In general, seed germination is improved by low-pressure plasma treatment using precursors such as air, nitrogen, O₂, and argon, etc. For the first time, low-pressure O₂ plasma was used to treat chili seeds in this study. When compared to untreated and vacuum-treated seeds, O₂ plasma treatment using the discharge power of 80 W for 60 s significantly improves chili seed germination and growth. The effect of vacuum on the germination and growth of chili seeds was also studied and shown to be negligible. The physical and chemical changes induced by O₂ plasma treatment were investigated to understand the plasma treatment to germination improvement. Combinatory etching and chemical modification aided imbibition and increased germination percentage in this O₂ plasma treatment on chili seeds. The success of this method has the potential to be scaled up to solve food security issues with seeds that would otherwise struggle to germinate.

In general, cold plasma treatment improves crop germination and growth. The purpose of this research is to examine the impact of low-pressure O2 plasma treatment on the germination and growth kinetics of papaya seeds. Seeds were treated for 40 s at a discharge power of 80 W using O2 as a monomer. Physical and chemical changes were studied to understand the mechanism of germination and growth improvement. Furthermore, changes in phytohormones and antioxidant activity that were beneficial to germination were also examined. O2 plasma treatment improved wettability, surface etching, and oxidation, and affected other molecular-level changes leading to a 16% germination improvement in papaya.

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.

Plasma hydrophilization and subsequent hydrophobic recovery in Bambara groundnuts are studied for the first time. Bambara groundnut seeds were treated with cold plasma (CP) for 10 seconds at 10 watts using water as a monomer. The contact angle, as well as physical and chemical changes, were used to determine the kinetics of hydrophobic recovery. The hydrophilic state of Bambara groundnut seeds had decreased after 60 days, but not to original hydrophobicity, and also the recovery rate is slower than those observed on synthetic polymer. However, this slower hydrophobic recovery makes CP treatment as an effective method for long-term seed storage.

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.

Theoretical investigations on the micellization of mixtures of (i) amino acid-based anionic surfactants [AAS: N-dodecyl derivatives of aminomalonate, -aspartate, and -glutamate] and (ii) hexadecyltrimethylammonium bromide (HTAB), were carried out at different mole ratios. Variation in the theoretical values of critical micelle concentration (CMC), mole fraction of surfactants in the micellar phase (X), at the interface (X-sigma), interaction parameters at the bulk/interface (beta(R)/beta(sigma)), ideality/nonideality of the mixing processes, and activity coefficients (f) were evaluated using Rubingh, Rosen, Motomora, and Sarmoria-Puvvada-Blankschtein models. CMC values significantly deviate from the theroretically calculated values, indicating associative interaction. With increasing mole fraction of AAS (alpha(AAS)), the magnitude of the (beta(R)/beta(sigma)) values gradually decreased, considered to attributable to hydrophobic interactions. With increasing alpha(AAS), the micellar mole fraction of HTAB (X-2) decreased insignificantly and X-2 values were higher than those compared to AAS for all combinations, due to the dominance of HTAB in micelles. Micellar mole fraction at the ideal state of AAS (X1ideal) differed from micellar mole fraction of AAS (X-1), indicating nonideality in the mixed micellization process. Gibbs free energy of micellization ( increment G(m)) values are more negative than the free energy of micellization for ideal mixing ( increment Gmideal), indicating the micellization process is spontaneous. With increasing alpha(AAS), the enthalpy of micellization (Delta H-m) and entropy of micellization (Delta S-m) values gradually increased, which indicates micellization is exothermic. The different physicochemical parameters of the mixed micelles are correlated with the variation in the spacer length between the two carboxylate groups of AAS.

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.

