Página 1 dos resultados de 594 itens digitais encontrados em 0.010 segundos

Hydrophilic and hydrophobic cyclodextrins in a new sustained release oral formulation of nicardipine: in vitro evaluation and bioavailability studies in rabbits

Fernandes, Catarina Marques; Ramos, Pedro; Falcão, Amílcar; Veiga, Francisco José Baptista
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
36.19%
The feasibility of using complexes with cyclodextrins (CDs) in nicardipine (NC) controlled delivery has been examined, with a view to extending the pharmaceutical applications spectrum of these carriers. For a fast release fraction, a hydrophilic [beta]-cyclodextrin derivative (hydroxypropyl-[beta]-cyclodextrin) was employed to form a water-soluble complex. For the sustained-releasing portion, triacetyl-[beta]-cyclodextrin (TA[beta]CD) was used to provide complexes with appropriate hydrophobicity. An optimal formulation was designed by the combination of each fraction in different mixing ratios. The release behaviour of the complexes, as well as of their mixtures, was examined in simulated gastric (pH 1.2) and intestinal (pH 6.8) fluids. The formulations released the drug rapidly at the initial stage, followed by a slow release. The drug release rate was markedly retarded in the increasing order of the amount of NC/TA[beta]CD complex. When NC was administered to rabbits, its absorption was very rapid with a short elimination half-life, while a prolonged maintenance of the plasma levels was obtained for the two selected formulations. The drug bioavailability was considerably improved especially after the administration of the mixture of hydrophilic and hydrophobic complexes...

Estudos de interações hidrofóbicas em substâncias húmicas e componentes do solo utilizando análises espectroscópicas.; Study of hydrophobic interactions in humic substances and soil fractions using spectroscopic analyses.

Simões, Marcelo Luiz
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/08/2005 PT
Relevância na Pesquisa
36.32%
A avaliação da ocorrência de interações hidrofóbicas em substâncias húmicas toma-se importante pois este tipo de interação pode afetar a dinâmica e a reatividade de contaminantes apoIares no ambiente e influenciar no controle biogeoquímico do carbono no solo, podendo contribuir para a mitigação do efeito estufa. Entretanto, devido à heterogeneidade química das substâncias húmicas associada à baixa energia envolvida neste tipo de interação, evidências ou detecções experimentais são difíceis. Neste trabalho avaliou-se a ocorrência de interações hidrofóbicas em substâncias húmicas e também em alguns componentes do solo utilizando a metodologia de marcador de spin, detectável por ressonância paramagnética eletrônica, e a supressão de fluorescência. A utilização de diferentes marcadores de spin (TEMPO, 5-SASL, 16-SASL e 5-MSSL) possibilitou avaliar que a interação estabelecida com o ácido húmico é predominantemente hidrofóbica. A forte imobilização do marcado r 5SASL no ácido húmico foi confirmada pela diminuição dos valores da taxa de difusão rotacional obtida por simulação espectral (109 s-1 em água e 106 s-1 em presença do ácido húmico). Da análise do comportamento espectral do marcador de spin...

Moléculas bioativas em quilópodes.; Bioactive molecules in chilopods.

Aguirre, Elisa Chaparro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 27/09/2011 PT
Relevância na Pesquisa
26.12%
Os artrópodes constituem o grupo mais diverso do Reino Animal, apresentando uma distribuição muito ampla nos ecossistemas e habitats. O fato de esses animais terem mudado muito pouco durante sua evolução e estarem bem adaptados aos ambientes inóspitos e com uma alta presença de microorganismos patogênicos, torna interessante a realização de estudos sobre o seu sistema imunológico. Parte importante deste sistema são os peptídeos antimicrobianos, que controlam a invasão dos diferentes patógenos. Estas moléculas não só podem fornecer informação sobre o sistema imune e o funcionamento deste, como também pode ajudar a buscar alternativas nas lutas contra as doenças infecciosas. Sendo assim, se torna interessante a purificação e a caracterização dos peptídeos antimicrobianos presentes nesses animais como também o conhecimento do funcionamento de seu sistema imune. Neste trabalho foram utilizadas duas espécies da ordem quilópoda: Scolopendra viridicornis e Otostigmus cavalcanti como modelo experimental. Foi avaliada a presença de moléculas bioativas na hemolinfa (plasma e hemócitos) e no extrato total do corpo, bem como a produção destas moléculas após o animal receber um estímulo ou injúria. Foi observada a presença de diferentes frações com atividade antimicrobiana na hemolinfa (plasma e hemócitos) e no extrato total de animais desafiados e não desafiados em Otostigmus cavalcanti...

