Kinetics of Reactions of α,β-Unsaturated Surfactants with Secondary Amines in a Solution

The kinetics of reactions of acrylamide derivatives (acrylamidotrihydroxymethylmethane (TA), sodium 4-acrylamidobutanoate (AA₃), sodium 6-acrylamidohexanoate (AA₅), and sodium 11-acrylamido-undecanoate (AA10)) with piperidine and morpholine in water (for TA, also in DMF, DMSO, and formamide) is studied at 293 K. These compounds are weak surfactant monomers. The critical concentrations of micelle formation (CCM) for them are determined. The self-association of AA₃, AA₅, and AA₁₀ producing micelles results in a decrease in their reactivity compared to the monomeric forms. The rates of the reactions of surfactant monomers (SM) with morpholine and piperidine are described by the second-order rate law w ₀ = k[SM]₀[Amine]₀. An empirical equation is derived that relates the CCM values to the rate constant for the reaction of a surfactant monomer with a secondary amine with charges on the -carbon and oxygen atoms of the amide group of a surfactant monomer. The rates of the reactions of TA with piperidine and morpholine are determined by the electrophilicity (acidity) of the medium, which is favorable for the Michael reaction.     

Downstream processing of inulinase

Candida kefyr DSM 70106 was cultivated in a medium containing inulin as a carbon source. About 92% of the inulinase was recovered directly from the medium. Different concentration (C_f) and enrichment (E_f) factors were obtained, using the following methods: Cross-flow filtration (microfiltration and cell diafiltration were carried out using a rotary filter; enzyme ultrafiltration and diafiltration were performed using a cassette module): C_f = 7.5 and E_f = 2.2; liquid-liquid extraction ofN-Benzyl-N-Dodecyl-N-bis[2-hydroxyethyl] ammonium chloride (BDBAC) reversed micelles: C_f = 2.5 and E_f = 2.7; and expanded-bed adsorption: C_f = 2.8 and E_f = 4.3.     

The molecular weight dependence of intrinsic viscosity of rod-like micelles of dodecyldimethylammonium chloride

It is shown that the non-linear logarithmic dependence of the intrinsic viscosity on the molecular weight for rod-like micelles of dodecyldimethylammonium chloride (as reported by Ozeki and Ikeda [1]) can be interpreted in terms of the Yamakawa-Fujii theory of worm-like chains. Characteristic parameters of the micelles are estimated: persistence length (a=14 nm), linear mass density (M _L=4800 nm^–1), diameter (d=3 nm), molecular pitch (b=0.052), and the number of surfactant chains in a layer of rod-like micellen=12. The results are compared with those derived from light-scattering measurements.     

Microphase Separation within a Comb Copolymer with Attractive Side Chains: A Computer Simulation Study

Computer simulation modelling of a flexible comb copolymer with attractive interactions between the monomer units of the side chains is performed. The conditions for the coil‐globule transition, induced by the increase of attractive interaction, ε, between side chain monomer units, are analysed for different values of the number of monomer units in the backbone, N, in the side chains, n, and between successive grafting points, m. It is shown that the coil‐globule transition of such a copolymer corresponds to a first‐order phase transition. The energy of attraction (ε) required for the realisation of the coil‐globule transition decreases with increasing n and decreasing m. The coil‐globule transition is accompanied by significant aggregation of side chain units. The resulting globule has a complex structure. In the case of a relatively short backbone (small value of N), the globule consists of a spherical core formed by side chains and an enveloping shell formed by the monomer units of the backbone. In the case of long copolymers (large value of N), the side chains form several spherical micelles while the backbone is wrapped on the surfaces of these micelles and between them.     

