Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Neutron Diffraction”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
PubMed2003

Size and shape of the repetitive domain of high molecular weight wheat gluten proteins. I. Small-angle neutron scattering.

The solution structure of the central repetitive domain of high molecular weight (HMW) wheat gluten proteins has been investigated for a range of concentrations and temperatures using mainly small-angle neutron scattering. A representative part of the repetitive domain (dB1) was studied as well as an "oligomer" basically consisting of four dB1 units, which has a length similar to the complete central domain. The scattering data over the entire angular range of both proteins are in quantitative agreement with a structural model based on a worm-like chain, a model frequently used in polymer theory. This model describes the "supersecondary structure" of dB1 and dB4 as a semiflexible cylinder with a length of about 235 and 900 A, respectively, and a cross-sectional diameter of about 15 A. The flexibility of both proteins is characterized by a persistence length of about 13 A. Their structures are thus quantitatively identical, which implies that the central HMW domain can be elongated while retaining its structural characteristics. It seems conceivable that the flexible cylinder results from a helical structure, which resembles the beta-spiral observed in earlier studies on gluten proteins and elastin. However, compared to the previously proposed structure of a (stiff) rod, our experiments clearly indicate flexibility of the cylinder.

Biopolymers↗
PubMed2006

Drug-excipient interactions in ketoprofen: a vibrational spectroscopy study.

Ketoprofen (3-benzoyl-alpha-methylbenzeneacetic acid) is a widely used nonsteroidal anti-inflammatory drug (NSAID), always administered in the form of drug-excipient physical mixtures (PMs). The occurrence of possible interactions between ketoprofen and two commonly used excipients-lactose (LAC) and polyvinylpyrrolidone (PVP)-was evaluated, through vibrational spectroscopy techniques [both Raman and Inelastic Neutron Scattering (INS)]. Spectral evidence of drug:excipient close contacts, which were enhanced by aging, was verified for the (1:1) (w:w) (ketoprofen:PVP) and (ketoprofen:LAC) PMs, both by Raman and INS. These interactions were found to involve mainly the central carbonyl and the terminal methyl-carboxylic moieties of the ketoprofen molecule, this being reflected in particular vibrational modes, such as the methyl torsion, the out-of-plane C-OH bending, and the inter-ring C=O stretching.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2007

Nanostructures by self-assembling peptide amphiphile as potential selective drug carriers.

The self-assembling behavior, at physiological pH, of the amphiphile peptide (C18)(2)L5CCK8 in nanostructures is reported. Stable aggregates presenting a critical micellar concentration of 2 x 10(-6) mol kg(-1), and characterized by water exposed CCK8 peptide in beta-sheet conformation, are obtained. Small angle neutron scattering experiments are indicative for a 3D structure with dimensions > or =100 nm. AFM images confirm the presence of nanostructures. Fluorescence experiments indicating the sequestration of pyrene, chosen as drug model, and the anticancer Doxorubicin within the nanostructures are reported.

Antineoplastic Agents↗
PubMed2004

Crystal refinement and magnetic structure of KNi4(PO4)3: a novel example of three interacting magnetic sub-lattices.

KNi(4)(PO(4))(3) has been synthesised following a method previously reported by some of us and studied on the basis of magnetization and neutron powder diffraction (NPD) data. Magnetization measurements suggest the coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) interactions: magnetization versus magnetic field curves present a remanent magnetization of around 2.15 micro(B) at T=2 K. The magnetic structure of the KNi(4)(PO(4))(3) has been determined at low temperature from the NPD data. These measurements show that there are three magnetic sub-lattices of Ni(2+) ions, which interact through common oxygen or phosphate groups, giving rise to FM and AFM couplings. The resulting interactions are FM in nature. Such a complex behaviour could provide an interesting model to analyse magnetic interactions in more condensed systems, such in mixed metal oxides.

Journal Article↗
PubMed2004

Compressed octahedral coordination in chain compounds containing divalent copper: structure and magnetic properties of CuFAsF6 and CsCuAlF6.

