Exchange Of Hydrogen Atoms Research Articles

The Exchange of Hydrogen Atoms between Water Hydrogen Atoms and Hydrogen Atoms on Carbon in Hot Water

The Exchange of Hydrogen Atoms between Water Hydrogen Atoms and Hydrogen Atoms on Carbon in Hot Water

InnTl4-nH+ (n = 0∼4): Tetracoordinate Hydrogen in a Planar Fashion?

The recent report of planar tetracoordinate hydrogen (ptH) in In4H+ is very intriguing in planar hypercoordinate chemistry. Our high-level CCSD(T) calculations revealed that the proposed D4h-symmetric ptH In4H+ is a first-order saddle point with an imaginary frequency in the out-of-plane mode of the hydrogen atom. In fact, at the CCSD(T)/aug-cc-pV5Z/aug-cc-pV5Z-PP level, the C4v isomer, with the H atom located 0.70 Å above the In4 plane, is 0.5 kcal/mol more stable than the D4h isomer. However, given the small perturbation from planarity and essentially barrierless C4v ↔ D4h ↔ C4v transition, the vibrationally averaged structure can still be considered as a planar. Extending our exploration to the InnTl4-nH+ (n = 0-3) systems, we found all these ptH structures, except for In2Tl2H+, to be the putative global minimum. The single σ-delocalized interaction between the central hydrogen atom and InnTl4-n ligand rings proves pivotal in establishing planarity and aromaticity and conferring substantial stability upon these rule-breaking ptH species.

Carboxylesterase Activatable Molecular Probe for Personalized Treatment Guidance by Analyte-Induced Molecular Transformation.

Accurate visualization of tumor microenvironment is of great significance for personalized medicine. Here, we develop a near-infrared (NIR) fluorescence/photoacoustic (FL/PA) dual-mode molecular probe (denoted as NIR-CE) for distinguishing tumors based on carboxylesterase (CE) level by an analyte-induced molecular transformation (AIMT) strategy. The recognition moiety for CE activity is the acetyl unit of NIR-CE, generating the pre-product, NIR-CE-OH, which undergoes spontaneous hydrogen atom exchange between the nitrogen atoms in the indole group and the phenol hydroxyl group, eventually transforming into NIR-CE-H. In cellular experiments and in vivo blind studies, the human hepatoma cells and tumors with high level of CE were successfully distinguished by both NIR FL and PA imaging. Our findings provide a new molecular imaging strategy for personalized treatment guidance.

Carboxylesterase Activatable Molecular Probe for Personalized Treatment Guidance by Analyte‐Induced Molecular Transformation

AbstractAccurate visualization of tumor microenvironment is of great significance for personalized medicine. Here, we develop a near‐infrared (NIR) fluorescence/photoacoustic (FL/PA) dual‐mode molecular probe (denoted as NIR−CE) for distinguishing tumors based on carboxylesterase (CE) level by an analyte‐induced molecular transformation (AIMT) strategy. The recognition moiety for CE activity is the acetyl unit of NIR−CE, generating the pre‐product, NIR−CE−OH, which undergoes spontaneous hydrogen atom exchange between the nitrogen atoms in the indole group and the phenol hydroxyl group, eventually transforming into NIR−CE−H. In cellular experiments and in vivo blind studies, the human hepatoma cells and tumors with high level of CE were successfully distinguished by both NIR FL and PA imaging. Our findings provide a new molecular imaging strategy for personalized treatment guidance.

Pushing The Extreme of Multicentre Bonding: Planar Pentacoordinate Hydride.

