Particulate and bulk bicontinuous cubic phases obtained from mixtures of glyceryl monooleate and copolymers bearing blocks of lipid-mimetic anchors in water

Copolymers based on poly(ethylene glycol) bearing one or more lipid-mimetic anchors were mixed with glycerylmonooleate (GMO)-a lipid with nonlamellar propensity-to form bulk and particulate bicontinuous cubic phases in water. The particulate phase was obtained via a liquid precursor method. Three forms of copolymer/GMO mixtures were investigated-precursor dispersions in glycerol and bulk and particulate phases in water-by visual observations, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM). The bulk phases were found to very slowly develop a macroscopic appearance that can be associated with the bicontinuous cubic phase. They were prepared in a slight excess of water, which became opalescent in some of the preparations. Cryo-TEM investigation of the excess showed that vesicles and particles with a dense interior coexisted. The precursors were prepared as solutions in glycerol. The viscous liquid material was investigated by DLS. Diffusion coefficients and the corresponding hydrodynamic radii, ranging from about 10 to 30 nm, were calculated. The particles are presumably of a structure similar to that of conventional emulsion droplets with GMO in the interior and copolymer molecules in the outer regions. The particulate phase in water was obtained upon hydration of the liquid precursors. The dispersions were investigated by DLS and cryo-TEM. DLS revealed the formation of nanosized particles. The size was found to increase with increasing copolymer content for copolymers with only one lipid-mimetic anchor, whereas the opposite trend was observed for the formulations with copolymers bearing more than one lipid-mimetic anchor. The shape and interior of the particles were studied by cryo-TEM. It was found that most particles were globular. For some of the compositions, particles with a dense internal structure dominated. The texture of the internal structures was assigned to dispersed bicontinuous cubic or L3 phases. In other compositions, the interior seemingly consists of arrays of interlamellar attachments.     

Theoretical study of the o-OH participation in catechol ester ammonolysis

The possible catalytic effect of the vicinal hydroxyl group during the ammonolysis of acetylcatechol has been studied by first principle calculations. A very efficient intramolecular catalysis was found to occur when the catechol ester o-OH group is deprotonated: the activation energy of the ammonolysis decreases by 24 kcal mol(-1) as compared to that of acetylphenol ammonolysis. Using this value, the o-oxyanion-catalysed intramolecular ammonolysis was estimated to be orders of magnitude faster than the ammonolysis of acetylphenol or nonionised acetylcatechol. The analogy with the aminolysis of peptidyl-tRNA that occurs during protein biosynthesis implies several orders of magnitude acceleration due to complete or partial deprotonation of its 3'-terminal adenosine 2'-OH providing a mechanistic possibility for general acid-base catalysis by the ribosome.     

Rapid adiabatic passage without level crossing

We present a method for achieving complete population transfer in a two-state quantum system via adiabatic time evolution in which, contrary to conventional rapid adiabatic passage produced by chirped pulses, there occurs no crossing of diabatic energy curves: there is no sign change of the detuning. Instead, we use structured pulses, in which, in addition to satisfying conditions for adiabatic evolution, there occurs a sign change of the Rabi frequency when the detuning is zero. We present simulations that offer simple geometrical interpretation of the two-dimensional motion of the Bloch vector for this system, illustrating how both complete population inversion and complete population return occur for different choices of structured pulses.     

The syn-oriented 2-OH provides a favorable proton transfer geometry in 1,2-diol monoester aminolysis: implications for the ribosome mechanism

A computational study of 1-formyl 1,2-ethanediol aminolysis predicts a stepwise mechanism involving syn-2-OH-assisted proton transfer. The syn-oriented 2-OH takes over the catalytic role of the external water or amine molecule previously observed in 2-deoxy ester aminolysis. It provides more favorable, that is, more linear, proton transfer geometry for the rate-limiting transition state resulting in an almost billion-fold rate acceleration of the overall reaction. These findings provide structural basis for explanation of the efficiency of the proton shuttling mechanism and imply double proton transfer catalysis by peptidyl tRNA A76 2'-OH as a possible catalytic strategy used by ribosome.     

