Alkylammonium Moieties Research Articles

Reducing Ice Adhesion to Polyelectrolyte Surfaces by Counterion-Mediated Nonfrozen Hydration Water.

Hydrophilic anti-icing coatings can be energy-effective passive solutions for combating ice accretion and reducing ice adhesion. However, their underlying mechanisms of action remain inferential and are ill-defined from a molecular perspective. Here, we systematically investigate the influence of the counterion identity on the shear ice adhesion strength to cationic polymer coatings having quaternary alkyl ammonium moieties as chargeable groups. Temperature-dependent molecular information on the hydrated polymer films is obtained using total internal reflection (TIR) Raman spectroscopy, complemented with differential scanning calorimetry (DSC) and ellipsometry. Ice adhesion measurements show a pronounced counterion-specific behavior with a sharp increase in adhesion at temperatures that depend on the anion identity, following the order Cl- < F- < SCN- < Br- < I-. Linked to the freezing of hydration water, the specific ordering results from differences in ion pairing and the amount of water present within the polymer film. Moreover, similar effects can be promoted by varying the cross-linking density in the coating while keeping the anion identity fixed. These findings shed new light on low ice adhesion mechanisms and may inspire novel approaches for improved anti-icing coatings.

An Activatable Host-Guest Conjugate as a Nanocarrier for Effective Drug Release through Self-Inclusion.

There is a challenge in supramolecular chemotherapy for constructing a system equipped with both sufficient protection and high-efficiency release of drugs. To this end, a new strategy of an activatable host-guest conjugate with self-inclusion property is proposed. Based on the binding affinity gain of intramolecular host-guest self-inclusion, an activatable host-guest conjugate was designed, bearing cucurbit[7]uril as the host, an alkyl ammonium moiety as the guest, and the redox-responsive disulfide linkage. Oxaliplatin, a clinical antitumor drug, could be firmly encapsulated by the activatable host-guest conjugate to form the supramolecular drug with high stability. Moreover, oxaliplatin loaded in the activatable host-guest conjugate could be almost completely released by self-inclusion triggered by glutathione in a tumor microenvironment, thus exhibiting comparable antitumor bioactivity with naked oxaliplatin through in vitro cell experiments. It is highly anticipated that this line of research may open new horizons for programmable and on-demand supramolecular chemotherapy with high antitumor efficiency.

Laser-induced inter-ion migration and the effect of different long alkylammonium halide functionalization on CH3NH3Pb(BrxI1−x)3 colloidal nanoparticles

The laser-induced phase segregation effect and dynamic evolution of room-temperature photoluminescence (PL) from mixed halide colloidal nanoparticles of CH3NH3Pb(Br0.5I0.5)3 are presented. UV laser-assisted compositional changes are observed in PL when the nanoparticles are surface-functionalized with different halide based long alkylammonium moieties (C8H17NH3X; X = Cl, Br or I). The C8H17NH3Cl passivation produced a remarkable 100 nm relative blue shift in the mixed-phase PL peak position, while C8H17NH3Br shows a 15 nm blue-shift and C8H17NH3I produced a red-shift of about 10 nm. The results are direct evidence of laser-assisted reversible phase segregation, halide ion diffusion from surface ligand to nanoparticles, and the effect of surface functionalization on photo-assisted bandgap engineering. These studies provide a broad understanding of various dynamically evolving emission pathways in such mixed hybrid materials when they are functionalized with diverse halide based organic moieties.

Fluorine-substituted tetracationic ABAB-phthalocyanines for efficient photodynamic inactivation of Gram-positive and Gram-negative bacteria

Herein, we report the synthesis and characterization of new amphiphilic phthalocyanines (Pcs), the study of their singlet oxygen generation capabilities, and biological assays to determine their potential as photosensitizers for photodynamic inactivation of bacteria. In particular, Pcs with an ABAB geometry (where A and B refer to differently substituted isoindole constituents) have been synthesized. These molecules are endowed with bulky bis(trifluoromethylphenyl) groups in two facing isoindoles, which hinder aggregation and favour singlet oxygen generation, and pyridinium or alkylammonium moieties in the other two isoindoles. In particular, two water-soluble Pc derivatives (PS-1 and PS-2) have proved to be efficient in the photoinactivation of S. aureus and E. coli, selected as models of Gram-positive and Gram-negative bacteria.

