Search results for "Complex."
showing 10 items of 5824 documents
Simultaneous endo and exo Complex Formation of Pyridine[4]arene Dimers with Neutral and Anionic Guests
2017
The formation of complexes between hexafluorophosphate (PF6- ) and tetraisobutyloctahydroxypyridine[4]arene has been thoroughly studied in the gas phase (ESI-QTOF-MS, IM-MS, DFT calculations), in the solid state (X-ray crystallography), and in chloroform solution (1 H, 19 F, and DOSY NMR spectroscopy). In all states of matter, simultaneous endo complexation of solvent molecules and exo complexation of a PF6- anion within a pyridine[4]arene dimer was observed. While similar ternary complexes are often observed in the solid state, this is a unique example of such behavior in the gas phase.
Anionic Organic Guests Incorporated in Zeolites: Adsorption and Reactivity of a Meisenheimer Complex in Faujasites
2005
Zeolites are suitable microporous hosts for positively charged organic species, but it is believed that they cannot adsorb organic anions. Pure Meisenheimer complex, derived from reduction of 2,4-dinitroaniline with NaBH4, was adsorbed inside faujasite cavities. Evidence for the internal incorporation of this negatively charged reaction intermediate comes from 1) XPS elemental analysis as a function of the depth of penetration into the particle, 2) the remarkable blue shift in lambda(max) of the Meisenheimer complex adsorbed on zeolite (ca. 470 nm) as compared to that in acetonitrile (580 nm) and 3) from the lack of reactivity with size-excluded hydride-acceptor reagents. Evidence is provid…
Water Structure Recovery in Chaotropic Anion Recognition: High-Affinity Binding of Dodecaborate Clusters to γ-Cyclodextrin
2015
Dodecaborate anions of the type B12X12(2-) and B12X11Y(2-) (X=H, Cl, Br, I and Y=OH, SH, NH3(+), NR3(+)) form strong (K(a) up to 10(6) L mol(-1), for B12Br12(2-)) inclusion complexes with γ-cyclodextrin (γ-CD). The micromolar affinities reached are the highest known for this native CD. The complexation exhibits highly negative enthalpies (up to -25 kcal mol(-1)) and entropies (TΔS up to -18.4 kcal mol(-1), both for B12I12(2-)), which position these guests at the bottom end of the well-known enthalpy-entropy correlation for CDs. The high driving force can be traced back to a chaotropic effect, according to which chaotropic anions have an intrinsic affinity to hydrophobic cavities in aqueous …
Detection of mitochondrial electron chain carrier redox status by transhepatic light intensity during rat liver reperfusion.
2003
The aim of the study was to investigate mitochondrial electron transfer during rat liver reperfusion after cold storage and hypothermic machine perfusion. Livers from male Brown Norway rats were preserved (UW) for 10h either by cold storage (CS) or by hypothermic oxygenated perfusion extracorporal (HOPE). Transhepatic photometric analysis allowed determination of the redox status of mitochondrial cytochromes during preservation, rewarming and reperfusion. Mitochondrial electron chain carriers were inhibited at different sites with rotenone and cyanide in some experiments. reversed transcriptional polymerase chain reaction (RT-PCR) was performed after reperfusion concerning transcription of …
Polyfunctional recognition of pyridinedicarboxylate anions with macrocyclic polyamine receptors containing heteroaromatic groups.