Light scattering and cryogenic transmission electron microscopy of vesicles and other structures formed in water by mixtures of copolymers bearing lipid-mimetic units

The phase behavior of mixtures of a vesicle-forming copolymer and related to it copolymers of different phase propensities was studied by light scattering and cryogenic transmission electron microscopy. The vesicle-forming copolymer and the copolymeric additives are based on poly(ethylene glycol) (PEG) and comprise from 1 to 8 lipophilic lipid-mimetic anchors which form hydrophobic moieties. The ability of the additives to control the vesicle size and particle morphology was examined as a function of their content, composition, and phase propensity. At the lower guest to host molar ratios, the bilayer organization is preserved and changes in the vesicle dimensions are not observed. At a certain ratio which is dependent on the composition and phase propensity of the guest copolymer the particle dimensions start to change, and typically, transitions from low- to high-curvature structures are observed. The critical value of the mean PEG interfacial area at which the particles undergo size, size distribution, and phase transitions slightly depends on the composition of the guest copolymer and is found to be roughly 3 nm2.     

Triblock and Radial Star-Block Copolymers Comprised of Poly(ethoxyethyl glycidyl ether), Polyglycidol,Poly(propylene oxide) and Polystyrene Obtained by Anionic Polymerization Initiated by Cs Initiators

The anionic polymerization of ethoxyethyl glycidyl ether (EEGE) initiated by cesium alkoxide was studied. The ring-opening polymerization of EEGE in the presence of cesium alkoxide of 1-methoxy-2-ethanol does not involve any side reactions. The presence of an additional alcohol leads to a significant increase of the initiator efficiency. Aqueous solutions of poly (ethoxyethyl glycidyl ether) (PEEGE) exhibit lower critical solution temperature (LCST), and the polymer solubility in water is extremely sensitive to its MW. Two novel types of block copolymers based on PEEGE were synthesized: triblock-copolymers of ABA (A′:BA′) structure, where A is the PEEGE block, A′ polyglycidol (PG) and B the polypropylene oxide (PPO) block, and A₂S (A′₂S) and A₄S (A′₄S) heteroarm stars, where S is the polystyrene block. The synthesis of the ABA block was performed by polymerization of EEGE initiated by bi-functional PPO/Cesium alkoxide macroinitiator. The PEEGE blocks were converted into PG blocks by successful cleavage of the ethoxyethyl group. Polystyrene/PEEGE and polystyrene/PG three- and five- heteroarm star copolymers were synthesized by a coupling reaction between well-defined chain-end-functionalized polystyrenes carying dendritic benzyl bromide moieties with living anionic polymers of PEEGE with one cesium alkoxide terminal group. The coupling reaction proceeds quantitatively without any side reactions, and thus series of star-branched polymers can be systematically synthesized. Polystyrenes with two or four PG arms have been obtained after the cleavage of the protecting group. The compact structure of these multi-arm star polymers and their amphiphilic character leads to the formation of nanoparticles in aqueous solution with rather uniform size distribution and a mean diameter of 15 nm.     

Influence of the precursor nature and deposition mode on the oxygen sensing properties of Ru(II) complex immobilized in a SiO2-based matrix

Films are deposited by dip- or spin-coating in gels produced from tetraethoxysilane (TEOS), octyltriethoxysilane (OtEOS) or mixtures of TEOS and OtEOS (mole ratio1:1) as well as TEOS and methyltriethoxysilane (MtEOS) (mole ratio 1:3). The Stern–Volmer constants and the response to oxygen of Ru(II)-tris(4,7-diphenyl-1,10-phenathroline) dichloride immobilized in the produced matrices are calculated. The oxygen sensitivity of the film depends on the chemical nature of the precursors, the Ru(II) concentration, the film deposition technology, and the film thickness. The uncertainty of the results obtained with films of different production batches varies between 1.5% and 3% of the measured value for oxygen content for gas mixtures between 10% and 90% oxygen content. The sonication of the sol has a strong positive effect on the sensitivity of the films and the linearity of the calibration curves.     

