Self‐Assembly of Amphiphilic Janus Dendrimers into Mechanically Robust Supramolecular Hydrogels for Sustained Drug Release

Compounds that can gelate aqueous solutions offer an intriguing toolbox to create functional hydrogel materials for biomedical applications. Amphiphilic Janus dendrimers with low molecular weights can readily form self‐assembled fibers at very low mass proportion (0.2 wt %) to create supramolecular hydrogels (G′?G′′) with outstanding mechanical properties and storage modulus of G′>1000 Pa. The G′ value and gel melting temperature can be tuned by modulating the position or number of hydrophobic alkyl chains in the dendrimer structure; thus enabling exquisite control over the mesoscale material properties in these molecular assemblies. The gels are formed within seconds by simple injection of ethanol‐solvated dendrimers into an aqueous solution. Cryogenic TEM, small‐angle X‐ray scattering, and SEM were used to confirm the fibrous structure morphology of the gels. Furthermore, the gels can be efficiently loaded with different bioactive cargo, such as active enzymes, peptides, or small‐molecule drugs, to be used for sustained release in drug delivery.     

Ordered *-Algebras with an Order Unit

We develop a theory of ordered *-algebras with an order unit. These are complex algebras equipped with a conjugate-linear vector space involution whose hermitian elements form an ordered real algebra with an order unit but not necessarily with a multiplicative identity. Our main result is a representation theorem for ordered *-algebras with an order unit. This can be viewed as the complex and the non-unital version of the representation theorem of Stone and Kadison for ordered real algebras containing an order unit which is a multiplicative identity. A key role in our approach is played by certain weighted function algebras.     

Radio-frequency single-electron refrigerator

We propose a cyclic refrigeration principle based on mesoscopic electron transport. Synchronous sequential tunneling of electrons in a Coulomb-blockaded device, a normal metal-superconductor single-electron box, results in a cooling power of approximately k(B)T x f at temperature T over a wide range of cycle frequencies f. Electrostatic work, done by the gate voltage source, removes heat from the Coulomb island with an efficiency of approximately k(B)T/Delta, where Delta is the superconducting gap parameter. The performance is not affected significantly by nonidealities, for instance by offset charges. We propose ways of characterizing the system and of its practical implementation.     

Experimental and quantum-chemical determination of the (2)H quadrupole coupling tensor in deuterated benzenes

Deuterium Quadrupole Coupling Constant (DQCC) in benzene was determined both experimentally by Nuclear Magnetic Resonance spectroscopy in Liquid Crystalline solutions (LC NMR) and theoretically by ab initio electronic structure calculations. DQCCs were measured for benzene-d(1) and 1,3,5-benzene-d(3) using several different liquid crystalline solvents and taking vibrational and deformational corrections into account in the analysis of experimental dipolar couplings, used to determine the orientational order parameter of the dissolved benzene. The experimental DQCC results for the isotopomers benzene-d(1) and 1,3,5-benzene-d(3) are found to be 187.7 kHz and 187.3 kHz, respectively, which are essentially equal within the experimental accuracy (+/-0.4 kHz). Theoretical results were obtained at different C-D bond lengths, and by applying corrections for electron correlation and rovibrational motion on top of large-basis-set Hartree-Fock results. The computations give a consistent DQCC of ca. 189 kHz for three different isotopomers; benzene-d(1), 1,3,5-benzene-d(3), and benzene-d(6), revealing that isotope effects are not detectable within the present experimental accuracy. Calculations carried out using a continuum solvation model to account for intermolecular interaction effects result in very small changes as compared to the data obtained in vacuo. The comparison of theoretical and experimental results points out the selection of the underlying molecular geometry as the most likely source of the remaining discrepancy of less than 2 kHz. Such an agreement between the calculated and the experimental DQCC results can only be achieved if rovibrational effects are considered on one hand in the experimental direct dipolar coupling data, and on the other hand in the theoretical property calculation, as is done presently.     

Photocrosslinkable polyesters and poly(ester anhydride)s for biomedical applications

Crosslinking is a feasible way to prepare biodegradable polymers with potential in biomedical applications such as controlled release of active agents and tissue engineering. A synthesis route in which functional telechelic aliphatic polyester oligomers are used as precursors for the preparation of crosslinked polyesters and poly(ester anhydride)s is described. Mechanical properties, degradation characteristics and rate, and bioactivity can be modified widely by controlling the chemical composition and architecture of the crosslinkable oligomers. In tissue engineering, photocrosslinking allows to use crosslinkable oligomers in advanced manufacturing techniques like micromolding in capillaries, stereolithography and two-photon polymerization.     

