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Thienoguanosine (thG) is an isomorphic guanosine (G) surrogate that almost perfectly mimics G in nucleic acids. To exploit its full potential and lay the foundation for future applications, 20 DNA duplexes, where the bases facing and neighboring thG were systematically varied, were thoroughly studied using fluorescence spectroscopy, molecular dynamics simulations, and mixed quantum mechanical/molecular mechanics calculations, yielding a comprehensive understanding of its photophysics in DNA. In matched duplexes, thG's hypochromism was larger for flanking G/C residues but its fluorescence quantum yield (QY) and lifetime values were almost independent of the flanking bases. This was attributed to high duplex stability, which maintains a steady orientation and distance between nucleobases, so that a similar charge transfer (CT) mechanism governs the photophysics of thG independently of its flanking nucleobases. thG can therefore replace any G residue in matched duplexes, while always maintaining similar photophysical features. In contrast, the local destabilization induced by a mismatch or an abasic site restores a strong dependence of thG's QY and lifetime values on its environmental context, depending on the CT route efficiency and solvent exposure of thG. Due to this exquisite sensitivity, thG appears ideal for monitoring local structural changes and single nucleotide polymorphism. Moreover, thG's dominant fluorescence lifetime in DNA is unusually long (9-29 ns), facilitating its selective measurement in complex media using a lifetime-based or a time-gated detection scheme. Taken together, our data highlight thG as an outstanding emissive substitute for G with good QY, long fluorescence lifetimes, and exquisite sensitivity to local structural changes.

The thienoguanine nucleobase (thGb) is an isomorphic fluorescent analogue of guanine. In aqueous buffer at neutral pH, thGb exists as a mixture of two ground-state H1 and H3 keto-amino tautomers with distinct absorption and emission spectra and high quantum yield. In this work, we performed the first systematic photophysical characterization of thGb as a function of pH (2 to 12). Steady-state and time-resolved fluorescence spectroscopies, supplemented with theoretical calculations, enabled us to identify three additional thGb forms, resulting from pH-dependent ground-state and excited-state reactions. Moreover, a thorough analysis allowed us to retrieve their individual absorption and emission spectra as well as the equilibrium constants which govern their interconversion. From these data, the complete photoluminescence pathway of thGb in aqueous solution and its dependence as a function of pH was deduced. As the identified forms differ by their spectra and fluorescence lifetime, thGb could be used as a probe for sensing local pH changes under acidic conditions.

La conception et la gestion des frontières diffèrent quand il s’agit de l’Afrique ou de l’Europe ou de tout autre continent ou région du monde. L’on pouvait penser que l’heure des invasions territoriales ou de la conquête d’espaces est déjà surannée, mais la réalité actuelle en Afrique et en Europe témoigne le contraire. Ces deux continents ont un parcours historique intimement lié, c’est-à-dire l’Afrique est la mère nourricière de l’Europe et l’Europe est le père créateur de l’Afrique. Toutefois, l’on constate qu’en Europe l’approche est de supprimer totalement les frontières pour une unification du Continent, c’est le cas avec l’Union Européenne. En Afrique, malgré la prolifération des regroupements sous-régionaux d’intégration, la tendance est de créer d’autres Etats, bref la multiplication d’autres frontières par le bais de la proclamation de l’autonomisation de certaines provinces vis-à-vis du pouvoir central. Beaucoup de pays ont vu le jour en Afrique de cette manière, notamment : l’Erythrée face à l’Ethiopie, le Sud Soudan vis-à-vis du Grand Soudan. Et d’autres cas encore sont en pleine gestation, notamment le Casamance face au Sénégal, le Sahara occidental face au Royaume de Maroc. Par ailleurs, ce qui se passe en Afrique, se passe aussi en Europe, beaucoup d’autres pays sont menacés par les différents indépendantistes tels que la Catalogne face à l’Espagne, l’Ecosse face au Royaume Uni. Les guerres anciennes et actuelles, essayent de rapprocher la réalité de ces deux continents, au point de dire que c’est une même réalité et de tous les temps. Les Etats en Afrique défendent et soutiennent l’approche du respect de la souveraineté et de l’intégrité territoriale, et des frontières héritées de la colonisation avec pour conséquence l’immuabilité des frontières nationales. Tandis qu’en Europe, les Etats sont dans une dynamique d’abolir les frontières, qui permettrait de rapprocher les uns les autres. Ainsi, l’Afrique a des problèmes propres à ses frontières, et la façon de les gérer diffère de celle de l’Europe.

Light‐harvesting is a fundamental process in nature, which inspires researchers to develop artificial systems for photocatalysis, photovoltaics, and biosensing. A previously introduced light‐harvesting nanoantenna, based on polymeric nanoparticles (NPs) loaded with rhodamine dyes and bulky hydrophobic counterions, provides a record‐breaking antenna effect ≈1000. However, the high dye cooperativity of its thousands of encapsulated dyes causes energy losses by traces of self‐quenched dye aggregates. Here, it is found that these imperfections can be suppressed by blank hydrophobic salts (BHS) formed by the same bulky counterion (fluorinated tetraphenylborate) with an optically inactive cation, analogs of ionic liquids. The presence of BHS increases twofold the fluorescence quantum yields and fluorescence lifetimes of NPs and suppresses their fluorescence blinking. This study assumes that BHS provides an excess of bulky counterions that excludes traces of dye aggregates. As a result, an efficient Forster resonance energy transfer (FRET) is achieved from 40 000 dye donors to a single acceptor within a 70 nm particle, leading to the antenna effect of 4800, which is by far the highest value reported to date. Using this nanoantenna, a single‐molecule detection of the FRET acceptor is realized at low excitation power using an RGB camera of a smartphone. [ABSTRACT FROM AUTHOR]

We herein present a new concept to produce dual‐color photoconvertible probes based on a mechanism called Directed Photooxidation Induced Conversion (DPIC). As a support of this mechanism, styryl‐coumarins (SCs) bearing Aromatic Singlet Oxygen Reactive Moieties (ASORMs) like furan and pyrrole have been synthesized. SCs are bright fluorophores, which undergo a hypsochromic conversion upon visible light irradiation due to directed photooxidation of the ASORM that leads to the disruption of conjugation. SC‐P, a yellow emitting probe bearing a pyrrole moiety, converts to a stable blue emitting coumarin with a 68 nm shift allowing the photoconversion and tracking of lipid droplet in live cells. This new approach might pave the way to a new generation of photoconvertible dyes for advanced bioimaging applications. [ABSTRACT FROM AUTHOR]