Variation Of Solvent Composition Research Articles

Observing atomically precise nanocluster aggregates in solution by mass photometry.

We report the first mass photometric characterization of nanoaggregates of atomically precise nanoclusters (NCs) in solution. The differently-sized nanoaggregates of silver-gold alloy NCs, [Ag11-xAux(DPPB)5Cl5O2]2+ [x = 1-5 and DPPB = 1,4-bis(diphenylphosphino)butane], formed in solution, were examined by mass photometry (MP) with a protein calibration. In addition, we conducted MP studies of varying solvent composition to understand the structural evolution of nanoaggregates. The masses of nanoaggregates were correlated to structures of 15 to 50 nm diameter observed in cryo-electron microscopy.

Dynamic coassembly of nanodiamonds and block copolymers in organic solvents

Nonaqueous suspensions of nanoparticles have potential value in a wide range of applications, from coatings to environmental remediation. However, organic solvents often lead to nanoparticle agglomeration, and few methods developed to counteract this phenomenon. We present a novel approach to achieve stable nanoparticle suspensions in both nonpolar and polar aprotic solvents. Our method utilizes nanodiamonds (NDs) as a model system, due to the rich nature of their surface chemistry. This technique involves three key steps: (1) ultrasonication of air-oxidized NDs (OXNDs) in dimethylacetamide (DMAc), (2) the introduction of amphiphilic dispersants primarily composed of PVA-b-PMMA block copolymers (BCPs), and (3) exchanging DMAc with organic solvents to promote composite micelle formation, where BCP forms the micelle corona encapsulating OXND as the micelle core. Our method yields stable suspensions with particle sizes strongly influenced by thermokinetic interactions between OXND, BCP, and the solvent. Dynamic light scattering measurements of OXND–PVA-b-PMMA suspensions demonstrate that stabilization in toluene is governed by steric hindrance, while in THF or CHCl3 both electrostatic repulsion and steric hindrance contribute to particle stabilization. Characterization through electron microscopy and AFM reveals the efficacy of our coassembly method for producing uniformly-sized composite micelles. We identify a critical BCP:OXND weight ratio, analogous to the critical micelle concentration in surfactant-stabilized suspensions, crucial for effective particle stabilization. By analyzing the evolution of particle size distribution with varying solvent composition, we propose a dynamic coassembly mechanism between OXND and BCP, wherein OXND particles and encapsulating BCP chains dynamically rearrange to reach an equilibrium structure as the thermodynamic quantities of the surrounding medium change. Furthermore, BCP micellization is shown to play a vital role in preventing OXND aggregation during solvent exchange, resulting in uniformly sized particles. This enhanced understanding of the OXND–BCP coassembly mechanism in organic solvents holds promise for the development of novel functional materials. Our study provides insights into fabricating stable nanoparticle suspensions with diverse applications to coatings, lubricants, drug delivery, nanocomposite materials, biosensing, medical imaging, and environmental remediation.

LCST/UCST transition of acrylate copolymer with cosolvency behaviors in alcohol aqueous solutions

Though the mechanism of temperature-induced lower critical solution temperature (LCST) in water is clear for the classic homopolymer poly(N-isopropylacrylamide) (PNIPAM), the LCST of other homopolymer or copolymer remains to be understood. In this work, a novel random copolymer poly(2-hydroxyethyl-co-methyl acrylate) (P(HEA-co-MA)) was prepared. The LCST of the copolymer P(HEA-co-MA) can vary from 11 °C to 65 °C by adjusting flexibly the ratio of the two monomers, showing a broad tunable range. The experimental results showed that the balance of hydrogen bond bridge formed by P(HEA-co-MA) in water and the hydrophobic interaction between polymers can cause the LCST transition of P(HEA-co-MA). An interesting observation is that the sharp phase transition (cosolvency) of P(HEA-co-MA) exists when a rather small amount of alcohol or water is added in polymer solutions at constant temperatures. Moreover, it was found that the increase of LCST is correlated with the increase of alcohol concentration in the water-rich regime, but the decrease of upper critical solution temperature (UCST) is related to the increase of water concentration in the alcohol-rich regime. This work shed light on the understanding of cosolvency by studying the solution behavior of copolymer P(HEA-co-MA) in mixed solvents, which can be of interest for the design of stimuli-responsive polymer materials by variation in solvent composition.