Crystal structures and magnetic investigations of CuFAsF6 and CsCuAlF6 are reported. Together with KCuAlF6, these appear to be the only examples of Jahn-Teller pure Cu(II) compounds containing only one type of ligand that exhibits a compressed octahedral coordination geometry. The Rietveld method has been used for refining the CsCuAlF6 structure based on neutron powder diffraction data at 4 K. The compound crystallizes in space group Pnma (no. 62) with a=7.055(1), b=7.112(1), c=10.153(1) A and Z=4 at 4 K. The structure is built from infinite [CuF5]n(3n-) chains of [CuF6]4- octahedra running along the [1 0 0] direction and (AlF6)3- octahedra connected by corners in the trans position, thus giving rise to chains oriented along the [0 1 0] direction. Single crystals of CuFAsF6 were prepared under solvothermal conditions in AsF5 above its critical temperature. The structure was determined from single-crystal data. CuFAsF6 crystallises in the orthorhombic space group Imma (No. 74) with a=10.732(5), b=6.941(3), c=6.814(3) A and Z=4 at 200 K. The structure can also be described in terms of one-dimensional infinite [CuF5]n(3n-) chains of tilted [CuF6](4-) octahedra linked by trans-vertices running along the b axis. The [CuF5]n(3n-) chains are connected through [AsF6]- units sharing joint vertices. The compressed octahedral coordination of CuII atoms in CuFAsF6 and CsCuAlF6 compounds at room temperature is confirmed by Cu K-edge EXAFS (extended x-ray absorption fine structure) analysis. For both compounds strong antiferromagnetic interactions within the [CuF5]n(3n-) chains were observed (theta(p)=-290+/-10 K and theta(p)=-390+/-10 K for CuFAsF6 and CsCuAlF6, respectively). The peculiar magnetic behaviour of chain compounds containing divalent copper at low temperature could be related to uncompensated magnetic moments in the one-dimensional network.

Journal Article↗
PubMed2006

Structural effects of crosslinking a biopolymer hydrogel derived from marine mussel adhesive protein.

In an effort to explore new biocompatible substrates for biomedical technologies, we present a structural study on a crosslinked gelatinous protein extracted from marine mussels. Prior studies have shown the importance of iron in protein crosslinking and mussel adhesive formation. Here, the structure and properties of an extracted material were examined both before and after crosslinking with iron. The structures of these protein hydrogels were studied by SEM, SANS, and SAXS. Viscoelasticity was tested by rheological means. The starting gel was found to have a heterogeneous porous structure on a micrometer scale and, surprisingly, a regular structure on the micron to nanometer scale. However disorder, or "no periodic structure", was deduced from scattering on nanometer length scales at very high q. Crosslinking with iron condensed the structure on a micrometer level. On nanometer length scales at high q, small angle neutron scattering showed no significant differences between the samples, possibly due to strong heterogeneity. X-ray scattering also confirmed the absence of any defined periodic structure. Partial crosslinking transformed the viscoelastic starting gel into one with more rigid and elastic properties.

Animals↗
PubMed2003

Hydration in proteins observed by high-resolution neutron crystallography.

It is well known that water molecules surrounding a protein play important roles in maintaining its structural stability. Water molecules are known to participate in several physiological processes through the formation of hydrogen bonds. However, the hydration structures of most proteins are not known well at an atomic level at present because X-ray protein crystallography has difficulties to localize hydrogen atoms. In contrast, neutron crystallography has no problem in determining the position of hydrogens with high accuracy.1 In this article, the hydration structures of three proteins are described- myoglobin, wild-type rubredoxin, and a mutant rubredoxin-the structures of which were solved at 1.5- or 1.6-A resolution by neutron structure determination. These hydration patterns show fascinating features and the water molecules adopt a variety of shapes in the neutron Fourier maps, revealing details of intermolecular hydrogen bond formation and dynamics of hydration. Our results further show that there are strong relationships between these shapes and the water environments.

Hydrogen↗
PubMed2004

Biomolecular and amphiphilic films probed by surface sensitive X-ray and neutron scattering.

In this review article we discuss the thin film analytical techniques of interface sensitive X-ray and neutron scattering applied to aligned stacks of amphiphilic bilayers, in particular phospholipid membranes in the fluid L(alpha) phase. We briefly discuss how the structure, composition, fluctuations and interactions in lipid or synthetic membranes can be studied by modern surface sensitive scattering techniques, using X-rays or neutrons as a probe. These techniques offer an in-situ approach to study lipid bilayer systems in different environments over length scales extending from micrometer to nanometer, both with and without additional membrane-active molecules such as amphiphilic peptides or membrane proteins.

