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The potential antibacterial activity of secondary metabolites produced by Streptomyces sp. 156A isolated from Lake Baikal was investigated. The selective liquid-liquid extraction method was applied to obtain a mixture of nactins (polynactin) produced by the strain. The polynactin consisted of nonactin (3%), monactin (18%), dinactin (36%), trinactin (31%) and tetranactin (12%). The compounds were identified by MS/MS, 1H and 13C NMR methods. The loss of neutral 184 and 198 Da fragments from a sodiated molecular ion, [M + Na]+, of nactins was observed in the MS/MS spectrum. The polynactin was shown to possess the antibiotic activity against Gram-positive strains including opportunistic strains and strains isolated from various ecosystems of Lake Baikal.

Activity coefficients of NH4Cl in methanol–water mixtures containing respectively 0, 10, 20, 30, 40, and 50 weight percent MeOH 25°C were determined using the Pitzer ion-interaction model and the electromotive force (emf) data of the following galvanic cell without a liquid junction: . The experimental emf data were obtained using a solvent polymeric PVC ammonium selective membrane electrode containing a mixture of nonactin/monactin as ionophore and an Ag/AgCl electrode. Activity coefficients were determined over the molality range from dilute solution to near salt saturation (i.e. about 5.15 mol/kg in pure water or 2.44 mol/kg in 50% mixed MeOH–water solvent).

An optical urea biosensor was developed by immobilizing an urease enzyme layer on a thin ammonium-selective polymer membrane. The ammonium optical membrane utilized dichlorofluorescein octadecyl ester (DCFOE) as anionic chromophore and nonactin as neutral ionophore. The urease layer was coated on the top of the ammonium layer by gelatin entrapment combined with glutaradehyde cross-linking. Hydrolysis of urea catalyzed by urease produced ammonium ion, which was extracted into the-polymer film to form complexes with nonactin. A proton was released which resulted in a color change of the optical membrane due to charge neutrality principle. The biosensor

An analytical reverse phase HPLC separation of Nonactin and its homologues: Monactin, Dinactin, Trinactin and Tetranactin using Evaporative Light Scattering Detection is described.

The developed potentiometric urea biosensor is based on a modified PVC-nonactin NH3 -sensitive gas electrode. Membrane resistance has been optimised by incorporating lipophilic salt. The coefficient of variation for the standard urea solution is 2.45. The sensor performance has been compared with a photometric method for blood samples.

The stability constants of several alkali metal ion complexes with the macrotetrolides were determined polarographically in acetonitrile. For any single alkali metal ion the stability constant increased in the order nonactin < monactin < dinactin < trinactin. Their values are larger than those found in methanol. The Stoke's radii estimated from the limiting diffusion currents of the complexes increase with increasing crystallographic radius of the cation. The increasing strain on the ligand causes a decrease of stability constant for Rb+ and Cs+.

A micro ammonia sensor, consisting of an ISFET covered with a dry membrane which is made from nonactin and substituted poly-γ-methyl-L-glutamate (PMG) is described. The gate output voltage of the micro ammonia sensor increased with NH4OH addition. The response time of the sensor was 2 min at 30°C, and the sensor exhibited superior selectivity for NH4 + compared to a pH sensitive ISFET.

A new sensitive, accurate and reproducible method has been developed for the assay of L-aspartase (aspartate ammonia-lyase, EC 4.3.1.1) activity. Ammonium ion selective elctrodes were used to measure the increase in activity of ammonium ion produced during the deamination of L-aspartate, a reaction catalyzed by L-aspartase. The sensitive electrode membrane was prepared by immobilizing nonactin in polyvinyl chloride (PVC). Our potentiometric studies indicate an optimum substrate concentration of 0.05 M for L-aspartate and an optimum pH of 8.4. Also, a linear calibration curve of the electrode response towards enzyme activity was obtained in which activity units as low as 0.007 units/ml were detected. These findings were confirmed using spectrophotometric techniques. The increase in absorbance at 240 nm was used to measure the increase in fumarate during the deamination of L-aspartate. The interference from potassium ion was eliminated by dialyzing the enzyme preparation against water.

A PVC matrix nonactin based membrane electrode assembled with a solid carbon-epoxy inner electric contact has been successfully used in ammonium and urea analysis. Different buffers have been tested and sodium and potassium interferences have been evaluated in order to obtain the best calibration curve for determination of ammonium and urea in serum samples. Three immobilization techniques for the enzyme urease have been compared. Nylon net immobilization procedure was found to have the best analytical features when coupled with this electrode and it has been selected for urea determination in sera. Results were in good agreement with those obtained with the clinical standard spectrophotometric method.