Using molecular dynamics modeling,the change in the shape and density of the macromolecular corona consisting of two oppositely charged polyelectrolytes,including those combined into one block copolymer,on the surface...Using molecular dynamics modeling,the change in the shape and density of the macromolecular corona consisting of two oppositely charged polyelectrolytes,including those combined into one block copolymer,on the surface of a polarized spherical metal nanoparticle was studied.A mathematical model of the structure of the block copolymer chain adsorbed on a polarized spherical nanoparticle is presented for the cases of polyelectrolyte blocks of large and small length.Based on the modeling results,radial and angular distributions of the density of atoms of polyelectrolyte polypeptides adsorbed on the surface of a spherical nanoparticle were calculated depending on its dipole moment.As the dipole moment of the nanoparticle increased,the dense macromolecular shell was destroyed,forming caps of polyelectrolyte macro molecules or fragments of block copolymer of different types on the poles of the polarized nanoparticle.In this case,the macromolecular corona in the region of the poles of the polarized nanoparticle swelled the more strongly,the greater the distance between the charged links in the polymer.展开更多
The assembly behaviors of two low-symmetric carboxylic acid molecules(50-(6-carboxynaphthalen-2-yl)-[1,10:30,100-triphenyl]-3,400,5-tricarboxylic acid(CTTA)and 30,50-bis(6-carboxynaphthalen-2-yl)-[1,10-biphenyl]-3,5-d...The assembly behaviors of two low-symmetric carboxylic acid molecules(50-(6-carboxynaphthalen-2-yl)-[1,10:30,100-triphenyl]-3,400,5-tricarboxylic acid(CTTA)and 30,50-bis(6-carboxynaphthalen-2-yl)-[1,10-biphenyl]-3,5-dicarboxylic acid(BCBDA))containing naphthalene rings on graphite surfaces have been investigated using scanning tunneling microscopy(STM).The transformation of nanostructures induced by the second components(EDA and PEBP-C4)have been also examined.Both CTTA and BCBDA molecules self-assemble at the 1-heptanoic acid(HA)/HOPG interface,forming porous network structures.The dimer represents the most elementary building unit due to the formation of double hydrogen bonds.Moreover,the flipping of naphthalene ring results in the isomerization of BCBDA molecule.The introduction of carboxylic acid derivative EDA disrupts the dimer,which subsequently undergoes a structural conformation to form a novel porous structure.Furthermore,upon the addition of pyridine derivative PEBP-C4,N–H⋯O hydrogen bonds are the dominant forces driving the three coassembled structures.We have also conducted density functional theory(DFT)calculations to determine the molecular conformation and analyze the mechanisms underlying the formation of nanostructures.展开更多
To regulate the sodium chloride content in Jinhua ham,the impact of NaCl on the activity and conformation of cathepsin B was investigated using spectroscopy and computational methods.The results showed that the activi...To regulate the sodium chloride content in Jinhua ham,the impact of NaCl on the activity and conformation of cathepsin B was investigated using spectroscopy and computational methods.The results showed that the activity of cathepsin B decreased with an increase in Na^(+)cation content and temperature.Additionally,decreasedα-helix content and increasedβ-sheet content were observed.The increase in sulfhydryl group content was attributed to the breaking of original disulfide bonds in the molecular structure or the release of embedded groups.Furthermore,the surface hydrophobicity gradually declined,which was consistent with the analysis of endogenous fluorescence spectroscopy.At the molecular level,the number of hydrogen bonds formed in NaCl-treated samples decreased,and the interactions between the hydrogen bonding were less powerful,which caused instability in the binding of the protein and substrate.The conformation of cathepsin B accurately characterized its activity,and the structural changes had a macroscopic effect on the decrease in protease activity.展开更多
For chromosome abnormalities(CAs),such as Down syndrome(DS),the influence of genomic variations on chromosome conformation and gene transcription remains elusive.Based on the complete genomic sequences from the parent...For chromosome abnormalities(CAs),such as Down syndrome(DS),the influence of genomic variations on chromosome conformation and gene transcription remains elusive.Based on the complete genomic sequences from the parents of a DS trisomy patient,we systematically delineated an atlas of parental-specific,haplotype-resolved single nucleotide polymorphisms(SNPs),copy number variations(CNVs),threedimensional(3D)genome architecture,and RNA expression profiles in the diencephalon of the DS patient.The integrated haplotype-resolved multi-omics analysis demonstrated that one-dimensional(1D)genomic variations including SNPs and CNVs in the DS patient are highly correlated with the alterations in the 3D genome organization and the subsequent changes in gene transcription.This correlation remains valid at the haplotype level.Moreover,we revealed the 3D genome alteration-associated dysregulation of DS-related genes,which facilitates understanding the pathogenesis of CAs.Together,our study contributes to deciphering the coding from 1D genomic variations to 3D genome architecture and the subsequent gene transcription outcomes in both health and disease.展开更多
