Electrochemical and in situ FTIR studies on the adsorption and oxidation of glycine and lysine in alkaline medium

doi:10.1016/S0022-0728(98)00015-1

Journal of Electroanalytical Chemistry

Volume 449, Issues 1–2, June 1998, Pages 101-109

https://doi.org/10.1016/S0022-0728(98)00015-1 Get rights and content

Abstract

The electrochemical oxidation of glycine and lysine in strongly alkaline solution has been studied, and the nature of the adsorbed species disclosed by means of an in situ FTIR spectroscopic method. The oxidation of water was strongly suppressed by the adsorption of the amino acids and the subsequent oxidative decomposition. The adsorption of amino acid onto the electrode was achieved through the terminal COO⁻ group of fully unprotonated anions from +0.4 V vs. Ag|AgCl, and the concentration of the adsorbent attained the maximum at +0.9 V. Beyond this potential, the adsorption strength was weakened, and the oxidative decomposition to CO₂, NH₃, acids, etc., occurred from +1.1 V.

Introduction

Electrochemical investigations on aliphatic amino acids have been performed for many years 1, 2, 3, 4, 5, 6. The major interest of this work is to make clear the nature of adsorbed species and the scheme of the redox reaction, since an amino acid on an electrode may be used as a model to disclose the part fulfilled by the different functional groups such as –COOH, –NH₂ and –CH₃ in the electrochemical performance of small organic molecules. Marangoni et al. have investigated the electrochemical oxidation of glycine on a platinum electrode using steady-state current–potential measurements, and proposed a mechanism involving adsorption through the carboxyl group followed by decarboxylation [5]. However, this work is not based on direct information about the nature of the adsorbed species, and there is still much to unravel in terms of adsorption and oxidation schemes.

Recently, Huerta et al. have reported the nature and bonding of the adsorbed species formed from glycine on a Pt(111) electrode in acid medium by using an in situ FTIR spectroscopic method [7]. They claim that cyanide ions generated in the electrooxidation of glycine adsorb strongly on the electrode surface and that this species inhibits further oxidation of glycine. In our experiments, however, cyanide formed by the oxidation of glycine in alkaline solution dissolved into the solution, and further oxidation of amino acids proceeded without being hindered by cyanide ions. Hence, the situation of adsorbed amino acids on the electrode surface in alkaline solution may be considerably different from that in acid solution. In this paper, the nature of adsorbed species and the reaction scheme in the oxidation of glycine and lysine at high pH values were investigated by electrochemical and in situ FTIR methods.

Section snippets

Experimental

Cyclic voltammetric (CV) measurements were performed in a Pyrex H-type cell (50 cm³) equipped with a Pt wire working electrode, a Pt auxiliary electrode, and an Ag|AgCl|saturated KCl reference electrode. For the pretreatment, the working electrode was polarized at +2.5 V in 0.1 M H₂SO₄ until it gave a reproducible voltammogram. The prepared electrode showed a large overpotential for oxygen evolution. The apparent area of the working electrode was 1.26 mm². The solution was prepared by

CV curves and galvanostatic oxidation of glycine and lysine

Cyclic voltammograms of glycine (a) and lysine (b) at various concentrations in the solutions of pH 13 are shown in Fig. 1. In the absence of glycine (Fig. 1a, curve 1), the oxygen evolution was observed from +0.65 V, which is considerably more positive than the theoretical value (E=+0.258 V vs. Ag|AgCl). This is attributed to the enhanced overpotential of oxygen evolution exhibited by the pretreated electrode. The addition of glycine or lysine leads to the appearance of an anodic peak,

Conclusions

Electrochemical and in situ FTIR spectroscopic studies on glycine and lysine oxidation were performed in alkaline medium, and the following results were obtained.

(1) The oxidation of water was extremely repressed by the adsorption of the amino acids and the subsequent decomposition reactions. The adsorption of the amino acids occurred from +0.4 V, and their oxidation from +1.1 V.

(2) The concentration of unprotonated glycine anions adsorbed on the electrode was a maximum at +0.9 V. The

Acknowledgements

This work was funded by a Grant-in-Aid for Scientific Research on Priority Area of `Electrochemistry of Ordered Interfaces' from the Japanese Ministry of Education, Science, Sports and Culture.

References (13)

G. Horányi et al.
J. Electroanal. Chem.
(1975)
G. Horányi et al.
J. Electroanal. Chem.
(1986)
M. Heyrovský et al.
J. Electroanal. Chem.
(1997)
F. Huerta et al.
J. Electroanal. Chem.
(1997)
H. Kawashima et al.
J. Electroanal. Chem.
(1991)
C. Stuhlmann
Surf. Sci.
(1995)

There are more references available in the full text version of this article.