Planar hypercoordination has sparkled interest among the researchers from last few decades. Most of the elements in the Periodic Table have shown this remarkable structural feature. However, the smallest element, hydrogen, is missing in the list. No evidence is there in the literature. Herein, we introduce the first planar pentacoordinate hydrogen atom (ppH) in the global minimum geometry of Li5 H6 - cluster. Bonding analysis indicates that the central hydrogen atom is stabilized by multicentre bonding with five surrounding Li atoms. Natural charge analysis reveals that the central hydrogen is acting like a hydride which is strongly attracted by the positively charged surrounding lithium centres. The ppH structure is stabilized by strong electrostatic attraction as well as extensive multicentre bonding. Aromaticity has no role to play here. The cluster is dynamically stable and is expected to be detected in gas phase.

Pushing The Extreme of Multicentre Bonding: Planar Pentacoordinate Hydride

AbstractPlanar hypercoordination has sparkled interest among the researchers from last few decades. Most of the elements in the Periodic Table have shown this remarkable structural feature. However, the smallest element, hydrogen, is missing in the list. No evidence is there in the literature. Herein, we introduce the first planar pentacoordinate hydrogen atom (ppH) in the global minimum geometry of Li5H6− cluster. Bonding analysis indicates that the central hydrogen atom is stabilized by multicentre bonding with five surrounding Li atoms. Natural charge analysis reveals that the central hydrogen is acting like a hydride which is strongly attracted by the positively charged surrounding lithium centres. The ppH structure is stabilized by strong electrostatic attraction as well as extensive multicentre bonding. Aromaticity has no role to play here. The cluster is dynamically stable and is expected to be detected in gas phase.

Characteristics of Intermolecular Interactions between Encapsulated Molecules and the Lantern-Like Carcerand Superphanes

The main topic of the article is to provide the characteristics of individual intermolecular interactions present between three lantern-like superphanes and the H2O, NH3, HF, HCN, and MeOH molecules trapped inside them. Despite the large cavity, the freedom of the trapped molecules is significantly limited by the presence of numerous interaction sites on the side chains of the superphane molecule. It is shown that the molecule trapped inside the superphane is stabilized mainly by only one or, less often, two strong hydrogen bonds involving the imino nitrogen atom, but QTAIM calculations also suggest the presence of many other intermolecular interactions, mainly hydrogen bonds involving imino or central hydrogen atoms from the side chains of the superphane molecule. Moreover, it is also shown that the structural simplification of the side chains does not significantly affect both the size of the superphane molecule and the obtained encapsulation energies, which is important in modeling this type of carceplexes. Noticeably, the parent superphane considered here was previously synthesized by the group of Qing He, so the results obtained will help in understanding this type and similar systems.

Planar Tetracoordinate Hydrogen: Pushing the Limit of Multicentre Bonding

AbstractAmong the list of planar tetracoordinate atoms, the smallest element hydrogen is missing. No experimental and theoretical evidence have ever been put forwarded. Herein, we introduce the first planar tetracoordinate hydrogen atom (ptH) in the global minimum geometry of In4H+ cluster. Bonding analysis indicates that the central hydrogen atom is acting like a proton and significant charge transfer from the surrounding In4 framework results in a negative charge of the central hydrogen atom. The proposed global minimum geometry possesses σ‐aromaticity and the central hydrogen atom forms unusual multicentre bond with more than three centres.

Planar Tetracoordinate Hydrogen: Pushing the Limit of Multicentre Bonding.

Among the list of planar tetracoordinate atoms, the smallest element hydrogen is missing. No experimental and theoretical evidence have ever been put forwarded. Herein, we introduce the first planar tetracoordinate hydrogen atom (ptH) in the global minimum geometry of In4 H+ cluster. Bonding analysis indicates that the central hydrogen atom is acting like a proton and significant charge transfer from the surrounding In4 framework results in a negative charge of the central hydrogen atom. The proposed global minimum geometry possesses σ-aromaticity and the central hydrogen atom forms unusual multicentre bond with more than three centres.

Alkali Metal Decorated Planar Tetracoordinate Hydrogen.

