Surfactant Micelles Research Articles

Denaturants and Solutol® HS15 in ophthalmic formulations: Insights into their combined effects

In the field of ophthalmology, significant attention is dedicated to developing micellar carriers to enhance ocular drug delivery. Urea is a well-known denaturant and has been used as an excipient in several ocular formulations due to its efficacy as an ocular hypotensive agent. The presence of urea as an excipient may influence the characteristics of the micellar nanocarrier in the formulation and needs to be investigated. Solutol® HS15, a well-known nonionic surfactant and a commonly used nanocarrier in drug formulations, enhances the solubilization and stability of ocular drugs. However, a detailed study of its interaction with various pharmaceutical excipients is still lacking. With this intention, the present study focuses on comprehending the interaction between Solutol® HS15 micelles with urea and its derivatives. Here, we present a detailed analysis on the influence of urea and its derivatives (methylurea, dimethylurea) on Solutol® HS15 using small-angle neutron scattering (SANS), dynamic light scattering (DLS), and cloud point (CP) measurements. The presence of urea and its derivatives strongly affects the CP, leading to a significant increase in its values when urea derivatives are present. Additionally, the SANS and DLS results also indicate a significant decrease in micellar size, suggesting demicellization. The observed effects of urea derivatives on Solutol® HS15 micelles underscore the importance of considering solvent-surfactant interactions in understanding the behavior of surfactant-based systems. This research will provide greater insight into the interactions between urea and its derivatives and Solutol® HS15, which will assist in understanding the morphology and size distribution of surfactant micelles for drug delivery applications.

The role of presence of wormlike micelles of ionic surfactants on the sterilization efficiency of sodium hypochlorite

Abstract This paper describes an attempt to increase the sterilising efficacy of sodium hypochlorite (SH) by prolonging its shelf life in gel mode through the presence of wormlike micelles. No effect was observed on the presence of SH on the ratio of highest viscosity peak of 20:80 of 3 % (w/w) sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB). On the other side, the presence of SH has a relatively negative effect on transformation process from spherical (three-dimensional, 3D) micelles to wormlike (one-dimensional, 1D) micelles. The gel state of the aqueous SH solution is maintained even at a ratio of 20:80 SDS:CTAB 3 % (w/w). Measurements of the biological activity of the gel using Staphylococcus aureus bacteria show that the sterilizing efficiency of SH is enhanced by the presence of 1D micelles. In contrast, the stability of SH using the kinetic method shows a sudden decrease in its stability due to the presence of 1D micelles, and the same is the case when both SDS and CTAB micelles are present. It was concluded that the increase in the biological activity of SH due to presence of micelles in gel or liquid mode resulted from their chemical interference, which acts as an antibacterial formulation.

Distinct Solubilization Mechanisms of Medroxyprogesterone in Gemini Surfactant Micelles: A Comparative Study with Progesterone

The solubilization behavior of medroxyprogesterone (MP) within gemini surfactant micelles (14-6-14,2Br−) was investigated and compared with that of progesterone to uncover distinct solubilization mechanisms. We employed 1H-NMR and 2D ROESY spectroscopy to elucidate the spatial positioning of MP within the micelle, revealing that MP integrates more deeply into the micellar core. This behavior is linked to the unique structural features of MP, particularly its 17β-acetyl group, which promotes enhanced interactions with the hydrophobic regions of the micelle, while the 6α-methyl group interacts with the hydrophilic regions of the micelle. The 2D ROESY correlations specifically highlighted interactions between the hydrophobic chains of the surfactant and two protons of MP, H22 and H19. Complementary machine learning and electron density analyses supported these spectroscopic findings, underscoring the pivotal role of the molecular characteristics of MP in its solubilization behavior. These insights into the solubilization dynamics of MP not only advance our understanding of hydrophobic compound incorporation in gemini surfactant micelles but also indicate the potential of 14-6-14,2Br− micelles for diverse drug delivery applications.

Direct Synthesis of Artificial Esterase through Molecular Imprinting Using a Substrate-Mimicking Acylthiourea Template.

