RESUMEN
Most oxidation processes in common organic synthesis and chemical biology require transition metal catalysts or metalloenzymes. Herein, we report a detailed mechanistic study of a metal-free oxygen (O2) activation protocol on benzylamine/alcohols using simple quaternary alkylammonium-based ionic liquids to produce products such as amide, aldehyde, imine, and in some cases, even aromatized products. NMR and various control experiments established the product formation and reaction mechanism, which involved the conversion of molecular oxygen into a hydroperoxyl radical via a proton-coupled electron transfer process. Detection of hydrogen peroxide in the reaction medium using colorimetric analysis supported the proposed mechanism of oxygen activation. Furthermore, first-principles calculations using density functional theory (DFT) revealed that reaction coordinates and transition state spin densities have a unique spin conversion of triplet oxygen leading to formation of singlet products via a minimum energy crossing point. In addition to DFT, domain-based local pair natural orbital coupled cluster, (DLPNO-CCSD(T)), and complete active space self-consistent field, CASSCF(20,14) methods complemented the above findings. Partial density of states analysis showed stabilization of π* orbital of oxygen in the presence of ionic liquid, making it susceptible to hydrogen abstraction in a mild, metal-free condition. Inductively coupled plasma atomic emission spectroscopic (ICP-AES) analysis of reactant and ionic liquids clearly showed the absence of any significant transition metal contamination. The current results described the origin of O2 activation within the context of molecular orbital (MO) theory and opened up a new avenue for the use of ionic liquids as inexpensive, multifunctional and high-performance alternative to metal-based catalysts for O2 activation.
RESUMEN
BACKGROUND: There are very few published reports of upper cervical spine injuries from our country and there is a heavy bias towards operative treatment of these injuries. We present below our experience of upper cervical injuries over the last four years. MATERIALS AND METHODS: Twenty eight patients (20 males, 8 females) with upper cervical spine injury (including Occiput, Atlas and Axis) were treated and were followed-up for an average of 11.2 months. The data was analyzed retrospectively with regards to the location and type of injury, the treatment offered (conservative or operative) as well as the final clinical and radiological outcome. RESULTS: The clinico-radiological outcome of treatment of these injuries is mostly very good with few complications. Other than a single case of mortality due to associated head injury there were no major complications. CONCLUSION: Management of these patients needs a proper evaluation to arrive at the type of injury and prompt conservative or operative treatment. Treatment is usually safe and effective with good clinical and radiological outcome.