Practical syntheses of [1,3,5]‐triazine dendritic molecules on solid supports

A practical and divergent synthesis of supported [1,3,5]‐triazine dendritic molecules on Wang resin, PEGA resin, SynPhase? Lanterns, and silica gel is described. The alkylamine linkers used allow derivatization with functionality for both synthetic (e.g., supported reagent and scavenger activity) and chemical biology applications. The use of supported intermediates allows differentiation of symmetric linkers without the need for protecting group chemistry. The synthetic route uses inexpensive, readily available starting materials in a straightforward and scaleable strategy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2248–2259, 2006     

Surface functionalization of ultrananocrystalline diamond films by electrochemical reduction of aryldiazonium salts

The surface functionalization of ultrananocrystalline diamond (UNCD) thin films via the electrochemical reduction of aryl diazonium cations is described. The one-electron-transfer reaction leads to the formation of solution-based aryl radicals, which in turn react with the UNCD surface forming stable covalent C-C bonds. Cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), ac impedance spectroscopy, and contact angle measurements have been employed to characterize the organic overlayer and estimate the surface coverage. The grafting of 3,5-dichlorophenyl groups renders the UNCD surface hydrophobic, whereas the attachment of 4-aminophenyl groups makes the surface relatively hydrophilic. The surface coverage, estimated from the electrochemical and XPS measurements, is as high as 70% of a compact monolayer. The aminophenyl terminated surface was obtained by electrochemical reduction of the tethered nitrophenyl groups. This two-step approach yields a UNCD surface with functional moieties available for the potential covalent coupling of a wide variety of biomolecules (e.g., DNA and proteins).     

The crystal and molecular structure of a dinuclear copper(II) complex of a Robson-type macrocycle, [Cu2(C26H30N4O2)(H2O)2](BF4)2

Summary The crystal structure of the dinuclear complex [Cu₂(C₂₆H₃₀-N₄O₂)(H₂O)₂](BF₄)₂ was determined by x-ray crystallography. The crystals are triclinic, P¯1, witha = 10.945(5),b = 8.703(5),c = 8.495(5) Å, = 103.86(3)°, = 105.73(3)°, = 85.77(3)°, V = 756 ų D_c = 1.65 g cm^–3 for Z = 1. The copper(II) atoms are 5-coordinate and square-pyramidal. Selected bond distances are: Cu-N, 1.91 Å (mean); Cu-O(base) = 1.90(1) and 1.91(1) Å; Cu-O(apical) = 2.47(1) Å; There are O(water)-H ... F interionic hydrogen bonds in the structure. The Cu .. Cu distance is 2.847 Å.     

Cholesteric liquid crystal displays as optical sensors of barbiturate binding

The influence on the optical properties of cholesteric liquid crystal displays (LCDs) was examined for neutral molecule binding by mesogen/receptors in the mesomorphic phase. The motivation was to prepare neutral molecule sensors that use a colour change to signal analyte binding. A receptor that binds barbiturate analytes was modified with two or one cholesteryl groups to yield compounds 2 and 3, respectively. LCDs were prepared by incorporating one of the receptor/mesogen compounds into a cholesteric LC blend along with a potential H‐bonding guest. The optical properties of the LCDs were then determined by measuring the absorbance of the displays. For various LCDs, the colour of the display depended upon several factors: the amount of guest molecule used, the number of cholesteryl side chains on the receptor and the mole concentration of receptor/mesogen in the blend. In particular, complementary host/guest binding of H‐bonding analytes by the bis(cholesteryl) receptor 2 in a cholesteric LCD caused a change of up to +70 nm, which was observed by the naked eye as a blue‐to‐orange colour change. Control experiments confirm that the colour of an LCD is a consequence of molecular recognition in the mesomorphic phase.     

In search of a new class of stable nitroxide: synthesis and reactivity of a peri-substituted N,N-bissulfonylhydroxylamine

Acyclic bissulfonylnitroxides have never been isolated, and degrade through fragmentation. In an approach to stabilising a bissulfonylnitroxide radical, the cyclic, peri-substituted N,N-bissulfonylhydroxylamine, 2-hydroxynaphtho[1,8-de][1,3,2]dithiazine 1,1,3,3-tetraoxide (1), has been prepared by formal nitrogen insertion into the sulfur-sulfur bond of a sulfinylsulfone, naphtho[1,8-cd][1,2]dithiole 1,1,2-trioxide. The heterocyclic ring of 1 is shown to adopt a sofa conformation by X-ray crystallography, with a pseudo-axial hydroxyl group. N,N-Bissulfonylhydroxylamine 1 displays high thermal, photochemical and hydrolytic stability compared to acyclic systems. EPR analysis reveals formation of the corresponding bissulfonylnitroxide 2 upon oxidation of 1 with the Ce(IV) salts CAN and CTAN. Although 2 does not undergo fragmentation, it cannot be isolated, since hydrogen atom abstraction to reform 1 occurs in situ. The stability and reactivity of 1 and 2 are compared with the known cyclic benzo-fused N,N-bissulfonylhydroxylamine, N-hydroxy-O-benzenedisulfonimide (6), for which the X-ray data, and EPR of the corresponding nitroxide 10, are also reported for the first time.     

Crystal and molecular structure of 24,25-dibromolanost-8-en-3β-yl acetate ‘A’

The crystal and molecular structure of the thermodynamically more stable isomer of 24,25-dibromolanost-8-en-3-yl acetate, the A form, has been solved by the heavy-atom method and refined by full-matrix least-squares methods to a finalR-value of 0.153 for 2354 reflections. The crystals are orthorhombic:P2₁2₁2₁,a = 40.889,b = 9.990,c = 7.839Å,Z = 4. Some difficulties were encountered owing to both radiation damage and the unusual positions of the bromine atoms. The analysis shows the configuration at C(24) to be 24S, and the rest of the structure does not reveal any unexpected features.