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PubMed2005

Improving packaged food quality and safety. Part 1: synchrotron X-ray analysis.

The objective was to demonstrate, as an example of an application, the potential of synchrotron X-ray analysis to detect morphological alterations that can occur in barrier packaging materials and structures. These changes can affect the packaging barrier characteristics when conventional food preservation treatments are applied to packaged food. The paper presents the results of a number of experiments where time-resolved combined wide-angle X-ray scattering and small-angle X-ray scattering analysis as a function of temperature and humidity were applied to ethylene-vinyl alcohol co-polymers (EVOH), polypropylene (PP)/EVOH/PP structures, aliphatic polyketone terpolymer (PK) and amorphous polyamide (aPA) materials. A comparison between conventional retorting and high-pressure processing treatments in terms of morphologic alterations are also presented for EVOH. The impact of retorting on the EVOH structure contrasts with the good behaviour of the PK during this treatment and with that of aPA. However, no significant structural changes were observed by wide-angle X-ray scattering in the EVOH structures after high-pressure processing treatment. These structural observations have also been correlated with oxygen permeability measurements that are of importance when guaranteeing the intended levels of safety and quality of packaged food.

Environmental Exposure↗

PubMed2004

The role of hydrophobic interactions in catalysis of RNA cleavage by 1,4-diazabicyclo[2.2.2]-octane based artificial ribonucleases.

Molecular interactions of RNA cleaving compounds-conjugates of 1,4-diazabicyclo[2.2.2.]octane substituted at the bridge position with tetradecamethylene fragment and imidazole were investigated using light scattering and small angle x-ray scattering methods. The compounds are known to efficiently cleave RNA and one source of the activity could result from micellar catalysis. It was found that the compounds indeed are capable of forming complex aggregates in solution. However, maximal efficacy of RNA cleavage by the conjugates is observed at concentrations well below the concentration required for micelle formation.

Catalysis↗

PubMed2006

Small-angle x-ray scattering study of flow alignment of a thermotropic liquid crystal in the nematic and smectic phases.

The capillary flow alignment of the thermotropic liquid crystal 4-n-octyl-4'-cyanobiphenyl in the nematic and smectic phases is investigated using time-resolved synchrotron small-angle x-ray scattering. Samples were cooled from the isotropic phase to erase prior orientation. Upon cooling through the nematic phase under Poiseuille flow in a circular capillary, a transition from the alignment of mesogens along the flow direction to the alignment of layers along the flow direction (mesogens perpendicular to flow) appears to occur continuously at the cooling rate applied. The transition is centered on a temperature at which the Leslie viscosity coefficient alpha3 changes sign. The configuration with layers aligned along the flow direction is also observed in the smectic phase. The transition in the nematic phase on cooling has previously been ascribed to an aligning-nonaligning or tumbling transition. At high flow rates there is evidence for tumbling around an average alignment of layers along the flow direction. At lower flow rates this orientation is more clearly defined. The layer alignment is ascribed to surface-induced ordering propagating into the bulk of the capillary, an observation supported by the parallel alignment of layers observed for a static sample at low temperatures in the nematic phase.

Journal Article↗

PubMed2000

Effective screening of hydrodynamic interactions in charged colloidal suspensions.

We investigate the hydrodynamic interaction in suspensions of charged colloidal silica spheres. The volume fraction as well as the range of the electrostatic repulsion between the spheres is varied. Using a combination of dynamic x-ray scattering, cross-correlated dynamic light scattering, and small angle x-ray scattering, the hydrodynamic function H(q) is determined experimentally. The effective hydrodynamic interactions are found to be screened, if the range of the direct interaction is relatively long and the static density correlations are strong. This observation of effective hydrodynamic screening is in marked contrast to hard-sphere-like systems.

Journal Article↗

PubMed1993

Investigations of the architecture of tamarind seed polysaccharide in aqueous solution by different scattering techniques.

