Cationic Ammonium Groups Research Articles

Donor-acceptor star-shaped conjugated macroelectrolytes: synthesis, light-harvesting properties, and self-assembly-induced Förster resonance energy transfer.

A novel series of donor-acceptor star-shaped conjugated macroelectrolytes (CMEs), denoted as 4FTs, including anionic carboxylic acid sodium groups (4FNaT), neutral diethanolamine groups (4FNOHT), and cationic ammonium groups (4FNBrT), were designed, synthesized, and explored as an excellent platform to investigate the impact of various polar pendent groups on self-assembly behaviors. The resulting CMEs with donor-acceptor star-shaped architectures exhibited distinct light-harvesting properties. The interactions between 4FTs and TrNBr, a star-shaped monodisperse CME grafted with cationic quaternary ammonium side chains, were investigated in H2O and CH3OH using steady-state, time-resolved fluorescence, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Highly favored energy transfer has been proven by the excellent spectral overlap between TrNBr fluorescence and 4FTs absorptions which can be tuned by adjusting the pendent polar groups and solvents. It is suggested that self-assembled structures are formed between TrNBr and 4FNaT, while there is no obvious change for TrNBr/4FNOHT and TrNBr/4FNBrT in both H2O and CH3OH at low concentrations (<10(-6) M). This result is confirmed by the change of the TrNBr and 4FTs fluorescence properties and the time-resolved fluorescence data. The overall results manifest that at low concentrations the self-assembly between TrNBr and 4FTs is dominated by the electrostatic interactions. This study suggests that the functionalization of pendent polar groups of star-shaped CMEs has proven to be effective to modulate the self-assembly behaviors in dilute solutions and thus provide a strategy to further manage the optoelectronic properties.

Synthesis and optical properties of pH-responsive conjugated polyampholytes

Conjugated polyampholytes (CPAs) containing both positive and negative ionic groups in their side-chains were designed and synthesized. Two types of random copolymers were prepared by the incorporation of fluorene, phenylene and 2,1,3-benzothiadiazole (BT) moieties in the main chain. Both quaternary ammonium bromide and carboxylic acid functionalities were introduced successfully in the side-chain through sequential protection, quaternization and deprotection reactions. The resulting ionic polymers were soluble in water and their optical characteristics were examined by changing pH. The fluorescence resonance energy transfer (FRET)-sensitized BT emission of the polymers increased with increasing solution pH. Under basic conditions, deprotonation of the carboxylic acid groups induced intra- and/or interchain aggregation via electrostatic complexation between the cationic ammonium and anionic carboxylate groups. The FRET ratio between the green and blue emissions showed a linear relationship with solution pH. This new type of water-soluble fluorescent bioassays and bioimaging applications through bioconjugation with a targeting moiety.

Chitosan finishing nonwoven textiles loaded with silver and iodide for antibacterial wound dressing applications

Polyethylene terephtalate (PET) and Polypropylene (PP) textiles are widely used in biomedical application such as wound dressings and implants. The aim of this work was to develop an antibacterial chitosan (CHT) coating activated by silver or by iodine. Chitosan was immobilized onto PET and PP supports using citric acid (CTR) as a crosslinking agent through a pad-dry-cure textile finishing process. Interestingly, depending on the CHT/CTR molar ratio, two different systems were obtained: rich in cationic ammonium groups when the CTR concentration was 1%w/v, and rich in anionic carboxylate groups when the CTR concentration was 10%w/v. As a consequence, such samples could be selectively loaded with iodine and silver nitrate, respectively.Both types of coatings were analyzed using SEM and FTIR, their sorption capacities were evaluated toward iodide/iodate anions (I−/IO3−) and the silver cations (Ag+) were evaluated using elemental analysis. Finally, in vitro evaluations were carried out to evaluate the cytocompatibility on the epithelial cell line. The silver loaded textile reported a stronger antibacterial effect against E.coli (5 log10 reduction) than toward S. aureus (3 log10) while the antibacterial effect of the iodide loaded textiles was limited to 1 log10 to 2 log10 on both strains.

