Hydrophobic Alkyl Chain Length Research Articles

Supramolecular Organo/hydrogel-Fabricated Long Alkyl Chain α-Amidoamides as a Smart Soft Material for pH-Responsive Curcumin Release.

Low-molecular-mass gelators, due to their excellent biocompatibility, low toxicological profile, innate biodegradability and ease of fabrication have garnered significant interest as they self-assemble through non-covalent interactions. In this study, we have designed and synthesized a series of six α-amidoamides by varying the hydrophobic alkyl chain length (C12-C22), which were well characterized using different spectral techniques. These α-amidoamides formed self-assembled aggregates in a DMSO/water solvent system affording organo/hydrogels at 0.66% w/v, which is the minimum gelation concentration (MGC) making them as remarkable supergelators. The various functionalities present in these gelators such as amides and alkyl chain length pave the way toward excellent gelation mechanism through hydrogen bonding and van der Waals interaction as evidenced from FTIR spectroscopy. Notably, as the chain length increased, organo/hydrogels became more thermally stable. Rheological results showed that the stability and strength of these gelators were considerably impacted by variations in chain length. The SEM morphology revealed dense sheet architectures of the organo/hydrogel samples. Organo/hydrogels have a significant impact on the advancement of innovative drug delivery systems that respond to various stimuli, ushering in a new era in pharmaceutical technology. Inspired by this, we encapsulated curcumin, a chemopreventive medication, into the gel core and further released via gel-to-sol transition induced by pH variation at 37 °C, without any alteration in structure-activity relationship. The drug release behavior was observed by UV-vis spectroscopy. Moreover, cell viability and cell invasion experiments demonstrate that the gel formulations exhibit high biocompatibility and low cytotoxicity. Among the tested formulations, 5e+Cur exhibited remarkable efficacy in controlling A549 cell migration, suggesting significant potential for applications in the pharmaceutical industry.

Self-Assembled Metal-Coordination Nanohelices as Efficient and Robust Chiral Supramolecular Catalysts for Enantioselective Reactions.

The development of chiral nanostructures-based supramolecular catalysts with satisfied enantioselectivity remains a significantly more challenging task. Herein, the synthesis and self-assembly of various amino acid amphiphiles as chiral supramolecular catalysts after metal ion coordination is reported and systematically investigate their enantioselectivity in asymmetric Diels-Alder reactions. In particular, the self-assembly of l/d-phenylglycine-based amphiphiles (l/d-PhgC16 ) and Cu(II) into chiral supramolecular catalysts in the methanol/water solution mixture is described, which features the interesting M/P nanohelices (diameter ≈8nm) and mostly well-aligned M/P nanoribbons (NRs). The M/P supramolecular catalysts show both high but inverse enantioselectivity (>90% ee) in Diels-Alder reactions, while their monomeric counterparts display nearly racemic products. Analysis of the catalytic results suggests the outstanding enantioselectivities are closely related to the specific stereochemical microenvironment provided by the arrangement of the amphiphiles in the supramolecular assembly. Based on the experimental evidence of chirality transfer from supramolecular nanohelices to coordinated Cu(II) and substrate aza-chalcone and the molecular dynamics simulations, the enantioselective catalytic mechanisms are proposed. Moreover, the relationships between molecular structures of amino acid amphiphiles (the hydrophilic head group and hydrophobic alkyl chain length) in supramolecular catalysts and enantioselectivity in Diels-Alder reactions are elaborated.

The structure effect on the physicochemical properties of Gemini surfactants used as viscosity reducer for heavy oil

