Unprotonated Amines Research Articles

A new method of simultaneous determination of atmospheric amines in gaseous and particulate phases by gas chromatography-mass spectrometry

As more attention is being paid to the characteristics of atmospheric amines, there is also an increasing demand for reliable detection technologies. Herein, a method was developed for simultaneous detection of atmospheric amines in both gaseous and particulate phases using gas chromatography-mass spectrometry (GC-MS). The amine samples were collected with and without phosphoric acid filters, followed by derivatization with benzenesulfonyl chloride under alkaline condition prior to GC-MS analysis. Furthermore, the method was optimized and validated for determining 14 standard amines. The detection limits ranged from 0.0408-0.421 µg/mL (for gaseous samples) and 0.163-1.69 µg/mL (for particulate samples), respectively. The obtained recoveries ranged from 68.8%-180% and the relative standard deviation was less than 30%, indicating high precision and good reliability of the method. Seven amines were simultaneously detected in gaseous and particulate samples in an industrial park using the developed method successfully. Methylamine, dimethylamine and diethylamine together accounted for 76.7% and 75.6% of particulate and gaseous samples, respectively. By comparing the measured and predicted values of gas-particle partition fractions, it was found that absorption process of aqueous phase played a more important role in the gas-partition of amines than physical adsorption. Moreover, the reaction between unprotonated amines and acid (aq.) in water phase likely promoted water absorption. Higher measured partition fraction of dibutylamine was likely due to the reaction with gaseous HCl. The developed method would help provide a deeper understanding of gas-particle partitioning as well as atmospheric evolution of amines.

L-Type Ligand-Assisted Acid-Free Synthesis of CsPbBr3 Nanocrystals with Near-Unity Photoluminescence Quantum Yield and High Stability.

X-type ligands, for example, the pair of oleylamine (OAm) and oleic acid (OA), have been widely used to prepare CsPbX3 nanocrystals (NCs). However, the proton exchange between coordinated OAm and OA may induce the detachment of ligands, resulting in poor performance after cleaning or long-time storage. Herein, density functional theory calculations predict that primary amines (L-type ligands) can stabilize a PbBr x-rich surface and yield a trap-free material with fully delocalized valence band maximum and conduction band minimum states, which can significantly improve the photophysical properties and stability of CsPbBr3 NCs. Along this prediction, a room-temperature reprecipitation method using L-type ligands (OAm, n-octylamine, or undecylamine) as the sole capping ligand has been developed to synthesize high-quality CsPbBr3 NCs with near-unity photoluminescence quantum yield and dramatically improved stability against purification and water treatment. The enhancement can be attributed to the strong binding of unprotonated amines to lead atoms and the effective surface passivation provided by the resulted PbBr x-rich surface, which are highly consistent with the theoretical predictions. This work not only offers an approach to synthesize high-quality perovskite NCs but also provides an in-depth understanding of the surface modification of CsPbX3 NCs for practical applications.

Unusual Salt and pH Induced Changes in Polyethylenimine Solutions.

Linear PEI is a cationic polymer commonly used for complexing DNA into nanoparticles for cell-transfection and gene-therapy applications. The polymer has closely-spaced amines with weak-base protonation capacity, and a hydrophobic backbone that is kept unaggregated by intra-chain repulsion. As a result, in solution PEI exhibits multiple buffering mechanisms, and polyelectrolyte states that shift between aggregated and free forms. We studied the interplay between the aggregation and protonation behavior of 2.5 kDa linear PEI by pH probing, vapor pressure osmometry, dynamic light scattering, and ninhydrin assay. Our results indicate that:At neutral pH, the PEI chains are associated and the addition of NaCl initially reduces and then increases the extent of association.The aggregate form is uncollapsed and co-exists with the free chains.PEI buffering occurs due to continuous or discontinuous charging between stalled states.Ninhydrin assay tracks the number of unprotonated amines in PEI.The size of PEI-DNA complexes is not significantly affected by the free vs. aggregated state of the PEI polymer.Despite its simple chemical structure, linear PEI displays intricate solution dynamics, which can be harnessed for environment-sensitive biomaterials and for overcoming current challenges with DNA delivery.

