RH Logo

All
My Hubs

Analytical Chemistry

Trending
Today
All
Papers
Posts
Hypotheses

Sign in to discover all of the research papers you care about, live as they're published.

9
Date Added: Oct 5, 2021
Date Added: Oct 5, 2021
Despite essentially identical crystallography and equilibrium structuring of water, nanoscopic channels composed of hexagonal boron nitride and graphite exhibit an order-of-magnitude difference in fluid slip. We investigate this difference using molecular dynamics simulations, demonstrating that its origin is in the distinct chemistries of the two materials. In particular, the presence of polar bonds in hexagonal boron nitride, absent in graphite, leads to Coulombic interactions between the polar water molecules and the wall. We demonstrate that this interaction is manifested in a large typical lateral force experienced by a layer of oriented hydrogen atoms in the vicinity of the wall, leading to the enhanced friction in hexagonal boron nitride. The fluid adhesion to the wall is dominated by dispersive forces in both materials, leading to similar wettabilities. Our results rationalize recent observations that the difference in frictional characteristics of graphite and hexagonal boron nitride cannot be explained on the basis of the minor differences in their wettabilities.
7
Date Added: Oct 5, 2021
Date Added: Oct 5, 2021
Bond breaking and forming are essential components of chemical reactions. Recently, the structure and formation of covalent bonds in single molecules have been studied by non-contact atomic force microscopy (AFM). Here, we report the details of a single dative bond breaking process using non-contact AFM. The dative bond between carbon monoxide and ferrous phthalocyanine was ruptured via mechanical forces applied by atomic force microscope tips; the process was quantitatively measured and characterized both experimentally and via quantum-based simulations. Our results show that the bond can be ruptured either by applying an attractive force of ~150 pN or by a repulsive force of ~220 pN with a significant contribution of shear forces, accompanied by changes of the spin state of the system. Our combined experimental and computational studies provide a deeper understanding of the chemical bond breaking process.
2
Date Added: Aug 5, 2021
Date Added: Aug 5, 2021
Understanding the differences between reactions driven by elevated temperature or electric potential remains challenging, largely due to materials incompatibilities between thermal catalytic and electrocatalytic environments. We show that Ni, N-doped carbon (NiPACN), an electrocatalyst for the reduction of CO2 to CO (CO2R), can also selectively catalyze thermal CO2 to CO via the reverse water gas shift (RWGS) representing a direct analogy between catalytic phenomena across the two reaction environments. Advanced characterization techniques reveal that NiPACN likely facilitates RWGS on dispersed Ni sites in agreement with CO2R active site studies. Finally, we construct a generalized reaction driving-force that includes temperature and potential and suggest that NiPACN could facilitate faster kinetics in CO2R relative to RWGS due to lower intrinsic barriers. This report motivates further studies that quantitatively link catalytic phenomena across disparate reaction environments.
12
Date Added: Jul 21, 2021
Date Added: Jul 21, 2021
Background The World Health Organization has warned that cigarette smoking is an avoidable risk factor for endothelial injury. Myogenin might play a role in muscle metabolism and energy utilization. Electrolytes and minerals are involved in most cellular activities. The objective of this study was to compare myogenin and electrolyte levels between adult male cigarette smokers (CS) and non-smokers (NS). Methods A cross-sectional study was conducted involving 90 subjects, consisting of 55 CS and 35 NS. The sandwich enzyme-linked immunosorbent assay was used to determine myogenin levels while the ion-selective electrode method was used to determine electrolyte levels. The levels of sodium, potassium, and chloride and the body mass index (BMI) were measured. Mann-Whitney and independent t-test were used to analyse the data. Results The BMI of CS was significantly lower than that of NS (p
2
Date Added: Nov 2, 2020
Date Added: Nov 2, 2020
The electrogenerated chemiluminescence (ECL) of Ru(bpy)32+ and tripropylamine, tributylamine, triethylamine, trimethylamine, or sodium oxalate encapsulated within sol−gel-derived silica monoliths have been investigated using an immobilized ultramicroelectrode assembly. The major purpose of this study was to investigate the role of the reductant on the magnitude and stability of the ECL in this solid host matrix. For gel-entrapped Ru(bpy)32+/tertiary amines, the shape and intensity of the ECL−potential curves were highly dependent on scan rate. At 10 mV/s, the ECL intensity was ca. 6-fold higher relative to that observed at 500 mV/s. When the ECL acquired at low scan rates was normalized by that obtained in solution under similar conditions, a value of 0.03−0.06 was obtained. In direct contrast, the ECL of the Ru(bpy)32+-oxalate system showed little dependence on scan rate, and the ECL was ca. 65−75% of that measured in solution. These differences can be attributed to differences in rotational and translational mobility between the reductants (amines vs oxalate) trapped in this porous solid host. For both systems, the ECL was found to be stable upon continuous oxidation or upon drying the gels in a high-humidity environment for over 10 days.
