The interface interactions between surfactants oleic acid and oleylamine and magnetic nanoparticles are studied via molecular mechanics and dynamics. Mixtures of these two surfactants are widely advocated in the chemical synthesis of nanoparticles. However, the exact dynamic mechanism remains unclear. Here we report, for the first time, a comprehensive qualitative model showing the importance of acid-base complex formation between oleic acid and oleylamine as well as the presence of free protons in the engineering of nanoparticles of specific shapes and sizes. We show why critical parameters such as surfactant concentration may modify iron oxide nanoparticle shape and size and how this can be understood in the light of acid-base complex pair formation. We report on the influence these parameters have on both the in situ nanoparticle surface charge and zeta potential. Transmission electron microscopy (TEM), FTIR, and pH studies are used to confirm the validity of the calculated binding energies and number of acid-base pairs.

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Due to increased antimicrobial resistance against current drugs, new alternatives are sought. Endophytic bacteria associated with medicinal plants are recognized as valuable sources of novel secondary metabolites possessing antimicrobial, antitumor, insecticidal, and antiviral activities. In this study, five bacterial endophytes were isolated and identified from the medicinal plant, Alectra sessiliflora, and their antibacterial and antitumor activities were investigated. In addition, the crude extracts of the endophytes were analyzed using gas chromatography (GC) coupled with time-of-flight mass spectrometry (TOF-MS). The identified bacterial endophytes belong to three genera viz Lysinibacillus, Peribacillus, and Bacillus, with the latter as the dominant genus with three species. Ethyl acetate extracts from the endophytes were used for antimicrobial activity against eleven pathogenic strains through minimum inhibitory concentration (MIC). The antitumor activity against the Hela cervical, Hek 293 kidney, and A549 lung carcinoma cells was determined by the MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxy-phenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay. Lysinibacillus sp. strain AS_1 exhibited broad antibacterial activity against the pathogenic strains with MIC values ranging from 4 to 8 mg/ml, while Bacillus sp. strain AS_3 displayed MIC of 0.25 mg/ml. Crude extracts of Lysinibacillus sp. strain AS_1, Peribacillus sp. strain AS_2, and Bacillus sp. strain AS_3 showed growth inhibition of more than 90% against all the cancer cell lines at a concentration of 1,000 μg/ml. Untargeted secondary metabolite profiling of the crude extracts revealed the presence of compounds with reported biological activity, such as antimicrobial, antioxidant, anti-inflammatory, antitumor, and antidiabetic properties. This study reported for the first time, bacterial endophytes associated with A. sessiliflora with antibacterial and antitumor activities.

Magnetic nanoparticles with tailored surface chemistry are widely used for a number of different in vivo applications, ranging from tissue repair and magnetic cell separation through to cancer-hyperthermia, drug delivery and magnetic resonance imaging contrast enhancement. A major requirement for all these biomedical applications is that these nanoparticles must have high magnetization values and sizes smaller than 100 nm with a narrow particle size distribution. Thus nanoparticles must have uniform physical and chemical properties. For these applications, a tailored surface coating/shell needs to be engineered, which has to be non-toxic, biocompatible and make allowance for targetable drug delivery with particle localization in a targeted area. Most work in this field has been done on improving the biocompatibility of the nanoparticles. Only a few scientific investigations have been carried out on improving the quality of magnetic nanoparticles with specific focus on the nanoparticle's surface chemistry, size distribution and shape (which directly influences the magnetic properties). All these particles also need to be properly characterized in order to get a protocol for the quality control of these particles, the nature of the surface coatings and their subsequent geometric arrangement. This will ultimately determine the overall size of the colloids and also plays a significant role in biokinetics and biodistribution of nanoparticles in the body. This review highlights recent advances in the synthetic chemistry, magnetic characterization and biological applications of inorganic/organic - core/shell FexOy based magnetic nanoparticles with specific focus on using the two popular surfactants for producing MNPs namely oleic acid and/or oleylamine as capping agents. Although the main nano-magnets under discussion are magnetite (Fe3O4) nanoparticles, maghemite (γ-Fe2O3) is also briefly mentioned.