Acetone Water Research Articles

Reducing the Induction Time Using Ultrasound and High-Shear Mixing in a Continuous Crystallization Process

Continuous crystallization in tubular crystallizers is of particular interest to the pharmaceutical industry to accurately control average particle size, particle size distribution, and (polymorphic) shape. However, these types of crystallizers require fast nucleation, and thus, short induction times at the beginning of the flow process, which is challenging for larger and complex organic molecules. High shear and/or the presence of bubbles were identified to influence the nucleation behavior. This work investigates the effects of both high-shear mixing and ultrasound on the anti-solvent crystallization of paracetamol in acetone–water. Both devices generate intense amounts of shear and gas bubbles. Generally, the results show that increasing input power decreases the induction time significantly for both the rotor–stator mixer and ultrasound probe. However, the induction time is almost independent of the supersaturation for the ultrasound probe, while the induction time significantly increases with decreasing supersaturation for the rotor–stator mixer. In contrast, the particle size distribution for the rotor–stator mixer is independent of the supersaturation, while increasing supersaturation decreases the particle size for the ultrasound probe.

Study of Organic Substance (Myrmecodia pendans) Extraction Using Soxhletation Method as an Organic Inhibitor

Extract of natural substance is currently being developed as an organic inhibitor. Organic inhibitor can be used to inhibit corrosion rate of metallic material especially steel. The purpose of this study is to analyze the effectiveness of soxhletation extraction methods and the quality of inhibitor of Sarang Semut (Myrmecodia pendans) extract. The variations implemented in this research were the composition of the solvent-material and the content comparison of flavonoid compounds. The results of Sarang Semut (Myrmecodia pendans) extract inhibitor using soxhletation extraction method was observed qualitatively and quantitatively This research used soxhletation extraction method, simplicia Sarang Semut (Myrmecodia pendans) powder as the organic substance, and a mixture of acetone and distilled water as the solvent. Ratio variation of the solvent-substance composition used are 1:10, 1:15, and 1:20. Tests used in this study were Extract Parameters, FTIR, TLC and UV-Vis Spectrophotometry and weight loss. The highest yield was shown when using 1:10 ratio which was 13.943%, the total ash content and the lowest extracted water content shown at a ratio of 1:10 with amount of 4.26% and 4.2483%. FTIR test results indicated functional groups of flavonoids compounds and TLC test showed positive results of Flavonoid compounds which were characterized by blackish discoloration. The highest percentage of flavonoid compounds of 0.22025% found at the 1:10 ratio. The highest efficiency inhibition happened when weight loss testing showed 500ppm with the result of 84.3%.

Mass transfer studies in an L-shaped pulsed sieve-plate extraction column

ABSTRACTIn the process of our research, the mass transfer performance of an L-shaped pulsed sieve-plate extraction column for toluene–acetone–water and n-butyl acetate–acetone–water systems is investigated using the back flow model. The volumetric overall mass transfer coefficients are determined with respect to the variation of the mean drop size and the dispersed phase holdup in the column and the effects of the operating parameters are evaluated. Furthermore, a new empirical correlation is proposed for the prediction of the overall continuous phase Sherwood number based on the Reynolds number, the Schmidt number, and the values of holdup, denoting a satisfactory agreement with the experimental data.

Optimization study of polyethylene glycol and solvent system for gas permeation membranes

Cellulose acetate (CA) membranes blended with Polyethylene glycol (PEG) in acetone–water solvent system were synthesized by using solution-casting method that resulted in the formation of flexible, white membranes. Different molecular weight (MW) grades of PEG (including MW 1000, 10,000 and 20,000 g/mol) were used. Cast membranes were tested for tensile strength and permeability at different loading of PEG MW 10,000 and 20,000 g/mol. Excellent flexible membranes were produced in acetone–water solvent system in the presence of PEG, which were otherwise brittle. Surface structure and morphology were analysed using scanning electron microscopy. The presence of different functional groups was confirmed using Fourier transform infra-red spectroscopy and the mechanical characteristics were studied by tensile testing. The introduction of PEG caused an increase in permeability of the membranes. The increase in permeability is due to the opening up of pores as the membrane becomes more flexible, when the plasticizer is added. The permeability continues to increase with the addition of PEG. Moreover, the resulting membranes are not only more flexible, but also have largely improved tensile strength as compared to the CA membranes without PEG. This improved tensile strength can also be attributed to the improved flexibility of the membrane. A trade-off is reached between tensile strength and permeability as increasing amount of PEG improves tensile strength but the resulting membrane becomes too permeable to be used for gas separation. Moreover, using PEG of higher MW resulted in porous membranes, even at low amounts of PEG. Therefore, we concluded that CA membrane with less amount of low-MW PEG (i.e. 5% PEG of MW 1000 g/mol) must be used to optimize both permeability and tensile strength of the membrane.

