Occurrence Of Proton Transfer Research Articles

Proton transfer in Quantum well and Potential barrier models of adenine-thymine and deazaadenine-thymine radical cation: A QM/MM dynamics study

Proton transfer within DNA base pairs has significant implications for charge transport and its potential applications in semiconductor devices. Also, it can provide a deeper understanding of the fundamental reactions that occur in biology and acid–base chemistry. Through QM/MM calculations, it was discovered that proton transfer occurs in Quantum well and Potential barrier made up of adenine-thymine and deazaadenine-thymine radical cation base pairs. Although various cases can influence proton transfer, an analysis of water polarity within a specific range shows a correlation between the occurrence of proton transfer and water polarity.

Ferroelectric SbSI nanowires for ammonia detection at a low temperature

For the first-time, an ammonia (NH3) gas sensor has been fabricated using antimony sulfoiodide (SbSI). A few aligned SbSI nanowires have been bonded to Au microelectrodes on a glass substrate. The fabricated sensor has been tested for various concentrations of NH3 in N2 at operating temperatures below (T = 280 K) and above (T = 304 K) Curie point of SbSI. A significantly higher response and sensitivity of the sensor is observed, when the operating temperature is lower than Curie temperature. However, comparable values of the low detection limits (6.0 ± 2.4) ppm and (6.3 ± 3.9) ppm have been determined at operating temperatures of 280 K and 304 K, respectively. The current response, as well as the sensitivity versus ammonia concentration, follow the power laws known for conductometric gas sensors. SbSI nanosensor exhibits good stability, short term response reversibility, and does not require a heating system for recovery. This device also demonstrates a high selectivity to NH3 against other interfering gases. The ammonia sensing mechanism has been explained by considering the formation of NH4+ ions on the nanowire surface and the occurrence of proton transfer according to Grotthuss's chain reaction.

Aromatic versus Aliphatic Carboxyl Group as a Hydrogen Bond Donor in Salts and Cocrystals of an Asymmetric Diacid and Pyridine Derivatives

A series of 15 salts and cocrystals of an asymmetric aromatic–aliphatic dicarboxylic diacid, N-(2-carboxyphenyl)glycine, and pyridine derivatives was synthesized in order to study whether there is a preference of pyridine binding to either of the carboxylic groups. In nine structures the pyridine was bonded to the aliphatic group, in three to both carboxylic groups, and in three to the aromatic group alone. The preference of pyridine derivatives to bond to the aliphatic group correlates with the more positive electrostatic potential on the aliphatic carboxyl hydrogen atom. The occurrence of proton transfer within the structures was found to follow the basicity of the pyridine derivative, four of the least basic pyridines forming cocrystals, two intermediate bases solids with proton disorder and the more basic pyridine derivatives salts. Proton transfer had a considerable effect on the crystal packing, cocrystals mostly comprising discrete molecular complexes, and salt chains of monoanions.

Hydrated alizarin complexes: hydrogen bonding and proton transfer

We investigated the hydrogen bonding structures and proton transfer for the hydration complexes of alizarin (Az) produced in a supersonic jet using fluorescence excitation (FE), dispersed laser induced fluorescence (LIF), visible-visible hole burning (HB), and fluorescence detected infrared (FDIR) spectroscopy. The FDIR spectrum of bare Az with two O-H groups exhibits two vibrational bands at 3092 and 3579 cm(-1), which, respectively, correspond to the stretching vibration of O1-H1 that forms a strong intramolecular hydrogen bond with the C9=O9 carbonyl group and the stretching vibration of O2-H2 that is weakly hydrogen-bonded to O1-H1. For the 1:1 hydration complex Az(H(2)O)(1), we identified three conformers. In the most stable conformer, the water molecule forms hydrogen bonds with the O1-H1 and O2-H2 groups of Az as a proton donor and proton acceptor, respectively. In the other conformers, the water binds to the C10=O10 group in two nearly isoenergetic configurations. In contrast to the sharp vibronic peaks in the FE spectra of Az and Az(H(2)O)(1), only broad, structureless absorption was observed for Az(H(2)O)(n) (n≥ 2), indicating a facile decay process, possibly due to proton transfer in the electronic excited state. The FDIR spectrum with the wavelength of the probe laser fixed at the broad band exhibited a broad vibrational band near the O2-H2 stretching vibration frequency of the most stable conformer of Az(H(2)O)(1). With the help of theoretical calculations, we suggest that the broad vibrational band may represent the occurrence of proton transfer by tunnelling in the electronic ground state of Az(H(2)O)(n) (n≥ 2) upon excitation of the O2-H2 vibration.

