Aylin Uslu

The structural and stereogenic properties of pentaerythritoxy-bridged cyclotriphosphazene derivatives: spiro-spiro, spiro-ansa and ansa-ansa isomers.

Reactions of pentaerythritol with hexachlorocyclotriphosphazene, N3P3Cl6, and gem-disubstituted cyclotriphosphazene derivatives, N3P3Cl4R2 [R = Ph, NHBu(t) or (OCH2CF2CF2CH2O)0.5] gave a series of pentaerythritol-bridged derivatives linked spiro-spiro, spiro-ansa and ansa-ansa. The structures and stereogenic properties of the products were characterised by X-ray crystallography and 31P NMR spectroscopy on addition of the chiral solvating agent, (S)-(+)-2,2,2-trifluoro-1-(9-anthryl)ethanol. Molecules with spiro-spiro and spiro-ansa bridged gem-disubstituted cyclophosphazenes [R = Ph, NHBu(t) or (OCH2CF2CF2CH2O)0.5] are found to be chiral and exist as racemates. Molecules with ansa-ansa bridged cyclophosphazenes [R = Cl or (OCH2CF2CF2CH2O)0.5] have been characterised for the first time and are shown to have meso configurations. Analysis of crystal structure data shows that the six-membered chair form of the spiro rings and the eight-membered boat-chair form of the ansa rings in the bridged compounds are similar to analogous spiro and ansa exocyclic ring conformations of 1,3-propanedioxy-derivatives of cyclophosphazenes.

Structural investigations of phosphorus-nitrogen compounds. 4. Steric and electronic effects in dibenzylamino derivatives of hexachlorocyclotriphosphazatriene and 4,4,6,6-tetrachloro-2,2-diphenylcyclotriphosphazatriene

A systematic study is presented on the products of aminolysis of N(3)P(3)Cl(6) (1) and N(3)P(3)Ph(2)Cl(4) (4) with dibenzylamine. Two series of mono- and disubstituted derivatives of compounds (1) and (4), namely N(3)P(3)Cl(5)[N(CH(2)Ph)(2)] (2) and N(3)P(3)Cl(4)[N(CH(2)Ph)(2)](2) (3) and N(3)P(3)Ph(2)Cl(3)[N(CH(2)Ph)(2)] (5) and N(3)P(3)Ph(2)Cl(2)[N(CH(2)Ph)(2)](2) (6) [where (2), (3), (5) and (6) are new structures], are investigated in order to determine whether steric or electronic effects prevail in the formation of dibenzylamino-substituted cyclophosphazenes. The influence of an electron-releasing group (i.e. phenyl) on the stereochemistry and degree of substitution of the product is analysed by comparison of the above two series. The difference in unsymmetrically substituted endocyclic P-N bond lengths, Delta, is used as a measure of the degree of the electronic contribution, in combination with basicity constants, to quantify the degree of the electron-releasing capacity of the R group. In order to compare geminal versus non-geminal substitution, a difunctional secondary amine was used to form the compound N(3)P(3)Cl(4)[NMe(CH(2))(3)NMe] (7) (a reinvestigation) for inclusion in this study. It is shown that electron-releasing groups have a greater effect on the lengthening of P-Cl bonds as opposed to endocyclic P-N bonds and that this effect is greater in the non-geminal PRCl case than for geminal PCl(2). However, steric effects are shown to be dominant in the reactions of dibenzylamine with N(3)P(3) derivatives, with a disposition to a trans stereochemistry in bisdibenzylamino derivatives.

The investigation of structural and thermosensitive properties of new phosphazene derivatives bearing glycol and amino acid

In this study, hexachlorocyclotriphosphazene, N(3)P(3)Cl(6) (cylotriphosphazene), was reacted with hydrophilic and hydrophobic groups to synthesize amphiphilic phosphazene derivatives (4-12). Cylotriphosphazene was reacted triethylene glycol monomethyl ether (TEGME), dipropylene glycol monomethyl ether (DPGME), diethylene glycol monobutyl ether (DEGBE), (1 : 3 mole proportion) in the presence of sodium hydride and using tetrahydrofuran (THF) as solvent at -60 °C. Three isomers (nongeminal cis-2,4,6 (1a-3a); nongeminal trans-2,4,6 (1b-3b); geminal 2,2,4 (1c-3c)) were isolated from the reaction of hexachlorocyclotriphosphazatriene (trimer) (1) with TEGME, DPGME and DEGBE. The substitution reactions of cis-tris isomers (1a-3a) with 4-amino butyric acid, 5-amino valeric acid and 6-amino hexanoic acid were separately done to provide amphiphilic phosphazenes (4-12). All compounds were characterized by using elemental analysis, (31)P NMR and mass spectroscopy. Thermosensitive properties of compounds were studied. The compounds (4-12) were soluble in both water and organic media that shows they are amphiphilic molecules. Concentration-dependent LCST (Lower Critical Solution Temperature) behaviours of new compounds (4-12) were measured in water. Compounds 7, 9, 11 and 12 exhibited a reversible and thermosensitive phase transition in aqueous medium, from soluble to insoluble states.

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.

Characterisation of temperature-dependent phase transitions in 2,2-trimethylenedioxy- 4,4,6,6-tetrachlorocyclotriphosphazene, N3P3Cl4[O(CH2)3O]

BackgroundThe crystal structure of 2,2-trimethylenedioxy-4,4,6,6-tetrachlorocyclo triphosphazene has been determined at 120, 274 and 293 K. The result at 293 K confirms the room temperature Cmc21 structure, but at the lower temperatures the space group is Pna21. Nevertheless the basic structure remains the same, with only small displacements of the atoms, amounting to an average of 25 pm between 120 and 293 K.ResultsX-ray diffraction and DSC results indicate that the phase transition takes place in two steps between 274 – 293 K and provides an understanding of previous NQR results. In the intermediate temperature range the molecules are displaced from their room temperature positions in such a way as to give an average structure with Cmc21 symmetry.ConclusionThe overall phase transition is consistent with the occurrence of a soft lattice mode at room temperature in which a large displacement of the molecule in the x-direction is coupled with a flexing motion about an axis defined by the nitrogen atoms in the N1 and N3 positions.

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.

New Synthetic Approach to Molecular Rods Using Cyclophosphazene-Based Oligospiranes

A synthetic approach was developed to prepare a new type of highly functionalized inorganic-organic heterocyclic molecular rod (3a and 3b) consisting of cyclophosphazene and carbocyclic units. Single-crystal X-ray diffraction analysis of 3a revealed that the molecular length was ca. 2.5 nm. The products of this high-yield process have the potential for derivatization via known phosphazene reactions.