Multiresidue method for the analysis of emerging contaminants in wastewater by ultra performance liquid chromatography-time-of-flight mass spectrometry

A multiresidue method for screening of emerging contaminants in aquatic environments was developed. The method was based on sample pretreatment with solid phase extraction (SPE) and analysis with an ultra performance liquid chromatograph-time-of-flight mass spectrometer (UPLC-TOF-MS). The method was optimized and tested with standard solutions of model compounds containing 84 pesticides and pharmaceuticals. Four different SPE sorbents were evaluated to gain maximum recovery for the analytes. For the final procedure a combination of two different sorbents was chosen. In spite of high matrix suppression, the method quantification limits (MQLs) were acceptable. Therefore, the method can be used for screening known target compounds. The applicability of the method for posttarget and nontarget screening will be reported later. To preliminarily assess the quantitative performance of the method, some compounds in wastewater effluent were quantified using the standard addition method. Three pesticides and eight pharmaceuticals were found in concentrations up to ～2200 ng/L.     

Surface functionalization of nanofibrillated cellulose using click-chemistry approach in aqueous media

In the present work, amino functionalized nanofibrillated cellulose (NFC) was prepared using click-chemistry in aqueous reaction conditions. First, reactive azide groups were introduced on the surface of NFC by the etherification of 1-azido-2,3-epoxypropane in alkaline water/isopropanol-mixture at ambient temperature. Then the azide groups were reacted with propargyl amine utilizing copper catalyzed azide-alkyne cycloaddition (CuAAC), leading to pH-responsive 1,2,3-triazole-4-methanamine decorated NFC. The reaction products were characterized using Fourier transform infrared spectroscopy, elemental analysis and X-ray photoelectron spectroscopy. The presence of the attached azide groups was also confirmed by reacting them with 5-(dimethylamino)-N-(2-propyl)-1-naphthalenesulfonamide by CuAAC, yielding highly fluorescent NFC. In addition, atom force microscopy and rheology studies confirmed that the original NFC nanostructure was maintained during the synthesis.     

Lipase-Catalyzed Polyester Synthesis

Abstract

The use of lipase as biocatalyst in polyesterification of aliphatic diacids or their derivatives, and diols in an organic solvent has been discussed. We have demonstrated that bis(2-chloroethyl) esters of succinic, fumaric, and maleic acid, and bis(2,2,2-trifluoroethyl) sebacate and -dodecanedioate can be polymerized by lipase-catalyzed polytransesterification. Maleate was isomerized to fumarate even under mild reaction conditions, resulting in poly(1,4-butyl fumarate). In order to obtain a high mass-average molar mass of the polyester, solid Mucor miehei lipase was found to be the best lipase and diphenyl ether the best solvent of several investigated. There was no clear relationship with the log P value of the solvent and the polyesterification activity of lipase. The highest degree of polymerization (DP = 184) of poly(1,4-butyl sebacate) with a mass-average molar mass of 46,600 g·mol^?1 was obtained in polytransesterification of bis(2,2,2-trifluoroethyl) sebacate and 1,4-butanediol using a programmed vacuum profile. However, a mass-average molar mass as high as about 42,000 g·mol^?1 (DP = 167) was also obtained with free sebacic acid when vacuum was employed to remove the water formed during esterification. The mass average molar mass of the polyester increased with an increase in the relative quantity of lipase up to 1 g per 1.5 mmol of diacid, with an increase in the molar mass of the aliphatic diol up to 1,5-pentanediol, and with an increase in the concentration of substrates up to 0.83 M.     

The Effect of Pure Component Characteristic Parameters on Sanchez–Lacombe Equation‐of‐State Predictive Capabilities

The dependence of predictive capabilities of SL EOS on the pure characteristic parameters of monomers and polymers is investigated. A sensitivity analysis study is carried out to understand the effect of these parameters on the predictive capability of SL EOS for different α‐olefin/polyolefins systems. Among all pure component characteristic parameters, the monomer characteristic temperature (T*_monomer) has the largest impact on SL EOS predictive capability; whereas the polymer characteristic density (ρ*_polymer) is found to have the smallest impact.

     

Quenched point-to-point free energy for random walks in random potentials

We consider a random walk in a random potential on a square lattice of arbitrary dimension. The potential is a function of an ergodic environment and steps of the walk. The potential is subject to a moment assumption whose strictness is tied to the mixing of the environment, the best case being the i.i.d. environment. We prove that the infinite volume quenched point-to-point free energy exists and has a variational formula in terms of entropy. We establish regularity properties of the point-to-point free energy, and link it to the infinite volume point-to-line free energy and quenched large deviations of the walk. One corollary is a quenched large deviation principle for random walk in an ergodic random environment, with a continuous rate function.