Mila Nocentini

Spectroscopic investigation of tetracycline interaction with phospholipid Langmuir–Blodgett films

Abstract A widely used veterinary antibiotic, tetracycline (TC), has been incorporated in Langmuir–Blodgett (LB) films of dipalmitoylphosphatidic acid (DPPA) by means of two different procedures: co-transfer and incubation in solution. The resulting structures were characterized by means of contact angle and ellipsometric measurements. The presence of the antibiotic in the phospholipid film was evidenced by means of UV–Vis electronic absorption and infrared vibrational spectroscopy. The two sets of measurements unambiguously indicated the presence of the drug in the LB layer films obtained with both methods, although incubation led to a smaller content of immobilized tetracycline. In both cases, the drug was found to reside in the hydrophilic portion of the layers due to specific interactions of the dimethylamino group of the molecule with the polar head groups of the phospholipid.

Antibiotic interaction with phospholipid monolayers

Abstract We studied the interactions of tetracycline (TC) antibiotic molecules with phospholipid monolayers with the two-fold aim of elucidating the mechanism of action and providing a first step for the realization of bio-mimetic sensors for such drugs by means of the Langmuir–Blodgett technique. We examined spreading monolayers of three phospholipids in the presence of tetracycline in the subphase by means of surface pressure–area and surface potential–area isotherms as a function of bulk pH. We selected phospholipids with hydrophobic chains of the same length but polar head groups differing either in dimensions and protonation equilibria, i.e. dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE) and dipalmitoylphosphatidic acid (DPPA). The interaction of tetracycline with the three phospholipids was found to be highly dependent on the electric charge of the antibiotic and on the ionization state of the lipid. Significant interactions are established between the negatively charged form of dipalmitoylphosphatidic acid and the zwitterionic form of tetracycline. The drug was found to migrate at the interface where it is adsorbed underneath or/and among the head groups, depending on the surface pressure of the film, whereas penetration through the hydrophobic layer was excluded for all the three phospholipids.

High throughput headspace GC-MS quantitative method to measure the amount of carbon monoxide in treated tuna fish†

A robust and dependable headspace HS-GC-MS method has been developed for the determination of carbon monoxide (CO) treated tuna fish. The performance of the method has been evaluated by analyzing spiked and blank samples. The proposed method uses a programmed temperature vaporizing (PTV) injector to implement the HS injection and overcome the negative effects on the column of water contained in the sample. The level of CO could be easily detected in the treated samples, its amount differing markedly from that detected in the untreated samples. Proper oven temperature programming prevented any deterioration of chromatographic performance caused by the accumulation of water, carbon dioxide and other low molecular weight hydrocarbons in the column during serial analyses. The introduction of PTV injection and the restoring of GC column, by oven temperature programming, were crucial for obtaining the required robustness. This procedure assures the run-to-run repeatability necessary for high throughput applications. The method affords linear calibration curves ranging from 50 to 2500 ng/g of CO content in tuna sample.