Scaling law for the radius of gyration of poly[bis(2-naphthoxyphosphazene)] (PBNP)

1992 ◽  
Vol 29 (3-4) ◽  
pp. 469-475 ◽  
Author(s):  
Maria P. Tarazona ◽  
Julio Bravo ◽  
Enrique Saiz
Keyword(s):  
Scaling Law ◽  
Radius Of Gyration

scholarly journals Forward Flux Sampling of Polymer Desorption Paths from a Solid Surface into Dilute Solution

Polymers ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2275
Author(s):  
Kyle J. Huston ◽  
Christina E. Rice ◽  
Ronald G. Larson
Keyword(s):  
Interaction Energy ◽  
Solid Wall ◽  
Scaling Law ◽  
Rare Event ◽  
Degree Of Polymerization ◽  
Radius Of Gyration ◽  
Exponential Dependence ◽  
Excluded Volume Effects ◽  
Desorption Time ◽  
Wall Interaction

We compute desorption rates for isolated polymers adsorbed to a solid wall with a rare event sampling technique called multilevel splitting, also known as forward flux sampling. We interpret computed rates with theories based on the conjecture that the product tdesDRg2 of the desorption time tdes and diffusivity D divided by squared radius of gyration Rg scales with exp(h/Rg) where h is the equilibrium ratio of adsorbed surface concentration of polymer Γ to bulk concentration of polymer c. As the polymer–wall interaction energy is increased, the slope of lntdesDRg2 vs. NVMFkBT nearly approaches unity, as expected for strongly-adsorbing chains, where N is the degree of polymerization and VMF is the height-averaged monomer–wall interaction energy for a strongly adsorbed chain. However, we also find that this scaling law is only accurate when adsorption strength per monomer exceeds a threshold value on the order of 0.3–0.5 kBT for a freely jointed chain without or with excluded volume effects. Below the critical value, we observe that tdesDRg2 becomes nearly constant with N, so that tdes∝Nα, with α≈2. This suggests a crossover from “strong” detachment-controlled to a “weak” diffusion-controlled desorption rate as VMF/kBT drops below some threshold. These results may partially explain experimental data, that in some cases show “strong” exponential dependence of desorption time on chain length, while in others a “weak” power-law dependence is found. However, in the “strong” adsorption case, our results suggest much longer desorption times than those measured, while the reverse is true in the weak adsorption limit. We discuss possible reasons for these discrepancies.

scholarly journals Variants of intrinsic disorder: structural characterization

2019 ◽  
Author(s):  
Sergio Forcelloni ◽  
Antonio Deiana ◽  
Andrea Giansanti
Keyword(s):  
Amino Acids ◽  
Structural Model ◽  
Intrinsically Disordered Proteins ◽  
Scaling Law ◽  
Intrinsically Disordered Protein ◽  
Accessible Surface Area ◽  
Human Proteome ◽  
Disordered Proteins ◽  
Radius Of Gyration ◽  
Intrinsically Disordered

AbstractIn a recent study, we have introduced an operational classification of the human proteome in three variants of disorder: ordered proteins (ORDPs), structured proteins with intrinsically disordered protein regions (IDPRs), intrinsically disordered proteins (IDPs). That classification was useful in functionally separating IDPRs from IDPs, which up until now have been generally considered as a whole. In this study, we corroborate this distinction by considering different physical-chemical and structural properties. Both ORDPs and IDPRs are enriched in order-promoting amino acids, whereas only IDPs show an enrichment in disordered-promoting amino acids. Consistently, ORDPs and IDPRs are preferentially located in the ordered phase of the charge-hydropathy plot, whereas IDPs are widespread over the disordered phase. We introduce the mean packing - mean pairwise energy (MP-MPE) plane to structurally characterize these variants even in the absence of a structural model. As expected for well-packed proteins, a negative linear correlation is observed between MP and MPE for ORDPs and IDPRs, whereas IDPs break this linear dependence. Finally, we find that IDPs have a more extended conformation as measured by the scaling law between the radius of gyration and the length of these proteins, and accordingly they have higher solubility and accessible surface area than ORDPs and IDPRs. Overall, our results confirm the relevance of our operational separation of IDPRs from IDPs and provide further validation of our criteria to separate IDPs from the rest of human proteome.