The structure of surfactants is a key factor affecting their physicochemical properties. Our earlier work synthesized Gemini surfactants CEA-n with different structures. In this paper, the effects of polyether chain length, spacer groups number and the hydrophobic alkyl chain length of surfactants CEA-n on the interfacial properties, wettability, rheological properties and emulsion stability were fully studied in detail, and the effects of surfactant structure on their temperature tolerance and salt resistance properties were explored. The results showed that the variation of polyether chain length of surfactant molecules had the greatest impact on the interfacial tension (IFT), and the surfactants with longer alkyl chains had better interfacial film strength. The wettability of various surfactant systems was investigated by the sessile drop method, and the contact angle decreased remarkably from 92.6° to 17.9° in a short time (300 s) after adding surfactant CEA-6. Judging from the fluid type, each heavy oil emulsion system exhibited pseudoplastic fluid characteristics, and dilute shear phenomenon was observed in the range of 0–50 s−1 with an increasing shear ratio. The particle size, dispersibility and coalescence of the heavy oil O/W emulsion droplets of each system were observed through the microscopic images of the emulsions, and the factors affecting the stability of the emulsions were systematically studied by bottle test. It was found that the increase of oil-water ratio, surfactant concentration and mixing speed would improve the stability of O/W emulsions, while high temperature would accelerate the demulsification process. All these results established the structure-property relationship of surfactant molecules.

Solubility tuning of alkyl amine functionalized carbon quantum dots for selective detection of nitroexplosive

The major issue of luminescent carbon quantum dots (CQDs) is the solubility in wide range of solvent and disappearance of luminescence behavior in its solid state due to aggregation caused quenching. To resolve this issue, in the present work, we have tuned the solubility of carbon quantum dots in different kinds of solvents through surface functionalization technique. Here, we have synthesized three sets of alkyl amine functionalized carbon quantum dots from citric acid and alkyl amine by solvothermal method. We have observed that the solubility of CQDs increases from aqueous medium to organic medium with increasing length of hydrophobic alkyl chains attached at the surface of CQDs. It is seen that n-butyl amine functionalized CQDs (C4-CQD) are soluble in any type of solvents. Here we have also observed that the C4-CQD shows aggregation induced emission instead of aggregation caused quenching in solid state and shows bright yellow luminescence color upon excitation. Besides this, we also report selective detection of both dinitroaniline (DNA) and dinitrophenol (DNP) using this C4-CQD via fluorescence quenching and colorimetric methods. In organic medium both shows significant quenching with emission peak of carbon quantum dots is red shifted (∼30 nm) in presence of DNP whereas no significant peak shift is observed for DNA. CQDs containing paper strip shows yellow spot in presence of DNP but no such characteristic color is appeared after addition of DNA. Using these two techniques, we have selectively identified both DNA and DNP among other nitro compounds by our as-synthesized carbon dots.

Hydrophobically Associating Polyacrylamide “Water-in-Water” Emulsion Prepared by Aqueous Dispersion Polymerization: Synthesis, Characterization and Rheological Behavior

The hydrophobically associating polyacrylamide (HAPAM) is an important kind of water-soluble polymer, which is widely used as a rheology modifier in many fields. However, HAPAM products prepared in a traditional method show disadvantages including poor water solubility and the need for hydrocarbon solvents and appropriate surfactants, which lead to environmental pollution and increased costs. To solve these problems, we reported a novel kind of HAPAM "water-in-water" (w/w) emulsion and its solution properties. In this work, a series of cationic hydrophobic monomers with different alkyl chain lengths were synthesized and characterized. Then, HAPAM w/w emulsions were prepared by the aqueous dispersion polymerization of acrylamide, 2-methylacryloylxyethyl trimethyl ammonium chloride and a hydrophobic monomer. All these emulsions can be stored more than 6 months, showing excellent stability. An optical microscopy observation showed that the particle morphology and the particle size of the HAPAM emulsion were more regular and bigger than the emulsion without the hydrophobic monomer. The solubility tests showed that such HAPAM w/w emulsions have excellent solubility, which took no more than 180 s to dilute and achieve a homogeneous and clear solution. The rheology measurements showed that the HAPAM association increases with a hydrophobe concentration or the length of hydrophobic alkyl chains, resulting in better shear and temperature resistances. The total reduced viscosity was 124.42 mPa·s for cw101, 69.81 mPa·s for cw6-1, 55.38 mPa·s for cw8-0.25, 48.95 mPa·s for cw12-0.25 and 28 mPa·s for cw16-0.25 when the temperature increased from 30 °C to 90 °C. The cw8-2.0 that contains a 2 mol% hydrophobe monomer has the lowest value at 19.12 mPa·s due to the best association. Based on the excellent stability, solubility and rheological properties, we believe that these HAPAM w/w emulsions could find widespread applications.