The architecture of tamarind seed polysaccharide (TSP) has been investigated by light scattering (LS), small angle X-ray scattering (SAXS) and synchrotron radiation scattering (SRSAXS). The experimental data show that TSP in aqueous solution consists of multi stranded aggregates, with a high degree of particle stiffness. The angular dependence of the scattered intensity is typical for wormlike chains. Data evaluation on the basis of this model yields a statistical Kuhn segment length lK = 150 nm. The cross sectional radius of gyration is estimated as Rgcs = 6.0 +/- 0.5 A, which is more than twice the value, published for single stranded polysaccharides. Correspondingly, the experimental value of the linear mass density, measured by LS, is about five times higher than the theoretical value calculated from the primary structure.

Light↗

PubMed2006

Effective phase function for light scattered by blood.

The scattering process induced in blood by a collimated laser beam is theoretically investigated. An individual red blood cell (RBC) has a scattering phase function strongly peaked in the forward direction. For far-field experiments, the small scattering volumes can be considered as "macroscopic particles" characterized by an effective scattering phase function. Using the single-cell phase function as "input data" the angular distribution of light scattered at small angles by the whole scattering volume, containing RBCs in suspension, is calculated analytically. The angular dispersion of the light scattered by blood can be approximately described by the same formula used to characterize the light scattered by a single cell but with an effective, hematocrit-dependent anisotropy parameter.

Anisotropy↗

PubMed1991

Neutron and x-ray scatter studies of the histone octamer and amino and carboxyl domain trimmed octamers.

The structure of the nucleosome has been under intense investigation using neutron crystallography, x-ray crystallography, and neutron solution scattering. However the dimension of the histone octamer inside the nucleosome is still a subject of controversy. The radius of gyration (Rg) of the octamer obtained from solution neutron scattering of core particles at 63% 2H2O, 37% 1H2O is 33 A, and x-ray crystallography study of isolated histone octamer gives a Rg of 32.5 A, while the reported values using x-ray crystallography of core particles from two individual studies are 29.7 and 30.4 A, respectively. We report here studies of isolated histone octamer and trypsin-limited digested octamer using both neutron solution scattering and small angle x-ray scattering. The Rg of the octamer obtained is 33 A, whereas that of the trimmed octamer is 29.8 A, similar to the structure obtained from the crystals of the core particles. The N-terminal domains of the core histones in the octamer have been shown by high resolution nuclear magnetic resonance (Schroth, G.P., Yau, P., Imai, B.S., Gatewood, J.M., and Bradbury, E.M. (1990) FEBS Lett. 268, 117-120) to be mobile and flexible; it is likely that these regions are disordered and "not seen" by x-ray crystallography.

Animals↗

PubMed2005

Small-angle X-ray scattering, light scattering, and NMR study of PEO-PPO-PEO triblock copolymer/cationic surfactant complexes in aqueous solution.

The formation of triblock copolymer/surfactant complexes upon mixing a nonionic Pluronic polymer (PEO-PPO-PEO) with a cationic surfactant, hexadecyltrimethylammonium chloride (CTAC), has been studied in dilute aqueous solutions using small-angle X-ray scattering, static and dynamic light scattering, and self-diffusion NMR. The studied copolymer (denoted P123, EO(20)PO(68)EO(20)) forms micelles with a radius of 10 nm and a molecular weight of 7.5 x 10(5), composed of a hydrophobic PPO-rich core of radius 4 nm and a water swollen PEO corona. The P123/CTAC system has been investigated between 1 and 5 wt % P123 and with varying surfactant concentration up to approximately 170 mM CTAC (or a molar ratio n(CTAC)/n(P123) = 19.3). When CTAC is mixed with micellar P123 solutions, two different types of complexes are observed at various CTAC concentrations. At low molar ratios (>/=0.5) a "P123 micelle-CTAC" complex is obtained as the CTAC monomers associate noncooperatively with the P123 micelle, forming a spherical complex. Here, an increased interaction between the complexes with increasing CTAC concentration is observed. The interaction has been investigated by determining the structure factor obtained by using the generalized indirect Fourier transformation (GIFT) method. The interaction between the P123 micelle-CTAC complexes was modeled using the Percus-Yevick closure. For the low molar ratios a small decrease in the apparent molecular weight of the complex was obtained, whereas the major effect was the increase in electrostatic repulsion between the complexes. Between molar ratios 1.9 and 9 two coexisting complexes were found, one P123 micelle-CTAC complex and one "CTAC-P123" complex. The latter one consists of one or a few P123 unimers and a few CTAC monomers. As the CTAC concentration increases above a molar ratio of 9, the P123 micelles are broken up and only the CTAC-P123 complex that is slightly smaller than a CTAC micelle exists. The interaction between the P123/CTAC complexes was modeled with the hypernetted-chain closure using a Yukawa type potential in the GIFT analysis, due to the stronger electrostatic repulsion.

