Hazendonk, Paul
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- ItemChalcogen versus dative bonding in [SF3] + Lewis acid−base adducts: [SF3(NCCH3)2] +, [SF3(NC5H5)2] +, and [SF3(phen)]+ (phen = 1,10-phenanthroline)(American Chemical Society, 2021) Turnbull, Douglas; Chaudhary, Praveen; Hazendonk, Paul; Wetmore, Stacey D.; Gerken, MichaelThe Lewis-acid behavior of [SF3][MF6] (M = Sb, As) salts toward mono- and bidentate nitrogen bases was explored. Reactions of [SF3][MF6] with excesses of CH3CN and C5H5N yielded [SF3(L)2]+ (L = CH3CN, C5H5N) salts, whereas the reaction of [SF3][SbF6] with equimolar 1,10-phenanthroline (phen) in CH3CN afforded [SF3(phen)][SbF6]·2CH3CN. Salts of these cations were characterized by low-temperature X-ray crystallography and Raman spectroscopy in the solid state as well as by 19F NMR spectroscopy in solution. In the solid state, the geometries of [SF3(NC5H5)2]+ and [SF3(phen)]+ are square pyramids with negligible cation–anion contacts, whereas the coordination of CH3CN and [SbF6]− to [SF3]+ in [SF3(NCCH3)2][SbF6] results in a distorted octahedral coordination sphere with a minimal perturbation of the trigonal-pyramidal SF3 moiety. 19F NMR spectroscopy revealed that [SF3(L)2]+ is fluxional in excess L at −30 °C, whereas [SF3(phen)]+ is rigid in CH2Cl2 at −40 °C. Density functional theory (DFT-B3LYP) calculations suggest that the S–N bonds in [SF3(NC5H5)2]+ and [SF3(phen)]+ possess substantial covalent character and result in a regular AX5E VSEPR geometry, whereas those in [SF3(NCCH3)2]+ are best described as S···N chalcogen-bonding interactions via σ-holes on [SF3]+, which is consistent with the crystallographic data.
- ItemCoupling of CpCr(CO)3 and heterocyclic dithiadiazolyl radicals: synthetic, X-ray diffraction, dynamic NMR, EPR, CV and DFT studies(ACS Publications, 2008) Lau, Hiu F.; Ang, Chwee Y.; Ng, Victor W. L.; Kuan, Seah L.; Goh, Lai Y.; Borisov, Alexey S.; Hazendonk, Paul; Roemmele, Tracey L.; Boeré, René T.; Webster, Richard D.The reaction of 1,2,3,5-dithiadiazolyls, (4-R-C6H4CN2S2)2 (R = Me, 2a; Cl, 2b; OMe, 2c; and CF3, 2d) and (3-NC-5-tBu-C6H3CN2S2)2 (2e) with (CpCr(CO)3]2 (Cp = η5-C5H5) (1) at ambient temperature, yielded respectively the complexes CpCr(CO)2(η2-S2N2CC6H4R) (R = 4-Me, 3a; 4Cl, 3b; 4-OMe, 3c; and 4-CF3, 3d) and CpCr(CO)2(η2-S2N2CC6H3-3-(CN)-5-(tBu)) (3e) in 35 – 72 % yields. The complexes 3c and 3d were also synthesized via a salt metathesis method from the reaction of NaCpCr(CO)3 (1B) and the 1,2,3,5-dithiadiazolium chlorides, 4-R-C6H4CN2S2Cl (R = OMe, 8c; CF3, 8d) with much lower yields of 6 and 20 %, respectively. The complexes were characterized spectroscopically, and also by single crystal X-ray diffraction analysis. Cyclic voltammetry experiments were conducted on 3a-e, EPR spectra were obtained of one-electron reduced forms of 3a-e, and variable temperature 1H NMR studies were carried out on complex 3d. Hybrid DFT calculations were performed on the model system [CpCr(CO)2S2N2CH] and comparisons are made with the reported CpCr(CO)2(π-allyl) complexes.
