Carbonic acid is an important species in a variety of fields and has long been regarded to be non-existing in isolated state, as it is thermodynamically favorable to decompose into water and carbon dioxide. In this work, we systematically studied a novel ionic complex [H2CO3·HSO4]− using density functional theory calculations, molecular dynamics simulations, and topological analysis to investigate if the exotic H2CO3 molecule could be stabilized by bisulfate ion, which is a ubiquitous ion in various environments. We found that bisulfate ion could efficiently stabilize all the three conformers of H2CO3 and reduce the energy differences of isomers with H2CO3 in three different conformations compared to the isolated H2CO3 molecule. Calculated isomerization pathways and ab initio molecular dynamics simulations suggest that all the optimized isomers of the complex have good thermal stability and could exist at finite temperatures. We also explored the hydrogen bonding properties in this interesting complex and simulated their harmonic infrared spectra to aid future infrared spectroscopic experiments. This work could be potentially important to understand the fate of carbonic acid in certain complex environments, such as in environments where both sulfuric acid (or rather bisulfate ion) and carbonic acid (or rather carbonic dioxide and water) exist. 相似文献
The possibility to synthesize stereoregular tris-cis-tris-trans- dodeca[(phenyl)(hydroxy)]cyclododecasiloxane (tris-cis-tris-trans-[PhSi(O)OH]12) in an inorganic liquid medium – aqueous carbonic acid solution – was shown. The interaction of polyhedral phenylcoppersodiumsiloxane, {[(C6H5Si(O)O?]12(Cu2+)4(Na+)4}*(L)m (L?=?BunOH, H2O), with carbonic acid can be considered as a new ‘green’ method to obtain functional organosiloxane macrocycles. In contrast to the known methods, no organic solvents were used during the reaction. The identification of the structure of the end compound was performed by means of NMR and Infrared spectroscopy as well as X-ray crystallography. 相似文献
Using pressure-jump, concentration-jump, and stopped-flow methods, we have studied the rate of dehydration (k–1) of carbonic acid as a function of temperature (0–40°C) and ionic strength (0.005–3M NaCl, 3M LiBr) in both H2O and D2O. A new design of pressure-jump cell with reliable temperature control, as well as improved sensitivity in the spectrophotometric detection for stopped flow, enabled k–1 values to be determined with an accuracy better than ±8%, based on a comparison of results obtained using five different techniques. The influence of ionic strength, temperature, and isotope effects are discussed. 相似文献
The kinetics of the formation of hydrogen peroxide by the sonolysis of light and heavy water in argon and oxygen atmospheres
was investigated. The sonochemical reaction has a zero order with respect to hydrogen peroxide (H2O2, D2O2, or DHO2). The measurement of the kinetic isotope effect (α), defined as the ratio of the reaction rates in H2O and D2O, carried out under argon gave a value of 2.2±0.3. The observed isotope effect decreases with an increase in the concentration
of light water in H2O−D2O mixtures. No isotope effect is displayed in the oxygen atmosphere (α=1.05±0.10). The isotope effect is determined presumably
by the mechanism of sonochemical decomposition of water molecules, which includes the H2O−Ar* and D2O−Ar* energy exchange (where Ar* are argon atoms in the3P2.0 excited state) in the nonequilibrium plasma generated by a shock wave, arising upon a cavitation collapse.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 645–649, April, 2000. 相似文献
An anti trihydroxycarbenium ion is revealed to be the gas‐phase structure of protonated carbonic acid by IR multiple‐photon dissociation spectroscopy (see picture for calculated structure and comparison of experimental and computed spectra). Deprotonation yields anti‐H2CO3 with a nominal gas‐phase basicity of 724 kJ mol?1.
Stabilization by salt formation : carbonic acid, which is not available as a pure substance, was isolated in the form of its trihydroxycarbenium salts, C(OH)3+ MF6− (M=As, Sb), from the reaction of carbonic acid bis(trimethylsilyl) ester in the superacids HF/MF5. The structure of the cation is shown in the picture. The ion was also characterized by vibrational spectroscopic studies. 相似文献
Carbonic anhydrase II (CA II) is an important enzyme complex with Zn2+, which is involved in many physiological and pathological processes, such as calcification, glaucoma and tumorigenicity.
In order to search for novel inhibitors of CA II, inhibition assay of carbonic anhydrase II was performed, by which seven
natural phenolic compounds, including four phenolics (grifolin, 4-O-methyl-grifolic acid, grifolic acid, and isovanillic acid) and three flavones (eriodictyol, quercetin and puerin A), showed
inhibitory activities against CA II with IC50s in the range of 6.37–71.73 μmol/L. Grifolic acid is the most active one with IC50 of 6.37 μmol/L. These seven phenolic compounds were proved to be novel natural carbonic anhydrase II inhibitors, which were obtained
in flexible docking study with GOLD 3.0 software. Results indicated that the aliphatic chain and polar groups of hydroxyl
and carboxyl are important to their inhibitory activities, providing a new insight into study on CA II potent inhibitors.
