Effect of cationic dendrimer on membrane mimetic systems in the form of monolayer and bilayer.

Interactions between a zwitterionic phospholipid, 1, 2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and four anionic phospholipids dihexadecyl phosphate (DHP), 1, 2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG), 1, 2-dipalmitoyl-sn-glycero-3-phosphate (DPP) and 1, 2-dipalmitoyl-sn-glycero-3-phospho ethanol (DPPEth) in combination with an additional amount of 30 mol% cholesterol were separately investigated at air-buffer interface through surface pressure (π) - area (A) measurements. π-A isotherm derived parameters revealed maximum negative deviation from ideality for the mixtures comprising 30 mol% anionic lipids. Besides the film functionality, structural changes of the monomolecular films at different surface pressures in the absence and presence of polyamidoamine (PAMAM, generation 4), a cationic dendrimer, were visualised through Brewster angle microscopy and fluorescence microscopic studies. Fluidity/rigidity of monolayers were assessed by surface dilatational rheology studies. Effect of PAMAM on the formation of adsorbed monolayer, due to bilayer disintegration of liposomes (DPPC:anionic lipids= 7:3 M/M, and 30 mol% cholesterol) were monitored by surface pressure (π) - time (t) isotherms. Bilayer disintegration kinetics were dependent on lipid head group and chain length, besides dendrimer concentration. Such studies are considered to be an in vitro cell membrane model where the alteration of molecular orientation play important roles in understanding the nature of interaction between the dendrimer and cell membrane. Liposome-dendrimer aggregates were nontoxic to breast cancer cell line as well as in doxorubicin treated MDA-MB-468 cell line suggesting their potential as drug delivery systems.

Atmospheric Pressure Plasma Polymerisation of D-Limonene and Its Antimicrobial Activity.

Antibacterial coating is necessary to prevent biofilm-forming bacteria from colonising medical tools causing infection and sepsis in patients. The recent coating strategies such as immobilisation of antimicrobial materials and low-pressure plasma polymerisation may require multiple processing steps involving a high-vacuum system and time-consuming process. Some of those have limited efficacy and durability. Here, we report a rapid and one-step atmospheric pressure plasma polymerisation (APPP) of D-limonene to produce nano-thin films with hydrophobic-like properties for antibacterial applications. The influence of plasma polymerisation time on the thickness, surface characteristic, and chemical composition of the plasma-polymerised films was systematically investigated. Results showed that the nano-thin films deposited at 1 min on glass substrate are optically transparent and homogenous, with a thickness of 44.3 ± 4.8 nm, a smooth surface with an average roughness of 0.23 ± 0.02 nm. For its antimicrobial activity, the biofilm assay evaluation revealed a significant 94% decrease in the number of Escherichia coli (E. coli) compared to the control sample. More importantly, the resultant nano-thin films exhibited a potent bactericidal effect that can distort and rupture the membrane of the treated bacteria. These findings provide important insights into the development of bacteria-resistant and biocompatible coatings on the arbitrary substrate in a straightforward and cost-effective route at atmospheric pressure.

A study to examine the ageing behaviour of cold plasma-treated agricultural seeds.

Cold plasma (low pressure) technology has been effectively used to boost the germination and growth of various crops in recent decades. The durability of these plasma-treated seeds is essential because of the need to store and distribute the seeds at different locations. However, these ageing effects are often not ascertained and reported because germination and related tests are carried out within a short time after the plasma-treatment. This research aims to fill that knowledge gap by subjecting three different types of seeds (and precursors): Bambara groundnuts (water), chilli (oxygen), and papaya (oxygen) to cold plasma-treatment. Common mechanisms found for these diverse seed types and treatment conditions were the physical and chemical changes induced by the physical etching and the cold plasma on the seeds and subsequent oxidation, which promoted germination and growth. The high glass transition temperature of the lignin-cellulose prevented any physical restructuring of the surfaces while maintaining the chemical changes to continue to promote the seeds germination and growth. These changes were monitored over 60 days of ageing using water contact angle (WCA), water uptake, electrical conductivity, field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS). The vacuum effect was also investigated to separate its effect from cold plasma (low pressure). This finding offers a framework for determining how long agricultural seeds that have received plasma treatment can be used. Additionally, there is a need to transfer this research from the lab to the field. Once the impact of plasma treatment on seeds has been estimated, it will be simple to do so.

