Antimicrobial properties of benzalkonium chloride derived polymerizable deep eutectic solvent.

Benzalkonium chloride (BC) is a quaternary ammonium antimicrobial agent used in a variety of applications. In this work, BC was prepared into deep eutectic solvent (DES) with acrylic acid (AA) or methacrylic acid (MA). Within the newly prepared DES, BC is responsible for antimicrobial properties, while AA and MA are responsible for polymerization. Three types of microorganisms, E. coli (gram-negative bacilli), S. aureus (gram-positive cocci) and C. albicans (fungi), were assessed for antimicrobial properties through agar diffusion test. DES viscosity measurements and polymerizations were also conducted to assist the antimicrobial performance analysis. From this study, stronger antimicrobial effectiveness of BC-AA DES towards S. aureus and C. albicans was observed, while smaller inhibition zone widths were obtained for BC-AA DES polymer compared to BC-AA DES monomer which may due to the limited active component transportation after polymerization. When changing AA to MA, increased structural complexity and decreased linearity may limit the molecule movement thus reduce the inhibition zone width, which could be proved by the calculated activation energy results. Accurately determined eutectic ratio of DES is recommended to get optimized drug release control. This work offers a new sight for preparation of antimicrobial materials with stronger effectiveness and limited release.

Bacterial Cellulose Ionogels as Chemosensory Supports.

To fully leverage the advantages of ionic liquids for many applications, it is necessary to immobilize or encapsulate the fluids within an inert, robust, quasi-solid-state format that does not disrupt their many desirable, inherent features. The formation of ionogels represents a promising approach; however, many earlier approaches suffer from solvent/matrix incompatibility, optical opacity, embrittlement, matrix-limited thermal stability, and/or inadequate ionic liquid loading. We offer a solution to these limitations by demonstrating a straightforward and effective strategy toward flexible and durable ionogels comprising bacterial cellulose supports hosting in excess of 99% ionic liquid by total weight. Termed bacterial cellulose ionogels (BCIGs), these gels are prepared using a facile solvent-exchange process equally amenable to water-miscible and water-immiscible ionic liquids. A suite of characterization tools were used to study the preliminary (thermo)physical and structural properties of BCIGs, including no-deuterium nuclear magnetic resonance, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction. Our analyses reveal that the weblike structure and high crystallinity of the host bacterial cellulose microfibrils are retained within the BCIG. Notably, not only can BCIGs be tailored in terms of shape, thickness, and choice of ionic liquid, they can also be designed to host virtually any desired active, functional species, including fluorescent probes, nanoparticles (e.g., quantum dots, carbon nanotubes), and gas-capture reagents. In this paper, we also present results for fluorescent designer BCIG chemosensor films responsive to ammonia or hydrogen sulfide vapors on the basis of incorporating selective fluorogenic probes within the ionogels. Additionally, a thermometric BCIG hosting the excimer-forming fluorophore 1,3-bis(1-pyrenyl)propane was devised which exhibited a ratiometric (two-color) fluorescence output that responded precisely to changes in local temperature. The ionogel approach introduced here is simple and has broad generality, offering intriguing potential in (bio)analytical sensing, catalysis, membrane separations, electrochemistry, energy storage devices, and flexible electronics and displays.

Incorporation of antibacterial agent derived deep eutectic solvent into an active dental composite.

OBJECTIVE: To incorporate an antibacterial agent derived deep eutectic solvent (DES) into a dental resin composite, and investigate the resulting mechanical properties and antibacterial effects. METHOD: The DES was derived from benzalkonium chloride (BC) and acrylic acid (AA) and was incorporated into the dental resin composite through rapid mixing. A three-point bending test was employed to measure the flexural strength of the composite. An agar diffusion test was used to investigate antibacterial activity. Artificial (accelerated) aging was undertaken by immersing the composites in buffer solutions at an elevated temperature for up to 4 weeks. UV-vis spectrophotometry and NMR analysis were conducted to study BC release from the composite. Finally, the biocompatibility of the composite materials was evaluated using osteoblast cell culture for 7 days. Results were compared to those of a control composite which contained no BC. RESULT: The DES-incorporated composite (DES-C) displayed higher flexural strength than a similar BC-incorporated composite BC (BC-C) for the same level of BC. The inclusion of BC conferred antibacterial activity to both BC-containing composites, although BC-C produced larger inhibition halos than DES-C at the same loading of BC. Control composites which contained no BC showed negligible antibacterial activity. After artificial aging, the DES-C composite showed better maintenance of the mechanical properties of the control compared with BC-C, although a decrease was observed during the three-point bending test, particularly upon storage at elevated temperatures. No BC release was detected in the aged solutions of DES-C, whereas the BC-C showed a linear increase in BC release with storage time. Significantly, cell viability results indicated that DES-C has better biocompatibility than BC-C. SIGNIFICANCE: The incorporation of a BC-based DES into a dental resin composite provides a new strategy to develop antibacterial dental materials with better biocompatibility and longer effective lifetimes without sacrificing the intrinsic mechanical properties of the composite structure.

