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Absolute rate constants and their temperature dependence were determined by time‐resolved electron spin resonance for the addition of the radicals PhĊH2 and PhĊMe2 to a variety of alkenes in toluene solution. To vinyl monomers CH2=CXY, PhĊH2 adds at the unsubstituted C‐atom with rate constants ranging from 14 M−1S−1 (ethoxyethene) to 6.7 · 103 M−1S−1 (4‐vinylpyridine) at 296 K, and the frequency factors are in the narrow range of log (A/M−1S−1) = 8.6 ± 0.3, whereas the activation energy varies with the substituents from ca. 51 kJ/mol to ca. 26 kJ/mol. The rate constants and the activation energies increase both with increasing exothermicity of the reaction and with increasing electron affinity of the alkenes and are mainly controlled by the reaction enthalpy, but are markedly influenced also by nucleophilic polar effects for electron‐deficient substrates. For 1,2‐disubstituted and trisubstituted alkenes, the rate constants are affected by additional steric substituent effects. To acrylate and styrenes, PhĊMe2 adds with rate constants similar to those of PhĊH2, and the reactivity is controlled by the same factors. A comparison with relative‐rate data shows that reaction enthalpy and polar effects also dominate the copolymerization behavior of the styrene propagation radical.

Phosphorus-doped TiO2 nanoparticles with visible light activity were prepared by sol–gel method by using Ti(IV) isopropoxide and phosphoric acid as precursors. As prepared samples were calcined at different temperatures, and the obtained samples were characterized by X-ray diffraction, UV–vis spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis, X-ray photoelectron spectroscopy, scanning emission microscopy, electron paramagnetic resonance (EPR) spectroscopy, the photodegradation of methyleneblue (MB). The results indicate that phosphorus-doping into TiO2 lattice decreases the particle size, increases the thermal stability of titania, and retards the phase transition from anatase to rutile. UV–vis absorption of the P-doped samples shows the redshift in its absorption edge. Doped phosphorus exists in a pentavalent oxidation state by replacing part of lattice Ti4+ by the formation of Ti–O–P bonds. MB degradation profiles with visible light irradiation show that the photocatalytic activity of P-doped Titania is much enhanced and superior to undoped TiO2 and commercial Degussa P25. Low temperature EPR studies with in situ visible light irradiation on the samples heated at different temperatures clearly demonstrates that enhanced charge separation is the major reason for the enhanced photocatalytic activity.

The triplet state properties of 7-azatryptophan (7AW), 5-hydroxytryptophan (5HW), and the 5HW anion (pH ) 12.3) have been investigated by optically detected magnetic resonance, ODMR, in zero applied field. Also the triplet state properties of tryptophan (Trp) have been reexamined. Analysis of "slow-passage" ODMR responses during phosphorescence decay (delayed ODMR) that contain the effects of fast passage is introduced using Marquardt-Levenberg nonlinear least-squares fitting. The parameters determined by the analysis of delayed ODMR are the band center frequency (ν 0 ) and bandwidth (ν 1/2 ) of the inhomogeneously broadened ODMR band, the apparent decay constants of the triplet sublevels, and their relative radiative rate constants. The values of ν 0 and ν 1/2 are obtained with greater accuracy than is possible with analysis that does not account for fast passage effects on the band shape. The kinetic parameters are influenced somewhat by residual spin-lattice relaxation (SLR) effects, however. The zero-field magnetic resonance frequencies and band widths have been determined for Trp, 7AW, 5HW, and 5HW anion, along with the apparent kinetic parameters for Trp and 7AW. Microwave-induced delayed phosphorescence transient responses of 5HW and its anion are analyzed globally to give kinetic parameters free of residual effects. The ODMR band widths of 5HW and its anion greatly exceed those of Trp, while those of 7AW are significantly narrower. The zero-field-splitting (ZFS) parameter E is reduced in 5HW and its anion to about half its value in Trp, while the E-parameter of 7AW increases by about 10%. Sublevel decay constants relative to Trp are hardly changed in 5HW, but increase significantly in the anion. Decay constants of Trp increase moderately with 7-aza substitution, as expected from introduction of spin-orbit coupling at the N atom. The pattern of ODMR bandwidths of Trp and 7AW is consistent with a positive correlation of solvent induced shifts in the ZFS Dand E-parameters.

