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Quenching
Kinds of Quenching Terms modified by Quenching Selected AbstractsFormation and Stability of Near Convoluted Structure Obtained in the Ti,46Al,8Ta Alloy Via Air Quenching and Ageing,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2010Valery Imayev Abstract Microstructure evolution after air quenching and variable ageing treatment has been investigated in small-sized ingot bars of the Ti,46Al,8Ta alloy. It was found that air quenching and subsequent ageing at 1200,1260,°C led to the formation of a homogeneous refined near convoluted microstructure. To increase the stability of the near convoluted structure, very slow cooling after high-temperature ageing and final long-term ageing at around 900,°C can be recommended. [source] Energy- and Charge-Transfer Processes in a Perylene,BODIPY,Pyridine Tripartite ArrayEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2008Mohammed A. H. Alamiry Abstract A novel boron dipyrromethene (BODIPY) dye has been synthesized in which the F atoms, usually bound to the boron center, have been replaced with 1-ethynylperylene units and a 4-pyridine residue is attached at the meso -position. The perylene units function as photon collectors over the wavelength range from 350 to 480 nm. Despite an unfavorable spectral overlap integral, rapid energy transfer takes place from the singlet-excited state of the perylene unit to the adjacent BODIPY residue, which is itself strongly fluorescent. The mean energy-transfer time is 7,±,2 ps at room temperature. The dominant mechanism for the energy-transfer process is Dexter-type electron exchange, with Förster-type dipole,dipole interactions accounting for less than 10,% of the total transfer probability. There are no indications for light-induced electron transfer in this system, although there is evidence for a nonradiative decay channel not normally seen for F -type BODIPY dyes. This new escape route is further exposed by the application of high pressure. The meso -pyridine group is a passive bystander until protons are added to the system. Then, protonation of the pyridine N atom leads to complete extinction of fluorescence from the BODIPY dye and slight recovery of fluorescence from the perylene units. Quenching of BODIPY-based fluorescence is due to charge-transfer to the pyridinium unit whereas the re-appearance of perylene-based emission is caused by a reduction in the Förster overlap integral upon protonation. Other cations, most notably zinc(II) ions, bind to the pyridine N-atom and induce similar effects but the resultant conjugate is weakly fluorescent.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Diastereoselective Alkylation of (Arene)tricarbonylchromium and Ferrocene Complexes Using a Chiral, C2 -Symmetrical 1,2-Diamine as AuxiliaryEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2005Alexandre Alexakis Abstract The aminal of (benzaldehyde)tricarbonylchromium and en-antiopure bipyrrolidine undergoes diastereoselective ortho -metallation with butyllithium. Quenching with various electrophiles, followed by hydrolysis of the aminal, affords ortho -substituted (benzaldehyde)tricarbonylchromium compounds with high ee (91,99,%). When quenched with Ph2PCl, a new chiral P,N-bidentate ligand is obtained, which shows efficiency in Pd- and Cu-catalysed reactions. The aminal of ferrocenecarbaldehyde could also be formed, but the ortho -deprotonation occurs with only moderate diastereoselectivity (70,%). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Helically ,-Stacked Conjugated Polymers Bearing Photoresponsive and Chiral Moieties in Side Chains: Reversible Photoisomerization-Enforced Switching Between Emission and Quenching of Circularly Polarized FluorescenceADVANCED FUNCTIONAL MATERIALS, Issue 8 2010Hiroyuki Hayasaka Abstract Novel multifunctional conjugated polymers, [poly(p -phenylene)s and poly(bithienylene-phenylene)s with (R)- and (S)-configurations], which have fluorescence, chirality, and photoresponsive properties, have been designed and synthesized. The polymers are composed of ,-conjugated main chains, where poly(p -phenylene) and poly(bithienylene-phenylene) are fluorescence moieties, and the side chains of the photochromic dithienylethene moiety are linked with chiral alkyl groups. The polymer films exhibit right- or left-handed circularly polarized fluorescence (CPF) and also show reversible quenching and emitting behaviors as a result of photochemical isomerization of the dithienylethene moiety upon irradiation with ultraviolet and visible light. This is the first report realizing the reversible switching of CPF using chirality and photoresponsive properties. [source] Photoluminescence-Based Sensing With Porous Silicon Films, Microparticles, and NanoparticlesADVANCED FUNCTIONAL MATERIALS, Issue 20 2009Michael J. Sailor Abstract Here, chemical sensors made from porous Si are reviewed, with an emphasis on systems that harness photoluminescence and related energy- and charge-transfer mechanisms available to porous Si-derived nanocrystallites. Quenching of luminescence by molecular adsorbates involves the harvesting of energy from a delocalized nanostructure