Flavonoids are a class of polyphenolic secondary metabolites found in plants. Due to their ubiquity in our daily dietary intake and their major anti-oxidative, anti-inflammatory and anti-mutagenic activities, they have been a major focus of wide-ranging research for the past two decades. Mass spectrometry combined with liquid chromatography is one of the most popular techniques for the analysis of flavonoids.
View Article and Find Full Text PDFDespite growing interest in 2,1,3-benzothiadiazole (BTD) as an integral component of many functional molecules, methods for the functionalization of its benzenoid ring have remained limited, and many even simply decorated BTDs have required synthesis. We show that regioselective Ir-catalyzed C-H borylation allows access to versatile 5-boryl or 4,6-diboryl BTD building blocks, which undergo functionalization at the C4, C5, C6, and C7 positions. The optimization and regioselectivity of C-H borylation are discussed.
View Article and Find Full Text PDFA MeDalPhos-ligated gold(III) metallafluorene complex, generated via C-C oxidative addition of biphenylene, reacts with CO to produce 9-fluorenone. Experimental and computational studies show that this proceeds via a hitherto unknown migratory insertion of CO into a Au(III)-C bond. This process is more energetically challenging compared to other M-C bonds, but once achieved, the product is comparatively stable with respect to retro-carbonylation.
View Article and Find Full Text PDFObjective: There is a lack of diversity in the dental workforce. Efforts to enhance underrepresented minority (URM) recruitment and retention within dental school exist, but little effort has been made to track URM providers through education and practice. This study assesses the status of workforce diversity in the dental specialties and the predictors of URM dentist specialization.
View Article and Find Full Text PDFObjective: Little is known about the scope and role of discriminatory experiences in dentistry. The purpose of this study is to document the experiences that American Indian/Alaska Native (AI/AN), Black, and Hispanic dentists have had with discrimination.
Methods: This study reports data from a 2012 nationally representative study of dentists documenting experiences with discrimination during their dental careers or during dental school by the setting of the discrimination, the providers' education, and geographic location.
J Phys Chem C Nanomater Interfaces
March 2022
Boron-nitrogen substitutions in polycyclic aromatic hydrocarbons (PAHs) have a strong impact on the optical properties of the molecules due to a significantly more heterogeneous electron distribution. However, besides these single-molecule properties, the observed optical properties of PAHs critically depend on the degree of intermolecular interactions such as π-π-stacking, dipolar interactions, or the formation of dimers in the excited state. Pyrene is the most prominent example showing the latter as it exhibits a broadened and strongly bathochromically shifted emission band at high concentrations in solution compared to the respective monomers.
View Article and Find Full Text PDFRationale: In the lubrication industry, commercial base oils are commonly made up of blends of base oil stocks from different sources in different ratios to reduce production costs and modulate rheological properties. This practice introduces complexity in lubricant design because as the chemistry of the base oil becomes more complicated, it can become harder to formulate the base oil - particularly when the ratio of the original base oil stocks is unknown.
Methods: In this study, field ionisation mass spectrometry is used to collect chemical information on a range of base oil mixtures.
Matrix-assisted laser desorption/ionisation mass spectrometry has always suffered from matrix interference at low-masses making it an unsuitable method for the analysis of low molecular weight analytes. In recent years, there has been considerable interest in the use of graphite as a matrix. In this study, we demonstrate the application of colloidal graphite for the analysis of lanthanides in the positive ion mode.
View Article and Find Full Text PDFNatural products with novel chemistry are urgently needed to battle the continued increase in microbial drug resistance. Mushroom-forming fungi are underutilized as a source of novel antibiotics in the literature due to their challenging culture preparation and genetic intractability. However, modern fungal molecular and synthetic biology tools have renewed interest in exploring mushroom fungi for novel therapeutic agents.
View Article and Find Full Text PDFEur J Mass Spectrom (Chichester)
February 2021
The routine analysis of low molecular weight analytes by mass spectrometry is often complicated by the lability of the analyte's functional groups and/or the lack of moieties that can be easily charged. If a molecule is too labile this precludes analysis by techniques such as electron ionisation or chemical ionisation as the analyte will undergo thermal decomposition prior to ionisation as well as spontaneous fragmentation during the ionisation process. If the analyte has a low propensity to form ions in electrospray ionisation (i.
View Article and Find Full Text PDFThe removal of plant pigments such as β-carotene is an aspect of vegetable oil processing often desired by the food and pharmaceutical industries. Adsorption of β-carotene to acid-activated clay (AAC) is a well-established method for purification. Despite this, the removal mechanism of β-carotene is not well understood.
View Article and Find Full Text PDFNovel N-methylated ebselenamine antioxidants were prepared from the corresponding diselenides with iodomethane. All ebselenamines showed excellent chain-breaking and glutathione peroxidase (GPx)-like activities. They could also inhibit lipid peroxidation much more efficiently than α-tocopherol.
