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1.
J Phys Chem B ; 128(28): 6940-6950, 2024 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-38956449

RESUMO

Two ionic liquids (ILs) with amphiphilic properties composed of 1-butyl-3-methylimidazolium dioctylsulfosuccinate (bmim-AOT) and 1-hexyl-3-methylimidazolium dioctylsulfosuccinate (hmim-AOT) form unilamellar vesicles spontaneously simply by dissolving the IL-like surfactant in water. These novel vesicles were characterized using two different and highly sensitive fluorescent probes: 6-propionyl-2-(dimethylaminonaphthalene) (PRODAN) and trans-4-[4-(dimethylamino)-styryl]-1-methylpyridinium iodide (HC). These fluorescent probes provide information about the physicochemical properties of the bilayer, such as micropolarity, microviscosity, and electron-donor capacity. In addition, the biocompatibility of these vesicles with the blood medium was evaluated, and their toxicity was determined using Dictyostelium discoideum amoebas. First, using PRODAN and HC, it was found that the bilayer composition and the chemical structure of the ions at the interface produced differences between both amphiphiles, making the vesicles different. Thus, the bilayer of hmim-AOT vesicles is less polar, more rigid, and has a lower electron-donor capacity than those made by bmim-AOT. Finally, the results obtained from the hemolysis studies and the growth behavior of unicellular amoebas, particularly utilizing the D. discoideum assay, showed that both vesicular systems do not produce toxic effects up to a concentration of 0.02 mg/mL. This elegant assay, devoid of animal usage, highlights the potential of these newly organized systems for the delivery of drugs and bioactive molecules of different polarities.


Assuntos
Líquidos Iônicos , Tensoativos , Lipossomas Unilamelares , Líquidos Iônicos/química , Tensoativos/química , Lipossomas Unilamelares/química , Lipossomas Unilamelares/metabolismo , Nanomedicina , Corantes Fluorescentes/química , Compostos de Piridínio/química , Imidazóis/química , Bicamadas Lipídicas/química
2.
Langmuir ; 40(1): 657-667, 2024 01 09.
Artigo em Inglês | MEDLINE | ID: mdl-38100549

RESUMO

Vesicles formed by phospholipids are promising candidates for drug delivery. It is known that the lipid composition affects properties such as the rigidity-fluidity of the membrane and that it influences the bilayer permeability, but sometimes sophisticated techniques are selected to monitor them. In this work, we study the bilayer of different unilamellar vesicles composed of different lipids (1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC, and lecithin) and diverse techniques such as extruder and electrospun templates and using 6-propionyl-2-(N,N-dimethyl) aminonaphthalene (PRODAN) and its photophysics. Moreover, we were able to monitor the influence of cholesterol on the bilayers. We demonstrate that the bilayer properties can be evaluated using the emission feature of the molecular probe PRODAN. This fluorescent probe gives relevant information on the polarity and fluidity of the microenvironment for unilamellar vesicles formed by two different methods. The PRODAN emission at 434 nm suggests that the bilayer properties significantly change if DOPC or lecithin is used in the vesicle preparation especially in their fluidity. Moreover, cholesterol induces alterations in the bilayer's structural and microenvironmental properties to a greater or lesser degree in both vesicles. Thus, we propose an easy and elegant way to evaluate physicochemical properties, which is fundamental for manufacturing vesicles as a drug delivery system, simply by monitoring the molecular probe emission band centered at 434 nm, which corresponds to the PRODAN species deep inside the bilayer.


Assuntos
Fosfolipídeos , Lipossomas Unilamelares , Fosfolipídeos/química , Lipossomas Unilamelares/química , Lecitinas , Bicamadas Lipídicas/química , Sondas Moleculares , Colesterol/química , Fosfatidilcolinas/química
3.
Pharm Res ; 39(10): 2379-2390, 2022 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-35854078

RESUMO

The present review describes the state of the art in the conversion of pharmaceutically active ingredients (API) in amphiphilic Ionic Liquids (ILs) as alternative drug delivery systems. In particular, we focus our attention on the compounds generated by ionic exchange and without original counterions which generate different systems in comparison with the simple mixtures. In water, these new amphiphiles show similar or even better properties as surfactants in comparison with their precursors. Cations such as 1-alkyl-3-methyl-imidazolium and anions such as dioctyl sulfosuccinate or sodium dodecyl sulfate appear as the amphiphilic components most studied. In conclusion, this work shows interesting information on several promissory compounds and they appear as an interesting challenge to extend the application of ILs in the medical field.