that can be much larger than the molecule being sensed, providing a means to amplify the sensory event. The interaction of chemical species on the surface of porous Si can exert a pronounced influence on this process, and examples of some of the key chemical reactions that modify either the surface or the bulk properties of porous Si are presented. Sensors based on micron-scale and smaller porous Si particles are also discussed. Miniaturization to this size regime enables new applications, including imaging of cancerous tissues, indirect detection of reactive oxygen species (ROS), and controlled drug release. Examples of environmental and in vivo sensing systems enabled by porous Si are provided. [source] Ionic Iridium(III) Complexes with Bulky Side Groups for Use in Light Emitting Cells: Reduction of Concentration QuenchingADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Carsten Rothe Abstract Here, the photophysics and performance of single-layer light emitting cells (LECs) based on a series of ionic cyclometalated Ir(III) complexes of formulae and where ppy, bpy, and phen are 2-phenylpyridine, substituted bipyridine and substituted phenanthroline ligands, respectively, are reported. Substitution at the N,N ligand has little effect on the emitting metal-ligand to ligand charge-transfer (MLLCT) states and functionalization at this site of the complex leads to only modest changes in emission color. For the more bulky complexes the increase in intermolecular separation leads to reduced exciton migration, which in turn, by suppressing concentration quenching, significantly increases the lifetime of the excited state. On the other hand, the larger intermolecular separation induced by bulky ligands reduces the charge carrier mobility of the materials, which means that higher bias fields are needed to drive the diodes. A brightness of ca. 1000,cd,m,2 at 3,V is obtained for complex 5, which demonstrates a beneficial effect of bulky substituents. [source] Quenching of Singlet Oxygen by Tertiary Aliphatic Amines.HELVETICA CHIMICA ACTA, Issue 10 2006Products, Structural Effects on Rates Abstract A kinetic and product study of the reaction of a series of , -methyl-substituted N -methylpiperidines with thermally generated 1O2 in MeCN was carried out. It was found that as the number of , -methyl groups (Me in , -position relative to the N-atom) increases, the rate of 1O2 quenching (physical plus chemical) slightly decreases. This finding shows that, with respect to the reaction rate, steric effects are much more important than electronic effects as the latter should have produced the opposite result. The opposite outcome was instead found for the chemical quenching that leads to the N -demethylation products and N -formyl derivatives. The same trend was observed for the ratio between N -demethylation and formation of the N -formyl derivatives (NH/NCHO ratio). All these results are consistent with the mechanism reported in Scheme,1 where an exciplex is first formed that by a H-atom transfer process produces an , -amino-substituted C-radical. The latter forms the product of N -demethylation by one electron oxidation, or affords the N -formyl derivative by radical coupling (Scheme,1). Similar results were obtained with N,N -dimethylcyclohexanamine. However, this ,acyclic' amine exhibited behaviors quite distinct from those of the N -methylpiperidines series, with respect to reaction rate, extent of chemical quenching, and NH/NCHO ratio. [source] Correlation of Heterojunction Luminescence Quenching and Photocurrent in Polymer-Blend Photovoltaic DiodesADVANCED MATERIALS, Issue 38-39 2009Astrid Gonzalez-Rabade Charge generation in organic solar cells proceeds via photogeneration of excitons in the bulk that form geminate electron,hole pairs at the heterojunction formed between electron donor and acceptors. It is shown that an externally applied electric field increases the number of free charges formed from the geminate pair, and quenches the luminescence from the relaxed exciplex with one-to-one correspondence. [source] Crack Patterns in Ceramic Plates after QuenchingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Yingfeng Shao The crack patterns generated in a real ceramic plate and in a plate stacked by ceramic slabs under quenching are experimentally studied. The results here reveal that there are some distinct differences between the two crack patterns. The reasons that caused the differences are the size and boundary effects of the slabs. These crack patterns are very useful to understand the failure mechanisms of ceramic materials in thermal shock. [source] Flavonol glycosides and antioxidant capacity of various blackberry and blueberry genotypes determined by high-performance liquid chromatography/mass spectrometryJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 13 2005Mi Jin Cho Abstract Flavonol glycoside composition and content in blueberry and blackberry extracts were determined using a high-performance liquid chromatographic (HPLC) separation method coupled with photodiode array (PDA) and mass spectrometric (MS) detection. The hydrophilic antioxidant capacities of crude and fractionated flavonol extracts