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Photoinduced Electron Transfer (Photoinduce + electron_transfer)
Selected AbstractsOligonucleotide Duplexes with Tethered Photoreactive Ruthenium(II) Complexes: Influence of the Ligands and Their Linker on the Photoinduced Electron Transfer and Crosslinking Processes of the Two StrandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2009Stéphanie Deroo Abstract The photoreactivity of new RuII -oligonucleotide conjugates is investigated in the presence of their complementary strands. The goal is to determine the origins of different effects of parameters that control the photocrosslinking process of the two strands. Therefore, two RuII compounds, either [Ru(tap)3]2+or [Ru(tap)2phen]2+ (tap = 1,4,5,8-tetraazaphenanthrene, phen = 1,10-phenanthroline) with different oxidation powers, were tethered with different linkers to either the 5,- or 3,-phosphate end of the probe strand before hybridization with the complementary strand. These systems were studied by time-resolved emission spectroscopy, UV/Vis absorption experiments, PAGE and MS (ESI) analyses. The best yields of photocrosslinking (45,%) obtained with [Ru(tap)3]2+ tethered to the 3,-position are due to (i) a higher oxidation power of the complex and (ii) its attachment at the 3,-position. Indeed, this tethering favours the interaction of the Ru compound with the duplex and, therefore, inhibits its photodechelation. This work allows better design of sequence-specific DNA photodamaging agents prior to biological applications.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Cationic Dye,sensitized Degradation of Sodium Hyaluronate Through Photoinduced Electron Transfer in the Upper Excited State,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2001Masanobu Kojima ABSTRACT The formation of ground-state complexes of methylene blue (MB) and thionine (TN) with sodium hyaluronate (NaHA) was clearly observed by means of absorption spectra in aqueous solution. Irradiation of the complexes using 313 nm light caused significant degradation of NaHA under oxygen and argon. However, the use of visible light over 400 nm, which gives the lowest excited singlet state of the cationic dyes, caused no degradation. MB and TN were more efficient sensitizers for the degradation of NaHA than rose bengal (RB), although RB is a more efficient singlet oxygen (1O2) sensitizer than the cationic dyes. Under similar conditions the polysaccharides with carboxyl groups, such as alginic acid and polygalacturonic acid, also photodecomposed. However, the polysaccharides without carboxyl groups, such as pullulan and methyl cellulose, did not. The irradiation of the polysaccharides in the presence of powdered titanium dioxide as a photocatalyst to generate the hydroxyl radical (·OH) in aerated aqueous solution caused the fragmentation of all the polymers. It was confirmed that methyl viologen, an electron-accepting sensitizer, formed a charge-transfer complex with NaHA, the irradiation of which caused the efficient degradation of NaHA. In the presence of ,- and ,-cyclodextrins the MB- and TN-sensitized photodegradation of NaHA was markedly suppressed. This was probably due to the formation of the inclusion complexes comprising the cationic dyes and the cyclodextrins. On the basis of the results obtained we propose that the cationic dye,sensitized degradation of NaHA involves a photoinduced electron-transfer process between the upper excited dyes and the ground-state NaHA and that ·OH and 1O2 do not participate in the degradation. [source] Reversible Thermally and Photoinduced Electron Transfer in a Cyano-Bridged {Fe2Co2} Square Complex,ANGEWANDTE CHEMIE, Issue 22 2010Yuanzhu Zhang Dr. Spektroskopische, (photo)magnetische und Strukturstudien belegen reversible thermische und lichtinduzierte Änderungen der optischen und magnetischen Eigenschaften für den abgebildeten {Fe2Co2}-Cyanometallat-Vierkernkomplex. Die beobachtete Bistabilität ist das Ergebnis eines intramolekularen Elektronentransfers, wie er auch in dreidimensionalen Co/Fe-Preußischblau-Derivaten auftritt. [source] ChemInform Abstract: Highly Stereoselective Carbon-Functionalization of Electron-Deficient Arylalkenes by Use of Organosilicon Compounds via Photoinduced Electron Transfer.CHEMINFORM, Issue 27 2001Tomoo Hayamizu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Systematic Investigation of Photoinduced Electron Transfer Controlled by Internal Charge Transfer and Its Consequences for Selective PdCl2 CoordinationCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2010Thomas Schwarze Abstract Fluoroionophores of fluorophore,spacer,receptor format were prepared for detection of PdCl2 by fluorescence enhancement. The fluorescent probes 1,13 consist of a fluorophore group, an alkyl spacer and a dithiomaleonitrile PdCl2 receptor. First, varying the length of the alkylene spacer (compounds 1,3) revealed a dominant through-space pathway for oxidative photoinduced electron transfer (PET) in CH2 -bridged dithiomaleonitrile fluoroionophores. Second, fluorescent probes 4,9 containing two anthracene or pyrene fragments connected through CH2 bridges to the dithiomaleonitrile unit were synthesized. Modulation of the oxidation potential (EOx) through electron-withdrawing or -donating groups on the anthracene