Most reported artificial esterases hydrolyze only activated esters. We here report a one-pot synthesis of artificial esterases via molecular imprinting. An acylthiourea template hydrogen bonds with 4-vinylbenzoic acid and coordinates to a polymerizable zinc complex inside a cross-linkable surfactant micelle. Double cross-linking of the micelle yields a polymeric nanoparticle catalyst that mimics a metalloenzyme to activate a water molecule for nucleophilic attack on the bound ester. The catalyst hydrolyzes both activated and unactivated esters under mild conditions with selectivity.

Investigating the interactions between an industrial lipase and anionic (bio)surfactants

In laundry formulations, synergies between amphiphiles and other additives such as enzymes increase sustainability through a large decrease in energy consumption. However, traditional surfactants are derived from petroleum, requiring chemical modifications (sulfonation, ethoxylation, or esterification) and generating environmental pollution through toxicity and low degradability. Use of biosurfactants removes these issues. To provide a firmer basis for the use of biosurfactants, we report on the interactions between the industrial lipase LIPEX® and three common biosurfactants, rhamnolipids, sophorolipids, and surfactin. The model surfactant sodium dodecyl sulfate (SDS) is included in the study for comparison. A thorough characterization by Small-angle X-ray scattering (SAXS) provides valuable information on the enzyme’s oligomerization and the surfactant micelles’ ellipsoidal morphology. Additionally, the enzymatic activity and complex formation in different surfactant mixtures are studied using isothermal titration calorimetry, activity assays, and SAXS. SDS activates the enzyme while promoting a controlled association of monomers while the biosurfactants inhibit the enzyme, independent of their effects on its quaternary structure. Rhamnolipids and surfactin promote lipase dimerization while sophorolipids have no significant effect on lipase quaternary structure. Based on these data, we propose a partial replacement that allows the enzyme to retain enzymatic activity while improving the environmental footprint of the formulation.

Precision picric acid detection via a fluorenone-amide functionalized fluorescent micellar probe

Detection of picric acid (PA) in aqueous solutions is crucial for pollution control, extending beyond national security and military applications. Herein, a binary ensemble AM@SDS has been assembled by encapsulating a fluorenone functionalized amide-based probe (AM) within the micelles of an anionic surfactant, sodium dodecyl sulphate (SDS) in an aqueous medium. A range of spectroscopic techniques, including high-resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), and fluorescence spectroscopy (FL), have been employed to characterize the formation of micelles of AM@SDS. A remarkable increase in fluorescence intensity was observed upon interactions of AM with the microenvironment of SDS micelles. Conversely, the fluorescence intensity at 358 nm was significantly quenched in the presence of PA compared to other nitroaromatic compounds (NACs). The detection limit for PA was found to be 368 nM. Furthermore, the binary ensemble AM@SDS has demonstrated remarkable efficacy in detecting PA in real water samples from diverse sources such as lake, river, and tap water, achieving an exceptional recovery rate of up to 99.9 %.

Oppositely charged polymer-surfactant nanoparticles stabilized by triblock copolymers for enhanced oil loading

When oppositely charged polymers and surfactants combine, they can form a concentrated phase rich in micelles interconnected by polymer chains. Dispersing this concentrated phase as nanoparticles in an aqueous media can be a way to load and deliver hydrophobic ingredients. This study employed triblock copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), EOxPOyEOx, also known as poloxamers or pluronics, to disperse the concentrated phase, forming nanoparticles of aggregated micelles connected by the polyion chains. We showed that nanoparticles formed by hexadecyltrimethylammonium bromide (CTAB), poly(acrylic acid) (PAA), and different EOxPOyEOx copolymers can enhance the loading of oily ingredients compared to pure surfactant micelles. Dispersions with 1.6 wt% of nanoparticles exhibited water-like viscosity and loaded up to 0.48 wt% of oil. Characterization techniques, including dynamic light scattering (DLS), electrophoretic mobility, small-angle X-ray scattering (SAXS), and cryogenic transmission electronic microscopy (cryo-TEM), revealed positively charged spherical 50–180 nm nanoparticles with a core formed by concentrated micelles, that were stable for at least 4 months. Variations in the EO and PO block lengths did not impact morphology, showing that different EOxPOyEOx copolymers were suitable for dispersing the nanoparticles. Increasing EO block length size decreased the diameter of nanoparticles and enhanced stability, providing a means to control their properties. In conclusion, nanoparticles formed by oppositely charged polymer-surfactant mixtures and stabilized by triblock copolymers showed potential for applications, such as sprays, due to their effective oil loading, high stability, and facile preparation.

