Beta-Lactamases (EC 3.5.2.6, 'penicillinases') are a family of enzymes that protect bacteria against the lethal effects of cell-wall synthesis of penicillins, cephalosporins and related antibiotic agents, by hydrolysing the beta-lactam antibiotics to biologically inactive compounds. Their production can, therefore, greatly contribute to the clinical problem of antibiotic resistance. Three classes of beta-lactamases--A, B and C--have been identified on the basis of their amino-acid sequence; class B beta-lactamases are metalloenzymes, and are clearly distinct from members of class A and C beta-lactamases, which both contain an active-site serine residue involved in the formation of an acyl enzyme with beta-lactam substrates during catalysis. It has been predicted that class C beta-lactamases share common structural features with D,D-carboxypeptidases and class A beta-lactamases, and further, suggested that class A and class C beta-lactamases have the same evolutionary origin as other beta-lactam target enzymes. We report here the refined three-dimensional structure of the class C beta-lactamase from Citrobacter freundii at 2.0-A resolution and confirm the predicted structural similarity. The refined structure of the acyl-enzyme formed with the monobactam inhibitor aztreonam at 2.5-A resolution defines the enzyme's active site and, along with molecular modelling, indicates a mechanism for beta-lactam hydrolysis. This leads to the hypothesis that Tyr 150 functions as a general base during catalysis.

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The structure of triphenylphosphorus, PPh,, has been determined by single-crystal X-ray diffraction methods. A three-dimensional least-squares refinement has been carried out. The molecule has the expected pyramidal configuration about the phosphorus atom but, owing to the unequal rotation o f the benzene rings about the P-C bonds, possesses no symmetry. The mean P-C bond length is 1-828 '4; none of these three bonds differs significantly from the mean.The final values of R and R' were 0.101 and 0.018, respectively .

Effective clinical leadership is offered as the key to healthy, functional and supportive work environments for nurses and other health professionals. However, as a concept it lacks a standard definition and is poorly understood. This paper reports on an integrative review undertaken to uncover current understandings of defining attributes of contemporary clinical leadership in nursing. Data collection involved a search of relevant electronic databases for a 10-year period. Keywords for the search were 'clinical leadership' and 'nursing'. Ten research papers met the inclusion criteria for the integrative review. Analysis of these studies indicated clinical leadership attributes had a clinical focus, a follower/team focus or a personal qualities focus; attributes necessary to sustain supportive workplaces and build the capacity and resilience of nursing workforces. The small number of research-based studies yielded for the review indicates the need for further research in the area of clinical leadership.

~~It is shown that dimethyl 7-isopropyl-5, IO-dimethylheptalene-1,2-dicarboxylate (1) and dimethyl 5,6,8,10-tetramethylheptalene-l,2-dicarboxylate (2) can be resolved via the corresponding mono-acids and with the aid of optically active primary or secondary amines such as I-phenylethylamine or ephedrine into the (-)-(P)-and (+)-(M)-enantiomeres, respectively. Characteristic for the (P)-chirality of the heptalene n-skeleton with C, or pseudo-C, symmetry are two (-)-CE's at the long wavelength region (450-300 nm) followed by at least one intense (+)-CE at wavelengths about or below 300 nm. The absolute configuration of the heptalenes was correlated with the well-established absolute configuration of (+)-(R)-and (-)-(S)-l -phenylethanol.