The strength of non-covalent intermolecular interactions between dithiadiazolyl (DTDA) radicals XCNSSN (X = F, Cl, Br, CN) were benchmarked using a high-level post-Hartree−Fock ab initio CCSD(T) theory with a complete basis set and corrected with a counterpoise (CP) correction for basis-set superposition error (BSSE). A range of density functional theory (DFT) functionals and basis sets were then screened to identify appropriate DFT methods which would reflect the benchmark data. These identified that minimal basis sets tended to overestimate the interaction energies, whereas inclusion of additional diffuse and polarization functions led to underestimation of these energies. The application of a CP correction for BSSE generally led to inferior performances in relation to uncorrected data for DFT calculations. The relative strengths of the intermolecular interactions were implemented to rationalize the trends in packing within the series XCNSSN (X = F, Cl, Br, CN). The nature of these interactions was also probed through an Atoms in Molecules approach which reveals intermolecular bond critical points for the different types of interactions, which are all diagnostic of non-covalent interactions between DTDA radicals. These are compared with previous experimental charge-density studies on related DTDA radicals. The best-performing DFT methods were then applied to the αand β-polymorphs of the larger radical p-NCC 6 F 4 CNSSN which was too large for benchmark studies. These confirmed the small energetic differences between α and β phases with the top five best-performing methods and functionals correctly reflecting the relative phase stabilities.

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Cocrystallization of the dithiadiazolyl (DTDA) radicals p-XC 6 F 4 CNSSN (X=F, Cl, Br, I, CN) with TEMPO afforded the 2 : 1 cocrystals [p-XC 6 F 4 CNSSN] 2 [TEMPO] (1-5) whose structures all reflect a common S 4 •••O supramolecular motif.The nature of this interaction was probed by DFT calculations (M06/aug-cc-pVDZ) on 1 which revealed that the enthalpy of formation of the [C 6 F 5 CNSSN] 2 [TEMPO] supramolecular motif from [C 6 F 5 CNSSN] 2 and TEMPO is substantial (À 54.0 kJ mol À 1 ). Electronic structure calculations revealed a TEMPO-based doublet S = 1 = 2 configuration as the ground state with limited spin density on the DTDA rings (2.4 %). The corresponding spin quartet state is + 78.9 kJ mol À 1 higher in energy. An atoms-in-molecules analysis reveals four bond critical points (BCPs) between the TEMPO O and the DTDA S atoms as well as additional BCPs between selected DTDA S atoms and methyl H atoms of the TEMPO molecule. Herein, the structures of 2-5 are considered within the context of a hierarchical view of competing and complementary intermolecular interactions; in particular, the established supramolecular CN•••SÀ S synthon is sacrificed in order to form the new S 4 •••O interaction.

The heavier chalcogens sulfur and selenium are important in organic and inorganic chemistry, and the role of such chalcogens in biological systems has recently gained more attention. Sulfur and, to a lesser extent selenium, are involved in diverse reactions from redox signaling to antioxidant activity and are considered essential nutrients. We investigated the ability of the DFT functionals (B3LYP, B3PW91, ωB97XD, M06-2X, and M08-HX) relative to electron correlation methods MP2 and QCISD to produce reliable and accurate structures as well as thermochemical data for sulfur/selenium-containing systems. Bond lengths, proton affinities (PA), gas phase basicities (GPB), chalcogen–chalcogen bond dissociation enthalpies (BDE), and the hydrogen affinities (HA) of thiyl/selenyl radicals were evaluated for a range of small polysulfur/selenium compounds and cysteine per/polysulfide. The S–S bond length was found to be the most sensitive to basis set choice, while the geometry of selenium-containing compounds was less sensitive to basis set. In mixed chalcogens species of sulfur and selenium, the location of the sulfur atom affects the S–Se bond length as it can hold more negative charge. PA, GPB, BDE, and HA of selenium systems were all lower, indicating more acidity and more stability of radicals. Extending the sulfur chain in cysteine results in a decrease of BDE and HA, but these plateau at a certain point (199 kJ mol−1 and 295 kJ mol−1), and PA and GPB are also decreased relative to the thiol, indicating that the polysulfur species exist as thiolates in a biological system. In general, it was found that ωB97XD/6-311G(2d,p) gave the most reasonable structures and thermochemistry relative to benchmark calculations. However, nuances in performance are observed and discussed.

Current research has identified S-nitrosoglutathione reductase (GSNOR) as the central enzyme for regulating protein S-nitrosylation. In addition, the dysregulation of GSNOR expression is implicated in several organ system pathologies including respiratory, cardiovascular, hematologic, and neurologic, making GSNOR a primary target for pharmacological intervention. This study demonstrates the kinetic activation of GSNOR by its substrate S-nitrosoglutathione (GSNO). GSNOR kinetic analysis data resulted in nonhyperbolic behavior that was successfully accommodated by the Hill–Langmuir equation with a Hill coefficient of +1.75, indicating that the substrate, GSNO, was acting as a positive allosteric affector. Docking and molecular dynamics simulations were used to predict the location of the GSNO allosteric domain comprising the residues Asn185, Lys188, Gly321, and Lys323 in the vicinity of the structural Zn2+-binding site. GSNO binding to Lys188, Gly321, and Lys323 was further supported by hydrogen–deuterium exchange mass spectroscopy (HDXMS), as deuterium exchange significantly decreased at these residues in the presence of GSNO. The site-directed mutagenesis of Lys188Ala and Lys323Ala resulted in the loss of allosteric behavior. Ultimately, this work unambiguously demonstrates that GSNO at large concentrations activates GSNOR by binding to an allosteric site comprised of the residues Asn185, Lys188, Gly321, and Lys323. The identification of an allosteric GSNO-binding domain on GSNOR is significant, as it provides a platform for pharmacological intervention to modulate the activity of this essential enzyme.

Thiazole derivatives R 0260 Aqueous-Phase Synthesis of 2-Aminothiazole and 2-Iminothiazolidine Derivatives Catalyzed by Diammonium Hydrogen Phosphate and DABCO. -The advantages of the new procedure are easy work-up, short reaction times and environmental friendliness. -(BALALAIE*, S.; NIKOO, S.; HADDADI, S.; Synth. Commun. 38 (2008) 15, 2521-2528; Dep. Chem., K. N. Toosi Univ. Technol., Tehran, Iran; Eng.) -K. Woydowski 52-134

A series of 7-methylenedehydrobenzo[7]annulen-5-ol hexacarbonyldicobalt complexes were generated by Hosomi–Sakurai reactions of allylsilanes containing o-alkynylarylaldehyde-Co2(CO)6 complexes. One of the cyclization products was converted into its corresponding dihydrobenzo[7]annulen-7-ol hexacarbonyldicobalt complex, an immediate precursor to a benzodehydrotropylium–Co2(CO)6. The cation was generated in situ and reacted with four nucleophiles, and its aromatic stabilization was determined by computational methods.