1H and 13C NMR spectral assignments of four dammarane triterpenoids from carnauba wax

The phytochemical investigation of carnauba wax led to the isolation of three new dammarane triterpenoids 1, 2 and 4, together with the known triterpene 3. The structures of the new compounds were determined by 1D and 2D NMR spectroscopy and by comparison with published data for closely related compounds.     

Electronic sputtering produced by fission fragments on condensed CO and CO2

Condensed CO and CO2 are bombarded by approximately 65 MeV 252Cf fission fragments and the desorbed ions are analyzed by time-of-flight mass spectrometry as a function of target temperature, in the ranges 25-33 K and 75-91 K, respectively. Absolute desorption yields are measured up to complete ice sublimation. The mass spectra of both ice targets reveal the emission of: (1) low mass ions, produced by direct Coulomb interaction of the highly charged projectiles and delta-electrons with CO and CO2, and (2) pronounced series of cluster ions. The basic ice cluster structures (CO)n and (CO2)n are present in the emitted cluster series such as (CO)nCO+, (CO2)nCO2+, or (CO2)nCO3-. In the case of CO ice, however, the intense production of the series Cn+, Cn-, and (CO)mCn+ shows that Cn is the main cluster structure, consequence of a higher concentration of free carbon atoms in the nuclear track plasma of CO ice than in that of CO2 ice. Ion cluster abundance is observed to decrease exponentially with cluster mass. The decay constant is k(n) congruent with 0.13, about the same for series based on (CO)n and (CO2)n, but a factor 3.3 higher for the Cn series. The Cn clusters are formed by gas-phase condensation, but the (CO)n and (CO2)n clusters are produced by fracturing of the highly excited solid around the nuclear track. A dramatic reduction of the ion desorption yield is observed near T = 29 K for CO and near T = 85 K for CO2, when fast sublimation occurs and ice thickness vanishes. Close to sublimation temperature, the decay constant of the (CO)2Cn+ series increases due to a decreasing formation probability of large Cn clusters.     

Thermal characterization of the intermediary products of the synthesis of Zn-substituted barium hexaferrite

The focus of this work is the use of thermal analyses and Fourier Transform Infrared Spectroscopy (FTIR) for characterization of the gel decomposition, resulting from the formation of Y-barium hexaferrite substituted by Zn ions (Zn-Y-barium hexaferrite). Samples with Ba₂Zn₂Fe₁₂O₂₂ composition were synthesized by the citrate auto-combustion method. During the TG experiments the highest mass loss was attributed to citrate decomposition owing to the self-combustion reaction, confirmed by the disappearance of –OH band, and the drastic decrease of –CO₂ ⁻and –NO₃ ⁻ bands. Zn substitution resulted in an X-band microwave absorber material.     

Antihydrogen formation by autoresonant excitation of antiproton plasmas

In efforts to trap antihydrogen, a key problem is the vast disparity between the neutral trap energy scale ( $\sim\!50\,\upmu\mathrm{eV}$ ), and the energy scales associated with plasma confinement and space charge (~1 eV). In order to merge charged particle species for direct recombination, the larger energy scale must be overcome in a manner that minimizes the initial antihydrogen kinetic energy. This issue motivated the development of a novel injection technique utilizing the inherent nonlinear nature of particle oscillations in our traps. We demonstrated controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm or tenuous plasma can be similarly excited. Antihydrogen was produced and trapped by using this technique to drive antiprotons into a positron plasma, thereby initiating atomic recombination. The nature of this injection overcomes some of the difficulties associated with matching the energies of the charged species used to produce antihydrogen.     

