Non-Equilibrium Potential Responses towards Neutral Orcinol Using All-Solid-State Potentiometric Sensors Integrated with Molecularly Imprinted Polymers

Molecularly imprinted polymer (MIP) receptors have been synthesized, characterized, and applied as new selective receptors in solid-contact ion selective electrodes (ISEs) towards non-dissociated 3,5-dihydroxytoluene (orcinol). Two monomers, namely methacrylic acid (MAA) and acrylamide (AA), were used in the preparation of MIP receptors. Graphene (Gr) was used as the solid contact material between the sensing membrane and the electrical contact substrate. Based on non-equilibrium sensing mechanism, the proposed sensors reveal observably enhanced detection sensitivity towards orcinol with detection limits 1.7 × 10⁻⁵ and 3.3 × 10⁻⁶ M for sensors based on MIP/MAA and MIP/AA, respectively. The selectivity coefficients measured by the modified separate solution method (MSSM) for the proposed sensors showed good selectivity towards orcinol over most common other phenols and inorganic anions. All measurements were made in the presence of 30 mM phosphate buffer solution (PBS) with a pH of 7.0. Potential stability for the proposed sensors was tested by constant-current chronopotentiometry. No water films were formed between the sensing membrane and the electron conductor substrate. The applicability of MIP/MAA incorporated ISE has been checked by recovery test of orcinol in the presence of soil matrix and by standard addition method.

Constituents of Ramalina capitata (Ach.) Nyl. extracts

The aim of this work was to determine the chemical composition of the ether, ethyl acetate and dichloromethane extracts of Ramalina capitata by GC-FID and GC-MS for the first time. The main identified components in the ether, ethyl acetate and dichloromethane extracts were everninic acid (24.7, 33.7 and 22.2%), orcinol (25.8, 16.7 and 11.9%), orcinol monomethyl ether (11.6, 7.6 and 4.8%), 3-methylorsellinic acid (10.2, 7.1 and 9.0%) and usnic acid (4.4, 8.2 and 25.8%), respectively. Considerable amount (10.4%) of 2-hydroxy-4-methoxy-3,5,6-trimethylbenzoic acid was detected in ethyl acetate extract. Additionally, palmitic acid, linoleic acid, oleic acid and stearic acid and their esters were observed in the dichloromethane and ethyl acetate extracts in the range of 4.1-0.1%, while their amount was below 0.05% in the ether extract. According to the results reported here R. capitata predominantly biosynthesises derivatives of orcinol and, in much lesser extent, derivatives of β-orcinol.

A Novel Class of Plant Type III Polyketide Synthase Involved in Orsellinic Acid Biosynthesis from Rhododendron dauricum

Rhododendron dauricum L. produces daurichromenic acid, the anti-HIV meroterpenoid consisting of sesquiterpene and orsellinic acid (OSA) moieties. To characterize the enzyme responsible for OSA biosynthesis, a cDNA encoding a novel polyketide synthase (PKS), orcinol synthase (ORS), was cloned from young leaves of R. dauricum. The primary structure of ORS shared relatively low identities to those of PKSs from other plants, and the active site of ORS had a unique amino acid composition. The bacterially expressed, recombinant ORS accepted acetyl-CoA as the preferable starter substrate, and produced orcinol as the major reaction product, along with four minor products including OSA. The ORS identified in this study is the first plant PKS that generates acetate-derived aromatic tetraketides, such as orcinol and OSA. Interestingly, OSA production was clearly enhanced in the presence of Cannabis sativa olivetolic acid cyclase, suggesting that the ORS is involved in OSA biosynthesis together with an unidentified cyclase in R. dauricum.