Wei G. Wycoff

Solution-phase structures of gallium-containing pyrogallol[4]arene scaffolds.

The variations in architecture of gallium-seamed (PgC4Ga) and gallium-zinc-seamed (PgC4GaZn) C-butylpyrogallol[4]arene nanoassemblies in solution (SANS/NMR) versus the solid state (XRD) have been investigated. Rearrangement from the solid-state spheroidal to the solution-phase toroidal shape differentiates the gallium-containing pyrogallol[4]arene nanoassemblies from all other PgCnM nanocapsules studied thus far. Different structural arrangements of the metals and arenes of PgC4Ga versus PgC4GaZn have been deduced from the different toroidal dimensions, C–H proton environments and guest encapsulation of the two toroids. PGAA of mixed-metal hexamers reveals a decrease in gallium-to-metal ratio as the second metal varies from cobalt to zinc. Overall, the combined study demonstrates the versatility of gallium in directing the selfassembly of pyrogallol[4]arenes into novel nanoarchitectures.

15N nuclear magnetic resonance relaxation studies on rat β‐parvalbumin and the pentacarboxylate variants, S55D and G98D

15N relaxation data for Ca2+‐bound rat β‐parvalbumin (a.k.a. oncomodulin) were analyzed using the Lipari‐Szabo formalism and compared with existing data for rat α‐parvalbumin. Although the average S2 values for the two proteins are very similar (0.85 for α, 0.84 for β), residue‐by‐residue inspection reveals systematic differences. α tends to have the lower S2 value in helical regions; β tends to have the lower value in the loop regions. Rat β was also examined in the Ca2+‐free state. The 59 assigned residues displayed an average order parameter (0.90) significantly greater than the corresponding residues in the Ca2+‐loaded form. The pentacarboxylate variants of rat β—S55D and G98D—also were examined in the Ca2+‐bound state. Although both mutations significantly heighten Ca2+ affinity, they utilize distinct energetic strategies. S55D improves the Ca2+‐binding enthalpy; G98D improves the binding entropy. They also show disparate peptide backbone dynamics. Whereas β G98D displays an average order parameter (0.87) slightly greater than that of the wild‐type protein, β S55D displays an average order parameter (0.82) slightly lower than wild‐type β. Furthermore, whereas just two backbone N‐H bonds in β G98D show internal motion on the 20–200‐psec timescale, fully 52 of the 93 residues analyzed in β S55D show this behavior. These findings suggest that the increased electrostatic repulsion attendant to introduction of an additional carboxylate into the CD site ligand array impedes backbone vibrational motion throughout the molecule.

Solution structures of polcalcin Phl p 7 in three ligation states: Apo‐, hemi‐Mg2+‐bound, and fully Ca2+‐bound

Polcalcins are small EF‐hand proteins believed to assist in regulating pollen‐tube growth. Phl p 7, from timothy grass (Phleum pratense), crystallizes as a domain‐swapped dimer at low pH. This study describes the solution structures of the recombinant protein in buffered saline at pH 6.0, containing either 5.0 mM EDTA, 5.0 mM Mg2+, or 100 μM Ca2+. Phl p 7 is monomeric in all three ligation states. In the apo‐form, both EF‐hand motifs reside in the closed conformation, with roughly antiparallel N‐ and C‐terminal helical segments. In 5.0 mM Mg2+, the divalent ion is bound by EF‐hand 2, perturbing interhelical angles and imposing more regular helical structure. The structure of Ca2+‐bound Phl p 7 resembles that previously reported for Bet v 4—likewise exposing apolar surface to the solvent. Occluded in the apo‐ and Mg2+‐bound forms, this surface presumably provides the docking site for Phl p 7 targets. Unlike Bet v 4, EF‐hand 2 in Phl p 7 includes five potential anionic ligands, due to replacement of the consensus serine residue at –x (residue 55 in Phl p 7) with aspartate. In the Phl p 7 crystal structure, D55 functions as a helix cap for helix D. In solution, however, D55 apparently serves as a ligand to the bound Ca2+. When Mg2+ resides in site 2, the D55 carboxylate withdraws to a distance consistent with a role as an outer‐sphere ligand. 15N relaxation data, collected at 600 MHz, indicate that backbone mobility is limited in all three ligation states. Proteins 2013.

Conversion of Pregabalin to 4-Isobutylpyrrolidone-2

Solid-state studies of C-butyl-resorcin[4]arene with pregabalin (Lyrica, Nervalin) in nitrobenzene yielded a cocrystal of C-butyl-resorcin[4]arene with 4-isobutylpyrrolidone-2. A combined experimental and quantum chemical investigation was implemented to further our understanding of the factors affecting the conversion process.

Erratum to “Conversion of Pregabalin to 4-Isobutylpyrrolidone-2”

Erratum to “Conversion of Pregabalin to 4-Isobutylpyrrolidone-2” Amanda M. Drachnik, Harshita Kumari, Collin M. Mayhan, Drew A. Fowler, Wei G. Wycoff, Charles L. Barnes, John E. Adams, Carol A. Deakyne, Jerry L. Atwood [J Pharm Sci 2017;106(10):3095-3102] The authors wish to include 3 corresponding authors: Correspondence to: Jerry L. Atwood (Telephone: 573-882-9606); Carol A. Deakyne (Telephone: 573-882-1347); Harshita Kumari (Telephone: 513-558-1872). E-mail addresses: AtwoodJ@missouri.edu (J. Atwood), DeakyneC@missouri.edu (C. Deakyne), kumariha@ucmail.uc.edu (H. Kumari).

Pertechnetate-Induced Addition of Sulfide in Small Olefinic Acids: Formation of [TcO(dimercaptosuccinate)2]5– and [TcO(mercaptosuccinate)2]3– Analogues

Technetium-99 (99Tc) is important to the nuclear fuel cycle as a long-lived radionuclide produced in ∼6% fission yield from 235U or 239Pu. In its most common chemical form, namely, pertechnetate (99TcO4-), it is environmentally mobile. In situ hydrogen sulfide reduction of pertechnetate has been proposed as a potential method to immobilize environmental 99TcO4- that has entered the environment. Reactions of 99TcO4- with sulfide in solution result in the precipitation of Tc2S7 except when olefinic acids, specifically fumaric or maleic acid, are present; a water-soluble 99Tc species forms. NMR (1H, 13C, and 2D methods) and X-ray absorption spectroscopy [XAS; near-edge (XANES) and extended fine structure (EXAFS)] studies indicate that sulfide adds across the olefinic bond to generate mercaptosuccinic acid (H3MSA) and/or dimercaptosuccinic acid (H4DMSA), which then chelate(s) the 99Tc to form [99TcO(MSA)2]3-, [99TcO(DMSA)2]5-, or potentially [99TcO(MSA)(DMSA)]4-. 2D NMR methods allowed identification of the products by comparison to 99Tc and nonradioactive rhenium standards. The rhenium standards allowed further identification by electrospray ionization mass spectrometry. 99TcO4- is essential to the reaction because no sulfide addition occurs in its absence, as determined by NMR. Computational studies were performed to investigate the structures and stabilities of the potential products. Because olefinic acid is a component of the naturally occurring humic and fulvic acids found in soils and groundwater, the viability of in situ hydrogen sulfide reduction of environmental 99TcO4- as an immobilization method is evaluated.