Cooperative Intramolecular Hydrogen Bonding Effect and Basicity –An Ab Initio and DFT Study of the Superbasic Properties ofN‐[(Dimethylamino)alkyl]‐2,3‐diaminocycloprop‐2‐ene‐1‐imines
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Abstract The MP2(fc)/6‐311+G**//HF/6‐31G* and B3LYP/6‐311+G**//HF/6‐31G* calculations show that N ‐[3‐(dimethylamino)propyl] and N ‐[4‐(dimethylamino)butyl] derivatives of 2,3‐diamino‐cycloprop‐2‐ene‐1‐imine (CPI) possess high gas phase proton affinities (PA) and pronounced basicities in acetonitrile (MeCN). Tris[ N ‐dimethylaminopropyl(‐butyl)]‐CPI derivatives achieve superbasic PA and p K a values. The reason behind these remarkable features is the stability of the resulting conjugate acids. They are stabilized by aromatization of the three‐membered ring accompanied by the cationic resonance between the cyclopropyl ring and amino nitrogen atoms of the side chains, and, last but not least, by the cooperative multiple intramolecular hydrogen bonding effect. The latter is particularly enhanced in tris‐substituted CPIs. It was found that the N ‐[4‐(dimethylamino)butyl] side chains contribute more to the stability of the conjugate acids than those of the corresponding compound with a propyl chain, because they undergo a somewhat larger relaxation upon protonation. The studied compounds might be helpful in building up a dense ladder of strong bases and superbases, which could contribute to the development of the chemistry of superacids and superbases. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)Keywords:
Aromatization
Imine
Proton affinity
Cationic polymerization
The protonation/deprotonation constants for uracil (U) (pK 1 and pK 2 ), thymine (T) (pK 1 ) and cytosine (C) (pK 1 and pK 2 ) in water have been determined from emf measurements of Harned–Ehler type cells comprising H 2 and Ag–AgI electrodes at five equidistant temperatures ranging from 15–35 °C. The pK a values were fitted in the temperature equation pK a = AT −1 + B + CT by the method of least squares and the standard free energies (ΔG 0 ), entropies (ΔS 0 ), and enthalpies (ΔH 0 ) of protonation/deprotonation processes in water were evaluated using the values of the coefficients A, B, and C of the respective acids. The second step deprotonation constant for T was determined using precise spectrophotometric method. The results have been duly compared with the existing literature data and are also shown to derive important reflections on the sites of protonation/deprotonation in the light of pK values of some acids and bases of comparable functional groups and especially the entropies of protonation/deprotonation of the key DNA–RNA base molecules.
Thymine
Uracil
Cytosine
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The protonation of diphosphinoamines attached to pyridine at the ortho-position quantitatively affords the corresponding iminobiphosphine isomers. The starting material can be recovered quantitatively by deprotonation with base. The system represents a new type of molecular switch.
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Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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본 논문에서는 산화 환원 효소의 최적 pH를 예측해 보았다. Boltzman 분배를 이용하여 어떤 아미노산의 side chain이 물에서 발견될수 있는 상대적 확률이나 물에 대한 상대적 친화력을 구하였으며 p$K_R$ 을 이용해 protonated 아미노산의 양과 deprotonated 아미소산의 양을 계산하였다. 효소의 최적 pH는 아미노산의 side chain이 물에서 발견될수 있는 상대적 확률과 protonated 또는 deprotonated된 아미노산 양의 곱인 유효 protonated된 양과 유효 depotonated된 양이 같아지는 pH로 예측하였다. 문헌 값과 비교해 보았을 때 예측치는 상당히 일치하는 경향을 보였으며 이 결과 로 효소 자체의 전도도가 생물학적 기능에 있어 매우 중요한 역할을 하는 것을 알 수있다. For various oxidoreductases, the optimum pHs of the enzymes can be calculated using the rule based on proton transfer. Relative probability of a certain amino acid side chain to be in the water, or the relative affinity to the water was calculated using Boltzman distribution. Also, the protonated and deprotonated portions of a certain amino acid side chain were calculated using p$K_R$ of that and the effective protonated and deprotonated protions were the product of relative probability and the protonated and deproteonated protions. Where the total effective protonated portion was equal to the effective deprotonated portion of amino acid side chains, it was expected that oxidoreductases have max-imum activities. The optimum pHs calculated by our rule were compared with the experimental results.