The effect of Fe-doping on superconductivity of YBa2Cu30 y

In the present paper, an approximate band-structure treatment based on the EHMO approach is suggested and used to calculate the electronic structures of the Fe-doped superconductors YBa₂Cu_3–x Fe _x O _y . The present treatment gives, indeed, average band structures and average densities of states as the doping fraction increases. From investigations of the influence of the Fe-doping at the Cu-site on their properties, it is shown that as the Fe-doping fractionx in YBa₂Cu_3–x Fe _x O _y is raised from 0.0 to 0.5, (i) the broad anisotropic bands arising from the 1D Cu-O chains and the 2D Cu-O planes are displaced and depart from the Fermi levelE _f toward the high-energy zone by degrees, while the total electronic densities of states nearE _f are drastically decreased; (ii) the band arising from the Cu-O chains doped by Fe is gradually separated from the broad anisotropic bands arising from the 2D Cu-O planes; (iii) at the doping fractionx = 0.5, the Fe-doping results in an energy gap (about 0.2 eV) near E_f; (iv) the oxygen content is not a predominant factor for the superconducting properties of the Fe-doped Y-Ba-Cu-O system; (v) the total densities of states atE _f,N(E _f), and their decrease caused by the Fe-doping arise mainly from the 2D Cu-O planes, which implies the important role of the 2D Cu-O planes in the Y-Ba-Cu-O superconducting system.     

Evolution of defect states in doped polythiophene: A study based on the method of simulated annealing

A modified Su–Schrieffer–Heeger Hamiltonian‐based model is used to compute the electronic and geometric structures of fairly long polythiophene (PT) chains, neutral as well as doped. The geometry optimization is carried out by the simulated annealing method. Both Metropolis and Glauber functions are used for sampling. It is shown that a bipolaron can be structurally represented by a fragment of the PT chain containing 14 thiophene units. As a series of bipolaronic defects are introduced in a long PT chain (50–100 rings), the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap energy (Δ) becomes vanishingly small, a feature not present in the PT chains of similar sizes containing polaronic defects. The Fermi energy level (E_F) also moves into the valency band and nonzero density of states at ? = E_F are created. Once again, this feature is shown to be missing in PT chains containing polaronic defects. Implications of these findings are analyzed. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Some properties of the Lagrange multiplier μ in density functional theory

Some new properties of the Lagrange multiplier μ introduced through the normalization constraint on ρ in the variations of energy density functionals are determined. Through arguments concerning the homogeneity properties of these functionals with respect to μ, it is demonstrated that at the point of variation μ = μ₀ = E₀/N, where E₀ is the ground state energy and N is the total particle number. It is also shown that the value of μ₀ is independent of the normalization imposed on ρ. The interpretation of μ₀ as a chemical potential is discussed in the light of these findings.     

Polymer chains confined into tubes with attractive walls: A Monte Carlo simulation

A bead-spring off-lattice model of a polymer chain with repulsive interactions among repeating units confined into straight tubes of various cross sections, D_T², is studied by Monte Carlo simulation. We are also varying the chain length from N = 16 to 128 and the strength of a short-range attractive interaction between the repeating units and the walls of the tube. Longitudinal and perpendicular static linear dimensions of the chains are analyzed, as well as the density profile of repeating units across the tube. These data are interpreted in terms of scaling concepts describing the crossover between three-dimensional and quasi-one-dimensional chain conformations and the adsorption transition of chains at flat infinite walls, respectively. We also study the time-dependent mean-square displacements of repeating units and obtain various relaxation times. It is shown that both relaxation times scaling proportional to N² and to N³ play a role in the reptative motion of the chain in the tubes.     

Preparation of substituted ionic carbohydrate polymers and their interactions with ionic surfactants

The formation of micelles of hexadecyltrimethylammonium chloride (CTAC) and sodium dodecylsulfate (SDS) in aqueous solutions containing charged polysaccharides was studied by steady-state and time-resolved fluorescence measurements using pyrene as a photophysical probe. Micropolarity studies using the I₁/I₃ ratio of the vibronic emission bands of pyrene and the behaviour of the I_E/I_M ratio between the excimer and monomer emissions show the formation of hydrophobic domains. The interactions between the polyelectrolytes and surfactants of opposite charge lead to the formation of induced pre-micelles at surfactant concentrations lower than the critical micellar concentration (cmc) of the surfactants. At similar concentrations, the I_E/I_M ratio shows a peak. This aggregation process is assumed to be due to electrostatic attractions. At higher surfactant concentrations, near the critical micellar concentration, micelles with the same properties as those found in pure aqueous solution are formed. On the other hand, systems containing polyelectrolytes and surfactants of the same charge do not show this behaviour at low concentrations. The presence of long alkyl chains bound to the polyelectrolytes also induces the formation of free micelles at concentrations somewhat below the aqueous cmc.     

