Bušić, V.; Roca, S.; Vrandečić, K.; Ćosić, J.; Siber, T.; Gašo-Sokač, D. Comparison of Conventional and Ultrasound-Assisted Green Synthesis of Quaternary Pyridinium Salts and Their Antifungal Activity. Appl. Sci. 2026, 16, 3470. https://doi.org/10.3390/app16073470
Usporedba konvencionalne i ultrazvučno potpomognute zelene sinteze kvaternih piridinijevih soli i njihove antifungalne aktivnosti
OPIS ISTRAŽIVANJA
Ovo istraživanje bavi se razvojem ekološki prihvatljivih metoda sinteze kvaternih piridinskih soli, s naglaskom na principe zelene kemije, te njihovom antifungalnom aktivnošću. Cilj rada bio je ispitati učinkovitost kvaternizacijskih reakcija između piridin-3- i piridin-4-aldoksima i supstituiranih 2-bromoacetofenona u različitim reakcijskim medijima, uključujući konvencionalna otapala (etanol) i zelene alternative poput niskotemperaturnih eutektičnih otapala (DES), uz primjenu ultrazvučne sinteze.
DES-ovi su pripremljeni kombinacijom kolin-klorida kao akceptora vodikove veze i različitih donora (urea, glicerol te organske kiseline). Njihova prednost leži u biorazgradivosti, niskoj toksičnosti i jednostavnoj pripremi bez stvaranja značajnog otpada. U istraživanju je po prvi put ispitan njihov potencijal u kvaternizacijskim reakcijama, pri čemu su pokazali ograničenja zbog viskoznosti i slabije difuzije reaktanata, što je rezultiralo nižim prinosima u usporedbi s klasičnim otapalima.
Rezultati su pokazali da ultrazvučna sinteza značajno poboljšava učinkovitost reakcije u odnosu na konvencionalne metode, skraćujući vrijeme reakcije s 3 sata na 1 sat te povećavajući ukupne prinose. Najbolji rezultati postignuti su kombinacijom ultrazvuka i DES-a, posebno u sustavu kolin-klorid:urea, koji se pokazao kao najpovoljniji medij za kvaternizaciju.
Sintetizirano je ukupno 18 spojeva, čija je struktura potvrđena spektroskopskim metodama (NMR, IR, MS i elementarna analiza). Svi spojevi su zatim ispitani na antifungalnu aktivnost prema četiri fitopatogena: Botrytis cinerea, Fusarium culmorum, Macrophomina phaseolina i Sclerotinia sclerotiorum. Rezultati su pokazali značajnu inhibiciju rasta micelija, pri čemu je B. cinerea bio najosjetljiviji (do 70,7% inhibicije), dok je F. culmorum pokazao najmanju osjetljivost (≤32%).
Zanimljivo je da niža koncentracija spojeva (10 µg/mL) u nekim slučajevima pokazuje veću učinkovitost od više koncentracije, što se objašnjava fizikalno-kemijskim svojstvima i mogućom agregacijom molekula. Statistička analiza potvrdila je značajne razlike između spojeva i patogena, pri čemu su pojedini derivati pokazali izraženiji antifungalni potencijal. Zaključno, rad pokazuje da kombinacija ultrazvuka i DES-a predstavlja održivu i učinkovitu alternativu klasičnim metodama sinteze, uz istovremeno dobivanje biološki aktivnih spojeva s potencijalnom primjenom u zaštiti bilja.
Comparison of Conventional and Ultrasound-Assisted Green Synthesis of Quaternary Pyridinium Salts and Their Antifungal Activity
ABOUT THIS RESEARCH
This study focuses on the development of environmentally friendly synthesis methods for quaternary pyridinium salts, emphasizing the principles of green chemistry, as well as their antifungal activity. The aim was to investigate the efficiency of quaternization reactions between pyridine-3- and pyridine-4-aldoximes and substituted 2-bromoacetophenones in different reaction media, including conventional solvents (ethanol) and green alternatives such as deep eutectic solvents (DES), with the assistance of ultrasound irradiation.
DES were prepared by combining choline chloride as a hydrogen bond acceptor with various donors (urea, glycerol, and organic acids). Their advantages include biodegradability, low toxicity, and simple preparation without significant waste generation. In this study, their potential in quaternization reactions was investigated for the first time. However, they showed certain limitations due to high viscosity and reduced diffusion of reactants, which resulted in lower yields compared to conventional solvents.
The results demonstrated that ultrasound-assisted synthesis significantly improves reaction efficiency compared to conventional methods, reducing reaction time from 3 hours to 1 hour while increasing overall yields. The best results were achieved by combining ultrasound irradiation with DES, particularly in the choline chloride:urea system, which proved to be the most effective medium for quaternization.
A total of 18 compounds were synthesized and structurally confirmed using spectroscopic techniques (NMR, IR, MS, and elemental analysis). All compounds were subsequently tested for antifungal activity against four phytopathogenic fungi: Botrytis cinerea, Fusarium culmorum, Macrophomina phaseolina, and Sclerotinia sclerotiorum. The results showed significant inhibition of mycelial growth, with B. cinerea being the most sensitive species (up to 70.7% inhibition), while F. culmorum showed the lowest sensitivity (≤32%).
Interestingly, in some cases, lower concentrations of the compounds (10 µg/mL) exhibited higher antifungal activity than higher concentrations. This behavior is attributed to physicochemical properties of the compounds and possible aggregation effects. Statistical analysis confirmed significant differences among compounds and pathogens, with certain derivatives showing particularly strong antifungal potential. In conclusion, the study demonstrates that the combination of ultrasound irradiation and deep eutectic solvents represents a sustainable and efficient alternative to classical synthetic methods, while also yielding biologically active compounds with potential applications in plant protection.