Electron exchange in conformationally restricted donor-spacer-acceptor dyads: angle dependence and involvement of upper-lying excited States

The rate constant for triplet energy transfer (k(TET)) has been measured in fluid solution for a series of mixed-metal Ru-Os bis(2,2':6',2'-terpyridine) complexes built around a tethered biphenyl-based spacer group. The length of the tether controls the central torsion angle for the spacer, which can be varied systematically from 37 to 130 degrees . At low temperature, but still in fluid solution, the spacer adopts the lowest-energy conformation and k(TET) shows a clear correlation with the torsion angle. A similar relationship holds for the inverse quantum yield for emission from the Ru-terpy donor. Triplet energy transfer is more strongly activated at higher temperature and the kinetic data require analysis in terms of two separate processes. The more weakly activated step involves electron exchange from the first-excited triplet state on the Ru-terpy donor and the size of the activation barrier matches well with that calculated from spectroscopic properties. The pre-exponential factor derived for this process correlates remarkably well with the torsion angle and there is a large disparity in electronic coupling through pi and sigma orbitals on the spacer. The more strongly activated step is attributed to electron exchange from an upper-lying triplet state localized on the Ru-terpy donor. Here, the pre-exponential factor is larger but shows the same dependence on the geometry of the spacer. Strangely, the difference in coupling through pi and sigma orbitals is much less pronounced. Despite internal flexibility around the spacer, k(TET) shows a marked dependence on the torsion angle computed for the lowest-energy conformation.     

Hartree-Fock-Bogoliubov calculations of the rotational band of the very heavy 254No nucleus

We report on Hartree-Fock-Bogoliubov (HFB) calculations of the ground-state rotational band of the heavy nucleus ²⁵⁴No recently observed experimentally. The calculated quadrupole deformation is consistent with the experimental value of β = 0.27 and is almost constant over the whole band. We also reproduce fairly well the excitation spectra and moments of inertia of this isotope up to the maximal experimentally observed state of spin 20. The rather high stability of this nucleus against fission is illustrated by the deformation energy curve providing very high fission barriers at zero spin within the HFB and HFB plus Lipkin-Nogami formalisms. The variation of these barriers with increased angular velocities is also studied. Received: 23 November 2000 / Accepted: 24 October 2001     

158 A Ge V p-Pb Pb-Pb碰撞中的单奇异和多奇异粒子产生

用描写相对论性核 核碰撞的LUCIAE模型及相应的MonteCarlo事例产生器分析了WA97最近发表的 1 5 8AGeVp Pb和Pb Pb碰撞中单奇异粒子 (Λ ,Λ)和多奇异粒子 (Ξ-,Ξ-,Ω-,Ω-)的多重数和横质量分布 .由于LUCIAE模型包含了弦碎裂微观过程中奇异夸克压低因子随碰撞体系的能量、中心度和质量的增大而增大 ,以及由它导致的相对论性核 核碰撞宏观过程中奇异粒子产额随上述三因素之增而增的物理机制 ;LUCIAE模型计算结果能较好描写WA97实验所揭示的相对论性核 核碰撞中奇异粒子产额随中心度之增而增和奇异粒子增强随奇异夸克数之增而增的实验事实 ,以及单奇异和多奇异粒子的横质量分布 .     

Solid-phase synthesis of 1,2,4-oxadiazoles

The synthesis of 3,5-substituted 1,2,4-oxadiazoles on solid support is described. Benzoic acids bound to the Wang linker on a polystyrene resin are activated and allowed to react with N-hydroxyamidines. The resulting acylated N-hydroxyamidines are converted into 1,2,4-oxadiazoles at 125°C.     

Saturation Effects and the Colored Pump Noise in a Dye Laser

We investigate the statistical properties of two single-mode dye-laser models-the colored-loss-noise model and the colored-gain-noise model. Analytic expressions of the probability,the mean and the variance of the steady-state laser intensity are obtained through the unified expansion theory [Phys. Rev. A43 (1991) 700]. By comparison we find that when the cavity decay rate for the electric field is large and the pump parameter a₀ is small, the differences of the results of the two laser models are small. Otherwise, the differences are large. And the correlation time of the noise has very obvious influence on the results of the two models.     