The chain conformation of polymers in binary solvent mixtures is a key issue in the study of functional soft matter and lies at the heart of various applications such as smart soft materials.Based on a minimal lattice...The chain conformation of polymers in binary solvent mixtures is a key issue in the study of functional soft matter and lies at the heart of various applications such as smart soft materials.Based on a minimal lattice model,we employ Monte Carlo(MC)simulation to systematically investigate the effects of solvent qualities on the conformation of a single homopolymer chain in binary mixed solvents.We also perform calculations using a Flory-type mean-field theory.We focus on how the introduction of a second solvent B affects the dependence of chain conformation on the quality of solvent A.We mainly examine the effects of the composition of solvent B,denoted by x,and the interactions between the two solvents.First,when x is low,the mean-square chain radius of gyration exhibits qualitatively similar behaviors to those in an individual solvent A,with a slight chain contraction when solvent A is very good.Second,in equal-molar mixtures with x=0.5,a homopolymer chain collapses when solvent A is either poor or very good,while expands at intermediate qualities.Lastly,at large x,a chain undergoes a coil-to-globule transition with the increasing quality of solvent A when solvent B is good,but mainly adopts the collapsed conformation when solvent B is poor.Our findings not only improve our understanding on the chain conformation in binary solvent mixtures,but also provide valuable guidance on the rational design of stimuli-responsive polymeric materials.展开更多
Dynamic adaptability is a key feature in biological macromolecules,enabling selective binding and catalysis[1].From DNA supercoiling to enzyme conformational changes,biological systems have evolved intricate ways to d...Dynamic adaptability is a key feature in biological macromolecules,enabling selective binding and catalysis[1].From DNA supercoiling to enzyme conformational changes,biological systems have evolved intricate ways to dynamically adjust their structures to accommodate functional needs.Mimicking this adaptability in synthetic systems is an ongoing challenge in supramolecular chemistry.展开更多
Gaining insights into charge transport related to conformational changes and ion transport in valinomycin(VM)is crucial for understanding the underlying physiological processes and advancing ion carrier applications.O...Gaining insights into charge transport related to conformational changes and ion transport in valinomycin(VM)is crucial for understanding the underlying physiological processes and advancing ion carrier applications.Observing these processes in single molecules provides deeper insights and precision than those obtained through conventional ensemble measurements.Herein,we employed a single-molecule conductance measurement method based on the scanning tunneling microscopy break-junction(STM-BJ)to measure the charge transport of individual VM molecules in both non-polar and polar solvents,as well as when mediated by K^(+)ions.Single-molecule conductance measurements revealed that the bracelet and propeller-type conformations of VM in both non-polar and polar solvents significantly affect its conductance.In polar solvents,the propeller-type conformation of VM demonstrated a well-defined conductance signature,single-molecule rectification feature,and through-space transmission mechanism.Specifically,the introduction of K^(+)ions in polar solvents induced a conformational transition from the propeller-type to the bracelet-type form,facilitating K^(+)binding recognition.These observations were further supported by density functional theory combined with non-equilibrium Green’s function calculations.This study enhanced the fundamental understanding of the electronic transport mechanisms in VM and valinomycin-K^(+)molecular junctions,offering insights into VM ionophores and promoting supramolecular sensing applications.展开更多
