Novel drug delivery systems based on the complexes of block ionomers and surfactants of opposite charge

In this paper we have evaluated a novel family of polymer-surfactant complexes formed between block ionomers and oppositely charged surfactants. Complexes between cationic copolymer poly(ethylene oxide)-g-polyethyleneimine (PEO-g-PEI) and sodium salt of oleic acid, natural nontoxic surfactant, are prepared and characterized. These systems self-assemble in aqueous solutions into particles with average size of 50–60 nm, which can solubilize hydrophobic dyes (Yellow OB) and drug molecules (paclitaxel). The use of the biologically active surfactants as components of block ionomer complexes is demonstrated for the complexes from PEO-g-PEI and all-trans-retinoic acid. Binding of relatively soluble drugs with block ionomers is illustrated using PEO-b-poly(sodium methacrylate) and doxorubicin. Overall these studies suggest that block ionomer complexes can be used to prepare a variety of soluble and stable formulations of biologically active compounds, and have potential application as drug delivery systems     

The Greek banking system: Reanalysis of performance

Zopounidis et al. used an ordinal regression analysis to assess an additive utility model and to obtain final ranking of a representative sample of commercial Greek banks [C. Zopounidis, D.K. Despotis, E. Stavropoulou, Multiattribute evaluation of Greek banking performance, Applied Stochastic Models and Data Analysis 11 (1995) 97–107]. In this paper, we reanalyze their data by means of a new multivariate analysis method called Co-plot, a two-dimensional graphic display technique designed to analyze observations (e.g., 16 banks) and attributes (e.g., 7 attributes) simultaneously. The method produces three results: (1) similarity among the banks by the composite of all attributes involved (five clusters are obtained), (2) the structure of correlations among the attributes (three clusters are obtained), and (3) the mutual relationships between the banks and the attributes. The banks are mapped into a partial order according to their (increased) performance to obtain their rating. The final ranking obtained by the Co-plot method differed from that obtained by Zopounidis et al.     

Surface modification strategies for multicomponent polymer systems,Part I: Use of diblock copolymers as surface modifiers of rutile

Various functional diblock copolymers have been used as surface modifiers for rutile pigment in an effort to condition the solid for eventual use in multicomponent polymer systems. Coated surfaces were analyzed by inverse gas chromatography at infinite and finite dilution of the vapor phase, and by XPS. At high coverages (about 10% by weight of the pigment), the diblocks were randomly oriented at the air interface, effectively masking the surface of the rutile. At low diblock concentrations acid/base interactions dominated the orientation of the adsorbed molecule at the rutile interface, thereby also affecting the orientational states at the air interface. In this condition, the performance of the pigment in specified host polymer systems may be expected to vary with the selection of the diblock copolymer modifier. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1793–1805, 1997     

Computability in Harmonic Analysis

Foundations of Computational Mathematics - We study the question of constructive approximation of the harmonic measure $$\omega _x^\varOmega $$ of a bounded domain $$\varOmega $$ with respect to a...     

Deterministic algorithms for matrix completion

The goal of the matrix completion problem is to retrieve an unknown real matrix from a small subset of its entries. This problem comes up in many application areas, and has received a great deal of attention in the context of the Netflix challenge. This setup usually represents our partial knowledge of some information domain. Unknown entries may be due to the unavailability of some relevant experimental data. One approach to this problem starts by selecting a complexity measure of matrices, such as rank or trace norm. The corresponding algorithm outputs a matrix of lowest possible complexity that agrees with the partially specified matrix. The performance of the above algorithm under the assumption that the revealed entries are sampled randomly has received considerable attention (e.g., Refs. Srebro et al., 2005; COLT, 2005; Foygel and Srebro, 2011; Candes and Tao, 2010; Recht, 2009; Keshavan et al., 2010; Koltchinskii et al., 2010). Here we ask what can be said if the observed entries are chosen deterministically. We prove generalization error bounds for such deterministic algorithms, that resemble the results of Refs. Srebro et al. (2005); COLT (2005); Foygel and Srebro (2011) for the randomized algorithms. We still do not understand which sets of entries in a given matrix can be used to properly reconstruct it. Our hope is that the present work sheds some light on this problem. © 2013 Wiley Periodicals, Inc. Random Struct. Alg., 45, 306–317, 2014     

Harnessing the Oxidation Susceptibility of Deubiquitinases for Inhibition with Small Molecules

Deubiquitinases (DUBs) counteract ubiquitination by removing or trimming ubiquitin chains to alter the signal. Their diverse role in biological processes and involvement in diseases have recently attracted great interest with regard to their mechanism and inhibition. It has been shown that some DUBs are regulated by reactive oxygen species (ROS) in which the catalytic Cys residue undergoes reversible oxidation, hence modulating DUBs activity under oxidative stress. Reported herein for the first time, the observation that small molecules, which are capable of generating ROS efficiently, inhibit DUBs by selective and nonreversible oxidation of the catalytic Cys residue. Interestingly, the small molecule beta‐lapachone, which is currently in clinical trials for cancer, is among the potent inhibitors, thus suggesting possible new cellular targets for its therapeutic effects. Our study describes a novel mechanism of DUBs inhibition and opens new opportunities in exploiting them for cancer therapy.     

