Synthesis, structural characterization and biological activity of helicin thiosemicarbazone monohydrate and a copper(II) complex of salicylaldehyde thiosemicarbazone

Single Crystal Diffraction Studies of Structure I, II and H Hydrates: Structure, Cage Occupancy and Composition

Esterases form a diverse class of enzymes of largely unknown physiological role. Because many drugs and pesticides carry ester functions, the hydrolysis of such compounds forms at least one potential biological function. Carboxylesterases catalyze the hydrolysis of short chain aliphatic and aromatic carboxylic ester compounds. Esterases, D-alanyl-D-alanine-peptidases (DD-peptidases) and beta-lactamases can be grouped into two distinct classes of hydrolases with different folds and topologically unrelated catalytic residues, the one class comprising of esterases, the other one of beta-lactamases and DD-peptidases. The chemical reactivities of esters and beta-lactams towards hydrolysis are quite similar, which raises the question of which factors prevent esterases from displaying beta-lactamase activity and vice versa. Here we describe the crystal structure of EstB, an esterase isolated from Burkholderia gladioli. It shows the protein to belong to a novel class of esterases with homology to Penicillin binding proteins, notably DD-peptidase and class C beta-lactamases. Site-directed mutagenesis and the crystal structure of the complex with diisopropyl-fluorophosphate suggest Ser75 within the "beta-lactamase" Ser-x-x-Lys motif to act as catalytic nucleophile. Despite its structural homology to beta-lactamases, EstB shows no beta-lactamase activity. Although the nature and arrangement of active-site residues is very similar between EstB and homologous beta-lactamases, there are considerable differences in the shape of the active site tunnel. Modeling studies suggest steric factors to account for the enzyme's selectivity for ester hydrolysis versus beta-lactam cleavage.

EstB from Burkholderia gladioli: a novel esterase with a beta-lactamase fold reveals steric factors to discriminate between esterolytic and beta-lactam cleaving activity

The reaction of the Er3+ ion with polycarboxylate ligands in gel media leads to coordination polymers exhibiting various structural types and dimensionalities. Five Er3+/1,4-benzenedicarboxylate-based coordination polymers have been obtained in such conditions. Four out of the five are new. Their crystal structures are reported and compared herein. Compound 1, namely, Er2Ter3(H2O)6, where H2Ter symbolizes the terephthalic acid, crystallizes in the space group P1 (No. 2) with a = 7.8373(10) A, b = 9.5854(2) A, c = 10.6931(2) A, α = 68.7770(8)°, β = 70.8710(8)°, and γ = 75.3330(12)°. It has already been reported elsewhere. The last four compounds are new. Compound 2, namely, Er2Ter3(H2O)6·2H2O, crystallizes in the space group P121/a1 (No. 14) with a = 6.7429(2) A, b = 22.4913(7) A, c = 9.6575(3) A, and β = 91.6400(18)°. Compound 3, namely Er2Ter3(H2O)8·2H2O crystallizes in the space group P1 (No. 2) with a = 7.5391(2) A, b = 10.0533(3) A, c = 10.4578(3) A, α = 87.7870(10)°, β = 82.5510(11)°, and γ = 86.28...

Synthesis, crystal structure, and porosity estimation of hydrated erbium terephthalate coordination polymers.

A New Method for the Synthesis of Aromatic Sulfurpentafluorides and Studies of the Stability of the Sulfurpentafluoride Group in Common Synthetic Transformations

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SHELXL-92 a new least-squares refinement program for use with single-crystal diffraction data

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SHELXL-92 a new least-squares refinement program for use with single-crystal diffraction data