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https://www.readbyqxmd.com/read/29136324/proton-transfer-reaction-dynamics-of-pyranine-in-dmso-water-mixture
#1
Prabhat Kumar Singh, Ankur Awasthi
Photo-induced intermolecular excited-state proton transfer (ESPT) reactions are ubiquitous in chemistry and biology. ESPT reactions are extremely sensitive to the nature of water molecules in its microenvironment and thus serve as a sensitive reporter for the water structure and dynamics in a system. Herein, the photo-induced intermolecular ESPT reaction of 8-Hydroxy pyrene-1, 3, 5-trisulfonic acid (HPTS, also known as Pyranine) has been investigated in various DMSO-water mixtures using steady-state and time-resolved emission spectroscopy...
November 14, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
https://www.readbyqxmd.com/read/29131927/direct-evidence-for-the-origin-of-bis-gold-intermediates-probing-gold-catalysis-with-mass-spectrometry
#2
Mei Lu, Yijin Su, Pengyi Zhao, Xiaohan Ye, Yi Cai, Xiaodong Shi, Eric Masson, Fengyao Li, J Larry Campbell, Hao Chen
Gold-catalyzed alkyne hydration was studied using in-situ reacting mass spectrometry (MS) technology. By monitoring the reaction process in solution under different conditions (regular and very diluted catalyst concentrations, different pHs) and examining the reaction occurrence in the early reaction stage (1-2 ms after mixing) with MS, we collected a series of experimental evidence to support that the bisgold complex is a key reaction intermediate. Furthermore, both experimental and computational studies confirmed that the σ,π-bisgold complexes are not active intermediate toward nucleophilic addition...
November 13, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29092603/the-phonetics-and-phonology-of-geminate-consonants
#3
Donna Erickson
No abstract text is available yet for this article.
October 2017: Journal of the Acoustical Society of America
https://www.readbyqxmd.com/read/29077238/%C3%AE-%C3%AE-alkylation-halogenation-and-dihalogenation-of-sulfoxonium-ylides-a-direct-preparation-of-geminal-difunctionalized-ketones
#4
Rafael Gallo, Anees Ahmad, Gustavo Metzker, Antonio Carlos Bender Burtoloso
A one-pot alkylation-halogenation of ketosulfoxonium ylides in the presence of alkylhalides is described. The method furnishes several gem-difunctionalized haloketones (an alkyl and F, Cl, Br, or I) in good yields. Replacing alkyhalides with a mixture of electrophilic halogen species and various halide anions led to gem-dihalogenated ketones containing a combination of the same or two different halogens. Kinetic isotopic effects as well as reaction kinetic experiments give insight to the mechanism of these reactions...
October 27, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29053262/carotenoid-singlet-fission-reactions-in-bacterial-light-harvesting-complexes-as-revealed-by-triplet-excitation-profiles
#5
Jie Yu, Li-Min Fu, Long-Jiang Yu, Ying Shi, Peng Wang, Zheng-Yu Wang-Otomo, Jian-Ping Zhang
Carotenoids (Cars) in bacterial photosynthesis are known as accessory light harvesters and photoprotectors. Recently, the singlet fission (SF) reaction initiated by Car photoabsorption has been recognized to be an effective excitation deactivation channel disfavoring the light harvesting function. Since the SF reaction and the triplet sensitization reaction underlying photoprotection both yield triplet excited state Cars ((3)Car*), their contribution to the overall (3)Car* photoproduction are difficult to disentangle...
November 8, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29048161/effects-of-temperature-and-concentration-on-the-rate-of-photobleaching-of-erythrosine-in-water
#6
Joshua K G Karlsson, Owen J Woodford, Roza Al-Aqar, Anthony Harriman
Erythrosine, a popular food dye, undergoes fast O2-sensitive bleaching in water when subjected to visible light illumination. In dilute solution, erythrosine undergoes photobleaching via first-order kinetics, where the rate of bleaching depends critically on the rate of photon absorption and on the concentration of dissolved oxygen. Kinetic studies indicate that this inherent bleaching is augmented by self-catalysis at higher concentrations of erythrosine and on long exposure times. Under the conditions used, bleaching occurs by way of geminate attack of singlet molecular oxygen on the chromophore...
