1558 cm-1 is the C=N quinonoid
stretching mode of vibration .
Raman shift Assignments ([cm.sup.-1]) 1598 [v.sub.C=C] stretching vibration in the quinonoid
rings [2, 9, 10] 1562 N-H deformation vibration of the semiquinonoid structures [2, 11] 1470 [v.sub.C=N] stretching vibrations in quinonoid
unit [11, 12] 1398 [v.sub.C-N+] ring-stretching vibrations of substituted 1347 N-phenylphenazines [2, 4] 1220 Symmetric uC-N stretching [3, 4, 11] 1164 [[delta].sub.C-H] bending vibration [2, 3, 11] 821 781 750 Various deformations modes of polyaniline 608 [9, 12] 526 419 311 Terminal halogen atoms stretching vibrations ([v.sub.Ag-Cl])  250 Stretching vibrations of the bridging halogen metal ([[delta].sub.Cl-Ago] and/or [[delta].sub.N-AgO]) [8, 13]
The Raman features of semiquinone radical structures typical for protonated emeraldine salt are enhanced by near-infrared excitation; in contrast, the Raman features of quinonoid
units typical for the PANI base are enhanced with a red excitation line .
A decrease in the degree of oxidation of the polyaniline chain was observed with an increasing of Co content on the surface, by reducing the quinonoid
units to benzenoid ones.
The peaks corresponding to benzenoid (NH-B-NH) and quinonoid
(NH-Q-NH) rings are observed around 1590,1500, and 1300 [cm.sup.-1], respectively [30, 31].
metal complexes: Toward molecular switches.
Aurine, on the other hand, because of ionization of its hydroxyl groups, resists further hydroxylation and shows reduction of the quinonoid
form up to at least pH 11.7.
Synthesis and antitumor activity of quinonoid
derivatives of cannabinoids.
Such molecules participate in different pathways yielding various types of phenoxy radicals, which lead to chain cleavage or colored quinonoid
The antimycobacterial activity of quinonoid
compounds, particularly those isolated from natural sources, has remained unexplained.
The activity of this enzyme was assayed, as described previously (24), by monitoring the oxidation of NADH during the reduction of 6,7-dimethyldihydropterin (quinonoid
isomer) to 6,7-dimethyltetrahydropterin, catalyzed by DHPR.
Chemical modifications were performed on these compounds to address this issue and modification of the quinonoid
center of [alpha]-lapachone followed by epoxidation generated the epoxy-[alpha]-lapachone (Figure 1(e)) and epoxymethoxy-lawsone (Figure 1(f)), derivatives potentially less toxic for mammalian cells [22, 23].