Homogeneous Aqueous Medium Research Articles

Photo-induced electron transfer between carbon dots and menadione in non-ionic micelles: A triplet states study with magnetic field

Compared to homogeneous surroundings, the kinetics of ultrafast photo-induced processes gets perturbed in self-assemblies. Herein, we attempt to unveil the photophysical alterations in highly luminescent carbon dots (CDs) with menadione (MQ-Vitamin K3), in homogeneous aqueous medium and nonionic Brij-35 self-assemblies. With a series of steady-state and time-resolved studies, we report photoinduced electron transfer between the CDs and MQ for Brij-35. Host-guest-like encapsulation in micelles can severely deter the diffusion dynamics of the transient intermediates. With an external magnetic field, we trace an enhancement in the radical products with controlled diffusion and spin dynamics for Brij-35 than the aqueous surrounding.

Catalytic cyclohexane oxidation to KA oil using novel hydrosoluble copper(I) complexes bearing aminophosphine ligands: Water as a selectivity promoter

Reacting the alkylated 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane (PTA), namely (PTA-CH2-C6H4-p-COOH)Br (1) or (PTA-CH2-C6H3-p-OH-m-CHO)Cl (2), with CuBr, CuI or [Cu(CH3CN)4]BF4, under mild conditions using different stoichiometric ratios resulted in the formation of the new water soluble copper complexes [CuBr2(PTA-CH2-C6H4-p-COOH)2]X (X = Br {3a}, I {3b} or BF4 {3c}), [CuBr(PTA-CH2-C6H4-p-COOH)3]Br3 (4) and [CuCl2(PTA-CH2-C6H3-p-OH-m-CHO)2]X (X = I {5a} or Cl {5b}). The compounds were characterized using multinuclear NMR, FTIR, ESI-MS and elemental analysis. The molecular structure of the neutral form of 3 was established by single crystal X-ray diffraction. In a homogeneous aqueous medium, the catalytic activity of the hydrophilic complexes was assessed for the cyclohexane oxidation to the KA oil (a mixture of cyclohexanone and cyclohexanol). The selectivity towards cyclohexanone is controlled by water, increasing with the H2O amount, and becoming higher than that of cyclohexanol for the 25–75% range of water in the solvent composition. Complex 5a exhibited the highest catalytic activity, achieving up to 21% conversion after 4 h at 50 °C using 0.5 mol% of the catalyst. Utilizing a similar loading of 5a, under microwave irradiation, afforded 18% of yield after 1.5 h at 70 °C.

Synthesis and Characterization of a Novel Composite Edible Film Based on Hydroxypropyl Methyl Cellulose Grafted with Gelatin

A novel composite edible film was synthesized by grafting gelatin chain onto hydroxypropyl methyl cellulose (HPMC) in the presence of glycerol (used as a plasticizer) using a solution polymerization technique. The reaction was carried out in homogeneous aqueous medium. Thermal properties, chemical structure, crystallinity, surface morphology, and mechanical and hydrophilic performance changes of HPMC caused by the addition of gelatin were investigated by differential scanning calorimetry, thermogravimetric, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, universal testing machine and water contact angle. The results shows that HPMC and gelatin are miscible and the hydrophobic property of the blending film can be enhanced with the introduction of the gelatin. Moreover, the HPMC/gelatin blend films are flexible, and exhibit excellent compatibility, good mechanical properties and also thermal stability, and could be promising candidates for food packaging materials.

UVB light influence on the laccase enzyme catalytic activity in reverse micelles and in homogeneous aqueous medium.

Laccase is a versatile enzyme widely used for the oxidation of environmental contaminants and exhibits great potential in many others applications; however, it undergoes photo-degradation when irradiated with UVB light. The photo-stability of this biomolecule can be improved by immobilization in different encapsulation media and reverse micelles have been employed with this purpose. The laccase activity using syringaldazine as substrate has been studied in the absence and in the presence of reverse micelles of 0.15M of sodium 1,4-bis (2-ethylhexyl) sulfosuccinate (AOT) in isooctane at W0 ([H2O]/[AOT]) = 30, before and after irradiation of the enzyme with UVB light. The kinetic parameters, i.e., Michaelis-Menten constant (KM), catalytic constant (kCAT), and catalytic efficiency (kCAT/KM), were determined by spectroscopic measurements in the micellar system and in homogeneous aqueous medium. The distribution of the substrate in two pseudo-phases (micelle and organic solvent) was taking into account inthe kinetic parameters' determinations. The results obtained indicate that the nano-aggregate system confers a solubilization media in the water core of the micelle, both for the enzyme and the substrate, in which the catalytic function of the enzyme is preserved. On the other hand, in homogeneous aqueous medium kCAT/KM value, it is reduced by ~50% after UVB irradiation of the enzyme, while in micellar medium, less than 10% of the activity was affected. This mean that the enzyme achieves a considerably photo-protection when it is irradiated with UVB light in reverse micelles as compared with the homogeneous aqueous medium. This phenomenon can be mainly due to the confinement of the biomolecule inside the micelle. Physical properties of the nano-environment could affect photochemical reactions.