PANF supported polymeric ionic liquids: Amphiphilic microenvironment for efficient preparation of biodiesel

Efficient and green production is extremely essential to the development of society and environment, and supported polymeric ionic liquids as heterogeneous catalysts are the current research hotspot for chemists. In this study, imidazolium ionic liquids were supported on modified polyacrylonitrile fiber (PANF) by reversible addition fragmentation chain transfer (RAFT) polymerization, and a series of fiber-supported basic catalysts (PANF@VIm-nX) were obtained by ion exchange with different anions. The modified fibers were characterized by FT-IR, XRD, TGA, SEM, 13C CP-MAS NMR and ICP-MS. The results show that the modified fibers are successful and the catalysts have sufficient active sites and mechanical strength to meet the application requirements. Several supported poly(ionic liquid)s catalysts were used to promote the transesterification of methanol and soybean oil to produce biodiesel. The effects ofionicliquidswith different structures on the reaction yield were sufficiently investigated. The anions of ionic liquids and the length of hydrophobic alkyl chains have synergistic effects on the catalytic performance of the catalyst. The fiber catalyst (PANF@VIm-8OMe) with 8 carbon alkyl chains and OMe anion showed the optimal catalytic efficiency. The yield of biodiesel was as high as 95.4 % within 6 h with a catalyst dosage of 4 wt% and a methanol to oil ratio of 30:1 at 60 ℃. In addition, the fiber catalyst had excellent stability and durability, which could be recycled more than 6 times. Finally, the fiber could be twined on the stirring impeller of the reactor, indicating its potential industrial application prospect.

Molecular engineering of complexation between RNA and biodegradable cationic gemini surfactants: role of the hydrophobic chain length

The effects of the hydrophobic alkyl chain length of Cm-E2O-Cm gemini surfactants (m = 12, 14 and 16) on ribonucleic acid were investigated using different methods. The various calculated parameters revealed that complexation occurs via an intercalative binding mode.

Small-angle X-ray scattering as an effective tool to understand the structure and rigidity of the reverse micelles with the variation of surfactant

This study is aimed to utilize the small-angle X-ray scattering technique for getting new insights on the effect of the structure of surfactants on the shape, size, thickness of the diffusion layer, and rigidity of the reverse micelles, formed within a water-in-oil microemulsion. For this study, two important features of the structure of the surfactant i.e. hydrophobic alkyl chain length and the nature of the hydrophilic head group (cationic, anionic, and non-ionic) are taken into consideration. The primary information regarding the shape, diffusion length, and internal structure of reverse micelles was evaluated using the model-free approach. It was found that the reverse micelles formed in the case of cationic and anionic surfactants were spherical whereas cylindrical-shaped reverse micelles were formed with non-ionic surfactants. After critically analyzing the inferences from the model-free approach, an appropriate model for fitting the SAXS data was selected. For cationic and anionic surfactant-based microemulsions, the spherical shell model was chosen while the cylindrical shell model was used for microemulsions formed using non-ionic surfactants. We believe that this study will give a systematic approach to analyze the SAXS data and further add to our understanding of the relation between the surfactant and the structure of the reverse micelles.

Effect of Alkyl Chain Length on Adsorption and Release of Hydrophobic Drug to/from Hydrophobically-modified Gelatin Hydrogel

Hydrogels have become popular as drug carriers. Controlled release of the drugs from hydrogels can reduce dosage, inducing prevention of side effects. However, the hydrophilicity of hydrogels interferes with controlled release of hydrophobic drugs such as anticancer agents or antibiotics. In this study, we developed hydrophobically-modified gelatin (HMG) hydrogel, which was cross-linked only by hydrophobic interaction. HMG does not require toxic chemical cross-linkers to form hydrogel. In addition, the HMG hydrogel has hydrophobic chambers in its structure which hydrophobic drugs can adsorb to and desorb from. In order to control the amount of hydrophobic drugs adsorbed into the hydrogel, hydrophobic alkyl chains with different lengths (C4-C12) were incorporated into gelatin molecules. Uranine was used as a model for hydrophobic drugs. The adsorption test exhibited that the amount of uranine adsorbed in HMG hydrogels could be controlled by varying hydrophobic alkyl chain length and that the drug could be released in a controlled manner. These results show that HMG hydrogels are promising carriers of hydrophobic drugs.

