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Presents an undergraduate biochemistry laboratory experiment on the synthesis of Brome mosaic virus (BMV) proteins in a rabbit reticulocyte cell-free system. Phases in the translation of cellular messenger RNA (mRNA) in eukaryotic systems; Demonstration of the importance of adenosine 5'-triphosphate (ATP) and guanosine 5'-triphosphate (GTP) for protein synthesis.

Carbon nanodots (CNDs) are nanosized light-harvesters emerging as next-generation photosensitizers in photocatalytic reactions. Despite their ever-increasing potential applications, the intricacies underlying their photoexcited charge carrier dynamics are yet to be elucidated. In this study, nitrogen-doped graphitic CNDs (NgCNDs) are selectively excited in the presence of methyl viologen (MV 2+ , redox mediator) and different electron donors (EDs), namely ascorbic acid (AA) and ethylenediaminetetraacetic acid (EDTA). The consequent formation of the methyl viologen radical cation (MV •+ ) is investigated, and the excited charge carrier dynamics of the photocatalytic system are understood on a 0.1 ps-1 ms time range, providing spectroscopic evidence of oxidative or reductive quenching mechanisms experienced by optically excited NgCNDs (NgCNDs*) depending on the ED implemented. In the presence of AA, NgCNDs* undergo oxidative quenching by MV 2+ to form MV •+ , which is short-lived due to dehydroascorbic acid, a product of photoinduced hole quenching of oxidized NgCNDs. The EDTA-mediated reductive quenching of NgCNDs* is observed to be at least 2 orders of magnitude slower due to screening by EDTA-MV 2+ complexes, but the MV •+ population is stable due to the irreversibly oxidized EDTA preventing a back reaction. In general, our methodology provides a distinct solution with which to study charge transfer dynamics in photocatalytic systems on an extended time range spanning 10 orders of magnitude. This approach generates a mechanistic understanding to select and develop suitable EDs to promote photocatalytic reactions., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Four-dimensional printing with embedded photoluminescence is emerging as an exciting area in additive manufacturing. Slim polymer films patterned with three-dimensional lattices of multimode cylindrical waveguides (waveguide-encoded lattices, WELs) with enhanced fields of view can be fabricated by localizing light as self-trapped beams within a photopolymerizable formulation. Luminescent WELs have potential applications as solar cell coatings and smart planar optical components. However, as luminophore-photoinitiator interactions are expected to change the photopolymerization kinetics, the design of robust luminescent photopolymer sols is nontrivial. Here, we use model photopolymer systems based on methacrylate-siloxane and epoxide homopolymers and their blends to investigate the influence of the luminophore Lumogen Violet ( LV ) on the photolysis kinetics of the Omnirad 784 photoinitiator through UV-vis absorbance spectroscopy. Initial rate analysis with different bulk polymers reveals differences in the pseudo-first-order rate constants in the absence and presence of LV , with a notable increase (∼40%) in the photolysis rate for the 1:1 blend. Fluorescence quenching studies, coupled with density functional theory calculations, establish that these differences arise due to electron transfer from the photoexcited LV to the ground-state photoinitiator molecules. We also demonstrate an in situ UV-vis absorbance technique that enables real-time monitoring of both waveguide formation and photoinitiator consumption during the fabrication of WELs. The in situ photolysis kinetics confirm that LV -photoinitiator interactions also influence the photopolymerization process during WEL formation. Our findings show that luminophores play a noninnocent role in photopolymerization and highlight the necessity for both careful consideration of the photopolymer formulation and a real-time monitoring approach to enable the fabrication of high-quality micropatterned luminescent polymeric films., Competing Interests: The authors declare the following competing financial interest(s): Some of the authors are co-inventors of patent filings covering selected aspects in this article., (© 2024 The Authors. Published by American Chemical Society.)