Mechanically interlocked molecules (MIMs) have unique properties with broad applications, yet constructing both knotted and linked topologies from the same ligand remains challenging due to their distinct geometric de...Mechanically interlocked molecules (MIMs) have unique properties with broad applications, yet constructing both knotted and linked topologies from the same ligand remains challenging due to their distinct geometric demands. To address this, we design and synthesize a conformationally adaptive ligand 4,7-bis(3-(pyridin-4-yl) phenyl) benzo[c][1,2,5]thiadiazole (L1) with a tunable torsional angle θ of N1C1C2N2 ranging from 7.5° to 108.9°. Utilizing coordination-driven self-assembly at ambient temperature, L1 selectively assembles with binuclear half-sandwich units RhB1, RhB2, RhB3, and RhB4 featuring Cp*^(Rh^(Ⅲ)) (Cp* = η^(5)-pentam-ethylcyclopentadienyl) into distinct topologies: Solomon links Rh-1, trefoil knots Rh-2, molecular tweezers Rh 3, and Rh-4, respectively. Crucially, the self-adaptability of ligand L1 directs topology formation through pro-gramming different combination of noncovalent interactions (π-x stacking, CH..π interaction, and lone pair-π interaction), thus navigating divergent assembly pathways by conformational switching, as evidenced by X-ray crystallography analysis, independent gradient model (IGM) analysis, detailed nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization time-of-flight/mass spectrometry (ESI-TOF/MS). This strategy can also be extended to construct Cp*^(Irl^(Ⅲ)) analogs (Solomon links Ir-1, trefoil knots Ir-2, molecular tweezers Ir-3 and Ir-4), demonstrating metal-independent control and achieving intricate topologies in a high yield.展开更多
Understanding the conformational characteristics of polymers is key to elucidating their physical properties.Cyclic polymers,defined by their closed-loop structures,inherently differ from linear polymers possessing di...Understanding the conformational characteristics of polymers is key to elucidating their physical properties.Cyclic polymers,defined by their closed-loop structures,inherently differ from linear polymers possessing distinct chain ends.Despite these structural differences,both types of polymers exhibit locally random-walk-like conformations,making it challenging to detect subtle spatial variations using conventional methods.In this study,we address this challenge by integrating molecular dynamics simulations with point cloud neural networks to analyze the spatial conformations of cyclic and linear polymers.By utilizing the Dynamic Graph CNN(DGCNN)model,we classify polymer conformations based on the 3D coordinates of monomers,capturing local and global topological differences without considering chain connectivity sequentiality.Our findings reveal that the optimal local structural feature unit size scales linearly with molecular weight,aligning with theoretical predictions.Additionally,interpretability techniques such as Grad-CAM and SHAP identify significant conformational differences:cyclic polymers tend to form prolate ellipsoid shapes with pronounced elongation along the major axis,while linear polymers show elongated ends with more spherical centers.These findings reveal subtle yet critical differences in local conformations between cyclic and linear polymers that were previously difficult to discern,providing deeper insights into polymer structure-property relationships and offering guidance for future polymer science advancements.展开更多
We present a comprehensive investigation of the vibrational spectra and conformational distribution of neutral and cationic monoethanolamine(MEA)in the gas phase.Using infrared-vacuum ultraviolet non-resonant ionizati...We present a comprehensive investigation of the vibrational spectra and conformational distribution of neutral and cationic monoethanolamine(MEA)in the gas phase.Using infrared-vacuum ultraviolet non-resonant ionization fragmentation detected IR spectroscopy(NRIFD-IR),we obtained vibrational spectra in the 2500-3800 cm^(−1)range for both neutral and cationic MEA.Density functional theory(DFT)calculations at the B3LYPD3(BJ)/def2-TZVPP level were employed to elucidate the molecular structures and vibrational modes.Our analysis revealed twelve distinct conformers for neutral MEA,with N1gʹGgʹbeing the most stable,while cationic MEA exhibited four conformers,among which C1gʹGt conformer was found to be the primary contributor to the observed spectra.The experimental spectra were interpreted through comparison with anharmonic calculations,allowing for detailed assignment of vibrational modes.Notably,we observed significant differences in the OH stretch region between neutral and cationic species,reflecting changes in intramolecular hydrogen bonding upon ionization.Furthermore,our study highlights the necessity for distinct scaling factors when calculating harmonic frequencies for neutral and cationic substances.展开更多
