Cross-sectional Radius Of Gyration Research Articles

Conformation and hydration property of low-acetyl gellan gum under microwave irradiation: Experiments and molecular dynamics simulations

The effect of microwave irradiation on the conformation and hydration properties of low-acetyl gellan gum was investigated to reveal the mechanism using experimental methods and molecular dynamics (MD) simulations. The experimental data showed that cross-sectional radius of gyration of the gellan chain treated by microwave or water bath were identical and microwave treatment could improve the water holding capability and restrict water mobility. On the other hand, results of root-mean-square deviation (RMSD) and root-mean-square fluctuation (RMSF) showed that microwave irradiation had little impact on the structural conformation of the low-acetyl gellan molecule. The analysis of radial distribution function and interaction energy demonstrated that microwaves modified the gellan-water molecules structure by energy transfer, making hydration shells of the gellan molecule become more structured. In addition, there was an enhancement of the average hydrogen bond number and lifetime under microwave irradiation due to rearrangement and reorient of molecules. These findings can explain the mechanism of microwave-promoted gellan gum gelation to some extent, which enhance industrial applications of low-acetyl gellan.

New AISC and EC3 design for S690 plate girders at elevated temperatures

Recently, the determination of the strengths of bridge girders exposed to fire has become of great importance as a result of the failure of some famous bridges for the same reason (e.g. Birmingham and MacArthur Maze Bridges (USA)). On the other hand, S690 high strength steel is widely examined and used in bridges all over the world, such as Mttådalen Bridge in Sweden. With respect to the effect of elevated temperatures on the strength of flexural members, stocky I-section beams have been studied in the literature. On the opposite, the lateral-torsional buckling (LTB) strengths of laterally-unrestrained plate girders with slender webs, which are used extensively in bridges such as those of Birmingham and MacArthur Maze Bridges (USA), and particularly formed from S690 at elevated temperatures have not been addressed. Additionally, AISC (2016) and EC3–1-2 (2005) do not neither cover S690 steel elements nor IPGs with slender webs. Therefore, these girders are simulated in this paper using ABAQUS programme. Currently, the simplified finite element method used successfully by Chen and Young (2008) and Fang and Chan (2019), which utilises the reduced material properties of S690 above the room temperature, is used, which means assuming a balanced structure and a uniform temperature range. The parametric studies consider the variations of the cross-sectional radius of gyration and elastic section modulus. Since the main focus of this paper is strength predictions, strengths are first compared to design models initially proposed according to AISC and EC3–1-2, which are found to yield very conservative predictions. Then, modified AISC and EC3–1-2 design models are recommended, which can safely predict the strengths of S690 IPGs with slender webs at elevated temperatures.

Conformational characteristics of regioselectively PEG/PS-grafted cellulosic bottlebrushes in solution: cross-sectional structure and main-chain stiffness

Cellulosic bottlebrushes with polystyrene (PS) and poly(ethylene glycol) (PEG) side chains at the O-6 and O-2,3 positions, respectively (PEG-PS-cellulose), were synthesized and characterized in diluted solution to reveal the second structure of heterografted bottlebrushes. The regioselectivity and degree of substitution were evaluated by 1H- and 13C-nuclear magnetic resonance spectroscopy and size-exclusion chromatography (SEC). The cross-sectional structure of PEG-PS-cellulose was evaluated from the cross-sectional radius of gyration determined by the small angle X-ray scattering technique as a function of the molecular weight of the PS side chain. As a result, PEG-PS-cellulose was found to show a core-shell-corona structure, in which PEG and PS side chains formed a homogeneous shell layer surrounding the cellulosic core and the outer segments of PS chains formed an outer corona layer. The stiffness parameter (λ−1) of the main chain was analyzed by the SEC–multiangle light scattering technique along with the Kratky-Porod wormlike chain model. In comparison with a previously reported cellulosic bottlebrush with a PS side chain at the O-6 position, it is suggested that the observed increase in λ−1 with increasing molecular weight of PS is mainly derived from the interaction among PS side chains located in an outer layer, while the PEG side chains at the O-2,3 position effectively suppressed the internal rotation of the cellulosic main chain. Cellulosic bottlebrush regioselectively possessing poly(ethylene glycol) (PEG) and polystyrene (PS) side chains (PEG-PS-cellulose) was synthesized, and its secondary structure in dilute solution was investigated with SAXS and SEC-MALS. The relationship between the cross-sectional mean squared radius of gyration (〈Sc2〉) and molecular weight of PS chain (MWPS) showed that PEG-PS-cellulose has a core-shell-corona structure in cross section. The dependency of main-chain stiffness (λ−1) on MWPS was discussed on the basis of the interactions of the PS and PEG side chains as well as the restricted rotation of the cellulosic main chain.

