Crystallization and preliminary X-ray diffraction analysis of full-length spr1814, a response regulator ofStreptococcus pneumoniae, in complex with a phosphoryl analogue

Spr1814 ofStreptococcus pneumoniaeis a signal transduction response regulator belonging to the NarL/FixJ subfamily, which has a helix–turn–helix DNA-binding effector domain. To understand how the phosphorylation of the conserved aspartic acid residue induces conformational changes in spr1814 allowing binding to the target promoter, recombinant spr1814 expressed inEscherichia coliwas crystallized with the phosphoryl analogue beryllium fluoride BeF3−by the hanging-drop vapour-diffusion method. The crystals diffracted to 1.9 Å resolution and belonged to space groupP21, with unit-cell parametersa= 40.2,b= 114.5,c= 50.1 Å, β = 92.1°. Structure determination by the SAD method using the bromine derivative 5-amino-2,4,6-tribromoisophthalic acid (B3C) is under way.

The magic triangle goes MAD: experimental phasing with a bromine derivative

Experimental phasing is an essential technique for the solution of macromolecular structures. Since many heavy-atom ion soaks suffer from nonspecific binding, a novel class of compounds has been developed that combines heavy atoms with functional groups for binding to proteins. The phasing tool 5-amino-2,4,6-tribromoisophthalic acid (B3C) contains three functional groups (two carboxylate groups and one amino group) that interact with proteinsviahydrogen bonds. Three Br atoms suitable for anomalous dispersion phasing are arranged in an equilateral triangle and are thus readily identified in the heavy-atom substructure. B3C was incorporated into proteinase K and a multiwavelength anomalous dispersion (MAD) experiment at the Br Kedge was successfully carried out. Radiation damage to the bromine–carbon bond was investigated. A comparison with the phasing tool I3C that contains three I atoms for single-wavelength anomalous dispersion (SAD) phasing was also carried out.

Designing Adsorption Centres for Biological Active Molecules on a Silica Surface

The chemical interaction between the surface of hydroxylated or aminated silicas and β-cyclodextrin, mono-tosyl-β-cyclodextrin and the bromine derivative of heptakis-[6- O-( p-tosyl-β-cyclodextrin)] has been investigated using IR spectroscopy, thermogravimetric analysis with programmed heating, pH titration, weight adsorption method, elemental analysis and quantitative chemical analysis of the surface compounds. The optimum conditions for chemical grafting of β-cyclodextrins onto the silica surface were established. The formation of supramolecular structures, viz. inclusion complexes between immobilized β-cyclodextrin and the hormone of pineal gland (melatonin), on the surface of highly dispersed silicas of 1:1 composition was demonstrated.

Note: Synthesis of the Dinuclear Halogeno-Bridged Complexes [Re2(μ-X)2(CO)6(CH3CN)2], (X = Cl, Br)

Complexes [Re2(μ-X)2(CO)6(NCCH3)2] (X = Cl, Br) have been easily prepared in high yield by refluxing of fac- [ReX(CO)3(NCCH3)2] in toluene. The crystal and molecular structure of the bromine derivative have been determined by X-ray analysis. The molecule consists of two fac-Re(CO)3 fragments bridged by two bromine atoms. The acetonitrile molecules reside above and below the Re2Br2 plane.

Secondary Bonding Interactions in Some Halopyridinium and Dihalopyridinium Halides

The packing motifs of 2-and 3-chloropyridinium chloride can be interpreted in terms of classical hydrogen bonds N+-H···Cl- and non-classical C-H···Cl-" interactions, with halo-gen-halogen contacts playing a subordinate role. In the corresponding bromine derivatives, Br···Br interactions are much more important. Of the dihalo derivatives, 3,5-dichloropyridinium chloride crystallises with classical linear hydrogen bonds of the form N+-H···Cl- , but its chlorine-chlorine interactions are at best weak; the corresponding bromine derivative displays aggregates of bromine atoms and three-centre hydrogen bonds N+-H (···Br-)2 .