- ItemCurrent and future experimental strategies for structural analysis of trichothecene mycotoxins-a prospectus(M D P I A G, 2011) Shank, Roxanne A.; Foroud, Nora Afsaneh; Hazendonk, Paul; Eudes, François; Blackwell, Barbara A.Fungal toxins, such as those produced by members of the order Hypocreales, have widespread effects on cereal crops, resulting in yield losses and the potential for severe disease and mortality in humans and livestock. Among the most toxic are the trichothecenes. Trichothecenes have various detrimental effects on eukaryotic cells including an interference with protein production and the disruption of nucleic acid synthesis. However, these toxins can have a wide range of toxicity depending on the system. Major differences in the phytotoxicity and cytotoxicity of these mycotoxins are observed for individual members of the class, and variations in toxicity are observed among different species for each individual compound. Furthermore, while diverse toxicological effects are observed throughout the whole cellular system upon trichothecene exposure, the mechanism of toxicity is not well understood. In order to comprehend how these toxins interact with the cell, we must first have an advanced understanding of their structure and dynamics. The structural analysis of trichothecenes was a subject of major interest in the 1980s, and primarily focused on crystallographic and solution-state Nuclear Magnetic Resonance (NMR) spectroscopic studies. Recent advances in structural determination through solution- and solid-state NMR, as well as computation based molecular modeling is leading to a resurgent interest in the structure of these and other mycotoxins, with the focus shifting in the direction of structural dynamics. The purpose of this work is to first provide a brief overview of the structural data available on trichothecenes and a characterization of the methods commonly employed to obtain such information. A summary of the current understanding of the relationship between structure and known function of these compounds is also presented. Finally, a prospectus on the application of new emerging structural methods on these and other related systems is discussed.
- ItemHydrogen-bonding interactions in T-2 toxin studies using solution and solid-state NMR(M D P I A G, 2011) Chaudhary, Praveen; Shank, Roxanne A.; Montina, Tony; Goettel, James T.; Foroud, Nora Afsaneh; Hazendonk, Paul; Eudes, FrançoisThe structure of T-2 toxin in the solid-state is limited to X-ray crystallographic studies, which lack sufficient resolution to provide direct evidence for hydrogen-bonding interactions. Furthermore, its solution-structure, despite extensive Nuclear Magnetic Resonance (NMR) studies, has provided little insight into its hydrogen-bonding behavior, thus far. Hydrogen-bonding interactions are often an important part of biological activity. In order to study these interactions, the structure of T-2 toxin was compared in both the solution- and solid-state using NMR Spectroscopy. It was determined that the solution- and solid-state structure differ dramatically, as indicated by differences in their carbon chemical shifts, these observations are further supported by solution proton spectral parameters and exchange behavior. The slow chemical exchange process and cross-relaxation dynamics with water observed between the hydroxyl hydrogen on C-3 and water supports the existence of a preferential hydrogen bonding interaction on the opposite side of the molecule from the epoxide ring, which is known to be essential for trichothecene toxicity. This result implies that these hydrogen-bonding interactions could play an important role in the biological function of T-2 toxin and posits towards a possible interaction for the trichothecene class of toxins and the ribosome. These findings clearly illustrate the importance of utilizing solid-state NMR for the study of biological compounds, and suggest that a more detailed study of this whole class of toxins, namely trichothecenes, should be pursued using this methodology.
