Protonated Amine Groups Research Articles

Task-specific basic ionic liquid immobilized on mesoporous silicas: Efficient and reusable catalysts for Knoevenagel condensation in aqueous media

N-(3-aminopropyl), N(3)-(3-triethoxysilylpropyl)-4,5-dihydroimidazolium bromide hydrobromide was prepared and successively grafted onto mesoporous silicas of MCM-41 and SBA-15. Finally, the protonated amine groups in the resultant organic–inorganic hybrid mesoporous silicas were neutralized by treating with potassium bicarbonate, leading to the immobilized basic amino-containing task-specific ionic liquids (TSILs). Using Knoevenagel condensation as test reaction, the immobilized basic TSILs showed higher efficiency (particularly reusability) than that of similar pure basic TSIL of N-(3-aminopropyl), N(3)-(methyl)-imidazolium tetrafluoroborate or amino-functionalized mesoporous silicas in aqueous media. Much higher catalytic performance of the immobilized basic TSILs, as compared with the pure basic TSIL, could be due to the depressed reaction between amine groups and the hydrogen at C2 of imidazolium derivative cations in the immobilized basic TSILs and to the acid–base cooperativity between the silanols on the pore surface of the siliceous supports and amine groups. On the other hand, that amine groups nucleophilically attack the Si O Si bonds on the pore surface was suppressed due to steric hindrance resulted from the existence of dihydroimidazolium cations in the organic structure of the immobilized basic TSILs, leading to low leaching level of the active species in the immobilized TSILs during the reuse process. As such, the immobilized basic TSILs showed much better reusability in comparison with the amino-functionalized mesoporous silicas.

Cation exchange interaction between antibiotic ciprofloxacin and montmorillonite

Exploring the interactions between antibiotics and soils/minerals is of great importance in resolving their fate, transport, and elimination in the environment due to their frequent detection in wastewater, river water, sewage sludge and soils. This study focused on determining the adsorption properties and mechanisms of interaction between antibiotic ciprofloxacin and montmorillonite (SAz-1), a swelling dioctahedral mineral with Ca 2+ as the main interlayer cation. In acidic and neutral aqueous solutions, a stoichiometric exchange between ciprofloxacin and interlayer cations yielded an adsorption capacity as high as 330 mg/g, corresponding to 1.0 mmol/g. When solution pH was above its p K a2 (8.7), adsorption of ciprofloxacin was greatly reduced due to the net repulsion between the negatively charged clay surfaces and the ciprofloxacin anion. The uptake of ciprofloxacin expanded the basal spacing ( d 0 0 1 ) of montmorillonite from 15.04 to 17.23 Å near its adsorption capacity, confirming cation exchange within the interlayers in addition to surface adsorption. Fourier transform infrared results further suggested that the protonated amine group of ciprofloxacin in its cationic form was electrostatically attracted to negatively charged sites of clay surfaces, and that the carboxylic acid group was hydrogen bonded to the basal oxygen atoms of the silicate layers. The results indicate that montmorillonite is an effective sorbent to remove ciprofloxacin from water.

Facile synthesis of core–shell and Janus particles via 2-D dendritic growth of gold film

We report a facile method for the electroless deposition (ELD) of gold film via two-dimensional (2-D) dendritic growth. Our scheme employs protonated amine groups, which electrostatically attract both the negatively charged reducing agent and gold-precursor. This electrostatic interaction increases the local concentrations of gold-precursor and reducing agent near the silica surface to levels high enough for gold films with a 2-D fractal morphology to form directly on the surfaces of the amine-functionalized silica nanospheres by diffusion-limited aggregation. Our one-pot reaction avoids the need for seed attachment, which is typically employed for the growth of metallic shells on nanospheres. Therefore, the proposed method significantly reduces the number of processing steps required for the production of core–shell nanospheres. The gold morphologies were systematically investigated in terms of various synthesis variables, including solution pH, reducing agent concentration, and gold precursor injection speed. In addition, we synthesized gold-capped silica nanospheres via ELD of gold on a patterned array of silica nanospheres embedded in polystyrene (PS) film followed by dissolution of the PS matrix, thus demonstrating the potential utility of the proposed method in emerging fields of materials science such as patterning of noble metals and studies of nanometer-scale optics.

