Terminal Amine Groups Research Articles

Custom-tailoring metal-organic framework in thin-film nanocomposite nanofiltration membrane with enhanced internal polarity and amplified surface crosslinking for elevated separation property

A polyamide (PA) thin-film nanocomposite (TFN) membrane embedded with post-synthetically functionalized metal-organic framework (MOF) nanofillers of imidazole-2-carbaldehyde (ICA) decorated UiO-66-NH2 nanofillers (ICA_d_UiO-66-NH2) was developed using the interfacial polymerization method. The ICA_d_UiO-66-NH2 nanofiller couples a surface water-capturing ICA decoration, facilitating the rapid transport of water molecules owing to the enhanced internal polarity, while achieving an amplified crosslinking between the terminal amine groups of ICA and trimesoyl chloride, enabling the perfect incorporation of MOF nanofillers within the PA matrix. The resultant ICA_d_UiO-66-NH2@PA TFN membrane with elevated separation property performed comparably high water permeance of 9.4 l m−2 h−1 bar−1 (achieving a nearly 2-fold increase from the initial value of the thin-film composite membrane), and a favorable rejection ratio of 97.4% (Na2SO4). Owing to the unique hierarchical surface microstructure embedded with the intrinsically hydrophilic ICA_d_UiO-66-NH2 nanofillers, the newly-developed TFN membrane exhibited superior antifouling properties. Furthermore, the ICA_d_UiO-66-NH2@PA TFN membrane also retained excellent reusability and durability without significant compromise even after long-term salt, and acid/alkali treatments. Overall, this work provides an insight into the embedding of different functionalized nanofillers inside TFN membranes with elevated separation properties.

Engineering Heterostructured Thin-Film Nanocomposite Membrane with Functionalized Graphene Oxide Quantum Dots (GOQD) for Highly Efficient Reverse Osmosis.

In this study, custom-tailored graphene oxide quantum dots (GOQD) were synthesized as functional nanofillers to be embedded into the polyamide (PA) membrane for reverse osmosis (RO) via interfacial polymerization (IP). The heterostructured interface-functionalization of amine/sulfonic decoration on GOQD (N/S-d-GOQD) takes place via the tuning of the molecular design. The embedded N/S-d-GOQD inside the PA matrix contributes to facilitating water molecules quick transport due to the more accessible capturing sites with higher internal polarity, achieving a nearly 3-fold increase in water permeance when compared to the pristine thin-film composite (TFC) membrane. Covalent bonding between the terminal amine groups and the acyl chloride of trimesoyl chloride (TMC) enables the formation of an amplified selective layer, while the sulfonic part assists in maintaining a robust membrane surface negative charge, thus remarkably improving the membrane selectivity toward NaCl. As a result, the newly developed TFN membrane performed remarkably high water permeance up to 5.89 L m-2 h-1 bar-1 without the compromising of its favorable salt (NaCl) rejection ratio of 97.1%, revealing a comparably high separation property when comparing to the state-of-the-art RO membranes, and surpassing the permeability-selectivity trade-off limits. Furthermore, we systematically investigated the GOQDs with different surface decorations but similar configurations (including 3 different nanofillers of pristine GOQD, amine decorated GOQD (N-d-GOQD), and N/S-d-GOQD) to unveil the underlying mechanisms of the swing effects of internal geometry and polarity of the embedded nanofillers on contributing to the uptake, and/or release of aqueous molecules within TFN membranes, providing a fundamental perspective to investigate the impact of embedded nanofillers on the formation of an IP layer and the overall transporting behavior of the RO process.