Assuntos
Líquidos Iônicos , Ânions , Cátions , Ácido Dioctil Sulfossuccínico , Micelas , Dodecilsulfato de Sódio , Tensoativos , Água
4.
Phys Chem Chem Phys ; 24(3): 1692-1701, 2022 Jan 19.
Artigo em Inglês | MEDLINE | ID: mdl-34982075

RESUMO

In the synthesis of metallic nanoparticles in microemulsions, we hypothesized that the particle size is controlled by the reaction rate and not by the microemulsion size. Thus, the changes observed in the particle sizes as reaction conditions, such as concentrations, temperatures, the type of surfactant used, etc., are varied which should not be correlated directly to the modification of these conditions but indirectly to the changes they produce in the reaction rates. In this work, the microemulsions were formulated with benzene and water as continuous and dispersed phases, respectively, using n-dodecyltrimethylammonium bromide (DTAB) and n-octanol as the surfactant and cosurfactant. Using time-resolved UV-vis spectroscopy, we measured the reaction rates in the production of palladium (Pd) nanoparticles inside the microemulsions at different reactant concentrations and temperatures, keeping all the other parameters constant. The measured reaction rates were then correlated with the particle sizes measured by transmission electron microscopy (TEM). We found that the nanoparticle size increases linearly as the reaction rate increases, independently of the actual reactant concentration or temperature. We proposed a simple model for the observed kinetics where the reaction rate is controlled mainly by the diffusion of the reducing agent. With this model, we predicted that the particle size should depend indirectly, via the reaction kinetics, on the micelle radius, the water volume and the total microemulsion volume. Some of these predictions were indeed observed and reported in the literature.

5.
J Phys Chem B ; 125(48): 13203-13211, 2021 12 09.
Artigo em Inglês | MEDLINE | ID: mdl-34788537

RESUMO

Ionic liquids (ILs) have received attention for many years due to them being very promising as green solvent substitutes, but they are not fully understood, especially their behavior dissolved in other solvents, for example, water. Thus, the goal of this contribution is to show insight into the different IL-water mixtures interaction. In this way, two protic ILs (PILs), ethylammonium nitrate (EAN) and 1-methylimidazolium acetate (MIA), mixed with water were investigated. To study the PILs-water interaction, the unique spectroscopical behavior in water of the molecular probe 4-aminophthalimide (4-AP) was used. 4-AP emission spectra show hypsochromic shifting by changing the excitation wavelength and, using time-resolved spectroscopy, can be detected by a blue shifting with time. Also, the water mixture of an aprotic IL, 1-methyl-3-butylimidazolium tetrafluoroborate (bmimBF4), and three alcohols, methanol (MeOH), 2-propanol (2-PrOH), and t-butanol (t-BOH), were investigated for comparison. Our results show that the water-ILs interaction is dominated by the size of the IL components, in particular, the cation size. Thus, in MIA-water and bmimBF4-water mixtures, 4-AP is mostly solvated by the IL, even at a low IL molar fraction, as in the t-BOH-water mixture. This finding is especially interesting when ILs-water mixtures are used as a solvent in an organic reaction, where it may call attention to water probably not being the solvent that is interacting with the reactants.


