Presence Of L-lysine Research Articles

Lysine 2,3-Aminomutase and a Newly Discovered Glutamate 2,3-Aminomutase Produce β-Amino Acids Involved in Salt Tolerance in Methanogenic Archaea.

Many methanogenic archaea synthesize β-amino acids as osmolytes that allow survival in high salinity environments. Here, we investigated the radical S-adenosylmethionine (SAM) aminomutases involved in the biosynthesis of Nε-acetyl-β-lysine and β-glutamate in Methanococcus maripaludis C7. Lysine 2,3-aminomutase (KAM), encoded by MmarC7_0106, was overexpressed and purified from Escherichia coli, followed by biochemical characterization. In the presence of l-lysine, SAM, and dithionite, this archaeal KAM had a kcat = 14.3 s-1 and a Km = 19.2 mM. The product was shown to be 3(S)-β-lysine, which is like the well-characterized Clostridium KAM as opposed to the E. coli KAM that produces 3(R)-β-lysine. We further describe the function of MmarC7_1783, a putative radical SAM aminomutase with a ∼160 amino acid extension at its N-terminus. Bioinformatic analysis of the possible substrate-binding residues suggested a function as glutamate 2,3-aminomutase, which was confirmed here through heterologous expression in a methanogen followed by detection of β-glutamate in cell extracts. β-Glutamate has been known to serve as an osmolyte in select methanogens for a long time, but its biosynthetic origin remained unknown until now. Thus, this study defines the biosynthetic routes for β-lysine and β-glutamate in M. maripaludis and expands the importance and diversity of radical SAM enzymes in all domains of life.

Lysine‐2,3‐aminomutase and a newly discovered glutamate‐2,3‐aminomutase produce β‐amino acids to overcome salt stress in methanogenic archaea

Many methanogenic archaea synthesize N ε ‐acetyl‐β‐lysine and/or β‐glutamate as osmolytes that allow survival in high salinity environments. Methanococcus maripaludis C7 contains two genes, MmarC7_0106 and MmarC7_1783, encoding radical S‐adenosylmethionine(SAM) enzymes with sequence similarity to lysine‐2,3‐aminomutase (KAM). MmarC7_0106 is immediately upstream of an acetyltransferase and was expected to be the KAM involved in the biosynthesis of N ε ‐acetyl‐β‐lysine. To confirm this, the gene was cloned and expressed with a hexahistidine tag in E. coli, followed by anaerobic purification and biochemical characterization. Although the bacterial KAMs involved in lysine degradation in Clostridium subterminale and a post‐translational modification of elongation factor P in E. coli have been well‐characterized, the archaeal KAM involved in compatible solute biosynthesis had never been studied in vitro before. In the presence of L‐lysine, SAM, and dithionite at 37°C, this archaeal KAM had a k cat = 0.42 s ‐1 and a K m = 17.8 mM. The product was shown to be 3(S)‐β‐lysine, which is like the well‐characterized Clostridium KAM as opposed to the E. coli KAM that produces 3(R)‐β‐lysine. The archaeal KAM was highly specific for L‐lysine, with no activity observed with D‐lysine or most other amino acids. However, low aminomutase activity was observed with L‐arginine. We further report the function of MmarC7_1783, a putative radical SAM aminomutase with a ~160 amino acid extension at its N‐terminus. Bioinformatic analysis of possible substrate binding residues suggested a function as glutamate‐2,3‐aminomutase, which was confirmed here through heterologous expression in a methanogen followed by detection of β‐glutamate in cell extracts. Finally, we investigated the differences in amino acid compatible solute usage amongst M. maripaludis C7 (contains both aminomutase genes) and M. maripaludis S2 (contains only the canonical KAM gene) in different salt concentrations. Taken together, this work defines the biosynthetic routes for β‐amino acids in methanogenic archaea and expands the importance and diversity of radical SAM enzymes in all domains of life.

The Solubility and Structures of Porcine Myofibrillar Proteins under Low-Salt Processing Conditions as Affected by the Presence of L-Lysine.