Optical monitoring and screening of photocatalytic batch reactions using cuvettes ex situ is time-consuming, requires substantial amounts of samples, and does not allow the analysis of species with low extinction coefficients. Hollow-core photonic crystal fibers (HC-PCFs) provide an innovative approach for in situ reaction detection using ultraviolet-visible absorption spectroscopy, with the potential for high-throughput automation using extremely low sample volumes with high sensitivity for monitoring of the analyte. HC-PCFs use interference effects to guide light at the center of a microfluidic channel and use this to enhance detection sensitivity. They open the possibility of comprehensively studying photocatalysts to extract structure-activity relationships, which is unfeasible with similar reaction volume, time, and sensitivity in cuvettes. Here, we demonstrate the use of HC-PCF microreactors for the screening of the electron transfer properties of carbon dots (CDs), a nanometer-sized material that is emerging as a homogeneous light absorber in photocatalysis. The CD-driven photoreduction reaction of viologens (XV 2+ ) to the corresponding radical monocation XV •+ is monitored in situ as a model reaction, using a sample volume of 1 μL per measurement and with a detectability of <1 μM. A range of different reaction conditions have been systematically studied, including different types of CDs ( i.e. , amorphous, graphitic, and graphitic nitrogen-doped CDs), surface chemistry, viologens, and electron donors. Furthermore, the excitation irradiance was varied to study its effect on the photoreduction rate. The findings are correlated with the electron transfer properties of CDs based on their electronic structure characterized by soft X-ray absorption spectroscopy. Optofluidic microreactors with real-time optical detection provide unique insight into the reaction dynamics of photocatalytic systems and could form the basis of future automated catalyst screening platforms, where samples are only available on small scales or at a high cost., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

As generally acknowledged, terminal deoxynucleotidyl transferase (TdT) can only elongate DNA substrates from their 3'-OH ends. Herein, for the first time, we report that TdT-catalyzed DNA polymerization can directly proceed on the exosome membrane without the mediation of any nucleic acids. We prove that both the glycosyl and phenolic hydroxyl groups on the membrane proteins can initiate the DNA polymerization. Accordingly, we have developed powerful strategies for high-sensitive exosome profiling based on a conventional flow cytometer and an emerging CRISPR/Cas system. By using our strategy, the featured membrane protein distributions of different cancer cell-derived exosomes can be figured out, which can clearly distinguish plasma samples of breast cancer patients from those of healthy people. This work paves new ways for exosome profiling and liquid biopsy and expands the understanding of TdT, holding great significance in developing TdT-based sensing systems as well as establishing protein/nucleic acid hybrid biomaterials.

Nanoparticle-based contrast agents, when used in concert with imaging modalities such as computed tomography (CT), enhance the visualization of tissues and boundary interfaces. However, the ability to determine the physiological state of the tissue via the quantitative assessment of biochemical or biomechanical properties remains elusive. We report the synthesis and characterization of tantalum oxide (Ta 2 O 5 ) nanoparticle (NP) contrast agents for rapid, nondestructive, and quantitative contrast-enhanced computed tomography (CECT) to assess both the glycosaminoglycan (GAG) content and the biomechanical integrity of human metacarpal phalangeal joint (MCPJ) articular cartilage. Ta 2 O 5 NPs 3-6 nm in diameter and coated with either nonionic poly(ethylene) glycol (PEG) or cationic trimethylammonium ligands readily diffuse into both healthy and osteoarthritic MCPJ cartilage. The CECT attenuation for the cationic and neutral NPs correlates with the glycosaminoglycan (GAG) content ( R 2 = 0.8975, p < 0.05 and 0.7054, respectively) and the equilibrium modulus ( R 2 = 0.8285, p < 0.05 and 0.9312, p < 0.05, respectively). The results highlight the importance of the surface charge and size in the design of NP agents for targeting and imaging articular cartilage. Further, nanoparticle CECT offers the visualization of both soft tissue and underlying bone unlike plain radiography, which is the standard for imaging bone in musculoskeletal diseases, and the ability to provide a real-time quantitative assessment of both hard and soft tissues to provide a comprehensive image of the disease stage, as demonstrated herein.

