Preparation of N-alkylbis(3-aminopropyl)amines by the catalytic hydrogenation of N-alkylbis(cyanoethyl)amines

An improved process for the preparation of N-alkylbis(3-aminopropyl)amines is described. These triamines are of interest as monomers for the condensation polymerization with esterified carbohydrate diacids (aldaric acids) to generate the corresponding poly(4-alkyl-4-azaheptamethylene aldaramides). The triamine synthesis is comprised of two efficient steps and requires no chromatographic purification. Bisconjugate addition of alkylamines to acrylonitrile followed by catalytic hydrogenation of the N-alkylbis(cyanoethyl)amines over Raney nickel yields the target N-alkylbis(3-aminopropyl)amines. Much less solvent was used in the bisconjugate addition step then previously reported, and in the second step, a relatively low-pressure catalytic hydrogenation (50 psi of hydrogen) was employed using Raney nickel as the catalyst in a 7 N methanolic ammonia solvent system to afford the N-alkylbis(3-aminopropyl)amines of high purity in nearly quantitative yield.     

A Simple Synthesis of 1-Methylcyclobutene

Controlled thermal decomposition of the sodium salt of cyclopropyl methyl ketone tosylhydrazone gives 1-methylcyclobutene of excellent purity in good yield.     

Structure and Function of the α-Hydroxylation Bimodule of the Mupirocin Polyketide Synthase

Mupirocin is a clinically important antibiotic produced by a trans-AT Type I polyketide synthase (PKS) in Pseudomonas fluorescens. The major bioactive metabolite, pseudomonic acid A (PA−A), is assembled on a tetrasubstituted tetrahydropyran (THP) core incorporating a 6-hydroxy group proposed to be introduced by α-hydroxylation of the thioester of the acyl carrier protein (ACP) bound polyketide chain. Herein, we describe an in vitro approach combining purified enzyme components, chemical synthesis, isotopic labelling, mass spectrometry and NMR in conjunction with in vivo studies leading to the first characterisation of the α-hydroxylation bimodule of the mupirocin biosynthetic pathway. These studies reveal the precise timing of hydroxylation by MupA, substrate specificity and the ACP dependency of the enzyme components that comprise this α-hydroxylation bimodule. Furthermore, using purified enzyme, it is shown that the MmpA KS⁰ shows relaxed substrate specificity, suggesting precise spatiotemporal control of in trans MupA recruitment in the context of the PKS. Finally, the detection of multiple intermodular MupA/ACP interactions suggests these bimodules may integrate MupA into their assembly.     

Matrix effects demystified: Strategies for resolving challenges in analytical separations of complex samples

Matrix effects can significantly impede the accuracy, sensitivity, and reliability of separation techniques presenting a formidable challenge to the analytical process. It is crucial to address matrix effects to achieve accurate and precise measurements in complex matrices. The multifaceted nature of matrix effects which can be influenced by factors such as target analyte, sample preparation protocol, composition, and choice of instrument necessitates a pragmatic approach when analyzing complex matrices. This review aims to highlight common challenges associated with matrix effects throughout the entire analytical process with emphasis on gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, and sample preparation techniques. These techniques are susceptible to matrix effects that could lead to ion suppression/enhancement or impact the analyte signal at various stages of the analytical workflow. The assessment, quantification, and mitigation of matrix effects are necessary in developing any analytical method. Strategies can be implemented to reduce or eliminate the matrix effect by changing the type of ionization, improving extraction and clean-up methods, optimization of chromatography conditions, and corrective calibration methods. While development of an effective strategy to completely mitigate matrix effects remains elusive, an integrated approach that combines sample preparation, analytical extraction, and effective instrumental analysis remains the most promising avenue for identifying and resolving matrix effects.     

Electroanalytical performance of a Bismuth/Antimony composite glassy carbon electrode in detecting lead and cadmium

This work reports on the electroanalytical performance of a glassy carbon electrode (GCE) modified with antimony and bismuth (Sb/Bi-GCE) in detecting heavy metal ions using lead and cadmium as model analytes. The electroanalytical performance of the Sb/Bi-GCE surface was compared to the bismuth modified glassy carbon electrode (Bi-GCE) as well as the antimony modified glassy carbon electrode (Sb-GCE). The Sb/Bi-GCE exhibited excellent figures of merit compared to Bi-GCE and Sb-GCE surfaces. For example, the limit of detection for lead was 0.01 ppb using Sb/Bi-GCE and 0.1 and 1 ppb on Bi-GCE and Sb-GCE, respectively.     

Metal-like Charge Transport in PEDOT(OH) Films by Post-processing Side Chain Removal from a Soluble Precursor Polymer

Herein, a route to produce highly electrically conductive doped hydroxymethyl functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films, termed PEDOT(OH) with metal-like charge transport properties using a fully solution processable precursor polymer is reported. This is achieved via an ester-functionalized PEDOT derivative [PEDOT(EHE)] that is soluble in a range of solvents with excellent film-forming ability. PEDOT(EHE) demonstrates moderate electrical conductivities of 20–60 S cm⁻¹ and hopping-like (i.e., thermally activated) transport when doped with ferric tosylate (FeTos₃). Upon basic hydrolysis of PEDOT(EHE) films, the electrically insulative side chains are cleaved and washed from the polymer film, leaving a densified film of PEDOT(OH). These films, when optimally doped, reach electrical conductivities of ≈1200 S cm⁻¹ and demonstrate metal-like (i.e., thermally deactivated and band-like) transport properties and high stability at comparable doping levels.