title: Relationship between photosensitizing and emission properties of peat humic acid fractions obtained by tangential ultrafiltration.
abstract: Peat humic acid was fractionated by tangential ultrafiltration into six nominal molecular weight (NMW) fractions, HA5-10, HA10-20, HA20-50, HA50-100, HA100-300 and HA > 300, which were purified by dialysis using a 0.5 kDa membrane. The absorbing and emission properties of the separated fractions were compared and their ability to generate singlet oxygen under light excitation was evaluated, using furfuryl alcohol (FFA) as a singlet oxygen scavenger. The absorbance, the emission intensity, and the apparent first order rate constants of FFA loss were normalized per mole of organic carbon (a*, IF*, and k*, respectively). The fraction absorbance decreased with NMW, except for HA > 300 which was less absorbing than HA100-300. The low NMW fractions and the HA > 300 fraction generally showed lower k* and IF* values compared to the HA50-100 and HA100-300 fractions. A plot of k* versus IF* indicates that the first order rate constant of FFA photo-oxygenation increased with the intensity of fluorescence at 380, 430, and 500 nm (R2 = 0.77-0.84). This shows that the distribution of fluorescent centers among fractions paralleled that of photosensitizing centers. Plotting k* or IF* versus a* at365 nm reveals the apparent relative quantum efficiency of the different fractions. Higher values for low NMW fractions and HA50-100 are either due higher percentages of absorbing centers able to produce singlet oxygen or exhibit fluorescence or to lower quenching processes.
authors: Dipartimento di Scienze e Tecnologie Agroambientali, Alma Mater Studiorum-Università di Bologna, Viale Fanin 40, 40127 Bologna, Italy.
authors: Luciano
authors: L
authors: Cavani
authors: Sabrina
authors: S
authors: Halladja
authors: Alexandra
authors: A
authors: ter Halle
authors: Ghislain
authors: G
authors: Guyot
authors: Giampietro
authors: G
authors: Corrado
authors: Claudio
authors: C
authors: Ciavatta
authors: A
authors: A
authors: Boulkamh
authors: Claire
authors: C
authors: Richard
mesh_terms: D005663:Furans / Q000737:chemistry; D006812:Humic Substances / Q000032:analysis*; D010084:Oxidation-Reduction; D010777:Photochemistry; D010787:Photosensitivity Disorders; D012987:Soil / Q000032:analysis*; D014462:Ultrafiltration / Q000379:methods*
chemical_list: D005663:Furans; D006812:Humic Substances; D012987:Soil; C012986:furfuryl alcohol