Dicarboxylate metallosurfactants (AASM), synthesized by mixing N-dodecyl aminomalonate, -aspartate and -glutamate with CaCl2,MnCl2 and CdCl2, were characterized by XRD, FTIR, and NMR spectroscopy. Layered structures, formed by metallosurfactants, were evidencedfrom differential scanning calorimetry and thermogravimetric analyses. Solvent-spread monolayer of AASM in combination withsoyphosphatidylcholine (SPC) and cholesterol (CHOL) were studied using Langmuir surface balance. With increasing mole fraction of AASMmean molecular area increased and passed through maxima at ~60 mol% of AASMs, indicating molecular packing reorganization. Systems with20 and 60 mol% AASM exhibited positive deviations from ideal behavior signifying repulsive interaction between the AASM and SPC, whilesynergistic interactions were established from the negative deviation at other combinations. Dynamic surface elasticity increased with increasingsurface pressure signifying formation of rigid monolayer. Transition of monolayer from gaseous to liquid expanded to liquid condensed state wasestablished by Brewster angle microscopic studies. Stability of the hybrid vesicles, formed by AASM+SPC+CHOL, was established bymonitoring their size, zeta potential and polydispersity index values over 100 days. Size and spherical morphology of hybrid vesicles wereconfirmed by transmission electron microscopic studies. Biocompatibility of the hybrid vesicles were established by cytotoxicity studies revealingtheir possible applications in drug delivery and imaging.

In the last few decades, the prevalence of multidrug resistance and importunate virulence in bacteria emerged as one of the serious concerns in health-care system. Lantibiotics, the well-conserved antimicrobial peptides predominantly rich in atypical sulfur-containing amino acids, lanthionine (Lan), and 3-methyl-lanthionine (MeLan), synthesized ribosomally from bacterial cells and modified posttranslationally, have drawn considerable interest in the therapeutic management of infectious diseases because of their effectiveness against multidrug-resistant bacteria. So far studied, the other reasons remain their potency, broad-spectrum nature, and negligible cytotoxicity. The biosynthesis of the lantibiotics involves two major steps, the modification of precursor peptides and their proteolytic activation. The gene cluster constituting the biosynthetic machinery codes essentially for the prepeptide and modification enzymes besides the proteases, ATP-binding cassette transporters, immunity factors, and regulatory proteins required as accessory factors. Herein, in this chapter a comprehensive discussion has been made on the biosynthesis of lantibiotics, which may be noteworthy in biomedical science for technology advancement.

Due to the accumulation of cholesterol in arterial wall, clot-forming cascade activated in the blood capillaries lead to conditions like myocardial ischemia and heart failure. These clots are dissolved by the enzyme streptokinase (SK), produced by Streptococcus sp., a normal flora in the human body. In the present study, codon-dependent evolution of twenty-three SK from Streptococcus sp. bacteria, isolated from distinct geographical origins were analyzed. Besides, domain variation, compositional analysis, effective number of codons (ENc) plot, codon adaptation index (CAI), and effect of polymorphism on SK interaction with its substrate plasminogen (Plg) were analyzed. Codon usage bias varied within a tiny range. Studies also reveal that AT ending codons are preferred over GC ending codons. Analyses of the other parameters reveal that the mutational pressure is one of the main factors to shape codon usage biasness. Interfacing and polar contact forming amino acid residues of SK with Plg is identical for all Streptococcus dysgalactiae but not for all Streptococcus pyogenes. Changes of those interfacing amino acid sites exhibit a substantial effect on polar interaction between SK and Plg. The present in silico studies are expected to shed further light to characterize and moreover, to understand the various contributing factors to influence SK adaptation that will be fulfilling to develop efficient thrombolytic therapeutics.

