Abstract
Larix bark oligomeric proanthocyanidins (LOPC) were prepared from larix bark polymeric proanthocyanidins (LPPC) by catalytic hydrogenolysis using SO42−/ZrO2 solid superacid as the catalyst. The catalyst to polymeric proanthocyanidins ratio was 0.2:1 (m/m). The LOPC, obtained after hydrogenolysis at 100 °C for 4 h under 3 MPa hydrogen pressure, retained the structural characteristics of proanthocyanidins. The average degree of polymerization was reduced from 9.50% to 4.76% and the depolymerization yield was 53.85%. LOPC has good antioxidant properties and, at the same concentration, the reducing ability of LOPC was much higher than that of LPPC. The IC50 values of LOPC for scavenging DPPH• and ABTS•+ radicals were 0.046 mg/mL and 0.051 mg/mL, respectively. LOPC is biocompatible and has fluorescent properties that are affected by external factors, such as solvent polarity, pH and the presence of different metal ions. These features indicate that LOPC could be developed as a new biological fluorescent marker. The depolymerization of low-value polymeric proanthocyanidins to provide high-value oligomeric proanthocyanidins and the development of new applications for proanthocyanidins represent significant advances.
Highlights
Since China implemented the “Natural Forest Protection Project”, which completely bans the commercial harvesting of natural forests, the Russian Far East has exported a large amount of larch (Larix spp.) timber to China
1112 not cm−1destroy proanthocyanidin units but does not retains destroythe thestructural molecularcharacteristics structure of proanthocyanidin monomers monomers since the product data show that SO4 /ZrO2 solid superacid degrades larix bark polymeric proanthocyanidins (LPPC) mainly by breaking the C4-C8 bond of the since the product Larix bark oligomeric proanthocyanidins (LOPC) retains the structural characteristics of proanthocyanidins
The longer wavelength can mostly be attributed to π→π* transitions and intramolecular transfer polarity of the solvent affects the fluorescence intensity of the LOPC, the fluorescence intensity transitions, accompanied by rearrangement of electrons, which results in larger changes in dipole ofmomen
Summary
Since China implemented the “Natural Forest Protection Project”, which completely bans the commercial harvesting of natural forests, the Russian Far East has exported a large amount of larch (Larix spp.) timber to China. After processing at a local level, this imported larch produces a mountain of wood processing residues, including bark and wood flour, which are classed as low value resources and are typically used as fuel. The bark is, rich in procyanidins, which account for 10–16%. Procyanidins are multimeric polyphenolic compounds that are formed by connecting catechins (or epicatechins) through C4 -C6 or C4 -C8 bonds. Procyanidins can be considered to be flavonoids, with a flavan-3-ol monomer structure and tannin-like properties [5].
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