A Study of Azo-Hydrazone Tautomerism in 3-Phenyl-4-arylazo-5-isozaolones by $^H-NMR$ spectra of $^{15}N-labeled$ Compounds and HMO Method

Shawali, Ahmad S.,Salkaabi, harifia S.,Abdallah, Magda A. The Pharmaceutical Society of Korea 1991 Archives of Pharmacal Research Vol.14 No.3

The tautomerism in 3-phenyl-4-arylazo-5-isoxazolones 1 was examined by $^1H-NMR$ spectra of $^15N-labeled$ compound and by HMO method. Both spectra data $(^1H-NMR\;and\;IR)$ and bonding energies are in support of the assignment of the hydrazone structure to such compounds. It is further shown that intermolecular and intramolecular hydrogen bondings favor the hydrazone tautomer.

Experimental and Theoretical Investigations of Spectral, Tautomerism and Acid-Base Properties of Schiff Bases Derived from Some Amino Acids

Y. H. Ebead,H. M. A. Salman,M. A. Abdellah 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.4

The electronic absorption spectra of five Schiff bases derived from 2-hydroxy-1-naphthaldehyde with glycine, alanine,leucine, valine and phenylalanine have been measured in various solvents. The observed bands were assigned to the proper electronic transitions and compared with the predicted transitions at the semiempirical level of theory. The calculated equilibrium constants are in agreement with the experimental results, predicting the existence of all studied compounds predominantly or completely in keto-imine tautomerism. On the other hand, a correlation between ν (cm‒1) (main frequency of each compound) and the well known solvent parameters ET (30), εr, π* has been made. Furthermore, the acid dissociation constants, pKa, were determined by using three different spectrophotometric methods.

Experimental and Theoretical Investigations of Spectral, Tautomerism and Acid-Base Properties of Schiff Bases Derived from Some Amino Acids

Ebead, Y.H.,Salman, H.M.A.,Abdellah, M.A. Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.4

The electronic absorption spectra of five Schiff bases derived from 2-hydroxy-1-naphthaldehyde with glycine, alanine, leucine, valine and phenylalanine have been measured in various solvents. The observed bands were assigned to the proper electronic transitions and compared with the predicted transitions at the semiempirical level of theory. The calculated equilibrium constants are in agreement with the experimental results, predicting the existence of all studied compounds predominantly or completely in keto-imine tautomerism. On the other hand, a correlation between $\nu\;(cm^{-1})$ (main frequency of each compound) and the well known solvent parameters $E_T$ (30), $\varepsilon_T$, $\pi^*$ been made. Furthermore, the acid dissociation constants, $pK_a$, were determined by using three different spectrophotometric methods.

Tautomerism of Cytosine on Silver, Gold, and Copper: Raman Spectroscopy and Density Functional Theory Calculation Study

조광휘,주상우 대한화학회 2008 Bulletin of the Korean Chemical Society Vol.29 No.1

Tautomerism of pyrimidine base cytosine has been comparatively examined on nanoparticle and roughened plate surfaces of silver, gold, and copper by surface-enhanced Raman scattering (SERS). The SERS spectrum was found to be different depending on the metals and their substrate conditions suggesting the dissimilar population of various tautomers of cytosine on the surfaces. The ab initio calculations were performed at the levels of B3LYP, HF, and MP2 levels of theory with the LanL2DZ basis set to estimate the energetic stability of the tautomers with the metal complexes as well as the gas phase state. The amino group and N3-coordinated tautomer was predicted to be more favorable for bonding to Au, whereas the hydroxyl and N1-coordinated zwitter ionic form is most stable with Ag and Cu as a bidentate form from the DFT calculation. The binding energy with the Ag atom is calculated to be smaller than those with the Au and Cu atoms in line with the temperature-dependent SERS spectra of cytosine.

Tautomeric Effect of Histidine on the Structural Properties of Aβ40 heterodimers

( Li Hao ),( Salimi Abbas ),이진용 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1

Alzheimer’s disease (AD) is the most common form of dementia occurred in the elderly that affected more than 40 million people across the world resulting in enormous social and economic impact. The intrinsic origin of amyloid aggregation still remains to be considered. The aggregation mechanism affected by the tautomeric state (δ and ε) of histidine residues (H6, H13, and H14) was previously investigated in A β40 and Aβ42 monomers. Molecular dynamics simulation results show different aggregation trends in the different heterodimers formed by the (εεε) and other isomers. In the (εεε:δδδ) dimer, the highest β -sheet content was obtained in the (δδδ) chain, consistent with our previous studies that showed the (δδδ) monomer most easily form a β -sheet secondary structure in the monomer. Further analysis confirmed that the (εεε:δδδ) dimer is more likely to aggregate than other heterodimers. The current research helps to understand the pathology AD.

Crystal Structure and Tautomerism Study of the Mono-protonated Metformin Salt

Wei, Xiaodan,Fan, Yuhua,Bi, Caifeng,Yan, Xingchen,Zhang, Xia,Li, Xin Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.12

A novel crystal, the mono-protonated metformin acetate (1), was obtained and characterized by elemental analysis, IR spectroscopy and X-ray crystallography. It was found that one of the imino group in the metformin cation was protonated along with the proton transfer from the secondary amino group to the other imino group. Its crystal structure was then compared with the previously reported diprotonated metformin oxalate (2). The difference between them is that the mono-protonated metformin cations can be linked by hydrogen bonding to form dimers while the diprotonated metformin cations cannot. Both of them are stabilized by intermolecular hydrogen bonds to assemble a 3-D supermolecular structure. The four potential tautomer of the mono-protonated metformin cation (tautomers 1a, 1b, 1c and 1d) were optimized and their single point energies were calculated by Density Functional Theory (DFT) B3LYP method based on the Polarized Continuum Model (PCM) in water, which shows that the most likely existed tautomer in human cells is the same in the crystal structure. Based on the optimized structure, their Wiberg bond orders, Natural Population Analysis (NPA) atomic charges, molecular electrostatic potential (MEP) maps were calculated to analyze their electronic structures, which were then compared with the corresponding values of the diprotonated metformin cation (cation 2) and the neutral metformin (compound 3). Finally, the possible tautomeric mechanism of the mono-protonated metformin cation was discussed based on the observed phenomena.

