Mass overloading in the flow field-flow fractionation channel studied by the behaviour of the ultra-large wheat protein glutenin

Flow field-flow fractionation (FFF) has previously been used in successful fractionation and characterisation of the ultra-large wheat protein glutenin. The many parameters, which may influence the retention behaviour, especially when analysing extremely high-molecular-mass samples such as glutenin, are here reported. Size determination from the sample retention time, using FFF theory, will as a result have a very low accuracy. The need for direct molecular mass determination, such as by light scattering, in combination with FFF, in order to do accurate size measurements of glutenin is pointed out as well as the importance to minimise the overloading.     

Molecular mass distribution analysis of ethyl(hydroxyethyl)cellulose by size-exclusion chromatography with dual light-scattering and refractometric detection

Dual low-angle light scattering and refractometric detection coupled to size-exclusion chromatography provided proof for the presence of a low amount of stable aggregates/particles in ethyl(hydroxyethyl)cellulose. Unlike the correct size-exclusion chromatographic behavior of the parent polysaccharide itself, the aggregates exhibit variable size-dependent weak retention as a function of flow-rate and of ionic strength of the aqueous mobile phase. Therefore, determination of the molecular mass of non-aggregated polymer is possible in aqueous mobile phase containing 0.1 M NaCl under conditions at which aggregates are completely adsorbed on the column packing irrespective of the flow-rate used. Flow-rate and ionic strength-dependent variations of aggregate behavior as well as model size-exclusion experiments with latex particles indicate that they partly carry a minute charge and have a compact structure. Their weak retention under the separation conditions used suggests a difference in their surface chemistry when compared with the dissolved polymer coils which exhibit a correct size-exclusion behavior.     

Concurrent adsorption and complex formation in reversed-phase liquid-liquid chromatography with tri-n-octylphosphine oxide

Summary Reversed-phase liquid-liquid chromatographic systems consisting of an aqueous mobile phase and an organic liquid stationary phase of the proton acceptor tri-n-octylphosphine oxide (TOPO) inn-decane, coated on LiChrosorb RP-8, have been studied. The solutes were hydrophilic aromatic carboxylic acids and phenol. The retention of the carboxylic acids shows a minimum at 10 mM of TOPO, whereas increasingly tailing peaks have been obtained with decreasing concentrations of TOPO. This behaviour is due to a concurrent complex formation by hydrogen bonding with TOPO in the liquid stationary phase and adsorption at the interface between the support and the liquid stationary phase. The adsorption of TOPO, ketones and aromatic acids from hexane on Li-Chrosorb RP-8 has been studied, and seems to be due to residual silanol groups. The adsorption isotherm of TOPO has been determined and can be described by a two-site Langmuir adsorption model. Non polar solutes are not adsorbed. The influence of TOPO on the retention and the peak symmetry of carboxylic acids in the liquid-liquid chromatographic system appears to be due to a competition between TOPO and the acids for the same adsorption sites. No competition was found for phenol.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Cerebral abnormalities in Wilson''s disease as evaluated by ultra-low-field magnetic resonance imaging and computerized image processing

The cerebral involvement of a 13-yr-old boy with Wilson's disease was serially evaluated during the first 18 mo of D-penicillamine treatment. An ultra-low-field magnetic resonance imaging (ULF MRI) system, operating at 0.02 T, with computerized image processing was used. The half-yr period prior to the clinical diagnosis was set, the patient had showed poor school performance, emotional lability, deteriorating handwriting, progressively slow, gross, and fine motor functions, and a fixed rigid smile. No overt signs of liver disease were found. With D-penicillamine treatment (1–1.5 g/d) a continuous improvement was seen. The pretreatment MRI investigation showed pronounced pathological transformation in the basal ganglia. However, changes were seen also in most other parts of the brain indicating diffuse involvement. During treatment the computerized MR images became gradually more normal. The current magnetic resonance imaging system with computerized image processing is a sensitive and simple method for evaluation of subtle parenchymal changes of the brain.     

Size separations of starch of different botanical origin studied by asymmetrical-flow field-flow fractionation and multiangle light scattering

Asymmetrical-flow field-flow fractionation combined with multiangle light scattering and refractive index detection has been revealed to be a powerful tool for starch characterization. It is based on size separation according to the hydrodynamic diameter of the starch components. Starch from a wide range of different botanical sources were studied, including normal starch and high-amylose and high-amylopectin starch. The starch was dissolved by heat treatment at elevated pressure in a laboratory autoclave. This gave clear solutions with no granular residues. Amylose retrogradation was prevented by using freshly dissolved samples. Programmed cross flow starting at 1.0 mL min(-1) and decreasing exponentially with a half-life of 4 min was utilised. The starches showed two size populations representing mainly amylose and mainly amylopectin with an overlapping region where amylose and amylopectin were possibly co-eluted. Most of the first population had molar masses below 10(6) g mol(-1), and most of the second size population had molar masses above 10(7) g mol(-1). Large differences were found in the relative amounts of the two populations, the molar mass, and hydrodynamic diameters, depending on the plant source and its varieties.     

Dibenzothiophene-S,S-dioxide-fluorene co-oligomers. Stable, highly-efficient blue emitters with improved electron affinity

Incorporation of dibenzothiophene-S,S-dioxide units into conjugated fluorene oligomers changes the frontier orbital energy levels and presents an effective way to increase the electron affinity of these materials, which are highly fluorescent with bright blue emission in both solution and the solid state.     

Two-photon absorption and photoluminescence of europium based emissive probes for bioactive systems

Observation of two-photon excitation (760 nm) and emission of two responsive water soluble europium complexes is reported with cross-sections of up to 2 GM. Two-photon excitation spectra have also been measured, acquisition being achieved by the use of a cavity-dumped mode locked Ti-sapphire laser. Time-gated detection is used to differentiate the ligand fluorescence and metal centred emission in these europium complexes.     

Direct conjugation of semiconductor nanocrystals to a globular protein to study protein-folding intermediates

In this Article, we study the development of semiconductor nanocrystals (quantum dots of average diameter less than 2 nm) directly conjugated to a transporter protein human serum albumin (HSA) as fluorescent biological labels. F?rster resonance energy transfer (FRET) from the amino acid tryptophan (Trp214) to quantum dot in HSA is monitored to follow the local and global changes in the protein structure during thermal unfolding and refolding processes. This study is likely to attract widespread attention as a powerful tool for the study of protein folding.     

Programmed cross flow asymmetrical flow field-flow fractionation for the size separation of pullulans and hydroxypropyl cellulose

Different functions for the programming of the cross flow in asymmetrical flow field-flow fractionation were studied with the aim to find the flow conditions most suitable for the molar mass distribution analysis of high molecular weight polysaccharides. A mixture of four differently sized pullulans covering the molar mass range 5.8 x 10(3)-1.6 x 10(6) g mol(-1) were used as a model sample. Two types of programs were studied, linear and exponential decays, both with and without initial periods of a constant cross flow. For comparison, nonprogrammed runs, i.e. using constant cross flow, were studied. It was found that exponentially decaying cross flow gave the most uniform molar mass selectivity across the fractogram. The programmed cross flow was applied to the molar mass distribution analysis of a technical quality of hydroxypropyl cellulose.