Ionic liquid-assisted exfoliation and dispersion: stripping graphene and its two-dimensional layered inorganic counterparts of their inhibitions.

Research on graphene-monolayers of carbon atoms arranged in a honeycomb lattice-is proceeding at a relentless pace as scientists of both experimental and theoretical bents seek to explore and exploit its superlative attributes, including giant intrinsic charge mobility, record-setting thermal conductivity, and high fracture strength and Young's modulus. Of course, fully exploiting the remarkable properties of graphene requires reliable, large-scale production methods which are non-oxidative and introduce minimal defects, criteria not fully satisfied by current approaches. A major advance in this direction is ionic liquid-assisted exfoliation and dispersion of graphite, leading to the isolation of few- and single-layered graphene sheets with yields two orders of magnitude higher than the earlier liquid-assisted exfoliation approaches using surface energy-matched solvents such as N-methyl-2-pyrrolidone (NMP). In this Minireview, we discuss the emerging use of ionic liquids for the practical exfoliation, dispersion, and modification of graphene nanosheets. These developments lay the foundation for strategies seeking to overcome the many challenges faced by current liquid-phase exfoliation approaches. Early computational and experimental results clearly indicate that these same approaches can readily be extended to inorganic graphene analogues (e.g., BN, MoX2 (X = S, Se, Te), WS2, TaSe2, NbSe2, NiTe2, and Bi2Te3) as well.

Protein-templated gold nanoclusters sequestered within sol-gel thin films for the selective and ratiometric luminescence recognition of Hg2+.

Sequestration of bovine serum albumin (BSA)-stabilized gold nanoclusters (AuNCs@BSA) prepared using microwave assistance within sol-gel-derived mesoporous silica films permits the selective and highly sensitive quenchometric detection of aqueous Hg(2+) (limit of detection = 600 pM) with luminescence signal arising from oxidized BSA allowing for an analytically robust and reliable ratiometric detection. Overall, this work highlights a number of important advances, including the highest luminescence quantum yield reported to date for a protein-templated luminescent noble metal nanocluster (13%) made possible using a microwave-mediated synthesis followed by cold incubation. We also demonstrate the clear advantage of exploiting the luminescence signal arising from oxidized BSA as an internal reference to generate selectivity of response to Hg(2+). A careful Stern-Volmer quenching analysis reveals the persistence of two unique quenching sites for AuNCs@BSA entrapped within a sol-gel-derived glass, a minor population of which is unquenchable. Finally, based on these AuNCs@BSA nanosensors, we advise a path forward for paper-based indicator strip detection of heavy metals in aqueous streams, the implementation of which can be performed using the unaided eye, making it a meaningful approach for routine screening and in resource-limited situations.

Ranking solvent interactions and dielectric constants with [Pt(mesBIAN)(tda)]: A cautionary tale for polarity determinations in ionic liquids.

The solvatochromic properties of [Pt(mesBIAN)(tda)] are studied in traditional molecular solvents and ionic liquids and duly compared along established empirical solvent parameter scales. The charge-transfer absorption band of [Pt(mesBIAN)(tda)] is determined to be primarily dependent upon solvent acidity and dipolarity. Notably, ionic liquids do not obey the same well-behaved trend as molecular solvents, highlighting the complexity and domain (nano)segregation inherent to ionic liquids.

Nanosilica-supported polyethoxyamines as low-cost, reversible carbon dioxide sorbents.

