ABSTRACT
Galactomannans are polysaccharides obtained from legume seed extraction. They present a chemical structure consisting of D-mannose chains linked by glycosidic bonds and galactose branches. The main focus lies in their use as thickeners in the food industry, aimed at improving the dielectric properties of food during heating processes within the radiofrequency and microwave ranges. In this work, the prepared galactomannan samples were electrically analyzed through impedance spectroscopy, which is a powerful physical technique. From the experimental measurements, the dielectric permittivity and loss tangent of the galactomannan solutions were analyzed and the electrical modulus formalism was used to study the dielectric relaxations. Crude galactomannans exhibited higher values of permittivity, conductivity, and losses compared to purified galactomannans. Increasing ethanol concentration in galactomannan purification causes an increase in the permittivity and conductivity of galactomannan solutions. In a 1% solution, at 1 kHz, the permittivity increased from 378.56 to 538.09, while in the 2% solution, this increase was from 656.22 to 1103.24. Regarding the conductivity, at the same frequency, the increase was from 1.6 × 10-3 to 3.3 × 10-3 Ω-1m-1 and from 2.9 × 10-3 to 5.5 × 10-3 Ω-1m-1, respectively. The rise of the ethanol concentration in galactomannan purification led to a decrease in the relaxation time, from 448.56 to 159.15 µs and from 224.81 to 89.50 µs in the solution with 1 and 2%, respectively. The results suggest that galactomannan from Adenanthera pavonina L. has potential for use in the food industry.
ABSTRACT
Implementing additional optical (luminescent) properties into the well-known class of single-molecule magnets (SMMs) is considered as a promising route toward obtaining the next generation of optomagnetic materials for quantum information storage and computing. Herein, we report a joint optical and magneto-structural study for the two novel series of lanthanide(iii) complexes of general formula Bu4N[LnIII(HL)4(dmso)]·nH2O where H2L = N-(4-Xphenyl)oxamic acid with X = Cl and n = 2 [Ln = Eu (1_Cl), Gd (2_Cl), Dy (3_Cl), and Tb (4_Cl)] and X = F and n = 3 [Ln = Eu (1_F), Gd (2_F), Dy (3_F), and Tb (4_F)]. All these compounds are mononuclear species with each lanthanide(iii) cation in a low-symmetry nine-coordinate environment (LnO9) which is constituted by four didentate monoprotonated oxamate groups and one dmso molecule. Magnetic measurements show the occurrence of field-induced SMM behavior for the Gd3+ (2_Cl and 2_F), Dy3+ (3_Cl and 3_F), and Tb3+ complexes (4_Cl and 4_F). Solid-state photophysical measurements for the Eu3+ (1_Cl and 1_F) and Tb3+ complexes (4_Cl and 4_F) reveal that both monoprotonated chloro- and fluoro-substituted phenyl(oxamate) ligands are able to sensitize the lanthanide(iii)-based luminescence in the visible region, through an energy transfer process ("antenna effect"), as supported by theoretical calculations for Eu3+ compounds. In particular, 1_Cl and 1_F present a quantum efficiency of approximately 50%, being potentially suitable as efficient light conversion molecular devices (LCMDs).
