NADH-depletion triggered energy shutting with cyclometalated iridium (III) complex enabled bimodal Luminescence-SERS sensing and photodynamic therapy.

The nicotinamide adenine dinucleotide-reduced (NADH) function as a hydride (H) carrier to maintain cellular homeostasis. Herein, we report a quinoline appended iridium complex (QAIC) as a molecular probe in fluorescence and surface-enhanced Raman spectroscopy (SERS) modalities to evaluate the endogenous NADH status. NADH-triggered activation of QAIC enabled luminescence (turn-ON) and SERS (turn-OFF) switching phenomenon with a detection limit of 25.6 nM and 15 pM for NADH in luminescence and SERS respectively. Transition state modelling using density functional theory calculations proved that a facile migration of H from NADH to QAIC transformed the activated QAIC (N-QAIC) with an energy span of 19.7 kcal/mol. Furthermore, N-QAIC is probed as a photosensitizer to source singlet oxygen by blocking the photo induced electron transfer (PeT) and generate NAD radicals. Therefore, an efficient light triggered cyclometalated iridium-based molecular probe has been divulged to promote bimodal NADH sensing and multiphase photodynamic therapy.

Substituent Effect Parameters: Extending the Applications to Organometallic Chemistry.

Typically, metal complexes are constituted of an acceptor metal ion and one or more Iigands containing the donor atoms. Accordingly, the properties of a metal complex are equally dependent on the nature of the metal ion and the ligands. Minute structural variations in the ligand will may result in linear changes in the respective energetic parameters and such linear relationships have paramount importance in organometallic chemistry. The variation in ligands is virtually limitless and substantial because of the extent of organic chemistry available for the modelling of desirable ligands, apart from the variation in metal ions. Anyhow, there is still a need for new parameters for the design and quantification of new ligands which in turn leads to the synthesis of metal complexes with possibly predictable chemical properties. Previous studies have demonstrated that quantum chemically derived molecular electrostatic potential (MESP) parameters can be listed as one of the superior quantifiers in this regard, which can act as an effective ligand electronic parameter. The interaction between the ligand part and metal-containing part will be crucial in assessing the reactivity of organometallic complexes. Here we are applying MESP based substituent constants derived from substituted benzenes to forecast the interaction energies in (pyr* )W(CO)5 , (NHC* )Mo(CO)5 and (η6 -arene* )Cr(CO)3 complexes. Ligands and metal ions are varied in each case for better understanding and transparency.

Quantification and classification of substituent effects in organic chemistry: a theoretical molecular electrostatic potential study.

Substituent effects in organic chemistry are generally described in terms of experimentally derived Hammett parameters whereas a convenient theoretical tool to study these effects in π-conjugated molecular systems is molecular electrostatic potential (MESP) analysis. The present study shows that the difference between MESP at the nucleus of the para carbon of substituted benzene and a carbon atom in benzene, designated as ΔVC, is very useful to quantify and classify substituent effects. On the basis of positive and negative ΔVC values, a broad classification of around 381 substituents into electron withdrawing and donating categories is made. Each category is again sorted based on the magnitude of ΔVC into subcategories such as very strong, strong, medium, and weak electron donating/withdrawing. Furthermore, the data are used to show the transferability and additivity of substituent effects in π-conjugated organic molecules such as condensed aromatic, olefinic, acetylenic, and heterocyclic systems. The transferability properties hold good for ΔVC in all these molecular systems. The additive properties of substituent effects are strongly reflected on ΔVC and the predictive power of the data to assign the total substituent effects of multi-substituted systems is verified. The ΔVC data and the present classification of substituents are very useful to design π-conjugated organic molecular systems with desired electron rich/poor character.

Pincer Ligand Modifications To Tune the Activation Barrier for H2 Elimination in Water Splitting Milstein Catalyst.

Modifications on the ligand environment of Milstein ruthenium(II) pincer hydride catalysts have been proposed to fine-tune the activation free energy, ΔG(⧧) for the key step of H2 elimination in the water splitting reaction. This study conducted at the B3LYP level of density functional theory including the solvation effect reveals that changing the bulky t-butyl group at the P-arm of the pincer ligand by methyl or ethyl group can reduce the ΔG(⧧) by a substantial margin, ∼ 10 kcal/mol. The reduction in the steric effect of the pincer ligand causes exothermic association of the water molecule to the metal center and leads to significant stabilization of all the subsequent reaction intermediates and the transition state compared to those of the original Milstein catalyst that promotes endothermic association of the water molecule. Though electron donating groups on the pyridyl unit of the pincer ligand are advantageous for reducing the activation barrier in the gas phase, the effect is only 1-1.4 kcal/mol compared to that of an electron withdrawing group. The absolute minimum of the electrostatic potential at the hydride ligand and carbonyl stretching frequency of the catalyst are useful parameters to gauge the effect of ligand environment on the H2 elimination step of the water splitting reaction.