Ionic thermoresponsive fluorescent polymers for detecting countercharged surfactants without phase separation

Thermoresponsive polymers containing ionic and fluorescent groups were designed and synthesized for use as fluorescent probes to sense ionic surfactants without phase separation. The synthesized ionic thermoresponsive fluorescent polymers interact with countercharged surfactants, resulting in increases in their fluorescence intensities, even at temperatures lower than their phase-transition temperatures. The observed increases in the fluorescence intensities are attributable to the incorporation of fluorophores within the soluble aggregates formed by the polymers and ionic surfactants at temperatures lower than the phase-transition temperatures. The synergistic effects of the hydrophobic and ionic interactions between the two moieties lead to the formation of soluble aggregates, which enhance the fluorescence of the fluorophores bound to the polymers. The fluorescence intensities of cationic and anionic fluorescent polymer probes were found to be linearly dependent on the concentrations of sodium dodecyl sulfate (SDS) and zephilamine, respectively, at the 10−5 mol/L level. Moreover, the concentration of SDS, an anionic surfactant used commonly in detergents, as determined using the cationic fluorescent probe was in keeping with that determined by the conventional methylene blue method. Thus, it was confirmed that the synthesized thermoresponsive fluorescent polymers with ionic groups can function as probes for countercharged ionic surfactants in homogeneous aqueous media without any phase-separation processes, which require hazardous organic solvents.

Tunable Conductance of MoS2 and WS2 Quantum Dots by Electron Transfer with Redox-Active Quinone.

Due to their uniqueness in tunable photophysics, transition metal dichalcogenide (TMD) based quantum dots (QDs) have emerged as the next-generation quantum materials for technology-based semiconductor applications. This demands frontline research on the rational synthesis of the TMD QDs with controlled shape, size, nature of charge migration at the interface, and their easy integration in optoelectronic devices. In this article, with a controlled solution-processed synthesis of MoS2 and WS2 QDs, we demonstrate the disparity in their structural, optical, and electrical characteristics in bulk and confinement. With a series of steady-state and time-resolved spectroscopic measurements in different media, we explore the uncommon photophysics of MoS2 and WS2 QDs such as excitation-dependent photoluminescence and assess their excited state charge transfer kinetics with a redox-active biomolecule, menadione (MQ). In comparison to the homogeneous aqueous medium, photoinduced charge transfer between the QDs and MQ becomes more plausible in encapsulated cetyltrimethylammonium bromide (CTAB) micelles. Current sensing atomic force microscopy (CS-AFM) measurements at a single molecular level reveal that the facilitated charge transfer of QDs with MQ strongly correlates with an enhancement in their charge transport behavior. An increase in charge transport further depends on the density of states of the QDs directing a change in Schottky emission to Fowler-Nordheim (FN) type of tunneling across the metal-QD-metal junction. The selective response of the TMD QDs while in proximity to external molecules can be used to design advanced optoelectronic devices and applications involving rectifiers and tunnel diodes for future quantum technology.

Synthesis of a Novel Series of Cu(I) Complexes Bearing Alkylated 1,3,5-Triaza-7-phosphaadamantane as Homogeneous and Carbon-Supported Catalysts for the Synthesis of 1- and 2-Substituted-1,2,3-triazoles.

The N-alkylation of 1,3,5-triaza-7-phosphaadamantane (PTA) with ortho-, meta- and para-substituted nitrobenzyl bromide under mild conditions afforded three hydrophilic PTA ammonium salts, which were used to obtain a new set of seven water-soluble copper(I) complexes. The new compounds were fully characterized and their catalytic activity was investigated for the low power microwave assisted one-pot azide–alkyne cycloaddition reaction in homogeneous aqueous medium to obtain disubstituted 1,2,3-triazoles. The most active catalysts were immobilized on activated carbon (AC), multi-walled carbon nanotubes (CNT), as well as surface functionalized AC and CNT, with the most efficient support being the CNT treated with nitric acid and NaOH. In the presence of the immobilized catalyst, several 1,4-disubstituted-1,2,3-triazoles were obtained from the reaction of terminal alkynes, organic halides and sodium azide in moderate yields up to 80%. Furthermore, the catalyzed reaction of terminal alkynes, formaldehyde and sodium azide afforded 2-hydroxymethyl-2H-1,2,3-triazoles in high yields up to 99%. The immobilized catalyst can be recovered and recycled through simple workup steps and reused up to five consecutive cycles without a marked loss in activity. The described catalytic systems proceed with a broad substrate scope, under microwave irradiation in aqueous medium and according to “click rules”.