Host-guest complexes of local anesthetics with cucurbit[6]uril and para-sulphonatocalix[8]arene in the solid state

Here we describe the host-guest inclusion complexes of local anesthetic drugs with two macrocyclic hosts cucurbit[6]uril and para-sulphonatocalix[8]arene in the solid state. The anesthetic agents used in the co-crystallization with the supramolecular hosts are lidocaine, procaine, procainamide, prilocaine and proparacaine. Both macrocycles encapsulate the alkylammonium moieties of anestetics guests into their cavities although the mechanism of complexation, host-guest stoichiometry and geometry differ depending on the nature of the supramolecular host.

Effects of organic moieties on the photoluminescence spectra of perovskite-type tin bromide based compounds

The photoluminescence (PL) and optical absorption (OA) spectra of some compounds of the type (SC)SnBr3, (BC)2SnBr4, and (SC)(BC)2Sn2Br7 (where SC is CH3NH3+ or Cs+; BC is C4H9NH3+,CH3C6H4CH2NH3+,C12H25NH3+,C18H37NH3+ and 1-naphthylmethyl ammonium group), in the forms of thin deposits on several substrates, are investigated. Generally, using the 350nm as excitation line, the obtained PL spectra of compounds of the type (BC)2SnBr4 with short alkyl chain-length in the alkyl ammonium moiety, show broad and strong bands. For example, the PL spectra of compound (C4H9NH3)2SnBr4 exhibit a weak band at ca 475nm, attributed to free-excitons and a broad and strong band at ca 570 nm, attributed to radiative decay of self-trapped excitons in the inorganic moiety. This is a bright yellow-orange emission, which can be seen by naked eye, even at room temperature. In the case of the compounds with long alkyl chain-length in the alkyl ammonium moiety, the PL spectra are dominated by an excitonic band, which occurs close to the corresponding fundamental OA edge. The PL spectrum of (1-naphthylmethyl ammonium)2SnBr4 shows the strong red band with main maxima at ca 603 and 642nm, arising from tetramers of naphthyl moieties. Also, the PL spectra of the compounds of the type (SC)SnBr3 and (SC)(BC)2Sn2Br7, after grinding, show strong bands at 600–620nm.

Triply Stacked Heterogeneous Array of Porphyrins and Phthalocyanine through Stepwise Formation of a Fourfold Rotaxane and an Ionic Complex

We report the preparation and crystal structure of a triply stacked metal complex array in which a Cu-phthalocyanine is sandwiched between different Cu-porphyrins. The discrete heterogeneous assembly was prepared through formation of a fourfold rotaxane from a tetradactyl porphyrin with alkylammonium moieties and a phthalocyanine bearing four crown ethers and the subsequent formation of an ionic complex between the fourfold rotaxane and a tetraanionic porphyrin. The tetraanionic porphyrin, Cu-TPPS(4-), is selectively bound to the fourfold rotaxane through cooperative π-π and ionic interactions. The crystal structure revealed the columnar stacked array of the three planar building components in a precise order and spatial arrangement that promote intermolecular electronic communication.