2,4-Dimethylanilinium perchlorate

The crystal packing of the title compound, C8H12N+·ClO4 −, is stabilized by N—H⋯O hydrogen bonds, the protonated amine group acting as a hydrogen-bond donor with the perchlorate O atoms as acceptors. These connect neighbouring cations and anions, forming a two-dimensional network. Variable-temperature dielectric constant measurements on the salt indicated that no distinct phase transition occurred within the measured temperature range of 80–293 K.

Infrared multiple photon dissociation spectroscopy of cationized cysteine: Effects of metal cation size on gas-phase conformation

The gas-phase structures of cationized cysteine (Cys) including complexes with Li +, Na +, K +, Rb +, and Cs +, as well as protonated Cys, are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light generated by a free electron laser, in conjunction with quantum-chemical calculations. To identify the structures present in the experimental studies, measured IRMPD spectra are compared to spectra calculated at B3LYP/6-311G(d,p) (H +, Li +, Na +, and K + complexes) and B3LYP/HW*/6-311G(d,p) (Rb + and Cs + complexes) levels of theory, where HW* indicates that the Hay–Wadt effective core potential was used on the metals. On the basis of these experiments and calculations, the only conformation that reproduces the IRMPD action spectra for the complexes of the smaller alkali metal cations, Li +(Cys) and Na +(Cys), is a charge-solvated, tridentate structure where the metal cation binds to the amine and carbonyl groups of the amino acid backbone and the sulfur atom of the side chain, [N,CO,S], in agreement with the predicted ground states of these complexes. For the larger alkali metal cation complexes, K +(Cys), Rb +(Cys), and Cs +(Cys), the spectra have very similar spectral features that are considerably more complex than the IRMPD spectra of Li +(Cys) and Na +(Cys). For these complexes, the bidentate [COOH] conformer, in which the metal cation binds to both oxygens of the carboxylic acid group, is a dominant contributor, although features associated with the tridentate [N,CO,S] conformer remain and those for the zwitterionic [CO 2 −] conformer are also clearly present. Theoretical results for Rb +(Cys) and Cs +(Cys) indicate that both [COOH] and [N,CO,S] conformers are low-energy structures. For H +(Cys), the IRMPD action spectrum is reproduced by [N,CO] conformers, in which the protonated amine group hydrogen bonds to the carbonyl oxygen atom and the sulfur atom of the amino acid side chain. Several low-energy [N,CO] conformers that differ only in their side-chain orientations are found and therefore have very similar predicted spectra.

Molecular dynamics computer simulations of the effects of hydrogen bonding on the properties of layered double hydroxides intercalated with organic acids

Anion exchange capabilities of layered double hydroxides (LDHs) make them uniquely suitable for the creation of bio-inorganic nanocomposites, with amino acids and DNA fragments occurring as negatively charged species at most pH values. To better understand molecular-level structural, thermodynamic and kinetic aspects of their interactions with LDHs, we have performed molecular dynamics (MD) computer simulations of glutamate(1−) and glutamate(2−) intercalated in Mg–Al LDH. The results are compared with previous simulations of the hydration and swelling behaviour of similar LDHs intercalated with other organic anions (formate, acetate, propanoate and citrate). The MD simulations provide important insight into the interpretation of NMR and X-ray diffraction data for the same systems. The organic species interact with the LDH layers principally via electrostatic and van der Waal's forces, and the hydrated interlayer galleries are stabilised via the development of an integrated hydrogen-bonding network among the anions, water molecules and OH-groups of the LDH layers. Deprotonated carboxylate groups are the primary strong H-bond acceptors, whereas, for glutamate(2−), the amino groups are additional H-bond acceptors from the LDH surface. On the other hand, the protonated amine groups of glutamate(1−) serve as additional strong H-bond donors in the interlayer, responsible for up to 1/6 of all H-bonds formed by each carboxylic group in the interlayer. The organic species preferably accept H-bonds from H2O molecules rather than from surface OH-groups due to structural restrictions on the development of tetrahedrally coordinated H-bonding environments for the carboxylate groups at the surface.