2008
The interaction of the biologically relevant anions deriving from the six pyridinedicarboxylic acids (H2PDC) with two macrocyclic receptors containing a pentamine chain and a bipyridine (1) or a phenanthroline (2) moiety, as well as with the aliphatic analogue [21]aneN7 (3), was studied by means of spectroscopic methods (UV-vis, NMR) and potentiometric titrations affording the stability constants of the adducts formed. All three receptors form stable complexes with the substrates thanks to the formation of several salt bridges and hydrogen bond contacts, as observed in the crystal structure of the H8[3(2,6-PDC)4] x H2O x 0.5 EtOH solid compound. Additional pi-stacking interactions between t…
Experimental and Theoretical Studies of Nonclassical d 0 Cyclopentadienyl Polyhydride Complexes of Molybdenum and Tungsten
1998
Low-temperature protonation of compounds Cp{sup *}MH{sub 5}(PMe{sub 3}) (M = Mo, 1; W, 2) by HBF{sub 4}{center_dot}Et{sub 2}O in CD{sub 2}Cl{sub 2} or CDFCl{sub 2} affords the thermally unstable hexahydride derivatives [Cp{sup *}MH{sub 6}(PMe{sub 3})]{sup +} (M = Mo, 3; W, 4). The corresponding protonation of 1- and 2-d{sup 5} affords 3- and 4-d{sup 5}, respectively. The {Delta}{delta} on going from H{sub 6} to HD{sub 5} is small for both compounds, but positive for 3 and negative for 4, and no isotopic perturbation of resonance (IPR) is observed. The T{sub 1min} at 400 MHz for [Cp{sup *}MH{sub 6}(PMe{sub 3})]{sup +} apparently doubles on going from Mo to W (52 ms for 3 and approximately 10…
Influence of the anions on the structure and magnetic properties of a series of bis(µ-diphexono)-bridged linear trinuclear copper(II) complexes: an e…
2011
The reaction of H(2)L (N,N'-dimethyl-N,N'-bis(2-hydroxy-3-methoxy-5-methylbenzyl)-ethylenediamine) with different copper salts, in methanol and using a H(2)L/Cu = 2 : 3 molar ratio, led to four new bis(μ-diphenoxo)-bridged Cu(3) complexes of general formula [{Cu(S)(μ-L)}(2)Cu(H(2)O)(2n)]X(2) (S = CH(3)OH, n = 1 and X = BF(4)(-) for (1) or ClO(4)(-) for (2); S = Br(3)(-) anion and n = 1 without any X species for (3); S = H(2)O, n = 0 and X = NO(3)(-) for (4)). The use in the same reaction conditions of 4,4'-bipyridine (4,4'-bipy) as connector led to the chain complex [{Cu(μ-4,4'-bipy)(0.5)(μ-L)}(2)Cu(H(2)O)(2n)](ClO(4))(2)·17H(2)O (5). The structure of the centrosymmetric trinuclear unit in …
Anion Recognition by a Bioactive Diureidodecalin Anionophore: Solid-State, Solution, and Computational Studies
2018
Recent work has identified a bis-(p-nitrophenyl)ureidodecalin anion carrier as a promising candidate for biomedical applications, showing good activity for chloride transport in cells yet almost no cytotoxicity. To underpin further development of this and related compounds, a detailed structural and binding investigation is reported. Crystal structures of the transporter as five solvates confirm the diaxial positioning of urea groups while revealing a degree of conformational flexibility. Structures of complexes with Cl−, Br−, NO3 −, SO4 2− and AcO−, supported by computational studies, show how the binding site can adapt to accommodate these anions. 1H NMR binding studies revealed exception…
Synthesis, characterization and the first crystal structure of the Zn(II) complex of 4,6-O-ethylidine-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine
2001
4,6-O-Ethylidine-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine (H3L1) and N-(5-bromo-2-hydroxybenzylidene-4,6-O-ethylidine-β-D-glucopyranosylamine (H3L2) molecules possessing a–C-1–N=C(H)–moiety for metal-ion binding were synthesized by condensing the 4,6–O–ethylidene–β–D–glucopyranosylamine with salicylaldehyde or 5–bromosalicylaldehyde. Complexes of these ligands with Zn(II) were isolated and characterized using elemental analysis, FTIR, UV–Vis absorption, NMR spectroscopic and FAB mass spectrometric techniques. The structure of the Zn(II) complex derived from H3L1 was established for the first time by a single-crystal X-ray diffraction study. The anomeric nature of the saccharide moie…
Altered Mitochondrial Function and Oxidative Stress in Leukocytes of Anorexia Nervosa Patients
2014
ContextAnorexia nervosa is a common illness among adolescents and is characterised by oxidative stress.ObjectiveThe effects of anorexia on mitochondrial function and redox state in leukocytes from anorexic subjects were evaluated.Design and settingA multi-centre, cross-sectional case-control study was performed.PatientsOur study population consisted of 20 anorexic patients and 20 age-matched controls, all of which were Caucasian women.Main outcome measuresAnthropometric and metabolic parameters were evaluated in the study population. To assess whether anorexia nervosa affects mitochondrial function and redox state in leukocytes of anorexic patients, we measured mitochondrial oxygen consumpt…