Lindsay T. Byrne

Solvent inclusion in the structural voids of form II carbamazepine: single-crystal X-ray diffraction, NMR spectroscopy and Hirshfeld surface analysis

Single-crystal X-ray diffraction and solution 1H NMR spectroscopy, in conjunction with Hirshfeld surface analysis, give evidence of solvent inclusion in the trigonal polymorph of carbamazepine, which in the unsolvated form is characterised by the presence of large structural voids.

Octapi Interactions: Self-Assembly of a Pd-Based [2]Catenane Driven by Eightfold π Interactions

An unprecedented 2.5 nm array of pi interactions between eight aromatic rings drives the formation of a [2]catenane. Disruption of this array through the use of longer ligands results in the formation of only single, uncatenated rings. The catenated complex is shown to persist in solution alongside its constituent metallomacrocycles.

A phloracetophenone glucoside with choleretic activity from Curcuma comosa

Abstract Three known diarylheptanoids, 1,7-diphenyl-5-hydroxy-(1E)-1-heptene, 5-hydroxy-7-(4-hydroxyphenyl)-1-phenyl-(1E)-1-heptene and 7-(3,4-dihydroxyphenyl)-5-hydroxy-1-phenyl-(1E)-1-heptene, were isolated from the ethyl acetate extract of Curcuma comosa rhizomes. A phloracetophenone glucoside, 4,6- dihydroxy -2-O-(β- d -glucopyranosyl)acetophenone , was isolated from the ethyl acetate and n-butanol extracts. This compound exhibited choleretic activity in rats.

Synthesis of α-, γ-phosphorus functionalized alkyl lithium species; X-ray structures of [{Li(L)(Ch2PMeR)}2][L =NNN′N′-tetramethylethylenediamine (tmen), R = Me or Ph; L =(–)sparteine, R = Ph] and [Li(tmen){CH(SiMe3)C6H4PPh2-o}]

[{Li(L)(CH2PMeR)}2][L = tetramethylethylenediamine (tmen), R = Me (1) or Ph (2); L =(–)-sparteine (sp), R = Ph (3)], prepared by treating the appropriate phosphine with LiBun(L) in hexane or diethyl ether, are dimeric in the solid. The phosphinomethyl ligands bridge the two lithium atoms as part of six-atom heterocycles; Li–C, P 2.145, 2.604; 2.14, 2.64; 2.20, 2.72A, respectively; (2) and (3) are homochiral and thus have a meso configuration. In benzene (1), (2), and [Li(tmen)(CH2PPh2)](5), are monomeric (cryoscopy), and 7Li–31P coupling only below ca. –70 °C for (1)–(3) and (5) in toluene (1 : 1 doublet, 7Li; 1 : 1 : 1 : 1 quartet, 31P, JLip 44.0–53.4 Hz) is consistent with the presence of symmetrical dimers of the type found in the solid for (1)–(3). [[graphic omitted]Ph2-o}], (4), similarly prepared, has the lithium as part of a chelate ring in the solid, binding through the ipso carbon and PIII centre; Li–C,P 2.25(1), 2.65(1)A. Trilithio species based on P(C6H4CHR–)3(R = H or SiMe3) are generated via metallation using LiBun(tmen). Treating the monolithio species derived from P(O)Me2Ph and LiBun(sp) with Etl yields P(O)MePhPrn of 14% estimated optical purity.

Probing the catalytic roles of Arg548 and Gln552 in the carboxyl transferase domain of the Rhizobium etli pyruvate carboxylase by site-directed mutagenesis.

The roles of Arg548 and Gln552 residues in the active site of the carboxyl transferase domain of Rhizobium etli pyruvate carboxylase were investigated using site-directed mutagenesis. Mutation of Arg548 to alanine or glutamine resulted in the destabilization of the quaternary structure of the enzyme, suggesting that this residue has a structural role. Mutations R548K, Q552N, and Q552A resulted in a loss of the ability to catalyze pyruvate carboxylation, biotin-dependent decarboxylation of oxaloacetate, and the exchange of protons between pyruvate and water. These mutants retained the ability to catalyze reactions that occur at the active site of the biotin carboxylase domain, i.e., bicarbonate-dependent ATP cleavage and ADP phosphorylation by carbamoyl phosphate. The effects of oxamate on the catalysis in the biotin carboxylase domain by the R548K and Q552N mutants were similar to those on the catalysis of reactions by the wild-type enzyme. However, the presence of oxamate had no effect on the reactions catalyzed by the Q552A mutant. We propose that Arg548 and Gln552 facilitate the binding of pyruvate and the subsequent transfer of protons between pyruvate and biotin in the partial reaction catalyzed in the active site of the carboxyl transferase domain of Rhizobium etli pyruvate carboxylase.

