Quantification of small molecule organic acids from Mycobacterium tuberculosis culture supernatant using ion exclusion liquid chromatography/mass spectrometry

Quantitative analysis of cellular small molecule organic acids of intermediary metabolism can provide critical insight into bacterial metabolic pathways. The concentration of these metabolites in culture supernatant varies at different growth stages or under particular environmental conditions reflecting both the energy and the biosynthetic needs, yielding metabolic information about the microorganism. The method described here utilizes ion exclusion chromatography with formic acid, coupled with a mass-selective detector using selective ion monitoring with negative mode electrospray ionization (SIM ES-), to detect and quantify several small organic acids in culture supernatants. The microM limits of quantitation (LOQs) were found to be 5.5 +/- 0.9 for pyruvate, 7.0 +/- 0.4 for malate, 2.5 +/- 0.5 for succinate, 12.7 +/- 0.8 for lactate, and 6.6 +/- 0.2 for fumarate. The method was used to detect and quantify these acids in the culture supernatants from Mycobacterium tuberculosis. Supernatant samples were spiked with stable-isotope-labeled internal standards, and the organic acids were quantified by isotope ratiometry.     

Diastereomeric Xe chemical shifts in tethered cryptophane cages

Cryptophane cages serve as host molecules to a Xe atom. Functionalization of cryptophane-A has permitted the development of Xe as a biosensor. Synthetic routes used to prepare cryptophanes result in racemic mixtures of the chiral cages. In the preparation of a tethered cryptophane-A cage for biosensor applications, some achiral and chiral substituents such as left-handed amino acids have been used. When the substituent is achiral, the NMR signal of the Xe atom in the functionalized cage in solution is a single isotropic peak, since the Xe shielding tensor components in the R and L cages differ by no more than the signs of the off-diagonal elements. Chiral substituents can split the cage-encapsulated Xe NMR signal into one or more sets of doublets, depending on the number of asymmetric centers in the substituent. We carry out quantum mechanical calculations of Xe nuclear magnetic shielding for the Xe atom at the same strategic position within an L cryptophane-A cage, under the influence of chiral potentials that represent r or l substituents outside the cage. Calculations of the Xe shielding response in the Lr and Ll diastereomeric pairs permit the prediction of the relative order of the Xe chemical shifts in solutions containing the Rl and Ll diastereomers. Where the substituent itself possesses two chiral centers, comparison of the calculated isotropic shielding responses in the Llr, Lrl, Rll, and Lrr systems, respectively, permits the prediction of the Xe spectrum of diastereomeric systems in solutions containing Llr, Rlr, Lll, and Rll systems. Assignment of the peaks observed in the experimental Xe NMR spectra is therefore possible, without having to undertake the difficult synthetic route that produces a single optically pure enantiomer.     

A note on chirality in NMR spectroscopy

Using simple symmetry arguments we give proofs of the derivations of the manifestation of chirality in the chemical shift and spin-spin coupling constant in nuclear magnetic resonance and relate our proofs to earlier discussions.     

Selectivity Control in Gold‐Mediated Esterification of Methanol

The Midas touch : The low‐temperature transformation of methanol to methyl formate, formaldehyde, and formic acid is promoted by atomic oxygen adsorbed on metallic gold (see picture). The reactions occur with O‐containing Au nanoparticles formed on Au(111) upon oxidation with ozone at 200 K; the facile esterification to methyl formate occurs well below room temperature.

     

Developmental trajectory of the endocannabinoid system in human dorsolateral prefrontal cortex

ABSTRACT: BACKGROUND: Endocannabinoids provide control over cortical neurotransmission. We investigated the developmental expression of key genes in the endocannabinoid system across human postnatal life and determined whether they correspond to the development of markers for inhibitory interneurons, which shape cortical development. We used microarray with qPCR validation and in situ hybridisation to quantify mRNA for the central endocannabinoid receptor CB1R, endocannabinoid synthetic enzymes (DAGLalpha for 2-arachidonylglycerol [2- AG] and NAPE-PLD for anandamide), and inactivating enzymes (MGL and ABHD6 for 2- AG and FAAH for anandamide) in human dorsolateral prefrontal cortex (39 days - 49 years). RESULTS: CB1R mRNA decreases until adulthood, particularly in layer II, after peaking between neonates and toddlers. DAGLalpha mRNA expression is lowest in early life and adulthood, peaking between school age and young adulthood. MGL expression declines after peaking in infancy, while ABHD6 increases from neonatal age. NAPE-PLD and FAAH expression increase steadily after infancy, peaking in adulthood. CONCLUSIONS: Stronger endocannabinoid regulation of presynaptic neurotransmission in both supragranular and infragranular cortical layers as indexed through higher CB1R mRNA may occur within the first few years of human life. After adolescence, higher mRNA levels of the anandamide synthetic and inactivating enzymes NAPE-PLD and FAAH suggest that a late developmental switch may occur where anandamide is more strongly regulated after adolescence than earlier in life. Thus, expression of key genes in the endocannabinoid system changes with maturation of cortical function.     

Electrochemical Sulphenylation/Cyclization of Quinones: A Rapid,Green, and Efficient Access to Cytotoxic Compounds

Undivided electrochemical cells enable economical preparation of sulphur-containing naphthoquinones through electrochemical sulphenylation of quinoidal compounds. The environmentally friendly and efficient protocol eliminates the use of chemical oxidants and facilitates the synthesis of the desired molecules. This approach offers an efficient and versatile method to synthesize quinones that exhibit cytotoxicity against cancer cell lines.     

ChemInform Abstract: Potential Energy Surface of SCl3‐.

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