Comments on the papers recently published by M.M. Khandpekar and S.P. Pati

The effect of carboxylic acids on glycine polymorphism, salt and co-crystal formation. A comparison of different crystallisation techniques

“…[18][19][20] Glycine is also known to form both organic and inorganic salts with a variety of acids, many of which are considered to be promising optical, ferroelectric and piezoelectric materials. [21][22][23][24][25][26][27][28][29][30][31][32][33][34] The pharmaceutical industry also makes use of glycine both as an excipient and an active pharmaceutical ingredient, 35 therefore its salts and co-crystals can be of interest for pharmaceutical applications.…”

Can a ‘magnesium sulfate admixtured l-threonine’ crystal be grown by slow evaporation solution growth method?

“…Incidentally the same research group (Puhal Raj & Ramachandra Raja) had also reported l-valine under the name 'lvaline zinc sulfate' crystal. Since several instances of isolation and reporting of known amino acids under the name novel NLO crystal are well documented in the literature in the form of critical comments [1][2][3][4][5][6][7][8]11,12,15,[20][21][22][23], the report on l-threonine crystal with the name 'magnesium sulfate admixtured l-threonine' [16] is not very surprising. It is only unfortunate that the authors of the commented paper [16] could find MgSO 4 in crystals of l-threonine as evidenced by their claim, The presence of MgSO 4 in LTMS is confirmed from the EDAX spectrum.…”

“…In addition, Fleck and Petrosyan convincingly proved that many of the so called novel NLO materials, were actually not novel but in fact crystals of the starting amino acid used for crystal growth. In spite of publication of this case study, more cases of erroneous reports continue to appear in the literature in the area of crystal growth of NLO materials and have been extensively commented [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The recent paper by Puhal Raj et al [16] entitled, 'Structural, optical and mechanical property analysis of magnesium sulphate admixtured l-Threonine: A novel optoelectronic material', is one such erroneous paper reporting the growth of the well-known l-threonine crystal under the name viz.…”

Comments on the paper: ‘Growth structural, spectral, optical and mechanical studies of gamma bis glycinium oxalate (GBGOx) new NLO single crystal by SEST method’

“…In spite of this, glycine has been chosen by many research groups as a precursor material for new nonlinear material synthesis. The inappropriate choice of glycine as a precursor for NLO crystal work can be evidenced by the several improperly characterized glycine based compounds, many of which have been extensively commented in the literature [10][11][12][13][14][15][16][17][18][19][20][21][22]. The glycine/oxalic acid system has been the subject of recent research and a total of four compounds (Table 1), crystallizing in centrosymmetric space groups are well documented [7][8][9].…”