Diffusions of β-cyclodextrins in mucus studied by <Superscript>19</Superscript>F diffusion NMR

β-Cyclodextrin (β-CD) based materials have been widely used as drug carriers for pharmaceutical applications. To understand the diffusion of β-CDs in mucus is important for selecting β-CD based drug carriers for applications targeting mucosal absorption because the surfaces of many biological membranes are covered with a highly viscous aqueous mucus layer which forms relatively effective diffusion barriers for drugs. In this study, ¹⁹F self-diffusion NMR technique has been applied to study the self-diffusions of β-CDs in mucus. The ¹⁹F NMR signals arose from 1-fluoroadamantane molecules entrapped in the cavities of β-CDs. The diffusive abilities of different β-CDs in mucus were assessed through analyzing the diffusion coefficients using the presented kinetic model, and Ogston’s and Renkin’s diffusion models for hydrogel systems. The kinetic results show that 2-hydroxypropyl-β-CD and 2-Carboxyethyl-β-CD have the smallest binding affinities to bovine submaxillary mucin and human nasal mucin among five tested β-CDs. The mesh sizes of the bovine submaxillary mucus at different concentrations and that of the human nasal mucus were evaluated using the diffusion models. We hope that this ¹⁹F diffusion method will be useful to study the diffusion of β-CD based materials in other biological systems.     

Complexation of dodecyl‐substituted poly(acrylate) by linked β‐cyclodextrin dimers and trimers in aqueous solution

Two‐dimensional NOESY ¹H NMR, isothermal titration calorimetric (ITC), and rheological studies of host–guest complexation by β‐cyclodextrin, β‐CD, and the β‐CD groups of the linked β‐CD dimers, β‐CD₂ur and β‐CD₂su and trimers, β‐CD₃bz and β‐CDen₃bz, of the dodecyl, C12, substituents of the 3.0% substituted poly(acrylate), PAAC12, in aqueous solution are reported. Complexations by β‐CD, β‐CD₂ur, β‐CD₂su, β‐CD₃bz, and β‐CDen₃bz of the C12 substituents of PAAC12 in 0.2 wt % solution exhibit complexation constants 10^?4K₁₁ (298.2 K) = 0.83, 5.80, 4.40, 15.0, and 1.50 dm³ mol^?1, respectively. (The corresponding ΔH₁₁ and TΔS₁₁ show a linear relationship.) The rheologically determined zero‐shear viscosities of 3.3 wt % aqueous solutions of PAAC12 alone and in the presence of β‐CD, β‐CD₂ur, β‐CD₂su, β‐CD₃bz, and β‐CDen₃bz (where the β‐CD groups and C12 substituents are equimolar) are 0.016, 0.03, 0.12, 0.25, 0.12, and 0.08 Pa s (298.2 K), respectively, and show PAAC12 to form interstrand cross‐links through complexation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1278–1286     

Hybrid competitive Lotka–Volterra ecosystems: countable switching states and two-time-scale models

This work is concerned with competitive Lotka–Volterra model with Markov switching. A novelty of the contribution is that the Markov chain has a countable state space. Our main objective of the paper is to reduce the computational complexity by using the two-time-scale systems. Because existence and uniqueness as well as continuity of solutions for Lotka–Volterra ecosystems with Markovian switching in which the switching takes place in a countable set are not available, such properties are studied first. The two-time scale feature is highlighted by introducing a small parameter into the generator of the Markov chain. When the small parameter goes to 0, there is a limit system or reduced system. It is established in this paper that if the reduced system possesses certain properties such as permanence and extinction, etc., then the complex system also has the same properties when the parameter is sufficiently small. These results are obtained by using the perturbed Lyapunov function methods.     

Magnetic state of the bulk, surface and nanoclusters of CaMnO3: A DFT study

The electronic structures of bulk, 2D slabs and clusters of CaMnO₃ in various magnetic configurations are presented. The obtained results including optimized cell constant, band-gap, Mn magnetic moment, on-site Coulomb repulsion potential and p-d charge separation potential are in good agreement with experiment data. The energetically most preferable configuration was an insulating charge-transfer ground state with G-type antiferromagnetic (AF) configuration (classified according to Wollan and Koehler, Phys. Rev. 100 (1955) 545). For the finite 2D layers the C-type AF ground state was found to be most stable. The surface effect on magnetism of finite quasi 2D systems appeared to originate in the pyramidal field splitting of Mn 3d levels, which induced the formation of ferromagnetic (FM) regions within the AF matrix and the extension of FM correlation deep through 7 subsurface layers (2.7 nm from the surface). All finite systems (clusters and slabs) were found non-conducting due to the localization of electrons and the cancellation of surface excess carriers (holes) after surface relaxation, although the band-gaps of 2D systems were sufficiently reduced in comparison with that of the bulk.     

Tetrathiafulvalene hydrazone an efficient precursor of various chelating electroactive ligands

Novel bidentate electroactive ligands containing one or two tetrathiafulvalene (TTF) cores as redox active unit have been synthesized thanks to the condensation of various carbonyl derivatives with TTF hydrazone. The electron donating ability of these redox active ligands determined by cyclic voltammetry is described together with the investigations of their molecular structures by X-ray diffraction studies. The chelating ability of these ligands has been exemplified through the coordination to molybdenum carbonyl fragment or the complexation to difluoroboron moiety.     

Investigation by combined solid‐state NMR and SAXS methods of the morphology and domain size in polystyrene‐b‐polyethylene oxide‐b‐polystyrene triblock copolymers

The microphase structure of a series of polystyrene‐b‐polyethylene oxide‐b‐polystyrene (SEOS) triblock copolymers with different compositions and molecular weights has been studied by solid‐state NMR, DSC, wide and small angle X‐ray scattering (WAXS and SAXS). WAXS and DSC measurements were used to detect the presence of crystalline domains of polyethylene‐oxide (PEO) blocks at room temperature as a function of the copolymer chemical composition. Furthermore, DSC experiments allowed the determination of the melting temperatures of the crystalline part of the PEO blocks. SAXS measurements, performed above and below the melting temperature of the PEO blocks, revealed the formation of periodic structures, but the absence or the weakness of high order reflections peaks did not allow a clear assessment of the morphological structure of the copolymers. This information was inferred by combining the results obtained by SAXS and ¹H NMR spin diffusion experiments, which also provided an estimation of the size of the dispersed phases of the nanostructured copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 55–64, 2010     

Lipschitzian stability of parametric variational inequalities over perturbed polyhedral convex sets

In this paper we investigate the Lipschitz-like property of the solution mapping of parametric variational inequalities over perturbed polyhedral convex sets. By establishing some lower and upper estimates for the coderivatives of the solution mapping, among other things, we prove that the solution mapping could not be Lipschitz-like around points where the positive linear independence condition is invalid. Our analysis is based heavily on the Mordukhovich criterion (Mordukhovich in Variational Analysis and Generalized Differentiation. vol. I: Basic Theory, vol. II: Applications. Springer, Berlin, 2006) of the Lipschitz-like property for set-valued mappings between Banach spaces and recent advances in variational analysis. The obtained result complements the corresponding ones of Nam (Nonlinear Anal 73:2271–2282, 2010) and Qui (Nonlinear Anal 74:1674–1689, 2011).