Jari S. Kavakka

Noncovalent attachment of pyro-pheophorbide a to a carbon nanotube

Pyrene mediated noncovalent attachment of a chlorophyll derivative, pyro-pheophorbide a, to a soluble single wall carbon nanotube is reported and the resultant CD, UV-Vis absorbance, fluorescence and 1H NMR spectra are discussed.

Enhanced chromatographic NMR with polyethyleneglycol. A novel resolving agent for diffusion ordered spectroscopy

NMR analysis of complex mixtures can be significantly simplified using polyethyleneglycol (PEG) as resolving additive in DOSY NMR technique, which allows the extraction of individual spectra of mixture components with differing polarity. Resolving power of PEG‐assisted DOSY was demonstrated with natural product mixtures. Copyright

Reactive dissolution of cellulose and pulp through acylation in pyridine

The direct acylation of cellulose and different pulps with various acid chlorides was systematically screened. The syntheses were started in a heterogeneous solid–liquid reaction medium in hot pyridine with aliphatic and aromatic acid chlorides. After a few hours, depending on the reagent used, a homogenous solution was obtained. The obtained cellulose esters usually show a high degree of substitution (DS) and polymerization and are soluble in organic solvents. Esterification of softwood dissolving pulp, hardwood kraft pulp and hardwood kraft pulp-hemicellulose poor were also studied. The results show that almost identical DS were obtained for pulp derivatives compared to esters of microcrystalline cellulose. Thermogravimetric analysis and differential scanning calorimetry of the synthesized materials showed an improved thermal stability and various discrete thermal transitions compared to the original cellulose. The scanning electron microscopy images of derivatives showed a relatively flat and smooth surface with an absence of fibrous structure. The reactive dissolution of cellulose or pulp in pyridine is a straightforward and easy route to obtain long-chain aliphatic and aromatic cellulose esters.

Biomimetic zinc chlorin–poly(4-vinylpyridine) assemblies: doping level dependent emission–absorption regimes

To develop biomimetic dye–polymers for photonics, two different types of Zn chlorin–poly(4-vinylpyridine) (P4VP) assemblies were prepared by varying Zn pyro-pheophorbide a methylester (ZnPPME) and Zn 31-OH-pyro-pheophorbide a methylester (Zn-31-OH-PPME) doping levels. 1H NMR spectroscopy and diffusion ordered NMR spectroscopy (DOSY) studies revealed that a coordinative interaction between Zn chlorin and P4VP was predominant in solution (d5-nitrobenzene). Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) characterization of bulk samples of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) doped with variable amounts of Zn chlorin showed that the pigment doping transformed the native cylindrical block copolymer nanostructures to lamellar morphologies. The result indicates that the pyridine moiety–Zn chlorin coordination is stronger than the aggregation tendency between the pigment molecules even in the solid state. UV-Vis absorption spectroscopy studies of a Zn chlorin–P4VP thin film showed characteristic monomeric chlorin spectra, while steady-state fluorescence spectroscopy displayed quenching of fluorescence and time-resolved studies indicated shortening of fluorescence lifetimes with an increasing chlorin doping level. Notably, time-resolved fluorescence spectroscopy revealed that the lifetime decay changed from monoexponential to biexponential above 0.5 wt% (ca. 0.001 equiv.) loadings. The Forster analysis implies that excitonic chlorin–chlorin interactions are observed in the thin films when the distance between the pigment molecules is approximately 50 A. The Zn chlorin–P4VP solid films emit strongly up to 1 wt% (ca. 0.002 equiv.) doping level above which the chlorin–chlorin interactions start to linearly dominate with an increase of doping level, while with 10 wt% (ca. 0.02 equiv.) loading less than 10% of fluorescence remains. Doping levels up to 300 wt% (0.5 equiv.) can be used in absorbing materials without the formation of chlorin aggregates. These defined optical response regions pave the way for photonic materials based on biopigment assemblies.

Amination and thiolation of chloroacetyl cellulose through reactive dissolution in N,N-dimethylformamide.

The synthesis and characterization of aminoacetyl cellulose and thioacetyl cellulose is presented in this paper. Cellulose was first chemically modified with chloroacetyl chloride using N,N-dimethylformamide (DMF) as reaction medium. The maximum substitution of hydroxyl groups of cellulose was achieved reacting in the presence of 6 equiv. of chloroacetyl chloride over 24 h at 60 °C. DMF were then recovered by fractional distillation of the media. In the next step, chloroacetyl cellulose was reacted with either secondary amines or thiols. The reactions were initially heterogeneous in hot DMF. As the reactions proceeded, homogenous mixtures were obtained. Highly substituted cellulose derivatives were achieved via this method. The success of the reactions was confirmed by ATR-IR and NMR spectroscopy. Various pulps were used as cellulose source. The resulting products were found to be thermally stable and have glass transition temperatures around 120 °C. Gel permeation chromatography (GPC) indicated that degradation of the cellulose backbone had occurred. The cellulose derivatives were then processed into films. Their potential, as packaging films, was then studied from the view-point of their moisture and oxygen barrier properties, as well as their tensile properties.