Photoluminescent neodymium-doped ZnO nanocrystals prepared by laser ablation in solution for NIR-II fluorescence bioimaging

The work reports on the use of laser ablation and post-ablation irradiation techniques for the preparation Nd3+ doped ZnO nanoparticles (NPs). The focus has been made on photoluminescence of Nd-doped ZnO NPs in the second near infrared (NIR-II) spectral window (1000–1700 nm) of the biological transparency. Morphology, phase composition and optical properties of the synthesized NPs were studied by absorption and photoluminescence spectroscopy, X-Ray diffraction (XRD) and transmission (TEM) electron microscopy. Near-infrared luminescence of Nd3+ doped ZnO nanocrystals in the region of 1000–1400 nm was detected both upon excitation from the ground state (800 nm) and upon UV excitation. The latter proves the incorporation of the Nd3+ into ZnO lattice as photoluminescence occurs through the transfer of excitation energy from the ZnO matrix to the Nd3+ ion. The possibility of control over the luminescence properties by a variation of solvent composition and by additional laser irradiation was demonstrated.

Assessment of chimeric antigen receptor T cytotoxicity by droplet microfluidics in vitro.

Chimeric antigen receptor T (CAR-T) cells are cytotoxic T cells engineered to specifically kill cancer cells expressing specific target receptor(s). Prior CAR-T efficacy tests include CAR expression analysis by qPCR or ELISA, in vitro measurement of interferon-γ (IFNγ) or interleukin-2 (IL-2), and xenograft models. However, the in vitro measurements did not reflect CAR-T cytotoxicity, whereas xenograft models are low throughput and costly. Here, we presented a robust in vitro droplet microfluidic assay for CAR-T cytotoxicity assessment. This method not only enabled assessment of CAR-T cytotoxic activity under different fluid viscosity conditions, but also facilitated measurement of CAR-T expansion and dissection of mechanism of action via phenotype analysis in vitro. Furthermore, our data suggested that label-free cytotoxicity analysis is feasible by acquiring data before and after treatment. Hence, this study presented a novel in vitro method for assessment of cellular cytotoxicity that could potentially be applied to any cytotoxicity experiment with varying solvent composition.

Quantification of Synthetic Polyesters from Biodegradable Mulch Films in Soils.

Soil biodegradable mulch films composed of the polyester polybutylene adipate-co-terephthalate (PBAT) are being increasingly used in agriculture. Analytical methods to quantify PBAT in field soils are needed to assess its soil occurrence and fate. Here, we report an analytical method for PBAT in soils that couples Soxhlet extraction or accelerated solvent extraction (ASE) with quantitative protonnuclear magnetic resonance (q-1H NMR) spectroscopy detection. The 1H NMR peak areas of aromatic PBAT protons increased linearly with PBAT concentrations dissolved in deuterated chloroform (CDCl3), demonstrating accurate quantitation of PBAT by q-1H NMR. Spike-recovery experiments involving PBAT addition to model sorbents and soils showed increased PBAT extraction efficiencies into chloroform (CHCl3) with methanol (MeOH) as cosolvent, consistent with MeOH competitively displacing PBAT from H-bond donating sites on mineral surfaces. Systematic variations in solvent composition and temperatures in ASE revealed quantitative PBAT extraction from soil with 90/10 volume % CHCl3/MeOH at 110-120 °C. Both Soxhlet extraction and ASE resulted in the complete recovery of PBAT added to a total of seven agricultural soils covering a range of physicochemical properties, independent of whether PBAT was added to soils dissolved in CHCl3, as film, or as particles. Recovery was also complete for PBAT added to soil in the form of a commercial soil biodegradable mulch film with coextractable polylactic acid (PLA). The presented analytical method enables accurate quantification and biodegradation monitoring of PBAT in agricultural field soils.

