Mequinol

Mequinol

Development and evaluation of kinetic spectrophotometric assays for horseradish peroxidase by catalytic coupling of paraphenylenediamine and mequinol.[Pubmed:19822971]

Anal Sci. 2009 Oct;25(10):1243-8.

This paper presents a novel spectrophotometric method to measure peroxidase activity using paraphenylenediamine dihydrochloride (PPDD) and Mequinol (MQ). The PPDD traps the free radical, and gets oxidized to electrophilic 1,4-diimine; this couples with MQ to an give intense violet-colored chromogenic species with the maximum absorbance at 560 nm. This assay was adopted for the quantification of hydrogen peroxide between 10 x 10(-6) to 80 x 10(-6) M. From the kinetic data, a two-substrate ping-pong mechanism of peroxidase was established. Catalytic efficiency and catalytic power of commercial peroxidase were 0.204 x 10(6) M(-1) min(-1) and 2.86 x 10(-4) min(-1), respectively. The catalytic constant (k(cat)) of the proposed method was 0.2080 x 10(3) min(-1). As a simple, rapid, precise and sensitive technique, PPDD-MQ stands as a potential replacement for the traditional guaiacol method. Applications to the plant extracts increase its relevance in the field of biochemical analysis.

Mequinol 2%/tretinoin 0.01% topical solution for the treatment of melasma in men: a case series and review of the literature.[Pubmed:18441773]

Cutis. 2008 Feb;81(2):179-83.

Melasma is a common hyperpigmentation disorder that typically affects women, though up to 10% of white individuals seeking treatment for melasma are men. Melasma can be a source of embarrassment for men because of its association with women and pregnancy. We performed a case series assessing the use of Mequinol 2%/ tretinoin 0.01% topical solution in 5 men with melasma. Four of 5 patients achieved complete clearance of melasma at 12 weeks, and 1 patient showed moderate improvement. Side effects were minimal and consisted of stinging in one patient. All patients maintained results at the 16-week follow-up visit. Mequinol 2%/tretinoin 0.01% topical solution was an effective and well-tolerated treatment of melasma in men. The vehicle resulted in good compliance and minimal adverse effects in patients. This is the first report describing the use of Mequinol 2%/tretinoin 0.01% topical solution for the treatment of melasma in men; there are no reports in women.

Intramolecular structure and dynamics of mequinol and guaiacol in the gas phase: Rotationally resolved electronic spectra of their S1 states.[Pubmed:26342364]

J Chem Phys. 2015 Sep 7;143(9):094301.

The molecular structures of guaiacol (2-methoxyphenol) and Mequinol (4-methoxyphenol) have been studied using high resolution electronic spectroscopy in a molecular beam and contrasted with ab initio computations. Mequinol exhibits two low frequency bands that have been assigned to electronic origins of two possible conformers of the molecule, trans and cis. Guaiacol also shows low frequency bands, but in this case, the bands have been assigned to the electronic origin and vibrational modes of a single conformer of the isolated molecule. A detailed study of these bands indicates that guaiacol has a vibrationally averaged planar structure in the ground state, but it is distorted along both in-plane and out-of-plane coordinates in the first electronically excited state. An intramolecular hydrogen bond involving the adjacent -OH and -OCH3 groups plays a major role in these dynamics.

Competing 1pisigma* mediated dynamics in mequinol: O-H versus O-CH3 photodissociation pathways.[Pubmed:22948565]

Phys Chem Chem Phys. 2012 Oct 14;14(38):13415-28.

Deactivation of excited electronic states through coupling to dissociative (1)pisigma* states in heteroaromatic systems has received considerable attention in recent years, particularly as a mechanism that contributes to the ultraviolet (UV) photostability of numerous aromatic biomolecules and their chromophores. Recent studies have expanded upon this work to look at more complex species, which involves understanding competing dynamics on two different (1)pisigma* potential energy surfaces (PESs) localized on different heteroatom hydride coordinates (O-H and N-H bonds) within the same molecule. In a similar spirit, the work presented here utilizes ultrafast time-resolved velocity map ion imaging to study competing dissociation pathways along (1)pisigma* PESs in Mequinol (p-methoxyphenol), localized at O-H and O-CH(3) bonds yielding H atoms or CH(3) radicals, respectively, over an excitation wavelength range of 298-238 nm and at 200 nm. H atom elimination is found to be operative via either tunneling under a conical intersection (CI) (298 >/= lambda >/= 280 nm) or ultrafast internal conversion through appropriate CIs (lambda /= lambda >/= 245 nm, mediated H atom elimination is not observed. In contrast, we find that state driven CH(3) radical elimination is only observed in the excitation range 264 >/= lambda >/= 238 nm. Interpretation of these experimental results is guided by: (i) high level complete active space with second order perturbation theory (CASPT2) calculations, which provide 1-D potential energy cuts of the ground and low lying singlet excited electronic states along the O-H and O-CH(3) bond coordinates; and (ii) calculated excitation energies using CASPT2 and the equation-of-motion coupled cluster with singles and doubles excitations (EOM-CCSD) formalism. From these comprehensive studies, we find that the dynamics along the O-H coordinate generally mimic H atom elimination previously observed in phenol, whereas O-CH(3) bond fission in Mequinol appears to present notably different behavior to the CH(3) elimination dynamics previously observed in anisole (methoxybenzene).