moiety regulates the thermodynamic driving force for oxidative PET (,GPET) in bis(anthrylmethylthio)maleonitriles and therefore the fluorescence quantum yields (,f), too. The new concept was confirmed and transferred to pyrenyl ligands, and fluorescence enhancements (FE) greater than 3.2 in the presence of PdCl2 were achieved by 7 and 8 (FE=5.4 and 5.2). Finally, for comparison, monofluorophore ligands 10,13 were synthesized. [source] Carbon Nanotube,Acridine Nanohybrids: Spectroscopic Characterization of Photoinduced Electron TransferCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2009Nicolas Mackiewicz Dr. Abstract Change happens: Acridine,carbon nanotube nanohybrids were built (see figure) and their photoinduced electron-transfer properties investigated, showing variable behaviour depending on the acridine partner. Single-walled carbon nanotubes (NT) were covalently functionalized with either 9-phenyl acridine (PhA) or 10-methyl-9-phenyl acridinium (PhMeA+). Absorption and fluorescence properties of acridine derivatives tethered to the nanotubes were studied in homogeneous dispersions. Exciplex emission was observed for NT functionalized with 9-phenylacridine. This phenomenon was attributed to an "intramolecular" interaction between excited phenyl acridine and carbon nanotubes. Interestingly, reverse photoinduced electron transfer from the nanotube to 10-methyl-9-phenylacridinium was detected for the NT-PhMeA+ nanohybrid. This electron transfer led to a strong quenching of the acridinium fluorescence and to the formation of a metastable acridine radical. Evidence for the formation of this radical was obtained by ESR studies. [source] Selective Inclusion of Electron-Donating Molecules into Porphyrin Nanochannels Derived from the Self-Assembly of Saddle-Distorted, Protonated Porphyrins and Photoinduced Electron Transfer from Guest Molecules to Porphyrin DicationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2007Takahiko Kojima Prof. Abstract A doubly protonated hydrochloride salt of a saddle-distorted dodecaphenylporphyrin (H2DPP), [H4DPPP]Cl2, forms a porphyrin nanochannel (PNC). X-ray crystallography was used to determine the structure of the molecule, which revealed the inclusion of guest molecules within the PNC. Electron-donating molecules, such as p -hydroquinone and p -xylene, were selectively included within the PNC in sharp contrast to electron acceptors, such as the corresponding quinones, which were not encapsulated. This result indicates that the PNC can recognize the electronic character and steric hindrance of the guest molecules during the course of inclusion. ESR measurements (photoirradiation at ,>340,nm at room temperature) of the PNC that contains p -hydroquinone, catechol, and tetrafluorohydroquinone guest molecules gave well-resolved signals, which were assigned to cation radicals formed without deprotonation based on results from computer simulations of the ESR spectra and density functional theory (DFT) calculations. The radicals are derived from photoinduced electron transfer from the guest molecules to the singlet state of H4DPP2+. Transient absorption spectroscopy by femtosecond laser flash photolysis allowed us to observe the formation of 1(H4DPP2+)*, which is converted to H4DPP+. by electron transfer from the guest molecules to 1(H4DPP2+)*, followed by fast disproportionation of H4DPP+., and charge recombination to give diamagnetic species and the triplet excited state 3(H4DPP2+)*, respectively. [source] Dynamic Chemical Devices: Photoinduced Electron Transfer and Its Ion-Triggered Switching in Nanomechanical Butterfly-Type Bis(porphyrin)terpyridines,CHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2006Myriam Linke-Schaetzel Dr. Abstract A series of butterfly-type molecular constructs has been prepared in good yield by using a double Stille coupling synthetic protocol. They are composed of a terpyridine (terpy) scaffold and two wings composed of appended porphyrins that are capable of switching from an extended W geometry to a compact U geometry upon cation coordination of the terpy unit. The porphyrin moieties exist in the constructs either as free bases or they can be sequentially metallated, thus giving rise to wings of different "colours". Stationary and time-resolved emission studies of the HZn, ZnAu and Zn2Au constructs show that the electronic properties are strongly dependent on the geometry. In the extended W conformation an energy-transfer process is seen from the free base to the Zn-metallated porphyrin. In the U conformation in Zn2Au the donor luminescence resulting from the singlet excited state of the Zn wing is strongly, quenched not only due to the heavy atom effect but also due to a fast electron-transfer process to the ground state of the Au wing. Furthermore, the binding of (,,,)-diamine substrates to the ZnII,porphyrin sites can also influence the conformation of the system. For the Zn2Zn construct, single-crystal diffraction experiments with synchrotron radiation allowed the structure to be solved by direct methods and fully refined; it shows the expected U conformation. The central Zn atom is six-coordinate, whereby the zinc atom is coordinated by the ,3 -terpy ligand as well by monodentate and semi-chelating acetate anions. The structure is made rigid by hydrogen bonds