were also determined by the oxygen radical-absorbing capacity (ORACFL) and photochemiluminescence (PCL) assays. Eight flavonols of quercetin and quercetin,sugar conjugates were identified in Kiowa blackberry, namely rutinoside, galactoside, methoxyhexoside, glucoside, pentoside, [6,-(3-hydroxy-3-methylglutaroyl)]-,-galactoside, glucosylpentoside and oxalylpentoside. Thirteen flavonols were detected in Ozarkblue blueberry. Of these, myricetin 3-hexoside and 12 quercetin,sugar conjugates, namely rutinoside, galactoside, methoxyhexoside, glucoside, pentoside, glucosylpentoside, caffeoylglucoside, oxalylpentoside, rhamnoside, dimethoxyrhamnoside, acetylgalactoside and acetylglucoside, were identified. In Bluecrop blueberry, two additional quercetin,sugar conjugates were identified, namely glucuronide and caffeoylgalactoside. Quercetin glycosides accounted for 75% of total flavonols in the blueberry genotypes. Total flavonol contents ranged from 99 to 150 mg kg,1 for blackberries and from 192 to 320 mg kg,1 for blueberries. Quenching of peroxyl and superoxide anion radicals by the flavonol fractions ranged from 1.5 to 2.3 mmol Trolox equivalents (TE) kg,1 and from 0.5 to 0.7 mmol TE kg,1 respectively for blackberries and from 2.9 to 5.2 mmol TE kg,1 and from 0.8 to 1.4 mmol TE kg,1 respectively for blueberries. The HPLC method allowed for complete separation and identification of flavonols commonly found in blackberries, and blueberries. Our results showed that blueberry and blackberry genotypes varied significantly in flavonol content and antioxidant capacity. Even though total flavonol content did not correlate well with antioxidant capacity, their ability to scavenge peroxyl and superoxide anion radicals was apparent. Copyright © 2005 Society of Chemical Industry [source] Quenching with fluid jetsMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 5-6 2009S. Schuettenberg Verzugskompensation; Distortion Engineering; Jetabschreckung; Flüssigkeitsabschreckung Abstract The quenching process within the heat treatment of workpieces can be optimized by applying locally adapted quenching conditions. Locally variable heat transfer conditions at the workpiece surface are realizable by impressing and regulation of adjustable flexible flow fields on the basis of arrays for jet flow impingings on surfaces inside the quenching media. With use of these adapted jet fields it is possible to generate spatially and or timewise varying quenching conditions with high cooling intensities for a systematic locally heat transfer during the quenching process. For the analysis of workpiece distortion activated by heat treatment, the heat transfer and hardening process by quenching in adapted flexible flow fields is modelwise described. By controlled quenching with liquid media, the quenching intensities can be increased for specific local hardening results on massive workpieces. By that, the heat treatment process and the quenching result can be affected and optimized by controlling the boiling process and the establishing of the rewetting front on the workpiece surface. Abschrecken mit Flüssigkeitsjets Der Abschreckprozess bei der Wärmebehandlung von Werkstücken kann durch die Aufprägung lokaler Abschreckbedingungen optimiert werden. Lokal variable Wärmeübergangsbedingungen an der Werkstückoberfläche sind hier innerhalb des Abschreckmediums durch die Aufprägung und Regelung flexibler Strömungsfelder auf der Grundlage von Jetfeldern mit Prallströmungen auf die Oberflächen möglich. Mit der Anwendung dieser angepassten Jetfelder ist es möglich, räumlich und zeitlich variable Abschreckbedingungen mit hohen Kühlintensitäten für einen gezielten, lokalen Wärmeübergang während des Abschreckprozesses zu generieren. Zur Analyse des durch die Wärmebehandlung aktivierten Bauteilverzugs wird der Härteprozess durch Abschreckung in angepassten, flexiblen Strömungsfeldern modellmäßig beschrieben. Durch gesteuertes Abschrecken mit flüssigen Medien können die Abschreckintensitäten für bestimmte lokale Härteergebnisse an massiven Werkstücken erhöht werden. Damit kann das Abschreckergebnis durch die Steuerung des Siedeprozesses und des Verlaufs der Wiederbenetzungsfront an der Werkstückoberfläche beeinflusst und optimiert werden. [source] Flavin-sensitized Photo-oxidation of Lysozyme and Serum AlbuminPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Yazhou Zhang The excited state processes of riboflavin, flavin mononucleotide and flavin adenine dinucleotide in argon-saturated aqueous solution were studied in the presence of lysozyme or bovine serum albumin (BSA). UV,Vis absorption and fluorescence spectroscopy indicates that the noncovalent flavin-protein binding is relatively weak. Quenching of the flavin triplet state by BSA, observed by time-resolved photolysis, is less efficient than by lysozyme. Light-induced oxidation of the two proteins and reduction of the three flavins were studied. The quantum yields of the former and latter in the absence of oxygen are up to 0.1 and 0.04, respectively. The effects of pH and sensitizer and protein concentrations were examined in greater detail. The proposed reaction is electron transfer from the tryptophan moiety