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Towards Eumelanin@Zeolite Hybrids: Pore‐Size‐Controlled 5,6‐Dihydroxyindole Polymerization
Author(s) -
Prasetyanto Eko Adi,
Manini Paola,
Napolitano Alessandra,
Crescenzi Orlando,
d'Ischia Marco,
De Cola Luisa
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201303682
Subject(s) - zeolite , chemistry , polymerization , mesoporous material , dimer , polymer , sublimation (psychology) , spectroscopy , density functional theory , organic chemistry , catalysis , computational chemistry , psychology , psychotherapist , physics , quantum mechanics
5,6‐Dihydroxyindole ( 1 ) and its N ‐methyl derivative ( 2 ), key eumelanin building blocks, were inserted into zeolite L by sublimation at 175 °C for 5 days. At a 10 mg/300 mg indole/zeolite ratio, the resulting hybrids displayed a stable deep red coloration. CP/MAS 13 C NMR and UV/Vis spectroscopy of the red species suggested the generation and accommodation of quinonoid biindole derivative(s) within the void space of the acidic zeolite channels. Removal of the zeolite matrix by treatment with HF gave a stable species that could be separated by HPLC and characterized by mass spectrometry as an oxygenated biindole derivative (or a mixture of isomers), suggesting addition of water to the original dimer and subsequent re‐oxidation. The characterization was corroborated by optimized molecular geometries and simulated UV spectra with density functional calculations. Loading 1 or 2 into the larger pores of SBA‐15 type mesoporous silica resulted in black eumelanin‐type polymers, confirming channel size dependence over the polymerization process.