The development of highly active catalyst in pH-neutral media for oxygen evolution reaction(OER)is critical in the field of renewable energy storage and conversion.Nevertheless,the slow kinetics of proton-coupled elec...The development of highly active catalyst in pH-neutral media for oxygen evolution reaction(OER)is critical in the field of renewable energy storage and conversion.Nevertheless,the slow kinetics of proton-coupled electron transfer(PCET)hinders the overall OER efficiency.Herein,we report an ionic liquid(IL)modified CoSn(OH)_(6)nanocubes(denoted as CoS-n(OH)_(6)-IL),which could be prepared through a facile strategy.The modified IL would not change the structural character-istics of CoSn(OH)_(6),but could effectively regulate the local proton activity near the active sites.The CoSn(OH)_(6)-IL exhibited higher intrinsic OER performances than the pristine CoSn(OH)_(6)in neutral media.For example,the current density of CoS-n(OH)_(6)-IL at 1.8 V versus reversible hydrogen electrode(RHE)was about 4 times higher than that of CoSn(OH)_(6).According to the pH-dependent kinetic investigations,operando electrochemical impedance spectroscopic,chemical probe tests,and deuterium kinetic isotope effects,the interfacial layer of IL could be utilized as a proton transfer mediator to promote the proton transfer,which enhances the surface coverage of OER intermediates and reduces the activation barrier.Consequent-ly,the sluggish OER kinetics would be efficiently accelerated.This study provides a facile and effective strategy to facilitate the PCET processes and is beneficial to guide the rational design of OER electrocatalysts.展开更多
Fisetin attracts intense attention not only due to its antioxidant and anticancer properties but also be-cause of wide applications in fluo-rescence probes and sensors,which are based on the dual fluorescence induced ...Fisetin attracts intense attention not only due to its antioxidant and anticancer properties but also be-cause of wide applications in fluo-rescence probes and sensors,which are based on the dual fluorescence induced by excited-state proton transfer(ESPT).However,to date,its ESPT dynamics remains unknown yet.In this study,we give a comprehensive investiga-tion on ESPT dynamics of fisetin in both protic methanol and aprot-ic acetonitrile by using femtosecond transient absorption spectroscopy combined with time-dependent density functional theory calculations.In acetonitrile,the ESPT time constant of fisetin is 1.2 ps.In methanol,two distinct intermolecular hydrogen bonding configurations contribute to a fast(<90 fs)and slow ESPT(11.1 ps),respectively.The slow ESPT in methanol explains the higher emission intensity of normal species than in acetonitrile.The ex-cited-state relaxation of fisetin involves two main vibrational modes:rotation between B and C rings and butterfly-like motion of C ring.Our results give insight into the effect of solvent-solute hydrogen bonding interaction on the dual fluorescence,providing a fundamental guide-line for the development of fluorescent probes and sensors based on ESPT.展开更多
The slow-proton-fast-electron process severely limits the catalytic efficiency of oxygen evolution reaction.A method is proposed to accelerate proton transfer by building up local electric fields.Modifying acetic,etha...The slow-proton-fast-electron process severely limits the catalytic efficiency of oxygen evolution reaction.A method is proposed to accelerate proton transfer by building up local electric fields.Modifying acetic,ethanedioic and propanetricarboxylic(C_(6)H_(8)O_(6))ligands on BiVO_(4)surface results in a potential difference between BiVO_(4)and ligands that generates a local electric field which serves as a driving force for proton transfer.Among the ligands,carrying the strongest electron-withdrawing ability,the modification of C_(6)H_(8)O_(6) forms the strongest local electric field and leads to the fastest proton transfer and the smallest thermodynamic overpotential.C_(6)H_(8)O_(6)-BiVO_(4)exhibits 3.5 times photocurrent density as high as that of pure BiVO_(4),which is 3.50 mA cm^(-2)at 1.23 VRHE.The onset potential of C_(6)H_(8)O_(6)-BiVO_(4)shifts negatively from 0.70 to 0.38 VRHE.The mechanism for OER transitions from thermodynamically high energy proton-coupled electron transfer to thermodynamically low energy electron transfer as proton transfer is accelerated.展开更多
The excited state intramolecular proton transfer （ESIPT） coupled charge transfer of baicalein has been investigated using steady-state spectroscopic experiment and quantum chemistry calculations. The absence of the ...The excited state intramolecular proton transfer （ESIPT） coupled charge transfer of baicalein has been investigated using steady-state spectroscopic experiment and quantum chemistry calculations. The absence of the absorption peak from S1 excited state both in the experi-mental and calculated absorption spectra indicates that S1 is a dark state. The dark excited state S1 results in the very weak fluorescence of solid baicalein in the experiment. The fron- tier molecular orbital and the charge difference densities of baicalein show clearly that the S1 state is a charge-transfer state whereas the S2 state is a locally excited state. The only one stationary point on the potential energy profile of excited state suggests that the ESIPT reaction of baicalein is a barrierless process.展开更多
