Allosteric Regulation in Carbon Monoxide (CO) Release: Anion Responsive CO-Releasing Molecule (CORM) Derived from (Terpyridine)phenol Manganese Tricarbonyl Complex with Colorimetric and Fluorescence Monitoring

Rational design of co-ordination compounds in combination of bipyridine type of ligands and group 7 metal (M = Mn, Re) for photoCORM: a DFT study

CONTEXT

A large number of manganese and rhenium tricarbonyl complexes are known in literature along with various applications in different fields. CO-releasing molecules (CORMs) got recent research attention because CO can act as a prodrug for different diseases. CORMs offer the promising prospect of a safe and controllable amount of CO release. In this research work, we have explored the electronic properties of compounds such as bipyridine-related [Mn(CO)3] and [Re(CO)3] and we have compared the electronic properties of both manganese and rhenium tricarbonyl complexes in the light of carbon monoxide releasing tendency. The chosen Mn and Re metals have enough possibility to vary or play with ligands and design a new and novel CORM molecule. In this context, we have taken a range of 4,4'-disubstituted 2,2' bipyridyl ligands (Rbpy, where R = NH2, tBu, OCH3, H, CF3, CN, NO2) to investigate CO's liberation ability to identify and study such molecules. The calculated absorbance of designed complexes (1-14) shows visible/near-IR region (350-850 nm). The HOMO-LUMO energy gap of 7 (ΔE=2.40 eV) complex and for complex 14 (ΔE=2.28 eV) which is lesser in all complexes but the MLCT percentage is greater in Mn tricarbonyl complexes in comparison to Re tricarbonyl complexes. The calculated results of the FMO approach revealed that complex 7 and 14 have the lowest energy gap which is also in good agreement with DOSs and TDM results. The theoretically calculated results revealed that the both Mn and Re tricarbonyl complexes have a tendency for labialization of CO, but Mn tricarbonyl complexes are more prone to CO release because they have higher MLCT percentage.

METHODS

In this research work, we have performed density functional theory (DFT) calculations to explore the physical properties of compounds such as bipyridine-related [Mn(CO)3] and [Re(CO)3] and we have compared the physical properties of both manganese and rhenium tricarbonyl complexes in the light of carbon monoxide releasing tendency. DFT-based calculations were performed by using B3LYP/LANL2DZ basis set followed by acetonitrile solvent using the conductor-like polarizable continuum model (CPCM) for different calculations. Various geometrical calculations were performed using the Gaussian16 suite of programs and the output results obtained from Gaussian16 were visualized using GaussView 5.0.16. The same level of theory was used for various calculations, including frontier molecular orbital (FMO) analysis, metal to ligand charge transfer (MLCT), density of state (DOS) calculations, and transition density of matrix (TDM) calculations. For specific calculations, GaussSum 2.2 software package was used to calculate the density of states, and the Multiwfn 3.8 program was used to analyze the transition density matrix, which is presented using heat maps for both electrons and holes.

Photochemistry of transition metal carbonyls

The purpose of this Tutorial Review is to outline the fundamental photochemistry of metal carbonyls, and to show how the advances in technology have increased our understanding of the detailed mechanisms, particularly how relatively simple experiments can provide deep understanding of complex problems. We recall some important early experiments that demonstrate the key principles underlying current research, concentrating on the binary carbonyls and selected substituted metal carbonyls. At each stage, we illustrate with examples from recent applications. This review first considers the detection of photochemical intermediates in three environments: glasses and matrices; gas phase; solution. It is followed by an examination of the theory underpinning these observations. In the final two sections, we briefly address applications to the characterization and behaviour of complexes with very labile ligands such as N₂, H₂ and alkanes, concentrating on key mechanistic points, and also describe some principles and examples of photocatalysis.

Syntheses and structure of dinuclear metal complexes containing naphthyl-Ir bichromophore

A series of novel metal complexes were synthesized containing an Ir-cyclometalated bichromophore as a visible-light sensitizer. A new bichromophoric unit containing a naphthyl substituent and methyl substituents on the 2-phenylpyridine chelating ligand was synthesized and characterized for the first time. According to the increased crystallinity of the bichromophoric unit, novel Ir-M metal complexes (M = Pd, Mn, and Ir) were synthesized and fully characterized. The novel Ir-Pd complex maintained photocatalytic activity toward styrenes under visible-light irradiation, and polymerization with p-chlorostyrene, copolymerization with styrene and p-chlorostyrene furnished corresponding polymers.

Sensitive and Direct Optical Monitoring of Release and Cellular Uptake of Aqueous CO from CO-Releasing Molecules

Dynamics of release and cellular uptake of aqueous CO from CO-releasing molecules (CORMs) significantly affect signaling and cell viability. So far, it has been mainly observed by IR, UV-visible, and fluorescence techniques, which suffer from poor sensitivity and slow response time. Here, we show how to directly probe the mass transfer of aqueous CO from CORMs to cells using a fluidic chamber integrated with live cells and Raman reporters of large-area Au@Pd core-shell nanoparticle assembly to emulate a physiologically relevant microenvironment. We sensitively and directly detect CO release from trace CORMs of as low as 100 nM by measuring the Raman transitions of CO via rapid chemisorption onto the surface of the Au@Pd nanoparticles. By using our method, we successfully observe the dynamics of CO release from CORM-2 despite its very short half-life. We also reveal that the initial rate of CO release from CORM-3 is dramatically decreased by tens to hundreds of times when exposed to physiologically relevant pH variations from 7.4 to 2.5, which can be attributed to the acid hydrolysis of the CO ligand. CORM-2 tends to quickly release CO regardless of pH, probably because of its rapid cleavage into two monomeric Ru complexes by the co-solvent. The decrease in the initial rate at lower temperatures is more significant for CORM-3 than for CORM-2. Finally, we observe that the cellular uptake of aqueous CO from CORM-3 by lung cancer cells is approximately 2 times higher than that of normal lung cells.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

Hydrosilylation of Aldehydes by a Manganese α-Diimine Complex

This paper describes the catalytic activity of air stable and easy to handle manganese complexes towards the hydrosilylation of aldehydes. These catalysts incorporate a bulky diazabutadiene ligand and exhibit good functional group tolerance and chemoselectivity in the hydrosilylation of aldehydes, utilizing primary silanes as the reducing agent. The reactions proceed with turnover frequencies approaching 150 h−1 in some instances, similar to those observed for other manganese-based catalysts. The conversion of aromatic aldehydes to the corresponding alcohols was found to be more efficient than that for the analogous aliphatic systems.