DAMMIF, a revised implementation of the ab-initio shape-determination program DAMMIN for small-angle scattering data, is presented. The program was fully rewritten, and its algorithm was optimized for speed of execution and modified to avoid limitations due to the finite search volume. Symmetry and anisometry constraints can be imposed on the particle shape, similar to DAMMIN. In equivalent conditions, DAMMIF is 25–40 times faster than DAMMIN on a single CPU. The possibility to utilize multiple CPUs is added to DAMMIF. The application is available in binary form for major platforms.

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DAMMIF, a program for rapid ab-initio shape determination in small-angle scattering

Small-angle scattering (SAS) of x-rays and neutrons is a fundamental tool in the study of biological macromolecules. The major advantage of the method lies in its ability to provide structural information about partially or completely disordered systems. SAS allows one to study the structure of native particles in near physiological environments and to analyse structural changes in response to variations in external conditions. In this review we concentrate on SAS studies of isotropic systems, in particular, solutions of biological macromolecules, an area where major progress has been achieved during the last decade. Solution scattering studies are especially important, given the challenge of the ‘post-genomic’ era with vast numbers of protein sequences becoming available. Numerous structural initiatives aim at large-scale expression and purification of proteins for subsequent structure determination using x-ray crystallography and NMR spectroscopy. Because of the requirement of good crystals for crystallography and the low molecular mass requirement of NMR, a significant fraction of proteins cannot be analysed using these two high-resolution methods. Progress in SAS instrumentation and novel analysis methods, which substantially improve the resolution and reliability of the structural models, makes the method an important complementary tool for these initiatives. The review covers the basics of x-ray and neutron SAS, instrumentation, mathematical methods used in data analysis and major modelling techniques. Examples of applications of SAS to different types of biomolecules (proteins, nucleic acids, macromolecular complexes, polyelectrolytes) are presented. A brief account of the new opportunities offered by third and fourth generation synchrotron radiation sources (time-resolved studies, coherent scattering and single molecule scattering) is also given.

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Small-angle scattering studies of biological macromolecules in solution

Polymers for gas separations: the next decade

The surface structures and properties of a membrane largely determine its in-service performance during a filtration process. Here we report a facile hydrophilization method via co-deposition of mussel-inspired polydopamine (PDA) and polyethyleneimine (PEI) on a polypropylene microfiltration membrane. The deposition time is greatly shortened and the surface hydrophilicity is significantly improved compared to those membranes decorated only by PDA. The dopamine/PEI deposition solution can be reused several times with negligible effect on the surface hydrophilicity of membranes. Moreover, the PDA/PEI coating endows the membranes with ultra-high water permeability, allowing microfiltration separation of oil-in-water emulsions under atmospheric pressure.

Mussel-inspired modification of a polymer membrane for ultra-high water permeability and oil-in-water emulsion separation

Permeability and permselectivity of gases in fluorinated and non-fluorinated polyimides

/pdf/the-system-e8-a-special-class-of-simple-polyhedra-and-gas-2p2v38l5ee.pdf

The system E8, a special class of simple polyhedra and gas hydrate structures

https://iopscience.iop.org/article/10.1070/RCR4932/pdf

Supercritical fluids in chemistry

Conformational parameters for a wide variety of aromatic cyclochain polymers have been computed assuming free rotation about virtual bonds. The flexibility with free rotation is shown to be determined by the geometry of the repeat unit and can vary over a wide range (15–1500 A). Experimental values of the Kuhn segment length A are calculated from literature data on the hydrodynamic behavior of polymeric macromolecules of this class in solution. For most polymers Afr for free rotation is equal to the experimental Aexp, and hindered rotation is mainly due to bulky substituents. © 1993 John Wiley & Sons, Inc.

On the flexibility of cyclochain polymers

In order to relate the microstructure of polymer chains to the gas permeation properties, a novel method is proposed for the calculation of the van der Waals (V w ), occupied (V occ ), and accessible (V acc ) volumes of polymers, using polyimides as examples. In this approach, V occ and V acc values are obtained as characteristics of polymer-gas systems. Correlations between V occ and the gas permeability (P) and diffusion (D) coefficients are demonstrated. Accessible volume, V acc , determined experimental densities, and V occ calculated using a Monte Carlo technique, as well as the fractional accessible volume (FAV) (V acc /V sp ), where V sp is the specific volume of polymers, also correlate well with the P and D value. The slopes of these correlations increase with increasing molecular size of the diffusing molecules. In addition, the parameters of the equations for D(FAV) and P(FAV) strongly depend on conformation rigidity (Kuhn segment) of the polyimides. An interpretation of the results obtained is presented.

Inga A. Ronova

Papers

The system E8, a special class of simple polyhedra and gas hydrate structures

Supercritical fluids in chemistry

On the flexibility of cyclochain polymers

Occupied and accessible volumes in glassy polymers and their relationship with gas permeation parameters

Electron diffraction study of the molecular structure of trimethylcyclopentadienylsilane