Palladium and platinum sorption using chitosan-based hydrogels

Two chitosan hydrogels (prepared by NaOH neutralization and by polyphosphate ionotropic gelation) have been tested in the dry state for Pd(II) and Pt(IV) sorption at pH 2. Similar sorption isotherms with maximum sorption capacities close to 190 mg Pd g−1 and 235 mg Pt g−1 were achieved. The sorption mechanism involves electrostatic attraction of the chloro-anionic species onto protonated amine groups; the drastic decrease of sorption capacity with the addition of chloride ions supports this hypothesis. SEM-EDAX analysis suggests that sorption proceeds, in kinetic terms, through a shrinking core mechanism. Metal ions can diffuse throughout all the sorbent volume. The main differences between the sorbents are revealed by kinetics. The hydrogels prepared by ionotropic gelation in polyphosphate (C-PPh) allows reaching equilibrium much faster than the hydrogels prepared by the neutralization process (C-NaOH). While for C-PPh sorbent the chemical reaction rate seems to control sorption profiles, in the case of C-NaOH a combination of mechanisms including intraparticle diffusion resistance controls uptake kinetics. Metal desorption from loaded sorbents is possible using thiourea alone or in association with HCl solutions. The recycling of the sorbents is possible but for a limited number of cycles.

Palladium and platinum sorption on a thiocarbamoyl‐derivative of chitosan

AbstractImmobilizing thiourea onto chitosan allowed using the polymer for the recovery of platinum groups metals (PGMs) in acidic solutions (up to 1–2M HCl concentrations). At low HCl concentration protonated amine groups may sorb chloroanionic metal species (electrostatic attraction mechanism); however, most of sorption proceeds through chelation on sulfur containing groups (less sensitive to acidic conditions). The bi‐site Langmuir equation was used for fitting sorption isotherms. The sorption of PGMs was weakly affected by the composition of the solution (presence of high concentration of anions and base metals). Maximum sorption capacities for Pd(II) and Pt(IV) ranged between 274 and 330 mg g−1 in 0.25M HCl solutions and decreased to 150–198 mg g−1 in 2M HCl solutions: Pd(II) sorption was systematically higher than Pt(IV) sorption. The pseudo‐second rate equation was used for modeling the uptake kinetics. Agitation speed hardly affected uptake kinetics indicating that external diffusion resistance is not the rate controlling step. Desorption yield higher than 85% were obtained using thiourea in 0.1M HCl solution. The adsorbents could be reused for at least three cycles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

2-Carb-oxy-1-(3-nitro-phen-yl)ethanaminium perchlorate.

In the title compound, C9H11N2O4 +·ClO4 −, the organic cations form centrosymmetric dimers via a pair of O—H⋯O hydrogen bonds between the carboxyl groups. In the crystal, N—H⋯O inter­actions between the protonated amine group and the perchlorate anions and the nitro group connect the components into a two-dimensional network parallel to (001).

Solvent‐dependent fluorescence emission in heterocyclic compounds having isoquinoline backbone

Abstract magnified imageFew amino derivatives of benzo[de]benzo[4,5]imidazo[2,1‐a]isoquinolin‐7‐one having amino groups at different positions of the rings are prepared and characterized. Solvent‐dependent emission and changes in emission properties on protonation of amine group are observed. J. Heterocyclic Chem., (2010).

Coordination Reactions and Noncovalent Interactions of Polyamines with Nucleotides in Binary Systems and with Nucleotides and Copper(II) Ion in Ternary Systems.

Interactions of nucleotides (AMP, CMP) and 1,2-diaminopropane (tn-1) or 2-methyl-1,2-diaminopropane (tn-2) in metal-free systems as well as in the systems including copper(II) ions were studied. The composition and overall stability constants of the complexes formed were determined by the potentiometric method, whereas the interaction centres and coordination sites were identified by spectroscopic methods. It was found that phosphate groups of nucleotides and the protonated amine groups of polyamines are the centres of interaction. The differences in the interactions with the polyamines which act as models of biogenic amines are impacted by the presence of lateral chains (methylene groups) in tn-1 and tn-2. In the ternary systems with Cu(II) ions, the heteroligand complexes are mainly of the ML⋯L' type, in which the protonated polyamine is engaged in noncovalent interactions with the anchoring Cu(II)-nucleotide complex. The complexes formed in the Cu/NMP)/tn-1 system are more stable than those formed in the system with tn-2. The mode of coordination in the complex is realised mainly through the phosphate groups of the nucleotide with involvement of the endocyclic nitrogen atoms in a manner which depends upon the steric conditions and in particular on the number of the methylene groups in the polyamine molecule.

