Studies of microgel formation in aqueous and organic solvents by light scattering and analytical ultracentrifugation

2007 ◽  
pp. 144-153 ◽  
Author(s):  
W. Mächtle ◽  
G. Ley ◽  
J. Streib
Keyword(s):  
Light Scattering ◽  
Organic Solvents ◽  
Analytical Ultracentrifugation

scholarly journals The mechanism of assembly of Acanthamoeba myosin-II minifilaments: minifilaments assemble by three successive dimerization steps.

1989 ◽  
Vol 109 (4) ◽  
pp. 1537-1547 ◽  
Author(s):  
J H Sinard ◽  
W F Stafford ◽  
T D Pollard
Keyword(s):  
Electron Microscopy ◽  
Light Scattering ◽  
Ionic Strength ◽  
Analytical Ultracentrifugation ◽  
Myosin Ii ◽  
Alkaline Ph ◽  
Predominant Species ◽  
Assembly Mechanism ◽  
Rapid Equilibrium ◽  
Low Ionic Strength

We used 90 degrees light scattering, analytical ultracentrifugation, and electron microscopy to deduce that Acanthamoeba myosin-II minifilaments, composed of eight molecules each, assemble by a novel mechanism consisting of three successive dimerization steps rather than by the addition of monomers or parallel dimers to a nucleus. Above 200 mM KCl, Acanthamoeba myosin-II is monomeric. At low ionic strength (less than 100 mM KCl), myosin-II polymerizes into bipolar minifilaments. Between 100 and 200 mM KCl, plots of light scattering vs. myosin concentration all extrapolate to the origin but have slopes which decrease with increasing KCl. This indicates that structures intermediate in size between monomers and full length minifilaments are formed, and that the critical concentrations for assembly of these structures is very low. Analytical ultracentrifugation has confirmed that intermediate structures exist at these salt concentrations, and that they are in rapid equilibrium with each other. We believe these structures represent assembly intermediates and have used equilibrium analytical ultracentrifugation and electron microscopy to identify them. Polymerization begins with the formation of antiparallel dimers, with the two tails overlapping by approximately 15 nm. Two antiparallel dimers then associated with a 15-nm stagger to form an antiparallel tetramer. Finally, two tetramers associate with a 30-nm stagger to form the completed minifilament. At very low ionic strengths, the last step in the assembly mechanism is largely reversed and antiparallel tetramers are the predominant species. Alkaline pH, which can also induce minifilament disassembly, produces the same assembly intermediates as are found for salt induced disassembly.

scholarly journals Size and Shape of Human Fibrinogen in Solution

1977 ◽  
Author(s):  
V. Hofmann ◽  
P.W. Straub ◽  
T. Binkert ◽  
E. Serrallach ◽  
W. Känzig ◽  
...  
Keyword(s):  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Analytical Ultracentrifugation ◽  
Rotational Diffusion ◽  
Axial Ratio ◽  
Major Axis ◽  
Fluorescence Depolarization ◽  
Human Fibrinogen ◽  
Size And Shape ◽  
Rotational Diffusion Coefficients

In order to obtain information on size and shape of the fibrinogen molecule in solution the translational diffusion coefficient (DT), the rotational diffusion coefficients (DR⊥ and DR//) and the sedimentation coefficients (S) have been measured on human fibrinogen with a clottaoility above 95%. The methods used were dynamic light scattering, nanosecond fluorescence depolarization and analytical ultracentrifugation. Dynamic light scattering yields DT = 2.0 ± 3% x 10-7 cm2sec–1 at a concentration of 7 mg/ml in 0.15 M Tris-NaCl, pH 7.4. DT is strongly dependent on concentration, being 3.4 ± 10% × 10-7 cm2 sec-1 at 0.1 mg/ml. The rotation along the minor axis as measured with the same method is DR = // 1.5 × 106 sec-1 at 0.1 mg/ml. The rotation along the major axis as measured on fibrinogen labeled with dansylchloride is DR// = 1.5 x106 sec–1. S is also strongly dependent on concentration, being 7.9 S at 0.1 mg/ml, 8.1 S at 1 mg/ml and 6.6 S at 10 mg/ml.These results fit with an elongated molecule having an axial ratio of 7. They are compatible with a MW of 340’000 only for concentrations above 2 mg/ml, while at lower concentrations (0.1 mg/ml) they agree with a MW of approximately half the accepted value.

Photo-Crosslinking of Copolymeric Methacrylates Bearing Stilbene Chromophores

2012 ◽  
Vol 67 (11) ◽  
pp. 1132-1136
Author(s):  
Angelika Jahnke ◽  
Herbert Meier
Keyword(s):  
Light Scattering ◽  
Methyl Methacrylate ◽  
Radical Polymerization ◽  
Organic Solvents ◽  
Imaging Techniques ◽  
Ester Group ◽  
Cast Films ◽  
The Cross ◽  
Group Yield

Radical polymerization of methyl methacrylate (2) as major component and the methacrylates 1a or 1b, which contain an (E)-stilbene unit fixed by a tether to the ester group, yield easily soluble copolymers 3a, b. Whereas the dominant photoreactions in solution are (E)⇄Z) isomerizations and intra-chain [2π +2π] cycloadditions, cast films of 3a, b give an inter-chain photo-crosslinking on irradiation. Compared to homopolymers, the copolymers are not only better soluble and more easily processible, their films show less undesired light scattering. The cross-linked material is completely insoluble in organic solvents. Thus, it represents the basis for negative photoresists and the corresponding imaging techniques.

Light scattering and viscosity study of Poly-L-methionine

1970 ◽  
Vol 23 (9) ◽  
pp. 1801 ◽  
Author(s):  
JH Bradbury ◽  
BE Chapman
Keyword(s):  
Light Scattering ◽  
Organic Solvents ◽  
Trifluoroacetic Acid ◽  
Dichloroacetic Acid ◽  
Random Coil ◽  
Ethylene Dichloride ◽  
Viscosity Study ◽  
Polyelectrolyte Effect

Poly-L-methionine samples have been produced by polymerization of L- methionine-N-carboxyanhydride and their properties studied by light scattering and viscometry in organic solvents. In trifluoroacetic acid viscosity studies reveal a polyelectrolyte effect, hence the poly-L-methionine is charged. Furthermore, it is a random coil and fits the same Mark-Houwink equation as does poly-γ-benzyl-L-glutamate in dichloroacetic acid. Poly-L-methionine is a helical rod in ethylene dichloride + 2% dichloroacetic acid and shows the same viscometric behaviour as poly-y-benzyl-L-glutamate in dimethylformamide. Comparison of five different organic soluble polypeptides shows that there is an approximate correlation between the rigidity of the helix and its stability.

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