143 research outputs found
Synthesis and alkyne-coupling chemistry of cyclomanganated 1- and 3-acetylindoles, 3-formylindole and analogues
The syntheses are reported of new cyclomanganated indole derivatives (1-acetyl-κO-indolyl-κC2)dicarbonylbis(trimethylphosphite)manganese (2), (1-methyl-3-acetyl-κO-indolyl-κC2)tetracarbonylmanganese (4), (3-formyl-κO-indolyl-κC2)tetracarbonylmanganese (5a) and (1-methyl-3-formyl-κO-indolyl-κC2)tetracarbonylmanganese (5b). The unusually complicated crystal structure of 5b has been determined, the first for a cyclomanganated aryl aldehyde.
The preparations of a mitomycin-related pyrrolo-indole and related products by thermally promoted and oxidatively (Me3NO) initiated alkyne-coupling reactions of the previously known complex (1-acetyl-κO-indolyl-κC2)tetracarbonylmanganese (1) are reported for different alkynes and solvents. X-ray crystal structures are reported for the dimethyl acetylenedicarboxylate coupling product of 1 (dimethyl 1-methyl-l-hydroxypyrrolo[1,2a]-indole-2,3-dicarboxylate; 6a), and an unusually-cyclised triple insertion product 8 from the coupling of acetylene with 4, in which a cyclopentadiene moiety is η3-allyl-coordinated to Mn through only one double bond and an exocyclic carbon, but which rearranges on heating to an η5-cyclopentadienyl complex
Structure, Oligomerisation and Interactions of β-Lactoglobulin
β-Lactoglobulin (βLg), as the most abundant whey protein in ruminant milk and as a useful model protein, is the subject of countless biophysical studies in the literature, yet its physiological role is hitherto unknown. This chapter deals with studies that focus on the structure of βLg, its oligomeric behaviour and the interactions that this protein participates in. These and further studies are necessary to understand how the protein’s physicochemical properties may influence the processing, digestion and immunogenicity of ruminant milks and their products. However, there is also a need for research into the interactions that occur naturally between βLg and other components in milk, as this may give us insight into the physiological role of the protein
Synthesis and Characterization of Symmetrically versus Unsymmetrically Proton-Bridged Hexa-Iron Clusters
Syntheses and magnetic and structural characterization of hexa-iron complexes of derivatized salicylaldoximes are discussed. Complexation of Fe(BF4)2·6H2O with each ligand (H2 L1 and H4 L2) in a methanolic-pyridine solution resulted in hexa-iron compounds (C1 and C2, respectively), which each contain two near-parallel metal triangles of [Fe3-μ3-O], linked by six fluoride bridges and stabilized by a hydrogen-bonded proton between the μ3-O groups. Within each metal triangle of C2, Fe(III) ions are connected via the amine "straps" of (H4 L2-2H). Variable-temperature magnetic susceptibility and Mössbauer data of C1 and C2 indicate the presence of dominant antiferromagnetic interactions between the high-spin (S = 5/2) Fe(III) centers. For C1, two quadrupole doublets are observed at room temperature and 5 K, consistent with structural data from which discrete but disordered [Fe3-μ3-O] and [Fe3-μ3-OH] species were inferred. For C2, a single sharp quadrupole doublet with splitting intermediate between those determined for C1 was observed, consistent with the symmetric [Fe3-μ3-O···H···μ3-O-Fe3] species inferred crystallographically from the very short μ3-O···μ3-O separation. The differences in the physical properties of the complexes, as seen in the Mössbauer, X-ray, and magnetic data, are attributed to the conformational flexibility imparted by the nature of the linkages between the closely related ligands
Interpenetration isomers in isoreticular amine-tagged zinc MOFs
The effect of increasing steric size of pendant amine substituents on structural isoreticulation has been studied systematically in a series of Zn-MOFs. Linear biphenyl dicarboxylic acids tagged with pendant primary amine (H2bpdc-NH2), allylamine (H2bpdc-NHallyl), diallylamine (H2bpdc-N(allyl)2) and dimethylamine (H2bpdc-NMe2) groups react with zinc nitrate in DMF to yield a set of interpenetrated MOFs, WUF-11-14, respectively, that are structurally akin to IRMOF-9. The allylated amine ligands undergo C-N cleavage reactions under the synthesis conditions, yielding WUF-12 and WUF-13 as multivariate MOFs. The single crystal X-ray crystallography on this set of MOFs was not straightforward and we give a salutary account of the difficulties encountered. Gas adsorption measurements combined with surface area calculations provide invaluable support for the crystallographic assignments. The crystallographic analyses reveal subtle differences in the relative positions of the interpenetrating frameworks, and we present a classification system for this type of MOF and analyse related examples available in the literature. CO2 adsorption measurements revealed that WUF-14, which features the strongest Brønsted basic dimethylamine tag group, has the highest capacity, isosteric heat of adsorption, and CO2/N2 selectivity.</p
A review of the mechanisms and models of bubble-particle detachment in froth flotation
