Resonant oscillators with carbon-nanotube torsion springs

We report on the characterization of nanometer-scale resonators. Each device incorporates one multiwalled carbon nanotube (MWNT) as a torsional spring. The devices are actuated electrostatically, and their deflections, both low frequency and on resonance, are detected optically. These are some of the smallest electromechanical devices ever created and are a demonstration of practical integrated MWNT-based oscillators. The results also show surprising intershell mechanical coupling behavior in the MWNTs.     

Hysteresis modeling of two-way shape memory effect in NiTi alloys

In the present study the two-way shape memory effect (TWSME) of a Ni-51 at.% Ti alloy was investigated and a numerical model, able to simulate its hysteretic behaviour in the strain-temperature response, is proposed. In particular, the TWSME was induced through a proper thermo-mechanical training, carried out at increasing number of training cycles and for two values of training deformation, and the thermal hysteretic behaviour, between M _f (Martensite finish temperature) and A _f (Austenite finish temperature), was recorded. The experimental measurements were used to develop a phenomenological model, based on the Prandtl-Ishlinksii hysteresis operator, which was implemented in a Matlab^® function and a Simulink^® model. A systematic comparison between experimental results and numerical predictions is illustrated and a satisfactory accuracy and efficiency has been observed, therefore the method looks suitable for real-time control of NiTi based actuators.     

Probing the spin multiplicity of gas-phase polycyclic aromatic hydrocarbons through their infrared emission spectrum: A theoretical study

The anharmonic infrared emission spectrum following an optical excitation has been calculated for a variety of polycyclic aromatic hydrocarbon molecules in their ground singlet electronic state or in their triplet state. The computational protocol relies on second-order perturbation theory and involves a quartic vibrational Hamiltonian, the vibrational quantum numbers being sampled according to a Monte Carlo procedure. In the case of neutral naphthalene, the IR spectrum obtained in the (ground) singlet state differs significantly from the spectrum in the triplet state, especially for out-of-plane CH bending modes. Although not as prominent, spectral differences in larger molecules are still observable.     

Coherent two dimensional infrared spectroscopy of a cyclic decapeptide antamanide. A simulation study of the amide-I and A bands

The two-dimensional infrared photon echo spectrum of Antamanide (- (1)Val- (2)Pro- (3)Pro- (4)Ala- (5)Phe- (6)Phe- (7)Pro- (8)Pro- (9)Phe- (10)Pro-) in chloroform is calculated using an explicit solvent molecular dynamics (MD) simulation combined with a density functional theory (DFT) map for the effective vibrational Hamiltonian. Evidence for a strong intramolecular hydrogen bonding network is found. Comparison with experimental absorption allows the identification of the dominant conformation. Multidimensional spectroscopy reveals intramolecular couplings and gives information on its dynamics. A two-color amide-I and amide-A crosspeak is predicted and analyzed in terms of local structure.     

Novel Concepts of MS-Cleavable Cross-linkers for Improved Peptide Structure Analysis

The chemical cross-linking/mass spectrometry (MS) approach is gaining increasing importance as an alternative method for studying protein conformation and for deciphering protein interaction networks. This study is part of our ongoing efforts to develop innovative cross-linking principles for a facile and efficient assignment of cross-linked products. We evaluate two homobifunctional, amine-reactive, and MS-cleavable cross-linkers regarding their potential for automated analysis of cross-linked products. We introduce the bromine phenylurea (BrPU) linker that possesses a unique structure yielding a distinctive fragmentation pattern on collisional activation. Moreover, BrPU delivers the characteristic bromine isotope pattern and mass defect for all cross-linker-decorated fragments. We compare the fragmentation behavior of the BrPU linker with that of our previously described MS-cleavable TEMPO-Bz linker (which consists of a 2,2,6,6-tetramethylpiperidine-1-oxy moiety connected to a benzyl group) that was developed to perform free-radical-initiated peptide sequencing. Comparative collisional activation experiments (collision-induced dissociation and higher-energy collision-induced dissociation) with both cross-linkers were conducted in negative electrospray ionization mode with an Orbitrap Fusion mass spectrometer using five model peptides. As hypothesized in a previous study, the presence of a cross-linked N-terminal aspartic acid residue seems to be the prerequisite for the loss of an intact peptide from the cross-linked products. As the BrPU linker combines a characteristic mass shift with an isotope signature, it presents a more favorable combination for automated assignment of cross-linked products compared with the TEMPO-Bz linker.

Open image in new window

?

     

Vibron-polaron in alpha-helices. II. Two-vibron bound states

The two-vibron dynamics associated to amide-I vibrations in a three-dimensional (3D) alpha-helix is described according to a generalized Davydov model. The helix is modeled by three spines of hydrogen-bonded peptide units linked via covalent bonds. It is shown that the two-vibron energy spectrum supports both a two-vibron free states continuum and two kinds of bound states, called two-vibron bound states (TVBS)-I and TVBS-II, connected to the trapping of two vibrons onto the same amide-I mode and onto two nearest-neighbor amide-I modes belonging to the same spine, respectively. At low temperature, nonvanishing interspine hopping constants yield a three-dimensional nature of both TVBS-I and TVBS-II which the wave functions extend over the three spines of the helix. At biological temperature, the pairs are confined in a given spine and exhibit the same features as the bound states described within a one-dimensional model. The interplay between the temperature and the 3D nature of the helix is also responsible for the occurrence of a third bound state called TVBS-III which refers to the trapping of two vibrons onto two different spines. The experimental signature of the existence of bound states is discussed through the simulation of their infrared pump-probe spectroscopic response. Finally, the fundamental question of the breather-like behavior of two-vibron bound states is addressed.