Electron correlation in one dimension: Coupled cluster approaches to cyclic polyene π-electron models

Methods accounting for correlation effects in quasi-one-dimensional π-electron systems and based on the restricted Hartree–Fock (RHF ) single determinantal reference state are briefly reviewed as well as their role in the bond length alternation (or dimerization) problem in polyactylene-like systems, as described by the semiempirical Hamiltonians of the Pariser–Parr–Pople (PPP ) type. Particular attention is given to the π-electron model of cyclic polyene homologous series C_NH_N, N = 2n = 4v + 2, v = 1,2,…, which can be regarded as an idealized model of one-dimensional metallic-like systems with imposed Born–von Kármán boundary conditions when N ∞. These models provide a useful bridge between the typical aromatic systems, represented by benzene (N = 6) π-electron model, and long linear polyenic chains, since the properties of these systems hardly change once a sufficiently large N (?26 or 30) is reached. It is shown that due to the quasidegenerate character of the RHF reference employed, and the related prominence of connected quadruply excited cluster components in the exact wave function, most of the standard technieques suffer a singular behavior break down entirely for large enough systems, particularly in the strongly correlated regime. The approximate coupled pair theory that accounts for quadruply excited clusters (ACPQ method) is shown to be free of these shortcomings and is extended to include also approximately the effects of connected triexcited cluster components. These results are compared with other recently examined approximate methods accounting for the tri- and quadruply excited clusters and the proposed ACPQ +T (ACPQ ) procedure is shown to provide the best results in the whole range of the coupling constant.     

Dual‐responsive crosslinked micelles of a multifunctional graft copolymer for drug delivery applications

A novel multifunctional amphiphilic graft copolymer has been synthesized consisting of a biodegradable poly(l ‐aspartic acid) backbone that was decorated by water‐soluble poly(ethylene glycol) (PEG) and pH‐responsive poly(N,N‐diethylaminoethyl methacrylate) (PDEAEMA) side‐chains as well as thiol pendant groups. This graft copolymer together with doxorubicin (DOX) formed micelles in water at pH = 10.0 with PDEAEMA and DOX acting as the core and PEG serving as the micellar corona. Upon oxidation, the thiol groups dimerized to form disulfide bonds, thus “locking in” the micellar structure. These crosslinked micelles expanded as the pH was decreased from 7.4 to 5.0 or upon the addition, at pH = 7.4, of glutathione (GSH), a thiol‐containing oligopeptide that is present in cancerous cells and cleaves disulfide bonds. At pH = 5.0, GSH addition triggered the disassembly of the micelles. The expansion and disassembly of the micelles have been determined via in vitro experiments to evaluate their DOX release behavior. More importantly, the graft copolymer micelles could enter cells by means of endocytosis and deliver DOX to the nuclei of ovarian cancer BEL‐7402 cells. Thus, this polymer and its micelles are promising candidates for drug delivery applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1536–1546     

Study on the chain conformation of polymers.: II. Conformational characteristics of 1,2-polybutadiene and its characteristic ratio

In this work, improvement was made for conformational analysis of 1,2-polybutadiene by means of the molecular mechanics force field program (MM2). Thus the first and the second order interaction energies obtained are much more reasonable. The characteristic ratio of isotactic 1,2-polybutadiene was emphasized properly, which varied with energy E (E = E_η + E_ω″). In the same time, the characteristic ratios for isotactic chain of polystyrene and so on were noticed, which varied with energy E according to the same way as that for isotactic 1,2-polybutadiene. It is shown that there is a general rule or a common feature for isotactic chains of poly -α-olefine and vinyl polymer.     

Structural aspects in self-assembled systems of polyoxyethylene surfactants, as studied by the spin probe technique

Typical examples of structural characterization of self-assembled systems by the spin probes technique, selected from our representative results accumulated in the last years of systematic studies, are presented. The choice of the examples has aimed at emphasizing the potentiality of this technique in the study of self-assembled systems, in general, and of those of PEO surfactants, in particular. By using specific ESR parameters (the nitrogen hyperfine splitting (hfs), a_N, the rotational correlation time, τ_c, the order parameter, S) of a variety of properly chosen nitroxides, problems such hydration degree and profile of the PEO chains, ordering and order profile along these chains, their penetrability by the oil solvent, role of the terminal OH in the micellization, as well as differences in these quantities vs. the nature of the aggregate (micelle, reverse micelle, lamellar phase, etc.), nature of the surfactants (conventional or triblock copolymer), solubilizates (water in reverse micelles or various alcohols in micelles) and temperature have been discussed.     

