Influence of sodium fluoride (NaF) on the crystallization and spectral properties of l-tyrosine

l-Tyrosine (C9H11NO3) is an essential amino acid in living organisms. It is also a building unit in protein, takes part in bio-synthesis of hormones, neurotransmitters, pigments and one of the organic chemical constituents of urinary stones. l-Tyrosine has been crystallized in silica gel by double diffusion technique with and without the addition of NaF. The crystals had rosette-like shape. In case of fluoride addition, two types of crystals have formed: rosette like crystallites, at the gel–solution interface and reticulate type crystallites beneath the interface. XRD results confirmed that both the products are of l-tyrosine with identical crystal structures. Crystal structure, morphology, thermal and spectral properties are analyzed using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric and differential thermal analysis (TG–DTA), Fourier transform infrared spectroscopy (FTIR) and UV–vis transmittance studies. The TG–DTA results suggest that the thermal stability of l-tyrosine has markedly improved due to fluoride doping. Optical band gap energy of NaF grown l-tyrosine crystallite is estimated as 4.28 eV. Second harmonic generation efficiency test indicates that l-tyrosine crystals can be used for application in nonlinear optical devices.

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► The influence of F on the crystallization of l-tyrosine have been studied.
► Reticulate crystallites are also observed along with the pure rosette type of l-tyrosine.
► TG–DTA results suggests that the thermal stability of l-tyrosine has improved remarkably.
► The results are significant in view of the excessive intake of ‘F’ through drinking water.