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We report on the functionalization of wet bacterial cellulose sheets towards photo-bactericidal materials that produce singlet oxygen (1O2) upon illumination. Pre-modification was carried out by a silane chemistry approach in order to make the cellulosic material accessible to Cu(I)-catalyzed azide-alkyne click chemistry. This way, two xanthene-derived photosensitizers were covalently grafted onto the surface of the silanized bacterial cellulose sheets. The obtained materials and photosensitizers were comprehensively characterized by means of FTIR, NMR, elemental analysis, UV/Vis absorption and fluorescence techniques, including nanosecond laser flash photolysis, for the determination of respective triplet state and singlet oxygen quantum yields. The photomicrobicidal activity was tested under white light illumination against gram-negative as well as gram-positive bacteria, including Escherichia coli, Bacillus subtilis and Staphylococcus aureus, as well as fungi (Candida albicans and Aspergillus brasiliensis). The results show type II photochemical antimicrobial activity against S. aureus and B. subtilis, but no effect against gram-negative bacteria and fungi.

In the present work, bacterial cellulose (BC) was analyzed for its chromophore content with the chromophore release and identification (CRI) method. In aged BC, seven chromophores were unambiguously identified, despite their very low (ppb) presence. The compounds contain 2-hydroxy-[1,4]benzoquinone, 2-hydroxyacetophenone and 5,8-dihydroxy-naphthoquinone moieties. These three classes of key chromophores had also been found in other celluloses such as bleached pulp, fiber and derivatives. The detection of chromophores in lignin-free BC confirms that the chromophores are formed from oxidized and degraded carbohydrate material rather than lignin fragments. Samples that were insufficiently purified before the aging step also yielded three N-heterocyclic compounds. They originated from tryptophan moieties in residual adhering protein and protein degradation products. N-Heteropentacycles 9 and 10 showed strong adsorption onto cellulosic surfaces, and that adsorption aided oxidation of cyclohexadiene derivative 9 into the corresponding aromatic and intensely yellow system 10, consistent with the strain-induced bond localization theory. In purified fresh BC, no chromophores were detectable by the CRI method. The present contribution is the first report on defined chromophoric structures isolated from BC.