A novel liquid hyperbranched polyether epoxy （HBPEE） based on commercially available hydroquinone （HQ） and 1,1,1-trihydroxymethylpropane triglycidyl ether （TMPGE） was synthesized through an A2 ＋ B3 one-step pro...A novel liquid hyperbranched polyether epoxy （HBPEE） based on commercially available hydroquinone （HQ） and 1,1,1-trihydroxymethylpropane triglycidyl ether （TMPGE） was synthesized through an A2 ＋ B3 one-step proton transfer polymerization. In order to improve the toughness, the synthesized HBPEE was mixed with diglycidyl ether of bisphenol A （DGEBA） in different ratios to form hybrids and cured with triethylenetetramine （TETA）. Thermal and mechanical properties of the cured hybrids were evaluated. Results show that addition of HBPEE can improve the toughness of cured hybrids remarkably at 〈 20 wt% loading, without compromising the tensile strength. However, the glass transition temperature （Tg） of the cured hybrids decreases with increasing HBPEE content. Fracture surface images from scanning electron microscope show oriented fibrils in hybrids containing HBPEE. The formation and orientation of the fibrils can absorb energy under impact and lead to an improvement of toughness. Furthermore, based on the morphology of fractured surfaces and the single Tg in each hybrid, no sign of phase separation was found in the cured hybrid systems. As a result, the toughening mechanism could be explained by in situ homogeneous toughening mechanism rather than phase separation mechanism.展开更多
The geometries of glycine-nH2O （n = 1-5） complexes and the transition states of proton transfer in glycine-H2O system were calculated at the MP2/6-31＋＋G＊＊//MP2/6-31G＊ level, upon which we discovered the proton ...The geometries of glycine-nH2O （n = 1-5） complexes and the transition states of proton transfer in glycine-H2O system were calculated at the MP2/6-31＋＋G＊＊//MP2/6-31G＊ level, upon which we discovered the proton transfer mechanisms, including the number of water molecules necessary for the stabilization of zwitterions and the effect of increasing water molecules on the proton transfer. To our interest, we found that only one water molecule can stabilize the zwitterions; in addition, with the increment of water molecules, the activation energy of positive reaction decreases and that of reverse reaction increases gradually. Glycine will be ionized completely while the water molecules reach to a certain number.展开更多
The conversion between anamorphoses of the dihydrated glycine complex was studied by means of B3LYP/6-31＋＋G^＊＊. It was found that proton transfer was accompanied by hydrogen bond transfer in the process of convers...The conversion between anamorphoses of the dihydrated glycine complex was studied by means of B3LYP/6-31＋＋G^＊＊. It was found that proton transfer was accompanied by hydrogen bond transfer in the process of conversion between different kinds of anamorphoses. With proton transfer, the electrostatic action was notably increased and the hydrogen-bonding action was evidently strengthened when the dihydrated neutral glycine complex converts into dihydrated zwitterionic glycine complex. The activation energy required for hydrogen bond transfer between dihydrated neutral glycine complexes is very low （6.32 kJ·mol^-1）; however, the hydrogen bond transfer between dihydrated zwitterionic glycine complexes is rather difficult with the required activation energy of 13.52 kJ·mol^-1 due to the relatively strong electrostatic action. The activation energy required by proton transfer is at least 27.33 kJ·mol^-1, higher than that needed for hydrogen bond transfer. The activation energy for either hydrogen bond transfer or proton transfer is in the bond-energy scope of medium-strong hydrogen bond, so the four kinds of anamorphoses of the dihydrated glycine complex could convert mutually.展开更多
In computational physics proton transfer phenomena could be viewed as pattern classification problems based on a set of input features allowing classification of the proton motion into two categories： transfer ＇occu...In computational physics proton transfer phenomena could be viewed as pattern classification problems based on a set of input features allowing classification of the proton motion into two categories： transfer ＇occurred＇ and transfer ＇not occurred＇. The goal of this paper is to evaluate the use of artificial neural networks in the classification of proton transfer events, based on the feed-forward back propagation neural network, used as a classifier to distinguish between the two transfer cases. In this paper, we use a new developed data mining and pattern recognition tool for automating, controlling, and drawing charts of the output data of an Empirical Valence Bond existing code. The study analyzes the need for pattern recognition in aqueous proton transfer processes and how the learning approach in error back propagation （multilayer perceptron algorithms） could be satisfactorily employed in the present case. We present a tool for pattern recognition and validate the code including a real physical case study. The results of applying the artificial neural networks methodology to crowd patterns based upon selected physical properties （e.g., temperature, density） show the abilities of the network to learn proton transfer patterns corresponding to properties of the aqueous environments, which is in turn proved to be fully compatible with previous proton transfer studies.展开更多
Epoxy-terminated hyperbranched polymers （EHBPs） were prepared by proton transfer polymerization and characterized by FT-IR, 1H-NMR and GPC. The solution and thermal properties of the uncured samples and mechanical p...Epoxy-terminated hyperbranched polymers （EHBPs） were prepared by proton transfer polymerization and characterized by FT-IR, 1H-NMR and GPC. The solution and thermal properties of the uncured samples and mechanical properties of cured samples were examined. The thermo-stable products had good solubility in polar solvents, low solution viscosity and Tgs ranging from 15℃ to 33℃ depending on their molecular weights. The mechanical properties of cured films were studied and compared with those of a bisphenol-A type epoxy resin. The films of EHBPs had good impact resistance and high gloss values without sacrificing hardness and adhesion.展开更多
