39 results on '"Susumu Fujiwara"'
Search Results
2. Image processing method for automatic measurement of number of DNA breaks
- Author
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Hiroaki Nakamura, Yuichi Tamura, Yasuhisa Oya, Seiki Saito, Susumu Fujiwara, Takahiro Kenmotsu, Yuji Hatano, and Hiroaki Ohtani
- Subjects
chemistry.chemical_compound ,Materials science ,chemistry ,Dna breaks ,Fluorescence microscope ,Image processing ,Biological system ,DNA - Published
- 2021
3. Hydrogen bond analysis of confined water in mesoporous silica using the reactive force field
- Author
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Katsumi Hagita, Susumu Fujiwara, Takeshi Yamada, and Tomoko Mizuguchi
- Subjects
Properties of water ,Materials science ,General Chemical Engineering ,FOS: Physical sciences ,02 engineering and technology ,Condensed Matter - Soft Condensed Matter ,01 natural sciences ,Force field (chemistry) ,Quantitative Biology::Subcellular Processes ,chemistry.chemical_compound ,Molecular dynamics ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,General Materials Science ,Confined water ,Condensed Matter - Materials Science ,Physics::Biological Physics ,Quantitative Biology::Biomolecules ,Condensed Matter - Mesoscale and Nanoscale Physics ,010304 chemical physics ,Nanoporous ,Hydrogen bond ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,Mesoporous silica ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,chemistry ,Chemical engineering ,Modeling and Simulation ,Soft Condensed Matter (cond-mat.soft) ,ReaxFF ,0210 nano-technology ,Information Systems - Abstract
The structural and dynamical properties of water confined in nanoporous silica with a pore diameter of 2.7 nm were investigated by performing large-scale molecular dynamics simulations using the reactive force field. The radial distribution function and diffusion coefficient of water were calculated, and the values at the center of the pore agreed well with experimental values for real water. In addition, the pore was divided into thin coaxial layers, and the average number of hydrogen bonds, hydrogen bond lifetime, and hydrogen bond strength were calculated as a function of the radial distance from the pore central axis. The analysis showed that hydrogen bonds involving silanol (Si-OH) have a longer lifetime, although the average number of hydrogen bonds per atom does not change from that at the pore center. The longer lifetime, as well as smaller diffusion coefficient, of these hydrogen bonds is attributed to their greater strength.
- Published
- 2019
4. Cavitation in thin films of amorphous polymers from the static melt induced by thermal treatment
- Author
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Nan Lin, Atsushi Doi, Masato Hashimoto, Tomoko Mizuguchi, Susumu Fujiwara, Nozomi Katayama, and Junki Ootani
- Subjects
chemistry.chemical_classification ,010407 polymers ,Materials science ,Polymers and Plastics ,Polymer ,Thermal treatment ,01 natural sciences ,0104 chemical sciences ,Annealing (glass) ,Amorphous solid ,Viscous fingering ,chemistry.chemical_compound ,chemistry ,Cavitation ,Materials Chemistry ,Polystyrene ,Composite material ,Glass transition - Abstract
We discover a new cavitation phenomenon in amorphous polymers sandwiched between two thick slide glasses from the static melt induced by thermal treatment. By quenching atactic polystyrene (aPS) samples from the static melt under the glass transition temperature (Tg) and annealing them above Tg for thick slide glasses, cavities are created to relax the negative pressure. Cavity growth undergoes an Ostwald ripening-like process in cases of large molecular weight, while it undergoes a viscous fingering process in cases of small molecular weight. The induction time for cavity formation is found to decrease with the increase of the annealing temperature and with the decrease of molecular weight. In contrast, no cavities are observed in an aPS sample between two thin cover glasses because the negative pressure can be relaxed by bending the whole thin cover glasses. We discover a new cavitation phenomenon in amorphous polymers sandwiched between two thick slide glasses from the static melt induced by thermal treatment. By quenching atactic polystyrene samples from the static melt under the glass transition temperature (Tg) and annealing them above Tg, cavities are created to relax the negative pressure. Cavity growth undergoes an Ostwald ripening-like process in cases of large molecular weight while it undergoes a viscous fingering process in cases of small molecular weight.
- Published
- 2019
5. Icosahedral order in liquid and glassy phases of cyclohexane
- Author
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Susumu Fujiwara, Tomoko Mizuguchi, and Soichi Tatsumi
- Subjects
Materials science ,Cyclohexane ,Icosahedral symmetry ,General Chemical Engineering ,Thermodynamics ,FOS: Physical sciences ,02 engineering and technology ,Computer Science::Computational Geometry ,Condensed Matter::Disordered Systems and Neural Networks ,01 natural sciences ,chemistry.chemical_compound ,Molecular dynamics ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Physics::Chemical Physics ,Supercooling ,010304 chemical physics ,Order (ring theory) ,General Chemistry ,Disordered Systems and Neural Networks (cond-mat.dis-nn) ,Condensed Matter - Disordered Systems and Neural Networks ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Condensed Matter::Soft Condensed Matter ,chemistry ,Modeling and Simulation ,0210 nano-technology ,Voronoi diagram ,Information Systems - Abstract
We performed all-atom molecular dynamics simulations for bulk cyclohexane and analysed the short- and medium-range structures in supercooled and glassy states by using the Voronoi tessellation technique. From the analyses of both the potential energy of the system and the radial distribution function of molecules, cyclohexane was found to be vitrified as the temperature decreased. Furthermore, the icosahedral-like structures are dominant at all temperatures and grow in a supercooled liquid, whereas the face-centred cubic structures do not grow when the temperature decreases. It was also ascertained that the icosahedral-like structure is more dominant than the full-icosahedral one. The network of the distorted icosahedron spreads throughout the system at low temperatures. Our simulation demonstrates the stability of the icosahedral structure even in a non-spherical molecule such as cyclohexane., 12 pages, 7 figures
- Published
- 2020
6. Exacerbation and Prolongation of Psoriasiform Inflammation in Diabetic Obese Mice: A Synergistic Role of CXCL5 and Endoplasmic Reticulum Stress
- Author
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Chikako Nishigori, Haruki Jimbo, Susumu Fujiwara, Hiroshi Nagai, and Noriko Shimoura
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0301 basic medicine ,Chemokine CXCL5 ,medicine.medical_specialty ,Mice, Obese ,Inflammation ,Dermatology ,Biochemistry ,Diabetes Mellitus, Experimental ,Palmitic acid ,Mice ,03 medical and health sciences ,chemistry.chemical_compound ,Dermis ,Internal medicine ,Diabetes mellitus ,Psoriasis ,medicine ,Animals ,Secretion ,Obesity ,Endoplasmic Reticulum Chaperone BiP ,Molecular Biology ,Cells, Cultured ,business.industry ,Endoplasmic reticulum ,Cell Biology ,Endoplasmic Reticulum Stress ,medicine.disease ,Mice, Inbred C57BL ,030104 developmental biology ,Endocrinology ,medicine.anatomical_structure ,chemistry ,Metabolic syndrome ,medicine.symptom ,business - Abstract
Accumulating evidence suggests that psoriasis is frequently accompanied by metabolic disorders, such as obesity and diabetes. However, the mechanisms underlying the association between increased psoriasis severity and concomitant metabolic syndrome have not been fully clarified. Herein, we show that imiquimod-induced psoriasiform inflammation was exacerbated and prolonged in diabetic obese mice compared to that in control mice, accompanied by remarkably increased lesional expressions of Cxcl5 and Il-1b. Notably, a large number of CXCL5+ Ly6G+ cells infiltrated the dermis and subcutaneous fat tissue of the diabetic obese mice. Most macrophages in the subcutaneous fat tissues of the diabetic obese mice were positive for expression of IL-1β and GRP78/Bip, an endoplasmic reticulum stress marker. Depletion of Ly6G+ cells and macrophages diminished the imiquimod-induced psoriasiform inflammation. Further, CXCL5 potentiated the secretion of IL-1β from macrophages and palmitic acid, a fatty acid released from subcutaneous adipocytes, further enhanced IL-1β secretion via endoplasmic reticulum stress induction. Combined with the fact that the serum levels of both CXCL5 and palmitic acid are significantly elevated in patients with metabolic syndrome, our results suggest a role for CXCL5 and endoplasmic reticulum stress in the increase of psoriasis severity of patients with concomitant metabolic syndrome.