A facile method to mussel-inspired superhydrophobic thiol-textiles@polydopamine for oil/water separation

Due to the poor mechanical stability, the practical applications of superhydrophobic materials are limited. Inspired by the excellent adhesion of polydopamine (PDA), a kind of superhydrophobic coating is successfully fabricated on the textile. Herein, under weak acidic conditions (pH = 5.0), sodium periodate is selected as oxidant and the concentration of dopamine is controlled at 8 mg/mL, which leads to the fast and homogeneous deposition of PDA nanoaggregates on the pristine textile. Subsequently, the nanoaggregates are modified by octadecyl thiol. The PDA nanoaggregates work as a stable bond between the pristine textile and hydrophobic groups introduced from thiol, which contributes to the mechanical stability of the superhydrophobic textile. In addition, the superhydrophobic textiles display resistance to acetone, UV irradiation, and hot water. Significantly, the textiles can be used for oil/water separation with flux around 4500 Lm−2 h−1 and the separation efficiency more than 97%. These advantages provide the superhydrophobic textiles with multiple applications.

Scientific rationale for traditional use of plants to treat tuberculosis in the eastern region of the OR Tambo district, South Africa

Ethnopharmacological relevanceTuberculosis (TB) remains a major health problem for humans worldwide, and was responsible for 1.4 million human deaths in 2015 alone. Although there is treatment for TB, emerging multi-drug, extensively drug and totally drug resistant forms of this disease, as well as co-infection with human immunodefiency virus (HIV) continue to worsen the situation. South Africa is among countries with reported traditional use and published documentation of such knowledge concerning the use of plants against TB. Based on a previous study where plants used traditionally for treating TB in the eastern region of OR Tambo district, South Africa, were documented, the present study aimed to determine the antimycobacterial effect, cytotoxicity and genotoxicity of plants selected from that list. Material and methodsAcetone, 70% ethanol, cold and hot water extracts were tested for antimycobacterial activity against saprophytic Mycobacterium species including M. aurum, M. bovis BCG, M. gordonae, M. fortuitum, and M. smegmatis using a microdilution method. Extracts with MIC values less than 1 mg/ml against at least three Mycobacterium strains were evaluated for antimycobacterial activity against pathogenic Mycobacterium strains including M. tuberculosis H37RV, M. tuberculosis and M. bovis, cytotoxicity (against Vero monkey kidney and bovine dermis cells), and genotoxicity (against Salmonella typhimurium TA98 and TA100). ResultsThe MIC values of the extracts ranged from 0.02 to 2.50 mg/ml, LC50 values of twenty-nine extracts ranged from 0.001 to > 1 mg/ml and the highest selectivity index was 79.50, an extremely promising value. Phymaspermum acerosum roots and leaves (ethanol and water) extracts had the best MIC value (0.02 mg/ml) against at least one Mycobacterium strain. It was interesting to note the lack of cytotoxicity of these extracts with the highest selectivity index value of 39.75. Pterocelastrus echinatus bark acetone and Protorhus longifolia leaf hot water extracts were the most cytotoxic with LC50 = 0.001 and 0.008 mg/ml, respectively, whereas Pittosporum viridiflorum bark water extract was genotoxic. Among non-pathogenic strains, M. gordonae, M. aurum, M. smegmatis showed good correlation of activity with pathogenic M. tuberculosis H37Rv, M. tuberculosis and M. bovis, however, M. aurum was the best predictor with Mycobacterium tuberculosis H37Rv (correlation coefficient value = 0.73). ConclusionThe results indicate that Heteromorpha trifoliata and Phymaspermum acerosum should be investigated further for antimycobacterial efficacy against drug resistant strains of Mycobacterium.