Effect of pH on Homogeneous Photodegradation of Eosin Y Dye

Eosin Y (EY), an anionic dye, also known as Eosin Yellow or Bromoeosin, or Acid red 27 is an industrial dye. The residual dye, discharged as one of the components of the untreated effluent, into the adjacent surface and causes water pollution. Photodegradation of EY was investigated at 29 oC in homogeneous aqueous media using UVA light (≈400 – 320 nm) in acetate buffer solution as a function of pH (3.08-7.08). At higher pH, there was no effect of this light on the dye in the solution. Results show that the initial rate of photocolorization increased with decreasing the pH of the dye solution.

Photochemically induced cyclic morphological dynamics via degradation of autonomously produced, self-assembled polymer vesicles

Autonomous and out-of-equilibrium vesicles synthesised from small molecules in a homogeneous aqueous medium are an emerging class of dynamically self-assembled systems with considerable potential for engineering natural life mimics. Here we report on the physico-chemical mechanism behind a dynamic morphological evolution process through which self-assembled polymeric structures autonomously booted from a homogeneous mixture, evolve from micelles to giant vesicles accompanied by periodic growth and implosion cycles when exposed to oxygen under light irradiation. The system however formed nano-objects or gelation under poor oxygen conditions or when heated. We determined the cause to be photoinduced chemical degradation within hydrated polymer cores inducing osmotic water influx and the subsequent morphological dynamics. The process also led to an increase in the population of polymeric objects through system self-replication. This study offers a new path toward the design of chemically self-assembled systems and their potential application in autonomous material artificial simulation of living systems.

Detection of Tetraplex DNA and Detection by Tetraplex DNA.

G-quardruplex (G4) DNA forms through the gathering together of G-quartet planes formed with four guanine (G) bases. G4 DNA stabilizes with potassium ions (K+) by coordination with the G-quartet center. Fluorometric G4 DNA carrying the fluorescence resonance energy transfer (FRET) chromophore pair at both termini has been applied for the fluorometric sensing or imaging of K+ under a homogeneous aqueous medium. This system has realized non-conventional K+ selectivity over the sodium ion (Na+). The selectivity of the fluorescence G4 was converted to Na+ from K+ with a modification of its sequence. On the other hand, G4 DNA detection has been achieved in terms of cancer diagnosis because of a strong relationship of G4 DNA and cancer development. Ligands interacting with G4 are expected to have anti-cancer potential. In addition, fluorometric G4 ligands have been developed and tested as tools for the dynamic monitoring of G4 in living cells. Moreover, fluorometric G4 DNA has been utilized to evaluate the G4 ligand performance.

Eco-friendly synthesis of an alkyl chitosan derivative

Chitosan (CH) was N-alkylated via Schiff base formation and further reduced via sodium borohydride. The reaction was carried out at room temperature, in a homogeneous aqueous medium, using as a source of alkyl group an essential oil (Eucalyptus staigeriana) containing an unsaturated aldehyde (3,7-dimethylocta-2,6-dienal). Derivatives were characterized by Infrared Spectroscopy, proton and carbon Nuclear Magnetic Resonance, XRD, particle size distribution and zeta potential. Chitosan hydrophobization evidence was given by FTIR as new bands at 2929 cm−1 due to methyl groups, along with the presence of strong band at 1580 cm−1 owing to N substitution. Moreover, carbon and proton NMR corroborated the insertion of methyl groups in chitosan backbone. The degree of substitution was found to be in the range 0.69–1.44. X-ray diffractograms revealed that the insertion of alkyl substituents in chitosan backbone led to a less crystalline material. Data from antibacterial activity revealed that chitosan and derivatives were effective against Gram-positive bacteria, whereby derivatives exhibited greater inhibitory effect than CH. Derivatives are likely candidates for use as carriers for active principles of interest of food, pharmacy and medicine.

