Properties of polyethylene glycol (23) lauryl ether with cetyltrimethylammonium bromide in mixed aqueous solutions studied by self-diffusion coefficient NMR

NMR self-diffusion coefficient measurements have been used to study the properties of polyethylene glycol (23) lauryl ether (Brij-35) with cetyltrimethylammonium bromide (CTAB) in the mixed aqueous solutions with different mole fractions of CTAB. By fitting the self-diffusion coefficients to the two-state exchange model, the critical micelle concentrations of the two solutes in the mixed solutions (cmc*1 and cmc*2) were obtained. The critical mixed micelle concentrations (cmc*) were then evaluated by the sum of cmc*1 and cmc*2, which are in good agreement with the results measured by the surface tension method. The cmc* values are lower than those of the ideal case of mixing, which indicates that the behavior of the CTAB/Brij-35 system is nonideal. Moderate interactions between CTAB and Brij-35 in their mixtures can be deduced from the interaction parameters (betaM) based on the cmc* obtained by the NMR self-diffusion method. The compositions (x1) of the mixed micelles at different total surfactant concentrations were also evaluated. By using these results, a possible mechanism of mixed micellar formation and a picture of the formation of nonsimultaneous CTAB/Brij-35 binary mixed micelle were proposed. In contrast to the case of CTAB/TX-100 system, Brij-35 molecules have a tendency to form micelles first at any mole fraction of CTAB. The mixed micellar self-diffusion coefficients (Dm) increase slightly at lower CTAB molar ratios, and then speed up with increasing CTAB mole fraction.     

Conformation and dynamics of polyoxyethylene lauryl ether (Brij-35) chains in aqueous micellar solution studied by 2D NOESY and 1H NMR relaxation

Spin-lattice relaxation time, spin-spin relaxation time and two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY) experiments of polyoxyethylene lauryl ether (Brij-35) micelles in aqueous solutions at a concentration of 100 times the critical micellar concentration (cmc) give direct evidence that the hydrophilic polyoxyethylene chains, staying in the exterior of the micellar core, are coiled, bent and aligned around the micellar core with a certain number of water molecules included. This hydrophilic layer is in contact with the solvent, water, keeping the micellar solution stable. 1H NMR relaxation time measurements show that the first oxyethylene group next to the alkyl chain participates in the formation of the surface area of the micellar core. The motion of the hydrophilic polyoxyethylene chains is less restricted as compared with the hy-drophobic alkyl chains.     

Conformation and dynamics of polyoxyethylene lauryl ether (Brij- 35) chains in aqueous micellar solution studied by 2D NOESY and <Superscript>1</Superscript>H NMR relaxation

Spin-lattice relaxation time, spin-spin relaxation time and two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY) experiments of polyoxyethylene lauryl ether (Brij-35) micelles in aqueous solutions at a concentration of 100 times the critical micellar concentration (cmc) give direct evidence that the hydrophilic polyoxyethylene chains, staying in the exterior of the micellar core, are coiled, bent and aligned around the micellar core with a certain number of water molecules included. This hydrophilic layer is in contact with the solvent, water, keeping the micellar solution stable. ¹H NMR relaxation time measurements show that the first oxyethylene group next to the alkyl chain participates in the formation of the surface area of the micellar core. The motion of the hydrophilic polyoxyethylene chains is less restricted as compared with the hydrophobic alkyl chains.     

Quantitative analysis of three phases of high-density polyethylene with 2D time-domain proton NMR

With two-dimensional time-domain NMR analysis in the proton spin rotating frame, three phases are identifiable in the solid polyethylene. The major proton magnetization fraction is due to the polymer's crystalline region, where the motion is least isotropic and slowest. A magnetization fraction with intermediate relaxation rate is also intermediate in magnitude. This component is proposed to comprise chain loops on the surfaces of crystallites and effectively entangled chain segments. The most mobile fraction, which is most liquid-like with a T₂ of near 1 ms at 120°C, is also the smallest. It is proposed that it is due to polymer chains in the amorphous phase. In the crystalline phase the chain motion is an unexpectedly effective relaxation mechanism at ∼50 KHz. This process, which involves propagation of a twisted region along the crystallite, as has been suggested before, is either not present in the other two phases of the HDPE or is less efficient because of the lower polymer density. The activation energies for the crystalline, intermediate and amorphous phases are estimated to be 34 ± 3, 13 ± 3, and 8 ± 2 Kcal/mol, respectively. The frequencies of the relaxation process at 120°C are 43 KHz, 350 KHz, and 1.5 MHz, respectively. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2551–2558, 1997     