- ItemLewis acid behavior of SF4: synthesis, characterization, and computational study of adducts of SF4 with pyridine and pyridine derivatives(Wiley, 2015) Chaudhary, Praveen; Goettel, James T.; Mercier, Hélène P. A.; Sowlati-Hashjin, Shahin; Hazendonk, Paul; Gerken, MichaelSulfur tetrafluoride was shown to act as a Lewis acid towards organic nitrogen-bases, such as pyridine, 2,6-dimethylpyridine, 4-methylpyridine, and 4-dimethylaminopyridine. The SF4·NC5H5, SF4·2,6-NC5H3(CH3)2, SF4·4-NC5H4(CH3), and SF4·4-NC5H4N(CH3)2 adducts can be isolated as solids that are stable below –45 °C. The Lewis acid-base adducts were characterized by low temperature Raman spectroscopy and the vibrational bands were fully assigned with the aid of density-functional-theory (DFT) calculations. The electronic structures obtained from the DFT calculations were analyzed by the quantum theory of atoms in molecules (QTAIM). The crystal structures of SF4·NC5H5, SF4·4-NC5H4(CH3), and SF4·4-NC5H4N(CH3)2 revealed weak S---N dative bonds with nitrogen coordinating in the equatorial position of SF4. Based on the QTAIM analysis, the non-bonded valence shell charge concentration on sulfur, which represents the lone pair, is only slightly distorted by the weak dative S---N bond. No evidence for adducts between quinoline or isoquinoline with SF4 was found by low-temperature Raman spectroscopy.
- ItemReactions of molybdenum and tungsten oxide tetrafluoride with sulfur(IV) Lewis bases: structure and bonding in [WOF4]4, MOF4(OSO), and [SF3][M2O2F9] (M = Mo, W)(American Chemical Society, 2020) Turnbull, Douglas; Chaudhary, Praveen; Leenstra, Dakota; Hazendonk, Paul; Wetmore, Stacey D.The structure of [WOF4]4 has been reinvestigated by low-temperature X-ray crystallography and DFT (MN15/def2- SVPD) studies. Whereas the W4F4 ring of the tetramer is planar and disordered in the solid state, the optimized gas-phase geometry prefers a disphenoidally puckered W4F4 ring and demonstrates asymmetric fluorine bridging. Dissolution of MOF4 (M = Mo, W) in SO2 and SF4 results in the formation of MOF4(OSO) and [SF3][M2O2F9], respectively. Both SO2 adducts and [SF3]- [Mo2O2F9] have been characterized by X-ray crystallography. The crystal structure of [SF3][Mo2O2F9] reveals dimerization of the ion pair that results in a rare heptacoordinate sulfur center. Optimization of the {[SF3][M2O2F9]}2 dimers in the gas phase, however, results in the elongation of one contact such that the sulfur centers are effectively hexacoordinate. Meanwhile, the crystal structure of [SF3][W2O2F9]·HF instead demonstrates hexacoordinate sulfur centers and a highly unusual coordination to [SF3]+ from [W2O2F9]−through an oxido ligand. While [SF3][W2O2F9] does not decompose at ambient temperature, MOF4(OSO) and [SF3][Mo2O2F9] are unstable toward evolution of SO2 or SF4. Computational studies reveal that the monomerization of [WOF4]4 in the gas phase at 25 °C is thermodynamically unfavorable using SO2, but favorable using SF4, consistent with the relative thermal stabilities of WOF4(OSO) and [SF3][W2O2F9].
- ItemSDS-induced hexameric oligomerization of myotoxin-II from Bothrops asper assessed by sedimentation velocity and nuclear magnetic resonance(Springer, 2023) Henrickson, Amy; Montina, Tony; Hazendonk, Paul; Lomonte, Bruno; Neves-Ferreira, Ana Gisele C.; Demeler, BorriesWe report the solution behavior, oligomerization state, and structural details of myotoxin-II purified from the venom of Bothrops asper in the presence and absence of sodium dodecyl sulfate (SDS) and multiple lipids, as examined by analytical ultracentrifugation and nuclear magnetic resonance. Molecular functional and structural details of the myotoxic mechanism of group II Lys-49 phospholipase A2 homologues have been only partially elucidated so far, and conflicting observations have been reported in the literature regarding the monomeric vs. oligomeric state of these toxins in solution. We observed the formation of a stable and discrete, hexameric form of myotoxin-II, but only in the presence of small amounts of SDS. In SDS-free medium, myotoxin-II was insensitive to mass action and remained monomeric at all concentrations examined (up to 3 mg/ml, 218.2 μM). At SDS concentrations above the critical micelle concentration, only dimers and trimers were observed, and at intermediate SDS concentrations, aggregates larger than hexamers were observed. We found that the amount of SDS required to form a stable hexamer varies with protein concentration, suggesting the need for a precise stoichiometry of free SDS molecules. The discovery of a stable hexameric species in the presence of a phospholipid mimetic suggests a possible physiological role for this oligomeric form, and may shed light on the poorly understood membrane-disrupting mechanism of this myotoxic protein class.