This study aimed to investigate the presence of L-lysine (Lys) on the solubility and structures of myofibrillar proteins (MFPs) at different ionic strengths. Porcine MFPs were incubated at 4 °C with various levels of ionic strengths (0.15, 0.3, or 0.6 M NaCl) with or without the presence of 20 or 40 mM Lys. After 24 h of incubation, MFP solubility and turbidity were determined, and the particle size distribution, circular dichroism spectra, and intrinsic tryptophan fluorescence of MFP were analyzed to obtain their secondary and tertiary structure. Results showed that the solubilization effects of Lys on MFPs are dependent on the ionic strength. Particularly, the presence of Lys could improve MFP solubility at 0.3 M, which resembles salt-reducing processing conditions. Concomitantly, the secondary and tertiary structures were observed to change as a result of the varying ionic strengths and the addition of Lys, including myofibril swelling, dissociation of myosin filaments, uncoiling of α-helix, and unfolding of the tertiary structure. The possible mechanisms underlying the solubilization effects of Lys on MFPs at low ionic strengths are discussed from the perspective of protein structural changes.

Biochemical Characterization of Aminomutases Involved in Salt Tolerance in Methanogenic Archaea

Lysine-2,3-aminomutase (LAM) catalyzes the conversion of L-α-lysine to L-β-lysine, which entails the transfer of an α-amino group to the b-carbon alongside the migration of a β-hydrogen to the α-carbon. This enzyme plays a role in combating salt stress in methanogenic archaea by carrying out the first step in the biosynthesis of Ne-acetyl-β-lysine, a well-studied osmolyte synthesized and accumulated in methanogens. LAM is of special interest as it belongs to the radical S-adenosyl-L-methionine (SAM) superfamily of enzymes which perform diverse and complex chemistry that often produces valuable compounds. Radical SAM enzymes utilize a reduced [4Fe-4S] cluster to initiate the homolytic cleavage of SAM, yielding a highly reactive 5’-deoxyadenosyl radical that then abstracts a hydrogen atom from an otherwise unreactive substrate. Although the bacterial LAM involved in lysine degradation in Clostridium subterminale has been well-characterized, the archaeal LAM involved in osmolyte biosynthesis has never been studied in vitro. Here, we report on the recombinant expression, purification, and enzymatic properties of LAM from Methanococcus maripaludis. The gene encoding LAM from M. maripaludis C7 (MmarC7_0106) was cloned and the his-tagged protein was overexpressed in Escherichia coli. After purification by metal-affinity chromatography under strictly anaerobic conditions, the protein was brown in color, had UV-Vis spectrum characteristics of a [4Fe-4S] cluster that was capable of being reduced to an active state, and had 3.9 mol of iron per monomer. A wide ranged temperature profile study revealed that enzymatic activity was highest at 37°C. The enzyme reaction in the presence of L-lysine, SAM, and dithionite at 37°C had a Kcat = 0.42 s-1 and a Km = 17.8 mM. Finally, alternative substrates for the aminomutation reaction were investigated. There exists another gene annotated as LAM in M. maripaludis C7 due to its close sequence similarity with the bacterial LAM; however, this gene (MmarC7_1783) lacks lysine binding residues and has a 164 amino acid N-terminal extension and as such is referred to as a “long-LAM”. The presence of a “long-LAM” such as MmarC7_1783 in a methanogen is not uncommon as there are several annotated in thermophilic methanogenic species that are known to solely use β-glutamate, another beta-amino acid, as their osmolyte. Given that the only known pathway for the biosynthesis of β-glutamate is through the use of a glutamate-2,3-aminomutase (GAM) and that these thermophilic methanogens do not have an annotated GAM, we proposed that these long-LAMs were in fact GAM which we have now confirmed through heterologous expression studies. Thus, in addition to the biochemical characterization of an archaeal LAM (MmarC7_0106) described above, we have determined that long-LAMs are in fact GAMs required in the biosynthesis of an alternative osmolyte used for survival in high salt concentrations by halotolerant methanogenic archaea.

L-lysine-assisted hydrothermal synthesis of β-NaGdF4:Eu3+ microcrystals: Morphology evolution, luminescence and magnetic properties

Eu3+ doped β-NaGdF4 microcrystals were prepared by using an L-lysine-assisted hydrothermal synthetic method and the morphology evolution was successfully controlled. Hierarchical β-NaGdF4:Eu3+ microcrystals with different morphologies were obtained by changing the moles of L-lysine and the volume of H2O, respectively. The photoluminescence properties of the β-NaGdF4:Eu3+ samples with different morphology were comparatively discussed, in which the hollow hexagonal tube-like β-NaGdF4:Eu3+ exhibited the strongest fluorescence emission intensity owing to the high crystallinity. The characteristic luminescence properties of Tb3+-single doped, Yb3+/Er3+-, and Yb3+/Tm3+-codoped NaGdF4 microcrystals obtained in the presence of L-lysine under hydrothermal condition were also investigated. The superparamagnetic performance of β-NaGdF4:Eu3+ samples at 3 K were characterized in comparison to their paramagnetic property at 300 K, and the results indicated that all samples are paramagnetic at room temperature and the hollow tube-like β-NaGdF4:Eu3+ microcrystals exhibits best saturation magnetization values of 111.11 emu/g at 3 K. The results imply that the morphology-tunable β-NaGdF4:Eu3+ microcrystals are expected to have promising applications for micro/nano optical/magnetic functional devices.

