Octadecyl Moieties Research Articles

Hydrophobic Magnetite Nanoparticles for Bioseparation: Green Synthesis, Functionalization, and Characterization

In this study, three types of hydrophobized alkyl-modified magnetic nanoparticles (MNPs) comprising direct alkylated-MNPs (A-MNPs), silica-mediated alkyl MNPs (A-SiMNPs), and arginine (Arg)-mediated alkyl MNPs (A-RMNPs) were synthesized successfully. For this purpose, the co-precipitation method was used to synthesize, and octadecyl trimethoxy silane (OTMS) was used as a functionalizing agent. Accordingly, the hydrophobic octadecyl moieties were connected to MNPs. The nanoparticles (NPs) were characterized by XRD, SEM, FTIR, CHN, DLS, and zeta potential analyses. The synthesized coated MNPs represented a decrease in surface charge and magnetization alongside increased surface hydrophobicity and size. It was revealed that the alkylation process was successfully performed to all three MNPs, but A-SiMNPs showed the highest hydrophobicity. Additionally, the novel A-RMNPs, as the most biocompatible type, and A-MNPs showed the highest magnetization among the synthesized MNPs. The results indicate that synthesized NPs can play an important role in bio applications. However, it was revealed that alkyl chains are easily connected to all three MNPs, and that A-MNPs contained the highest alkyl chains and could affect the re-folding and denaturation process of recombinant proteins.

Liquid-crystalline behavior and ion transport properties of block-structured molecules containing a perfluorinated ethylene oxide moiety complexed with a lithium salt

The liquid-crystalline behavior of fluorinated block-structured molecules and the ion transport properties of their complexes with a Li salt have been examined. The block-structured molecules comprise a perfluorinated oligo (ethylene oxide) moiety containing a terminal methyl carbonate or a terminal hydroxyl group and an octadecyl moiety. These molecules exhibit highly ordered smectic phases. The fluorinated molecule with a terminal methyl carbonate possesses an isotropization temperature lower than that of the analogous non-fluorinated molecule. The fluorinated molecule complexed with a Li salt shows ionic conductivities on the order of 10−6 S cm−1 in the smectic phase formed at ambient temperature, while conductivities on the order of 10−5 S cm−1 are observed in the isotropic phase. A perfluorinated oligo (ethylene oxide) monoalkyl ether containing a terminal methyl carbonate has been developed for potential application as quasi-solid-state electrolytes for Li-ion batteries. The fluorinated block-structured molecule self-assembles to form nanosegregated bilayer structures, which can be used for anisotropic Li ion transport when complexed with a Li salt. The complex shows ionic conductivities on the order of 10−6 S cm−1 in the ordered smectic phase formed at ambient temperature.

Enhancement of Thermal Stability and Selectivity by Introducing Aminotriazine Comonomer to Poly(Octadecyl Acrylate)-Grafted Silica as Chromatography Matrix

This paper introduces a poly(octadecyl acrylate) (pODA)-based organic phase on silica, which is assisted by 2-vinyl-4,6-diamino-1,3,5-triazine (AT), for a chromatography stationary phase. The ODA-AT copolymer grafting onto silica surface was characterized by elemental analysis, FT-IR spectroscopy, scanning electron microscopy, thermo gravimetric analysis and differential scanning calorimeter (DSC). An endothermic peak top of the copolymer-grafted silica was increased to 46 °C from 38 °C, which was a peak top of pODA homopolymer. For high performance liquid chromatography (HPLC) application, the molecular selectivity increased with an increase in the AT contents of the ODA-AT copolymer as organic phase. The co-existence of an aminotriazine moiety in the copolymer promoted side-chain ordering of the poly(octadecyl) moiety, thus enhancing molecular planarity selectivity for PAHs in reversed-phase liquid chromatography.

