Structural evidence of an intramolecular proton transfer leading to keto-amine tautomer in the crystals of Schiff bases derived from tyrosine and histidine esters

Núñez-Montenegro, Ara; Pino-Cuevas, Arantxa; Carballo, Rosa; Vázquez‐López, Ezequiel M.

doi:10.1016/j.molstruc.2014.01.023

Cited by 11 publications

(7 citation statements)

References 20 publications

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“…[52] In the literature only ah andful structurally characterized Nsalicylidene a-amino acid esters, exhibiting both enol-imine and keto-enamine structures, are known( Figure 1). [46,[52][53][54][55] However,its till remains unclear which factorsdetermine the stability of tautomers:w hether it is defined by the nature of an ester group or as ubstituent at the benzene ring of salicylaldehyde or at the a-position of an amino acid moiety.Equally important is that theses ystems contain extra stabilization stemming from p-electrons delocalization, the so-called resonance-assisted hydrogen bonding( RAHB),w hich might influencef ormation of varioust automeric forms.A lthought his effect is well recognized in the literature, its fundamentalm echanism and impact on photophysical properties are not well understood. [56][57][58][59][60][61][62][63][64][65][66][67][68] With all this in mind, we have directed our attention to a new family of N-salicylidene aniline derivatives 1-4 differing in donor-acceptor properties and their luminescence activity, which are fabricated from the ethyl ester of glycine and corresponding salicyladehyde derivatives (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

“…Diagrams of the reported crystal structures of N-salicylidene aamino acid esters. [45,[51][52][53][54] Scheme1.Possible tautomeric forms of 1 (X = H), 2 (X = OMe), 3 (X = Br), 4 (X = NO 2 ). presenceo fc atalytic amountso fs ubstituted salicylaldehydes.…”

Section: Introductionmentioning

confidence: 99%

“…In the literature only a handful structurally characterized N‐salicylidene α‐amino acid esters, exhibiting both enol‐imine and keto‐enamine structures, are known (Figure ) . However, it still remains unclear which factors determine the stability of tautomers: whether it is defined by the nature of an ester group or a substituent at the benzene ring of salicylaldehyde or at the α‐position of an amino acid moiety.…”

Section: Introductionmentioning

confidence: 99%

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Resonance Assisted Hydrogen Bonding Phenomenon Unveiled through Both Experiments and Theory: A New Family of Ethyl N‐Salicylideneglycinate Dyes

Shapenova

Shiryaev

Bolte

et al. 2020

Chemistry A European J

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Extensive experimental and theoretical investigations are reported on the nature of resonance-assisted hydrogen bonding phenomenon (RAHB) and its influenceo n photophysical properties of the newly designed dyes differing in donor-acceptor properties, namely ethyl N-salicylideneglycinate (1), ethyl N-(5-methoxysalicylidene)glycinate (2), ethyl N-(5-bromosalicylidene)glycinate (3)a nd ethyl N-(5-nitrosalicylidene)glycinate(4). All compounds are thermochromic in the solid state and they contain at ypical intramolecular OÀH•••N hydrogen bond formed between the hydroxyl hydrogen atom and the imine nitrogen atom, yielding the enol form in the solid state. It is unveiled, that the magnitude of RAHB effect fine tunes the strength of the OÀH•••N bondinga nd accordingly the relativep opulations of the enol, cis-keto and trans-keto formsl eading to variation of the photophysical properties of 1-4.I ti sd etermined, that the electron-withdrawing NO 2 in 4 amplifies the mostR AHB effectc ausing the breaking of the OÀH•••N hydrogenb ond and accordingly formation of the dominant cis-keto isomer in both the solid state and EtOH. To this end, the UV/Vis spectra of 1-3 in EtOH revealed the exclusive presence of the enol form, while the prevalent contribution of the cisketo form was found for 4.F urthermore, only compound 4 is emissive in the solids tate in ambient condition due to dual emissiona rising from the cis-keto* and trans-keto* forms,w hile 2 was found to be highly emissive in EtOH. It is revealed qualitativelya nd quantitatively,b ased on the ETS-NOCV charge and energy decomposition scheme and the EDDB population-based method, that RAHB is strongly a non-local phenomenon based on electrons pumping or suckingt hrough both the p-a nd s-channels, which accordingly exerts chemicalb ondingc hanges at both the phenyl ring and predominantly ad istant OÀH•••N area.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Resonance Assisted Hydrogen Bonding Phenomenon Unveiled through Both Experiments and Theory: A New Family of Ethyl N‐Salicylideneglycinate Dyes

Shapenova

Shiryaev

Bolte

et al. 2020

Chemistry A European J

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“…The proposed mechanism for this racemization reaction is initiated by proton abstraction from the α‐carbon, whose acidity can be increased after forming the C=N bond by condensation , . In addition, a compound of methyl ( E )‐2‐[(2,4‐dihydroxybenzylidene)amino]‐3‐(1 H ‐imidazol‐4‐yl)propanoate has also been found to exhibit a racemization, which was confirmed by CD measurement and single‐crystal X‐ray diffraction analysis . It was reported that the racemization proceeded in refluxing methanol within 2 h, but not in dichloromethane.…”

