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Scattering Data (scattering + data)
Kinds of Scattering Data Selected AbstractsScattering from laterally heterogeneous vesicles.JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2007Despite growing interest in the formation of domains or `rafts' in cell and model membranes, there have been relatively few attempts to characterize such systems via scattering techniques. Previously [Pencer et al. (2006). J. Appl. Cryst.39, 293,303], it was demonstrated that the Porod invariant, Q, could be used to detect lateral segregation. Here, the general theory for scattering from laterally heterogeneous vesicles is outlined and form factors are derived for vesicles containing either single circular or annular domains. These form factors are then applied to the analysis of neutron scattering data from heterogeneous vesicles. Potential advantages and limitations of this technique are also discussed. [source] Iron K -edge anomalous small-angle X-ray scattering at 15-ID-D at the Advanced Photon SourceJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Nigel Kirby Small-angle X-ray scattering (SAXS) is an ideal technique for characterizing inorganic nanoparticles in biological specimens large enough to be representative of tissues. As tissues consist of complex mixtures of structures, identifying particular structural features from single-wavelength scattering data can be problematic. Synchrotron SAXS can supply element-specific structural information in complex samples, using anomalous scattering close to absorption edges. Anomalous dispersion is a secondary effect that produces relatively subtle changes in scattering patterns. In order to utilize this effect for anomalous SAXS analysis, stringent control of instrument performance is required. This work outlines the development of high-quality data collection and processing strategies for Fe K -edge anomalous SAXS on the ChemMatCARS beamline at the Advanced Photon Source (APS), Chicago, with an emphasis on intensity normalization. The methods reported here were developed during a study of iron-loaded mammal tissues, but could equally well be applied to other complex specimens. [source] PRINSAS, a Windows-based computer program for the processing and interpretation of small-angle scattering data tailored to the analysis of sedimentary rocksJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2004Alan L. Hinde PRINSAS is a Windows program that takes as input raw (post-reduction) small-angle neutron and small-angle X-ray scattering (SANS and SAXS) data obtained from various worldwide facilities, displays the raw curves in interactive log,log plots, and allows processing of the raw curves. Separate raw SANS and ultra-small-angle neutron scattering (USANS) curves can be combined into complete scattering curves for an individual sample. The combined curves can be interpreted and information inferred about sample structure, using built-in functions. These have been tailored for geological samples and other porous media, and include the ability to obtain an arbitrary distribution of scatterer sizes, the corresponding specific surface area of scatterers, and porosity (when the scatterers are pores), assuming spherical scatterers. A fractal model may also be assumed and the fractal dimension obtained. A utility for calculating scattering length density from the component oxides is included in the program. [source] Elucidation of zeolite microstructure by synchrotron X-ray diffuse scatteringJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2004B. J. Campbell Single-crystal diffuse scattering measurements can now rapidly probe the three-dimensional structure of subtle defects in microporous framework materials. Diffuse scattering data from natural mordenite crystals are shown to exhibit a complex distribution of weak features which have been mapped out using a synchrotron X-ray source and a CCD detector. Comparison with computer-simulated diffuse scattering patterns yields a detailed three-dimensional columnar defect structure and reveals that roughly one third of the mordenite's columnar defects cooperate to form a block-mosaic pattern of {110} stacking faults. [source] Low-resolution structure of immunoglobulins IgG1, IgM and rheumatoid factor IgM-RF from solution X-ray scattering dataJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003Vladimir V. Volkov Low-resolution structures of immunoglobulins IgG, IgM and rheumatoid factor IgM-RF in solution were analyzed using synchrotron radiation small-angle X-ray scattering and the macromolecular shapes were restored ab initio from the scattering data. The shape of IgG agrees well with the distorted Y-type crystallographic model but has a swollen appearance reflecting flexibility of the molecule in solution. The structures of pentameric IgM and IgM-RF were reconstructed assuming a five-fold symmetry. The IgM displays a flat star-like shape with observable F(ab)2 regions. The overall shape of the IgM-RF is similar to that of the IgM but with distinctly asymmetric F(ab)2 regions. This result agrees with the earlier observed functional dissimilarity of the Fab fragments in the rheumatoid factor and points to their structural dissimilarity. [source] Evaluation