Antibiofilm and anticancer activities of unripe and ripe Azadirachta indica (neem) seed extracts.

BACKGROUND: Antibiotic resistances of pathogens and breast cancer warrant the search for new alternative strategies. Phytoextracts can eradicate microbe-borne diseases as well as cancer with lower side effects compared to conventional antibiotics. AIM: Unripe and ripe Azadirachta indica (neem) seed extracts were explored as potential antibiofilm and anticancer agents in combating multidrug-resistant infectious bacteria as well as anticancer agents against the MDR breast cancer cell lines. METHODS: Shed-dried neem seeds (both unripe and ripe) were pulverized and extracted using methanol. The chemical components were identified with FTIR and gas chromatography - mass spectrometry. Antibiofilm activity of neem seed extracts were assessed in terms of minimum biofilm inhibitory concentration (MBIC), minimum biofilm eradication concentration (MBEC), and fluorescence microscopic studies on Staphylococcus aureus and Vibrio cholerae. Bacterial cells were studied by fluorescence microscopy using acridine orange/ethidium bromide as the staining agents. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were evaluated to observe the antibacterial activities. Cytotoxicity of the extracts against human blood lymphocytes and the anticancer activity against drug-resistant breast cancer cell lines were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and fluorescence-activated cell sorting (FACS) studies. RESULTS: 4-Ethyl-2-hydroxy-2-cyclopentene-1-one, phthalic acid, and 2-hexyl-tetrahydro thiophane were the major compounds in unripe neem seed, whereas 3,5-dihydroxy-6-methyl-2,3-dihydro-4-H-pyran-4-one and 4-ethylbenzamide were predominant in ripe neem seed. Triazine derivatives were also common for both the extracts. MBIC values of unripe and ripe neem seed extracts for S. aureus are 75 and 100 µg/mL, respectively, and for V. cholerae, they are 100 and 300 µg/mL, respectively. MBEC values of unripe and ripe seed extracts are 500 and 300 µg/mL, respectively for S. aureus and for V. cholerae the values are 700 and 500 µg/mL, respectively. Fluorescence microscopic studies at 16 and 24 h, after bacterial culture, demonstrate enhanced antibiofilm activity for the ripe seed extract than that of the unripe seeds for both the bacteria. MTT assay reveals lower cytotoxicity of both the extracts towards normal blood lymphocytes, and anticancer activity against breast cancer cell line (MDA-MB-231) with superior activity of ripe seed extract. FACS studies further supported higher anticancer activity for ripe seed extract. CONCLUSIONS: Methanolic extract of neem seeds could substantially inhibit and eradicate biofilm along with their potent antibacterial and anticancer activities. Both the extracts showed higher antibiofilm and antibacterial activity against S. aureus (gram-positive) than V. cholerae (gram-negative). Moreover, ripe seed extract showed higher antibiofilm and anticancer activity than unripe extracts.

Micro-structural investigations on oppositely charged mixed surfactant gels with potential dermal applications.

Dicarboxylic amino acid-based surfactants (N-dodecyl derivatives of -aminomalonate, -aspartate, and -glutamate) in combination with hexadecyltrimethylammonium bromide (HTAB) form a variety of aggregates. Composition and concentration-dependent mixtures exhibit liquid crystal, gel, precipitate, and clear isotropic phases. Liquid crystalline patterns, formed by surfactant mixtures, were identified by polarizing optical microscopy. FE-SEM studies reveal the existence of surface morphologies of different mixed aggregates. Phase transition and associated weight loss were found to depend on the composition where thermotropic behaviours were revealed through combined differential scanning calorimetry and thermogravimetric studies. Systems comprising more than 60 mol% HTAB demonstrate shear-thinning behaviour. Gels cause insignificant toxicity to human peripheral lymphocytes and irritation to bare mouse skin; they do not display the symptoms of cutaneous irritation, neutrophilic invasion, and inflammation (erythema, edema, and skin thinning) as evidenced by cumulative irritancy index score. Gels also exhibit substantial antibacterial effects on Staphylococcus aureus, a potent causative agent of skin and soft tissue infections, suggesting its possible application as a vehicle for topical dermatological drug delivery.