to the flavin triplet rather than excited singlet state. [source] The Occurrence of the psbS Gene Product in Chlamydomonas reinhardtii and in Other Photosynthetic Organisms and Its Correlation with Energy Quenching,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2008Giulia Bonente To avoid photodamage, photosynthetic organisms have developed mechanisms to evade or dissipate excess energy. Lumen overacidification caused by light-induced electron transport triggers quenching of excited chlorophylls and dissipation of excess energy into heat. In higher plants participation of the PsbS protein as the sensor of low lumenal pH was clearly demonstrated. Although light-dependent energy quenching is a property of all photosynthetic organisms, large differences in amplitude and kinetics can be observed thus raising the question whether a single common mechanism is in action. We performed a detailed study of PsbS expression/accumulation in Chlamydomonas reinhardtii and investigated its accumulation in other algae and plants. We showed that PsbS cannot be detected in Chlamydomonas under a wide range of growth conditions. Overexpression of the endogenous psbs gene showed that the corresponding protein could not be addressed to the thylakoid membranes. Survey of different unicellular green algae showed no accumulation of anti-PsbS reactive proteins differently from multicellular species. Nevertheless, some unicellular species exhibit high energy quenching activity, suggesting that a PsbS-independent mechanism is activated. By correlating growth habitat and PsbS accumulation in different species, we suggest that during the evolution the light environment has been a determinant factor for the conservation/loss of the PsbS function. [source] Photophysics of Aminoxanthone Derivatives and Their Application as Binding Probes for DNA,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2006Tamara C. S. Pace ABSTRACT Xanthones with amino substituents were synthesized to diminish the photoreactivity of the xanthone chromophore with DNA, with the objective of using these molecules to study their binding dynamics with DNA. The aminoxanthones showed a strong solvatochromic effect on their singlet and triplet excited-state photophysics, where polar solvents led to a decrease of the energies for the excited states. Quenching of the triplet excited states by nitrite anions was used to determine the binding dynamics, and a residence time in the microsecond time domain was estimated for the bound 2-aminoxanthone with DNA. The quenching experiments performed showed that this methodology will not be applicable to study the binding dynamics of a wide variety of guests with DNA. [source] Environmental Effects on the Photochemistry of A2-E, a Component of Human Retinal Lipofuscin,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2001Laura Ragauskaite ABSTRACT Several retinal dystrophies are associated with the accumulation of lipofuscin, a pigment mixture, in the retinal pigment epithelium (RPE). One of the major fluorophores of this mixture has been identified as the bis-retinoid pyridinium compound, A2-E. Because this compound absorbs incident radiation that is transmitted by the anterior segment of the human eye, photophysical and photochemical studies were performed to determine if A2-E could photosensitize potentially damaging reactions. Steady-state fluorescence measurements indicate that the fluorescence emission maximum and quantum yield are very sensitive to the chemical environment and a correlation between these two parameters and the solvent dielectric constant is observed. Time-resolved absorption experiments of A2-E in pure organic solvents showed no formation of transient species on the timescale of our experiments. However, when these measurements were repeated for A2-E in Triton X-100 micelles, a short-lived (,, 14 ,s), weak absorption was observed. This species is quenched by oxygen (k= 2 × 109M,1 s,1) and by the addition of the antioxidants, cysteine and N,N,N,,N, -tetramethylphenylenediamine. Quenching of this species by 2,3,5-trimethylhydroquinone results in the formation of the 2,3,5-trimethylsemiquinone free radical and an increase in yield of the A2-E,derived species. Sensitization of the A2-E triplet excited state indicates that the species observed in micelles upon direct excitation is not consistent with the triplet excited state. Based on these data we tentatively assign this absorption to a free radical. In the RPE these initial processes can ultimately lead to damage to the tissue through the formation of peroxides and other oxidized species. [source] Coherent Quenching of a Fluorophore for the Design of a Highly Sensitive In-Stem Molecular Beacon,ANGEWANDTE CHEMIE, Issue 32 2010Yuichi Hara Excitonische Wechselwirkung wurde beim Design eines hochempfindlichen ,molekularen Beacons" genutzt, der in seiner Stammregion D -Threoninole mit Fluorophor und Fluoreszenzlöscher als Pseudobasenpaare trägt (ISMB; siehe Schema: optimierte Kombination mit Cy3 und modifiziertem Methylrot). Durch Minimierung der Differenz zwischen ,max von Fluorophor und Fluoreszenzlöscher wurde die Löscheffizienz maximiert. [source] Discrimination of Single-Nucleotide Alterations by G-Specific Fluorescence QuenchingCHEMBIOCHEM, Issue 6 2005Chikara Dohno Dr. Abstract A new strategy for the detection of single-base alterations through fluorescence quenching by guanine (G) is described. We have devised a novel base-discriminating fluorescent (BDF) nucleoside, 4,PyT, that contains a pyrenecarboxamide fluorophore at the thymidine sugar's C4,-position. 