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Synthesising Schiff Base Antimicrobial Copper Complexes With Unprecedented Speed

Researchers at the Tokyo University of Science have developed a method that synthesises amino acid derivatives of Schiff base copper complexes in 10 minutes, a step up from previous reaction times that spanned from a few hours to days.

Schiff bases are a group of organic compounds that contain a carbon-nitrogen double-bond (imine bond). These compounds and their derivatives have fascinated researchers since their discovery in the 19th century due to their multitude of chemical properties that have shown promise for use in chemical catalysts, dyes, and even environmental sensors.

In particular, the metal derivatives of Schiff bases have been under scrutiny in recent years because of their biological activity. Research is currently underway to examine their anticancer, antioxidant, and antimicrobial properties. It has also been found that amino acid Schiff base copper complexes have the highest potential for antibacterial activity. However, it takes from hours to days to produce these compounds, which is extremely time inefficient.

Fortunately, in a discovery by scientists from the Tokyo University of Science, led by Professor Takashiro Akitsu, with input from Dr. Estelle Léonard and Dr. Antoine Fayeulle from ESCOM, TIMR (Integrated Transformations of Renewable Matter), Centre de Recherche Royallieu, University of Technology of Compiègne, France, a new two-step procedure to synthesise amino acid Schiff base Cu(II) complexes in 10 minutes was found.

Prof. Akitsu hopes that his team’s research may make synthesis for amino acid Schiff base Cu(II) complexes more time-efficient for their use in a wider variety of applications.

In the team’s optimised process, microwave irradiation was used during the preparation as it heats the reaction mixture in a controlled manner, increasing the rate of reaction and allowing for fewer by-products, higher purity, and increased yields. Furthermore, the chosen solvent for the reaction was methanol, which has a high loss tangent — a measure of a substance’s ability to convert energy from microwaves to heat energy — of 0.659, and has a high tendency to absorb microwaves. These properties of methanol were key to the drastic reduction of global reaction time to 10 minutes.

To gain a better understanding of the antimicrobial properties of the compounds, different types of bacteria were exposed to them. The experimental results show that mono and disubstituted complexes with chlorine were more effective against bacteria, especially against ;E. coli as compared to chlorine-unsubstituted compounds. Some chlorine-substituted complexes also had light antioxidant activity. The scientists also hope to verify the toxicity of these compounds toward the kidney, liver, and skin cells, such that the safety risk of these compounds is properly evaluated before conducting more research into the biological applications of these compounds.

The outcomes of this study may be used to develop time-efficient synthesis for amino acid derivatives of different Schiff base metal complexes. “Bacterial infectious diseases are a major threat to public health. Our study aims to contribute towards the improvement of health care systems in developing nations that are often affected by infectious epidemics,” concludes Prof Akitsu. [APBN]

Source: Otani et al. (2022). Synthesis, Identification and Antibacterial Activities of Amino Acid Schiff Base Cu (II) Complexes with Chlorinated Aromatic Moieties. ;Applied Microbiology, ;2(2), 438-448.