Abstract:We report a method to control the conformation of a weak polyampholyte (the protein β-casein) in Langmuir monolayers by light, even though the protein is not photosensitive. Our approach is to couple the monolayer state to a photochemical reaction excited in the liquid subphase. The conformational transition of the protein molecule is triggered through its sensitivity to a subphase bulk field (pH in this study), changing in the course of the photochemical process. Thus, reaction of photoaquation of the ferrocy… Show more
“…If one takes into account that β-casein is a nonglobular protein with a flexible polypeptide chain and contains hydrophobic groups, it is possible to assume that β-casein also forms pancakes initially. This idea is really used in numerous studies and agrees with the scaling description. − ,− ,− ,,, Figure a shows a very simplified scheme of the corresponding conformation where the hydrophobic and hydrophilic parts of the molecule are represented by two pairs of blocks. 8 Schematic of conformational changes of a single β-casein molecule upon surface pressure increase in the range below the first maximum (a), close to the local minimum (b), and beyond the second local maximum (c).…”
Section: Discussionmentioning
confidence: 57%
“…The dynamic surface elasticity as a function of surface age goes through a local minimum at π ∼ 11 mN/m. The first minimum for the β-casein solutions is also usually explained by the formation of loops and tails. − ,− ,− , Results from neutron and X-ray reflectivity, and also self-consistent field numerical calculations confirm the existence of loops and tails. , Obviously, the loops and tails are formed by the more hydrophilic parts of the molecule, the N-terminal ends first of all (Figure b).…”
Section: Discussionmentioning
confidence: 91%
“…The adsorbed and spread layers of β-casein at the interface between a liquid and a fluid phase have been studied by surface tensiometry, ,− radiotracer methods, ellipsometry, ,,, the methods of X-ray 17 and neutron 2,4,17 reflection, infrared reflection−absorption spectroscopy, , atomic force microscopy, , Brewster angle microscopy, , surface shear ,− and dilational − ,,,,,− ,,− rheology. The dilational viscoelasticity of β-casein surface layers probably was investigated to the greatest extent as compared with other polymeric systems.…”
The nonmonotonic kinetic dependencies of the dynamic elasticity of adsorbed and spread β-casein layers at the liquid-gas interface have been determined by the oscillating barrier method. While two local maxima in the surface elasticity versus concentration dependence are well documented in literature, these features have not been reported for kinetic curve. The surface elasticity in the time range of the second maximum depended on the β-casein bulk concentration and deviated from the elasticity of spread β-casein layers at the same surface pressures. In parallel to the surface viscoelasticity of PEO-PPO-PEO block copolymers, the experimental findings for β-casein can be explained by a separation of relatively hydrophobic groups of the polypeptide chain during the slow process of protein adsorption.
“…If one takes into account that β-casein is a nonglobular protein with a flexible polypeptide chain and contains hydrophobic groups, it is possible to assume that β-casein also forms pancakes initially. This idea is really used in numerous studies and agrees with the scaling description. − ,− ,− ,,, Figure a shows a very simplified scheme of the corresponding conformation where the hydrophobic and hydrophilic parts of the molecule are represented by two pairs of blocks. 8 Schematic of conformational changes of a single β-casein molecule upon surface pressure increase in the range below the first maximum (a), close to the local minimum (b), and beyond the second local maximum (c).…”
Section: Discussionmentioning
confidence: 57%
“…The dynamic surface elasticity as a function of surface age goes through a local minimum at π ∼ 11 mN/m. The first minimum for the β-casein solutions is also usually explained by the formation of loops and tails. − ,− ,− , Results from neutron and X-ray reflectivity, and also self-consistent field numerical calculations confirm the existence of loops and tails. , Obviously, the loops and tails are formed by the more hydrophilic parts of the molecule, the N-terminal ends first of all (Figure b).…”
Section: Discussionmentioning
confidence: 91%
“…The adsorbed and spread layers of β-casein at the interface between a liquid and a fluid phase have been studied by surface tensiometry, ,− radiotracer methods, ellipsometry, ,,, the methods of X-ray 17 and neutron 2,4,17 reflection, infrared reflection−absorption spectroscopy, , atomic force microscopy, , Brewster angle microscopy, , surface shear ,− and dilational − ,,,,,− ,,− rheology. The dilational viscoelasticity of β-casein surface layers probably was investigated to the greatest extent as compared with other polymeric systems.…”
The nonmonotonic kinetic dependencies of the dynamic elasticity of adsorbed and spread β-casein layers at the liquid-gas interface have been determined by the oscillating barrier method. While two local maxima in the surface elasticity versus concentration dependence are well documented in literature, these features have not been reported for kinetic curve. The surface elasticity in the time range of the second maximum depended on the β-casein bulk concentration and deviated from the elasticity of spread β-casein layers at the same surface pressures. In parallel to the surface viscoelasticity of PEO-PPO-PEO block copolymers, the experimental findings for β-casein can be explained by a separation of relatively hydrophobic groups of the polypeptide chain during the slow process of protein adsorption.
“…Self-avoiding, intrinsically curved chains may also show interesting behavior in two dimensions, as in the case of a chain adsorbed on a monolayer interface , where helix formation is impossible and one expects frustration between the chain's desire to curl upon itself and the need for constant curvature. This competition should result in the formation of “curvature kinks” corresponding to inflection points or straightened segments of the chain, and which to our knowledge have not yet been studied on or off the lattice.…”
We treat polymer chains with an intrinsic curvature, which we model by a continuum extension
of a microscopic model with preferred bending angle. From this model, we obtain a modified form of the mean-field Hamiltonian used to describe semiflexible chains. We then employ an auxiliary field operator to enforce the
mean curvature constraint along with a torsional constraint. Using this formalism, we provide analytic results for
the tangent-tangent correlator 〈
u
(s)·
u
(s‘)〉, mean square radius of gyration 〈S
2〉, and mean square separation 〈R
2〉.
We also obtain approximate results for the force−extension behavior of these chains, and discuss possible extensions
to curved polymers with excluded volume and other self-interactions.
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