Journal Article↗

PubMed2000

pH-dependent unfolding of aspergillopepsin II studied by small-angle X-ray scattering.

Aspergillopepsin II (EC 3.4.23.6) secreted from the fungus Aspergillus niger var. macrosporus is a non-pepsin-type acid proteinase. It consists of two polypeptide chains (i.e., a heavy chain and a light chain), which are bound noncovalently to each other. The pH titration analysis using small-angle X-ray scattering (SAXS) as well as circular dichroism (CD) and gel filtration indicated that the enzyme was unfolded around a neutral pH with concomitant dissociation of the two chains. Detailed analyses showed that the midpoint pH values for the unfolding are not coincident with one another (pH 6.1 in circular dichroism and gel filtration, pH 6.4 in zero-angle intensity of SAXS, pH 6.8 in radius of gyration). The difference between these values suggested the existence of an intermediate state during the unfolding. Further analyses of the SAXS data showed that the heavy chain just after the dissociation still kept molecular compactness and that it gradually increased its dimensions as the pH was further raised. Noncoincidence of the two phenomena (i.e., chain dissociation and swelling) led to elucidation of a novel intermediate state during unfolding, which was confirmed by the subsequent singular value decomposition (SVD) analysis.

Aspartic Acid Endopeptidases↗

PubMed2001

Crystallization of a recombinant form of the complete sequence of human gamma-interferon: characterization by small-angle X-ray scattering, mass spectrometry and preliminary X-ray diffraction studies.

The crystallization conditions of a recombinant form of the complete sequence of human gamma-interferon, designated r-hu IFN-gamma (RU 42369), have been determined after studying the behaviour of this protein in solution by small-angle X-ray scattering (SAXS) as a function of pH and salt type. IFN-gamma is difficult to crystallize without truncating at least the last five amino acids of the C-terminus; the SAXS results suggest viable crystallization conditions that led to crystals of r-hu IFN-gamma suitable for X-ray diffraction analysis. The crystals were grown in the presence of ammonium sulfate using vapour-diffusion techniques. The crystals, which diffract to 5 A resolution at best, belong to the primitive tetragonal space group P42(1)2 and have unit-cell parameters a = b = 123.4, c = 93.4 A. The protein contained in these crystals was analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), which verified the presence of the complete amino-acid sequence of r-hu IFN-gamma.

Crystallization↗

PubMed2001

Small-angle X-ray scattering analysis of stearic acid modified lipase.

Stearic acid modified lipase (from Rhizopus japonicus) exhibited remarkable interesterification activity in n-hexane, but crude native lipase did not. The structure of the fatty acid modified lipase had not been analyzed until now. We analyzed the modified lipase by small-angle X-ray scattering (SAXS) measurements in order to clarify the structure. SAXS measurements showed that the modified lipase consisted of a lipid lamellar structure and implied that the lipase was incorporated into the lamellar structure of stearic acid. The long spacings in the lamellar structures of the modified lipase and stearic acid were measured.

Algorithms↗

PubMed2004

Activation mechanisms of transcriptional regulator CooA revealed by small-angle X-ray scattering.