Synthesis and Characterization of Water Dispersible Iron Oxide (�a-Fe2O3) Nanoparticles for Biomedical Applications

In this study, L-lysine coated �a-Fe2O3 nanoparticles were synthesized by a chemical approach in two steps. In the first step �a-Fe2O3 nanoparticles were synthesized by a polyol-reduction method. XRD analysis confirmed the presence of cubic maghemite phase with an average crystallite size of 9.2 nm. SEM analysis showed that the prepared �a-Fe2O3 nanoparticles have a spherical structural morphology with the tendency of agglomeration and with size in the range 8.36- 10.69 nm. The �a-Fe2O3 nanoparticles were coated with L-lysine in the second stage in an aqueous dispersion with ultrasonication followed by a gentle heating at 40��C. FT-IR spectroscopy confirmed the presence of L-lysine on the nanoparticles surface and the Zeta potential also supported the coating of nanoparticles with a hydrophilic layer of amino acid (L-lysine) and a good stability in aqueous medium. Hysteresis loop shows a ferromagnetic behavior at room temperature for both samples.

Electrochemical Oxidation of Catechol in the Presence of L-Lysine at Different pH

The reaction of electrochemically produced o-benzoquinone from oxidation of catechol as Michael acceptor with L-lysine as nucleophiles has been studied in aqueous solution with various pH values, different electrodes and different concentration of L-lysine using cyclic voltammetry, controlled potential coulometry and differential pulse voltammetry. The participation of reaction of o-benzoquinone with L-lysine at higher concentration of nucleophiles in the second scan of potential was observed. The products generated from the reaction are assumed to be 2-amino-6-((3,4-dihydroxyphenyl)amino)hexanoic acid that undergo electron transfer at more negative potentials than the catechol. The effect of pH of catechol in presence of L-lysine was studied by varying pH from 5 to 11. The reaction was strongly influenced by the pH as well as concentration of L-lysine. The reaction was mostly favorable in 2 mM of catechol and 70 mM of L-lysine at pH 7. The behavior of the reaction mechanism was of electron transfer, chemical reaction and electron transfer (ECE) type.

L-lysine determination in animal feed using microbiological microtiter plate assay

Chromatographic methods are most commonly used for the analysis of amino acids; however, there is growing need for faster, simpler and more price-effective assays. In this paper, the applicability of a rapid microbiological assay for quantification of the total content of L-lysine in feed samples was evaluated. The assay relies on the dependency of bacterial growth of Pediococcus acidilactici on the presence of L-lysine. Microbiological microtiter plate assay method for the quantitative determination of total (added and natural) L-lysine in feed samples has been verified, and parameters such as accuracy, precision, limit of detection, and limit of determination were evaluated. Results of total L-lysine determination in different feed samples have been compared with results of validated HPLC method. The microbiological microtiter plate assay method can be employed as a qualitative and quantification method for total L-lysine determination with detection and determination limit of 0.040 % and 0.085 %, respectively. However, further research on the influence of sample matrix on the determination of low lysine levels is required.

Influence of nitrogen sources on growth and mycotoxin production by isolates of Pyrenophora tritici-repentis from wheat