6
Date Added: Jun 3, 2021
Date Added: Jun 3, 2021
With a sharp increase in the cases of multi-drug resistant (MDR) bacteria all over the world, there is a huge demand to develop a new generation of antibiotic agents to fight against them. As an alternative to the traditional drug discovery route, we have designed an effective antibacterial agent by modifying an existing commercial antibiotic, kanamycin, conjugated on the surface of gold nanoparticles (AuNPs). In this study, we report a single-step synthesis of kanamycin-capped AuNPs (Kan-AuNPs) utilizing the combined reducing and capping properties of kanamycin. While Kan-AuNPs have increased toxicity to a primate cell line (Vero 76), antibacterial assays showed dose-dependent broad spectrum activity of Kan-AuNPs against both Gram-positive and Gram-negative bacteria including Kanamycin resistant bacteria. Further, a significant reduction in the minimum inhibitory concentration (MIC100) of Kan-AuNPs was observed when compared to free kanamycin against all the bacterial strains tested. Mechanistic studies using transmission electron microscopy and fluorescence microscopy indicated that at least part of Kan-AuNPs increased efficacy may be through disrupting the bacterial envelope, resulting in the leakage of cytoplasmic content and the death of bacterial cells. Results of this study provide critical information about a novel method for the development of antibiotic capped AuNPs as potent next-generation antibacterial agents.
5
Date Added: May 15, 2021
Date Added: May 15, 2021
The reaction of hydroxy peroxy radicals (RO2) with NO represents one of the most crucial tropospheric processes, leading to terrestrial ozone formation or NOx removal and chain termination. We investigate the formation of hydroxy peroxy nitrites (ROONO) and nitrates (RONO2) from the OH−isoprene reactions using DFT and ab initio theories and variational RRKM/master equation (vRRKM/ME) formalism. The binding energies of ROONO from NO addition to RO2 are determined to be in the range of 20−22 kcal mol-1, and the bond dissociation energies of ROONO to form an alkoxy radical (RO) and NO2 range from 6 to 9 kcal mol-1. Isomerization of ROONO to RONO2 is exothermic by 22−28 kcal mol-1. The entrance and exit channels of the RO2−NO reaction are found to be barrierless, and the rate constants to form ROONO are calculated to be 3 × 10-12 to 2 × 10-11 cm3 molecule-1 s-1 using the canonical variational transition state theory. The vRRKM/ME analysis reveals negligible stabilization of excited ROONO and provides an assessment of ROONO isomerization to RONO2.
8
Date Added: Dec 21, 2020
Date Added: Dec 21, 2020
Untargeted metabolomics analysis captures chemical reactions among small molecules. Common mass spectrometry-based metabolomics workflows first identify the small molecules significantly associated with the outcome of interest, then begin exploring their biochemical relationships to understand biological fate or impact. We suggest an alternative by which general chemical relationships including abiotic reactions can be directly retrieved through untargeted high-resolution paired mass distance (PMD) analysis without a priori knowledge of the identities of participating compounds. PMDs calculated from the mass spectrometry data are linked to chemical reactions obtained via data mining of small molecule and reaction databases, i.e. ‘PMD-based reactomics’. We demonstrate applications of PMD-based reactomics including PMD network analysis, source appointment of unknown compounds, and biomarker reaction discovery as complements to compound discovery analyses used in traditional untargeted workflows. An R implementation of reactomics analysis and the reaction/PMD databases is available as the pmd package.
10
Date Added: Nov 8, 2020
Date Added: Nov 8, 2020
Cannabidiol (CBD) is a naturally occurring, non-psychotropic cannabinoid of the hemp plant Cannabis sativa L. and has been known to induce several physiological and pharmacological effects. While CBD is approved as a medicinal product subject to prescription, it is also widely sold over the counter (OTC) in the form of food supplements, cosmetics and electronic cigarette liquids. However, regulatory difficulties arise from its origin being a narcotic plant or its status as an unapproved novel food ingredient. Regarding the consumer safety of these OTC products, the question whether or not CBD might be degraded into psychotropic cannabinoids, most prominently tetrahydrocannabinol (THC), under in vivo conditions initiated an ongoing scientific debate. This feature review aims to summarize the current knowledge of CBD degradation processes, specifically the results of in vitro and in vivo studies. Additionally, the literature on psychotropic effects of cannabinoids was carefully studied with a focus on the degradants and metabolites of CBD, but data were found to be sparse. While the literature is contradictory, most studies suggest that CBD is not converted to psychotropic THC under in vivo conditions. Nevertheless, it is certain that CBD degrades to psychotropic products in acidic environments. Hence, the storage stability of commercial formulations requires more attention in the future.