Synthesis and Biological Evaluation of New Imidazolium and Piperazinium Salts of Pyropheophorbide-a for Photodynamic Cancer Therapy

We have designed imidazolium and piperazinium salts of pyropheophorbide-a in order to develop effective photosensitizers which have good solubility in polar and non polar media and to reveal the possible influences of the piperazine and imidazole moieties on the biological activities of pyropheophorbide-a. The phototoxicity of those pyropheophorbide-a salts against A549 cells was studied in vitro and compared with that of pyropheophorbide-a. The result showed that complexing piperazine and imidazole into pyropheophorbide-a decreases its dark toxicity without greatly decreasing phototoxicity and, enhances its phototoxicity without greatly increasing dark toxicity, respectively. This work not only describes novel amphiphilic salt complexes of pyropheophobide-a which retain the biological activities of the parent compound pyropheophorbide-a and could be effective candidate for PDT, but also reveals the possibility of developing effective photosensitizers by complexing imidazole and piperazine into other hydrophobic photosensitizers

Green Synthesis of Sustainable Solar Cell Materials

As world energy consumption continues to grow, so does the priority to develop sustainable energy sources, such as solar energy, the most abundant of these sources. Large scale production of solar cell materials demands the use of more sustainable starting materials and greener methods to assemble light-harvesting devices. Our project aims to design new solar cell materials using greener chemical reaction conditions, with the ultimate goal of implementing our materials in organic photovoltaic cells (OPVs). Commercially available solar cell materials, while engineered to efficiently harvest solar energy, involve wasteful and expensive processes. In contrast, our focus is to develop greener methods for production of materials to employ in OPVs. Beginning with the first step of a 3-step method to assemble our target polymer for use in an OPV cell, we compared the same reaction using solution, mechanochemical, and microwave methods. Mechanochemistry initiates chemical reactions by use of mechanical force in the absence of a solvent as opposed to traditional solution methods that use a wasteful or toxic solvent. Microwave chemistry involves controlled, rapid, uniform heating and can reduce reaction times dramatically. The products of the first reaction step, a Knoevenagel condensation, synthesized by each of the three methods, were identified using structural techniques including nuclear magnetic resonance and X-ray crystallography. Comparison of the reaction products obtained using these three methods shows that the greener mechanochemical and microwave conditions resulted in similar or higher yields, shorter reaction times, and allowed for replacement of a toxic base with a more benign base. Our results indicate that greener approaches to synthesizing solar energy materials are possible. Our next step will be to investigate applying greener approaches for the additional steps needed to reach our target polymer. Greener approaches can help significantly minimize environmental impacts and decrease costs associated with assembling OPV materials

Green methods for synthesis of solar cell materials

Silicon is the most common material used in solar cells in part due to its abundance in the earth’s crust as well its intrinsic semiconductor properties. However, there are some drawbacks of silicon solar cellsincluding toxicity in processing, difficulty in purification, high cost of fabrication, and rigidity. Materials used in bulk heterojunction organic photovoltaics (BHJ OPVs) have many advantages over silicon as they can be less expensive, have more tunable properties, and are flexible. Donor polymers for incorporation in OPVs made using furfural, an extract of corn stover, have the potential to be semi-sustainable. While furan polymers areless widely studied than their thiophene analogs, both heterocycles were studied in monomers for use in conjugated donor polymers. Two greener synthetic methods for monomer synthesis, mechanochemistry andmicrowave chemistry, were compared to traditional solution methods. A Knoevenagel condensation was carried out using an indole and an aldehyde employing the more toxic base piperidine as well as benign potassiumcarbonate. The products were characterized by H-NMR, elemental analysis, X-ray crystallography, and electrospray mass spectrometry. Both of the greener methods gave higher yields and required less time than thetraditional solution synthesis. NMR and elemental analysis of the products from both the mechanochemical and microwave reactions confirmed both condensation and further deprotonation of the indole N-H proton. Thisunexpected result is important because the next synthetic step to form our target monomer for the desired polymer is installing a long alkyl chain for polymer solubility. Current work focuses on the alkylation of the indole group of our monomer using these greener methods. Preliminary mass spectral results suggest alkylation of Knoevenagel products are possible via mechanochemistry and microwave chemistry