The Effect of H-bonding and Proton Transfer on the Voltammetry of 2,3,5,6-Tetramethyl-p-phenylenediamine in Acetonitrile. An Unexpectedly Complex Mechanism for a Simple Redox Couple. | LitMetric
The voltammetry of 2,3,5,6-tetramethyl-p-phenylenediamine, HPD, has been studied and compared to that of its isomer N,N,N'N'-tetramethyl-p-phenylenediamine, MePD. Both undergo two reversible electron transfer processes in acetonitrile that nominally correspond to 1e- oxidation to the radical cations, MePD and HPD, and a second 1e- oxidation at more positive potentials to the quinonediimine dications, MePD and HPD. While the voltammetry of MePD agrees with this simple mechanism, that of HPD does not. The second voltammetric wave is too small. UV/Vis spectroelectrochemical experiments indicate that the second wave does correspond to oxidation of HPD to HPD in solution. The fact that the second wave is not present at all at the lowest concentrations (5 µM), and that it increases at longer times and higher concentrations, indicates that HPD is not the initial solution product of the first oxidation. A number of lines of evidence suggest instead that the initial product is a mixed valent, H-bonded dimer between one HPD in the the full reduced, fully protonated state, HPD, and another in the fully oxidized, fully deprotonated state, PD. A mechanism is proposed in which this dimer is formed on the electrode surface through proton transfer and H-bonding. Once desorbed into solution, it breaks apart via reaction with other HPD's, to give 2 HPD, which is the thermodynamically favored species in solution.
Background: Occiput-posterior (OP) position is associated with labor arrest, need of operative delivery and failed instrumental vaginal delivery with resulting adverse peripartum outcomes. Vacuum extraction (VE) is the most commonly performed type of instrumental delivery worldwide. This study aimed to investigate the outcome of VE in fetuses with sonographically confirmed OP position prior to the procedure.
Institute of Food Science and Technology, Chinese Academy of Agricultural Sciences, Key Laboratory of Agro-Products Processing, Ministry of Agriculture and Rural Affairs, Beijing 100193, China. Electronic address:
The binary solution (sucrose/erythritol solution) and ternary solution (compound sucrose/erythritol with maltitol/fructooligosaccharide) were prepared as osmotic dehydration (OD) pretreatment before hot-pump-dried (HPD). Based on the analysis of OD solutions, the analysis of quality of dehydrated yellow peach slices (DYPS) were emphasized on the soluble sugar content, macro-µ-structure and thermal stability. Following with sucrose and maltitol (SM)-OD pretreatment, DYPS showed the decreased free sugar content and improved cohesiveness (0.
The acoustic noise outputs of MR equipment typically require a hearing protection device (HPD) to minimize the likelihood of patient hearing loss. Several different ways to quantify HPD performance have been developed and adopted over many years in different countries across the world (eg, NRR, SNR, SLC80). These HPD evaluations are done in controlled laboratory conditions, following different standardized methodologies, producing different performance ratings for the same HPD, and consequently of a variable relationship with achieved real-world usage performance assessments.
Background: Fibromyalgia is a chronic pain condition characterized by widespread musculoskeletal pain, fatigue, and cognitive difficulties, affecting individuals across all age groups. Positive affect (PA) interventions have shown promise in enhancing emotional well-being and pain management in patients with diverse chronic pain conditions. However, the efficacy of internet-delivered PA interventions for individuals with fibromyalgia remains understudied.
The rock lizard genus Laudakia is representative agamid species from the arid zone, and its genus division has not been resolved yet. Laudakia stoliczkana, which occurs in both Xinjiang, China, and the Gobi Altai, Mongolia, is divided into two subspecies, Laudakia stoliczkana stoliczkana and Laudakia stoliczkana altaica, based on morphological differences, but little is known about the molecular genetic differences between the two subspecies. This study reconstructs the phylogenetic tree of Laudakia and analyses molecular differences between two subspecies of L.