A gemini quaternary ammonium poly (ether ether ketone) anion-exchange membrane for alkaline fuel cell: design, synthesis, and properties.

To reconcile the tradeoff between conductivity and dimensional stability in AEMs, a novel Gemini quaternary ammonium poly (ether ether ketone) (GQ-PEEK) membrane was designed and successfully synthesized by a green three-step procedure that included polycondensation, bromination, and quaternization. Gemini quaternary ammonium cation groups attached to the anti-swelling PEEK backbone improved the ionic conductivity of the membranes while undergoing only moderate swelling. The grafting degree (GD) of the GQ-PEEK significantly affected the properties of the membranes, including their ion-exchange capacity, water uptake, swelling, and ionic conductivity. Our GQ-PEEK membranes exhibited less swelling (≤ 40 % at 25-70 °C, GD 67 %) and greater ionic conductivity (44.8 mS cm(-1) at 75 °C, GD 67 %) compared with single quaternary ammonium poly (ether ether ketone). Enhanced fuel cell performance was achieved when the GQ-PEEK membranes were incorporated into H2 /O2 single cells.

Stable synthetic mono-substituted cationic bacteriochlorins mediate selective broad-spectrum photoinactivation of drug-resistant pathogens at nanomolar concentrations

Three stable synthetic mono-substituted cationic bacteriochlorins (BC37, BC38 and BC39) were recently reported to show exceptional activity (low nanomolar) in mediating photodynamic killing of human cancer cells after a 24h incubation upon excitation with near-infrared light (730nm). The presence of cationic quaternary ammonium groups in each compound suggested likely activity as antimicrobial photosensitizers. Herein this hypothesis was tested against a panel of pathogenic microorganisms that have all recently drawn attention due to increased drug-resistance (Gram-positive bacteria, Staphylococcus aureus and Enterococcus faecalis; Gram-negative bacteria, Escherichia coli and Acinetobacter baumannii; and fungal yeasts, Candida albicans and Cryptococcus neoformans). All three bacteriochlorins were highly effective against both Gram-positive species (>6 logs of eradication at ⩽200nM and 10J/cm2). The dicationic bacteriochlorin (BC38) was best against the Gram-negative species (>6 logs at 1–2μM) whereas the lipophilic monocationic bacteriochlorin (BC39) was best against the fungi (>6 logs at 1μM). The bacteriochlorins produced substantial singlet oxygen (and apparently less Type-1 reactive-oxygen species such as hydroxyl radical) as judged by activation of fluorescent probes and comparison with 1H-phenalen-1-one-2-sulfonic acid; the order of activity was BC37>BC38>BC39. A short incubation time (30min) resulted in selectivity for microbial cells over HeLa human cells. The highly active photodynamic inactivation of microbial cells may stem from the amphiphilic and cationic features of the bacteriochlorins.

Functionalized fullerenes in photodynamic therapy.

Since the discovery of C60 fullerene in 1985, scientists have been searching for biomedical applications of this most fascinating of molecules. The unique photophysical and photochemical properties of C60 suggested that the molecule would function well as a photosensitizer in photodynamic therapy (PDT). PDT uses the combination of non-toxic dyes and harmless visible light to produce reactive oxygen species that kill unwanted cells. However the extreme insolubility and hydrophobicity of pristine CO60, mandated that the cage be functionalized with chemical groups that provided water solubility and biological targeting ability. It has been found that cationic quaternary ammonium groups provide both these features, and this review covers work on the use of cationic fullerenes to mediate destruction of cancer cells and pathogenic microorganisms in vitro and describes the treatment of tumors and microbial infections in mouse models. The design, synthesis, and use of simple pyrrolidinium salts, more complex decacationic chains, and light-harvesting antennae that can be attached to C60, C70 and C84 cages are covered. In the case of bacterial wound infections mice can be saved from certain death by fullerene-mediated PDT.