Assuntos
Líquidos Iônicos , Álcoois , Fluorescência , Ftalimidas , Água
6.
Polymers (Basel) ; 13(9)2021 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-33922597

RESUMO

In this review, we deal with the formation and application of biocompatible water-in-oil microemulsions commonly known as reverse micelles (RMs). These RMs are extremely important to facilitate the dissolution of hydrophilic and hydrophobic compounds for biocompatibility in applications in drug delivery, food science, and nanomedicine. The combination of two wisely chosen types of compounds such as biocompatible non-polar solvents and ionic liquids (ILs) with amphiphilic character (surface-active ionic liquids, SAILs) can be used to generate organized systems that perfectly align with the Green Chemistry concepts. Thus, we describe the current state of SAILs (protic and aprotic) to prepare RMs using non-polar but safe solvents such as esters derived from fatty acids, among others. Moreover, the use of the biocompatible solvents as the external phase in RMs and microemulsions/nanoemulsions with the other commonly used biocompatible surfactants is detailed showing the diversity of preparations and important applications. As shown by multiple examples, the properties of the RMs can be modified by changes in the type of surfactant and/or external solvents but a key fact to note is that all these modifications generate novel systems with dissimilar properties. These interesting properties cannot be anticipated or extrapolated, and deep analysis is always required. Finally, the works presented provide valuable information about the use of biocompatible RMs, making them a green and promising alternative toward efficient and sustainable chemistry.

7.
Langmuir ; 37(1): 445-453, 2021 01 12.
Artigo em Inglês | MEDLINE | ID: mdl-33373249

RESUMO

Herein, we report the effect of employing two different alcohols, such as n-pentanol and 2,2,3,3,4,4,5,5-octafluoro pentanol (from now on F-pentanol), into 1,4-bis-2-ethylhexylsulfosuccinate (AOT) reverse micelles (RMs), to determine the interfacial activity and establish the best candidate to act as a cosurfactant in supercritical RMs. Dynamic light scattering (DLS), Fourier transform infrared (FT-IR), and fluorescence emission spectroscopy allowed us to determine and understand the behavior of alkanols in RMs. As a result, we found interesting displacements of alkanol molecules within the RMs, suggesting that the electrostatic interaction between SO3- and Na+ weakens because of new interactions of n-pentanol with SO3- through H-bonds, changing the curvature of the micellar interface. According to FT-IR and DLS studies, F-pentanol forms a RM polar core interacting through intermolecular H-bonds, suggesting no perturbations of the AOT RM interface. Hence, n-pentanol was selected as a cosurfactant to form supercritical RMs, which is confirmed by red edge excitation shift studies, using C343 as a molecular probe. Herein, we were able to create RMs under supercritical conditions without the presence of modified surfactants, fluorinated or multitailed compounds, which, to the best of our knowledge, was not shown before.

8.
J Org Chem ; 85(23): 15006-15014, 2020 12 04.
Artigo em Inglês | MEDLINE | ID: mdl-33147953

RESUMO

In this work, two hydrolysis reactions were used as a probe to investigate the properties of reverse micelles (RMs) formed by the ionic liquid-surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT). The results were compared with those found for RMs generated with sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT). As external nonpolar solvents, n-heptane (n-Hp), isopropyl myristate (IPM), and methyl laurate (ML) were used. Thus, the effect of changing the Na+ cation by bmim+ was analyzed, as well as the impact of the replacement of a conventional external nonpolar solvent by biocompatible solvents. The kinetics of the hydrolysis reactions of 4-methoxybenzoyl chloride (OMe) and 4-(trifluoromethyl)benzoyl chloride (CF3) were studied. The results indicate that the replacement of the Na+ counterion by bmim+ in AOT RMs alters the rates of reactions carried out in them and produces changes in the reaction mechanism. In bmim-AOT RMs, the bmim+ cation is located between the surfactant molecules; this has an important influence on the reaction intermediates' stability and, therefore, in the reaction rates and mechanisms. Also, the results indicate that when IPM is used as an external solvent instead of ML or n-Hp, interfacial water molecules have larger nucleophilicity due to the higher interface penetration of IPM.

