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101.
A. Després V. Lejeune E. Migirdicyan C. Mijoule G. Marconi G. Orlandi W. Siebrand M.Z. Zgierski 《Chemical physics》1984,88(2):229-245
An attempt is reported to explain the main intensity patterns in the phosphorescence spectra of 2,4-, 2,5- and 3,4-dimethyl-benzaldehyde-1h1 and -1d1, observed previously. The analysis is based on CNDO and MINDO calculations of (transition) dipole moments, spin-orbit couplings, vibronic couplings, state energies, normal coordinates and vibrational frequencies. Where possible these quantities are empirically checked and corrected. Additional information, especially about the separation of the closely spaced T1(3ππ*) and T2(3nπ*) states, is obtained from phosphorescence excitation spectra reported here for all six isomers. The phosphorescence spectra consist of two components, an “allowed” component of 3ππ* and a “forbidden” component of 3nπ* symmetry. It is concluded that the allowed component is partly induced by the crystal field. The forbidden component is vibronically induced by out-of-plane vibrations among which the aldehydic CH(CD)-wag mode is the most active. The observed intensity patterns for this component are ascribed to interference between two mechanisms, one involving vibronic coupling between S0 and S1(1nπ*) and spin-orbit coupling between S1 and T1, the other involving vibronic coupling between T1 and T2 and spin-orbit coupling between S0 and T2. Within the groups of either 1h1 or 1d1 isomers, the main changes in the spectrum are shown to be due to the change in T1–T2 energy separation. The changes observed upon deuterium substitution in the aldehyde group involve, in addition to changes in the T1–T2 gap, changes in vibronic coupling due to normal-coordinate mixing. All these spectral changes are reproduced by calculations based on a mixture of theoretical and empirical input parameters, derived from, or at least consistent with, other observations, including excitation spectra, dipole moments and zero-field splittings. It is concluded that the mechanisms underlying these calculations offer a satisfactory explanation of the observed intensity patterns in the phosphorescence spectra of dimethylbenzaldehydes. 相似文献
102.
Salvatore Sortino Salvatore Petralia Giuseppe Condorelli Giancarlo Marconi 《Helvetica chimica acta》2003,86(2):266-273
The photoreactivity of the phototoxic anticancer drug flutamide (FM) in the presence of bovine serum albumin (BSA) has been investigated. The presence of BSA induces a remarkable modification of the photochemical outcome of the drug with respect to that observed in aqueous solution. Induced circular dichroism (ICD) measurements combined with theoretical calculations provide strong evidence that the new photochemical scenario is tuned by changes of the molecular geometry of FM when incorporated in the protein microenvironment. This behavior presents close analogies to that found in the presence of either cyclodextrin or phospholipid vesicles, chosen as models for biological systems, and delineates a quite general photochemical picture that can be useful for a more appropriate understanding of the adverse phototoxic effects induced by this drug. 相似文献
103.
We study the behavior of two particles moving in a bistable potential, colliding inelastically with each other and driven by a stochastic heat bath. The system has the tendency to clusterize, placing the particles in the same well at low drivings, and to fill all of the available space at high temperatures. We show that the hopping over the potential barrier occurs following the Arrhenius rate, where the heat bath temperature is replaced by the granular temperature. Moreover, within the clusterized "phase" one encounters two different scenarios: For moderate inelasticity, the jumps from one well to the other involve one particle at a time, whereas for strong inelasticity the two particles hop simultaneously. 相似文献
104.
105.
Cherrine K. Pires Andr F. Lavorante Luciana M.T. Marconi Silvia R.P. Meneses Elias A.G. Zagatto 《Microchemical Journal》2006,83(2):70-74
A multi-pumping flow-based procedure with chemiluminescent detection is proposed for the determination of ascorbic acid, AA, in fruit juices (powdered form). The method relies on the inhibitory effect of AA on the oxidation of luminol by hydrogen peroxide in alkaline medium. The system comprises several discretely actuated solenoid pumps as the only active components. It handles 100 samples per hour, and requires 96 μl of sample, 42 μg of luminol and 105 μg of potassium hexacyanoferrate(III) per determination. The analytical curve is linear up to about 11 mmol l− 1 AA, and detection limit is 0.17 mmol l− 1 AA. The system yields precise measurements (r.s.d. < 1%; n = 11), and recovery ranges from 94% to 106%. Results are in agreement with the reference method (AOAC) at the 95% confidence level. 相似文献
106.
