Deenan Santhiya

Effect of polymer molecular weight on the absorption of polyacrylic acid at the alumina-water interface

The absorption and electrokinetic characteristics of alumina suspensions in the presence of polyacrylic acid as a dispersant have been studied. The adsorption isotherms exhibit high-affinity Langmuirian behaviour. The adsorption density decreases with increasing in pH, while it increases with increasing molecular weight of the polymer. Electrokinetic studies indicate specific adsorption at and above the isoelectric point of the alumina sample. Possible mechanisms of interaction between alumina and polyacrylic acid are discussed.

Surface Chemical Studies on Galena and Sphalerite in the Presence of Thiobacillus Thiooxidans with Reference to Mineral Beneficiation

Adsorption and electrokinetic studies were carried out to examine the surface chemical changes on galena and sphalerite before and after interaction with Thiobacillus thiooxidans (T. thiooxidans). The adsorption density of bacterial cells onto the two sulphide minerals was found to be independent of pH, although an increased number of cells was adsorbed onto galena compared to sphalerite. The adsorption isotherms of the cells with respect to the two minerals conform to the Langmuir equation. Zeta potential measurements revealed that the isoelectric points of the sulphide minerals were shifted to higher pH values after bacterial interaction, suggestive of specific adsorption. Both the sulphide minerals as well as the cells became less electronegative as a function of time after interaction with each other. Selective flotation and flocculation studies highlighted that galena could be separated from sphalerite after bacterial interaction. These tests confirmed that galena was depressed while sphalerite was made hydrophobic after interaction with the cells. Fourier transform infrared spectroscopic studies provided evidence in support of hydrogen bonding for the mineral-cell adsorption process. Possible mechanisms of interaction between galena/sphalerite and the cells of T. thiooxidans are discussed.

Bio-modulation of galena and sphalerite surfaces using Thiobacillus thiooxidans

The interaction of Thiobacillus thiooxidans (T. thiooxidans) with sphalerite and galena has been investigated through adsorption, electrokinetic, and flotation studies. The amount of T. thiooxidans cells adsorbed onto galena and sphalerite is found to be almost independent of pH. However, a greater amount of cells is adsorbed onto galena compared to sphalerite. The adsorption isotherms of T. thiooxidans onto both galena and sphalerite exhibit Langmuirian behaviour. Electrokinetic measurements reveal that the isoelectric points (iep) of galena and sphalerite are located around pH 2, while that of T. thiooxidans is around pH 3. The isoelectric points of the minerals are shifted to higher pH values after interaction, consequent to bacterial cell attachment, indicating specific adsorption. Additionally, the electrophoretic mobilities are found to become less negative as a function of time after bacterial interaction. Such a trend is also followed in the case of the cells after interaction with the minerals for different time intervals. On a comparative basis, the cells after interaction with sphalerite are less negative vis-a-vis those after interaction with galena. The flotation recovery of sphalerite, beyond 1 h of interaction with T. thiooxidans cells is not affected but galena is totally depressed in the presence of T. thiooxidans cells, in the pH range 5–11. The differential flotation tests on a synthetic mixture of galena and sphalerite reveal that sphalerite can be selectively floated from galena in the presence of T. thiooxidans.

Surface chemical studies on alumina suspensions using ammonium poly(methacrylate)

The interaction of \alpha-alumina with ammonium poly(methacrylate) (APMA) has been investigated through adsorption and electrokinetic measurements. The adsorption isotherms exhibit high affinity, Langmuirian behaviour at highly acidic pH and the adsorption density is found to decrease with increasing pH. On the contrary, the percentage desorption increases with increasing pH. Electrokinetic studies indicate specific adsorption between alumina and APMA resulting in a shift of the isoelectric point to acidic pH values. Electrophoretic mobility values indicate that the alumina suspension could be well dispersed in the pH range 5-11, consequent to polymer adsorption. These results were corroborated by the dispersion tests. Dissolution tests reveal the release of aluminium species from alumina while co-precipitation experiments confirm the chemical interaction of aluminium species with APMA in the bulk solution. Hydrogen bonding, electrostatic and chemical interactive forces are postulated to govern the adsorption process. FTIR spectroscopic data lend further support to the interaction mechanisms proposed.

Role of linker groups between hydrophilic and hydrophobic moieties of cationic surfactants on oligonucleotide-surfactant interactions.

The interaction between DNA and amino-acid-based surfactants with different linker groups was investigated by gel electrophoresis, ethidium bromide exclusion assays, circular dichroism, and melting temperature determinations. The studies showed that the strength of the interaction between the oligonucleotides and the surfactants is highly dependent on the linker of the surfactant. For ester surfactants, no significant interaction was observed for surfactant-to-DNA charge ratios up to 12. On the other hand, amide surfactants were shown to interact strongly with the oligonucleotides; these surfactants could displace up to 75% of the ethidium bromide molecules bound to the DNA and induced significant changes in the circular dichroism spectra. When comparing the headgroups of the surfactants, it was observed that surfactants with more hydrophobic headgroups (proline vs alanine) interacted more strongly with the DNA, in good agreement with previous studies.