Intramolecular excimer formation and delayed fluorescence in sterically constrained pyrene dimers

The synthesis is described for a series of five molecular dyads comprising pyrene-based terminals covalently linked through a 1,3-disubstituted phenylene spacer. The extent of through-space communication between the pyrene units is modulated by steric interactions imposed by bulky moieties attached at the 6,8-positions of each pyrene unit. For the control compound, only hydrogen atoms occupy the 6,8 positions (DP1), whereas the remaining compounds incorporate ethynylene groups terminated with either triisopropylsilyl (DP2), 1-tert-butylbenzene (DP3), 2,6-di-tert-butylbenzene (DP4) or 1-tert-butyl-3,5-dimethylbenzene (DP5) units. Each compound shows a mixture of monomer and excimer fluorescence in fluid solution at room temperature, but only monomer emission in a glassy matrix at 77 K. The ratio of monomer to excimer fluorescence depends markedly on the molecular structure; DP1 is heavily biased in favour of the excimer and DP4 is enriched with monomer fluorescence. Photophysical properties, including laser induced and delayed fluorescence data, are reported for each compound. Delayed fluorescence occurs by both intramolecular and bimolecular steps, but these events take place on different timescales. The possibility is raised for using intramolecular triplet-triplet annihilation as a means of molecular imaging.     

UPLC-MS/MS Method for the Identification of Recombinant Human Erythropoietin Analogues in Horse Plasma and Urine

Recombinant human erythropoietin (rhEPO) analogues are known to have been used in horse sports for their assumed performance enhancing properties. Recently, several authors have published liquid chromatographic-tandem mass spectrometric (LC-MS/MS) methods for confirming the presence of rhEPO analogues in horse plasma. In the current study, an improved LC-MS/MS confirmatory procedure for rhEPO, darbepoetin (DPO) and continuous erythropoietin receptor activator (CERA) in horse plasma was developed and validated. The method was also adapted for and applied to urine samples for the first time. Similar to previously published plasma assays, the methods utilise size exclusion and immunoaffinity extraction prior to tryptic cleavage, enzymatic deglycosylation and LC-MS/MS analysis of the resulting signature tryptic peptides (rhEPO/CERA T5, rhEPO/CERA/DPO T6 and DPO T9). However, the novel application of UPLC chromatography significantly improves the run time of the method compared to nano- or micro-LC and its robustness compared to nano-LC. Furthermore, recombinant canine EPO was found to serve as an effective internal standard, thus allowing confidence in interpretation of the success/failure of every step in the procedure. Limits of detection for confirming the presence of rhEPO, CERA and DPO in plasma were 0.1, 0.25 and 0.05 ng mL^?1, respectively, which were equal to or lower than limits achieved using previously published LC-MS/MS based methods. Limits of detection for confirming the presence of rhEPO, CERA and DPO in urine were 0.05, 0.15 and 0.025 ng mL^?1 and the analysis of urine samples collected from horses administered rhEPO (Eprex?) or DPO (Aranesp?) demonstrated the use of this matrix as a suitable alternative in situations where plasma is not available.     

An apparent angle dependence for the nonradiative deactivation of excited triplet states of sterically constrained, binuclear ruthenium(II) bis(2,2':6',2' '-terpyridine) complexes

The photophysical properties are reported for a series of binuclear ruthenium(II) bis(2,2':6',2"-terpyridine) complexes built around a geometrically constrained, biphenyl-based bridge. The luminescence quantum yield and lifetime increase progressively with decreasing temperature, but the derived rate constant for nonradiative decay of the lowest-energy triplet state depends on the length of a tethering strap attached at the 2,2'-positions of the biphenyl unit. Since the length of the strap determines the dihedral angle for the central C-C bond, the rate of nonradiative decay shows a pronounced dependence on angle. The minimum rate of nonradiative decay occurs when the dihedral angle is 90 degrees, but there is a maximum in the rate when the dihedral angle is about 45 degrees. This effect does not appear to be related to the extent of electron delocalization at the triplet level but can be explained in terms of variable coupling with a low-frequency vibrational mode associated with the strapped biphenyl unit.     

Diode laser spectra of the ν2 band of H212CO and H213CO

The Q-branches of the ν₂ (CO stretch) band of H₂¹²CO and H₂¹³CO have been studied in high resolution using an infrared diode laser. Accurate upper state constants, including A, B, C, Δ_J, Δ_JK, Δ_K, and H_K, were determined from an analysis of the data for 97 lines of H₂¹²CO and 79 lines and H₂¹³CO and compared with previous reported values. Band centers were also determined and reported as 1746.009 ± 0.002 cm^?1 for H₂¹²CO and 1707.981 ± 0.002 cm^?1 for H₂¹³CO.