Optimization of the geometry and calculation of the normal vibrations of the dendrimer with amine terminal groups

The structure of the first generation dendrimer Gi constructed from a hexafunctional cyclotriphosphazene core with six branches -O-C6H4-CH=N-N(CH3)-P(S)< and twelve 4-hydroxyphenethylamine end groups O-C6H4-(CH2)2-NH2 was studied. Structural optimization and analysis of normal vibrations were performed for the Gi dendrimer. The Gi dendrimer molecule has a convex lens structure with flat -O-C6H4-CH=N-N(CH3)-P(S)< fragments and a slightly nonplanar cyclotriphosphazene core. Full optimization shows that the conformation of terminal 4-hydroxyphenethylamine groups O-C6H4-(CH2)2-NH2 with dihedral angles C(13)-C(22)-C(23)-N(6) and C(22)-C(23)-N(6)-H(23): 63.7 and 46.8° is predominant. The flat and anisotropic form of the cyclotriphosphazene core determines the ability of dendrimers to pack with each other in the most likely disk-like form. The spatial distribution of electron density for the core and end groups allows estimating the magnitude of electrostatic interactions on the surface of the dendrimer in the guest-host complexes.

Synthesis of organic iron chelates and evaluation of their efficiency in improving the growth and yield of Blackgram

Supplying a sufficient amount of available iron (Fe) for plant growth in pot culture is a great challenge. The chelators commonly used to supply Fe in pot culture have several advantages and positively affect plant growth. In this research study we have synthesized certain Fe – amino acid and Fe – organic acid chelates, including Fe – glycinate, Fe – citrate and Fe – EDTA and evaluated their efficacy as a Fe source for blackgram grown in pot culture. FTIR analysis shows unbound glycine from chelated one. Free glycine exhibit a vibration peak at 2920 cm-1 that disappear upon chelate formation. The peak at 2920 cm-1 due to twisting vibrating of NH2 groups. Disappearing of this peak indicates that new coordinate bond is formed through the terminal amine groups. The peak at 3153.04 cm-1 and 1327.75 cm-1 is due to weak stretching of symmetric and asymmetric amine vibration. As compared to the position of bands in the spectrum of iron glycinate confirms the chelation of said amino acid with Fe2+ ions. The pot experiment was conducted to study the effect of foliar and soil application of amino acid and organic acid chelated iron on growth of blackgram. The results showed that the foliar spraying of 1% ferrous glycinate resulted in maximum Fe, Zn content, leaf active iron, Catalase and Peroxidase activity. Higher activity of Catalase and Peroxidase confirmed the improvement in plant Fe status. Between the soil and foliar application foliar spraying is better in improving the plant micronutrient content which was evidenced from higher enzyme activities.

Comparison of Protein-Repellent Behavior of Linear versus Dendrimer-Structured Surface-Immobilized Polymers.

For many biomedical applications, material surfaces should not only prevent unspecific protein adsorption and bacterial attachment as in many other applications in the food, health, or marine industry, but they should also promote the adhesion of tissue cells. In order to take a first step toward the challenging development of protein and bacteria-repelling and cell-adhesion-promoting materials, polyamine and poly(amido amine) surface coatings with terminal amine groups and varying structure (dendrimer, oligomer, polymer) were immobilized on model surfaces via silane chemistry. Physicochemical analysis showed that all modifications are hydrophilic (contact angles <60°) and possess similar surface free energies (SFEs, ∼46-54 mN/m), whereas their amine group densities and zeta potentials at physiological conditions (pH 7.4) varied greatly (-50 to +75 mV). In protein adsorption experiments with single proteins (human serum albumin (HSA) and lysozyme) as well as complex physiological fluids (fetal bovine serum (FBS) and human saliva), the amounts of adsorbed protein were found to correlate strongly with the zeta potential of the surface coatings. Both modifications based on linear polymers exhibited good protein repellency toward all proteins examined and are thus promising for testing in cell adhesion studies.

Azido-Desferrioxamine Siderophores as Functional Click-Chemistry Probes Generated in Culture upon Adding a Diazo-Transfer Reagent.