Phosphorylcholine Phosphatase: A Peculiar Enzyme of Pseudomonas aeruginosa

Pseudomonas aeruginosa synthesizes phosphorylcholine phosphatase (PchP) when grown on choline, betaine, dimethylglycine or carnitine. In the presence of Mg2+ or Zn2+, PchP catalyzes the hydrolysis of p-nitrophenylphosphate (p-NPP) or phosphorylcholine (Pcho). The regulation of pchP gene expression is under the control of GbdR and NtrC; dimethylglycine is likely the metabolite directly involved in the induction of PchP. Therefore, the regulation of choline metabolism and consequently PchP synthesis may reflect an adaptive response of P. aeruginosa to environmental conditions. Bioinformatic and biochemistry studies shown that PchP contains two sites for alkylammonium compounds (AACs): one in the catalytic site near the metal ion-phosphoester pocket, and another in an inhibitory site responsible for the binding of the alkylammonium moiety. Both sites could be close to each other and interact through the residues 42E, 43E and 82YYY84. Zn2+ is better activator than Mg2+ at pH 5.0 and it is more effective at alleviating the inhibition produced by the entry of Pcho or different AACs in the inhibitory site. We postulate that Zn2+ induces at pH 5.0 a conformational change in the active center that is communicated to the inhibitory site, producing a compact or closed structure. However, at pH 7.4, this effect is not observed because to the hydrolysis of the [Zn2+L2 −1L2 0(H2O)2] complex, which causes a change from octahedral to tetrahedral in the metal coordination geometry. This enzyme is also present in P. fluorescens, P. putida, P. syringae, and other organisms. We have recently crystallized PchP and solved its structure.

Different Effects of Mg2+ and Zn2+ on the Two Sites for Alkylammonium Compounds in Pseudomonas aeruginosa Phosphorylcholine Phosphatase

Pseudomonas aeruginosa phosphorylcholine phosphatase (PchP) catalyzes the hydrolysis of phosphorylcholine (Pcho), is activated by Mg2+ or Zn2+, and is inhibited by high concentrations of substrate. This study has shown that PchP contains two sites for alkylammonium compounds (AACs): one in the catalytic site near the metal ion-phosphoester pocket, and the other in an inhibitory site responsible for the binding of the alkylammonium moiety. The catalytic mechanism for the entry of Pcho in both sites and Zn2+ or Mg2+ follows a random sequential mechanism. However, Zn2+ is more effective than Mg2+ at alleviating the inhibition produced by the entry of Pcho or different AACs in the inhibitory site. We postulate that Zn2+ induces a conformational change in the active center that is communicated to the inhibitory site, producing a compact or closed structure. In contrast, Mg2+ produces a relaxed or open conformation.

Counterion‐Dependent Proton‐Driven Self‐Assembly of Linear Supramolecular Oligomers Based on Amino‐Calix[5]arene Building Blocks

Self-assembly of a calix[5]arene bearing a 12-aminododecyl pendant group on the lower rim into supramolecular oligomers through intermolecular iterative inclusion events is readily triggered by contact with acid solutions and is reversed to the amino monomer precursor by treatment with a base. 1H NMR data are consistent with the formation of head-to-tail assemblies derived from endo-cavity inclusion of the alkylammonium moiety. Diffusion NMR and light-scattering studies provide evidence for the presence of oligomers in solution and show that different counterions and concentrations result in different oligomer sizes, whereas ESI-MS and SEM investigations, respectively, indicate that self-assembly also takes place in the gas phase and in the solid state. The growth of these supramolecular oligomers is concentration-dependent; however, as a consequence of the saline nature of the monomer, it also shows a distinct counterion-dependence owing to ion-pairing/solvation effects.

Low-Defect Neutral, Cationic, and Anionic Conducting Polymers from Electrochemical Polymerization of N-Substituted Bipyrroles. Synthesis, Characterization, and EQCM Analysis

Various 2,2‘-bipyrroles N-substituted with alkyl, alkylsulfonate, or alkylammonium moieties have been anodically coupled to polymers. The polymers were characterized by cyclic voltammetry, UV−vis and FTIR spectroscopies, EQCM, and in situ conductivity. Coupling of dipyrroles instead of pyrroles minimizes the introduction of overoxidative defects into the polymer chain (from FTIR spectroscopy). The polymer of N-alkylammonium-N-hexyldipyrrole is soluble in acetonitrile. EQCM analysis of the oxidative doping process of the polymers in acetonitrile has shown that the alkyl- and alkylammonium-substituted polymers increase their mass with doping, whereas the mass decreases in the case of alkylsulfonate-substituted polymers provided with tetralkylammonium counterions. Electrochemical muscles built from the most representative polymers show marked deflections that follow the EQCM mass/charge changes.