Preparation of cationic functional starch/Na+‐MMT composite and its application for effective removal of three hazardous metal anionic ions with different valence

The design of cost‐effective biopolymers‐based adsorbents is of particular interest. In our work, a cationic functional starch (CFS)/Na+‐montmorillonite (Na+‐MMT) composite was prepared by combining 5 wt% modified starch containing quaternary ammonium cationic functional groups and 0.5% w/v Na+‐MMT dispersed solution together. Its microstructure was characterized by FTIR and XRD. Removal of three metal anionic ions with different valence like: , , and by the composite was compared. Adsorption equilibrium, kinetics, and thermodynamic models were also investigated. The adsorption capacity was very high and followed the sequence of &gt; &gt; , which could be demonstrated with strong electrostatic interaction between active cationic functional groups and metal anionic ions. The Langmuir isotherm gave satisfying fits to equilibrium data of ions indicating monolayer adsorption to monovalent anionic ion, while the Freundlich equation fitting equilibrium data of and ions better predicated multilayer adsorption to polyvalent anionic ion. There was a better matching accuracy between the experimental data and the pseudo second order model. The removal percentages for the three ions of , , by the composite were 96.84, 94, and 89.84%, respectively.

Water-soluble copolymeric materials: switchable NIR two-photon fluorescence imaging agents for living cancer cells.

A simple one-pot multi-component ROMP of hydrophilic, spiropyran (SP) and tert-butyloxycarbonyl-protected (Boc-protected) amino-functionalized norbornenes was developed, and a series of water-soluble copolymeric materials were provided. The photochromic SP moiety endows the copolymers the properties of switchable fluorescence imaging with alternating near-IR (NIR) two-photon and visible single-photon excitations; thereby the copolymers can serve as a promising NIR two-photon fluorescent probe for living cancer cells. The cationic ammonium group enhances the cell transporting capability of the copolymers as well. The present strategy of one-pot ROMP also makes polynorbornene a modular and flexible scaffold in designing and synthesizing specifically biocompatible polymers with applications in imaging, diagnosis and therapy.

Comparative study of encapsulation of vitamins with native and modified soy protein

Microencapsulation of hydrophobic (α-tocopherol) and hydrophilic (ascorbic acid) vitamins by native (non-modified) and modified soy protein isolate (SPI) was carried out using a spray-drying technique. Proteins' functional properties were modified by acylation and cationization reactions in aqueous alkaline media. The results obtained demonstrated that SPI modification resulted in decreased emulsion droplet size and viscosity. All preparations with ascorbic acid (AA) had lower viscosity and microparticle size than those with α-tocopherol (T). Moreover, grafting of fatty acid chains to SPI by acylation improved its amphiphilic character and affinity with hydrophobic substances. Thus, the microencapsulation efficiency of T was increased from 79.7% to 94.8% and the microencapsulation efficiency of AA was reduced from 91.8% to 57.3% compared to native SPI. Conversely, attachment of quaternary ammonium cationic groups to proteinic chains by cationization, increased SPI solubility and favored the AA microencapsulation. This study illustrated that an appropriate modification of SPI can improve the microencapsulation efficiency of suitable active cores.

Oxidative cleavage of DNA by pentamethine carbocyanine dyes irradiated with long-wavelength visible light

Here we report the synthesis of seven symmetrical carbocyanine dyes in which two nitrogen-substituted benz[e]indolium rings are joined by a pentamethine bridge that is meso-substituted with chlorine or bromine versus hydrogen. The heteroatom of benz[e]indolium is modified with a phenylpropyl, methyl, or cationic quaternary ammonium group. In reactions containing micro molar concentrations of halogenated dye, irradiation at 575, 588, 623, or 700nm produces good photocleavage of plasmid DNA. UV–visible spectra show that the carbocyanines are in their H-aggregated and monomeric forms. Scavenger experiments point to the involvement of singlet oxygen and hydroxyl radicals in DNA photocleavage.