CooA, a heme-containing transcriptional activator, binds CO to the heme moiety and then undergoes a structural change that promotes the specific binding to the target DNA. To elucidate the activation mechanism coupled to CO binding, we investigated the CO-dependent structural transition of CooA with small-angle X-ray scattering (SAXS). In the absence of CO, the radius of gyration Rg and the second virial coefficient (A2) were 25.3(+/-0.5)A and -0.39(+/-0.25) x 10(-4)ml mol g(-2), respectively. CO binding caused a slight increase in Rg (by 0.5A) and a marked decrease in A2 (by 5.09 x 10(-4)ml mol g(-2)). The observed decrease in A2 points to higher attractive interactions between CO-bound CooA molecules in solution compared with CO-free CooA. Although the minor alternation of Rg rules out changes in the overall structure, the marked change in the surface properties points to a CO-induced conformational transition. The experimental Rg and SAXS curves of the two states did not agree with the crystal structure of CO-free CooA. We thus simulated the solution structures of CooA based on the experimental data using rigid-body refinements as well as low-resolution model reconstructions. Both results demonstrate that the hinge region connecting the N-terminal heme domain and C-terminal DNA-binding domain is kinked in CO-free CooA, so that the two domains are positioned close to each other. The CO-dependent structural change observed by SAXS corresponds to a slight swing of the DNA-binding domains away from the heme domains coupled with their rotation by about 8 degrees around the axis of 2-fold symmetry.

Amino Acids↗

PubMed2005

Studies of the structural change during deformation in Cryptomeria japonica by time-resolved synchrotron small-angle X-ray scattering.

A definite proportional limit which has been observed typically in metallic materials during the transition from elastic deformation into plastic one was also detected in the load-displacement curve of the compression wood with the water content about 100% from Cryptomeria japonica D. Don. Time-resolved small-angle X-ray scattering studies demonstrated a large structural change, that is, a strong decrease in the microfibril angle in the cell wall occurring with increasing the displacement beyond the proportional limit for the compression wood loaded in uniaxial tension. Correspondingly, the mechanical properties are changed and high elongations begin to be seen. For the dried normal wood, on the other hand, only a weak decrease in the microfibril angle was observed with increasing the elongation until the fracture is initiated, where the elastic behavior was maintained.

Cryptomeria↗

PubMed2004

Structural insights into the mechanism of formation of cellulosomes probed by small angle X-ray scattering.

Exploring the mechanism by which the multiprotein complexes of cellulolytic organisms, the cellulosomes, attain their exceptional synergy is a challenge for biologists. We have studied the solution structures of the Clostridium cellulolyticum cellulosomal enzyme Cel48F in the free and complexed states with cohesins from Clostridium thermocellum and Clostridium cellulolyticum by small angle x-ray scattering in order to investigate the conformational events likely to occur upon complexation. The solution structure of the free cellulase indicates that the dockerin module is folded, whereas the linker connecting the catalytic module to the dockerin is extended and flexible. Remarkably, the docking of the different cohesins onto Cel48F leads to a pleating of the linker. The global structure determined here allowed modeling of the atomic structure of the C. cellulolyticum dockerin-cohesin interface, highlighting the local differences between both organisms responsible for the species specificity.

Amino Acid Sequence↗

PubMed2005

Structure and interactions of block copolymer micelles of Brij 700 studied by combining small-angle X-ray and neutron scattering.

Spherical micelles of the diblock copolymer/surfactant Brij 700 (C(18)EO(100)) in water (D(2)O) solution have been investigated by small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). SAXS and SANS experiments are combined to obtain complementary information from the two different contrast conditions of the two techniques. Solutions in a concentration range from 0.25 to 10 wt % and at temperatures from 10 to 80 degrees C have been investigated. The data have been analyzed on absolute scale using a model based on Monte Carlo simulations, where the micelles have a spherical homogeneous core with a graded interface surrounded by a corona of self-avoiding, semiflexible interacting chains. SANS and SAXS data were fitted simultaneously, which allows one to obtain extensive quantitative information on the structure and profile of the core and corona, the chain interactions, and the concentration effects. The model describes the scattering data very well, when part of the EO chains are taken as a "background"contribution belonging to the solvent. The effect of this becomes non-negligible at polymer concentrations as low as 2 wt %, where overlap of the micellar coronas sets in. The results from the analysis on the micellar structure, interchain interactions, and structure factor effects are all consistent with a decrease in solvent quality of water for the PEO block as the theta temperature of PEO is approached.