This work aimed to undertake the in situ conversion of the terminal amine groups of bacterial desferrioxamine (DFO) siderophores, including desferrioxamine B (DFOB), to azide groups to enable downstream click chemistry. Initial studies trialed a precursor-directed biosynthesis (PDB) approach. Supplementing Streptomyces pilosus culture with blunt-end azido/amine non-native substrates designed to replace 1,5-diaminopentane as the native diamine substrate in the terminal amine position of DFOB did not produce azido-DFOB. Addition of the diazo-transfer reagent imidazole-1-sulfonyl azide hydrogen sulfate to spent S. pilosus medium that had been cultured in the presence of 1,4-diaminobutane, as a viable native substrate to expand the suite of native DFO-type siderophores, successfully generated the cognate suite of azido-DFO analogues. CuI -mediated or strain-promoted CuI -free click chemistry reactions between this minimally processed mixture and the appropriate alkyne-bearing biotin reagents produced the cognate suite of 1,4-disubstituted triazole-linked DFO-biotin compounds as potential molecular probes, detected as FeIII -loaded species. The amine-to-azide transformation of amine-bearing natural products in complex mixtures by the direct addition of a diazo-transfer reagent to deliver functional click chemistry reagents adds to the toolbox for chemical proteomics, chemical biology, and drug discovery.

Highly selective epoxidation of olefins using vanadium (IV) schiff base- amine-tagged graphene oxide composite

Catalysts are of great importance in the petrochemical industry, so the design and synthesis of heterogeneous catalysts for this purpose is the most important field in catalysts. In this context, 3-aminopropyltriethoxysilane was grafted into graphene oxide via the condensation reaction, and then the amine terminal groups were utilized to produce azomethine (–C = N–) group using the 3-formyl 4-hydroxy benzoic acid compound. The post-modification approach was used to fabricate the novel vanadium (IV) Schiff-base complex. Characterization was carried out to achieve chemical composition and physical properties such as Raman spectroscopy, FTIR, XRD, XPS, elementary analysis, TGA, FESEM-EDX, AFM, HRTEM, and nitrogen sorption have been performed to realize the grafting vanadium (IV) Schiff base complex on GO. The value of the prepared material as a catalyst was examined for the epoxidation of cyclohexene, cyclooctene, 1-octene, styrene, allyl bromide, and ally alcohol, and styrene. Also, the impact of pH, time, temperature, and catalyst dose was observed. The results showed that the novel catalyst for the epoxidation reaction showed distinct catalytic efficiency. Besides, owing to the strong interaction between the V(IV) ions and chelating moieties in GO, the novel catalyst showed outstanding recycling effectiveness after being used for six subsequent cycles.

Robust phase transfer, 3D-assembly and SERS application of multi-shaped gold nanoparticles

A robust, fast and versatile phase transfer approach to the transfer of large hydrophilic multi-shaped gold nanoparticles from aqueous to organic phase was systematically investigated. The procedure uses the amphiphilic surfactant bis-(amidoethylcarbamoylethyl) octadecylamine (C18N3), which consists of a long alkane chain to provide hydrophobic properties and terminal amine groups for hydrophilic properties. Furthermore, the 3D-assembly behavior, plasmonic properties and surface-enhanced Raman scattering properties of the hydrophobic multi-shaped gold nanoparticles derived from the phase transfer method on the surface of mercapto-silica colloidal spheres were systematically investigate. The surfaces of mercapto-silica spheres immobilize gold nanoparticles through strong coordination interactions between gold cations and thiol groups and allow the direct assembly of large multi-shaped nanoparticles on supporting colloidal spheres. The size of the gold nanoparticles used in both 3D-assembly and phase transfer is much larger (as large as 55 nm) than any known reports to date. This assembly strategy will provide the research community with a highly versatile, configurable, and reproducible process for the preparation of various structures and great flexibility in incorporating multiple nanoparticle components.

Conformations of poly(propylene imine) dendrimers in an ionic liquid at different pH.