9.
ACS Omega ; 5(41): 26562-26572, 2020 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-33110984

RESUMO

A series of ionic liquids (ILs) composed by choline (Ch) as a cation and different amino acids (AA) as anions and their respective aqueous mixtures were prepared using different [Ch][AA] contents in a range of 0.4-46 mol % IL. These solvents were used for the first time to achieve an eco-friendlier Paraoxon degradation. The results show that [Ch][AA]/water mixtures are an effective reaction medium to degrade Paraoxon, even when the IL content in the mixture is low (0.4 mol % IL) and without the need of an extra nucleophile. Both the kinetics and the degradation pathways of pesticides depend on the nature of the AA on [Ch][AA] and the amount of an IL present in the mixture. We have demonstrated that in those mixtures with a low amount of [Ch][AA], the hydrolysis reaction is the main pathway for Paraoxon degradation, showing a catalytic effect of the IL. However, as the percentage of [Ch][AA] increases in the mixture, the nucleophilic attack of [Ch][AA] is evident. Finally, the aim of this study was to provide evidence of a promising and biocompatible methodology to degrade a toxic compound (Paraoxon) using a minimal quantity of an IL designed totally from natural resources.

10.
Langmuir ; 36(36): 10785-10793, 2020 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-32830497

RESUMO

The impact of the imidazolium counterion structure on the organized systems formed by the surfactant 1,4-bis-2-ethylhexylsulfosuccinate, AOT, both in aqueous solutions and in nonpolar solvents is investigated. With this in mind, we investigated if the ionic liquid-like (IL-like) surfactant 1-ethyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate, emim-AOT, forms direct micelles or vesicles in water. Dynamic light scattering, zeta potential, conductivity, fluorescence spectroscopy, and UV-visible spectroscopy measurements were performed to characterize the organized systems in aqueous solutions. We also studied the self-aggregation of emim-AOT, 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate, bmim-AOT, and of 1-hexyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate, hmim-AOT, in nonpolar solvents. The results obtained showed that the IL-like surfactant emim-AOT forms direct micelles in water, as sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) does. However, emim-AOT aggregates are larger, have a lower surface charge, are more stable, and have a more polar and less fluid micellar interface than Na-AOT micelles. It was also observed that emim-AOT and hmim-AOT form reverse micelles in nonpolar solvents. The size of the imidazolium cations dramatically influences the size of the reverse micelles and their ability to solubilize water.

11.
Carbohydr Polym ; 224: 115158, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31472856

RESUMO

In this study, water-soluble chitosan (Ch) derivatives were synthesized by the Maillard reaction between Ch and lactose. The Ch derivatives were characterized by FT-IR, 1H-NMR and SLS to determine their structure, degree of deacetylation (DD), and molecular weight (Mw). The solubility at physiological pH, the in vitro antioxidant activity against hydroxyl radical, anion superoxide radical and ABTS cation radical, and the cytotoxicity against epithelial cells of the rat ileum (IEC-18) were also evaluated. The Maillard reaction, derivatives with lower Mw and DD and greater solubility than Ch were obtained. The biological properties of the derivatives were dependent on the concentration, Mw and DD, with antioxidant activity greater than or equal to that of Ch and non-cytotoxic in a wide range of concentrations. The results indicate that Ch derivatization with lactose produces new water-soluble polysaccharides, with antioxidant activity and non-cytotoxic, which can be used as biomaterials for food and pharmaceutical applications.


Assuntos
Fenômenos Químicos , Quitosana/química , Citotoxinas/química , Sequestradores de Radicais Livres/química , Lactose/química , Água/química , Animais , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , Citotoxinas/toxicidade , Sequestradores de Radicais Livres/toxicidade , Ratos , Solubilidade
12.
Langmuir ; 35(41): 13332-13339, 2019 10 15.
Artigo em Inglês | MEDLINE | ID: mdl-31510743

RESUMO

The goal of this work is to understand the influence of the counterion nature on the organized systems formed by 1,4-bis-2-ethylhexylsulfosuccinate surfactants in aqueous solutions and how these aggregates will influence the deoxyribonucleic acid (DNA)-surfactant interactions. With this in mind, two ionic liquid-like surfactants were investigated: 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) and 1-hexyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (hmim-AOT). Measurements of dynamic light scattering, ζ-potential, transmission electron microscopy, and fluorescence and UV-visible spectroscopy were performed to study the characteristics of the vesicles formed by bmim-AOT and hmim-AOT. Regarding the determination of the interaction of the surfactants with DNA, circular dichroism was used. The results obtained showed that bmim-AOT and hmim-AOT ionic liquid-like surfactants spontaneously form unilamellar vesicles in water at very low surfactant concentrations. The characteristics of these aggregates are dependent on the length of the tail of the counterions. The length of the hydrophobic chains of the counterions also influences the DNA-surfactant interactions through hydrophobic effects.

