Theoretically obtained insight into the effect of basic amino acids on Cypridina bioluminescence.

The spectroscopic properties of acylamino form of Cypridina oxyluciferin are modulated by the covalent character of the N 4 -H 5 bond. With N 4 -H 5 bond length increasing, the weight of amide ion in the complex increase, the emission spectra shift to red. • In polar medium, the emission wavelengths varied little with solvent polarity. • Basic amino acid only slightly affect the structure and spectroscopic properties. • Because of the different electron distribution, the emission spectra is shifted to blue. • Amide ion was not taken into consideration as a possible emitter. • The spectroscopic properties of acylamino are modulated by the covalent character. Because of high bioluminescent quantum yields, independent cofactors, high signal-to-noise ratio, Cypridina bioluminescence has been successfully applied to gene reporter assays, enzyme immunoassays, immunohistology and imaging. Although the chemical reaction that transforms Cypridina luciferin into Cypridina oxyluciferin is clearly defined, the environmental effects on the spectrochemistry of Cypridina oxyluciferin continue to be a particularly intriguing aspect. In this paper, the solvent effect on the fluorescent spectrum, the basicity of amino acids and the degree of covalent character of hydrogen bond were studied by a theoretical Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT) approach. Our results demonstrate that the emission wavelengths varied little with solvent polarity. The compositive effects of basic amino acid and polarity of the environment only slightly affected the structure and spectroscopic properties. The fluorescent properties of Cypridina oxyluciferin can be modulated by the covalent character of the hydrogen bond. [ABSTRACT FROM AUTHOR]