Promoting sustainability: Micellization and surface dynamics of recycled monoethanolamine surfactants

The purpose of this work is to explore the micellization and surface characteristics of recycled monoethanolamine (MEA) surfactants, designated as MK-1, MK-2, and MK-3, and to assess their potential in promoting sustainability. Traditional surfactants contribute to environmental pollution due to their non-renewable sources and persistence in nature. This study addresses the knowledge gap in sustainable surfactant development by investigating the efficacy of recycled MEA surfactants. Its novelty lies in its innovative recycling process, which not only reduces waste, but also produces surfactants with superior properties. This study also investigates the distillation-based separation of MEA from degraded compounds, showcasing its potential in waste management. It was found that a maximum MEA separation of 17 % was achieved with a resulting purity of 83 %. Optimal conditions, including the use of catalysts and a temperature of 393K, led to enhanced oleic acid conversion. Similarly, reactions conducted with catalysts at 433K for 3 h demonstrated favorable outcomes. Surfactant MK-1 exhibited superior foam and emulsifying abilities, generating a foam height of 60 cm with only 8 cm lost after 10 min. Regarding emulsifying properties, the sunflower oil/water system with a 0.1% MK-1 solution exhibited delayed water separation from the emulsion. MK-3 displayed the highest pC20 value at 2.91. Among the MEA-based surfactants, MK-1 reduced surface tension to 33.1 mN/m. The maximum surface excess concentration (Γmax) for all surfactants was consistent. This demonstrates that recycled MEA surfactants exhibited favorable micellization properties, with a critical micelle concentration (CMC) comparable to that of virgin counterparts. Over ten cycles of use and regeneration, the performance of recycled MEA surfactants remained stable. Surface tension measurements indicated improved interfacial activity, while emulsification capacity tests revealed an enhanced performance in forming stable emulsions. This implies the potential of recycled MEA surfactants to produce high-performance surfactants, thereby promoting sustainability in the chemical industry.

Effective Detoxification of Olive Mill Wastewater Using Multi-Step Surfactant-Based Treatment: Assessment of Environmental and Health Impact.

Olive mill wastewater (OMW) poses a significant environmental challenge and health concern in olive-producing countries, including Jordan. Surfactant micelles are frequently employed as solubilizing agents to enhance the water solubility of chemical compounds. This study aims to leverage the sodium dodecyl sulfate (SDS) micelles in a multi-step process to detoxify OMW for agricultural and industrial uses and reduce its impact. The OMW was treated in multiple steps: screening, coagulation with different chemicals, and distillation with different surfactants. The treatment steps were monitored using LC-MS, GC-MS, ICP-MS, chemical oxygen demand contents, and total phenolic compounds. The detoxification of OMW was evaluated using standard germination assays, MTT assays using tissue culture, and toxicity assays using fluorescence bacteria. Following the treatment, the seed growth rate improved significantly from 0% to 100%. The GC-MS revealed a substantial decrease in pollutants. The concentration of polyphenols was reduced to 2.5%, while the COD level decreased to 35%. The toxicity in bacteria was significantly reduced in a time-dependent manner, and the toxicity in human cells decreased by 95%. Additionally, between 50% and 95% of metals in OMW were removed. The multi-step SDS-based approach successfully detoxified the OMW and enhanced water quality, which would pave the road for its direct application in industry and agriculture.

