Single‐Chain Self‐Folding of Synthetic Polymers Induced by Metal–Ligand Complexation

The controlled folding of a single polymer chain is for the first time realized by metal‐ complexation. α,ω‐Bromine functional linear polymers are prepared via activators regenerated by electron transfer (ARGET) ATRP (_,SEC = 5900 g mol⁻¹, Đ = 1.07 and 12 000 g mol⁻¹, Đ = 1.06) and the end groups of the polymers are subsequently converted to azide functionalities. A copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction is carried out in the presence of a novel triphenylphosphine ligand and the polymers to afford homotelechelic bis‐triphenylphosphine polymeric‐macroligands (MLs) (_,SEC = 6600 g mol⁻¹, Đ = 1.07, and 12 800 g mol⁻¹, Đ = 1.06). Single‐chain metal complexes (SCMCs) are formed in the presence of Pd(II) ions in highly diluted solution at ambient temperature. The results derived via ¹H and ³¹P{¹H} NMR experiments, SEC, and DLS unambiguously evidence the efficient formation of SCMCs via metal ligand complexation.

     

Comprehensive native glycan profiling with isomer separation and quantitation for the discovery of cancer biomarkers

Glycosylation is highly sensitive to the biochemical environment and has been implicated in many diseases including cancer. Glycan compositional profiling of human serum with mass spectrometry has already identified potential biomarkers for several types of cancer and diseases; however, composition alone does not fully describe glycan stereo- and regioisomeric diversity. The vast structural heterogeneity of glycans presents a formidable analytical challenge. We have developed a method to identify and quantify isomeric native glycans using nanoflow liquid chromatography (nano-LC)/mass spectrometry. A microfluidic chip packed with graphitized carbon was used to chromatographically separate the glycans. To determine the utility of this method for structure-specific biomarker discovery, we analyzed serum samples from two groups of prostate cancer patients with different prognoses. More than 300 N-glycan species (including isomeric structures) were identified, corresponding to over 100 N-glycan compositions. Statistical tests established significant differences in glycan abundances between patient groups. This method provides comprehensive, selective, and quantitative glycan profiling.     

New Amperometric Cholesterol Biosensors Using Poly(ethyleneoxide) Conducting Polymers

Accumulation of cholesterol in human blood can cause several health problems such as heart disease, coronary artery disease, arteriosclerosis, hypertension, cerebral thrombosis, etc. Therefore, simple and fast cholesterol determination in blood is clinically important. In this study, two types of amperometric cholesterol biosensors were designed by physically entrapping cholesterol oxidase in conducting polymers; thiophene capped poly(ethyleneoxide)/polypyrrole (PEO-co-PPy) and 3-methylthienyl methacrylate-co-p-vinyl benzyloxy poly(ethyleneoxide)/polypyrrole (CP-co-PPy). PEO-co-PPy and CP-co-PPy were synthesized electrochemically and cholesterol oxidase was immobilized by entrapment during electropolymerization. The amperometric responses of the enzyme electrodes were measured by monitoring oxidation current of H₂O₂ at +0.7 V in the absence of a mediator. Kinetic parameters, such as Km and Imax, operational and storage stabilities, effects of pH and temperature were determined for both entrapment supports. Km values were found as 1.47 and 5.16 mM for PEO-co-PPy and CP-co-PPy enzyme electrodes, respectively. By using these Km values, it can be observed that ChOx immobilized in PEO-co-PPy shows higher affinity towards the substrate.     

Intercalation of graphite and hexagonal boron nitride by lithium

Although graphite and hexagonal form of BN (h-BN) are isoelectronic and have very similar lattice structures, it has been very difficult to intercalate h-BN while there are hundreds of intercalation compounds of graphite. We have done a comparative first principles investigation of lithium intercalation of graphite and hexagonal boron nitride to provide clues for the difficulty of h-BN intercalation. In particular lattice structure, cohesive energy, formation enthalpy, charge transfer and electronic structure of both intercalation compounds are calculated in the density functional theory framework with local density approximation to the exchange-correlation energy. The calculated formation enthalpy of the considered forms of Li intercalated h-BN is found to be positive which rules out h-BN intercalation without externally supplied energy. Also, the Li(BN)₃ form of Li-intercalated h-BN is found to have a large electronic density of states at the Fermi level and an interlayer state that crosses Fermi level at the zone center; these properties make it an interesting material to investigate the role of interlayer states in the superconductivity of alkali intercalated layered structures. The most pronounced change in the charge distribution of the intercalated compounds is found to be charge transfer from the planar σ states to the π states.     