Section: Resultsmentioning

confidence: 73%

Schiff Base Ligands Derived from l‐Histidine Methyl Ester: Characterization, Racemization, and Dimerization of Their Transition‐Metal Complexes

2018

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Reactions of methyl (S)‐2‐[(2‐hydroxybenzylidene)amino]‐3‐(1H‐imidazol‐4‐yl)propanoate (S‐H2LMe) and various transition‐metal(II) salts (MX2: M = Mn, Fe, Co, and Ni; X = ClO4, Cl, OAc, etc.) are examined. During the reactions with MnII and CoII salts, the MII ion is oxidized by air to form a cationic complex with two mono‐deprotonated ligands, [MIII(S‐HLMe)2]X [M, X = Mn, ClO4 (S‐1ClO4); Co, ClO4 (S‐3ClO4); and Co, Cl (S‐3Cl)], where (S‐HLMe)– is coordinated to a MIII center in a tridentate κ3O,N,N′ mode with a mer configuration. In contrast, the NiII ion is not oxidized; only one of the ligands is deprotonated to form a similar monocationic complex, [NiII(S‐HLMe)(S‐H2LMe)]PF6 (S‐6PF6), which forms a dimer structure by double hydrogen bonds between the coordinating phenoxide and phenol groups in the crystal. Interestingly, the above complexes show slow racemization of the ligand, as confirmed by circular dichroism spectroscopy. Racemic NiII complexes of [Ni(HLMe)(H2LMe)](PF6 or Cl) (rac‐6PF6 or rac‐6Cl) are isolated and their crystal structures are confirmed by X‐ray diffraction analysis. In the case where Co(OAc)2 is used as the metal(II) salt, a new ligand dimerization reaction takes place to afford a complex of [Co(H2LLMe)]Cl (7Cl, H4LLMe = methyl (E)‐3‐{[3‐(1H‐imidazol‐4‐yl)‐1‐methoxy‐1‐oxopropano‐2‐yl]amino}‐2‐[(1H‐imidazol‐4‐yl)methyl]‐2‐[(2‐hydroxybenzylidene)amino]‐3‐(2‐hydroxyphenyl)propanoate).

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“…Another class of compounds of interest are amino acids, due to their relevant biological role and structural diversity. Amino acids such as tyrosine and cysteine can be chemically modified using straightforward methodologies [ 41 , 42 , 43 , 44 , 45 ] and provide sufficiently reactive functional side chains that can bind covalently onto the porphyran chain.…”

Section: Introductionmentioning

confidence: 99%

Enhancement of the Antioxidant and Antimicrobial Activities of Porphyran through Chemical Modification with Tyrosine Derivatives

et al. 2021

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The chemical modification of porphyran hydrocolloid is attempted, with the objective of enhancing its antioxidant and antimicrobial activities. Sulfated galactan porphyran is obtained from commercial samples of the red algae Porphyra dioica using Soxhlet extraction with water at 100 °C and precipitation with isopropyl alcohol. The extracted porphyran is then treated with modified L-tyrosines in aqueous medium in the presence of NaOH, at ca. 70 °C. The modified tyrosines L1 and L2 are prepared through a Mannich reaction with either thymol or 2,4-di-tert-butylphenol, respectively. While the reaction with 2,4-di-tert-butylphenol yields the expected tyrosine derivative, a mixture of products is obtained with thymol. The resulting polysaccharides are structurally characterized and the respective antioxidant and antimicrobial activities are determined. Porphyran treated with the N-(2-hydroxy-3,5-di-tert-butyl-benzyl)-L-tyrosine derivative, POR-L2, presents a noticeable superior radical scavenging and antioxidant activity compared to native porphyran, POR. Furthermore, it exhibited some antimicrobial activity against S. aureus. The surface morphology of films prepared by casting with native and modified porphyrans is studied by SEM/EDS. Both POR and POR-L2 present potential applicability in the production of films and washable coatings for food packaging with improved protecting characteristics.

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Structural evidence of an intramolecular proton transfer leading to keto-amine tautomer in the crystals of Schiff bases derived from tyrosine and histidine esters

Cited by 11 publications

References 20 publications

Resonance Assisted Hydrogen Bonding Phenomenon Unveiled through Both Experiments and Theory: A New Family of Ethyl N‐Salicylideneglycinate Dyes

Resonance Assisted Hydrogen Bonding Phenomenon Unveiled through Both Experiments and Theory: A New Family of Ethyl N‐Salicylideneglycinate Dyes

Schiff Base Ligands Derived from l‐Histidine Methyl Ester: Characterization, Racemization, and Dimerization of Their Transition‐Metal Complexes

Enhancement of the Antioxidant and Antimicrobial Activities of Porphyran through Chemical Modification with Tyrosine Derivatives

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