4,PyT-containing oligodeoxynucleotides only exhibited enhanced fluorescence in response to the presence of a complementary adenine base. In contrast, the fluorescence of mismatched duplexes containing 4,PyT/N base pairs (N=C, G, or T) was considerably weaker. This highly A-selective fluorescence was a product of guanine-specific quenching efficiency; when the complementary base to 4,PyT was a mismatch, the pyrenecarboxamide fluorophore was able to interact intimately with neighboring G bases (the most likely interaction in the case of intercalation), so effective quenching by the G bases occurred in the mismatched duplexes. In contrast, duplexes containing 4,PyT/A base pairs exhibited strong emission, since in this case the fluorophores were positioned in the minor groove and able to escape fluorescence quenching by the G bases. [source] Hybridization-Sensitive On,Off DNA Probe: Application of the Exciton Coupling Effect to Effective Fluorescence QuenchingCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2008Shuji Ikeda Dr. Abstract The design of dyes that emit fluorescence only when they recognize the target molecule, that is, chemistry for the effective quenching of free dyes, must play a significant role in the development of the next generation of functional fluorescent dyes. On the basis of this concept, we designed a doubly fluorescence-labeled nucleoside. Two thiazole orange dyes were covalently linked to a single nucleotide in a DNA probe. An absorption band at approximately 480,nm appeared strongly when the probe was in a single-stranded state, whereas an absorption band at approximately 510,nm became predominant when the probe was hybridized with the complementary strand. The shift in the absorption bands shows the existence of an excitonic interaction caused by the formation of an H aggregate between dyes, and as a result, emission from the probe before hybridization was suppressed. Dissociation of aggregates by hybridization with the complementary strand resulted in the disruption of the excitonic interaction and strong emission from the hybrid. This clear change in fluorescence intensity that is dependent on hybridization is useful for visible gene analysis. [source] Model Systems for Fluorescence and Singlet Oxygen Quenching by MetalloporphyrinsCHEMMEDCHEM, Issue 3 2007Jason Abstract Next-generation photodynamic therapy agents will minimize extraneous phototoxicity by being active only at the target site. To this end, we have developed a model system to systematically investigate the excited-state quenching ability of a number of metalloporphyrins. Central metal ions that prefer four-coordinate, square planar orientations (AgII, CuII, NiII, PdII, and ZnII) were used. Porphyrin dimers based on 5-(4-aminophenyl)-10,15,20-triphenylporphyrin and comprising both a free base porphyrin and a metalloporphyrin covalently linked through a five-carbon alkyl chain were synthesized. The fluorescence and singlet oxygen quantum yields for the dimers were probed at 630 and 650,nm, respectively, resulting in the excitation of only the free base porphyrin and allowing a comparison of the quenching efficacy of each central metal ion. These results demonstrate that metalloporphyrins can serve as efficient quenchers, and may be useful in the design of novel light-activated therapeutic agents. [source] A Close Look at Fluorescence Quenching of Organic Dyes by TryptophanCHEMPHYSCHEM, Issue 11 2005Sören Doose Dr. Abstract Understanding fluorescence quenching processes of organic dyes by biomolecular compounds is of fundamental importance for in-vitro and in-vivo fluorescence studies. It has been reported that the excited singlet state of some oxazine and rhodamine derivatives is efficiently and almost exclusively quenched by the amino acid tryptophan (Trp) and the DNA base guanine via photoinduced electron transfer (PET). We present a detailed analysis of the quenching interactions between the oxazine dye MR121 and Trp in aqueous buffer. Steady-state and time-resolved fluorescence spectroscopy, together with fluorescence correlation spectroscopy (FCS), reveal three contributing quenching mechanisms: 1) diffusion-limited dynamic quenching with a bimolecular quenching rate constant kdof 4.0×109s,1,M,1, 2) static quenching with a bimolecular association constant Ksof 61,M,1, and 3) a sphere-of-action contribution to static quenching described by an exponential factor with a quenching constant , of 22,M,1. The latter two are characterized as nonfluorescent complexes, formed with ,30,% efficiency upon encounter, that are stable for tens of nanoseconds. The measured binding energy of 20,30 kJmol,1is consistent with previous estimates from molecular dynamics simulations that proposed stacked complexes due to hydrophobic forces. We