Interfacial and Aggregation Behavior of Dicarboxylic Amino Acid-Based Surfactants in Combination with a Cationic Surfactant.

The interfacial and micellization behavior of three dicarboxylic amino acid-based anionic surfactants, abbreviated as AAS (N-dodecyl derivative of -aminomalonate, -aspartate, and -glutamate) in combination with hexadecyltrimethylammonium bromide (HTAB) were investigated by surface tension, conductance, UV-vis absorption/emission spectroscopy, dynamic light scattering (DLS), and viscosity studies. Critical micelle concentration (CMC) values of the surfactant mixtures are significantly lower than the predicted values, indicating associative interaction between the components. Surface excess, limiting molecular area, surface pressure at the CMC, and Gibbs free energy indicate spontaneity of the micellization processes compared to the pure components. CMC values were also determined from the sigmoidal variation in the plot of micellar polarity and pyrene UV-vis absorption/emission intensities with surfactant concentration. The aggregation number, determined by static fluorescence quenching method, increases with decreasing mole fraction of the AAS (αAAS), where the micelles are mainly dominated by the HTAB molecules. The size of the micelle increases with decreasing αAAS, leading to the formation of larger and complex aggregates, as also supported by the viscosity studies. Micelles comprising 20-40 mol % AAS are highly viscous, in consonance with their sizes. Some of the mixed surfactant systems show unusual viscosity (shear thickening and increased viscosity with increasing temperature). Such mixed surfactant systems are considered to have potential in gel-based drug delivery and nanoparticle synthesis.

Flotation selectivity of novel alkyl dicarboxylate reagents for apatite-calcite separation.

The investigation aims to demonstrate the conceptual thoughts behind developing mineral specific reagents for use in flotation of calcium containing ores. For this purpose, a series of dicarboxylate-based surfactants with varying distance between the carboxylate groups (one, two or three methylene groups) was synthesized. A surfactant with the same alkyl chain length but with only one carboxylate group was also synthesized and evaluated. The adsorption behavior of these new reagents on pure apatite and pure calcite surfaces was studied using Hallimond tube flotation, FTIR and ζ potential measurements. The relation between the adsorption behavior of a given surfactant at a specific mineral surface and its molecular structure over a range of concentrations and pH values, as well as the region of maximum recovery, was established. It was found that one of the reagents, with a specific distance between the carboxylate groups, was much more selective for a particular mineral surface than the other homologues. For example, out of the four compounds synthesized, only the one where the carboxylate groups were separated by a single methylene group floated apatite but not calcite, whereas calcite was efficiently floated with the monocarboxylic reagent, but not with the other reagents synthesized. This selective adsorption of a given surfactant to a particular mineral surface relative to other mineral surfaces as evidenced in the flotation studies was substantiated by ζ potential and infra-red spectroscopy data.

Design of pyrimidine-based photoresponsive surfaces and light-regulated wettability.

Photoresponsive surfaces were prepared by attaching pyrimidine-terminated molecules to flat gold substrates (as thiol self-assembled monolayers) or by dip-coating quartz surfaces. Both types of films underwent photodimerization (two pyrimidine rings react with one another and form a cyclobutane type dimer through the C5=C6 double bond) when irradiated with light of 280 nm wavelength. The reverse reaction was carried out by irradiating the dimerized surface with light of 240 nm wavelength. The photoinduced chemical changes are accompanied by a change in the physical properties of the surface (e.g., wettability and acidity), and are highly dependent on the structure of the photoactive molecules. The surface dimerization reaction follows a pseudo-first order reaction. The rate constant is determined by the structure of the pyrimidine headgroup. In self-assembled monolayers, uracil derivatives dimerize faster than thymine derivatives due to a reduced steric repulsion near the reaction center. In dip-coated films, however, uracil derivatives appear to be less ordered and, correspondingly, the efficiency of the reaction is lower. The reaction rate is also very sensitive to the ordering within the layer, which can be manipulated through the structure of the tail. In SAMs, faster dimerization occurs with molecules containing flexible chains. In dip-coated films, the presence of a polar group at the chain terminus favors dimerization.