Automated peak width measurements for targeted analysis of ion mobility unresolved species

Peak broadening in ion mobility (IM) is a relatively predictable process and abnormally broad peaks can be indicative of the presence of unresolved species. Here, we introduce a new ion mobility peak fitting (IM_FIT) software package for automated and systematic determination of traveling wave ion mobility (TWIM) unresolved species. To identify IM unresolved species, the IM_FIT software generates a trend line by plotting ions' mobility peak widths as a function of their arrival times. Utilizing user-defined thresholds, IM_FIT allows for automated and rapid detection of ions that deviate from the peak width trend line. To demonstrate the advantages of IM_FIT for automated detection of IM unresolved species, IM-mass spectrometry (IM-MS) data from a sample mixture containing polypropylene glycol and multiple peptides were analyzed. A total of 14 out of the 34 observed singly-charged IM peaks above 5% relative abundance (i.e., signal-to-noise ratios above ∼200) were tagged as potentially co-eluting ions by IM_FIT. Subsequently, the 14 IM peaks tagged as potentially unresolved (presumably, peaks corresponding to co-eluting compounds), were further analyzed by automated IM deconvolution (AIMD), liquid chromatography-IM-MS (LC-IM-MS), and/or ultra-high resolution mass spectrometry. Using the aforementioned techniques, more than 85% of the tagged IM peaks (12 out of 14) were confirmed to contain co-eluting ions. As an additional new finding, IM_FIT facilitated the discovery of an unexpected sequence-scrambled y-type fragment ion.     

Synthesis and functionalization study of hierarchical ZnO nanowires for potential nitroaromatic sensing applications

In this work, we synthesize hierarchical ZnO nanowires in a customized atmospheric CVD furnace and investigate their surface modification behavior for prospective nitroaromatic sensing applications. The morphology and crystal structure of pristine nanowires are characterized through FE-SEM, TEM, X-ray diffraction and EDAX studies. Photoluminescence behavior of pristine nanowires is also reported. Surface modification behavior of synthesized nanowires on a ZnO–oleic acid system is studied by utilizing Raman and FT-IR spectroscopy. Based on these findings, 1-pyrenebutyric acid (PBA) has been identified as an appropriate fluorescent receptor for sensing p-nitrophenol. Fluorescence quenching experiments on a PBA–p-nitrophenol system are reported and a detection limit of up to 28 ppb is envisaged for PBA-grafted ZnO nanowire-based optical sensor.     

Chemical reactions modulated by mechanical stress: extended Bell theory

A number of recent studies have shown that mechanical stress can significantly lower or raise the activation barrier of a chemical reaction. Within a common approximation due to Bell [Science 200, 618 (1978)], this barrier is linearly dependent on the applied force. A simple extension of Bell's theory that includes higher order corrections in the force predicts that the force-induced change in the activation energy will be given by -FΔR - ΔχF(2)∕2. Here, ΔR is the change of the distance between the atoms, at which the force F is applied, from the reactant to the transition state, and Δχ is the corresponding change in the mechanical compliance of the molecule. Application of this formula to the electrocyclic ring-opening of cis and trans 1,2-dimethylbenzocyclobutene shows that this extension of Bell's theory essentially recovers the force dependence of the barrier, while the original Bell formula exhibits significant errors. Because the extended Bell theory avoids explicit inclusion of the mechanical stress or strain in electronic structure calculations, it allows a computationally efficient characterization of the effect of mechanical forces on chemical processes. That is, the mechanical susceptibility of any reaction pathway is described in terms of two parameters, ΔR and Δχ, both readily computable at zero force.     

Communication: uncovering molecule-TiO2 interactions with nonlinear spectroscopy

Femtosecond transient grating experiments are used to investigate electronic structures and transport mechanisms in dye-sensitized nanocrystalline TiO(2) films. This study examines two molecular sensitizers spanning the weak (a phosphonated Ruthenium complex) and strong (catechol) molecule-TiO(2) coupling regimes. It is shown that strong molecule-TiO(2) interactions give rise to photoinduced vibrational coherences at the interface between species. We suggest that the amplitudes of these coherences reflect the molecule-TiO(2) coupling strength and signify the delocalization of excited state wavefunctions.     

A Self-Bracketing Search Technique for the Classical Dispersion Analysis of Infrared Reflectance Data

If an observed infrared reflectance band corresponds to a harmonic vibrational mode, then it is feasible by means of well known dispersion relationships to calculate reflectance values R_c for an ideal reflectance curve that agrees with the curve obtained from experimentally observed R_x values. The technique of comparing R_c with R_x has been denoted as “classical dispersion,” or CD analysis. In the obtaining of dispersion parameters, such as oscillator strength (S_j), damping constant (Y_j), and resonant frequency (v_j) through CD analysis of infrared reflectance data, a number of methods have been used.     

Electrochemical and surface behavior of hydyroxyapatite/Ti film on nanotubular Ti-35Nb-xZr alloys

In this paper, we investigated the electrochemical and surface behavior of hydroxyapatite (HA)/Ti films on the nanotubular Ti-35Nb-xZr alloy. The Ti-35Nb-xZr ternary alloys with 3-10 wt.% Zr content were made by an arc melting method. The nanotubular oxide layers were developed on the Ti-35Nb-xZr alloys by an anodic oxidation method in 1 M H₃PO₄ electrolyte containing 0.8 wt% NaF at room temperature. The HA/Ti composite films on the nanotubular oxide surfaces were deposited by a magnetron sputtering method. Their surface characteristics were analyzed by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS) and an X-ray diffractometer (XRD). The corrosion behavior of the specimens was examined through potentiodynamic and AC impedance tests in 0.9% NaCl solution. From the results, the Ti-35Nb-xZr alloys showed a solely β phase microstructure that resulted from the addition of Zr. The nanotubular structure formed with a diameter of about 200 nm, and the HA/Ti thin film was deposited on the nanotubular structure. The HA/Ti thin film-coated nanotubular Ti-35Nb-xZr alloys showed good corrosion resistance in 0.9% NaCl solution.