November 1, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29031266/effects-of-external-electric-field-and-anisotropic-long-range-reactivity-on-charge-separation-probability
#7
Kyusup Lee, Seonghoon Lee, Cheol Ho Choi, Sangyoub Lee
We consider the effects of external electric field and anisotropic long-range reactivity on the recombination dynamics of a geminate charge pair. A closed-form analytic expression for the ultimate separation probability of the pair is presented. In previous theories, analytic expressions for the separation probability were obtained only for the case where the recombination reaction can be assumed to occur at a contact separation. For this case, Noolandi and Hong obtained an exact solution, but their expression for the separation probability was too complicated to evaluate...
October 14, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29031255/compressed-representation-of-dispersion-interactions-and-long-range-electronic-correlations
#8
Jérôme F Gonthier, Martin Head-Gordon
The description of electron correlation in quantum chemistry often relies on multi-index quantities. Here, we examine a compressed representation of the long-range part of electron correlation that is associated with dispersion interactions. For this purpose, we perform coupled-cluster singles and doubles (CCSD) computations on localized orbitals, and then extract the portion of CCSD amplitudes corresponding to dispersion energies. Using singular value decomposition, we uncover that a very compressed representation of the amplitudes is possible in terms of occupied-virtual geminal pairs located on each monomer...
October 14, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29019511/acetylenic-scaffolding-with-subphthalocyanines-synthetic-scope-and-elucidation-of-electronic-interactions-in-dimeric-structures
#9
Henrik Gotfredsen, Line Broløs, Thomas Holmstrøm, Jacob Sørensen, Alberto Viñas Muñoz, Martin Drøhse Kilde, Anders B Skov, Marco Santella, Ole Hammerich, Mogens Brøndsted Nielsen
Boron subphthalocyanines (SubPcs) are powerful chromophoric heterocycles that can be synthetically modified at both axial and peripheral positions. Acetylenic scaffolding offers the possibility of building large, unsaturated carbon-rich frameworks that can exhibit excellent electron-accepting properties, and when combined with SubPcs it presents a convenient method for preparing interesting chromophore-acceptor architectures. Here we present synthetic methodologies for the post-functionalization of the relatively sensitive SubPc chromophore via acetylenic coupling reactions...
October 11, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28933802/invesigation-of-prevalence-of-dental-anomalies-by-using-digital-panoramic-radiographs
#10
Nebiha Hilal Bilge, Selin Yeşiltepe, Kübra Törenek Ağırman, Fatma Çağlayan, Osman Murat Bilge
BACKGROUND: This study was performed to evaluate the prevalence of all types and subtypes of dental anomalies among 6 to 40 year-old patients by using panoramic radiographs. MATERIALS AND METHODS: This cross-sectional study was conducted by analyzing digital panoramic radiographs of 1200 patients admitted to our clinic in 2014. Dental anomalies were examined under 5 types and 16 subtypes. Dental anomalies were divided into five types: (a) number (including hypodontia, oligodontia and hyperdontia); (b) size (including microdontia and macrodontia); (c) structure (including amelogenesis imperfecta, dentinogenesis imperfecta and dentin dysplasia); (d) position (including transposition, ectopia, displacement, impaction and inversion); (e) shape (including fusion-gemination, dilaceration and taurodontism); RESULTS: The prevalence of dental anomalies diagnosed by panoramic radiographs was 39...