Structural characteristics and flocculation properties of amphoteric starch

Starch ampholytes (AmS) – cationic starch succinates – with the degree of substitution according to cationic groups of 0.29 or 0.36 and the degree of substitution according to anionic groups from 0.11 to 0.34 were prepared by succinylation of precationized starch. FT-IR spectra confirmed the incorporation of carboxylic groups into the backbone of cationic starch. Scanning electron microscopy was used for evaluation of the granular structure and surface morphology of modified polysaccharides. The decrease in accessibility of cationic quaternary ammonium groups in AmS was detected by means of polyelectrolyte titration. Colloidal dispersions of AmS were verified in the flocculation of kaolin suspensions and the sedimentation of wastewater sludge. Their flocculation performance was studied in connection with ξ-potential measurements and compared with that of cationic starch. The main advantage of AmS application is broadening of the flocculation window. The mechanism of flocculation by starch ampholytes has been proposed.

Poly(phenylene oxide) copolymer anion exchange membranes

Poly(phenylene oxide) block and random copolymers are synthesized by oxidative polymerization of 2,6‐dimethylphenol and 2,6‐diphenylphenol for potential alkaline exchange membrane application. The copolymers are functionalized on the methyl substituted repeat units through a two‐step process to produce pendent quaternary ammonium cationic groups. The amount of quaternary ammonium cations and the ion exchange capacity are quantified through titration measurements. Ionic conductivity of the copolymer membranes is measured by electrochemical impedance spectroscopy. Block copolymers show increased bromide conductivity at higher ion exchange capacities compared with the random copolymer analogs. The bromide conductivity for a block copolymer film with an ion exchange capacity of 1.27 mequiv/g reaches 26 mS/cm at 90 °C and 95% relative humidity. The hydroxide conductivity for the same film was measured to be 84 mS/cm at 80 °C and 95% relative humidity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1770–1778, 2013

Supramolecular cooperative-assembly of polyelectrolyte films

In this report we investigate and compare the characteristics of the cooperative-assembly of double-stranded DNA and random coil poly(styrene sulfonate) mixed with didodecyldimethylammonium bromide (DDAB). Film formation is attributed primarily to electrostatic interactions between anionic phosphate or sulfonate groups (DNA or PSS) and cationic ammonium groups of DDAB. It appears that the elasticity and morphology of such films are dependent on the length and the structure of polymers. Ethidium bromide (a nucleic acid stain and intercalating agent) was employed to probe the structure of polymers based on the photoluminescence response of this dye.

Exploring the interesting interaction between graphene oxide, Aliquat-336 (a room temperature ionic liquid) and chromium(vi) for wastewater treatment

We report an interesting interaction between exfoliated graphene oxide (EGO), ionic liquid (IL) Aliquat-336 and hexavalent chromium. Graphene oxide was impregnated with the ionic liquid and the interaction primarily involves electrostatic affinity between the quaternary ammonium cation and surface hydroxyl groups in EGO. The IL-EGO combination functions as an effective adsorbent for hexavalent chromium. The IL-EGO adsorbent acts as a good host in welcoming the incoming guest, hydrochromate anion and several interesting interactions such as cation–π, electrostatic as well as anion–π could be conceptualized in this process. The adsorbent features are ably supported by various physico-chemical characterization techniques and the effect of various analytical parameters affecting the adsorption is examined in detail. A high Langmuir adsorption capacity of 285.71 mg g−1 is augmented by the thermodynamically favourable adsorption process. Kinetic studies confirm the pseudo second order model and furthermore, the process could be upgraded by column study to a sample volume of 1200 mL. Effective regeneration of the adsorbent could be accomplished with ammonium hydroxide and the potential of this novel adsorbent material has been examined in the total removal of chromium from a tannery effluent sample.

