Fast Acquisition of <Superscript>13</Superscript>C NMR Spectra using the Steady-state Free Precession Sequence

In this paper, we show that the steady-state free precession sequence can be used to acquire ¹³C high-resolution nuclear magnetic resonance spectra and applied to qualitative analysis. The analysis of brucine sample using this sequence with 60o flip angle and time interval between pulses equal to 300 ms (acquisition time, 299.7 ms; recycle delay, 300 ms) resulted in spectrum with twofold enhancement in signal-to-noise ratio, when compared to standard ¹³C sequence. This gain was better when a much shorter time interval between pulses (100 ms) was applied. The result obtained was more than fivefold enhancement in signal-to-noise ratio, equivalent to more than 20-fold reduction in total data recording time. However, this short time interval between pulses produces a spectrum with severe phase and truncation anomalies. We demonstrated that these anomalies can be minimized by applying an appropriate apodization function and plotting the spectrum in the magnitude mode.     

HR‐MAS NMR metabolomics of ‘Swingle’ citrumelo rootstock genetically modified to overproduce proline

The accumulation of proline is a typical physiological response to abiotic stresses in higher plants. ‘Swingle’ citrumelo, an important rootstock for citrus production, has been modified with a mutated Δ¹‐pyrroline‐5‐carboxylate synthetase gene (VaP5CSF129A) linked to the cauliflower mosaic virus 35S promoter to induce the overproduction of free proline. This paper presents a comparative metabolomic study of nontransgenic versus transgenic ‘Swingle’ citrumelo plants with high endogenous proline. ¹H high‐resolution magic angle spinning nuclear magnetic resonance spectroscopy and multivariate analysis showed significant differences in some metabolites between the nontransgenic and transgenic leaves and roots. The overproduction of proline has reduced the sucrose content in transgenic leaves, revealing a metabolic cost for these plants. In roots, the high level of free proline acts for the adjustment of cation–anion balance, causing the reduction of acetic acid content. The same sucrose level in roots indicates that they can be considered as sucrose sink. Similar behavior may be waited for fruits produced on transgenic rootstock. Copyright © 2014 John Wiley & Sons, Ltd.     

Efficient Technique to Control the Zero-Dispersion Wavelength of a Microstructured Optical Fiber

Abstract

An efficient technique to control the zero-dispersion wavelength of a microstructured optical fiber is proposed and numerically demonstrated in this article. This technique is based on the variation of the linear refractive index and the thickness of a thin film covering the microstructured optical fiber holes' inner surfaces. A powerful and accurate code based on a full-vector finite-element method formulation in conjunction with perfectly matched layers was used. A maximum of 570-nm zero-dispersion wavelength displacement is demonstrated. This thin film can be included after the microstructured optical fiber has been fabricated, as that means the zero dispersion of such fiber can be tailored as needed.     

Kinetic resolution of iodophenylethanols by Candida antarctica lipase and their application for the synthesis of chiral biphenyl compounds

The kinetic resolution of (±)-iodophenylethanols was carried out using lipase from Candida antarctica and in some cases the enantiomeric excesses were high (up to >98%). Enantiomerically enriched (S)-iodophenylethanols produced by the enzymatic resolution process were used in the synthesis of chiral biphenyl compounds by the Suzuki reaction with good yields (63–65%).     

Enzymatic kinetic resolution of organochalcogenides in supercritical CO2

1-(Phenylthio)-, 1-(phenylseleno)- and 1-(phenyltelluro)-propan-2-ol were efficiently resolved by CAL-B in sc-CO₂.     

Influence of lead dioxide electrodes morphology on kinetics and current efficiency of oxygen-ozone evolution reactions

Influence of electrode morphology on electrochemical properties of lead dioxide electrodes (β-PbO₂) for oxygen-ozone evolution reactions in acid medium was investigated using scanning electronic microscopy (SEM), cyclic voltammetry (CV), polarization curves (PC), and determination of the current efficiency (Φ). Experimental findings revealed that application of high electrodeposition current densities furnishes more rough β-PbO₂ films. Surface characteristics were verified by SEM images and the analysis of interfacial pseudo-capacitances and morphology factor (φ). Kinetic study of the overall electrode process (O₂ + O₃) based on the analysis of the Tafel slope revealed that the electrode morphology and electrolyte composition considerably affect the electrode kinetics. In most cases, the existence of two Tafel slopes distributed in the low and high overpotential domains was observed. Abnormal Tafel slopes (b ≠ 120 mV) obtained for the primary water discharge step during water electrolysis were interpreted considering the apparent charge transfer coefficient (α _apa). Optimum conditions for the ozone production were obtained for the less rough β-PbO₂ electrode immersed in a sulfuric acid solution (1.0 mol dm⁻³) containing KPF₆ (30 × 10⁻³ mol dm⁻³), where the current efficiency of 15 mass % for the ozone production was obtained.     

Investigation of tetracaine complexation with beta-cyclodextrins and p-sulphonic acid calix[6]arenes by nOe and PGSE NMR

Cyclodextrins (CD) and calixarenes are complexing agents that have been successfully used as pharmaceutical drug carriers, to improve the bioavailability of medicines. The aim of this work was to investigate the complexation of the local anesthetic tetracaine 1 with β-cyclodextrin 2, as well as with p-sulphonic acid calix[6]arene 3. ¹H NMR experiments were carried out in D₂O, i.e., with the charged tetracaine species 1. HR-DOSY ¹H NMR allowed determination of the fraction of complexed population (%p _bound = 55% and 70%) and the apparent association constants (K _a = 1358 and 3889 M⁻¹), respectively, for 1/2 and 1/3. These results confirm that a strong association takes place between 1 and 2, while the 1/3 complex is even more stable, due to the negatively charged sulphonic groups of 3. Studies conducted at pH 10 revealed that the association of the uncharged form of 1 with 3 is considerably weaker, while that with 2 increased significantly (K _a = 6597 M⁻¹), protecting the anesthetic against alkaline hydrolysis. ¹H-ROESY 1D NMR experiments allowed determination of the host-guest relative positions, revealing that the proposed topologies for the 1/2 and 1/3 complexes were quite different. The complexation of 1 with either 2 or 3 is being investigated in view of its potential use in new therapeutic formulations, designed to increase the bioavailability and/or to decrease the systemic toxicity of tetracaine, in anesthesia procedures.