Phosphazene base,t-BuP2,was employed to catalyze the proton transfer polymerization(PTP)of 2-hydroxyethyl acrylate(HEA),and PTP was further combined with ring-opening polymerization(ROP)to exploit a new type of hybrid...Phosphazene base,t-BuP2,was employed to catalyze the proton transfer polymerization(PTP)of 2-hydroxyethyl acrylate(HEA),and PTP was further combined with ring-opening polymerization(ROP)to exploit a new type of hybrid copolymerization.The studies on homopolymerization showed that t-BuP2 was a particularly efficient catalyst for the polymerization of HEA at room temperature,giving an excellent monomer conversion.Throughout the polymerization,transesterification reactions were unavoidable,which increased the randomness in the structures of the resulting polymers.The studies on copolymerization showed that t-BuP2 could simultaneously catalyze the hybrid copolymerization via the combination of PTP and ROP at 25°C.During copolymerization,HEA not only provided hydroxyl groups to initiate the ROP ofε-caprolactone(CL)but also participated in the polymerization as a monomer for PTP.The copolymer composition was approximately equal to the feed ratio,demonstrating the possibility to adjust the polymeric structure by simply changing the monomer feed ratio.This copolymerization reaction provides a simple method for synthesizing degradable functional copolymers from commercially available materials.Hence,it is important not only in polymer chemistry but also in environmental and biomedical engineering.展开更多
Semi-empirical molecular orbital theory AMI method is employed to study the ortho-position substituent impact on intramolecular proton transfer reaction of perylenequinone. The calculation demonstrates that the peryle...Semi-empirical molecular orbital theory AMI method is employed to study the ortho-position substituent impact on intramolecular proton transfer reaction of perylenequinone. The calculation demonstrates that the perylenequinone molecule is of stable structure. and all substituents may cause the decrease of barriers for the hydrogen transfer reaction.展开更多
Intramolecular proton transfer of hypomycin A in the ground state S0 and singlet excited state S1 were calculated by high level quantum chemical method in this letter. It was found that the IPT barriers for I→TS1 ar...Intramolecular proton transfer of hypomycin A in the ground state S0 and singlet excited state S1 were calculated by high level quantum chemical method in this letter. It was found that the IPT barriers for I→TS1 are 38.56 kJ/mol in S0 and 8.19 kJ/mol in S1, while those for I→TS4 get approximately 17 kJ/mol higher in S0 and 28 kJ/mol higher in S1. The calculation of IPT rate constants suggests that the experiment observed process of PQD is in S1. The height of the IPT barriers correlate not only with the variance of charge for labile hydrogen, the change of H-bonds length, the change of O-H bonds length and the change of O-O distance, but also with the reactant molecular H-bonds length. Moreover, the correlations are the same for S0 and S1.展开更多
The mp2/6-31＋＋g^＊＊//b3lyp/6-31＋＋g^＊＊ method has been employed to study the proton transfer mechanism in 4H2O-glycine complexes（4W-G）.Compared with bare glycine the four-water hydrated neutral glycine comple...The mp2/6-31＋＋g^＊＊//b3lyp/6-31＋＋g^＊＊ method has been employed to study the proton transfer mechanism in 4H2O-glycine complexes（4W-G）.Compared with bare glycine the four-water hydrated neutral glycine complexes（4W-GN） can turn into the corresponding zwitterionic glycine（4W-GZ） through proton transfer.The most stable conformation of 4W-GZ has a ＂double water-chain＂ structure and is more stable than its corresponding precursor 4W-GN by 0.97 KJ/mol though it is less stable than the most stable 4W-GN by 7.80 KJ/mol.It is a spontaneous reaction to form the most stable conformation of 4W-GZ,and the potential barrier is only 1.97 KJ/mol,so the probability of this reaction is very high and the most stable 4W-GZ may be detected in experiment or in the early stage of experiment.展开更多
The proton transfer isomerization of pyrazole and the water assisting effect by looping 1 to 4 water molecules on the singlet state potential energy surface have been investigated by using hybrid density functional th...The proton transfer isomerization of pyrazole and the water assisting effect by looping 1 to 4 water molecules on the singlet state potential energy surface have been investigated by using hybrid density functional theory method （B3PW91） with a 6-311＋＋G^＊＊ basis set. Two mechanisms were proposed to explain the mono- and multi-water assisting effects, respectively. The reactants and products of all groups have been characterized on their potential energy surfaces. For the isomerizafion of monomolecule pyrazole, the isomeriz＇ation energy barrier is 46.4 kcal·mol^-1. For the monohydration assisting mechanism, the reactant complex is connected to the product complex via two saddle points. The corresponding isomerization barriers are 46.7and 23.0 kcal·mol^-1, respectively. As to the multihydration assisting mechanism, the isomerization barriers are 12.0, 10.9 and 13.14 kcal·mol^-1 accordingly, when the number of water molecules is 2, 3 and 4, respectively. The multihydration assisting isomerization can occur in water-dominated environments, for example, in the organism, and thereby is crucial to energy transference. The deproton and dehydrogen energies of monomolecule pyrazole and various hydrated pyrazoles were calculated and then found much bigger than the isomerization barriers of their relative complexes, suggesting the impossibility of deprotonation or dehydrogenation. The isomerization of pyrazole is a proton-coupling-electron-migration process, but two different mechanisms are noticed, viz. σ- and π-type mechanisms. The π-bond of pyrazole participates in isomerization in the π-type mechanism, whereas only o-electron takes part in isomerization in the σ-type mechanism.展开更多
Electrocatalytic CO_(2) reduction has attracted growing attention as a promising route to realize artificial carbon recycling.Proton transfer plays an essential role in CO_(2) reduction and dramatically impacts produc...Electrocatalytic CO_(2) reduction has attracted growing attention as a promising route to realize artificial carbon recycling.Proton transfer plays an essential role in CO_(2) reduction and dramatically impacts product distribution.However,the precise control of proton transfer during CO_(2) reduction remains challenging.In this study,we present a well-controlled proton transfer through the modification of several purines with similar molecular structures,and reveal a direct correlation between surface proton transfer capability and CO_(2) reduction selectivity over Cu electrode.With a moderate proton transfer capability,the guanine modification can remarkably boost CH_(4) production and suppress C2 products formation.In-situ ATR-SEIRAS suggests a weakened^(*)CO intermediate adsorption and a relatively low local pH environment after the guanine modification,which facilitates the^(*)CO protonation and detachment for CH_(4) generation.展开更多
