Photophysical Properties of Indotricarbocyanine Dyes Complexed with Lipid-Transfer Protein Ns-LTP1

The interaction of indotricarbocyanine dyes with lipid-transfer protein Ns-LTP1 in Dulbecco's phosphate-buffered saline (PBS) was studied. An orthophenylene bridge with a chlorine in the meso-position of the dye was shown to be ineffective as a linker for protein macromolecules without a free cysteine residue. The indotricarbocyanine dye was modified into the N-hydroxysuccinimide ester to obtain a complex of the indotricarbocyanine dye with the Ns-LTP1 protein. A complex of dye molecules with the Ns-LTP1 protein was obtained by mixing a two-phase system of the protein in PBS and the dye activated ester in 1,2-dichloroethane. The half-width of the absorption spectrum increased from 56 to 61 nm; the fluorescence decay time, from 0.3 to 0.5 ns; and the degree of polarization, from 27 to 31% upon formation of the complex. It was established that HCl at concentrations equivalent to its content in gastric juice (0.1–0.5%) led to irreversible destruction of the dye. Capsules that can withstand stomach acid and dissolve in the intestines could be used to treat erosive and ulcerative lesions with peroral administration of the complex.