Despite the long list of planar tetracoordinate atoms, hydrogen is elusive. This is especially due to the inherent ability of hydrogen to form multicenter bonds with other centers. Herein, we introduce the first planar tetracoordinate hydrogen atom (ptH) in the global minimum geometry of a C2v symmetric Li4H4- cluster. Bonding analysis indicates that the central hydrogen atom is stabilized by multicenter bonding with four surrounding Li atoms. Natural charge analysis reveals that the central hydrogen is acting like a hydride, which is strongly attracted by the positively charged surrounding lithium centers. The ptH structure is stabilized by strong electrostatic attraction as well as extensive multicenter bonding. Aromaticity has no role to play here. The cluster is dynamically stable and is expected to be detected in the gas phase. Introduction of a heavier alkali metal such as sodium makes the planar C2v cluster a local minimum with slightly higher energy than the linear global minimum geometry.

Электронное влияние ароматического кольца в положении 2 на H/D обмен метильных протонов в пиримидине

The H/D exchange of hydrogen atoms of methyl groups in pyrimidines containing a phenyl or substituted pyrazole ring in position 2, namely, 2-phenyl-4-methyl-5-ethoxycarbonyl-, 2-phenyl-4-methyl-5-acetyl and 2-(3,5 dimethylpyrazolyl-1-)-4-methyl-5-acetylpyrimidines was studied. It has been shown that the rate of deuterium exchange depends on the electronic influence of the lateral aromatic ring associated with pyrimidine. When a phenyl group is introduced into position 2 of the pyrimidine ring almost immediately after adding deuterated sodium methoxide (CD3ONa) to the CD3OD solution, the signals from the protons of the ester or acetyl groups disappear.

Enhancing perovskite solar cell performance through dynamic hydrogen-mediated polarization of nitrogen and sulfur in phthalocyanine

Perovskite defect passivation has been researched extensively as an essential technique to improve the efficiency and stability of perovskite solar cells (PSCs) and thus drive their future commercialization. Three phthalocyanines named NP-SC6-ZnPc, NP-SC6-CuPc, and NP-SC6-H2Pc were synthesized and use for PSCs passivation. Theoretical calculations and experimental verifications confirmed that NP-SC6-H2Pc had the best passivation effect on perovskites. The phthalocyanine ring’s central hydrogen atoms are transferred dynamically from NP-SC6-H2Pc and interact with the formamidinium lead iodide (FAPbI3) perovskite through nitrogen-hydrogen bonding, resulting in α-FAPbI3 perovskite formation and increasing the sulfur/nitrogen (S/N) passivation capability. FAPbI3-based PSCs treated with NP-SC6-H2Pc demonstrated the highest power conversion efficiency (PCE) of 24.03 % (certified PCE of 23.78 %) with excellent stability. This significant finding represents the first observation of dynamic transfer of the hydrogen atoms in phthalocyanine and provides a thorough investigation of the perovskite passivation mechanism.

1-Methyl-5-nitro-imidazolium chloride.

The title salt, C4H6N3O2 +·Cl-, exhibits multiple hydrogen-bonding inter-actions involving the nitro-imidazolium cation and the chloride anion. Strong hydrogen bonds between the amine hydrogen atom and the chloride anion link the ionic moieties. Of note, with respect to H⋯Cl inter-actions, the central aromatic hydrogen atom displays a shorter inter-action than the other aromatic hydrogen atom. Finally, inter-actions are observed between the nitro moiety and methyl H atoms. While no π-π stacking is observed, anion-π inter-actions are present. The crystal was refined as a two-component twin.