Synthesis and oxidative stability of phenolic antioxidants immobilized by cellulose nanocrystals

Antioxidants are immobilized by attaching them as functional groups to cellulose nanocrystals. The synthesis route includes a carboxymethylation step followed by covalent grafting of di-tert-butylphenol moieties (first product). To improve solubility within non-polar polymeric matrices additional octadecyl groups are added (second product). Both products are fully characterized using FT-IR, solid-state NMR, and thermogravimetric analyses. The degree of substitution in each functionalization step is determined by conductometric titration. The syntheses are successful, with moderate degrees of functionalization due to limited accessibility of the hydroxyl groups, which correlates with the geometric shape of cellulose nanocrystals. The stabilization effect is determined by oxidation induction time measurements in squalane. Further, the influence of additional octadecyl moieties grafted to cellulose nanocrystals is assessed.

Evaluation of adsorption and desorption steps in the solid-phase extraction of explosives using carbon/silica gel nanocomposites.

New series of carbon/silica gel nanocomposites, carbosils, prepared by the carbonization of starch bound to silica gel, and carbosils additionally silylated with octadecyldimethylchlorosilane were synthesized. These materials were applied as adsorbents in the solid-phase extraction of explosive nitrate esters and nitroaromatics from aqueous solutions. The adsorption and desorption steps were evaluated separately. It was found that both the molecular properties of explosives (dipole moments, orbital energies, solvation effects) and textural properties influenced by carbon deposits or octadecyl moieties have a large impact on the recovery rates. It was shown that the composites with moderate content of carbon deposits or with the highest amounts of carbon deposits and additionally silylated can be used as materials tailored for extraction of explosives from the aqueous solutions.

Organic-sulfur-zinc hybrid nanoparticle for optical applications synthesized via polycondensation of trithiol and Zn(OAc)2

Organic-sulfur-zinc hybrid materials were prepared via polycondensation of Zn(OAc)2 and trithiols bearing various alkyl groups. A soluble nanoparticle could be obtained by the polycondensation using a trithiol bearing octadecyl moieties. The good dispersing ability as nano-scaled particles was confirmed by dynamic light scattering and atomic force microscopy analyses. This hybrid nanoparticle was miscible with poly(methyl methacrylate) and served as a refractive additive to increase refractive indexes. The calculated refractive index value for the nanoparticle was 1.58.

Dual targeting folate-conjugated hyaluronic acid polymeric micelles for paclitaxel delivery

A series of novel self-assembled hyaluronic acid derivatives (HA-C18) grafted with hydrophobic octadecyl moiety and further dual targeting folic acid-conjugated HA-C18 (FA-HA-C18) were synthesized. With the increase in the degree of substitution of octadecyl group from 12.7% to 19.3%, the critical micellar concentration of HA-C18 copolymers decreased from 37.3 to 10.0μg/mL. Paclitaxel (PTX) was successfully encapsulated into the hydrophobic cores of the HA-C18 and FA-HA-C18 micelles, with encapsulation efficiency as high as 97.3%. The physicochemical properties of the polymeric micelles were measured by DLS, TEM and DSC. Moreover, in vitro release behavior of PTX was investigated by dialysis bag method and PTX was released from micelles in a near zero-order sustained manner. In vitro antitumor activity tests suggested PTX-loaded HA-C18 and FA-HA-C18 micelles exhibited significantly higher cytotoxic activity against MCF-7 and A549 cells compared to Taxol at a lower PTX concentration. The cellular uptake experiments were conducted by quantitative assay of PTX cellular accumulation and confocal laser scanning microscopy imaging of coumarin-6 labeled HA-C18 and FA-HA-C18 micelles in folate receptor overexpressing MCF-7 cells. Folate and CD44 receptor competitive inhibition studies performed by fluorescence microscopy imaging suggested intracellular delivery of HA-C18 and FA-HA-C18 micelles were efficiently taken up via CD44 receptor-mediated endocytosis. The folate receptor-mediated endocytosis further enhanced internalized amounts of FA-HA-C18 micelles in MCF-7 cells, as compared with HA-C18 micelles. The internalization pathways of PTX-loaded HA-C18 and FA-HA-C18 micelles might include clathrin-mediated endocytosis, caveolae-mediated endocytosis and macropinocytosis. Therefore, the present study suggested that HA-C18 and FA-HA-C18 copolymers as biodegradable, biocompatible and cell-specific targetable nanostructure carriers, are promising nanosystems for cellular and intracellular targeting delivery of hydrophobic anticancer drugs.

