• 제목/요약/키워드: Molecular electrostatic potential

검색결과 48건 처리시간 0.02초

용매 극성도의 이론적 예측 연구 (An ab Initio Predictive Study on Solvent Polarity)

  • 박민규;조수경
    • 한국군사과학기술학회지
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    • 제11권3호
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    • pp.154-160
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    • 2008
  • We investigated molecular polarity by using theoretical means and comparing empirical solvent polarity. Our approach employed electrostatic potentials at the molecular surface calculated by density functional methods. A number of molecular descriptors related to molecular polarities were computed from molecular surface electrostatic potentials. Among computed molecular descriptors, the most positive electrostatic potential provided the best correlation with the empirical solvent polarities. A regression equation was developed in order to predict molecular polarities of molecules whose experimental solvent polarities were unknown. The new regression equations were utilized in estimating solvent polarities of cubane derivatives which are considered important precusors of high-energy density meterials.

부분 전하의 의미와 정의 (Meaning and Definition of Partial Charges)

  • 조승주
    • 통합자연과학논문집
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    • 제3권4호
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    • pp.231-236
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    • 2010
  • Partial charge is an important and fundamental concept which can explain many aspects of chemistry. Since a molecule can be regarded as neclei surrounded by electron cloud, there is no way to define a partial charge accurately. Nevertheless, there have been many attempts to define these seemingly impossible parameters, since they would facilitate the understanding of molecular properties such as molecular dipole moment, solvation, hydrogen bonding, molecular spectroscopy, chemical reaction, etc. Common methods are based on the charge equalization, orbital occupancy, charge density, and electric multipole moments, and electrostatic potential fitting. Methods based on the charge equalization using electronegativity are very fast, and therefore they have been used to study many compounds. Methods to subdivide orbital occupancy using basis set conversion, relies on the notion that molecular orbitals are composed of atomic orbitals. The main idea is to reduce overlap integral between two nuclei using converted orthogonal basis sets. Using some quantum mechanical observables like electrostatic potential or charge multipole moments. Using potential grids obtained from wavefunction, partial charges can be fitted. these charges are most useful to describe intermolecular electrostatic interactions. Methods to using dipole moment and its derivatives, seems to be sensitive the level of theory, Dividing electron density using density gradient being the most rigorous theoretically among various schemes, bears best potential to describe the charge the most adequately in the future.

Theoretical Study of the N-(2,5-Methylphenyl)salicylaldimine Schiff Base Ligand: Atomic Charges, Molecular Electrostatic Potential, Nonlinear Optical (NLO) Effects and Thermodynamic Properties

  • Zeyrek, Tugrul C.
    • 대한화학회지
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    • 제57권4호
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    • pp.461-471
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    • 2013
  • Optimized geometrical structure, atomic charges, molecular electrostatic potential, nonlinear optical (NLO) effects and thermodynamic properties of the title compound N-(2,5-methylphenyl)salicylaldimine (I) have been investigated by using ab initio quantum chemical computational studies. Calculated results showed that the enol form of (I) is more stable than keto form. The solvent effect was investigated for obtained molecular energies, hardneses and the atomic charge distributions of (I). Natural bond orbital and frontier molecular orbital analysis of the title compound were also performed. The total molecular dipole moment (${\mu}$), linear polarizability (${\alpha}$), and first-order hyperpolarizability (${\beta}$) were calculated by B3LYP method with 6-31G(d), 6-31+G(d,p), 6-31++G(d,p), 6-311+G(d) and 6-311++G(d,p) basis sets to investigate the NLO properties of the compound (I). The standard thermodynamic functions were obtained for the title compound with the temperature ranging from 200 to 450 K.

캘빈방전 효과를 이용한 초순수 및 전해이온수의 정전기 방전 연구 (A Study on Electrostatic Discharging in Ultrapure and Electrolyzed Waters Using Kelvin's Thunderstorm Effect)

  • 김형원;정윤원;최인식;최병선;최동현;유근걸
    • 반도체디스플레이기술학회지
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    • 제21권1호
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    • pp.5-11
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    • 2022
  • Despite the increasing importance of manufacturing and application R&D for ultrapure deionized water and electrolyzed ion water, various and systematic studies have not been conducted until now. In this study, the electrostatic discharge (ESD) behavior of electrolyzed ion water using a proton exchange membrane(PEM) was evaluated according to the type, flow rate, and bubble of electrolyzed ion water. In addition, by observing that Oxidation Reduction Potential (ORP) value returns to the unique value of electrolyzed ion water after electrostatic discharge, the possibility of two types of ions participating in electrostatic discharge ((H2O)n+ (assumed)) and ions for maintaining the characteristics of electrolyzed water could be inferred. In order to confirm the chemical structure and characteristics of the cations, in-depth research related to water molecular orbital energy or band gap should be followed.

Quantitative Structure-Activity Relationships (QSAR) Study on C-7 Substituted Quinolone

  • 이근우;권순영;황선구;이재욱;김호징
    • Bulletin of the Korean Chemical Society
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    • 제17권2호
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    • pp.147-152
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    • 1996
  • To see the quantitative relationship between the structures of the C-7 substituted quinolones and their antibacterial activities, theoretical parameters such as the molecular van der Waals volume, surface area and some electrostatic parameters based on the molecular electrostatic potential, which represent lipophilicity, and some quantum mechanical parameters are introduced as descriptors. The sixteen substituted quinolone derivatives and twenty bacteria are used for the study. It is found that the QSARs of C-7 substituted quinolones are obtained for eleven bacteria and our descriptors are more useful for Gram positive organisms than negative ones. It is also shown that molecular surface area (or molecular Waals volume) of the C-7 substituent and net charge of C-7 atom of the quinolones are the descriptors of utmost importance.