Thermotropic Mesomorphism via Self‐Assembly of Cationic Dendritic Polymers with an Anionic Polar Carboxylic Acid

AbstractThe synthesis and characterization of ionic liquid crystalline dendritic polymers based on the ammonium salts of commercially available poly(propylene imine) (PPI), poly(amidoamine) (PAMAM), poly(ethyleneimine) (PEI), and the fully methylated PEI (PEIMe) with 5‐(4‐cyanobiphenoxy)pentanoic acid (CBPA) are reported. The occurrence of proton transfer from the carboxylic acid to the amine groups is confirmed using IR and NMR techniques. The mesomorphic behavior is investigated by means of differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffractometry. Although CBPA exhibits monotropic nematic mesomorphism, all ionic complexes display enantiotropic liquid crystal properties. The relationship between the mesomorphism of the complexes and their structure is discussed.

Photosensitive Ionic Nematic Liquid Crystalline Complexes Based on Dendrimers and Hyperbranched Polymers and a Cyanoazobenzene Carboxylic Acid

The synthesis and characterization of ionic liquid crystal dendrimers and hyperbranched polymers based on the ammonium salts of commercially available dendrimers poly(propylene imine) [PPI-(NH2) n ] (with n = 16), and poly(amidoamine) [PAMAM-(NH2) n ] (with n = 16), and random hyperbranched poly(ethyleneimine) (PEI) and the prepared fully methylated PEI (namely PEIMe) with 5-(4-cyanophenylazophenyloxy)pentanoic acid (CAzPA) are reported. The occurrence of proton transfer from the carboxylic acid to the amine groups was confirmed by IR and NMR measurements. 5-(4-Cyanophenylazophenyloxy)pentanoic acid does not show mesogenic properties. However, all synthesized ionic complexes displayed a nematic mesophase. The liquid crystalline behavior was investigated by means of differential scanning calorimetry, polarizing light optical microscopy, and X-ray diffractometry. Themogravimetry analysis was carried out in order to determine the stability of the complexes, all of which have their mesophase−isotropic liquid ...

Isomeric dependence of the formation of ion/neutral complexes in dissociation reactions of ionized propoxypyridines

The mechanistic aspects of the dissociation reactions of the molecular ions of isomeric propoxypyridines have been examined with the use of deuterium labelling and tandem mass spectrometry. The ionized 2- and 3-propoxypyridines dissociate predominantly by the loss of propene, whereas the molecular ions of 4-propoxy- and 4-isopropoxypyridine react by the competing losses of a propene molecule and an allyl radical. The loss of propene from the metastable molecular ions of the 2-isomer involves a 1,5-H shift from the 2-position of the propyl group to the ring as evidenced by the labelling experiments. For the metastable molecular ions of 3-propoxypyridine, the results are in agreement with propene loss by a pathway involving formation of a [C 5H 4NO ·/(CH 3) 2CH +] complex which reacts further by proton transfer prior to dissociation. In contrast to these findings, interchange between the hydrogen atoms at the 2-position of the propyl group, and the 3- or 5-position of the pyridine ring, occurs in ionized 4-propoxypyridine. This interchange can precede the formation of a [C 5H 4NO ·/(CH 3) 2CH +] complex and the occurrence of proton transfer within this species. The [C 5H 5NO +·/C 3H 6] complex formed in the proton transfer step may either expel propene or react by hydrogen atom transfer prior to the loss of an allyl radical. For the metastable ions of 4-isopropoxypyridine, interchange between a hydrogen atom from one of the methyl groups of the alkyl chain and the aromatic ring appears to be of minor importance.

Lamellar Mesophases Formed by Thermotropic Liquid Crystalline Ionic Polymer Systems without Mesogenic Units

Mixtures consisting of polyamine (branched polyethyleneimine (PEI) and polyallylamine (PAA)) and n-alkanoic acid (C n: n = the carbon number of alkanoic acid) were prepared and their thermal and liquid crystalline properties were examined. The occurrence of proton transfer from the carboxylic acid to the amine groups was found by IR measurement of the mixtures. The polyamines and C n exhibited no mesophase. Also, PEI/C n with n = 3, 4, 5, which are mixtures of PEI and C n, did not show a liquid crystalline phase. However, PEI/C n with n> 5 clearly displayed a lamellar fluid liquid crystal phase having a layer structure with low order inside the layer, due to ion–ion interactions. In the lamellar mesophase, PEI/C n showed a focal-conic fan texture which resembles the fan-shaped textures in smectic A and C phases. PEI/C n with 5 < n < 13 formed a bilayer structure in the lamellar mesophase. On the other hand, a tilted bilayer structure is proposed as a packing model of PEI/C n with 13 < n< 19. PAA/C18 consisting of polyallylamine and C18 also showed a lamellar fluid mesophase and formed a similar layer structure to PEI/C18.

