Polymer brush collapse under shear flow

Shear responsive surfaces offer potential advances in a number of applications. Surface functionalisation using polymer brushes is one route to such properties, particularly in the case of entangled polymers. We report on neutron reflectometry measurements of polymer brushes in entangled polymer solutions performed under controlled shear, as well as coarse-grained computer simulations corresponding to these interfaces. Here we show a reversible and reproducible collapse of the brushes, increasing with the shear rate. Using two brushes of greatly different chain lengths and grafting densities, we demonstrate that the dynamics responsible for the structural change of the brush are governed by the free chains in solution rather than the brush itself, within the range of parameters examined. The phenomenon of the brush collapse could find applications in the tailoring of nanosensors, and as a way to dynamically control surface friction and adhesion

QUANTITATIVE STRUCTURE-ACTIVITY-RELATIONSHIPS FOR 1,4-DIHYDROPYRIDINE CALCIUM-CHANNEL ANTAGONISTS (NIFEDIPINE ANALOGS) - A QUANTUM CHEMICAL/CLASSICAL APPROACH

A quantum chemical (AM1) combined with a classical study of structure-activity relationships for 1,4-dihydropyridines (nifedipine analogues) was performed. The biological data were taken from the literature. The quantum chemical parameters tested were energies of HOMO and LUMO, dipole moment (total and partial), hardness, Mulliken electronegativity, frontier orbital indices, and others. Also tested were classical parameters like Hansch hydrophobic constant, pi; Hammett electronic constant for the mete position, sigma(m); and the Verloop sterimol parameters, B-1 and L. The van der Waals volume was also tested. The pharmacological activities of the para monoderivatives are negatively correlated with the molecular volume, i.e. a steric factor. The meta position of the phenyl ring is affected by steric and electronic parameters, whereas the ortho position seems to be affected by hydrophobic and electronic parameters.8381110111

Conformational Analysis Of The 1,4-dihydropyridines Linking The Structural Aspects To The Biological Binding Event: A Study Of The Receptor-site Conformation

A conformational analysis involving a set of 45 2,6-dimethyl-3,5-dicarbomethoxy-4-X-phenyl-1,4-dihydropyridine derivatives was performed. The potential energy surfaces of the rotation of the phenyl ring around the pyridine ring were constructed for each compound. These were arranged in groups of five in descending order of biological activity. The energy level below 99% of the molecular population for each molecule was superimposed on those groups. The conformationally stable regions permitted to this molecular population were found and compared. The analysis of each group of potential energy surfaces thus constructed revealed that in the biologically active conformation the phenyl ring bisects the pyridine ring and the ortho/meta phenyl substituents are spatially away from the pyridine ring. © 1994.303C255263Janis, Silver, Triggle, (1987) Adv. Drug Res., 16, p. 309Fleckenstein, (1977) Annu. Rev. Pharmacol. Toxicol., 17, p. 149Janis, Triggle, (1983) J. Med. Chem., 26, p. 775Triggle, Comprehensive Medicinal Chemistry. The Rational Design (1990) Mechanistic Study and Therapeutic Application of Chemical Compounds, 3, p. 1047. , C. Hansch, P.G. Sammos, J.B. Taylor, Pergamon, New YorkCoburn, Wierzba, Suto, Solo, Triggle, Triggle, (1988) J. Med. Chem., 31, p. 2103Loev, Goodman, Snader, Tedeschi, Macko, (1974) J. Med. Chem., 17, p. 956Triggle, Shefter, Triggle, (1980) J. Med. Chem., 23, p. 1442Fossheim, Svarteng, Mostad, Rømming, Shefter, Triggle, (1982) J. Med. Chem., 25, p. 126Seidel, Meyer, Born, Kazda, Dompert, (1984) Proc. 5th Eur. Symp. Quant. Struct. Act. Relat., p. 366. , J.K. Scidel, VCH, WeinheimMahmoudian, Richards, (1986) J. Pharm. Pharmacol., 38, p. 272Baldwin, Claremon, Lumma, McClure, Rosenthal, Winquist, Faison, Smith, (1987) J. Med. Chem., 30, p. 690Höltje, Marrer, Qualitative and Quantitative Structure-Activity Relationships for Calcium Channel Modulating 1,4-Dihydropyridine Derivatives: A Hypothetical Molecular Receptor Model (1988) Quantitative Structure-Activity Relationships, 7, p. 174Hofmann, Cimiraglia, (1990) J. Mol. Struct. (Theochem), 205, p. 1Höltje, Molecular Modelling Studies on 1,4-Dihydropyridines Acting at the Ca-Channel (1992) Quantitative Structure-Activity Relationships, 11, p. 224Dewar, Zoebisch, Healy, Stewart, (1985) J. Am. Chem. Soc., 107, p. 3902Stewart, (1990) J. Comput. Aided Mol. Des., 4, p. 1Richards, (1983) Quantum Pharmacology, p. 145. , 2nd Edn., Butterworths, LondonFarnell, Richards, Ganellin, (1975) J. Med. Chem., 18, p. 66

CONFORMATIONAL-ANALYSIS OF THE 1,4-DIHYDROPYRIDINES LINKING THE STRUCTURAL ASPECTS TO THE BIOLOGICAL BINDING EVENT - A STUDY OF THE RECEPTOR-SITE CONFORMATION

A conformational analysis involving a set of 45 2,6-dimethyl-3,5-dicarbomethoxy-4-X-phenyl-1,4-dihydropyridine derivatives was performed. The potential energy surfaces of the rotation of the phenyl ring around the pyridine ring were constructed for each compound. These were arranged in groups of five in descending order of biological activity. The energy level below 99% of the molecular population for each molecule was super-imposed on those groups. The conformationally stable regions permitted to this molecular population were found and compared. The analysis of each group of potential energy surfaces thus constructed revealed that in the biologically active conformation the phenyl ring bisects the pyridine ring and the ortho/meta phenyl substituents are spatially away from the pyridine ring.10925526

Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces: a statistical analysis of the scattering contributions

Grazing incidence neutron scattering experiments offer surface sensitivity by reflecting from an interface at momentum transfers close to total external reflection. Under these conditions the penetration depth is strongly non-linear and may change by many orders of magnitude. This fact imposes severe challenges for depth resolved experiments, since the brilliance of neutron beams is relatively low in comparison to e.g. synchrotron radiation. In this article we use probability density functions to calculate the contribution of scattering at different distances from an interface to the intensities registered on the detector. Our method has the particular advantage that the depth sensitivity is directly extracted from the scattering pattern itself. Hence for perfectly known samples exact resolution functions can be calculated and visa versa. We show that any tails in the resolution function, e.g. Gaussian shaped, hinders depth resolved experiments. More importantly we provide means for a descriptive statistical analysis of detector images with respect to the scattering contributions and show that even for perfect resolution near surface scattering is hardly accessible