Preparation of cellulose and pulp carbamates through a reactive dissolution approach

Carbamoylation of various cellulosic materials was systematically studied, using a reactive dissolution approach. Reactions with cellulose, or pulp and aromatic isocyanates, were initiated as heterogeneous mixtures in hot pyridine. As the reaction proceeded, homogeneous solutions were obtained. However, attempts to synthesize highly substituted cellulose carbamates, with aliphatic isocyanates in pyridine, failed as homogeneous solutions were not achieved, even after long reaction times. Consequently, aliphatic cellulose carbamates were prepared via reactive dissolution in dimethylacetamide (DMA), with dibutyltin dilaurate (DBTL) as catalyst. Reactions of cellulose with aliphatic isocyanates in DMA/DBTL at elevated temperature also ended up as homogeneous solutions. The success of the carbamoylation reaction was assessed by means of FTIR, 1H, 13C, 31P and diffusion-ordered spectroscopy (DOSY) NMR. Carbamoylation of pre-hydrolysis hardwood kraft pulp (PHK), hardwood kraft pulp (HKP) and hemicellulose-poor hardwood kraft pulp (HPHKP) were also studied under similar conditions. Highly soluble carbamates were also obtained with the pulp derivatives. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) of the derivatives showed no significant improvement in the thermal properties compared with the untreated cellulose. However, DSC thermograms of some samples showed a phase change, which is attributed to a glass transition temperature (Tg). Also, a two-step decomposition process was observed in the TGA curves for the derivatives, which is attributed to the cleavage of carbamate substituents through a retro-carbamoylation and degradation of the cellulose backbone. Aromatic carbamates of cellulose showed similar molecular weight distributions compared to intact cellulose. However, for aliphatic cellulose carbamates the derivatization led to products with lower molecular weight.

Synthesis and in vitro phantom NMR and MRI studies of fully organic free radicals, TEEPO-glucose and TEMPO-glucose, potential contrast agents for MRI

Two organic radical contrast agents, TEMPO-Glc and TEEPO-Glc, were synthesized and their stabilities and contrast enhancing properties were tested with in vitro NMR and MRI experiments. Owing to the glucose moieties in the prepared compounds, this study presents potential candidates for a tumor targeting fully organic contrast agents for MRI.

Cationic cellulose betainate for wastewater treatment

Abstract High molecular-weight, cationic and water-soluble cellulose-based polyelectrolytes were synthesized and their performance in water purification was tested. Dissolving pulp samples were acylated with chlorobetainyl chloride in dimethylacetamide/lithium chloride to obtain betaine esters of cellulose (cellulose betainates). A series of application tests was carried out with samples of different degree of substitution to examine the performance of these cellulose derivatives as flocculants. Commercial synthetic polyacrylamide and polyamine flocculants were used as reference materials to obtain a realistic picture about the performance of cellulose betainates. According to the fixing test, one of the derivatives exhibited a performance equal to, or better than the reference flocculant. In addition, the cellulose betainates exhibited excellent floc strength in the flocculation testing. In the capillary suction test, the performance of the derivatives was also relatively good. In all, this research demonstrated that the cationic cellulose betainate can be successfully used in flocculation and other water purification applications. The current approach for wastewater treatment with bio-based polymers offers a sustainable and biodegradable alternative to conventional synthetic polymers.

Chlorophyll tailored 20-trifluoroacetamide and its azacrown derivative as pH sensitive colorimetric sensor probe with response to AcO−, F− and CN− ions

Chlorophyll derivatives were functionalized with a trifluoroamide (TFA) group to obtain colorimetric ion sensors. Prior to this, a NO2BF4*pyridine based, chlorin nitration method was developed. The base strength dependent sensing of AcO−, F− and CN− ions was detected in aqueous media, which was enhanced in nonprotic solvents by an integration of the ditopic chelation capable amine crown-6 moiety.

The Reactivity of Thymine and Thymidine 5,6-Epoxides with Organometallic Reagents – A Route to Thymidine (6-4) Photoproduct Analogues

This report describes an efficient procedure for the generation and isolation of various thymine and thymidine 5,6-epoxides from the corresponding trans-5,6-bromohydrins by reaction with triethylamine. The quantitative isolation of the epoxides, accomplished by solvent precipitation of triethylamine hydrobromide, enabled their regiospecific ring-opening at C6 position by organometallic nucleophiles. The reaction was amenable to a broad range of alkyl, aryl, alkenyl, and alkynyl organomagnesium, -zinc, -aluminum, or -boron reagents, although the reactivity was strongly affected by the electronic effects of N3 protecting group. Additionally, the reaction featured excellent cis-diastereoselectivity providing access to C6-carbon-functionalized dihydrothymidine cis-alcohols, which are synthetic derivatives of UV-induced DNA lesions, namely, thymidine (6-4) photoproducts.