(Co)polymers of oligo(ethylene glycol) methacrylates—temperature‐induced aggregation in aqueous solution

The synthesis and aggregation behavior of well‐defined thermosensitive (co)polymers of oligo(ethylene glycol) methacrylates (POEGMA) in aqueous solutions were investigated. The cloud points of the POEGMAs solutions were determined by turbidimetry and dynamic light scattering. For POEGMA (co)polymers the cloud point temperature (T_CP) increased linearly with increasing content of more hydrophilic comonomer. The mesoglobules formed by POEGMAs in dilute aqueous solutions above T_CP were studied by light scattering. The size of mesoglobules depended on the concentration and the heating procedures. The aggregates became smaller with decreasing initial concentration of polymer and increasing rates of temperature change. By selecting the proper heating and dilution procedures, the influence of the (co)polymer structure on the size of the mesoglobules could be determined. The size of the mesoglobules decreased with the length of the OEG side chains and increased with increasing content of more hydrophilic comonomer. The light scattering parameters of the mesoglobules—A₂ values and shape factors ${R_{\rm g}\over R_{\rm h}}$ —suggested that the hydrophilic OEG side chains placed at the periphery of the mesoglobules in direct contact with the surrounding water controlled the size of mesoglobules and their stability. Shape factors for all POEGMA mesoglobules indicated that the mesoglobules remained highly hydrated after formation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Hydrodynamic behavior of high molar mass linear polyglycidol in dilute aqueous solution

Six high molar mass polyglycidol samples were obtained by fractionation of polyglycidol synthesized by means of cationic polymerization of ethoxyethyl glycidyl ether followed by cleavage of the protective groups. The fractions covering the molar mass range from 0.1 to 2.4 x 10(6) were studied by dynamic and static light scattering. The weight-average molar masses (Mw), second virial coefficients (A2), radii of gyration (Rg), diffusion coefficients (D0), hydrodynamic radii (Rh), and dynamic virial coefficients (kDphi) were determined for the single coil in dilute aqueous solution at 25 degrees C, and scaling equations were established. It was found that polyglycidol in water does not exhibit the expected asymptotic good solvent behavior. The scaling exponents for A2, D0, and Rh are even closer to those for polymer coils in marginal solvents than to the expected ones in the excluded-volume region. The values of the interpenetration parameter, psi, and kDphi are far from reaching limiting values even for the fractions of the highest molar masses. The scaling exponent for Rg as well as the Rg/Rh ratio, which was found to increase with increasing molar mass, imply elongated coil conformation in the high molar mass region.     

Nano-Templates from Thermoresponsive Poly(ethoxytriethyleneglycol acrylate) for Polymeric Nano-Capsules

Temperature responsive poly(ethoxytriethyleneglycol acrylate) (PETEGA) of Mn = 8000 and M_w/M_n = 2.30 was synthesized by ATRP. Dilute aqueous solutions of PETEGA exhibit lower critical solution temperature (LCST) at around 34 °C. We found that PETEGA can form nano-sized uniform colloidal aggregates (50-200 nm) above LCST either with or without an additional surfactant. Therefore PETEGA nano-aggregates were used as templates for the seeded free radical copolymerization of acrylamides or methacrylates together with a cross-linker to form acrylamide or methacrylate based core-shell particles. The formation of the PETEGA templates was investigated by dynamic light scattering (DLS) in order to find optimal conditions for obtaining narrow dispersed aggregates of desired sub-micron dimensions. Core-shell particles were characterized by DLS and scanning electron microscopy.