Electronic relaxation mechanism of 9-methyl-2,6-diaminopurine and 2,6-diaminopurine-2'-deoxyribose in solution.

Prolonged ultraviolet exposure results in the formation of cyclobutane pyrimidine dimers (CPDs) in RNA. Consequently, prebiotic photolesion repair mechanisms should have played an important role in the maintenance of the structural integrity of primitive nucleic acids. 2,6-Diaminopurine is a prebiotic nucleobase that repairs CPDs with high efficiency when incorporated into polymers. We investigate the electronic deactivation pathways of 2,6-diaminopurine-2'-deoxyribose and 9-methyl-2,6-diaminopurine in acetonitrile and aqueous solution to shed light on the photophysical and excited state properties of the 2,6-diaminopurine chromophore. Evidence is presented that both are photostable compounds exhibiting similar deactivation mechanisms upon the population of the S1 (ππ* La ) state at 290 nm. The mechanism involves deactivation through the C2- and C6-reaction coordinates and >99% of the excited state population decays through nonradiative pathways involving two conical intersections with the ground state. The radiative and nonradiative lifetimes are longer in aqueous solution compared to acetonitrile. While τ1 is similar in both derivatives, τ2 is ca. 1.5-fold longer in 2,6-diaminopurine-2'-deoxyribose due to a more efficient trapping in the S1 (ππ* La ) minimum. Therefore, 2,6-diaminopurine could have accumulated in significant quantities during prebiotic times to be incorporated into non-canonical RNA and play a significant role in its photoprotection.

Low-cost, 3D printed irradiation system for in vitro photodynamic therapy experiments.

The development of a suitable irradiation setup is essential for in vitro experiments in photodynamic therapy (PDT). While various irradiation systems have been developed for PDT, only a few offer practical and high-quality setups for precise and reproducible results in cell culture experiments. This report introduces a cost-effective illumination setup designed for in vitro photodynamic treatments. The setup consists of a commercially available light-emitting diode (LED) lamp, a cooling unit, and a specially designed 3D-printed enclosure to accommodate a multiwell plate insert. The LED lamp is versatile, supporting various irradiation wavelengths and adjustable illumination fields, ensuring consistent and reliable performance. The study evaluates the setup through various parameters, including photon flux density, illumination uniformity, photon distribution across the multiwell plate, and temperature changes during irradiation. In addition, the effectiveness of the LED-based illumination system is tested by treating mouse mammary breast carcinoma cells (4T1) with Rose Bengal and LED irradiation at around 525 nm. The resulting IC50 of 5.2 ± 0.9 µM and a minimum media temperature change of ca. 1.2°C indicate a highly promising LED-based setup that offers a cost-effective and technically feasible solution for achieving consistent, reproducible, and uniform irradiation, enhancing research capabilities and potential applications.

2-Oxopurine Riboside: A Dual Fluorescent Analog and Photosensitizer for RNA/DNA Research.

There is significant interest in developing suitable nucleoside analogs exhibiting high fluorescence and triplet yields to investigate the structure, dynamics, and binding properties of nucleic acids and promote selective photosensitized damage to DNA/RNA, respectively. In this study, steady-state, laser flash photolysis, time-resolved IR luminescence, and femtosecond broad-band transient absorption spectroscopies are combined with quantum chemical calculations to elucidate the excited-state dynamics of 2-oxopurine riboside in aqueous solution and to investigate its prospective use as a fluorescent or photosensitizer analog. The Franck-Condon population in the S1 (ππ*) state decays through a combination of solvent and conformational relaxation to its minimum in 1.9 ps. The population trapped in the 1ππ* minimum bifurcates to either fluoresce or intersystem cross to the triplet manifold within ca. 5 ns, while another fraction of the population decays nonradiatively to the ground state. It is demonstrated that 2-oxopurine riboside exhibits both high fluorescent (48%) and significant triplet (between 10% and 52%) yields, leading to a yield of singlet oxygen generation of 10%, making this nucleoside analog a dual fluorescent and photosensitizer analog for DNA and RNA research.

A New Compound for Sequential Sensing of Picric Acid and Aliphatic Amines: Physicochemical Details and Construction of Molecular Logic Gates.

Picric acid (PA) at low concentration is a serious water pollutant. Alongside, aliphatic amines (AAs) add to the queue to pollute surface water. Plenty of reports are available to sense PA with an ultralow limit of detection (LOD). However, only a handful of works are testified to detect AAs. A new fluorescent donor-acceptor compound has been synthesized with inherent intramolecular charge transfer (ICT) character that enables selective and sensitive colorimetric quantitative detection of PA and AAs with low LODs in non-aqueous as well as aqueous solutions. The synthesized compound is based on a hemicyanine skeleton containing two pyridenylmethylamino groups at the donor and a benzothiazole moiety at the acceptor ends. The detailed mechanisms and reaction dynamics are explained spectroscopically along with computational support. The fluorescence property of the detecting compound changes due to protonation of its pyridinyl centers by PA leading to quenching of fluorescence and subsequently de-protonation by AAs to revive the signal. We have further designed logic circuits from the acquired optical responses by sequential interactions.

Surfactant and Cyclodextrin Induced Vesicle to Micelle to Vesicle Transformation in Aqueous Medium.

The physicochemical behavior and characteristics of lipid vesicles and micelles in aqueous medium are greatly tuned by changing the ambient physical parameters, such as temperature, pH, and ionic strength. The process is also controlled by external additives and the nature of the surfactants. In this work, we have used water-soluble surfactant and cyclodextrin to transform lipid vesicles to micelles to vesicles without changing the physical ambience. In this regard, we have used a special pyrene-tagged guest compound that readily forms excimer in water and thus acts as a reporter for the process. Giant lipid vesicles (biological cell mimics) are disrupted by cationic surfactants to form mixed elongated micelles that transform to vesicles on applying a cyclodextrin host.

Undulation induced tuning of electron acceptance by edge-oxidized graphene oxide.

Edge-oxidized graphene oxide (EOGO) nanosheets are good acceptors of electrons. We have employed a suitably designed pyrene-tailed fluorescent probe to establish that the electron acceptability of EOGO can be tuned by undulation of the GO sheet. Comparison between EOGO and single-walled carbon nanotubes (SWCNT) on electron acceptance from the probe molecule shows that the efficiency of π-π stacking between pyrene and the graphene sheet plays the key role.