of anisotropic small-angle neutron scattering data; a faster approachJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003Pavel Strunz An improvement of the anisotropic small-angle neutron scattering (SANS) data evaluation program is presented. The program is particularly suited for treatment of data from dense precipitate systems like those appearing in single crystal Ni-base superalloys. A new model of the precipitate microstructure was implemented allowing for a significant shortening of the evaluation time which is necessary mainly for in-situ studies. The change concerns the mode in which the size distribution is calculated. The local random smearing of the size as well as the distance of particles was introduced, too, which leads to a more realistic look of the microstructure model. The form of individual cuboidal particle was changed as well. The characteristics of the new microstructure model with respect to the SANS data modeling are tested on several measured as well as simulated data. [source] Modelling of small-angle X-ray scattering data using Hermite polynomialsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2001A. K. Swain A new algorithm, called the term-selection algorithm (TSA), is derived to treat small-angle X-ray scattering (SAXS) data by fitting models to the scattering intensity using weighted Hermite polynomials. This algorithm exploits the orthogonal property of the Hermite polynomials and introduces an error-reduction ratio test to select the correct model terms or to determine which polynomials are to be included in the model and to estimate the associated unknown coefficients. With no a priori information about particle sizes, it is possible to evaluate the real-space distribution function as well as three- and one-dimensional correlation functions directly from the models fitted to raw experimental data. The success of this algorithm depends on the choice of a scale factor and the accuracy of orthogonality of the Hermite polynomials over a finite range of SAXS data. An algorithm to select a weighted orthogonal term is therefore derived to overcome the disadvantages of the TSA. This algorithm combines the properties and advantages of both weighted and orthogonal least-squares algorithms and is numerically more robust for the estimation of the parameters of the Hermite polynomial models. The weighting feature of the algorithm provides an additional degree of freedom to control the effects of noise and the orthogonal feature enables the reorthogonalization of the Hermite polynomials with respect to the weighting matrix. This considerably reduces the error in orthogonality of the Hermite polynomials. The performance of the algorithm has been demonstrated considering both simulated data and experimental data from SAXS measurements of dewaxed cotton fibre at different temperatures. [source] Bayesian estimation of hyperparameters for indirect Fourier transformation in small-angle scatteringJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2000Steen Hansen Bayesian analysis is applied to the problem of estimation of hyperparameters, which are necessary for indirect Fourier transformation of small-angle scattering data. The hyperparameters most frequently needed are the overall noise level of the experiment and the maximum dimension of the scatterer. Bayesian methods allow the posterior probability distribution for the hyperparameters to be determined, making it possible to calculate the distance distribution function of interest as the weighted mean of all possible solutions to the indirect transformation problem. Consequently no choice of hyperparameters has to be made. The applicability of the method is demonstrated using simulated as well as real experimental data. [source] Advanced solution scattering data analysis methods and their applicationsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000D. I. Svergun A method for ab initio low-resolution shape and internal structure retrieval from contrast variation solution scattering data is described. The method uses a multiphase model of a particle build from densely packed dummy atoms and employs simulated annealing to find a compact interconnected configuration of phases that fits the available experimental data. In the particular case of a single phase particle (shape determination) the method is compared to another ab initio method using low resolution envelope functions. Examples of the shape determination of several proteins from experimental X-ray scattering data are presented. [source] A software system for rigid-body modelling of solution scattering dataJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000M.B. Kozin A computer system for rigid body modelling against solution scattering data is described. Fast algorithms to compute scattering from a complex of two arbitrary positioned subunits are implemented and coupled with the graphics program ASSA (Kozin, Volkov & Svergun, 1997, J. Appl. Cryst.30, 811-815). Mutual positions and orientations of the subunits (represented by low-resolution envelopes or by atomic models) can be determined by interactively fitting the experimental scattering curve from the complex. The system runs on the major Unix platforms (SUN, SGI and DEC