Optimization of Solution Condition for an Effective Electrochemical Reduction of N2O

AbstractAn effective electrochemical reduction of nitrous oxide (N2O) is established by controlling solution compositions in this study. N2O was electrochemically reduced varying solvent composition and supporting electrolytes (K2SO4 and Na2SO4) concentrations. The differences in reduction current density and solution resistance were analyzed via linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS), respectively, depending on solution conditions. UV‐Vis spectroscopy was adopted to measure the solubility of N2O. As a result, among the conditions investigated in this study, 300 mM of K2SO4 and aqueous based solution were revealed as an optimum condition for the electrochemical N2O reduction. At 300 mM of K2SO4, the highest current density was obtained due to a high conductance of the electrolyte and a moderate solubility of N2O.

Phenolic Composition, Antimicrobial and Antioxidant Properties of Belgian Apple Wood Extracts

Each year, fruit growers have hundreds of tons of bark and pruning waste. Despite their potential for chemical recycling, residues from this waste are frequently used for applications with low added value. By converting the waste stream into a valuable source, this study emphasizes waste valorisation and engenders re-use strategies for the production of higher value products. The aim of the present work is the optimization of the solvent extraction of phenolic compounds from apple trees, more specifically bark and core wood. Solvent extractions, with a varying solvent composition, are assessed based on the extraction efficiency of the total polyphenols and flavonoids (spectrophotometry). The extracts are further characterized by their antimicrobial properties and antioxidant activities. Bark extracts obtained by a 40 v/v % acetone/ water mixture presented the highest phenolic (22.84 ± 0.56 mg GAE/g DW) and flavonoid (12.16 ± 0.06 mg QC/g DW) content, and antioxidant activity (1.068 ± 0.005 mM FeSO4.7H2O/g DW for the FRAP assay), while the extract also inhibited growth of the gram-positive bacteria Enterococcus faecalis and Staphylococcus aureus by 100 %. The results indicate that warm solvent extraction (WSE) proved to be an efficient way to extract polyphenols with a high reducing ability from bark and core wood of apple trees.

Adhesion and Separation of Nanoparticles on Polymer-Grafted Porous Substrates.

This work explores interactions of functionalized nanoparticles (NP) with polymer brushes (PB) in a binary mixture of good and poor solvents. NP-PB systems are used in multiple applications, and we are particularly interested in the problem of chromatographic separation of NPs on polymer-grafted porous columns. This process involves NP flow through the pore channels with walls covered by PBs. NP-PB adhesion is governed by adsorption of polymer chains to NP surface and entropic repulsion caused by the polymer chain confinement between NP and the channel wall. Both factors depend on the solvent composition, variation of which causes contraction or expansion of PB. Using dissipative particle dynamics simulations in conjunction with the ghost tweezers free energy calculation technique, we examine the free energy landscapes of functionalized NPs within PB-grafted channels depending on the solvent composition at different PB grafting densities and polymer-solvent affinities. The free energy landscape determines the probability of NP location at a given distance to the surface, positions of equilibrium adhesion states, and the Henry constant that characterizes adsorption equilibrium and NP partitioning between the stationary phase of PB and mobile phase of flowing solvent. We analyze NP transport through a polymer-grafted channel and calculate the mean velocity and retention time of NP depending on the NP size and solvent composition. We find that, with the increase of the bad (poor) solvent fraction and respective PB contraction, NP separation exhibits a transition from the hydrodynamic size exclusion regime with larger NPs having shorter retention time to the adsorption regime with smaller NPs having shorter retention time. The observed reversal of the sequence of elution is reminiscent of the critical condition in polymer chromatography at which the retention time is molecular weight independent. This finding suggests the possibility of the existence of an analogous special regime in nanoparticle chromatography at which NPs with like surface properties elute together regardless of their size. The latter has important practical implications: NPs can be separated by surface chemistry rather than by their size employing the gradient mode of elution with controlled variation of solvent composition.