Experimental and Computational Approaches to the Molecular Structure of 3-(2-Mercaptopyridine)phthalonitrile

  • Tanak, Hasan;Koysal, Yavuz;Isik, Samil;Yaman, Hanifi;Ahsen, Vefa
    • Bulletin of the Korean Chemical Society
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    • 제32권2호
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    • pp.673-680
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    • 2011
  • The compound 3-(2-Mercaptopyridine)phthalonitrile has been synthesized and characterized by IR, UV-vis, and X-ray single-crystal determination. The molecular geometry from X-ray determination of the title compound in the ground state has been compared using the Hartree-Fock (HF) and density functional theory (DFT) with the 6-31G(d) basis set. The calculated results show that the DFT and HF can well reproduce the structure of the title compound. The energetic behavior of the title compound in solvent media was examined using the B3LYP method with the 6-31G(d) basis set by applying the Onsager and polarizable continuum model. Using the TD-DFT and TD-HF methods, electronic absorption spectra of the title compound have been predicted and good agreement with the TD-DFT method and the experimental determination was found. The predicted nonlinear optical properties of the title compound are much greater than those of urea. Besides, molecular electrostatic potential of the title compound were investigated by theoretical calculations. The thermodynamic properties of the compound at different temperatures have been calculated and corresponding relations between the properties and temperature have also been obtained.

치환 피리딘의 치환기 효과에 대한 Ab initio 연구 (Ab Initio Studies on Substituent Effects of Substituted Pyridines)

  • 이갑용;장만식
    • 대한화학회지
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    • 제43권4호
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    • pp.378-383
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    • 1999
  • 파라-치환 피리딘의 치환기 효과를 조사하기 위하여 Ab initio 계산을 수행하였다. 여러 치환 피리딘의 최적화 된 구조로부터 정전기전위를 계산한 결과 피리딘의 질소 원자에서 최소값을 나타내었으며, 최소정전기전위 값은 Hammett 치환기 상수, ${\sigma}_p$${\Delta}pKa$와 홀륭한 상관성이 있음을 알았다. 그 결과 최소정전기전위가 치환기 효과를 나타내는 척도로 사용될 수 있음을 알 수 있었다.

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Thermodynamic Model for Partition Coefficients in the Two Protein Systems

  • Jung, Chang-Min;Bae, Young-Chan;Kim, Jae-Jun
    • Macromolecular Research
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    • 제15권7호
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    • pp.682-687
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    • 2007
  • The equation of state developed herein is predicated on a hard-sphere reference with perturbations introduced via a potential function to account for electrostatic forces and for attraction between protein particles. During this process, the generalized Lennard-Jones (GLJ) pair potential function is employed. The GLJ pair potential function is employed to represent the protein-protein interaction in two-protein systems. Via the use of the relation between the equation of state and the chemical potential, the phase behavior in the aqueous two-protein system can be estimated. The partition coefficients can be obtained via these processes. The calculated values of the coefficients agree fairly well with the experimental data in the given pH and ionic strength range, with no additional adjustable model parameters.

다이옥신의 인체 독성에 영향을 미치는 물리화학적 인자에 대한 이론적 접근 (Theoretical Approach for Physicochemical Factors Affecting Human Toxicity of Dioxins)

  • 황인철;박형석
    • Environmental Analysis Health and Toxicology
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    • 제14권1_2호
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    • pp.65-73
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    • 1999
  • Dioxins refer to a family of chemicals comprising 75 polychlorinated dibenzo-p-dioxin (PCDD) and 135 polychlorinated dibenzo-p-furan (PCDF) congeners, which may cause skin disorder, human immune system disruption, birth defects, severe hormonal imbalance, and cancer. The effects of exposure of dioxin-like compounds such as PCBs are mediated by binding to the aryl hydrocarbon receptor (AHR), which is a ligand-activated transcription factor. To grasp physicochemical factors affecting human toxicity of dioxins, six geometrical and topological indices, eleven thermodynamic variables, and quantum mechanical descriptors including ESP (electrostatic potential) were analyzed using QSAR and semi-empirical AM1 method. Planar dioxins with high lipophilicity and large surface tension show the probability that negative electrostatic potential in the lateral oxygen may make hydrogen bonding with DNA bases to be a carcinogen.

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Characteristics of the Multi-Hydrogen Bonded Systems: DFT Description on the Solvated Electrons

  • Xu, Jun
    • Bulletin of the Korean Chemical Society
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    • 제34권11호
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    • pp.3265-3268
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    • 2013
  • The multi-hydrogen bonded systems with the solvated electrons are investigated at the B3LYP/6-311++$G^{**}$ basis set level. The symmetrical linear geometrical characteristic is common for the dimer systems, while for the tetramer system, the tetrahedron configuration is generated. The NBO charge analyses demonstrate that the multi-hydrogen-multi-electron (mH-ne) coupling exist in these anion systems, as is supported by the electrostatic potential and the molecular orbital analyses. The positive chemical shift value of the central hydrogen ($H_c$) and the negative chemical shift value of the terminal hydrogen ($H_t$) indicate that the $H_c$ is electronegative while the $H_t$ is electropositive, respectively. Strong coupling between two central hydrogen atoms is demonstrated by the large spin-spin coupling constants. The solvated electron donates significant contributions for the stability of these systems.