A Formalism for Scattering of Complex Composite Structures. 2 Distributed Reference Points

Recently we developed a formalism for the scattering from linear and acyclic branched structures build of mutually non-interacting sub-units.{[}C. Svaneborg and J. S. Pedersen, J. Chem. Phys. 136, 104105 (2012){]} We assumed each sub-unit has reference points associated with it. These are well defined positions where sub-units can be linked together. In the present paper, we generalize the formalism to the case where each reference point can represent a distribution of potential link positions. We also present a generalized diagrammatic representation of the formalism. Scattering expressions required to model rods, polymers, loops, flat circular disks, rigid spheres and cylinders are derived. and we use them to illustrate the formalism by deriving the generic scattering expression for micelles and bottle brush structures and show how the scattering is affected by different choices of potential link positions.Comment: Paper no. 2 of a serie

A Formalism for Scattering of Complex Composite Structures. 1 Applications to Branched Structures of Asymmetric Sub-Units

We present a formalism for the scattering of an arbitrary linear or acyclic branched structure build by joining mutually non-interacting arbitrary functional sub-units. The formalism consists of three equations expressing the structural scattering in terms of three equations expressing the sub-unit scattering. The structural scattering expressions allows a composite structures to be used as sub-units within the formalism itself. This allows the scattering expressions for complex hierarchical structures to be derived with great ease. The formalism is furthermore generic in the sense that the scattering due to structural connectivity is completely decoupled from internal structure of the sub-units. This allows sub-units to be replaced by more complex structures. We illustrate the physical interpretation of the formalism diagrammatically. By applying a self-consistency requirement we derive the pair distributions of an ideal flexible polymer sub-unit. We illustrate the formalism by deriving generic scattering expressions for branched structures such as stars, pom-poms, bottle-brushes, and dendrimers build out of asymmetric two-functional sub-units.Comment: Complete rewrite generalizing the formalism to arbitrary functional sub-units and including a new Feynmann like diagrammatic interpretatio

Structure of PEP-PEO block copolymer micelles: Exploiting the complementarity of small-angle X-ray scattering and static light scattering

The structure of large block copolymer micelles is traditionally determined by small-angle neutron scattering (SANS), covering a large range of scattering vectors and employing contrast variation to determine the overall micelle morphology as well as the internal structure on shorter length scales. The present work shows that the same information can be obtained by combining static light scattering (SLS) and small-angle X-ray scattering (SAXS), which provide information on, respectively, large and short length scales. Micelles of a series of block copolymers of poly(ethylene propylene)-b-poly(ethylene oxide) (PEP–PEO) in a 70% ethanol solution are investigated. The polymers have identical PEP blocks of 5.0 kDa and varying PEO blocks of 2.8–49 kDa. The SLS contrasts of PEP and PEO are similar, providing a homogeneous contrast, making SLS ideal for determining the overall micelle morphology. The SAXS contrasts of the two components are very different, allowing for resolution of the internal micelle structure. A core–shell model with a PEP core and PEO corona is fitted simultaneously to the SAXS and SLS data using the different contrasts of the two blocks for each technique. With increasing PEO molecular weight, a transition from cylindrical to spherical micelles is observed. This transition cannot be identified from the SAXS data alone, but only from the SLS data.</jats:p

Complementary substrate specificity and distinct quaternary assembly of the Escherichia coli aerobic and anaerobic beta-oxidation trifunctional enzyme complexes

The trifunctional enzyme (TFE) catalyzes the last three steps of the fatty acid beta-oxidation cycle. Two TFEs are present in Escherichia coli, EcTFE and anEcTFE. EcTFE is expressed only under aerobic conditions, whereas anEcTFE is expressed also under anaerobic conditions, with nitrate or fumarate as the ultimate electron acceptor. The anEcTFE subunits have higher sequence identity with the human mitochondrial TFE (HsTFE) than with the soluble EcTFE. Like HsTFE, here it is found that anEcTFE is a membrane-bound complex. Systematic enzyme kinetic studies show that anEcTFE has a preference for medium- and long-chain enoyl-CoAs, similar to HsTFE, whereas EcTFE prefers short chain enoyl-CoA substrates. The biophysical characterization of anEcTFE and EcTFE shows that EcTFE is heterotetrameric, whereas anEcTFE is purified as a complex of two heterotetrameric units, like HsTFE. The tetrameric assembly of anEcTFE resembles the HsTFE tetramer, although the arrangement of the two anEcTFE tetramers in the octamer is different from the HsTFE octamer. These studies demonstrate that EcTFE and anEcTFE have complementary substrate specificities, allowing for complete degradation of long-chain enoyl-CoAs under aerobic conditions. The new data agree with the notion that anEcTFE and HsTFE are evolutionary closely related, whereas EcTFE belongs to a separate subfamily.Peer reviewe

The role of nanoparticle structure and morphology in the dissolution kinetics and nutrient release of nitrate‑doped calcium phosphate nanofertilizers

Bio-inspired synthetic calcium phosphate (CaP) nanoparticles (NPs), mimicking the mineral component of bone and teeth, are emergent materials for sustainable applications in agriculture. These sparingly soluble salts show self-inhibiting dissolution processes in undersaturated aqueous media, the control at the molecular and nanoscale levels of which is not fully elucidated. Understanding the mechanisms of particle dissolution is highly relevant to the efcient delivery of macronutrients to the plants and crucial for developing a valuable synthesis-by-design approach. It has also implications in bone (de)mineralization processes. Herein, we shed light on the role of size, morphology and crystallinity in the dissolution behaviour of CaP NPs and on their nitrate doping for potential use as (P,N)-nanofertilizers. Spherical fully amorphous NPs and apatite-amorphous nanoplatelets (NPLs) in a core-crown arrangement are studied by combining forefront Small-Angle and Wide-Angle X-ray Total Scattering (SAXS and WAXTS) analyses. ­Ca2+ ion release rates difer for spherical NPs and NPLs demonstrating that morphology plays an active role in directing the dissolution kinetics. Amorphous NPs manifest a rapid loss of nitrates governed by surface-chemistry. NPLs show much slower release, paralleling that of ­Ca2+ ions, that supports both detectable nitrate incorporation in the apatite structure and dissolution from the core basal faces.Fondazione Cariplo 2016-0648FEDER/Ministerio de Ciencia, Innovacion y Universidades-Agencia Estatal de Investigacion (FEDER/MCIU/AEI, Spain) through the project NanoVIT RTI-2018-095794-A-C22FEDER/Ministerio de Ciencia, Innovacion y Universidades-Agencia Estatal de Investigacion (FEDER/MCIU/AEI, Spain) through the project NanoSmart RYC-2016-21042FEDER/MCIU/AEI within the Juan de la Cierva Program (JdC2017

Structural Basis for Dityrosine-Mediated Inhibition of α-Synuclein Fibrillization

[Image: see text] α-Synuclein (α-Syn) is an intrinsically disordered protein which self-assembles into highly organized β-sheet structures that accumulate in plaques in brains of Parkinson’s disease patients. Oxidative stress influences α-Syn structure and self-assembly; however, the basis for this remains unclear. Here we characterize the chemical and physical effects of mild oxidation on monomeric α-Syn and its aggregation. Using a combination of biophysical methods, small-angle X-ray scattering, and native ion mobility mass spectrometry, we find that oxidation leads to formation of intramolecular dityrosine cross-linkages and a compaction of the α-Syn monomer by a factor of √2. Oxidation-induced compaction is shown to inhibit ordered self-assembly and amyloid formation by steric hindrance, suggesting an important role of mild oxidation in preventing amyloid formation