Hydrophobic fraction of Taenia saginata metacestodes, rather than hydrophilic fraction, contains immunodominant markers for diagnosing human neurocysticercosis

Gonçalves,Flávia de Assunção; Machado,Gleyce Alves; Oliveira,Heliana Batista; Rezende,Maria Teresa Nunes Pacheco; Mineo,José Roberto; Costa-Cruz,Julia Maria
Fonte: Sociedade Brasileira de Medicina Tropical - SBMT Publicador: Sociedade Brasileira de Medicina Tropical - SBMT
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2010 EN
Relevância na Pesquisa
36.06%
INTRODUCTION: Considering that alternative antigens for diagnosing neurocysticercosis continue to be a challenge because of the increasing difficulty in obtaining parasites from naturally infected pigs for preparation of Taenia solium homologous antigen, the aim of the present study was to evaluate the detergent (D) and aqueous (A) fractions from saline extract of Taenia saginata metacestodes for diagnosing neurocysticercosis. METHODS: Taenia saginata was obtained from naturally infected bovines in the Triângulo Mineiro region, State of Minas Gerais, Brazil. The carcasses came from cold storage units and had been slaughtered in accordance with the inspection technique recommended by the Federal Inspection Service. The D and A fractions were obtained by using Triton X-114 (TX-114). Serum samples were obtained from 40 patients with a diagnosis of neurocysticercosis, 45 with other parasitic diseases and 30 from apparently normal individuals. IgG antibody levels were evaluated using the ELISA and immunoblotting assays. RESULTS: The ELISA sensitivity and specificity were 95% and 73.3%, when using saline extract; 95% and 82.6% for the D fraction; and 65% and 61.3% for the A fraction, respectively. The immunoblotting assay confirmed the ELISA results...

Determination of the hydrophobic fraction of Ca, Fe, Mg and Zn in dark color honeys using solid phase extraction and flame atomic absorption spectrometry

Pohl,Pawel; Stecka,Helena; Greda,Krzysztof; Jamroz,Piotr
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2012 EN
Relevância na Pesquisa
66.38%
In this study, the hydrophobic fraction of Ca, Fe, Mg and Zn in dark honeys was assessed by means of solid phase extraction using silica gel based material with monomerically bonded phenyl active groups (Discovery® DSC-Ph tubes). It was found that Fe is associated with this fraction, likely polyphenolic compounds, to the highest degree. The contribution of the hydrophobic fraction to the total content of this element in analyzed honeys accounted for 7-43%. The reliability of these results was verified using for solid phase extraction silica gel based material with polymerically bonded octadecyl active groups (SupercleanÔ ENVI DSC-18). Additionally, a strong positive correlation was established between the concentration of Fe in the hydrophobic fraction assessed and the optical density of dark honeys, indicating a possible contribution of blue complexes of this metal with phenolic substances to the overall color of honey.

A study of calf thymus histone fraction F2(b) by gel filtration

Edwards, P. A.; Shooter, K. V.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1970 EN
Relevância na Pesquisa
26.12%
The gel-filtration behaviour of calf thymus histone fraction F2(b) was studied at three different salt concentrations (0.01m-, 0.10m- and 1.00m-sodium chloride) and two different pH ranges (pH3–4 and pH6.7–7.1). Other histone fractions [F1, F2(a) and F3] were also utilized to assist interpretation of the data. It was found that the Stokes radius of histone fraction F2(b) was not significantly changed when the salt concentration was increased, implying that the aggregation of the individual histone molecules (Edwards & Shooter, 1969) resulted in only relatively minor changes in the hydrodynamic volume. Aggregation would appear to be due to the salting out of hydrophobic regions giving rise, in the aggregate, to a compact core of hydrophobic groups from which protrude the remaining basic parts of the molecule. Repulsion between charged groups on the basic regions of individual histone molecules would give the aggregate approximately spherical symmetry, the diameter of the aggregate approximating to the length of a single histone molecule.