- Published
- 2018
7. Coarse-grained Molecular Simulations for Structure Formation of Polymers
- Author
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Susumu Fujiwara
- Subjects
chemistry.chemical_classification ,Materials science ,Structure formation ,chemistry ,Chemical physics ,Polymer - Published
- 2017
8. An accelerated united-atom molecular dynamics simulation on the fast crystallization of ring polyethylene melts
- Author
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Katsumi Hagita, Nobuyuki Iwaoka, and Susumu Fujiwara
- Subjects
Materials science ,010304 chemical physics ,Crystallization of polymers ,General Physics and Astronomy ,Thermodynamics ,Polyethylene ,010402 general chemistry ,01 natural sciences ,Bond order ,Force field (chemistry) ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,Molecular dynamics ,Monomer ,chemistry ,Homogeneous ,law ,0103 physical sciences ,Physical and Theoretical Chemistry ,Crystallization - Abstract
To investigate crystallinities based on trans-structures, we determined the differences in the crystallization properties of ring and linear polymers by performing united-atom-model molecular dynamics (MD) simulations of homogeneous polyethylene melts of equal length, N, which refers to the number of monomers per chain. Modified parameters based on the DREIDING force field for the CH2 units were used in order to accelerate the crystallization process. To detect polymer crystallization, we introduced some local-order parameters that relate to trans-segments in addition to common crystallinities using neighboring bond orders. Through quenching MD simulations at 5 K/ns, we roughly determined temperature thresholds, Tth, at which crystallization is observed although it was hard to determine the precise Tth as observed in the laboratory time frame with the present computing resources. When N was relatively small (100 and 200), Tth was determined to be 320 and 350 K for the linear- and ring-polyethylene melts, respectively, while Tth was found to be 330 and 350 K, respectively, when N was 1000. Having confirmed that the crystallization of a ring-polyethylene melt occurs faster than that of the analogous linear melt, we conclude that the trans-segment-based crystallinities are effective for the analysis of local crystal behavior.
- Published
- 2019
9. Structural change of damaged polyethylene by beta-decay of substituted tritium using reactive force field
- Author
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Tomoko Mizuguchi, Haolun Li, Shinji Saito, Hiroaki Nakamura, Susumu Fujiwara, Ayako Nakata, and Tsuyoshi Miyazaki
- Subjects
chemistry.chemical_compound ,Materials science ,Physics and Astronomy (miscellaneous) ,Structural change ,chemistry ,Force field (physics) ,General Engineering ,General Physics and Astronomy ,Tritium ,Atomic physics ,Polyethylene ,Beta decay - Abstract
The molecular mechanism of structural change caused by the beta-decay of substituted tritium on DNA or polymeric materials is still being unsolved and it is hard to study the decay effect of tritium solely by experiment. In order to study the structural changes of damaged polyethylene caused by the decay effect of tritium, we randomly removed hydrogen atoms from the polyethylene chain and performed molecular dynamics (MD) simulations using the reactive force field (ReaxFF). We adopted two parameter sets of ReaxFF and evaluated their reliability by comparing the atomic forces with density functional theory calculations. The results of MD simulations at a low temperature of 100 K show that the structure of polyethylene will be less ordered when losing more hydrogen atoms. It is observed that a double bond or a cyclic structure will be formed when two carbon atoms, which are the nearest or next-nearest neighbors, lose hydrogen atoms.
- Published
- 2020
10. Molecular dynamics study on DNA damage by tritium disintegration
- Author
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Yuji Hatano, Takuo Yasunaga, Tomoko Mizuguchi, Tsuyoshi Miyazaki, Takahiro Kenmotsu, Hisanori Miyanishi, Takao Otsuka, Susumu Fujiwara, Shinji Saito, Ayako Nakata, and Hiroaki Nakamura
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Guanine ,DNA damage ,General Engineering ,General Physics and Astronomy ,Charge density ,Thermodynamics ,Force field (chemistry) ,chemistry.chemical_compound ,Molecular dynamics ,chemistry ,Density functional theory ,Root-mean-square deviation ,DNA - Abstract
Using molecular dynamics (MD) simulation, we simulate the structural change of a telomeric DNA by β-decay of substituted tritium to helium-3. The configuration of the telomeric DNA is obtained by removing TRF2 protein from the TRF2-Dbd-DNA complex (Protein Data Bank ID is 3SJM). We assume that hydrogens (H) of guanines in the telomeric DNA are replaced to helium-3. Since this replacement of the H atoms to the 3He atoms changes the charge distribution significantly, the charge distribution used in the MD simulation for the modified guanine is obtained by the density functional theory calculations. We adopt, as the MD simulation, nanoscale molecular dynamics code with CHARMM36 force field using Langevin thermostat and Nosé–Hoover Langevin piston to control the temperature and pressure of the system, respectively. Moreover, changing both the number of replaced guanine N and the temperature of the system T, we calculate the root mean square deviation RMSD to quantify the dependence of the durability of the telomeric DNA on the β-decays. From the MD simulation, it is found that as N or T becomes larger, the RMSD of the DNA becomes also larger. Namely, it denotes that as the intensity of the β-decays becomes larger or as the temperature is increased, the DNA structure becomes more fragile.