Capillary electrochromatographic testing of monolithic silica columns synthesized according to an experimental design approach

Monolithic silica capillary columns synthesized following a three-level design were evaluated for the electrochromatographic separation of acidic and neutral compounds. The influences of four factors in the sol-gel synthesis, i.e. the concentrations of tetramethylorthosilicate (TMOS) and PEG in the starting mixture, the gelation temperature and the silanization modifying time, on the electrochromatographic performance of the resulting C18-silica capillary monoliths were studied. The considered responses were retention factor, resolution, symmetry factor, column efficiency, electrokinetic porosity and the equivalent length of the monolith. The four factors were varied to change the pore structure and the surface coverage with octadecyl moieties, resulting in nine stationary phases. The retentive properties of the columns were initially characterized with alkylbenzenes. Next, the separation for acetylsalicylic acid (ASA) and its related compounds was optimized and used to evaluate the performance of the nine stationary phases considering six responses. A compromise between the different responses was found around higher concentrations of tetramethylorthosilicate and PEG with a lower gelation temperature and a modifying time of 2 h. Column efficiencies up to 96,000 plates/m and resolutions above 1.9 were obtained for the acetylsalicylic acid separation, with a sufficient EOF to yield rapid analysis, which showed improvements over the center-point stationary phase.

Bioanalysis of pentoxifylline and related metabolites in plasma samples through LC‐MS/MS

Analytical aspects related to the assay of pentoxifylline (PTX), lisofylline (M1) and carboxypropyl dimethylxanthine (M5) metabolites are discussed through comparison of two alternative analytical methods based on liquid chromatography separation and atmospheric pressure electrospray ionization tandem mass spectrometry detection. One method is based on a 'pure' reversed-phase liquid chromatography mechanism, while the second one uses the additional polar interactions with embedded amide spacers linking octadecyl moieties to the silicagel surface (C-18 Aqua stationary phase). In both cases, elution is isocratic. Both methods are equally selective and allows separation of unknowns (four species associated to PTX, two species associated to M1) detected through specific mass transitions of the parent compounds and owning respective structural confirmation. Plasma concentration-time patterns of these compounds follow typical metabolic profiles. It has been advanced that in-vivo formation of conjugates of PTX and M1 is possible, such compounds being cleaved back to the parent ones within the ion source. The first method was associated with a sample preparation procedure based on plasma protein precipitation by strong organic acid addition. The second method used protein precipitation by addition of a water miscible organic solvent. Both analytical methods were fully validated and used to assess bioequivalence between a prolonged release generic formulation and the reference product, under multidose and single dose approaches.

Selectivity comparisons of monolithic silica capillary columns modified with poly(octadecyl methacrylate) and octadecyl moieties for halogenated compounds in reversed-phase liquid chromatography

Stationary phase selectivities for halogenated compounds in reversed-phase HPLC were compared using C18 monolithic silica capillary columns modified with poly(octadecyl methacrylate) (ODM) and octadecyl moieties (ODS). The preferential retention of halogenated benzenes on ODM was observed in methanol/water and acetonitrile/water mobile phases. In selectivity comparison of selected analytes on ODM and ODS, greater selectivities for halogenated compounds were obtained with respect to alkylbenzenes on an ODM column, while similar selectivities were observed with a homologous series of alkylbenzenes on ODM and ODS columns. These data can be explained by greater dispersive interactions by more densely packed octadecyl groups on the ODM polymer coated column together with the contribution of carbonyl groups in ODM side chains. For the positional isomeric separation of dihalogenated benzenes ( ortho-, meta-, para-), the ODM column also provided better separation of these isomers for the adjacently eluted isomers that cannot be completely separated on an ODS column in the same mobile phase. These results imply that the ODM column can be used as a better alternative to the ODS column for the separation of other halogenated compounds.