Exploration of micellization and phase separation nature of surfactants in metformin hydrochloride + additives media: An experimental and DFT study

The study explores the aggregation and phase separation of a newly synthesized cationic surfactant − octadecyltriethylammonium bromide (OTEAB) and triton X-100 (TX-100) respectively with/without metformin hydrochloride (MMH) drug in absence/presence of NaCl. The conductivity measurements were performed to investigate the aggregation of cationic OTEAB at temperatures between 298.15 and 323.15 K with a 5 K gap. The micelle development of OTEAB in pure state and with MMH drug has been assessed by determining the critical micelle concentration (CMC). The reduction of CMC of OTEAB has been detected owing to the introduction of the MMH drug. The CMC was further decreased in attendance of NaCl. The CMC values also demonstrate the dependency on the change of temperature in all situations investigated. The decrease of CP values of triton X-100 and MMH mixture in aqueous NaCl was attained with the augmentation of the concentration of NaCl. The negative and positive values of free energy of micellization (ΔGm0) and clouding (ΔGc0) indicate the spontaneous and nonspontaneous nature of the respective processes. The enthalpy (ΔHm0) and entropy(ΔSm0) changes of the micellization were negative (exothermic) and positive, respectively. The enthalpy (ΔHc0) and entropy(ΔSc0) changes of the clouding were negative (exothermic) and positive, respectively, at lesser and higher concentrations of NaCl. The values of ΔHm0/ΔHc0 and ΔSm0/ΔSc0 designated that both hydrophobic and electrostatic interaction are present as important forces among the components under investigation. The thermodynamics of transfer and the enthalpy-entropy compensation parameters for the two processes were also computed and explained appropriately. Herein, we have also performed the computational analysis to find out the optimized structures, HOMO-LUMO orbitals, and the band gaps of OTEAB, MMH, and OTEAB+MMH mixture.

Surfactant Micelles as Catalysts: Kinetic Modeling and Key Models

Surfactant molecules possess both hydrophilic and hydrophobic properties, featuring a hydrophilic head and a hydrophobic tail. When surfactants reach a critical micellar concentration, they assemble into stable molecular aggregates called micelles. These micelles serve as effective catalysts for a range of chemical reactions. To elucidate and make sense of experimental data related to micelle-catalyzed reactions, researchers often employ kinetic modeling as a valuable tool. Several kinetic models have been introduced to describe the reaction rates within micellar environments. In this discussion, we will provide a concise overview of four widely utilized models: The Berezin model, the pseudophase model, the ion exchange model, and the Piskiewicz model.

Effect of cationic surfactants on titration behavior of isotactic and atactic poly(methacrylic acid)

By forming strong complexes with oppositely charged polyelectrolytes, cationic surfactants significantly affect their solution properties. We investigated the effect of bound surfactant on the titration behavior of two isomer forms of poly(methacrylic acid), PMA, atactic and isotactic PMA, aPMA and iPMA, respectively, which are known for the cooperative change in chain conformation in water. The bound surfactant micelles increase the initial degree of ionization, α, of carboxyl groups on PMA, shift the conformational transition to higher α and make it narrower, and exclude the complexed chains from the solution. The titration curves were analyzed in the framework of the Henderson-Hasselbalch theory and the Gibbs free energy change of the conformational transition was calculated. The results were discussed in the context of a complex influence of surfactant on the PMA chain conformation in solution. It is proposed that the PMA-surfactant interaction changes from a so-called hydrophobic mode, which is responsible for the solubilization of the unionized and water-insoluble iPMA at low α, to a predominantly electrostatic one at high α, which leads to the precipitation of both aPMA and iPMA from solution. Constant pH simulations using simple coarse-grained models for the PMA polymers and individual surfactants were performed to rationalize the titration behavior of PMAs in the absence and presence of surfactant. By inducing an attractive interaction between PMA monomers, an excellent agreement between the experimental and numerical titration curves was obtained. Such agreement becomes poorer upon the addition of surfactant; however, the main features of the PMA titration curves are preserved, which supports the role of hydrophobic interactions in PMA-surfactant association at low pH values and that of electrostatics at higher pH.

