Thermo‐ and pH‐induced phase transitions and network parameters of poly(N‐isopropylacrylamide‐ co‐2‐acrylamido‐2‐methyl‐propanosulfonic acid) hydrogels

Dual temperature‐ and pH‐sensitive hydrogels composed of N‐isopropylacrylamide (NIPAM) and 2‐acrylamido‐2‐methyl‐propanosulfonic acid (AMPS) were prepared by free‐radical crosslinking copolymerization in aqueous solution at 22 °C. The mole percent of AMPS in the comonomer feed was varied between 0.0 and 7.5, while the crosslinker ratio was fixed at 5.0/100. The effect of AMPS content on thermo‐ and pH‐ induced phase transitions as well as equilibrium swelling/deswelling, interior morphology and network structure was investigated. The volume phase transition temperature (VPT‐T) was determined by both swelling/deswelling measurements and differential scanning calorimetry (DSC) technique. In addition, the volume phase transition pH (VPT‐pH) was detected from the derivative of the curves of the swelling ratio (dQ_v/dpH) versus pH. The polymer‐solvent interaction parameter (χ) and the average molecular mass between crosslinks ( ) of hydrogels were calculated from swelling ratios in buffer solutions at various pHs. The enthalpy (ΔH) and entropy (ΔS) changes appearing in the χ parameter of hydrogels were also determined by using the modified Flory–Rehner equation. The negative values for ΔH and ΔS indicated that the hydrogels had a negative temperature‐sensitive property in water, that is, swelling at a lower temperature and shrinking at a higher temperature. It was observed that the experimental swelling data of hydrogels at different temperature agreed with the modified Flory‐Rehner approach based on the affine network model. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1713–1724, 2008     

4,4,6,6‐Tetra­chloro‐2,2‐(ethyl­ene­di­oxy­di‐o‐phenyl­enedi­imino)‐2λ5,4λ5,6λ5‐cyclo­triphosphazene

The title ligand, C₁₄H₁₄Cl₄N₅O₂P₃, is a cyclo­phosphazene lariat (PNP pivot) ether with a spiro‐cyclic 11‐membered macrocyclic ring containing two ether O and two N atoms; the phosphazene ring is nearly planar. The macrocyclic ring contains a four‐centred (trifurcate) N—H⋯O/N—H⋯N hydrogen bond, and the relative inner‐hole size of the macrocycle is ∼1.14 Å in radius. The mol­ecules are linked about inversion centres by N—H⋯N hydrogen bonds into centrosymmetric dimers.     

The synthesis of chromophore ended glycoles,part IV. Bis‐coumarin derivatives ended polyglycols

The coumarin derivatives of bis‐resorcin ended polyglycols were prepared in two ways: Bis‐4‐alkyl‐7‐oxycoumarin ended mono and diethyleneglycols were prepared starting from bis(3‐hydroxyphenyl)glycols by coumarin condensation using relevant β‐ketoesters. Accordingly, 4‐methyl, 4‐trifluoromethyl, 4‐n‐propyl and 4‐phenyl derivatives of 7‐hydroxycoumarins were prepared in good yields. They were then converted to bis‐coumarin ended three and tetraethylenglycol derivatives by reacting with three and tetraethyleneglycols dichlorides in Na₂CO₃/DMF, respectively. The products were identified using IR, ¹H nmr and low resolution mass spectrometry. The Li⁺, Na⁺ and Rb⁺ metal/Ligand selectivities of cation binding behaviour of products in acetonitrile were studied with steady state fluorescence spectroscopy.     

Spatiotemporal Patterns of a Reaction–Diffusion Substrate–Inhibition Seelig Model

In this paper, the spatiotemporal patterns of a reaction–diffusion substrate–inhibition chemical Seelig model are considered. We first prove that this parabolic Seelig model has an invariant rectangle in the phase plane which attracts all the solutions of the model regardless of the initial values. Then, we consider the long time behaviors of the solutions in the invariant rectangle. In particular, we prove that, under suitable “lumped parameter assumption” conditions, these solutions either converge exponentially to the unique positive constant steady states or to the spatially homogeneous periodic solutions. Finally, we study the existence and non-existence of Turing patterns. To find parameter ranges where system does not exhibit Turing patterns, we use the properties of non-constant steady states, including obtaining several useful estimates. To seek the parameter ranges where system possesses Turing patterns, we use the techniques of global bifurcation theory. These two different parameter ranges are distinguished in a delicate bifurcation diagram. Moreover, numerical experiments are also presented to support and strengthen our analytical analysis.     