Tuning Biocompatible Block Copolymer Micelles by Varying Solvent Composition: Dynamics and Populations of Micelles and Unimers

Optimization of micellar molecular encapsulation systems, such as drug delivery vehicles, can be achieved through fundamental understanding of block copolymer micelle structure and dynamics. Herein, we present a study of PEO–PCL block copolymer spherical micelles that self-assemble at 1% wt/vol in D2O–THF-d8 mixtures. Varying solvent composition as a function of cosolvent THF-d8 at constant polymer concentration (1% wt/vol) allows sensitive study of how small molecule additives influence micelle structure and dynamics. We conduct nuclear magnetic resonance spectroscopy and diffusometry on two block copolymer (2k series: PEO2k–PCL3k; 5k series: PEO5k–PCL8k) spherical micelles that show drastically different behaviors. Unimers and micelles coexist in solution from 10–60 vol % THF-d8 for the 2k series but only coexist at 60 vol % THF-d8 for the 5k series. At ≥ 60 vol % THF-d8 micelles disassemble into free unimers for both series. We observe relatively flat micelle diffusion coefficients (∼1 × 10–10 m2/s) wi...

Morphology and physical properties of graphene nanoplatelet embedded poly(vinyl alcohol) composite aerogel

Three dimensional carbon nanomaterial reinforced composite aerogel was fabricated using a freeze-drying method. Graphene nanoplatelets (GNPs) were used as the reinforcement and poly vinyl alcohol (PVA) as the organic binding material to produce the composite aerogel. Two different methods were employed to control the internal structure of the aerogel: a variation of solvent composition and the formation of cross-linking. The internal structure of the aerogel was affected by the types and composition of the solvent. In addition, the subsequent cross-linking of the aerogel influenced the morphology and physical properties. It is expected that this study can provide a simple and efficient way to control the internal structure and resulting properties of the GNP aerogel.

Structural color of polymeric physical gels

In this study, the coloration mechanism of isotactic poly(1-butene) (iPB) in o-xylene and o-xylene/ethyl alcohol mixture gels were carried out. iPB gel becomes yellow because of transmitted light or blue because of reflected light. Changing the temperature, solvent composition, or even the thickness of samples of this gel continuously changes its color to blue, violet, purple, red, and yellow. Structural characterization, electron microscopy, and transmittance measurements were carried out for iPB dissolved in o-xylene to form a three-dimensional sponge-like network with different mesh sizes under various conditions. Subsequently, the relative refractive index between the solvent and gel network produces incoherent Tyndall blue scattering. Finally, color change due to variations in solvent composition or temperature contributes to the interplay between the refractive index of network structure nnetwork and solvent ns. For a Tyndall medium with ns/nnetwork >1, normal reflection creates a blue gel; when ns/nnetwork ≒1, strong transmittance of light passing through the medium leads to a yellowish gel. This is the first report on the concept of structural color for polymeric physical gel systems.

Molecular-Based Theory for Electron-Transfer Reorganization Energy in Solvent Mixtures.

Using statistical-field techniques, we develop a molecular-based dipolar self-consistent-field theory (DSCFT) for charge solvation in liquid mixtures under equilibrium and nonequilibrium conditions, and apply it to compute the solvent reorganization energy of electron-transfer reactions. In addition to the nonequilibrium orientational polarization, the reorganization energy in liquid mixtures is also determined by the out-of-equilibrium solvent composition around the reacting species due to preferential solvation. Using molecular parameters that are readily available, the DSCFT naturally accounts for the dielectric saturation effect and the spatially varying solvent composition in the vicinity of the reacting species. We identify three general categories of binary solvent mixtures, classified by the relative optical and static dielectric permittivities of the solvent components. Each category of mixture is shown to produce a characteristic local solvent composition profile in the vicinity of the reacting species, which gives rise to the distinctive composition dependence of the reorganization energy that cannot be predicted using the dielectric permittivities of the homogeneous solvent mixtures.

Tailored conditions for controlled and fast growth of surface-grafted PNIPAM brushes

Abstract Surface-initiated Atom Transfer Radical Polymerization is an established technique for synthesis of polymer brushes via “grafting from” method. However, dynamic behavior of surface-tethered macromolecules during their growth requires more detailed studies to obtain uniform polymer brush films. It was addressed here by varying solvent composition in grafting of poly(N-isopropylacrylamide) brushes. Complementary in situ (quartz crystal microbalance) and ex situ (atomic force microscope, spectroscopic ellipsometry) techniques were employed to investigate the influence of methanol molar fraction (xMe) in methanol/water polymerization mixture on the brush growth. Grazing-angle polarized FT-IR spectroscopy was used to monitor macromolecular arrangement in the brushes. While achieving controlled, uniform and relatively fast growth of macromolecules is challenging a compromise may be reached by tuning solvent composition. The most balanced conditions with this respect were found in a narrow solvent composition window at ca. xMe ≈ 0.16 and below 0.31. The results may be applied for tailoring polymerization conditions of other polymer brush systems.