Knowledge of the solid state is of great importance in the development of a new active pharmaceutical ingredient, since the solid form often dictates the properties and performance of the drug. In the present study, solid state characteristics of the sodium salt of the candidate cholesterol reducing compound eritadenine, 2(R), 3(R))-dihydroxy-4-(9-adenyl)-butanoic acid, were investigated. The compound was crystallized by slow cooling from water and various aqueous ethanol solutions, at different temperatures. Further, the compound solution was subjected to lyophilization and to high vacuum drying. The resulting solids were screened for polymorphism by micro Raman spectroscopy (λex = 830 nm) and the crystallinity was investigated by X-ray powder diffraction. Further, thermal analysis was applied to study possible occurrence of solvates or hydrates. Solids obtained from slow cooling showed crystallinity, whereas rapid cooling gave rise to more amorphous solids. Analysis of difference spectra of the Raman data for solids obtained from slow cooling of solution revealed subtle differences in the structures between crystals derived from pure water and crystals derived from aqueous ethanol solutions. Finally, from the thermal analysis it was deduced that crystals obtained from pure water were stoichiometrically dihydrates whereas crystals obtained from aqueous ethanol solutions were 2.5 hydrates; this formation of different hydrates were supported by the Raman difference analysis.

We have reported for the first time a solvated electron mediated reduction of silver ion (Ag+) in presence of extract of Murraya koenigii (Mk) leaf as a surfactant to produce silver nanoparticles (AgNPs). Synthesized NPs show efficient ascorbic acid sensing at the µM range along with selective detection of different metal ions due to the presence of different biomolecules on the surface which are present in the extract. Synthesized nontoxic AgNPs will also exhibit proficient photocatalytic behavior for the degradation of toxic dyes due to the effective coupling between surface plasmon of AgNPs and the excited state continuum of the dye fluorophores. AgNPs will also exhibit substantial antibacterial activities. Altogether, our biosynthesized nontoxic NPs could be effectively used as both chemical and biosensor, catalyst as well as antibacterial agent.

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.

A series of amino acid-based surfactants with a fixed alkyl chain length and with two carboxyl groups separated by a spacer of one, two or three carbon atoms have been synthesized and evaluated as potential collectors for flotation of calcite and fluorite. A monocarboxylate amino acid-based surfactant having the same length of the hydrocarbon tail was also included in the study. Experiments using a Hallimond flotation tube showed that although the flotation reagents solely differs in terms of spacer, their efficacy in terms of flotation recovery varied very much. Whereas on calcite at pH 10.5 only the monocarboxylate collector gave a high yield, on fluorite at the same pH both the monocarboxylate and the dicarboxylate collectors with one carbon between the carboxyl groups gave good results. On calcite at the natural pH the monocarboxylate collector was most efficient but the dicarboxylate collectors with a two- and a three-carbon spacer also gave a reasonable recovery. On fluorite at the natural pH the dicarboxylate collectors with a two- and a three-carbon spacer were most efficient. The potential and the flotation recovery of the mineral particles as afunction of added collector was assessed and the adsorption was also monitored by diffuse reflectance infra-red spectroscopy. Taken together, the results showed that small changes in the head group region of the collector can radically affect flotation recovery. This type of knowledge is important to understand flotation selectivity in a mixture of similar minerals.

The present investigation aims to develop and distinguish mineral specific reagents with two functional groups for use in flotation of calcium containing minerals. For this purpose, a series of dicarboxylate-based surfactants with varying length between the carboxylate groups (one, two or three methylene groups) were synthesized. As reference, a surfactant with the same alkyl chain length but with only one carboxylate group in the polar part was synthesized. The adsorption behavior of these new reagents on pure apatite and calcite mineral surfaces was studied using Hallimond tube flotation, FTIR and ζ potential measurements. The relation between the adsorption behavior of a given surfactant on a specific mineral surface and its molecular structure over a range of concentration and pH values, as well as the region of maximum recovery were 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 synthesized. This selective adsorption of a given surfactant to a particular mineral surface relative to other mineral surfaces as evidenced in flotation studies is substantiated by ζ potential and infra-red spectroscopy data.