Radiation synthesis and uranyl‐ion adsorption of poly(2‐hydroxyethyl methacrylate/maleic acid) hydrogels

A new kind of copolymeric hydrogel adsorbent containing hydrophilic groups that both provides swelling in water and chelates with uranyl ions was synthesized, and its adsorptive ability for recovering uranium from aqueous media was investigated. The uranyl adsorption capacities of poly(2‐hydroxyethyl methacrylate/maleic acid) hydrogels were determined with a polarographic technique to be 3.2–4.8 (mg UO/g dry gel) from a 15‐ppm uranyl nitrate solution at pH, 6 depending on the molar content of maleic acid in the hydrogel. Adsorption studies showed that other stimuli, the temperature, and the ionic strength of the solution also have important roles in the uranyl‐ion adsorption capacity of these hydrogels. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 277–283, 2001     

Multilevel Deep Feature Generation Framework for Automated Detection of Retinal Abnormalities Using OCT Images

Optical coherence tomography (OCT) images coupled with many learning techniques have been developed to diagnose retinal disorders. This work aims to develop a novel framework for extracting deep features from 18 pre-trained convolutional neural networks (CNN) and to attain high performance using OCT images. In this work, we have developed a new framework for automated detection of retinal disorders using transfer learning. This model consists of three phases: deep fused and multilevel feature extraction, using 18 pre-trained networks and tent maximal pooling, feature selection with ReliefF, and classification using the optimized classifier. The novelty of this proposed framework is the feature generation using widely used CNNs and to select the most suitable features for classification. The extracted features using our proposed intelligent feature extractor are fed to iterative ReliefF (IRF) to automatically select the best feature vector. The quadratic support vector machine (QSVM) is utilized as a classifier in this work. We have developed our model using two public OCT image datasets, and they are named database 1 (DB1) and database 2 (DB2). The proposed framework can attain 97.40% and 100% classification accuracies using the two OCT datasets, DB1 and DB2, respectively. These results illustrate the success of our model.     

Phosphorus‐nitrogen compounds. Part 39. Syntheses and Langmuir‐Blodgett thin films and antimicrobial activities of N/N and N/O spirocyclotriphosphazenes with monoferrocenyl pendant arm

The Cl substitution reactions of the N/N ( 1 ‐ 3 ) and N/O ( 4 and 5 ) spirocyclic monoferrocenylphosphazenes with 1,4‐dioxa‐8‐azaspiro[4,5]decane (DASD) produce the mono‐ ( 1a ‐ 5a ), geminal‐ ( 1b ‐ 5b ) and tetrakis‐DASD‐substituted ferrocenylspirocyclotriphosphazenes ( 1c ‐ 5c ). The mono‐ and geminal‐DASD‐substituted phosphazenes have two and one stereogenic P‐centers, respectively. The structures of the compounds were established by spectroscopic techniques. The molecular structures of 3a and 2b were evaluated using X‐ray crystallography. Additionally, the ultrathin and highly ordered Langmuir‐Blodgett (LB) films of 3a and 2b were also prepared. The characterizations of the LB films were done using p‐polarized grazing angle (GAIR) and horizontal attenuated total reflectance (HATR) techniques. On the other hand, the antimicrobial activities of the eight phosphazene derivatives against G(+) and G(‐) bacteria and fungi were investigated. Furthermore, the interactions between the compounds and plasmid DNA were studied by agarose gel electrophoresis.     

Synthesis of superparamagnetic and thermoresponsive hybrid nanoparticles via surface‐mediated RAFT polymerization of di(ethylene glycol) ethyl ether acrylate and (oligoethylene glycol) methyl ether acrylate

A reversible addition‐fragmentation chain transfer (RAFT) agent was directly anchored onto superparamagnetic Fe₃O₄ nanoparticles (SPNPs) in a simple procedure using a ligand exchange reaction of 2‐[(dodecylsulfanylcarbonylthiolsulfanyl) propionic acid] (DCPA) with oleic acid initially present on the surface of Fe₃O₄ nanoparticles. The DCPA‐modified SPNPs were then used for the surface‐mediated RAFT polymerization of di(ethylene glycol) ethyl ether acrylate and (oligoethylene glycol) methyl ether acrylate to fabricate structurally well‐defined hybrid SPNPs with temperature‐responsive poly[di(ethylene glycol) ethyl ether acrylate‐co‐(oligoethylene glycol) methyl ether acrylate] shell and magnetic Fe₃O₄ core. Evidence of a well‐controlled surface‐mediated RAFT polymerization was gained from a linear increase of number‐average molecular weight with overall monomer conversions and relatively narrow polydispersity indices of the copolymers grown from the SPNPs. The resultant hybrid nanoparticles exhibited superparamagnetic property with a saturation magnetization of 55.1–19.4 emu/g and showed a temperature‐responsive phenomenon as the temperature changed between 25 and 40 ^°C. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3420–3428     

On Pointwise Convergence of q-Bernstein Operators and Their q-Derivatives

Pointwise convergence of q-Bernstein polynomials and their q-derivatives in the case of 0 < q < 1 is discussed. We study quantitative Voronovskaya type results for q-Bernstein polynomials and their q-derivatives. These theorems are given in terms of the modulus of continuity of q-derivative of f which is the main interest of this article. It is also shown that our results hold for continuous functions although those are given for two and three times continuously differentiable functions in classical case.