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Dissecting Hydrophobic Hydration and Association  [PDF]
Richard C. Remsing,John D. Weeks
Physics , 2015, DOI: 10.1021/jp4053067
Abstract: We use appropriately defined short ranged reference models of liquid water to clarify the different roles local hydrogen bonding, van der Waals attractions, and long ranged electrostatic interactions play in the solvation and association of apolar solutes in water. While local hydrogen bonding in- teractions dominate hydrophobic effects involving small solutes, longer ranged electrostatic and dis- persion interactions are found to be increasingly important in the description of interfacial structure around large solutes. The hydrogen bond network sets the solute length scale at which a crossover in solvation behavior between these small and large length scale regimes is observed. Unbalanced long ranged forces acting on interfacial water molecules are also important in hydrophobic association, illustrated here by analysis of the association of model methane and buckminsterfullerene solutes.
Synthesis of New Thickener Based on Carbohydrate Polymers for Printing Cotton Fabrics with Reactive Dyes
Kh.M. Mostafa,Abdul Rahim Samarkandy
Journal of Applied Sciences , 2005,
Abstract: Tailoring of new thickener via graft copolymerization of methacrylonitrile (MAN) onto pregelled starch (PGS) as a carbohydrate polymer was synthesized and the reaction conditions were optimized using potassium monopersulphate (PMPS) in presence of ferrous ion redox pair as initiator. Emphasis was directed towards preparing new thickener for printing cotton fabrics with reactive dyes. The grafting parameter was studied with respect to Graft Yield (GY) and Graft Reaction Efficiency Percent (GRE%). On the other hand, the newly prepared poly (MAN)-pregelled starch graft copolymers were used as a thickener for printing cotton fabrics with reactive dyes, to see their suitability as pastes for printing cotton with the latter dyes. Based on the results obtained, appropriate conditions for grafting methacrylonitrile onto pregelled starch was established and the graft yield is higher under the following conditions: using 0.004 mol L-1 potassium monopersulphate as initiator, 0.005 mol L-1 ferrous ion concentration, 0.002 mol L-1, sulphuric acid; 50% methacrylonitrile concentration (based on weight of substrate), material to liquor ratio, 1:2.5, reaction time, 60 min and polymerization temperature, 40 °C. Finally, utilization of poly (MAN)-pregelled starch graft copolymers as a new thickener for printing cotton with reactive dyes proved to be a potential thickener as evidenced by excellent color strength as well as overall fastness properties.
Synthesis of New Thickener Based on Carbohydrate Polymers for Printing Cotton Fabrics with Reactive Dyes  [PDF]
Kh.M. Mostafa,Abdul Rahim Samarkandy
Journal of Biological Sciences , 2004,
Abstract: Tailoring of new thickener via graft copolymerization of methacrylonitrile (MAN) onto pregelled starch (PGS) as a carbohydrate polymer was synthesized and the reaction conditions were optimized using potassium monopersulphate (PMPS) in presence of ferrous ion redox pair as initiator. Emphasis was directed towards preparing new thickener for printing cotton fabrics with reactive dyes. The grafting parameter was studied with respect to graft yield (G.Y.) and graft reaction efficiency percent (G.R.E.%). On the other hand, the newly prepared poly (MAN)-pregelled starch graft copolymers were used as a thickener for printing cotton fabrics with reactive dyes, to see their suitability as pastes for printing cotton with the latter dyes. Based on the results obtained, appropriate conditions for grafting methacrylonitrile onto pregelled starch was established and the graft yield is higher under the following conditions: using 0.004 mmol L-1 potassium monopersulphate as initiator, 0.005 mmol L-1 ferrous ion concentration, 0.002 mmol L-1, sulphuric acid; 50% methacrylonitrile concentration (based on weight of substrate), material to liquor ratio, 1:2.5, reaction time, 60 min and polymerization temperature, 40 C. Finally, utilization of poly (MAN)-pregelled starch graft copolymers as a new thickener for printing cotton with reactive dyes proved to be a potential thickener as evidenced by excellent color strength as well as overall fastness properties.