Lipid Bilayers↗
PubMed2003

Determination of bilayer thickness and lipid surface area in unilamellar dimyristoylphosphatidylcholine vesicles from small-angle neutron scattering curves: a comparison of evaluation methods.

Small-angle neutron scattering (SANS) experiments were performed on unilamellar 1,2-dimyristoylphosphatidylcholine (DMPC) vesicles prepared in heavy water by extrusion through polycarbonate filters with 500 A pores. The data obtained at 30+/-0.1 degrees C were evaluated using a five-strip function model of the bilayer coherent neutron scattering length density, three different approximate form factors describing scattering from vesicles, and different methods of evaluation of the experimental data. It is shown that the results obtained from the SANS data in the range of scattering vector values 0.0316 A(-1)< q<0.0775 A(-1) are not sensitive to the vesicle form factor, nor to the evaluation method. Using the hollow sphere model of vesicles convoluted with the Gaussian distribution of their sizes, a constrained bilayer polar region thickness of 9 A and a DMPC headgroup volume of 325.5 A(3), it was possible to obtain from the experimental data the DMPC surface area as 58.9+/-0.8 A(2), the bilayer thickness as 44.5+/-0.3 A and the number of water molecules as 6.8+/-0.2 per DMPC located in the bilayer polar region.

Algorithms↗
PubMed2004

Protein dynamics in solution and powder measured by incoherent elastic neutron scattering: the influence of Q-range and energy resolution.

Incoherent elastic neutron scattering (IENS) has been widely used to measure intramolecular atomic mean square displacements (MSDs) of proteins in powder and in solution. The instrumental energy resolution and the wave vector transfer (Q-range) determine, respectively, the time and length scales of observable motions. In order to investigate contributions of diffusive motions to MSDs measured by this method, we calculated the elastic intensity for several simple scattering functions. We showed that continuous translational diffusion contributes to MSDs in a Q-range where the energy width of the scattering function is of the order of the instrumental energy resolution. We discuss the choice of instruments adapted to focus on intramolecular motions in the presence of solvent or global macromolecular diffusion. The concepts developed are applied to interpret experimental data from H(2)O- and D(2)O-hydrated proteins. Finally, analogies between the Gaussian approximation in IENS and the Guinier approximation in small-angle scattering are discussed.

Computer Simulation↗
PubMed2004

Polymer-cushioned lipid bilayers in porous alumina.

Using small-angle neutron scattering (SANS) and cyclic voltammetry (CV), we show that model biological membranes can be deposited on a polymer cushion confined in highly regular porous alumina. The thicknesses of the dilute polymer cushion chemically bound to the alumina and of the supported bilayer are obtained for two polyethylene glycol cushions (PEG(5000) and PEG(20000)) and for a cushion made of chains bearing a lipid anchor at their free end (DSPE-PEG(3400)). The bilayers are studied well below and well above the chain melting temperature of the lipid mixture (DMPC/DMPE: 80/20), using a coenzyme (Ubiquinone, UQ(10)) as a redox probe for the voltammetry experiments. Analysis of the SANS form factor of the bilayers shows that the bilayer thickness can be extracted in this particular geometry. Using PEG chains grafted at a low surface density (D < 2R(g)), the thickness of the complete molecular construction is obtained by CV, which shows (after subtracting the bilayer thickness) that the polymer cushion thickness can be varied from 50 to 150 Angstroms. The values obtained with three different chain lengths, are in perfect agreement with the radius derived from the Flory theory.

Aluminum Oxide↗
PubMed2005

Multilamellarity, structure and hydration of extruded POPC vesicles by SANS.

