Covalent and noncovalent interactions for [metal(dien)nucleobase](2+) complexes with L-tryptophan derivatives: formation of palladium-tryptophan species by nucleobase substitution under biologically relevant conditions

The interaction of the complexes [Pd(dien)(1-MeCyt)]2+ (2) and [Pd(dien)(9-EtGH)]2+ (3) with the amino acids L-tryptophan (Trp) and N-acetyltryptophan (N-AcTrp) was studied and compared with the previously studied platinum analogues [Pt(dien)(1-MeCyt)]2+ (4) and [Pt(dien)(9-EtGH)]2+ (5). Solid-state structures for 2 and 4 are reported. For the palladium complexes, the interaction is pH sensitive. Below pH 5, the noncovalent interaction with stacking between the aromatic amino acid residue and the metalated nucleobase was observed. Fluorescence quenching experiments indicated similar association constants for platinum and palladium derivatives 2-5. Unusual substitution of the model nucleobases 1-methylcytosine (1-MeCyt) and 9-ethylguanine (9-EtGH) by tryptophan was observed in the range of pH 5-11. The resulting species [Pd(dien)(Trp)]+ (6) and [Pd(dien)(N-AcTrp)]+ (7) were characterized using 1H NMR, 13C NMR, and ESI-MS spectroscopy with coordination indicated through the amino and deprotonated amido nitrogens, respectively. Complexes 6 and 7 were also obtained from a solution of [Pd(dien)Cl]+ (1) incubated with either Trp or N-AcTrp, respectively.     

Electron attachment to higher fullerenes and to Sc3N@C80

We report on attachment of free electrons to fullerenes C(n) (n = 60, 70, 76, 78, 80, 82, 84, 86) and to Sc(3)N@C(80). The attachment cross sections exhibit a strong resonance at 0 eV for all species. The overall shape of the anion yield versus electron energy is quite similar for the higher fullerenes, with a minimum around 1 eV and a maximum which gradually shifts from 6 eV for C(60) to approximately 4 eV for large n. The endohedral Sc(3)N@C(80) exhibits a particularly shallow minimum and a maximum below 4 eV. We model autoionization of the anions with due consideration of the internal energy distributions. The relatively low electron affinity of Sc(3)N@C(80) is reflected in its reduced ion yield at higher attachment energies.     

Linearized forward and inverse problems of the resonant ultrasound spectroscopy for the evaluation of thin surface layers

In this paper, linearized approximations of both the forward and the inverse problems of resonant ultrasound spectroscopy for the determination of mechanical properties of thin surface layers are presented. The linear relations between the frequency shifts induced by the deposition of the layer and the in-plane elastic coefficients of the layer are derived and inverted, the applicability range of the obtained linear model is discussed by a comparison with nonlinear models and finite element method (FEM), and an algorithm for the estimation of experimental errors in the inversely determined elastic coefficients is described. In the final part of the paper, the linearized inverse procedure is applied to evaluate elastic coefficients of a 310 nm thick diamond-like carbon layer deposited on a silicon substrate.     

Inverse problems in cancellous bone: estimation of the ultrasonic properties of fast and slow waves using Bayesian probability theory

Quantitative ultrasonic characterization of cancellous bone can be complicated by artifacts introduced by analyzing acquired data consisting of two propagating waves (a fast wave and a slow wave) as if only one wave were present. Recovering the ultrasonic properties of overlapping fast and slow waves could therefore lead to enhancement of bone quality assessment. The current study uses Bayesian probability theory to estimate phase velocity and normalized broadband ultrasonic attenuation (nBUA) parameters in a model of fast and slow wave propagation. Calculations are carried out using Markov chain Monte Carlo with simulated annealing to approximate the marginal posterior probability densities for parameters in the model. The technique is applied to simulated data, to data acquired on two phantoms capable of generating two waves in acquired signals, and to data acquired on a human femur condyle specimen. The models are in good agreement with both the simulated and experimental data, and the values of the estimated ultrasonic parameters fall within expected ranges.     

169 MHz repetition frequency all-fiber passively mode-locked erbium doped fiber laser

Passively mode-locked stretched-pulse erbium fiber laser is presented. With all-fiber configuration 111 fs pulses were achieved with the fundamental repetition rate of 169 MHz and an average output power of more than 30 mW. Proposed setup shows excellent stability, reliability and ‘turn-key’ operation. The impact of the pump power on laser parameters is described.     

Controlling the frequency of the frequency-shifted feedback fiber laser using injection-seeding technique

In this paper we describe the stabilization of the optical frequency comb (OFC) generated by the frequency-shifted feedback (FSF) erbium fiber laser. Frequency of the comb is controlled using the distributed feedback laser diode seeded into the cavity of the FSF laser. When the DFB diode is stabilized to the molecular absorption line of hydrogen cyanide frequency stabilized OFC is obtained.