Gas-Phase Reactivity of Carboxylic Acid Functional Groups with Carbodiimides

Gas-phase modification of carboxylic acid functionalities is performed via ion/ion reactions with carbodiimide reagents [N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide (CMC) and [3-(3-Ethylcarbodiimide-1-yl)propyl]trimethylaminium (ECPT)]. Gas-phase ion/ion covalent chemistry requires the formation of a long-lived complex. In this instance, the complex is stabilized by an electrostatic interaction between the fixed charge quaternary ammonium group of the carbodiimide reagent cation and the analyte dianion. Subsequent activation results in characteristic loss of an isocyanate derivative from one side of the carbodiimide functionality, a signature for this covalent chemistry. The resulting amide bond is formed on the analyte at the site of the original carboxylic acid. Reactions involving analytes that do not contain available carboxylic acid groups (e.g., they have been converted to sodium salts) or reagents that do not have the carbodiimide functionality do not undergo a covalent reaction. This chemistry is demonstrated using PAMAM generation 0.5 dendrimer, ethylenediaminetetraacetic acid (EDTA), and the model peptide DGAILDGAILD. This work demonstrates the selective gas-phase covalent modification of carboxylic acid functionalities.

Degradation of Imidazolium- and Quaternary Ammonium-Functionalized Poly(fluorenyl ether ketone sulfone) Anion Exchange Membranes

Imidazolium and quaternary ammonium-functionalized poly(fluorenyl ether ketone sulfone)s were synthesized successfully with the same degree of cationic functionalization and identical polymer backbones for a comparative study of anion exchange membranes (AEMs) for solid-state alkaline membrane fuel cells (AMFCs). Both anion exchange membranes were synthesized using a new methyl-containing monomer that avoided the use of toxic chloromethylation reagents. The polymer chemical structures were confirmed by ¹H NMR and FTIR. The derived AEMs were fully characterized by water uptake, anion conductivity, stability under aqueous basic conditions, and thermal stability. Interestingly, both the cationic groups and the polymer backbone were found to be degraded in 1 M NaOH solution at 60 °C over 48 h as measured by changes of ion exchange capacity and intrinsic viscosity. Imidazolium-functionalized poly(fluorenyl ether ketone sulfone)s had similar aqueous alkaline stability to quaternary ammonium-functionalized materials at 60 °C but much lower stability at 80 °C. This work demonstrates that quaternary ammonium and imidazolium cationic groups are not stable on poly(arylene ether sulfone) backbones under relatively mild conditions. Additionally, the poly(arylene ether sulfone) backbone, which is one of the most common polymers used in ion exchange membrane applications, is not stable in the types of molecular configurations analyzed.

Perturbing Peptide Cation-Radical Electronic States by Thioxoamide Groups: Formation, Dissociations, and Energetics of Thioxopeptide Cation-Radicals

Thioxodipeptides Gly-thio-Lys (GtK), Ala-thio-Lys (AtK), and Ala-thio-Arg (AtR) in which the amide group has been modified to a thioxoamide were made into dications by electrospray ionization and converted to cation-radicals, (GtK + 2H)(+•), (AtK + 2H)(+•), and (AtR + 2H)(+•), by electron transfer dissociation (ETD) tandem mass spectrometry using fluoranthene anion-radical as an electron donor. The common and dominant dissociation of these cation-radicals was the loss of a hydrogen atom. The dissociation products were characterized by collision-induced dissociation (CID) multistage tandem mass spectrometry up to CID-MS(5). The ground electronic states of several (GtK + 2H)(+•), (AtK + 2H)(+•), and (AtR + 2H)(+•) conformers were explored by extensive ab initio and density functional theory calculations of the potential energy surface. In silico electron transfer to the precursor dications, (GtK + 2H)(2+), (AtK + 2H)(2+), and (AtR + 2H)(2+), formed zwitterionic intermediates containing thioenol anion-radical and ammonium cation groups that were local energy minima on the potential energy surface of the ground electronic state. The zwitterions underwent facile isomerization by N-terminal ammonium proton migration to the thioenol anion-radical group forming aminothioketyl intermediates. Combined potential energy mapping and RRKM calculations of dissociation rate constants identified N-C(α) bond cleavages as the most favorable dissociation pathways, in a stark contrast to the experimental results. This discrepancy is interpreted as being due to the population upon electron transfer of low-lying excited electronic states that promote loss of hydrogen atoms. For (GtK + 2H)(+•), these excited states were characterized by time-dependent density functional theory as A-C states that had large components of Rydberg-like 3s molecular orbitals at the N-terminal and lysine ammonium groups that are conducive to hydrogen atom loss.