The small-angle neutron scattering (SANS) data of 12 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) dispersions at low lipid concentration (1 mg per 100-mg heavy water) prepared by 5, 9 and 29 extrusions through filters of pores with 50, 100, 200 and 400 nm diameter are presented. They were analyzed within a theory that permits the determination of both structural and hydration parameters of the bilayers as well as the portions of multilamellar vesicles in dispersions with negligible long-range order between the vesicles. The scattering length density profile across the bilayers is approximated by assuming a central hydrocarbon core surrounded by a water-accessible coat. It is modeled by two different forms of functions. In the boat model, the scattering length density of the coat changes linearly from core to water, whereas in the strip model it is constant across the water-accessible coat. It was found that the boat model reflects the reality better than the strip model. The decrease of the multilamellar vesicle portions, either with increasing the number of extrusions at same filter size and with decreasing the filter size, was characterized quantitatively.

Lipid Bilayers↗
PubMed2006

What can we learn about the lipid vesicle structure from the small-angle neutron scattering experiment?

Small-angle neutron scattering (SANS) on the unilamellar vesicle (ULV) populations (diameter 500 and 1,000 A) in D2O was used to characterize lipid vesicles from dimyristoylphosphatidylcholine (DMPC) at three phases: gel Lbeta', ripple Pbeta' and liquid Lalpha. Parameters of vesicle populations and internal structure of the DMPC bilayer were characterized on the basis of the separated form factor (SFF) model. Vesicle shape changes from nearly spherical in the Lalpha phase to elliptical in the Pbeta' and Lbeta' phases. This is true for vesicles prepared via extrusion through pores with the diameter 500 A. Parameters of the internal bilayer structure (thickness of the membrane and the hydrophobic core, hydration and the surface area of the lipid molecule) were determined on the basis of the hydrophobic-hydrophilic (HH) approximation of neutron scattering length density across the bilayer rhox and of the step function (SF) approximation of rhox. DMPC membrane thickness in the Lalpha phase (T = 30 degrees C) demonstrates a dependence on the membrane curvature for extruded vesicles. Prepared via extrusion through 500 A diameter pores, vesicle population in the Lalpha phase has the following characteristics: average value of minor semi-axis 266 +/- 2 A, ellipse eccentricity 1.11 +/- 0.02, polydispersity 26%, thickness of the membrane 48.9 +/- 0.2 A and of the hydrophobic core 19.9 +/- 0.4 A, surface area 60.7 +/- 0.5 A2 and number of water molecules 12.8 +/- 0.3 per DMPC molecule. Vesicles prepared via extrusion through pores with the diameter 1,000 A have polydispersity of 48% and membrane thickness of 45.5 +/- 0.6 A in the Lalpha phase. SF approximation was used to describe the DMPC membrane structure in Lbeta' (T = 10 degrees C) and Pbeta' (T = 20 degrees C) phases. Extruded DMPC vesicles in D2O have membrane thickness of 49.6 +/- 0.5 A in the Lbeta' phase and 48.3 +/- 0.6 A in the Pbeta' phase. The dependence of the DMPC membrane thickness on temperature was restored from the SANS experiment.

Biophysical Phenomena↗
PubMed2006

Comparison of hydrogen determination with X-ray and neutron crystallography in a human aldose reductase-inhibitor complex.

Protonation states determination by neutron (2.2 A at room temperature) and X-ray (0.66 A at 100 K) crystallographic studies were compared for a medium size enzyme, human aldose reductase (MW=36 kDa), complexed with its NADP+ coenzyme and a selected inhibitor of therapeutic interest. The neutron resolution could be achieved only with the ab initio fully deuterated protein and the subsequent crystallization in D2O of the complex. We used the largest good-quality crystal (1.00x0.67x0.23 mm, i.e. volume of 0.15 mm3) that we were able to grow so far. Both studies enable the determination of protonation states, with a clear advantage for neutrons in the case of less-ordered atoms (B>5 A2). Hydrogen atoms are best determined by a complementary analysis of the Fourier maps obtained from both methods.

Aldehyde Reductase↗
PubMed1993

Pigmenting agents in Martian soils: inferences from spectral, Mossbauer, and magnetic properties of nanophase and other iron oxides in Hawaiian palagonitic soil PN-9.