- Published
- 2019
11. Single-chain folding of a quenched isotactic polypropylene chain through united atom molecular dynamics simulations
- Author
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Katsumi Hagita and Susumu Fujiwara
- Subjects
Quenching ,Quantitative Biology::Biomolecules ,Materials science ,Polymers and Plastics ,Hydrogen ,Organic Chemistry ,chemistry.chemical_element ,02 engineering and technology ,Single chain ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Molecular dynamics ,Rigidity (electromagnetism) ,chemistry ,Chemical physics ,Tacticity ,Atom ,Materials Chemistry ,0210 nano-technology ,Torsional angle - Abstract
The single-chain folding of an isotactic polypropylene (iPP) chain through united atom (UA) molecular dynamics simulations under quenching was investigated using force fields (FFs) based on TraPPE-UA. We estimated the degree of local rigidity of the folded chain along iPP undergoing single-chain folding. To maintain the tacticity of iPP, we introduced improper torsional angle potentials and/or explicit hydrogen atoms bonded to backbone carbon atoms. In the simulation using modified TraPPE-UA FFs with added hydrogen atoms, folded structures were observed. In the cases using modified TraPPE-UA FFs with only improper torsional potentials, folding of the quenched iPP chain was not observed. Moreover, to clarify the folding behavior of the iPP chain, we studied the chirality of a single iPP chain and subsequently observed spontaneous chirality selection during the quenched folding process. We also examined the effect of the angle and torsional potentials of the added hydrogen on the folding behavior of a single iPP chain into local crystals. Therefore, we confirmed that the strength of the angle and torsional potentials contributed to the acceleration of the folding behavior.
- Published
- 2019
12. Melt memory of a spherulite nucleus formed through a seeding process in the crystal growth of isotactic polystyrene
- Author
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Junko O'ishi, Susumu Fujiwara, Masato Hashimoto, and Sayoko Moriya
- Subjects
Number density ,Materials science ,Polymers and Plastics ,Crystal growth ,law.invention ,chemistry.chemical_compound ,Crystallography ,chemistry ,Spherulite ,Optical microscope ,law ,Scientific method ,Tacticity ,Materials Chemistry ,Seeding ,Polystyrene ,Composite material - Abstract
The melt memory of isotactic polystyrene spherulites from the melt is investigated using optical microscopy. When the melting–recrystallization processes are repeated by raising and lowering the temperature after the reset of the melt and the subsequent seeding process, the number of the spherulites is found to decrease with the cumulative melting time. The spherulites appear at the same positions as the original ones, and the higher the melt temperature is, the faster their number decreases. At the initial stage, the number density of spherulites rapidly decreases with the cumulative melting time. After the initial stage, the number density of spherulites exponentially decays with the cumulative melting time and approaches a finite value. This asymptotic value decreases with the melt temperature.
- Published
- 2015
13. Single-molecule imaging reveals topological isomer-dependent diffusion by 4-armed star and dicyclic 8-shaped polymers
- Author
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Takuya Yamamoto, Susumu Fujiwara, Satoshi Habuchi, and Yasuyuki Tezuka
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chemistry.chemical_classification ,Quantitative Biology::Biomolecules ,Materials science ,Polymers and Plastics ,Gaussian ,Organic Chemistry ,Bioengineering ,Polymer ,Star (graph theory) ,Topology ,Biochemistry ,Single Molecule Imaging ,symbols.namesake ,Crystallography ,chemistry ,Chain (algebraic topology) ,symbols ,Molecule ,Diffusion (business) ,Threading (protein sequence) - Abstract
Diffusion dynamics of topological isomers of polymer molecules was investigated at the single-molecular level in the melt state by employing the fluorophore-incorporated 4-armed star and the corresponding doubly-cyclized, 8-shaped poly(THF) chains. While the single-molecule fluorescence imaging experiment revealed that the diffusion of the 4-armed star polymer was described by a single Gaussian distribution, the diffusion of the 8-shaped polymer exhibited a double Gaussian distribution behaviour. We reasoned that the two 8-shaped polymeric isomers have distinct diffusion modes in the melt state, although ensemble-averaged experimental methods cannot detect differences in the overall conformational state of the isomers. The single-molecule experiments suggested that one of the 8-shaped polymeric isomers, having the horizontally oriented form, causes an efficient threading with the linear matrix chains which leads to slower diffusion compared with the corresponding 4-armed star polymer, while the other 8-shaped polymeric isomer, having the vertically oriented form, displayed faster diffusion by the suppression of effective threading with the linear matrix chains due to its contracted chain conformation.
- Published
- 2015
14. Novel serum metabolomics-based approach by gas chromatography/triple quadrupole mass spectrometry for detection of human skin cancers: Candidate biomarkers
- Author
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Chikako Nishigori, Shin Nishiumi, Takeshi Fukumoto, Masaru Yoshida, and Susumu Fujiwara
- Subjects
0301 basic medicine ,Male ,Pathology ,medicine.medical_specialty ,Skin Neoplasms ,Sebacic acid ,Human skin ,Dermatology ,Gas Chromatography-Mass Spectrometry ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,Metabolomics ,medicine ,Biomarkers, Tumor ,Humans ,Melanoma ,Aged ,Aged, 80 and over ,Principal Component Analysis ,business.industry ,General Medicine ,Glutamic acid ,Middle Aged ,medicine.disease ,030104 developmental biology ,chemistry ,030220 oncology & carcinogenesis ,Cancer research ,Carcinoma, Squamous Cell ,Biomarker (medicine) ,Female ,Skin cancer ,Suberic acid ,business - Abstract
Skin cancer incidence rates are continuing to rise; however, if detected at an early stage, they can be cured with minimally invasive treatment. Therefore, the identification of novel and robust biomarkers for the early detection of skin cancer is required to improve the quality of life of the patient after treatment. In the present study, we aimed to identify novel biomarkers of skin cancers. We carried out serum metabolomics using gas chromatography/triple quadrupole mass spectrometry for two types of skin cancer: squamous cell carcinoma and melanoma. The changes in the expression of metabolites compared with healthy volunteers were analyzed by principal component analysis. Among all 118 metabolites, 27 in patients with squamous cell carcinoma and 33 in patients with melanoma showed significant changes in comparison with healthy volunteers. Principal component analysis showed that both skin cancer groups could be distinguished from the healthy volunteers group. We further investigated the specific metabolites most useful for these distinctions. In the squamous cell carcinoma group, these metabolites were glycerol, 4-hydroxybenzoic acid, sebacic acid, fucose and suberic acid. In the melanoma group, these metabolites were glutamic acid, sebacic acid, suberic acid, 4-hydroxybenzoic acid and phenylalanine. The present study identified several metabolites that were distinct for certain skin cancer types, which could potentially be used as diagnostic biomarkers leading to novel clinical management strategies.