Molecular structure and anti-diabetic activity of a polysaccharide extracted from pumpkin Cucurbita pepo

In this work, structure and anti-diabetic effect of a polysaccharide (PP-PE) obtained by hot-water extraction from Cucurbita pepo was studied. The results showed that PP-PE was composed of α-(1→6)-glucan branched at C3 position and α-(1→4)-galactan. The polysaccharide molecule had a local rod-like conformation in solution with the cross-sectional radius of gyration of 0.27 nm and the chain aggregation was also observed from SAXS measurements. For alloxan-diabetic mice, blood glucose level was decreased by 29.8 % after 7 days PP-PE treatment at a dose of 100mg/kg/day. The histological examination indicated that degeneration and necrosis of pancreas tissues were observed in diabetic mice, however, histopathological changes were restored to near normal by PP-PE treatment. PP-PE also showed α-glucosidase and α-amylase inhibited activities with an IC50 value of 110.32±7.08 mg/mL and 103.06±1.60 mg/mL, respectively.

Solution structure of deglycosylated human IgG1 shows the role of CH2 glycans in its conformation

The human immunoglobulin G (IgG) class is the most prevalent antibody in serum, with the IgG1 subclass being the most abundant. IgG1 is composed of two Fab regions connected to a Fc region through a 15-residue hinge peptide. Two glycan chains are conserved in the Fc region in IgG; however, their importance for the structure of intact IgG1 has remained unclear. Here, we subjected glycosylated and deglycosylated monoclonal human IgG1 (designated as A33) to a comparative multidisciplinary structural study of both forms. After deglycosylation using peptide:N-glycosidase F, analytical ultracentrifugation showed that IgG1 remained monomeric and the sedimentation coefficients s020,w of IgG1 decreased from 6.45 S by 0.16–0.27 S. This change was attributed to the reduction in mass after glycan removal. X-ray and neutron scattering revealed changes in the Guinier structural parameters after deglycosylation. Although the radius of gyration (RG) was unchanged, the cross-sectional radius of gyration (RXS-1) increased by 0.1 nm, and the commonly occurring distance peak M2 of the distance distribution curve P(r) increased by 0.4 nm. These changes revealed that the Fab-Fc separation in IgG1 was perturbed after deglycosylation. To explain these changes, atomistic scattering modeling based on Monte Carlo simulations resulted in 123,284 and 119,191 trial structures for glycosylated and deglycosylated IgG1 respectively. From these, 100 x-ray and neutron best-fit models were determined. For these, principal component analyses identified five groups of structural conformations that were different for glycosylated and deglycosylated IgG1. The Fc region in glycosylated IgG1 showed a restricted range of conformations relative to the Fab regions, whereas the Fc region in deglycosylated IgG1 showed a broader conformational spectrum. These more variable Fc conformations account for the loss of binding to the Fcγ receptor in deglycosylated IgG1.

Influence of water on the intrinsic characteristics of cellulose dissolved in an ionic liquid

The local structure of cellulose, dissolved in the frequently used ionic liquid EMIm-OAc, is modelled by a coaxial double layer cylinder. The cylinder’s core consists of a cellulose chain while the sheath is formed by a solvent layer with lower electron density than the bulk solvent. We studied 2% cellulose solutions in EMIm-OAc and their behavior upon addition of increasing amounts of water. At this cellulose concentration, 15 wt% of water induced the precipitation of cellulose. Water molecules did not form an independent phase, but were bound to EMIm-OAc in the cellulose/water/EMIm-OAc solution. The conformational of a cellulose chain changes by adding water into the solution, and the square of the apparent cross-sectional radius of gyration of the cellulose chain becomes zero to negative. This phenomenon is explained by the formation of a solvation shell with lower electron density than the bulk solvent around the cellulose chain.

