Hypochromic shifts

Hassan et al. [39] used a sensitive color reaction method for the determination of primaquine in pharmaceutical preparation. Primaquine was treated with diazo-p-nitroaniline in acidic medium to give an orange-yellow product with an absorbance maximum at 478 nm. When the medium was made alkaline, bathochromic, and hypochromic shifts occurred the new maximum was located at 525 nm. The mean percentage recoveries for authentic samples amounted to 100 and 100.21 by the acid and alkaline procedures, respectively (P = 0.05). Both reactions could be used to determine primaquine salts in pharmaceutical preparations. The results obtained were in good agreement with those of the official methods. Recoveries were quantitative by both methods. 

The method of preparation of this complex is simple enough and consists of mixing of fullerene solution in toluene with solution of PVP in chloroform with the following evaporation of organic solvents and dissolution of the residue in water. It was shown that the complex formation caused the bathochromic and hypochromic shifts of the fullerene absorption bands in UV-VIS spectra (Yamakoshi et al., 1994). 

In order to prepare the complexes with low association of fullerene molecules it is necessary to start with diluted solutions of C60 (in toluene) and PVP (in CHCy, but the goal can be achieved only at relatively low content of fullerene in the complex. Thus, the degree of association of C60 molecules depends also on the molecular mass of PVP, and low associated complexes can be obtained only with PVP 10,000 and fullerene low concentration. It must be mentioned however that such complexes are relatively unstable - during their storage for about several months the association of fullerene molecules changes what can be seen from the shift of the band in UV-VIS spectra between 330 and 340 ran (bathochromic and hypochromic shifts). 

We have recently prepared a new chromophoric and redox-responsive ionophore (4) containing a tricyanovinyl redox-active moiety (35) (Scheme 2). Electronic absorption spectra of (4) exhibit hypochromic shifts on binding Group IA and IIA metal cations and cyclic voltamme-tric electrochemical investigations reveal that (4) electrochemically recognizes Na+ and K+ guest cations, resulting in one-wave CV shifts of the tricyanovinyl reduction wave (80 and 20 mV, respectively) to more anodic potentials. 

M. Mayot, and G. Berthier The occurrence of hypochromic shifts on alkyl substitution Structure and color of methylated derivatives of azulene. J. Chem. Phys. 18, 257 (1950). 

Denaturation results in decreased absorption at 260 nm (hypochromic shift). 

From Table II it appears that the long-wave absorption maximum is increasingly shifted at longer wavelengths in the order O, S, Se, Te. 2,4,6-triphenyl-substituted cations 8-10 appear to be an exception, but the seemingly hypsochromic shift in going from O to Se is probably due to a simultaneous bathochromic shift of the L band and hypochromic shift of the Lft band. The latter appears as a shoulder of the L band in 9 and is probably submerged by the L band in 10. Thus X ax refers to the L, band for cations 8 and 9, and to the L band for cation 10. 

Picrasidine O (33) has been isolated from the root wood of P. quassioides (48). The UV spectrum shows, like 3, a hypochromic shift on addition of acid. The H-NMR spectrum shows signals arising from a methyl (8 3.82, 377, s) and a methoxyl (S 4.26, 377, s) but lacks the aromatic proton at H-4, and hence structure 33 was proposed. Since the synthetic compound obtained through methylation of 28 agrees with naturally produced 33, structure 33 was confirmed. 

UV spectra of canthin-5,6-dione alkaloids 3 and 33, which were isolated by Ohmoto and Koike (3,48) from Picrasma quassioides, showed a characteristic absorption between 400 and 500 nm. This absorption was hypochromically shifted under acidic conditions. The UV spectrum of 3 in acidic solvents resembles that of 5-hydroxycanthin-6-one (16) (Fig. 3). This fact, that is, that 3 undergoes chemical shift in acidic solvents, indicates that the carbonyl at position 5 of the canthin-5,6-dione skeleton in 16 is protonated, producing 42a. On the basis of the above observations, Ohmoto and Koike refluxed 16 and 33 with dimethyl sulfate in acetone and synthesized 3 and 28 (Scheme 3). 

While chaetomellic acids were isolated in the anhydride form [71] the integrity of the anhydride form in the aqueous assay environment was questionable. This raised questions as to which form, the diacid or the anhydride, was the species that inhibited FPTase enzyme activity. This uncertainty was resolved by demonstrating that the equilibrium between the diacid and the anhydride forms was pH dependent (Figure 12). The UV spectrum of the anhydride in CH3CN exhibited a maximum for a cyclic anhydride at 254 nm. When the anhydride was treated either with O.IN NaOH or HEPES buffer (pH = 7.5) the maximum shifted to X.max 243 nm with a concurrent hypochromic shift. As expected, the process could be reversed by addition of mineral acid indicating that the active species are the open dicarboxylates [71]. 

The absolute sense of twist between the two amino groups of the diaminocyclohexane of kasugamin 85 can be determined from the signs of exciton-split c.d. corves of derivatives 86 bearing two chromophoric imino groups. The protonated forms lead to strong bathochromic and hypochromic shifts. Similar derivatizations were applied to methyl a-L-acosaminide and daunosamine. The effects of stereochemistry and solvent on o.r.d., c.d. and u.v. spectra of 1-nitrophenyl D-galactopyranosides has been described. 

A different approach to dendritic sensors involves modification of a sensor core unit with dendritic substituents to confer beneficial solubility properties. An example of a sensor core unit is the porphyrin macrocycle, a heterocycle that has been employed extensively in prototypical photochemical sensor systems. Vinogradov and co-workers have exploited the versatile photoactive porphyrin sensor unit as a fluorescence-based pH indicator for use in biological assays [73], by attaching acid terminated polyamide-ether dendrons as substituents (Figure 8.12). The two imino nitrogen atoms present in the free-base porphyrin are susceptible to stepwise protonation to afford initially a cation and then a dication, respectively. Upon protonation, both the emission and absorption fluorescence spectroscopic characteristics of the porphyrin core are subject to dramatic hypochromic shifts. This spectroscopic phenomenon formed the basis for an accurate pH indicator with potential applications in proton gradient determination studies in biological systems. 

Hyperchromic shift Hypochromic shift Hypsochromic shift Ion pair... 

Hypochromic shift A decrease in the of a chio-mophore resulting in a less intense color. 

N-Oxidation has an important effect on the absorption spectrum of N,N-dialkylanilines (e.g., 12, see Equation 99.7). The substituent is no longer an electron-donating group and both a hypso- and a hypochromic shift take place. ° In this case, irradiation causes hydrogen transfer to the solvent, as well as attack on the side chain leading to amides and dealkylated anilines. ... 

---