Related Experiment Video
Updated: Jun 13, 2026
Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
Published on: October 5, 2019
Axial Coordination of Melatonin in Magnesium Porphyrin: Structural Insights, Excited-State Dynamics, and
Abdul K Choudhury1, Jagannath Bhuyan1,2
1Department of Chemistry, North Eastern Regional Institute of Science and Technology, Nirjuli, Arunachal Pradesh 791109 India.
Abstract:
Axial coordination of biologically relevant ligands offers an effective strategy for tuning the photophysical and redox behavior of magnesium porphyrins, widely used as models for chlorophyll a. Herein, we report the first example of a melatonin-coordinated magnesium porphyrin, [MgT(4-Cl)PP(MT)],1 [T(4-Cl)PP = 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin, MT = melatonin], in which melatonin binds axially to the Mg(II) center through its carbonyl oxygen atom with the Mg-OMT distance of 2.008 Å, resulting in a penta-coordinated square-pyramidal geometry. Compound 1 was characterized by UV-visible spectroscopy, NMR, MALDI-TOF, FTIR, and single-crystal XRD. Moreover, the redox properties were studied using cyclic voltammetry. Photophysical studies reveal that melatonin coordination significantly alters the excited-state dynamics of the porphyrin, resulting in reduced fluorescence lifetime and suppressed singlet oxygen generation, which correlate with enhanced resistance toward photoinduced degradation. The melatonin-bound complex also exhibits improved antioxidant activity relative to the parent magnesium porphyrin. Notably, freshly isolated spinach chlorophyll a exhibits similar resistance to oxidative stress and photodegradation in the presence of melatonin. Complementary density functional theory calculations and electrostatic analyses provide insight into ligand-induced modulation of the porphyrin π-electronic framework. Overall, these results demonstrate that axial coordination of melatonin offers an effective strategy for tuning the photochemical stability and reactivity of magnesium porphyrins.
Related Concept Videos
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
01:26Variables Affecting Phosphorescence and Fluorescence
02:42Valence Bond Theory
01:02The Pineal Gland
The primary secretion of the pineal gland is the hormone melatonin, derived from serotonin. The concentration of melatonin in the...
02:52Stereoisomerism
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
01:26Photochemical Electrocyclic Reactions: Stereochemistry
Selection Rules: Photochemical Activation