No abstract

Plant biostimulants, an emerging class of agricultural inputs, are complex products. The reproducibility of their specific action on plant metabolism and plant physiology, which lead to an enhanced nutrient use efficiency, stress tolerance and edible yield quality, is still a challenge. Development of quality insurance systems for plant biostimulants need complex investigation based on adapted analytical, physico-chemical and chemical methods. The objective of this work was to characterize commercial humate biostimulants through different analytical techniques (Fourier transform infrared spectroscopy - FTIR, thermogravimetric analysis- TGA) and to evaluate their textural and chemical (pH, C, N, humic acids, inorganic components) parameters. The first derivative curve from TG analysis showed decomposition of different compounds, classified according to the results obtained by FTIR. The humic substances determined by TGA method was comparable with the results obtained by gravimetric reference method. The inductively coupled plasma-optical emission spectrometry (ICP-OES) technique was applied to determine the inorganic elements either from the production process of humate or from raw materials, as well as for the control of humate in terms of requirements for safety and quality. Their complementary properties obtaining through different analytical techniques provide essential information on the chemical characteristics of the humate plant biostimulant formulations.

The aim of this work is the synthesis of calcium carbonate (CaCO3) nano and microparticles and their application as biomaterials (vehicles) for the sustained release of doxycycline. CaCO3 micro particles were synthesized by water-in oil (W/O) emulsion method using emulsion liquid membranes with bis (2-ethylhexyl) phosphate (D2EHPA) as carrier, Span 80 as surfactant, and toluene and kerosene as organic solvents. The aqueous phases contained 1 M CaCl2, and 1 M Na2CO3, respectively. The Dynamic Light Scattering (DLS) data showed CaCO3 particles with sizes ranging from around 100 nm to 3500 nm. The CaCO3 particles with the average diameters around 600 nm attained an adsorbtion of doxycycline of maximum 97.9%, and a slow and steady release with a cumulative value of approximative 50% after ten days.

The hydroxyapatite (HA) nano and microparticles were synthesized by wet-chemical precipitation in order to use them as drug carriers for biomedical applications. Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS) and Fourier Transform Infrared Spectroscopy (FTIR) were performed to assess their size, external morphology and chemical composition. The properties of HA particles as drug carriers for antibiotics delivery were evaluated with doxycycline and chloramphenicol. The amount of drug loading and release was determined by UV-Visible spectrophotometry. The antibacterial properties of loaded HA particles were evaluated using gram-positive Bacillus subtilis bacteria and gram-negative Pseudomonas aeruginosa bacteria. The synthesized particles of HA exhibit a high adsorption capacity (around 99%) and good controlled release properties for doxycycline. The adsorption of chloramphenicol on HA was extremely low (about 2%). According to the results, the compatibility between the drug and substrate is an important factor in the absorption process, and the hydroxyapatite is a very promising carrier for controlled release of antibiotics.