A simple and rapid flow system for the determination of lactulose in milk samples was developed. It is based on the hydrolysis of lactulose to galactose and fructose by the enzyme beta-galactosidase immobilised in a reactor. The amount of fructose produced was measured with an electrochemical biosensor based on the fructose dehydrogenase enzyme, K3[Fe(CN)6] as mediator and a platinum based electrochemical transducer. Parameters such as the enzyme immobilisation in the reactor and under the electrode surface, the lifetime of the beta-galactosidase reactor and of the dehydrogenase biosensor and the flow parameters were studied and optimised. Fructose was determined in the range 1 x 10(-6)-5 x 10(-3) mol l-1 with an RSD of about 2% and a detection limit of 5 x 10(-7) mol l-1. The use of a microdialysis probe as the sampling system permitted the direct measurement of lactulose in milk samples without pre-treatment in the range 1 x 10(-5)-5 x 10(-3) mol l-1. The sensitivity of the procedure allowed pasteurised, UHT and in-container sterilised milk to be distinguished. 相似文献
107.
Susana Encinas Miguel A. Miranda Giancarlo Marconi Sandra Monti 《Photochemistry and photobiology》1998,67(4):420-425
The 2-benzoylthiophene chromophore of the photosensitizing drug tiaprofenic acid and of its decarboxylated derivative is characterized by a unusually high energy gap between the T1 (π,π*) and T2 (n,π*) excited states, which makes this a unique system to study the intrinsic photo-reactivity of the two states. Weak fluorescence and phosporescence emission were detected at room temperature. Tiaprofenic acid undergoes photodecarboxylation from the triplet manifold as the main reaction. The photoprocess is temperature dependent with activation energy of 7–10 kcal/mol, close to the energy gap between T1 and T2 . The decarboxylated product abstracts hydrogen in type I reactions. The involvement of T2 in the above processes is proposed. Moreover the decarboxylated derivative exhibits reactivity toward phenols, consistent with a participation of the T1 state as electron acceptor. The observed photoprocesses can account for biological photosensitization reactions, like membrane damage and protein modification. 相似文献
108.
Vibronic coupling integrals governing the induced absorption of the first nπ* excited state have been evaluated theoretically. The calculations, based on the CNDO/S method, confirm the b1g assignment of the 918 cm?1 vibration, its prominent role in the intensity borrowing and its anharmonic character in the B3u state. Furthermore they suggest that non-BO coupling and borrowing from higher electronic states cannot be neglected. 相似文献
109.
Armaroli N Boudon C Felder D Gisselbrecht JP Gross M Marconi G Nicoud JF Nierengarten JF Vicinelli V 《Angewandte Chemie (International ed. in English)》1999,38(24):3730-3733
Virtual inaccessibility to external contact was revealed by electrochemical investigations for a bis(1,10-phenanthroline)copper(I) core embedded in dendrimers with up to 16 peripheral fullerene units (shown schematically). With increasing numbers of fullerene units, less and less light is available to the core, and the small quantity of light energy that reaches the central Cu(I) complex is returned to the external fullerenes by energy transfer-the central core is buried in a dendritic black box. 相似文献
110.
A simple model of inelastic hard rods subject to a one-dimensional array of identical wells is introduced. The energy loss due to inelastic collisions is balanced by the work supplied by an external stochastic heat bath. We explore the effect of the spatial nonuniformity on the steady states of the system. The spatial variations of the density, granular temperature, and pressure induced by the gradient of the external potential are investigated and compared with the analogous variations in an elastic system. Finally, we study the clustering process by considering the relaxation of the system starting from a uniform homogeneous state. 相似文献