Polymers often exhibit multi-state conformational transitions with multiple pathways as temperature varies.However,characterizing the inherent features of these pathways is hindered by the lack of physical characteriz...Polymers often exhibit multi-state conformational transitions with multiple pathways as temperature varies.However,characterizing the inherent features of these pathways is hindered by the lack of physical characterizations that can distinguish various transition pathways between complex and disordered states.In this work,we introduced a machine-learning framework based on spatiotemporal point-cloud neural networks to identify and analyze conformational transition pathways in polymer chains.As a case study,we applied this framework to the temperature-induced unfolding of a single semi-flexible polymer chain,simulated via coarse-grained molecular dynamics.We first combined spatiotemporal point cloud neural networks and contrastive learning to extract features of conformational evolution,and then we employed unsupervised learning methods to cluster distinct transition pathways and unfolding trajectories.Our results reveal that,with increasing temperature,semi-flexible polymer chains exhibit five distinct unfolding pathways:rigid rod→random coil;small toroid→large toroid→hairpin→random coil;rod bundle→hairpin→random coil;hairpin→random coil;and tailed structure→random coil.We further calculated the structural order parameters of those typical conformations with distinct transition pathways,we distincted five transition mechanisms,including the straightening of rigid rods,tightening of small rings,expansion of hairpin ends,symmetrization of rod bundles,and retraction of tailed structures.These findings demonstrate that our framework presents a promising data-driven approach for analyzing complex conformational transitions in disordered polymers,which might be potentially extendable to other heterogeneous systems like intrinsically disordered proteins.展开更多
基金the financial support of the Ministry of Science and Higher Education of the Russian Federation within the framework of a grant for conducting large scientific projects in priority areas of scientific and technological development 075-15-2024-550。
文摘Using molecular dynamics modeling,the change in the shape and density of the macromolecular corona consisting of two oppositely charged polyelectrolytes,including those combined into one block copolymer,on the surface of a polarized spherical metal nanoparticle was studied.A mathematical model of the structure of the block copolymer chain adsorbed on a polarized spherical nanoparticle is presented for the cases of polyelectrolyte blocks of large and small length.Based on the modeling results,radial and angular distributions of the density of atoms of polyelectrolyte polypeptides adsorbed on the surface of a spherical nanoparticle were calculated depending on its dipole moment.As the dipole moment of the nanoparticle increased,the dense macromolecular shell was destroyed,forming caps of polyelectrolyte macro molecules or fragments of block copolymer of different types on the poles of the polarized nanoparticle.In this case,the macromolecular corona in the region of the poles of the polarized nanoparticle swelled the more strongly,the greater the distance between the charged links in the polymer.
基金financially supported by the National Natural Science Foundation of China(No.22272039)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB36000000)+1 种基金the Youth Program of the Liaoning Education Department(No.LJKQZ20222280)the Jilin Chinese Academy of Sciences-Yanshen Technology Co.,Ltd.
文摘The assembly behaviors of two low-symmetric carboxylic acid molecules(50-(6-carboxynaphthalen-2-yl)-[1,10:30,100-triphenyl]-3,400,5-tricarboxylic acid(CTTA)and 30,50-bis(6-carboxynaphthalen-2-yl)-[1,10-biphenyl]-3,5-dicarboxylic acid(BCBDA))containing naphthalene rings on graphite surfaces have been investigated using scanning tunneling microscopy(STM).The transformation of nanostructures induced by the second components(EDA and PEBP-C4)have been also examined.Both CTTA and BCBDA molecules self-assemble at the 1-heptanoic acid(HA)/HOPG interface,forming porous network structures.The dimer represents the most elementary building unit due to the formation of double hydrogen bonds.Moreover,the flipping of naphthalene ring results in the isomerization of BCBDA molecule.The introduction of carboxylic acid derivative EDA disrupts the dimer,which subsequently undergoes a structural conformation to form a novel porous structure.Furthermore,upon the addition of pyridine derivative PEBP-C4,N–H⋯O hydrogen bonds are the dominant forces driving the three coassembled structures.We have also conducted density functional theory(DFT)calculations to determine the molecular conformation and analyze the mechanisms underlying the formation of nanostructures.
