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. 2018 Sep 25;23(10):2445.
doi: 10.3390/molecules23102445.

Antioxidant and Fluorescence Properties of Hydrogenolyzised Polymeric Proanthocyanidins Prepared Using SO₄2-/ZrO₂ Solid Superacids Catalyst

Liwen Ni  1 , Fanbin Zhao  2 , Bolun Li  3 , Tong Wei  4 , Hang Guan  5 , Shixue Ren  6
Affiliations

Antioxidant and Fluorescence Properties of Hydrogenolyzised Polymeric Proanthocyanidins Prepared Using SO₄2-/ZrO₂ Solid Superacids Catalyst

Liwen Ni et al. Molecules. .

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.

Keywords: SO42−/ZrO2 solid superacid; antioxidant activity; catalytic hydrogenolysis; fluorescence; proanthocyanidins.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript and in the decision to publish the results.

Figures

Figure 1
Figure 1
Polymeric procyanidin units containing C4-C8 bonds (left) and C4-C6 bonds (right).
Figure 2
Figure 2
Molecular weight distribution of LPPC and LOPC.
Figure 3
Figure 3
UV spectra of catechin standard (1), LOPC (2) and LPPC (3).
Figure 4
Figure 4
IR spectra of catechin standard (1), LOPC (2) and LPPC (3).
Figure 5
Figure 5
Comparison of reducing power of proanthocyanidins with different mass concentrations.
Figure 6
Figure 6
DPPH• free radical scavenging ability of BHT, LPPC and LOPC with different mass concentrations.
Figure 7
Figure 7
Half-maximal DPPH• free radical scavenging rate (IC50) of BHT, LPPC and LOPC.
Figure 8
Figure 8
ABTS•+ free radical scavenging ability of LPPC and LOPC with different mass concentrations.
Figure 9
Figure 9
Half-maximal ABTS•+ free radical scavenging rate (IC50) of LPPC and LOPC.
Figure 10
Figure 10
Effect of solvent polarity on fluorescence intensity of LOPC. Ethanol concentration: 1, 5%; 2, 25%; 3, 50%; 4, 75%; 5, 100%.
Figure 11
Figure 11
Effect of pH on fluorescence intensity of LOPC.
Figure 12
Figure 12
Effect of (a) Cu2+, (b) Ba2+, (c) Al3+, (d) Fe3+ and (e) Ni2+ ions on fluorescence intensity of LOPC.
Figure 12
Figure 12
Effect of (a) Cu2+, (b) Ba2+, (c) Al3+, (d) Fe3+ and (e) Ni2+ ions on fluorescence intensity of LOPC.
Figure 13
Figure 13
Stern-Volmer curves for quenching of LOPC fluorescence by Cu2+, Ba2+, Al3+, Fe3+ and Ni2+ ions.
See this image and copyright information in PMC

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