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Aggregation Number (aggregation + number)
Selected AbstractsPolymeric alkenoxy amino acid surfactants: I. Highly selective class of molecular micelles for chiral separation of ,-blockersELECTROPHORESIS, Issue 15 2003Syed A. A. Rizvi Abstract Two amino acid-based alkenoxy micelle polymers were synthesized for this study. These include polysodium N -undecenoxy carbonyl- L -leucinate (poly- L -SUCL) and polysodium N -undecenoxy carbonyl- L -isoleucinate (poly- L -SUCIL). The polymerization time and concentration of the synthesized micelle polymers were optimized by 1H-nuclear magnetic resonance (NMR) and capillary electrophoresis (CE) experiments. Detailed physicochemical properties (1H NMR, critical micelle concentration (CMC), optical rotation, partial specific volume, aggregation number, and polarity) were determined, and these molecular micelles were introduced as a pseudostationary phase in micellar electrokinetic chromatography to study the molecular recognition and to develop a method for simultaneous separation of eight chiral ,-blockers. It is found that poly- L -SUCL gives overall better chiral resolution and wider chiral window than poly- L -SUCIL. After optimizing the type of micelle polymer, injection size and temperature, simultaneous separation and enantioseparation of eight ,-blockers were achieved in less than 35 min. A comparison with the amide-type surfactants of the same polar head group and alkyl chain length showed that carbamate-type surfactants always work better than the corresponding amide-type surfactant. [source] Self-assembly of well-defined amphiphilic polymeric miktoarm stars, dendrons, and dendrimers in water: The effect of architectureJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2009Daria E. Lonsdale Abstract Five polymeric architectures with a systematic increase in architectural complexity were synthesized by "click" reactions from a toolbox of functional linear polymers and small molecule linkers. The amphiphilic architectures ranged from a simple 3-miktoarm star block copolymer to the more complex third generation dendrimer-like block copolymer, consisting of polystyrene (PSTY) and polyacrylic acid (PAA). Micellization of these architectures in water at a pH of 7 under identical ionic strength gave spherical micelles ranging in size from 9 to 30 nm. Subsequent calculations of the PSTY core density, average surface area per PAA arm on the corona-core interface, and the relative stretching of the PAA arms provided insights into the effect of architecture on the self-assembly processes. A particular trend was observed that with increased architectural complexity the hydrodynamic diameter, radius of the core in the dry state and the aggregation number also increased with the exception of the third generation dendrimer. On the basis of these observations, we postulate that thermodynamic factors controlling self-assembly were the entropic penalty of forming PSTY loops in the core counterbalanced by the reduction in repulsive forces through chain stretching. This results in a greater number of aggregating unimers and consequently larger micelle sizes. The junction points within the architecture also play an important role in controlling the self-assembly process. The G3 dendrimer showed results contradictory to the aforementioned trend. We believe that the self-assembly process of this architecture was dominated by the increased attractive forces due to stretching of the PSTY core chains to form a more compact core. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6292,6303, 2009 [source] A New View of the Anionic Diene Polymerization MechanismMACROMOLECULAR SYMPOSIA, Issue 1 2004A.Z. Niu Abstract We investigated the anionic polymerization of butadiene in d-heptane solvent using tert -butyl lithium as initiator. Two complementary techniques were used to follow the polymerization processes: 1H NMR and small angle neutron scattering (SANS). The time resolved 1H NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The initiation event commences slowly and then progressively accelerates. This indicates an autocatalytic mechanism. The microstructure of the first monomer units attached is to a high extent 1,2. The disappearance of initiator --- at about 10% monomer conversion --- signals the onset of the normal ,6% vinyl content of the chain. Small angle neutron scattering was used to study the aggregation behavior of the carbon lithium head groups. It is well known that the polar head groups aggregate and form micellar structures. For dienes in non-polar solvents the textbook mechanism assumes the formation of only tetramers during the propagation reaction. By combining 1H NMR and SANS results we were able to determine quantitatively the aggregation number during all stages of the polymerization. Our measurements show the existence of large-scale structures during the initiation