Identification of oxygen in dental enamel following tooth bleaching using confocal micro Raman spectroscopy

Oxygen is a polymerization inhibitor of 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloxypropoxy) phenyl]propane (Bis‐GMA) and triethylene glycol dimethacrylate, a basic constituent of most dental adhesive materials. Some hypothesis that oxygen remains in tooth mineralized tissues following some dental treatments and thus reducing adhesive forces and compromising the restorative treatments, have been advanced, but no experimental demonstration has been conducted. We used for the first time a confocal micro Raman technique to successfully identify the presence of oxygen generated by tooth bleaching products in tooth enamel surface, hence, helping to provide confirmation for this theory. This new data result from a multidisciplinary research approach between physics and dentistry is pioneering and could in the future support dental treatment protocol changes, increasing productivity and patient's benefits. Copyright © 2012 John Wiley & Sons, Ltd.     

Temperature‐dependent Raman spectroscopy study in MoO3 nanoribbons

This paper reports a study of vibrational, structural and morphological properties of molybdenum oxide nanoribbons. Temperature‐dependent Raman spectroscopy measurements in MoO₃ nanoribbons revealed morphological changes in the 150–350 °C temperature range. No structural phase transitions were observed, thus showing that the orthorhombic phase is stable from room temperature (nanoribbons) up to 650 °C (bulk‐like phase) where large plates have been formed by the coalescence of the nanoribbons. The interpretation of temperature‐dependent Raman data (wavenumber and linewidths) is supported by scanning electron microscopy that is used to directly probe the morphological changes in MoO₃ samples. The observed phenomena in the Raman data for MoO₃ nanoribbons can be applied to other nanomaterials. Copyright © 2012 John Wiley & Sons, Ltd.     

Photophysics of aminobenzazole dyes in silica-based hybrid materials

In this work two aminobenzazole derivatives (5-AHBT and 5-AHBI) were dispersed in silica-based hybrid materials with different surface hydrophobicity, which were obtained by the sol?Cgel process using tetraethylorthosilicate as inorganic precursor and dimethyldimethoxysilane as organic precursor, with a molar percent of organic precursor changing from 0 to 50%. The photophysics of the obtained doped silica hybrid materials was investigated by means ultraviolet?Cvisible diffuse reflectance and steady-state fluorescence emission spectroscopy in the solid state. The materials present absorption maxima located around 353 and 318?nm when doped with 5-AHBT and 5-AHBI, respectively. The red shifted absorption maxima of the 5-AHBT can be explained by the better electron delocalization allowed by the sulfur atom in relation to the nitrogen. The fluorescence emission spectra are located in the blue-green regions and the high Stokes shift indicates that the ESIPT mechanism occurs in the excited state for both dyes. The photophysical behavior of 5-AHBT shows that this dye is more affected by the matrix polarity due to specific interactions that take place in the ground state.     

Structure elucidation and NMR assignments of new spirosolane alkaloids from Solanum campaniforme

From the leaves of Solanum campaniforme, two new spirosolane alkaloids β‐acetoxyl‐(25S)‐22βN‐spirosol‐4‐en‐3‐one (1) and β‐hydroxyl‐(25S)‐22βN‐spirosol‐4‐en‐3‐one (4) were isolated along with two other known alkaloids of the same class (25S)‐22βN‐spirosol‐1,4‐dien‐3‐one (2) and (25S)‐22βN‐spirosol‐4‐en‐3‐one (3), which are reported for the first time as natural products. The structures of all alkaloids were established after an extensive analysis by 1D and 2D NMR spectroscopy (COSY, HSQC, HMBC and NOESY) as well as HRESIMS. Copyright © 2012 John Wiley & Sons, Ltd.     

Neodymium two-step optogalvanic spectroscopy in a hollow cathode lamp

This paper presents the results of Doppler-limited optogalvanic spectroscopy in commercial neodymium hollow cathode lamp, ranging from 580 to 600 nm. Using the laser multistep excitation technique, five transitions for the first step excitation from the neodymium ground state and seven transitions related to the second step of photoionization scheme were observed. Within these results, for the first time, a new line, 596.645 nm, was observed which could be attributed to a possible two-step transition to neodymium energy level from the 16 979.352 cm^? 1 to 33 735.4 cm^? 1. The simulated (synthetic) spectra of a mixture of neon (Ne I) and neodymium (Nd I) in this region are compared with experiments in order to facilitate data analysis.