Surface modification studies on sulphide minerals using bioreagents

The interaction of galena and sphalerite minerals with the metabolite obtained from Bacillus polymyxa has been examined through adsorption, electrokinetic, microflotation and flocculation tests. The adsorption density of the carbohydrate component of the metabolite for sphalerite exhibits a characteristic maximum in the pH range of 6–7, while in the case of galena the amount adsorbed increases with increase of pH. On the other hand, the adsorption density of the bacterial protein shows a continuous decrease with increase of pH, for both the minerals. The adsorption affinity of both the metabolic components is higher for galena vis-a-vis sphalerite. The electrophoretic mobility of the chosen minerals becomes less negative after interaction with the metabolite, in proportion with the time of interaction. Interestingly, the isoelectric point of sphalerite is shifted to less acidic values after treatment with the metabolite, but that of galena is unaltered. Bioflotation and bioflocculation studies on a synthetic mixture of galena and sphalerite demonstrate that galena can be selectively depressed or flocculated from sphalerite under appropriate conditions. Co-precipitation tests confirm complexation of lead and zinc species with the metabolic products, in the bulk solution. Possible mechanisms of interaction between the chosen sulphide minerals and the bioreagents are discussed.

Kinetic Studies of Amino Acid-Based Surfactant Binding to DNA

In this work, the binding kinetics of amino acid-based surfactants, presenting different linkers and head groups, with calf thymus (CT)-DNA was studied using stopped-flow fluorescence spectroscopy. The kinetic studies were carried out as a function of Na(+) concentration and surfactant-to-DNA charge ratio. The surfactant binding on DNA took place in two consecutive steps, for which the corresponding first and second relative rate constants (k(1) and k(2)) were determined. The fast step was attributed to the surfactant binding to DNA and micelle formation in its vicinity, the slower step to DNA condensation and possible rearrangement of the surfactant aggregates. In general, both relative rate constants increase with surfactant concentration and decrease with the ionic strength of the medium. The architecture of the surfactant was found to have a significant impact on the kinetics of the DNA-surfactant complexation. Surfactants with amide linkers showed larger relative rate constants than those with ester linkers. The variation of the relative rate constants with the head groups of the surfactants, alanine and proline, was found to be less obvious, being partially dependent on the surfactant concentration.

Bio-inspired synthesis of microporous bioactive glass-ceramic using CT-DNA as a template

We report, for the first time, bio-inspired synthesis of a bioactive glass-ceramic with superior textural properties in atmospheric conditions using CT-DNA as template. The phase composition, structure, morphology, and textural properties of the bioactive glass sample were evaluated with various analytical techniques before and after in vitro tests. The BET surface area analysis of the obtained glass-ceramic sample reveals that it possesses a high surface area with a range of (micro- to meso-) pore sizes. The TEM analysis of the glass-ceramic phase indicates that the amorphous phase consists of spherical particles, whereas the crystalline phase is found to have needle-like shape. In the glass-ceramic, we find a new type of crystalline phase (Na0.11Ca0.89)(P0.11Si0.89)O3, which is different from the earlier observation on 45S5® glass-ceramic sample. The accelerated in vitro bioactivity of the glass-ceramic is evidenced based on the hydroxyl carbonate apatite (HCA) layer formation on the glass-ceramic surface after immersing the bioglass sample in simulated body fluid (SBF), by FTIR, SEM and EDX analysis. Additionally, the ion release kinetics of the bioglass sample in SBF is followed by ICP-AES with simultaneous pH measurements. The in vitro cytotoxicity experiments on the glass-ceramic sample using osteosarcoma cells by following the MTT assay method indicate that the sample has good biocompatibility and may serve as an effective biomaterial for bone tissue engineering.

Non-invasive topical delivery of plasmid DNA to the skin using a peptide carrier.

Topical delivery to skin is an essential step in non-invasive application of nucleic acid therapeutics for cutaneous disorders. The barrier posed by different layers of the skin - stratum corneum on top followed by the viable epidermis below - makes it extremely challenging for large hydrophilic molecules like nucleic acids to efficiently enter the uncompromised skin. We report an amphipathic peptide Mgpe9 (CRRLRHLRHHYRRRWHRFRC) that can penetrate the uncompromised skin, enter skin cells and deliver plasmid DNA efficiently as nanocomplexes in vitro and in vivo without any additional physical or chemical interventions prevalent currently. We observe efficient gene expression up to the highly proliferating basal layer of the skin without observable adverse reactions or toxic effects after delivery of reporter plasmids. The entry mechanism of nanocomplexes possibly involves reversible modulation of junction proteins accompanied by transient changes in skin structure. This peptide holds potential to be used as an efficient transporter of therapeutic nucleic acids to the skin.

Dendrimer templated bioactive glass-ceramic nanovehicle for gene delivery applications

In the present investigation, multifunctional nanocrystalline microporous 45S5 bioglass particles were synthesized using poly(amidoamine) (PAMAM) dendrimer generation 3 as a template. Apart from bone regeneration ability, special focus has been placed on its application as a nanocarrier in gene delivery. Considering bio-inspired nanoscale microporous 45S5 bioglass (BG) as a bone regenerative material, evaluating the biocompatibility and mechanical properties are essential parameters. Initially, the characterization of BG was carried out through morphology, composition and textural studies. Interestingly, a polygonal shape was observed by TEM and microporosity was further confirmed by BET analysis. The mechanical properties of the obtained glass-ceramic were evaluated using a dynamic mechanical analyzer (DMA) which revealed its stiffness and good damping property. The nanocrystalline BG was observed to be osteoproductive through the hydroxycarbonated apatite (HCA) formation in simulated body fluid (SBF). The biocompatibility of the material was confirmed by MTT assay and furthermore, the U2OS osteosarcoma cell proliferation on the surface of the BG was visualized by FESEM. The material was found to be highly cell proliferative. In addition to this, in vitro studies were carried out to evaluate the therapeutic pDNA compaction ability of the bioglass material. Furthermore, the transfection ability of the material was also investigated against the CHO-K1 cell line. This investigation provides a new insight into the application of bioactive glass as an efficient non-viral nanocarrier for gene therapy.