基金supported by the National Natural Science Foundation of China(31972097)Jiangsu Key Research and Development Plan(Modern Agriculture)(BE2020302)+1 种基金the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(24KJB550003)2024 Huaiyin Institute of Technology Talent Recruitment Research Startup Fund Project(Z301B24521)。
文摘To regulate the sodium chloride content in Jinhua ham,the impact of NaCl on the activity and conformation of cathepsin B was investigated using spectroscopy and computational methods.The results showed that the activity of cathepsin B decreased with an increase in Na^(+)cation content and temperature.Additionally,decreasedα-helix content and increasedβ-sheet content were observed.The increase in sulfhydryl group content was attributed to the breaking of original disulfide bonds in the molecular structure or the release of embedded groups.Furthermore,the surface hydrophobicity gradually declined,which was consistent with the analysis of endogenous fluorescence spectroscopy.At the molecular level,the number of hydrogen bonds formed in NaCl-treated samples decreased,and the interactions between the hydrogen bonding were less powerful,which caused instability in the binding of the protein and substrate.The conformation of cathepsin B accurately characterized its activity,and the structural changes had a macroscopic effect on the decrease in protease activity.
基金supported by the National Natural Science Foundation of China(Grant Nos.32221005 to Gang Cao and 81900063 to He Long)the Natural Science Foundation of Hubei Province,China(Grant No.2022CFB180 to Zhijun Zhang).
文摘For chromosome abnormalities(CAs),such as Down syndrome(DS),the influence of genomic variations on chromosome conformation and gene transcription remains elusive.Based on the complete genomic sequences from the parents of a DS trisomy patient,we systematically delineated an atlas of parental-specific,haplotype-resolved single nucleotide polymorphisms(SNPs),copy number variations(CNVs),threedimensional(3D)genome architecture,and RNA expression profiles in the diencephalon of the DS patient.The integrated haplotype-resolved multi-omics analysis demonstrated that one-dimensional(1D)genomic variations including SNPs and CNVs in the DS patient are highly correlated with the alterations in the 3D genome organization and the subsequent changes in gene transcription.This correlation remains valid at the haplotype level.Moreover,we revealed the 3D genome alteration-associated dysregulation of DS-related genes,which facilitates understanding the pathogenesis of CAs.Together,our study contributes to deciphering the coding from 1D genomic variations to 3D genome architecture and the subsequent gene transcription outcomes in both health and disease.
基金financially supported by the National Natural Science Foundation of China(Nos.22473024,22073016 and 21803011)the award of Shanghai Dongfang Scholar。
文摘The chain conformation of polymers in binary solvent mixtures is a key issue in the study of functional soft matter and lies at the heart of various applications such as smart soft materials.Based on a minimal lattice model,we employ Monte Carlo(MC)simulation to systematically investigate the effects of solvent qualities on the conformation of a single homopolymer chain in binary mixed solvents.We also perform calculations using a Flory-type mean-field theory.We focus on how the introduction of a second solvent B affects the dependence of chain conformation on the quality of solvent A.We mainly examine the effects of the composition of solvent B,denoted by x,and the interactions between the two solvents.First,when x is low,the mean-square chain radius of gyration exhibits qualitatively similar behaviors to those in an individual solvent A,with a slight chain contraction when solvent A is very good.Second,in equal-molar mixtures with x=0.5,a homopolymer chain collapses when solvent A is either poor or very good,while expands at intermediate qualities.Lastly,at large x,a chain undergoes a coil-to-globule transition with the increasing quality of solvent A when solvent B is good,but mainly adopts the collapsed conformation when solvent B is poor.Our findings not only improve our understanding on the chain conformation in binary solvent mixtures,but also provide valuable guidance on the rational design of stimuli-responsive polymeric materials.