A consistent variational formulation of Bishop nonlocal rods

Thick rods are employed in Nanotechnology to build modern electro mechanical systems. Design and optimization of such structures can be carried out by nonlocal continuum mechanics which is computationally convenient when compared to atomistic strategies. Bishop's kinematics is able to describe small-scale thick rods if a proper mathematical model of nonlocal elasticity is formulated to capture size effects. In all papers on the matter, nonlocal contributions are evaluated by replacing Eringen's integral convolution with the consequent (but not equivalent) differential equation governed by Helmholtz's differential operator. As notorious in integral equation theory, this replacement is possible for convolutions, defined in unbounded domains, governed by averaging kernels which are Green's functions of differential operators. Indeed, Eringen himself, in order to study nonlocal problems defined in unbounded domains, such as screw dislocations and wave propagations, suggested to replace integro-differential equations with differential conditions. A different scenario appears in Bishop rod mechanics where nonlocal integral convolutions are defined in bounded structural domains, so that Eringen's nonlocal differential equation has to be supplemented with additional boundary conditions. The objective is achieved by formulating the governing nonlocal equations by a proper variational statement. The new methodology provides an amendment of previous contributions in literature and is illustrated by investigating the elastostatic behavior of simple structural schemes. Exact solutions of Bishop rods are evaluated in terms of nonlocal parameter and cross-section gyration radius. Both hardening and softening structural responses are predictable with a suitable tuning of the parameters.

Cysteine-rich protein 2 accelerates actin filament cluster formation.

Filamentous actin (F-actin) forms many types of structures and dynamically regulates cell morphology and movement, and plays a mechanosensory role for extracellular stimuli. In this study, we determined that the smooth muscle-related transcription factor, cysteine-rich protein 2 (CRP2), regulates the supramolecular networks of F-actin. The structures of CRP2 and F-actin in solution were analyzed by small-angle X-ray solution scattering (SAXS). The general shape of CRP2 was partially unfolded and relatively ellipsoidal in structure, and the apparent cross sectional radius of gyration (Rc) was about 15.8 Å. The predicted shape, derived by ab initio modeling, consisted of roughly four tandem clusters: LIM domains were likely at both ends with the middle clusters being an unfolded linker region. From the SAXS analysis, the Rc of F-actin was about 26.7 Å, and it was independent of CRP2 addition. On the other hand, in the low angle region of the CRP2-bound F-actin scattering, the intensities showed upward curvature with the addition of CRP2, which indicates increasing branching of F-actin following CRP2 binding. From biochemical analysis, the actin filaments were augmented and clustered by the addition of CRP2. This F-actin clustering activity of CRP2 was cooperative with α-actinin. Thus, binding of CRP2 to F-actin accelerates actin polymerization and F-actin cluster formation.

