Serkan Yeşilot

Separation and mesogenic properties of tetraalkoxy-substituted phthalocyanine isomers

The main aim of this paper is to describe the separation and properties of four possible structural isomers of non-peripherally substituted nickel(II) phthalocyanine. Two isomers (C4h and D2h) of this compound were separated by preparative thin layer chromatography; however the other two isomers (C2v and Cs) were separated by HPLC only with an analytical chiral column. The individual isomers and symmetry were assigned on the basis of the 1H NMR signals of the aromatic protons of the phthalocyanine ring system. The pure C4h isomer exhibited liquid crystalline properties at room temperature while the isomeric mixture containing four structural isomers was liquid. The other three isomers were liquid under the same conditions. The mesogenic properties of pure C4h isomer were determined by differential scanning calorimetry, optical polarizing microscopy and X-ray diffractometry. This is the first report of the separation of a liquid crystalline pure isomer in the field of phthalocyanine chemistry.

Azole substituted polyphosphazenes as nonhumidified proton conducting membranes

Novel nonhumidified proton conducting membranes have been prepared from the reactions of triazole (Tri) and aminotriazole (Atri) compounds with poly[(4-methylphenoxy)chlorophosphazene] (PMPCP). The composition of the novel polymers (TriP and AtriP) was verified by elemental analysis (EA) and the structure was characterized by FT-IR, 1H and 31P NMR. Size exclusion chromatography was used to confirm the polymer formation. Thermogravimetric analysis (TGA) showed that the samples are thermally stable up to approximately 150 °C. Differential scanning calorimetry (DSC) results illustrated the homogeneity of the materials. To obtain sufficient proton conductivity at high temperatures in the anhydrous state, the polymers were doped with trifluoromethanesulfonic acid (TA) at various molar ratios, x = 0.5, 1, 2 and 3 with respect to the azole unit. The proton conductivity of the polymer electrolytes was measured using high resolution dielectric-impedance analyzer. The proton conductivity of these materials increased with dopant concentration and temperature. Maximum proton conductivity of TriP2TA and AtriP2TA were obtained as 3 × 10−3 S cm−1 at 50 °C and 0.0412 S cm−1 at 130 °C respectively, in the anhydrous state.

Absolute structure determination as a reference for the enantiomeric resolution of racemic mixtures of cyclophosphazenes via chiral high-performance liquid chromatography

Reversed-phase chiral high-performance liquid chromatography (HPLC) is a potentially powerful technique for the enantiomeric resolution of racemic mixtures, although the elution order of enantiomers is only relative and it is necessary to fully characterize reference systems for this method to provide absolute configurational information. The enantiomeric resolution of a series of racemic di-spiro cyclotriphosphazene derivatives, N3P3X2[O(CH2)(3)NH]2 (X = Cl, Ph, SPh, NHPh, OPh) [(1)-(5), respectively] was carried out by reversed-phase chiral HPLC on a commercially available Pirkle-type chiral stationary phase (R,R)-Whelk-01 using 85:15 (v/v) hexane-thf as the mobile phase. The absolute configurations of the resulting enantiomers of compounds (3) (X = SPh) and (5) (X = OPh) were determined unambiguously by X-ray crystallography. For both (3) and (5) it was found that the SS enantiomer eluted before the RR enantiomer, indicating a convenient method to determine the absolute configurations of enantiomers of this series of cyclophosphazene derivatives and providing the first set of enantiomeric reference compounds for cyclophosphazene derivatives. These structures demonstrate an interesting anomaly in that the pair of enantiomers of (3) crystallize in enantiomorphically paired space groups whilst, under the same conditions, the solid-state forms of the enantiomers of (5) form structures in Sohncke space groups that are not enantiomorphous.

