The chemokine CXC ligand 8 (CXCL8)͞IL-8 and related agonists recruit and activate polymorphonuclear cells by binding the CXC chemokine receptor 1 (CXCR1) and CXCR2. Here we characterize the unique mode of action of a small-molecule inhibitor (Repertaxin) of CXCR1 and CXCR2. Structural and biochemical data are consistent with a noncompetitive allosteric mode of interaction between CXCR1 and Repertaxin, which, by locking CXCR1 in an inactive conformation, prevents signaling. Repertaxin is an effective inhibitor of polymorphonuclear cell recruitment in vivo and protects organs against reperfusion injury. Targeting the Repertaxin interaction site of CXCR1 represents a general strategy to modulate the activity of chemoattractant receptors. L eukocyte trafficking into tissue sites of inflammation is directed by chemokines. Chemokines are grouped into four families based on a cysteine motif in the amino terminus of the protein (1, 2). Human CXC ligand 8 (CXCL8)͞IL-8 and related molecules are polymorphonuclear cells (PMN) chemoattractants. Two high-affinity human CXCL8 receptors are known, CXC chemokine receptor 1 (CXCR1) and CXC chemokine receptor 2 (CXCR2). Only one corresponding receptor has been identified in the mouse, and this is recognized by ligands that act as neutrophil attractant, although a mouse orthologue of CXCL8 has not been identified. By recruiting and activating PMN, CXCL8 and related rodent molecules have been implicated in a wide range of disease states characterized by PMN infiltration in organs, including reperfusion injury (RI) (3).G protein-coupled receptors (GPCR) are a prime target for the development of new strategies to control diverse pathologies (4-6). Antichemokine strategies include antibodies, N-terminal modified chemokines, and small-molecule antagonists (7-9). Here we describe a class of GPCR inhibitors that specifically block the inflammatory CXCL8 chemokine receptors CXCR1 and CXCR2 by means of an allosteric noncompetitive mode of interaction and protection against RI. Materials and MethodsReagents. Repertaxin (R)(Ϫ)-2-(4-isobutylphenyl)propionyl methansulfonamide) salified with L-lysine was dissolved in saline. Chemokines were from PeproTech (London). Chemicals, cell culture reagents, and protease inhibitors were from Sigma.Migration. Cell migration of human PMN and monocytes and rodent peritoneal PMN were evaluated in a 48-well microchemotaxis chamber with or without Repertaxin. Agonists (1 nM CXCL8, 10 nM N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), 10 nM CXCL1, 2.5 nM CCL2, 1 nM C5a, 5 nM rat and mouse CXCL1, and 2.5 nM rat and mouse CXCL2) were seeded in the lower compartment. The chemotaxis chamber was incubated for 45 min (human PMN), 1 h (rodent PMN), or 2 h (monocytes). L1.2 migration was evaluated by using 5-m pore-size Transwell filters (Costar) (10). Mutation Analysis of CXCR1 and Signaling. The human CXCR1 ORF was PCR amplified from a CXCR1͞pCEP4 plasmid (kindly provided by P. M. Murphy, National Institutes of Health, Bethesda). Receptor mutants and chimeric re...

Bimetallic silver-gold clusters offer an excellent opportunity to study changes in metallic versus ''ionic'' properties involving charge transfer as a function of the size and the composition, particularly when compared to pure silver and gold clusters. We have determined structures, ionization potentials, and vertical detachment energies for neutral and charged bimetallic Ag m Au n ͓3р(mϩn)р5͔ clusters. Calculated VDE values compare well with available experimental data. In the stable structures of these clusters Au atoms assume positions which favor the charge transfer from Ag atoms. Heteronuclear bonding is usually preferred to homonuclear bonding in clusters with equal numbers of hetero atoms. In fact, stable structures of neutral Ag 2 Au 2 , Ag 3 Au 3 , and Ag 4 Au 4 clusters are characterized by the maximum number of hetero bonds and peripheral positions of Au atoms. Bimetallic tetramer as well as hexamer are planar and have common structural properties with corresponding one-component systems, while Ag 4 Au 4 and Ag 8 have 3D forms in contrast to Au 8 which assumes planar structure. At the density functional level of theory we have shown that this is due to participation of d electrons in bonding of pure Au n clusters while s electrons dominate bonding in pure Ag m as well as in bimetallic clusters. In fact, Au n clusters remain planar for larger sizes than Ag m and Ag n Au n clusters. Segregation between two components in bimetallic systems is not favorable, as shown in the example of Ag 5 Au 5 cluster. We have found that the structures of bimetallic clusters with 20 atoms Ag 10 Au 10 and Ag 12 Au 8 are characterized by negatively charged Au subunits embedded in Ag environment. In the latter case, the shape of Au 8 is related to a pentagonal bipyramid capped by one atom and contains three exposed negatively charged Au atoms. They might be suitable for activating reactions relevant to catalysis. According to our findings the charge transfer in bimetallic clusters is responsible for formation of negatively charged gold subunits which are expected to be reactive, a situation similar to that of gold clusters supported on metal oxides.