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

Large efforts are being made to streamline the conventional (chemical and physical) technological schemes of ore processing, remediation and environmental protection towards reducing overall costs, limiting the use of dangerous substances, decreasing waste streams and improving waste disposal and recycling practice. Hitherto, search for such innovations has been performed mainly empirically and there is an urgent need to shift these technologies to be more innovative and effective. Alternative biotechnological solutions and solutions mimicking natural processes are also being proposed. However, except for bioleaching, practical exploitation of the biotechnological potential in extractive industries and accompanying environmental protection measures remains far from feasibility.Understanding of the fundamental concepts of aquatic chemistry of minerals–selective adsorption and selective redox reactions at mineral–bacteria–solution interfaces, impact innovating conventional and bio-flotation, as well as (bio)remediation/detoxification of mineral and chemical wastes. Molecular-level knowledge and coherent understanding of minerals contacted with aqueous solutions is required that underlie great opportunities in controlling abiotic and biotic mineral–solution interfaces towards the grand challenge of tomorrow’s science and mineral processing technology.

Large efforts are being made to streamline the conventional (chemical and physical) technological schemes of ore processing, remediation and environmental protection towards reducing overall costs, limiting the use of dangerous substances, decreasing waste streams and improving waste disposal and recycling practice. Hitherto, search for such innovations has been performed mainly empirically and there is an urgent need to shift these technologies to be more innovative and effective. Alternative biotechnological solutions and solutions mimicking natural processes are also being proposed. However, except for bioleaching, practical exploitation of the biotechnological potential in extractive industries and accompanying environmental protection measures remains far from feasibility. Understanding of the fundamental concepts of aquatic chemistry of minerals–selective adsorption and selective redox reactions at mineral– bacteria–solution interfaces, impact innovating conventional and bio-flotation, as well as (bio) remediation/detoxification of mineral and chemical wastes are necessary. Molecular-level knowledge and coherent understanding of minerals contacted with aqueous solutions is required that underlie great opportunities in controlling abiotic and biotic mineral– solution interfaces towards the grand challenge of tomorrow’s science and mineral processing technology

Flame retardants are commonly used as a way to reduce the risk of fire. However, many of the currently used flame retardants are toxic and hazardous to the environment. Therefore, there are incentives to find safer alternatives. In nature, there are many substances that can function as non-toxic and environmentally friendly flame retardants. Phytic acid is the main storage form of phosphorus in plants and can be found in e.g. nuts and cereals. Amino acids are the building blocks of enzymes and proteins. Many common metal ions are important nutrients.

Phosphorus based flame retardants are considered to be the best for cellulose-based materials such as cotton and wood. A non-toxic naturally occurring substance with high phosphorus content is phytic acid, which is used by plants as the main storage of phosphorus. It is prevalent in grains and seeds, so we eat it every day. Phytic acid and phytate complexes with various common and non-toxic metal ions or ammonia have been studied on cotton and wood in orderto systematically assess their performance as flame retardants and elucidate their mechanismsof action.

Simple combustion tests have been used to gain a first overview of the relative performance of the flame retardants depending on which ion is combined with the phytic acid, and in which proportions. Analytical methods such as TGA and calorimetry have been used to investigate the thermal properties and thermal degradation of the samples. Spectroscopic techniques suchas MAS NMR have been used to explain the chemistry behind the thermal degradation mechanisms in molecular detail. The main focus has been on cotton samples, but an efficient methodology to control the humidity of wood samples in lab scale has been developed for future investigations on wood.

Phytic acid and its complexes have a flame retarding effect on both cotton and wood. The thermal process is similar on both materials. The mechanism is low-temperature charring giving less combustible degradation products, followed by cooling polymerization of the phosphate groups in the phytic acid, and formation of a second barrier to prevent the mixture of combustible volatiles and oxygen. It is important to have ionizable protons available in the flame retardant to induce the main mechanism of charring. Cone calorimeter tests on cotton samples show that the samples self-extinguish. Sodium phytates have a better performance than calcium phytates, as shown from combustion tests and FIGRA index on cotton samples. Possibly the superior flame retarding effect of sodium compared to the other ions is because ofthe radical quenching ability of alkali metals, but further investigations are needed into thisissue.

