Molecular Recognition Using Ruthenium(II) Porphyrin Thiol Complexes as Probes

A Theoretical Probe for Structures, Metal–Metal Bonding, and Electronic Spectra of Paramagnetic Tetrapyrrolic RuII Complex

Dimeric complexes (RuIIPz)2 have been investigated using density functional theory (DFT), where Pz is a porphyrazine ligand that features a 16-atom, 18-π-electron cyclic polyene aromatic skeleton. Structural optimizations in various configurations and spin states indicate that (RuPz)2 favours a Pz–Pz staggered conformer over an eclipsed one; the paramagnetic triplet state with the staggered configuration is found as the global ground state. This agrees with experimental magnetic results of (RuOEPor)2 (OEPor = octaethylporphyrin) and (RuPc)2 (Pc = phthalocyanine). The Ru–Ru bond length was optimized to be 2.38 Å, close to the experimental bond length of 2.40–2.41 Å. The Ru2 doubly bonded nature has been evidenced by the Ru–Ru stretching vibrational frequency of 202 cm–1, bond energy of 30.7 kcal mol–1, and electronic arrangement of σ2π4(nonbonding-δ)4(π*)2. Further confirmation was obtained from high-level wave function theory calculations (complete active space self-consistent field and n-electron valence state second-order perturbation theory). Associated with the solvation of the explicit pyridine accounting for the first coordination sphere and the implicit continuum model for the long-range interaction, the electronic spectra of tetrapyrrolic ruthenium complex were calculated at the time-dependent DFT level.

Acid-Activatable Michael-Type Fluorescent Probes for Thiols and for Labeling Lysosomes in Live Cells

A Michael addition is usually taken as a base-catalyzed reaction. Most fluorescent probes have been designed to detect thiols in slightly alkaline solutions (pH 7-9). The sensing reactions of almost all Michael-type fluorescent probes for thiols are faster in a high pH solution than in a low pH solution. In this work, we synthesized a series of 7-substituted 2-(quinolin-2-ylmethylene)malonic acids (QMAs, substituents: NEt2, OH, H, Cl, or NO2) and their ethyl esters (QMEs) as Michael-type fluorescent probes for thiols. The sensing reactions of QMAs and QMEs occur in distinct pH ranges, pH < 7 for QMAs and pH > 7 for QMEs. On the basis of experimental and theoretic studies, we have clarified the distinct pH effects on the sensing reactivity between QMAs and QMEs and demonstrated that two QMAs (NEt2, OH) are highly sensitive and selective fluorescent probes for thiols in acidic solutions (pH < 7) and promising dyes that can label lysosomes in live cells.

Chemically reversible reactions of hydrogen sulfide with metal phthalocyanines

Hydrogen sulfide (H₂S) is an important signaling molecule that exerts action on various bioinorganic targets. Despite this importance, few studies have investigated the differential reactivity of the physiologically relevant H₂S and HS^– protonation states with metal complexes. Here we report the distinct reactivity of H₂S and HS^– with zinc(II) and cobalt(II) phthalocyanine (Pc) complexes and highlight the chemical reversibility and cyclability of each metal. ZnPc reacts with HS^–, but not H₂S, to generate [ZnPc-SH]⁻, which can be converted back to ZnPc by protonation. CoPc reacts with HS^–, but not H₂S, to form [Co^IPc]⁻, which can be reoxidized to CoPc by air. Taken together, these results demonstrate the chemically reversible reaction of HS^– with metal phthalocyanine complexes and highlight the importance of H₂S protonation state in understanding the reactivity profile of H₂S with biologically relevant metal scaffolds.

The protonation state of H₂S influences its reactivity with different metal phthalocyanine (Pc) complexes. Both ZnPc and CoPc react with H₂S in a chemically reversible manner, with redox-inactive ZnPc binding HS⁻ and redox-active CoPc undergoing reduction. The [ZnPc-SH]⁻ product can be reverted to ZnPc by protonation, and [Co^IPc]⁻ can be redoxidized to CoPc with air.

Studies of iron(III) porphyrinates containing silanethiolate ligands

The chemistry of several iron(III) porphyrinates containing silanethiolate ligands is described. The complexes are prepared by protonolysis reactions of silanethiols with the iron(III) precursors, [Fe(OMe)(TPP)] and [Fe(OH)(H2O)(TMP)] (TPP = dianion of meso-tetraphenylporphine; TMP = dianion of meso-tetramesitylporphine). Each of the compounds has been fully characterized in solution and the solid state. The stability of the silanethiolate complexes versus other iron(III) porphyrinate complexes containing sulfur-based ligands allows for an examination of their reactivity with several biologically relevant small molecules including H2S, NO, and 1-methylimidazole. Electrochemically, the silanethiolate complexes display a quasi-reversible one-electron oxidation event at potentials higher than that observed for an analogous arenethiolate complex. The behavior of these complexes versus other sulfur-ligated iron(III) porphyrinates is discussed.