CRYSTAL ENGINEERING STUDIES ON THE MOLECULAR SALTS AND SILVER(I) COORDINATION COMPOUNDS FOR [2+2] CYCLOADDITION REACTION IN THE SOLID STATE

Ph.DDOCTOR OF PHILOSOPH

Para-N-Methylpyridinium Pyrenes: Impact of Positive Charge on ds- DNA/RNA and Protein Recognition, Photo-Induced Bioactivity, and Intracellular Localisation

The 2- and 2, 7- substituted para-N-methylpyridinium pyrene cations show high-affinity intercalation into ds-DNAs, whereas their non- methylated analogues interacted with ds-DNA/RNA only in the protonated form (at pH 5), but not at physiological conditions (pH 7). The fluorescence from non-methylated analogues was strongly dependent on the protonation of the pyridines ; con- sequently, they act as fluorescence ratiometric probes for simultaneous detection of both ds-DNA and BSA at pH 5, relying on the ratio between intensities at 420 nm (BSA specific) and 520 nm (DNA specific), whereby exclusively ds-DNA sensing could be switched-off by adjustment to pH 7. Only methylated, permanently charged pyrenes show photoinduced cleavage of circular DNA, at- tributed to pyrene- mediated irradiation-induced production of singlet oxygen. Consequently, the moderate toxicity of these cations against human cell lines is strongly increased upon irradiation. Detailed studies revealed increased total ROS production in cells treated by the compounds studied, accompanied by cell swelling and augmentation of cellular complexity. The most photo-active 2- para-N- methylpyridinium pyrene showed significant localization at mitochondria, its photo-bioac- tivity likely due to mitochondrial DNA damage. Other derivatives were mostly non-selectively dis- tributed between various cytoplasmic organelles, thus being less photoactive

Methyl Viologens of Bis-(4'-pyridylethynyl)arenes - Structures, Photophysical and Electrochemical Studies, and their Potential Application in Biology

A series of bis-(4'-pyridylethynyl)arenes (arene = benzene, tetrafluorobenzene, and anthracene) were synthesized and their bis-N-methylpyridinium compounds were investigated as a class of π-extended methyl viologens. Their structures were determined by single crystal X-ray diffraction, and their photophysical and electrochemical properties (cyclic voltammetry), as well as their interactions with DNA/RNA were investigated. The dications showed bathochromic shifts in emission compared to the neutral compounds. The neutral compounds showed very small Stokes shifts, which are a little larger for the dications. All of the compounds showed very short fluorescence lifetimes (< 4 ns). The neutral compound with an anthracene core has a quantum yield of almost unity. With stronger acceptors, the analogous bis-N-methylpyridinium compound showed a larger two-photon absorption cross-section than its neutral precursor. All of the dicationic compounds interact with DNA/RNA ; while the compounds with benzene and tetrafluorobenzene cores bind in the grooves, the one with an anthracene core intercalates as a consequence of its large, condensed aromatic linker moiety, and it aggregates within the polynucleotide when in excess over DNA/RNA

Isomerization of cyclobutane ligands in the solid state and solution

10.1016/j.jics.2022.100630JOURNAL OF THE INDIAN CHEMICAL SOCIETY99

Rotation of a helical coordination polymer by mechanical grinding

Anisotropic cell volume expansion by mechanical grinding of the solid facilitates the concerted rotation of the photo-inert helical coordination polymer, which causes the misaligned arms containing olefin functional groups in the neighbouring strands to align to undergo [2+2] cycloaddition reaction in 83% yield.Ministry of Education (MOE)This work was financially supported by the Ministry of Education, Singapore (Grant No. Tier 1 WBS R-143-000-A12-114 and R-143-000-B13-114)

Photoreactivity of Ag(I) Complexes and Coordination Polymers of Pyridyl Acrylic Acids

An attempt has been made to orient the CC bonds in <i>trans</i>-3-(3′-pyridyl)acrylic acid (3-PAH) and <i>trans</i>-3-(4′-pyridyl)acrylic acid (4-PAH) in the hydrogen-bonded coordination complexes and coordination polymers of Ag(I), utilizing the argentophilic interaction. Both neutral and deprotonated ligands were employed to synthesize the following compounds: [Ag(3-PAH)₂](BF₄) (<b>1</b>), [Ag(3-PAH)₂](ClO₄) (<b>2</b>), [Ag(4-PAH)₂](ClO₄)·H₂O (<b>3</b>), [Ag(3-PA)]·1.5H₂O (<b>4</b>), and [Ag(4-PA)] (<b>5</b>). Of these, <b>1–2</b> are isotypical hydrogen-bonded polymers of Ag(I) complexes and <b>3</b> is a hydrogen-bonded dimer, whereas <b>4</b> and <b>5</b> are coordination polymers. Compounds <b>1–4</b> undergo photodimerization in <i>head-to-head</i> fashion in the solid state. The photoreactivity of these compounds in solution was also investigated. The <i>head-to-head</i> photodimerized product of 4-PAH, namely, 3,4-bis(4′-pyridyl)cyclobutane-1,2-dicarboxylic acid (HH-4,4-BPCD), has been shown to be a potential ligand for synthesizing coordination polymers, by the isolation of [Ag₂(HH-4,4-BPCD)(H₂O)]·(2H₂O)(¹/₂MeOH), which has a two-dimensional polymeric structure in the solid state

Photoreactivity of Ag(I) Complexes and Coordination Polymers of Pyridyl Acrylic Acids