Herein we have employed high-level multi-reference CASSCF and MS-CASPT2 electronic structure methods to systematically study the photochemical mechanism of intramolecularly hydrogen-bonded 2-(2'-hydroxyphenyl)-4-m...Herein we have employed high-level multi-reference CASSCF and MS-CASPT2 electronic structure methods to systematically study the photochemical mechanism of intramolecularly hydrogen-bonded 2-(2'-hydroxyphenyl)-4-methyloxazole.At the CASSCF level,we have optimized minima,conical intersections,minimum-energy reaction paths relevant to the excited-state intramolecular proton transfer(ESIPT),rotation,photoisomerization,and the excited-state deactivation pathways.The energies of all structures and paths are refined by the MS-CASPT2 method.On the basis of the present results,we found that the ESIPT process in a conformer with the OH...N hydrogen bond is essentially barrierless process;whereas,the ESIPT process is inhibited in the other conformer with the OH...O hydrogen bond.The central single-bond rotation of the S1 enol species is energetically unfavorable due to a large barrier.In addition,the excited-state deactivation of the S1 keto species,as a result of the ultrafast ESIPT,is very efficient because of the existence of two easily-approached keto S1/S0 conical intersections.In stark contrast to the S1 keto species,the decay of the S1 enol species is almostly blocked.The present theoretical study contributes valuable knowledge to the understanding of photochemistry of similar intramolecularly hydrogen-bonded molecular and biological systems.展开更多
Intracellular pH is a key parameter related to various biological and pathological processes.In this study,a ratiometric pH fluorescent sensor ABTT was developed harnessing the amino-type excited-state intramolecular ...Intracellular pH is a key parameter related to various biological and pathological processes.In this study,a ratiometric pH fluorescent sensor ABTT was developed harnessing the amino-type excited-state intramolecular proton transfer(ESIPT) process.Relying on whether the ESIPT proceeds normally or not,ABTT exhibited the yellow fluorescence in acidic media,or cyan fluorescence in basic condition.According to the variation,ABTT behaved as a promising sensor which possessed fast and reversible response to pH change without interference from the biological substances,and exported a steady ratiometric signal(I_(478)/I_(546)).Moreover,due to the ESIPT effect,large Stokes shift and high quantum yield were also exhibited in ABTT.Furthermore,ABTT was applied for monitoring the pH changes in living cells and visualizing the pH fluctuations under oxidative stress successfully.These results elucidated great potential of ABTT in understanding pH-dependent physiological and pathological processes.展开更多
Excited-state intramolecular proton transfer(ESIPT)is favored by researchers because of its unique optical properties.However,there are relatively few systematic studies on the effects of changing the electronegativit...Excited-state intramolecular proton transfer(ESIPT)is favored by researchers because of its unique optical properties.However,there are relatively few systematic studies on the effects of changing the electronegativity of atoms on the ESIPT process and photophysical properties.Therefore,we selected a series of benzoxazole isothiocyanate fluorescent dyes(2-HOB,2-HSB,and 2-HSe B)by theoretical methods,and systematically studied the ESIPT process and photophysical properties by changing the electronegativity of chalcogen atoms.The calculated bond angle,bond length,energy gap,and infrared spectrum analysis show that the order of the strength of intramolecular hydrogen bonding of the three molecules is 2-HOB<2-HSB<2-HSe B.Correspondingly,the magnitude of the energy barrier of the potential energy curve is 2-HOB>2-HSB>2-HSe B.In addition,the calculated electronic spectrum shows that as the atomic electronegativity decreases,the emission spectrum has a redshift.Therefore,this work will offer certain theoretical guidance for the synthesis and application of new dyes based on ESIPT properties.展开更多
Proton transfer plays a key role in the applications of advanced energy materials as well as in the functionalities of biological systems.In this work,based on the transfer matrix method,we study the quantum effects o...Proton transfer plays a key role in the applications of advanced energy materials as well as in the functionalities of biological systems.In this work,based on the transfer matrix method,we study the quantum effects of proton transfer in a series of one-dimensional(1 D) model potentials and numerically calculate the quantum probability of transferring across single and double barriers(wells).In the case of single barriers,when the incident energies of protons are above the barrier height,the quantum oscillations in the transmission coefficients depend on the geometric shape of the barriers.It is found that atomic resonant tunneling(ART) not only presents in the rectangular single well and rectangular double barriers as expected,but also exists in the other types of potential wells and double barriers.For hetero-structured double barriers,there is no resonant tunneling in the classical forbidden zone,i.e.,in the case when the incident energy(E_(i)) is lower than the barrier height(E_(b)).Furthermore,we have provided generalized analysis on the characteristics of transmission coefficients of hetero-structured rectangular double barriers.展开更多
基金supported by the National Natural Science Foundation of China(22209040,22202063).