Cited by (53)

Electrochemical quantification of glycine using amorphous iron vanadate nanoparticles modified pencil electrode
2023, Inorganic Chemistry Communications
The quest of stable, environmentally benign and highly electro-active inorganic electrode modifiers is of great research interest in the field of biomolecules detection. In this regard, a simple precipitation method, operating at room temperature and completes in a few minutes, has been employed to prepare FeVO₄. The FeVO₄ prepared at room temperature exhibits amorphous structure with spherical particles of size 40–60 nm. Thus, the prepared amorphous FeVO₄ nanoparticles were coated on pencil electrode by drop-casting. The electrochemical activity of FeVO₄ nanoparticles modified pencil electrode towards glycine detection has been carried out in presence of potassium ferricyanide and potassium chloride electrolyte using cyclic voltammetry and chronoamperometric techniques. The linear decrease in current against increased concentration of glycine reveals that the amorphous FeVO₄ nanoparticles could be used to detect glycine. The experimental results successfully demonstrate that amorphous FeVO₄ nanoparticles exhibit a low detection limit of 5.9 μM with a linear concentration range of 0 μM–72 μM.
Selective separation of hematite from quartz with sodium oleate collector and calcium lignosulphonate depressant
2021, Journal of Molecular Liquids
Citation Excerpt :
Fig. 6(b) exhibits the FTIR spectra of hematite treated with different reagents. After treatment with NaOl, new peaks occurred at 2922.3 cm−1 and 2850.9 cm−1, which were assigned to the stretching vibration of the –CH2– and –CH3 groups respectively, while the peaks appearing at 1560.5 cm−1 and 1458.2 cm−1 corresponded to the stretching vibration of –COOC– (i.e., the characteristic peak of iron oleate) [34,37]. All these characteristic peaks proved the adsorption of NaOl on hematite surface.
Iron ions activation of quartz is a tricky issue for efficiently sorting of target minerals in ferrous minerals flotation. The selection of an effective depressant is one of the most significant approaches to addressing this problem. In this study, the effects of calcium lignosulphonate (CLS), a widely studied novel depressant, on the flotation of Fe³⁺-activated quartz were investigated. The potential depression role of CLS in separating hematite from Fe³⁺-activated quartz in a sodium oleate (NaOl) flotation system was further explored. The flotation results indicated that the separation of hematite from quartz could be achieved by the selective depression of quartz in the presence of CLS. The results of zeta potential and spectroscopy analysis showed that CLS could absorb onto the surfaces of both hematite and Fe³⁺-activated quartz. The presence of CLS hindered the further adsorption of NaOl on quartz, whereas the NaOl adsorption onto hematite surfaces was limitedly affected. Compared with hematite, CLS might be more prone to react with the Fe sites on the surface of Fe³⁺-activated quartz, resulting in a relatively high final adsorption density on quartz surfaces, which was confirmed by X-ray photoelectron spectroscopy analysis and adsorption tests.
Extraction of copper and the co-leaching behaviour of other metals from waste printed circuit boards using alkaline glycine solutions
2020, Resources, Conservation and Recycling
Waste printed circuit boards (WPCBs) are a complicated and valuable fraction of electric and electronic waste. The recycling of them is critical to avoid environmental pollutions and to reuse resources. In particular, the e-waste import bans have been implemented in many traditional waste-importing countries in recent years, which is making the sustainable recycling essential and crucial for the advanced economies. In this study, a sustainable approach using alkaline glycine solution for the extraction of copper (Cu) from WPCBs, and the leaching behaviour of other metals (Ni, Al, Fe, Pb, Sn, Co, Zn, Au, Ag and Pd) is presented. Various leaching parameters, including initial pH, glycine concentration, solid content, oxidant, particle size, temperature and time were investigated. A maximum Cu extraction of 96.5 % was achieved, with high co-extraction of base metals (BMs). The extraction of BMs was dependent on the pH of leaching solution, which was highly correlated with other variables. BMs extraction was largely influenced by glycine concentration and solid content, while the sensitivity to H₂O₂, temperature, and particle size was insignificant. SEM-EDS analysis of leaching residue indicated that the unleached Cu may be locked in inert layers, e.g. Sn/solder materials. The kinetic analysis showed that the extraction of Cu from WPCBs (100 % <2 mm) at room temperature with ambient O₂ in air as an oxidant was mainly controlled by internal diffusion.
