Publications by authors named "Randolph Thummel"
Article Synopsis
- * This study focuses on dimeric Cu(I) complexes connected by polyethylene bridges of varying lengths, examining how these differences affect their excited-state properties and structural changes when excited.
- * The results show that longer bridges require more rearrangement for a flattened structure upon excitation, and the behavior of these complexes was analyzed using vibrational wavepacket analysis and TDDFT calculations, offering insights into tuning excited-state dynamics through metal interactions.
Article Synopsis
- Two new ruthenium complexes, [Ru(tpy)(qdppz)](PF) and [Ru(qdppz)](PF), were studied as potential phototherapeutic agents due to their ability to produce singlet oxygen when exposed to visible light.
- These complexes display strong metal-to-ligand charge transfer (MLCT) absorption, with specific absorption maxima indicating effective energy transfer capabilities; however, only one complex shows measurable luminescence at room temperature.
- The differences in ligand geometry impact the lifetimes of MLCT states and photocleavage abilities, with [Ru(qdppz)] being more effective at intercalating DNA and producing singlet oxygen for DNA photocleavage.
Article Synopsis
- * The quantum yield, or efficiency, of this reaction varies significantly based on the surrounding environment, being notably lower in protic solvents like methanol compared to aprotic ones like acetonitrile or n-hexane.
- * The decrease in quantum yield in methanol is attributed to hydrogen bonding interactions that reduce the formation efficiency of triplet states, ultimately leading to less singlet oxygen generation.
A family of complexes of the type [Ru(tpbn)(IP-R)(4-pic)]Cl (tbpn=2,2'-(4-(-butyl)pyridine-2,6-diyl)bis(1,8-napthyridine); 4-pic=4-picoline; IP-R=imidazo[4,5-][1,10]phenanthroline attached to an aromatic group R for - and H for ) were prepared as near-infrared (NIR) absorbing coordination complexes to test whether triplet intraligand excited states (IL) of higher energy than the lowest-lying triplet metal-to-ligand charge transfer excited states (MLCT) could effectively generate cytotoxic singlet oxygen (O) and elicit in vitro photodynamic therapy (PDT) effects. Aromatic groups ranged from benzene to anthracene, with corresponding triplet state energies that were all significantly higher (approximately 3.7-1.
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- - Two series of ruthenium complexes were developed, utilizing various polypyridyl ligands, with one series featuring tetradentate ligands and the other combining tridentate ligands with additional bipyridine or picoline molecules.
- - The complexes were fully characterized using NMR spectra and x-ray crystallography, and their electronic absorption and redox properties were measured.
- - Among the eight complexes studied, three were found to effectively catalyze electrochemical CO reduction, achieving a turnover frequency over 1000 s, primarily utilizing a quaterpyridine ligand and suggesting a specific binding interaction with the CO substrate.
Article Synopsis
- * The research involved screening 22 dirhodium and ruthenium complexes against various macrophage subtypes and cancer cells using both 2D and 3D co-culture systems, finding that some complexes exhibited specific toxicity to macrophages or cancer cells.
- * Notably, certain complexes enhanced the effectiveness of the chemotherapy drug doxorubicin and increased the presence of calreticulin, which is linked to immunogenic cell death, while reducing an M2 macrophage
Article Synopsis
- Researchers synthesized and characterized novel cobalt and zinc complexes using a specific ligand called ppq, which features a unique phenanthroline and pyridine structure.
- Electrochemical studies revealed that a cobalt complex underwent two ligand-based reductions, leading to a new species that was identified as a low-spin Co(II) center interacting with a reduced ppq radical.
- The study demonstrates that this cobalt complex efficiently drives electrocatalytic hydrogen evolution in the presence of a proton donor, highlighting an important mechanism in the process and the significance of redox-active ligands in transition metal catalysis.
Article Synopsis
- Over the last 20 years, photodynamic therapy (PDT) has shown potential not just as a local cancer treatment, but also for triggering a systemic immune response that helps prevent tumor recurrence, particularly in aggressive cancers like melanoma.
- Researchers have developed nine new near-infrared (NIR) photosensitizers (PSs) based on a specific chemical structure that demonstrate strong effectiveness against melanoma cells, achieving low concentrations for significant phototoxic effects with NIR light.
- When tested in mice, PDT treatment with one of the PSs activated a pro-inflammatory response and induced immunogenic cell death, resulting in substantial protection from tumor growth and improved survival rates after vaccination and subsequent tumor challenges.