Open tubular capillary electrochromatography migration behavior of enkephalins in etched chemically modified fused silica capillaries

Fused silica capillaries for use in electrophoretic analyses are etched with ammonium bifluoride in the presence of a second inorganic salt (CuCl 2, CrCl 3, NaNO 3, or (NH 4) 2CO 3). The effects of the presence of these inorganic components in the surface matrix on the electromigration behavior of enkephalins are evaluated. Resolution, efficiency and peak shape are used to compare the various columns. In some cases the etched surface is then modified by the addition of an octadecyl moiety using a silanization/hydrosilation procedure. The surface properties of the etched capillaries can also be evaluated by electroosmotic flow measurements. RSDs of migration times under identical experimental conditions were <1%.

A new method for evaluation of the mobility of silica-grafted alkyl chains by suspension-state 1H NMR

Although molecular mobility is usually probed by measurement of the T1 relaxation time, it is not the case for methylene groups of grafted acyl chains because each methylene group has a different mobility and hence, a different T1 relaxation time depending on the distance from the junction between organic molecule and nonorganic particle. Therefore, we devised a very simple method that can semiquantitatively determine the extent of mobility in the grafted acyl chains. Silica-supported poly(octadecylacrylate) (Sil-ODAn), polymeric octadecylsilyl silica (polymeric ODS), and monomeric octadecylsilyl silica (monomeric ODS) were studied by comparing the intensity of NMR peaks from grafted molecules with the same amount of nongrafted molecules. In the case of Sil-ODAn, with a gradual increase in temperature, the intensity of the proton signals (1H NMR) of the octadecyl moieties (mainly methylene groups) rose dramatically. This dramatic rise was at the same temperature as that of an endothermic peak detectable in its DSC thermogram, indicating a relatively complete solid to liquid phase transition. Sil-ODAn, as the stationary phase in RP-HPLC, showed analogous temperature dependencies of the separation factor between naphthacene and triphenylene (as a simple indicator of shape selectivity). Using this method we determined the liquid phase percentage (LPP) in Sil-ODAn, polymeric ODS, and monomeric ODS at various temperatures. We suggest LPP as a semiquantitative index of mobility for grafted organic layers.Key words: comb-shaped polymer, nanocomposite, alkyl chain mobility, NMR, liquid chromatography.

Universal Approach for Selective Trace Metal Determinations via Sequential Injection−Bead Injection−Lab-on-Valve Using Renewable Hydrophobic Bead Surfaces as Reagent Carriers

A new concept is presented for selective and sensitive determination of trace metals via electrothermal atomic absorption spectrometry based on the principle of bead injection (BI) with renewable reversed-phase surfaces in a sequential injection-lab-on-valve (SI-LOV) mode. The methodology involves the use of poly(styrene-divinylbenzene) beads containing pendant octadecyl moieties (C18-PS/DVB), which are preimpregnated with a selective organic metal chelating agent prior to the automatic manipulation of the beads in the microbore conduits of the LOV unit. By adapting this approach, the immobilization of the most suitable chelating agent can be effected irrespective of the kinetics involved, optimal reaction conditions can be used for implementing the chelating reaction of the target metal analyte with the immobilized re-agent, and an added degree of freedom is offered in selecting the most favorable elution mode in order to attain the highest sensitivity. The potential of the SI-BI-LOV scheme is demonstrated by taking Cr(VI) as a model analyte, using a 1,5-diphenylcarbazide (DPC)-loaded bead column as the active microzone. As this reaction requires the use of high acidity, it is also shown that the bead material exhibits excellent chemical stability at low pH values. On-line pH sample adjustment prevents alteration of the original distribution of chromium species while ensuring fast rates for the DPC-Cr(VI) reaction. The proposed procedure was successfully applied to the determination of trace levels of Cr(VI) in natural waters containing high levels of dissolved salts (such as seawater and hard tap water) without requiring any dilution step. Method validation was performed by determination of total chromium in an NIST standard reference material (NIST 1640, natural water) after Cr(III) oxidation, and the results were in good agreement with the certified value.