workstations). [source] Cationic, water-soluble, fluorene-containing poly(arylene ethynylene)s: Effects of water solubility on aggregation, photoluminescence efficiency, and amplified fluorescence quenching in aqueous solutionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2006Yan-Qin Huang Abstract Three novel fluorene-containing poly(arylene ethynylene)s with amino-functionalized side groups were synthesized through the Sonogashira reaction. They were poly{9,9-bis[6,-(N,N -diethylamino)hexyl]-2,7-fluorenylene ethynylene}- alt - co -{2,5-bis[3,-(N,N -diethylamino)-1,-oxapropyl]-1,4-phenylene} (P1), poly{9,9-bis[6,-(N,N -diethylamino)hexyl]-2,7-fluorenylene ethynylene} (P2), and poly({9,9-bis[6,-(N,N -diethylamino)hexyl]-2,7-fluorenylene ethynylene}- alt - co -(1,4-phenylene)) (P3). Through the postquaternization treatment of P1,P3 with methyl iodide, we obtained their cationic water-soluble conjugated polyelectrolytes (WSCPs): P1,,P3,. The water solubility was gradually improved from P3, to P1, with increasing contents of hydrophilic side chains. After examining the ultraviolet,visible absorption and photoluminescence (PL) spectra, fluorescence lifetimes, and dynamic light scattering data, we propose that with the reduction of the water solubility from P1, to P3,, they exhibited a gradually increased degree of aggregation in H2O. The PL quantum yields of P1,,P3, in H2O displayed a decreasing tendency consistent with the increased degree of aggregation, suggesting that the pronounced degree of aggregation was an important reason for the low PL quantum yields of WSCPs in H2O. Two structurally analogous water-soluble trimers of P2, and P3,, model compounds 2,7-bis(9,,9,-bis{6,-[(N,N -diethyl)- N -methylammonium] hexyl}-2,-fluorenylethynyl)-9,9-bis{6,-[(N,N -diethyl)- N -methylammonium]hexyl}fluorene hexaiodide and 1,4-bis(9,,9,-bis{6,-[(N,N -diethyl)- N -methylammonium]hexyl}-2,-fluorenylethynyl)benzene tetraiodide, were synthesized. The amplified fluorescence quenching of these WSCPs by Fe(CN)64, in H2O was studied by comparison with a corresponding analogous trimer. The effects of aggregation on the fluorescence quenching may be two-edged in these cases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5778,5794, 2006 [source] High-resolution wide-angle X-ray scattering of protein solutions: effect of beam dose on protein integrityJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2003Robert F. Fischetti Wide-angle X-ray scattering patterns from proteins in solution contain information relevant to the determination of protein fold. At relevant scattering angles, however, these data are weak, and the degree to which they might be used to categorize the fold of a protein is unknown. Preliminary work has been performed at the BioCAT insertion-device beamline at the Advanced Photon Source which demonstrates that one can collect X-ray scattering data from proteins in solution to spacings of at least 2.2,Å (q = 2.8,Å,1). These data are sensitive to protein conformational states, and are in good agreement with the scattering predicted by the program CRYSOL using the known three-dimensional atomic coordinates of the protein. An important issue in the exploitation of this technique as a tool for structural genomics is the extent to which the high intensity of X-rays available at third-generation synchrotron sources chemically or structurally damage proteins. Various data-collection protocols have been investigated demonstrating conditions under which structural degradation of even sensitive proteins can be minimized, making this technique a viable tool for protein fold categorization, the study of protein folding, unfolding, protein,ligand interactions and domain movement. [source] Soliton solutions of the Toda hierarchy on quasi-periodic backgrounds revisitedMATHEMATISCHE NACHRICHTEN, Issue 4 2009Iryna Egorova Abstract We investigate soliton solutions of the Toda hierarchy on a quasi-periodic finite-gap background by means of the double commutation method and the inverse scattering transform. In particular, we compute the phase shift caused by a soliton on a quasi-periodic finite-gap background. Furthermore, we consider short range perturbations via scattering theory. We give a full description of the effect of the double commutation method on the scattering data and establish the inverse scattering transform in this setting (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Chemical bonding of nitrogen in dilute InAsN and high In-content GaInAsNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007D. N. Talwar Abstract To assess the preferential chemical bonding of N in dilute InAsN and high In content GaInNAs alloys we have analyzed the recent infrared absorption and Raman scattering data by using a comprehensive Green's function theory within an 11 parameter rigid-ion-model. Our theoretical results provided firm corroboration to some of the observed N- related modes to specific bonding (micro clusters) configurations. