Squaric acid, white to beige granular crystal, with strong acidity, pkl = 1.5; pK2=3.5。 With ferric chloride, an aqueous solution produces dark purple. It can be oxidized by bromine and potassium permanganate and does not react with phenylhydrazine. Like carboxylic acid in nature, it can be salted with alkali to produce ester, acyl chloride, amide and mixed anhydride. It can be used as an acylation reagent for acylation reaction with an electrically activated aromatic ring. It reacts with active double bonds and methyl groups to produce new compounds with special properties. It is prepared from 1,1,2,2-tetrafluoro-3,3,4,4-tetrachlorocyclobutane or perchloric-1,3-butadiene.
Used as acylation reagent for acylation reaction with an electrically activated aromatic ring; React with active double bonds and active methyl groups to form new compounds with unique properties. It can be used as an acylation reagent for acylation reaction with an electrically activated aromatic ring. It reacts with active double bonds and methyl groups to produce new compounds with unique properties. It is used as an intermediate in synthesizing organic photoconductor, liquid crystal display material, laser writing and recording material and electrostatic photography light receptor material.
Application of square cyanine dye in protein labeling imaging: molecular imaging method has rapidly become a powerful tool for biological research, drug development and clinical diagnosis. It can be used for natural targets and fluorescence imaging methods and has selectivity and molecular imaging sensitivity. However, for tissue or cell imaging in vivo, fluorescent dyes' maximum absorption and emission are preferred in the near-infrared region because this wavelength region has minor biomolecular interference, low spontaneous fluorescence, good tissue penetration, and low phototoxicity to cells. Because squaric acid can be labeled in proteins, it plays a crucial role in treating tumors and warts.
Application of square cyanine dye in tumor marker diagnosis and treatment: in detecting fluorescence imaging of tumor lesions, a near-infrared fluorescent dye can be modified to target molecules that recognize the specific receptors of tumor cells. When applied to the diagnosis and treatment of a tumor, the modified near-infrared probe will target the tissue or compartment where the cancer is located. The typical target molecules are antibodies, some polypeptide molecules. With its specificity, the sensitivity of fluorescence detection is greatly improved. If cancer cells can be detected in the early stage of cancer, it will be very conducive to treatment. However, identifying cancer cells from normal cells and selectively killing cancer cells is still the primary goal of the development of science and technology. Some square cyanine dyes have been proved to be photosensitizers for PDT (photodynamic therapy). PDT is a new technology for disease diagnosis and treatment using photodynamic effects. The basic principle is to produce toxic substances and reactive oxygen species under the excitation of a sensitizer. The process is that the squaric acid absorbed by the tissue is excited under the irradiation of the excitation light of a specific wavelength. The photosensitizer transmits the energy to the surrounding oxygen to generate highly active singlet oxygen. The singlet oxygen reacts with the adjacent biological macromolecules to produce cytotoxicity, which destroys the normal function of the cell and causes cell death.