Protonation thermochemistry of selected hydroxy- and methoxycarbonyl molecules

The gas-phase basicities of a representative set of hydroxy- and methoxycarbonyl compounds (hydroxyacetone, 1, 3-hydroxybutanone, 2, 3-hydroxy-3-methylbutanone, 3, 1-hydroxy-2-butanone, 4, 4-hydroxy-2-butanone, 5, 5-hydroxy-2-pentanone, 6, methoxyacetone, 7, 3-methoxy-2-butanone, 8, 4-methoxy-2-butanone, 9, and 5-methoxy-2-pentanone, 10) were experimentally determined by the equilibrium method using Fourier transform ion cyclotron resonance and high-pressure mass spectrometry techniques. The latter method allows the measurement of proton transfer equilibrium constants at various temperatures and thus the estimate of both the proton affinities and the protonation entropies of the relevant species. Quantum chemical calculations at the G3 and the B3LYP/6-311+G(3df,2p)//6-31G(d) levels of theory were undertaken in order to find the most stable structures of the neutrals 1-10 and their protonated forms. Conformational and vibrational analyses have been done with the aim of obtaining a theoretical estimate of the protonation entropies.     

Evaluation of inoculum of Candida guilliermondii grown in presence of glucose on xylose reductase and xylitol dehydrogenase activities and xylitol production during batch fermentation of sugarcane bagasse hydrolysate

The effect of glucose on xylose-xylitol metabolism in fermentation medium consisting of sugarcane bagasse hydrolysate was evaluated by employing an inoculum of Candida guilliermondii grown in synthetic media containing, as carbon sources, glucose (30 g/L), xylose (30 g/L), or a mixture of glucose (2 g/L) and xylose (30 g/L). The inoculum medium containing glucose promoted a 2.5-fold increase in xylose reductase activity (0.582 IU/mg_prot) and a 2-fold increase in xylitol dehydrogenase activity (0.203 IU/mg_prot) when compared with an inoculum-grown medium containing only xylose. The improvement in enzyme activities resulted in higher values of xylitol yield (0.56 g/g) and productivity (0.46 g/[L·h]) after 48 h of fermentation.     

Framework fluxionality of organometallic oxides: synthesis, crystal structure, EXAFS, and DFT studies on [[Ru(eta6-arene)]4Mo4O16] complexes

Reactions of the molybdates Na(2)MoO4.2 H2O and (nBu(4)N)2[Mo2O7] with [[Ru(arene)Cl(2)](2)] (arene=C(6)H5CH3, 1,3,5-C6H3(CH3)(3), 1,2,4,5-C6H2(CH3)4) in water or organic solvents led to formation of the triple-cubane organometallic oxides [[Ru(eta(6)-arene)](4)Mo4O16], whose crystal and molecular structures were determined. Refluxing triple cubane [[Ru(eta(6)-C6H5CH3)](4)Mo4O16] in methanol caused partial isomerization to the windmill form. The two isomers of [[Ru(eta(6)-C6H5CH3)](4)Mo4O16] were characterized by Raman and Mo K-edge X-ray absorption spectroscopy (XAS), both in the solid-state and in solution. This triple-cubane isomer was also used as a spectroscopic model to account for isomerization of the p-cymene windmill [[Ru(eta(6)-1,4-CH3C6H4CH(CH3)2)](4)Mo4O16] in solution. Using both Raman and XAS techniques, we were then able to determine the ratio between the windmill and triple-cubane isomers in dichloromethane and in chloroform. Density functional calculations on [[Ru(eta(6)-arene)](4)Mo4O16] (arene=C6H6, C6H5CH3, 1,3,5-C6H3(CH3)3, 1,4-CH3C6H4CH(CH3)2, C6(CH3)6) suggest that the windmill form is intrinsically more stable, provided the complexes are assumed to be isolated. Intramolecular electrostatic interactions and steric bulk induced by substituted arenes were found to modulate but not to reverse the energy difference between the isomers. The stability of the triple-cubane isomers should therefore be accounted for by effects of the surroundings that induce a shift in the energy balance between both forms.     

Investigation into the formation of heteronuclear clusters of formula [{Ru<Subscript>6</Subscript>C(CO)<Subscript>16</Subscript>Ag<Subscript>2</Subscript>X}<Subscript>2</Subscript>]<Superscript>2−</Superscript> (X = Cl,Br or I)

Reaction of [Ru₆C(CO)₁₆]²⁻ with an excess of AgX (X = Cl, Br or I) affords heteronuclear clusters of formula [{Ru₆C(CO)₁₆Ag₂X}₂]²⁻ in 80% yield, which for X = I and X = Br/Cl were crystallographically characterised. The formation of the cluster was followed in solution using electrospray ionisation mass spectrometry (ESI-MS), which revealed the presence of a wide range of clusters with the general formula [{Ru₆C(CO)₁₆} _x Ag _y X _z ]^{(2x−y+z)−} where x = 1 or 2, y = 1, 2, 3 or 4 and z = 0, 1 or 2. The high yield of the product despite the evident complicated solution speciation is attributed to selective crystallisation of the observed compound driving the equilibrium toward this product.     