Graft Density Dependence of Main Chain Stiffness in Molecular Rod Brushes

The graft density dependence of main chain stiffness in rod brushes composed of a flexible linear polystyrene (PS) main chain and poly(n-hexyl isocyanate) (PHIC) rod side chains has thoroughly been investigated by static light (LS) and small-angle X-ray scattering (SAXS) measurements in tetrahydrofuran (THF) at 25 °C. A series of statistical graft copolymers having different graft densities (σ) and graft chain lengths (PS-g-HIC-Ns-lg, where Ns is the weight-averaged degree of polymerization of HIC and lg is the average distance (spacing) of the main chain between the side chain joints) were prepared by the nearly azeotrope radical copolymerizations of styrene (M1) with PHIC macromonomers (M2) (r1 = 0.84 ± 0.1 and r2 = 1.1 ± 0.3) in n-hexane or the bulk at 60 °C. The compositional heterogeneities of the graft copolymers were carefully characterized by the ratio of the UV to RI signal in the SEC traces and the comparison with those predicted from the theory by Stejskal and Kratochvil [Macromolecules 1987, 20, 2624], implying that they were sufficiently small enough to allow one to study their dimensional characterizations. The graft density dependence of the root-mean-square cross-section radius of gyration (⟨Sc2⟩1/2) and the z-averaged root-mean-square radius of gyration (⟨S2⟩z1/2) of PS-g-HIC-Ns-lg was studied and rationalized as the function of σ and Ns. The σ-dependence of ⟨Sc2⟩1/2 could be quantitatively described by the theory for the semiflexible comb whose main and side chains have different chain stiffness. The weight-averaged degree of polymerization of the main chain (NM) dependence of ⟨S2⟩z1/2 was also quantitatively described by the cylindrical wormlike chain model. It was found that the change in the main chain stiffness (λb–1) resulting from the interactions among the side chains increases in proportion to the scaling law of λb–1 ∝ Ns1σ1.

Fibrinogen species as resolved by HPLC-SAXS data processing within the UltraScan Solution Modeler (US-SOMO) enhanced SAS module.

Fibrinogen is a large heterogeneous aggregation/degradation-prone protein playing a central role in blood coagulation and associated pathologies, whose structure is not completely resolved. When a high-molecular-weight fraction was analyzed by size-exclusion high-performance liquid chromatography/small-angle X-ray scattering (HPLC-SAXS), several composite peaks were apparent and because of the stickiness of fibrinogen the analysis was complicated by severe capillary fouling. Novel SAS analysis tools developed as a part of the UltraScan Solution Modeler (US-SOMO; http://somo.uthscsa.edu/), an open-source suite of utilities with advanced graphical user interfaces whose initial goal was the hydrodynamic modeling of biomacromolecules, were implemented and applied to this problem. They include the correction of baseline drift due to the accumulation of material on the SAXS capillary walls, and the Gaussian decomposition of non-baseline-resolved HPLC-SAXS elution peaks. It was thus possible to resolve at least two species co-eluting under the fibrinogen main monomer peak, probably resulting from in-column degradation, and two others under an oligomers peak. The overall and cross-sectional radii of gyration, molecular mass and mass/length ratio of all species were determined using the manual or semi-automated procedures available within the US-SOMO SAS module. Differences between monomeric species and linear and sideways oligomers were thus identified and rationalized. This new US-SOMO version additionally contains several computational and graphical tools, implementing functionalities such as the mapping of residues contributing to particular regions of P(r), and an advanced module for the comparison of primary I(q) versus q data with model curves computed from atomic level structures or bead models. It should be of great help in multi-resolution studies involving hydrodynamics, solution scattering and crystallographic/NMR data.

Fracture toughness of open-cell Kelvin foam

Brittle fracture behavior of a perfect open-cell Kelvin foam is considered. The foam is modeled as a spatial lattice consisting of brittle elastic struts rigidly connected to each other at the nodal points. The fracture toughness is determined from the analysis of a quasi-plane problem for a slice of the foam with an embedded finite length crack generated by broken struts. The crack plane is chosen on the basis of a previous study of crack nucleation phenomenon, and the crack length, which assures the self-similar K-field in the tip vicinity, is established by numerical experiments. For the considered densities range the crack includes several hundreds of broken struts and, consequently, the portion of the foam to be considered in the analysis has a very large number of nodal degrees of freedom. The computational cost is reduced significantly by using for the analysis the representative cell method based on the discrete Fourier transform. As a result, the initial problem for the foam slice is reduced to the problem for the repetitive cell which includes 12 struts.The dependence of the Mode I and Mode II fracture toughness of the considered bending dominated foam upon its relative density is determined and found to be different from known results for the stretch dominated cubic cell lattice. On the other hand, the results obtained for Mode I meet the experimental data and theoretical predictions for random foams. For the case of struts with hollow cross-section the analysis predicts linear dependence of the fracture toughness upon cross-section gyration radius.

