A spectroscopic study of folic acid (AB), pterin (A) and para‐aminobenzamide (B), using absorption, fluorescence, phosphorescence and electron spin resonance techniques, indicates the occurrence of spectroscopic differences between the behavior of solution of folic acid AB and equimolar solution of (A + B).The experimental evidence may be summarized as follows: a probable hypochromic effect on the highest energy bands, and a bathochromic shift (8 nm) over the whole absorption spectrum of AB, compared to that of (A + B); highly efficient quenching (more than 95%) of the fluorescence of components A and B in AB, compared to (A + B); disappearance of phosphorescent and paramagnetic signal of B in AB, but not in (A + B). The experiments are carried out on samples in aqueous solution at pH 5.6 (neutral, sparingly soluble, form of A and AB) and at pH 10.5 (ionic form of A and AB).These spectroscopic differences, observed between solutions AB and (A + B), suggest important intramolecular interactions between the two chromophores A and B in the molecule AB.A folded configuration, in which pterin A and the aromatic ring of B are held in proximity by several hydrogen bonds, seems in better a
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