The role of tyrosine at the ligand-binding site of the nicotinic acetylcholine receptor

Identification of the critical residues in a receptor's ligand-binding site provides valuable structural information important for understanding the basis for ligand recognition. The design of specific ligands targeted for receptor action will depend to a great extent on detailed structural knowledge of this kind. Although the nicotinic acetylcholine receptor (nAChR) is perhaps the best characterized of all receptors, the detailed configuration of the ligand-binding site remains unknown. Structural comparisons of nicotinic agonists and antagonists have long predicted a negative subsite on the receptor to interact with the positively charged alkyl-ammonium moiety common to nearly all nicotinic agents. We have used intrinsic fluorescence spectroscopic analyses together with binding studies of selectively modified peptide fragments of the nAChR to suggest that one or two invariant tyrosine residues at positions 190 and 198 on the alpha-subunit provide the critical negative subsite required for ligand binding. Tyrosines may similarly be part of the negative subsite of muscarinic receptors and other neurotransmitter receptors that bind cationic ligands.

Mesomorphic-like character of long-chain amine salts formed by template neutralization on polyacids

Abstract Several examples of monomeric and polymerized surfactants exhibiting liquid-crystalline behaviour have recently been reported. In the present investigation a novel process for the formation of liquid crystals is introduced, according to which certain functionalized polymers induce mesomorphism when they react with appropriate amines. For instance, neutralization of polyacrylic or polymaleic acid with long-chain amines forms alkylammonium salt surfactants which exhibit mesomorphic-like character. In this type of experiment, however, the known lamellar structure of alkylammonium salts was modified by this so-called template neutralization. The carboxylate groups, due to their location on the polymeric chain, appear to exert a topochemical effect on alkylammonium moieties which in turn affect the mesomorphic behaviour compared with that of common surfactants. The mesomorphic behaviour of these materials was established by optical microscopy and differential scanning calorimetry.

Alkylammonium dialkylarsiante surfactants in organic solvents: Aggregation and water solubilization studies

The aggregation of butyl-, octyl-, and dodecylammonium di-2-ethylhexylarsinate in C 6D 6, CDCl 3, and CCl 4 was studied by PMR spectroscopy. The variation of the chemical shifts of the magnetically discrete protons as a function of the stoichiometric concentration of the surfactants indicates that the − N + H 3 and −AsO 2 − ions are located at the aggregate interior. A multiple equilibrium aggregation model was applied to the PMR data, the equilibrium constant for aggregation, and the aggregates distribution calculated. Both quantities depend on the chain length of the alkylammonium moiety, and on the solvent polarity. Compared to the corresponding alkylammonium diethylarsinates the title surfactants show higher aggregation tendency, probably due to the diminished solvent-head-ions interactions. The polarity (Z value) of the water solubilized by dodecylammonium dietyl-, and di-2-ethylhexylarsinates in chloroform showed marked dependence on the [water]/[surfactant] ratio. Higher Z values were obtained in the case of the latter surfactant, reflecting weaker interactions of the head-ions with the solubilized water. The obtained Z values indicate micellar cores whose polarities lie between those of dichloromethane, and acetonitrile or t-butanol.