文摘The development of highly active catalyst in pH-neutral media for oxygen evolution reaction(OER)is critical in the field of renewable energy storage and conversion.Nevertheless,the slow kinetics of proton-coupled electron transfer(PCET)hinders the overall OER efficiency.Herein,we report an ionic liquid(IL)modified CoSn(OH)_(6)nanocubes(denoted as CoS-n(OH)_(6)-IL),which could be prepared through a facile strategy.The modified IL would not change the structural character-istics of CoSn(OH)_(6),but could effectively regulate the local proton activity near the active sites.The CoSn(OH)_(6)-IL exhibited higher intrinsic OER performances than the pristine CoSn(OH)_(6)in neutral media.For example,the current density of CoS-n(OH)_(6)-IL at 1.8 V versus reversible hydrogen electrode(RHE)was about 4 times higher than that of CoSn(OH)_(6).According to the pH-dependent kinetic investigations,operando electrochemical impedance spectroscopic,chemical probe tests,and deuterium kinetic isotope effects,the interfacial layer of IL could be utilized as a proton transfer mediator to promote the proton transfer,which enhances the surface coverage of OER intermediates and reduces the activation barrier.Consequent-ly,the sluggish OER kinetics would be efficiently accelerated.This study provides a facile and effective strategy to facilitate the PCET processes and is beneficial to guide the rational design of OER electrocatalysts.
基金supported by the National Natural Science Foundation of China(No.22003066)。
文摘Fisetin attracts intense attention not only due to its antioxidant and anticancer properties but also be-cause of wide applications in fluo-rescence probes and sensors,which are based on the dual fluorescence induced by excited-state proton transfer(ESPT).However,to date,its ESPT dynamics remains unknown yet.In this study,we give a comprehensive investiga-tion on ESPT dynamics of fisetin in both protic methanol and aprot-ic acetonitrile by using femtosecond transient absorption spectroscopy combined with time-dependent density functional theory calculations.In acetonitrile,the ESPT time constant of fisetin is 1.2 ps.In methanol,two distinct intermolecular hydrogen bonding configurations contribute to a fast(<90 fs)and slow ESPT(11.1 ps),respectively.The slow ESPT in methanol explains the higher emission intensity of normal species than in acetonitrile.The ex-cited-state relaxation of fisetin involves two main vibrational modes:rotation between B and C rings and butterfly-like motion of C ring.Our results give insight into the effect of solvent-solute hydrogen bonding interaction on the dual fluorescence,providing a fundamental guide-line for the development of fluorescent probes and sensors based on ESPT.
文摘The slow-proton-fast-electron process severely limits the catalytic efficiency of oxygen evolution reaction.A method is proposed to accelerate proton transfer by building up local electric fields.Modifying acetic,ethanedioic and propanetricarboxylic(C_(6)H_(8)O_(6))ligands on BiVO_(4)surface results in a potential difference between BiVO_(4)and ligands that generates a local electric field which serves as a driving force for proton transfer.Among the ligands,carrying the strongest electron-withdrawing ability,the modification of C_(6)H_(8)O_(6) forms the strongest local electric field and leads to the fastest proton transfer and the smallest thermodynamic overpotential.C_(6)H_(8)O_(6)-BiVO_(4)exhibits 3.5 times photocurrent density as high as that of pure BiVO_(4),which is 3.50 mA cm^(-2)at 1.23 VRHE.The onset potential of C_(6)H_(8)O_(6)-BiVO_(4)shifts negatively from 0.70 to 0.38 VRHE.The mechanism for OER transitions from thermodynamically high energy proton-coupled electron transfer to thermodynamically low energy electron transfer as proton transfer is accelerated.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.61137005 and No.10974023）, the Program for Liaoning Excellent Talents in University （No.LJQ2012002）, and the Program for New Century Excellent Talents in University （No.NCET-12-0077）.
文摘The excited state intramolecular proton transfer （ESIPT） coupled charge transfer of baicalein has been investigated using steady-state spectroscopic experiment and quantum chemistry calculations. The absence of the absorption peak from S1 excited state both in the experi-mental and calculated absorption spectra indicates that S1 is a dark state. The dark excited state S1 results in the very weak fluorescence of solid baicalein in the experiment. The fron- tier molecular orbital and the charge difference densities of baicalein show clearly that the S1 state is a charge-transfer state whereas the S2 state is a locally excited state. The only one stationary point on the potential energy profile of excited state suggests that the ESIPT reaction of baicalein is a barrierless process.
