Gunnar Westman

Cationic surface functionalization of cellulose nanocrystals

The surface of cellulose nanocrystals, prepared by sulfuric acid hydrolysis of cotton, was rendered cationic through a reaction with epoxypropyltrimethylammonium chloride. The resultant nanocrystal suspensions were characterized by ζ-potential, conductometric titration and polarized light microscopy. Atomic force microscopy (AFM) showed no change in the size or shape of the nanocrystals, but the functionalization process reversed the surface charge and led to a reduction of the total surface charge density. These modifications led to stable aqueous suspensions of nanocrystalline cellulose with unexpected gelling and rheological properties. Shear birefringence was observed, but no liquid crystalline chiral nematic phase separation was detected.

C60 embedded in γ-cyclodextrin: a water-soluble fullerene

A water-soluble complex of C60 is formed on refluxing a solution of γ-cyclodextrin with solid C60; the lifetime of the triplet excited state of C60 in the complex is 83 µs in an oxygen free solution.

A gas phase container for C60; a γ-cyclodextrin dimer

Abstract A molecular complex consisting of two molecules of γ-cyclodextrin and one molecule of C 60 has been identified by negative FAB/LSIMS mass spectroscopy.

Clusters of C60-fullerene in a water solution containing γ-cyclodextrin : a photophysical study

Abstract γ-CD has been used to dissolve C 60 in water. Depending on the concentration of cyclodextrin two forms of solutions can exist. At high γ -CD:C 60 ratio a complex that is monomeric in C 60 is stable whereas at lower γ -CD:C 60 ratio a cluster of several C 60 molecules surrounded by γ-CD can exist. We propose that clusters of different sizes can be formed. The γ -CD:C 60 complex have an electronic absorption spectrum similar to that of an organic solution of C 60 and the cluster have an electronic absorption spectrum similar to that of a thin film of C 60 . For the γ -CD:C 60 complex the photophysical properties are similar to those of an organic solution with the exceptions for quenching of the triplet state by molecular oxygen and annihilation of the triplet state. The rate constant for quenching of the triplet is reduced by a factor two and the rate constant for annihilation of triplets is reduced by a factor four when compared to those expected for a “free” C 60 , respectively. The properties of the clusters are different from those of an organic solution of C 60 . For water solutions of small clusters, decay of the excited state of the cluster is clearly dependent on the intensity of the excitation laser pulse; at high laser intensity there is both a fast and a slow component in the decay process whereas at low laser intensity only the slow process is observed. For excitation of larger clusters we could only detect a fast decay process.

Host-guest chemistry of fullerenes; a water-soluble complex between C70 and γ—cyclodextrin

Abstract A water-soluble complex between C70 and γ—cyclodextrin has been prepared by boiling a conc. solution of γ—cyclodextrin (0.8M) in water with solid C70 suspended in water. The complex has been characterised by its UV/VIS spectrum and by photophysical methods.

Diastereoselective nitrile oxide and nitrone additions

Abstract With simple chiral esters, cycloaddition reactions are performed in high yields with considerable diastereoselectivities. Evidence for the preferred conformation of the enoates in the transition state of the nitrile oxide addition is provided and the stereoselectivity of nitrone additions is discussed.

Regioselective nitration of phenols and anisols in microemulsion

Abstract A nitration reaction was performed in a cationic surfactant-based microemulsion system with four different aromatic compounds, and the ortho-to-para ratio was examined. The results have been compared with a reference reaction performed in a two-phase system without surfactant and with previous work done with reactions in microemulsions. We report almost selective para-nitration of the chosen compounds when the reactions were performed in the microemulsion. Reaction in a two-phase system gave approximately equal ortho- and para nitration. The difference in reaction rate between the microemulsion system and the two-phase system was examined as well. Using diluted HNO3 the reaction in microemulsion went to completion in 30 min. The two-phase system demanded concentrated HNO3; with dilute HNO3, there was almost no reaction after 24 h. 1H-NMR techniques were used to characterise the microemulsion and to determine the ortho-to-para ratio of the reaction products.

Synthesis and DNA binding studies of a new asymmetric cyanine dye binding in the minor groove of [poly(dA-dT)]2.

A new asymmetric cyanine dye has been synthesised and its interaction with different DNA has been investigated. In this dye, BEBO, the structure of the known intercalating cyanine dye BO has been extended with a benzothiazole substituent. The resulting crescent-shape of the molecule is similar to that of the well-known minor groove binder Hoechst 33258. Indeed, comparative studies of BO illustrate a considerable change in binding mode induced by this structural modification. Linear and circular dichroism studies indicate that BEBO binds in the minor groove to [poly (dA-dT)](2), but that the binding to calf thymus DNA is heterogeneous, although still with a significant contribution of minor groove binding. Similar to other DNA binding asymmetric cyanine dyes, BEBO has a large increase in fluorescence intensity upon binding and a relatively large quantum yield when bound. The minor groove binding of BEBO to [poly (dA-dT)](2) affords roughly a 180-fold increase in intensity, which is larger than to that of the commonly used minor groove binding probes DAPI and Hoechst 33258.

Solid-phase synthesis of asymmetric cyanine dyes

Abstract An efficient solid-phase synthesis of asymmetric cyanine dyes is described. Combinatorial synthesis and spectroscopic analysis of four dyes was carried out. The yields are quantitative after 20 h, but the reaction can be halted earlier, since it is shown that the starting material does not disturb the fluorescence measurements in these binding studies.

NMR and UV–VIS Investigation of water-soluble fullerene-60–γ-cyclodextrin complex

Fullerene-60 can be made water-soluble by forming an inclusion complex with γ-cyclodextrin (γ-CD). The complex between C60 and γ-CD is selectively formed; neither β- or α-CD, nor C70 takes part in complex formation. The UV–VIS and 13C NMR spectra of C60 in the complex are almost identical to those of C60 in organic solvents. The 1H NMR spectrum of the host, γ-CD, in the complex has been identified. Only small differences to the spectrum of the free host are observed; this is interpreted as being due mainly to a conformational change to a more conical structure in the host. Both 2 : 1 and 1 : 1 complexes between γ-CD and C60 are believed to exist in water. On heating in water, the complexes are transformed into water-soluble aggregates containing several fullerenes and γ-CD molecules. On addition of excess γ-CD to this solution and further heating, the initial complexes, monomeric in C60, are reformed.