Self‐diffusion and interactions in mixtures of imidazolium bis(mandelato)borate ionic liquids with polyethylene glycol: 1H NMR study

We used ¹H nuclear magnetic resonance pulsed‐field gradient to study the self‐diffusion of polyethylene glycol (PEG) and ions in a mixture of PEG and imidazolium bis(mandelato)borate ionic liquids (ILs) at IL concentrations from 0 to 10 wt% and temperatures from 295 to 370 K. PEG behaves as a solvent for these ILs, allowing observation of separate lines in ¹H NMR spectra assigned to the cation and anion as well as to PEG. The diffusion coefficients of PEG, as well as the imidazolium cation and bis(mandelato)borate (BMB) anion, differ under all experimental conditions tested. This demonstrates that the IL in the mixture is present in at least a partially dissociated state, while the lifetimes of the associated states of the ions and ions with PEG are less than ~30 ms. Generally, increasing the concentration of the IL leads to a decrease in the diffusion coefficients of PEG and both ions. The diffusion coefficient of the anion is less than that of the cation; the molecular mass dependence of diffusion of ions can be described by the Stokes–Einstein model. NMR chemical shift alteration analysis showed that the presence of PEG changes mainly the chemical shifts of protons belonging to imidazole ring of the cation, while chemical shifts of protons of anions and PEG remain unchanged. This demonstrated that the imidazolium cation interacts mainly with PEG, which most probably occurs through the oxygen of PEG and the imidazole ring. The BMB anion does not strongly interact with PEG, but it may be indirectly affected by PEG through interaction with the cation, which directly interacts with PEG. Copyright © 2015 John Wiley & Sons, Ltd.     

Aggregation behavior of acrylamide/2-phenoxyethyl acrylate and its interaction with sodium dodecyl sulfate in aqueous solution studied by proton 1D and 2D NMR

¹H NMR self-diffusion coefficient, spin-lattice relaxation time, spin-spin relaxation time, and two-dimensional nuclear Overhauser enhancement (2D NOESY) measurements have been used to study the association behavior of a novel hydrophobically associating copolymer composed of acrylamide (AM) and a small amount of 2-phenoxyethyl acrylate (POEA), and its interaction with the anionic surfactant sodium dodecyl sulfate (SDS). Three sets of copolymers with approximately the same composition but with different hydrophobic POEA contents were investigated. The POEA contents for these copolymers were about 1.41, 1.03, and 0.56 mol% respectively, as validated by ¹H NMR spectra. Self-diffusion coefficient measurements show that the aggregation process occurs in a relative narrow concentration range and the critical association concentrations (cacs), of these copolymers are within this narrow concentration range, which are in agreement with those measured by viscosity measurements (6 g L^–1). Above this concentration, the hydrophobic POEA moieties are found to associate and possibly build a transitory three-dimensional network along the polyacrylamide (PAM) backbones, which induces a strong decrease in NMR parameters including self-diffusion coefficients and relaxation times. The surfactant SDS showed a significant interaction with the copolymer in the dilute solution. Addition of SDS resulted in the binding of SDS on copolymer POEA-PAM segments and reinforced the interchain transient network formation of copolymer at a concentration below its cac. In the SDS/POEA-PAM mixed systems, the hydrophobic methylene groups of the SDS molecules were preferentially located in the vicinity of the phenoxy groups of the POEA hydrophobes.     

Preparation and evaluation of poly(polyethylene glycol methyl ether acrylate-co-polyethylene glycol diacrylate) monolith for protein analysis

A poly(polyethylene glycol methyl ether acrylate-co-polyethylene glycol diacrylate) monolith was prepared by UV-initiated polymerization. Methanol and ethyl ether were selected as porogens from a variety of organic solvents to achieve the desirable characteristics of the monolith. The preparation of the monolith could be achieved within 10 min. The monolith was macroscopically homogeneous, had low flow resistance, and did not swell or shrink significantly in tetrahydrofuran. Inverse size-exclusion data indicate that the monolith had a total porosity of 75.4% and an internal porosity of 9.1%. The monolith could be used for size-exclusion separation of peptides, although it could not separate proteins with molecular masses between 10 and 100 K due to its unique pore size distribution. It was found to resist adsorption of proteins in capillary liquid chromatography when using 100 mM phosphate buffer (pH 7.0) containing 0.5 M NaCl. Complete recovery of both acidic and basic proteins was achieved. The monolith can be used for applications in which inert materials are required for protein analysis.     

