Search results for "Spectrophotometry"
showing 10 items of 644 documents
Matrix Isolation and Ab Initio Study of Trans−Trans and Trans−Cis Dimers of Formic Acid
2010
Six trans-trans and five trans-cis dimeric structures of formic acid (HCOOH) are revealed by ab initio calculations. Four trans-trans and two trans-cis dimers are identified in the IR absorption spectra in argon matrices. The trans-cis dimers are obtained by narrow-band IR excitation of the vibrational transitions of the trans-trans dimers. Two trans-trans (tt3 and tt6) and one trans-cis (tc4) dimer are characterized experimentally for the first time. The tunneling decay rates of two trans-cis dimers (tc1 and tc4) are evaluated at different temperatures. A greater lifetime of the trans-cis dimers at elevated temperatures compared to the cis-monomer suggests that the high-energy conformers c…
Face-to-face held Pacman type porphyrin-fullerene dyads: design, synthesis, charge transfer interactions and photophysical studies
2008
Pacman-type face-to-face zinc-porphyrin-fullerene dyads have been newly synthesized and studied. Owing to the close proximity of the donor and acceptor entities, strong pi-pi intramolecular interactions between the porphyrin and fullerene entities resulted in modulating the spectral and electrochemical properties of the dyads. New absorption and emission bands that correspond to the charge-transfer interactions were observed in the near-IR region. Time-resolved transient absorption studies revealed efficient photoinduced electron transfer from the singlet excited porphyrin to the fullerene entity. The rate constants for photoinduced electron transfer are analyzed in terms of the Marcus theo…
Transient IR spectroscopy identifies key interactions and unravels new intermediates in the photocycle of a bacterial phytochrome.
2020
Phytochromes are photosensory proteins in plants, fungi, and bacteria, which detect red- and far-red light. They undergo a transition between the resting (Pr) and photoactivated (Pfr) states. In bacterial phytochromes, the Pr-to-Pfr transition is facilitated by two intermediate states, called Lumi-R and Meta-R. The molecular structures of the protein in these states are not known and the molecular mechanism of photoconversion is not understood. Here, we apply transient infrared absorption spectroscopy to study the photocycle of the wild-type and Y263F mutant of the phytochrome from Deinococcus radiodurans (DrBphP) from nanoto milliseconds. We identify two sequentially forming Lumi-R states …
Autonomous artificial nanomotor powered by sunlight
2006
Light excitation powers the reversible shuttling movement of the ring component of a rotaxane between two stations located at a 1.3-nm distance on its dumbbell-shaped component. The photoinduced shuttling movement, which occurs in solution, is based on a “four-stroke” synchronized sequence of electronic and nuclear processes. At room temperature the deactivation time of the high-energy charge-transfer state obtained by light excitation is ≈10 μs, and the time period required for the ring-displacement process is on the order of 100 μs. The rotaxane behaves as an autonomous linear motor and operates with a quantum efficiency up to ≈12%. The investigated system is a unique example of an artif…
Crystallization, spectral, crystallographical, and thermoanalytical studies of succinobucol polymorphism.
2011
Four different polymorphs, A, C, D, and E, of succinobucol were isolated and characterized by means of solid-state nuclear magnetic resonance spectroscopy, single crystal and powder X-ray diffraction, differential scanning calorimetry, thermogravimetry, and attenuated total reflection–infrared spectroscopy. From a number of experiments, the same polymorphs (C, D, and E) and an equilibrium phase mixture B consisting of polymorphs C and D were repeatedly gained using different solvents or their mixtures. Although polymorph A was obtained directly from recrystallization only on few occasions, polymorphs C, D, and E proved to be metastable kinetic polymorphs, which slowly transform to a thermod…
Geometric Isomerism in Pentacoordinate Cu2+ Complexes: Equilibrium, Kinetic, and Density Functional Theory Studies Reveal the Existence of Equilibriu…
2009
A ligand (L1) (bis(aminoethyl)[2-(4-quinolylmethyl)aminoethyl]amine) containing a 4-quinolylmethyl group attached to one of the terminal amino groups of tris(2-aminoethyl)amine (tren) has been prepared, and its protonation constants and stability constants for the formation of Cu(2+) complexes have been determined. Kinetic studies on the formation of Cu(2+) complexes in slightly acidic solutions and on the acid-promoted complex decomposition strongly suggest that the Cu(2+)-L1 complex exists in solution as a mixture of two species, one of them showing a trigonal bipyramidal (tbp) coordination environment with an absorption maximum at 890 nm in the electronic spectrum, and the other one bein…
Fluorescent substituted amidines of benzanthrone: synthesis, spectroscopy and quantum chemical calculations.
