Post‐Plasma Grafting of AEMA as a Versatile Tool to Biofunctionalise Polyesters for Tissue Engineering

In the last decade, substantial research in the field of post‐plasma grafting surface modification has focussed on the introduction of carboxylic acids on surfaces by grafting acrylic acid (AAc). In the present work, we report on an alternative approach for biomaterial surface functionalisation. Thin poly‐ε‐caprolactone (PCL) films were subjected to a dielectric barrier discharge Ar‐plasma followed by the grafting of 2‐aminoethyl methacrylate (AEMA) under UV‐irradiation. X‐ray photoelectron spectroscopy (XPS) confirmed the presence of nitrogen. The ninhydrin assay demonstrated, both quantitatively and qualitatively, the presence of free amines on the surface. Confocal fluorescence microscopy (CFM), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to visualise the grafted surfaces, indicating the presence of pAEMA. Static contact angle (SCA) measurements indicated a permanent increase in hydrophilicity. Furthermore, the AEMA grafted surfaces were applied for comparing the physisorption and covalent immobilisation of gelatin. CFM demonstrated that only the covalent immobilisation lead to a complete coverage of the surface. Those gelatin‐coated surfaces obtained were further coated using fibronectin. Osteosarcoma cells demonstrated better cell‐adhesion and cell‐viability on the modified surfaces, compared to the pure PCL films.

     

Synthesis and NMR Analysis in Solution of Oligo(3‐hydroxyalkanoic acid) Derivatives with the Side Chains of Alanine,Valine, and Leucine (β‐Depsides): Coming Full Circle from PHB to β‐Peptides to PHB

Oligomers of 3‐hydroxyalkanoic acids that contain two, three, and six residues with and without O‐terminal (tBu)Ph₂Si and C‐terminal PhCH₂ protection have been synthesized in such a way that the side chains on the oligoester backbone were those of the proteinogenic amino acids Ala (Me), Val (CHMe₂), and Leu (CH₂CHMe₂). The enantiomerically pure 3‐hydroxyalkanoates were obtained by Noyori hydrogenation of the corresponding 3‐oxo‐alkanoates with [Ru((R)‐binap)Cl₂](binap=2,2′bis(diphenylphosphanyl)‐1,1′‐binaphthalene)/H₂ (Scheme 1), and the coupling was achieved under the conditions (pyridine/(COCl)₂, CH₂Cl₂, −78°) previously employed for the synthesis of various oligo(3‐hydroxybutanoic acids) (Schemes 2 and 3). The Cotton effects in the CD spectra of the new oligoesters provided no hints about chiral conformation (cf. a helix) in MeOH, MeCN, octan‐1‐ol, or CF₃CH₂OH solutions (Figs. 1 and 2). Detailed NMR investigations in CDCl₃ solution (Figs. 3–6, and Tables 1–5) of the hexa(3‐hydroxyalkanoic acid) with the side chains of Val (HC), Ala (HB), Leu (HH), Val, Ala, Leu (from O‐ to C‐terminus; 3 ) gave, on the NMR time‐scale, no evidence for the presence of any significant amount of a 2₁‐ or a 3₁‐helical conformation, comparable to those identified in stretched fibers of poly[(R)‐3‐hydroxybutanoic acid], or in lamellar crystallites and in single crystals of linear and cyclic oligo[(R)‐3‐hydroxybutanoic acids], or in the corresponding β‐peptide(s) (the oligo(3‐aminoalkanoic acid) analogs; 1 – 3 ). Thus, the extremely high flexibility (averaged or ‘random‐coil' conformation) of the polyester chain (CO−O rotational barrier ca. 13 kcal/mol; no hydrogen bonding), as compared to polyamide chains (CO−NH barrier ca. 18 kcal/mol; hydrogen bonding) has been demonstrated once again. The possible importance of this structural flexibility, which goes along with amphiphilic properties, for the role of PHB in biology, in evolution, and in prebiotic chemistry is discussed. Structural similarities of natural potassium‐channeling proteins and complexes of oligo(3‐hydroxybutanoates) with Na⁺, K⁺, or Ba²⁺ are alluded to (Figs. 7–9).     