Effect of hydrophobic surfactant proteins SP-B and SP-C on phospholipid monolayers. Protein structure studied using 2D IR and beta correlation analysis.

Shanmukh, Saratchandra; Howell, Phillip; Baatz, John E; Dluhy, Richard A
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/2002 EN
Relevância na Pesquisa
36.24%
We have applied two-dimensional infrared (2D IR) and betanu correlation spectroscopy to in-situ IR spectroscopy of pulmonary surfactant proteins SP-B and SP-C in lipid-protein monolayers at the air-water interface. For both SP-B and SP-C, a statistical windowed autocorrelation method identified two separate surface pressure regions that contained maximum amide I intensity changes: 4-25 mN/m and 25-40 mN/m. For SP-C, 2D IR and betanu correlation analyses of these regions indicated that SP-C adopts a variety of secondary structure conformations, including alpha-helix, beta-sheet, and an intermolecular aggregation of extended beta-sheet structure. The main alpha-helix band split into two peaks at high surface pressures, indicative of two different helix conformations. At low surface pressures, all conformations of the SP-C molecule reacted identically to increasing surface pressure and reoriented in phase with each other. Above 25 mN/m, however, the increasing surface pressure selectively affected the coexisting protein conformations, leading to an independent reorientation of the protein conformations. The asynchronous 2D IR spectrum of SP-B showed the presence of two alpha-helix components, consistent with two separate populations of alpha-helix in SP-B-a hydrophobic fraction associated with the lipid chains and a hydrophilic fraction parallel to the membrane surface. The distribution of correlation intensity between the two alpha-helix cross peaks indicated that the more hydrophobic helix fraction predominates at low surface pressures whereas the more hydrophilic helix fraction predominates at high surface pressures. The different SP-B secondary structures reacted identically to increasing surface pressure...

Hydrophobic folding units derived from dissimilar monomer structures and their interactions.

Tsai, C. J.; Nussinov, R.
Fonte: Cold Spring Harbor Laboratory Press Publicador: Cold Spring Harbor Laboratory Press
Tipo: Artigo de Revista Científica
Publicado em /01/1997 EN
Relevância na Pesquisa
26.2%
We have designed an automated procedure to cut a protein into compact hydrophobic folding units. The hydrophobic units are large enough to contain tertiary non-local interactions, reflecting potential nucleation sites during protein folding. The quality of a hydrophobic folding unit is evaluated by four criteria. The first two correspond to visual characterization of a structural domain, namely, compactness and extent of isolation. We use the definition of Zehfus and Rose (Zehfus MH, Rose GD, 1986, Biochemistry 25:35-340) to calculate the compactness of a cut protein unit. The isolation of a unit is based on the solvent accessible surface area (ASA) originally buried in the interior and exposed to the solvent after cutting. The third quantity is the hydrophobicity, equivalent to the fraction of the buried non-polar ASA with respect to the total non-polar ASA. The last criterion in the evaluation of a folding unit is the number of segments it includes. To conform with the rationale of obtaining hydrophobic units, which may relate to early folding events, the hydrophobic interactions are implicitly and explicitly applied in their generation and assessment. We follow Holm and Sander (Holm L, Sander C, 1994, Proteins 19:256-268) to reduce the multiple cutting-point problem to a one-dimensional search for all reasonable trial cuts. However...