The valley pseudospin at the K and K' high-symmetry points in monolayer transition metal dichalcogenides (TMDs) has potential as an optically addressable degree of freedom in next-generation optoelectronics. However, intervalley scattering and relaxation of charge carriers leads to valley depolarization and limits practical applications. In addition, enhanced Coulomb interactions lead to pronounced excitonic effects that dominate the optical response and initial valley depolarization dynamics but complicate the interpretation of ultrafast spectroscopic experiments at short time delays. Employing broadband helicity-resolved two-dimensional electronic spectroscopy (2DES), we observe ultrafast (∼10 fs) intervalley coupling between all A and B valley exciton states that results in a complete breakdown of the valley index in large-area monolayer MoS 2 films. These couplings and subsequent dynamics exhibit minimal excitation fluence or temperature dependence and are robust toward changes in sample grain size and inherent strain. Our observations strongly suggest that this direct intervalley coupling on the time scale of optical excitation is an inherent property of large-area MoS 2 distinct from dynamic carrier or exciton scattering, phonon-driven processes, and multiexciton effects. This ultrafast intervalley coupling poses a fundamental challenge for exciton-based valleytronics in monolayer TMDs and must be overcome to fully realize large-area valleytronic devices.

Optical signals come from coherences between quantum states, with spectral line widths determined by the coherences' dephasing dynamics. Using a 2D electronic spectrometer, we observe weak coherence- and rephasing-time-domain signals persisting to 1 ps in the Fenna-Matthews-Olson complex at 77 K. These are coherences between the ground and excited states prepared after the complex interacts once or three times with light, rather than zero-quantum coherences that are more frequently investigated following two interactions. Here, we use these small but persistent signal components to isolate spectral contributions with narrowed peaks and reveal the system's eigenenergies.

Performing quantitative in situ spectroscopic analysis on minuscule sample volumes is a common difficulty in photochemistry. To address this challenge, we use a hollow-core photonic crystal fiber (HC-PCF) that guides light at the center of a microscale liquid channel and acts as an optofluidic microreactor with a reaction volume of less than 35 nL. The system was used to demonstrate in situ optical detection of photoreduction processes that are key components of many photocatalytic reaction schemes. The photoreduction of viologens (XV 2+ ) to the radical XV •+ in a homogeneous mixture with carbon nanodot (CND) light absorbers is studied for a range of different carbon dots and viologens. Time-resolved absorption spectra, measured over several UV irradiation cycles, are interpreted with a quantitative kinetic model to determine photoreduction and photobleaching rate constants. The powerful combination of time-resolved, low-volume absorption spectroscopy and kinetic modeling highlights the potential of optofluidic microreactors as a highly sensitive, quantitative, and rapid screening platform for novel photocatalysts and flow chemistry in general.

DNA scaffolds enable base-pair-specific positioning of fluorescent molecules, allowing for nanometer-scale precision in controlling multidye interactions. Expanding on this concept, DNA-based molecular photonic wires (MPWs) allow for light harvesting and directional propagation of photonic energy on the nanometer scale. The most common MPW examples exploit Förster resonance energy transfer (FRET), and FRET between the same dye species (HomoFRET) was recently shown to increase the distance and efficiency at which MPWs can function. Although increased proximity between adjacent fluorophores can be used to increase the energy transfer efficiency, FRET assumptions break down as the distance between the dye molecules becomes comparable to their size (∼2 nm). Here we compare dye conjugation with single versus dimer Cy5 dye repeats as HomoFRET MPW components on a double-crossover DNA scaffold. At room temperature (RT) under low-light conditions, end-labeled uncoupled dye molecules provide optimal transfer, while the Cy5 dimers show ultrafast (<100 ps) nonradiative decay that severely limits their functionality. Of particular interest is the observation that through increased excitation fluence as well as cryogenic temperatures, the dimeric MPW shows suppression of the ultrafast decay, demonstrating fluorescence lifetimes similar to the single Cy5 MPWs. This work points to the complex dynamic capabilities of dye-based nanophotonic networks, where dye positioning and interactions can become critical, and could be used to extend the lengths and complexities of such dye-DNA devices, enabling multiparameter nanophotonic circuitry.