Some of the results are also available in Bachelor and Master theses, and in a recently accepted paper in Green Materials Special Issue on Sustainable Flame Retardants.

The results may be of interest to the scientific community as well as for companies and organizations that work for a fire-safe and sustainable living environment.

Effect of 1-butyl-3-methylimidazolium chloride ionic liquid ([bmim]Cl, IL) on the monolayer/bilayer of either soy-phosphatidylcholine (SPC) or hydrogenated soy-phosphatidylcholine (HSPC), in combination with 30 ​mol% cholesterol (Chol), were investigated. Impact of IL on monolayers were explored by measuring the surface pressure (π)-area (A) isotherm with a Langmuir-surface balance. Lift-off area (A₀) of the monomolecular films gradually increased [A_0(HSPC+IL) ​> ​A_0(SPC+IL)], collapse pressures (π_c) decreased and passed through minima [π_c(HSPC+IL) ​> ​π_c(SPC+IL)] with increasing IL concentration ([IL]). Minimum molecular area (A_min) increased monotonously and compression moduli (C_s⁻¹) followed the sequence (HSPC+IL) ​> ​(SPC+IL) at a particular π with respect to [IL]. Dynamic light scattering studies were carried out to determine the hydrodynamic diameter (d_h), zeta potential (Z.P.) and polydispersity index (PDI) values while fluorescence anisotropy studies, using 7-hydroxycoumarin and 1,6-diphenyl-1,3,5-hexatriene, could reveal the micro-viscosity of liposomes. Increased size and rigidity, induced by IL, suggest the formation of leak-proof, condensed liposomes. Disruption of vesicles induced by IL were observed from transmission electron microscopic (TEM) studies. IL induced disintegration of liposome and kinetics of subsequent formation of adsorbed monolayer were accomplished by surface pressure-time isotherms. IL-induced liposomes were substantially less toxic as revealed by MTT assay. These liposomes are considered to be safely used as effective and controlled drug delivery systems.

The production of suitable coating with excellent antibacterial performance has now become a viable technique for enhancing the functional qualities of various biomedical materials. Here, pulsed plasma polymerisation was used to produce an antibacterial coating from carvone oil of spearmint plant. The coating films have adjustable chemical and physical properties based on the deposition parameter, i.e., duty cycles (DC). The static water contact angle (WCA) values of PW ppCar increase with the increase of DC. FTIR and XPS showed that the molecular structure of the carvone is less fragmented, retaining moieties associated with C-O and C=O when the DC is reduced. These C-O and C=O moieties likely reduced the measured static water contact angle. This surface chemical composition with predominantly C-O and C=O also showed a stronger bactericidal effect, based on the biofilm assay with bacteria (E. coli and S. aureus), compared to those coating with C-C and C-H produced at higher DC. According to the AFM images, the lower DC resulted in smoother and more homogeneous coating than those produced with the higher DC, while FE-SEM images show that when E. coli and S. aureus membranes were attached to the PW ppCar, they ruptured and distorted with a pore created, and that these distortions and ruptures increased as the DC was reduced.

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.

Medical devices are often vulnerable to colonization by nosocomial pathogens (bacteria), leading to infections. Traditional sterilization methods may not always be effective, and as a result, alternative options are being explored to prevent microbial contamination. Recently, scientists are emphasizing using plant-derived essential oils that possess inherent antibacterial properties to produce antimicrobial coatings using plasma polymerization technology carried out at atmospheric pressure (AP). This approach shows promise compared to other coating strategies that need several processing steps, including a high-vacuum system, and are laborious, such as the immobilization of antimicrobial materials on precoated layers in the low-pressure plasma polymerization approach. The present study demonstrates the potential of AP plasma polymerization for producing thin films with excellent antibacterial properties and surface characteristics. The resulting coatings are stable, smooth, and have high wettability, making them ideal for repelling bacteria. The calculated zeta potential and deposition rate for the films are also favorable. These AP plasma-polymerized thin films created from carvone show a reduction rate of more than 90% for Escherichia coli and Staphylococcus aureus bacteria. Our computational docking studies also reveal strong binding interactions between the original carvone monomer and both bacteria. The study suggests that these AP plasma-produced coatings have great potential as antibacterial coatings for biomedical devices.

