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A polymorph of dipeptide halide glycyl-L-alanine hydroiodide monohydrate: crystal structure, optical second harmonic generation, piezoelectricity and pyroelectricity

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Resumo:A polymorph of glycyl-L-alanine HI.H2O is synthesized from chiral cyclo-glycyl-L-alanine dipeptide. The dipeptide is known to show molecular flexibility in different environments, which leads to polymorphism. The crystal structure of the glycyl-L-alanine HI.H2O polymorph is determined at room temperature and indicates that the space group is polar (P21), with two molecules per unit cell and unit cell parameters a = 7.747 Å, b = 6.435 Å, c = 10.941 Å, α = 90◦, β = 107.53(3)◦,γ = 90◦ and V = 520.1(7) Å3. Crystallization in the polar point group 2, with one polar axis parallel to the b axis, allows pyroelectricity and optical second harmonic generation. Thermal melting of the glycyl-L-alanine HI.H2O polymorph starts at 533 K, close to the melting temperature reported for cyclo-glycyl-L-alanine (531 K) and 32 K lower than that reported for linear glycyl-L-alanine dipeptide (563 K), suggesting that although the dipeptide, when crystallized in the polymorphic form, is not anymore in its cyclic form, it keeps a memory of its initial closed chain and therefore shows a thermal memory effect. Here, we report a pyroelectric coefficient as high as 45 µC/m2K occurring at 345 K, one order of magnitude smaller than that of semi-organic ferroelectric triglycine sulphate (TGS) crystal. Moreover, the glycyl-L-alanine HI.H2O polymorph displays a nonlinear optical effective coefficient of 0.14 pm/V, around 14 times smaller than the value from a phase-matched inorganic barium borate (BBO) single crystal. The new polymorph displays an effective piezoelectric coefficient equal to deff = 280 pCN−1, when embedded into electrospun polymer fibers, indicating its suitability as an active system for energy harvesting.
Autores principais:Baptista, Rosa Maria Ferreira
Outros Autores:Gomes, Clara S. B.; Silva, Bruna Machado; Oliveira, joão; Almeida, B. G.; Castro, Maria Cidália Rodrigues; Rodrigues, Pedro António Veiga; Machado, A. V.; Freitas, Ruben Brandão; Rodrigues, Manuel José Lima Ferreira; de Matos Gomes, Etelvina; Belsley, M.
Assunto:Glycyl-L-alanine iodide Polymorphism Crystal structure Cyclic dipeptides Optical second harmonic generation Pyroelectricity
Ano:2023
País:Portugal
Tipo de documento:artigo
Tipo de acesso:acesso aberto
Instituição associada:Universidade do Minho
Idioma:inglês
Origem:RepositóriUM - Universidade do Minho

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