Transition-metal dichalcogenides (TMDs) such as MoS 2 display promising electrical and optical properties in the monolayer limit. Due to strong quantum confinement, TMDs provide an ideal environment for exploring excitonic physics using ultrafast spectroscopy. However, the interplay between collective excitation effects on single excitons such as band gap renormalization/exciton binding energy (BGR/EBE) change and multiexciton effects such biexciton formation remains poorly understood. Using two-dimensional electronic spectroscopy, we observe the dominance of single-exciton BGR/EBE signals over optically induced biexciton formation. We make this determination based on a lack of strong PIA features at T = 0 fs in the cryogenic spectra. By means of nodal line slope analysis, we determine that spectral diffusion occurs faster than BGR/EBE change, indicative of distinct processes. These results indicate that at higher sub-Mott limit fluences, collective effects on single excitons dominate biexciton formation.

The noninvasive and real-time detection of glucose sugar from tears is promising for the early diagnosis and treatment of chronic diseases such as diabetes. However, its realization is a big challenge. A suitable biosensor electrode that can closely fit the eye and be electrochemically sensitive is still unrealized. In this work, nitrogen-doped graphene (N-G) was used as an ophthalmic electrode in a high-performance intraocular biosensor. The use of N-G has been reported elsewhere before as it is highly electroactive and so has a particular use in biosensors. We hereby present a novel procedure for making carboxylated chitosan-functionalized nitrogen-containing graphene (GC-COOH) by using a one-step ball-milling process. This process does not use toxic chemicals, flammable gases, or a high temperature. It is thus particularly easy to perform. The fabricated nanomaterial had a high electroactivity and was easily assembled as a glucose biosensor by the immobilization of glucose oxidase. The thus constructed biosensor has a high sensitivity at 9.7 μA mM -1 cm -2 , a broad linear range at 12 mM, and a good detection limit of 9.5 μM. It was able to maintain this activity after a month of storage. We also report the intraocular use of this constructed biosensor. The as-prepared GC-COOH was found to be highly biocompatible to ophthalmologic cells such as corneal epithelial and retinal pigment epithelium cells. No change in the intraocular pressure or the corneal structure was measured in a New Zealand white rabbit model. The as-assembled sensor was worn by the animals for more than 24 h without undue impact. This result confirmed the biosensor's potential for intraocular application in the clinic. Its assembly into a useful sensor shown here has great potential to provide real-time monitoring of glucose levels in tear fluids of patients with high sugar levels.

Ethanol is a principle ingredient of alcoholic beverages with potential neurotoxicity and genotoxicity, and the ethanol-associated oxidative DNA damage in the central nervous system is well documented. Natural source compounds may offer new options to protect the brain against ethanol-induced genotoxicity. Veratrum maackii Regel is a toxic rangeland plant linked to teratogenicity which is also used in traditional Chinese medicine as "Lilu" and is reported to contain a family of compounds called stilbenes that can have positive biological activity. In this study, nine stilbenes were isolated from the aerial parts of V. maackii Regel, and their structures were identified as cis-mulberroside A (1), resveratrol-4,3'- O-β-d-diglucopyranoside (2), mulberroside A (3), gentifolin K (4), resveratrol-3,5- O-β-d-diglucopyranoside (5), oxyresveratrol- 4'- O-β-d-glucopyranoside (6), oxyresveratrol-3- O-β-d-glucopyranoside (7), oxyresveratrol (8), and resveratrol (9) using ESI-MS and NMR techniques. The total concentration of extracted compounds 2-9 was 2.04 mg/g, suggesting that V. maackii Regel is a novel viable source of these compounds. In an in vivo comet assay, compounds 1-9 were observed to decrease DNA damage in mouse cerebellum and cerebral cortex caused by acute ethanol administration. Histological observation also revealed decreased brain injury in mice administered with compounds 1-9 after acute ethanol administration. The protective effects of compound 6 were associated with increasing T-SOD and GSH-PX activities and a decrease in NO and MDA concentrations. These findings suggest that these compounds are potent inhibitors of ethanol-induced brain injury possibly via the inhibition of oxidative stress and may be valuable leads for future therapeutic development.

