Presence Of CTA Research Articles

Incorporation of tyrosine in the Co/MCM-41: Green and efficient peroxidase mimetic

Tyrosine (Tyr) was incorporated in the Co/MCM-41 channels by adding template-containing Co/MCM-41 and Tyr solution via a simple green approach. The prepared material was characterized using UV–vis, FT-IR, XRD, TGA-DTG, EDX, and N2 adsorption/desorption analytical techniques. For comparison, Co-Tyr/[CTA]MCM-41 (CTA: Cetyltrimethylammonium bromide) was also synthesized by mixing a solution of Co-Tyr with [CTA]MCM-41. The prepared samples were used as a peroxidase mimetic in the presence of H2O2. Co-Tyr/[CTA]MCM-41 prepared by the first method was found to be highly active for the oxidation of 3,3ʹ,5,5ʹ-tetramethylbenzidine (TMB), following the typical Michaelis-Menten kinetics and exhibiting the excellent peroxidase-like catalytic performance. This high activity was due to the phenol hydroxyl group of the Tyr, the presence of CTA+ cations, and hydrophobicity induced by the organic template.

Adsorption of CTAB on Sapphire-c at High pH: Surface and Zeta Potential Measurements Combined with Sum-Frequency and Second-Harmonic Generation.

The adsorption of cetyltrimethylammonium bromide (CTA+Br-) on sapphire-c surfaces was studied at pH 10 below the surfactants' critical micelle concentration. The evolution of interfacial potentials as a function of CTAB concentration was characterized by surface and zeta potential measurements and complemented by molecular dynamic (MD) simulations as well as by second-harmonic (SHG) and vibrational sum-frequency generation (SFG) spectroscopy. The changes in interfacial potentials suggest that the negative interfacial charge due to deprotonated surface aluminols groups is neutralized and can be even overcompensated by the presence of CTA+ cations at the interface. However, SFG intensities from strongly hydrogen-bonded interfacial water molecules as well as SHG intensities decrease with both increasing CTAB concentration and the magnitude of the surface potential. They do not suggest a charge reversal at the interface, while the change in zeta potential is actually consistent with an apparent charge inversion. This can be qualitatively explained by results from MD simulation, which reveal adsorbed CTA+ cations outside a first strongly bound hydration layer of water molecules, where they can locally distort the structural order and replace some of the interfacial water molecules adjacent to the first layer. This is proposed to be the origin for the significant loss in SFG and SHG intensities with increasing CTAB concentration. Moreover, we propose that CTA+ can act as a counterion and enhance the occurrence of deprotonated surface aluminols that is consistent with the decrease in surface potential.

A new nanocomposite catalyst based on clay‐supported heteropolyacid for the green synthesis of 2,4,5‐trisubstituted imidazoles

Intercalation of cetyltrimethylammonium (CTA+) cations within the nanolayers of montmorillonite (MMT) clay followed by reaction with Keggin‐type phosphomolybdic acid (PMo) resulted in the synthesis of (CTA)3PMo‐MMT nanocomposite catalyst. The prepared nanocomposite catalyst was characterized using different physicochemical methods such as Fourier‐transform infrared and inductively coupled plasma–optical emission spectroscopies, X‐ray diffraction, and nitrogen adsorption–desorption (Brunauer–Emmett–Teller method) analyses. Characterization techniques demonstrated the intercalation of (CTA)3PMo species into the nanolayers of MMT. The resulting (CTA)3PMo‐MMT nanocomposite catalyst efficiently catalyzed the synthesis of 2,4,5‐trisubstituted imidazoles under solvent‐free conditions. The efficiency is due to the fact that the presence of CTA+ species makes the nanocomposite catalyst hydrophobic and facilitates the accessibility of hydrophobic reactants to active sites in the course of the reaction. High activity and selectivity were achieved in the presence of the prepared nanocomposite catalyst. The nanocomposite catalyst was readily isolated from the reaction mixture using simple filtration, washed with ethanol, and recycled five times without a major loss of activity.

Toughening Cellulose: Compatibilizing Polybutadiene and Cellulose Triacetate Blends.