Hydrophobic flavonoids from Scutellaria baicalensis induce colorectal cancer cell apoptosis through a mitochondrial-mediated pathway

WANG, CHONG-ZHI; CALWAY, TYLER D.; WEN, XIAO-DONG; SMITH, JACOB; YU, CHUNHAO; WANG, YUNWEI; MEHENDALE, SANGEETA R.; YUAN, CHUN-SU
Fonte: D.A. Spandidos Publicador: D.A. Spandidos
Tipo: Artigo de Revista Científica
Publicado em 16/01/2013 EN
Relevância na Pesquisa
26.14%
Scutellaria baicalensis extract (SbE) has been shown to exert chemopreventive effects on several types of cancer. Baicalin, a hydrophilic flavonoid found in SbE, may have opposing effects that decrease the antitumor potential of SbE against colorectal cancer. In this study, after removing baicalin, we prepared an aglycone-rich fraction (ARF) of SbE and evaluated its anti-proliferative activity and mechanisms of action. The flavonoids found in ARF, baicalin fraction (BF) and SbE were determined by high-performance liquid chromatography (HPLC). The effects of ARF, BF, SbE and representative flavonoids on the proliferation of HCT-116 and HT-29 human colorectal cancer cells were determined by an MTS assay. The cell cycle, the expression of cyclins A and B1 and cell apoptosis were assayed using flow cytometry. Apoptosis-related gene expression was visualized by quantitative real-time polymerase chain reaction (PCR), and mitochondrial membrane potential was estimated following staining with JC-1. HPLC analysis showed that ARF contained two hydrophobic flavonoids, baicalein and wogonin, and that BF contained only baicalin. SbE had little anti-proliferative effect on the colorectal cancer cells; cancer cell growth was even observed at certain concentrations. ARF exerted potent anti-proliferative effects on the cancer cells. By contrast...

A novel diblock of copolymer of (monomethoxy poly [ethylene glycol]-oleate) with a small hydrophobic fraction to make stable micelles/polymersomes for curcumin delivery to cancer cells

Erfani-Moghadam, Vahid; Nomani, Alireza; Zamani, Mina; Yazdani, Yaghoub; Najafi, Farhood; Sadeghizadeh, Majid
Fonte: Dove Medical Press Publicador: Dove Medical Press
Tipo: Artigo de Revista Científica
Publicado em 28/11/2014 EN
Relevância na Pesquisa
36.01%
Curcumin is a potent natural anticancer agent, but its effectiveness is limited by properties such as very low solubility, high rate of degradation, and low rate of absorption of its hydrophobic molecules in vivo. To date, various nanocarriers have been used to improve the bioavailability of this hydrophobic biomaterial. This study investigates the encapsulation of curcumin in a novel nanostructure of monomethoxy poly(ethylene glycol)-oleate (mPEG-OA) and its anticancer effect. Tests were done to determine the critical micelle concentration (CMC), encapsulation efficiency, drug-loading efficiency, and cytotoxicity (against U87MG brain carcinoma cells and HFSF-PI3 cells as normal human fibroblasts) of some nanodevice preparations. The results of fluorescence microscopy and cell-cycle analyses indicated that the in vitro bioavailability of the encapsulated curcumin was significantly greater than that of free curcumin. Cytotoxicity evaluations showed that half maximal inhibitory concentrations of free curcumin and curcumin-loaded mPEG-OA for the U87MG cancer cell line were 48 μM and 24 μM, respectively. The Annexin-V-FLUOS assay was used to quantify the apoptotic effect of the prepared nanostructures. Apoptosis induction was observed in a dose-dependent manner after curcumin-loaded mPEG-OA treatments. Two common self-assembling structures...

The association of low-molecular-weight hydrophobic compounds with native casein micelles in bovine milk

Cheema, M.; Mohan, M. S.; Campagna, S. R.; Jurat-Fuentes, J. L.; Harte, F. M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/2015 EN
Relevância na Pesquisa
26.13%
The agreed biological function of the casein micelles in milk is to carry minerals (calcium, magnesium, and phosphorus) from mother to young along with amino acids for growth and development. Recently, native and modified casein micelles were used as encapsulating and delivery agents for various hydrophobic low-molecular-weight probes. The ability of modified casein micelles to bind certain probes may derive from the binding affinity of native casein micelles. Hence, a study with milk from single cows was conducted to further elucidate the association of hydrophobic molecules into native casein micelles and further understand their biological function. Hydrophobic and hydrophilic extraction followed by ultraperformance liquid chromatography-high resolution mass spectrometry analysis were performed over protein fractions obtained from size exclusion fractionation of raw skim milk. Hydrophobic compounds, including phosphatidylcholine, lyso-phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin, showed strong association exclusively to casein micelles as compared with whey proteins, whereas hydrophilic compounds did not display any preference for their association among milk proteins. Further analysis using liquid chromatography-tandem mass spectrometry detected 42 compounds associated solely with the casein-micelles fraction. Mass fragments in tandem mass spectrometry identified 4 of these compounds as phosphatidylcholine with fatty acid composition of 16:0/18:1...