Authors with the equal contribution
Supported by the National Natural Science Foundation of China (Grant No. 30725048) and the Foundation of Chinese Academy of
Sciences (West Light Program). 相似文献
Protein design will ultimately allow for the creation of artificial enzymes with novel functions and unprecedented stability. To test our current mastery of nature’s approach to catalysis, a ZnII metalloenzyme was prepared using de novo design. α3DH3 folds into a stable single‐stranded three‐helix bundle and binds ZnII with high affinity using His3O coordination. The resulting metalloenzyme catalyzes the hydration of CO2 better than any small molecule model of carbonic anhydrase and with an efficiency within 1400‐fold of the fastest carbonic anhydrase isoform, CAII, and 11‐fold of CAIII. 相似文献
We present pseudo-potential calculations of geometrical structures of stable isomers of LiArn clusters with both an electronic ground state and excited states of the lithium atom. The Li atom is perturbed by argon atoms
in LiArn clusters. Its electronic structure obtained as the eigenfunctions of a single-electron operator describing the electron in
the field of a Li+Arn core, the Li+ and Ar atoms are replaced by pseudo-potentials. These pseudo-potentials include core-polarization operators to account for
the polarization and correlation of the inert core with the valence Lithium electron [J Chem Phys 116, 1839 1]. The geometry optimization of the ground and excited states of LiArn (n = 1–12) clusters is carried out via the Basin-Hopping method of Wales et al. [J Phys Chem 101, 5111 2; J Chem Phys 285, 1368 3]. The geometries of the ground and ionic states of LiArn clusters were used to determine the energy of the high excited states of the neutral LiArn clusters. The variation of the excited state energies of LiArn clusters as a function of the number of argon atoms shows an approximate Rydberg character, corresponding to the picture
of an excited electron surrounding an ionic cluster core, is already reached for the 3s state. The result of optical transitions calculations shows that the absorption spectral features are sensitive to isomer
structure. It is clearly the case for transitions close to the 2p levels of Li which are distorted by the cluster environment. 相似文献
The isotope exchange reactions of malonic acid and a malonate ion were investigated in acidic and basic D2O solutions, respectively, using 1H NMR spectroscopy. The isotope exchange reaction of malonic acid is inhibited by the presence of DNO3 (0–3 M) and DSO4? ion (0–0.1 M), whereas it is catalyzed by the presence of DSO4? ion (> 0.2 M), D3PO4, D2PO4? ion or DPO42– ion. The order of relative reactivity for catalyzing the isotope reaction of malonic acid in D2O is DPO42– > D2PO4? > D3PO4 > DSO4? > DNO3. The rate of the isotope exchange reaction of malonate ion in D2O decreases to a minimum and then increases with increased [NaOD]0. The mechanism of the isotope exchange reaction of malonic acid in acidic D2O is different from the general acid-catalyzed mechanism generally observed for organic acids like acetic and dichloroacetic acids. The bimalonate ion plays an important role in the isotope exchange reactions of this system. 相似文献
The design of molecular catalysts that mimic the behavior of enzymes is a topical field of activity in emerging technologies, and can lead to an improved understanding of biological systems. Herein, we report how the bulky arms of the cations in [(n C4H9)4N]+[HCO3]‐ give rise to a host scaffold that emulates the substrate binding sites in carbonic anhydrase enzymes, affording a unique glimpse of an arrested intermediate in the base‐mediated binding and activation of CO2. 相似文献
Two ionic carbon nitride type compounds containing the ammelinium cation, ammelinium sulfate cyanuric acid (6C3N5H6O+ · 3SO42– · 1?C3N3H3O3 · H2O) ( 1 ) and ammelinium sulfate monohydrate (2C3N5H6O+ · SO42– · H2O) ( 2 ) were synthesized through hydrolysis of melam (C6N11H9) in diluted sulfuric acid. 1 crystallizes in hexagonal space group P63 (no. 173) with lattice parameters of a = 14.642(3), c = 13.113(4), and Z = 2. The structure is comprised of protonated ammelinium ions and neutral cyanuric acid molecules, which form a layered structure, as well as sulfate ions that span through these layers. 2 crystallizes in the triclinic space group P1 with lattice parameters of a = 7.404(3), b = 9.673(4), c = 10.040(4), α = 91.098(15), β = 109.884(10), γ = 92.567(13), and Z = 2. As for 1 , the ammelinium rings form layers with the sulfate ions located in between. In both structures, no extended hydrogen bond networks between the respective triazine‐based molecules are formed. Instead, single molecules or small building blocks occur isolated and interact primarily with sulfate anions. Compound 1 , which was obtained phase pure, was further investigated by FTIR spectroscopy, solid‐state NMR spectroscopy and powder X‐ray diffractometry. 相似文献
An original method was developed for the synthesis of functional derivatives of triallylmethane (CH2=CH-CH2)3C-X (X = OH, NH2, or SCOPh) based on reactions of triallylborane with the corresponding derivatives of carbonic acid (ethylene carbonate, diethylcyanamide, and 0,S-dimethyidithio carbonate) at 110–120 °C.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp 2739–2742, November, 1996. 相似文献