period. The initial degree of aggregation of more than 100 living polymer chains diminished as the polymerization progressed. In addition, even larger, giant structures with Nagg >>1000 and Rg , 1000Å were found. [source] Surface activity,thermodynamic properties and light scattering studies for some novel aliphatic polyester surfactantsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2004R. A. El-Ghazawy Abstract The preparation of 12 new polyester surfactants based on aliphatic amines and different ethylene oxide content is described. These surfactants were characterized by determining their molecular weights and polydispersity by gel permeation chromatography (GPC) and nitrogen content. Drop volume tensiometry (DVT) was used to measure the surface tension at 25, 35, 45 and 55°C. The surface tension isotherms were used to determine critical micelle concentration (CMC), maximum Gibb's adsorption (,max), minimum area per molecule (Amin), the effectiveness of surface tension reduction (,cmc) and the efficiency (pC20). The thermodynamic parameters of micellization (,Gmic, ,Hmic, ,Smic) and of adsorption (,Gad, ,Had, ,Sad) were calculated and the data showed that these surfactants favor micellization to adsorption. The static scattered light intensity measurements provide the calculation of the molecular weight of micelle and the aggregation number (N°), while the dynamic light scattering provide the hydrodynamic radius of micelle (RH) and the diffusion coefficient at different surfactant concentrations. The hydrodynamic radius of micelle (RH) at different surfactant concentrations could be used also to determine the CMC giving results that are comparable to those obtained by surface tension measurements. All the data are discussed regarding the chemical structure of the polymeric surfactants. Copyright © 2004 John Wiley & Sons, Ltd. [source] A metal-chelate affinity reverse micellar system for protein extractionBIOTECHNOLOGY PROGRESS, Issue 1 2010Xiao-Yan Dong Abstract A new nonionic reverse micellar system is developed by blending two nonionic surfactants, Triton X-45 and Span 80. At total surfactant concentrations lower than 60 mmol/L and molar fractions of Triton X-45 less than 0.6, thermodynamically stable reverse micelles of water content (W0) up to 30 are formed. Di(2-ethylhexyl) phosphoric acid (HDEHP; 1,2 mmol/L) is introduced into the system for chelating transition metal ions that have binding affinity for histidine-rich proteins. HDEHP exists in a dimeric form in organic solvents and a dimer associated with one transition metal ion, including copper, zinc, and nickel. The copper-chelate reverse micelles (Cu-RM) are characterized for their W0, hydrodynamic radius (Rh), and aggregation number (Nag). Similar with reverse micelles of bis-2-ethylhexyl sodium sulfosuccinate (AOT), Rh of the Cu-RM is also linearly related to W0. However, Nag is determined to be 30,90 at W0 of 5,30, only quarter to half of the AOT reverse micelles. Then, selective metal-chelate extraction of histidine-rich protein (myoglobin) by the Cu-RM is successfully performed with pure and mixed protein systems (myoglobin and lysozyme). The solubilized protein can be recovered by stripping with imidazole or ethylinediaminetetraacetic acid (EDTA) solution. Because various transition metal ions can be chelated to the reverse micelles, it is convinced that the system would be useful for application in protein purification as well as simultaneous isolation and refolding of recombinant histidine-tagged proteins expressed as inclusion bodies. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] A New Method for Simultaneous Estimation of Micellization Parameters from Conductometric DataCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004Nenad Jal, enjak Dr. Abstract A simple method for determination of the counterion binding parameter (,) and aggregation number (N) from conductivity data is proposed. The method is based on fitting the values of the first derivative of conductivity (,) versus total surfactant concentration (ct) function according to the equation derived from the mass action model (MAM) by using different conductivity models. Sodium dodecylsulphate (SDS) and dodecyltrimethylammonium bromide (DTAB) were chosen for validation of the proposed method. It was shown that the method gives a fairly accurate values for micellisation parameters of SDS (N=51,64, ,=0.74,0.75) and DTAB (N=56,62, ,=0.77,0.79), both in good agreement with the literature data. In addition, application of the proposed method does not require the value of the critical micelle concentration (cmc). [source] Bending Energetics of Tablet-Shaped Micelles: A Novel Approach to Rationalize Micellar SystemsCHEMPHYSCHEM, Issue 3 2007L. Magnus Bergström Prof. Abstract A novel approach to rationalize micellar systems is expounded in which the structural behavior of tablet-shaped micelles is theoretically investigated as a function