Search results for "Spectrophotometry"
showing 10 items of 644 documents
Multinuclear Cytotoxic Metallodrugs: Physicochemical Characterization and Biological Properties of Novel Heteronuclear Gold-Titanium Complexes
2011
An unprecedented series of titanocene-gold bi- and trimetallic complexes of the general formula [[(η(5)-C(5)H(5))(μ-η(5):κ(1)-C(5)H(4)(CH(2))(n)PPh(2))TiCl(2)](m)AuCl(x)](q+) (n = 0, 2, or 4; m = 1, x = 1, q = 0 or m = 2, x = 0, q = 1) have been prepared and characterized spectroscopically. The luminescence spectroscopy and photophysics of one of the compounds, [[(η(5)-C(5)H(5))(μ-η(5):κ(1)-C(5)H(4)PPh(2))TiCl(2)](2)Au]PF(6), have been investigated in 2MeTHF solution and in the solid state at 77 and 298 K. Evidence for interfragment interactions based on the comparison of electronic band positions and emission lifetimes, namely, triplet energy transfer (ET) from the Au- to the Ti-containing…
Oxidative DNA cleavage induced by an iron(III) flavonoid complex: synthesis, crystal structure and characterization of chlorobis(flavonolato)(methano…
2006
A flavonol iron(III) complex, [Fe(flavonolato)(2)Cl(MeOH)], has been prepared. The compound has been characterized by X-ray crystallography, spectroscopy, magnetism and electronic paramagnetic resonance (EPR) at X- and Q-band. The geometrical environment around the metal is best described as rhombic distorted octahedral. This distortion has also been inferred from the magnetic measurements and from the EPR spectra at different temperatures, E/D(rhombicity parameter) approximately 0.06. The DNA cleavage activity of the iron(III) complex with and without ascorbate/hydrogen peroxide is reported. Mechanisms of the oxidative cleavage have been proposed when DNA strand scission is performed both …
Vibrational spectrum of the spin crossover complex [Fe(phen)(2)(NCS)(2)] studied by IR and Raman spectroscopy, nuclear inelastic scattering and DFT c…
2006
The vibrational modes of the low-spin and high-spin isomers of the spin crossover complex [Fe(phen)(2)(NCS)(2)] (phen = 1,10-phenanthroline) have been measured by IR and Raman spectroscopy and by nuclear inelastic scattering. The vibrational frequencies and normal modes and the IR and Raman intensities have been calculated by density functional methods. The vibrational entropy difference between the two isomers, DeltaS(vib), which is--together with the electronic entropy difference DeltaS(el)--the driving force for the spin-transition, has been determined from the measured and from the calculated frequencies. The calculated difference (DeltaS(vib) = 57-70 J mol(-1) K(-1), depending on the m…
Experimental and Computational Studies of Hydrogen Bonding and Proton Transfer to [Cp*Fe(dppe)H]
2005
The present contribution reports experimental and computational investigations of the interaction between [Cp*Fe(dppe)H] and different proton donors (HA). The focus is on the structure of the proton transfer intermediates and on the potential energy surface of the proton transfer leading to the dihydrogen complex [Cp*Fe(dppe)(H2)]+. With p-nitrophenol (PNP) a UV/Visible study provides evidence of the formation of the ion-pair stabilized by a hydrogen bond between the nonclassical cation [Cp*Fe(dppe)(H2)]+ and the homoconjugated anion ([AHA]-). With trifluoroacetic acid (TFA), the hydrogen-bonded ion pair containing the simple conjugate base (A-) in equilibrium with the free ions is observed…
Comparative Studies on IR, Raman, and Surface Enhanced Raman Scattering Spectroscopy of Dipeptides Containing ΔAla and ΔPhe
2012
Three dipeptides containing dehydroresidues (\DeltaAla, \Delta (Z)Phe, and \Delta (E)Phe) were examined by IR, Raman, and surface-enhanced Raman techniques for the first time. The effect of the size and isomer type of the β -substituent in the dehydroresidue on the conformational structure of the peptide was evaluated by using the analysis of IR and Raman bands. Additionally, SERS spectroscopy provided insight into the adsorption mechanism of these species on the metal surface. SERS spectra were recorded at alkaline pH on the silver sol using visible light excitation. The dehydroresidues studied here strongly influenced the SERS profile of the peptides. The most pronounced SERS signal for a…