Catanionic Gels Based on Cholic Acid Derivatives

In this paper, the preparation and characterization of an anionic and a cationic surfactant obtained by chemical modifications of a natural bile acid (cholic acid) are reported. The bile acid was modified by introducing a diamine or a dicarboxylic aromatic residue on the lateral chain. The pure cationic surfactant self-assembles in a network of fibers with a cross-section gyration radius of about 15.1 Å, providing hydrogels with a pH-dependent compactness. On the other hand, the anionic molecule gives rise to prolate ellipsoid micelles. Homogeneous catanionic mixtures have also been obtained, with molar fraction of each surfactant ranging from 0.125 to 0.875. At total surfactant concentration of 0.05% (w/v), the mixtures form gels of fibrils partially arranged in secondary twisted superstructures. Comparison of this concentration with the minimum gelation concentration of the pure cationic derivative (0.16% w/v) suggests that, in the mixtures, the presence of the electrostatic component in self-assembly of the molecules allows the formation of gels starting from more dilute samples. In view of these achievements, this work suggests that catanionic mixtures can be exploited to enhance the efficiency of gelators.

Difference in hydration structures between F-actin and myosin subfragment-1 detected by small-angle X-ray and neutron scattering.

Hydration structures around F-actin and myosin subfragment-1 (S1), which play central roles as counterparts in muscle contraction, were investigated by small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). The radius of gyration of chymotryptic S1 was evaluated to be 41.3±1.1 Å for SAXS, 40.1±3.0 Å for SANS in H2O, and 37.8±0.8 Å for SANS in D2O, respectively. The values of the cross-sectional radius of gyration of F-actin were 25.4±0.03 Å for SAXS, 23.4±2.4 Å for SANS in H2O, and 22.6 ± 0.6 Å for SANS in D2O, respectively. These differences arise from different contributions of the hydration shell to the scattering curves. Analysis by model calculations showed that the hydration shell of S1 has the average density 10–15% higher than bulk water, being the typical hydration shell. On the other hand, the hydration shell of F-actin has the average density more than 19% higher than bulk water, indicating that F-actin has a denser, unusual hydration structure. The results indicate a difference in the hydration structures around F-actin and S1. The unusual hydration structure around F-actin may have the structural property of so-called “hyper-mobile water” around F-actin.

The internal organization of mycobacterial partition assembly: does the DNA wrap a protein core?

Before cell division in many bacteria, the ParBs spread on a large segment of DNA encompassing the origin-proximal parS site(s) to form the partition assembly that participates in chromosome segregation. Little is known about the structural organization of chromosomal partition assembly. We report solution X-ray and neutron scattering data characterizing the size parameters and internal organization of a nucleoprotein assembly formed by the mycobacterial chromosomal ParB and a 120-meric DNA containing a parS-encompassing region from the mycobacterial genome. The cross-sectional radii of gyration and linear mass density describing the rod-like ParB-DNA assembly were determined from solution scattering. A “DNA outside, protein inside” mode of partition assembly organization consistent with the neutron scattering hydrogen/deuterium contrast variation data is discussed. In this organization, the high scattering DNA is positioned towards the outer region of the partition assembly. The new results presented here provide a basis for understanding how ParBs organize the parS-proximal chromosome, thus setting the stage for further interactions with the DNA condensins, the origin tethering factors and the ParA.

Heat-induced structural transitions of alpha-crystallin studied by small-angle neutron scattering

Alpha-crystallin from the bovine eye lens was studied by small-angle neutron scattering (SANS) in 90% D2O buffer solution at 20, 50, 60, 65, 75, 85 and 95°C. The temperature points for this study were specified on the basis of differential scanning calorimetric analysis of alpha-crystallin solutions which has shown two endothermic transitions with midpoints at 64.5 and 86°C. The SANS study revealed no significant alpha-crystallin quaternary structure alterations at 50°C as compared with 20°C. At 60-65°C the SANS data confirmed substantial alpha-crystallin quaternary structure rearrangements which resulted in the formation of alpha-crystallin oligomers with a similar shape but approximately twofold increased molecular weight as compared to the native state at 20°C. At higher temperatures (75, 85 and 95°C) the SANS patterns were very similar and were consistent with the scattering by rod-like particles with a cross-section radius of gyration ∼55 This transformation of alpha-crystallin to the rod-like particles was evidently irreversible as these particles remained in solution after cooling to 20°C. Ab initio shape models of the native and high-temperature alpha-crystallin were retrieved with DAMMIN and DAMAVER software. Schematic model of alpha-crystallin heat-induced quaternary structure transitions was considered.

