in the monomer as central to maintaining extensive hydrogen-bonding networks, giving rise to the excellent Young's modulus. This work provides the foundation for knowledge-based strategies to systematically improve the structure/property relationships in FR bio-based epoxy resins.     

Systematic Investigation of Tri- and Tetrametaphosphimates

A systematic investigation of tri- and tetrametaphosphimates based on single-crystals is reviewed and results of a conformation analysis of the cyclic six- and eight-membered P-N rings of the (PO₂NH)₃ ^3- and (PO₂NH)₄ ^4- ions are given.     

The assessment of π-π selective stationary phases for two-dimensional HPLC analysis of foods: Application to the analysis of coffee

Differences between alkyl, dipole-dipole, hydrogen bonding, and π-π selective surfaces represented by non-resonance and resonance π-stationary phases have been assessed for the separation of ‘Ristretto’ café espresso by employing 2DHPLC techniques with C18 phase selectivity detection. Geometric approach to factor analysis (GAFA) was used to measure the detected peaks (N), spreading angle (β), correlation, practical peak capacity (n_p) and percentage usage of the separations space, as an assessment of selectivity differences between regional quadrants of the two-dimensional separation plane. Although all tested systems were correlated to some degree to the C18 dimension, regional measurement of separation divergence revealed that performance of specific systems was better for certain sample components. The results illustrate that because of the complexity of the ‘real’ sample obtaining a truly orthogonal two-dimensional system for complex samples of natural origin may be practically impossible.