Mixtures of quasi-two and three dimensional hybrid organic-inorganic semiconducting perovskites for single layer LED

New blends of simply synthesized quasi two-dimensional (quasi-2D) hydrophobic perovskite semiconductors, employed in high performance light emitting diodes (LEDs) which function due to excitonic energy transfer effects, are reported. These materials are self-assembled blends of 2D, quasi-2D and three-dimensional (3D) hybrid organic-inorganic semiconductors (HOIS). Moreover, shown for the first time, crude mixing of 3D perovskite and unprotonated amines provides similar semiconductors. HOIS reported here are based on the organic cations CH3NH3+, CH3(CH2)7CHCH(CH2)8NH3+ or C6H5CH2CH2NH3+ and inorganic networks formed out of PbX42− anions (X = I, Br, Cl). HOIS exhibit strong bound excitonic states with increased oscillator strength at room temperature, tunable via simple halide substitution. HOIS blends manifest energy transfer effects, where adjacent nanoparticles of different band gap energies (Eg) transfer optical energy to those with the lowest Eg; the suggested light emission mechanism here. LED fabrication is attained via a single deposition of the hydrophobic mixture, reducing device complexity, cost and degradability. LED's diodic behavior is observed even under light albeit its photovoltaic and photoconductive quasi-2D and 3D components. LED devices exposed for over than four months under adverse laboratory conditions, showed stable light emission. Further research on this class of quasi-2D/3D HOIS mixtures is expected to lead to novel quantum electronic devices.

Formation potential of nine nitrosamines from corresponding secondary amines by chloramination

Nitrosamines, a group of emerging disinfection by-products (DBPs) in drinking water, have recently caused significant concern because of their higher carcinogenic potential than that of currently regulated DBPs. In this study, the formation of nine representative nitrosamines by chloramination of their corresponding secondary amines was investigated under various conditions. All nine nitrosamines were detected in the corresponding reaction solutions, which confirmed that all the investigated secondary amines were the potential precursors of corresponding nitrosamines. The molar yields of nitrosamines from the corresponding secondary amines were quite different, depending on the structural characteristics of the secondary amines. The maximum molar yields for the formation of all nine nitrosamines occurred in the pH range of 7.0–9.0 and at the Cl/N molar ratio of 0.7 for chloramines, suggesting that monochloramine and unprotonated secondary amines may play a major role in the formation of nitrosamines. The molar yields of nitrosamines also exhibited a moderate upward tendency with rising temperature, but no consistent correlation was observed between the formation of nitrosamine and the initial concentrations of secondary amines and chloramines. The results of this study could be useful for devising strategies for controlling the formation of nitrosamines during the disinfection processes of drinking water.

Ion/ion reactions of MALDI-derived peptide ions: increased sequence coverage via covalent and electrostatic modification upon charge inversion.

Atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI)-derived tryptic peptide ions have been subjected to ion/ion reactions with doubly deprotonated 4-formyl-1,3-benzenedisulfonic acid (FBDSA) in the gas-phase. The ion/ion reaction produces a negatively charged electrostatic complex composed of the peptide cation and reagent dianion, whereupon dehydration of the complex via collision-induced dissociation (CID) produces a Schiff base product anion. Collisional activation of modified lysine-terminated tryptic peptide anions is consistent with a covalent modification of unprotonated primary amines (i.e., N-terminus and ε-NH(2) of lysine). Modified arginine-terminated tryptic peptides have shown evidence of a covalent modification at the N-terminus and a noncovalent interaction with the arginine residue. The modified anions yield at least as much sequence information upon CID as the unmodified cations for the small tryptic peptides examined here and more sequence information for the large tryptic peptides. This study represents the first demonstration of gas-phase ion/ion reactions involving MALDI-derived ions. In this case, covalent and electrostatic modification charge inversion is shown to enhance MALDI tandem mass spectrometry of tryptic peptides.

Gas-Phase Conjugation to Arginine Residues in Polypeptide Ions via N-Hydroxysuccinimide Ester-Based Reagent Ions

Gas-phase conjugation to unprotonated arginine side-chains via N-hydroxysuccinimide (NHS) esters is demonstrated through both charge reduction and charge inversion ion/ion reactions. The unprotonated guanidino group of arginine can serve as a strong nucleophile, resulting in the facile displacement of NHS from NHS esters with concomitant covalent modification of the arginine residue. This reactivity is analogous to that observed with unprotonated primary amines such as the N-terminus or ε-amino group of lysine. In solution, however, the arginine residues tend to be protonated at pH values low enough to prevent hydrolysis of NHS esters, which would render them relatively unreactive with NHS esters. This work demonstrates novel means for gas-phase conjugation to arginine side chains in polypeptide ions.