ESR and NMR studies of poly (amidoamine) dendrimers with ionic surfactants in different media

The electron paramagnetic resonance (EPR) study has been carried out for the micellar solutions of various ionic surfactant solutions as well as various generations of aqueous dendrimer both in their respective presence as well as their absence at 25°C and in different media. From these measurements, the rotation correlation time (τ_B) have been calculated for all the ionic surfactant + PAMAM + water system. A variation in the τ_Bvalue remains mostly constant for the dodecyltrimethyammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) + PAMAM + water ternary mixtures. The τ_Bvalue shows an increase with the increase in the amount of PAMAM for SDS in basic medium and for 12-2-12 in acidic medium. It has been concluded from these results that SDS undergo complexation with all generations of PAMAM in basic medium and 12-2-12 in acidic medium and produce stronger hydrophobic environment. The nuclear magnetic resonance study (NMR) allowed us to evaluate the spin–spin relaxation (T₁) times of SDS in the presence of all generations of PAMAM. The T₁ values for all the tail protons of SDS showed a slight decrease with the increase in the constant amount of PAMAM suggesting the adsorption of PAMAM molecules on the micelle surface.     

Solubilization of n-alkylbenzenes into octaethylene glycol mono-n-tetradecyl ether (C14E8) micelles

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, and n-pentylbenzene into the micelles of octaethylene glycol monotetradecyl ether (C(14)E(8)) was studied, where equilibrium concentrations of all the solubilizates were determined spectrophotometrically at 298.2, 303.2, and 308.2 K. The concentration of the above solubilizates except benzene remained constant below the critical micelle concentration (cmc) and increased linearly with an increase in C(14)E(8) concentration above the cmc, whereas benzene concentration was found to remain constant over the whole concentration range of C(14)E(8). The Gibbs energy change (DeltaG(0)) for their solubilization was evaluated by the partitioning of the solubilizates between the aqueous phase and the micellar phase because of the large aggregation number of the C(14)E(8) micelle. Furthermore, enthalpy and entropy changes for their solubilization were evaluated from the temperature dependence of the DeltaG(0) values. From these thermodynamical parameters and the change in absorption spectra of the solubilizates due to their incorporation into the micelles, the solubilization site was found to move into the inner core of the micelle with increasing alkyl chain length of the solubilizates.     

13C and proton NMR spectra of 2(1H)pyrazinones

¹³C and proton NMR spectra data are given for eleven 2(1H)pyraziones. Assignments of chemical shifts were made by methods which included: deuterium exchange with certain protons of 3-alkyl substituents; change of chemical shifts of certain carbon atoms with change in pH; the use of long-range coupling constants for ¹³C to protons; and various correlations among assigned spectra.     

Effect of polyethylene glycol (PEG-400) on the 1-butyl-3-methylimidazolium tetrafluoroborate-in-cyclohexane ionic liquid microemulsion

The effect of a common polymer, polyethylene glycol with molecular weight of 400 (PEG-400) on the microstructure of 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF₄)/Triton X-100/cyclohexane ionic liquid (IL) reverse microemulsion has been investigated. The addition of PEG-400 leaded to the linear increase of the microemulsion droplet size, in accordance with the observation of dispersed phase, showing that PEG-400 was only solubilized into the polar interior of the IL microemulsions. FTIR spectroscopic analysis indicated that the addition of PEG-400 decreased the electrostatic interaction between the oxygen atoms of OE units and the positive electrical charged imidazolium cation of bmimBF₄. At the same time, the oxygen atoms of PEG-400 can also interact with the imidazolium cation. These results suggested that small amounts of PEG-400 entered the palisade layers of the IL microemulsion. The conductivity of the IL reverse microemulsions was decreased owing to the dilution of conducting polar cores by the addition of insulative PEG-400, indicating that PEG-400 was only solubilized into the reverse IL microemulsion interior. The conclusion was further supported by viscosity measurement.     

Separation of cationic analytes by nonionic micellar electrokinetic chromatography using polyoxyethylene lauryl ether surfactants with different polyoxyethylene length

Although nonionic micellar electrokinetic chromatography is used for the separation of charged compounds that are not easily separated by capillary zone electrophoresis, the effect of the hydrophilic moiety of the nonionic surfactant has not been studied well. In this study, the separation of ultraviolet‐absorbing amino acids was studied in electrokinetic chromatography using neutral polyoxyethylene lauryl ether surfactants (Adekatol) in the separation solution. The effect of the polyethylene moiety (the number of repeating units was from 6.5 to 50) of the hydrophobic test amino acids (methionine, tryptophan, and tysorine) was studied using a 10 cm effective length capillary. The separation mechanism was based on hydrophobic as well as hydrogen bonding interactions at the micellar surface, which was made of the polyoxyethylene moiety. The length of the polyoxyethylene moiety of the surfactants was not important in nonionic micellar electrokinetic chromatography mode.     