Critical conditions of polymer adsorption and chromatography on non-porous substrates

We present a novel thermodynamic theory and Monte Carlo simulation model for adsorption of macromolecules to solid surfaces that is applied for calculating the chain partition during separation on chromatographic columns packed with non-porous particles. We show that similarly to polymer separation on porous substrates, it is possible to attain three chromatographic modes: size exclusion chromatography at very weak or no adsorption, liquid adsorption chromatography when adsorption effects prevail, and liquid chromatography at critical conditions that occurs at the critical point of adsorption. The main attention is paid to the analysis of the critical conditions, at which the retention is chain length independent. The theoretical results are verified with specially designed experiments on isocratic separation of linear polystyrenes on a column packed with non-porous particles at various solvent compositions. Without invoking any adjustable parameters related to the column and particle geometry, we describe quantitatively the observed transition between the size exclusion and adsorption separation regimes upon the variation of solvent composition, with the intermediate mode occurring at a well-defined critical point of adsorption. A relationship is established between the experimental solvent composition and the effective adsorption potential used in model simulations.

Particle size tailoring of ursolic acid nanosuspensions for improved anticancer activity by controlled antisolvent precipitation

The present study was aimed at tailoring the particle size of ursolic acid (UA) nanosuspension for improved anticancer activity. UA nanosuspensions were prepared by antisolvent precipitation using a four-stream multi-inlet vortex mixer (MIVM) under defined conditions of varying solvent composition, drug feeding concentration or stream flow rate. The resulting products were characterized for particle size and polydispersity. Two of the UA nanosuspensions with mean particle sizes of 100 and 300nm were further assessed for their in-vitro activity against MCF-7 breast cancer cells using fluorescence microscopy with 4′,6-diamidino-2-phenylindole (DAPI) staining, as well as flow cytometry with propidium (PI) staining and with double staining by fluorescein isothiocyanate. It was revealed that the solvent composition, drug feeding concentration and stream flow rate were critical parameters for particle size control of the UA nanosuspensions generated with the MIVM. Specifically, decreasing the UA feeding concentration or increasing the stream flow rate or ethanol content resulted in a reduction of particle size. Excellent reproducibility for nanosuspension production was demonstrated for the 100 and 300nm UA preparations with a deviation of not more than 5% in particle size from the mean value of three independent batches. Fluorescence microscopy and flow cytometry revealed that these two different sized UA nanosuspensions, particularly the 300nm sample, exhibited a higher anti-proliferation activity against the MCF-7 cells and afforded a larger population of these cells in both early and late apoptotic phases. In conclusion, MIVM is a robust and pragmatic tool for tailoring the particle size of the UA nanosuspension. Particle size appears to be a critical determinant of the anticancer activity of the UA nanoparticles.

Significant enhancement of curcumin photoluminescence by a photosensitizing organogel: An optical sensor for pyrrole detection

A curcumin organogel was prepared using an organogelator of N′1,N′6-bis(3-(1-pyrrolyl)propanoyl) hexanedihydrazide (DPH), and its photoluminescence properties were examined for sensor applications. The organogelator created a yellow curcumin organogel and considerably enhanced curcumin photoluminescence through the photosensitization effect. Specifically, the DPH organogel allowed the curcumin organogel to be excited over a wider range of visible light. Due to the organogelator, the quantum yield of curcumin photoluminescence increased to around 50%. A series of control experiments with variations in solvent composition and concentrations of organogelator verified that both the solvent composition and the phase transition from solution to organogel remarkably enhanced photoluminescence. The curcumin organogel was exploited as a sensor material that selectively recognizes pyrrole among heterocyclic compounds because of the molecular similarity of DPH with pyrrole. Due to the properties of a gel, nonlinear photoluminescence quenching behavior suggests both static and dynamic quenching mechanisms. In summary, the curcumin organogel showed significantly enhanced photoluminescence due to the DPH organogelator, and this material could be utilized as a soft solid platform for optical pyrrole detection.