Novel hybrid quasi-solid-state sorbents pairing inexpensive CO(2)-reactive polyethoxyamine (Jeffamine®) fluids with an abundantly available silica support have been investigated for carbon capture. The highest performance sorbent was capable of reversibly capturing close to 70 mg of CO(2) per gram of sorbent at 45°C, could be almost fully (~90%) regenerated by simple vacuum swing, and was stable over many sequential capture-release cycles. The new supports can be handled as solventless, free-flowing powders even post-CO(2) capture, obviating the mass flow problems arising from viscous liquid (or solid, gel, or wax) formation frequently attending carbamate formation. Our results have important ramifications for reducing the high costs of thermal regeneration in conventional carbon capture schemes, particularly in comparison with the aqueous monoethanolamine-based system currently favoured industrially. The strategy of uniformly dispersing a functional fluid onto a solid nanosupport in a manner that allows intimate contact with and diffusion of external gaseous species is additionally projected to find value in a range of gas separation and sensing endeavours.

Optically responsive switchable ionic liquid for internally-referenced fluorescence monitoring and visual determination of carbon dioxide.

Modulation in the local viscosity and polarity within a reversible carbamate ionic liquid system forms the basis for the fluorescence excimer-based estimation of CO(2). Inherently self-referencing, the photonic response to CO(2) recognition shows excellent sensitivity and complete reversibility, making possible a striking visual display discernible to the naked eye.

Fluorescent probe studies of polarity and solvation within room temperature ionic liquids: a review.

Ionic liquids display an array of useful and sometimes unconventional, solvent features and have attracted considerable interest in the field of green chemistry for the potential they hold to significantly reduce environmental emissions. Some of these points have a bearing on the chemical reactivity of these systems and have also generated interest in the physical and theoretical aspects of solvation in ionic liquids. This review presents an introduction to the field of ionic liquids, followed by discussion of investigations into the solvation properties of neat ionic liquids or mixed systems including ionic liquids as a major or minor component. The ionic liquid based multicomponent systems discussed are composed of other solvents, other ionic liquids, carbon dioxide, surfactants or surfactant solutions. Although we clearly focus on fluorescence spectroscopy as a tool to illuminate ionic liquid systems, the issues discussed herein are of general relevance to discussions of polarity and solvent effects in ionic liquids. Transient solvation measurements carried out by means of time-resolved fluorescence measurements are particularly powerful for their ability to parameterize the kinetics of the solvation process in ionic liquids and are discussed as well.

Binding of the ionic liquid cation 1-alkyl-3-methylimidazolium to p-tetranitrocalix[4]arene probed by fluorescent indicator displacement.

Acridine orange (AO) was used as a fluorescent probe molecule to study the encapsulation of an alkylimidazolium cation from a water-soluble ionic liquid (IL) within two cavitand species, p-tetranitrocalix[4]arene (1) and calix[4]resorcinarene (2), both in alkaline aqueous media. The addition of IL to the preformed [1·AO] adduct resulted in significantly increased fluorescence due to the expulsion of AO from the inclusion complex to the aqueous phase by competitive recognition of the 1-alkyl-3-methylimidazolium cation ([C(n)mim](+), n = 4 and 6) by 1. Conversely, the fluorescence signal dropped upon the addition of IL to the [2·AO] host-guest complex due to unfavorable binding between [C(n)mim](+) and 2. The formation of these postulated adducts is corroborated using ab initio calculations, which also provide evidence for the location of [bmim](+) at the lower external rim of [2·AO], providing an explanation for the observed luminescence quenching in the latter case. These results point to a number of different paths for exploration, ranging from the fluorescence monitoring of IL contamination in groundwater to the "daisy chaining" of macrocyles toward supramolecular ionic networks. They also broadly encourage the exploration of ILs in host-guest-based optical and mass spectrometric sensory systems.

Computational prediction of ionic liquid 1-octanol/water partition coefficients.

Wet 1-octanol/water partition coefficients (log K(ow)) predicted for imidazolium-based ionic liquids using adaptive bias force-molecular dynamics (ABF-MD) simulations lie in excellent agreement with experimental values. These encouraging results suggest prospects for this computational tool in the a priori prediction of log K(ow) values of ionic liquids broadly with possible screening implications as well (e.g., prediction of CO(2)-philic ionic liquids).

Pronounced hydrogen bonding giving rise to apparent probe hyperpolarity in ionic liquid mixtures with 2,2,2-trifluoroethanol.

