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Angewandte Chemie (International Ed. in... Dec 2019This report details the development of a masked N-centered radical strategy that harvests the energy of light to drive the conversion of cyclopropylimines to...
This report details the development of a masked N-centered radical strategy that harvests the energy of light to drive the conversion of cyclopropylimines to 1-aminonorbornanes. This process employs the N-centered radical character of a photoexcited imine to facilitate the homolytic fragmentation of the cyclopropane ring and the subsequent radical cyclization sequence that forms two new C-C bonds en route to the norbornane core. Achieving bond-forming reactivity as a function of the N-centered radical character of an excited state Schiff base is unique, requiring only violet light in this instance. This methodology operates in continuous flow, enhancing the potential to translate beyond the academic sector. The operational simplicity of this photochemical process and the structural novelty of the (hetero)aryl-fused 1-aminonorbornane products are anticipated to provide a valuable addition to discovery efforts in pharmaceutical and agrochemical industries.
Topics: Imines; Models, Molecular; Molecular Structure; Photochemistry
PubMed: 31701606
DOI: 10.1002/anie.201909492 -
Organic & Biomolecular Chemistry Feb 2010Dihydrobiopterin (H(2)Bip) and its oxidized analogue, biopterin (Bip), accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder in...
Dihydrobiopterin (H(2)Bip) and its oxidized analogue, biopterin (Bip), accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder in which the protection against UV radiation fails. The photochemistry of H(2)Bip was studied in neutral aqueous solutions upon UV-A irradiation (320-400 nm) at room temperature. The photochemical reactions were followed by UV/vis spectrophotometry, HPLC and enzymatic methods for hydrogen peroxide (H(2)O(2)) determination. Photoproducts were analyzed by means of electrospray ionization mass spectrometry. Under anaerobic conditions, excitation of H(2)Bip leads to the formation of at least two isomeric dimers with molecular masses equal to exactly twice the molecular mass of the reactant. This reaction takes place from the singlet excited state of the reactant. To the best of our knowledge, this is the first time that the photodimerization of a dihydropterin is reported. In the presence of air, the dimers are again the main photoproducts at the beginning of the reaction, but a small proportion of the reactant is converted into Bip. As the reaction proceeds and enough Bip accumulates in the solution, a photosensitized process starts, where Bip photoinduces the oxidation of H(2)Bip to Bip, and H(2)O(2) is formed. As a consequence, the rates of H(2)Bip consumption and Bip formation increase as a function of irradiation time, resulting in an autocatalytic photochemical process. In this process, Bip in its triplet excited state reacts with the ground state of H(2)Bip. The mechanisms involved are analyzed and the biological implications of the results are discussed.
Topics: Biopterins; Chromatography, High Pressure Liquid; Humans; Hydrogen Peroxide; Oxidation-Reduction; Oxygen; Pharmaceutical Solutions; Photochemistry; Solutions; Spectrophotometry, Ultraviolet; Water
PubMed: 20135037
DOI: 10.1039/b913095k -
Proceedings of the National Academy of... Jul 2012
Topics: DNA; Electrochemistry; History, 20th Century; History, 21st Century; Microelectrodes; Nanostructures; Photochemistry
PubMed: 22802653
DOI: 10.1073/pnas.1209943109 -
Physical Chemistry Chemical Physics :... Jun 2007The first postulated structure of the N(3) moiety appeared in a scientific journal in 1890 and was reported as a cyclic triangle with one N,N double bond and two N,N... (Review)
Review
The first postulated structure of the N(3) moiety appeared in a scientific journal in 1890 and was reported as a cyclic triangle with one N,N double bond and two N,N single bonds. Only in the last several years has our understanding of azides advanced to the point that we can now claim to know how to synthesize this prototypical bonding motif. This article examines the experiments and theory that were essential in reaching this point and suggests future directions of research on cyclic-N(3).
Topics: Azides; Computer Simulation; Light; Models, Chemical; Models, Molecular; Molecular Conformation; Nitrogen; Photochemistry; Photolysis
PubMed: 17612730
DOI: 10.1039/b704782g -
ACS Applied Materials & Interfaces Jan 2020A novel approach for the photolabeling of proteins by a BODIPY fluorophore is reported that is based on an anti-Kasha photochemical reaction from an upper singlet...