- Published
- 2017
15. Synthesis of core-fluorescent four-armed star and dicyclic 8-shaped poly(THF)s by electrostatic self-assembly and covalent fixation (ESA–CF) protocol
- Author
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Takuya Yamamoto, Susumu Fujiwara, Yasuyuki Tezuka, and Satoshi Habuchi
- Subjects
Polymers and Plastics ,General Chemical Engineering ,General Chemistry ,Biochemistry ,Fluorescence ,Toluene ,chemistry.chemical_compound ,chemistry ,Diimide ,Covalent bond ,Polymer chemistry ,Materials Chemistry ,Environmental Chemistry ,Self-assembly ,Bifunctional ,Tetrahydrofuran ,Perylene - Abstract
A pair of four-armed star and dicyclic 8-shaped poly(tetrahydrofuran)s, poly(THF)s, possessing a perylene diimide group at the core position (Ia and Ib, respectively) were synthesized by means of an electrostatic self-assembly and covalent fixation (ESA–CF) protocol. Mono- and bifunctional poly(THF)s having N-phenylpiperidinium salt end groups accompanying a perylene diimide tetracarboxylate as a counteranion were prepared by the ion-exchange reaction, and the subsequent covalent conversion by reflux in toluene afforded the corresponding core-fluorescent four-armed star and dicyclic 8-shaped poly(THF)s, (Ia and Ib, respectively) for the use of single-molecule fluorescence microscopy measurements.
- Published
- 2014
16. Structure formation of a quenched single polyethylene chain with different force fields in united atom molecular dynamics simulations
- Author
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Nobuyuki Iwaoka, Katsumi Hagita, and Susumu Fujiwara
- Subjects
Quenching ,Materials science ,Structure formation ,General Physics and Astronomy ,02 engineering and technology ,Polyethylene ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,lcsh:QC1-999 ,0104 chemical sciences ,law.invention ,Folding (chemistry) ,Molecular dynamics ,chemistry.chemical_compound ,Crystallinity ,chemistry ,law ,Atom ,Crystallization ,0210 nano-technology ,lcsh:Physics - Abstract
The differences in the structure formations of a single polyethylene (PE) chain in united atom molecular dynamics (UAMD) simulations under quenching was investigated with varying force fields (FFs) that included torsional potential. We estimated the crystallinity of the folded structures undergoing local crystallization of the single PE chain. In simulations with DREIDING FF, highly folded structures were observed with fast quenching at the rate of 50 K/ns. From the viewpoint of crystallinity, we clarified that it was easy to achieve folding of the PE chains into local crystals with DREIDING FFs. With recent commonly used general FFs such as OPLS-UA and TraPPE-UA, highly folded structures were observed by quenching at the rate of 1 K/5 ns. In the present paper, we examine the Rigby–Roe (RR) FF optimized by Theodorou and coworkers and Paul–Yoon–Smith (PYS) FF optimized by Rutledge and coworkers. With the RR-Theodorou and PYS-Rutledge FFs, crystallization was observed with quenching at 1 K/ns and 1 K/5 ns, respectively. Consequently, it was relatively easier to achieve folding with the RR-Theodorou FF than with the PYS-Rutledge, OPLS-UA, and TraPPE-UA FFs.The differences in the structure formations of a single polyethylene (PE) chain in united atom molecular dynamics (UAMD) simulations under quenching was investigated with varying force fields (FFs) that included torsional potential. We estimated the crystallinity of the folded structures undergoing local crystallization of the single PE chain. In simulations with DREIDING FF, highly folded structures were observed with fast quenching at the rate of 50 K/ns. From the viewpoint of crystallinity, we clarified that it was easy to achieve folding of the PE chains into local crystals with DREIDING FFs. With recent commonly used general FFs such as OPLS-UA and TraPPE-UA, highly folded structures were observed by quenching at the rate of 1 K/5 ns. In the present paper, we examine the Rigby–Roe (RR) FF optimized by Theodorou and coworkers and Paul–Yoon–Smith (PYS) FF optimized by Rutledge and coworkers. With the RR-Theodorou and PYS-Rutledge FFs, crystallization was observed with quenching at 1 K/ns and 1 K/5 ns, ...
- Published
- 2018
17. Single-Molecule Study on Polymer Diffusion in a Melt State: Effect of Chain Topology
- Author
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Satoshi Habuchi, Susumu Fujiwara, Takuya Yamamoto, Martin Vacha, and Yasuyuki Tezuka
- Subjects
chemistry.chemical_classification ,Polymers ,Surface Properties ,Chemistry ,Polymer ,Topology ,Phase Transition ,Analytical Chemistry ,Diffusion ,Condensed Matter::Soft Condensed Matter ,Mean squared displacement ,Motion ,chemistry.chemical_compound ,Chain (algebraic topology) ,Diimide ,Polymer physics ,Molecule ,Diffusion (business) ,Perylene - Abstract
We report a new methodology for studying diffusion of individual polymer chains in a melt state, with special emphasis on the effect of chain topology. A perylene diimide fluorophore was incorporated into the linear and cyclic poly(THF)s, and real-time diffusion behavior of individual chains in a melt of linear poly(THF) was measured by means of a single-molecule fluorescence imaging technique. The combination of mean squared displacement (MSD) and cumulative distribution function (CDF) analysis demonstrated the broad distribution of diffusion coefficient of both the linear and cyclic polymer chains in the melt state. This indicates the presence of spatiotemporal heterogeneity of the polymer diffusion which occurs at much larger time and length scales than those expected from the current polymer physics theory. We further demonstrated that the cyclic chains showed marginally slower diffusion in comparison with the linear counterparts, to suggest the effective suppression of the translocation through the threading-entanglement with the linear matrix chains. This coincides with the higher activation energy for the diffusion of the cyclic chains than of the linear chains. These results suggest that the single-molecule imaging technique provides a powerful tool to analyze complicated polymer dynamics and contributes to the molecular level understanding of the chain interaction.