Influence of 1-alkyl-3-methylimidazolium tetrafluoroborate on the lamellar liquid crystal formed by tetraethylene glycol lauryl ether and water

Lyotropic liquid crystals (LLCs) formed in tetraethylene glycol lauryl ether–water system by the addition of 1-alkyl-3-methylimidazolium tetrafluoroborate ([C _n Mim][BF₄], n?=?2, 4, 6, 8, 10) are characterised by polarised optical microscopy and small-angle X-ray scattering techniques. A small number of [C _n Mim][BF₄] molecules can be solubilised in the liquid crystal without changing the lamellar type. These imidazolium salts are considered as an ideal kind of modifiers for the ordered structure. With different lengths of alkyl chains, [C _n Mim][BF₄] molecules appear in various domains of ordered assemblies: in the water layer for [C₂Mim][BF₄], in the water layer as well as in the polar domain for [C₄Mim][BF₄] and in the apolar domain for the other imidazolium salts with long alkyl chains. Diverse distributions of [C _n Mim][BF₄] molecules in the inner structure bring about their specific influence on the lamellar phase. These results enlighten the use of diverse alkyl-substituted imidazolium salts in modulating LLC and other assemblies and also enrich the aggregation behaviour of these assemblies.     

Model of drug-loaded fluorocarbon-based micelles studied by electron-spin induced (19)f relaxation NMR and molecular dynamics simulation

Rf-IPDU-PEGs belong to a class of fluoroalkyl-ended poly(ethylene glycol) polymers (Rf-PEGs), where the IPDU (isophorone diurethane) functions as a linker to connect each end of the PEG chain to a fluoroalkyl group. The Rf-IPDU-PEGs form hydrogels in water with favorable sol-gel coexistence properties. Thus, they are promising for use as drug delivery agents. In this study, we introduce an electron-spin induced 19F relaxation NMR technique to probe the location and drug-loading capacity for an electron-spin labeled hydrophobic drug, CT (chlorambucil-tempol adduct), enclosed in the Rf-IPDU-PEG micelle. With the assistance of molecular dynamics simulations, a clear idea regarding the structures of the Rf-IPDU-PEG micelle and its CT-loaded micelle was revealed. The significance of this research lies in the finding that the hydrophobic drug molecules were loaded within the intermediate IPDU shells of the Rf-IPDU-PEG micelles. The molecular structures of IPDU and that of CT are favorably comparable. Consequently, it appears that this study opens a window to modify the linker between the Rf group and the PEG chain for achieving customized structure-based drug-loading capabilities for these hydrogels, while the advantage of the strong affinity among the Rf groups to hold individual micelles together and to interconnect the micellar network is still retained in hopes of maintaining the sol-gel coexistence of the Rf-PEGs.     

Structure of pravastatin and its complex with sodium dodecyl sulfate micelles studied by NMR spectroscopy

The aim of this work was to study the mechanisms of interaction between pravastatin and cell membranes using model membranes (sodium dodecyl sulfate micelles) by nuclear magnetic resonance spectroscopy methods. On the basis of the nuclear magnetic resonance experiments, it was established that pravastatin can form intermolecular complexes with sodium dodecyl sulfate micelles by the interaction of its hydrophilic groups with the polar surface of the micelle. Conformational features of pravastatin molecule were also studied. Copyright © 2014 John Wiley & Sons, Ltd.     

丙交脂与聚四亚甲基醚二醇共聚的研究

合成了具有含不同量聚四亚甲基醚二醇(PTMG)的PTMG-PLA嵌段共聚物,并以IR,GPC,′H-NMR,和DSC进行了表征。通过应力-应变曲线研究了共聚物的力学性能。结果表明,共聚物的GPC曲线上只出现单一的流出体积峰,分子量分布多分散系数(?)_n/(?)_n小于2.0;另外,共聚物的T_g随其中的PTMG含量增加而降低,断裂伸长率随共聚物中PTMG含量的增加而增大,而应力,模量等力学性能则随共聚物中PTMG含量增加而降低。共聚物的体外降解速度较PLA均聚物的降解速度平缓。     

Hydrocarbon chain packing in the micellar core of surfactants studied by 1H NMR relaxation

