• 제목/요약/키워드: dissociation of acid

검색결과 136건 처리시간 0.024초

Computational Study on Protolytic Dissociation of HCl and HF in Aqueous Solution

  • Kim, Chang Kon;Park, Byung Ho;Sohn, Chang Kook;Yu, Yu Hee;Kim, Chan Kyung
    • Bulletin of the Korean Chemical Society
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    • 제35권4호
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    • pp.1029-1035
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    • 2014
  • The protolytic dissociation process of hydrochloric acid (HCl) and hydrofluoric acid (HF) is studied using the B3LYP and MP2 methods with the 6-311+G(d,p) basis set in the gas phase and in aqueous solution. To study the phenomena in detail, discrete and discrete/continuum models were applied by placing water molecules in various positions around the acid. The dissociation process was studied using the thermodynamic cycle involving the structures optimized both in the gas phase and in aqueous solution and was analyzed with two key energy factors, relaxation free energy (${\Delta}G_{Rex(g)}$) and solvation free energy (${\Delta}G_s$). Based on the results, we could understand the dissociation mechanism and wish to propose the best way to study acid dissociation process using the CPCM methodology in aqueous solution.

Ascorbic Acid가 Carboxyhemoglobin의 해리속도항수에 미치는 영향 (Influence of Ascorbic Acid on Velocity Constant of Carboxyhemoglobin Dissociation)

  • 심길순
    • 약학회지
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    • 제8권3호
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    • pp.62-68
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    • 1964
  • Author has determined the dissociation velocity constant of carboxyhemoglobin in cattle blood solution by addition of ascorbic acid at $36-38{\deg}.$ It was found that these kinetic data are concordant with Roughton's equation d[COHb]/dt = $m^{'}[CO][O_{2}Hb]/[O_{2}$ - m[COHb] and that the dissociation velocity constant of carboxyhemoglobin was accelerated by the presence of ascorbic acid from 0.119 to 0.135.

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유기산의 해리평형에 미치는 치환기 효과와 그의 온도 및 압력의 영향 (제 7 보). 수용액중에서 몇가지 ${\omega}$-아미노산의 해리 (The Effects of Substituent, Pressure and Temperature on the Dissociation Constants of Organic Acids (VII). Dissociation Constants of Some ${\omega}$-Amino Acid in Aqueous Solution)

  • 황정의;곽영우;정재원
    • 대한화학회지
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    • 제33권4호
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    • pp.343-349
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    • 1989
  • ${\omega}$-아미노산인 ${\beta}$-alanine과 ${\gamma}$-aminobutyric acid의 해리상수를 전도도법을 이용하여 온도($20{\sim}40^{\circ}C$)와 압력($1{\sim}2500$ bar)을 변화시키면서 측정하였다. 각각 아미노산의 두 가지 해리상수는 온도가 증가하면 증가하지만 압력이 증가하면 $K_1$은 증가하지만 $K_2$는 감소하였다. 해리상수를 이용하여 여러 가지 열역학적 성질들을 계산하고 이들로부터 해리반응의 특성을 알아보았다. ${\omega}$-아미노산의 해리상수를 해리기와 치환기간의 거리의 상관관계로 알아보았다. 반응특성을 알아보기 위해 Hammett 법칙을 적용하여 반응의 치환기 상수와 압력에 따른 반응상수를 계산하였다. ${\omega}$-아미노산의 특성을 치환기 효과로 설명하고 반응유형을 반응상수로서 알아보았다.

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Thermal Dissociation and Conformational Lock of Superoxide Dismutase

  • Hong, J.;Moosavi-Movahedi, A.A.;Ghourchian, H.;Amani, M.;Amanlou, M.;Chilaka, F.C.
    • BMB Reports
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    • 제38권5호
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    • pp.533-538
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    • 2005
  • The kinetics of thermal dissociation of superoxide dismutase (SOD) was studied in 0.05 M Tris-HCl buffer at pH 7.4 containing $10^{-4}\;M$ EDTA. The number of conformational locks and contact areas and amino acid residues of dimers of SOD were obtained by kinetic analysis and biochemical calculation. The cleavage bonds between dimers of SOD during thermal dissociation and type of interactions between specific amino acid residues were also simulated. Two identical contact areas between two subunits were identified. Cleavage of these contact areas resulted in dissociation of the subunits, with destruction of the active centers, and thus, lost of activity. It is suggested that the contact areas interact with active centers by conformational changes involving secondary structural elements.

Electron Capture Dissociation Mass Spectrometry for Gaseous Protonated Melittin Ions and Its Single Amino Acid Substituted Variants

  • Yu, Seonghyun;Jang, Hwa-yong;Oh, Han Bin
    • Mass Spectrometry Letters
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    • 제10권4호
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    • pp.117-122
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    • 2019
  • This study demonstrated the sensitivity of electron capture dissociation mass spectrometry (ECD-MS) to probe subtle conformational changes in gaseous melittin ions induced by the substitution of an amino acid. ECD-MS was performed for triply and quadruply-protonated melittin and its variants obtained by a single amino acid substitution, namely, D-Pro14, Pro14Ala, and Leu13Ala. Although native triply-protonted melittin showed only a few peptide backbone cleavage products, the D-Pro14 and Pro14Ala variants exhibited extensive backbone fragments, suggesting the occurrence of a significant structural or conformational change induced by a single amino acid substitution at Pro14. On the contrary, the substitution at Leu13, namely Leu13Ala (+3), did not cause significant changes in the ECD backbone fragmentation pattern. Thus, the sensitivity of ECD-MS is demonstrated to be good enough to probe the aforementioned conformational change in melittin.

