The collapse of monolayers of 10,12-pentacosadiyonic acid at the air/water interface has been stu... more The collapse of monolayers of 10,12-pentacosadiyonic acid at the air/water interface has been studied by measurements of isotherms as a function of temperature, compression speed, and spreading solvent. Films on the water surface have been examined by X-ray reflectivity, and atomic force microscopy (AFM) images have been obtained of films transferred to mica by the Langmuir-Blodgett method. At constant temperature, collapse occurs at constant pressure, which increases with the logarithm of the compression speed, suggesting an activation controlled process. Both the AFM and reflectivity measurements are consistent with the formation of a trilayer upon collapse. A mechanical model for collapse is discussed.
Monolayers of the polymerizable 10-12 pentacosadiyonic acid amphiphile spread on a basic buffer a... more Monolayers of the polymerizable 10-12 pentacosadiyonic acid amphiphile spread on a basic buffer are studied both before and after polymerization. We have established the phase diagram of the unpolymerized Langmuir film by isotherm measurements, Brewster angle microscopy, and grazing incidence X-ray diffraction experiments. Diffuse scattering experiments performed at the European Synchrotron Radiation Facility allowed us to investigate the structure and elastic properties of the different monomer phases and the modifications induced by polymerization.
The second virial coefficients of 13 binary gas mixtures have been measured at 90°I,2. A new expe... more The second virial coefficients of 13 binary gas mixtures have been measured at 90°I,2. A new experimental method is described and the data are compared with calculations using the Lennard-Jones 6-12 potential and combination rules.
Throughout the previous chapters, attention has been focused on the wide variety of structures an... more Throughout the previous chapters, attention has been focused on the wide variety of structures and phase behaviors characterizing the self-assembly of amphiphilic molecules in aqueous solution (Chapters 1 to 6) and in oil/water mixtures (Chapters 6 to 11). In all cases the organization of amphiphilic (surfactant) molecules has involved one or more three-dimensional aggregates, i.e., globular or cylindrical micelles, vesicles or undulating bilayers, and droplets or bicontinuous phases of microemulsions. As a consequence, elastic (curvature) free energy has played a crucial role in determining the relative stabilities of competing geometries, and the associated phase transitions have been naturally compared and contrasted with those familiar from the usual fluids, liquid crystals, and solids in bulk.
A majority of viruses are composed of long single-stranded genomic RNA molecules encapsulated by ... more A majority of viruses are composed of long single-stranded genomic RNA molecules encapsulated by protein shells with diameters of just a few tens of nanometers. We examine the extent to which these viral RNAs have evolved to be physically compact molecules to facilitate encapsulation. Measurements of equal-length viral, non-viral, coding and non-coding RNAs show viral RNAs to have among the smallest sizes in solution, i.e., the highest gel-electrophoretic mobilities and the smallest hydrodynamic radii. Using graph-theoretical analyses we demonstrate that their sizes correlate with the compactness of branching patterns in predicted secondary structure ensembles. The density of branching is determined by the number and relative positions of 3-helix junctions, and is highly sensitive to the presence of rare higher-order junctions with 4 or more helices. Compact branching arises from a preponderance of base pairing between nucleotides close to each other in the primary sequence. The density of branching represents a degree of freedom optimized by viral RNA genomes in response to the evolutionary pressure to be packaged reliably. Several families of viruses are analyzed to delineate the effects of capsid geometry, size and charge stabilization on the selective pressure for RNA compactness. Compact branching has important implications for RNA folding and viral assembly.
Physica A: Statistical Mechanics and its Applications, 1994
Abstract Quantitative studies are described of striped textures in Langmuir monolayers of tetrade... more Abstract Quantitative studies are described of striped textures in Langmuir monolayers of tetradecanoic and pentadecanoic acids. The textures, which are the result of modulations of the tilt azimuths of the molecules, have been visualized with polarized fluorescence microscopy. The stripe widths change with pressure and temperature. When the monolayer is compressed beyond a threshold pressure, the stripes become unstable and form a zig-zag pattern, which is likely the result of a crossover between the bend and splay elastic ...
... The translational correlation length in the S phase is less than half as large; in the LS ...... more ... The translational correlation length in the S phase is less than half as large; in the LS ... but broader in L;. Pershan and coworkers (22) have raised questions about the meta stability of phases ... A unique feature of this phase is the broken symmetry that results from the locking of the ...