Reversible redox activity of {Mo72Fe30} nano-polyoxometalate cluster in three crystalline forms

The {Mo72Fe30} cluster is the basic unit of three crystalline materials rhombohedral [Mo72Fe30O252(CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91]·150H2O (1), orthorhombic [H4Mo72Fe30O254(CH3COO)10{Mo2O7(H2O)}{H2Mo2O8(H2O)}3(H2O)87]·80H2O (2) and host guest system [HxPMo12O40 ⊂ H4MoVI72FeIII30(CH3COO)15-O254(H2O)98]·ca.60H2O (3). The {Mo72Fe30} Keplerate cluster in all the three crystalline compounds actively undergoes reversible redox cycles without any significant structural disintegration. Hydrogen peroxide/molecular oxygen and ascorbic acid/sodium dithionite are found to be suitable oxidizing and reducing agents, respectively. Compound 1 (reasonably soluble in water) shows reversible electron transfer reactions in a homogeneous aqueous medium, whereas, compounds 2 and 3 (having extended structures, thereby insoluble in water) undergo reversible electron transfer reactions in heterogeneous manner in solid-liquid interface reactions.

Chemo‐ and Magnetotaxis of Self‐Propelled Light‐Emitting Chemo‐electronic Swimmers

AbstractMiniaturized autonomous chemo‐electronic swimmers, based on the coupling of spontaneous oxidation and reduction reactions at the two poles of light‐emitting diodes (LEDs), are presented as chemotactic and magnetotactic devices. In homogeneous aqueous media, random motion caused by a bubble‐induced propulsion mechanism is observed. However, in an inhomogeneous environment, the self‐propelled devices exhibit positive chemotactic behavior, propelling themselves along a pH or ionic strength gradient (∇pH and ∇I, respectively) in order to reach a thermodynamically higher active state. In addition, the intrinsic permanent magnetic moment of the LED allows self‐orientation in the terrestrial magnetic field or following other external magnetic perturbations, which enables a directional motion control coupled with light emission. The interplay between chemotaxis and magnetotaxis allows fine‐tuning of the dynamic behavior of these swimmers.

Chemo- and Magnetotaxis of Self-Propelled Light-Emitting Chemo-electronic Swimmers.

Miniaturized autonomous chemo-electronic swimmers, based on the coupling of spontaneous oxidation and reduction reactions at the two poles of light-emitting diodes (LEDs), are presented as chemotactic and magnetotactic devices. In homogeneous aqueous media, random motion caused by a bubble-induced propulsion mechanism is observed. However, in an inhomogeneous environment, the self-propelled devices exhibit positive chemotactic behavior, propelling themselves along a pH or ionic strength gradient (∇pH and ∇I, respectively) in order to reach a thermodynamically higher active state. In addition, the intrinsic permanent magnetic moment of the LED allows self-orientation in the terrestrial magnetic field or following other external magnetic perturbations, which enables a directional motion control coupled with light emission. The interplay between chemotaxis and magnetotaxis allows fine-tuning of the dynamic behavior of these swimmers.

Mobility of pectin methylesterase in pectin/cellulose gels is enhanced by the presence of cellulose and by its catalytic capacity

The pectin methylesterase action is usually studied in a homogeneous aqueous medium in the presence of a large excess of soluble substrate and water. However in the cell wall, the water content is much lower, the substrate is cross-linked with itself or with other polymers, and the enzyme has to diffuse through the solid matrix before catalysing the linkage breakdown. As plant primary cell walls can be considered as cellulose-reinforced hydrogels, this study investigated the diffusion of a fungal pectin methylesterase in pectin/cellulose gels used as cell wall-mimicking matrix to understand the impact of this matrix and its (micro) structure on the enzyme’s diffusion within it. The enzyme mobility was followed by synchrotron microscopy thanks to its auto-fluorescence after deep-UV excitation. Time-lapse imaging and quantification of intensity signal by image analysis revealed that the diffusion of the enzyme was impacted by at least two criteria: (i) only the active enzyme was able to diffuse, showing that the mobility was related to the catalytic ability, and (ii) the diffusion was improved by the presence of cellulose in the gel.

Sustainable Modification of Carboxymethyl Cellulose by Passerini Three-Component Reaction and Subsequent Adsorption onto Cellulosic Substrates

The present work describes the chemical modification of carboxymethyl cellulose (CMC), a widely diffused commercial cellulose ether, by means of the Passerini three-component reaction (P-3CR). The reaction, performed in homogeneous aqueous medium, was proven to be effective at combining the carboxyl groups of CMC with different aldehydes and isocyanides, leading to the formation of a wide library of Passerini-modified CMC derivatives, in a simple and environmentally friendly one-pot process. The derivatized CMC products were thoroughly characterized to confirm the modification and determine the degrees of substitution (DS). The impact of experimental parameters (i.e., reaction T, time and pH, amount of employed reagents) and structure of the reactants (different aldehydes and isocyanides) on the reaction outcome was also discussed to explore the potential of this original approach for polysaccharide modification. Finally, the adsorption ability of selected CMC samples onto a model cellulosic surface was characterized by means of quartz crystal microbalance with energy dissipation monitoring (QCM-D). The analysis confirmed the successful adsorption of the Passerini-modified CMC derivatives and highlighted a positive effect of the derivatization on the amount of adsorbed polymer. Not only does the developed strategy appear as a mild and sustainable route for CMC functionalization, but also the promising adsorption ability of the functionalized derivatives opens the path toward the straightforward modification of surface properties of cellulosic substrates.