Evaluation of microstructural features of a new polymeric organic stationary phase grafted on silica surface: A paradigm of characterization of HPLC-stationary phases by a combination of suspension-state 1H NMR and solid-state 13C-CP/MAS-NMR

Silica-supported poly(octadecylacrylate) (Sil-ODA n ), polymeric octadecylsilyl silica (polymeric ODS), and monomeric octadecylsilyl silica (monomeric ODS) were studied by a combination of suspension-state 1H NMR and solid-state 13C CP/MAS-NMR to probe the mechanisms underlying their functions as stationary phases for RP-HPLC. Sil-ODA n , with a strong temperature dependent separation behaviour showed correspondent temperature dependent manifestations in both suspension-state 1H NMR and solid-state 13C CP/MAS-NMR experiments. With a gradual increase in temperature, intensity of proton signals ( 1H NMR) of octadecyl moieties (mainly methylene groups) rose dramatically. This dramatic rise was at the same temperature of an endothermic peak detectable in its DSC thermogram indicating a relatively complete solid to liquid phase transition. In addition temperature dependencies of the ratio of trans to gauche conformed well to temperature dependencies of the separation factor between naphthacene and triphenylene (as a simple indicator of shape selectivity). Therefore NMR spectra of Sil-ODA n were used as a reference for ascertaining percentage of octadecyl moieties of liquid type mobility in the two other stationary phases. Using this method we determined percentage of liquid phase in polymeric ODS and monomeric ODS at various temperatures. We suggest a combination of suspension-state 1H NMR and solid-state 13C CP/MAS-NMR for structure-dynamic characterization of various kinds of hydrocarbon chains grafted onto the silica particles.

Use of inorganic salts during the etching process in the fabrication of chemically modified capillaries for open tubular electrochromatography

Capillaries for use in electrophoretic analyses are etched with ammonium bifluoride and in some cases a second inorganic salt is included in the process. The effects of the presence of these inorganic components in the surface matrix on the electromigration of heterocyclic aromatic amines and enkephalins are evaluated. Resolution, efficiency, and peak shape are used to compare the various columns. In one instance, the etched surface is then modified by the addition of an octadecyl moiety using a silanization/hydrosilation procedure. The surface properties of the various etched capillaries are also compared by electroosmotic flow measurements.

Preparation and characterization of alkylated polymethacrylate monolithic columns for micro‐HPLC of proteins

Protein separations were carried out by micro-high performance liquid chromatography (micro-HPLC) with surface alkylated monolithic columns, which were prepared by in situ copolymerization of glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA) in the presence of dodecanol and toluene as porogens. First, glycidyl groups at the surface of the porous monolith were hydrolyzed with sulfuric acid. The hydroxyl groups thus formed were then reacted with n-alkyl chloride to form alkylated stationary phase. Separation performance for proteins on columns with C18 and C8 stationary phases was compared. The results showed that a poly(GMA-EGDMA) support derivatized with octadecyl moieties could achieve much better resolution than one with octyl groups. A protein mixture was separated with the octadecylated poly-(GMA-EGDMA) monolithic column, and the effluent peaks were collected and analyzed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The physical properties of the monolithic columns such as column morphology, surface area, mesopore size distribution, and column permeability were further characterized by scanning electron microscopy (SEM), multipoint BET nitrogen adsorption/desorption, and Darcy's law, respectively.

Capillary electrochromatography with monolithic silica column: I. Preparation of silica monoliths having surface-bound octadecyl moieties and their chromatographic characterization and applications to the separation of neutral and charged species.