The collapse of monolayers of 10,12-pentacosadiyonic acid at the air/water interface has been stu... more The collapse of monolayers of 10,12-pentacosadiyonic acid at the air/water interface has been studied by measurements of isotherms as a function of temperature, compression speed, and spreading solvent. Films on the water surface have been examined by X-ray reflectivity, and atomic force microscopy (AFM) images have been obtained of films transferred to mica by the Langmuir-Blodgett method. At constant temperature, collapse occurs at constant pressure, which increases with the logarithm of the compression speed, suggesting an activation controlled process. Both the AFM and reflectivity measurements are consistent with the formation of a trilayer upon collapse. A mechanical model for collapse is discussed.
Monolayers of the polymerizable 10-12 pentacosadiyonic acid amphiphile spread on a basic buffer a... more Monolayers of the polymerizable 10-12 pentacosadiyonic acid amphiphile spread on a basic buffer are studied both before and after polymerization. We have established the phase diagram of the unpolymerized Langmuir film by isotherm measurements, Brewster angle microscopy, and grazing incidence X-ray diffraction experiments. Diffuse scattering experiments performed at the European Synchrotron Radiation Facility allowed us to investigate the structure and elastic properties of the different monomer phases and the modifications induced by polymerization.
The second virial coefficients of 13 binary gas mixtures have been measured at 90°I,2. A new expe... more The second virial coefficients of 13 binary gas mixtures have been measured at 90°I,2. A new experimental method is described and the data are compared with calculations using the Lennard-Jones 6-12 potential and combination rules.
Throughout the previous chapters, attention has been focused on the wide variety of structures an... more Throughout the previous chapters, attention has been focused on the wide variety of structures and phase behaviors characterizing the self-assembly of amphiphilic molecules in aqueous solution (Chapters 1 to 6) and in oil/water mixtures (Chapters 6 to 11). In all cases the organization of amphiphilic (surfactant) molecules has involved one or more three-dimensional aggregates, i.e., globular or cylindrical micelles, vesicles or undulating bilayers, and droplets or bicontinuous phases of microemulsions. As a consequence, elastic (curvature) free energy has played a crucial role in determining the relative stabilities of competing geometries, and the associated phase transitions have been naturally compared and contrasted with those familiar from the usual fluids, liquid crystals, and solids in bulk.
A majority of viruses are composed of long single-stranded genomic RNA molecules encapsulated by ... more A majority of viruses are composed of long single-stranded genomic RNA molecules encapsulated by protein shells with diameters of just a few tens of nanometers. We examine the extent to which these viral RNAs have evolved to be physically compact molecules to facilitate encapsulation. Measurements of equal-length viral, non-viral, coding and non-coding RNAs show viral RNAs to have among the smallest sizes in solution, i.e., the highest gel-electrophoretic mobilities and the smallest hydrodynamic radii. Using graph-theoretical analyses we demonstrate that their sizes correlate with the compactness of branching patterns in predicted secondary structure ensembles. The density of branching is determined by the number and relative positions of 3-helix junctions, and is highly sensitive to the presence of rare higher-order junctions with 4 or more helices. Compact branching arises from a preponderance of base pairing between nucleotides close to each other in the primary sequence. The density of branching represents a degree of freedom optimized by viral RNA genomes in response to the evolutionary pressure to be packaged reliably. Several families of viruses are analyzed to delineate the effects of capsid geometry, size and charge stabilization on the selective pressure for RNA compactness. Compact branching has important implications for RNA folding and viral assembly.
Physica A: Statistical Mechanics and its Applications, 1994
Abstract Quantitative studies are described of striped textures in Langmuir monolayers of tetrade... more Abstract Quantitative studies are described of striped textures in Langmuir monolayers of tetradecanoic and pentadecanoic acids. The textures, which are the result of modulations of the tilt azimuths of the molecules, have been visualized with polarized fluorescence microscopy. The stripe widths change with pressure and temperature. When the monolayer is compressed beyond a threshold pressure, the stripes become unstable and form a zig-zag pattern, which is likely the result of a crossover between the bend and splay elastic ...
... The translational correlation length in the S phase is less than half as large; in the LS ...... more ... The translational correlation length in the S phase is less than half as large; in the LS ... but broader in L;. Pershan and coworkers (22) have raised questions about the meta stability of phases ... A unique feature of this phase is the broken symmetry that results from the locking of the ...
Uploads
Papers by C. Knobler