The fungus Pyrenophora tritici-repentis (Died.) Drechs. infects the leaves and kernels of wheat, causing tan spot and red smudge, respectively. Isolates of P. tritici-repentis have been reported to be both phytopathogenic and mycotoxigenic. This research investigates the influence of nitrogen sources on growth and production of mycotoxins by eight different isolates of P. tritici-repentis. A synthetic agar medium (SAM) was used with different nitrogen sources, both inorganic [(NH4Cl, NH4NO3 and (NH4)2SO4)] and organic (l-alanine, l-histidine, and l-lysine), at a concentration of 37.5mmolL−1. Individual isolates exhibited different growth rates that varied according to the nitrogen source added to the medium. The choice of nitrogen source also had a major effect on production of the mycotoxins emodin, catenarin and islandicin. The highest concentrations of emodin, 54.40±4.46μgg−1, 43.07±23.39μgg−1 and 28.91±4.64μgg−1 of growth medium, were produced on the complex medium (V8-potato dextrose agar) by the isolates Alg-H2, 331-2 and TS93-71B, respectively. A relatively high concentration of emodin also was produced by isolates Az35-5 (28.29±4.71μgg−1 of medium) and TS93-71B (27.03±4.09μgg−1 of medium) on synthetic medium supplemented with l-alanine. The highest concentrations of catenarin (174.54±14.46μgg−1 and 104.87±6.13μgg−1 of medium) were recorded for isolates TS93-71B and Alg-H2 on synthetic medium supplemented with l-alanine and NH4Cl, respectively. The highest concentration of islandicin (4.64±0.36μgg−1 medium) was observed for isolate 331-2 in the presence of l-lysine. There was not a close relationship between mycelial growth and mycotoxin production by the fungal isolates. This is the first report on the influence of nitrogen sources on the production of mycotoxins by P. tritici-repentis.

Cloning, expression, purification, crystallization and preliminary X-ray diffraction of a lysine-specific permease from Pseudomonas aeruginosa.

The prokaryotic lysine-specific permease (LysP) belongs to the amino acid-polyamine-organocation (APC) transporter superfamily. In the cell, members of this family are responsible for the uptake and recycling of nutrients, for the maintenance of a constant internal ion concentration and for cell volume regulation. The detailed mechanism of substrate selectivity and transport of L-lysine by LysP is not understood. A high-resolution crystal structure would enormously facilitate such an understanding. To this end, LysP from Pseudomonas aeruginosa was recombinantly expressed in Escherichia coli and purified to near homogeneity by immobilized metal ion-affinity chromatography (IMAC) and size-exclusion chromatography (SEC). Hexagonal- and rod-shaped crystals were obtained in the presence of L-lysine and the L-lysine analogue L-4-thialysine by vapour diffusion and diffracted to 7.5 Å resolution. The diffraction data were indexed in space group P21, with unit-cell parameters a = 169.53, b = 169.53, c = 290.13 Å, γ = 120°.

The solubility and conformational characteristics of porcine myosin as affected by the presence of l-lysine and l-histidine

The influence of l-lys and l-his on the solubility, surface hydrophobicity, sulphydryl content and conformational characteristics of porcine myosin solubilised in high (0.6M), physiological (0.15M) and low (1mM) ionic strength solutions were explored. The solubility of myosin was increased in the presence of l-his and/or l-lys in all ionic strength solutions used. The presence of l-his and l-lys caused increases in the surface hydrophobicity and reactive sulphydryl content (p<0.05). Circular dichroism revealed a significant decrease of α-helical content with an increase of random coils, β-turns and β-sheets in the presence of l-his and/or l-lys. These results demonstrate that the introduction of l-lys and l-his causes the unfolding of myosin, resulting in loss of α-helical structure, which is followed by increases in random coils, β-turns and β-sheets, which exposes buried hydrophobic and sulphydryl groups to the myosin surface, ultimately increasing the solubility of porcine myosin.

Synthesis of a nitrogen-doped porous carbon monolith and its use for CO2 capture

Monolithic nitrogen-doped porous carbon was synthesized by the copolymerization of resorcinol and formaldehyde in the presence of l-lysine as the catalyst at the ambient conditions. The carbon is designated RFL. In order to increase the active nitrogen content, nitrogen-rich melamine was added, and the resulting material (RFLM) has more nitrogen-containing functional groups, and a higher specific surface area and pore volume than the original RFL. Glutamic acid was used to control the rate of polymerization, resulting in a porous carbon (RFLMG) with optimized texture properties. However, samples of RFLM and RFLMG show lower CO2 adsorption capacities than do the RFL series, indicating that there is no explicit linear relationship between the nitrogen content and CO2 adsorption capacity. This may be directly caused by the different form of the nitrogen-containing functional groups. [New Carbon Materials 2013, 28(4): 267–272]

Intra-tissue localization of an antibacterial l-amino acid oxidase in the rockfish Sebastes schlegeli

The rockfish Sebastes schlegeli skin mucus contains a potent antibacterial protein, SSAP (S. schlegeli antibacterial protein), a novel l-amino acid oxidase with strict substrate specificity that acts against water-borne Gram-negative bacteria. We previously demonstrated that SSAP distributes in the skin and gills. Here we investigated the intra-tissue localization of SSAP in the tissues by in situ hybridization. Skin and gill sections were hybridized with digoxigenin-conjugated SSAP-specific RNA probe. SSAP mRNA-positive cells located near the basal membrane of skin epidermis and the gill epithelium. Furthermore, skin section was analyzed by immunohistochemistry and reacted with anti-SSAP antiserum as a primary antibody. The mucus layer and mucous cells in the skin were immunopositive. Skin and gill extracts produced hydrogen peroxide, responsible for antibacterial activity, in the presence of l-lysine. These results suggested that SSAP functions locally as a humoral defense factor in S. schlegeli skin and gills and prevents pathogenic bacterial invasion.