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Interface and confined polar optical phonons in spherical ZnO quantum dots with wurtzite crystal structurePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004Vladimir A. Fonoberov Abstract We derive analytically the interface and confined polar optical-phonon modes for spherical quantum dots with wurtzite crystal structure. While the frequency of confined optical phonons in zincblende nanocrystals is equal to that of the bulk crystal phonons, the confined polar optical phonons in wurtzite nanocrystals are shown to have a discrete spectrum of frequencies different from those in bulk crystal. The calculated frequencies of confined polar optical phonons in wurtzite ZnO quantum dots are found to be in excellent agreement with experimental resonant Raman scattering data. The derived analytical expression for phonon modes can facilitate interpretation of experimental data obtained for ZnO quantum dots. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Analysis of time-resolved X-ray scattering data from solution-state systemsACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2010Kristoffer Haldrup As ultrafast time-resolved studies of liquid systems with the laser pump/X-ray scattering probe method have come of age over the past decade, several groups have developed methods for the analysis of such X-ray scattering data. The present article describes a method developed primarily with a focus on determining structural parameters in the excited states of medium-sized molecules (~30 atoms) in solution. The general methodology is set in a maximum-likelihood framework and is introduced through the analysis of the photoactive platinum compound PtPOP, in particular the structure of its lowest triplet excited state (3A2u). Emphasis is put on structure determination in terms of model comparisons and on the information content of difference scattering signals as well as the related experimental variables. Several suggestions for improving the accuracy of these types of measurements are presented. [source] Structural characterization of unphosphorylated STAT5a oligomerization equilibrium in solution by small-angle X-ray scatteringPROTEIN SCIENCE, Issue 4 2009Pau Bernadó Abstract Signal transducer and activator of transcription (STAT) proteins play a crucial role in the activation of gene transcription in response to extracellular stimuli. The regulation and activity of these proteins require a complex rearrangement of the domains. According to the established models, based on crystallographic data, STATs convert from a basal antiparallel inactive dimer into a parallel active one following phosphorylation. The simultaneous analysis of small-angle X-ray scattering data measured at different concentrations of unphosphorylated human STAT5a core domain unambiguously identifies the simultaneous presence of a monomer and a dimer. The dimer is the minor species but could be structurally characterized by SAXS in the presence of the monomer using appropriate computational tools and shown to correspond to the antiparallel assembly. The equilibrium is governed by a moderate dissociation constant of Kd , 90 ,M. Integration of these results with previous knowledge of the N-terminal domain structure and dissociation constants allows the modeling of the full-length protein. A complex network of intermolecular interactions of low or medium affinity is suggested. These contacts can be eventually formed or broken to trigger the dramatic modifications in the dimeric arrangement needed for STAT regulation and activity. [source] Miranda cargo-binding domain forms an elongated coiled-coil homodimer in solution: Implications for asymmetric cell division in DrosophilaPROTEIN SCIENCE, Issue 5 2008Mohammad S. Yousef Abstract Miranda is a multidomain adaptor protein involved in neuroblast asymmetric division in Drosophila melanogaster. The central domain of Miranda is necessary for cargo binding of the neural transcription factor Prospero, the Prospero-mRNA carrier Staufen, and the tumor suppressor Brat. Here, we report the first solution structure of Miranda central "cargo-binding" domain (residues 460,660) using small-angle X-ray scattering. Ab initio modeling of the scattering data yields an elongated "rod-like" molecule with a maximum linear dimension (Dmax) of ,22 nm. Moreover, circular dichroism and cross-linking experiments indicate that the cargo-binding domain is predominantly helical and forms a parallel coiled-coil homodimer in solution. Based on the results, we modeled the full-length Miranda protein as a double-headed, double-tailed homodimer with a long central coiled-coil region. We discuss the cargo-binding capacity of the central domain and propose a structure-based mechanism for cargo release and timely degradation of Miranda in developing neuroblasts. [source] Determination of a one-electron reduced density matrix using a coupled pseudo-atom model and a set of complementary scattering dataACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2007Jean-Michel Gillet A possible model of one-electron reduced density matrices is presented, adapted from the Hansen,Coppens pseudo-atomic description of electron density [Hansen & Coppens (1978). Acta Cryst. A34, 909,913]. Potential benefits from a joint refinement of the model from X-ray diffraction and deep inelastic scattering data are illustrated. [source] Simultaneous fitting of X-ray and neutron diffuse scattering dataACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2007D. J. Goossens