PMC:2812708 / 1442-7329 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/2812708","sourcedb":"PMC","sourceid":"2812708","source_url":"https://www.ncbi.nlm.nih.gov/pmc/2812708","text":"Introduction\nAnalytical Ultracentrifugation is an analytical absolute technique applying centrifugal force to fractionate the sample and optical detection systems to detect the concentration distribution of the sample inside the ultracentrifuge cell. These experiments yield a number of important physico-chemical quantities of the sample like size, shape, density, molar mass, sedimentation and diffusion coefficient, interaction constants and stoichiometry etc. and many of them in form of distributions. However, often the available information depends on the applied optical detection system. Optical systems that have been constructed are UV/vis absorption, Rayleigh interference, Schlieren and the Lavrenko Optics (Lavrenko et al. 1999; Lloyd 1974). Development of new optical detection systems can expand the possible use of AUC for different types of samples. Size distributions can be determined with Turbidity optics (Mächtle 1992; Müller 1989; Scholtan and Lange 1972). Fluorescence optics has expanded the use for extremely diluted labeled samples even in presence of other solutes at a much higher concentration (MacGregor et al. 2004; Schmidt and Riesner 1992). The only commercially available machine at the moment is the Beckman XL-I which is equipped with a UV/vis absorption optics and Rayleigh interference optics (Giebeler 1992). Recently, the UV/vis absorption detection was significantly improved by the development of a multiwavelength UV/vis absorption detector (MWL-AUC). By essentially replacing the monochromator with a spectrograph, the MWL-AUC delivers an entire UV/vis spectrum for each radial point instead of a single wavelength reading (Bhattacharyya et al. 2006; Strauss et al. 2008). This technology has a number of advantages over the commercial absorption optics detecting at a single wavelength with time-consuming wavelength scanning, thus excluding the study of all fast processes, Obtaining full UV/vis spectra at each point in the ultracentrifuge cell rather than a radial concentration profile at a single wavelength can give much more structural information about the sample, allows for averaging and can even decrease the experimental time when modern fast CCD based spectrometers are used (Bhattacharyya et al. 2006; Strauss et al. 2008). Successful optical, mechanical, radial scan, linearity and noise tests of the MWL detector have been published recently (Strauss et al. 2008).\nCombined with the fractionating power of the AUC, application of the MWL detector with its additional structural and/or compositional information on light absorbing samples can yield distributions of the individual components in complex mixtures with respect to composition and size/density related to different chromophores. This can start with relatively straightforward issues like sample homogeneity and purity but can then get increasingly complex in case of composite and/or interacting samples. Especially for such complex samples MWL-AUC has a huge potential, as spectral discrimination can synergistically enhance the hydrodynamic resolution (Balbo et al. 2005). This is also an important issue for any colored industrial product composed of at least two components which at least slightly differ in their UV/vis spectra. In this work, we will show the capabilities of MWL-AUC for the analysis of an industrial composite sample of β-carotene and gelatin. This system was investigated before with X-ray scattering, UV/vis absorption spectroscopy, FOQELS (Fiber-optic quasi-elastic light scattering), microelectrophoresis and on basis of these results, a core-shell structure was presented (Auweter et al. 1999), as shown in Fig. 2. The core structure with 120 nm diameter consists of partially crystallized, partially amorphous β-carotene as active ingredient. The shell structure consists of gelatin, functioning as bio-degradable protection colloid. This hybrid structure self-assembles in a carefully tuned co-precipitation of gelatin (from an aqueous solution) and the active ingredient (from a lipophilic solvent). Such particulate formulations can transport an active ingredient that is not water soluble across an aqueous phase with high bioavailability, in this case provitamin A. These particles are not persistent, but disassemble and get digested quickly in biological media.