Infrared multiple photon dissociation spectroscopy of cationized methionine: effects of alkali-metal cation size on gas-phase conformation

The gas-phase structures of alkali-metal cation complexes of the amino acid methionine (Met) as well as protonated methionine are investigated using infrared multiple photon dissociation (IRMPD) spectroscopy utilizing light generated by a free electron laser. Spectra of Li(+)(Met) and Na(+)(Met) are similar and relatively simple, whereas the spectra of K(+)(Met), Rb(+)(Met), and Cs(+)(Met) include distinctive new bands. Measured IRMPD spectra are compared to spectra calculated at the B3LYP/6-311+G(d,p) level of theory to identify the conformations present in the experimental studies. For Li(+) and Na(+) complexes, the only conformation present is a charge-solvated, tridentate structure that binds the metal cation to the amine and carbonyl groups of the amino acid backbone and the sulfur atom of the side chain, [N,CO,S]. In addition to the [N,CO,S] conformer, bands corresponding to alkali-metal cation binding to a bidentate zwitterionic structure, [CO(2)(-)], are clearly present for the K(+), Rb(+), and Cs(+) complexes. Theoretical calculations of the lowest energy conformations of Rb(+) and Cs(+) complexes suggest that the experimental spectra could also include contributions from two additional charge-solvated structures, tridentate [COOH,S] and bidentate [COOH]. For H(+)(Met), the IRMPD action spectrum is reproduced by multiple low-energy [N,CO,S] conformers, in which the protonated amine group hydrogen bonds to the carbonyl oxygen atom and the sulfur atom of the amino acid side chain. These [N,CO,S] conformers only differ in their side-chain orientations.

Synthesis and chemical properties of photoluminescent self-doped polyanilines

Fluorescent self-doped polyanilines (PAS-AntPy-a and PAS-AntPy-b) were obtained by the pyridinium sulfonation of poly(2-methoxyaniline-5-sulfonic acid) (PAS) with 4-(2-anthracene-9-yl-vinyl)pyridine (AntPy). The degrees of pyridinium sulfonation in PAS-AntPy-a and PAS-AntPy-b were 0.70 and 0.97, respectively. A neutral polyaniline with an AntPy side unit (PANI-AntPy) was synthesized by the oxidative polymerization of N-(2-aminophenyl)-4-(2-anthracene-9-yl-vinyl)pyridinium chloride. The UV-vis spectra of PAS-AntPy-a and PAS-AntPy-b exhibited an absorption due to the polaron band that was derived from the protonation of amine groups in the polyaniline backbone with the remaining sulfonic acid proton. In contrast, PANI-AntPy did not exhibit absorption due to the polaron band. PAS-AntPy-a, PAS-AntPy-b, and PANI-AntPy were photoluminescent in a solution. The electric conductivity of PAS-AntPy-a was σ = 1.5 × 10−7 S cm−1, which was higher than that of H2SO4 doped PANI (4.2 × 10−9 S cm−1) reported previously.

Adsorption of copper–citrate complexes on chitosan: Equilibrium modeling

The effects of complexes on the adsorption of copper from citrate solutions using chitosan were investigated. Various copper to citrate ratios and solution pHs were used to determine the copper adsorption capacity on the chitosan and a mathematical model was developed to simulate the copper adsorption process. According to the model, the three parameters influencing the copper adsorption capacity are the fraction of protonated amine groups ( RNH 3 + ) , the fraction of anionic copper–citrate complexes (CuL − and CuL 2 4 - ), and the fraction of anionic citrate complexes (HL 2−, H 2L −, and L 3−). The copper adsorption capacities onto chitosan at varying copper–citrate ratios and solution pHs can be predicted by the mathematical model. With such a model to facilitate understand the copper adsorption mechanisms at varying copper–citrate ratios and solution pHs, the copper adsorption efficiency can be increased by the adjustment of the copper–citrate ratio and solution pH.