For photochromic molecules, the ability to switch reversibly between two states is controlled largely by structural effects. The photodimerization of 5-methyluracil, commonly known as thymine, a member of the pyrimidine family and one of the DNA bases, is a particularly important reaction in photobiology, one which occurs when the molecule is subjected to UV irradiation. Dimerization takes place through the C5=C6 bond of thymine and results in the formation of a cyclobutane ring. Various analogues of thymine behave in a similar manner. In solution, for the majority of molecules in the pyrimidine family, excitation is accompanied by an accumulation of lone electrons at C5 and C6 and a marked reduction in bond order. Dimerization occurs through the generation of a singlet state, followed by intersystem crossing and decay to a triplet state, from which the dimer is formed. The lifetime of the excited triplet state is much longer than the singlet state and energy is normally dissipated by chemical routes, since there is ample opportunity for molecules to diffuse and collide in solution. When a molecule is tethered at an interface, reaction can readily occur through the singlet state. The impact of this is that uracils which do not photoreact in solution, i.e., 5-nitrouracil, will photoreact when immobilized in the solid state. To produce photoactive materials that display both high sensitivity and reversibility, it is necessary to control the orientation of the thymine molecule. Nature dictates this in the case of DNA, and only the cis-syn isomer is formed upon dimerization. The cis-syn dimer exhibits the greatest ease of photosplitting, apparently due to steric repulsion of the methyl groups attached to C5 in thymine. In the case of photoactive materials, the necessary orientation can be achieved through the formation of a thin solid film. Irradiation with monochromatic light at 280 nm leads to dimerization, a process which can be reversed again by irradiation at 240 nm. Depending upon the nature of the molecule this process can be performed reversibly over many cycles. Photosplitting in the case of thin solid films is apparently induced by crystal lattice strain. Inefficiencies in the photosplitting process are caused by misalignment in the thin solid films and/or the formation of a photoinactive conformer. One very attractive way of obtaining the appropriate orientation at an interface is through the formation of self-assembled monolayers (SAMs) or through the formation of thin solid films by alternative techniques such as dip-coating. The first objective of the thesis, was to form such films, exploring how chemical structure influenced the photodimerization process and associated surface physical properties. Photoresponsive surfaces were prepared by attaching synthesized pyrimidine-terminated molecules to flat gold substrates (as thiol self-assembled monolayers) or quartz surfaces (by dip-coating). 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. The second objective was to explore how photosensitizers could be used to alter the wavelength at which dimerization occurred, giving greater flexibility to the entire process. Thin solid films of thymine and uracil derivatives, incorporating a photosensitizer in the film, were prepared on quartz surfaces using a dip-coating technique. Photosensitized dimerization in this thin solid film was investigated for the first time and compared with the conventional, non-photosensitized reaction. p-Aminobenzoic acid (PABA) and N-dodecyl PABA (PABA-C12) were selected as photosensitizers. It was found that PABA and PABA-C12 were effective in causing the photosensitized dimerization of thymine, upon exposure to light of wavelength 313 nm. Uracil surfaces, however, do not photodimerize under these conditions. The concentration of photosensitizer and the solvent selected in the dip-coating process strongly influenced the dimerization process. The reaction rate of sensitized dimerization follows a pseudo-first order reaction.