Environment of the Al3+ ion in Water–Acetone Solutions of Aluminum Chloride

Water–acetone solutions in the AlCl3–(CH3)2CO–H2O and AlCl3–(CH3)2CO–H2O–HCl systems were obtained and studied. In both cases, the solution separated into layers to form liquid fractions of lower and higher density. The IR spectra of the fractions were studied. In the light fraction, no AlCl3 was present, but hydrogen-bonded acetone–water complexes were detected. The spectra of the heavy fraction exhibited a broad band at ~3020–3040 cm–1 corresponding to the OH groups of water from aluminum hexahydrate. As the solvent is evaporated, the band narrows down, with its position being retained. The IR spectrum of the obtained solid becomes identical to the IR spectrum of the crystal hydrate AlCl3.(H2O)6. The structures and spectral and energetic parameters of Al(H2O) 6 3+ , Al(H2O) 6+12 3+ , Al((CH3)2CO) 6 3+ , Al((CH3)2CO) 4 3+ , and (CH3)2CO.H2O were calculated by the density functional theory method (B3LYP/6-31++G(d,p)). Relying on the results, an explanation was proposed for the experimentlly observed absence of acetone molecules in the Al3+ first coordination shell.

Synthesis of Substituted Quinolinyl Ether‐based Inhibitors of PI3K as Potential Anticancer Agents

A new strategy for the preparation of 8‐quinolyl ethers 3(a–g), 5(a–g), and 7(a–d) was studied by copper (II)‐catalyzed methodology in the presence of Cs2CO3 and acetone–water mixture (1:1). Screening of quinolinyl‐8‐ethers was investigated against anticancer expressive studies to validate new chemical entity in medicinal chemistry. Approaches were evaluated against breast cancer (MCF‐7), skin cancer (G‐361), and colon cancer (HCT 116) cell lines. Inhibitory potentials against phosphoinositide‐3‐kinase (PI3K) enzyme responsible for cancer development have been evaluated by competitive ELISA studies. In PI3K assay, 3a–c were inactive (IC50 > 5 μM), while 3e–g, 5a, 5c–e, 5g, 7a, and 7d showed a moderate activity (IC50 ≥ 0.05 μM). Compounds (5b, 5f, 7b, and 7c) showed significant activity (IC50 < 1.0 μM); thus, their anticancer activities were carried out. Anticancer activity was found to be selective towards breast cancer (MCF‐7); 5b, 5f, 7b, and 7c showed predominant relative percentage activities of 74.12%, 79.04%, 72.56%, and 78.47%, with IC50 values of 5b (2.27 ± 0.88 μM), 5f (1.38 ± 0.60 μM), 7b (2.64 ± 0.86 μM), and 7c (1.87 ± 0.68 μM) compared with the standard doxorubicin 73.14% inhibition (IC50 = 1.98 ± 0.75 μM). Docking study also conducted to find out the binding interactions with p110α (PDB ID: 3T8M) enzyme. Compounds 5b, 5f, 7b, and 7c showed best docking score into the active site of PI3K 12.59, 10.51, 56.52, and 8.61 nM. Structure–activity relationship studies demonstrated that the synthesized compounds are the potential PI3K inhibitors to treat various cancer‐related diseases.

Noxious to ecosystems, but relevant to pharmacology: Four South African alien invasive plants with pharmacological potential

Alien invasive plants pose a huge threat to natural and semi-natural ecosystems in their introduced ranges thereby compromising ecosystem integrity. However, anecdotal and empirical evidence suggests that some invasive alien plants are used in traditional medicine due to their pharmacological activities. Here, we evaluated the antimicrobial activity of 70% ethanol, dichloromethane, acetone and hot water extracts of four invasive alien plants in South Africa viz. Dolichandra unguis-cati, Cardiospermum grandiflorum, Chromolaena odorata and Gomphrena celosioides against pathogenic and non-pathogenic microbes. The test organisms included Staphylococcus aureus, Salmonella enterica serovar Typhimurium (S. Typhimurium), Salmonella Dublin, Klebsiella pneumoniae, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, Mycobacterium aurum, M. fortuitum, M. smegmatis, Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans. Phytochemicals that may be responsible for antimicrobial activity were determined using standard phytochemical methods. A further objective was to investigate the safety of these plants by conducting cytotoxicity and genotoxicity tests. All solvent extracts of plants investigated exhibited a broad spectrum of antibacterial activity with minimum inhibitory concentration (MIC) values ranging from 0.039 to 2.5 mg/ml, with the acetone and dichloromethane extracts showing better activity against E. coli, K. pneumoniae and E. faecalis (MIC between 0.039 and 0.078 mg/ml). Of all extracts tested, only the ethanol extracts of C. grandiflorum showed good antimycobacterial activity with MIC of 0.078 mg/ml against M. smegmatis. In contrast, C. grandiflorum only showed moderate antifungal activity, while dichloromethane and acetone extracts of the other three plants were very effective against C. neoformans and A. fumigatus with MIC values ranging from 0.019 to 0.078 mg/ml. All four plants moderately inhibited C. albicans at MIC of 0.156 mg/ml. The plant species were rich in phenolics, flavonoids and tannins in varying amounts and had relatively low levels of cytotoxicity and none was mutagenic. Promising selectivity index values (between 10 and 50) highlight the potential of these plant species as sources of antimicrobial remedies. Despite the ecological noxiousness of these alien invasive plants, our findings suggest that they possess some antimicrobial properties that are too pharmacologically relevant to ignore.