The fascinating and attractive features of ionic liquids (ILs) can be considerably expanded by mixing with suitable cosolvents, opening their versatility beyond the pure materials. We show here that mixtures of the IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 2,2,2-trifluoroethanol (TFE) display the intriguing phenomenon of hyperpolarity, examples of which are notably sparse in the literature. From the perspective of the E(T)(N) polarity scale and Kamlet-Taft parameters for hydrogen bond acidity (α) and basicity (ß), the polarity of this mixture exceeds that of either neat component. Fluorescent molecular probes capable of engaging in hydrogen bonds (e.g., 2-(p-toluidino)naphthalene-6-sulfonate, TNS; 6-propionyl-2-(dimethylamino)naphthalene, PRODAN) also exhibit this curious behavior. The choice of IL anion appears to be essential as hyperpolarity is not observed for mixtures of TFE with ILs containing anions other than hexafluorophosphate. The complex solute-solvent and solvent-solvent interactions present in the [bmim][PF6] + TFE mixture were further elucidated using infrared absorbance, dynamic viscometry, and density measurements. These results are discussed in terms of Coulombic interactions, disruption of TFE multimers, formation of hyperanion preference aggregates, and "free" [bmim]⁺. It is our intent that these results open the door for computational exploration of related solvent mixtures while inspiring practical questions, such as whether such systems might offer the potential for stabilization of highly charged transition states or ionic clusters during (nano)synthesis.

Contrasting behavior of classical salts versus ionic liquids toward aqueous phase J-aggregate dissociation of a cyanine dye.

The effect of addition of ionic liquids (ILs) on the aggregation behavior of a cyanine dye, 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC), was investigated. In basic aqueous buffer solutions (pH ≥ 10), TDBC preferably exists in its J-aggregated form. Addition of hydrophilic ILs > 5 wt % is observed to disrupt the TDBC J-aggregates, converting them to monomer form most likely because of the interaction between bulky IL cation and the J-aggregates in a time-dependent fashion. This is evidenced by the observed increase in monomer band absorbance at the expense of the absorbance band due to J-aggregates over time. Inorganic salts at similar molar concentrations do not cause this phenomenon but instead induce TDBC precipitation. At low concentrations (<5 wt %), the added IL acts similarly to the inorganic salts, reducing the overall absorbance of TDBC in the solution most likely due to cation exchange causing TDBC precipitation. Addition of a molecular solvent, ethanol, at 15 wt % results in an initial increase in monomer absorbance, albeit to a much lesser extent than for the corresponding molar fraction of IL, which then decreases over time with recovery of J-aggregate absorbance--quite opposite the time-dependent behavior seen for TDBC in PB at pH 12.0 with >5 wt % IL. The unique and dual behavior of ILs as an additive toward affecting cyanine dye aggregation is demonstrated.

Fluorescence energy transfer efficiency in labeled yeast cytochrome c: a rapid screen for ion biocompatibility in aqueous ionic liquids.

A fluorescence energy transfer "de-quenching" assay was implemented to follow the equilibrium unfolding behaviour of site-specific tetramethylrhodamine-labelled yeast cytochrome c in aqueous ionic liquid solutions; additionally, this approach offers the prospect of naked eye screening for biocompatible ion combinations in hydrated ionic liquids.

Luminescent carbon nanodots: emergent nanolights.

Similar to its popular older cousins the fullerene, the carbon nanotube, and graphene, the latest form of nanocarbon, the carbon nanodot, is inspiring intensive research efforts in its own right. These surface-passivated carbonaceous quantum dots, so-called C-dots, combine several favorable attributes of traditional semiconductor-based quantum dots (namely, size- and wavelength-dependent luminescence emission, resistance to photobleaching, ease of bioconjugation) without incurring the burden of intrinsic toxicity or elemental scarcity and without the need for stringent, intricate, tedious, costly, or inefficient preparation steps. C-dots can be produced inexpensively and on a large scale (frequently using a one-step pathway and potentially from biomass waste-derived sources) by many approaches, ranging from simple candle burning to in situ dehydration reactions to laser ablation methods. In this Review, we summarize recent advances in the synthesis and characterization of C-dots. We also speculate on their future and discuss potential developments for their use in energy conversion/storage, bioimaging, drug delivery, sensors, diagnostics, and composites.

J-aggregation of ionic liquid solutions of meso-tetrakis(4-sulfonatophenyl)porphyrin.