基金supported by the Natural Science Foundation of Beijing(No.2092023)National Natural Science Foundation of China(No.51173012)the Fundamental Research Funds for the Central Universities(No.ZZ0912)
文摘A novel liquid hyperbranched polyether epoxy （HBPEE） based on commercially available hydroquinone （HQ） and 1,1,1-trihydroxymethylpropane triglycidyl ether （TMPGE） was synthesized through an A2 ＋ B3 one-step proton transfer polymerization. In order to improve the toughness, the synthesized HBPEE was mixed with diglycidyl ether of bisphenol A （DGEBA） in different ratios to form hybrids and cured with triethylenetetramine （TETA）. Thermal and mechanical properties of the cured hybrids were evaluated. Results show that addition of HBPEE can improve the toughness of cured hybrids remarkably at 〈 20 wt% loading, without compromising the tensile strength. However, the glass transition temperature （Tg） of the cured hybrids decreases with increasing HBPEE content. Fracture surface images from scanning electron microscope show oriented fibrils in hybrids containing HBPEE. The formation and orientation of the fibrils can absorb energy under impact and lead to an improvement of toughness. Furthermore, based on the morphology of fractured surfaces and the single Tg in each hybrid, no sign of phase separation was found in the cured hybrid systems. As a result, the toughening mechanism could be explained by in situ homogeneous toughening mechanism rather than phase separation mechanism.
基金supported by the Fund of Education Committee of Hebei Province (No. Z2007205)Application Theoretical Foundation of Tangshan (No. 06234501A-10)+1 种基金Research Foundation of Tangshan Normal College (No. 06D08)the Scientific Research Fund of Hunan Provincial Education Department (B30865)
文摘The geometries of glycine-nH2O （n = 1-5） complexes and the transition states of proton transfer in glycine-H2O system were calculated at the MP2/6-31＋＋G＊＊//MP2/6-31G＊ level, upon which we discovered the proton transfer mechanisms, including the number of water molecules necessary for the stabilization of zwitterions and the effect of increasing water molecules on the proton transfer. To our interest, we found that only one water molecule can stabilize the zwitterions; in addition, with the increment of water molecules, the activation energy of positive reaction decreases and that of reverse reaction increases gradually. Glycine will be ionized completely while the water molecules reach to a certain number.
基金The project was supported by Tangshan Fundamental Research Fund (0612345A-10)
文摘The conversion between anamorphoses of the dihydrated glycine complex was studied by means of B3LYP/6-31＋＋G^＊＊. It was found that proton transfer was accompanied by hydrogen bond transfer in the process of conversion between different kinds of anamorphoses. With proton transfer, the electrostatic action was notably increased and the hydrogen-bonding action was evidently strengthened when the dihydrated neutral glycine complex converts into dihydrated zwitterionic glycine complex. The activation energy required for hydrogen bond transfer between dihydrated neutral glycine complexes is very low （6.32 kJ·mol^-1）; however, the hydrogen bond transfer between dihydrated zwitterionic glycine complexes is rather difficult with the required activation energy of 13.52 kJ·mol^-1 due to the relatively strong electrostatic action. The activation energy required by proton transfer is at least 27.33 kJ·mol^-1, higher than that needed for hydrogen bond transfer. The activation energy for either hydrogen bond transfer or proton transfer is in the bond-energy scope of medium-strong hydrogen bond, so the four kinds of anamorphoses of the dihydrated glycine complex could convert mutually.
基金Dr. Steve Jones, Scientific Advisor of the Canon Foundation for Scientific Research (7200 The Quorum, Oxford Business Park, Oxford OX4 2JZ, England). Canon Foundation for Scientific Research funded the UPC 2013 tuition fees of the corresponding author during her writing this article
文摘In computational physics proton transfer phenomena could be viewed as pattern classification problems based on a set of input features allowing classification of the proton motion into two categories： transfer ＇occurred＇ and transfer ＇not occurred＇. The goal of this paper is to evaluate the use of artificial neural networks in the classification of proton transfer events, based on the feed-forward back propagation neural network, used as a classifier to distinguish between the two transfer cases. In this paper, we use a new developed data mining and pattern recognition tool for automating, controlling, and drawing charts of the output data of an Empirical Valence Bond existing code. The study analyzes the need for pattern recognition in aqueous proton transfer processes and how the learning approach in error back propagation （multilayer perceptron algorithms） could be satisfactorily employed in the present case. We present a tool for pattern recognition and validate the code including a real physical case study. The results of applying the artificial neural networks methodology to crowd patterns based upon selected physical properties （e.g., temperature, density） show the abilities of the network to learn proton transfer patterns corresponding to properties of the aqueous environments, which is in turn proved to be fully compatible with previous proton transfer studies.
基金supported by the Natural Science Foundation of Beijing(No.2092023)the Program of Introducing Talents Discipline to Universities(No.B08003)
文摘Epoxy-terminated hyperbranched polymers （EHBPs） were prepared by proton transfer polymerization and characterized by FT-IR, 1H-NMR and GPC. The solution and thermal properties of the uncured samples and mechanical properties of cured samples were examined. The thermo-stable products had good solubility in polar solvents, low solution viscosity and Tgs ranging from 15℃ to 33℃ depending on their molecular weights. The mechanical properties of cured films were studied and compared with those of a bisphenol-A type epoxy resin. The films of EHBPs had good impact resistance and high gloss values without sacrificing hardness and adhesion.