Monolithic silica columns with surface-bound octadecyl (C18) moieties have been prepared by a sol-gel process in 100 microm ID fused-silica capillaries for reversed-phase capillary electrochromatography of neutral and charged species. The reaction conditions for the preparation of the C18-silica monoliths were optimized for maximum surface coverage with octadecyl moieties in order to maximize retention and selectivity toward neutral and charged solutes with a sufficiently strong electroosmotic flow (> 2 mm/s) to yield rapid analysis time. Furthermore, the effect of the pore-tailoring process on the silica monoliths was performed over a wide range of treatment time with 0.010 M ammonium hydroxide solution in order to determine the optimum time and conditions that yield mesopores of narrow pore size distribution that result in high separation efficiency. Under optimum column fabrication conditions and optimum mobile phase composition and flow velocity, the average separation efficiency reached 160 000 plates/m, a value comparable to that obtained on columns packed with 3 microm C18-silica particles with the advantages of high permeability and virtually no bubble formation. The optimized monolithic C18-silica columns were evaluated for their retention properties toward neutral and charged analytes over a wide range of mobile phase compositions. A series of dimensionless retention parameters were evaluated and correlated to solute polarity and electromigration property. A dimensionless mobility modulus was introduced to describe charged solute migration and interaction behavior with the monolithic C18-silica in a counterflow regime during capillary electrochromatography (CEC )separations. The mobility moduli correlated well with the solute hydrophobic character and its charge-to-mass ratio.

Capillary electrochromatography with monolithic-silica columns. II. Preparation of amphiphilic silica monoliths having surface-bound cationic octadecyl moieties and their chromatographic characterization and application to the separation of proteins and other neutral and charged species.

Three different synthetic routes have been introduced and evaluated for the preparation of amphiphilic silica-based monoliths possessing surface-bound octadecyl ligands and positively charged groups. The amphiphilic silica monoliths (designated as cationic C18-monoliths) have been designed for use in reversed-phase capillary electrochromatography (RP-CEC) with hydro-organic mobile phases. These amphiphilic stationary phases yielded anodic electroosmotic flow (EOF) over a wide range of mobile phase pH. The magnitude of EOF remained constant up to pH 4.0 and then decreased at pH > 4.0 due to the ionization of silanol groups and the subsequent decrease in the net positive surface charge density of the amphiphilic monoliths. The cationic C18-monoliths exhibited reversed-phase chromatography (RPC) behavior toward non-polar solutes (e.g., alkyl benzenes), which parallels that observed with octadecyl-silica (ODS) monoliths. On the other hand, the amphiphilic stationary phases exhibited both non-polar and polar interactions toward slightly polar solutes such as anilines and PTH-amino acids. CEC retention factor k* and velocity factor k*e, which reflects the contribution of the electrophoretic mobility, were evaluated for charged solutes such as anilines and proteins.

Organo-silica nano-particles used in ultrahigh-pressure liquid chromatography.

A simple one-step process was used to synthesize uniform, spherical organosilica nano-particles containing octadecyl moieties. These nano-particles, having a diameter of 670 nm, were slurry packed into fused-silica capillary tubes of 50 microm internal diameter and tested for use in ultrahigh-pressure liquid chromatography (UHPLC) at inlet pressures of about 50,000 psi (approximately 3,500 bar), providing for the use of HPLC with nano-particle packed columns. The retention characteristics of a column packed with the organo-nano-particles were shown to be stable under acidic (pH < 1) and basic (pH > 11) conditions. Fast analysis times and relatively high separation efficiencies (approximately 500,000 plates m(-1)) were obtained under the conditions used.

Applications of chemically modified and coated etched capillaries for the separation of basic molecules

A comparison of the migration behavior of two antibiotics is made between several types of etched columns used in the open tubular format of capillary electrochromatography. The types of columns evaluated are: (1) etched and unmodified; (2) etched and bonded with an octadecyl moiety; (3) etched and bonded with a cholesterol moiety; (4) etched and coated with an anionic surfactant; and (5) etched and coated with a neutral (zwitterionic) surfactant. In addition to evaluating the influence of the stationary phase, the effect of buffer pH is also measured. Each of the antibiotic samples consist of several components and the resolution capabilities of the various columns are tested in order to determine how OTCEC can be optimized for the analysis of small basic compounds.