Molecular structure and dynamics of poly(methacrylic acid) and poly(acrylic acid) complexes with dodecyl-substituted poly(ethylene glycol)

The molecular dynamics and the structure of molecular complexes formed by micelles of dodecyl-substituted poly(ethylene glycol) with poly(methacrylic acid) and poly(acrylic acid) in aqueous solutions were studied by viscosimetry, pH measurement, and electron spin resonance spin-probe techniques. At low surfactant concentrations, the conformation of the complex is a compact globule. The local mobility of surfactant molecules in such a complex is much slower than that in the free micelle. At high surfactant concentration, the nonionic micelles and polyacids form hydrophilic associates. The associates have the conformation of extended coils. In an associate, a major part of the micellar poly(ethylene glycol) groups is free. The local mobility of the micellar phase depends on the number of micelles involved in an associate. The mobility of surfactant molecules is slower in the complexes of poly(methacrylic acid) than in the complexes of poly(acrylic acid).     

Macromolecular surfactant as a pseudo-stationary phase in micellar electrokinetic capillary chromatography

We examined polymers of sodium 11-acrylamidoundecanoate [poly(Na 11-AAU)] with a very high molecular mass (>10(6)) for their potential use as a pseudo-stationary phase in micellar electrokinetic capillary chromatography (MEKC). Size-exclusion chromatography and capillary electrophoresis studies reveal that the polymers are highly charged, and have a densely packed chain structure. For aromatic compounds, the polymeric surfactant showed significantly different selectivity than sodium dodecyl sulfate (SDS). It was suggested that one molecule of poly(Na 11-AAU) forms one micelle. The structural stability of this pseudo-stationary phase permitted its use with relatively high percentages of organic modifiers in the buffer medium, allowing the separation of highly hydrophobic compounds which are difficult to analyze by conventional MEKC with SDS.     

Polymeric sulfated surfactants with varied hydrocarbon tail: II. Chemical selectivity in micellar electrokinetic chromatography using linear solvation energy relationships study

The effect of hydrocarbon chain length on chemical selectivity in micellar electrokinetic chromatography (MEKC) was investigated using polymeric sulfated surfactants: poly-(sodium 7-octenyl sulfate), poly(sodium 8-nonenyl sulfate), poly(sodium 9-decenyl sulfate), and poly(sodium 10-undecenyl sulfate). Linear solvation energy relationships (LSERs) and free energy of transfer studies were conducted to predict the selectivity differences between the four polymeric surfactants. The overall nature of the solute/ polymeric micelle interactions was found to be different despite the fact that all polymeric surfactants have the same head group. The polar character and acidic strength of the polymeric surfactant are found to decrease as the hydrocarbon chain length of the surfactant is increased. On the other hand, the polarizability of the polymeric sulfated surfactants increases (upon interacting with solute lone-pair electrons) with increasing hydrocarbon chain length. The LSER results show that the solute size and hydrogen bond accepting ability play the key roles in MEKC retention.     

Chelating DTPA amphiphiles: ion-tunable self-assembly structures and gadolinium complexes