基金financially supported by the Natural Science Foundation for Excellent Young Scholar of Jiangsu Province (No. BK20170056)the National Natural Science Foundation of China(No. 21304010)+1 种基金the Opening Project of Key Laboratory of Polymer Processing Engineering (South China University of Technology)Ministry of Education, and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘Phosphazene base,t-BuP2,was employed to catalyze the proton transfer polymerization(PTP)of 2-hydroxyethyl acrylate(HEA),and PTP was further combined with ring-opening polymerization(ROP)to exploit a new type of hybrid copolymerization.The studies on homopolymerization showed that t-BuP2 was a particularly efficient catalyst for the polymerization of HEA at room temperature,giving an excellent monomer conversion.Throughout the polymerization,transesterification reactions were unavoidable,which increased the randomness in the structures of the resulting polymers.The studies on copolymerization showed that t-BuP2 could simultaneously catalyze the hybrid copolymerization via the combination of PTP and ROP at 25°C.During copolymerization,HEA not only provided hydroxyl groups to initiate the ROP ofε-caprolactone(CL)but also participated in the polymerization as a monomer for PTP.The copolymer composition was approximately equal to the feed ratio,demonstrating the possibility to adjust the polymeric structure by simply changing the monomer feed ratio.This copolymerization reaction provides a simple method for synthesizing degradable functional copolymers from commercially available materials.Hence,it is important not only in polymer chemistry but also in environmental and biomedical engineering.
文摘Semi-empirical molecular orbital theory AMI method is employed to study the ortho-position substituent impact on intramolecular proton transfer reaction of perylenequinone. The calculation demonstrates that the perylenequinone molecule is of stable structure. and all substituents may cause the decrease of barriers for the hydrogen transfer reaction.
文摘Intramolecular proton transfer of hypomycin A in the ground state S0 and singlet excited state S1 were calculated by high level quantum chemical method in this letter. It was found that the IPT barriers for I→TS1 are 38.56 kJ/mol in S0 and 8.19 kJ/mol in S1, while those for I→TS4 get approximately 17 kJ/mol higher in S0 and 28 kJ/mol higher in S1. The calculation of IPT rate constants suggests that the experiment observed process of PQD is in S1. The height of the IPT barriers correlate not only with the variance of charge for labile hydrogen, the change of H-bonds length, the change of O-H bonds length and the change of O-O distance, but also with the reactant molecular H-bonds length. Moreover, the correlations are the same for S0 and S1.
基金Project supported by the Fund of Education Committee of Hebei Province (No. Z2007205)the Application & Theoretical Foundation of Tangshan (No. 06234501A-10)
文摘The mp2/6-31＋＋g^＊＊//b3lyp/6-31＋＋g^＊＊ method has been employed to study the proton transfer mechanism in 4H2O-glycine complexes（4W-G）.Compared with bare glycine the four-water hydrated neutral glycine complexes（4W-GN） can turn into the corresponding zwitterionic glycine（4W-GZ） through proton transfer.The most stable conformation of 4W-GZ has a ＂double water-chain＂ structure and is more stable than its corresponding precursor 4W-GN by 0.97 KJ/mol though it is less stable than the most stable 4W-GN by 7.80 KJ/mol.It is a spontaneous reaction to form the most stable conformation of 4W-GZ,and the potential barrier is only 1.97 KJ/mol,so the probability of this reaction is very high and the most stable 4W-GZ may be detected in experiment or in the early stage of experiment.
基金supported by the National Natural Science Foundation of China (20633060)
文摘The proton transfer isomerization of pyrazole and the water assisting effect by looping 1 to 4 water molecules on the singlet state potential energy surface have been investigated by using hybrid density functional theory method （B3PW91） with a 6-311＋＋G^＊＊ basis set. Two mechanisms were proposed to explain the mono- and multi-water assisting effects, respectively. The reactants and products of all groups have been characterized on their potential energy surfaces. For the isomerizafion of monomolecule pyrazole, the isomeriz＇ation energy barrier is 46.4 kcal·mol^-1. For the monohydration assisting mechanism, the reactant complex is connected to the product complex via two saddle points. The corresponding isomerization barriers are 46.7and 23.0 kcal·mol^-1, respectively. As to the multihydration assisting mechanism, the isomerization barriers are 12.0, 10.9 and 13.14 kcal·mol^-1 accordingly, when the number of water molecules is 2, 3 and 4, respectively. The multihydration assisting isomerization can occur in water-dominated environments, for example, in the organism, and thereby is crucial to energy transference. The deproton and dehydrogen energies of monomolecule pyrazole and various hydrated pyrazoles were calculated and then found much bigger than the isomerization barriers of their relative complexes, suggesting the impossibility of deprotonation or dehydrogenation. The isomerization of pyrazole is a proton-coupling-electron-migration process, but two different mechanisms are noticed, viz. σ- and π-type mechanisms. The π-bond of pyrazole participates in isomerization in the π-type mechanism, whereas only o-electron takes part in isomerization in the σ-type mechanism.
