Search results for "Proton"
showing 10 items of 5886 documents
2-Acylamino- and 2,4-bis(acylamino)pyrimidines as supramolecular synthons analysed by multiple non-covalent interactions. DFT, X-ray diffraction, and…
2012
Intermolecular interactions of ten 2-acylamino and 2,4-bis(acylamino)pyrimidines (7 of which are previously unknown) have been investigated by X-ray structural, quantum chemical (DFT), and NMR spectral methods. Especially the concentration dependencies of the (1)H NMR chemical shifts and titrations with other molecules capable of multiple hydrogen bonding provided useful information regarding their association via triple or quadruple hydrogen bonding, which is controlled by the conformational preferences of 2-acylamino- and 2,4-bis(acylamino)pyrimidines. On comparison of the properties of 2-acylamino- and 2,4-bis(acylamino)pyrimidines with the corresponding pyridines, an additional nitrogen…
Conformational studies of hexapeptides containing two dehydroamino acid residues in positions 2 and 5 in peptide chain
2008
Conformational preferences of a group of hexapeptides containing two dehydroamino acid residues in Positions 2 and 5 in peptide chain were investigated by means of spectroscopic methods (NMR and CD) and theoretical calculations. In the case of dimethylsulfoxide (DMSO) solution, only peptide with free N-termini adopted rigid 310-helical conformation, for the rest of examined peptides extended and “zig-zag” conformers were predominant. CD measurements showed that only in chloroform solution the conformational freedom of investigated peptides was restricted. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 691–699, 2008. This article was originally published online as an accepted preprint. The “…
Design and characterization of bi-functional electrocatalytic layers for application in PEM unitized regenerative fuel cells
2010
Abstract Results concerning the development and characterization of bi-functional electrocatalytic layers for application in unitized regenerative fuel cells (URFCs) based on proton exchange membrane (PEM) technology are reported. Carbon-supported hydrophobic (10 wt.% of PTFE) Pt catalysts (40 wt.% of Pt), and Pt and Ir black powders of large specific areas have been synthesized. Their structure, morphology and electrochemical properties have been investigated using SEM, TEM, XRD analysis, and by measurements of polarization curves and cyclic voltammograms. Current–voltage curves have been recorded during water electrolysis and H 2 /O 2 fuel cell experiments to evaluate their performances a…
Proton Conducting Membrane Prepared by Cross-Linking Highly Sulfonated Peek for PEMFC Application
2009
The proton conducting membrane was prepared by cross-linking highly sulfonated and sulfinated poly(etheretherketone) (SsPEEK). The cross-linked membrane is low cost due to its use of non-expensive chemical and simple production procedure. The membrane exhibited high proton conductivity (0.04 S/cm at 60 °C), extremely reduced water uptake, enhanced strength and stability compared with that of non-cross-linked membrane. These results suggested that the cross-linked PEEK membrane is a suitable candidate of proton conducting membranes for polymer electrolyte membrane fuel cell (PEMFC) applications, particularly promising to be used in direct methanol fuel cell (DMFC) due to its lower methanol c…
Insights into the Dynamics of Grotthuss Mechanism in a Proton-Conducting Chiral bioMOF
2016
Proton conduction in solids attracts great interest, not only because of possible applications in fuel cell technologies, but also because of the main role of this process in many biological mechanisms. Metal–organic frameworks (MOFs) can exhibit exceptional proton-conduction performances, because of the large number of hydrogen-bonded water molecules embedded in their pores. However, further work remains to be done to elucidate the real conducting mechanism. Among the different MOF subfamilies, bioMOFs, which have been constructed using biomolecule derivatives as building blocks and often affording water-stable materials, emerge as valuable systems to study the transport mechanisms involve…
The deprotonative metalation of [1,2,3]triazolo[1,5-a]quinoline. Synthesis of 8-haloquinolin-2-carboxaldehydes
2009
New highly functionalized triazoloquinolines were synthesized by applying polar organometallic methods. Double metalation and functionalization provided 3,9-dihalogenated triazoloquinolines. Ring opening of the triazole with loss of nitrogen has been performed for the first time with 3,9-dihalogenated triazoloquinolines allowing the access toward 8-haloquinolin-2-carboxaldehydes under oxidant-free conditions. This approach demonstrates that the triazole ring can be used as protecting group of 2-quinolinecarboxaldehydes, activating the C9-position for lithiation and functionalization by triazole ring opening. 8-Haloquinoline-2-carbaldehydes become in this way readily available.