The conformational behavior of poly(propylene imine) (PPI) dendrimers at three different solution pH is studied in an ionic liquid (IL) solvent, 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), through molecular dynamics (MD) simulations. The size, shape, density distribution, structure factor, and the scattering intensity are evaluated to probe the conformational transition of dendrimers as a function of pH. The results of the radial atomic and terminal amine group density distribution at low pH indicate a shift in the density towards the periphery of the dendrimers due to the electrostatic repulsion between the charged tertiary amine groups within the dendrimers. The [BMIM] cations are not encapsulated within dendrimers and predominantly reside near the periphery. The extensive back-folding of the outer branches due to the electrostatic repulsion between the solvent cations and the peripheral charged amine groups at neutral and low pH results in a dense compact structure in [BMIM]Cl as compared to that in water, as evident from the results of the structure factor and scattering intensity. The structural analysis in terms of the fractal dimension reveals that the lower generation dendrimers exhibit conformational transition as a function of pH, while the higher generations exhibit a highly compact structure at all solution pH. However, PPI dendrimers at low pH exhibit more free volume as compared to that at high pH, which may be utilized to accommodate specific guest molecules.

Coordination properties of diethylenetriamine in relation to zinc phthalocyanine

The coordination properties of diethylenetriamine (DETA) as a ligand containing three donor nitrogen atoms, two terminal primary amino groups and one secondary central amino group, with respect to divalent zinc ion in ZnPc were examined. The ZnPcDETA complex in the powder form was obtained by the solvothermal reaction of ZnPc with DETA. Recrystallization of the crude product from 3,4-lutidine yields non-centrosymmetric monoclinic solvated crystals (ZnPcDETA)3·3,4-lut (1) with the space group of Cc. As show the X-ray single crystal analysis in ZnPcDETA complex, the DETA coordinates via terminal amine group to the divalent zinc ion of a planar ZnPc molecule in axial position. Interaction of the N atom of DETA containing a lone electron pair with divalent zinc ion of ZnPc and the formation of the Zn-N coordination bond leads to deviation of the Zn from the N4-isoindole plane of Pc by ~ 0.5 Å toward the N-atom of the axial DETA ligand as well as to saucer-shaped distortion of the Pc macrocycle. Arrangement of ZnPcDETA molecules in the 3,4-lutidine solvate crystal with the composition of (ZnPcDETA)3·(3,4-lutidine) - (1) is determined by the van der Waals forces and by the weak NH⋯N hydrogen bonds. The lack of the π⋯π interaction between the phthalocyaninate(2-) macrocycles in the crystals (1) is clearly evidenced by the Hirshfeld surface analysis, and increases significantly their solubility in most common solvents, even in water, when comparing to the parent ZnPc pigment with limited solubility in solvents and insoluble in water. This feature together with the strong absorption in the therapeutic window within the 600–900 nm makes it a potentially good photosensitizer. DFT calculations performed for the ZnPc-derivatives with DETA, coordinated via terminal or central amine group of DETA as well as for the bridged complex (through the terminal amino groups of the DETA ligand of two ZnPc molecules) show the possibility to obtain all three of these complexes. UV–Vis absorption spectra ZnPcDETA complex (1) in solutions as well as the diffuse reflectance spectroscopy (DSR) supported by the TD-DFT calculations were used for the characterization of the spectroscopic properties. SHG efficiency of 1 is ~10% in relation to that of KDP.

Effective enhancement of Cu ions adsorption on porous polyurea adsorbent by carboxylic modification of its terminal amine groups