A pH-Responsive Molecular Switch with Tricolor Luminescence

Ahn, Hyungmin,Hong, Jaewan,Kim, Sung Yeon,Choi, Ilyoung,Park, Moon Jeong American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.1

<P>We developed a new ratiometric pH sensor based on poly(<I>N-</I>phenylmaleimide) (PPMI)-containing block copolymer that emits three different fluorescent colors depending on the pH. The strong solvatochromism and tautomerism of the PPMI derivatives enabled precise pH sensing for almost the entire range of the pH scale. Theoretical calculations have predicted largely dissimilar band gaps for the keto, enol, and enolate tautomers of PPMI owing to low-dimensional conjugation effects. The tunable emission wavelength and intensity of our sensors, as well as the reversible color switching with high-luminescent contrast, were achieved using rational molecular design of PPMI analogues as an innovative platform for accurate H<SUP>+</SUP> detection. The self-assembly of block copolymers on the nanometer length scale was particularly highlighted as a novel prospective means of regulating fluorescence properties while avoiding the self-quenching phenomenon, and this system can be used as a fast responsive pH sensor in versatile device forms.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-1/am5070188/production/images/medium/am-2014-070188_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5070188'>ACS Electronic Supporting Info</A></P>

Crystal Structure and Tautomerism Study of the Mono-protonated Metformin Salt

Xiaodan Wei,Yuhua Fan,Caifeng Bi,Xingchen Yan,Xia Zhang,Xin Li 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.12

A novel crystal, the mono-protonated metformin acetate (1), was obtained and characterized by elemental analysis, IR spectroscopy and X-ray crystallography. It was found that one of the imino group in the metformin cation was protonated along with the proton transfer from the secondary amino group to the other imino group. Its crystal structure was then compared with the previously reported diprotonated metformin oxalate (2). The difference between them is that the mono-protonated metformin cations can be linked by hydrogen bonding to form dimers while the diprotonated metformin cations cannot. Both of them are stabilized by intermolecular hydrogen bonds to assemble a 3-D supermolecular structure. The four potential tautomer of the monoprotonated metformin cation (tautomers 1a, 1b, 1c and 1d) were optimized and their single point energies were calculated by Density Functional Theory (DFT) B3LYP method based on the Polarized Continuum Model (PCM) in water, which shows that the most likely existed tautomer in human cells is the same in the crystal structure. Based on the optimized structure, their Wiberg bond orders, Natural Population Analysis (NPA) atomic charges, molecular electrostatic potential (MEP) maps were calculated to analyze their electronic structures, which were then compared with the corresponding values of the diprotonated metformin cation (cation 2) and the neutral metformin (compound 3). Finally, the possible tautomeric mechanism of the monoprotonated metformin cation was discussed based on the observed phenomena.

Ethyl 2-Methyl-3-Pyrazinyl-3-oxopropionate의 합성과 케토-엔올 토토머화현상

권순경,박명숙,박해선 德成女子大學校 藥學硏究所 2002 藥學論文誌 Vol.13 No.1

Ethyl 2-methyl-3-pyrazinyl-3-oxopropionate is a key intermediate for the development of new drugs and can be synthesized through Claisen condensation from methyl pyrazine carboxylate and ethyl propionate. Even though in β-diketones esters in general the amount of enol form present at equilibrium is far higher than keto form, this key compound showes that the keto concentration is high. It can be explained because of the electron-releasing effect of α-methyl group.

새로운 헤테로고리 화합물에 대한 연구(2) -Pyrrolo[1,2-a]quinoxaline류의 토토머화 현상-

김연옥 ( Yeon Ok Kim ),송영대 ( Young Dae Song ),이갑용 ( Gab Yong Lee ) 대구가톨릭대학교 자연과학연구소 2015 자연과학연구논문집 Vol.13 No.1

The reaction of (4-methyl-1-oxo-l,5-dihydropyrrolo[1,2-a]quinoxalin-2-yl)acetic acid with ethanol afforded ethyl(4-methyl-1-oxo-1,5-dihydropyrrolo[1,2-a]quinoxalin-2-yl)acetate. This compound with hydrazine hydrate gave 2-(4-methyl-1-oxo-1,5-dihydropyrrolo[1,2-a]quinoxalin-2-yl)acetohydrazide(7). The reaction of compound 7 with substituted benzaldehydes, heteroaryl aldehydes, substituted benzoyl chlorides, heteroacyl chlorides, substituted phenylacetyl chlorides and sulfonyl chlorides gave 2-substituted-pyrrolo[1,2-a]quinoxalines(8-16), respectively. The reaction of compound 7 with alkyl (ethoxymethylene)cyanoacetates resulted in the intramolecular cyclization to give pyrazolyl-pyrrolo[1,2-a]quinoxalines(17). The pyrrolo[l,2-a]quinoxalines have been shown the tautomerism between the oxo (A) and hydroxy (B) forms in dimethyl sulfoxide solution.