Solvent colorimetric paper-based polydiacetylene sensors from diacetylene lipids

A well known unique property of polydiacetylenes (PDAs) is the colorimetric response to external stimuli making it one of the most studied conjugated polymers for sensing applications. Here we report the synthesis of a novel series of diacetylene acids from the condensation of pentacosa-10,12-diynylamine (PCDAmine) and dicarboxylic acid or its anhydrides. One of these diacetylene lipids, 4-(pentacosa-10,12-diynylamino)-4-oxobutanoic acid (PCDAS), is used in combination with pentacosa-10,12-diynoic acid (PCDA) for dropcasting on pieces of filter paper which are consequently irradiated by UV light to generate a paper based sensor array for solvent detection and identification. Upon the exposure to various types of organic solvents, the blue colored sensors colorimetrically respond to give different shades of colors between blue to red. The color patterns of the sensor array are recorded as RedGreenBlue (RGB) values and statistically analyzed by principal component analysis (PCA). The PCA score plot reveals that the array is capable of identifying eleven common organic solvents.     

Treatment of oxidized cellulose fabric with chitosan and its surface activity towards anionic reactive dyes

The surface modification of cellulose fabric with chitosan was achieved through an oxidation of the fabric with KIO₄ followed by reductive ammination with chitosan. The chitosan content in the fabric determined by Kjeldahl nitrogen analysis technique was 1.69%. The scanning electron micrograph revealed submicron particles of chitosan attached on the fabric surface. Dyeing of the modified fabrics with mono-chloro-triazine and vinyl sulfone anionic reactive dyes, showed vastly improved exhaustion and color yield (K/S) indicating that this method of surface modification is effective for changing surface activity of the fabric. The enhancement of the dye uptake brought about an improved dyeing process in which the dye and salt used could be reduced by half and 14%, respectively. A Significant drop in burst strength upon the oxidation but no discernable adverse color fastness property was observed for the chitosan-modified fabric.     

Investigation of the carrier saturation in facilitated transport of unsaturated hydrocarbons

Single-component facilitated transports of ethylbenzene, styrene, cyclohexene and 1-hexene were carried out using the feed concentrations ranging from 0.5 M to pure. Equilibrium constants of the Ag⁺-solute complex formation, determined by distribution method, were 0.7, 2.2, 32.0, 129.1 M⁻¹, respectively. Carrier saturation was not found with the membrane incorporated with 2.67 M Ag⁺-ion. As the carrier concentration was reduced to 0.51 M, increase in the feed concentration beyond 4.5 M had very little effect on ethylbenzene flux, suggesting the onset of carrier saturation. Styrene and cyclohexene underwent the carrier saturation when the carrier loading was 0.25 M, while a complete saturation was not observed with 1-hexene. Extraction of solute from the membranes revealed that less than 50% of Ag⁺-ions were occupied when the carrier saturation occurred. It was also found that the ability of solute to use available Ag⁺-ions in the membrane was dependent on the equilibrium constant.     

Novel synthetic route to 1,4-dihydropyridines from β-amino acrylates by using titanium(IV) chloride under facile conditions

The reactions of Boc-β-amido- and β-amino acrylates, in which the CC possesses both nucleophilic and electrophilic sites, were investigated under acidic conditions. The trifluoroacetic-acid induced cyclization of the β-amido acrylates to the corresponding oxazolidin-2-ones involves a rarely seen nucleophilic attack of the carbamate carbonyl group. The cyclotrimerization of β-amino acrylates to N-substituted 1,4-dihydropyridines was observed in the presence of a Lewis acid. High yields of 1,4-dihydropyridines (70–83%) were readily obtained by using substoichiometric amount TiCl₄ under mild condition. The cyclotrimerization is presumably occurring via a Hantzsch related mechanism involving three addition/elimination reactions of the amphiphilically reactive CC.     

Direct synthesis of oxazolidin-2-ones from tert-butyl allylcarbamate via halo-induced cyclisation

A novel synthetic pathway towards the 2-oxazolidinone derivatives involving the halo-induced cyclisation of tert-butyl allyl(phenyl)carbamate was successfully developed. Various halogenating reagents were evaluated under different reaction conditions for the reaction optimisation. Interestingly, the synthetic route to 2-oxazolidinone derivatives containing one halogen atom in the aliphatic site or two halogen atoms including the extra halogen atom substituted in the aryl group at the para position, were thoroughly established for all chloro-, bromo- and iodo compounds. Either halo-unsubstituted-aryl oxazolidinone or p-halo-substituted-aryl oxazolidinone could be selectively produced by selecting the appropriate choices of halogenated reagents and reaction conditions e.g. reaction time and temperature. Toloxatone, a commercial antidepressant, was successfully synthesized by using this developed method.     

Selective fluorescent sensor for mercury ions in aqueous media using a 1,4-dihydropyridine derivative

Novel 1,4-dihydropyridine (DHP) derivatives containing 3 carboxylic acid units are synthesized via cyclotrimerization of N-substituted β-aminoacrylates followed by basic hydrolysis of the triester. These DHP derivatives are readily soluble in aqueous media buffered at pH 8.0 and the solutions give blue fluorescent signals with quantum yields of 7–23%. One of these compounds, bearing a p-methoxyphenyl N-substituted group, shows specific fluorescent quenching with the mercuric ion (Hg²⁺). The fluorescent signal of the DHP derivative decays over a period of minutes to hours depending on the Hg²⁺ concentration, which implies that the sensing mechanism involves chemical reaction between the Hg²⁺ ion and the DHP compound. The ¹H NMR and MS data suggest that Hg²⁺ mediates the oxidation of the DHP ring into a pyridinium ring. The event is useful for fluorescent detection of Hg²⁺ at the micromolar level within 30 min, with a detection limit of 0.2 μM in aqueous medium.     

Reaction Mechanism of Methanol to Formaldehyde over Fe‐ and FeO‐Modified Graphene

We employed periodic DFT calculations (PBE‐D2) to investigate the catalytic conversion of methanol over graphene embedded with Fe and FeO. Two possible pathways of dehydrogenation to formaldehyde and dehydration to dimethyl ether (DME) over these catalysts were examined. Both processes are initiated with the activation of methanol over the catalytic center through O?H cleavage. As a result, a methoxo‐containing intermediate is formed. Subsequently, H‐transfer from the methoxy to the adjacent ligand leads to the formation of formaldehyde. Conversely, the activation of the second methanol over the intermediate gives DME and H₂O. Over Fe/graphene, the dehydration process is kinetically and thermodynamically preferable. Unlike Fe/graphene, FeO/graphene is predicted to be an efficient catalyst for the dehydrogenation process. Oxidative dehydrogenation over FeO/graphene takes place through two steps with free energy barriers of 5.7 and 10.2 kcal mol^?1.