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Insights into the origin of the fluorescence responsive to protonation-deprotonation stimuli were provided through the study on the crystals of a new stimuli-responsive molecule BP3VA. And the transformation between microcrystals demonstrated the varying emissions of the BP3VA powder.
Organic molecules
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Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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Anthraquinones
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Two new C,N,N-type ligands (HL(2) and HL(3)), containing a C(phenyl), a N(pyridyl), and a N(imidazolyl) donor, and their cycloplatinated complexes, [Pt(L(2))Cl] (1), [Pt(L(3))Cl] (2), [Pt(L(2))(PPh(3))](+) (3) and [Pt(L(3))(PPh(3))](+) (4), have been successfully synthesized and characterized. Spectroscopic and (3)MLCT luminescent properties of these Pt(II) cyclometalated complexes were found to be pH dependent. This was attributed to the protonation/deprotonation of the acidic 1-imidazolyl-NH moieties on the ligands. All the cycloplatinated complexes (both protonated and deprotonated forms) possessed two-photon excitability with two-photon absorption cross-sections ranging from 6.0 to 30.0 GM (protonated forms) and from 16.2 to 24.9 GM (deprotonated forms).
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Abstract Solution and solid state properties of 1,4‐diketo‐3,6‐bis‐(4'‐pyridyl)‐pyrrolo‐[3,4‐c]‐pyrrole (DPPP: red pigment) have been investigated with respect to protonation and deprotonation. DPPP undergoes both protonation and deprotonation, because it behaves not only as a base due to electron lone pairs of the nitrogen in the pyridyl ring but also as an acid due to the NH group in the heterocyclic chromophore. Protonation at the pyridyl nitrogen and deprotonation at the NH group induce large bathochromic shifts in solution. These are interpreted in terms of Pariser‐Parr‐Pople calculations, using the variable β, γ‐approximation. Protonation in the solid state due to acid vapor brings about significant changes in photoelectrical properties, such as a reduction in electrical resistivity from about 10 10 to 10 5 Ωcm and strong photoconduction enhancement. The protonated solid state has been characterized systematically through spectroscopy, crystallography and thermo‐analysis with particular attention to its potential applications, e.g., to proton sensors and optical information storage systems.
Pyrrole
Bathochromic shift
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Abstract PPP, CNDO/S and INDO/S calculations have been carried out on the title compounds (abbreviated to DPPP, DPP and DTPP, respectively; industrially important pigments) in order to study spectroscopically the diketopyrrolopyrrole chromophore on protonation and deprotonation. Protonation which takes place at the pyridyl nitrogen (DPPP only) and deprotonation (in all three molecules) which occurs at the NH group induce large spectral shifts in solution towards longer wavelengths (protonation: 35 nm (ca. 1236 cm −1 ); deprotonation: 77–150 nm (ca. 1820–4380 cm −1 )). Geometry optimization by the AM1 method showed that the pyridyl rings in DPPP and the phenyl rings in DPP and DTPP are twisted, in the same direction, out of the plane of the planar heterocyclic system by 15–21°. The deviation is asymmetrically reduced due to mono‐deprotonation: the ring on the deprotonated side is less twisted than the other. Di‐deprotonation makes the molecule completely planar. On mono‐protonation of DPPP, the protonated pyridyl ring becomes less twisted while the unprotonated remains almost unchanged. In contrast, on di‐protonation, the two pyridyl rings become even more twisted than in the initial state. The electronic spectra calculated on the basis of the optimized structures reproduce well qualitatively the trends of the optical absorption, but generally underestimate the experimental values.
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