Andreas S. Kalogirou

PVP-crosslinked electrospun membranes with embedded Pd and Cu2O nanoparticles as effective heterogeneous catalytic supports

Palladium(0) (Pd) and copper(I) oxide (Cu2O) nanoparticles (NPs) were successfully embedded in electrospun polyvinylpyrrolidone (PVP) fibrous membranes. The fabrication process involved the synthesis of stable, PVP-capped Pd and Cu2O colloidal hybrid solutions in methanol that on subsequent electrospinning afforded PVP–Pd and PVP–Cu2O fibrous mats. The morphology of the as-prepared nanocomposite fibers was characterised using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM revealed the presence of bead-free, cylindrical fibers with diameters in the submicrometer range while TEM revealed the presence of spherical Pd and Cu2O NPs with diameters below 10 nm that were evenly distributed within the fibers. Thermal treatment of the PVP–Pd and the PVP–Cu2O membranes afforded crosslinked fibrous mats as supported by SEM. Furthermore, the presence of homogeneously distributed Pd and Cu2O NPs within the crosslinked polymer fibers was confirmed by HRTEM/EDX analyses. The above-mentioned nanocomposite fibers demonstrated high catalytic efficacy as heterogeneous catalytic supports in Heck, Suzuki (PVP–Pd) and click (PVP–Cu2O) reactions. Finally, the reusability of the membranes was briefly investigated with up to three consecutive runs being effective.

4H-1,2,6-Thiadiazin-4-one-containing small molecule donors and additive effects on their performance in solution-processed organic solar cells

The optical, electrochemical, morphological and transport properties of a series of thiadiazinone (acceptor) and (thienyl)carbazoles (donor) containing π-extended donor–acceptor–donors (D–A–D) are presented. Systematic variations in the number of the thienyl units, the choice of branched or straight alkyl side chains and the use of a processing additive demonstrate their use as electron donors in bulk heterojunction solar cells blended with fullerene acceptors. The best power conversion efficiency (PCE) of 2.7% is achieved by adding to the D–A–D 3 : fullerene blend a polydimethylsiloxane (PDMS) additive, that improves the morphology and doubles the hole mobility within the D–A–D : fullerene blend.

Ring transformation of (4-chloro-5H-1,2,3-dithiazol-5-ylidene)acetonitriles to 3-haloisothiazole-5-carbonitriles

Ring transformation of readily prepared (4-chloro-5H-1,2,3-dithiazol-5-ylidene)acetonitriles afford 3-haloisothiazole-5-carbonitriles in good to excellent yields. The transformation can be mediated using HBr (g), HCl (g) or BnEt3NCl. Mechanisms for the transformations are discussed, together with rationalizations for the formation of side products. Furthermore, single crystal X-ray structures are provided for (Z)-2-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)acetonitrile and (E)-2-bromo-2-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)acetonitrile confirming the stereochemistry of the exocyclic ethene bond.

Synthesis of N-Aryl-3,5-dichloro-4H-1,2,6-thiadiazin-4-imines from 3,4,4,5-Tetrachloro-4H-1,2,6-thiadiazine.

Condensation of 3,4,4,5-tetrachloro-4H-1,2,6-thiadiazine with a range of anilines gave 22 N-aryl-3,5-dichloro-4H-1,2,6-thiadiazin-4-imines in 43-96% yields. The scope and limitations of this condensation are briefly investigated. Furthermore, mono- and bis-substitution of the C-3 and C-5 chlorines of 3,5-dichloro-N-phenyl-4H-1,2,6-thiadiazin-4-imine by amine and alkoxide nucleophiles is explored. Finally, Stille coupling chemistry is used to prepare several N-phenyl-3,5-diaryl-4H-1,2,6-thiadiazin-4-imines.

A Qualitative Comparison of the Reactivities of 3,4,4,5-Tetrachloro-4H-1,2,6-thiadiazine and 4,5-Dichloro-1,2,3-dithiazolium Chloride

The high yielding transformations of 3,4,4,5-tetrachloro-4H-1,2,6-thiadiazine into 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (up to 85%) and 2-(3,5-dichloro-4H-1,2,6-thiadiazin-4-ylidene)malononitrile (up to 83%) have been investigated and compared to the analogous transformations of the closely-related 4,5-dichloro-1,2,3-dithiazolium chloride (Appel’s salt) into 4-chloro-5H-1,2,3-dithiazol-5-one and 2-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)malononitrile. Furthermore, cyclocondensation of 3,4,4,5-tetrachloro-4H-1,2,6-thiadiazine with 2-aminophenol and 1,2-benzenediamines gave fused 4H-1,2,6-thiadiazines in 68%–85% yields.