Conventional crystallographic refinement uses the Bragg-peak intensities and gives the single-site average crystal structure. Information about short-range order and local order is contained in the diffuse scattering that is distributed throughout reciprocal space. Models of the short-range order in materials can now be automatically refined. The complementarity of X-ray and neutron diffraction data, and the value of simultaneously refining a structural model against both types of data, has long been known. This paper presents the first refinement of a short-range-order model against comprehensive X-ray and neutron diffuse scattering data simultaneously. The sample is the organic molecular crystal benzil, C14H10O2 (for neutron work H is replaced by D). The technique gives new insights into local order in crystalline materials, including the dynamic correlation structure indicative of the dynamics of molecules in the crystalline state, and successfully overcomes limitations of using only the X-ray data set. [source] Single-crystal diffuse scattering studies on polymorphs of molecular crystals.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2009The drug benzocaine (ethyl 4-aminobenzoate), commonly used as a local anaesthetic, is a bimorphic solid at room temperature. Form (I) is monoclinic P21/c, while the metastable form (II) is orthorhombic P212121. Three-dimensional diffuse X-ray scattering data have been collected for the two forms on the 11-ID-B beamline at the Advanced Photon Source (APS). Both forms show strong and highly structured diffuse scattering. The data have been interpreted and analysed using Monte Carlo (MC) modelling on the basis that the scattering is purely thermal in origin and indicates the presence of highly correlated molecular motions. In both forms (I) and (II) broad diffuse streaks are observed in the 0kl section which indicate strong longitudinal displacement correlations between molecules in the ,031, directions, extending over distances of up to 50,Å. Streaks extending between Bragg peaks in the hk0 section normal to [100] correspond to correlated motions of chains of molecules extending along a that are linked by N,H...O=C hydrogen bonds and which occur together as coplanar ribbon pairs. The main difference between the two forms is in the dynamical behaviour of the ribbon pairs and in particular how they are able to slide relative to each other. While for form (I) a model involving harmonic springs is able to describe the motion satisfactorily, as simple excursions away from the average structure, there is evidence in form (II) of anharmonic effects that are precursors of a phase transition to a new low-temperature phase, form (III), that was subsequently found. [source] Structure of the sporulation histidine kinase inhibitor Sda from Bacillus subtilis and insights into its solution stateACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2009David A. Jacques The crystal structure of the DNA-damage checkpoint inhibitor of sporulation, Sda, from Bacillus subtilis, has been solved by the MAD technique using selenomethionine-substituted protein. The structure closely resembles that previously solved by NMR, as well as the structure of a homologue from Geobacillus stearothermophilus solved in complex with the histidine kinase KinB. The structure contains three molecules in the asymmetric unit. The unusual trimeric arrangement, which lacks simple internal symmetry, appears to be preserved in solution based on an essentially ideal fit to previously acquired scattering data for Sda in solution. This interpretation contradicts previous findings that Sda was monomeric or dimeric in solution. This study demonstrates the difficulties that can be associated with the characterization of small proteins and the value of combining multiple biophysical techniques. It also emphasizes the importance of understanding the physical principles behind these techniques and therefore their limitations. [source] The endoproteinase furin contains two essential Ca2+ ions stabilizing its N-terminus and the unique S1 specificity pocketACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2005Manuel E. Than The mammalian prohormone/proprotein convertase (PC) furin is responsible for the maturation of a great variety of homeostatic but also many pathogenic proteins within the secretory pathway and the endosomal pathway and at the cell surface. Similar to other members of the PC family, furin requires calcium for catalytic activity. In a previous paper, the structural association of the catalytic and the P-domain of furin was shown and data were presented indicating two or three calcium-binding sites. The exact number and the three-dimensional localization of the essential calcium sites within furin have now been determined by collecting X-ray diffraction data on either side of the Ca,K absorption edge and by calculating a novel type of double difference map from these anomalous scattering data. Two calcium ions were unambiguously identified: the purely structural Ca-1 also conserved in the bacterial digestive subtilisins and the Ca-2 site specific to PCs and essential for the formation of the P1 specificity-determining S1-binding pocket. In addition, these