Control of the pore wall thickness and thermal stability in low-cost bimodal porous silicas

A new hierarchical bimodal mesoporous silica, labelled as UVM-12 (acronym of University of Valencia Materials), has been prepared by using a solution of sodium silicate as low-cost silicon source. The final self-assembling between cationic micelles of CTAB and anionic inorganic Si-based oligomers occurs in a homogeneous aqueous medium. The reaction is carried out from low-sized building blocks through a bottom-up approach. The UVM-12 solids combine two mesopore systems according to N2 adsorption–desorption isotherms, what is corroborated by TEM micrographs and XRD patterns. This material has been inorganically modified by incorporation of Al or Ti (M-UVM-12, M = Al, Ti) without alteration of the parent architecture. Moreover, we have carried out a study of the UVM-12 thermal stability by means of N2 adsorption–desorption and XRD. For comparison, in this analysis we have included other two nanoparticulated bimodal silicas that share structure and morphology with UVM-12 (UVM-7 and UVM-10). Both the mesopore wall thickness and the condensation degree (measured through NMR) in the silica framework of each type of material successfully correlates with the thermal stability of their samples.

Quenching of Luminol Fluorescence at Nano-Bio Interface: Towards the Development of an Efficient Energy Transfer System.

Surface modified colloidal gold (Au) and silver (Ag) nanoparticles (NPs) were used as efficient quenchers of luminol (LH2) fluorescence either in homogeneous aqueous medium or its noncovalent assembly with bovine serum albumin (BSA). The mechanism as well as the extent of fluorescence quenching was found to be strongly dependent on the nature of the nanoparticles. While simple static type fluorescence quenching mechanism was perceived with AuNP, a more complex protocol involving quenching sphere model was envisaged for AgNP quenching. Nevertheless, the magnitude of Stern-Volmer (SV) quenching constant (KSV ~ 108-1010M-1) was calculated to be ca. 104 times more for surface quoted NPs in comparison with BSA-NP bioconjugates system. On the other hand, a highly efficient (E ≈ 95%) energy transfer (ET) process was predicted for LH2 captured in the hydrophobic assembly with BSA in presence of AgNP as an acceptor. The ET efficiency is critically dependent on the concentration of BSA and nicely correlated with the extent of NP surface coverage. However, fluorescence quenching on AuNP surface is relatively less responsive towards protein concentration, primarily due to the difference in surface activity as well as the mode of interaction of the protein with NPs. Graphical Abstract Energy transfer from excited luminol to metal nanoparticles is strongly modulated in presence of serum albumins.

Investigation of Backward Reflection from Aqueous Media at Arbitrary Grazing Angles

A model of backward reflection is presented which is distinguished by the fact that it takes account of excitation of counterpropagating waves in bounding media. For the case of a homogeneous aqueous medium, it is shown that the proposed model describes distinguishing features of the angular dependence of the backward reflection coefficients for all angles of incidence of the waves on the air–water interface. Characteristic regions of the angular dependence, associated with different mechanisms of formation of the backward reflection, are elucidated.

Homogeneous synthesis of Ag nanoparticles-doped water-soluble cellulose acetate for versatile applications

We report a facile and efficient approach for synthesis of well-dispersed and stable silver nanoparticles (Ag NPs) using water-soluble cellulose acetate (CA) as both reductant and stabilizer. Partially substituted CA with highly active hydroxyl groups and excellent water-solubility is able to reduce silver ions in homogeneous aqueous medium effectively. The synthesized Ag NPs were characterized by UV⿿vis spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and energy dispersive X-ray spectroscope analysis. The as-prepared Ag NPs were well-dispersed, showing a surface plasmon resonance peak at 426nm. The resulted Ag NPs@CA nanohybrids exhibit high catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4. Meanwhile, the nanohybrids are also effective in inhibiting the growth of bacterial. This environmentally friendly method promotes the use of renewable natural resources to prepare a variety of inorganic-organic materials for catalysis, antibacterial, sensors and other applications.