A tailored positively-charged hydrophobic surface reduces the risk of implant associated infections

Implant-associated infections is one of the most challenging post-operative complications in bone-related implantations. To tackle this clinical issue, we developed a low-cost and durable surface coating for medical grade titanium implants that uses positively charged silane molecules. The in vitro antimicrobial tests revealed that the titanium surface coated with (3-aminopropyl) triethoxysilane, which has the appropriate length of hydrophobic alkyl chain and positive charged amino group, suppressed more than 90% of the initial bacterial adhesion of S. aureus, P. aeruginosa, and E. coli after 30 min of incubation. In terms of growth inhibitory rate, the treated surface was able to reduce 75.7% ± 11.9% of bacterial growth after a 24-hour culturing, thereby exhibiting superior anti-biofilm formation in the late stage. When implanted into the rat model infected by S. aureus, the treated surface eliminated the implant-associated infection through the mechanism of inhibition of bacterial adhesion on the implant surface. Additionally, the treated surface was highly compatible with mammalian cells. In general, our design demonstrated its potential for human clinical trials as a low-cost and effective antibacterial strategy to minimize post-operative implant-related bacterial infection.

Structural insights into conformation of amphiphilic quaternary ammonium chitosans to control fungicidal and anti-biofilm functions

Fungal biofilm formation is an emerging problem in a wide range of health-related applications. This study aims to design and synthesize amphiphilic quaternary ammonium chitosans (AQACs) that could bind onto fungal biofilms to kill adherent fungal cells, and establish their structural/fungicidal activity relationships. AQACs with different hydrophobic alkyl chain length (C4, C8, and C12) were synthesized by quaternization of 3-bromopropionic acid with the corresponding tertiary amines, followed by reacting with chitosan using the EDC/NHS chemistry. The new AQACs were soluble in water, yet formed self-aggregates in the solution with different sizes. In antifungal tests against free-floating Candida albicans, shorter alkyl chains (C4) in the AQACs resulted in the most potent fungicidal effect. However, in the treatment of Candida biofilms formed on solid surfaces, AQACs with longer alkyl chains (C8 and C12) were much more effective than their shorter chain counterpart (C4). The effects of alkyl chain self-aggregation on the opposite trend in fungicidal and anti-biofilm activities were discussed. All the AQACs showed excellent cytocompatibility with mammalian cells.

Directed 2D nanosheet assemblies of amphiphilic lignin derivatives: Formation of hollow spheres with tunable porous structure

Synthesis of polymeric hollow spheres with porous structures has attracted significant attention in material applications. In the present work, without requiring any template and core removal, hollow spheres with tunable porous structures from amphiphilic lignin polymers were synthesized by directing the different length of hydrophobic alkyl chains. Remarkably, the results from scanning electron microscope (SEM) showed that lignin hollow sphere possessed only one hole by acetylation, while it became porous structures with the increase of alkyl chain length by acylation of propionylation, butyrylation and valerylation. Amazingly, all the LHSs exhibited strong emission peaks in visible spectral range as excitated with wavelength from 260 to 340 nm. In addition, as revealed by SEM and transmission electron microscope (TEM) images, the formation mechanism for the porous hollow spheres was proposed. The presence of hydrophobic and π–π interactions between the aromatic groups resulted in the lignin molecules gathering mutually to form the bilayers (nanosheets) with some imperfection sites. Then, the 2D patches intended to reduce their total energy via curling, which favored the formation of initial sphere structures, and other 2D patches kept continuously stacking on the surface of spheres, resulting in formation of porous lignin hollow spheres. Our study established a new method for fabricating porous hollow spheres from amphiphilic lignin polymers.