We report the synthesis of an ABA triblock copolymer of the structure CTA-b-PB-b-CTA (CTA = cellulose triacetate and PB = polybutadiene) and its ability to compatibilize immiscible CTA/PB polymer blends. CTA-b-PB-b-CTA was synthesized via ring-opening metathesis polymerization of cyclooctadiene (COD) in the presence of CTA containing a single olefin on the reducing end. The ABA triblock copolymer was incorporated into CTA/PB blends, resulting in films that were clear, tough, and creaseable, and increases in modulus, elongation at break, and toughness were observed with addition of as little as 1 wt % compatibilizer. Scanning electron microscopy revealed well-defined PB phases in the CTA matrix that decreased in domain size as more compatibilizer was added. This work may enhance the application scope of CTA and other cellulose-derived renewable polymers.

Synthesis of Ni(OH)2 in micellar environment: structural, spectroscopic, and electrochemical studies

This work describes the chemical synthesis of nickel hydroxide in the presence of cationic and anionic surfactants (dodecyl benzene sulfonate, DBS−, and cetyltrimethylammonium, CTA+). The materials were characterized by X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. Our findings highlighted that the synthesis in the presence of anionic DBS−, the α-Ni(OH)2 structure was preferentially formed. This material showed a high structural disorder and a high amount of intercalated species, suggesting the presence of both micelles and individual surfactants. On the other hand, the synthesis performed in the presence of CTA+ has not showed any drastic change in the material structure compared with pure Ni(OH)2; nevertheless, the intercalated cationic surfactant was identified by FTIR measurements. The enhanced electrochemical response found for the Ni(OH)2/DBS− over the Ni(OH)2/CTA+ modified electrodes can be attributed to the enhancement of the ionic diffusion through the solid material as an effect of the high structural disorder and the presence of the excess of the negative electric charge in the Ni(OH)2 sheets.

One-Pot Synthesis and Physicochemical Properties of an Organo-Modified Saponite Clay

An organo-saponite clay containing intercalated cetyltrimethylammonium (CTA(+)) cations was synthesized by an efficient one-step hydrothermal method and was compared with a CTA-exchanged saponite prepared by a classical postsynthesis intercalation route. In both hybrid samples, surfactant loading up to 10% was achieved. A comparative investigation of the physicochemical properties of both solids was carried out by a multidisciplinary approach, by using a combination of spectroscopic, structural, and thermal characterization tools. Powder X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) data indicated that the one-pot-prepared solid showed that the presence of CTA(+) molecules in the synthesis gel did not affect the clay structure. In addition, thermal analysis suggested that the inorganic layers play an active role in stabilizing and protecting the surfactant molecules by increasing their thermal stability. A different arrangement of intercalated CTA(+) ions in the two hybrid clays was observed by solid state NMR in combination with Fourier transform infrared (FTIR) spectroscopy and assigned to a different all-trans/gauche conformation ratio of the surfactant depending on the synthetic method used to prepare the two final materials. The surfactant organization is also influenced by the lamellae charge density, which is different in the two organo-modified materials as found by (27)Al and (29)Si MAS NMR experiments.

Reversible Addition−Fragmentation Chain Transfer Polymerization of N-Isopropylacrylamide: A Comparison between a Conventional and a Fast Initiator

The reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) was studied to determine the reasons for deviation of experimental molecular weights to lower molecular weight at high monomer conversion when S-1-dodecyl-S-(alpha,alpha'-dimethyl-alpha' '-acetic acid)trithiocarbonate (CTAm) and S,S-bis(alpha,alpha'-dimethyl-alpha' '-acetic acid)trithiocarbonate (CTAd) were used as RAFT agents at 65 degrees C. For this purpose, experiments were performed in N,N'-dimethylformamide (DMF) at the NIPAM/CTA ratio of 200 with initiators capable of yielding fast and slow initiation, respectively by photochemical and thermal process, either at ambient temperature or at 65 degrees C. When the polymerization of NIPAM was conducted under these conditions with Irgacure-2959 (IRGC) as photoinitiator, a continuing supply of primary radicals by incremental initiator addition was required to achieve reasonably high conversion. This effect was also apparent by the loss of linearity of the first-order kinetic plot with a conventional initiator (4,4-azobis(4-cyanovaleric acid) (ACVA) as azo-initiator, 10h (t1/2) decomposition at 65 degrees C) indicating that steady-state concentration of the macroradical decreases significantly with the initiator consumption. Nevertheless, polymers with predictable number-average molecular weight Mn (i.e., based on [monomer]/([CTA] + [initiator]) ratio) and narrow polydispersities were obtained (PDIs << 1.2) with CTAm indicating that the process of chain growth was controlled. When CTAd was used, instead of CTAm, the polymers obtained were characterized by a larger polydispersity (1.2 < PDIs < 1.3). The so-called "living steady-state concentration" in chain equilibration together with the linear dependence of Mn vs conversion was observed only when the 200/1 NIPAM/CTA mixture in DMF was subjected to a permanent photoirradiation at 65 degrees C. With ACVA, the deviation of the experimentally measured molecular weights at high conversion was accounted for by the simultaneous self-initiated polymerization of NIPAM with the controlled process in the presence of CTA at 65 degrees C. Similar drift from the linear dependence Mn vs conversion was also observed at 65 degrees C when a significant number of low molecular weight polymer chains were generated intentionally by photodecomposition of IRGC.