2012
Abstract Several new substituted amidine derivatives of benzanthrone were synthesized by a condensation reaction from 3-aminobenzo[de]anthracen-7-one and appropriate aromatic and aliphatic amides. The obtained derivatives have a bright yellow or orange fluorescence in organic solvents and in solid state. The novel benzanthrone derivatives were characterized by TLC analysis, 1H NMR, IR, MS, UV/vis, and fluorescence spectroscopy. The solvent effect on photophysical behaviors of these dyes was investigated, and the results showed that the Stoke’s shift increased, whereas quantum yield decreased with the growth of the solvent polarity. The structure of some dyes was confirmed by the X-ray singl…
Mapping the fluorophilicity of a hydrophobic pocket: synthesis and biological evaluation of tricyclic thrombin inhibitors directing fluorinated alkyl…
2006
In the completion of our fluorine scan of tricyclic inhibitors to map the fluorophilicity/fluorophobicity of the thrombin active site, a series of 11 new ligands featuring alkyl, alkenyl, and fluoroalkyl groups was prepared to explore fluorine effects on binding into the hydrophobic proximal (P) pocket, lined by Tyr 60A and Trp 60D, His 57, and Leu 99. The synthesis of the tricyclic scaffolds was based on the 1,3-dipolar cycloaddition of azomethine ylides, derived from L-proline and 4-bromobenzaldehyde, with N-(4-fluorobenzyl)maleimide. Introduction of alkyl, alkenyl, and partially fluorinated alkyl residues was achieved upon substitution of a sulfonyl group by mixed Mg/Zn organometallics f…
Triphenyltin(IV) 2-[(E)-2-(aryl)-1-diazenyl]benzoates as anticancer drugs: Synthesis, structural characterization, in vitro cytotoxicity and study of…
2009
Summary: Triphenyltin(IV) complexes of composition [Ph3SnL 1H]n (1) and [Ph3SnL2H]n (2) (where L1H=2-[(E)-2-(3-formyl-4-hydroxyphenyl)-1-diazenyl] benzoate and L2H = 2-[(E)-2-(4-Hydroxy-5-methylphenyl)-1-diazenyl] benzoate) were synthesized and characterized by spectroscopic (1H, 13C and 119Sn NMR, IR, 119Sn Mössbauer) techniques in combination with elemental analysis. The molecular structures and geometries of the complexes (1 and 2) were fully optimized using the quantum mechanical method (PM3). Complexes (1 and 2) were found to exhibit stronger cytotoxic activity in vitro across a panel of human tumour cell lines viz., A498, EVSA-T, H226, IGROV, M19 MEL, MCF-7 and WIDR. The test compound…
Synyhesis, structure, spectroscopy and redox chemistry of square-planar nickel(II) complexes with tetradentate o-phenylenedioxamidates and related li…
2005
[EN] A series of four-coordinate square-planar nickel(II) complexes of o-phenylenebis(N¿-methyloxamidate) (L1) and related o-phenylene(N¿-methyloxamidate)oxamate (L2) and o-phenylenebis(oxamate) (L3) tetradentate ligands have been synthesized and characterized structurally, spectroscopically and electrochemically. The parent nickel(II)¿L1 complex presents an intense MLCT band in the UV region (¿max = 357 nm) and a distinctive 1 s ¿ 4p CT satellite in the Ni K-edge XANES spectrum (E = 8339.2 eV). These features together with the short Ni¿N(amidate) bond lengths (1.85¿1.93 Å) as revealed by the analysis of the Ni K-edge EXAFS spectrum and confirmed by single-crystal X-ray diffraction are typi…