A series of chelating amphiphiles and their gadolinium (Gd(iii)) metal complexes have been synthesized and studied with respect to their neat and lyotropic liquid crystalline phase behavior. These amphiphiles have the ability to form ion-tunable self-assembly nanostructures and their associated Gd(III) complexes have potential as magnetic resonance imaging (MRI) contrast enhancement agents. The amphiphiles are composed of diethylenetriaminepentaacetic acid (DTPA) chelates conjugated to one or two oleyl chain(s) (DTPA-MO and DTPA-BO), or isoprenoid-type chain(s) of phytanyl (DTPA-MP and DTPA-BP). The thermal phase behavior of the neat amphiphiles was examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and cross polarizing optical microscopy (POM). Self-assembly of neat amphiphiles and their associated Gd complexes, as well as their lyotropic phase behavior in water and sodium acetate solutions of different ionic strengths, were examined by POM and small and wide angle X-ray scattering (SWAXS). All neat amphiphiles exhibited lamellar structures. The non-complexed amphiphiles showed a variety of lyotropic phases depending on the number and nature of the hydrophobic chain in addition to the ionic state of the hydration. Upon hydration with increased Na-acetate concentration and the subtle changes in the effective headgroup size, the interfacial curvature of the amphiphile increased, altering the lyotropic liquid crystalline structures towards higher order mesophases such as the gyroid (Ia3d) bicontinuous cubic phase. The chelation of Gd with the DTPA amphiphiles resulted in lamellar crystalline structures for all the neat amphiphiles. Upon hydration with water, the Gd-complexed mono-conjugates formed micellar or vesicular self-assemblies, whilst the bis-conjugates transformed only partially into lyotropic liquid crystalline mesophases.     

Polymerisation of liquid crystalline phases in binary surfactant/water systems

The polymerisation of a polymerisable fatty acid surfactant (sodium 10-undecenoate) has been studied in both its self-assembled and non self-assembled forms. Polymerisation in non self-assembled solution was achieved to near completion. The polymerisation produces a surface active polymer. The self-assembling behaviour of this pre-polymerised form differs markedly from that observed for the monomeric surfactant [1]. A lamellar phase only is formed in the polymeric phase diagram with no hexagonal or lamellar gel phases being observed. Polymerisation in the different self-assembled forms of sodium 10-undecenoate reached a limit of approximately 30% only, i.e., the surfactant aggregates act to inhibit the polymerisation. The nature of the hydrocarbon chain was found to play a critical role in determining the effect that polymerisation had on the underlying geometry of the surfactant molecules. When the chains are in a fluid-like state (as for the micellar and hexagonal phases) the original monomeric matrix remains largely unchanged. Whereas partial polymerisation of the lamellar gel phase results in a phase transformation.In addition the hydrolysis of the fatty acid soap at low concentrations (close to the critical micelle concentration) has been investigated. Hydrolysis was shown to produce both the parent fatty acid and an acid soap dimer. The presence of these species greatly affects the solution behaviour in this region of the phase diagram shifting the critical micelle concentration to very high concentrations of sodium 10-undecenoate (ca. 0.4 M).     

Complexes of polyelectrolyte-neutral double hydrophilic block copolymers with oppositely charged surfactant and polyelectrolyte

Complexes between sodium (sulfamate-carboxylate)isoprene/ethylene oxide double hydrophilic diblock copolymers (SCIEO) and dodecyltrimethylammonium bromide (DTMAB), as well as quaternized poly(2-vinylpyridine) (QP2VP), were studied in aqueous solutions, at pH 7. The complexes are formed due to electrostatic interactions between the anionic groups of the polyelectrolyte block of the copolymers and the cationic groups of the surfactant or the homopolyelectrolyte. The structure of the complexes was investigated as a function of the mixing ratio of the two components in solution and ionic strength by static, dynamic, and electrophoretic light scattering, atomic force microscopy, and fluorescence spectroscopy. The mass and size of the complexes depend on the mixing ratio between the components. A transition from intrachain to an interchain association was observed for block copolymer/ surfactant complexes. SCIEO/QP2VP complexes were found to respond to increasing concentrations of added salt. Spherical and ellipsoid shaped complexes with a core-shell micellar like structure were formed in the systems studied.     