Aggregation behaviors of amine-oxide gemini surfactants

ABSTRACTThe micellar aggregation of a series of gemini surfactants [N, N’-dimethyl-N, N’-bis(2-alkylamideethyl)-ethylenediamine oxide (alkyl = C11H23, C13H27, C15H31)] in aqueous media has been investigated. The results show that there is an excellent agreement among the critical micelle concentration (CMC) values obtained by surface tension and steady-state fluorescence methods. Because of the occurrence of self-coiling or the formation of pre-micellization, the CMC values, the I1/I3 values, and the micelle aggregation numbers (Nagg) at CMC (Nm) increase with the hydrophobic alkyl chain length increasing. Besides, vesicles are observed above the CMC for all these surfactants.

Alkyl Chain Length Dependent Structural and Orientational Transformations of Water at Alcohol-Water Interfaces and Its Relevance to Atmospheric Aerosols.

Although the hydrophobic size of an amphiphile plays a key role in various chemical, biological, and atmospheric processes, its effect at macroscopic aqueous interfaces (e.g., air-water, oil-water, cell membrane-water, etc.), which are ubiquitous in nature, is not well understood. Here we report the hydrophobic alkyl chain length dependent structural and orientational transformations of water at alcohol (CnH2n+1OH, n = 1-12)-water interfaces using interface-selective heterodyne-detected vibrational sum frequency generation (HD-VSFG) and Raman multivariate curve resolution (Raman-MCR) spectroscopic techniques. The HD-VSFG results reveal that short-chain alcohols (CnH2n+1OH, n < 4, i.e., up to 1-propanol) do not affect the structure (H-bonding) and orientation of water at the air-water interface; the OH stretch band maximum appears at ∼3470 cm-1, and the water H atoms are pointed toward the bulk water, that is, "H-down" oriented. In contrast, long-chain alcohols (CnH2n+1OH, n > 4, i.e., beyond 1-butanol) make the interfacial water more strongly H-bonded and reversely orientated; the OH stretch band maximum appears at ∼3200 cm-1, and the H atoms are pointed away from the bulk water, that is, "H-up" oriented. Interestingly, for the alcohol of intermediate chain length (CnH2n+1OH, n = 4, i.e, 1-butanol), the interface is quite unstable even after hours of its formation and the time-averaged result is qualitatively similar to that of the long-chain alcohols, indicating a structural/orientational crossover of interfacial water at the 1-butanol-water interface. pH-dependent HD-VSFG measurements (with H2O as well as isotopically diluted water, HOD) suggest that the structural/orientational transformation of water at the long-chain alcohol-water interface is associated with the adsorption of OH- anion at the interface. Vibrational mapping of the water structure in the hydration shell of OH- anion (obtained by Raman-MCR spectroscopy of NaOH in HOD) clearly shows that the water becomes strongly H-bonded (OH stretch max. ≈ 3200 cm-1) while hydrating the OH- anion. Altogether, it is conceivable that alcohols of different hydrophobic chain lengths that are present in the troposphere will differently affect the interfacial electrostatics and associated chemical processes of aerosol droplets, which are critical for cloud formation, global radiation budget, and climate change.

The effect of hydrophobic alkyl chain length on the mechanical properties of latex particle hydrogels

The hydrogels with optimal alkyl segments reinforced by LPs exhibited the maximum fracture stress of 1.2 MPa and elongation of 2336%.

Structural features and surfactant properties of core–shell type micellar aggregates formed by gemini piperidinium surfactants

Abstract Aqueous micellar solution of piperidinium gemini surfactants was investigated by small angle X-ray scattering (SAXS) and the real space structural information of the micelles was deduced by indirect Fourier transformation (IFT) method. The maximum dimension of the micelles and their shape were determined by evaluating the pair distance distribution function (PDDF) and the electron density profile of the aqueous surfactant solution. These gemini surfactants formed core–shell type micelles in the aqueous solution above their cmc values having ellipsoidal structure. The dilute aqueous solutions of these surfactants were further investigated to determine their surfactant properties by surface tension and conductivity method. The self-aggregation and thermodynamic properties as well as the shape, size and internal structure of the micelles formed by these surfactants were found to be dependent on the methylene spacer units and hydrophobic alkyl chain length of the gemini surfactants.

