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RISS 인기검색어
- 검색키워드
- 저자 : Rekharsky, Mikhail V. (검색결과 3 건)
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Rekharsky, Mikhail V.,Yamamura, Hatsuo,Mori, Tadashi,Sato, Akihiro,Shiro, Motoo,Lindeman, Sergey V.,Rathore, Rajendra,Shiba, Kouhei,Ko, Young Ho,Selvapalam, Narayanan,Kim, Kimoon,Inoue, Yoshihisa WILEY-VCH Verlag 2009 Chemistry Vol.15 No.8
<P>Water seeds: Complex stoichiometry/composition and degree of oligomerization (oligomeric supramolecular complex formation) of cucurbit[6]uril (CB[6]) with N-alkyl- and N,N′-dialkylpiperazine were investigated in aqueous solutions by means of isothermal titration calorimetry (ITC), ESI-MS, NMR and light scattering measurements. <img src='wiley_img/09476539-2009-15-8-CHEM200800398-content.gif' alt='wiley_img/09476539-2009-15-8-CHEM200800398-content'> </P><P>Complex stoichiometry/composition and degree of oligomerization (oligomeric supramolecular complex formation) of cucurbit[6]uril (CB[6]) with N-alkyl- and N,N′-dialkylpiperazine were investigated in aqueous solutions by means of isothermal titration calorimetry (ITC), ESI-MS, NMR and light scattering measurements. It was found that the complex stability and the degree of oligomerization increase with elongating the alkyl chain attached to the piperazine core. X-ray crystallographic studies revealed a clear correlation between the structure of CB[6]–alkylpiperazine crystals obtained from aqueous solutions and the molecular weight/properties of host–guest oligomers existed in the solution as supramolecular “seeds” of crystal formation.</P> <B>Graphic Abstract</B> <P>Water seeds: Complex stoichiometry/composition and degree of oligomerization (oligomeric supramolecular complex formation) of cucurbit[6]uril (CB[6]) with N-alkyl- and N,N′-dialkylpiperazine were investigated in aqueous solutions by means of isothermal titration calorimetry (ITC), ESI-MS, NMR and light scattering measurements. <img src='wiley_img/09476539-2009-15-8-CHEM200800398-content.gif' alt='wiley_img/09476539-2009-15-8-CHEM200800398-content'> </P>
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Rekharsky, Mikhail V,Mori, Tadashi,Yang, Cheng,Ko, Young Ho,Selvapalam, N,Kim, Hyunuk,Sobransingh, David,Kaifer, Angel E,Liu, Simin,Isaacs, Lyle,Chen, Wei,Moghaddam, Sarvin,Gilson, Michael K,Kim, Kimo National Academy of Sciences 2007 Proceedings of the National Academy of Sciences Vol.104 No.52
<P>The molecular host cucurbit[7]uril forms an extremely stable inclusion complex with the dicationic ferrocene derivative bis(trimethylammoniomethyl)ferrocene in aqueous solution. The equilibrium association constant for this host-guest pair is 3 x 10(15) M(-1) (K(d) = 3 x 10(-16) M), equivalent to that exhibited by the avidin-biotin pair. Although purely synthetic systems with larger association constants have been reported, the present one is unique because it does not rely on polyvalency. Instead, it achieves its extreme affinity by overcoming the compensatory enthalpy-entropy relationship usually observed in supramolecular complexes. Its disproportionately low entropic cost is traced to extensive host desolvation and to the rigidity of both the host and the guest.</P>
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Kim, Youngkook,Kim, Hyunuk,Ko, Young Ho,Selvapalam, Narayanan,Rekharsky, Mikhail V.,Inoue, Yoshihisa,Kim, Kimoon WILEY-VCH Verlag 2009 Chemistry Vol.15 No.25
<P>Without interference: The complexation of aliphatic ammonium ions with a water-soluble cucurbit[6]uril (CB[6]) derivative, CB*[6] (see picture), in pure water is investigated by isothermal titration calorimetry, NMR spectroscopy, and X-ray crystallography. The binding affinity of the host in pure water is 2–5 orders of magnitude higher than that in the presence of interfering ions, such as protons and alkali metal ions. <img src='wiley_img/09476539-2009-15-25-CHEM200900305-content.gif' alt='wiley_img/09476539-2009-15-25-CHEM200900305-content'> </P><P>Complexation of a water-soluble cucurbituril (CB) derivative, cyclohexanocucurbit[6]uril (CB*[6]), the cavity dimensions of which are essentially the same as those of CB[6], with various organic mono- and diammonium ions has been studied by isothermal titration calorimetry and <SUP>1</SUP>H NMR spectroscopy. The binding affinity of CB*[6] with the guest molecules in water is 3–5 and 2–3 orders of magnitude higher than those of CB[6] in 50 % formic acid and in 0.05 m NaCl solution, respectively, which is mainly due to the larger enthalpic gains upon complex formation in the absence of interfering ions, such as protons and Na<SUP>+</SUP>. In particular, the binding constant (K) of spermine to CB*[6] was measured to be 3.4×10<SUP>12</SUP> m<SUP>−1</SUP>, which is the highest binding constant ever reported for CB[6] or its derivatives. We also obtained the X-ray crystal structures of α,ω-alkanediammonium ions (C<SUB>n</SUB>DA<SUP>2+</SUP>, n=4–8) and spermine complexes with CB[6], in which the aliphatic chains of the guest molecules take an extended or partially bent conformation inside the CB[6] cavity, depending on the chain length. The hexamethylene chain of C<SUB>6</SUB>DA<SUP>2+</SUP> takes a twisted conformation, which not only allows strong ion–dipole interactions between the ammonium groups and the carbonyl groups at the portals, but also increases hydrophobic interactions between the alkyl part of the guest and the inner wall of the host, which results in the largest enthalpic gain among α,ω-alkanediammonium ions. The thermodynamic parameters associated with the complexation are discussed in relation to the binding modes and conformations of the aliphatic chain of the guest molecules inside the host, which were investigated by <SUP>1</SUP>H NMR spectroscopy and X-ray crystallography.</P> <B>Graphic Abstract</B> <P>Without interference: The complexation of aliphatic ammonium ions with a water-soluble cucurbit[6]uril (CB[6]) derivative, CB*[6] (see picture), in pure water is investigated by isothermal titration calorimetry, NMR spectroscopy, and X-ray crystallography. The binding affinity of the host in pure water is 2–5 orders of magnitude higher than that in the presence of interfering ions, such as protons and alkali metal ions. <img src='wiley_img/09476539-2009-15-25-CHEM200900305-content.gif' alt='wiley_img/09476539-2009-15-25-CHEM200900305-content'> </P>
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