The title porphyrin was dissolved in the hydrophilic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF(4)], and triggered to assemble into J-aggregates by the addition of incremental volumes of water containing various amounts of acid (0.1, 0.2, or 1.0 M HCl). In contrast to recent studies, the current investigation is unique in that it centers on media that contain a predominant ionic liquid component (2.9-5.4 M [bmim][BF(4)]), as opposed to an aqueous electrolyte containing a small fraction of ionic liquid as dissociated solute. Complex aggregation and underlying photophysical behavior are revealed from absorption spectroscopy, steady-state fluorescence, and resonance light scattering studies. Upon addition of aqueous HCl, the efficient formation of H(4)TPPS(2-) J-aggregates from the diprotonated form of meso-tetrakis(4-sulfonatophenyl)porphyrin (H(2)TPPS(4-)) occurs in [bmim][BF(4)]-rich media in a manner highly dependent upon the acidity, TPPS concentration, and solvent composition. The unique features of TPPS aggregation in this ionic liquid were elucidated, including the surprising disassembly of J-aggregates at higher aqueous contents, and our results are described qualitatively in terms of the molecular exciton theory. Finally, the potential of this system for the optical sensing of water at a sensitivity below 0.5 wt% is demonstrated. Overall, our findings accentuate how little is known about functional self-assembly within ionic liquids and suggest a number of avenues for exploring this completely untouched research landscape.

On the behavior of indole-containing species sequestered within reverse micelles at sub-zero temperatures.

We report on the effects of temperature (+30 to -100 degrees C) on the fluorescence from N-acetyl tryptophanamide (NATA) and human serum albumin (HSA) sequestered within Aerosol-OT (AOT) reversed micelles. NATA reports simultaneously from the polar and non-polar side of the reverse micelle interface. As the sample temperature decreases, the relative fraction of NATA molecules associated with the polar side increases. This redistribution process is characterized by DeltaH = -14.8 +/- 0.6 kJ/mol and DeltaS = -54 +/- 2 J/(K mol). The activation energy for thermal quenching (E(a,TQ)) associated with the polar side NATA molecules is 6.7 kJ/mol before the micelles have shed water and 1.0 kJ/mol after water shedding (below approximately -20 degrees C). The time-resolved fluorescence intensity decay for tryptophan-214 in HSA is triple exponential. We suggest that these lifetimes arise from three indole residue conformations in equilibrium. Cooling the sample causes a freezing-in of the least quenched conformer; the other conformers are frozen out. The E(a,TQ) value for the shortest lifetime component is 6 kJ/mol. The E(a,TQ) for the long and intermediate lifetime components are equivalent (approximately 1.5 kJ/mol).

Comparison of dansylated aminopropyl controlled pore glass solvated by molecular and ionic liquids.

We compare how (i) four ionic liquids (ILs) (1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4mim][Tf2N]), 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpy][Tf2N]), and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P(C6)3C14][Tf2N])) and (ii) two conventional molecular liquids (methanol and 1-octanol) solvate/wet luminescent organic moieties that are covalently attached to the surface of silica controlled pore glass (CPG). A series of aminopropyl CPG particles that have been covalently tagged with the solvatochromic fluorescent probe group dansyl were used in this study. The results demonstrate that ILs solvate/wet the silica surface differently in comparison to molecular liquids (MLs). Specifically, when comparing ILs and MLs that appear to solvate the free probe, dansylpropylsulfonamide (DPSA), equally in solution, we find that ILs do not solvate/wet the silica surfaces as well as the corresponding MLs. The cation component in these ILs is the significant factor in how the ILs solvate/wet silica surfaces. Solvation/wetting of surface-bound species at a silica surface depends on the cation size. Chlorosilane end-capping of the surface silanol and amine residues attenuates the cation's affects.

Surface confined ionic liquid as a stationary phase for HPLC.

Trimethoxysilane "ionosilane" derivatives of room temperature ionic liquids based on alkylimidazolium bromides were synthesized for attachment to silica support material. The derivatives 1-methyl-3-(trimethoxysilylpropyl)imidazolium bromide and 1-butyl-3-(trimethoxysilylpropyl)imidazolium bromide were used to modify the surface of 3 microm diameter silica particles to act as the stationary phase for HPLC. The modified particles were characterized by thermogravimetric analysis (TGA) and (13)C and (29)Si NMR spectroscopies. The surface modification procedure rendered particles with a surface coverage of 0.84 micromol m(-2) for the alkylimidazolium bromide. The ionic liquid moiety was predominantly attached to the silica surface through two siloxane bonds of the ionosilane derivative (63%). Columns packed with the modified silica material were tested under HPLC conditions. Preliminary evaluation of the stationary phase for HPLC was performed using aromatic carboxylic acids as model compounds. The separation mechanism appears to involve multiple interactions including ion exchange, hydrophobic interaction, and other electrostatic interactions.