Ivan I. Vorontsov

Bio: Ivan I. Vorontsov is an academic researcher from University of Arizona. The author has contributed to research in topics: Clathrochelate & Crystal structure. The author has an hindex of 22, co-authored 69 publications receiving 1421 citations. Previous affiliations of Ivan I. Vorontsov include State University of New York System & Moscow State University.

Capturing and Analyzing the Excited-State Structure of a Cu(I) Phenanthroline Complex by Time-Resolved Diffraction and Theoretical Calculations

Abstract: Time-resolved crystallography and density functional theory calculations are used to analyze the geometric and electronic changes that occur upon photoexcitation of [Cu(I)(dmp)(dppe)]+ in crystalline [Cu(I)(dmp)(dppe)][PF6] [dmp = 2,9-dimethyl-1,10-phenanthroline; dppe = 1,2-bis(diphenylphosphino)ethane]. In the pump−probe experiment, laser and X-ray pulses are synchronized to capture an image of the instantaneous molecular distortions in the transient triplet state. Parallel theoretical calculations, with the phenyl groups replaced by methyl groups, yield information on the distortion of the isolated cation and the change in electron density upon excitation. The experimental distortions are significantly less than the calculated values and are different for the two independent molecules in the asymmetric unit; these findings are attributed to the constraining influence of the crystal matrix. The calculations indicate that the electron transfer upon excitation is mostly from the dmpe ligand to the dmp lig...

Structure and metal binding properties of ZnuA, a periplasmic zinc transporter from Escherichia coli

Abstract: ZnuA is the periplasmic Zn2+-binding protein associated with the high-affinity ATP-binding cassette ZnuABC transporter from Escherichia coli. Although several structures of ZnuA and its homologs have been determined, details regarding metal ion stoichiometry, affinity, and specificity as well as the mechanism of metal uptake and transfer remain unclear. The crystal structures of E. coli ZnuA (Eco-ZnuA) in the apo, Zn2+-bound, and Co2+-bound forms have been determined. ZnZnuA binds at least two metal ions. The first, observed previously in other structures, is coordinated tetrahedrally by Glu59, His60, His143, and His207. Replacement of Zn2+ with Co2+ results in almost identical coordination geometry at this site. The second metal binding site involves His224 and several yet to be identified residues from the His-rich loop that is unique to Zn2+ periplasmic metal binding receptors. Electron paramagnetic resonance and X-ray absorption spectroscopic data on CoZnuA provide additional insight into possible residues involved in this second site. The second site is also detected by metal analysis and circular dichroism (CD) titrations. Eco-ZnuA binds Zn2+ (estimated Kd < 20 nM), Co2+, Ni2+, Cu2+, Cu+, and Cd2+, but not Mn2+. Finally, conformational changes upon metal binding observed in the crystal structures together with fluorescence and CD data indicate that only Zn2+ substantially stabilizes ZnuA and might facilitate recognition of ZnuB and subsequent metal transfer.

Shedding light on the structure of a photoinduced transient excimer by time-resolved diffraction.

Abstract: Time-resolved single-crystal diffraction performed with synchrotron radiation shows that the $53(1)\text{ }\ensuremath{\mu}\mathrm{s}$ phosphorescent state, generated in the crystalline phase of trimeric ${[3,5\mathrm{\text{\ensuremath{-}}}({\mathrm{CF}}_{3}{)}_{2}\mathrm{\text{Pyrazolate}}]\mathrm{Cu}{}}_{3}$ molecules by exposure to 355 nm of light at 17 K, is due to the formation of an excimer rather than the shortening of the intramolecular $\mathrm{Cu}\ensuremath{\cdots}\mathrm{Cu}$ distances within the trimeric units, or the formation of a continuous chain of interacting molecules. One of the intermolecular $\mathrm{Cu}\ensuremath{\cdots}\mathrm{Cu}$ distances contracts by 0.56 \AA{} from 4.018(1) to 3.46(1) \AA{}, whereas the interplanar spacing of the trimers is reduced by 0.65 \AA{} from 3.952(1) to 3.33(1) \AA{}. Density-functional theory calculations support the formation of a $\mathrm{Cu}\ensuremath{\cdots}\mathrm{Cu}$ bond through the intermetallic transfer of a Cu $3d$ electron to a molecular orbital with a large $4p$ contribution on the reacting Cu atoms.

The structure of short-lived excited states of molecular complexes by time-resolved X-ray diffraction.

Abstract: Experimental and computational methods for time-resolved (TR) diffraction now allow the determination of geometry changes on molecular excitation. The first results indicate significant changes in the interatomic distances and molecular shape on photo-excitation, but also a dependence of the induced changes on the molecular environment. Though the use of high-brightness synchrotron sources is essential, it limits the time resolution to the width of the synchrotron pulse which is currently 70–100 ps. The experiments discussed fall into two categories: (i) picosecond powder diffraction experiments on the molecular excitation to a singlet state, and (ii) microsecond experiments on the excited states of inorganic complexes. Both involve reversible processes for which a stroboscopic technique can be applied.

SAMHD1 restricts the replication of human immunodeficiency virus type 1 by depleting the intracellular pool of deoxynucleoside triphosphates.

Abstract: SAMHD1 restricts the infection of dendritic cells by human immunodeficiency virus type 1. Margottin-Goguet and colleagues show that SAMHD1 limits viral DNA synthesis by hydrolyzing intracellular dNTPs.