FT-IR and nuclear overhauser enhancement study of the state of urea confined in AOT-reversed micelles
2003
Abstract The system urea/sodium-bis(2-ethylhexyl)sulfosuccinate (AOT) dispersed in CCl 4 and benzene-d6 was investigated by viscosimetry, FT-IR and high-resolution 1 H NMR spectroscopy, as a function of urea/AOT molar ratio ( R urea ) at fixed AOT molal concentration (0.3467 mol kg −1 ) and as a function of AOT concentration at fixed R urea (0.5) at 25 °C. The experimental data are consistent with the hypothesis that urea is encapsulated as small-size hydrogen-bonded cluster in the hydrophilic micellar core of the AOT-reversed micelles and that this structure is maintained well above the volume fraction of the dispersed phase, where a percolative transition occurs. Intermolecular nuclear ov…
Normal-phase (temperature gradient) interaction chromatography – A powerful tool for the characterisation of high molecular weight chain-end function…
2015
Abstract We report here, for the first time, quantitative analysis of end-group functionalisation and the extent of end-group modification of polymers with molar mass up to 200,000 g mol −1 , using a combination of isothermal and temperature gradient interaction chromatography. At such high molecular weights, other common analytical techniques such as MALDI-ToF-MS and NMR spectroscopy are simply unable to offer any quantitative insight into the end-group functionality of polymers. Thus, normal phase isothermal interaction chromatography (NP-IIC) has been used to characterise a series of polystyrene samples, with identical molar mass (c. 90,000 g mol −1 ), each carrying a single chain-end fu…
Mn(II) complexes with sulfonamides as ligands.
2012
Abstract Sulfonamides derived from 8-aminoquinoline react with Mn(II) and Mn(III) salts to form Mn(II) complexes; the Mn(III) species are reduced to the divalent state in the presence of 1,10 phenanthroline and bipyridine. Their molecular structure, determined by single crystal X‐ray diffraction, show that all the complexes present a distorted octahedral geometry, in which the deprotonated sulfonamide acts as a bidentate ligand. UV–visible spectroscopy and changes in the melting temperature (Tm) of calf thymus DNA show a strong interaction of these complexes with DNA. The significant hypochromicity of the charge transfer transition at 370 nm without an appreciable change in wavelength and t…
Reactivity of the di-μ-hydroxo-complexes [{Pd(NN)}2(μ-OH)2][ClO4]2 (NN=bis(pyrazol-1-yl)alkanes) towards protic electrophiles. Hydration of coordin…
2000
Abstract The hydroxo-complexes [{Pd(μ-OH)(NN)}2][ClO4]2 (NN=bpzm:bis(pyrazol-1-yl) methane: a-compounds, bpzm*:bis(3,5-dimethylpyrazol-1-yl)methane; b-compounds) react with a wide variety of weak protic electrophiles H(LL) in a 1:2 molar ratio to give the mononuclear cationic palladium(II) derivatives of general formula [Pd(LL)(NN)][ClO4] [LL=2-pyridine-methoxo (OCH2-py) (1a,b); picolinate (pic) (2a,b); 8-hydroxiquinolinate (oxin) (3a,b)] or the dinuclear complexes [{Pd(NN)}2(μ-ox)][ClO4]2 [ox=oxalate: (4a,b)] and [{Pd(μ-LL)(NN)}2][ClO4]2 [LL=pyrazolate (pz) (5a,b); p-thiocresolate (SC6H4Me-p) (6a,b); triazolate (tz) (7b); thiophenolate (SPh) (8b)] when reacting with oxalic acid, azole…