13.
Langmuir ; 35(39): 12744-12753, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31495176

RESUMO

The present study investigated how the presence of butylmethylimidazolium cation (bmim+) alters the interfacial properties of reverse micelles (RMs) created with the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT), in comparison to sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) RMs, employing dynamic light scattering (DLS) and 1H NMR techniques. Moreover, through the hydrolysis reaction of bis(4-nitrophenyl)carbonate inside both RMs as reaction probe, interfacial properties changes were explored in more detail. The kinetic solvent isotope effect was also analyzed. Micellar systems were formed using n-heptane as external nonpolar solvent and water as the polar component. According to the DLS studies, water is encapsulated inside the organized media; however, a different tendency is observed depending on the cationic component of the surfactant. For Na-AOT system, the results suggest that the micellar shapes are probably spherical, while in the case of bmim-AOT, a transition from ellipsoidal to spherical micelles could be occurring when water is added. 1H NMR data show that water is structured differently when Na+ cation is replaced by bmim+; in bmim-AOT RMs, the interaction of water with the surfactant is weaker and the water hydrogen-bonding network is less disturbed than in Na-AOT RMs. Kinetic studies reveal that the hydrolysis reaction in bmim-AOT RMs was much more favorable in comparison to Na-AOT RMs. In addition, when water content decreases in bmim-AOT RMs, the hydrolysis reaction rate increases and the solvent isotope effect remains constant, while for Na-AOT solutions, both the reaction rate and the solvent isotope effect decrease. Our results indicate that bmim+ cation would be located in the surfactant layer in such a way the negative charge density in the interface is less than that in Na-AOT RMs, and the reaction is more favorable. Additionally, as 1H NMR studies reveal, the interfacial water molecules would be more available in bmim-AOT RMs to participate in the nucleophilic attack. Therefore, the present study evidences how the replacement of Na+ counterion by bmim+ alters the composition of the interface of AOT RMs.

14.
Soft Matter ; 15(5): 947-955, 2019 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-30644504

RESUMO

The behavior of the interfacial water entrapped in reverse micelles (RMs) that were formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) was investigated with the use of UV-Vis absorption spectroscopy and nuclear magnetic resonance (NMR) relaxometry. The solvatochromism of two molecular probes, namely, 1-methyl-8-oxyquinolinium betaine (QB) and N,N,N',N'-tetramethylethylenediamine copper(ii)acetylacetonate tetraphenylborate ([Cu(acac)(tmen)][B(C6H5)4]), was investigated. As a comparison, the analog RMs formed by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) were also explored. By varying the water content inside the RMs and consequently the different magnitude of the water-surfactant interactions at the interface, interesting properties were observed by comparing bmim-AOT and Na-AOT RMs. From the solvatochromic behavior of ([Cu(acac)(tmen)][B(C6H5)4]), we found that the interface in bmim-AOT RMs shows a smaller electron donating capacity than that in Na-AOT RMs. QB revealed that the interfacial region is a weaker hydrogen bond donor and less polar than the corresponding Na-AOT RMs. NMR experiments showed that the molecular motion of water in bmim-AOT RMs is less restricted than that of the water molecules confined in Na-AOT RMs. In summary, the results show how the nature of the bmim+ cation affects the interaction between the entrapped water and the RM interface, greatly modifying the interfacial water structure in comparison with the results known for Na-AOT.