Are Oxazolidinones Really Unproductive,Parasitic Species in Proline Catalysis? – Thoughts and Experiments Pointing to an Alternative View

The N,O‐acetal and N,O‐ketal derivatives (oxazolidinones) formed from proline, and aldehydes or ketones are well‐known today, and they are detectable in reaction mixtures involving proline catalysis, where they have been considered ‘parasitic dead ends’. We disclose results of experiments performed in the early 1970's, and we describe more recent findings about the isolation, characterization, and reactions of the oxazolidinone derived from proline and cyclohexanone. This oxazolidinone reacts (THF, room temperature) with the electrophiles β‐nitrostyrene and chloral (=trichloroacetaldehyde), to give the Michael and aldol adduct, respectively, after aqueous workup (Scheme 5). The reactions occur even at ?75° when catalyzed with bases such as 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) or EtN(i‐Pr)₂ (DIPEA) (10%; Table 1). It is shown by NMR (Figs. 1 and 3) and IR analysis (Figs. 2 and 4) that the primarily detectable product (before hydrolysis) of the reaction with the nitro‐olefin is again an oxazolidinone. When dissolved in hydroxylic solvents such as MeOH, ‘hexafluoroisopropanol’ ((CF₃)₂CHOH; HFIP), AcOH, CF₃COOH, or in LiBr‐saturated THF, the ring of the oxazolidinone from cyclohexanone and proline opens up to the corresponding iminium ion (Tables 2–4), and when treated with strong bases such as DBU (in (D₈)THF) the enamino‐carboxylate derived from proline and cyclohexanone is formed (Scheme 8). Thus, the two hitherto putative participants (iminium ion and enamine) of the catalytic cycle (Scheme 9) have been characterized for the first time. The commonly accepted mechanism of the stereoselective C,C‐ or C,X‐bond‐forming step (i.e., A – D ) of this cycle is discussed and challenged by thoughts about an alternative model with a pivotal role of oxazolidinones in the regio‐ and diastereoselective formation of the intermediate enamino acid (by elimination) and in the subsequent reaction with an electrophile (by trans‐addition with lactonization; Schemes 11–14). The stereochemical bias between endo‐ and exo‐space of the bicyclo[3.3.0]octane‐type oxazolidinone structure (Figs. 5 and 6) is considered to possibly be decisive for the stereochemical course of events. Finally, the remarkable consistency, with which the diastereotopic Re‐face of the double bond of pyrrolidino‐enamines (derived from proline) is attacked by electrophiles (Schemes 1 and 15), and the likewise consistent reversal to the Si‐face with bulky (Aryl)₂C‐substituents on the pyrrolidine ring (Scheme 16) are discussed by invoking stereoelectronic assistance from the lone pair of pyramidalized enamine N‐atoms.     

Clustering in carboxylated polysulfone ionomers: A characterization by dynamic mechanical and small-angle X-ray scattering methods

The dynamic mechanical properties and morphology of carboxylated polysulfone ionomers were investigated by dynamic mechanical thermal analysis and small-angle X-ray scattering (SAXS) techniques. It was found that at 25 mol % of ions, ionomers show two glass transitions: one at about 200 °C (the matrix T_g) and the other at about 235 °C (the cluster T_g). It was also found that with increasing ion content up to about 37 mol %, the matrix T_g shifted to higher temperatures and the size of tan δ peak decreased. The cluster T_g did not change. From the results, it is suggested that even at high ion content, the ionomers contain a significant amount of unclustered material, but that the increase in the ion content does not increase the amount of clustered material. SAXS profiles showed the ionic peak, which represents the presence of multiplets in the cluster regions. In addition, the difference in the matrix and cluster T_g's of this ionomer system was found to be about 35°. Thus, it is postulated that ionic group aggregation is subject to steric hindrance owing to the bulkiness of benzene ring, and tension on polymer chains surrounding the multiplet owing to chain rigidity, which limit the size and stability of the multiplet significantly. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3226–3232, 1999