Molecular Recognition of Phosphate Esters: A Balance of Hydrogen Bonding and Proton Transfer Interactions

AbstractThe interaction of different phosphate esters with a series of hydrogen bonding receptors has been studied using UV‐visible and NMR spectroscopies and X‐ray crystallography. Critical for binding is a combination of an acidic proton and the potential for bidentate hydrogen bonding either between charged or uncharged components. Phosphotriesters show no binding to the receptors. Phosphodiesters bind to both bis‐(2, 6–diacylaminopyridine) and mono‐(2, 6–diacylaminopyridine) receptors in chlorocarbon solvent via proton transfer to form the pyridinium phosphate ion pair and bidentate hydrogen bonding between the anion and the cation. Titration experiments as well as Job's analyses show that for cyclic and acyclic bis‐(2, 6–diacylaminopyridine) receptors 2: 1 complexes can be formed. X‐ray crystal structures demonstrate that in the solid state two different binding arrangements are present; either a direct bidentate interaction or intramolecular hydrogen bonding with self‐assembly of an oligomeric structure. Phosphomonoesters bind to mono‐(2, 6–diacylaminopyridines) in a similar way to the diesters, via proton transfer and bidentate hydrogen bonding. In this, as in the diester case, only a single acid‐base interaction is possible and proton transfer is preferred. However, in the interaction of phosphomonoesters with bis‐(2, 6–diacylaminopyridine) derivatives two acid‐base interactions are possible between the two pyridines and two POH groups, and little proton transfer is seen. Strong binding (Ka = 1.0 × 105M−1) occurs via tetrahydrogen bond formation. Thus, there appears to be a balance between the occurrence of proton transfer and the number of hydrogen bonds formed between receptor and substrate.

ChemInform Abstract: The Collision‐Induced Dissociations of Deprotonated Amines in the Gas Phase

The major collision-induced fragmentations of deprotonated primary and secondary amines are best rationalized as proceeding through the intermediacy of ion complexes. For example, the characteristic fragmentation of deprotonated ethylamine isMeCH2NH- → [Me-(CH2=NH)] → CH2N- + CH4 Secondary alkylamines behave in a similar fashion. The occurrence of proton transfer as a prelude to fragmentation is rare: the only example observed in this study is the probable reaction PhNEt →→ PhNHCHMe → [(PhNH=CH)Me-] → C7H6N- + CH4 which is preceded or accompanied by proton transfer between the methylene and phenyl substituents. Deprotonated aniline undergoes specific elimination of CNH from the 1-position to form the cyclopentadienyl anion. Finally, retro reactions are observed for the piperazine anion, e.g. HN(CH2CH2)2N → -CH2CH2N=CH2+CH2NH

Photophysical studies of luminarosine—A new, highly fluorescent ribonucleoside with pteridine-like betaine as the aglycone

The solvent and pH dependence of the absorption and fluorescence spectra, fluorescence quantum yields and lifetimes, and fluorescence quenching behaviour of 4-(2,3,5-tri-O-acetyl-β-D-ribofuranosylamino)pyrido[2,1-h]pteridin-11-ium-6-olate, its α-anomer, the parent ribonucleoside 4-(β-D-ribofuranosylamino)-pyrido[2,1-h]-pteridin-11-ium-5-olate (luminarosine) and the aglycone 4-aminopyrido[2,1-h]-pteridin-11-ium-5-olate (luminarine) are reported. Spectroscopic properties of these compounds in solvents of different polarities are characterized by evidence of the occurrence of a highly dipolar, charge-transfer excited state within the heterocyclic betaine system. The pH dependence of the absorption spectra of luminarosine and luminarine infer the occurrence of ground state prototropic equilibria in solution involving protonation of the negatively charged oxygen atom followed by tautomerism to a lactam. The excited state prototropic equilibria, as shown by fluorescence properties, seem to be more complex and suggest the possible occurrence of proton-transfer and/or phototautomerization reactions.

The Collision-Induced Dissociations of Deprotonated Amines in the Gas Phase

The major collision-induced fragmentations of deprotonated primary and secondary amines are best rationalized as proceeding through the intermediacy of ion complexes. For example, the characteristic fragmentation of deprotonated ethylamine isMeCH2NH- → [Me-(CH2=NH)] → CH2N- + CH4 Secondary alkylamines behave in a similar fashion. The occurrence of proton transfer as a prelude to fragmentation is rare: the only example observed in this study is the probable reaction PhNEt →→ PhNHCHMe → [(PhNH=CH)Me-] → C7H6N- + CH4 which is preceded or accompanied by proton transfer between the methylene and phenyl substituents. Deprotonated aniline undergoes specific elimination of CNH from the 1-position to form the cyclopentadienyl anion. Finally, retro reactions are observed for the piperazine anion, e.g. HN(CH2CH2)2N → -CH2CH2N=CH2+CH2NH