PHOTOSYNTHETICA

Photosynthetica X:X | DOI: 10.32615/ps.2026.032

Organic compounds as Photosystem II inhibitors and Cu²⁺ ligands: insights from primary screening

M.S. SHABANOVA¹, E.V. ZADNEPROVSKAYA², S.K. ZHARMUKHAMEDOV³, R.G. VASILOV⁴, M.S. KARACAN⁵, S.I. ALLAKHVERDIEV^{2, 3, 6}

¹ Institute of Molecular Biology, Ministry of Science and Education of the Republic of Azerbaijan, 11 Izzat Nabiev Street, AZ1073 Baku, Azerbaijan

² K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, 35 Botanicheskaya Street, 127276 Moscow, Russia

³ Institute of Basic Biological Problems, Russian Academy of Sciences, 2 Institutskaya Street, 142290 Pushchino, Moscow Region, Russia

⁴ National Research Center 'Kurchatov Institute', 1 Akademika Kurchatova Square, 123182 Moscow, Russia

⁵ Department of Chemistry, Science Faculty, Gazi University, Teknikokullar, 06500 Ankara, Turkey

⁶ Faculty of Engineering and Natural Sciences, Bahçeşehir University, Çirağan Caddesi 4-6 Osmanpaşa Mektebi, 34353 Istanbul, Turkey

The search for novel organic compounds as PSII inhibitors and copper (Cu²⁺) ligands addresses key agricultural challenges. Three novel compounds were synthesized and evaluated for PSII photochemical activity inhibition and Cu²⁺-chelating ability. Primary screening was performed by recording effects on minimal and maximal chlorophyll fluorescence levels in isolated thylakoids. Testing employed both direct (thylakoids + Cu²⁺ + compound) and reverse (thylakoids + compound + Cu²⁺) addition sequences, with measurements performed under short illumination (<10 s) to avoid photodynamic artifacts. The tested compounds showed no pronounced inhibitory activity toward PSII photochemistry and exhibited no strong Cu-chelating capacity. Nevertheless, these data enable formulation of more stringent structural requirements for candidate molecules and confirm the high information content of the proposed combined screening approach for further biologically active substance design.

Additional key words: chlorophyll fluorescence; copper ions; ligands; novel organic compounds; photosystem II; thylakoids.

Received: August 28, 2026; Revised: September 15, 2026; Accepted: September 16, 2026; Prepublished online: October 2, 2026