- Published
- 2013
18. Molecular Dynamics Simulations for Structure Formation of Polymers and Self-Assembly of Amphiphilic Molecules
- Author
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Susumu Fujiwara, Masato Hashimoto, and Takashi Itoh
- Subjects
chemistry.chemical_classification ,Amphiphilic molecule ,Structure formation ,Materials science ,Polymers and Plastics ,Materials Science (miscellaneous) ,Crystallization of polymers ,Polymer ,Molecular dynamics ,Chemical engineering ,chemistry ,Computational chemistry ,Chemical Engineering (miscellaneous) ,Self-assembly ,General Environmental Science - Published
- 2009
19. Molecular dynamics simulation of micelle formation in amphiphilic solution
- Author
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Takashi Itoh, Masato Hashimoto, Yuichi Tamura, and Susumu Fujiwara
- Subjects
Coalescence (physics) ,Chemistry ,General Chemical Engineering ,Bilayer ,General Chemistry ,Condensed Matter Physics ,Micelle ,Condensed Matter::Soft Condensed Matter ,Hydrophobic effect ,Molecular dynamics ,Chemical physics ,Computational chemistry ,Lyotropic liquid crystal ,Modeling and Simulation ,Amphiphile ,Molecule ,General Materials Science ,Physics::Chemical Physics ,Information Systems - Abstract
The micelle formation in amphiphilic solution is investigated by molecular dynamics (MD) simulation of coarse-grained rigid amphiphiles with explicit solvent molecules. In our simulation model, the intensity of the hydrophilic interaction and the hydrophobic interaction can be varied independently. Our simulations show that various kinds of micellar structures are formed at a lower temperature by quenching from a random configuration of amphiphilic molecules in solution at a higher temperature. The micellar shape changes from a disc (bilayer) into a cylinder and then into a sphere as the intensity of the hydrophilic interaction increases. It is also found that the micelle formation proceeds in a stepwise fashion through the coalescence of smaller micelles. From the analysis of the orientational order for the amphiphilic molecules, it is concluded that the orientational order parameters can be used to distinguish the micellar shapes clearly.
- Published
- 2007
20. Thermal, Structural and Ferroelectric Properties of Amorphous Phases in Quenched Nylon 6 Film
- Author
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Takashi Itoh, Yasuo Saruyama, Teruaki Yanagisawa, and Susumu Fujiwara
- Subjects
Materials science ,Annealing (metallurgy) ,Analytical chemistry ,General Physics and Astronomy ,Dielectric ,Ferroelectricity ,Amorphous solid ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Nylon 6 ,Nuclear magnetic resonance ,Differential scanning calorimetry ,chemistry ,Liquid crystal ,Glass transition - Abstract
Three types of amorphous phases (ferroelectric metastable phase A with large remanent polarization, ferroelectric metastable phase B with small remanent polarization and paraelectric stable phase C) are identified in as-quenched and/or annealed nylon 6 films on the basis of the thermal data obtained by light-modulated differential scanning calorimetry (LMDSC) as well as X-ray data, which show different glass transition temperatures and d -spacings. The irreversible exothermic anomaly at 328 K observed through heating process in the conventional DSC is attributed to transition from phases A and/or B to nematic phase. The transition from phase A to phase B is considered to complete after 15 min annealing at 320 K on the basis of the LMDSC data, which corresponds to abrupt diminution of the remanent polarization by the correspondent annealing condition. Such results suggest that ferroelectricity of nylon 6 film is mainly attributed to phase A (frozen state of the melt) formed in the quenched nylon 6 thin film.
- Published
- 2004
21. Phase Transition in Even–Even Nylon Crystals
- Author
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Hiroya Ishikawa, Susumu Fujiwara, Masato Hashimoto, and Takashi Itoh
- Subjects
Diffraction ,Phase transition ,Materials science ,digestive, oral, and skin physiology ,General Physics and Astronomy ,Crystal structure ,Thermal expansion ,Pressure range ,chemistry.chemical_compound ,Crystallography ,chemistry ,Melting point ,Moiety ,Methylene - Abstract
Temperature dependence of crystal structures is examined with X-ray diffraction at normal pressure or elevated pressures for solution-grown nylons with octamethylene moiety between amino or carboxy groups (nylons 82, 410, 610, 810). Although octamethylene moiety between amino groups has the potential to cause the phase transition, the low melting point veils the transition appearance. Considering this comprehensively with previous results, it is concluded for all even–even nylons, that the phase transition in the two-dimensional methylene layer system can be experimentally observed only in nylon 6Y (Y≤8) crystals at normal and/or high pressures, where the hexamethylene moiety between amino groups plays an intrinsic role. The so-called `Brill transition' widely reported for melt-crystallized nylons is not a phase transition but an abrupt thermal expansion.
- Published
- 2004
22. Micellar Shape Change in Amphiphilic Solution: A Molecular Dynamics Study
- Author
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Susumu Fujiwara, Ritoku Horiuchi, Takashi Itoh, and Masato Hashimoto
- Subjects
Molecular dynamics ,Chromatography ,Shape change ,Chemistry ,Chemical physics ,Amphiphile ,General Chemistry - Abstract
Micellar shape change in amphiphilic solution after sudden change in the solvophilic interaction is studied by molecular dynamics simulations of coarse-grained, rigid amphiphiles. Our simulations d...
- Published
- 2012
23. Structure Formation of a Single Polymer Chain in Solution: A Molecular Dynamics Study
- Author
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Susumu Fujiwara and Tetsuya Sato
- Subjects
Quenching ,chemistry.chemical_classification ,Materials science ,Structure formation ,Toroid ,Polymers and Plastics ,General Chemistry ,Polymer ,Condensed Matter Physics ,Molecular dynamics ,Chain (algebraic topology) ,chemistry ,Chemical physics ,Polymer solution ,Metastability ,Materials Chemistry ,Physical chemistry - Abstract
Molecular dynamics simulations are carried out to study the structure formation of a single polymer chain in solution. A random conformation of a polymer chain in solution at high temperature (550K) is quenched to several lower temperatures (300, 350, and 400K). Our simulations show the following characteristics: 1) At lower quenching temperature (300K), local orientationally ordered domains are formed first, and they grow to be a folded orientationally ordered structure. 2) At a higher quenching temperature (400K), a toroidal structure can be formed. 3) At an intermediate quenching temperature (350K), a toroidal structure can be formed before a folded orientationally ordered structure is formed. The last characteristic indicates that an intermediate toroidal structure at 350K is in a metastable state. We also find that it depends on the initial conformation of a polymer chain, whether a toroidal structure is formed or not.