Only when the process of particle detachment is well understood and modelled can minerals recovery using the flotation process be modulated to achieve a high efficiency by suitably changing the operating parameters. This is vitally necessary for the recovery of coarse particles in an energy efficient way, as detachment is the key limiting factor in the successful recovery of large particles. However, until the detachment mechanism is more fully understood, an upper limit on the floatable particle diameter still remains unidentified. To assess the current state of knowledge available in this area, a comprehensive literature review on the mechanisms and models of the bubble-particle detachment process in froth flotation is presented. In general, the detachment process is considered to be a stochastic process, and is usually attributed to the dynamic interactions with the turbulent flow structures (eddies) in the flotation environment which cause particles to detach because of dissipating energy. In this paper, previous studies on bubble-particle detachment have been critically analyzed with respect to the formulation of the models in predicting the detachment probability of particles. The models are classified into three different categories: force balance analysis; energy balance analysis and empirical analysis of particle size compared to maximum floatable particle size. Attention is also paid to an understanding of the mechanisms of bubble-particle detachment in quiescent and turbulent liquid flow fields. The predictions of all these models have been compared with the published experimental data and it was found that models which take an accurate consideration of the influence of eddies on a particle's detachment give the closest predictions. The generally held concept of bubble-particle detachment inside an eddy was experimentally validated, where a particle was observed to rotate on the surface of a bubble, resulting in a centrifugal acceleration 20 times that of gravitational acceleration. The aim of this paper is to review the developments and limitations of the existing models. The experimental work is reviewed so as to reveal the mechanisms of bubble-particle detachment. Therefore, the future development of models is identified in order to successfully predict particle detachment
A structural and catalytic model for zinc phosphoesterases
A structural model for the active site of phosphoesterases, enzymes that degrade organophosphate neurotoxins, has been synthesised. The ligand 2-((2-hydroxy-3-(((2-hydroxyethyl)(pyridin-2-ylmethyl)amino)methyl)-5-methylbenzyl)(pyridin-2-ylmethyl)amino)acetic acid (H(3)L1) and two Zn(ii) complexes have been prepared and characterised as and The ligand (H(3)L1) and complex were characterised through (1)H NMR, (13)C NMR, mass spectroscopy and microanalysis. The X-ray crystal structure of revealed a tetramer of dinuclear complexes, bridged by two phosphate molecules and bifurcating acetic acid arms. Functional studies of the zinc complex with the substrate bis(4-nitrophenyl)phosphate (bNPP) determined the complex with HL1(2-) to be a competent catalyst with k(cat) = 1.26 0.06 x 10(-6) s(-1)
Dust and gas in the magellanic clouds from the heritage Herschel Key Project. I. Dust properties and insights into the origin of the submillimeter excess emission
The dust properties in the Large and Small Magellanic clouds (LMC/SMC) are studied using the HERITAGE Herschel Key Project photometric data in five bands from 100 to 500 μm. Three simple models of dust emission were fit to the observations: a single temperature blackbody modified by a power-law emissivity (SMBB), a single temperature blackbody modified by a broken power-law emissivity (BEMBB), and two blackbodies with different temperatures, both modified by the same power-law emissivity (TTMBB). Using these models, we investigate the origin of the submillimeter excess, defined as the submillimeter emission above that expected from SMBB models fit to observations <200 μm. We find that the BEMBB model produces the lowest fit residuals with pixel-averaged 500 μm submillimeter excesses of 27% and 43% for the LMC and SMC, respectively. Adopting gas masses from previous works, the gas-to-dust ratios calculated from our fitting results show that the TTMBB fits require significantly more dust than are available even if all the metals present in the interstellarmedium (ISM) were condensed into dust. This indicates that the submillimeter excess ismore likely to be due to emissivity variations than a second population of colder dust. We derive integrated dust masses of (7.3 ± 1.7) × 105 and (8.3 ± 2.1) × 104 M⊙ for the LMC and SMC, respectively. We find significant correlations between the submillimeter excess and other dust properties; further work is needed to determine the relative contributions of fitting noise and ISM physics to the correlation
New salicylaldoximato-borate ligands resulting from anion hydrolysis and their respective copper and iron complexes
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