We present isolable examples of formal zinc hydride cations supported by N-heterocyclic carbene (NHC) donors, and investigate the dual electrophilic and nucleophilic (hydridic) character of the encapsulated [ZnH](+) units by computational methods and preliminary hydrosilylation catalysis.

Acidocin B, a bacteriocin produced by Lactobacillus acidophilus M46, was originally reported to be a linear peptide composed of 59 amino acid residues. However, its high sequence similarity to gassericin A, a circular bacteriocin from Lactobacillus gasseri LA39, suggested that acidocin B might be circular as well. Acidocin B was purified from culture supernatant by a series of hydrophobic interaction chromatographic steps. Its circular nature was ascertained by matrix-assisted laser desorption ionizationtime of flight (MALDI-TOF) mass spectrometry and tandem mass spectrometry (MS/MS) sequencing. The peptide sequence was found to consist of 58 amino acids with a molecular mass of 5,621.5 Da. The sequence of the acidocin B biosynthetic gene cluster was also determined and showed high nucleotide sequence similarity to that of gassericin A. The nuclear magnetic resonance (NMR) solution structure of acidocin B in sodium dodecyl sulfate micelles was elucidated, revealing that it is composed of four ␣-helices of similar length that are folded to form a compact, globular bundle with a central pore. This is a three-dimensional structure for a member of subgroup II circular bacteriocins, which are classified based on their isoelectric points of ϳ7 or lower.Comparison of acidocin B with carnocyclin A, a subgroup I circular bacteriocin with four ␣-helices and a pI of 10, revealed differences in the overall folding. The observed variations could be attributed to inherent diversity in their physical properties, which also required the use of different solvent systems for three-dimensional structural elucidation. C ircular bacteriocins are antimicrobial peptides that are ribosomally synthesized by bacteria and are posttranslationally modified to release a leader peptide and form a peptide bond between the N and C termini. These peptides exhibit antimicrobial activity against a broad range of Gram-positive bacteria, including Listeria spp. and Clostridium spp., which are common pathogens causing food-borne diseases (1). In addition, the circular nature of these bacteriocins imparts enhanced stability against proteolytic degradation and denaturation due to extreme temperature and pH conditions relative to linear forms (2). They thus serve as promising alternatives to traditional antimicrobial agents for food, medical, and industrial applications (3).A number of circular bacteriocins that are composed of 58 to 70 amino acid residues have been identified to date, including enterocin AS-48 (4), gassericin A (5), circularin A (6), butyrivibriocin AR10 (7), uberolysin (8), carnocyclin A (9), lactocyclicin Q (10), garvicin ML (11), leucocyclicin Q (12), amylocyclicin (13), and aureocyclicin 4185 (14). Another peptide exhibiting Nto C-terminal cyclization is subtilosin A (15). It is, however, considered a member of the sactipeptides, which represent a class of peptides containing cross-links between cysteine sulfurs and ␣-carbons (16). The structure and genetics of circular bacteriocins were reviewed previously (2). More recently, a re...

Phenol-soluble modulins (PSMs) are peptide virulence factors produced by staphylococci. These peptides contribute to the overall pathogenicity of these bacteria, eliciting multiple immune responses from host cells. Many of the α-type PSMs exhibit cytolytic properties and are able to lyse particular eukaryotic cells, including erythrocytes, neutrophils, and leukocytes. In addition, they also appear to contribute to the protection of the bacterial cell from the host immune response through biofilm formation and detachment. In this study, three of these peptide toxins, PSMs α1, α3, and β2, normally produced by Staphylococcus aureus, have been synthesized using solid-supported peptide synthesis (SPPS) (PSMα1 and PSMα3) or made by heterologous expression in Escherichia coli (PSMβ2). Their three-dimensional structures were elucidated using nuclear magnetic resonance spectroscopy. PSMα1 and PSMα3 each consist of a single amphipathic helix with a slight bend near the N- and C-termini, respectively. PSMβ2 contains three amphipathic helices, which fold to produce a "v-like" shape between α-helix 2 and α-helix 3, with α-helix 1 folded over such that it is perpendicular to α-helix 3. The availability of three-dimensional structures permits spatial analysis of features and residues proposed to control the biological activity of these peptide toxins.

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Mono- or dideprotonation at the N-H groups of the Noyori ketone hydrogenation catalyst trans-[RuH2((R)-BINAP)((R,R)-dpen)] (1a) yields trans-M[RuH2((R,R)-HNCH(Ph)CH(Ph)NH2)((R)-BINAP)], where M = K(+)(8-K) or Li(+) (8-Li), or trans-M2[RuH2((R,R)-HNCH(Ph)CH(Ph)NH)((R)-BINAP)], where M = Li(+) (8-M'2), which have unprecedented activity toward the hydrogenation of amide and imide carbonyls at low temperatures in THF-d8. Details of the origins of the enantioselection for the desymmetrization of meso-cyclic imides by hydrogenation with 8-K are also described herein.