- Published
- 2003
24. Adenosine triphosphate accelerates recovery from hypoxic/hypoglycemic perturbation of guinea pig hippocampal neurotransmission via a P2 receptor
- Author
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Tomoyuki Nishizaki, Hidetoshi Tozaki, Hitoshi Tada, Yukio Yajima, Ikuko Mizuta, Takeshi Kondoh, Susumu Fujiwara, Takeshi Kanno, Hideo Aihara, Kaoru Nagai, Yasuhiko Motooka, and Kazuhide Inoue
- Subjects
Adenosine monophosphate ,medicine.medical_specialty ,Patch-Clamp Techniques ,medicine.drug_class ,Guinea Pigs ,Biology ,P2 receptor ,Hippocampus ,Synaptic Transmission ,chemistry.chemical_compound ,Adenosine Triphosphate ,Organ Culture Techniques ,Internal medicine ,medicine ,Animals ,PPADS ,Hypoxia, Brain ,Molecular Biology ,Cells, Cultured ,gamma-Aminobutyric Acid ,Neurons ,Dose-Response Relationship, Drug ,Receptors, Purinergic P2 ,General Neuroscience ,Neural Inhibition ,Bicuculline ,Receptors, GABA-A ,Receptor antagonist ,Adenosine ,Hypoglycemia ,Adenosine diphosphate ,Endocrinology ,chemistry ,Astrocytes ,Neurology (clinical) ,Adenosine triphosphate ,Developmental Biology ,medicine.drug - Abstract
The present study was designed to assess the effects of adenosine triphosphate (ATP) on hippocampal neurotransmissions under the normal and hypoxic/hypoglycemic conditions. ATP reversely depressed population spikes (PSs), which were monitored in the dentate gyrus of guinea pig hippocampal slices, in a dose-dependent manner at concentrations ranged from 0.1 micro M to 1 mM. A similar depression was obtained with the P(2) receptor agonist, alpha,beta-methylene ATP (alpha,beta-MeATP), and the effect was inhibited by the P(2) receptor antagonists, suramin and PPADS. The inhibitory action of ATP or alpha,beta-MeATP was inhibited by the gamma-aminobutyric acid(A) (GABA(A)) receptor antagonist, bicuculline, but it was not affected by theophylline, a broad inhibitor of adenosine (P(1)) receptors, tetraethylammonium, a broad inhibitor of K(+) channels, or ecto-protein kinase inhibitors. ATP or alpha,beta-MeATP enhanced GABA release from guinea pig hippocampal slices, that was inhibited by deleting extracellular Ca(2+) or in the presence of tetrodotoxin, while ATP had no effect on GABA release from cultured rat hippocampal astrocytes or postsynaptic GABA-gated channel currents in cultured rat hippocampal neurons. Twenty-minutes deprivation of glucose and oxygen from extracellular solution abolished PSs, the amplitude recovering to about 30% of basal levels 50 min after returning to normal conditions. ATP or alpha,beta-MeATP accelerated the recovery after hypoxic/hypoglycemic insult (approximately 80% of basal levels). Adenosine diphosphate and adenosine monophosphate accelerated the recovery, but to a much lesser extent, and adenosine had no effect. The results of the present study thus suggest that ATP inhibits neuronal activity by enhancing neuronal GABA release via a P(2) receptor, perhaps a P2X receptor, thereby protecting against hypoxic/hypoglycemic perturbation of hippocampal neurotransmission.
- Published
- 2002
25. Molecular dynamics simulation of a single polymer chain in vacuum and in solution
- Author
-
Tetsuya Sato and Susumu Fujiwara
- Subjects
Persistence length ,chemistry.chemical_classification ,Quenching ,Structure formation ,Materials science ,Computer simulation ,General Physics and Astronomy ,Polymer ,Molecular dynamics ,Chain (algebraic topology) ,chemistry ,Correlation function ,Hardware and Architecture ,Chemical physics ,Physical chemistry - Abstract
Molecular dynamics simulations are carried out to study the structure formation of a single polymer chain in vacuum and in solution. We find that, in both cases, the folded orientationally ordered structure is formed at a low temperature by quenching from a random configuration at a higher temperature. It is also found that the stem length of the folded orientationally ordered structure formed in solution is longer than that formed in vacuum. This result is caused by the fact that the persistence length of a polymer chain in solution becomes longer than that in vacuum.
- Published
- 2002
26. Interleukin (IL)-17 versus IL-27: opposite effects on tumor necrosis factor-α-mediated chemokine production in human keratinocytes
- Author
-
Susumu Fujiwara, Hiroshi Nagai, Takayuki Yoshimoto, Shuntaro Oniki, and Chikako Nishigori
- Subjects
CXCL2 ,Interleukin 20 ,IL1A ,Chemistry ,Immunology ,Interleukin 12 ,CCL17 ,Dermatology ,CCL13 ,CCL7 ,Molecular Biology ,Biochemistry ,CXCL16 - Abstract
Tumor necrosis factor (TNF)-α is known to play a pivotal role in the pathogenesis of psoriasis. TNF-α has been shown to act directly on keratinocytes, thereby inducing the production of various kinds of chemokines, which contributes to the infiltration of leucocytes into the psoriatic lesions. Recent studies have shown that both interleukin (IL)-17 and IL-27 are increased in psoriatic lesional tissue. However, the interactions between TNF-α, IL-17 and IL-27 in chemokine production by keratinocytes have not been fully elucidated. Here, we examined in human keratinocytes how TNF-α, IL-17 and IL-27 affect production of chemokines that are involved in the pathogenesis of psoriasis. We found that IL-17 and IL-27 exert opposite effects on TNF-α-mediated chemokine production. This suggests that lesional balance of IL-17 and IL-27 is involved in the recruitment of T cells, natural killer cells, neutrophils, monocytes or dendritic cells, thereby affecting inflammation in skin diseases.
- Published
- 2011
27. Molecular dynamics study of structure formation of a single polymer chain by cooling
- Author
-
Tetsuya Sato and Susumu Fujiwara
- Subjects
Quenching ,chemistry.chemical_classification ,Molecular dynamics ,chemistry.chemical_compound ,Materials science ,Structure formation ,Chain (algebraic topology) ,chemistry ,Hardware and Architecture ,Chemical physics ,General Physics and Astronomy ,Polymer ,Methylene - Abstract
Structure formation of a single polymer chain with 500 methylene groups is investigated by means of a molecular dynamics simulation. We find that the folded orientationally ordered structure is formed at a low temperature by gradual stepwise cooling or by quenching from a random configuration at a higher temperature. It is also found that the global orientational order grows in a gradual manner in the case of gradual stepwise cooling, whereas it grows in a stepwise manner in the case of quenching.