The Solution Structure of Heparan Sulfate Differs from That of Heparin: IMPLICATIONS FOR FUNCTION

The highly sulfated polysaccharides heparin and heparan sulfate (HS) play key roles in the regulation of physiological and pathophysiological processes. Despite its importance, no molecular structures of free HS have been reported up to now. By combining analytical ultracentrifugation, small angle x-ray scattering, and constrained scattering modeling recently used for heparin, we have analyzed the solution structures for eight purified HS fragments degree of polymerization 6-18 (dp6-dp18) and dp24, corresponding to the predominantly unsulfated GlcA-GlcNAc domains of heparan sulfate. Unlike heparin, the sedimentation coefficient s(20,)(w) of HS dp6-dp24 showed a small rotor speed dependence, where similar s(20,)(w) values of 0.82-1.26 S (absorbance optics) and 1.05-1.34 S (interference optics) were determined. The corresponding x-ray scattering measurements of HS dp6-dp24 gave radius of gyration (R(G)) values from 1.03 to 2.82 nm, cross-sectional radius of gyration (R(XS)) values from 0.31 to 0.65 nm, and maximum lengths (L) from 3.0 to 10.0 nm. These data showed that HS has a longer and more bent structure than heparin. Constrained scattering modeling starting from 5000-8000 conformationally randomized HS structures gave best fit dp6-dp16 molecular structures that were longer and more bent than their equivalents in heparin. No fits were obtained for HS dp18 or dp24, indicating their higher flexibility. We conclude that HS displays an extended bent conformation that is significantly distinct from that for heparin. The difference is attributed to the different predominant monosaccharide sequence and reduced sulfation of HS, indicating that HS may interact differently with proteins compared with heparin.

Formation and Thermally-Induced Disruption of Nanowhiskers in Poly(3-hexylthiophene)/Xylene Gel Studied by Small-Angle X-ray Scattering

We identified the formation of nanowhiskers of poly(3-hexylthiophene) (P3HT) in the gel with xylene in situ by means of small-angle X-ray scattering (SAXS). In the freshly prepared solution, the rodlike segments of P3HT were found to form local network aggregates characterized by the mass fractal dimension of ca. 2.5. Upon prolonged aging at room temperature, the originally viscous liquid solution transformed into a gel, in which a rodlike entity with the cross-sectional radius of gyration of 7.31 nm was disclosed. Real-space observation of the morphology of the film cast from the gel revealed the presence of long nanowhiskers. The fact that the width and height of these whiskers closely agreed with those of the rodlike entity in the gel deduced from model fitting of the SAXS profile indicated that the nanowhiskers were present in the wet gel. Time-resolved SAXS experiment revealed that the nanowhisker formation was accompanied by the crystallization of P3HT. The ultimate crystallinity attained in the nan...

Conformational Properties of Cylindrical Rod Brushes Consisting of a Polystyrene Main Chain and Poly(n-hexyl isocyanate) Side Chains

Conformational properties of cylindrical rod brushes consisting of a flexible polystyrene main chain and poly(n-hexyl isocyanate) (PHIC) rod side chains have thoroughly been studied by static light and small-angle X-ray scattering (SAXS) in tetrahydrofuran (THF) at 25 °C. These rod brushes were prepared by radical homopolymerization of 4-vinylbenzyloxy-ended PHIC macromonomers (1) (VB-HIC-Ns, where Ns is the weight-averaged degree of polymerization of HIC and in a range from 21 to 80) in n-hexane at 60 °C. The mean-square cross-sectional radius of gyration (⟨Rc2⟩0) of the brush at an infinite dilution is determined by SAXS measurement and rationalized as a function of Ns. The experimental value of ⟨Rc2⟩0 gradually increases with Ns but above Ns higher than 20 increases to follow the scaling law of ⟨Rc2⟩0 ∝ Ns0.87. The experimental Ns dependence of ⟨Rc2⟩0 is compared to that from the wormlike comb model whose main and side chains have different stiffness parameters. The molecular weight dependence of z-ave...