Journal Article↗

PubMed2005

Small-angle X-ray scattering from a dual-component organogel to exhibit a charge transfer interaction.

The structure of a dual-component organogel consisting of methyl 4,6-O-(p-aminobenzylidene)-alpha-D-glucopyranoside and methyl 4,6-O-(p-nitrobenzylidene)-alpha-D-glucopyranoside in diphenyl ether was investigated with small-angle X-ray scattering (SAXS). The individual components gelatinized the solvent to yield a colorless gel and the gel fiber consisted of the crystal, providing the crystalline peaks at the same diffraction angles as those of the solid samples. When the components were mixed in equimolar ratio and dissolved in diphenyl ether, a yellow gel was formed and the crystalline peaks disappeared. For all compositions, the SAXS profiles were well fitted by a cylinder model. The cross-sectional radius of gyration, r(c), was determined from the cross-sectional Guinier plot (qI vs q(2), where I and q are the scattering intensity and the magnitude of the scattering vector). The value of r(c) reached a minimum of 3.0 nm at the equimolar composition. By correcting the data for the thermal scattering background, we obtained the entire SAXS profile for the equimolar dual-component gel. From this profile, the radial electron density distribution was determined and the radius of the cylinder was estimated to be 2.6 nm. The electron density distribution thus obtained revealed that four gelator molecules are packed in the sectional direction. This model was consistent with the size of the gelator molecules.

Journal Article↗

PubMed1982

Small-angle x-ray scattering study of halophilic malate dehydrogenase.

Malate dehydrogenase from the organism Halobacterium marismortui was studied in solutions of varying salt concentration by using a small-angle X-ray system employing a linear position sensitive detector. Considerations pertaining to the study of absorbing multicomponent solutions are presented. The radius of gyration of halophilic malate dehydrogenase was found to be 31.8 +/- 0.6 A and the shape of the molecule spheroidal. The scattering from prolate ellipsoids of eccentricity between 1 and 2 best fitted the data while for oblate ellipsoids the scattering was best fitted for eccentricities between 1 and 0.5. No significant change in the radius of gyration or anisotropy of halophilic malate dehydrogenase was found in the range of NaCl concentrations studied (1-4 M). The contrast matching electron density was found to be 0.407 +/- 0.002 e/A3. A parallel study of bovine serum albumin yielded within experimental error a similar contrast matching electron density of 0.404 +/- 0.006 e/A3. This information combined with the diffusion coefficient and the amount of water and salt associated with halophilic malate dehydrogenase renders the existence of an outer hydration shell unlikely. The data are rather consistent at low resolution with a spheroidal particle of uniform electron density.

Halobacterium↗

PubMed1977

Studies by small-angle x-ray scattering of the quaternary structure of dissociation products of the beta-haemocyanin of Helix pomatia.

Helix pomatia beta-haemocyanin was split into dissociation products by varying the pH and the ionic strength. The purity of the solution was checked in an ultracentrifuge. Two defined dissociation products were studied in solution by small-angle X-ray scattering. In Tris-HC1 buffer, pH 8.0 and ionic strength 1 M, the following parameters of the dissociation product (tenths) could be determined: molecular weight = 7 x 10(5), volume = 1350 nm3, radius of gyration = 9.0 nm, maximal distance = 28.3 nm, radius of the spherical subunits about 2.6 nm, number of the subunits approximately 19. Tris-HC1 buffer, pH 8.7 and ionic strength 0.01 M, yielded dissociation products (twentieths) with the following parameters: molecular weight = 3.5 x 10(5), volume = 635 nm3, radius of gyration = 7.5 nm, maximal distance = 21.9 nm, radius of the spherical subunits about 2.5 nm. With this information, the assumption that the larger fragment was double the smaller one and the latest biochemical and morphological results, theoretical scattering curves of models were calculated and compared with the experimental curves. Two models are suggested which argee well with the dissociation products in radius of gyration and scattering.

Animals↗