An attempt has been made to orient the CC bonds in <i>trans</i>-3-(3′-pyridyl)acrylic acid (3-PAH) and <i>trans</i>-3-(4′-pyridyl)acrylic acid (4-PAH) in the hydrogen-bonded coordination complexes and coordination polymers of Ag(I), utilizing the argentophilic interaction. Both neutral and deprotonated ligands were employed to synthesize the following compounds: [Ag(3-PAH)₂](BF₄) (<b>1</b>), [Ag(3-PAH)₂](ClO₄) (<b>2</b>), [Ag(4-PAH)₂](ClO₄)·H₂O (<b>3</b>), [Ag(3-PA)]·1.5H₂O (<b>4</b>), and [Ag(4-PA)] (<b>5</b>). Of these, <b>1–2</b> are isotypical hydrogen-bonded polymers of Ag(I) complexes and <b>3</b> is a hydrogen-bonded dimer, whereas <b>4</b> and <b>5</b> are coordination polymers. Compounds <b>1–4</b> undergo photodimerization in <i>head-to-head</i> fashion in the solid state. The photoreactivity of these compounds in solution was also investigated. The <i>head-to-head</i> photodimerized product of 4-PAH, namely, 3,4-bis(4′-pyridyl)cyclobutane-1,2-dicarboxylic acid (HH-4,4-BPCD), has been shown to be a potential ligand for synthesizing coordination polymers, by the isolation of [Ag₂(HH-4,4-BPCD)(H₂O)]·(2H₂O)(¹/₂MeOH), which has a two-dimensional polymeric structure in the solid state

Solid State Packing and Photoreactivity of Alkali Metal Salts of <i>trans</i>,<i>trans</i>-Muconate

Three alkali-metal salts of <i>trans</i>,<i>trans</i>-muconate (<i>muco</i>) <i>viz</i>. Li₂<i>muco</i> (<b>1</b>), Na₂<i>muco</i> (<b>2</b>), and K₂<i>muco</i> (<b>3</b>) have been prepared, and the influence of the crystal packing on the solid state photoreactivity has been investigated. Although the CC bonds of the <i>muco</i> ligands are oriented infinitely parallel in <b>1</b>, it was found to be photoinert. In contrast, the <i>muco</i> ligands of <b>2</b> and <b>3</b> in the crystalline state undergo photodimerization yielding cycloocta-3,7-diene-1,2,5,6-tetracarboxylate which has been formed stepwise via the [2 + 2] cycloaddition reaction of a single pair of CC bonds and subsequent Cope rearrangement. This study demonstrates how the size of the metal ion can influence the crystal packing in metal organic salts

Making Photoreactive <i>trans</i>-3‑(<i>n</i>′‑Pyridyl)acrylic Acid (<i>n</i> = 2, 3) with Head-to-Tail Orientation in the Solid State by Salt Formation

This work demonstrates that the photoinert <i>trans</i>-3-(2′-pyridyl)­acrylic acid (2-PA) can be made photoreactive by salt formation with HCl, CF₃CO₂H, and H₂SO₄. All three salts undergo photodimerization in head-to-tail (HT) fashion resulting in the formation of the corresponding dimer, 2,4-bis­(2′-pyridyl)-cyclobutane-1,3-dicarboxylic acid (HT-<i>rctt</i>-2,2′-BPCD), of which the former two salts, namely, [2-PAH]­Cl·H₂O and [(2-PAH)]­(CF₃CO₂) undergo single-crystal-to-single-crystal (SCSC) conversion. <i>trans</i>-3-(3′-Pyridyl)­acrylic acid (3-PA), on the other hand, is known to be photoreactive and undergoes photodimerization in head-to-head (HH) fashion producing the dimer HH-<i>rctt</i>-3,3′-BPCD. The HH-orientation of 3-PA can be flipped to HT by forming the ClO₄^– salt, which upon photodimerization produces HT-<i>rctt</i>-3,3′-BPCD. While HT-<i>rctt</i>-2,2′-BPCD exhibits isomerization in the presence of acid in solution, both the HH- and HT-<i>rctt</i>-3,3′-BPCD were inert under similar conditions. Our work demonstrates how the noncovalent intermolecular interactions can play a crucial role in the stereoselective synthesis and also emphasizes that the position of the nitrogen atom in the pyridyl ring is vital for the isomerization to occur in solution

Solid-State Photodimerization Reaction with Photosalient Effect and Photophysical and Electrochemical Properties of <i>N</i>‑Methylated 1‑Naphthylvinyl-4-Quinoline

Crystal packing-dependent photochemical reactions of several functional olefins have been explored, but not for 1-naphthylvinyl-4-quinoline (NVQ) and analogous N-methylated 1-naphthylvinyl-4-quinoline cation (MNVQ). Herein, crystal structure elucidation and photophysical and electrochemical properties for both NVQ and MNVQ, and photodimerization reaction with a photosalient effect for MNVQ have been investigated for the first time. The neutral compound NVQ stacks parallel in its crystal; however, having a distance of 4.43 Å between the CC bonds, it remained photoinert. Upon methylation at the quinoline-N, the resulting MNVQ cations stack parallel in a head-to-tail fashion with a distance of 3.6 Å between the CC bonds, and consequently it underwent [2 + 2] photocycloaddition reaction quantitatively to MQNCB dication, when irradiated under visible light (∼410 nm). Monitoring closely the single crystals of MNVQ under blue light showed that they burst upon exposure for 1 min, signifying a photosalient behavior. Measurements of photophysical properties showed that MNVQ exhibited a bathochromic shift in both absorption (by 4772 cm–1) and emission (by 6198 cm–1) compared to the neutral NVQ. Upon photodimerization, the MQNCB dication exhibited a hypsochromic and hypochromic shift both in absorption and emission compared to the MNVQ cation, a signature of cessation of conjugation. Cyclic voltammetry (CV) measurements showed that all three compounds are redox active and exhibit a reversible reduction event in the range of −0.6 to −0.9 V (vs Ag/AgCl). Experimental results have been substantiated by theoretical calculations