Effect of cyclodextrin modification on complexation thermodynamics with hexadecyltrimethylammonium cation with emphasis on subsequent surfactant micellization

Surfactant-cyclodextrin based complexes, are ideal guest-hosts for fundamental studies since both surfactant hydrophobic region with head group, and cyclodextrin cavity can be systematically varied. This allows, better understanding of the contributions that different chemical entities do to the stabilization of the complex and subsequent surfactant micellization. We studied systematically the interaction of hexadecyltrimethylammonium bromide (▪) with native α-, β- and γ-CDs, 2-hydroxypropylated and methylated α- and β-CDs, using isothermal titration calorimetry (ITC), measuring below critical micellization concentration (CMC) at least at three temperatures in the range (288.15 to 318.15) K. Data were treated simultaneously allowing the estimation of thermodynamically consistent temperature dependences of the equilibrium constant, the enthalpy and heat capacity for the inclusion complex formation. The data for cation/CD interaction were analysed mostly by the sequential binding model with 1:1 and 1:2 (cation:CD) stoichiometries, while some cation-CD combinations were examined using only 1:1, or more complicated 1:1, 2:1 and 2:2 stoichiometries. Thermodynamic quantities for complexation are discussed in terms of structural features, their temperature dependence with previous literature being examined. The shift of the CMC in presence of CDs was calculated founding large discrepancies with data in the literature. An extended mass-action chemical equilibrium model is proposed including free surfactant, free CD, complexes of the above mention stoichiometries, also including micelle, surfactant-cyclodextrin complexes of higher order stoichiometry, similar to that found for sodium dodecylsulfate-CDs systems. The new model provides a qualitative match with our own calorimetric titration curves measured above CMC for all studied ▪/CD combinations, and matches quantitatively with literature CMC values.

Degradation of sodium dodecyl benzene sulfonate in aqueous solution by electron beam radiation and changes in surfactant micelle property

In this study, we investigated the degradation of surfactant sodium dodecyl benzene sulfonate (SDBS) in aqueous solution using electron beam radiation. The removal efficiency of SDBS approached nearly 100%, achieving a COD removal rate of 7–20% with an absorbed dose of 5.0 kGy. Upon irradiation, several notable changes in SDBS micelles were observed. The absolute value of zeta potential and the average diameter size decreased. SEM observations revealed that the clustered aggregates of SDBS micelles fragmented into irregular filamentous pieces. Moreover, the interfacial tension increased remarkably and approached the level of pure water at 2.5 kGy for SDBS in a pure water solution and 5.0 kGy for SDBS in a brine water solution. The foaming power disappeared for SDBS in pure water and decreased to 20 mm for SDBS in brine water at 10 kGy. The defoaming rate of SDBS solution increased incrementally from an initial range of 1–2 mm/min to 3.0–5.6 mm/min at 5.0 kGy. In summary, when SDBS is decomposed, new system is created with new properties. Electron beam radiation offers a clean and sustainable approach to degrade SDBS in wastewater.

Development of MOF-derived Co3O4 microspheres composed of fiber stacks for simultaneous electrochemical detection of Pb2+ and Cu2+

