Novel C2-symmetric macrocycles bearing diamide-diester groups: synthesis and enantiomeric recognition for primary alkyl ammonium salts

We synthesized a series of novel macrocycles with diamide-diester groups (S,S)-1, (S,S)-2, (S,S)-3, and (R,R)-1, derived from dimethyloxalate and amino alcohols by high dilution technique, and evaluated enantiomeric recognition properties of these macrocycles toward primary alkyl ammonium salts by 1H NMR titration. Taking into account the host employed, important differences were observed in the Ka values of (R)-Am and (S)-Am for (S,S)-1 and (R,R)-1 hosts, KS/KR = 5.55 and KR/KS = 3.65, Delta Delta Go = 0.43 and -0.32 kJ mol-1, respectively. There seems a general tendency for the host to include the guests with the same absolute configuration.     

Thermal Analysis of Micro- and Nano-Lignocellulosic Reinforced Styrene Maleic Anhydride Composite Foams

The aim of this study was to measure the thermal properties of foamed nano/macro filler–reinforced styrene maleic anhydride (SMA) composites. SMA (66%) as a polymer matrix (10% maleic anhydride content) and various fillers including wood flour, starch, α-cellulose, microcrystalline cellulose and cellulose nanofibrils as reinforcing agents (30%) and lubricant (4%) were used to manufacture the composites in a twin-screw extruder. According to the thermogravimetric analysis (TGA) results, thermal degradation of all the foamed composites was found to be lower than that of SMA composites. The storage modulus values were negatively affected with a second time foaming (reprocessing [recycling] the initially processed composites a second time), as were loss modulus and T_g. As a result, second-time-foamed composite modulus values were lower than those of the foamed composites. According to the melt flow index (MFI) results, viscosity of the SMA was found to increase with the addition of fillers.     

Investigation of proton conductivity of anhydrous proton exchange membranes prepared via grafting vinyltriazole onto alkaline‐treated PVDF

This work uses a simple “grafting through” approach in the preparation of anhydrous poly(vinylidene fluoride) (PVDF)‐g‐PVTri polymer electrolyte membranes (PEMs). Alkaline‐treated PVDF was used as a macromolecule in conjunction with vinyltriazole in the graft copolymerization. The obtained polymer was subsequently doped with triflic acid (TA) at different stoichiometric ratios with respect to triazole units and the anhydrous PEMs (PVDF‐g‐PVTri‐(TA)_x) were prepared. All samples were characterized by FTIR and ¹H NMR. The composition of PVDF‐g‐PVTri was determined by energy dispersive spectroscopy. Thermal properties of the membranes were examined by thermogravimetric analysis and differential scanning calorimetry. The surface roughness and morphology of the membranes were studied using atomic force microscopy, X‐ray diffraction, and scanning electron microscopy. PVDF‐g‐PVTri‐(TA)₃ (C3‐TA₃) with a degree of grafting of 47.22% showed a maximum proton conductivity of 0.09 S cm^?1 at 150 °C and anhydrous conditions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1885–1897     

Voltammetric methods of reboxetine analysis and the mechanism of its electrode reactions

Reboxetine (RBX) electrochemical redox behavior at hanging mercury drop (HMDE) and glassy carbon electrodes (GCE) was studied in various pH Britton-Robinson universal buffers using cyclic voltammetry and square-wave voltammetry. RBX was reduced at the HMDE and oxidized at the GCE with reversible adsorption controlled and irreversible diffusion controlled processes respectively. The anodic peak is due to the amine and the cathodic peak may correspond to oxygen protonation. An oxidation reaction mechanism is proposed. The linear relation between peak currents and RBX concentration allowed simple, sensitive, precise and inexpensive voltammetric procedures to be developed. The limit of detection was 0.04 µM RBX. The procedures were successfully applied to human urine and RBX tablet assay. Therapeutic RBX concentrations in human serum were not detected due to strong drug-protein binding. Using bovine serum albumin, the methods were used to investigate the effect of serum protein binding on RBX determination.      

Solvatochromic rotaxane molecular shuttles

A strongly fluorescent bistable rotaxane is described in which the relative position of the macrocyclic ring with respect to a solvatochromic fluorophore gives a strong response in the spectral domain.     

Poly(p‐phenylene methylene)‐based block copolymers by mechanistic transformation

The synthesis of poly(p‐phenylene methylene) (PPM)‐based block copolymers such as poly(p‐phenylene methylene)‐b‐poly(ε‐caprolactone) and poly(p‐phenylene methylene)‐b‐polytetrahydrofuran by mechanistic transformation was described. First, precursor PPM was synthesized by acid‐catalyzed polymerization of tribenzylborate at 16 °C. Then, this polymer was used as macroinitiators in either ring‐opening polymerization of ε‐caprolactone or cationic ring‐opening polymerization of tetrahydrofuran to yield respective block copolymers. The structures of the prepolymer and block copolymers were characterized by GPC and ¹H NMR investigations. The composition of block copolymers as determined by ¹H NMR and TGA analysis was found to be in very good agreement. The thermal behavior and surface morphology of the copolymers were also investigated, respectively, by differential scanning calorimetry and atomic force microscopy measurements, and the contribution of the major soft segment has been observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Quantitative and sensitive detection of rare mutations using droplet-based microfluidics