The pollution by metal ions has been a key issue in environmental protection. Amine-rich porous polyurea (PPU), prepared by a simple one-step precipitation copolymerization of diisocyanate and diamine, is highly selective for Cu2+ adsorption, but associated with a poor reusability. We report here a chemically modified PPU by simply turning the amine groups of PPU to aminoacetic carboxyls. The results indicate that this carboxylation is an easy and effective pathway to polymer adsorbent, with high performance for Cu2+ adsorption and reusability superior to most of the reported adsorbents. Cu2+ adsorption capacity on PPU-M, i.e. PPU after carboxylation, increased to 2.84 mmol/g, an increase by 22% in comparison with PPU. The chemical modification process was optimized. The porosity and morphology of PPU-M were characterized using N2 adsorption, mercury intrusion, and scanning electron microscopy. The high Cu2+ adsorption was interpreted through a complex coordination mechanism of Cu2+ based on XPS analysis. The high performance of reusability of PPU-M, thanks to enhanced desorption of 99.5% or more of the adsorbed Cu2+ after each recycled use, was also interpreted based on the stability constants of acid-base equilibrium of amine and carboxyl towards Cu2+ and protons. Adsorption kinetics modelling demonstrated this adsorption followed the pseudo-second-order model. The adsorption analysis by isothermal adsorption showed this adsorption was well fitted by Freundlich equation and in good agreement with the suggested adsorption mechanism.

Linear Sulfur–Nylon Composites: Structure, Morphology, and Antibacterial Activity

Stabilization of sulfur in its linear form is highly challenging but recently developed inverse vulcanization method succeeded by reacting polysulfur terminals groups with organic cross-linkers. In present work, linear sulfur chains were stabilized in nylon matrix by forming amine-polysulfur complex. Composites were prepared by coextruding nylon with various amount of sulfur (2.5 to 30 wt %) under inert gas environment. Polysulfur chains produced under extrusion condition reacts with terminal amine groups of nylon in molten state and form polysulfur-amine complex. The color of these composites change from translucent to dark brown; which is due to formation of sulfur-amide complex based on FTIR spectroscopy. Furthermore the presence of NH3+ and sulfur anion peaks in XPS spectra confirms the formation of this complex. Disappearance of sulfur crystalline peak and absence of sulfur melt transition in XRD and DSC respectively suggests the conversion of crystalline sulfur into randomly arranged amorphous polys...

In situ synthesis of dendrimer-encapsulated palladium(0) nanoparticles as catalysts for hydrogen production from the methanolysis of ammonia borane

Addressed herein is the in situ synthesis of a PAMAM dendrimer-encapsulated palladium(0) NPs (Pd(0)/Dnd) during the methanolysis of ammonia borane (AB) and the catalytic performance of the yielded Pd(0)/Dnd nanocatalysts in hydrogen production from the methanolysis of AB under ambient conditions. A two-step procedure that includes the impregnation of Pd(II) ions via their coordination to –NH2 groups of the dendrimer and then reduction of Pd(II) ions into the dendrimer-encapsulated Pd(0) NPs by AB during the methanolysis reaction was followed for the synthesis of Pd(0)/Dnd nanocatalysts. However, apart from the existing reports on the synthesis of dendrimer-encapsulated metal NPs, the present study includes for the first time the examination of effect of generation size (G4-G6), core type (ethylene diamine (E) or Jeffamine (P)) and terminal groups (-NH2, –COOH and –OH) of a PAMAM dendrimer on the stability, particle size, morphology and catalytic activity of metal NPs. After finding the optimum Pd(0)/Dnd catalysts considering all these effects, a detailed kinetic study comprising the effect of catalyst and AB concentrations as well as temperature was conducted by monitoring the hydrogen production from the methanolysis of AB. The best catalytic activity in the methanolysis of AB was obtained by using a PAMAM dendrimer with generation G6, amine terminal groups and Jeffamine core (P6.NH2) encapsulated Pd(0) NPs, providing the highest initial turnover frequency (TOF) of 55.8 mol H2.mol Pd−1.min−1 and apparent activation energy (Eaapp) of 48 ± 3 kJ.mol−1 at room temperature.

Aggregation Induced Emission Switching Based Ultrasensitive Ratiometric Detection of Biogenic Diamines Using a Perylenediimide-Based Smart Fluoroprobe.