 ¹H NMR spin–lattice and spin–spin relaxation of different types (cationic cetyltrimethyl ammonium bromide, anionic sodium dodecyl sulfonate and nonionic Triton X-100) of surfactants in water solution were studied. Simulation of the decay curves of proton relaxation shows that the spin lattice relaxation of all the samples exhibits exponentially, while the spin–spin relaxation for several protons on the hydrophobic chains forming the micellar core is bi-exponential. The fast relaxing component is attributed to the part of the segments of the hydrophobic chain, situated near or on the surface of the micellar core, while the slower relaxing component is attributed to the rest part staying in the interior. The latter exchanges with the former in equilibrium. Thus, a part of each certain segment of the hydrophobic chain has an opportunity to stay in the surface layer of the micellar core and spend some time on the interface experiencing hydrophilic environment. Generally, the protons on the methylene carbon of the hydrophobic chain nearest to the polar head have more chance to spend time in the hydrophilic environment. However, it seems to be dependent on the chemical structure of the surfactant molecule. Large size of the polar group of CTAB shows steric hindrance on the packing of the hydrophobic chain. Quantitative results are given. The fact, that the fraction of slow relaxing protons on the hydrophilic ethylene oxide long chain of Triton X-100 dominates over that of fast relaxing protons, and that their T ₂ values are larger than those of the protons on the hydrocarbon chain in the interior of the micellar core, suggests that the ethylene oxide chain does not participate in the formation of the micellar core. Received: 10 March 1998 Accepted: 19 June 1998     

Intermicellar material exchange in reverse micelles formed by ionic AOT and nonionic Igepal surfactants studied by means of pulse radiolysis. Influence of the temperature

The recombination of thiocyanate anion radicals, (SCN) ₂ ⁻ , formed pulse radiolytically within the water pools of reverse micelles stabilized with anionic AOT and nonionic Igepal surfactants, was proved as an indicator reaction to study intermicellar exchange. It was found that the exchange process is slower inIgepal than in AOT reverse micelles with the same water to surfactant ratio. The apparent activation enthalpy and entropy of the exchange process were determined in different alkanes. For the AOT and Igepal reverse micelles the activation parameters increase with the droplet size, but for the AOT systems they do not significantly change with the increase of droplet concentration. For non-percolated systems the activation parameters for Igepal reverse micelles approach those for AOT reverse micelles. This result supports existing suggestions that the mechanism of intermicellar exchange does not differ in principle between reverse micelles stabilized with ionic and nonionic surfactants.     

NMR structure of two novel polyethylene glycol conjugates of the human growth hormone-releasing factor,hGRF(1-29)-NH2

Two novel mono-PEGylated derivatives of hGRF(1-29)-NH(2) [human growth hormone-releasing factor, fragment 1-29] have been synthesized by regio-specific conjugation of Lys(12) or Lys(21) to a monomethoxy-PEG(5000) chain (compounds Lys(12)PEG-GRF and Lys(21)PEG-GRF). The PEG moiety has been covalently linked at the amino group of a norleucine residue via a carbamate bond. The Lys(12)PEG-GRF regioisomer was found to be slightly less active in vitro than both the unmodified peptide and Lys(21)PEG-GRF. To assess whether the differences in the biological activity of the PEGylated analogues could be related to conformational rearrangements induced by the PEG moiety, the structure of these PEGylated derivatives has been worked out (TFE solution) by means of NMR spectroscopy and molecular dynamics. Secondary structure shifts, hydrogen/deuterium exchange kinetics, temperature coefficients of amide protons, and NOE-based molecular models point out that hGRF(1-29)-NH(2), Lys(21)PEG-GRF and Lys(12)PEG-GRF share a remarkably similar pattern of secondary structure. All three compounds adopt an alpha-helix conformation which spans the whole length of the molecule, and which becomes increasingly rigid on going from the N-terminus to the C-terminus. Residues Lys(12) and Lys(21) are enclosed in all the compounds considered into well-defined alpha-helical domains, indicating that PEGylation either at Lys(12) or Lys(21) does not alter the tendency of the peptide to adopt a stable alpha-helix conformation, nor does it induce appreciable conformational mobility in the proximity of the PEGylation sites. No significant variation of the amphiphilic organization of the alpha-helix is observed among the three peptides. Therefore, the different biological activities observed for the PEGylated analogues are not due to conformational effects, but are rather due to sterical hindrance effects. The relationship between the biological activitiy of the mono-PEGylated derivatives and sterical hindrance is discussed in terms of the topology of interaction between hGRF(1-29)-NH(2) and its receptor.