基金the Natural Science Foundation of China(No.22301131)the Natural Science Foundation of Jiangsu Province(Nos.BK20220781,BK20240679)the National Key Research and Development Program of China(No.2024YFB3815700)are greatly acknowledged.
文摘Dynamic adaptability is a key feature in biological macromolecules,enabling selective binding and catalysis[1].From DNA supercoiling to enzyme conformational changes,biological systems have evolved intricate ways to dynamically adjust their structures to accommodate functional needs.Mimicking this adaptability in synthetic systems is an ongoing challenge in supramolecular chemistry.
基金supported by the National Key R&D Program of China(Nos.2022YFB3204402,2020YFA0714703 and 2022YFC2205003)the National Natural Science Foundation of China(No.22204135)+2 种基金Hunan Provincial Natural Science Foundation of China(No.2023JJ40619)the Education Department of Hunan Province(No.23A0114)the Science and Technology Innovation Program of Hunan Province(No.2022RC3027)。
文摘Gaining insights into charge transport related to conformational changes and ion transport in valinomycin(VM)is crucial for understanding the underlying physiological processes and advancing ion carrier applications.Observing these processes in single molecules provides deeper insights and precision than those obtained through conventional ensemble measurements.Herein,we employed a single-molecule conductance measurement method based on the scanning tunneling microscopy break-junction(STM-BJ)to measure the charge transport of individual VM molecules in both non-polar and polar solvents,as well as when mediated by K^(+)ions.Single-molecule conductance measurements revealed that the bracelet and propeller-type conformations of VM in both non-polar and polar solvents significantly affect its conductance.In polar solvents,the propeller-type conformation of VM demonstrated a well-defined conductance signature,single-molecule rectification feature,and through-space transmission mechanism.Specifically,the introduction of K^(+)ions in polar solvents induced a conformational transition from the propeller-type to the bracelet-type form,facilitating K^(+)binding recognition.These observations were further supported by density functional theory combined with non-equilibrium Green’s function calculations.This study enhanced the fundamental understanding of the electronic transport mechanisms in VM and valinomycin-K^(+)molecular junctions,offering insights into VM ionophores and promoting supramolecular sensing applications.
基金Department of Chemistry,Fudan Uni-versity,the National Natural Science Foundation of China(22031003,21720102004)the Shanghai Science Technology Committee(19DZ227010O)the Alexander von Humboldt Foundation for a Humboldt Research Award.
文摘Mechanically interlocked molecules (MIMs) have unique properties with broad applications, yet constructing both knotted and linked topologies from the same ligand remains challenging due to their distinct geometric demands. To address this, we design and synthesize a conformationally adaptive ligand 4,7-bis(3-(pyridin-4-yl) phenyl) benzo[c][1,2,5]thiadiazole (L1) with a tunable torsional angle θ of N1C1C2N2 ranging from 7.5° to 108.9°. Utilizing coordination-driven self-assembly at ambient temperature, L1 selectively assembles with binuclear half-sandwich units RhB1, RhB2, RhB3, and RhB4 featuring Cp*^(Rh^(Ⅲ)) (Cp* = η^(5)-pentam-ethylcyclopentadienyl) into distinct topologies: Solomon links Rh-1, trefoil knots Rh-2, molecular tweezers Rh 3, and Rh-4, respectively. Crucially, the self-adaptability of ligand L1 directs topology formation through pro-gramming different combination of noncovalent interactions (π-x stacking, CH..π interaction, and lone pair-π interaction), thus navigating divergent assembly pathways by conformational switching, as evidenced by X-ray crystallography analysis, independent gradient model (IGM) analysis, detailed nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization time-of-flight/mass spectrometry (ESI-TOF/MS). This strategy can also be extended to construct Cp*^(Irl^(Ⅲ)) analogs (Solomon links Ir-1, trefoil knots Ir-2, molecular tweezers Ir-3 and Ir-4), demonstrating metal-independent control and achieving intricate topologies in a high yield.