Molecular weight effect on the complexation of poly(methacrylic acid) and poly(ethylene oxide) as studied by high-resolution solid-state C NMR spectroscopy

Complexes of poly(methacrylic acid) (PMAA) and poly(ethylene oxide) (PEO) with different PEO molecular weight were studied by solid-state high-resolution ¹³C NMR spectroscopy, with the emphasis on the PEO molecular weight effect on inter-polymer interaction, morphology and molecular motion. It is found that the crystalline phase of PEO is completely destroyed in the complex. The results of ¹H transverse relaxation times and ¹³C spin-lattice relaxation times indicate that the chain mobility of both PEO and PMAA are greatly restricted by inter-molecular hydrogen-bonding interactions, especially when the molecular weight of PEO is 1500. The bulk structures of the complexes are found to be closely dependent on the molecular weight of PEO. The fraction of “free” PEO segments without forming hydrogen-bonds with PMAA increases with increasing PEO molecular weight.     

Calorimetric investigation of the interaction between lithium perfluorononanoate and poly(ethylene glycol) oligomers in water

The interaction of lithium perfluorononanoate (LiPFN) with poly(ethylene glycol) (PEG) molecules of different molecular weights (300 < MW < 20000 Da) has been investigated in water at 298.15 and 308.15 K by isothermal titration calorimetry (ITC). Density, viscosity, and conductivity measurements were also performed at 298.15 K. The aggregation process of this surfactant on the PEG polymeric chain was found to be very similar to that exhibited by cesium perfluorooctanoate (CsPFO) and appears to be consistent with the necklace model. ITC titrations indicated that a fully formed LiPFN micellar cluster can be wrapped by a PEG chain having a molecular weight (MW) of approximately 3200 Da, longer than that required by the shorter perfluorooctanoate (MW approximately 2600 Da), and also suggested a stepwise mechanism for the aggregation of successive micelles. Viscosity data indicate that the formation of polymer-surfactant complexes between PEG and LiPFN involves a conformational change of the polymer. The aggregation of preformed micelles of LiPFN or CsPFO or SDS on the PEG polymeric chain always gives rise to further stabilization.     

Controlled stacking of charged block copolymer micelles

Using poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene (PAA-b-PMA-b-PS) triblock copolymers or a mixture of different molecular weight PAA-b-PS diblock copolymers, stacks of polymeric micellar assemblies, such as disks and Y-shaped cylinders, were formed through intermicellar interactions. Whereas micelles hierarchically stacked together, micellar interactions within the stack defined a uniform micelle geometry and size for up to micrometers in length. The kinetic pathway dependence and stability of the stacked assemblies were studied, and possible intermicellar interactions between micelles within the stacks are proposed.     

Role of polymer ligands in the oxygenation of metal chlorophyllins

In order to obtain information about the characteristics of polymer-(metal chlorophyllins), their redox and oxygenation reactions were studied. Complexes composed of metal chlorophyllins (MChn) and partially quaternized poly(4-vinylpyridine) (QPVP) exhibited an increased stability due to electrostatic interaction between polymer cation and carboxylate anions of side groups in the MChn. The reduction of these polymer complexes by S₂O₄^2- occurred easily with an decrease in their apparent reduction potentials. The resulting low-valence complexes had an ability to absorb molecular oxygen. The oxygenation of these polymer complexes was not completely reversible; however the rate of the irreversible reoxidation was less by a factor of 10¹⁰ for the polymeric complex than that for the monomeric MChn-pyridine complex. The stability of these oxygen complexes is discussed in relation to the hydrophobicity of QPVPs.     

Effects of the H-bond donor structure on the properties of supramolecular side chain liquid crystalline polymers based on poly(3-carboxypropylmethylsiloxane-co-dimethylsiloxane)s and stilbazoles

