Bathochromic shift, ultraviolet-visible

Purines absorb only ultraviolet light and they contribute to structural colors (white and silver) in animals. Pterines are generally yellow, orange, or red pigments. Because they are amphoteric molecules, the absorption spectra depend on the pH and present three or two absorption maxima, usually one in the visible region. Sepiapterin has an absorption maximum at 340 nm in O.IM NaOH and at 410 nm in O.IM HCl." Leucopterin has three maxima 240, 285, and 340 nm. Xanthopterin has two 255 and 391 nm. Because they are conjugated with proteins, pterins show bathochromic shifts in vivo. They also present fluorescence when excited with UV light. 

The ultraviolet-visible (UV-Vis) spectra of several isomeric pyrrolotetrazoles 12 and 13 in methanol have been compared. The spectra of ZH-pyrrolotetrazoles 13 are characterized by pronounced bathochromic shifts of the longest wavelength compared to those of 12 they also display green or blue fluorescence. The largest bathochromic shift for the 2/f-pyrrolotetrazole 13 (R1 = H, R2 = Ph, R3 = H, R4 = Ph) is ascribed to unhindered conjugative interaction of the phenyl group and the heterocycle, which is not possible to that extent for 12 (R1 = H, R2 = Ph, R3 = H, R4 = Ph) <2001J(P1)720>. 

A potentially new separation method called held flow fractionation has been introduced only on a preliminary basis for the determination of adsorbed substances to particles [182]. A novel method was developed by Ilium et al. [68] to determine both free and bound drug on PBCA nanoparticles without prior separation. For example, a bathochromic shift was observed in the ultraviolet/visible (UV/vis) spectrum of Rose Bengal after binding to PBCA nanoparticles. The amount of free drug was determined at 540 nm and bound drug at 548 nm. This type of analysis is very specific to the drug under investigation. 

The naturally occurring homoisoflavanones exhibit a uniform ultraviolet-visible absorption behaviour depending only on the presence or absence of the 3 (9)-double bond. The long wave absorption maxima in ethanol appear between 358 and 367 nm for unsaturated and between 285 and 297 nm for saturated systems. The logs values range from 4.2 to 4.7. Addition of sodium acetate induces bathochromic shifts of 20—40 nm if a free hydroxyl at C-7 is present. An analogous shift of 20—30 nm is observed with aluminum chloride if the compound contains a free hydroxyl at C-5 48). 

There are observed in the ultraviolet and visible spectra red (bathochromic) shifts for chromophores acting as proton donors and blue (hypsochromic) shifts for chromophores acting as proton acceptors. 

---