further evaluate the influence of glycerol and denaturant (guanidine hydrochloride) on the formation and stability of quenched complexes. Comparative measurements performed with two other dyes, ATTO 655 and Rhodamine 6G show similar results and thus demonstrate the general applicability of utilizing PET between organic dyes and Trp for the study of conformational dynamics of biopolymers on sub-nanometer length and nanosecond time-scales. [source] Magnetization Transfer from Laser-Polarized Xenon to Protons with Spin-Diffusion QuenchingCHEMPHYSCHEM, Issue 4 2003Hervé Desvaux Position of the prisoner: Accurate location of xenon atoms in cage molecules (see picture) is derived by specific through-space magnetization transfer from laser-polarized gas to protons using a new NMR pulse sequence. [source] Fluorescence Quenching of Pheophytin-a by Copper(II) IonsCHINESE JOURNAL OF CHEMISTRY, Issue 3 2009Mingbo HU Abstract A method was developed for determination of Cu(II) ions quantitatively by measuring fluorescent intensity of pheophytin-a (Pheoa) solution. The Pheoa was obtained by de-intercalation of magnesium from the porphyrin ring of chlorophyll-a (Chla) extracted from fresh spinach leaves. Its two UV-Vis absorption peaks at 505 and 535 nm in acetone solution have been observed but disappeared when the acetone solution of Pheoa was mixed with a Cu(II) ion aqueous solution. A fluorescence quenching phenomenon was thus observed when the acetone solution of Pheoa was mixed with an aqueous solution of Cu(II) ions. However, other physiologically relevant cations rarely caused any quenching fluorescence of Pheoa under the same experimental conditions. Kinetics of the fluorescence fading process was investigated by measuring the effects of Cu(II) ion concentration, reaction time and reaction temperature on the fluorescence intensity of the Pheoa acetone solution. An activation energy of (10±1) kJ·mol,1 was estimated from Arrhenius empirical relation assuming that the interaction between the Pheoa and the Cu(II) ions was the first order reaction. The calibration graph obtained with the fluorescence was linear over the Cu(II) concentration range of 8.0×10,5,8.0×10,7 mol·dm,3 with a detection limit of 8.0×10,7 mol·dm,3 for Cu(II) ion. [source] Synthesis and Photophysical Properties of Copper(I) Complexes Obtained from 1,10-Phenanthroline Ligands with Increasingly Bulky 2,9-SubstituentsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2010Gianluca Accorsi Abstract In this paper, we describe the synthesis and the electronic properties of a series of [Cu(NN)2]+ systems. The NN ligands investigated are 2,9-bis[(tert -butyldimethylsilyloxy)methyl]-1,10-phenanthroline (1), 2,9-bis[(triisopropylsilyloxy)methyl]-1,10-phenanthroline (2), 2,9-bis[(tert -butyldiphenylsilylmoxy)ethyl]-1,10-phenanthroline (3), 2,9-bis[2,6-bis(benzyloxy)phenethyl]-1,10-phenanthroline (4) and 2-(1,3-diphenylpropan-2-yl)-9-phenethyl-1,10-phenanthroline (5). The electrochemical properties and the ground state electronic absorption spectra of Cu(1)2,Cu(5)2 are in line with the classical behaviour of such [Cu(NN)2]+ derivatives. Whereas all the compounds exhibit MLCT luminescence centered around 630,650 nm, the emission quantum yields and the lifetimes are dramatically different as a function of stereoelectronic effects and/or the possibility of internal exciplex quenching when oxygen-containing functional groups are attached to the phenanthroline ligands. [source] Heterometallic CoIII,LnIII (Ln = Gd, Tb, Dy) Complexes on a p -Sulfonatothiacalix[4]arene Platform Exhibiting Redox-Switchable Metal-to-Metal Energy TransferEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 25 2008Viktoriya Skripacheva Abstract Nuclear magnetic relaxation along with pH metric data have been used to reveal pH-dependent heterometallic CoIII,LnIII (Ln = Gd, Tb, and Dy) complex formation on a p -sulfonatothiacalix[4]arene (TCAS) platform in aqueous solution. The previously obtained 1D and 2D 1H NMR spectroscopic and X-ray data prove the outer sphere binding of the CoIII block with the upper rim of TCAS, whereas the LnIII ion is coordinated with the phenolate groups of the lower rim of TCAS. The inclusive outer-sphere binding of CoIII tris(dipyridyl) and tris(ethylendiaminate) complexes with the upper rim of TCAS favors binding of the inner-sphere lanthanide ions through the lower rim of TCAS, whereas noninclusive binding of CoIII bis(histidinate) provides no effect on the binding of lanthanide ions. The emission properties of [Co(dipy)3]3+,LnIII (Ln = Gd, Tb, Dy) complexes indicate the quenching of 4f luminescence by the 3d block. This quenching can be switched off by electrochemical CoIII/CoII reduction with further switching on by reoxidation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Efficient Increase of DNA Cleavage Activity of a Diiron(III) Complex by a Conjugating Acridine GroupEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 34 2007Xiao-Qiang Chen Abstract A new diferric complex, Fe2Lb, in which a DNA intercalator (acridine) is linked to a precursor diferric complex (Fe2La), has been designed and synthesised as a hydrolytic cleaving agent of DNA. Compared