How interface geometry dictates water's thermodynamic signature in hydrophobic association  [PDF]
Joachim Dzubiella
Statistics , 2011, DOI: 10.1007/s10955-011-0217-8
Abstract: As a common view the hydrophobic association between molecular-scale binding partners is supposed to be dominantly driven by entropy. Recent calorimetric experiments and computer simulations heavily challenge this established paradigm by reporting that water's thermodynamic signature in the binding of small hydrophobic ligands to similar-sized apolar pockets is enthalpy-driven. Here we show with purely geometric considerations that this controversy can be resolved if the antagonistic effects of concave and convex bending on water interface thermodynamics are properly taken into account. A key prediction of this continuum view is that for fully complementary binding of the convex ligand to the concave counterpart, water shows a thermodynamic signature very similar to planar (large-scale) hydrophobic association, that is, enthalpy-dominated, and hardly depends on the particular pocket/ligand geometry. A detailed comparison to recent simulation data qualitatively supports the validity of our perspective down to subnanometer scales. Our findings have important implications for the interpretation of thermodynamic signatures found in molecular recognition and association processes. Furthermore, traditional implicit solvent models may benefit from our view with respect to their ability to predict binding free energies and entropies.
无皂种子乳液聚合制备新型增稠剂
Synthesis and Charaterized of Thickener by Soap-Free and Seeded Emulsion Polymerization
 [PDF]

杨润苗, 刘玉海, 邓瑶瑶, 黄磊, 秦莺莺
Material Sciences (MS) , 2013, DOI: 10.12677/MS.2013.31007
Abstract:
采用无皂种子乳液聚合方法制备了一种新型丙烯酸酯共聚物增稠剂。为了获得表面清洁和表面富含羧基的功能性聚合物乳胶粒子,首先合成了种子颗粒直径在250~300纳米的聚(苯乙烯-甲基丙烯酸)(P(St-MAA))种子乳液;然后,在无乳化剂的条件下,聚合丙烯酸乙酯(EA),甲基丙烯酸十二酯(LMA),苯乙烯(St)和甲基丙烯酸(MAA);最后,得到颗粒直径在380~440纳米的稳定乳液。重点研究了甲基丙烯酸十二酯含量对乳液颗粒大小和乳液稳定性的影响。研究表明,该聚合物乳液具有很好的增稠性能,良好的悬浮能力,透明性好,易于使用。采用傅里叶变换红外光谱仪(FT-IR)、示差扫描量热仪(DSC)、透射电子显微镜(TEM)对其结构和形貌进行了表征。
A kind of acrylates copolymer thickener was prepared by soap-free and seeded emulsion polymerization. In order to obtain functional polymer latex particles with clean surface and with surface carboxyl groups, Poly (styrene-methacrylic acid) (P (St-MAA)) seed particles with the diameter of 250 - 300 nm were synthesized via soap-free emulsion polymerization. Then the seeded emulsion
Evaluation of hydrophobic nanoparticulate delivery system for insulin  [cached]
Singnurkar P,Gidwani S
Indian Journal of Pharmaceutical Sciences , 2008,
Abstract: Insulin loaded hydrophobic nanoparticles were prepared by solvent diffusion followed by lyophilization. Nanoparticles were characterized for mean size by dynamic laser scattering and for shape by scanning electron microscopy. Insulin encapsulation efficiency, in vitro stability of nanoparticles in presence of proteolytic enzymes and in vitro release were determined by high pressure liquid chromatography analysis. The biological activity insulin from the nanopraticles was estimated by enzyme-linked immunosorbant assay and in vivo using Wister diabetic rats. Nanoparticles ranged 0.526±0.071 μm in diameter. Insulin encapsulation efficiency was 95.7±1.2%. Insulin hydrophobic nanoparticles suppressed insulin release promoted sustained release in pH 7.4 phosphate buffer and shown to protect insulin from enzymatic degradation in vitro in presence of chymotripsin. Nanoencapsulated insulin was bioactive, demonstrated through both in vivo and in vitro.
Simulations of HIV capsid protein dimerization reveal the effect of chemistry and topography on the mechanism of hydrophobic protein association  [PDF]
Naiyin Yu,Michael F. Hagan
Quantitative Biology , 2012, DOI: 10.1016/j.bpj.2012.08.016
Abstract: Recent work has shown that the hydrophobic protein surfaces in aqueous solution sit near a drying transition. The tendency for these surfaces to expel water from their vicinity leads to self assembly of macromolecular complexes. In this article we show with a realistic model for a biologically pertinent system how this phenomenon appears at the molecular level. We focus on the association of the C-terminal domain (CA-C) of the human immunodeficiency virus (HIV) capsid protein. By combining all-atom simulations with specialized sampling techniques we measure the water density distribution during the approach of two CA-C proteins as a function of separation and amino acid sequence in the interfacial region. The simulations demonstrate that CA-C protein-protein interactions sit at the edge of a dewetting transition and that this mesoscopic manifestation of the underlying liquid-vapor phase transition can be readily manipulated by biology or protein engineering to significantly affect association behavior. While the wild type protein remains wet until contact, we identify a set of in silico mutations, in which three hydrophilic amino acids are replaced with nonpolar residues, that leads to dewetting prior to association. The existence of dewetting depends on the size and relative locations of substituted residues separated by nm length scales, indicating long range cooperativity and a sensitivity to surface topography. These observations identify important details which are missing from descriptions of protein association based on buried hydrophobic surface area.