anomalous diffraction data show that no tightly bound K+ sites exist in furin. [source] Investigations of thermotropic phase behavior of newly developed synthetic PEGylated lipids using Raman spectro-microscopyBIOPOLYMERS, Issue 11 2008Rajan K. Bista Abstract In this article, a temperature-controlled Raman spectro-microscopic technique has been utilized to detect and analyze the phase behaviors of two newly developed synthetic PEGylated lipids trademarked as QuSomesÔ, which spontaneously form liposomes upon hydration in contrast to conventional lipids. The amphiphiles considered in this study differ in their hydrophobic hydrocarbon chain length and contain different units of polyethylene glycol (PEG) hydrophilic headgroups. Raman spectra of these new artificial lipids have been recorded in the spectral range of 500,3100 cm,1 by using a Raman microscope system in conjunction with a temperature-controlled sample holder. The gel to liquid phase transitions of the sample lipids composed of pure 1,2-dimyristoyl- rac -glycerol-3-dodecaethylene glycol (GDM-12) and 1,2-distearoyl- rac -glycerol-3-triicosaethylene glycol (GDS-23) have been revealed by plotting peak intensity ratios in the CH stretching region as a function of temperature. From this study, we have found that the main phase transitions occur at a temperature of ,5.2 and 21.2°C for pure GDM-12 and GDS-23, respectively. Furthermore, the lipid GDS-23 also shows a postphase transition temperature at 33.6°C. To verify our results, differential scanning calorimetry (DSC) experiments have been conducted and the results are found to be in an excellent agreement with Raman scattering data. This important information may find application in various studies including the development of lipid-based novel substances and drug delivery systems. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 1012,1020, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Radius of gyration of plasmid DNA isoforms from static light scatteringBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010David R. Latulippe Abstract Despite the extensive interest in applications of plasmid DNA, there have been few direct measurements of the root mean square radius of gyration, RG, of different plasmid isoforms over a broad range of plasmid size. Static light scattering data were obtained using supercoiled, open-circular, and linear isoforms of 5.76, 9.80, and 16.8,kbp plasmids. The results from this study extend the range of RG values available in the literature to plasmid sizes typically used for gene therapy and DNA vaccines. The experimental data were compared with available theoretical expressions based on the worm-like chain model, with the best-fit value of the apparent persistence length for both the linear and open-circular isoforms being statistically identical at 46,nm. A new expression was developed for the radius of gyration of the supercoiled plasmid based on a model for linear DNA using an effective contour length that is equal to a fraction of the total contour length. These results should facilitate the development of micro/nano-fluidic devices for DNA manipulation and size-based separation processes for plasmid DNA purification. Biotechnol. Bioeng. 2010;107: 134,142. © 2010 Wiley Periodicals, Inc. [source] Probing protein colloidal behavior in membrane-based separation processes using spectrofluorometric Rayleigh scattering dataBIOTECHNOLOGY PROGRESS, Issue 3 2010Rand Elshereef Abstract One of the primary problems in membrane-based protein separation is membrane fouling. In this study we explored the feasibility of employing Rayleigh light scattering data from fluorescence studies combined with chemometric techniques to determine whether a correlation could be established with membrane fouling phenomena. Membrane flux was measured in a dead-end UF filtration system and the effect of protein solution properties on the flux decline was systematically investigated. A variety of proteins were used as a test case in this study. In parallel, the colloidal behavior of the protein solutions was assessed by employing multiwavelength Rayleigh scattering measurements. To assess the usefulness of Rayleigh scattering measurements for probing the colloidal behavior of proteins, a protein solution of ,-lactoglobulin was used as a base-case scenario. The colloidal behavior of different ,-lactoglobulin solutions was inferred based on published data for this protein, under identical solution conditions, where techniques other than Rayleigh scattering had been used. Using this approach, good agreement was observed between scattering data and the colloidal behavior of this protein. To test the hypothesis that a high degree of aggregation will lead to increased membrane fouling, filtration data was used to find whether the Rayleigh scattering intensity correlated with permeate flux changes. It was found that for protein solutions which were stable and did not aggregate, fouling was reduced and these solutions exhibited reduced Rayleigh scattering. When the aggregation behavior of the solution was favored, significant flux declines occurred and were highly correlated with increased Rayleigh scattering. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | ||||||||||||||||