Hydrophobic and hydrophilic interactions in aqueous mixtures of alcohols at a hydrophobic surface

Ballal, Deepti; Chapman, Walter G.
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
26.19%
Aqueous solutions of alcohols are interesting because of their anomalous behavior that is believed to be due to the molecular structuring of water and alcohol around each other in solution. The interfacial structuring and properties are significant for application in alcohol purification processes and biomolecular structure. Here we study aqueous mixtures of short alcohols (methanol, ethanol, 1-propanol, and 2-propanol) at a hydrophobic surface using interfacial statistical associating fluid theory which is a perturbation density functional theory. The addition of a small amount of alcohol decreases the interfacial tension of water drastically. This trend in interfacial tension can be explained by the structure of water and alcohol next to the surface. The hydrophobic group of an added alcohol preferentially goes to the surface preserving the structure of water in the bulk. For a given bulk alcohol concentration, water mixed with the different alcohols has different interfacial tensions with propanol having a lower interfacial tension than methanol and ethanol. 2-propanol is not as effective in decreasing the interfacial tension as 1-propanol because it partitions poorly to the surface due to its larger excluded volume. But for a given surface alcohol mole fraction...

Caracterização da matéria orgânica natural em águas para consumo humano

Vieira, Raquel Filipa Moutinho
Fonte: Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto Publicador: Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto
Tipo: Dissertação de Mestrado
Publicado em //2010 POR
Relevância na Pesquisa
26.19%
O tratamento de água para consumo humano tem por objectivos não só a sua qualidade em termos de parâmetros químicos e físicos, como também microbiológicos. Considerando que a MON pode afectar os sistemas de tratamento, a sua redução minimiza a formação de subprodutos de desinfecção, como por exemplo os trihalometanos e diminui o crescimento de microrganismos ao longo do sistema de distribuição. Nesse sentido tem havido recentemente uma grande evolução na investigação relativamente à remoção de matéria orgânica natural. O principal objectivo deste trabalho foi o de caracterizar a matéria orgânica presente na água bruta e ao longo do processo de tratamento, assim como a sua evolução sazonal. Os dados obtidos a partir desta caracterização poderão contribuir para uma futura optimização no processo de tratamento de águas de consumo. O processo utilizado baseou-se na sorção da matéria orgânica dissolvida em diferentes tipos de resinas de permuta iónica, DAX-8, DAX-4 e IRA-958, permitindo a sua separação em várias fracções: ácidos muito hidrofóbicos (VHA), ácidos ligeiramente hidrofóbicos (SHA), compostos hidrofílicos carregados (CHA) e hidrofílicos neutros (NEU). De acordo com os resultados obtidos apenas a fracção NEU demonstrou ter uma tendência sazonal...

Simulación con dinámica molecular de polímeros anfifílicos: dependencia del pH, longitud de la cadena polimérica y cadena alquílica.

Suárez Vallejo, Catalina
Fonte: Universidad Icesi; Facultad de Ciencias Naturales; Química; Ciencias Químicas Publicador: Universidad Icesi; Facultad de Ciencias Naturales; Química; Ciencias Químicas
Tipo: bachelorThesis; Trabajo de grado Formato: pdf; 60 p.; Electrónico
SPA
Relevância na Pesquisa
26.14%
La microencapsulación de sustancias bioactivas es una alternativa para el desarrollo en química farmacéutica, medicina, bioquímica y ciencias de materiales. Uno de los mayores intereses de la investigación en este campo es la liberación controlada de fármacos a una diana biológica específica. Se busca proteger el fármaco de su degradación, disminuir su toxicidad, aumentar su eficacia biológica, entre otros. Adicionalmente, la mayoría de los nuevos agentes químicos que se usan para diferentes tratamientos exhiben baja solubilidad en agua así como una limitada disponibilidad para el suministro oral. Así, altas dosis de este tipo de fármacos son requeridas por los pacientes. Es necesario encontrar matrices de liberación que resuelvan los problemas mencionados anteriormente. Dentro de los sistemas que se han desarrollado se encuentran las cápsulas de polímeros y polielectrolitos, las microemulsiones de fluoroalcanos, las micelas y los hidrogeles. Los poliectrolitos son polímeros que tienen grupos ionizables. Estos sistemas poliméricos exhiben propiedades únicas para su aplicación no solo en el ámbito de química farmacéutica. Las propiedades de este tipo de polímeros dependen de la fracción de grupos iónicos disociados...