Supramolecular side chain liquid crystalline polymers (SCLCPs) based on poly(3-carboxypropylmethylsiloxane-co-dimethylsiloxane) (PSIX, X=100, 76, 60, 41 or 23, denoting the mole percentage of 3-carboxypropylmethylsiloxane unit in the polymer) and stilbazole derivatives have been obtained through intermolecular hydrogen bonding (H-bonding) interactions between the carboxylic acid and the pyridyl moieties. The formation of H-bonding and self-assembly results in the formation of new mesogenic units, in which H-bonds function as molecular connectors. FTIR shows the existence of H-bonding in the complexes. The polymeric complexes behave as single component liquid crystalline polymers and exhibit stable and enantiotropic mesophases. The liquid crystalline properties of the supramolecular SCLCPs were studied using differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction, and were found to exhibit smectic A phases with focal-conic textures. The thermal stability of the SCLCP increases on increasing the carboxylic acid content in the polysiloxane and the concentration of the stilbazole derivative in the complex. However, the thermal stability decreases on increasing the chain length of the stilbazole derivative. The crystal phase was not formed even on cooling to the glass transition temperature of the polymeric complex.     

Structure and dynamics of surfactin studied by NMR in micellar media

The NMR structure of the cyclic lipopeptide surfactin from Bacillus subtilis was determined in sodium dodecyl sulfate (SDS) micellar solution. The two negatively charged side chains of surfactin form a polar head opposite to most hydrophobic side chains, accounting for its amphiphilic nature and its strong surfactant properties. Disorder was observed around the fatty acid chain, and 15N relaxation studies were performed to investigate whether it originates from a dynamic phenomenon. A very large exchange contribution to transverse relaxation rate R(2) was effectively observed in this region, indicating slow conformational exchange. Temperature variation and Carr-Purcell-Meiboom-Gill (CPMG) delay variation relaxation studies provided an estimation of the apparent activation energy around 35-43 kJ x mol(-1) and an exchange rate of about 200 ms(-1) for this conformational exchange. 15N relaxation parameters were also recorded in dodecylphosphocholine (DPC) micelles and DMSO. Similar chemical exchange around the fatty acid was found in DPC but not in DMSO, which demonstrates that this phenomenon only occurs in micellar media. Consequently, it may either reflect the disorder observed in our structures determined in SDS or originate from an interaction of the lipopeptide with the detergent, which would be qualitatively similar with an anionic (SDS) or a zwitterionic (DPC) detergent. These structural and dynamics results on surfactin are the first NMR characterization of a lipopeptide incorporated in micelles. Moreover, they provide a model of surfactin determined in a more biomimetic environment than an organic solvent, which could be useful for understanding the molecular mechanism of its biological activity.     

EPR spin probe and spin label studies of some low molecular and polymer micelles

The rotational mobility of spin probes of different shape and size in low molecular and polymer micelles has been studied. Several probes having nitroxide fragment localized either in the vicinity of micelle interface or in the hydrocarbon core have been used. Upon increasing the number of carbon atoms in hydrocarbon chain of detergent from 7 to 13 (sodium alkyl sulfate micelles) or from 12 to 16 (alkyltrimethylammonium bromide micelles) the rotational mobility of spin probes is decreased by the factor 1.5–2.0. The spin probe rotational mobility in polymer micelles (the complexes of alkyltrimethylammonium bromides and polymethacrylic or polyacrylic acids) is less than mobility in free micelles of the same surfactants. The study of EPR-spectra of spin labeled polymethacrylic acid (PMA) indicated that formation of water soluble complexes of polymer and alkyltrimethylammonium bromides in alkaline solutions (pH 9) does not affect the polymer segmental mobility. On the other hand, the polymer complexes formation in slightly acidic water solution (pH 6) breaks down the compact PMA conformation, thus increasing the polymer segmental mobility. Possible structures of polymer micelles are discussed.     

The effect of the initial ratio of components in the formation of a ternary interpolymer complex on its composition and structure

The effect of the initial ratio of components in the formation of ternary interpolymer complexes with low-molecular-mass compounds of various chemical natures on the compositions and structures of polycomplexes has been studied. Complexes based on aniline, 4,4′-dipyridyl, lysine, poly(acrylic acid), and the sodium salt of polyphosphoric acid have been examined. It has been shown that an increase in the content of poly(acrylic acid) in the pristine reaction system results in a relative gain in its content in the reaction product.     