Ion-Association Aggregation of an Anionic Porphyrin at the Liquid/Liquid Interface Studied by Second Harmonic Generation Spectroscopy

Interfacial ion-association adsorption and aggregation of a water-soluble porphyrin, tetrakis(4-sulfonatephenyl)porphyrin (TPPS) diacid, which was promoted by a cationic cetyltrimethylammonium ion (CTA(+)), was studied by second harmonic generation (SHG) spectroscopy. Comparing the interfacial SH spectrum with the transmission absorption spectrum of TPPS in the aqueous solution elucidated the aggregation behavior of TPPS at the heptane/water interface. The time-dependent SHG spectra for TPPS aggregation and the interfacial tension lowering in the presence of CTA(+) were discussed on the basis of an electrostatic adsorption model. Then, it was suggested that TPPS diacid was highly concentrated by the ion-association with CTA(+) at the interface, which was the intermediate state before the final aggregated state.

Controlled Radical Polymerization of an Acrylamide Containing l-Phenylalanine Moiety via RAFT

Homopolymers of a monosubstituted acrylamide having an amino acid moiety in the side chain, N-acryloyl-l-phenylalanine methyl ester (A-Phe-OMe), have been synthesized by reversible addition−fragmentation chain transfer (RAFT) polymerization. Two dithioesters were used as chain transfer agents: benzyl 1-pyrrolecarbodithioate (CTA 1) and benzyl dithiobenzoate (CTA 2). The controlled character of the polymerization in the presence of CTA 1 in dioxane at 60 °C was confirmed by the formation of narrow polydispersity products, the molecular weight controlled by the monomer/CTA molar ratio, the linear relationship between the molecular weight and conversion, and the ability to increase the molecular weight by a second addition of monomer. Poly(A-Phe-OMe) with controlled molecular weight, low polydispersity, and enhanced isotacticity was also prepared by RAFT polymerization in the presence of catalytic amounts of Lewis acid, Y(OTf)3. The RAFT polymerizations of A-Phe-OMe in methanol at 45 °C and in methanol−tolu...

The interaction of cetyltrimethylammonium bromide and sodium dodecylbenzene sulfonate with polyvinyl alcohol. adsorption of the polymer—surfactant complexes on silica

The interaction of cetyltrimethylammonium bromide (CTABr) and sodium dodecylbenzene sulfonate (NaDBS) with polyvinyl alcohol (PVA) (12% acetate groups, M ̄ v = 42,000 ) has been investigated using surface tension, viscosity, conductivity and cloud point measurements. The results showed that the polymer-surfactant “complex” behaves as an association polyelectrolyte. The adsorption of PVA, CTABr, NaDBS and “complexes” of CTABr + PVA and NaDBS + PVA on silica was studied in aqueous solution at low and high pH. The adsorption of PVA was higher at pH 3.6 than at pH 9.1, because at low pH there are more undissociated silanol groups which act as adsorption sites for PVA. CTA + ions are adsorbed at low pH (3.6) in a more or less vertically oriented layer. At high pH (9.1) a bilayer of CTA + ions form at the silica-solution interface. The adsorption of NaDBS was low, increasing as the pH was lowered, and the adsorption isotherms deviated from the Langmuir equation. In the presence of preadsorbed CTA + ions at high pH, the PVA adsorption increased significantly relative to the value in absence of surfactant. It is believed that the CTA + ions act as “anchors” between the dissociated -SiO − sites on the surface and PVA chains. At low pH, CTA + ions are adsorbed to a greater extent in presence of preadsorbed PVA. It is assumed that under these conditions PVA acts as the “anchor” between the undissociated SiOH groups and CTA + ions. On a silica surface with preadsorbed DBS − ions at low and high pH PVA is adsorbed to a greater extent than in the absence of DBS − ions, but to a lesser extent than in the presence of CTA + ions. The adsorption of DBS − ions on a silica surface with preadsorbed PVA at low pH is complex, especially at high PVA concentration.