Pushing the Upper Limit of Nucleophilicity Scales by Mesoionic N-Heterocyclic Olefins

A series of mesoionic, 1,2,3-triazole-derived N-heterocyclic olefins (mNHOs), which have an extraordinarily electron-rich exocyclic CC-double bond, was synthesized and spectroscopically characterized, in selected cases by X-ray crystallography. The kinetics of their reactions with arylidene malonates, ArCH=C(CO₂Et)₂, which gave zwitterionic adducts, were investigated photometrically in THF at 20 °C. The resulting second-order rate constants k₂(20 °C) correlate linearly with the reported electrophilicity parameters E of the arylidene malonates (reference electrophiles), thus providing the nucleophile-specific N and s_N parameters of the mNHOs according to the correlation lg k₂(20 °C)=s_N(N+E). With 21<N<32, the mNHOs are much stronger nucleophiles than conventional NHOs. Some mNHOs even excel the reactivity of mono- and diacceptor-substituted carbanions. It is exemplarily shown that the reactivity parameters thus obtained allow to calculate the rate constants for mNHO reactions with further Michael acceptors and predict the scope of reactions with other electrophilic reaction partners including carbon dioxide, which gives zwitterionic mNHO-carboxylates. The nucleophilicity parameters N correlate linearly with a linear combination of the quantum-chemically calculated methyl cation affinities and buried volumes of mNHOs, which offers a valuable tool to tailor the reactivities of strong carbon nucleophiles.     

Liquid crystalline main chain polymers with a poly(p-phenyleneterephthalate) backbone. 2. Fiber spinning and mechanical properties of polyesters with alkoxy side chains

Fiber spinning and mechanical properties of four rigid polyesters with alkoxy substituents of different length and placement were evaluated. Properties of oriented fibers from the polymer with dodecyloxy substituents on the terephthalate moiety, PTA12HQ, were significantly affected by the crystal modification. At room temperature the following properties (tensile modulus E, tensile strength σ_b, and strain at break ε_b) could be obtained: E = 9.5 GPa, σ_b = 85 MPa and ε_b = 1.1% for phase L_f (the “frozen in layered mesophase”); E = 10.4 GPa, σ_b = 59 MPa and ε_b = 0.6% for modification A; E = 17.3 GPa, σ_b = 158 MPa and ε_b = 1.2% for modification B. Because of the higher amount of main chains per cross sectional area the polymer with hexyloxy side chains, PTA6HQ, showed better properties at a comparable degree of molecular orientation: E = 24 GPa, σ_b = 270 MPa, ε_b = 1.4%. Fibers obtained from the polyester with dodecyloxy substituents on the hydroquinone moiety, PTAHQ12, were too brittle to handle. The polyester with dodecyloxy substituents on both moieties, PTA12HQ12, was spun from the isotropic melt. Because of the obtained low degree of orientation, properties (E = 1 GPa, σ_b = 40 MPa, and ε_b = 6.3%) were governed by interactions between the chains (the main chains are not load-bearing). © 1993 John Wiley & Sons, Inc.     

Surface effects on the polarization reversal of the ferroelectric liquid crystal 8SI*

Abstract

The activation field for the switching time (τ_1/2) in the truly ferroelectric liquid crystal 8SI* (CE8; ΔS-(+)-4-(2′-methylbutyl) phenyl-4′-n-octylbiphenyl-4 carboxylate) has been studied for various surface conditions of the transparent electrode (SnO₂), in order to understand the memory effect, the polarization reversal mechanism and its surface effect. We prepared five different surfaces, namely one coated with polyvinyl alcohol (PVA) and the other four by scratching N-times(N = 0, 10, 20 and 30) with a paste made of Cr₂O₃ powder (about 0·1 μm). The number and the area of scratches on the electrode surface obviously increase with N. The polarization reversal processes are influenced by this treatment. τ_1/2 decreases with increasing N, but no change is observed in the contrast of the light transmittance. Two different activation fields, E _a1, for the applied field E > E ₀ and E _a2 for E < E ₀ are observed, where E ₀ is a certain field depending on the sample. Here E _a1 is much larger than E _a2; typically E _a1, = 260 kV cm^?1 and E _a2 = 144 kV cm^?1 for N = 0. This means that nucleation for the higher field needs a large activation energy which therefore has strong barriers. In contrast with this, nucleation for the low field occurs easily. Changing a surface condition, E _a2 clearly decreases with increasing N although E _a1 is almost independent of the surface scratching. This may suggest that E _a1 corresponds to the activation field for the bulk pinning and nucleation, and E _a2 for the surface pinning. The PVA treatment gives an intermediate influence between N = 0 and 10.     