Cationic polyvinylamine binding to anionic microgels yields kinetically controlled structures

Polyvinylamine (PVAm) binding (absorption and adsorption) to carboxylated microgels gave colloidally stable, cationic microgels that can be centrifuged, washed, freeze dried, and redispersed in water with no loss in colloidal stability. Because both PVAm and the carboxylated microgels are pH sensitive, changes in microgel swelling and electrophoretic mobility in response to pH change can be positive or negative depending upon pH and the PVAm content of the microgels. For a given PVAm molecular weight, the steady-state saturated mass fraction of bound PVAm in the microgels varied by a factor of four in our experiments. We proposed that the PVAm content at saturation was controlled by the relative rates of the initial attachment of PVAm chains versus the rate of attached chain spreading on and into the microgel structure. This explanation was further supported by a series of quartz crystal microbalance measurements.Finally, PVAm binding to two types of PNIPAM microgels shows general features recently reported for other polyelectrolyte types. Specifically: (1) for surface localized anionic charges on the microgels, the mass fraction of bound PVAm increased with PVAm molecular weight and vice versa; (2) in virtually all conditions, the quantity of adsorbed cationic ammonium groups was much greater than the carboxylate content of the microgel; and (3) sodium chloride additions lowered the mass fraction of bound PVAm.

Photochemical Modulation of DNA Conformation by Organic Dications

A group of azobenzene derivatives containing two quaternary ammonium groups with various intercharge distances between them was synthesised and used to control photochemically the conformation of genomic DNA by switching the distance between cationic ammonium groups in the dications. It was found that isomerisation of either dication from the trans form to cis resulted in an increase in the dication's efficiency for DNA compaction; this is associated with a decrease in intercharge distance between ammonium groups and leads to a better match of the binder's cationic groups to adjacent phosphate groups of DNA. Ammonium dications have several important advantages over the photosensitive surfactant type of diazobenzene reported earlier: they can be used at significantly lower (>100-fold) concentrations than photosensitive surfactants, and DNA conformation control can be performed over a broader concentration range of dications. The influence of intercharge distance in photosensitive dications on photo-induced DNA binding discrimination is discussed, and the molecular mechanism is proposed.

Uptake and Translocation Mechanisms of Cationic Amino Derivatives Functionalized on Pristine C60 by Lipid Membranes: A Molecular Dynamics Simulation Study

Bioactive molecules, cationic peptides among them, are nowadays well-recognized in modern pharmacology for their drug potential. However, they usually suffer from poor translocation across cell membranes, and specific drug carriers should be designed to circumvent this problem. In the present study, the uptake mechanism of fullerene bearing cationic ammonium groups by membranes modeled as lipid bilayers is investigated using extensive molecular dynamics simulations and free-energy calculations. Three main results issued from this work can be drawn. First, the fullerene core appears to be a good drug vector since it greatly enhances the uptake of the cationic groups by the membrane. Second, we show that the amino derivatives should be deprotonated at the lipid headgroup level in order to fully translocate the membrane by passive diffusion. Finally, the fullerenes bearing too many cationic groups display mostly a hydrophilic character; thus, the lipophilic fullerene core is not anymore effective as an insertion enhancer. Therefore, the lipid bilayer appears to be very selective with respect to the amount of amino groups conjugated with C(60).