Structural transition of asymmetric poly(ether imide) membrane prepared by wet phase inversion

The structure of membrane prepared by the phase inversion process shows a strong dependency on the casting thickness as well as composition of cast polymer solution. At the present work, these two factors are probed for poly(etherimide) (PEI) membranes prepared via the NIPS process. Three systematic variations in solvent composition from N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF) were applied; including pure NMP, 50NMP:50DMF, and 25NMP:75DMF. The critical thickness was determined by means of solution casting at a broad range of thickness. The scanning electron micrograph of cross-section membranes reveals that critical thickness of PEI membrane is taken place at thicknesses of 9.7, 19.2 and 22.5 µm when the ratios of 0:100, 50:50, and 25:75 for NMP:DMF are employed, respectively. Shrinkage values which are calculated via a novel method can subscribe the effect of casting thickness and also quality of solvent on final membrane structure. The shrinkage values are altered exponentially by increasing the cast solution thickness in pure NMP solvent system. Gradual addition of DMF to the solvent system takes the later trend to linear form. It has been argued that increase in DMF content of solvent system leads to a greater demixing gap in the ternary phase diagram; it can also result in a higher solvent/polymer interaction parameter.

Shape Control Synthesis, Characterizations, Mechanisms And Optical Properties Of Larg Scaled Metal oxide Nanostructures Of ZnO And TiO2

In the present study, ZnO and TiO2 nanostructures of different size have been synthesized in high yield with excellent repeatability by simple, economical and environmentally benign chemical route. ZnO quantum dots and nanorods of tuned aspect ratio were evolved by optimising the reaction conditions such as by varying solvent composition, precursor concentration and by using different additives. On the other hand, the synthesis of brookite, the rare phase, anatase and rutile, the stable phases of TiO2 were also achieved by just varying the annealing temperature from 400 to 615 °C. The obtained nanostructures were rationalized by various characterization techniques such as XRD, FTIR, Raman, SEM, HR- TEM, UV-Vis and PL. The Phase formation and structure determination were identified by using XRD, FTIR and Raman Spectra, SEM and HR-TEM were performed to determine the morphology and particle size. The aspect ratio was calculated to be in the range of 3.2-9.4 in case of ZnO NRs, and particle size was found to be 2-5 nm for ZnO QDs of wurtzite phase and ~ 10 nm for TiO2 (anatase phase) NPs, respectively. The UV-Vis optical absorption spectrum demonstrates the band gap value of 3.60, 4.02 and 3.40 eV for ZnO NRs, QDs and TiO2 NPs respectively. The UV-Vis optical absorption spectrum demonstrates the band gap and room temperature PL spectra illustrates about the various defects present in the sample. Various chemical reactions and mechanism involved in producing these nanostructures are dealt in detail. The future prospective of these metal oxide nanostructures lie in photocatalysis, sensors and biomedical applications. Copyright © 2015 VBRI press.

Kinetics and Mechanism of Micellar Catalyzed Oxidation of Dextrose by N-Bromosuccinimide in H2SO4 Medium

Kinetics and mechanism of micellar catalyzed N-bromosuccinimide oxidation of dextrose in H2SO4 medium was investigated under pseudo-first-order condition temperature of 40°C. The results of the reactions studied over a wide range of experimental conditions show that NBS shows a first order dependence, fractional order, on dextrose and negative fractional order dependence on sulfuric acid. The determined stoichiometric ratio was 1 : 1 (dextrose : N-bromosuccinimide). The variation of Hg(OAC)2 and succinimide (reaction product) has insignificant effect on reaction rate. Effects of surfactants, added acrylonitrile, added salts, and solvent composition variation have been studied. The Arrhenius activation energy and other thermodynamic activation parameters are evaluated. The rate law has been derived on the basis of obtained data. A plausible mechanism has been proposed from the results of kinetic studies, reaction stoichiometry, and product analysis. The role of anionic and nonionic micelle was best explained by the Berezin’s model.