A novel approach for the photolabeling of proteins by a BODIPY fluorophore is reported that is based on an anti-Kasha photochemical reaction from an upper singlet excited state () leading to the deamination of the BODIPY quinone methide precursor. On the other hand, the high photochemical stability of the dye upon excitation by visible light to allows for the selective fluorescence detection from the dye or dye-protein adduct, without concomitant bleaching or hydrolysis of the protein-dye adduct. Therefore, photolabeling and fluorescence monitoring can be uncoupled by using different excitation wavelengths. Combined theoretical and experimental studies by preparative irradiations, fluorescence, and laser flash photolysis fully disclose the photophysical properties of the dye and its anti-Kasha photochemical reactivity. The application of the dye was demonstrated on photolabeling of bovine serum albumin.
Topics: Boron Compounds; Fluorescence; Indolequinones; Photochemistry; Photolysis; Protein Structure, Secondary
PubMed: 31829548
DOI: 10.1021/acsami.9b19472 -
Analytical Chemistry Jan 2018
Review
Topics: Electrochemical Techniques; Immunoassay; Photochemistry
PubMed: 29135236
DOI: 10.1021/acs.analchem.7b04672 -
Photochemistry and Photobiology Jan 1997Photothermal beam deflection (PBD) calorimetry is a technique that measures changes in the solvent's refractive index that accompanies photothermal heating. This method... (Review)
Review
Photothermal beam deflection (PBD) calorimetry is a technique that measures changes in the solvent's refractive index that accompanies photothermal heating. This method is capable of extracting both kinetic and thermodynamic information from photochemical reactions. A qualitative description of physical basis of time-resolved PBD is presented. Several recent examples of its application to photochemical and photobiological problems are discussed. Finally, the advantages and limitations of PBD are described.
Topics: Calorimetry; Forecasting; Photochemistry; Solutions
PubMed: 9066285
DOI: 10.1111/j.1751-1097.1997.tb01870.x -
Angewandte Chemie (International Ed. in... Aug 2012Spatial and temporal control over chemical and biological processes plays a key role in life, where the whole is often much more than the sum of its parts. Quite... (Review)
Review
Spatial and temporal control over chemical and biological processes plays a key role in life, where the whole is often much more than the sum of its parts. Quite trivially, the molecules of a cell do not form a living system if they are only arranged in a random fashion. If we want to understand these relationships and especially the problems arising from malfunction, tools are necessary that allow us to design sophisticated experiments that address these questions. Highly valuable in this respect are external triggers that enable us to precisely determine where, when, and to what extent a process is started or stopped. Light is an ideal external trigger: It is highly selective and if applied correctly also harmless. It can be generated and manipulated with well-established techniques, and many ways exist to apply light to living systems--from cells to higher organisms. This Review will focus on developments over the last six years and includes discussions on the underlying technologies as well as their applications.
Topics: Chemistry, Organic; Optogenetics; Photochemistry
PubMed: 22829531
DOI: 10.1002/anie.201202134 -
Molecules (Basel, Switzerland) Jul 2020We present the first study to measure the dissociative photochemistry of 2-thiouracil (2-TU), an important nucleobase analogue with applications in molecular biology and...
We present the first study to measure the dissociative photochemistry of 2-thiouracil (2-TU), an important nucleobase analogue with applications in molecular biology and pharmacology. Laser photodissociation spectroscopy is applied to the deprotonated and protonated forms of 2-TU, which are produced in the gas-phase using electrospray ionization mass spectrometry. Our results show that the deprotonated form of 2-thiouracil ([2-TU-H]) decays predominantly by electron ejection and hence concomitant production of the [2-TU-H]· free-radical species, following photoexcitation across the UVA-UVC region. Thiocyanate (SCN) and a / 93 fragment ion are also observed as photodecay products of [2-TU-H] but at very low intensities. Photoexcitation of protonated 2-thiouracil ([2-TU·H]) across the same UVA-UVC spectral region produces the / 96 cationic fragment as the major photofragment. This ion corresponds to ejection of an HS· radical from the precursor ion and is determined to be a product of direct excited state decay. Fragment ions associated with decay of the hot ground state (i.e., the ions we would expect to observe if 2-thiouracil was behaving like UV-dissipating uracil) are observed as much more minor products. This behaviour is consistent with enhanced intersystem crossing to triplet excited states compared to internal conversion back to the ground state. These are the first experiments to probe the effect of protonation/deprotonation on thionucleobase photochemistry, and hence explore the effect of pH at a molecular level on their photophysical properties.
Topics: Electrons; Free Radicals; Ions; Photochemistry; Spectrum Analysis; Thiouracil
PubMed: 32664261
DOI: 10.3390/molecules25143157 -
Photochemical & Photobiological... Apr 2009
Topics: Humans; Microscopy; Photobiology; Photochemistry; Spectrometry, Fluorescence
PubMed: 19337655
DOI: 10.1039/b904005f