Dual Aperture Control on pH- and Anion-Driven Supramolecular Nanoscopic Hybrid Gate-like Ensembles

The development of gate-like systems able to perform certain programmed functions is an interesting way of taking chemistry to the frontiers of nanoscience. In relation to this field, we report a complete study of the behavior of a pH-driven and anion-controlled nano-supramolecular gate-like ensemble obtained by anchoring suitable polyamines on the pore outlets of mesoporous materials of the type MCM-41 (solid N3-S). The release of an entrapped dye (Ru(bipy)3(2+)) from the pore voids into the bulk solution allows us to study the gating effect. A pH-driven open/close mechanism was observed that arises from the hydrogen-bonding interaction between amines at neutral pH (open gate) and Coulombic repulsions at acidic pH between closely located polyammoniums at the pore openings (closed gate). Molecular dynamics simulations using force field methods have been carried out to explain the pH-driven open/close mechanism. For this purpose, a mesoporous silica structure was constructed, taking as base the (111) plane of the beta-crystoballite structure on which large hexagonal nanopores and anchored polyamines were included. From these calculations, it was observed how completely unprotonated amines display poor coverage of the pore (fully open gate), whereas completely protonated amines (simulating a pH 2 or lower) result in a clear reduction of the pore aperture, in agreement with the experimental results. In additional to the pH-driven protocol, opening/closing of the gate-like ensemble can also be modulated via an anion-controlled mechanism. This study was carried out by monitoring the dye released from the pore voids of the N3-S solid at a certain pH in the presence of a range of anions with different structural dimensions and charges, including chloride, sulfate, phosphate, and ATP (C(anion) = 1 x 10(-2) mol dm(-3)). The choice of a certain anionic guest results in a different gate-like ensemble behavior, ranging from basically no action (chloride) to complete (ATP) or partial pore blockage, depending on the pH (sulfate and phosphate). The remarkable anion-controllable response of the gate-like ensemble can be explained in terms of anion complex formation with the tethered polyamines. These experimental studies are also in agreement with computational simulations with fluoride, chloride, iodide, and dihydrogen phosphate anions. In the model, larger anions push the tethered polyamines toward the pore openings more efficiently, and therefore the pore aperture decreases. The studies also show that, for anions showing a strong tendency to form hydrogen-bonding networks (e.g., phosphate), complete pore blockage was observed at acidic pH. Finally, selectivity patterns have been discussed in terms of kinetic rates of the liberation of the Ru(bipy)3(2+) dye from the amine-functionalized dye-containing material N3-S.

Modified linear polyethylenimine-cholesterol conjugates for DNA complexation.

Linear polyethylenimine (LPEI) is an effective nonviral gene carrier with transfection levels equal or above branched polyethylenimine (BPEI) and exhibits a lower cytotoxicity profile than BPEI. High molecular weight LPEI M(w) 25 k was modified with cholesterol in three different geometries: linear shaped (L), T-shaped (T), and a combined linear/T-shaped (LT) forming the LPEI-cholesterol (LPC) conjugates LPC-L, LPC-T, and LPC-LT, respectively. Physical characterization of LPC/pDNA complexes included particle size, zeta potential, DNase protection, mIL-12 p70 expression, and cytotoxicity. The particle size was further confirmed by atomic force microscopy (AFM). The LPC-T/pDNA complexes were optimal at N/P 10/1 that resulted in a particle size of approximately 250 nm, which was confirmed by AFM, and a surface charge of +10 mV. These complexes also effectively protected the pDNA for up to 180 min in the presence of DNase I. B16-F0 cells transfected with LPC-L and LPC-T showed protein expression levels higher than LPEI alone and twice that of BPEI but without any significant loss in cell viability. These results were confirmed with EGFP flow cytometry and transfection of Renca cells. The differences in rates of transfection of the LPC/pDNA complexes is due in part to conformational changes from the point of complex formation to interaction with the plasma membrane. These conformation changes provide protection for unprotonated secondary amines in the LPEI backbone by hydrophobic protection of the cholesterol moiety that we termed "unprotonated reserves". Finally, we show that LPC conjugates exploit receptor-mediated endocytosis via the LDL-R pathway with transgene expression levels decreasing nearly 20% after saturating the LDL-R sites on MCF-7 cells with hLDL-R-Ab.

