Fluorescence-dip infrared spectroscopy and predissociation dynamics of OH A 2Sigma+ (v = 4) radicals

Fluorescence-dip infrared spectroscopy, an UV-IR double-resonance technique, is employed to characterize the line positions, linewidths, and corresponding lifetimes of highly predissociative rovibrational levels of the excited A (2)Sigma(+) electronic state of the OH radical. Various lines of the 4 <--2 overtone transition in the excited A (2)Sigma(+) state are observed, from which the rotational, centrifugal distortion, and spin-rotation constants for the A (2)Sigma(+) (v = 4) state are determined, along with the vibrational frequency for the overtone transition. Homogeneous linewidths of 0.23-0.31 cm(-1) full width at half maximum are extracted from the line profiles, demonstrating that the N = 0 to 7 rotational levels of the OH A (2)Sigma(+) (v = 4) state undergo rapid predissociation with lifetimes of < or =23 ps. The experimental linewidths are in near quantitative agreement with first-principles theoretical predictions.     

Synthesis of tricyclic phospholene oxides by cycloaddition of phosphorus halides with heterocyclic analogs of 1-vinyl-3,4-dihydronaphthalenes

Replacement of C-4 with a hetero substituent (NR,O,S) in the 1-vinyl-3,4-dihydronaphthalene system has provided a new type of diene for participation in the McCormack cycloaddition reaction with P(III) halides. The tricyclic phospholene oxides so obtained are the first to bear an additional heteroatom in the ring system. 1,2-Dihydro-7-methoxy-1-(p-toluenesulfonyl)-4-vinylquinoline is a stable solid that reacts with methylphosphonous dichloride to give, after hydrolysis of the cycloadduct, the 1,2,4,5-tetrahydro-1H-phospholo-[2,3-c]quinoline ring system. The dihydroquinoline moiety was aromatized by detosylation with potassium t-butoxide. The tendency of 4-vinyl-2H-benzopyran to dimerize was a serious complication in its use, and the cycloaddition with methylphosphonous dichloride proceeded only in low yield. The product, a 2,3,3a,4-tetra-hydrobenzo[3,2-d]pyran derivative, was a stable, easily purified and characterized substance. 4-Vinyl-2H-benzo[b]thiopyran was more stable than the pyran, but the phospholo derivative from reaction with methylphosphonous dichloride was more difficult to purify. All products were characterized by ¹³C-nmr spectroscopy.     

Quality assurance in research laboratories

During the last decade, it has become increasingly important that researchers demonstrate that research is conducted to the highest standards. The implementation of quality assurance for research laboratories will enable all fields of research and development to be judged impartially. There are no specific standards for research laboratories but where possible, existing standards can be adapted. This review is structured around two approaches. The first considers research to be a logical extension of testing, and it is assumed that testing standards can be applied methodically to each step in a research project. The second advocates a flexible approach, with research-specific criteria for assessing quality. The important papers published on this topic have been reviewed. The conclusions are that the general quality management approach, encompassed by the ISO 9000 series of standards with the emphasis on customer satisfaction and ‘fitness for purpose’, is suitable for implementing quality assurance in research laboratories.     

Bis[bis­(3‐phenyl­pyrazol‐1‐yl)­(pyrazol‐1‐yl)­methane]­copper(II) bis­(per­chlor­ate) acetonitrile disolvate

The title copper(II) complex, [Cu(C₂₂H₁₈N₆)₂](ClO₄)₂·2C₂H₃N, comprises two neutral substituted tris­(pyrazol‐1‐yl)­methane ligands bonded to a central Cu^II ion, which is positioned on a crystallographic inversion center. Six Cu—N bonds are arranged in a distorted octa­hedral fashion. The unsubstituted pyrazole rings on each ligand are oriented trans with respect to each other, inter­digitated with the two 3‐phenyl­pyrazole rings of the other ligand.     

Chimeric (alpha/beta + alpha)-peptide ligands for the BH3-recognition cleft of Bcl-XL: critical role of the molecular scaffold in protein surface recognition

Molecules that bind to specific surface sites on proteins are of great interest from both fundamental and practical perspectives. We are exploring a ligand development strategy that is based on oligomers with discrete folding propensities ("foldamers"); we target a specific cleft on the cancer-associated protein Bcl-xL because this system is well characterized structurally. In vivo, this cleft binds to alpha-helical segments (BH3 domains) of other proteins. We evaluated several types of helical foldamer, built entirely from beta-amino acid residues or from mixtures of alpha- and beta-amino acid residues, and ultimately identified foldamers in the latter class that bind very tightly to Bcl-xL. Our results suggest that combining different types of foldamer backbones will be an effective and general strategy for creating high-affinity and specific ligands for protein surface sites.     

A mass spectrometric investigation of non-covalent interactions between ruthenium complexes and DNA

Electrospray ionisation mass spectrometry was used to investigate reactions between six ruthenium compounds and three different non self-complementary duplex oligonucleotides containing 16 base pairs. Each of the compounds studied formed non-covalent complexes containing between one and five ruthenium molecules bound to DNA. Competition experiments involving duplex 16mers and pairs of ruthenium compounds were used to determine the order of relative binding affinities of the metal compounds. Other competition experiments involving ruthenium compounds, and the organic DNA binding agents daunomycin and distamycin, provided information about the sites and modes of DNA binding of the ruthenium compounds.     

Synthesis of Unsubstituted and 4,4′-Substituted Oligobipyridines as Ligand Strands for Helicate Self-Assembly

A general strategy for the synthesis of oligobipyridine ligands 2 – 5 containing from two to five 2,2′-bipyridine subunits, for helical metal complexes is described (sec Scheme). Both the unsubstituted parent strands ( a series) as well as their derivatives bearing fester or amide functions in the 4,4′-positions of the bipyridine moieties ( b – d series) have been obtained.     

Error estimates in the determination of rigid body displacements in protein crystals

We report the estimation of random errors in the refinement of the rigid body displacements of the -helices of the enzyme 6-phosphogluconate dehydrogenase. Least-squares refinement of the TLS parameters of the helices has been carried out using X-ray reflection data of 2.1 Å resolution, resulting in anR-factor of 19.5%. Standard deviations were estimated from the normal matrix. The results show that the translational mean-square displacements of nearly all the helices are significant at this resolution. However the libration parameters are only significant when the helices have at least four turns. Screw-rotation tensor values cannot be determined at this resolution.     

Relaxed chromatic numbers of graphs

Given any family of graphsP, theP chromatic number _p (G) of a graphG is the smallest number of classes into whichV(G) can be partitioned such that each class induces a subgraph inP. We study this for hereditary familiesP of two broad types: the graphs containing no subgraph of a fixed graphH, and the graphs that are disjoint unions of subgraphs ofH. We generalize results on ordinary chromatic number and we computeP chromatic number for special choices ofP on special classes of graphs.Research supported in part by ONR Grant N00014-85K0570 and by a grant from the University of Illinois Research Board.