Perovskite Oxide as A New Platform for Efficient Electrocatalytic Nitrogen Oxidation

Electrocatalytic nitrogen oxidation reaction (NOR) offers an efficient and sustainable approach for conversion of widespread nitrogen (N₂) into high-value-added nitrate (NO₃⁻) under mild conditions, representing a promising alternative to the traditional approach that involves harsh Haber–Bosch and Ostwald oxidation processes. Unfortunately, due to the weak absorption/activation of N₂ and the competitive oxygen evolution reaction, the kinetics of NOR process is extremely sluggish accompanied with low Faradaic efficiencies and NO₃⁻ yield rates. In this work, an oxygen-vacancy-enriched perovskite oxide with nonstoichiometric ratio of strontium and ruthenium (denoted as Sr_0.9RuO₃) was synthesized and explored as NOR electrocatalyst, which can exhibit a high Faradaic efficiency (38.6 %) with a high NO₃⁻ yield rate (17.9 μmol mg⁻¹ h⁻¹). The experimental results show that the amount of oxygen vacancies in Sr_0.9RuO₃ is greatly higher than that of SrRuO₃, following the same trend as their NOR performance. Theoretical simulations unravel that the presence of oxygen vacancies in the Sr_0.9RuO₃ can render a decreased thermodynamic barrier toward the oxidation of *N₂ to *N₂OH at the rate-determining step, leading to its enhanced NOR performance.     

Improvement of HS-SPME for analysis of volatile organic compounds (VOC) in water samples by simultaneous direct fiber cooling and freezing of analyte solution

The sensitivity and precision of headspace solid-phase micro extraction (HS-SPME) at an analyte solution temperature (T _as) of +35 °C and a fiber temperature (T _fiber) of +5 °C were compared with those for HS-SPME at T _as and T _fiber of −20 °C for analysis of the volatile organic compounds benzene, 1,1,1-trichloroethane, trichloroethylene, toluene, o-xylene, ethylbenzene, m/p-xylene, and tetrachloroethylene in water samples. The effect of simultaneous fiber cooling and analyte solution freezing during extraction was studied. The compounds are of different hydrophobicity, with octanol/water partition coefficients (Kow) ranging from 126 and 2511. During a first set of experiments the polydimethylsiloxane (PDMS) SPME fiber was cooled to +5 °C with simultaneous heating of the aqueous analyte solution to +35 °C. During a second set of experiments, both SPME fiber holder and samples were placed in a deep freezer maintained at −20 °C for a total extraction time of 30 min. After approximately 2 min the analyte solution in the vial began to freeze from the side inwards and from the bottom upwards. After approximately 30 min the solution was completely frozen. Analysis of VOC was performed by coupling HS-SPME to gas chromatography-mass spectrometry (GC-MS). In general, i.e. except for tetrachloroethylene, the sensitivity of HS-SPME increased with increasing compound hydrophobicity at both analyte solution and fiber temperatures. At T _as of +35 °C and T _fiber of +5 °C detection limits of HS-SPME were 0.5 μg L⁻¹ for benzene, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene, 0.125 μg L⁻¹ for toluene, and 0.025 μg L⁻¹ for ethylbenzene, m/p-xylene, and o-xylene. In the experiments with T _as and T _fiber of −20 °C, detection limits were reduced for compounds of low hydrophobicity (Kow<501), for example benzene, toluene, 1,1,1-trichloroethane, and trichloroethylene. In the concentration range 0.5–62.5 μg L⁻¹, the sensitivity of HS-SPME was enhanced by a factor of approximately two for all compounds by performing the extraction at −20 °C. A possible explanation is that freezing of the water sample results in higher concentration of the target compounds in the residual liquid phase and gas phase (freezing-out), combined with enhanced adsorption of the compounds by the cooled fiber. The precision of HS-SPME, expressed as the relative standard deviation and the linearity of the regression lines, is increased for more hydrophobic compounds (Kow>501) by simultaneous direct fiber cooling and freezing of analyte solution. Background contamination during analysis is reduced significantly by avoiding the use of organic solvents.     

A polynomial time approximation algorithm for the two-commodity splittable flow problem

We consider a generalization of the unsplittable maximum two-commodity flow problem on undirected graphs where each commodity ${i \in \{1, 2\}}$ can be split into a bounded number k _i of equally-sized chunks that can be routed on different paths. We show that in contrast to the single-commodity case this problem is NP-hard, and hard to approximate to within a factor of α > 1/2. We present a polynomial time 1/2-approximation algorithm for the case of uniform chunk size over both commodities and show that for even k _i and a mild cut condition it can be modified to yield an exact method. The uniform case can be used to derive a 1/4-approximation for the maximum concurrent (k ₁, k ₂)-splittable flow without chunk size restrictions for fixed demand ratios.