Phytochemical Investigation and Pharmacological Evaluation of Solanum xanthocarpum Endowed with their potential Activity

The study was done to assess the in-vitro antibacterial potential of various extracts was studied and compared with ciprofloxacin as the standard and shows significant action against E. coli, B. substilis S. aureus, S. pyrogenes, P. aeruginosa, and S. typhi. Anti-fungal potential of the aqueous extract also studied using miconazole as standard and shows significant action against A. niger and C. albicans. Anthelmintic potential of the aqueous and ethanolic extracts was also studied on earthworms, Eudrillus eugeniae using albendazole as standard and shows moderate activity. In the present study in-vitro free radical scavenging activity of whole plant material performed. Various crude extracts of S. xanthocarpum was prepared by successive maceration process using various solvents such as; chloroform, petroleum ether (60-80o), acetone, ethanol and distilled water. Each one extract have been chosen to study the free radical inhibitory activity by DPPH radical scavenging method. The preliminary phytochemical screening of extracts showed that sterols, alkaloids, glycosides, tannins, saponins, phenolic compounds, carbohydrates and proteins were present in the plant. Petroleum ether, chloroform, acetone, ethanol and distilled water extracts showed 52.69, 46.15, 21.08, 52.72 and 44.35 % respectively compared to standard ascorbic acid. Acetone extract showed poor inhibition of DPPH radical compared to standard and other extracts also.

Isobaric specific heat capacities of emulsified kerosene at high temperature and pressure

A flow calorimeter based on energy conservation was constructed for experimental measurements of isobaric specific heat capacity. The relative expanded uncertainty of isobaric specific heat capacity was identified as 2.32% (coverage factor k = 2). In the peak region, the relative expanded uncertainty of isobaric specific heat capacity increased to 7.10% (coverage factor k = 2). To verify the accuracy and reliability of the flow calorimeter, pure water and different mole-fraction binary mixtures of n-pentane and acetone were tested in the liquid and vapor phases. The maximum absolute deviation and average absolute deviation were 1.42% and 0.51%, respectively. The isobaric specific heat capacity of emulsified kerosene with different mass fractions was measured at temperatures ranging from 301 K to 878 K and at pressure p = 3 MPa. The effects of different mass frictions of water and temperature on the isobaric specific heat capacities were analyzed in detail. Finally, the isobaric specific heat capacity of RP-3 was compared with that of emulsified kerosene.

Extended Charge-On-Particle Optimized Potentials for Liquid Simulation Acetone Model: The Case of Acetone-Water Mixtures.

It is well-known that classical molecular dynamics simulations of acetone-water mixtures lead to a strong phase separation when using most of the standard all-atom force fields, despite the well-known experimental fact that acetone is miscible with water in any proportion at room temperature. We describe here the use of a charge-on-particle model for accounting for the induced polarization effect in acetone-water mixtures which can solve the demixing problem at all acetone molar fractions. The polarizability effect is introduced by means of a virtual site (VS) on the carbonyl group of the acetone molecule, which increases its dipole moment and leads to a better affinity with water molecules. The VS parameter is set by fitting the density of the mixture at different acetone molar fractions. The main novelty of the VS approach lies on the transferability and universality of the model because the polarizability can be controlled without modifying the force field adopted, like previous efforts did. The results are satisfactory also in terms of the transport properties, that is, diffusivity and viscosity coefficients of the mixture.

Mechanistic Elucidation of Hard Agglomerate Formation from Drying Kinetics in the Integrated Sorption Chamber

The formation of hard agglomerates during drying has impacts on the product quality, particle size distribution, and downstream formulation. Hence, understanding the cause of hard agglomerates and determining a remedy for them or preventing their formation are necessary. The integrated sorption chamber (ISC) has been successfully applied to the study of hard agglomerate formation. The design and development of this ISC are briefly described. The vapor-phase profile of a binary mixture of acetone and water without active pharmaceutical ingredient (API) was predicted using an analytical solution of a batch distillation and verified via mass spectrometry (MS). The drying of the API wet cake, which is very soluble in water, using a starting point of 5 wt % water in acetone was conducted in the ISC. A significant delay in water removal was observed from both the weight measurement and the MS signal. The slow removal of water was attributed to diffusion of water from a thin crust layer induced by the solution o...