In recent years, the widely explored phenomenon "aggregation-induced emission (AIE)" has played a crucial role in the development of luminescent materials for light-emitting applications. In the same direction, the contribution of its sister concept "AIE switching" has been impressive. In comparison, the application of this concept in the field of biosensing or bioimaging is still in its infancy. Therefore, to shed light into the sensing of bioanalytes, we have developed a new perylenediimide (PDI)-based small fluorescent probe, benzoannulated PDI (Bp(Im)2MA), that selectively detects diamines and biogenic amines (BAs) in solution via an "AIE-switching" phenomenon. The synthesized probe containing the bay-annulated anhydride moiety exhibits strong cyan emission in solution. In the mechanism, we have shown that the terminal free amine group of BAs readily reacts with a highly reactive anhydride moiety, which opens the cyclic anhydride moiety. In the open conformation, the free amine group along with a carboxylate group modulates the polarity of the system strikingly. Because of this induced polarity, the monomer of Bp(Im)2MA-BAs conjugate aggregated in solution, thereby exhibiting a significant change in emission property in solution. This method may also be called a very simple and straightforward "naked eye" detection of BAs in solution, with a nanomolar detection limit. A detailed spectroscopic and microscopic investigation demonstrated the existence of the aggregated state. As the reporter dye also emits strongly in the solid state (yellowish orange), it therefore instantly made vapor-phase detection of BAs feasible. Finally, this vapor-phase detection of BAs by the probe was applied very effectively in the determination of spoilage of raw fish.

Surface modification of polyester fabric using plasma-dendrimer for robust immobilization of glucose oxidase enzyme

Robust immobilization of glucose oxidase (GOx) enzyme was achieved on poly(ethylene terephthalate) nonwoven fabric (PN) after integration of favourable surface functional groups through plasma treatments [atmospheric pressure-AP or cold remote plasma-CRP (N2 + O2)] and/or chemical grafting of hyperbranched dendrimers [poly-(ethylene glycol)-OH or poly-(amidoamine)]. Absorption, stability, catalytic behavior of immobilized enzymes and reusability of resultant fibrous bio-catalysts were comparatively studied. Full characterization of PN before and after respective modifications was carried out by various analytical, instrumental and arithmetic techniques. Results showed that modified polyester having amine terminal functional groups pledged better surface property providing up to 31% enzyme loading, and 81% active immobilized enzymes. The activity of the enzyme was measured in terms of interaction aptitude of GOx in a given time to produce hydrogen peroxide using colorimetric assay. The immobilized GOx retained 50% of its original activity after being reused six (06) times and exhibited improved stability compared with the free enzyme in relation to temperature. The reaction kinetics, loading efficiency, leaching, and reusability analysis of enzyme allowed drawing a parallel to the type of organic moiety integrated during GOx immobilization. In addition, resultant fibrous bio-catalysts showed substantial antibacterial activity against pathogenic bacteria strains (Staphylococcus epidermidis and Escherichia coli) in the presence of oxygen and glucose. These results are of great importance because they provide proof-of-concept for robust immobilization of enzymes on surface-modified fibrous polyester fabric for potential bio-industrial applications.