The binding of p7 nucleocapsid protein of type 1 human immunodeficiency virus (HIV-1) to various oligonucleotides and polynucleotides has been investigated by phosphorescence and optically detected magnetic resonance (ODMR) spectroscopy. The intrinsic spectroscopic probe used in these studies is the photoexcited triplet state of Trp37, which is associated with the C-terminal zinc finger of p7 and is its only tryptophan residue. Complex formation produces a red-shift of the phosphorescence 0, 0-band (DeltaE0,0) of Trp37 as well as a reduction of the zero field splitting (zfs) D parameter. Increases of -DeltaE0,0 (A < C < U < G

Spectroscopic studies have been performed to characterize the solution structure of the V66W mutant of Staphylococcal nuclease and the corresponding 1-136 fragment, referred to as V66W'. Whereas wild-type nuclease has a single tryptophan residue at position 140, the V66W mutant has a second tryptophan residue at position 66, which is the only such residue in V66W'. Steady-state and time-resolved fluorescence studies show Trp-66 in V66W' to have a blue emission, a relatively large fluorescence quantum yield, a long lifetime, a significant degree of protection from solute quenchers, and to depolarize with a relatively long rotational correlation time. These results characterize Trp-66 in V66W' as being a buried residue, which indicates that this fragment retains some global structure. Circular dichroism (CD) data are consistent with the fragment having lost most of the alpha-helical content of the wild type, while retaining beta-sheet structure. The CD spectrum in the aromatic region also suggests that Trp-66 in the fragment experiences an asymmetric environment, which is not identical to that in the full length mutant, V66W. In addition, optical detection of triplet state magnetic resonance (ODMR) spectroscopy can clearly resolve the tryptophan residues and demonstrates differences between the local environment of Trp-66 in V66W and in V66W', as well as small differences in the Trp-140 environment in wild type and in V66W. Guanidine-HCl induced and thermally induced unfolding studies were performed by simultaneously acquiring CD and fluorescence data as a function of the perturbation and then performing a global analysis of such multiple data sets in terms of two-state and three-state unfolding models. Whereas data for wild-type nuclease and the V66W' fragment are well characterized by a two-state unfolding model, data for the V66W mutant are better characterized by a three-state process. That is, both the denaturant- and temperature-induced unfolding of V66W involves the significant population of an equilibrium unfolding intermediate. Our global analyses yield thermodynamic parameters for the unfolding transitions, and we show that the data for V66W can be described by a constrained three-state model in which the transition of the intermediate to the fully unfolded state is fixed to have the same thermodynamic parameters that describe the unfolding of the V66W' fragment.

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SUMMARYAn analytical model for high damping elastomeric isolation bearings is presented in this paper. The model is used to describe mathematically the damping force and restoring force of the rubber material and bearing. Ten parameters to be identiÿed from cyclic loading tests are included in the model. The sensitivity of the ten parameters in a ecting the model is examined. These ten parameters are functions of a number of in uence factors on the elastomer such as the rubber compound, Mullins e ect, scragging e ect, frequency, temperature and axial load. In this study, however, only the Mullins e ect, scragging e ect, frequency and temperature are investigated. Both material tests and shaking table tests were performed to validate the proposed model. Based on the comparison between the experimental and the analytical results, it is found that the proposed analytical model is capable of predicting the shear force-displacement hysteresis very accurately for both rubber material and bearing under cyclic loading reversals. The seismic response time histories of the bearing can also be captured, using the proposed analytical model, with a practically acceptable precision.