Metal(II) Complexes Based on Imidazo[4, 5‐f]‐1, 10‐phenanthroline and Bridging Dicarboxylato Ligands: Synthesis,Characterization and Photoluminescence

Eight metal(II) complexes based on imidazo[4, 5‐f]‐1, 10‐phenanthroline (HIMP) and bridging dicarboxylato ligands such as 4, 4′‐biphenyldicarboxylic acid (H₂BPDC), 1, 4‐benzenedicarboxylic acid (H₂BDC), thiophene‐2, 5‐dicarboxylic acid (H₂TDC), and 2, 6‐naphthalenedicarboxylic acid (H₂NDC) were hydrothermally synthesized and structurally characterized by single‐crystal X‐ray diffraction. Complexes 1 , 3 , 6 , and 7 are molecular dinuclear metal complexes. Complexes 2 , 4 , and 5 exhibit chain‐like structures. Compound 8 shows a novel 3D architecture, in which Zn^II dimers are connected by four NDC^2– anions. In the metal(II) complexes, HIMP exhibits a similar chelating coordination mode. Different π ··· π stacking interactions are observed in the complexes. The emission of HIMP is completely quenched in complexes 1 – 4 due to the strong π ··· π stacking interactions in the structures. Complexes 5 – 8 exhibit different photoluminescence properties. Firstly, we quantitatively investigated the effect of the strong HIMP–HIMP stacking interactions on the emission quenching of HIMP in the metal complexes. It was found that a higher extent of π ··· π stacking interactions in the complexes resulted in a higher extent of the emission quenching of HIMP. The introduction of aromatic conjugated carboxylate groups into metal(II)‐HIMP complexes changed the extent of the strong π ··· π stacking interactions in the structures and thus the photoluminescence properties of the complexes.     

聚合物复合物层层组装膜的高效负载及大分子和小分子药物的差别性释放

基于聚合物复合物和层层组装技术实现了大分子药物硫酸软骨素和小分子药物头孢曲松钠在聚合物膜中的高效负载以及差别性释放. 壳聚糖(CHI)和大分子药物硫酸软骨素(CSS)通过静电相互作用力复合, 制备了壳聚糖-硫酸软骨素复合物(CHI-CSS). 以CHI-CSS复合物和透明质酸(HA)为构筑基元, 通过层层组装构筑负载有硫酸软骨素的聚合物复合物膜. 利用后扩散的负载方法将小分子药物头孢曲松钠(CTX)负载到聚合物膜中, 从而实现大分子和小分子2种药物在聚合物膜中的负载. 聚合物膜中负载的CTX和CSS在生理条件下具有快慢不同的差别性释放动力学特性, CTX在6 h内快速释放, 而CSS长效缓释长达14 d. 快速释放的抗生素CTX能够有效抑制细菌感染, 而酶降解作用下缓慢释放的CSS可促进伤口愈合, 在包括头颈外科在内的外科术后感染防治领域有良好应用前景.     

An extended description of the effect of detergent monomers on migration in micellar electrokinetic chromatography

Three equilibria determine the interaction of a neutral analyte with the detergent in micellar electrokinetic chromatography and therefore its migration: (i) that of the free analyte in the aqueous phase with the micelle, (ii) its association with free detergent monomers in the aqueous phase, and (iii) the partition of the associate of analyte and monomer between the aqueous solution and the micelle. For the first equilibrium, non-stoichiometric partitioning between two phases is preferred in the present work over the assumption of complex formation between one molecule of the analyte with one micelle. The second equilibrium is described by the formation of a 1:1 associate of the analyte and monomer. In this paper, thirdly an additional equilibrium is introduced, namely, the distribution of the analyte-monomer associate between the aqueous and the micelle phase; it is expressed by the according partition coefficient. The three equilibrium constants are interrelated. Mobility data for a lipophilic fluorescent compound and a series of n-alkylphenones (differing in chain length) were measured as a function of the SDS concentration below and above the critical micellar concentration. Curve fitting enabled the derivation of the equilibrium constants. It was found that the association constants of the analytes with the detergent monomers are between 2 and 75 M(-1). Interestingly, the partition coefficient of the analyte-monomer associate between the aqueous and micellar phase is by a factor of 5-200 larger than that of the free analyte.     