Somatic mutations within tumoral DNA can be used as highly specific biomarkers to distinguish cancer cells from their normal counterparts. These DNA biomarkers are potentially useful for the diagnosis, prognosis, treatment and follow-up of patients. In order to have the required sensitivity and specificity to detect rare tumoral DNA in stool, blood, lymph and other patient samples, a simple, sensitive and quantitative procedure to measure the ratio of mutant to wild-type genes is required. However, techniques such as dual probe TaqMan(?) assays and pyrosequencing, while quantitative, cannot detect less than ～1% mutant genes in a background of non-mutated DNA from normal cells. Here we describe a procedure allowing the highly sensitive detection of mutated DNA in a quantitative manner within complex mixtures of DNA. The method is based on using a droplet-based microfluidic system to perform digital PCR in millions of picolitre droplets. Genomic DNA (gDNA) is compartmentalized in droplets at a concentration of less than one genome equivalent per droplet together with two TaqMan(?) probes, one specific for the mutant and the other for the wild-type DNA, which generate green and red fluorescent signals, respectively. After thermocycling, the ratio of mutant to wild-type genes is determined by counting the ratio of green to red droplets. We demonstrate the accurate and sensitive quantification of mutated KRAS oncogene in gDNA. The technique enabled the determination of mutant allelic specific imbalance (MASI) in several cancer cell-lines and the precise quantification of a mutated KRAS gene in the presence of a 200,000-fold excess of unmutated KRAS genes. The sensitivity is only limited by the number of droplets analyzed. Furthermore, by one-to-one fusion of drops containing gDNA with any one of seven different types of droplets, each containing a TaqMan(?) probe specific for a different KRAS mutation, or wild-type KRAS, and an optical code, it was possible to screen the six common mutations in KRAS codon 12 in parallel in a single experiment.     

Fast and stable photochromic oxazines for fluorescence switching

The stringent limitations imposed by diffraction on the spatial resolution of fluorescence microscopes demand the identification of viable strategies to switch fluorescence under optical control. In this context, the photoinduced and reversible transformations of photochromic compounds are particularly valuable. In fact, these molecules can be engineered to regulate the emission intensities of complementary fluorophores in response to optical stimulations. On the basis of this general design logic, we assembled a functional molecular construct consisting of a borondipyrromethene fluorophore and a nitrospiropyran photochrome and demonstrated that the emission of the former can be modulated with the interconversion of the latter. This fluorophore-photochrome dyad, however, has a slow switching speed and poor fatigue resistance. To improve both parameters, we developed a new family of photochromic switches based on the photoinduced opening and thermal closing of an oxazine ring. These compounds switch back and forth between ring-closed and -open isomers on nanosecond-microsecond timescales and tolerate thousands of switching cycles with no sign of degradation. In addition, the attachment of appropriate chromophoric fragments to their switchable oxazine ring can be exploited to either deactivate or activate fluorescence reversibly in response to illumination with a pair of exciting beams. Specifically, we assembled three dyads, each based on either a borondipyrromethene or a coumarin fluorophore and an oxazine photochrome, and modulated their fluorescence in a few microseconds with outstanding fatigue resistance. The unique photochemical and photophysical properties of our fluorophore-photochrome dyads can facilitate the development of switchable fluorophores for superresolution imaging and, ultimately, provide valuable molecular probes for the visualization of biological samples on the nanometer level.     

In vitro antiprotozoal activity of extracts of five Turkish Lamiaceae species

The in vitro antiprotozoal activities of crude methanolic extracts from the aerial parts of five Lamiaceae plants (Salvia tomentosa, S. sclarea, S. dichroantha, Nepeta nuda subsp. nuda and Marrubium astracanicum subsp. macrodon) were evaluated against four parasitic protozoa, i.e. Trypanosoma brucei rhodesiense, T. cruzi, Leishmania donovani and Plasmodium falciparum. The cytotoxic potentials of the extracts on L6 cells were also evaluated. Melarsoprol, benznidazole, miltefosine, chloroquine and podophyllotoxin were used as reference drugs. All crude MeOH extracts showed antiprotozoal potential against at least three parasites, so they were dispersed in water and partitioned against n-hexane and chloroform to yield three subextracts that were screened in the same test systems. The n-hexane extract of N. nuda was the most active against T. brucei rhodesiense while the CHCl3 extracts of S. tomentosa and S. dichroantha showed significant activity against L. donovani. All organic extracts displayed in vitro antimalarial and moderate trypanocidal activities against T. cruzi with the n-hexane extract of S. sclarea being the most active against the latter. The extracts displayed low or no cytotoxicity towards mammalian L6 cells.