Molecular mechanisms of nerve block by local anesthetics

Local anesthetics block nerve conduction by preventing the increase in membrane permeability to sodium ions that normally leads to a nerve impulse. Among anesthetics containing tertiary amine groups, the cationic, protonated form appears to be more active than the neutral form. However, the neutral forms, as well as uncharged molecules like benzocaine and the aliphatic alcohols, also depress sodium permeability. Studies of single myelinated nerves and squid axons show no direct interaction between calcium ions and local anesthetics, thus disproving theories based on competition between these two agents. Likewise, hypotheses attributing local anesthesia to changes in electrical potentials at the membrane-water interface are disproven by the demonstrated potencies of electrically uncharged anesthetics. Hypotheses that propose that local anesthetics act by expanding the nerve membrane and causing a change in protein conformation that blocks sodium permeability are vague in conception and difficult to test experimentally. Evidence from voltage-clamp studies of single nerve fibers indicates that anesthetic molecules interact with the sodium channels directly, from the inner side of the nerve membrane. Anesthetics bind within sodium channels which have opened during membrane depolarization, preventing the normal sodium ion flux. Anesthetic molecules can dissociate from open channels, but not from channels that remain closed when the nerve is kept at rest. The gating properties that regulate the opening and closing of sodium channels are reversibly modified during anesthesia. Specifically, the inactivation function responds more slowly and requires more negative membrane potential changes to reach the same values as in unanesthetized nerves. A second, slow inactivation is observed following external application of tertiary amine anesthetics. The selective binding of anesthetics to open sodium channels provides a simple explanation for Wedenski inhibition, in which the block increases with the frequency of nerve impulses. When impulses occur at higher frequencies more sodium channels are open over a period of time comparable to the time necessary for the anesthetic binding reaction, thus more channels are blocked. In addition the changes of the inactivation function result in a longer refractory period and, thus, a decrease of impulse height at higher frequencies. Charged anesthetic molecules may bind in the pore of the sodium channel. Their binding can be modulated by the electrical field in the membrane. The channel has a higher affinity for larger anesthetic molecules, but this may result from their greater hydrophobicity as well as from their size. The binding site favors molecules that contain more polar linkages between the amine group and the aromatic residue. Binding of amine anesthetics is weakly stereospecific and, surprisingly, shows no absolute requirement for the terminal alkyl ammonium moiety present in most local anesthetics...

Molecular mechanisms of nerve block by local anesthetics.

Local anesthetics block nerve conduction by preventing the increase in membrane permeability to sodium ions that normally leads to a nerve impulse. Among anesthetics containing tertiary amine groups, the cationic, protonated form appears to be more active than the neutral form. However, the neutral forms, as well as uncharged molecules like benzocaine and the aliphatic alcohols, also depress sodium permeability. Studies of single myelinated nerves and squid axons show no direct interaction between calcium ions and local anesthetics, thus disproving theories based on competition between these two agents. Likewise, hypotheses attributing local anesthesia to changes in electrical potentials at the membrane-water interface are disproven by the demonstrated potencies of electrically uncharged anesthetics. Hypotheses that propose that local anesthetics act by expanding the nerve membrane and causing a change in protein conformation that blocks sodium permeability are vague in conception and difficult to test experimentally. Evidence from voltage-clamp studies of single nerve fibers indicates that anesthetic molecules interact with the sodium channels directly, from the inner side of the nerve membrane. Anesthetics bind within sodium channels which have opened during membrane depolarization, preventing the normal sodium ion flux. Anesthetic molecules can dissociate from open channels, but not from channels that remain closed when the nerve is kept at rest. The "gating" properties that regulate the opening and closing of sodium channels are reversibly modified during anesthesia. Specifically, the inactivation function responds more slowly and requires more negative membrane potential changes to reach the same values as in unanesthetized nerves. A second, slow inactivation is observed following external application of tertiary amine anesthetics. The selective binding of anesthetics to open sodium channels provides a simple explanation for Wedenski inhibition, in which the block increases with the frequency of nerve impulses. When impulses occur at higher frequencies more sodium channels are open over a period of time comparable to the time necessary for the anesthetic binding reaction, thus more channels are blocked. In addition the changes of the inactivation function result in a longer refractory period and, thus, a decrease of impulse height at higher frequencies. Charged anesthetic molecules may bind in the pore of the sodium channel. Their binding can be modulated by the electrical field in the membrane. The channel has a higher affinity for larger anesthetic molecules, but this may result from their greater hydrophobicity as well as from their size. The binding site favors molecules that contain more polar linkages between the amine group and the aromatic residue. Binding of amine anesthetics is weakly stereospecific and, surprisingly, shows no absolute requirement for the terminal alkyl ammonium moiety present in most local anesthetics...