with Fe2La (without the DNA intercalator) (La: 2,6-bis{[(2-hydroxybenzyl)(pyridin-2-yl)methylamino]methyl}-4-methylphenol), Fe2Lb [Lb: 5-(acridin-9-yl)- N -(3,5-bis{[(2-hydroxybenzyl)(pyridin-2-yl)methylamino]methyl}-4-hydroxybenzyl)pentanamide] leads to a 14-fold increase in the cleavage efficiency of plasmid DNA due to the binding interaction between DNA and the acridine moiety. The interaction has been demonstrated by UV/Vis absorption, CD spectroscopy, viscidity experiments and thermal denaturation studies. The hydrolytic mechanism is supported by evidence from T4 DNA ligase assay, reactive oxygen species (ROS) quenching and BNPP [bis(4-nitrophenyl) phosphate, a DNA model] cleavage experiments. The pH dependence of the BNPP cleavage by Fe2La in aqueous buffer media shows a bell-shaped pH,kobs profile with an optimum point around a pH of 7.0 which is in good agreement with the maximum point of the pH-dependent relative concentration curve of active species from the pH titration experiments. The determination of the initial rates at a pH of 7.36 as a function of substrate concentration reveals saturation kinetics with Michaelis,Menten-like behaviour and Fe2La shows a rate acceleration increase of 4.7,×,106 times in the hydrolysis of BNPP. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Tagging (Arene)ruthenium(II) Anticancer Complexes with Fluorescent LabelsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2007Fabio Zobi Abstract Fluorescent (arene)ruthenium(II) complexes have been prepared by tagging a small fluorogenic reporter onto the chelating ligand of complexes of the type [(,6 -arene)RuCl(Z)]+ (Z = chelating ligand). Complexes [(,6 - p -cym)RuCl(NNO)](Cl) (2), [(,6 - p -cym)RuCl(L3)](Cl) (3) and [(,6 - p -cym)RuCl(L4)](Cl) (4) {p -cym = p- cymene, NNO = 2-[(2-aminoethyl)amino]ethanol, L3 = 2-[(2-aminoethyl)amino]ethyl-2-(methylamino)benzoate and L4 = N -{2-[(2-aminoethyl)amino]ethyl}-2-(methylamino)benzamide} were obtained in good yield from the reaction of the Ru dimer [(,6 - p -cym)RuCl2]2 (1) and the corresponding ligand. The compounds have been fully characterized and their X-ray crystal structures are reported. Compounds 3 and 4 show a photoluminescence response centered at 435 nm with partial fluorescence quenching of the fluorogenic reporters L3 and L4 upon coordination to the metal center. Species 2,4 show good solubility both in water and organic solvents. In water, 2,4 readily hydrolyze to form the aqua complexes. These are stable at acidic pH forming 10,15,% of the corresponding hydroxido complexes in buffered solution (25 mM HEPES) as the pH is raised to a physiological value (pH = 7.44). Under these conditions, 4 (but not 2 or 3) undergoes a fast pH-dependent reversible intramolecular rearrangement. Experimental data and semiempirical calculations indicate that the major species arising from this transformation is a complex with a tridentate chelating ligand following deprotonation at the nitrogen atom of the amide group. Esterase-catalyzed hydrolysis of 3 liberates isatoic acid (MIAH) and generates 2 indicating that the complex is a substrate for the enzyme. Complexes similar to 3 may have potential for esterase-activated Ru-based prodrug delivery systems.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] A PCP-Pincer RuII,Terpyridine Building Block as a Potential "Antenna Unit" for Intramolecular SensitizationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2007Marcella Gagliardo Abstract The redox- and photoactive mononuclear complex [Ru(PCP)(tpy,DTTANa4)]Cl {PCP = [C6H3(CH2PPh2)2 -2,6],; tpy,DTTA4, = 4,-(2,2,:6,,2,-terpyridine)-diethylenetriamine- N,N,N,,N, -tetraacetate} possesses an externally directed, vacant N3O4 polyaminocarboxylate-type binding site that coordinates to lanthanide(III) ions to give the neutral heterodinuclear RuII,LnIII complexes [Ru(PCP)(tpy,DTTA)Ln(H2O)2] (Ln = Gd3+, Eu3+). The photophysical properties of solutions of the mononuclear complex [Ru(PCP)(tpy,DTTANa4)]Cl were investigated in MeOH/EtOH (1:4) and compared to those of the solutions of heterodinuclear complexes [Ru(PCP)(tpy,DTTA)Ln(H2O)2] (Ln = Gd3+, Eu3+). Rigid matrix excitation at 77 K of the ,,* level of the ruthenium chromophore in the [Ru(PCP)(tpy,DTTA)Eu(H2O)2] complex results in a weak europium(III) emission pointing to a transfer of energy from Ru,Eu as a result of the metal-to-ligand charge-transfer (MLCT) excited state of the ruthenium component to the luminescent lanthanide ion. The excited state lifetime of the europium complex is 0.2 ms in methanol solution. In deuterated solvents, the lifetime increases to 0.4 ms, which indicates that the process is solvent-dependent as a result of the strongly coordinated molecules of water that are responsible for the quenching in nondeuterated solvents.