\nThere are two forms of hydrosol that are explained in Auweter et al. (1999). β-carotenes can precipitate as H-aggregate or J-aggregate; the two morphologies do not interconvert and are regarded to be kinetically stable over years. The H-aggregate is observed in precipitation of dilute solutions (0.3 weight%) whereas the J-aggregate is observed at higher concentration (1.0 weight%). Auweter et al. (1999) calculated a 40 nm hypsochromic shift observed for an H-aggregate and a bathochromic shift in J-aggregates. This results in a significant color change from yellow to red of the product depending on the precipitation conditions and hybrid particle size (Figs. 1, 2). This color change is the basis for the industrial application of the β-carotenes as pigments for food applications.\nFig. 1 Dashed line UV/vis spectrum of the core-shell β-carotene/gelatin sample with 0.05 g/l concentration; solid line UV/vis spectrum of gelatin at 1 g/l\nFig. 2 Left side Assumed structure of the β-carotene microparticle system (Auweter et al. 1999), right side color change of β-carotene/gelatin microparticles due to particle size and structure\nNot only the purity of the sample concerning the color characteristics (brilliance of color due to steep absorbance profiles) or sample homogeneity (different species or unbound gelatin) is of interest for the industrial application but furthermore any possible transitions between different structures. This is a problem which can be advantageously solved in a single MWL-AUC experiment, which we will describe in this work.","divisions":[{"label":"title","span":{"begin":0,"end":12}},{"label":"p","span":{"begin":13,"end":2427}},{"label":"p","span":{"begin":2428,"end":4322}},{"label":"p","span":{"begin":4323,"end":5461}},{"label":"figure","span":{"begin":5112,"end":5267}},{"label":"label","span":{"begin":5112,"end":5118}},{"label":"caption","span":{"begin":5119,"end":5267}},{"label":"p","span":{"begin":5119,"end":5267}},{"label":"figure","span":{"begin":5268,"end":5461}},{"label":"label","span":{"begin":5268,"end":5274}},{"label":"caption","span":{"begin":5275,"end":5461}},{"label":"p","span":{"begin":5275,"end":5461}}],"tracks":[{"project":"MyTest","denotations":[{"id":"19242689-15043928-28778234","span":{"begin":1143,"end":1147},"obj":"15043928"},{"id":"19242689-19816525-28778235","span":{"begin":1712,"end":1716},"obj":"19816525"},{"id":"19242689-19816525-28778236","span":{"begin":2278,"end":2282},"obj":"19816525"},{"id":"19242689-19816525-28778237","span":{"begin":2421,"end":2425},"obj":"19816525"},{"id":"19242689-15613487-28778238","span":{"begin":3093,"end":3097},"obj":"15613487"}],"namespaces":[{"prefix":"_base","uri":"https://www.uniprot.org/uniprot/testbase"},{"prefix":"UniProtKB","uri":"https://www.uniprot.org/uniprot/"},{"prefix":"uniprot","uri":"https://www.uniprot.org/uniprotkb/"}],"attributes":[{"subj":"19242689-15043928-28778234","pred":"source","obj":"MyTest"},{"subj":"19242689-19816525-28778235","pred":"source","obj":"MyTest"},{"subj":"19242689-19816525-28778236","pred":"source","obj":"MyTest"},{"subj":"19242689-19816525-28778237","pred":"source","obj":"MyTest"},{"subj":"19242689-15613487-28778238","pred":"source","obj":"MyTest"}]},{"project":"2_test","denotations":[{"id":"19242689-15043928-28778234","span":{"begin":1143,"end":1147},"obj":"15043928"},{"id":"19242689-19816525-28778235","span":{"begin":1712,"end":1716},"obj":"19816525"},{"id":"19242689-19816525-28778236","span":{"begin":2278,"end":2282},"obj":"19816525"},{"id":"19242689-19816525-28778237","span":{"begin":2421,"end":2425},"obj":"19816525"},{"id":"19242689-15613487-28778238","span":{"begin":3093,"end":3097},"obj":"15613487"}],"attributes":[{"subj":"19242689-15043928-28778234","pred":"source","obj":"2_test"},{"subj":"19242689-19816525-28778235","pred":"source","obj":"2_test"},{"subj":"19242689-19816525-28778236","pred":"source","obj":"2_test"},{"subj":"19242689-19816525-28778237","pred":"source","obj":"2_test"},{"subj":"19242689-15613487-28778238","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"MyTest","color":"#b993ec","default":true},{"id":"2_test","color":"#93ec9f"}]}]}}