Nanotechnology for Biosensing Applications

Nanomaterials, notable for their extremely small feature size (normally in the range of 1 - 100 nm), exhibit new chemical, physical and electronic properties that are different from those of bulk materials. Nanomaterials research is expected to present new possibilities for the development in many areas including energy, manufacturing, space exploration, medicineand medical devices, chemical analysis, and environmental monitoring. Nanotechnology has drawn much interest recently in the field of biomedical applications. Gold Nanoparticle (AuNP) and Magnetic Nanoparticle (MNP) are the two that have been studied most extensively due to its unique properties. For biomedical applications, AuNP is ideal for targets due to its low reactivity, high chemical stability, and biocompatibility, as well as its affinity for binding to amine (-NH2) or thiol (-SH) terminal groups of organic molecules.Magnetic nanoparticles (MNPs) have been receiving increasing attention because of its great potentials in separation. This talk will give an overview of biosensor researches that are taking place at the microfluidics and bionanotechnology lab at WPI. A system of adenosine/its aptamer that is tagged by Au NPs was used to construct a SPR sensor to detect adenosine. They also explored the ability of aptamer-Au NPs conjugates in increasing the sensitivity of SPR for the detection of large biomolecules. They further investigated the application of SPR spectroscopy for fast, ultrasensitive and in situ detection of the MNPs-enriched biomolecules. They have successfully developed an amplification technique using MNPs for enhanced SPR bioassay, for both small molecule detection and immunoassay. Clostridium difficileis a frequent cause of infectious colitis, usually occurring as a complication of antibiotic therapy, in elderly hospitalized patients. The diagnosis of C. difficileinfection still remains a challenge. Searching for a selective and specific technique for determination of its level in biological samples is crucial for regular clinical tests. The current diagnostic modalities mainly consist of the detection of the C. difficileorganisms and of their toxins in fecal samples. However, these methods are often time consuming and require sophisticated equipment. With recent advances in nanotechnology, various nanoparticles in different structures, shapes and composites provide good potential for their application in diagnostics and therapy. Nowadays, electrochemical biosensors based on nanoparticles have attracted extensive interest for sensing the formation of antigen–antibody, because of their fast and precise response, high sensitivity and simple pretreatment procedures. Herein, we developed an electrochemical sensor with gold nanoparticles labeled antibody as the amplifying probe for detecting clostridium difficiletoxins. Initially capture antibody was immobilized on gold electrode using conventional amine coupling chemistry. After clostridium difficiletoxins were attached on the capture antibody, gold nanoparticle labeled detect antibody as the amplifying probe was used to optimize the immunosensing performance by a sandwich immunoassay. In order to evaluate the electrochemical characteristics of modified electrode, cyclic voltammetry (CV) data were collected for each step. Compared with the traditional method, our method can be operated very simply and rapidly, thus it may possess great potential for clinical applications in the future.

Mechanistic Study on the Antibacterial Activity of Self-Assembled Poly(aryl ether)-Based Amphiphilic Dendrimers

The increased threat of bacterial resistance against conventional antibiotics has warranted the need for development of membrane targeting antibacterial agents. Several self-assembled cationic amphiphiles with different supramolecular structures have been reported in recent years for potent antibacterial activity with increased specificity. In this study, we describe the self-assembly and antibacterial activity of four lower generation poly(aryl ether)-based amphiphilic dendrimers (AD-1, AD-2, AD-3, and AD-4) containing terminal amine (PAMAM-based), ester, and hydrazide functional groups with varied hydrophobicity. Among the four dendrimers under study, the amine-terminated dendrimer (AD-1) displayed potent antibacterial activity. The ratio of surface cationic charge to hydrophobicity had a significant effect on the antibacterial activity, where AD-3 dendrimer with increased surface cationic charges exhibited a higher minimum inhibitory concentration (MIC) than AD-1. AD-2 (ester terminated) and AD-4 (hydrazide terminated) dendrimers did not show any bactericidal activity. The amphiphilic dendrimer-bacteria interactions, further validated by binding studies, also showed significant changes in bacterial morphology, effective membrane permeation, and depolarization by AD-1 in comparison with AD-3. Molecular dynamics simulations of AD-1 and AD-3 on bacterial membrane patches further corroborated the experimental findings. The structural conformation of AD-1 dendrimer facilitated increased membrane interaction compared to AD-3 dendrimer. AD-1 also displayed selectivity to bacterial membranes over fibroblast cells (4× MIC), corroborating the significance of an optimal hydrophobicity for potent antibacterial activity with no cytotoxicity. The self-assembled (poly(aryl ether)-PAMAM-based) dendrimer (AD-1) also exhibited potent antibacterial activity in comparison with conventional higher generation dendrimers, establishing the implication of self-assembly for bactericidal activity. Moreover, the detailed mechanistic study reveals that optimal tuning of the hydrophobicity of amphiphilic dendrimers plays a crucial role in membrane disruption of bacteria. We believe that this study will provide valuable insights into the design strategies of amphiphilic dendrimers as antibacterial agents for efficient membrane disruption.

