Fe(CO)4 and related compounds as isolobal fragments

The M(CO)(4) fragment can be assigned to be isolobal with both CH(3)(+) and CH(2). In order to investigate this ambiguous isolobal assignment, we report calculations on compounds of the type M(CO)(4)L(n), where M is Fe (n = 0), Mn (n = -1), and Co (n = +1) and L is an η(2) ligand with a π bond, generally an alkene. The L's are varied in electron-withdrawing ability, and patterns in computed structural parameters are investigated. We report that the equatorial OC-M-CO angle is sensitive to the electron-withdrawing ability of the alkene just as the isolobal prediction suggests. Other structural parameters that vary monotonically with electron-withdrawing ability of the alkene are the "bending back" of the alkene, the metal-ligand bond distances, and carbon-oxygen bond distances. Changing the metal from neutral Fe to a negatively charged Mn or positively charged Co has the result of increasing and decreasing, respectively, the OC-M-CO angle. Several compounds of Ni(CO)(3)L are also investigated as a further example of the ability of the isolobal concept to yield chemically useful information.     

Third-Order Phase Transition: Random Matrices and Screened Coulomb Gas with Hard Walls

Journal of Statistical Physics - Consider the free energy of a d-dimensional gas in canonical equilibrium under pairwise repulsive interaction and global confinement, in presence of a volume...     

Calcium ions tune the zinc-sequestering properties and antimicrobial activity of human S100A12

Human S100A12 is a host-defense protein expressed and released by neutrophils that contributes to innate immunity. Apo S100A12 is a 21 kDa antiparallel homodimer that harbors two Ca(ii)-binding EF-hand domains per subunit and exhibits two His₃Asp motifs for chelating transition metal ions at the homodimer interface. In this work, we present results from metal-binding studies and microbiology assays designed to ascertain whether Ca(ii) ions modulate the Zn(ii)-binding properties of S100A12 and further evaluate the antimicrobial properties of this protein. Our metal-depletion studies reveal that Ca(ii) ions enhance the ability of S100A12 to sequester Zn(ii) from microbial growth media. We report that human S100A12 has antifungal activity against Candida albicans, C. krusei, C. glabrata and C. tropicalis, all of which cause human disease. This antifungal activity is Ca(ii)-dependent and requires the His₃Asp metal-binding sites. We expand upon prior studies of the antibacterial activity of S100A12 and report Ca(ii)-dependent and strain-selective behavior. S100A12 exhibits in vitro growth inhibitory activity against Listeria monocytogenes. In contrast, S100A12 has negligible effect on the growth of Escherichia coli K-12 and Pseudomonas aeruginosa PAO1. Loss of functional ZnuABC, a high-affinity Zn(ii) import system, increases the susceptibility of E. coli and P. aeruginosa to S100A12, indicating that S100A12 deprives these mutant strains of Zn(ii). To evaluate the Zn(ii)-binding sites of S100A12 in solution, we present studies using Co(ii) as a spectroscopic probe and chromophoric small-molecule chelators in Zn(ii) competition titrations. We confirm that S100A12 binds Zn(ii) with a 2 : 1 stoichiometry, and our data indicate sub-nanomolar affinity binding. Taken together, these data support a model whereby S100A12 uses Ca(ii) ions to tune its Zn(ii)-chelating properties and antimicrobial activity.     

Free Fermions and the Classical Compact Groups

There is a close connection between the ground state of non-interacting fermions in a box with classical (absorbing, reflecting, and periodic) boundary conditions and the eigenvalue statistics of the classical compact groups. The associated determinantal point processes can be extended in two natural directions: (i) we consider the full family of admissible quantum boundary conditions (i.e., self-adjoint extensions) for the Laplacian on a bounded interval, and the corresponding projection correlation kernels; (ii) we construct the grand canonical extensions at finite temperature of the projection kernels, interpolating from Poisson to random matrix eigenvalue statistics. The scaling limits in the bulk and at the edges are studied in a unified framework, and the question of universality is addressed. Whether the finite temperature determinantal processes correspond to the eigenvalue statistics of some matrix models is, a priori, not obvious. We complete the picture by constructing a finite temperature extension of the Haar measure on the classical compact groups. The eigenvalue statistics of the resulting grand canonical matrix models (of random size) corresponds exactly to the grand canonical measure of free fermions with classical boundary conditions.