Article Synopsis
- - The study explores a catalytic pathway for turning water into oxygen using dinuclear transition metal complexes, particularly with two Ru centers at different separations.
- - Two new symmetrical bis-tridentate polypyridine ligands were designed, resulting in one catalyst with closely spaced Ru centers being more effective in water oxidation when reacting with Ce at pH 1.
- - The research highlights a bridging ligand that breaks down under Ce's influence to create catalyst fragments, while also noting a second less reactive catalyst due to its structural stability and warnings about using Ce due to possible catalyst decay.
Article Synopsis
- The study investigates how well the tetradentate ligand 2,2'-bi-1,10-phenanthroline (BIPHEN) can form stable complexes with various metal ions when dissolved in a 50% alcohol/water solution, showcasing its strong metal-ion-binding properties compared to similar ligands DPP and QPY.
- BIPHEN's enhanced stability is attributed to its two benzo groups that reinforce its structure, making it more effective at binding larger metal ions like cadmium (Cd) compared to smaller ones like zinc (Zn), demonstrating a significant difference in binding strength (log values: Cd = 12.7, Zn = 7.78).
The design of near-infrared (NIR)-active photosensitizers (PSs) for light-based cancer treatments such as photodynamic therapy (PDT) has been a challenge. While several NIR-Ru scaffolds have been reported, this approach has not been proven in cells. This is the first report of NIR-Ru PSs that are phototoxic to cancer cells, including highly pigmented B16F10 melanoma cells.
View Article and Find Full Text PDFPhotoinduced oxidation of an indole derivative: 2-(1'H-indol-2'-yl)-[1,5]naphthyridine.
Photochem Photobiol Sci
September 2019
The UV-induced oxidation of 2-(1'H-indol-2'-yl)-[1,5]naphthyridine acetonitrile solution in the presence of air leads to the formation of 2-(1,5-naphthyridin-2-yl)-4H-3,1-benzoxazin-4-one as a major product and N-(2-formylphenyl)-1,5-naphthyridine-2-carboxamide as a minor one. The probable reaction mechanisms are different for the two photoproducts and may involve both the reaction with singlet oxygen generated by the excited substrate or the reaction of the excited substrate with the ground state oxygen molecule. Electronic absorption and IR spectra indicate that both photoproducts are formed as mixtures of syn and anti-rotameric forms.
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- - The study focuses on the early photophysical events of the dinuclear metal complex [(ttb-terpy)(I)Ru(μ-dntpz)Ru(bpy)2]3+ using ultrafast pump-probe spectroscopy in acetonitrile solution to understand its photocatalytic water oxidation capabilities.
- - The researchers investigated several model species and analyzed their absorption spectra, redox behavior, and spectroelectrochemistry, noting different excited-state lifetimes across the compounds studied.
- - Significant findings include a fast energy transfer process in compound 2 occurring in 170 fs and differences in excited-state lifetimes, with 1 and 3 exhibiting ns lifetimes while 2 and 4 show ps lifetimes,
Article Synopsis
- - Transition metal complexes, particularly Ru(II) polypyridyl complexes, are becoming popular as photosensitizers for photodynamic therapy (PDT) and photochemotherapy (PCT) due to their unique properties that enable effective energy and electron transfer.
- - The design of these complexes, including TLD1433—the first Ru(II)-based photosensitizer in clinical trials—focuses on optimizing their excited-state configurations to enhance their effectiveness in treating cancers like non-muscle invasive bladder cancer.
- - The review addresses the challenges faced in integrating PDT into standard cancer treatment, emphasizing the need for innovative chemical and photophysical solutions and the collaborative effort required for drug development.
Article Synopsis
- The study focuses on 12,13-dihydro-5H-indolo[3,2-c]acridine (IA), a rigid molecule whose photophysics and stability change significantly based on its environment, particularly in the presence of alcohols.
- Hydrogen bonding with alcohols greatly reduces the formation of triplet states, leading to IA being around 200 times more photostable in methanol and 1-propanol compared to solvents like n-hexane.
- IA's rigid structure allows it to exist only in one form (syn), enhancing its photostability through a more efficient excited state transition process that prevents deactivation, unlike less rigid similar molecules.
Article Synopsis
- Light-activated compounds, especially ruthenium polypyridyl complexes, have medical potential by allowing control of biological effects through light activation, inducing cytotoxicity in targeted treatments.
- A study on various Ru(II) complexes showed that those with strain-inducing methyl groups could bond to biomolecules upon light activation, while unstrained complexes primarily generated reactive oxygen species (ROS).
