Search results for "Spectroscopy"
showing 10 items of 10293 documents
Stereoselective synthesis of the cytotoxic 14-membered macrolide aspergillide A.
2010
A stereoselective synthesis of the cytotoxic 14-membered macrolide aspergillide A has been performed. The preparation of a cis-2,6-disubstituted tetrahydropyran ring via stereoselective reduction of an intermediate cyclic hemiacetal was one key feature of the synthesis. The macrocyclic lactone ring was created by means of a ring-closing metathesis (RCM), whereby the new C=C bond displayed exclusively the undesired Z configuration. Conversion to the required E configuration was achieved via photochemical isomerization.
Electrospray ion mobility mass spectrometry of positively charged sodium bis[2-ethythexyl)sulfosuccinate aggregates.
2014
Collision cross-sections (CCS) of positively singly and multiply charged aggregates of the surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) in the gas phase have been measured by quadrupole ion mobility time-of-flight mass spectrometry. Calibration of the observed drift times to the CCS of the AOTNa non-covalent aggregates was achieved by collecting, under the same experimental conditions, the drift times of a range of singly and multiply charged polyalanine peptides whose CCS had been obtained by conventional ion mobility spectrometry. Together with an obvious increase of the aggregate cross-section with the aggregation number, it was found that the aggregate cross-section increa…
Expanding the 3d-4f heterometallic chemistry of the (py)2CO and pyCOpyCOpy ligands: structural, magnetic and Mössbauer spectroscopic studies of two F…
2011
Complex [Fe(II)Gd(III){pyCO(OEt)pyCOH(OEt)py}(3)](ClO(4))(2) (1) crystallizes in the Cc space group and contains one hexacoordinate ferrous ion and one enneacoordinate Gd(III) ion. Complex [Fe(2)(II)Gd(III){pyCO(OEt)py}(4)(NO(3))(H(2)O)][Gd(NO(3))(5)](0.5)(ClO(4)) (2) crystallizes in the C2/c space group and contains two hexacoordinate ferrous ions and one octacoordinate Gd(III) ion. Both complexes have been prepared by the metal-assisted ethanolysis of ligands di-2,6-(2-pyridylcarbonyl)pyridine (pyCOpyCOpy, dpcp) and di-2-pyridyl ketone ((py)(2)CO, dpk), which exhibit similar structures. Mössbauer spectroscopic studies of 2 revealed the presence of two quadrupole-split doublets of equal in…
Crystal structure of the bifunctional soybean Bowman-Birk inhibitor at 0.28-nm resolution. Structural peculiarities in a folded protein conformation.
1996
The Bowman-Birk inhibitor from soybean is a small protein that contains a binary arrangement of trypsin-reactive and chymotrypsin-reactive subdomains. In this report, the crystal structure of this anticarcinogenic protein has been determined to 0.28-nm resolution by molecular replacement from crystals grown at neutral pH. The crystal structure differs from a previously determined NMR structure [Werner, M. H. & Wemmer, D. E. (1992) Biochemistry 31, 999-1010] in the relative orientation of the two enzyme-insertion loops, in some details of the main chain trace, in the presence of favourable contacts in the trypsin-insertion loop, and in the orientation of several amino acid side chains. The p…
Physicochemical Properties of Copper(II) Bis(2-ethylhexyl) Sulfosuccinate Reversed Micelles
1998
Abstract Measurements of some physicochemical properties (density, viscosity, conductance, UV–vis spectra, IR spectra) of the water/copper(II) bis(2-ethylhexyl) sulfosuccinate (Cu(DEHSS) 2 )/CCl 4 microemulsions, at a fixed surfactant molal concentration ([Cu (DEHSS) 2 ] = 0.05003 mol kg −1 ), as function of the molar ratio R ( R = [water]/[DEHSS − ]) have been performed at 25°C. Information on some structural and dynamical properties of the water-containing Cu(DEHSS) 2 reversed micelles and of their evolution with R are derived from the experimental results. The comparison with the same properties of water-containing sodium bis(2-ethylhexyl) sulfosuccinate reversed micelles allows to evide…
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…
Fluorescence Correlation Spectroscopy in Dilute Polymer Solutions: Effects of Molar Mass Dispersity and the Type of Fluorescent Labeling
2015
Fluorescence correlation spectroscopy (FCS) has become an important tool in polymer science. Among various other applications the method is often applied to measure the hydrodynamic radius and the degree of fluorescent labeling of polymers in dilute solutions. Here we show that such measurements can be strongly affected by the molar mass dispersity of the studied polymers and the way of labeling. As model systems we used polystyrene and poly(methyl methacrylate) synthesized by atom transfer radical polymerization or free-radical polymerization. Thus, the polymers were either end-labeled bearing one fluorophore per chain or side-labeled with a number of fluorophores per chain proportional to…
Load-collapse-release cascades of amphiphilic guest molecules in charged dendronized polymers through spatial separation of noncovalent forces.
2012
The ability to pack guest molecules into charged dendronized polymers (denpols) and the possibility to release these guest molecules from subsequently densely aggregated denpols in a load-collapse-release cascade is described. Charged denpols, which constitute molecular objects with a persistent, well-defined envelope and interior, are capable of incorporating large amounts of amphiphilic guest molecules. Simultaneously, multivalent ions can coordinate to the surfaces of charged denpols, leading to counterion-induced aggregation of the already guest-loaded host structures. Thus, although the local guest concentration in denpol-based molecular transport might already be initially high due to…
Acylated triterpene saponins from the roots of Securidaca longepedunculata.
2009
Abstract Four triterpene saponins , 3- O -β- d -glucopyranosylpresenegenin 28- O -β- d -apiofuranosyl-(1 → 3)-β- d -xylopyranosyl-(1 → 4)-[β- d -apiofuranosyl-(1 → 3)]-α- l -rhamnopyranosyl-(1 → 2)-{4- O -[( E )-3,4,5-trimethoxycinnamoyl]}-β- d -fucopyranosyl ester, 3- O -β- d -glucopyranosylpresenegenin 28- O -β- d -apiofuranosyl-(1 → 3)-β- d -xylopyranosyl-(1 → 4)-[β- d -apiofuranosyl-(1 → 3)]-α- l -rhamnopyranosyl-(1 → 2)-[(6- O -acetyl)-β- d -glucopyranosyl-(1 → 3)]-{4- O -[( E )-3,4,5-trimethoxycinnamoyl]}-β- d -fucopyranosyl ester, 3- O -β- d -glucopyranosylpresenegenin 28- O -β- d -apiofuranosyl-(1 → 3)-β- d -xylopyranosyl-(1 → 4)-[β- d -apiofuranosyl-(1 → 3)]-α- l -rhamnopyranosyl-(…
Indanedione based binary chromophore supramolecular systems as a NLO active polymer composites
2010
Novel route to obtain EO material is proposed by supramolecular assembly of neutral-ground-state (NGS) and zwitterionic (ZWI) NLO chromophores in binary chromophore organic glass (BCOG) host–guest system. On a basis of our Langeven Dynamics (LD) molecular modeling combined with quantum chemical calculations, we have shown that anticipated enhancement NLO efficiency of BCOG material is possible via electrostatic supramolecular assembly of NGS with ZWI chromophore in antiparallel manner. Binding energy of such complex could be more dependent on molecular compatibility of components and local (atomic) charge distribution, then overall molecular dipole moments. According to our LD simulations t…