Growth saturation of unstable thin films on transverse-striped hydrophilic-hydrophobic micropatterns

Ledesma-Aguilar, Rodrigo; Hernandez-Machado, Aurora; Pagonabarraga, Ignacio
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/10/2011
Relevância na Pesquisa
26.24%
Using three-dimensional numerical simulations, we demonstrate the growth saturation of an unstable thin liquid film on micropatterned hydrophilic-hydrophobic substrates. We consider different transverse-striped micropatterns, characterized by the total fraction of hydrophilic coverage and the width of the hydrophilic stripes. We compare the growth of the film on the micropatterns to the steady states observed on homogeneous substrates, which correspond to a saturated sawtooth and growing finger configurations for hydrophilic and hydrophobic substrates, respectively. The proposed micropatterns trigger an alternating fingering-spreading dynamics of the film, which leads to a complete suppression of the contact line growth above a critical fraction of hydrophilic stripes. Furthermore, we find that increasing the width of the hydrophilic stripes slows down the advancing front, giving smaller critical fractions the wider the hydrophilic stripes are. Using analytical approximations, we quantitatively predict the growth rate of the contact line as a function of the covering fraction, and predict the threshold fraction for saturation as a function of the stripe width.; Comment: 11 pages, 5 figures

Random Hydrophilic-Hydrophobic Copolymers

Garel, T.; Leibler, L.; Orland, H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/06/1994
Relevância na Pesquisa
26.19%
We study a single statistical amphiphilic copolymer chain AB in a selective solvent (e.g.water). Two situations are considered. In the annealed case, hydrophilic (A) and hydrophobic (B) monomers are at local chemical equilibrium and both the fraction of A monomers and their location along the chain can vary, whereas in the quenched case (which is relevant to proteins), the chemical sequence along the chain is fixed by synthesis. In both cases, the physical behaviour depends on the average hydrophobicity of the polymer chain. For a strongly hydrophobic chain (large fraction of B), we find an ordinary continuous $\theta$ collapse, with a large conformational entropy in the collapsed phase. For a weakly hydrophobic, or a hydrophilic chain, there is an unusual first-order collapse transition. In particular, for the case of Gaussian disorder, this discontinuous transition is driven by a change of sign of the third virial coefficient. The entropy of this collapsed phase is strongly reduced with respect to the $\theta$ collapsed phase. Email contact: orland@amoco.saclay.cea.fr; Comment: Saclay-T94/077 Email: orland@amoco.saclay.cea.fr

Drag force on a sphere moving towards an anisotropic super-hydrophobic plane

Asmolov, Evgeny S.; Belyaev, Aleksey V.; Vinogradova, Olga I.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/06/2011
Relevância na Pesquisa
26.13%
We analyze theoretically a high-speed drainage of liquid films squeezed between a hydrophilic sphere and a textured super-hydrophobic plane, that contains trapped gas bubbles. A super-hydrophobic wall is characterized by parameters $L$ (texture characteristic length), $b_1$ and $b_2$ (local slip lengths at solid and gas areas), and $\phi_1$ and $\phi_2$ (fractions of solid and gas areas). Hydrodynamic properties of the plane are fully expressed in terms of the effective slip-length tensor with eigenvalues that depend on texture parameters and $H$ (local separation). The effect of effective slip is predicted to decrease the force as compared with expected for two hydrophilic surfaces and described by the Taylor equation. The presence of additional length scales, $L$, $b_1$ and $b_2$, implies that a film drainage can be much richer than in case of a sphere moving towards a hydrophilic plane. For a large (compared to $L$) gap the reduction of the force is small, and for all textures the force is similar to expected when a sphere is moving towards a smooth hydrophilic plane that is shifted down from the super-hydrophobic wall. The value of this shift is equal to the average of the eigenvalues of the slip-length tensor. By analyzing striped super-hydrophobic surfaces...