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Rare Earth Benzotriazolates: Coordination Polymers Incorporating Decomposition Products from Ammonia to 1,2-Diaminobenzene in,1[Ln(Btz)3(BtzH)] (Ln = Ce, Pr), ,1[Ln(Btz)3{Ph(NH2)2}] (Ln = Nd, Tb, Yb), and ,1[Ho2(Btz)6(BtzH)(NH3)],EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2006Klaus Müller-Buschbaum Abstract The solvent-free melt reactions of benzotriazole (BtzH, C6H4N2NH) with rare earth metals result in three different types of benzotriazolate coordination polymers. Early 4f metals yield ,1[Ln(Btz)3(BtzH)] [Ln = Ce (1), Pr (2)], from neodymium to ytterbium the type ,1[Ln(Btz)3{Ph(NH2)2}] is observed [Ln = Nd (3), Tb (4), Yb (5)], whereas the late 4f metal Ho gives ,1[Ho2(Btz)6(BtzH)(NH3)] (6). Depending on the reaction conditions and the respective rare earth element, ligand fragments originating from decomposition products are incorporated in the coordination polymers. Compounds 1,3 and 6 were obtained as single crystals and their crystal structures determined by single-crystal X-ray analysis, whilst 4 and 5 were obtained as powders. X-ray powder diffraction shows the isotypic character of polymers 3, 4, and 5. The benzotriazolates contain trivalent lanthanide ions with complete nitrogen coordination. Decomposition of the ligand accompanies the formation of the coordination polymers. X-ray analysis was combined with thermal analysis and mass spectrometry to investigate the influence of reaction temperatures on ligand decomposition. Ln-benzotriazolates exhibit aspects of materials science such as luminescence {5D4,7FJ, J = 4,6 for ,1[Tb(Btz)3{Ph(NH2)2}] (4)} without quenching by concentration. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Structural, Photophysical and Chiro-Optical Properties of Lanthanide Complexes with a Bis(benzimidazole)pyridine-Based Chiral LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2003Gilles Muller Abstract The neutral LnIII 1:1 nitrato complexes with the chiral ligand 2,6-bis(1- S -neopentylbenzimidazol-2-yl)pyridine (L11) have been synthesised and their stability constants measured in acetonitrile (log K1 = 4.0,6.4). The crystal and molecular structure of [Eu(NO3)3(L11)(MeCN)] shows the typical meridional planar coordination of L11 to the metal ion and low symmetry of the coordination polyhedron. The influence of the steric hindrance generated by the substituent at R2 on the crystal packing and bond lengths is discussed. Photophysical measurements show that ligand L11 induces a 3,,*-to-Ln energy-transfer process in the EuIII complex, while the TbIII compound is ten times less luminescent. Addition of a second molecule of L11 to give [Ln(ClO4)2(L11)2]+ leads to a large quenching of the EuIII luminescence (140-fold) due to several factors: a less efficient 1,,*,3,,* transfer (ca. fourfold), a smaller intrinsic quantum yield QEu (ca. threefold), and a substantially less efficient ligand-to-metal transfer (ca. 12-fold). In the case of the TbIII complex, the decrease in the energy of the triplet state reduces further the TbIII emission through increased back transfer. The specific rotary dispersion of the 1:1 and 1:2 complexes points to the chirality of the complexes arising mainly from the ligand, while the circularly polarized luminescence of these complexes with EuIII and TbIII displays a weak effect, pointing to a small diastereomeric excess in solution. Altogether, this study demonstrates that electronic, thermodynamic and photophysical properties of lanthanide complexes with aromatic terdentate ligands can be tuned by modifying the number and the arrangement of the ligands, as well as their substituents, particularly those in the R2 and R3 positions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] A Rigid Molecular Scaffold Affixing a (Polypyridine)ruthenium(II)- and a Nickel(II)-Containing Complex: Spectroscopic Evidence for a Weakly Coupled Bichromophoric SystemEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2003Yann Pellegrin Abstract The synthesis of DppztBuSalH2 (7), a rigid conjugated ditopic ligand containing a Dppz (dipyrido[3,2- a:2,,3,- c]phenazine) skeleton and a salophen-type chelate, is reported. The complexes DppztBuSalNi (10), [Ru(bpy)2(DppztBuSalH2)]2+ (11), and [Ru(bpy)2(DppztBuSalNi)]2+ (12) have been prepared and characterised using common spectroscopic methods. Electrochemical, UV/Vis spectroelectrochemical and EPR studies were conducted on compounds 7, 10, 11, and 12. The singly reduced radical forms of 7 and 10 can be generated electrochemically, with the lone electron located on the low-lying phenazine ,*-molecular orbital. Complexes 11 and 12 show several reduction waves and electronic and EPR data obtained for the electrogenerated singly reduced species show them to be closely related to the radical species 7·, and 10·,, respectively. The presence of nickel(II) in compound 12 renders the addition of the second electron on the phenazine group reversible. Both 11 and 12 show common features on the cathodic side of their cyclic voltammograms, with reversible one-electron ruthenium-centred oxidation. An additional low-potential reversible-oxidation wave is observed for 12, and this is ascribed to oxidation of the nickel(II) ion. The combined spectroscopic data best describe the ruthenium-containing complexes as weakly coupled bichromophoric systems. Photophysical studies attest to the formation of a charge-separated state for 11, whereas a strong quenching is detected for 12. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] | |||||||||||||||||||||||||||||||||||||||||||