A novel immunosensing platform for serotonin detection in complex real samples based on graphene oxide and chitosan

A novel, simple and versatile nanocomposite platform based on graphene-oxide/chitosan modified screen printed electrode was optimized and used for the development of an immunosensor for the sensitive and highly selective electrochemical detection of serotonin. Graphene oxide has been used for providing carboxylic groups which form covalent bonds with the terminal amine groups from the antibody units, thus ensuring the immobilization of the biocomponent at the electrode surface. The presence of chitosan is necessary to ensure the stability of the nanomaterial film deposited on the electrode’ surface during the modification steps. The platform development protocol was optimized throughout the study by using electrochemical methods (electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry) as well as scanning electron microscopy. The following steps, namely immobilization of the antibody, blocking of the active free sites from graphene template with bovine serum albumin and testing of the immunosensor after immobilization of the analyte molecules at the surface, were optimized based on the differential pulse voltammetry tests following the signal obtained for the electrochemical oxidation of serotonin. The newly customized sensor was found to have a detection range from 10 nM to 100 μM and a limit of detection of 3.2 nM, being used for serotonin detection from human serum, saliva, artificial tears and urine samples as well as in the presence of different interferences, when good recovery rates were obtained.

Preparation of PVDF/Hyperbranched-Nano-Palygorskite Composite Membrane for Efficient Removal of Heavy Metal Ions.

In this work, three kinds of hyperbranched polyamidoamine-palygorskite (PAMAM-Pal) were designed and synthesized by grafting the first generation polyamidoamine (G1.0 PAMAM), G2.0 PAMAM and G3.0 PAMAM onto Pal surfaces, respectively. Then, these PAMAM-Pals were used as additives to prepare polyvinylidene fluoride (PVDF)/hyperbranched polyamidoamine-palygorskite bicomponent composite membranes. The structures of the composite membranes were characterized by Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TEM), X-ray photoelectron spectroscopy (XPS), field-emission scanning electronmicroscopy (SEM), atomic force microscope (AFM) and Thermogravimetric analysis (TGA). The adsorption properties of composite membranes to heavy metal ions was studied, and the results found that the maximum adsorption capacities for Cu(II), Ni(II) and Cd(II) could reach 155.19 mg/g, 124.28 mg/g and 125.55 mg/g, respectively, for the PVDF/G3.0 PAMAM-Pal membrane, while only 23.70 mg/g, 17.74 mg/g and 14.87 mg/g could be obtained for unmodified membranes in the same conditions. The high adsorption capacity can be ascribed to the large number of amine-terminated groups, amide groups and carbonyl groups of the composite membrane. The above results indicated that the prepared composite membrane has a high adsorption capacity for heavy metal ions removal in water treatment.

Anatase TiO₂-Decorated Graphitic Carbon Nitride for Photocatalytic Conversion of Carbon Dioxide.

Three types of graphitic carbon nitride (gCN) nanosheets were derived from direct thermal condensation of urea, melamine, and dicyandiamide, respectively. As the sample (uCN) synthesized from urea exhibited porous morphology and highest surface area among other gCN, anatase TiO2 nanoparticles were then in-situ deposited on uCN via solvothermal process without further calcination. The resultant Ti/uCN_x samples remained with higher surface area and exhibited visible-light activity. The derived band structure of each sample also confirmed its ability to photoreduce CO2. XPS results revealed surface compositions of each sample. Those functional groups governed adsorption of reactant, interfacial interaction, electron transfer rate, and consequently influenced the yield of products. Carbon monoxide and methanol were detected from LED-lamp illuminated samples under appropriate moisture content. Samples with higher ratio of terminal amine groups produced more CO. The presence of hydroxyl groups promoted the initial conversion of methanol. The obtained Ti/uCN_0.5 and Ti/uCN_1.5 samples exhibited better quantum efficiency toward CO2 conversion and demonstrated stability to consistently produce CO under cycling photoreaction.