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Towards practical applications for molecular logic gates: “and” logic as an additional layer of selectivity in singlet oxygen release for photodynamic therapy

Özlem, Suriye
There have been many examples of individual molecular logic gates and molecular equivalents of more complex digital designs in recent years such as half adder, half subtractor, multiplexer. Neverethless, the unresolved issues of addressability and lack of communication between logic gates remain to be the Achille’s heel for molecular logic gates. A few years ago we have demonstrated that appropriately decorated bodipy dyes can be very efficient generators for singlet oxygen, thus act as a satisfactory photodynamic agents. As a bonus, these dyes absorb very strongly at 660 nm which is considered to be within the therapeutic window of mammalian tissue. So, combining our earlier experience in molecular logic gates and rational design of photodynamic agents, we proposed a photodynamic therapy agent that would release singlet oxygen at a much larger rate when the cancer related cellular parameters are above a threshold value at the same location. Following the survey of the relevant literature for cancer related parameters, we decided that sodium ion concentration and pH (H+ concentration) could be very promising targets. In the tumor regions the pH can drop below 6 and the Na+ concentration is also significantly higher then normal tissues. As a result, in the proposed logic system the chemical inputs could be Na+ and H+. The system in fact is an automaton which is to seek higher concentration of both hydrogen and sodium ions, and release the toxic agent (singlet oxygen) only when both concentrations are high. Thus, the proposed logic gate is an AND logic gate, the output of which is singlet oxygen. Keywords: Photodynamic therapy, singlet oxygen, molecular logic gates, AND logic operation.