September 21, 2017: Folia Morphologica (Warsz)
https://www.readbyqxmd.com/read/28931277/radical-cage-effects-the-prediction-of-radical-cage-pair-recombination-efficiencies-using-microviscosity-across-a-range-of-solvent-types
#11
Justin T Barry, Daniel J Berg, David R Tyler
This study reports a method for correlating the radical recombination efficiencies (FcP) of geminate radical cage pairs to the properties of the solvent. Although bulk viscosity (macroviscosity) is typically used to predict or interpret radical recombination efficiencies, the work reported here shows that microviscosity is a much better parameter. The use of microviscosity is valid over a range of different solvent system types, including nonpolar, aromatic, polar, and hydrogen bonding solvents. In addition, the relationship of FcP to microviscosity holds for solvent systems containing mixtures of these solvent types...
October 3, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28921980/benchmark-of-dynamic-electron-correlation-models-for-seniority-zero-wavefunctions-and-their-application-to-thermochemistry
#12
Katharina Boguslawski, Pawel Tecmer
Wave functions restricted to electron-pair states are promising models to describe static/nondynamic electron correlation effects encountered, for instance, in bond-dissociation processes and transition-metal and actinide chemistry. To reach spectroscopic accuracy, however, the missing dynamic electron correlation effects that cannot be described by electron-pair states need to be included a posteriori. In this article, we extend the previously presented perturbation theory models with an Antisymmetric Product of 1-reference orbital Geminal (AP1roG) reference function that allow us to describe both static/nondynamic and dynamic electron correlation effects...
September 18, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28921975/intricacies-of-van-der-waals-interactions-in-systems-with-elongated-bonds-revealed-by-electron-groups-embedding-and-high-level-coupled-cluster-approaches
#13
Ewa Pastorczak, Jun Shen, Michał Hapka, Piotr Piecuch, Katarzyna Pernal
Noncovalent interactions between molecules with stretched intramonomer covalent bonds are a fascinating, yet little studied area. This shortage of information stems largely from the inability of most of the commonly used computational quantum chemistry methods to accurately describe weak long-range and strong nondynamic correlations at the same time. In this work, we propose a geminal-based approach, abbreviated as EERPA-GVB, capable of describing such systems in a robust manner using relatively inexpensive computational steps...
October 12, 2017: Journal of Chemical Theory and Computation
https://www.readbyqxmd.com/read/28915031/unexpectedly-large-spin-coherence-effects-in-the-recombination-fluorescence-from-irradiated-highly-polar-solutions-on-a-nanosecond-time-scale
#14
Vsevolod I Borovkov
Spin correlation effects in the geminate recombination of radical ion pairs in irradiated highly polar liquids are typically believed to be negligible due to a high escape probability for the ions. This report presents the results of an exploratory study of organic polar solvents aimed at the searching for, and estimating the magnitude of, the time-resolved magnetic field effects (TR MFEs) in the delayed radiation-induced fluorescence from diluted solutions of a luminophore. It has been found that upon the high-energy irradiation of the solutions in polar liquids, such as dichloroethane (ε ≈ 10), methanol (ε ≈ 33), acetonitrile (ε ≈ 37), dimethylformamide (ε ≈ 37), dimethyl sulfoxide (ε ≈ 47), ethylene carbonate (ε ≈ 89), substantial spin coherence effects in the delayed fluorescence can be observed within a time range up to ∼100 ns...
September 29, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28906062/gemcitabine-pyrrologemcitabine-and-2-fluoro-2-deoxycytidines-synthesis-physical-properties-and-impact-of-sugar-fluorination-on-silver-ion-mediated-base-pairing
#15
Frank Seela, Xiurong Guo, Peter Leonard, Sachin Asaram Ingale
The stability of silver mediated "dC-dC" base pairs relies not only on the structure of the nucleobase but also is sensitive to structural modification on the sugar moiety. 2'-Fluorinated 2'-deoxycytidines with fluorine atoms in the arabino (up) and the ribo (down) configuration, as well as with geminal fluorine substitution (anticancer drug gemcitabine) and the novel fluorescent phenylpyrrolo-gemcitabine (phPyrGem) were synthesized. All nucleosides display the recognition face of naturally occurring 2'-deoxycytidine...