- Results indicated that strained complexes were more photoactive and cytotoxic than their unstrained counterparts, with specific ligand modifications enhancing activation by red light and photolabile complexes proving to be more effective in killing cells.
Article Synopsis
- - The study discusses a mononuclear ruthenium complex, [Ru(tpy)(bpg)HO], which acts as an effective catalyst for water oxidation at pH 1, utilizing Ce(IV) as a sacrificial oxidant.
- - This new complex exhibits a turnover number (TON) for water oxidation that is approximately five times greater than its predecessor, [Ru(tpy)(bpy)HO].
- - The enhanced catalytic performance is attributed to the intermolecular hydrogen bonding and the electronic effects of the functionalized bipyridine ligand within the complex.
Article Synopsis
- * The review categorizes these catalysts into four groups and addresses how they form O-O bonds, identify the rate-determining step in the catalytic cycle, and evaluate their efficiency using specific metrics.
- * Two main mechanisms for catalytic action are proposed: an acid-base mechanism involving high-valent Ru[double bond, length as m-dash]O species and a radical coupling mechanism; understanding these can help improve WOC design using various transition metals.
The realization of artificial photosynthesis carries the promise of cheap and abundant energy, however, significant advances in the rational design of water oxidation catalysts are required. Detailed information on the structure of the catalyst under reaction conditions and mechanisms of O-O bond formation should be obtained. Here, we used a combination of electron paramagnetic resonance (EPR), stopped flow freeze quench on a millisecond-second time scale, X-ray absorption (XAS), resonance Raman (RR) spectroscopy, and density functional theory (DFT) to follow the dynamics of the Ru-based single site catalyst, [Ru(NPM)(4-pic)(HO)] (NPM = 4-t-butyl-2,6-di(1',8'-naphthyrid-2'-yl)pyridine, pic = 4-picoline), under the water oxidation conditions.
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- The complex [Ru(pydppn)(biq)(py)](2+) shows unique photochemical behavior, including photodissociation and singlet oxygen production, with significantly lower efficiency in photodissociation compared to a previously studied complex.
- The dual reactivity is attributed to the presence of a long-lived (3) ππ* excited state, which competes with ligand exchange processes.
- This complex serves as a potential model for photochemotherapy applications due to its structural and functional properties.
A series of Ru(II) complexes that behave as water oxidation catalysts were prepared involving a tetradentate equatorial ligand and two 4-substituted pyridines as the axial ligands. Two of these complexes were derived from 2,9-di-(pyrid-2'-yl)-1,10-phenanthroline (dpp) and examine the effect of incorporating electron-donating amino and bulky t-butyl groups on catalytic activity. A third complex replaced the two distal pyridines with N-methylimidazoles that are more electron-donating than the pyridines of dpp and potentially stabilize higher oxidation states of the metal.
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- The ligand 2-(pyrid-2'-yl)-8-(1″,10″-phenanthrolin-2″-yl)-quinoline (ppq) has a unique structure that allows it to effectively bind first-row transition metals like iron (Fe), forming a stable, square planar complex.
- When reacted with FeCl3, ppq forms a μ-oxo-bridged dimer, which has a water molecule bound to one of its metal sites, and this structure, along with a comparison to another ligand (dpa), has been confirmed through X-ray analysis.
- In electrochemical studies, the ppq complex shows a two-electron oxidation process leading to oxygen evolution, with significantly higher
Article Synopsis
- A new series of tetradentate quaterpyridine-type ligands have been created by modifying the existing ppq ligand structure, impacting the planarity and flexibility of the ligands.
- Cobalt(II) complexes were formed and analyzed using various techniques, demonstrating effective light-driven hydrogen (H2) production, especially with the dimethylene-bridged ligand achieving the highest turnover frequency.
- The study indicates that a Co(II)-hydride intermediate plays a critical role in H2 generation and that the ligand's structure significantly affects both the catalytic activity and stability of these complexes.
Article Synopsis
- Molecules that can both donate and accept hydrogen bonds show different behaviors in protic (like water and alcohols) versus aprotic (like n-hexane and acetonitrile) solvents.
- The study focused on two specific compounds, analyzing their spectroscopy, photophysics, and stability in different solvents under 365 nm light exposure.
- Findings revealed that these compounds were more stable (lower photodegradation yield) in alcohols, and two forms of the molecules (syn and anti rotamers) were present, with the syn form being more prevalent across all solvents tested.