- ItemSF4·N(C2H5)3: the first conclusively characterized SF4 adduct with an organic base(Royal Society of Chemistry, 2012) Goettel, James T.; Chaudhary, Praveen; Hazendonk, Paul; Mercier, Hélène P. A.; Gerken, MichaelSulfur tetrafluoride and triethylamine react at low temperatures to form a 1 : 1 adduct. The unambiguous characterization of the SF4 N(C2H5)3, which is only stable at low temperature, proves the Lewis acid property of SF4 towards organic Lewis bases. The S–N bond has a length of 2.384(2) A ̊ and is an archetypical example of a dative SIV ’N bonding modality
- ItemSingle-core PAHs in petroleum- and coal-derived asphaltenes: size and distribution from solid-state NMR spectroscopy and optical absorption measurements(American Chemical Society, 2016) Majumdar, R. Dutta; Bake, K. D.; Ratna, Y.; Pomerantz, A. E.; Mullins, O. C.; Gerken, Michael; Hazendonk, PaulUsing solid-state 13C NMR spectroscopy of two different asphaltenes, one derived from petroleum and the other from coal liquids, it was shown that the asphaltene molecular architecture consists of a spectrum of sizes, ranging from smaller polyaromatic hydrocarbons (PAHs; <5 condensed rings) to much larger ones (>9 condensed rings), but their distribution varies between the two. It is shown that smaller PAHs are likely more abundant in the coal-derived asphaltenes, while the largest PAH cores of the two different asphaltenes are similar in size. These observations are reinforced by optical absorption. The coal-derived asphaltenes were found to contain a small fraction of archipelago-type structures, where a small PAH is tethered to the larger PAH core via an aryl linkage, which are less evident, and likely less abundant, in the petroleum asphaltenes. An important difference between the two asphaltenes lies in their alkyl fraction, with the petroleum asphaltenes possessing significantly longer and more mobile alkyl side chains, on average ∼7 carbons long, as opposed to an average chain length of ∼3–4 in the coal asphaltenes. The petroleum asphaltenes also possess a larger fraction of alicyclics. The longer length increases the propensity of the petroleum asphaltene alkyl side chains to intercalate between the aromatic rings of adjacent asphaltene aggregates, which is not observed in coal-derived asphaltenes. This work demonstrates the utility of combining cross-polarization dynamics and directly polarized 13C solid-state NMR spectroscopy in studying asphaltenes, while adding to the body of evidence supporting the single-core model of asphaltenes, which appears to be the dominant structural motif for this fraction of petroleum.
