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

• Published in: Materials Vol. 16; no. 10; pp. 1 - 20
• Main Authors: Baptista, Rosa Maria Ferreira, 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.
• Format: Journal Article
• Language: English
• Published: Switzerland Multidisciplinary Digital Publishing Institute 12-05-2023; MDPI AG; MDPI
• Subjects: Alanine; Amino acids; Aqueous solutions; Barium; Coefficients; Crystal structure; Crystallization; Crystals; Cyclic dipeptides; Dielectric properties; Displays; Electric power production; Energy harvesting; Ferroelectricity; glycyl-L-alanine iodide; Hydrogen bonds; Iodine; Melt temperature; Nonlinear optics; Optical second harmonic generation; Phase matching; Piezoelectricity; Polymers; Polymorphism; Pyroelectricity; Room temperature; Second harmonic generation; Single crystals; Software; Spectrum analysis; Structure; Symmetry; Temperature; Triglycine sulfate; Unit cell; United Kingdom; Portugal; Germany; United States > US; crystal structure; glycyl-L-alanine iodide; optical second harmonic generation; polymorphism; cyclic dipeptides; pyroelectricity
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma16103690

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.
This research was funded by Fundação para a Ciência e Tecnologia through FEDER (European Fund for Regional Development)-COMPETE-QREN-EU (ref. UID/FIS/04650/2013 and UID/FIS/04650/2019) and E-Field—“Electric-Field Engineered Lattice Distortions (E-FiELD) for optoelectronic devices”, ref. PTDC/NAN-MAT/0098/2020. C.S.B.G. acknowledges funding from Fundação para a Ciência e Tecnologia FCT/MCTES through projects UIDB/50006/2020, UIDP/50006/2020 and LA/P/0008/2020 of the Associate Laboratory for Green Chemistry—LAQV, UIDB/04378/2020, UIDP/04378/2020 and LA/P/0140/2020 of UCIBIO and Associate Laboratory i4HB, respectively.
We acknowledge national funds (OE), through FCT − Fundação para a Ciência e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of article 23 of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19.