Selective transport of amino acids into the gas phase: driving forces for amino acid solubilization in gas-phase reverse micelles

We report a study on encapsulation of various amino acids into gas-phase sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) reverse micelles, using electrospray ionization guided-ion-beam tandem mass spectrometry. Collision-induced dissociation of mass-selected reverse micellar ions with Xe was performed to probe structures of gas-phase micellar assemblies, identify solute-surfactant interactions, and determine preferential incorporation sites of amino acids. Integration into gas-phase reverse micelles depends upon amino acid hydrophobicity and charge state. For examples, glycine and protonated amino acids (such as protonated tryptophan) are encapsulated within the micellar core via electrostatic interactions; while neutral tryptophan is adsorbed in the surfactant layer. As verified using model polar hydrophobic compounds, the hydrophobic effect and solute-interface hydrogen-bonding do not provide sufficient driving force needed for interfacial solubilization of neutral tryptophan. Neutral tryptophan, with a zwitterionic structure, is intercalated at the micellar interface between surfactant molecules through complementary effects of electrostatic interactions between tryptophan backbone and AOT polar heads, and hydrophobic interactions between tryptophan side chain and AOT alkyl tails. Protonation of tryptophan could significantly improve its incorporation capacity into gas-phase reverse micelles, and displace its incorporation site from the micellar interfacial zone to the core; protonation of glycine, on the other hand, has little effect on its encapsulation capacity. Another interesting observation is that amino acids of different isoelectric points could be selectively encapsulated into, and transported by, reverse micelles from solution to the gas phase, based upon their competition for protonation and subsequent encapsulation within the micellar core.     

VARIATION OF STERN-VOLMER QUENCHING CONSTANTS IN MICELLAR SOLUTION AS A FUNCTION OF AQUEOUS OR MICELLAR QUENCHER

Abstract— The critical micelle concentration (CMC) of a fluorescent detergent may be measured by determining Stern-Volmer quenching parameters as a function of detergent concentration. The CMC's of a cationic detergent, 11-(3-hexyl-l-indolyI)undecyltrimethylamrnoniurn bromide (6-In-ll+), and an anionic detergent, sodium H-(3-hexyI-l-indoiyI) undecyl sulfate (6-In-ll⁻) were determined by this quenching procedure. Quenchers which were predominantly located in the aqueous phase (e.g. Co²+) or in the micellar phase (e.g. benzophenone) were employed. Aqueous phase quenchers are more effective below the CMC and cause a decrease in the long wavelength portion of the fluorescence band of the indole moiety. Quenchers located in the micellar phase are more effective above the CMC and decrease the short wavelength portion of the fluorescence band of the system.     

The mechanism of 2-methylbutene-2 hydrohalogenation in solid phase

Complexes and reactions of 2-methylbutene-2 with hydrohalogen (HCl, HBr) have been studied in solid phase at 80–150 K. It has been found that 2-methylbutene-2 forms with HX complexes of 1:1 and 1:2 composition. Hydrohalogenation proceeds via the rearrangement of complex 2HX·C₅H₁₀ into complex of the addition product with HX. Kinetic equation depends on the reagents ratio. In excess of HX (1< HX:C₅H₁₀< 10) reaction can be described by the first order kinetic equation. If the ratio HX:C₅H₁₀ is more than 10, reaction is described by polychronous kinetic law. The effective activation energy of solid phase hydrohalogenation does not exceed 20 kJ/mole. The molecular mechanism of hydrohalogenation in solid phase has been proposed.