文摘Electrocatalytic CO_(2) reduction has attracted growing attention as a promising route to realize artificial carbon recycling.Proton transfer plays an essential role in CO_(2) reduction and dramatically impacts product distribution.However,the precise control of proton transfer during CO_(2) reduction remains challenging.In this study,we present a well-controlled proton transfer through the modification of several purines with similar molecular structures,and reveal a direct correlation between surface proton transfer capability and CO_(2) reduction selectivity over Cu electrode.With a moderate proton transfer capability,the guanine modification can remarkably boost CH_(4) production and suppress C2 products formation.In-situ ATR-SEIRAS suggests a weakened^(*)CO intermediate adsorption and a relatively low local pH environment after the guanine modification,which facilitates the^(*)CO protonation and detachment for CH_(4) generation.
基金supported by the National Natural Science Foundation of China(No.21522302,No.21520102005,and No.21421003)financial support from the Recruitment Program of Global Youth Experts Youth Scholars Program of Beijing Normal UniversityFundamental Research Funds for Central Universities
文摘Herein we have employed high-level multi-reference CASSCF and MS-CASPT2 electronic structure methods to systematically study the photochemical mechanism of intramolecularly hydrogen-bonded 2-(2'-hydroxyphenyl)-4-methyloxazole.At the CASSCF level,we have optimized minima,conical intersections,minimum-energy reaction paths relevant to the excited-state intramolecular proton transfer(ESIPT),rotation,photoisomerization,and the excited-state deactivation pathways.The energies of all structures and paths are refined by the MS-CASPT2 method.On the basis of the present results,we found that the ESIPT process in a conformer with the OH...N hydrogen bond is essentially barrierless process;whereas,the ESIPT process is inhibited in the other conformer with the OH...O hydrogen bond.The central single-bond rotation of the S1 enol species is energetically unfavorable due to a large barrier.In addition,the excited-state deactivation of the S1 keto species,as a result of the ultrafast ESIPT,is very efficient because of the existence of two easily-approached keto S1/S0 conical intersections.In stark contrast to the S1 keto species,the decay of the S1 enol species is almostly blocked.The present theoretical study contributes valuable knowledge to the understanding of photochemistry of similar intramolecularly hydrogen-bonded molecular and biological systems.
基金the financial supports from National Natural Science Foundation of China (Nos.81971678 and 81671756)the Innovation Fund for Postgraduate Students of Central South University (No.2019zzts1019)。
文摘Intracellular pH is a key parameter related to various biological and pathological processes.In this study,a ratiometric pH fluorescent sensor ABTT was developed harnessing the amino-type excited-state intramolecular proton transfer(ESIPT) process.Relying on whether the ESIPT proceeds normally or not,ABTT exhibited the yellow fluorescence in acidic media,or cyan fluorescence in basic condition.According to the variation,ABTT behaved as a promising sensor which possessed fast and reversible response to pH change without interference from the biological substances,and exported a steady ratiometric signal(I_(478)/I_(546)).Moreover,due to the ESIPT effect,large Stokes shift and high quantum yield were also exhibited in ABTT.Furthermore,ABTT was applied for monitoring the pH changes in living cells and visualizing the pH fluctuations under oxidative stress successfully.These results elucidated great potential of ABTT in understanding pH-dependent physiological and pathological processes.
基金supported by the National Natural Science Foundation of China(No.21773238)the Fundamental Research Funds of Shandong University(2019GN025)。
文摘Excited-state intramolecular proton transfer(ESIPT)is favored by researchers because of its unique optical properties.However,there are relatively few systematic studies on the effects of changing the electronegativity of atoms on the ESIPT process and photophysical properties.Therefore,we selected a series of benzoxazole isothiocyanate fluorescent dyes(2-HOB,2-HSB,and 2-HSe B)by theoretical methods,and systematically studied the ESIPT process and photophysical properties by changing the electronegativity of chalcogen atoms.The calculated bond angle,bond length,energy gap,and infrared spectrum analysis show that the order of the strength of intramolecular hydrogen bonding of the three molecules is 2-HOB<2-HSB<2-HSe B.Correspondingly,the magnitude of the energy barrier of the potential energy curve is 2-HOB>2-HSB>2-HSe B.In addition,the calculated electronic spectrum shows that as the atomic electronegativity decreases,the emission spectrum has a redshift.Therefore,this work will offer certain theoretical guidance for the synthesis and application of new dyes based on ESIPT properties.
基金Project supported by the National Natural Science Foundation of China(Grant No.11474285)。
文摘Proton transfer plays a key role in the applications of advanced energy materials as well as in the functionalities of biological systems.In this work,based on the transfer matrix method,we study the quantum effects of proton transfer in a series of one-dimensional(1 D) model potentials and numerically calculate the quantum probability of transferring across single and double barriers(wells).In the case of single barriers,when the incident energies of protons are above the barrier height,the quantum oscillations in the transmission coefficients depend on the geometric shape of the barriers.It is found that atomic resonant tunneling(ART) not only presents in the rectangular single well and rectangular double barriers as expected,but also exists in the other types of potential wells and double barriers.For hetero-structured double barriers,there is no resonant tunneling in the classical forbidden zone,i.e.,in the case when the incident energy(E_(i)) is lower than the barrier height(E_(b)).Furthermore,we have provided generalized analysis on the characteristics of transmission coefficients of hetero-structured rectangular double barriers.