15.
J Org Chem ; 84(3): 1185-1191, 2019 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-30608687

RESUMO

The effect of interfacial water entrapped in two types of catanionic reverse micelles (RMs) on the kinetic parameters of the SN2 reaction between dimethyl-4-nitrophenylsulfonium trifluoromethanesulfonate (S+) and n-butylamine (BuNH2) was explored. Two catanionic surfactants, composed of a mixture of oppositely charged ionic surfactants without their original counterions, were used to create the RMs. Thus, benzyl- n-hexadecyldimethylammonium 1,4-bis(2-ethylhexyl) sulfosuccinate (BHD-AOT) and cetyltrimethylammonium 1,4-bis(2-ethylhexyl) sulfosuccinate (CTA-AOT) were formed. Also, the well-known anionic surfactant sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (Na-AOT) was employed as a comparison. Our results showed an important catalytic-like effect of all RMs investigated in comparison with a water-benzene mixture, and the rate constant values depend on the type of surfactant used. Faster reaction in BHD-AOT RMs than in CTA-AOT and Na-AOT RMs was observed. This behavior was attributed to the strong interaction (by hydrogen bonding with AOT anion and ion-dipole interaction with BHD+) between the entrapped water and the BHD-AOT interface, which reduces the solvation capacity of water on S+. In CTA-AOT (and Na-AOT) RMs, the water-interface interaction is weaker and the electron pairs of water can solvate S+ ions. In summary, the chemical structure of the counterion on the catanionic surfactant alters the interfacial region, allowing the progress of a reaction inside the RMs to be controlled.

16.
J Phys Chem B ; 122(15): 4366-4375, 2018 04 19.
Artigo em Inglês | MEDLINE | ID: mdl-29589933

RESUMO

The most critical problem regarding the use of reverse micelles (RMs) in several fields is the toxicity of their partial components. In this sense, many efforts have been made to characterize nontoxic RM formulations on the basis of biological amphiphiles and/or different oils. In this contribution, the microstructure of biocompatible mixed RMs formulated by sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) and tri- n-octylphosphine oxide (TOPO) surfactants dispersed in the friendly solvent methyl laurate was studied by using SAXS and 31P NMR and by following the solvatochromic behavior of the molecular probe 4-aminophthalimide (4-AP). The results indicated the presence of RM aggregates upon TOPO incorporation with a droplet size reduction and an increase in the interfacial fluidity in comparison with pure AOT RMs. When confined inside the mixed systems, 4-AP showed a red-edge excitation shift and confirmed the increment of interfacial fluidity upon TOPO addition. Also, the partition between the external nonpolar solvent and the RM interface and an increase in both the local micropolarity and the capability to form a hydrogen bond interaction between 4-AP and a mixed interface were observed. The findings have been explained in terms of the nonionic surfactant structure and its complexing nature expressed at the interfacial level. Notably, we show how two different approaches, i.e., SAXS and the solvatochromism of the probe 4-AP, can be used in a complementary way to enhance our understanding of the interfacial fluidity of RMs, a parameter that is difficult to measure directly.

17.
R Soc Open Sci ; 4(7): 170481, 2017 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-28791171

RESUMO

Herein we describe the synthesis of gold nanoparticles (Au-NPs) in presence of sulphonated imidazolium salts [1,3-bis(2,6-diisopropyl-4-sodiumsulfonatophenyl)imidazolium (L1), 1-mesityl-3-(3-sulfonatopropyl)imidazolium (L2) and 1-(3-sulfonatopropyl)imidazolium (L3)] in water and in a confinement environment created by reverse micelles (RMs). The Au-NPs were characterized-with an excellent agreement between different techniques-by UV-vis spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential. In homogeneous media, the Au-NPs interact with the imidazolium ring and the sulphonate groups were directed away from the NPs' surface. This fact is responsible for the Au-NPs' stability-over three months-in water. Based on the obtained zeta potential values we assume the degree of coverage of the Au-NPs by the imidazolium salts. In n-heptane/sodium 1,4-bis (2-ethylhexyl) sulfosuccinate (AOT)/water RMs, the Au-NPs formed in presence of sulphonated imidazolium salts present different patterns depending on the ligand used as stabilizer. Interestingly, the Au-NPs are more stable in time when the salts are present in AOT RMs (three weeks) in comparison with the same RMs system but in absence of ligands (less than an hour). Clearly, the sulphonated imidazolium salts are very effective Au-NPs stabilizers in a different medium and this generates a plus to be able to use them for multiple purposes.