Imaging of ribosomal RNA-protein interactions by dark-field STEM

1989 ◽  
Vol 47 ◽  
pp. 250-251
Author(s):  
M. Boublik ◽  
V. Mandiyan ◽  
S. Tumminia ◽  
J.F. Hainfeld ◽  
J.S. Wall
Keyword(s):  
Nucleic Acid ◽  
16S Rrna ◽  
Dark Field ◽  
Radius Of Gyration ◽  
Central Domain ◽  
The Core ◽  
16S Rna ◽  
30S Subunit ◽  
Core Particles

Success in protein-free deposition of native nucleic acid molecules from solutions of selected ionic conditions prompted attempts for high resolution imaging of nucleic acid interactions with proteins, not attainable by conventional EM. Since the nucleic acid molecules can be visualized in the dark-field STEM mode without contrasting by heavy atoms, the established linearity between scattering cross-section and molecular weight can be applied to the determination of their molecular mass (M) linear density (M/L), mass distribution and radius of gyration (RG). Determination of these parameters promotes electron microscopic imaging of biological macromolecules by STEM to a quantitative analytical level. This technique is applied to study the mechanism of 16S rRNA folding during the assembly process of the 30S ribosomal subunit of E. coli. The sequential addition of protein S4 which binds to the 5'end of the 16S rRNA and S8 and S15 which bind to the central domain of the molecule leads to a corresponding increase of mass and increased coiling of the 16S rRNA in the core particles. This increased compactness is evident from the decrease in RG values from 114Å to 91Å (in “ribosomal” buffer consisting of 10 mM Hepes pH 7.6, 60 mM KCl, 2 m Mg(OAc)2, 1 mM DTT). The binding of S20, S17 and S7 which interact with the 5'domain, the central domain and the 3'domain, respectively, continues the trend of mass increase. However, the RG values of the core particles exhibit a reverse trend, an increase to 108Å. In addition, the binding of S7 leads to the formation of a globular mass cluster with a diameter of about 115Å and a mass of ∽300 kDa. The rest of the mass, about 330 kDa, remains loosely coiled giving the particle a “medusa-like” appearance. These results provide direct evidence that 16S RNA undergoes significant structural reorganization during the 30S subunit assembly and show that its interactions with the six primary binding proteins are not sufficient for 16S rRNA coiling into particles resembling the native 30S subunit, contrary to what has been reported in the literature.

Scaling Law of Coupling Coefficient and Coil Size in Wireless Power Transfer Design via Magnetic Coupling

2017 ◽  
Vol 137 (4) ◽  
pp. 326-333
Author(s):  
Chiaki Nagai ◽  
Kenji Inukai ◽  
Masato Kobayashi ◽  
Tatsuya Tanaka ◽  
Kensho Abumi ◽  
...  
Keyword(s):  
Coupling Coefficient ◽  
Scaling Law ◽  
Magnetic Coupling ◽  
Wireless Power Transfer ◽  
Power Transfer ◽  
Wireless Power ◽  
Coil Size

The Reactive Formation of Diblock Copolymer at a Polymer/Polymer Interface and its Effect on Interfacial Structure

2000 ◽  
Vol 629 ◽  
Author(s):  
Jonathan S. Schulze ◽  
Timothy P. Lodge ◽  
Christopher W. Macosko
Keyword(s):  
Molecular Weight ◽  
Interfacial Structure ◽  
Root Mean Square Roughness ◽  
Radius Of Gyration ◽  
Interfacial Region ◽  
Force Microscopy ◽  
Amino Terminal ◽  
Polymer Interface ◽  
Atomic Force ◽  
Time Required

ABSTRACTThe reaction of perdeuterated amino-terminal polystyrene (dPS-NH2) with anhydrideterminal poly(methyl methacrylate) (PMMA-anh) at a PS/PMMA interface has been observed with forward recoil spectrometry (FRES). Bilayer samples were constructed by placing thin films of PS containing ∼8.5 wt % dPS-NH2 on a PMMA-anh layer. Significant reaction was observed only after annealing the samples at 174°C for several hours, a time scale at least two orders of magnitude greater than the time required for the dPS-NH2 chains to diffuse through the bulk PS layer. The topography of the interfacial region as copolymer formed was measured using atomic force microscopy (AFM). Roughening of the PS/PMMA interface was observed to varying degrees in all annealed samples. Furthermore, the extent of this roughening was found to depend on the PS matrix molecular weight. Reaction in the samples with a high molecular weight PS matrix resulted in a root mean square roughness approximately equal to the radius of gyration Rg of the copolymer. However, approximately twice as much roughening was observed in the low molecular weight PS matrix. This study reveals how the molecular weight of one of the phases can affect the rate of reaction at a polymer/polymer interface.

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