Formation and Dissociation Kinetics of Tetraaza-Crown-Alkanoic Acid Complexes of Cerium(Ⅲ)

  • 최기영;김동원;정용순;김창석;홍춘표;이용일
    • Bulletin of the Korean Chemical Society
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    • 제19권6호
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    • pp.671-676
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    • 1998
  • The formation and dissociation rates of $Ce^{3+}$ Complexes of the 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-NN', N",N"'-tetraacetic acid (1), 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-N,N',N",N"'-tetramethylacetic acid (2), and 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-N,N',N",N"'-tetrapropionic acid (3) have been measured by the use of stopped-flow spectrophotometry. Observations were made at 25.0±0.1 ℃ and at an ionic strength of 0.10 M $NaClO_4$. The complexation of $Ce^{3+}$ ion with 1 and 2 proceeds through the formation of an intermediate complex $(CeH_3L^{2+})^*$ in which the $Ce^{3+}$ ion is incompletely coordinated. This may then lead to be a final product in the rate-determining step. Between pH 4.76 and 5.76, the diprotonated $(H_2L^{2-})$ from is revealed to be a kinetically active species despite of its low concentration. The stability constants $(logK(CeH_3L^{2+}))$ and specific water-assisted rate constants $(k_{OH})$ of intermediate complexes have been determined from the kinetic data. The dissociation reactions of $Ce^{3+}$ complexes of 1, 2, and 3 were investigated with $Cu^{2+}$, ions as a scavenger in acetate buffer. All complexes exhibit acid-independent and acid-catalyzed contributions. The effect of buffer and $Cu^{2+}$ concentration on the dissociation rate has also been investigated. The ligand effect on the dissociation rate of $Ce^{3+}$ complexes is discussed in terms of the side-pendant arms and the chelate ring sizes of the ligands.

Temperature, Medium and Structural Effects on the Acid Dissociation Constants of Certain Schiff Bases Derived from Isatin with Some Amino Acids and Aroylhydrazines

  • Hassaan, Aly M.A.;Quenawy, M.T.A.
    • Archives of Pharmacal Research
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    • 제16권3호
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    • pp.180-185
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    • 1993
  • The acid dissociation constants of certain Schiff bases derived from isatin with p-substituted benzoyl hydrazines and somee amino acids of glycine, $\beta$-and $\alpha$-alanine, valine, $\beta$-phenyl-$\alpha$-alanine and anthranilic acid have been detemined potentiometrically at different temperatures in different aquo-organic solvent mixtures (ethnol, dioxane, dimethyl formamide, methanol, acetone and tetrahydrofurance). The pKa values were demonstrated on the light of the different electornic and steric effects of the substituents and the sovlent characteristics. In all the mixed media used, ionization of the compounds decreased by increasing the mole fraction of the organic cosolvent. Theemodynamic parameters $(\Delta{H}^\circ,\;\Delta{G}^\circ,\;\Delta{S}^\circ)$ were evaluated. The structural effects of the investigated compounds on these parameters were reported and discussed.

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Collisionally-Activated Dissociation of Peptides with a Disulfide Bond: Confirmation of the Mobile-Proton Model Based Explanation

  • Lee, Youn-Jin;Oh, Han-Bin
    • Mass Spectrometry Letters
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    • 제1권1호
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    • pp.5-8
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    • 2010
  • In the present study, collisionally-activated dissociation (CAD) experiments were performed under low energy collision conditions in six peptides containing a disulfide bond. Fragments produced as a result of the cleavage of a disulfide bond were obtained after CAD in four peptides (bactenecin, TGF-$\alpha$, cortistantin, and linearly linked peptide, Scheme 1) with basic amino acid residues. In contrast, the CAD analysis of two peptides with no basic residue (oxytocin and tocinoic acid) rarely produced fragments indicative of cleavage of a disulfide bond. These results are consistent with the mobile proton model suggested by the McLuckey and O'air groups (ref. 22 and 23); nonmobile protons sequestered at basic amino acid residues appear to promote the cleavage of disulfide bonds.

Dimethylformamide 수용액중에서의 Sulfa제-Cu 착화합물의 안정도정수 (Stability Constants of Copper Sulfa-Drug Complexes in Dimethylformamide Aqueous Solution)

  • 이왕규
    • 약학회지
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    • 제9권1_2호
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    • pp.4-7
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    • 1965
  • Acid dissociation constants of sulfamethoxypyridazine, sulfadimethoxine, sulfamerazine, sulfathiazole and sulfadiazine, and stability constants for formation of copper chelate were calculated from their titration curves in 80% dimethylformamide with ionic strength 0.1 at $25{\deg}$ It was found that the acid dissociation constants (pKa) of sulfa-drugs were in the range of 9.33 - 10.05, and the stability constants (log $k_{1}$, $k_{2})$ of their copper chelates were in the range of 9.33-9.71.

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