An electrochemical furosemide sensor based on pencil graphite surface modified with polymer film Ni-salen and Ni(OH)<inf>2</inf>/C nanoparticles
2018, Sensors and Actuators, B: Chemical
In this work, an advanced electrochemical sensor based on pencil graphite electrode modified via electropolymerization of the N,N′-bis(salicylidene) ethylenediaminonickel(II) monomer in the presence of carbon supported Ni(OH)₂ nanoparticles (here called as poly[Ni(salen)] and Ni(OH)₂/C) was developed and investigated for furosemide (FUR) quantification in alkaline medium. The electrochemical sensor and its components were extensively characterized by physico-chemical techniques, while the furosemide oxidation process was investigated by in situ Fourier transform infrared spectroscopy (in situ FTIR). These results indicate that the oxidation of furosemide leads to the formation of 2-amino-4-chloro-5-sulfamoylbenzoate and 5-hydroxy-furan-2-carboxylate in these conditions. The electrochemical response of the modified graphite electrode (MGE) for the determination of FUR was measured by cyclic voltammetry (CV). The calibration curve (change of voltammetric peak current vs. FUR concentration) presented a linear range from 2.5 × 10⁻¹⁰ M to 2.7 × 10⁻⁹ M with a calculated limit of detection as low as 1.4 × 10⁻¹⁰ M under the optimized conditions, which is lower than values reported in the literature. The ultra-low sensitivity obtained with the MGE sensor was attributed to an additiveeffect involving the poly[Ni(salen)] film and the high surface carbon-supported Ni(OH)₂ nanoparticles.
Electrochemical behaviour of copper in alkaline glycine solutions
2018, Hydrometallurgy
The fundamental electrochemical properties of the copper-glycine system were investigated in this study to understand the factors that affect the dissolution of metallic copper. Potentiodynamic polarisation measurements were carried out over the pH range 9.0 to 11.5, at temperatures of 22 °C and 60 °C and glycine concentrations 0.1 M and 0.3 M. A window for maximum corrosion current was determined to be between pH 10.0 and 10.5 with a maximum at 60 °C and 0.3 M glycine. Passivation was only observed at pH values >10.5, and then only at potentials above 0.4 V (vs SHE) for quiescent solutions. This passivation potential increased with the rotation speed of the copper electrode. The passive layer broke down after a short rest at the open circuit potential, which allowed reactivation of the surface and high initial currents to briefly flow until the layer re-formed. Potential-step and capacitance measurements are consistent with the formation of a duplex oxide layer of Cu₂O and CuO that thickens with increasing potential. The copper glycinate complex itself also acts as an oxidising agent, the effectiveness is increased with its concentration and the concentration of free glycine. Free glycine is oxidised irreversibly above 1.2 V (vs SHE).
Cytotoxic activity and structural features of Ru(II)/phosphine/amino acid complexes
2018, Journal of Inorganic Biochemistry
Thirteen new ruthenium amino acid complexes were synthesized and characterized. They were obtained by the reaction of α-amino acids (AA) with [RuCl₂(P-P)(N-N)], where P-P = 1,4-bis(diphenylphosphino)butane (dppb) or 1,3-bis(diphenylphosphino)propane (dppp) and N-N = 4,4′-dimethyl-2,2′-bipyridine (4′-Mebipy), 5,5′-dimethyl-2,2′-bipyridine (5′-Mebipy) or 4,4′-Methoxy-2-2′-bipyridine (4′-MeObipy). This afforded a family of complexes formulated as [Ru(AA-H)(P-P)(N-N)]PF₆, where AA = glycine (Gly), L-alanine (Ala), L-valine (Val), L-tyrosine (Tyr), L-tryptophan (Trp), L-histidine (His) and L-methionine (Met). All compounds were characterized by elemental analysis, spectroscopic and electrochemical techniques. The [Ru(AA-H)(P-P)(N-N)]PF₆ complexes are octahedral (the AA-H ligand binding involves N-amine and O-carboxylate), diamagnetic (low-spin d⁶, S = 0) and present bands due to electronic transitions in the visible region. ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectra of the complexes indicate the presence of C₂ symmetry, and the identification of diastereoisomers. In vitro cytotoxicity assays of the compounds and cisplatin were carried out using MDA-MB-231 (human breast) tumor cell line and a non-tumor breast cell line (MCF-10A). Most complexes present promising results with IC₅₀ values comparable with the reference drug cisplatin and high selectivity indexes were found for the complexes containing L-Trp. The binding of two Ru-precursors of the type [RuCl₂(dppb)(NN)] (N-N = 4′-MeObipy or 4′-Mebipy) to the blood transporter protein human serum albumin (HSA) was evaluated by fluorescence and circular dichroism spectroscopy. Both complexes bind HSA, probably in the hydrophobic pocket near Trp214, and the Ru-complex containing 4′-MeObipy shows higher affinity for HSA than the 4′-Mebipy one.