Synthesis and Crystal Structures of Diaryl Thioethers and Aryl Benzyl Thioethers Derived from Thiosalicylic Acid

Reaction of thiosalicylic acid and iodobenzene or 1-fluoro-2-nitrobenzene in the presence of two equiv. of K2CO3 in acetone–water afforded the according diaryl thioethers 1 and 2 bearing carboxyl groups. Treatment of thiosalicylic acid with benzyl bromide-type compounds under similar reaction conditions gave aryl benzyl thioethers 3–8 in excellent yields. Moreover, reactions of thiosalicylic acid and benzyl bromide in the presence of excess K2CO3 led to isolation of compound 9 (Leka et al. in Acta Cryst E69:o285–0286, 2013) through further esterification of the carboxyl group. Crystal structures of 2, 5–7 and 9 (Leka et al. in Acta Cryst E69:o285–0286, 2013), along with their spectroscopic properties are reported. Weak hydrogen-bonding interactions exist in compound 2 and isomers 5–7. Compounds 2 and 7 crystallize in the monoclinic space group P21/n and C2/c, respectively, with a = 12.04(3), b = 7.311(19), C=14.22(4) A, β = 93.94(3)°, and Z = 4 for 2, and a = 14.934(13), b = 5.116(5), C=33.76(3) A, β = 91.523(12)°, and Z = 8 for 7. The unit cell of 5 has triclinic P-1 symmetry with the cell parameters a = 5.4334(14), b = 7.7787(19), C=16.488(4) A, α = 76.601(3)°, β = 86.078(3)°, γ = 70.772(3)°, and Z = 2 for 5. Compound 6 crystallizes in the orthorhombic space group Pbca with a = 15.1881(12), b = 7.3288(6), C=23.7366(19) A, and Z = 8. Reactions of thiosalicylic acid and a series of aryl- or benzyl halides in the presence of K2CO3 in acetone–water resulted in the formation of according diaryl thioethers and aryl benzyl thioethers in excellent yields.

Effect of the Dielectric Constant on the Solubility of Acetone in Water

Molecular dynamics simulations for liquid acetone, the pure component and mixed with water, are performed to analyze the effect that the dielectric constant has on the solubility. The CGenFF and OPLS/AA force fields, together with two TraPPE_UA models, are used to simulate acetone, while the TIP4P/ϵ model is applied for water. The calculated dielectric constant of acetone models at room conditions follows a linear relation with their molecular dipole moment, allowing us to understand, in simulations, the miscibility problem of acetone in water. The experimental liquid and liquid–vapor properties as the pure component are reasonably well reproduced with those force fields. The TraPPE_UA04 and TraPPE_UA05 models predict dielectric constants for acetone in the liquid phase of 9 and 12, respectively. The experimental value is 21. The values obtained with the OPLS/AA and CGenFF models are 15 and 23, respectively. All of the models used, except CGenFF, give inhomogeneous mixtures at both low and moderate concen...

Influence of Solvent Composition on the Performance of Spray-Dried Co-Amorphous Formulations.

Ball-milling is usually used to prepare co-amorphous drug–amino acid (AA) mixtures. In this study, co-amorphous drug–AA mixtures were produced using spray-drying, a scalable industrially preferred preparation method. The influence of the solvent type and solvent composition was investigated. Mixtures of indomethacin (IND) and each of the three AAs arginine, histidine, and lysine were ball-milled and spray-dried at a 1:1 molar ratio, respectively. Spray-drying was performed at different solvent ratios in (a) ethanol and water mixtures and (b) acetone and water mixtures. Different ratios of these solvents were chosen to study the effect of solvent mixtures on co-amorphous formulation. Residual crystallinity, thermal properties, salt/partial salt formation, and powder dissolution profiles of the IND–AA mixtures were investigated and compared to pure crystalline and amorphous IND. It was found that using spray-drying as a preparation method, all IND–AA mixtures could be successfully converted into the respective co-amorphous forms, irrespective of the type of solvent used, but depending on the solvent mixture ratios. Both ball-milled and spray-dried co-amorphous samples showed an enhanced dissolution rate and maintained supersaturation compared to the crystalline and amorphous IND itself. The spray-dried samples resulting in co-amorphous samples were stable for at least seven months of storage.