Until now, polyvinyl alcohol (PVA) gel cylinders have been used in electrolyte diodes as a connecting element between the acidic and alkaline reservoirs. In this paper, a new connecting element is reported: a breath figure templated polyvinyl butyral (PVB) membrane prepared with dip-coating from a dichloromethane solution of the polymer in a humid atmosphere. The procedure gives a 1.5-2 μm thick membrane with a hexagonal pattern, the average characteristic length of which is 1 μm. After an acidic etching, it was found to be a good connecting element. The voltage-current characteristics and dynamic properties of PVA and PVB were measured and compared. The PVB membrane has a faster response to voltage changes than the PVA gel, but in both cases, there was a slow drift in the current that prevented it from reaching a steady state. Reproducible characteristics can be obtained, however, after the current reaches a well-defined quasi-steady state.

It was found that the inhibitory effect of resorcinol is less pronounced if it is added in a later stage of the Briggs-Rauscher reaction, which indicates that an accumulating intermediate--most probably iodomalonic acid--can suppress the inhibition. In fact, when iodomalonic acid was added to the reaction mixture, the inhibitory period was shortened considerably even at micromolar levels of the iodomalonic acid concentration. Moreover, iodomalonic acid can accelerate the rate of the reaction when applied in the same low concentrations, suggesting that it can be an autocatalytic intermediate of the Briggs-Rauscher reaction.

With Fenton-type experiments, it is shown that the intense CO2/CO evolution in the Briggs-Rauscher (BR) reaction is due to decarboxylation/decarbonylation of organic free radicals. The metal ion applied in the Fenton-type experiments was Fe2+ or Ti3+ or Mn2+ combined with H2O2 or S2O(8)(2-) as a peroxide, whereas the organic substrate was malonic acid (MA) or a 1:1 mixture of MA and iodomalonic acid (IMA). Experiments with a complete BR system applying MA or the MA/IMA mixture indicate that practically all CO2 and CO comes from IMA. The decarboxylation/decarbonylation mechanisms of various iodomalonyl radicals can be analogous to that of the bromomalonyl radicals studied already in the Belousov-Zhabotinsky (BZ) reaction. It is found that an intense CO2/CO evolution requires the simultaneous presence of H2O2, IO3-, Mn2+, and IMA. It is suggested that the critical first step of this complex reaction takes place in the coordination sphere of Mn2+. That first step can initiate a chain reaction where organic and hydroperoxyl radicals are the chain carriers. A chain reaction was already found in a BZ oscillator as well. Therefore, the analogies between the BR and BZ oscillators are due to the fact that in both mechanisms, free radicals and, in most cases, also transition-metal complexes play an important role.

Current chemotherapy protocols that include fluoropyrimidines, such as 5-fluorouracil (5-FU), are limited by the development of chemoresistance during the course of treatment. Our laboratory has developed a novel class of fluoropyrimidines, FdUMP[N], that are oligodeoxynucleotides (ODNs) composed of some number, N, of 5-fluoro-2'-deoxyuridine-5'-O-monphosphate (FdUMP) nucleotides. Novel synthetic procedures are described that permit conjugation of folic acid to the 5'-OH of FdUMP[10] via a phosphodiester linkage using automated synthesis. The synthetic methods developed are generally applicable for ODN conjugation with folic acid. The folic acid conjugate FA-FdUMP[10] showed improved cytotoxicity toward human colorectal tumor cells (H630), and 5-FU-resistant colorectal tumor cells (H630-10). Enhanced cytotoxicity was observed for FA-FdUMP[10] relative to nonconjugated FdUMP[10] for cells grown under folate-restricted conditions, consistent with cellular uptake being, in part, receptor-mediated. Folate receptor alpha (FRalpha) mRNA was shown by RT-PCR to be overexpressed 26.3-fold in 5-FU-resistant H630-10 cells relative to H630 cells. Thus, FA-FdUMP[N] may prove useful for the treatment of 5-FU-resistant malignancies.