involving the aqua ligands on the outer Zn centres and acetate oxygen atoms. The present system thus represents a double-trigger-modulated optomechanical switching device with selective substrate binding for either metal atoms or tailored ligands. Both energy- and electron-transfer processes can be controlled opening a means of improving the on/off ratio in future constructs. Une série d'architectures moléculaires, présentant une forme de papillon, a été préparée avec de bons rendements en utilisant une méthodologie synthétique comprenant comme étape clé un double couplage de Stille. Ces architectures sont composées d'un squelette terpyridine (terpy), qui compose le torse du papillon, sur lequel deux ailes porphyriniques ont été greffées; la géométrie peut varier entre une conformation étendue en forme de W, et une conformation compacte en forme de U, dû à la complexation du torse terpy par un cation de taille et coordination adéquate. Les ailes porphyriniques se présentent soit comme bases libres ou, peuvent être métallées successivement avec différentes métaux, pouvant ainsi avoir différentes "couleurs". Des études de fluorescence non seulement stationnaire mais aussi résolues dans le temps sur les architectures HZn, ZnAu et Zn2Au, montrent que les propriétés électroniques sont très dépendantes de la géométrie adoptée. Dans la conformation W étendue, nous avons mis en évidence un processus de transfert d'énergie de la porphyrine base libre vers la porphyrine metalée avec du Zn. Dans la conformation U de Zn2Au la luminescence de l'aile donneuse, à cause de l'état excité singulet, est fortement éteinte, non seulement à cause de l'effet d'atome lourd, mais aussi à cause d'un processus de transfert d'électron vers l'état fondamental de l'aile metalée avec de l'or. De plus, par compléxation avec des (,,,)-diamines des atomes de ZnIIdans les tetrapyrroles porphyrinques, la conformation induite du système peut être profondément influencée. Pour le composé Zn2Zn, que nous avons pu obtenir en monocristaux, des expériences de diffraction en utilisant comme source lumineuse un synchrotron, ont fourni des données qui ont permis de résoudre la structure par des méthodes directes et de la raffiner pour montrer la conformation en U attendue. L'atome central de Zn a une coordination de six dont trois provenant du ligand ,3 -terpy, et les autres de deux anions acetates, un monodenté et l'autre semi-chelatizé. La structure est ligotée par des multiples liaisons hydrogène entre des ligands aqueux sur les atomes de Zn externes et les atomes d'oxygène des anions acetates. Le système présenté est un double effecteur qui montre une commutation opto-mechanique dirigée soit par des ions métalliques, soit par d'autres ligands de taille adaptée. En même temps, les processus de transfert d'énergie et d'électrons peuvent être commuté en laissant de la place pour améliorer le rapport "on/off" dans de futures architectures. Abstract in Romanian:O serie de arhitecturi moleculare având o form, de fluture au fost preparate cu randamente bune utilizând o metodologie sintetic, cuprinzând ca etap, cheie un dublu cuplaj Stille. Aceste architecturi sunt compuse dintr-un schelet terpiridinic (terpy) alc,tuind trupul fluturelui, la care au fost implementate dou, aripi porfirinice care sunt capabile sa varieze între o conforma,ie extins, în forma de liter, W ,i o conformai,ie compact, în form, de litera U, datorit, complexarii trupului terpy printr-un cation de talie ,i coordina,ie adecvat,. Aripile porfirinice se prezintã fie ca base libere sau, datorita unei metalari succesive cu diferite metale, pot avea diferite "culori". Studii de fluorescen,a atât sta,ionar, cât ,i rezolvat, în timp, asupra arhitecturilor HZn, ZnAu ,i Zn2Au, arat, c, proprit,,ile electronice sunt foarte dependente de geometria adoptat,. In conforma,ia W extins,, am putut pune în eviden,, un proces de transfer de energie dinspre baza liber, c,tre porfirina metalat, cu Zn. In conforma,ia U a Zn2Au luminescen,a aripei donoare, datorate st,rii singulet excitate, este puternic stins, nu numai datorit, efectului de atom greu, cât ,i a unui proces de transfer de electron c,tre starea fundamental, a aripei metalat, cu aur. Pe deasupra, complexând (,,,)-diamine c,tre atomii de ZnIIîntre tetrapirolii porfirinici, sunt induse profunde influen,e asupra conforma,iei sistemului. Pentru compusul Zn2Zn, care a putut fi crescut monocristalin, experimente de difrac,ie folosind ca surs, luminoas, un sincrotron au condus la un set de date care a permis ca structura sa fie elucidat, prin metode directe ,i rafinat,, ar,tând conforma,ia în U a,teptat,. Atomul central de Zn are o coordina,ie de sase unde pe lang, lignadul ,3 -terpy, atomul de Zn este coordinat de c,tre doi anioni acetat, unul monodentat, iar cel,lalt semi-chelatizant. Structura este br,zdat, de leg,turi de hidrogen care implic, liganzii apo,i situa,i pe centrii de Zn exteriori, ,i atomii de oxigen din ionii acetat. Sistemul prezentat este un dutblu efector, ar,tând comutare opto-mecanic,, datorat, fie lig,rii prin ioni metalici, fie prin al,i liganzi perfect croitori,i. In acel,i timp, atât procese de transfer de energie, cât ,i de electroni, pot fi perfect comutate, l,sând loc pentru imbun,t,,irea raportului "on/off" în arhitecturi viitoare. [source] | ||||||||||