One-step hydrothermal synthesis of N-doped TiO2/C nanocomposites with high visible light photocatalytic activity

N-doped TiO(2) nanoparticles modified with carbon (denoted N-TiO(2)/C) were successfully prepared by a facile one-pot hydrothermal treatment in the presence of L-lysine, which acts as a ligand to control the nanocrystal growth and as a source of nitrogen and carbon. As-prepared nanocomposites were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR) spectra, and N(2) adsorption-desorption analysis. The photocatalytic activities of the as-prepared photocatalysts were measured by the degradation of methyl orange (MO) under visible light irradiation at λ≥ 400 nm. The results show that N-TiO(2)/C nanocomposites increase absorption in the visible light region and exhibit a higher photocatalytic activity than pure TiO(2), commercial P25 and previously reported N-doped TiO(2) photocatalysts. We have demonstrated that the nitrogen was doped into the lattice and the carbon species were modified on the surface of the photocatalysts. N-doping narrows the band gap and C-modification enhances the visible light harvesting and accelerates the separation of the photo-generated electrons and holes. As a consequence, the photocatalytic activity is significantly improved. The molar ratio of L-lysine/TiCl(4) and the pH of the hydrothermal reaction solution are important factors affecting the photocatalytic activity of the N-TiO(2)/C; the optimum molar ratio of L-lysine/TiCl(4) is 8 and the optimum pH is ca. 4, at which the catalyst exhibits the highest reactivity. Our findings demonstrate that the as-obtained N-TiO(2)/C photocatalyst is a better and more promising candidate than well studied N-doped TiO(2) alternatives as visible light photocatalysts for potential applications in environmental purification.

Hollow peanut-like m-BiVO4: facile synthesis and solar-light-induced photocatalytic property

Monoclinic bismuth vanadate (m-BiVO4) with novel hollow peanut-like morphology was synthesized for the first time using L-lysine as surfactant. The use of L-lysine and the crystallization procedure is indispensable in getting the peanut-like morphology. The photocatalytic activity of the m-BiVO4 samples under solar-light irradiation was evaluated for degradation of crystal violet and methylene blue. Crystallization and calcination temperature are important factors affecting the photocatalytic activity of m-BiVO4, and best performance was observed over the sample that crystallized at 160 °C in the presence of L-lysine and subsequently subjected to calcination at 550 °C. The as-prepared BiVO4 showed good stability in catalyst recycling. Based on the results of XRD, XPS, FESEM, TEM (HRTEM), UV-vis diffuse reflectance spectroscopy, and N2 adsorption–desorption characterization, the good photocatalytic activity of the m-BiVO4 sample is attributed to its unique hollow peanut-like morphology and pure monoclinic phase of high crystallinity.

Effect of amino acids on the crystal growth of hydroxyapatite

The purpose of this study was to investigate the effect of amino acid on the morphology and crystallinity of nano-sized hydroxyapatite (HAP) crystals via a chemical precipitation method in the presence of l-lysine and l-tyrosine at different concentrations. The products were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The results showed the effect of l-lysine and l-tyrosine on the crystal growth of HAP was at opposite poles, i.e., the crystal growth was inhibited by l-lysine but promoted by l-tyrosine depending on the amino acid content. The mechanism of HAP crystal growth was also proposed.

Stabilization of collagen with EDC/NHS in the presence of l-lysine: A comprehensive study

This paper reports the effect of l-lysine on the conformational, rheological, and thermal properties of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) cross linked collagen and investigates the influence of l-lysine on the self assembly processes of collagen. In the absence of l-lysine, the rheological characterization of collagen cross linked with EDC/NHS showed an increase in shearing stress with shearing speed indicating that the collagen chains become rigid and the molecules are reluctant to flow. On the other hand, the increase in shearing stress with shearing speed is comparatively much less in the presence of l-lysine indicating a greater flexibility of the collagen molecules. The self assembly processes of collagen treated with EDC/NHS in the absence and presence of l-lysine were characterized using powder XRD, FT-IR, polarizing optical microscopy and kinetic studies. XRD studies show an increase in peak intensity and sharpness in the presence of l-lysine indicating the enhancement of crystallinity of collagen nano-fibrils. FT-IR results suggest that the incorporation of l-lysine in the EDC/NHS cross linking favors the molecular stability of collagen. From the present study, it is possible to conclude that the pre-treatment of collagen with l-lysine enhances EDC/NHS cross linking and can be used for biomaterial applications.