Arylhydrazides, arylhydrazines, and N-alkyl-N-arylnitrosamines are metabolized to arenediazonium ions which yield C8-arylpurine adducts in calf thymus and cellular DNA. The mechanism of adduct formation has not been fully elucidated. C8-Arylguanine adducts likely form from direct aryl radical (Ar*) addition to the C8 position of guanine. However, the amounts of C8-aryladenine adducts measured here are inconsistent with direct radical attack at the C8 position of adenine. An intermediate product, an aryltriazene, is likely formed which then decomposes to the C8-aryladenine adduct. We have demonstrated that N1-aryl-N3-purinyltriazene adducts are formed from a variety of para-substituted arenediazonium ions with adenine. Decomposition of the N1-aryl-N3-purinyltriazene, at high pH and elevated temperatures, has been shown to give C8-aryladenine derivatives, and a free radical mechanism for this process has been proposed. Here we show that this process can occur under physiological conditions and that the C8-aryladenine adduct can be quantitated by HPLC. ESR studies, in which DMPO was used as a spin trap, have been used to demonstrate the intermediacy of aryl radicals during the decomposition of the N1-aryl-N3-purinyltriazenes and to demonstrate that this process also occurs in calf thymus (ct) DNA treated with arenediazonium ions. These results suggest the involvement of an aryl radical in the formation of the observed DNA adducts. Finally, we have found that the treatment of ct DNA with arenediazonium ions produces a significant amount of depurination. Both the formation of C8-arylguanine and C8-aryladenine adducts and the generation of apurinic sites may contribute to the genotoxicity of arylhydrazides, arylhydrazines, N-alkyl-N-arylnitrosamines, and arenediazonium ions.

Many arylhydrazines are genotoxins, although the mechanism of their genotoxicity is unknown. Previous studies have shown that arylhydrazines are metabolized to arenediazonium ions, which produce C8-arylguanine adducts in DNA suggesting the intermediacy of an aryl radical. Here we have looked for the formation of aryl radicals from arylhydrazines and microsomes by ESR spin trapping. Only hydroxyl radicals are trapped upon incubation of p-methylphenylhydrazine with rat liver microsomes and 5,5-dimethyl-1-pyrroline N-oxide (DMPO). However, hydroxyl and aryl radicals were trapped upon incubation of p-(methoxymethyl)phenylhydrazine with rat liver microsomes. Evidence for hydroperoxyl radical formation was also obtained. In contrast, when either of these substrates was incubated with microsomes from C5O cells, aryl and hydroxyl radicals were trapped. The ESR signal intensity of the spin-trapped aryl radicals parallels the extent of C8-arylguanine formation in DNA, and therefore, the aryl radical is likely the intermediate responsible for C8-arylguanine adduct formation. Aryl radicals and C8-arylguanine adducts may be related to the genotoxicity of arylhydrazines and related compounds that are oxidatively metabolized to arenediazonium ions, the precursor to aryl radicals, including arylalkyl nitrosamines, arylazo compounds, and triazenes.

A new technique has been applied to the study of the RNA secondary structure unwinding activity of the eukaryotic initiation factors (eIFs) 4F, 4A, and 4B. Secondary structures were generated at the 5' ends of reovirus and globin mRNA molecules by hybridization with 32P-labeled cDNA molecules 15 nucleotide residues long. The dissociation of the labeled cDNAs from the mRNAs was assayed by a gel filtration chromatography procedure which separates the free cDNAs from mRNAs and mRNA/cDNA hybrids. When the three factors were tested alone, only eIF-4F stimulated dissociation of hybrids. The combination of eIF-4A plus eIF-4B also exhibited a strong hybrid dissociating activity, which was markedly temperature dependent. Under optimum conditions, up to 90% of the hybrid structures are disrupted in 60 min. These results demonstrate for the first time that stable double-stranded regions can be melted and dissociated by eIFs. They also characterize more precisely the first step in the structure unwinding reaction.