- Published
- 2001
28. Structure formation of a single polymer chain. I. Growth of trans domains
- Author
-
Susumu Fujiwara and Tetsuya Sato
- Subjects
Quenching ,chemistry.chemical_classification ,Structure formation ,Chemistry ,General Physics and Astronomy ,Polymer ,Plasma ,Fundamental interaction ,Crystallography ,Molecular dynamics ,Chain (algebraic topology) ,Chemical physics ,Physical and Theoretical Chemistry ,Stable state - Abstract
Molecular dynamics simulations are carried out to study structure formation of a single polymer chain with 500 CH2 groups. Our simulations show that the orientationally ordered structure is formed at a low temperature both by gradual stepwise cooling and by quenching from a random configuration at a higher temperature. The growth of the global orientational order proceeds in a gradual manner in the case of gradual stepwise cooling, whereas it proceeds in a stepwise manner in the case of quenching. The latter feature endorses the previously proposed hypothetical grand view of self-organization [e.g., see T. Sato, Phys. Plasmas 3, 2135 (1996)]: when a system is driven far from equilibrium, it will evolve to a more stable state in a stepwise fashion irrespective of its fundamental interaction forces. From the microscopic analysis of the structure formation process, we find the following characteristic features: (i) In the case of gradual stepwise cooling, the global orientational order grows gradually throug...
- Published
- 2001
29. Molecular dynamics simulation of structure formation of short chain molecules
- Author
-
Susumu Fujiwara and Tetsuya Sato
- Subjects
Crystallography ,Molecular dynamics ,Quenching (fluorescence) ,Structure formation ,Chain (algebraic topology) ,Chemistry ,Chemical physics ,Phase (matter) ,Hexagonal phase ,General Physics and Astronomy ,Molecule ,Orthorhombic crystal system ,Physical and Theoretical Chemistry - Abstract
Molecular dynamics simulations are carried out to study the structure formation of 100 short chain molecules, each of which consists of 20 CH2 groups. Our simulations show that the orientationally ordered structure is formed from a random configuration by quenching. The global orientational order starts to increase suddenly after a certain duration and grow in a stepwise fashion afterwards. This behavior is also found in the growth process of the local orientationally-ordered domains. It is found from the microscopic analysis of the structure formation process, that parallel ordering of chain molecules starts to occur after the chain molecules stretch to some extent. From the analysis of the obtained orientationally ordered structure and the molecular mobility, we also find the following characteristic features: (i) The chain molecules are packed hexagonally at 400 K and the transition from the hexagonal phase toward the orthorhombic phase takes place as the temperature decreases. (ii) The gauche bonds in...
- Published
- 1999
30. Molecular Dynamics Study of the Structural Formation of Short Chain Molecules: Structure and Molecular Mobility
- Author
-
Susumu Fujiwara and Tetsuya Sato
- Subjects
Chemistry ,Hexagonal crystal system ,General Chemical Engineering ,Structure (category theory) ,General Chemistry ,Condensed Matter Physics ,Molecular dynamics ,Transverse plane ,Lattice constant ,Chain (algebraic topology) ,Computational chemistry ,Chemical physics ,Modeling and Simulation ,Monolayer ,Molecule ,General Materials Science ,Information Systems - Abstract
By carrying out molecular dynamics simulations of 100 short chain molecules, each of which consists of 20 CH2 groups, we show that the orientationally ordered structure is formed at low temperature by a sudden cooling from a random configuration at high temperature. The essentially extended chains form a monolayer structure. The ratio of the lattice constants a/b takes the hexagonal value ∼3 at 400 K and decreases as the temperature decreases. From detailed analysis of the local orientational order, it is found that the growth of the local ordered clusters proceeds in a stepwise fashion. From the analysis of the molecular mobility, we find that the longitudinal chain motion increases dramatically with increasing temperature while the transverse chain motion is not sensitive to the temperature variation.
- Published
- 1999
31. Freezing of High-Temperature Phase in Vinylidene Fluoride/Trifluoroethylene Copolymer Crystals on Vacuum-Evaporated Metal Surfaces
- Author
-
Thuy-Trang Hua, Jian-An Hou, Masato Hashimoto, Takashi Itoh, and Susumu Fujiwara
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Annealing (metallurgy) ,General Engineering ,Analytical chemistry ,General Physics and Astronomy ,Cyclohexanone ,Metal ,chemistry.chemical_compound ,chemistry ,Vinylidene fluoride-trifluoroethylene copolymer ,visual_art ,Polymer chemistry ,Copolymer ,visual_art.visual_art_medium ,Molecule ,Thin film ,Fluoride - Abstract
Vinylidene fluoride/trifluoroethylene copolymer thin films cast from dilute cyclohexanone solution on vacuum-evaporated Pt, Al, Cu, and Au were annealed at 420 K for 1 h. Transmission electron microscopic observation revealed that the high-temperature phase (HP) of the copolymers was frozen even at room temperature with molecular chains normal to the substrate after the annealing. The maximum lattice mismatch was 3.3% between the (001) plane of the HP of the copolymers and the {111} or {110} plane of the Pt crystals. Coulomb's interaction between the copolymer molecules and metallic atoms is suggested to have an important role in causing such phenomena.
- Published
- 2007
32. Molecular Dynamics Simulation of Structural Formation of Short Polymer Chains
- Author
-
Susumu Fujiwara and Tetsuya Sato
- Subjects
chemistry.chemical_classification ,Molecular dynamics ,Materials science ,chemistry ,Chemical physics ,General Physics and Astronomy ,Polymer - Published
- 1998
33. Molecular dynamics simulations of structural formation of a single polymer chain: Bond-orientational order and conformational defects
- Author
-
Susumu Fujiwara and Tetsuya Sato
- Subjects
chemistry.chemical_classification ,Quantitative Biology::Biomolecules ,Hexagonal symmetry ,Molecular dynamics ,Crystallography ,chemistry ,Chemical physics ,Surface change ,General Physics and Astronomy ,Polymer ,Physical and Theoretical Chemistry ,Anisotropy ,Gyration - Abstract
The structural formation of a single polymer chain with 500 CH2 groups is studied by the molecular dynamics simulations. Our simulations show that the bond-orientationally ordered structure at low temperatures is formed from a random-coil structure at high temperatures by a gradual stepwise cooling. From the radii of gyration and the bond-orientational order parameters, it is found that the anisotropy of a polymer chain also grows during the growth of the bond-orientational order. In the bond-orientationally ordered structure at low temperatures, 16 stems form a structure with deformed hexagonal symmetry and the stems in the outer layer have a tilted configuration. Furthermore, the gauche states are localized in the fold surface and the conformational states in the fold surface change more readily than those in the orientationally-ordered region.