- ItemSolvent and water mediated structural variations in deoxynivalenol and their potential implications on the disruption of ribosomal function(Frontiers Media, 2016) Foroud, Nora Afsaneh; Shank, Roxanne A.; Kiss, Douglas; Eudes, François; Hazendonk, PaulFusarium head blight (FHB) is a disease of cereal crops caused by trichothecene producing Fusarium species. Trichothecenes, macrocylicic fungal metabolites composed of three fused rings (A–C) with one epoxidef unctionality, area class of mycotoxins known to inhibit protein synthesis in eukaryotic ribosomes. These toxins accumulate in the kernels of infected plants rendering them unsuitable for human and animal consumption. Among the four classes of trichothecenes (A–D) A and B are associated with FHB, where the type B trichothecene deoxynivalenol (DON) is most relevant. While it is known that these toxins inhibit protein synthesis by disrupting peptidyl transferase activity, the exact mechanism of this inhibition is poorly understood. The three-dimensional structures and H-bonding behavior of DON were evaluated using one-and two-dimensional nuclear magnetic resonance (NMR) spectroscopy techniques. Comparisons of the NMR structure presented here with the recently reported crystal structure of DON bound in the yeast ribosome reveal insights into the possible toxicity mechanism of this compound. The work described herein identifies a waterbinding pocket in the core structure of DON, where the 3OH plays an important role in this interaction. These results provide preliminary insights into how substitution at C3 reduces trichothecene toxicity. Further investigations along these lines will provide opportunities to develop trichothecene remediation strategies based on the disruption of water binding interactions with 3OH.
- ItemStabilisation of [WF5]+ and WF5 by pyridine: facile access to [WF5(NC5H5)3]+ and WF5(NC5H5)2(Wiley, 2020) Turnbull, Douglas; Hazendonk, Paul; Wetmore, Stacey D.The enhanced reactivity of [WF5]+ over WF6 has been exploited to access a neutral derivative of elusive WF5. The reaction of WF6(NC5H5)2 with [(CH3)3Si(NC5H5)][O3SCF3] in CH2Cl2 results in quantitative formation of trigonal-dodecahedral [WF5(NC5H5)3]+, which has been characterised as its [O3SCF3]− salt by Raman spectroscopy in the solid state and variable-temperature NMR spectroscopy in solution. The salt is susceptible to slow decomposition in solution at ambient temperature via dissociation of a pyridyl ligand, and the resultant [WF5(NC5H5)2]+ is reduced to WF5(NC5H5)2 in the presence of excess C5H5N, as determined by 19F NMR spectroscopy. Pentagonal-bipyramidal WF5(NC5H5)2 was isolated and characterised by X-ray crystallography and Raman spectroscopy in the solid state, representing the first unambiguously characterised WF5 adduct, as well as the first heptacoordinate adduct of a transition-metal pentafluoride. DFT-B3LYP methods have been used to investigate the reduction of [WF5(NC5H5)2]+ to WF5(NC5H5)2, supporting a two-electron reduction of WVI to WIV by nucleophilic attack and diprotonation of a pyridyl ligand in the presence of free C5H5N, followed by comproportionation to WV.
- ItemThe structure of trimethyltin fluoride(Royal Society of Chemistry, 2015) Chaudhary, Praveen; Bieringer, Mario; Hazendonk, Paul; Gerken, MichaelThe solid-state structure of (CH3)3SnF was reinvestigated by X-ray diffraction techniques as well as by multi-nuclear solid-state NMR spectroscopy. Trimethyltin fluoride crystallizes from hot ethanol in the orthorhombic space group Pnma at room temperature and changes to a low-temperature orthorhombic phase (space group: Cmcm) below −70 °C. In both modifications, trimethyltin fluoride adopts a linear chain structure with symmetric fluorine bridges, in contrast to previous reports. During its synthesis, (CH3)3SnF precipitates in another, poorly crystalline modification, as shown by powder X-ray diffraction. Solid-state MAS NMR experiments of both room-temperature phases of (CH3)3SnF (non-recrystallized and recrystallized) were carried out for the 1H, 13C, 19F, and 119Sn nuclei. The 119Sn{19F, 1H} and 19F{1H} NMR spectra offer unambiguous determination for the 19F and 119Sn shielding tensors. The 119Sn{1H} solid-state NMR spectra are in agreement with pentacoordination of Sn in this compound for the non-recrystallized and the recrystallized modifications. Based on the solid-state NMR results, the non-recrystallized modification of (CH3)3SnF also consists of linear, symmetrically fluorine-bridged chains, and differs from the recrystallized orthorhombic phase only in packing of the chains.