Spectrophotometric determination of aliphatic primary and secondary amines by reaction with p-benzoquinone

Potentiometric PVC-Membrane-Based Sensor for Dimethylamine Assessment Using A Molecularly Imprinted Polymer as A Sensory Recognition Element

A new simple potentiometric sensor is developed and presented for sensitive and selective monitoring of dimethylamine (DMA). The sensor incorporates a molecularly imprinted polymer, with a pre-defined specific cavity suitable to accommodate DMA. The molecularly imprinted polymer (MIP) particles were dispersed in an aplasticized poly(vinyl chloride) matrix. The MIP is synthesized by using a template molecule (DMA), a functional monomer (acrylamide, AM), cross-linker (ethylene glycol dimethacrylate, EGDMA) and initiating reagent (benzoylperoxide, BPO). Using Trizma buffer solution (5 mmol L^-1, pH 7.1), the sensor exhibits a rapid, stable and linear response for 1.0 × 10^-5 to 1.0 × 10^-2 mol L^-1 DMA⁺ with a calibration slope of 51.3 ± 0.3 mV decade^-1, and a detection limit of 4.6 × 10^-6 mol L^-1 (0.37 µg mL^-1). The electrode exhibited a short response time (10 s) and stable potential readings (± 0.5 mV) for more than 2 months. Potentiometric selectivity measurements of the sensor reveal negligible interferences from most common aliphatic and aromatic amines. High concentration levels (100-fold excess) of many inorganic cations do not interfere. The sensor is successfully used for quantification of low levels of DMA down to 0.5 µg mL^-1. Verification of the presented method was carried out after measuring the detection limit, working linearity range, ruggedness of the method, accuracy, precision, repeatability and reproducibility. Under flow-through conditions, the proposed sensor in its tubular form is prepared and introduced in a two-channel flow injection setup for hydrodynamic determination of DMA. The sampling rate is 50-55 samples h^-1. The sensor is used to determine DMA in different soil samples with an accuracy range of 97.0-102.8%.

Synthesis and biological evaluation of 2,5-bis(alkylamino)-1,4-benzoquinones

A series of twelve 2,5-bis(alkylamino)-1,4-benzoquinones were prepared in yields ranging from 9–58% via the reaction between p-benzoquinone and various amines. The structures of the synthesized compounds were confirmed by IR, ¹H- and ¹³C-NMR and MS analyses. The phytotoxicity of the 2,5-bis(alkylamino)-1,4-benzoquinones was evaluated against two crop species, Cucumis sativus and Sorgum bicolor, at 1.0 × 10^-3 mol/L. In general, the quinones displayed inhibitory effects on the dicotyledonous species C. sativus (7–74%). On the other hand stimulatory effects were observed on S. bicolor (monocotyledonous). Similar results were observed in the biological assays carried out with the weed species Ipomoea grandifolia (dicotyledonous) and Brachiaria decumbens (monocotyledonous). In addition, the cytotoxicity of the 2,5-bis(alkylamino)-1,4-benzoquinones was assayed against HL-60 (leukemia), MDA-MB-435 (melanoma), SF-295 (brain) and HCT-8 (colon) human cancer cell lines and human peripheral blood mononuclear cells (PBMC), as representatives of healthy cells, using a MTT and an Alamar Blue assay. Compound 12 was the most active, displaying cytotoxicity against all cancer cell lines tested.

Spectrophotometric determination of diaminopyrimidines using benzoquinone

The diaminopyrimidine derivatives trimethoprim (TMP), pyrimethamine (PMA) and 2,4-diaminopyrimidine (2,4-DAP) are found to react readily and efficiently in an aqueous solution with p-benzoquinone (p-BQ) to form a colored product with an absorption optimum wavelength of about 500 nm. The optimum reaction time, pH, temperature, solvent, and [p-BQ] are determined by separate trials. These conditions are confirmed by a MultiSimplex optimization method. The molar absorptivities of the TMP, PMA, and 2,4-DAP reaction products at 500 nm are 10,830, 10,650, and 9660 l mol(-1) cm(-1), respectively. TMP shows a linear range between 5 and 100 mg/l while PMA and 2,4-DAP exhibit linearity between 15 and 75 mg l(-1) and 5 and 30 mg l(-1), respectively. There is some specificity to this reaction; 2-aminopyrimidine does not react. Under the optimum conditions, sulfamethoxazole (SM) reacts rather poorly with a molar absorptivity of about 110 l mol(-) cm(-1). Using p-BQ, TMP in a pharmaceutical sample can be determined in the presence of SM using derivative spectrophotometry. The TMP-p-BQ reaction is adaptable for flow injection analysis.