Molecular theory of hydrophobic mismatch between lipids and peptides

Duque, Daniel; Li, Xiao-jun; Katsov, Kirill; Schick, Michael
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/08/2001
Relevância na Pesquisa
26.13%
Effects of the mismatch between the hydrophobic length, d, of transmembrane alpha helices of integral proteins and the hydrophobic thickness, D_h, of the membranes they span are studied theoretically utilizing a microscopic model of lipids. In particular, we examine the dependence of the period of a lamellar phase on the hydrophobic length and volume fraction of a rigid, integral, peptide. We find that the period decreases when a short peptide, such that dD_h, is inserted. The effect is due to the replacement of extensible lipid tails by rigid peptide. As the peptide length is increased, the lamellar period continues to increase, but at a slower rate, and can eventually decrease. The amount of peptide which fails to incorporate and span the membrane increases with the magnitude of the hydrophobic mismatch |d-D_h|. We explicate these behaviors which are all in accord with experiment. Predictions are made for the dependence of the tilt of a single trans-membrane alpha helix on hydrophobic mismatch and helix density.; Comment: 14 pages, 5 figures

Correlation length of hydrophobic polyelectrolyte solutions

Baigl, D.; Ober, R.; Qu, D.; Fery, A.; Williams, C. E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/02/2003
Relevância na Pesquisa
26.14%
The combination of two techniques (Small Angle X-ray Scattering and Atomic Force Microscopy) has allowed us to measure in reciprocal and real space the correlation length $\xi$ of salt-free aqueous solutions of highly charged hydrophobic polyelectrolyte as a function of the polymer concentration $C_p$, charge fraction $f$ and chain length $N$. Contrary to the classical behaviour of hydrophilic polyelectrolytes in the strong coupling limit, $\xi$ is strongly dependent on $f$. In particular a continuous transition has been observed from $\xi \sim C_p^{-1/2}$ to $\xi\sim C_p^{-1/3}$ when $f$ decreased from 100% to 35%. We interpret this unusual behaviour as the consequence of the two features characterising the hydrophobic polyelectrolytes: the pearl necklace conformation of the chains and the anomalously strong reduction of the effective charge fraction.; Comment: 7 pages, 5 figures, submitted to Europhysics Letters

Atomic Force Microscopy Study of the Interaction between Adsorbed Poly(ethylene oxide) Layers: Effects of Surface Modification and Approach Velocity

McLean, Scott C; Lioe, Hadi; Meagher, Laurence; Craig, Vincent; Gee, Michelle L
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.19%
The interaction forces between layers of the triblock copolymer Pluronic F108 adsorbed onto hydrophobic radio frequency glow discharge (RFGD) thin film surfaces and hydrophilic silica, in polymer-free 0.15 M NaCl solution, have been measured using the atomic force microscope (ATM) colloid probe technique. Compression of Pluronic F108 layers adsorbed on the hydrophobic RFGD surfaces results in a purely repulsive force due to the steric overlap of the layers, the form of which suggests that the PEO chains adopt a brush conformation. Subsequent fitting of these data to the polymer brush models of Alexander-de Gennes and Milner, Witten, and Cates confirms that the adsorbed Pluronic F108 adsorbs onto hydrophobic surfaces as a polymer brush with a parabolic segment density profile. In comparison, the interaction between Pluronic F108 layers adsorbed on silica exhibits a long ranged shallow attractive force and a weaker steric repulsion. The attractive component is reasonably well described by van der Waals forces, but polymer bridging cannot be ruled out. The weaker steric component of the force suggests that the polymer is less densely packed on the surface and is less extended into solution, existing as polymeric isolated mushrooms. When the surfaces are driven together at high piezo ramp velocities...