18.
Carbohydr Polym ; 171: 85-93, 2017 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-28578974

RESUMO

It is known that Chitosan (Ch) can be used in several applications, such as antimicrobial agent or as drug delivery agent. However, being its water dispersibility very low at physiological pH it is necessary to find a way to improve it. One attractive strategy is to synthesize Chitosan Nanoparticles (Ch-NPs). In this work, a versatile method to obtain Ch-NPs with different and controlled sizes, that were successfully prepared by cross-linking reaction of glutaraldehyde and native chitosan inside of n-heptane/sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/water reverse micelles (RMs) is presented. Highly monodisperse NPs were synthesized as confirmed by Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM) techniques. The particle size was dependent on the reactants concentration, cross-linking degree and mainly the amount of water inside of the AOT RMs used as nanoreactors. While the cross-linking is quite difficult to control in bulk water, the reaction inside the RMs is more manageable and efficient.


Assuntos
Quitosana/síntese química , Micelas , Nanopartículas/química , Quitosana/química , Microscopia Eletrônica de Varredura , Nanopartículas/ultraestrutura , Tamanho da Partícula , Água/química
19.
Org Biomol Chem ; 14(11): 3170-7, 2016 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-26911404

RESUMO

In this work, we have explored how the confinement of the protic ionic liquid (IL) ethylammonium nitrate (EAN) inside toluene/benzyl-n-hexadecyldimethylammonium chloride (BHDC) reverse micelles (RMs) affects the Cl(-) nucleophilicity on the bimolecular nucleophilic substitution (SN2) reaction between this anion and dimethyl-4-nitrophenylsulfonium trifluoromethanesulfonate. To the best of our knowledge this is the first report where toluene/BHDC RMs use EAN as a polar component and it is used as a nanoreactor for carrying out kinetic experiments. Dynamic light scattering results reveal the formation of RMs containing the protic IL. The kinetic results show that upon confinement, EAN becomes a suitable solvent for the SN2 reaction while in homogeneous media it is a bad option. Entrapped in BHDC RMs, due to the strong hydrogen bond interactions, EAN behaves as an aprotic-like IL which cannot deactivate the nucleophilic power of Cl(-) and yet increases the substrate solubility. These facts show the versatility of this kind of organized system to alter the polar solvent entrapped and its influence on the reaction rate when it is used as a nanoreactor.

20.
J Phys Chem B ; 120(3): 467-76, 2016 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-26731512

RESUMO

The limited amount of information about reverse micelles (RMs) made with gemini surfactants, the effect of the n-alcohols in their interface, and the water-entrapped structure in the polar core motivated us to perform this work. Thus, in the present contribution, we use dynamic light scattering (DLS), static light scattering (SLS), and FT-IR techniques to obtain information on RMs structure created, with the gemini dimethylene-1,2-bis(dodecyldimethylammonium) bromide (G12-2-12) surfactant and compare the results with its monomer: dodecyltrimethylammonium bromide (DTAB). In this way, the size of the aggregates formed in different nonpolar organic solvents, the effect of the chain length of n-alcohols used as cosurfactants, and the water-entrapped structure were explored. The data show that the structure of the cosurfactant needed to stabilize the RMs plays a fundamental role, affecting the size and behavior of the aggregates. In contrast to what happens with the RMs formed with the monomer DTAB, water entrapped inside G12-2-12 RMs displays different interaction with the interface depending on the hydrocarbon chain length of the n-alcohol used as cosurfactant. Thus, n-pentanol and n-octanol molecules are located in different regions in the RMs interfaces formed with the gemini surfactant. n-Octanol locates at the RMs interface among the surfactant hydrocarbon tails increasing the water-surfactant polar headgroup interaction. On the other hand, n-pentanol locates at the RMs interface near the polar core, limiting the interaction of water with the micellar inner interface and favoring the water-water interaction in the polar core.

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