Analytical Evaluation of Omega 3 Fatty Acids Imbedded in Hydrophobic Starch in the Rumen  [PDF]
Malcolm Ballard
Open Journal of Animal Sciences (OJAS) , 2018, DOI: 10.4236/ojas.2018.84032
Abstract: Two experiments were conducted to assess the value of hydrophobic starch as a method to encapsulate a supplement consisting of refined fish oil intended for use as a feed supplement for ruminant animals. In Study 1, the product was incubated in vitro for 24 hours. The entire media was analyzed to determine fatty acid composition. In Study 2, the test material was incubated for 0, 2, 4, 6, 8, 10, 12 and 24 hours in order to determine rate of loss of dry matter, as well as the fatty acid profile of the dry matter remaining at 24 hours. Results from Study 1 indicated that 61.1 % of the eicosapentaenoic acid (C20:5) and 75.3% docosahexaenoic acid (C22:6) were still intact after the 24 hour incubation period. In Study 2, 39.1% of the test material was solubilized in the 24 hour period. However, the losses in C20:5 and C22:6 fatty acids were less (25.32% and 27.90% respectively) indicating that the majority of the test product was protected against biohydrogenation. It was concluded that hydrophobic starch can be used to ruminally protected fish oil and to deliver C20:5 and C22:6 fatty acids past the rumen.
The Rise and Fall of the Hydrophobic Effect in Protein Folding and Protein-Protein Association, and Molecular Recognition  [PDF]
Arieh Ben-Naim
Open Journal of Biophysics (OJBIPHY) , 2011, DOI: 10.4236/ojbiphy.2011.11001
Abstract: In the beginning everything was explained in Biochemistry in terms of hydrogen-bonds (HB). Then, the devastating blow, known as the HB-inventory argument came; hydrogen bonding with water molecules compete with intramolecular hydrogen-bonds. As a result, the HBs paradigm fell from grace. The void created was immediately filled by Kauzmann’s idea of hydrophobic (HφO) effect which reigned supreme in biochemical literature for over 50 years (1960-2010). Cracks in the HB-inventory argument on one hand, and doubts about the adequacy of Kauzmann’s model for the HφO effect, have led to a comeback of the HBs, along with a host of new hydrophilic (HφI) effects. The HφO effects lost much of its power - which it never really had - in explaining protein folding and protein-protein association. Instead, the more powerful and richer repertoire of HφI effects took over the reins. The interactions also offered simple and straightforward answers to the problems of protein folding, and protein-protein association.
Evaluation of association between hyperlipidemia and periodontitis
Moein Taghavi A.,Haerian Ardakani A.,Talebi Ardakani MR.,Tabatabai I
Journal of Dental Medicine , 2005,
Abstract: Statement of Problem: Hyperlipidemia is a major risk factor for cardiovascular disease. In recent years some evidence has been presented regarding the association between periodontal and cardiovascular diseases. Purpose: The aim of this study was the evaluation of association between hyperlipidemia and periodontitis. Materials and Methods: In this case-control study, levels of plasma lipids in 40 subjects with periodontitis (CPITN score III or IV) were measured and compared with 40 age and sex matched controls. Data were analyzed using t-student test with P<0.05 as the limit of significance. Results: Total cholesterol (CHL) and triglyceride (TG) were significantly higher in case group compared with control group. (P=0.045 and P=0.016 respectively). HDL and LDL cholesterols were higher in cases but showed no significant differences with controls. The relative frequency of pathologic values of CHL and TG were significantly greater in cases compared with control group (P=0.005 and P=0.001 respectively). Conclusion: Based on the findings of this study, hyperlipidemia may be associated with periodontitis in medically healthy peoples but whether periodontitis causes an increase in levels of serum lipids or whether hyperlipidemia is a risk factor for both periodontitis and cardiovascular disease need to be further investigated.
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