Regulation of intracellular pH during anoxia in rice coleoptiles in acidic and near neutral conditions

Rice coleoptiles, renowned for anoxia tolerance, were hypoxically pretreated, excised, ‘healed’, and then exposed to a combination of anoxia and pH 3.5. The putative acid load was confirmed by net effluxes of K+ to the medium, with concurrent net decreases of H+ in the medium, presumably mainly due to H+ influx. Yet the coleoptiles survived the combination of anoxia and pH 3.5 for at least 90 h, and even for at least 40 h when the energy crisis, inherent to anoxia, had been aggravated by supplying the coleoptiles with 2.5 mM rather than 50 mM glucose. Even in the case of coleoptiles with 2.5 mM glucose, an accumulation ratio of 6 for Cl– was attained at 4 h after the start of re-aeration, implying plasma membrane integrity was either maintained during anoxia, or rapidly restored after a return to aerated conditions. Cytoplasmic pH and vacuolar pH were measured using in vivo 31P nuclear magnetic resonance spectroscopy with 50 mM glucose in the basal perfusion medium. After 60 h in anoxia, external pH was suddenly decreased from 6.5 to 3.5, but cytoplasmic pH only decreased from 7.35 to 7.2 during the first 2 h and then remained steady for the next 16 h. During the first 3 h at pH 3.5, vacuolar pH decreased from 5.7 to 5.25 and then stabilized. After 18 h at pH 3.5, the initial values of cytoplasmic pH and vacuolar pH were rapidly restored, both upon a return to pH 6.5 while maintaining anoxia and after subsequent return to aerated solution. Summing up, rice coleoptiles exposed to a combination of anoxia and pH 3.5 retained pH regulation and cellular compartmentation, demonstrating tolerance to anoxia even during the acid load imposed by exposure to pH 3.5.

Reactions of metalloalkynes 3. Facile synthesis of pentanuclear ruthenium clusters. X-ray structures of [Ru5(μ5-CC)(η-C5H4R)2(dppm)(μ2-CO)2(CO)7] (R=H, CH3)

Abstract The reaction of the activated cluster compound, Ru3(CO)10(dppm), 1, with two ethyne-1,2-diyl compounds, [{Ru(CO)2(η-C5H4R)}2(μ-CC)], (2a, R=H; 2b, R=CH3) has resulted in a facile and high yielding synthesis of medium nuclearity cluster compounds, [Ru5(μ5-CC)(η-C5H4R)2(dppm)(μ2-CO)2(CO)7], (3a, R=H; 3b, R=CH3). The core of these compounds incorporate an open and accessible carbide ligand bound to a relatively rare example of a spiked butterfly metal framework. Both of these clusters, 3, have been characterised by X-ray crystallography.

Selective Binding of Imidazolium Cations in Building Multi-Component Layers

Addition of 1-alkyl-3-methylimidazolium (C(n)-mim) cations 3-5 to a mixture of bis-phosphonium cation 2 and sodium p-sulfonatocalix[4]arene (1) in the presence of lanthanide ions results in the selective binding of an imidazolium cation into the cavity of the calixarene. The result is a multi-layered solid material with an inherently flexible interplay of the components. Incorporating ethyl-, n-butyl- or n-hexyl-mim cations into the multi-layers results in significant perturbation of the structure, the most striking effect is the tilting of the plane of the bowl-shaped calixarene relative to the plane of the multi-layer, with tilt angles of 7.2, 28.9 and 65.5 degrees , respectively. The lanthanide ions facilitate complexation, but are not incorporated into the structures and, in all cases, the calixarene takes on a 5- charge, with one of the lower-rim phenolic groups deprotonated. ROESY NMR experiments and other (1)H NMR spectroscopy studies establish the formation of 1:1 supermolecules of C(n)-mim and calixarene, regardless of the ratio of the two components, and indicate that the supermolecules undergo rapid exchange on the NMR spectroscopy timescale.

Stable triazolylphosphonate analogues of phosphohistidine

Histidine-phosphorylated proteins and the corresponding kinases are important components of bacterial and eukaryotic cell-signalling pathways, and are therefore potential drug targets. The study of these biomolecules has been hampered by the lability of the phosphoramidate functional group in the phosphohistidines and the lack of generic antibodies. Herein, the design and concise synthesis of stable triazolylphosphonate analogues of N1- and N3-phosphohistidine, and derivatives suitable for bioconjugation, are described.

Reactions of metalloalkynes: Part 6. Synthesis of open tetrametallic clusters. Reaction of [Ru(CO)4(ethene)] with ethyne-1,2-diyl compounds. Single crystal X-ray structural determinations of [Ru4(μ4-CC)(η-C5H4R)2(μ-CO)2(CO)8] (R=H, Me)

Abstract The reactions between [Ru(CO)4(η2-C2H4)], generated in situ, and ruthenium ethyne-1,2-diyl complexes, [{Ru(CO)2(η-C5H4R)}2(μ-CC)] (R=H, Me) have provided the new air-sensitive complexes [Ru4(μ4-CC)(η-C5H4R)2(μ-CO)2(CO)8] (R=H, Me) with a permetallated ethene structure, in good yield. The complexes were characterized spectroscopically and by single-crystal X-ray diffraction studies. They have an almost planar open geometry, rendering the C22− ligand accessible to reaction. The resonances attributed to the C22− ligand in the 13C{1H}-NMR spectra of the complexes have been unequivocally assigned with the aid of labeling experiments.