Entropy‐Driven Selectivity for Chain Scission: Where Macromolecules Cleave

We show that, all other conditions being equal, bond cleavage in the middle of molecules is entropically much more favored than bond cleavage at the end. Multiple experimental and theoretical approaches have been used to study the selectivity for bond cleavage or dissociation in the middle versus the end of both covalent and supramolecular adducts and the extensive implications for other fields of chemistry including, e.g., chain transfer, polymer degradation, and control agent addition are discussed. The observed effects, which are a consequence of the underlying entropic factors, were predicted on the basis of simple theoretical models and demonstrated via high‐temperature (HT) NMR spectroscopy of self‐assembled supramolecular diblock systems as well as temperature‐dependent size‐exclusion chromatography (TD SEC) of covalently bonded Diels–Alder step‐growth polymers.     

Thermomechanical and structural characterization of polybutadiene/poly(ethylene oxide)/CNT stretchable electrospun fibrous membranes

It is difficult to produce rubbery polymer nanofibers, that is, polybutadiene, by the method of electrospinning, since during electrospinning rubbery polymer fibers join and entangles due to their low T_g. For this reason, it is not easy to achieve the fiber form out of these polymers. Homogeneously electrospun carbon nanotubes (CNT)‐filled polybutadiene (PBu) and poly(ethylene oxide) (PEO) composite elastomeric fibers exhibit distinctive physical features such as uniform fiber diameter and distribution with significant improvements in thermomechanical properties. Controlled hydrophilicity/hydrophobicity with the components allows to generate homogenous, thermally stable and stretchable bio‐composite scaffold, and fibrous antibacterial membrane scaffolds out of PBu/PEO/CNT composite. We have combined the exciting properties of PEO with high pore density with the rubber elasticity of PBu via dissolving them in a dichloromethane/ethyl acetate organic solvent, and subsequently producing electrospun woven fibers with different PBu/PEO ratios. Frequency‐dependent thermomechanical characterization via dynamic mechanical analysis reveals pronounced changes in the onset and extent of melting, as well as the storage and loss modulus values at the onset of melting, in particular when small amounts (1.25% by wt%) of CNTs are present. The characteristic bands were detected for the PBu/PEO and PBu/PEO/CNT samples by means of Raman and Fourier‐transform infrared spectroscopy. CNT addition increases the hydrophobicity via the increase in roughness as attained by atomic force microscopy.     

Microwave-assisted dilute acid pretreatment of different agricultural bioresources for fermentable sugar production

Microwave-assisted pretreatment can be used for fermentable sugar production from lignocellulosic biomass. In this study, the optimum hydrolysis conditions of barley husk, oat husk, wheat bran, and rye bran were determined in power level, treatment time, solid-to-liquid ratio and dilute acid ratio as follows: 700 W, 6.92 min, 1:18.26 w/v, and 3.67% for barley husk, 600 W, 6.96 min, 1:17.22 w/v, and 3.47% for oat husk, 600 W, 6.92 min, 1:16.69 w/v, and 1.85% for wheat bran, and 460 W, 6.15 min, 1:17.14 w/v, and 2.72% for rye bran. The fermentable sugar concentrations were 37.21 (0.68 g/g), 38.84 (0.67 g/g), 49.65 (0.83 g/g), and 36.27 g/L (0.62 g/g) under optimum conditions, respectively. The results showed that microwave-assisted pretreatment is a promising technology which can be successfully implemented for the hydrolysis of lignocellulosic biomass for high sugar yield. On the other hand, hydrolysates included some inhibitors such as organic acids, furans, and phenolic compounds. Lignocellulosic biomass used in this study can be employed as good feedstocks for value-added product production in the fermentation process, after the inhibitors have been detoxified/removed with different detoxification methods.     

Multi-residue determination of organochlorine pesticides in vegetables in Kirklareli,Turkey by gas chromatography–mass spectrometry

The aim of this study was to investigate the level of organochlorine pesticides use for treatment of tomatoes, eggplants and cucumbers in Kirklareli, Turkey. Eighteen organochlorine pesticides were identified in vegetable samples using microwave or Soxhlet extraction, and results were obtained by gas chromatography–mass spectrometry. The optimized conditions were 1 mL/min for flow rate in the mobile phase, 1 μL for injection volume and 70 V for fragmentation potential. The analytical parameters show that the microwave oven extraction procedure provided the best results when compared to the Soxhlet extraction procedure. Samples were prepared for analysis with hexane?dichlormethane (1: 1, v/v, 40 mL) using a solid-phase extraction method. The limits of detection and quantitation for the eighteen analytes were between 0.02–0.26 and 0.06–0.87 μg/L, respectively, and the relative standard deviations of the migration time ranged from 2.4 to 8.9%. The recoveries of surrogate spiked in vegetable samples ranged from 70 to 116%, respectively. The obtained concentrations of pesticides in all vegetables studied were proved in the range of ND–123 μg/kg. The organochlorine pesticide sum was below the legal limit, except for Endrin and Methoxychlor, which requires a further elucidation of the organochlorine pesticides pollution sources in the region. These studies on accumulation of organochlorine pesticides were necessary for accomplishing a comprehensive ecological risk assessment.