Energy-transfer studies on phthalocyanine–BODIPY light harvesting pentad by laser flash photolysis

A molecular pentad, comprised of zinc phthalocyanine (ZnPc) with four boron dipyrromethene units (BODIPY) have been examined by femtosecond and nanosecond laser flash photolysis to explore its photoinduced intramolecular events from the excited BODIPY. The geometry optimization showed that the phthalocyanine moiety is completely symmetric and form perfect square planar complex with zinc. The absorption spectrum of ZnPc-BODIPY pentad covers most of the visible region (ca. 300–750 nm), which clearly is an advantage for capturing solar energy. The excitation transfer from the singlet BODIPY to ZnPc is envisioned due to good spectral overlap of the BODIPY emission and ZnPc absorption spectra. Femtosecond laser flash photolysis studies provided concrete evidence for the occurrence of energy transfer from the singlet excited BODIPY to ZnPc in tetrahydrofuran. The kinetic study of energy transfer measured by monitoring the decay of the BODIPY emission revealed fast energy transfer (5.90 × 1010 s-1) in the molecular pentad. Since the electron transfer from the singlet ZnPc to BODIPY is thermodynamically not feasible, the singlet ZnPc decayed to populates the triplet ZnPc, in addition to the grounds state. These findings suggest the potential of the examined ZnPc-BODIPY pentad to be efficient photosynthetic antenna in the artificial photosynthetic systems.

Adsorption Kinetics for the Removal of Nitrite Ions from Aqueous Solutions by an Ion-exchange Resin

The adsorption kinetics of nitrite ions in aqueous solutions onto an anion-exchange resin A-250 was explored in a well-stirred tank. The capacity of the ion-exchange resin for the removal of nitrite ions from aqueous solution was investigated under different conditions, viz. initial concentration (10–50 mg/l), pH (2–8), particle size (565–850 μm) and resin dosage (2–8 g/l). A number of kinetic models such as those of external and intraparticle diffusion were applied to the results from this study in order to identify the adsorption mechanism. The results correlated well with the intraparticle diffusion model. The experimental parameters had an effect on the effective pore and surface diffusivities. Adsorption of nitrite ions onto the resin showed that the latter could be used as an efficient adsorbent material for the removal of nitrite ions from aqueous solutions.

Stereochemical Aspects of Polyphosphazenes

ABSTRACT Polyphosphazenes are the most important class of inorganic polymers having a backbone of alternating phosphorus and nitrogen atoms with phosphorus atoms bearing organic, inorganic or organometallic side groups. They are potentially optically active macromolecules because they may have a center of chirality anywhere in their structure. Although there have been a number of studies which deal with the polyphosphazenes having stereogenic P-moieties in the main chain, chiral groups in the side chain, optically active helical structure, and cyclolinear phosphazene polymers for over the last fifty years, there is little emphasis on the stereochemistry of phosphazene polymers to date. In this review the polyphosphazenes containing centers of chirality P- and/or C-moieties anywhere in their structure have been covered.

A systematic series of fluorescence chemosensors with multiple binding sites for Hg(II) based on pyrenyl-functionalized cyclotriphosphazenes and their application in live cell imaging

A systematic series of fluorescence chemosensors (1–3) having one, two and three-metal binding sites based on cyclotriphosphazene derivatives bearing bis-, tetra- and hexakis-2-(pyren-1-yl methylene amino) phenoxy units, respectively, were designed, synthesized, and evaluated for their sensing behaviors toward metal ions using UV/Vis and fluorescence spectroscopies. Upon the addition of Hg2+ in both the absence and presence of competitive metal ions, the chemosensors revealed highly selective and sensitive “turn-on” emission enhancement based on the combined effects of chelation-enhanced fluorescence (CHEF), CN isomerization and intramolecular pyrene excimer formation, as well as a color change from yellowish to colorless, which was readily detected by the naked eye. According to the Job plot method, the complexation ratios of chemosensors (1–3) with Hg2+ were found to be 1 : 1, 1 : 2 and 1 : 3 (ligand : metal), respectively, consistent with the proposed number of metal binding sites. Furthermore, the binding modes of chemosensors (1–3) with Hg2+ were supported by 1H NMR spectroscopy. The increasing complexation ratios from 1 : 1 to 1 : 3 for chemosensors (1–3) enabled proportionally decreasing values for the detection limit (LOD) with 0.223 μM, 0.114 μM and 0.050 μM, respectively. The cytotoxicity and fluorescence microscopy experiments also demonstrated that chemosensors (1–3) are non-cytotoxic, and can be used as fluorescence imaging sensors for Hg2+ in living cells.