of the three bending elasticity constants: spontaneous curvature (H0), bending rigidity (kc), and saddle-splay constant (k,c). As a result, experimentally accessible micellar properties, such as aggregation number, length-to-width ratio, and polydispersity, may be related to the different bending elasticity constants. It is demonstrated that discrete micelles or connected cylinders form when H0>1/4,, where , is the thickness of a surfactant monolayer, whereas various bilayer structures are expected to predominate when H0<1/4,. Our theory predicts, in agreement with experiments, a transition from discrete globular (tablet-shaped) micelles to a phase of ordered, or disordered, connected cylinders above a critical surfactant concentration. Moreover, a novel explanation for the mechanism of growth, from small globular to long rodlike or wormlike micelles, follows as a consequence from the theory. In accordance, polydisperse elongated micelles (large length-to-width ratio) form as the bending rigidity is lowered, approaching the critical point at kc=0, whereas monodisperse globular micelles (small length-to-width ratio) are expected to be present at large kc values. The spontaneous curvature mainly determines the width of tablet-shaped or ribbonlike micelles, or the radius of disklike micelles, whereas the saddle-splay constant primarily influences the size but not the shape of the micelles. [source] Study on the Radius of an Electrical Spherical Micelle: Functional Theoretical ApproachCHINESE JOURNAL OF CHEMISTRY, Issue 4 2004Zheng-Wu Wang Abstract For the purpose of eliminating restriction, the Poisson-Boltzmann (PB) equation, which represents the potential of the electrical double layer of spherical micelles, can be solved analytically only under the lower potential condition, a kind of iterative method in functional analysis theory has been used. The radius of the spherical particle can be obtained from the diagram of the second iterative solution of the potential versus the distance from the center of the particle. The influences of the concentration of the ions, the charge number of ions, the aggregation number of the particle, the dielectric constant of solvent and the temperature of system on the radius also have been studied. [source] On the determination of molecular weight distributions of asphaltenes and their aggregates in laser desorption ionization experimentsJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2006Ana R. Hortal Abstract Molecular weight distributions (MWD) of asphaltenes and their aggregates have been investigated in laser desorption ionization (LDI) mass spectrometric experiments. A systematic investigation of the dependence of the measured MWD on the asphaltene sample density and on the laser pulse energy allows the assignment of most probable molecular weights within 300,500 amu and average molecular weights of 800,1000 amu for the monomeric asphaltenes, as well as for the estimation of the contribution from asphaltene clusters in typical LDI measurements. The results serve to reconcile the existing controversy between earlier mass spectrometric characterizations of asphaltenes based on laser desorption techniques by different groups. Furthermore, the MWD measurements performed on particularly dense samples yield an additional differentiated broad band peaking around 9000,10 000 amu and extending over 20 000 amu, not observed previously in LDI experiments, thereby revealing a strong propensity of the asphaltenes to form clusters with specific aggregation numbers, which is in qualitative agreement with previous theoretical predictions and with the interpretation of measurements performed with other techniques. Copyright © 2006 John Wiley & Sons, Ltd. [source] Pulsed field gradient NMR investigation of solubilization equilibria in amino acid and dipeptide terminated micellar and polymeric surfactant solutionsMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2002Robin S. Hickok Abstract Pulsed field gradient NMR spectroscopy was used to investigate the association of toluene, chlorobenzene and benzyl alcohol with amino acid and dipeptide terminated polymerized surfactants (PS). The diffusion coefficient for each probe was measured in the presence and absence of the polymers and the mole fraction of bound probe molecules, fb, was calculated. For all solutions investigated, the probes associated more strongly with unpolymerized surfactant micelles than with corresponding PS. For example, the toluene fb values for association with sodium undecanoyl valinate micelles and the PS poly(sodium undecanoyl valinate) were 0.88 and 0.15, respectively. The relatively weak probe,polymer association was attributed to the polarity and fluidity of the polymers' hydrocarbon cores and to the fact that these PS have smaller aggregation numbers than the corresponding unpolymerized surfactant micelles. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||||||||