Study of the cloud point variation of amitriptyline hydrochloride solutions in presence of amines and amino acids

In this paper clouding phenomenon in aqueous solutions of an amphiphilic drug amitriptyline hydrochloride is reported. The effect of adding ethylamine, butylamine, hexylamine, heptylamine, octylamine, ethylenediamine, diethylenetriamine, tetraethylenepentramine, aniline, and benzylamine on the cloud point of solutions containing a fixed drug concentration (50 mM) was seen. All the amines decrease the cloud point by intercalating between the head groups with protonated amine groups at the micellar surface. The amino acids used (lysine, arginine, histidine) also behave similarly. The results are discussed in the light of a particular additive’s ability to remove water from the head group region of the drug micelles.

Preparation and acid dye adsorption behavior of polyurethane/chitosan composite foams

We prepared a series of polyurethane(PU)/chitosan composite foams with different chitosan content of 5∼20 wt% and investigated their adsorption performance of acid dye (Acid Violet 48) in aqueous solutions with various dye concentrations and pH values. It was observed that PU/chitosan composite foams exhibited well-developed open cell structures. Dye adsorption capacities of the composite foams increased with the increment of chitosan content in composite foams, because amine groups of chitosan serve as the binding sites for sulfonic ions of acid dyes in aqueous solutions. In addition, dye adsorption capacities of composite foams were found to increase with decreasing the pH value, which stems from the fact that the enhanced chemisorption between protonated amine groups of chitosan and sulfonic ions of acid dye is available in acidic solutions. The dye adsoption kinetics and equilibrium isotherm of the composite foams were well described with the pseudo-second order kinetic model and Langmuir isotherm model, respectively. The maximum adsorption capacity (qmax) for the PU/chitosan composite foams with 20 wt% chitosan content is evaluated to be ca. 30 mg/g.

Noncovalent interactions and coordination reactions in the systems consisting of copper(II) ions, aspartic acid and diamines

Interactions of aspartic acid between 1,3-diaminopropane (tn) and 1,4-diaminobutane (Put) in metal-free systems as well as in the systems including copper(II) ions were studied. The composition and overall stability constants of the complexes formed were determined by the potentiometric method. The interaction centres and coordination sites were identified by spectroscopic methods. Each of the ligands has both negative and positive interaction centres. In aspartic acid such centres are carboxyl groups and amine group, while in the polyamine molecules - protonated amine groups. The centres are also the potential sites of the coordination of metal ions. Analysis of the logK(e) values of the adducts in the systems with polyamines has shown that the stability of the adducts in the metal-free systems depends on a significant degree on the steric factor that is the length of the polyamine. In some species the inversion effect, hitherto not reported in literature, was found. In the ternary systems including Cu(II) ions, only protonated species are formed, including molecular complexes with intermolecular interactions and metallation through the oxygen atoms of carboxyl groups and amine groups of the amino acid. In the adducts the protonated diamine is in the outer coordination sphere and is involved in noncovalent interactions with the anchoring CuH(Asp) or Cu(Asp) complexes.

Morphosynthesis of Gold Nanoplates in Polypeptide Multilayer Films

Multilayer thin films formed from the layer-by-layer (LbL) assembly of cationic linear polyethyleneimide (LPEI) and anionic polyaspartic acid (pLAA) were used as reactive templates for in situ morphosynthesis of gold nanoplates. Size- and shape-controlled growth was made possible by the specific morphogenic action of the polypeptide pLAA and growth in a spatially confined environment. LPEI, in addition to serving as the counter polyelectrolyte for pLAA in the LbL assembly, also provided the facility for chloroaurate anion (AuCl4−) binding through its protonated amine groups (NH3+). The availability and accessibility of these binding sites were important to particle size control and could be varied by the pH of the pLAA solution used in the LbL assembly. Size-controlled synthesis of gold nanoplates was accomplished by controlling the secondary structure of pLAA in the multilayer film. In particular, an increase in the fraction of pLAA α-helices was found to increase the availability and accessibility of the reducing carboxyl side groups of pLAA, resulting in more facile reduction kinetics and smaller particle size in the product. The polypeptide-based reactive templates offered a finer level of kinetic control, enabling the formation of gold nanoplates in a size range (i.e., 50 nm) not possible in a solution phase synthesis (i.e., 500 nm), using reaction mixtures with the same overall composition (i.e., pLAA, LPEI, and HAuCl4) and under the same environmental conditions. The key parameters affecting the polypeptide film formation and their effects on the size-controlled synthesis of gold nanoplates were identified and discussed in detail in this report.