Synthesis of amphiphilic dendronized polymers to study their self‐assembly and transport behavior

Herein, we report on the synthesis of PEG‐1000‐diethyl ester and 2‐azido‐propane‐1,3‐diol‐based copolymers utilizing Novozym 435 (Candida antarctica lipase) using a biocatalytic method. The linear base copolymer was then functionalized with polyglycerol‐based regular [G1.0] and [G2.0] dendrons and C12/C14 hydrophobic alkyl chains via an efficient “Click approach.” The resulting amphiphilic dendronized polymers form well‐defined micelles in aqueous solutions. The transport behavior of these polymers was studied by using Nile red as a fluorescent model dye. The cytotoxicity profiles of a few representative polymers were evaluated, and the effect of hydrophobic alkyl chain length as well as the hydrophilic polyglycerol dendron's generation on the biocompatibility of polymeric systems was studied. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Self-Assembly of Hybridized Peptide Nucleic Acid Amphiphiles.

In this report, a series of peptide nucleic acid amphiphiles (PNAAs) with hybridization properties were designed and synthesized. Driven by hydrophobic interaction, the hybridized PNAAs can form uniform micelles, the base stacking interaction from PNA segments further stabilized the micelles. The effects of hydrophobic alkyl chain length, structure of hydrophilic peptides, concentration, and pH on the self-assembly behavior of partly complementing PNAA duplexes were explored.

Synthesis and self aggregation properties of ester-functionalized heterocyclic pyrrolidinium surfactants

Linear fatty alcohols on reaction with chloro/bromo acetic acid in the presence of catalytic amount of p-toluene sulphonic acid monohydrate under solvent-free conditions are converted into alkyl-2-haloacetate which on reaction with N-methyl pyrrolidine gives ester-functionalized pyrrolidinium surfactants. Thus, new series of ester-functionalized heterocyclic pyrrolidinium head group containing cationic surfactants have been synthesized by green approach via energy saving and cost effective methodology. These new surfactants have been investigated for their surface properties by surface tension, conductivity, and fluorescence method. Surface properties of these surfactants have been found to be far better compared to conventional heterocyclic cationic surfactants having similar hydrophobic alkyl chain length.

Effect of the spacer of gemini surfactants on reverse micellar extraction of bovine serum albumin

Reverse micellar extraction has the potential to overcome the hurdles associated with the conventional separation and purification procedures for proteins and hence has been considered as an alternative to conventional techniques. The surfactants used in protein extraction so far have been almost exclusively di-2-ethylhexyl sodium sulfosuccinate and cetyl trimethyl ammonium bromide. In the present paper, we extracted bovine serum albumin (BSA) by using a kind of novel surfactant – gemini surfactant Cm-s-Cm·2Br (m = 12 and 16, and s = 2, 5, 8, and 12). Compared with conventional surfactant reverse micelles, all the gemini surfactant reverse micelles show superior performance. The length and flexibility of spacer s of Cm-s-Cm·2Br contribute to the advantages of gemini surfactant reverse micelles, and increasing hydrophobic alkyl chain length weakens the effect of the spacer. As a result, the minimum content ([surfactant]min) of the surfactant needed for transferring protein into an organic phase is increased in the order of s being 5, 8, 12 (2) sequentially and [surfactant]min for C16-s-C16·2Br is higher than that for C12-s-C12·2Br. The loading capacity of C16-s-C16·2Br reverse micelle is lower than that of C12-s-C12·2Br reverse micelle and C12-12-C12·2Br reverse micelle can load the maximum amount of protein. In the backward extraction process, gemini surfactants with s being 8 and 12 are much more efficient than the other gemini surfactants at pH 4.3. With C12-8-C12·2Br and C12-12-C12·2Br reverse micelles, BSA can be recovered under neutral or basic conditions given a sufficient amount of salt present (while a pH of ca. 4.3 is prerequisite for the recovery of BSA from conventional surfactant reverse micelles) and the efficiency with C12-12-C12·2Br reverse micelle is higher. Since so far the reports about the effect of surfactant structure on protein extraction have been limited, this study should help us know more about how to optimize the surfactant structure.