As an ideal transition metal oxide, Co3O4 is a P-type semiconductor with excellent electrical conductivity, non-toxicity and low cost. This work reports the successful construction of Co3O4 materials derived from metal-organic frameworks (MOFs) using a surfactant micelle template-solvothermal method. The modified electrodes are investigated for their ability to electrochemically detect Pb2+ and Cu2+ in aqueous environments. By adjusting the mass ratios of alkaline modifiers, the morphological microstructures of Co3O4-X exhibit a transition from distinctive microspheres composed of fiber stacks to rods. The results indicate that Co3O4-1(NH4F/CO(NH2)2 = 1:0) has a distinctive microsphere structure composed of stacked fibers, unlike the other two materials. Co3O4-1/GCE is used as the active material of the modified electrode, it shows the largest peak response currents to Pb2+ and Cu2+, and efficiently detects Pb2+ and Cu2+ in the aqueous environment individually and simultaneously. The linear response range of Co3O4-1/GCE for the simultaneous detection of Pb2+ and Cu2+ is 0.5–1.5 μM, with the limits of detection (LOD, S/N = 3) are 9.77 nM and 14.97 nM, respectively. The material exhibits a favorable electrochemical response, via a distinctive Co3O4-1 microsphere structure composed of stacked fibers. This structure enhances the number of active adsorption sites on the material, thereby facilitating the adsorption of heavy metal ions (HMIs). The presence of oxygen vacancies (OV) can also facilitate the adsorption of ions. The Co3O4-1/GCE electrode also exhibits excellent anti-interference ability, stability, and repeatability. This is of great practical significance for detecting Pb2+ and Cu2+ in real water samples and provides a new approach for developing high-performance metal oxide electrochemical sensors derived from MOFs.Graphical abstract

Dissipative particle dynamics simulation and experimental studies of pseudo-gemini surfactants with different hydrophobic chain lengths

In this work new pseudo-gemini type surfactants are constructed via a simple, energy and material efficient way, using piperazine, propylene oxide and seven different fatty acids: capric, lauric, myristic, stearic, oleic and linolenic. The compounds are characterized by 1H NMR, 13C NMR and FTIR studies. Micellization and adsorption properties of the novel pseudo-gemini surfactants are investigated via surface tension and conductivity measurements. Antimicrobial properties are evaluated using the simple disk diffusion test method. Dissipative Particle Dynamics (DPD) simulations are performed to model aggregation behavior of the new pseudo-gemini surfactants. Experimental studies revealed that Critical Micelle Concentration (CMC) of the obtained pseudo-gemini surfactants are lower than 1 mmol/L. Theoretically calculated CMC values are slightly higher than experimental CMC values. However, overall, very good agreement between theoretical and experimental CMC values is observed. Radial Distribution Function (RDF) and radius of gyration (Rg) plots are analyzed to gain further insight into aggregation of the surfactant molecules in aqueous environment. The DPD model of the pseudo-gemini amphiphiles successfully predicts the most important traits of the aggregation process.

Determining the Role of Surfactant on the Cytosolic Delivery of DNA Cross-Linked Micelles.

Nucleic Acid Nanocapsules (NANs) are nucleic acid nanostructures that radially display oligonucleotides on the surface of cross-linked surfactant micelles. Their chemical makeup affords the stimuli-responsive release of therapeutically active DNA-surfactant conjugates into the cells. While NANs have so far demonstrated the effective cytosolic delivery of their nucleic acid cargo, as seen indirectly by their gene regulation capabilities, there remain gaps in the molecular understanding of how this process happens. Herein, we examine the enzymatic degradation of NANs and confirm the identity of the DNA-surfactant conjugates formed by using mass spectrometry (MS). With surface enhanced (resonance) Raman spectroscopy (SE(R)RS), we also provide evidence that the energy-independent translocation of such DNA-surfactant conjugates is contingent upon their release from the NAN structure, which, when intact, otherwise buries the hydrophobic surfactant tail in its interior. Such information suggests a critical role of the surfactant in the lipid disruption capability of the DNA surfactant conjugates generated from degradation of the NANs. Using NANs made with different tail lengths (C12 and C10), we show that this mechanism likely holds true despite significant differences in the physical properties (i.e., critical micelle concentration (CMC), surfactants per micelle, Nagg) of the resultant particles (C12 and C10 NANs). While the total cellular uptake efficiencies of C12 and C10 NANs are similar, there were differences observed in their cellular distribution and localized trafficking, even after ensuring that the total concentration of DNA was the same for both particles. Ultimately, C10 NANs appeared less diffuse within cells and colocalized less with lysosomes over time, achieving more significant knockdown of the target gene investigated, suggesting more effective endosomal escape. These differences indicate that the surfactant assembly and disassembly properties, including the number of surfactants per particle and the CMC can have important implications for the cellular delivery efficacy of DNA micelles and surfactant conjugates.