Spectroscopic characterization of C-4 substituted 3,5-dichloro-4H-1,2,6-thiadiazines

Three 3,5-dichloro-4H-1,2,6-thiadiazines, which differ according to the electron withdrawing nature of their substituent at C-4: (a) 3,5-dichloro-4-methylene-4H-1,2,6-thiadiazine (5a), (b) 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (5b) and (c) 2-(3,5-dichloro-4H-1,2,6-thiadiazin-4-ylidene)malononitrile (5c), are characterized using resonance Raman (RR), absorption (UV/vis) and photoluminescence (PL) spectroscopies. These weakly aromatic and electron-deficient heterocycles are potential components as acceptors in donor–acceptor systems for organic electronics. Experimental results, which include the synthesis, characterization and single crystal X-ray structure of 3,5-dichloro-4-methylene-4H-1,2,6-thiadiazine (5a), combined with theoretical calculations of their orbitals and vibrational frequencies, provide an understanding of the optical properties, on the basis of molecular geometry and electron distribution.

4H-1,2,6-Thiadiazine-containing donor–acceptor conjugated polymers: synthesis, optoelectronic characterization and their use in organic solar cells

π-Conjugated donor–acceptor (D–A) polymers containing electron withdrawing non-S-oxidized 4H-1,2,6-thiadiazines and electron donating (het)aryl-substituted indacenodithiophenes (IDTs) were prepared and used in organic solar cell (OSC) devices with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the fullerene acceptor. The non-S-oxidized 4H-1,2,6-thiadiazine containing polymers were wide bandgap absorbers (Eoptg 1.80–1.95 eV) with low-lying highest occupied molecular orbital energy levels (EHOMO −5.5 to −6.1 eV) affording high open circuit voltages (Vocs 0.82–0.96 V) for polymer:fullerene bulk heterojunction (BHJ) OSCs. Owing to enhanced short circuit currents (Jscs) and fill factors (FFs), the 1,2,6-thiadiazin-4(H)-one-based polymers had significantly higher performances (up to 3.83%) vs. the N-(perfluorophenyl)-1,2,6-thiadiazin-4(H)-imine based-polymers (up to 1.37%).

The Reaction of 4,5-Dichloro-1,2,3-dithiazolium Chloride with Sulfimides: A New Synthesis of N-Aryl-1,2,3-dithiazolimines

N-Aryl-S,S-dimethylsulfimides 3 (Ar = 4-NO2C6H4), 4 (Ar = Ph) and 5 (Ar = 4-Tol) react with Appel salt 1 to give the corresponding N-aryl-(4-chloro-5H-1,2,3-dithiazolylidene)benzenamines 8 (Ar = 4-NO2C6H4), 9 (Ar = Ph) and 10 (Ar = 4-Tol) in 84, 94 and 87% yields, respectively. The reaction proceeds in the absence of base and a proposed reaction mechanism is given.

1,2,6-Thiadiazinones as Novel Narrow Spectrum Calcium/Calmodulin-Dependent Protein Kinase Kinase 2 (CaMKK2) Inhibitors.

We demonstrate for the first time that 4H-1,2,6-thiadiazin-4-one (TDZ) can function as a chemotype for the design of ATP-competitive kinase inhibitors. Using insights from a co-crystal structure of a 3,5-bis(arylamino)-4H-1,2,6-thiadiazin-4-one bound to calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2), several analogues were identified with micromolar activity through targeted displacement of bound water molecules in the active site. Since the TDZ analogues showed reduced promiscuity compared to their 2,4-dianilinopyrimidine counter parts, they represent starting points for development of highly selective kinase inhibitors.

Evaluation of PVP/Au Nanocomposite Fibers as Heterogeneous Catalysts in Indole Synthesis.

Electrospun nanocomposite fibers consisting of crosslinked polyvinylpyrrolidone (PVP) chains and gold nanoparticles (Au NPs) were fabricated, starting from highly stable PVP/Au NP colloidal solutions with different NP loadings, followed by thermal treatment. Information on the morphological characteristics of the fibers and of the embedded Au NPs was obtained by electron microscopy. Cylindrical, bead-free fibers were visualized by Scanning Electron Microscopy (SEM) while Transmission Electron Microscopy (TEM) and Energy Diffraction X-ray (EDX) analysis supported the presence of Au NPs within the fibers and gave information on their morphologies and average diameters. These materials were briefly evaluated as heterogeneous catalytic supports for the gold-catalyzed intramolecular cyclisation of 2‑(phenylethynyl)aniline to form 2-phenyl-1H-indole. The performance of the gold catalyst was strongly dependent on the Au NP size, with the system containing the smallest Au NPs being the more effective. Moreover, a slight drop of their catalytic efficiency was observed after three consecutive reaction runs, which was attributed to morphological changes as a consequence of fiber merging.