Sensing of Carbon Dioxide by a Decrease in Photoinduced Electron Transfer Quenching

We described a new approach to sensing of carbon dioxide based on photoinduced electron transfer (PET) quenching. Fluorophores like naphthalene and anthracene are known to be quenched by unprotonated amines by the PET mechanism. We examined the fluorescence spectral properties of two amine-containing fluorophores, 1-naphthylmetylamine (NMA) and 9-ethanolaminomethylanthracene (EAA). When dissolved in an organic solvent, both fluorophores displayed increased intensity when equilibrated with gaseous carbon dioxide. In the case of NMA, we found that the mean lifetime increased with increasing partial pressures of CO2. The intensity and lifetime changes of NMA are completely reversible when CO2 is removed by purging with argon. Our results are consistent with decreased quenching by the covalently linked amino groups when CO2 is dissolved in the solution. At present, we are not certain whether the increased intensity is due to protonation of the amino groups or to carbamate formation. In either event, these results suggest that CO2 can be detected directly using amine-containing fluorophores without the use of bicarbonate and a pH-sensitive fluorophore.

Solvent influence upon complex formation between crown ethers and unprotonated amines

The complexation reactions of some primary and secondary amines with crown ethers have been studied by means of calorimetric titrations. Thus, the stability constants and values of the reaction enthalpies and entropies were obtained. The values of the stability constants are nearly identical in all solvents examined. However, the values of the reaction enthalpies and entropies are influenced by solvation effects. In non-polar solvents such as toluene, cyclohexane, and carbon tetrachloride, complex formation with the amines is only favoured by entropic contributions. The values of the reaction enthalpies are rather small and nearly identical in these solvents.

Complex formation between the macrocyclic ligand 18-crown-6 and unprotonated amines in methanol

The complexation reactions between different amines and the macrocyclic ligand 18-crown-6 have been studied in methanol. Calorimetric titrations have been performed in order to obtain the stability constants and the reaction enthalpies and entropies for these reactions. The stability constants of all amines studied are within the same order of magnitude. However, alkyl and aryl substituents strongly influence the values of the reaction enthalpies and entropies. In contrast, for all secondary and tertiary amines examined nearly identical values for the reaction enthalpies and entropies are observed. As a result, the number of hydrogen bonds formed between the crown ether and these amines is not the most important factor.

The Mechanisms of the Inactivation of Human Alpha-1-Proteinase Inhibitor by Gas-Phase Cigarette Smoke

Abstract Cigarette smoke, either directly or indirectly, causes alpha-1-proteinase inhibitor (a1PI) to lose elastase inhibitory capacity (EIC), leaving lung connective tissues susceptible to proteolytic degradation. This paper discusses possible mechanisms for inactivation by cigarette smoke (CS) and by a model system [NO, isoprene, and air] that duplicates much of CS free radical chemistry. Inactivation of a1PI by either CS or the model is biphasic; a fast inactivation is followed by a slower one. With pre-prepared extracts, only the slow inactivation is observed. Apparently short-lived species in the smoke itself and the model system cause the fast inactivation; they may be peroxynitrates, which form in smoke from nitrogen dioxide and peroxyl radicals. The slower inactivation appears to involve hydrogen peroxide and/or organic hydroperoxides or species produced by them. Incubation of a1PI with linoleic acid produces a slow loss of EIC, prevented by the presence of vitamin E, which supports the hypothesis of a route involving lipid hydroperoxides. Protection of a1PI by various types of compounds shows that unprotonated amines and amino acids protect, but the protonated or acylated compounds do not. Ascorbate and glutathione provide the strongest protection.

Mechanism of the periodate oxidation of ethane-1,2-diamine, NN′-dimethylethane-1,2-diamine, and 2-aminoethanol

The kinetics of the oxidation by periodate of ethane-1,2-diamine, NN′-dimethylethane-1,2-diamine, and 2-aminoethanol have been studied at pH 4–12 and 293.2 K. The reaction rates are highest at pH 9–11. It is assumed that periodate monoanion reacts with the unprotonated amines. The reactions of 1,2-diamines with periodate are catalysed by acids and bases. The oxidation of 2-aminoethanol is catalysed by bases, and at high concentration of catalysts the rate seems to approach a limiting value. The pH dependence of the rate of oxidation of these compounds can be explained in terms of multi-stage reactions similar to those in the oxidation of 1,2-diols by periodate.