Rheological behavior and solution pH response properties of nanoparticle-regulated low surface tension systems.

Regarding the rheological properties of fluids, certain nanoparticles can markedly modify the rheological behavior of low surface tension solutions by interacting with surfactant molecules. In this work, a low surface tension fluid with cetyltrimethylammonium chloride was prepared, and the silica nanoparticles were uniformly dispersed into it by ultrasonic dispersion. By adjusting the size, shape, and concentration of nanoparticles, the fluid behavior can be changed from Newtonian to non-Newtonian with finely tuned viscosity and characterized by a shear-thinning rheological behavior. In addition, this work explored how variations in environmental temperature and solution pH affect the rheological responses of the low surface tension suspension system. The experimental findings revealed that increasing the temperature substantially decreases the system's viscosity and induces a shear-thickening behavior. It is particularly significant that, under extreme pH conditions (either strongly acidic or alkaline), the viscosity of the nanoparticle suspensions was markedly enhanced at a particle concentration of 10 000 ppm. This interesting result coincided with a notable reduction in the zeta potential and an increase in the average particle size, suggesting an intensified aggregation of particles within the suspension system. A mechanism detailing the interaction between silica nanoparticles and surfactant micelles was proposed. This work indicates that the incorporation of nanoparticles into surfactant solutions offers a powerful approach to modulating fluid rheology across various conditions.

Investigation of micellization and thermodynamic properties of cationic gemini surfactant (12-2-O-2-12) in the presence of organic solvents

The micellization behaviour and thermodynamic properties of synthesized cationic gemini surfactant (12-2-O-12-12), N,N′-didodecyl-N,N,N′,N′-tetramethyl-N,N′-(oxybis(ethane-2,1-diyl))-diammonium dibromide were studied in the presence of organic solvents for four different temperatures (25, 30, 35 and 40 °C). Aqueous solutions of 10 % and 20 % methanol (MeOH), ethanol (EtOH), isopropanol (IPOH) and dimethyl sulfoxide (DMSO) were used as solvents. The critical micelle concentration (CMC) of cationic gemini surfactant and the degree of counterion dissociation (α) were determined by the conductometric method. Using the CMC and α values for each of the four temperatures, the values of the standard Gibbs free energy (ΔGmo), Gibbs free energy of transfer (ΔGm,transo), enthalpy (ΔHmo), and entropy (ΔSmo) of micellization were calculated. It was observed that the CMC and α values increased with increasing solvent percentage and temperature. It was found that in all cases, the standard Gibbs free energy and enthalpy values were negative while both the micellization entropy and the standard Gibbs free energy of transfer are positive. Negative Gibbs free energy values indicated that micellization was a spontaneous situation, while positive entropy values indicated the existence of a disordered situation. The positive ΔGm,transo values show that the presence of solvents makes the environment unfavorable for micelle formation.

Site-Selective Functionalization of Molecularly Imprinted Nanoparticles to Recognize Lysine-Rich Peptides.

Sequence-selective binding of peptides has been a long-standing goal of chemists. As one of the most abundant amino acids in proteins, lysine plays an important role in protein functions as well as in antimicrobial and cell-penetrating peptides. Herein, we report molecularly imprinted nanoparticles (NPs) with high sequence selectivity for lysine-rich peptides. The NPs are prepared from molecular imprinting of cross-linkable surfactant micelles and postmodification of the imprinted pockets by photoaffinity labeling. The method allows carboxylic acids to be installed precisely near the lysine amino side chains, greatly enhancing the binding strengths of lysine-rich peptides. Small variations in the peptide sequence can be distinguished, and the binding affinity correlates positively with the number of lysine groups in model tripeptides. The method applies to complex lysine-rich biological peptides, achieving hundreds of nanomolar binding affinities and excellent binding specificities.