Preparation of double decker {Li3(Cl−)(Hhp)}22− dianions and H2TPCor− monoanions by deprotonation of free-base trithiododecaazahexaphyrin (H3Hhp) and triphenylcorrole (H3TPCor) macrocycles

Deprotonation of free-base [30]trithia-2,3,5,10,12,13,15,20,22,23,25,30-dodecaazahexaphyrin (hemihexaphyrazine, H3Hhp) and 5, 10, 15- triphenylcorrole (H3TPCor) macrocycles by an excess of lithium diethylamide, LiNEt2, in the presence of three equivalents of cryptand[2.2.2] has been studied. Crystallization of the obtained products after the reaction allows the isolation of crystalline {Cryptand[2.2.2](Li)}2{Li3Cl(Hhp)}2·6C6H4Cl2 (1) and {Cryptand[2.2.2](Li)} {H2TPCor)·0.5C6H4Cl2 (2) salts. Compound 1 is the first example of lithium derivative of hemihexaphyrazine which additionally coordinates one Cl− anion per three lithium ions. There are five (Li+)⋯(Cl−) contacts of 2.389(4)-2.456(4) Å length for two independent {Li3Cl(Hhp)}− anions. However, one contact elongates to 2.557(4) Å due to shift of Cl− anions towards two hydrogen atoms of cryptand[2.2.2] providing the formation of weak hydrogen (Cl−)⋯H(cryptand) bonds. Two {Li3Cl(Hhp)}− anions are arranged in the double decker {Li3Cl(Hhp)}22− structure due to that the Cl− anion of one Li3Cl(Hhp) unit forms additional weak (Li+)⋯(Cl−) contacts of 2.586–2.617(4) Å with two lithium ions of the second {Li3Cl(Hhp)}− unit. In contrast to H3Hhp, H3TPCor splits only one hydrogen atom at deprotonation in the same experimental conditions forming a planar H2TPCor− anion and, therefore, H3Hhp has higher acidity of central hydrogen atoms in comparison with H3TPCor. Deprotonation preserves diamagnetic state of pristine macrocycles in salts 1 and 2. Their optical properties are also discussed. DFT calculations were carried out for 1 to discuss aromaticity of the macrocycles, electronic structure and optical spectrum of 1.

Nanoconfinement Raises the Energy Barrier to Hydrogen Atom Exchange between Water and Glucose.

In bulk aqueous environments, the exchange of protons between labile hydroxyl groups typically occurs easily and quickly. Nanoconfinement can dramatically change this normally facile process. Through exchange spectroscopy (EXSY) NMR measurements, we observe that nanoconfinement of glucose and water within AOT (sodium bis(2-ethylhexyl) sulfosuccinate) reverse micelles raises the energy barrier to labile hydrogen exchange, which suggests a disruption of the hydrogen bond network. Near room temperature, we measure barriers high enough to slow the process by as much as 2 orders of magnitude. Although exchange rates slow with decreasing temperatures in these nanoconfined environments, the barrier we measure below ∼285 K is 3-5 times lower than the barrier measured at room temperature, indicating a change in mechanism for the process. These findings suggest the possibility of hydrogen tunneling at a surprisingly high-temperature threshold. Furthermore, differences in exchange rates depend on the hydroxyl group position on the glucose pyranose ring and suggest a net orientation of glucose at the reverse micelle interface.

On-Surface Hydrogen/Deuterium Isotope Exchange in Polycyclic Aromatic Hydrocarbons.

Hydrogen plays important roles in the on-surface synthesis of carbon-based materials in ultra-high vacuum. The complex interplay between hydrogen and surface-adsorbed polycyclic aromatic hydrocarbons (PAHs) is tracked by in situ time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with isotope labeling. In situ deuterium labeling of prototypical PAHs, coronene (CR) and 7-armchair graphene nanoribbons (GNRs), on Au(111) is achieved by annealing either in D2 gas or in the vapor of perdeuterio-acenaphthene. By following the mass spectra of in situ deuterated CR mixed with hydrogen-CR, it is demonstrated that PAHs adsorbed at hot Au(111) surfaces continuously exchange hydrogen atoms. Also, D2 present during the Ullmann coupling step leads to incorporation of deuterium and to shorter GNRs.