September 14, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28886651/comparison-of-exciplex-generation-under-optical-and-x-ray-excitation
#16
A A Kipriyanov, A R Melnikov, D V Stass, A B Doktorov
Exciplex generation under optical and X-ray excitation in identical conditions is experimentally compared using a specially chosen model donor-acceptor system, anthracene (electron acceptor) and N,N-dimethylaniline (electron donor) in non-polar solution, and the results are analyzed and interpreted based on analytically calculated luminescence quantum yields. Calculations are performed on the basis of kinetic equations for multistage schemes of bulk exciplex production reaction under optical excitation and combination of bulk and geminate reactions of radical ion pairs under X-ray excitation...
September 7, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28880036/reactivity-of-the-geminal-phosphinoborane-tbu2pch2bph2-towards-alkynes-nitriles-and-nitrilium-triflates
#17
Evi R M Habraken, Lars C Mens, Martin Nieger, Martin Lutz, Andreas W Ehlers, J Chris Slootweg
The reactivity of the geminal phosphinoborane tBu2PCH2BPh2 towards terminal alkynes, nitriles and nitrilium salts is investigated. Terminal alkynes react via C-H bond splitting (deprotonation) resulting in the formation of phosphonium borates. In contrast, both nitriles and nitrilium salts undergo addition reactions resulting in the formation of five-membered heterocycles. All compounds were characterized by multinuclear NMR spectroscopy, and single-crystal X-ray structure determinations. Insight into the reaction mechanisms was gained by DFT calculations...
September 28, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28876955/synthesis-of-geminal-azido-halo-compounds-and-%C3%AE-azidoalkyl-esters-from-aldehydes-via-%C3%AE-azido-alcohols
#18
Klaus Banert, Christian Berndt, Kevin Weigand
α-Azido alcohols are generated by treating aldehydes with hydrazoic acid in chloroform. These adducts are transformed into geminal azido-halo compounds through the reaction with phosphorus trichloride or phosphorus tribromide, whereas α-azidoalkyl esters are isolated after interaction with acyl chlorides.
September 6, 2017: Organic Letters
https://www.readbyqxmd.com/read/28872310/mapping-the-binding-modes-of-hemilabile-pincer-crown-ether-ligands-in-solution-using-diamagnetic-anisotropic-effects-on-nmr-chemical-shift
#19
Andrew M Camp, Matthew R Kita, Javier Grajeda, Peter S White, Diane A Dickie, Alexander J M Miller
A protocol for identifying ligand binding modes in a series of iridium pincer complexes bearing hemilabile aza-crown ether ligands has been developed using readily accessible NMR methods. The approach was tested on a collection of 13 structurally diverse pincer-crown ether complexes that include several newly characterized species. New synthetic routes enable facile interconversion of coordination modes and supporting ligands. Detailed structural assignments of five complexes reveal that the difference in chemical shift (Δδ) between geminal protons in the crown ether is influenced by diamagnetic anisotropy arising from halides and other ligands in the primary coordination sphere...
September 5, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28853869/redox-based-photostabilizing-agents-in-fluorescence-imaging-the-hidden-role-of-intersystem-crossing-in-geminate-radical-ion-pairs
#20
Viktorija Glembockyte, Gonzalo Cosa
Here we report transient absorption studies on the ground-state recovery dynamics of the single-molecule fluorophore Cy3B in the presence of four different photostabilizing agents, namely β-mercaptoethanol (β-ME), Trolox (TX), n-propyl gallate (n-PG), and ascorbic acid (AA). These are triplet-state quenchers that operate via photoinduced electron transfer (PeT). While quantitative geminate recombination was recorded following PeT for β-ME (∼100%), for Trolox, n-propyl gallate, and ascorbic acid the extent of geminate recombination was >48%, >27%, and >13%, respectively...
September 8, 2017: Journal of the American Chemical Society
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