Electronic structure of long cumulene chains

The analysis of the equations of the unrestricted Hartree–Fock (UHF) method for polyenes C_NH_N+2 with even and odd N » 1 is carried out. The equations of the UHF method are shown to be the same in both cases. The comparison of the UHF method with the extended Hartree–Fock (EHF) method applied to large systems is performed. The ground state and π-electron spectra of long cumulene chains C_NH₄ are treated by the EHF Method. The end effects are taken into consideration. It is shown that the EHF method gives a finite value of the first optical transition frequency and, at the same time, zero value of torsion barrier of end CH₂–groups in long cumulene chains (N → ) in contrast to previous calculations of cumulenes by the Huckel method and the restricted Hartree–Fock method.     

Influence of Tetraethoxylated Nonylphenol on the Properties of Dodecaethoxylated Nonylphenol Micelles in Aqueous Medium

Properties of the mixed micelles of tetraethoxylated nonylphenol and dodecaethoxylated nonylphenol (NP₁₂) in water are studied by spectrophotometry, dynamic and static light scattering methods. Data on the composition, aggregation numbers (N), sizes (R _h), and hydration (n _OE) of mixed and individual micelles of NP₁₂ are obtained. Two NP₁₂ concentration regions are disclosed where mixed micelles of various compositions but with the close values of N, R _h, and n _OE are present. It is established that the sizes and aggregation numbers of mixed micelles are noticeably larger than those of individual micelles. Features of the mixing of two studied surfactants in a micellar state are analyzed in terms of the theory of phase separation.     

Isokinetic relationships in unimolecular heterolysis. Mechanism of ionization of covalent bond

Various types of isokinetic (isoparametric) relationships in heterolytic reactions were summarized and critically analyzed. It was presumed that the series of substrate reactivity is reversed after passing the isoparametric point, and the bimolecular reaction mechanism changes to unimolecular: S_N2-S_N1, S_N2-E1, S_E2-S_E1, S_E2-S_N1, and S_N2(SSIP)-S_N2(C⁺). Three particular cases of isoparametric relationships are discussed: (1) isoentropy (ΔS ^≠ = const) which reflects formation of contact ion pair; (2) isoenthalpy (ΔH ^≠ = const) which reflects formation of space-separated ion pair; and (3) isoenergy (ΔG ^≠ = const), when ΔH ^≠ = ΔG ^≠ = ΔE _r. The rate of heterolysis in cyclohexane does not depend on the substrate nature, and a universal minimal rate of heterolysis exists, k25 ≈ 10⁻¹⁰ s⁻¹, τ_1/2 = 220 years. There is no nucleophilic assistance by the solvent in unimolecular heterolysis.     

A potentiometric titration study on the dissociation of bile acids related to the mode of interaction between different head groups of nonionic surfactants with free bile salts upon mixed micelle formation in water

By constructing an elaborate set of potentiometric titration together with data analysis system, apparent acid dissociation indices (pK _a ^app ) for two bile acids were determined in the mixed surfactant system of bile salts (Sodium Deoxycholate, NaDC, and Sodium Chenodeoxycholate, NaCDC) with nonionic surfactants (Hexaethyleneglycol monon-dodecylether, C₁₂E₆, Decanoyl-N-methylglucamide, MEGA-10) in aqueous solution at ionic strength 1.5 as a function of mole fraction in the surfactant mixture. It was found that with increasing the bile salt concentration, pK _a ^app as well as pH showed an abrupt rise at a certain concentration of the bile salt being regardable as a critical micellization concentration (CMC) and reached a constant value at the range sufficiently higher than CMC for each pure bile salt system, meaning that the dissociation degree of carboxyl group in micelle is smaller than that in bulk. In the mixed systems of free bile salts with nonionic surfactants, the dissociation state of carboxyl groups in mixed micelles depends on the species of hydrophilic group of nonionic surfactants as well as on mole fraction in the surfactant mixture.