A new 18 F-labeled tetrazine derivative was developed aiming at optimal radiochemistry, fast reaction kinetics in inverse electron-demand Diels−Alder cycloaddition (IEDDA), and favorable pharmacokinetics for in vivo bioorthogonal chemistry. The radiolabeling of the tetrazine was achieved in high yield, purity, and specific activity under mild reaction conditions via conjugation with 5-[ 18 F]fluoro-5-deoxyribose, providing a glycosylated tetrazine derivative with low lipophilicity. The 18 F-tetrazine showed fast reaction kinetics toward the most commonly used dienophiles in IEDDA reactions. It exhibited excellent chemical and enzymatic stability in mouse plasma and in phosphate-buffered saline (pH 7.41). Biodistribution in mice revealed favorable pharmacokinetics with major elimination via urinary excretion. The results indicate that the glycosylated 18 F-labeled tetrazine is an excellent candidate for in vivo bioorthogonal chemistry applications in pretargeted PET imaging approaches.

Processes called pulping and bleaching are required for preparing industrial scale pure cellulose from biomass. Bleaching generally purifies the cellulose from components called hexenuronic acid (HexA) and lignin. Nevertheless, the oxidation reactions of these bleachable components generally consume stoichiometric volumes of oxidant and hours of retention time. The efficiency of the oxidants can be enhanced by catalysis. The present study focuses on increasing the selectivity of hypochlorous acid (HOCl) produced during chlorine dioxide bleaching toward oxidation of HexA and lignin with the help of a tertiary amine as a catalyst. A strong electrophile forms when HOCl reacts with tertiary amine, which further reacts selectively and efficiently with HexA and lignin. Catalytic oxidation experiments were conducted at broad range of pH, temperature, and oxidant dosage in conditions that are milder than used today in industry. Surprisingly, catalytic amounts of industrial tertiary amine were used, and the oxidation reactions took place in seconds. This study opens the door for future chemical pulp bleaching technologies with reduced oxidation time, less chemical consumption, and high chemical oxidation efficiency.

Bleaching processes remove residual lignin and hexenuronic acid from cellulosic pulps. The reactions taking place in several stages are slow and consume large amounts of chemicals. The present study demonstrates a novel three-stage pulp bleaching sequence that combines a tertiary amine-catalyzed hypochlorite oxidation with subsequent treatments with ozone and hydrogen peroxide. With this sequence, the residual lignin and hexenuronic acid contents of an oxygen-delignified eucalyptus pulp were decreased by ≫90%, and a full brightness (88% ISO) was achieved. The total reaction time was only ∼1 h, which is one-fifth of the retention time of the current industrial pulp bleaching sequences. The chemical need was low, and the viscosity of the pulp remained high. This study may open new doors to future pulp bleaching with fewer and smaller bleaching towers and diminished use of chemicals.

A totally chlorine free (TCF) bleaching sequence was studied for an acid sulfite pulp mill that produces dissolving pulps. Laboratory analyses of the last two bleaching stages, an oxidant-reinforced alkaline extraction stage (EOP), and a subsequent pressurized peroxide with oxygen stage (PO), were performed on a eucalypt pulp that had been delignified by an ozone (Z) stage in the pulp mill. The goal was to predict the optimal costs and operational conditions for the (EOP)(PO) partial bleach sequence for three different specialty pulp products. Four independent variables affecting the pulp quality properties were examined for each stage (i.e., reaction temperature, reaction time, NaOH dosage and H2O2 dosage). The dependent variables were various pulp properties, such as intrinsic pulp viscosity, alpha-cellulose content, kappa number, and GE brightness. Three scenarios were considered to optimize the bleaching process, which related to a regenerated cellulose product (viscose) that is widely commercialized, and to two novel products (nanocrystalline cellulose (NCC) and nanofibrillated cellulose (NFC). Statistical response surface models indicated that the bleaching behavior of the ozone-treated pulp could be represented by second-order polynomial equations. These non-linear optimization models predict cost savings of 62.2%, 73.4%, and 63.3% for producing viscose, NCC, and NFC pulp grades, respectively.

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