基金the National Key R&D Program of China(No.2022YFB3707303)National Natural Science Foundation of China(No.52293471)。
文摘Understanding the conformational characteristics of polymers is key to elucidating their physical properties.Cyclic polymers,defined by their closed-loop structures,inherently differ from linear polymers possessing distinct chain ends.Despite these structural differences,both types of polymers exhibit locally random-walk-like conformations,making it challenging to detect subtle spatial variations using conventional methods.In this study,we address this challenge by integrating molecular dynamics simulations with point cloud neural networks to analyze the spatial conformations of cyclic and linear polymers.By utilizing the Dynamic Graph CNN(DGCNN)model,we classify polymer conformations based on the 3D coordinates of monomers,capturing local and global topological differences without considering chain connectivity sequentiality.Our findings reveal that the optimal local structural feature unit size scales linearly with molecular weight,aligning with theoretical predictions.Additionally,interpretability techniques such as Grad-CAM and SHAP identify significant conformational differences:cyclic polymers tend to form prolate ellipsoid shapes with pronounced elongation along the major axis,while linear polymers show elongated ends with more spherical centers.These findings reveal subtle yet critical differences in local conformations between cyclic and linear polymers that were previously difficult to discern,providing deeper insights into polymer structure-property relationships and offering guidance for future polymer science advancements.
基金the Dalian Coherent Light Source (DCLS) for support and assistancesurported by the National Natural Science Foundation of China (No.22288201)+1 种基金the Chinese Academy of Sciences (GJJSTD20220001)the Innovation Program for Quantum Science and Technology (No.2021ZD0303305)。
文摘We present a comprehensive investigation of the vibrational spectra and conformational distribution of neutral and cationic monoethanolamine(MEA)in the gas phase.Using infrared-vacuum ultraviolet non-resonant ionization fragmentation detected IR spectroscopy(NRIFD-IR),we obtained vibrational spectra in the 2500-3800 cm^(−1)range for both neutral and cationic MEA.Density functional theory(DFT)calculations at the B3LYPD3(BJ)/def2-TZVPP level were employed to elucidate the molecular structures and vibrational modes.Our analysis revealed twelve distinct conformers for neutral MEA,with N1gʹGgʹbeing the most stable,while cationic MEA exhibited four conformers,among which C1gʹGt conformer was found to be the primary contributor to the observed spectra.The experimental spectra were interpreted through comparison with anharmonic calculations,allowing for detailed assignment of vibrational modes.Notably,we observed significant differences in the OH stretch region between neutral and cationic species,reflecting changes in intramolecular hydrogen bonding upon ionization.Furthermore,our study highlights the necessity for distinct scaling factors when calculating harmonic frequencies for neutral and cationic substances.
基金financially supported by the National Key R&D Program of China(No.2022YFB3707303)the National Natural Science Foundation of China(No.52293471)。
文摘Polymers often exhibit multi-state conformational transitions with multiple pathways as temperature varies.However,characterizing the inherent features of these pathways is hindered by the lack of physical characterizations that can distinguish various transition pathways between complex and disordered states.In this work,we introduced a machine-learning framework based on spatiotemporal point-cloud neural networks to identify and analyze conformational transition pathways in polymer chains.As a case study,we applied this framework to the temperature-induced unfolding of a single semi-flexible polymer chain,simulated via coarse-grained molecular dynamics.We first combined spatiotemporal point cloud neural networks and contrastive learning to extract features of conformational evolution,and then we employed unsupervised learning methods to cluster distinct transition pathways and unfolding trajectories.Our results reveal that,with increasing temperature,semi-flexible polymer chains exhibit five distinct unfolding pathways:rigid rod→random coil;small toroid→large toroid→hairpin→random coil;rod bundle→hairpin→random coil;hairpin→random coil;and tailed structure→random coil.We further calculated the structural order parameters of those typical conformations with distinct transition pathways,we distincted five transition mechanisms,including the straightening of rigid rods,tightening of small rings,expansion of hairpin ends,symmetrization of rod bundles,and retraction of tailed structures.These findings demonstrate that our framework presents a promising data-driven approach for analyzing complex conformational transitions in disordered polymers,which might be potentially extendable to other heterogeneous systems like intrinsically disordered proteins.