- Published
- 1997
34. Molecular dynamics simulation of amphiphilic molecules in solution: micelle formation and dynamic coexistence
- Author
-
Susumu Fujiwara, Takashi Itoh, Ritoku Horiuchi, and Masato Hashimoto
- Subjects
Coalescence (physics) ,Quenching (fluorescence) ,Chemistry ,General Physics and Astronomy ,Flory–Huggins solution theory ,Micelle ,Condensed Matter::Soft Condensed Matter ,Hydrophobic effect ,Molecular dynamics ,Chemical physics ,Computational chemistry ,Lyotropic liquid crystal ,Amphiphile ,Physics::Chemical Physics ,Physical and Theoretical Chemistry - Abstract
The micelle formation and the dynamic coexistence in amphiphilic solution are investigated by molecular dynamics simulation of coarse-grained rigid amphiphilic molecules with explicit solvent molecules. Our simulations show that three kinds of isolated micelles (disk, cylindrical, and spherical micelles) are observed at a lower temperature by quenching from a random configuration of amphiphilic molecules in solution at a higher temperature. The micellar shape changes from a disk into a cylinder, and then into a sphere as the hydrophilic interaction increases whereas it is not so sensitive to the variation of the hydrophobic interaction. This fact indicates that the hydrophilic interaction plays an important role in determining the micellar shape in the range of the interaction parameters used. It is also found that in a certain interaction parameter range, two kinds of micellar shapes coexist dynamically. From the detailed analyses of the dynamic coexistence, it is ascertained that the dynamic coexistence of a cylindrical micelle and a spherical micelle accompanies the coalescence and fragmentation of micelles while that of a disk micelle and a cylindrical micelle does not, but exhibits the continuous change between them.
- Published
- 2009
35. Novel Primary Dispersion in Viscoelastic Behavior of Ferroelectric Nylon 6
- Author
-
Masato Hashimoto, Tsutomu Takahashi, Takashi Itoh, and Susumu Fujiwara
- Subjects
Primary (chemistry) ,Materials science ,Polymers and Plastics ,Activation energy ,Ferroelectricity ,Viscoelasticity ,chemistry.chemical_compound ,Nylon 6 ,chemistry ,Polyamorphism ,Dispersion (optics) ,Polymer chemistry ,Materials Chemistry ,Composite material - Published
- 2009
36. Molecular dynamics simulation of the structural formation of polymer chains
- Author
-
Susumu Fujiwara and Tetsuya Sato
- Subjects
chemistry.chemical_classification ,Molecular dynamics ,Materials science ,Lennard-Jones potential ,chemistry ,Chemical physics ,Polymer ,Molecular physics - Published
- 1999
37. Shape transition of micelles in amphiphilic solution: A molecular dynamics study
- Author
-
Hiroaki Nakamura, Masato Hashimoto, Takashi Itoh, Yuichi Tamura, and Susumu Fujiwara
- Subjects
Quantitative Biology::Biomolecules ,History ,Chemistry ,Potential energy ,Micelle ,Computer Science Applications ,Education ,Condensed Matter::Soft Condensed Matter ,Solvent ,Molecular dynamics ,Lyotropic liquid crystal ,Chemical physics ,Computational chemistry ,Amphiphile ,Cylinder ,Molecule - Abstract
The shape transition of micelles in an amphiphilic solution is studied by a molecular dynamics simulation of coarse-grained rigid amphiphilic molecules with explicit solvent molecules. Our simulations show that the micellar shape changes from a disc into a cylinder, and then into a sphere as the hydrophilic interaction increases. We find that the potential energy decreases monotonically even during the micellar shape transition as the hydrophilic interaction increases. In contrast, it is ascertained that there exists a wide coexistence region in the intensity of the hydrophilic interaction between a cylinder and a sphere.
- Published
- 2013
38. Comparison of Hydrogen Adsorption on Diamond and Graphite Surfaces
- Author
-
Yuichi Tamura, Noriyasu Ohno, Atsuhi M. Ito, Susumu Fujiwara, Hiroaki Nakamura, Shin Kajita, and Seiki Saito
- Subjects
Materials science ,Hydrogen ,Material properties of diamond ,Analytical chemistry ,chemistry.chemical_element ,Nanotechnology ,engineering.material ,surface structure ,Molecular dynamics ,diamond ,Graphite ,armchair ,graphite ,carbon ,Diamond ,Hydrogen atom ,Condensed Matter Physics ,zigzag ,molecular dynamics simulation ,chemistry ,Zigzag ,edge state ,hydrogen ,engineering ,sputtering ,Carbon - Abstract
By a classical molecular dynamics (CMD) simulation with a modified Brenner's reactive empirical bond-order (REBO) potential, we found that graphite with zigzag (1010) and armchair (1120) edge states is destroyed more easily than other structures, i.e., graphite with the (0001) surface, and diamond with the (100), (111), (120), and (110) surfaces. Experimental results indicated that graphite is eroded under hydrogen atom injection with Ein = 0.3 eV, and that diamond is not eroded under the same conditions. Our simulation results are consistent with these experimental results. We also reveal the temperature and saturation dependence of the surface structure of carbon crystals.
- Published
- 2010
39. Molecular Dynamics Simulation for Structure Formation of Single Polymer Chain in Solution
- Author
-
Hiroaki Nakamura, Takashi Itoh, Masato Hashimoto, and Susumu Fujiwara
- Subjects
chemistry.chemical_classification ,Conformational change ,Materials science ,Quenching (fluorescence) ,Structure formation ,General Physics and Astronomy ,Polymer ,Solvent ,Molecular dynamics ,Chain (algebraic topology) ,chemistry ,Chemical physics ,Physical chemistry ,Molecule - Abstract
The structure formation of a single polymer chain in solution with explicit solvent molecules is investigated by molecular dynamics simulation. The orientationally ordered structure is formed at a low temperature by quenching from a random conformation at a high temperature. The growth of the global and local orientational order proceeds in a stepwise manner at T ≥350 K, whereas it proceeds in a gradual manner at T =300 K. From the detailed analyses of the parallel ordering process, it is found that a conformational change of the polymer chain occurs at first, and then parallel ordering starts to take place. In comparison with the simulation results of an isolated polymer chain in vacuum, it is ascertained that the stem length of the orientationally ordered structure formed in solution becomes 2–3 times longer than that formed in vacuum.
- Published
- 2006
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