Color Tuning of an Acidic Blue Dye by Intercalation into the Basic Interlayer Galleries of a Poly(allylamine)/Synthetic Fluoromica Nanocomposite

The intercalation of an acidic blue dye, Brilliant Blue FCF, into poly(allylamine) (PAA)/synthetic fluoromica (Na-TSM) was investigated as a function of the reaction pH (1.5−12.0) and the loading of the polyelectrolyte and acidic dye. Surprisingly, the colored solids so obtained show a variety of colors from the original blue to yellow through green with only a slight increase in the reaction pH. At low and neutral pH (1.5−9.5), the acidic blue dye molecules were adsorbed/intercalated on/in PAA/Na-TSM mainly through electrostatic interactions between protonated amine groups on the PAA chains and sulfonate groups of the dye, resulting in the original blue color. UV−visible spectroscopic data hint that the adsorbed/intercalated dye molecules were aggregated. The color shifted to blue-green at pH 10.0 and finally to yellow at pH 12.0. At high pH, the PAA layers have lower charge density and the dye is well-dispersed within the interlayer galleries. The fraction of neutral primary amine groups increases with ...

Theoretical and experimental sulfur K-edge X-ray absorption spectroscopic study of cysteine, cystine, homocysteine, penicillamine, methionine and methionine sulfoxide

The experimental sulfur K-edge X-ray absorption near-edge structure (XANES) spectra of the amino acids cysteine, homocysteine, penicillamine, methionine, including the oxidation products methionine sulfoxide and the disulfide cystine, have been analyzed by transition potential DFT calculations. The absolute energies and intensities of the main pre-edge sulfur 1s electron transitions have been computed to determine the character of the receiving unoccupied molecular orbitals (MO), and to investigate the influence of external interactions, especially by introducing water molecules hydrogen-bonded to the ionic species present in different pH ranges. When the thiol group deprotonates for cysteine, homocysteine and penicillamine and also for the cysteine residue in glutathione the energy of the main transition, to an MO with antibonding sigma*(S-H) character, reduces by approximately 1.1 eV and the receiving MO obtains sigma*(S-C) character. The changes in transition energy due to hydrogen-bonding were in most cases found to be relatively small, although the transition intensities could vary significantly due to the changes induced in the molecular charge distribution, thereby affecting the shapes of the spectral features. For the cysteine and penicillamine zwitterions deconvolution of the experimental spectra allowed the microscopic acid dissociation constants to be extracted separately for the thiol and the protonated amine groups, pK(a)(S) = 8.5 +/- 0.1 and 8.2 +/- 0.1, and pK(a)(N) = 8.9 +/- 0.1 and 8.8 +/- 0.1, respectively, with the thiol group in both cases being the more acidic. Coordination of cysteine to nickel(II) or mercury(II) introduced a new low energy transition involving metal ion orbitals in the receiving LUMO. The small experimentally observed energy differences between the similar main absorption features of the cysteine and methionine zwitterions, 0.2-0.3 eV in comparable surrounding, as well as a minor difference in their intensities, are reflected in the calculated transitions. The S K-edge XANES spectrum of the disulfide cystine displays a characteristic double peak with the lower energy transition (2469.9 eV) into the antibonding sigma*(S-S) MO. The second peak, at 2471.5 eV in aqueous solution, contains several transitions into MOs with sigma*(S-C) character involving also charge transfer to the water molecules hydrating the protonated amine groups (NH(3)(+)) of cystine. For solid cystine without hydrogen bonding the experimental energy difference between the two peaks is 0.2 eV larger, while no such increase occurs for the oxidized disulfide of glutathione, with a similar -S-S- bond between its cysteine residues as in cystine, because the amine groups are engaged in peptide bonds. This study shows that externally induced changes in the intramolecular bonding, e.g., by coordination, conformation geometry or hydrogen-bonding, can significantly influence the S K-edge spectra, and emphasizes the importance of a similar chemical surrounding when choosing the model compounds for standard spectra of sulfur functional groups, used to deconvolute composite experimental spectra.