Further characterization and mode of action of dactylomelin-P, an antibacterial protein isolated from the ink of the sea hare Aplysia dactylomela (Rang, 1828)

Sea hares are well known, nearly shell-less, marine opisthobranchs that use a complex repertoire of chemicals for defense and communication instead of a conventional gastropod shell. The most conspicuous characteristic of these invertebrates is the secretion of ink, which is rich in bioactive proteins. Many of these proteins belong to a family of L-amino acid oxidases (L-AAOs). In the current study, we aimed to determine whether dactylomelin-P, an antibacterial protein isolated from the ink of Aplysia dactylomela, could act as an L-AAO. We also investigated its biochemical properties and antibacterial mechanism of action. We found that dactylomelin-P is an acidic protein (pI=5.0), rich in glutamic acid/glutamine, aspartic acid/asparagine, tyrosine, serine, and proline. It was stable under a broad pH range (3.0–12.0), after heating to 55°C for 30min, and after treating with protease. Its N-terminal amino acid sequence was DGVCSNRRQCNKEVCGSSYDVAIVGA and showed high similarity to other sea hare proteins previously identified as L-AAOs. The L-AAO activity was confirmed in an enzymatic assay, which showed that dactylomelin-P could oxidize L-lysine and L-arginine. We also demonstrated that the bacteriostatic activity of dactylomelin-P was mediated by hydrogen peroxide generated in the enzymatic reaction, but it acted as a bactericide in the presence of L-lysine and L-arginine. Transmission electron microscopy analyses showed that dactylomelin-P bound to growth-phase bacteria without causing morphological alterations to the cells. The bactericidal effect seems to involve H2O2 and other reactive components since it was not counteracted by H2O2 scavengers. Our findings showed biochemical, functional, and phylogenetic similarities among L-AAOs isolated from sea hares; this offers new insight into the evolution of these proteins and their roles in chemical defense.

ChemInform Abstract: Catalysis by L‐Lysine: A Green Method for the Condensation of Aromatic Aldehydes with Acidic Methylene Compounds in Water at Room Temperature.

The condensation of aromatic aldehydes with acidic methylene compounds such as ethyl benzoylacetate, 2,4-pentanedione and dimedone proceeded efficiently in pure water in the presence of L-lysine at room temperature. Interestingly, there are two different reaction mechanisms taking place under the same green catalyst system. This provides a green and mild synthetic method for the preparation of these two classes of compounds.

L-lysine coated iron oxide nanoparticles: Synthesis, structural and conductivity characterization

l-lysine coated iron oxide (LCIO) nanoparticles were synthesized by a co-precipitation method in the presence of amino acid. XRD analysis confirmed the presence of cubic magnetite phase with an average crystallite size of 8 ± 4 nm. Particle size estimated from TEM, by log-normal fitting, is ∼114 nm. The difference between the crystallite size from XRD and particle size from TEM indicates polycrystalline nature of synthesized particles. FT-IR show that the binding of l-lysine on the surface of iron oxide through carboxyl groups is via unidentate linkage. The presence of l-lysine on iron oxide is also confirmed by zeta potential measurements on LCIO nanoparticles, revealing a partial coverage of iron oxide with l-lysine. In order to obtain chemically stable, well-dispersed and uniform sized nanoparticles, amino acids are suitable because they play a very important role in the body. Conductivity measurements were performed to investigate the influence of the coating on the conduction characteristics of iron oxide and results show the existence of a hopping conduction mechanism. Magnetic transition is observed at ∼70 °C for uncoated iron oxide and LCIO samples. Frequency (1 Hz to 3 MHz) and temperature (290–420 K) dependant AC conductivity measurements have resulted in AC activation energies between 0.048 and 0.041 eV for uncoated and 0.050–0.044 eV for LCIO nanoparticles. Temperature-dependant DC resistivity measurements of iron oxide and LCIO at high temperatures resulted in the DC activation energies of 0.22 and 0.43 eV respectively. The higher activation energy value for LCIO is the result of coating by insulating l-lysine layer.