The reaction of Fe 2 (S 2 C 2 H 4)(CO) 6 with cis-Ph 2 PCH=CHPPh 2 (dppv) yields Fe 2 (S 2 C 2 H 4) (CO) 4 (dppv), 1(CO) 4 , wherein the dppv ligand is chelated to a single iron center. NMR analysis indicates that in 1(CO) 4 , the dppv ligand spans axial and basal coordination sites. In addition to the axial-basal isomer, the 1,3-propanedithiolate and azadithiolate derivatives exist as dibasal isomers. Density functional theory (DFT) calculations indicate that the axial-basal isomer is destabilized by nonbonding interactions between the dppv and the central NH or CH 2 of the larger dithiolates. The Fe(CO) 3 subunit in 1(CO) 4 undergoes substitution with PMe 3 and cyanide to afford 1(CO) 3 (PMe 3) and (Et 4 N)[1(CN)(CO) 3 ], respectively. Kinetic studies show that 1(CO) 4 reacts faster with donor ligands than does its parent Fe 2 (S 2 C 2 H 4)(CO) 6. The rate of reaction of 1(CO) 4 with PMe 3 was first order in each reactant, k = 3.1 × 10 − 4 M −1 s −1. The activation parameters for this substitution reaction, ΔH ‡ = 5.8(5) kcal/mol and ΔS ‡ = −48(2) cal/deg•mol, indicate an associative pathway. DFT calculations suggest that, relative to Fe 2 (S 2 C 2 H 4)(CO) 6 , the enhanced electrophilicity of 1(CO) 4 arises from the stabilization of a "rotated" transition state, which is favored by the unsymmetrically disposed donor ligands. Oxidation of MeCN solutions of 1(CO) 3 (PMe 3) with Cp 2 FePF 6 yielded [Fe 2 (S 2 C 2 H 4)(μ-CO)(CO) 2 (dppv)(PMe 3)(NCMe)](PF 6) 2. Reaction of this compound with PMe 3 yielded [Fe 2 (S 2 C 2 H 4)(μ-CO)(CO)(dppv)(PMe 3) 2 (NCMe)](PF 6) 2 .

The one-electron oxidations of a series of diiron(I) dithiolato carbonyls were examined to evaluate the factors that affect the oxidation state assignments, structures, and reactivity of these lowmolecular weight models for the H ox state of the [FeFe]-hydrogenases. The propanedithiolates Fe 2 (S 2 C 3 H 6 )(CO) 3 (L)(dppv) (L = CO, PMe 3 , Pi-Pr 3 ) oxidize at potentials ~180 mV milder than the related ethanedithiolates (Angew. Chem. Int. Ed. 2007, 46, 6152). The steric clash between the central methylene of the propanedithiolate and the phosphine favors the rotated structure, which forms upon oxidation. EPR spectra for the mixed-valence cations indicate that the unpaired electron is localized on the Fe(CO)(dppv) center in both [Fe 2 (S 2 C 3 H 6 )(CO) 4 (dppv)]BF 4 and [Fe 2 (S 2 C 3 H 6 ) (CO) 3 (PMe 3 )(dppv)]BF 4 , as seen previously for the ethanedithiolate [Fe 2 (S 2 C 2 H 4 )(CO) 3 (PMe 3 ) (dppv)]BF 4 . For [Fe 2 (S 2 C n H 2n )(CO) 3 (Pi-Pr 3 )(dppv)]BF 4 , however, the spin is localized on the Fe (CO) 2 (Pi-Pr 3 ) center, although the Fe(CO)(dppv) site is rotated in the crystalline state. IR and EPR spectra, as well as redox potentials and DFT-calculations, suggest, however, that the Fe(CO) 2 (PiPr 3 ) site is rotated in solution, driven by steric factors. Analysis of the DFT-computed partial atomic charges for the mixed-valence species shows that the Fe atom featuring a vacant apical coordination position is an electrophilic Fe(I) center. One-electron oxidation of [Fe 2 (S 2 C 2 H 4 )(CN) (CO) 3 (dppv)] − resulted in 2e oxidation of 0.5 equiv to give the μ-cyano derivative [Fe I 2 (S 2 C 2 H 4 ) (CO) 3 (dppv)](μ-CN)[Fe II 2 (S 2 C 2 H 4 )(μ-CO)(CO) 2 (CN)(dppv)], which was characterized spectroscopically.