Abstract We propose the use of acetoxymethyl esters of pH-sensitive amphipathic photosensitizers (PS) for photodynamic therapy (PDT). These compounds may be applicable for PDT involving endocytosis of lipophilic carriers leading to lysosomal uptakc of the esterified PS by target cells. Partial and/or total enzymatic de-esterification may result in the extralysosomal distribution of the photoactive agents, possibly culminating in a multisite photochemical response. We report here the synthesis and properties of chlorin e6 triacetoxymethyl ester (CAME) and pheophorbide a acetoxymethyl ester (PAME). Chlorin e6 and pheophorbide a are photocytotoxic chlorins that possess free carboxylate groups and exhibit optimum wavelengths of excitation substantially red shifted relative to hematoporphyrin derivative. Acetoxymethyl esterification of chlorin e6 and pheophorbide a was accomplished with bromomethyl acetate. High-performance liquid chromatography allowed for the purification of PAME, in 87% purity, and CAME, in 63% yield and 94% purity, as well as the detection of the presumed mono- and diesters of chlorin e6 as transient intermediates in the synthesis of CAME. The ultraviolet-visible absorption, fluorescence excitation and emission, NMR and mass spectra of the chlorin e6 tnester are consistent with those expected for CAME. The pH-sensitive amphipathicity of pheophorbide a and chlorin e6 but not CAME was demonstrated using a water/1-octanol partition assay. The production of pheophorbide a from PAME and the sequential formation of the di- and monoesters and free chlorin e6 from CAME, by the action of lysosomal esterases obtained from cancer cells, demonstrate the potential of cellular enzymes to convert the lipophilic esters to pH-sensitive amphipathic PS. It is expected that the product of the esterases' action in the acidic lysosome will be hydrophobic and tend to diffuse into the organelle membrane. Contact with the neutral pH of the adjacent cytosol will result in conversion of the PS to a more hydrophilic anionic species, presumably allowing for it lo diffuse into that compartment and partition throughout the lipophilic and aqueous compartments of the cell. 相似文献
Summary. Three new complexes, namely [(nicotinic acid)2H]+I–, [(2-amino-6-methylpyridine)H]+ (NO3)–, and the 1:1 complex between 1-isoquinoline carboxylic acid (zwitter ion form) and L-ascorbic acid were synthesized. The IR spectra revealed different types of hydrogen bonds in these compounds. The X-ray structure determination has shown the first compound to consist of a packing of [(nicotinic acid)2H]+ cations and I– anions. In the dimeric cation the two nicotinic acid molecules (zwitter ions) are connected through hydrogen bonds (O–HO). Each dimer is further engaged in other hydrogen bonds with adjacent dimers giving 2D layers. The I– ion is located at the inversion center. In the second compound the cation and anion are connected via hydrogen bonds formed between oxygen atoms of the NO3– anion and NH and NH2 of the cation generating a layer structure. All atoms are coplanar on mirror planes. In the 1:1 complex the two molecules are connected through hydrogen bonds formed between the two oxygen atoms of the carboxylate group of 1-isoquinoline carboxylic acid (zwitter ion) and the oxygen atoms of the two adjacent hydrogen groups of the L-ascorbic acid molecule. These complex molecules are engaged in other hydrogen bonds with each other forming a 2D system normal to the long b-axis of the unit cell. 相似文献
Metaphosphorous acid (HOPO), a key intermediate in phosphorus chemistry, has been generated in syn- and anti-conformations in the gas phase by high-vacuum flash pyrolysis (HVFP) of a molecular precursor ethoxyphosphinidene oxide (EtOPO→C2H4+HOPO) at ca. 1000 K and subsequently trapped in an N2-matrix at 2.8 K. Unlike the two conformers of the nitrogen analogue HONO, the anti-conformer of HOPO undergoes spontaneous rotamerization at 2.8 K via hydrogen-atom tunneling (HAT) with noticeable kinetic isotope effects for H/D (>104 for DOPO) and 16O/18O (1.19 for H18OPO and 1.06 for HOP18O) in N2-matrices. 相似文献
The radiation kinetics of the plasma of barrier-torch disrcharge in argon flow in a capillary has been studied by cross-correlation
spectroscopy. It was established that the discharge emission spectrum consists of peaks of electronically excited states of
argon, bands of hydroxyl radicals, and a second positive system of nitrogen. An analysis of the spatio-temporal distributions
of emission intensity for the selected spectral indicators showed that the causes of the torch are ionization waves that extend
through the capillary from the electrode system with a speed of 105 m/s and project up to 3–4 mm. It was established that the formation of electronically excited molecules of nitrogen N2(C3Πu) in the torch of discharge occurs mainly on the reaction between metastable electronically excited atoms of argon and molecules
of nitrogen in the electronic ground state. 相似文献