Unphosphorylated Rhabdoviridae Phosphoproteins Form Elongated Dimers in Solution

The phosphoprotein (P) is an essential component of the replication machinery of rabies virus (RV) and vesicular stomatitis virus (VSV), and the oligomerization of P, potentially controlled by phosphorylation, is required for its function. Up to now the stoichiometry of phosphoprotein oligomers has been controversial. Size exclusion chromatography combined with detection by multiangle laser light scattering shows that the recombinant unphosphorylated phosphoproteins from VSV and from RV exist as dimers in solution. Hydrodynamic analysis indicates that the dimers are highly asymmetric, with a Stokes radius of 4.8-5.3 nm and a frictional ratio larger than 1.7. Small-angle neutron scattering experiments confirm the dimeric state and the asymmetry of the structure and yield a radius of gyration of about 5.3 nm and a cross-sectional radius of gyration of about 1.6-1.8 nm. Similar hydrodynamic properties and molecular dimensions were obtained with a variant of VSV phosphoprotein in which Ser60 and Thr62 are substituted by Asp residues and which has been reported previously to mimic phosphorylation by inducing oligomerization and activating transcription. Here, we show that this mutant also forms a dimer with hydrodynamic properties and molecular dimensions similar to those of the wild type protein. However, incubation at 30 degrees C for several hours induced self-assembly of both wild type and mutant proteins, leading to the formation of irregular filamentous structures.

Characterization of Rodlike Poly(n-hexyl isocyanate) Macromonomers and Their Polymacromonomers by Light Scattering, SAXS, Intrinsic Viscosity, and Scanning Force Microscopy

SEC-MALS, small-angle X-ray scattering (SAXS), and viscosity measurements were made on tetrahydrofuran (THF) and n-hexane of a series of 4-vinylbenzyl and methacrylate ended poly(n-hexyl isocyanate) (PHIC) macromonomers (VB-HIC-n and MA-HIC-n, where n is a degree of polymerization of HIC and in a range from 21 to 192), together with higher molecular weight PHIC chains than the macromonomers. The molecular weight dependence of z-average mean-square radius of gyration z and intrinsic viscosity [η] of the macromonomers and PHIC chains in THF at 25 °C were quantitatively described by the wormlike chain model with the stiffness parameter (λ−1)=63nm, the molecular weight per unit contour length (ML)=725 nm−1, and the hydrodynamic diameter (dB)=1.6 nm. The SAXS scattering profile of VB-HIC-57 in n-hexane at 25 °C was also perfectly described in terms of the straight cylinder model. The results imply that the macromonomers may be regarded as a rigid rod molecule in THF and n-hexane. Cylindrical brushes consisting of polystyrene as a main chain and PHIC chains as a side chain were prepared by homopolymerizations of VB-HIC-46 and their dimensional properties were investigated in THF at 25 °C by SAXS and SEC-MALS measurements. The molecular weight dependence of z of the brushes was quantitatively explained by the wormlike cylinder model with the parameters of λ−1=48 nm, ML=2.40×104 nm−1, the cross-sectional radius of gyration of the cylinder o1/2=4.66 nm, and the end effect (δ=16.7 nm) arising from side chains near the main-chain ends. It was concluded, therefore, that the main chain stiffness of the brush remarkably increases by the presence of densely located rodlike side chains. Direct observation of single brush of the poly(VB-HIC-46) deposited on a mica was made by scanning force microscopy (SFM) to reveal the cylindrical brushes consisting of rodlike side chains with ca. 15 nm in a thickness.