Monoamine oxidase—I: Specificity of some substrates and inhibitors

A number of synthetic substrates and inhibitors of monoamine oxidase have been studied, using the enzyme from porcine brain. K m and V max values have been calculated for substrates using Lineweaver-Burk plots. In many cases large variations in K m and V max were observed for relatively small changes in the structure of substrates. Similar observations were made concerning K i values for some competitive inhibitors. The effects of hydrogen-ion concentration on enzyme activity are consistent with the view that unprotonated amines are the species which bind to the enzyme. This finding, together with the observation that tertiary amines can act as substrates has led to formulation of a proposed mechanism of dehydrogenation which does not depend upon intermediate formation of Schiff base from the substrate amine.

Pulse radiolysis of ethyl, n-propyl, n-butyl and n-amyl amine in aqueous solutions

Pulse radiolysis of protonated and unprotonated ethyl (EA), n-propyl ( n-PA), n-butyl ( n-BA) and n-amyl amines ( n-AA) has been carried out. For all unprotonated amines k( e aq -+RNH 2) = (1·0 ± 0·1) × 10 6 dm 3 mol −1 s −1 was found, whereas the corresponding k-values for the protonated amines were higher by a factor of 2·5 to 3. With increasing chain length of the amine molecule the k(OH+RNH 3 +) values rise from 0·12 × 10 9 dm 3 mol −1s −1 (for EA) to 6·2 × 10 9 dm 3 mol −1s −1 (for n-AA). However, they are lower than the corresponding k(OH + RNH 2) values (6·2 × 10 9 dm 3 mol −1 s −1 for EA and 9 × 10 9 dm 3 mol −1 s −1 for n-AA). A chain length dependance was also observed for k(O aq − + RNH 2), starting with 8·65 x 10 9 dm 3 mol −1s −1 (EA) and reaching 15·2 x 10 9 dm 3 mol −1s −1 ( n-AA). The absorption spectra of the transients produced by reaction of OH radicals with the two forms of the amines show significant differences. The short-lived protonated species give absorption maxima between 212·5 and 215 nm ( ϵ max = 96−108 m 2 mol −1), while the corresponding data for the unprotonated transients are 222·5−225 nm ( ϵ max = 145−173 m 2 mol −1). The rate constants for the second-order disappearance of the protonated species decrease gradually with an increase of the molecule chain length (2 k = 1·2 × 10 9 dm 3 mol −1 for EA to 0·4 × 10 9 dm 3 mol −1 s −1 for n-AA) and are lower than the values for the unprotonated transients (2 k = 1·7 × 10 9 dm 3 mol −1 s −1 for EA to 0·7 × 10 9 dm 3 mol −1 s −1 for n- AA). In accordance with previous observations it can be stated that OH radicals attack protonated amines mainly on the C-atoms farthest from the —NH 3 + group, while in the case of unprotonated amines the H abstraction occurs preferentially on N-atom and α-C positions. The results are of particular interest for radiation biology.

Pulse radiolytic investigation of aliphatic amines in aqueous solution

The rates of reaction of hydroxyl radicals with various aliphatic amines have been determined as a function of pH. These include methyl, ethyl, isopropyl, t-butyl, trimethyl and triethyl amines. Rate constants of ap 3 × 10 8 dm 3 mol −1s −1 for protonated amines and ap 1 × 10 10 dm 3 mol −1s −1 for unprotonated amines have been obtained. This marked difference is attributed to the electrophilic character of the hydroxyl radical and its unfavorable interaction with the positive center. The transient absorption spectra of the various aminoalkyl and alkylamino radicals produced from the reaction of OH radicals with these amines were derived over the pH range 3–13. The transient species produced from trimethyl and triethyl amines have absorption maxima at ap 260 nm, all the other amines showed no maxima down to ap 230 nm, the limit imposed by experimental condictions. Strong pH dependence of the initial transient absorption is observed for all the amines examined. These changes are caused by the acid-base dissociation of the radicals, and by changes in the site of OH radical attack. Generally, it can be stated that hydrogen atom abstraction by OH radicals from unprotonated amines takes place mainly from an α-position and/or from hydrogen bonded to nitrogen, whereas abstraction from protonated amines occurs mainly at positions β- and/or γ-from the  ▪H group.