View Article and Find Full Text PDFThe mechanochemical, solvent-free, highly regioselective, rhodium-catalyzed C-H methylation of (hetero)arenes is reported. The reaction shows excellent functional-group compatibility and is demonstrated to work for the late-stage C-H methylation of biologically active compounds. The method requires no external heating and benefits from considerably shorter reaction times than previous solution-based C-H methylation protocols.
View Article and Find Full Text PDFCells of Mycobacterium alvei are known to contain a unique set of mycolic acids with a (ω-1)-methoxy group; although the various enzymes in the biosynthesis of other types of mycolic acid have been widely studied, the biosynthetic route to this substituent is unclear. We now define the stereochemistry of the (ω-1)-methoxy fragment as R, and describe the synthesis of a major R-(ω-1)-methoxy-mycolic acid and its sugar esters, and of two natural M. alvei diene mycolic acids.
View Article and Find Full Text PDFThe mass spectral analysis of metal salts, especially lanthanide and transition metal salts, can be challenging. Although getting information on the metal present is usually straightforward, obtaining information on the correct oxidation state and anion composition is challenging. Many ionisation techniques have some redox component to the ionisation process, which commonly results in changing the oxidation state of the metal and the associated loss of ligand and anion information.
View Article and Find Full Text PDFThe isomeric amino acids l-leucine, l-isoleucine and l-allo-isoleucine, are essential to many vital biological processes and are therefore of interest to the fields of metabolomics and proteomics. Their discrimination can be problematic however due to their isomeric natue. This study demonstrates a systematic investigation of the fragmentations of l-leucine, l-isoleucine and l-allo-isoleucine in combination with a thorough theoretical rationalisation.
View Article and Find Full Text PDFAn exceptionally mild and efficient method was developed for the preparation of (hetero)aryl-Au -L complexes using ethanol or water as the reaction medium at room temperature and Ar-B(triol)K boronates as the transmetalation partner. The reaction does not need an exogeneous base or other additives, and quantitative yields can be achieved through a simple filtration as the only required purification method, which obviates considerable waste associated with alternative workup methods. A broad reaction scope was demonstrated with respect to both the L and (hetero)aryl ligands on product Au complexes.
View Article and Find Full Text PDFA new, operationally simple approach is presented to access arynes and their fluoride-activated precursors based on Ru-catalyzed C-H silylation of arylboronates. Chromatographic purification may be deferred until after aryne capture, rendering the arylboronates de facto precursors. Access to various new arynes and their derivatives is demonstrated, including, for the first time, those based on a 2,3-carbazolyne and 2,3-fluorenyne core, which pave the way for novel derivatizations of motifs relevant to materials chemistry.
View Article and Find Full Text PDFWe have investigated gas-phase fragmentation reactions of protonated benzofuran neolignans (BNs) and dihydrobenzofuran neolignans (DBNs) by accurate-mass electrospray ionization tandem and multiple-stage (MS ) mass spectrometry combined with thermochemical data estimated by Computational Chemistry. Most of the protonated compounds fragment into product ions B ([M + H-MeOH] ), C ([B-MeOH] ), D ([C-CO] ), and E ([D-CO] ) upon collision-induced dissociation (CID). However, we identified a series of diagnostic ions and associated them with specific structural features.
View Article and Find Full Text PDFThree-coordinate bipyridyl complexes of gold, [(κ-bipy)Au(η-CH)][NTf], are readily accessed by direct reaction of 2,2'-bipyridine (bipy), or its derivatives, with the homoleptic gold ethylene complex [Au(CH)][NTf]. The cheap and readily available bipyridyl ligands facilitate oxidative addition of aryl iodides to the Au(I) center to give [(κ-bipy)Au(Ar)I][NTf], which undergo first aryl-zinc transmetalation and second C-C reductive elimination to produce biaryl products. The products of each distinct step have been characterized.
View Article and Find Full Text PDFWe describe two new types of reactivity involving silicon-bridged [1]ferrocenophanes. In an attempt to form a [1]ferrocenophane with a bridging silyl cation, the reaction of sila[1]ferrocenophane [Fe(η-CH)Si(H)TMP] (12) (TMP = 2,2,6,6-tetramethylpiperidyl) towards the hydride-abstraction reagent trityl tetrakis(pentafluorophenyl)borate ([CPh][B(CF)]) was explored. This yielded the unusual dinuclear species [Fe(η-CH)Si(TMP·H)(η-CH)Fe(η-CH)Si(H)TMP][B(CF)] [13][B(C6F5)4] in low yield.
View Article and Find Full Text PDFEur J Mass Spectrom (Chichester)
February 2018
There is still a need to develop reliable and robust matrix deposition methods for matrix-assisted laser desorption/ionisation mass spectrometry that are applicable to a range of matrices, solvents and analyte types. This paper presents a robust methodology for the airbrush application of matrices along with the implications of varying the set-up and airbrush parameters. A small number of organic analytes and metal salts are analysed in both positive and negative ion modes to exemplify this methodology.
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