Pharmacokinetic Profiling of Some Carbohydrate Derivatives and Their Structure Activity Relationship Evaluation

Background: Carbohydrates are of great interest for the synthesis of novel ribonucleosides and C-Nucleosides which often show different pharmacological potential including antiinflammatory and antineoplastic characteristics. Introduction: In this research twelve aldopentose derivatives were examined and their chromatographic properties were used to describe their pharmacokinetic profiles. Methods: Thin layer chromatography was performed using three mobile phases: acetone–water (φ = 0.5–0.7 v/v), dioxane–water (φ = 0.5–0.7 v/v) and methanol–water (φ = 0.5–0.7 v/v). Multiple linear regression was performed to examine correlation between lipophilicity and pharmacokinetic descriptors of the examined molecules. Results: Good oral absorption can be expected for all investigated compounds. Moderate volume of distribution indicates low to moderate probability of their accumulation in body tissues. All investigated molecules show good pharmacokinetic characteristics but compounds 2, 3, 5, 6 and 7 demonstrated the best biological potential and biochemical activity such as inhibition of protease and kinase (compound 7) and possibility to be a ligand for GPCR. Conclusion: Among the best candidates authors would emphasize structure 7 as the most promising molecule regarding its pharmacological potential. Keywords: Aldopentose, multiple linear regression, QSAR, pharmacokinetic, ADME, lipophilicity.

Comparative Investigation and Operational Performance Characteristics of a Wick Assisted and Axially Square Grooved Heat Pipe

The present work reported here involves the experimental investigation and performance evaluation of wick assisted and axially square grooved heat pipes of outer diameter 8mm, inner diameter 4mm with a length of 150mm.The objective of this work is to design, fabricate and test the heat pipes with and without an axial square groove for horizontal and gravity assisted conditions. The performance of the heat pipes was measured in terms of thermal resistance and heat transfer coefficients. In the present investigation four different working fluids were chosen namely acetone, ethanol, methanol and distilled water. Experiments were conducted by varying the heat load from 2 W to 10 W for different fill charge ratios in the range of 25% to 75% of evaporator volume for wick assisted heat pipe and 8 W to 18 W for axially square grooved heat pipe. From the experiments, it was found that there is a steady increase in temperature with the increase in heat input. The overall heat transfer coefficient was found to increase with the increase heat load for wick assisted heat pipe. In case of axially square grooved heat pipe, an attempt was made to experiment the heat pipe in different orientations. The maximum heat transfer coefficient of 7000 W/m2 °C is found for Acetone at 180° orientation.

Convenient synthesis of 2-(methylsulfonyl)pyrimidine derivatives

ABSTRACTAn efficient and convenient approach for the preparation of functionalized 2-(methylsulfonyl)pyrimidine derivatives has been developed through cyclic condensation of malonate derivatives with S-methylisothiouronium sulfate followed by derivation and oxidation in water–acetone mixture using oxone as the oxidant. This synthetic strategy provides an efficient and environmentally friendly approach for easy access to 2-(methylsulfonyl)pyrimidine derivatives with considerable yields.

Cosolvent effect on the dynamics of water in aqueous binary mixtures

ABSTRACTWater rotational dynamics in the mixtures of water and amphiphilic molecules, such as acetone and dimethyl sulfoxide (DMSO), measured by femtosecond infrared, often vary non-monotonically as the amphiphilic molecule's molar fraction changes from 0 to 1. Recent study has attributed the non-ideal water rotation with concentration in DMSO–water mixtures to different microscopic hydrophilic–hydrophobic segregation structure in water-rich and water-poor mixtures. Interestingly, the acetone molecule has very similar molecular structure to DMSO, but the extremum of the water rotational time in the DMSO-water mixtures significantly shifts to lower concentration and the rotation of water is much faster than those in acetone-water mixtures. The simulation results here shows that the non-ideal rotational dynamics of water in both mixtures are due to the frame rotation during the interval of hydrogen bond (HB) switchings. A turnover of the frame rotation with concentration takes place as the structure transition of mixture from the hydrogen bond percolation structure to the hydrophobic percolation structure. The weak acetone–water hydrogen bond strengthens the hydrophobic aggregation and accelerates the relaxation of the hydrogen bond, so that the structure transition takes places at lower concentration and the rotation of water is faster in acetone–water mixture than in DMSO–water mixture. A generally microscopic picture on the mixing effect on the water dynamics in binary aqueous mixtures is presented here.