We have examined a Hawaiian palagonitic tephra sample (PN-9) that has spectroscopic similarities to Martian bright regions using a number of analytical techniques, including Mossbauer and reflectance spectroscopy, X-ray diffraction, instrumental neutron activation analysis, electron probe microanalysis, transmission electron microscopy, and dithionite-citrate-bicarbonate extraction. Chemically, PN-9 has a Hawaiitic composition with alkali (and presumably silica) loss resulting from leaching by meteoric water during palagonitization; no Ce anomaly is present in the REE pattern. Mineralogically, our results show that nanophase ferric oxide (np-Ox) particles (either nanophase hematite (np-Hm) or a mixture of ferrihydrite and np-Hm) are responsible for the distinctive ferric doublet and visible-wavelength ferric absorption edge observed in Mossbauer and reflectivity spectra, respectively, for this and other spectrally similar palagonitic samples. The np-Ox particles appear to be imbedded in a hydrated aluminosilicate matrix material; no evidence was found for phyllosilicates. Other iron-bearing phases observed are titanomagnetite, which accounts for the magnetic nature of the sample; olivine; pyroxene; and glass. By analogy, np-Ox is likely the primary pigmenting agent of the bright soils and dust of Mars.

Evolution, Planetary↗
PubMed2005

Characterization of polyanion-protein complexes by frontal analysis continuous capillary electrophoresis and small angle neutron scattering: effect of polyanion flexibility.

The binding constant (K(obs)) for the beta-lactoglobulin-poly(vinylsulfate) (BLG-PVS) complex was measured by frontal analysis continuous capillary electrophoresis at pH values above the isoelectric point of BLG, and the persistence length (L(p)) of PVS was measured by small angle neutron scattering, to examine the effect of polyelectrolyte chain stiffness on its binding efficiency to proteins. The values of K(obs) and L(p) were compared with those of BLG-PSS and BLG-PAMPS (poly(2-acrylamido-2-methylpropanesulfonate)) reported previously. The relationship between K(obs) and L(p) was reciprocal, indicating that protein binding is enhanced by the flexibility of the polyanion, at least in the case where the net protein charge is negative. In addition, at a fixed pH, the polymer systems displayed a similar ionic strength dependence of K(obs). This similarity was consistent with the proposal that the binding properties of PVS and PAMPS polyanions are governed purely by electrostatic interactions and are independent of their molecular structure.

Electrophoresis, Capillary↗
PubMed2005

Divalent ion-dependent swelling of tomato bushy stunt virus: a multi-approach study.

Time-resolved small-angle X-ray and neutron scattering (SAXS and SANS) in solution were used to study the swelling reaction of TBSV upon chelation of its constituent calcium at mildly basic pH. SAXS intensities comprise contribution from the protein capsid and the RNA moiety, while neutron scattering, recorded in 72% D2O, is essentially due to the protein capsid. Cryo-electron micrographs of compact and swollen virus were used to produce 3D reconstructions of the initial and final conformations of the virus at a resolution of 13 A and 19 A, respectively. While compact particles appear to be very homogeneous in size, solutions of swollen particles exhibit some size heterogeneity. A procedure has been developed to compute the SAXS pattern from the 3D reconstruction for comparison with experimental data. Cryo-electron microscopy thereby provides an invaluable starting (and ending) point for the analysis of the time-resolved swelling process using the scattering data.

Cations, Divalent↗
PubMed2005

Bilayer thickness and thermal response of dimyristoylphosphatidylcholine unilamellar vesicles containing cholesterol, ergosterol and lanosterol: a small-angle neutron scattering study.

Small-angle neutron scattering (SANS) measurements are performed on pure dimyristoyl phosphatidylcholine (DMPC) unilamellar vesicles (ULV) and those containing either 20 or 47 mol% cholesterol, ergosterol or lanosterol. From the SANS data, we were able to determine the influence of these sterols on ULV bilayer thickness and vesicle area expansion coefficients. While these parameters have been determined previously for membranes containing cholesterol, to the best of our knowledge, this is the first time such results have been presented for membranes containing the structurally related sterols, ergosterol and lanosterol. At both molar concentrations and at temperatures ranging from 10 to 45 degrees C, the addition of the different sterols leads to increases in bilayer thickness, relative to pure DMPC. We observe large differences in the influence of these sterols on the membrane thermal area expansion coefficient. All three sterols, however, produce very similar changes to membrane thickness.

Cholesterol↗