On‐Surface Hydrogen/Deuterium Isotope Exchange in Polycyclic Aromatic Hydrocarbons

AbstractHydrogen plays important roles in the on‐surface synthesis of carbon‐based materials in ultra‐high vacuum. The complex interplay between hydrogen and surface‐adsorbed polycyclic aromatic hydrocarbons (PAHs) is tracked by in situ time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) combined with isotope labeling. In situ deuterium labeling of prototypical PAHs, coronene (CR) and 7‐armchair graphene nanoribbons (GNRs), on Au(111) is achieved by annealing either in D2 gas or in the vapor of perdeuterio‐acenaphthene. By following the mass spectra of in situ deuterated CR mixed with hydrogen‐CR, it is demonstrated that PAHs adsorbed at hot Au(111) surfaces continuously exchange hydrogen atoms. Also, D2 present during the Ullmann coupling step leads to incorporation of deuterium and to shorter GNRs.

Elucidating dynamic behavior of synthetic supramolecular polymers in water by hydrogen/deuterium exchange mass spectrometry.

A comprehensive understanding of the structure, self‐assembly mechanism, and dynamics of one‐dimensional supramolecular polymers in water is essential for their application as biomaterials. Although a plethora of techniques are available to study the first two properties, there is a paucity in possibilities to study dynamic exchange of monomers between supramolecular polymers in solution. We recently introduced hydrogen/deuterium exchange mass spectrometry (HDX‐MS) to characterize the dynamic nature of synthetic supramolecular polymers with only a minimal perturbation of the chemical structure. To further expand the application of this powerful technique some essential experimental aspects have been reaffirmed and the technique has been applied to a diverse library of assemblies. HDX‐MS is widely applicable if there are exchangeable hydrogen atoms protected from direct contact with the solvent and if the monomer concentration is sufficiently high to ensure the presence of supramolecular polymers during dilution. In addition, we demonstrate that the kinetic behavior as probed by HDX‐MS is influenced by the internal order within the supramolecular polymers and by the self‐assembly mechanism.

Substituent Effects on the N-H Bond Dissociation Enthalpies, Ionization Energies, Acidities, and Radical Scavenging Behavior of 3,7-Disubstituted Phenoxazines and 3,7-Disubstituted Phenothiazines.

The substituent effects on the N–H bond dissociation enthalpies (BDE), ionization energies (IE), acidities (proton affinity, PA), and radical scavenging behavior of 3,7-disubstituted phenoxazines (PhozNHs) and 3,7-disubstituted phenothiazines (PhtzNHs) were determined using density functional theory, with the M05-2X functional in conjunction with the 6-311++G(d,p) basis set. These thermochemical parameters calculated in both gas phase and benzene solution with respect to the changes in several different substituents including halogen, electron-withdrawing, and electron-donating groups at both 3 and 7 positions in both PhozNHs and PhtzNHs systems were analyzed in terms of the inherent relationships between them with some quantitative substituent effect parameters. The kinetic rate constants of hydrogen-atom exchange reactions between PhozNH and PhtzNH derivatives with the HOO• radical were also calculated, and the effects of the substituents on the kinetic behaviors of these reactions were thereby quantitatively evaluated.

IR Spectroscopy of the Cesium Iodide-Water Complex.

There has been much interest in I-(H2O) as a simple model for a hydrated iodide ion. Here we explore how this fundamental ion-solvent interaction is modified by the presence of a counterion, specifically Cs+. This has been achieved by forming the CsI(H2O) complex in superfluid helium nanodroplets and then probing this system using infrared spectroscopy. The complex retains the ionic hydrogen bond between the I- and a water OH group seen in I-(H2O), but the Cs+ ion substantially alters the anion-water interaction through formation of a cyclic Cs+-O-H-I- bonding motif. As with I-(H2O), the OH stretching band derived from the hydrogen-bonded OH group shows substructure, splitting into a clear doublet. However, in contrast to I-(H2O), where a tunneling splitting arising from hydrogen atom exchange plays a role, the doublet we observe is attributed solely to an anharmonic vibrational coupling effect.