Low pressure chemical ionization in ion trap mass spectrometry

This article presents the specificities of low pressure chemical ionization in ion trap mass spectrometry. One main feature is the ability to perform chemical ionization with liquid reagents as readily as with "conventional" gases (methane, isobutane and ammonia). The reactivities and analytical applications of gas and liquid reagents are summarized from literature data and are compared when possible.     

Etude théorique de la conformation des complexes moléculaires de type donneur accepteur d'électrons

The stabilisation energy of donor acceptor molecular complexes given by tetracyanoethylene with thiazole and phenylthiazoles have been calculated by several semiempirical approaches. The results obtained with the Extended Hückel theory, the CNDO/2 method and the PCILO method, the latter a perturbative one, are compared and this comparison shows that the PCILO method is well adapted to the study of molecular complexes. The different contributions to the stabilisation energy and the origin of the intermolecular forces have been discussed in relation to the geometry of the complex. For all the studied complexes, the calculated results obtained by the PCILO method agree very well with experiments.

     

Homochiral [2.2]Paracyclophane Self‐Assembly Promoted by Transannular Hydrogen Bonding

[2.2]paracyclophane (pCp), unlike many π‐building blocks, has been virtually unexplored in supramolecular constructs. Reported here is the synthesis and characterization of the first pCp derivatives capable of programmed self‐assembly into extended cofacial π‐stacks in solution and the solid state. The design employs transannular (intramolecular) hydrogen bonds (H‐bonds), hitherto unstudied in pCps, between pseudo‐ortho‐positioned amides of a pCp‐4,7,12,15‐tetracarboxamide (pCpTA) to preorganize the molecules for intermolecular H‐bonding with π‐stacked neighbors. X‐ray crystallography confirms the formation of homochiral, one‐dimensional pCpTA stacks helically laced with two H‐bond strands. The chiral sense is dictated by the planar chirality (R_p or S_p) of the pCpTA monomers. A combination of NMR, IR, and UV/Vis studies confirms the formation of the first supramolecular pCp polymers in solution.     

Chemical composition of the essential oil from the leaves of Anaxagorea brevipes (Annonaceae) and evaluation of its bioactivity

The essential oil obtained by hydrodistillation from leaves of Anaxagorea brevipes was analysed by gas chromatography fitted with a flame ionisation detector (GC–FID) and coupled to mass spectrometry (GC–MS). Thirty one components were identified, representing around 75.7% of total oil. The major components were β-eudesmol (13.16%), α-eudesmol (13.05%), γ-eudesmol (7.54%), guaiol (5.12%), caryophyllene oxide (4.18%) and β-bisabolene (4.10%). The essential oil showed antimicrobial activity against Gram-positive bacteria and yeast with the MIC values between 25.0 and 100 μg/mL. The highest antiproliferative activity was observed for the oil against MCF-7 (breast, TGI = 12.8 μg/mL), NCI-H460 (lung, TGI = 13.0 μg/mL) and PC-3 (prostate, TGI = 9.6 μg/mL) cell lines, while against no cancer cell line HaCat (keratinocyte) the TGI was 38.8 μg/mL. The oil exhibited a small antioxidant activity assessed through ORAC-FL assay (517 μmol TE/g). This is the first report regarding the chemical composition and bioactivity of A. brevipes essential oil.     

Insights Into the Allosteric Inhibition of the SUMO E2 Enzyme Ubc9

Conjugation of the small ubiquitin‐like modifier (SUMO) to protein substrates is an important disease‐associated posttranslational modification, although few inhibitors of this process are known. Herein, we report the discovery of an allosteric small‐molecule binding site on Ubc9, the sole SUMO E2 enzyme. An X‐ray crystallographic screen was used to identify two distinct small‐molecule fragments that bind to Ubc9 at a site distal to its catalytic cysteine. These fragments and related compounds inhibit SUMO conjugation in biochemical assays with potencies of 1.9–5.8 mm . Mechanistic and biophysical analyses, coupled with molecular dynamics simulations, point toward ligand‐induced rigidification of Ubc9 as a mechanism of inhibition.     

Charged ligands for catalyst immobilisation and analysis

Ligands involved in organometallic chemistry have been functionalised at locations somewhat removed from the binding site for diverse reasons, including modification of electronic and steric characteristics, improving solubility, to confer chirality, to add a spectroscopic "handle", to facilitate electron-transfer processes or for spin-labelling. Here, the focus is specifically on catalytically active metal complexes in which a charged or highly polar group has been appended to the periphery of one or more of the ligands. For the most part, the motivation has been to alter the solubility properties of the catalytic metal complex to which it is attached, for the purposes of immobilisation in another phase (water, ionic liquids, etc.) and improvement of the green credentials of the process. However, other uses are also becoming recognised, for example to aid in situ analysis of catalysts by electrospray ionisation mass spectrometry.