Tarantula Hemocyanin Shows Phenoloxidase Activity
1998
An enzyme generally catalyzes one well defined reaction with high specificity and efficiency. We report here in contrast that the copper protein hemocyanin of the tarantula Eurypelma californicum exhibits two different functions. These occur at the same active site. While hemocyanin usually is an oxygen carrier, its function can be transformed totally to monophenoloxidase and o-diphenoloxidase activity after limited proteolysis with trypsin or chymotrypsin. N-acetyldopamine (NADA) is more effectively oxidized than L-dopa or dopamine. This irreversible functional switch of tarantula hemocyanin function is limited to the two subunits b and c of its seven subunit types. A conserved phenylalani…
Characterization of Iron−Carbonyl-Protected Gold Clusters
2009
Ligand-stabilized nanometer-sized gold particles are interesting building blocks for molecular electronics, precursors for catalysts, optical labels for biomolecules and diagnosis, and potential nontoxic carriers for therapeutics. In this work we characterize for the first time, by means of near-infrared and Raman spectroscopy and time-dependent density functional calculations, gold clusters protected with iron-carbonyl ligands, such as {Au(22)[Fe(CO)(4)](12)}(6-) shown in the figure. Surprisingly, our results show that these novel compounds bear many analogues to another, well-studied, class of gold clusters, namely those of thiolate-monolayer-protected gold clusters. Our work adds a new d…
8-N(3)-3'-biotinyl-ATP, a novel monofunctional reagent: differences in the F(1)- and V(1)-ATPases by means of the ATP analogue.
2001
A novel photoaffinity label, 8-N(3)-3'-biotinyl-ATP, has been synthesized. The introduction of an additional biotin residue is advantageous for easy detection of labeled proteins. This could be first tested by reaction with the F(1)-ATPase from the thermophilic bacterium PS3 (TF(1)). UV irradiation of TF(1) in the presence of 8-N(3)-3'-biotinyl-ATP results in a nucleotide-dependent binding of the analogue in the noncatalytic alpha and the catalytic beta subunits of TF(1), demonstrating the suitability of this analogue as a potential photoaffinity label. Reaction with the V(1)-ATPase, however, led to labeling of subunit E, which has been suggested as a structural and functional homologue of …
A Tetracopper(II)-Tetraradical Cuboidal Core and Its Reactivity as a Functional Model of Phenoxazinone Synthase
2007
The coordination chemistry of the tridentate ligand N-(2-hydroxy-3,5-di-tert-butylphenyl)-2-aminobenzylalcohol H3L has been studied with the copper(II) ion. The ligand is noninnocent in the sense that it is readily oxidized in the presence of air to its o-iminobenzosemiquinonato [L*]2- radical form. The crystal structure of the synthesized tetracopper(II)-tetraradical complex [CuII4(L*)4] (1), has been determined by X-ray crystallography at 100 K. Variable-temperature (2-290 K) magnetic susceptibility measurements of complex 1 containing eight paramagnetic centers establish the spin ground state to be diamagnetic (St=0) arising from the antiferromagnetic interactions. Electrochemical measur…
Multiple Decay Mechanisms and 2D-UV Spectroscopic Fingerprints of Singlet Excited Solvated Adenine-Uracil Monophosphate
2016
The decay channels of singlet excited adenine uracil monophosphate (ApU) in water are studied with CASPT2//CASSCF:MM potential energy calculations and simulation of the 2D-UV spectroscopic fingerprints with the aim of elucidating the role of the different electronic states of the stacked conformer in the excited state dynamics. The adenine 1La state can decay without a barrier to a conical intersection with the ground state. In contrast, the adenine 1Lb and uracil S(U) states have minima that are separated from the intersections by sizeable barriers. Depending on the backbone conformation, the CT state can undergo inter-base hydrogen transfer and decay to the ground state through a conical …