Almost all of the flotation reagents used today were discovered by continued application of empirical methods and/or trial and error experimentation. Moreover, with the metal-ion specific approach used so far, it is difficult to separate the minerals containing the same constituent metal ion. A critical assessment of molecular recognition processes involved in biomineralization suggested the possibility of using reagents which are surface specific. The concept that the molecules consisting of two or more functional groups having appropriate spacing between those so as to achieve structural/stereochemical compatibility during interaction with the mineral surface exhibit structure-specificity is thought to be extended to the design of specific collectors in flotation processes. In the present study, for the first time, a rational design of surface active molecules, and thereby the recognition of crystal faces (of minerals) by these molecules through structural and stereochemical matching is being utilized successfully to selectively float various minerals. For this purpose, carboxylate-based collectors (for mineral specific flotation of calcium minerals) as well as xanthate-based collectors (for mineral specific flotation of sulphide minerals) with a fixed alkyl chain length but having two functional groups with varying geometrical distances (separated by a spacer of one, two and three carbon atoms) between them have been synthesized. In this article, we have discussed the design, synthesis, purification of these novel mineral specific collectors as well as their important solution parameters in relation to flotation processes.

Development of sustainable flame retardants for cotton-based materials has become an active research interest as many of the currently used flame retardants are harmful both to the environment and to human health. Phytic acid is a natural resource that has shown potential to be an environment-friendly flame retardant. In order to design highly efficient flame retardants based on phytic acid, detailed knowledge of the decomposition process is essential. In this study, cotton samples were prepared with pure phytic acid, as well as salts of sodium or calcium ions. All samples improved the fire performance, most notably sodium phytate, as shown by a simple burning test, as well as by thermogravimetric analysis. The formation of char prevents the degradation of cotton, leaving a residual mass. Phosphorus-31 nuclear magnetic resonance spectroscopy was used to characterize the intermediate products formed during the pyrolysis process. Both phytate salts polymerize, sodium to a higher degree than calcium.

Thin solid films of thymine and uracil derivatives, incorporating a photosensitizer in the film, were prepared on quartz surfaces using a dip-coating technique. Photosensitized dimerization in these thin solid films was investigated in this study and compared with the conventional, non-photosensitized reaction. Both carbonyl and p-aminobenzoic compounds were selected as photosensitizers. It was found that only p-aminobenzoic compounds such as p-aminobenzoic acid and N-dodecyl p-aminobenzoic acid were effective in causing the photosensitized dimerization of thymine, upon exposure to light of wavelength 313 nm. Uracil surfaces, however, do not photodimerize under these conditions. The concentration of photosensitizer and the solvent selected in the dip-coating process strongly influenced the dimerization process. The reaction rate of sensitized dimerization follows a pseudo-first order reaction.

A study was performed involving a series of double-headed carboxylate collectors with varying distance between the head groups (one, two or three carbon atoms). A collector with the same alkyl chain length but with only one carboxylate group was also included. All these were amino-acid based amphiphiles and the polar head group was connected to the hydrophobic tail via an amide linkage. Selective flotation recovery of different calcium minerals using these collectors was investigated. The double-headed collector with one carbon atom between the carboxylate groups was an apatite and fluorite specific reagent while the monocarboxylate surfactant showed high specificity for calcite. The flotation behavior of a simple conventional collector of the same alkyl chain length, a fatty acid salt, was also determined under identical flotation conditions in order to understand the effect of the amide group. Complementary experiments (ζ potential measurements, adsorption isotherm determinations) were also performed for these reagents. In order to shed light on the selectivity obtained with the dicarboxylate surfactants, the distances between the head groups were calculated and compared with the distances between neighboring calcium atoms on the surface of the minerals. It was found that the high degree of selectivity could be rationalized by perfect matching of these distances. To the best of our knowledge this is the first study where flotation selectivity in complex calcium mineral systems has been explained in terms of molecular recognition governing the interaction between the collector and the mineral surface.