Norbert Lihi - Academia.edu (original) (raw)
Papers by Norbert Lihi
Recent Highlights II, 2022
New Journal of Chemistry, 2022
Cysteine containing ligands with free amino- and amidated C-termini were studied and their nickel... more Cysteine containing ligands with free amino- and amidated C-termini were studied and their nickel(II), zinc(II) and cadmium(II) complexes were described in the aspect of their thermodynamic stability and structure, including...
Inorganic Chemistry Frontiers, 2022
Cu(ii) complexes formed with cross-bridged pentaazamacrocycle ligands exhibit high stability and ... more Cu(ii) complexes formed with cross-bridged pentaazamacrocycle ligands exhibit high stability and appropriate inertness, as well as fast complex formation auguring a bright future for this ligand family in radiotheranostic applications.
Chemistry – A European Journal, 2020
Detailed equilibrium, spectroscopica nd superoxide dismutase (SOD) activity studies are reported ... more Detailed equilibrium, spectroscopica nd superoxide dismutase (SOD) activity studies are reported on an ickel complex formed with an ew metallopeptide bearing two nickel binding loops of NiSOD. The metallopeptide exhibits unique nickel binding ability and the binuclear complex is a major speciesw ith 2 (NH 2 ,N amide ,S À ,S À)d onor set even in an equimolar solution of the metal ion and the ligand. Nickel(III) species were generated by oxidizing the Ni II complexes with KO 2 and the coordination modes were identified by EPR spectroscopy.T he binuclear complex formed with the binding motifs exhibits superior SOD activity,i nt his respect it is an excellent model of the native NiSOD enzyme.Adetailed kinetic model is postulated that incorporates spontaneous decomposition of the superoxide ion, the dismutation cycle and fast redox degradationo ft he binuclear complex. The latter process leads to the elimination of the SOD activity.A unique feature of this system is that the Ni III form of the catalyst rapidlya ccumulates in the dismutation cycle and simultaneously the Ni II form becomes am inor species.
Molecules, 2021
N-oxides of N-heteroaromatic compounds find widespread applications in various fields of chemistr... more N-oxides of N-heteroaromatic compounds find widespread applications in various fields of chemistry. Although the strictly planar aromatic structure of 1,10-phenanthroline (phen) is expected to induce unique features of the corresponding N-oxides, so far the potential of these compounds has not been explored. In fact, appropriate procedure has not been reported for synthesizing these derivatives of phen. Now, we provide a straightforward method for the synthesis of a series of mono-N-oxides of 1,10-phenanthrolines. The parent compounds were oxidized by a green oxidant, peroxomonosulfate ion in acidic aqueous solution. The products were obtained in high quality and at good to excellent yields. A systematic study reveals a clear-cut correlation between the basicity of the compounds and the electronic effects of the substituents on the aromatic ring. The UV spectra of these compounds were predicted by DFT calculations at the TD-DFT/TPSSh/def2-TZVP level of theory.
Inorganic Chemistry, 2021
Copper(II) complexes formed with sulfonated salan ligands (HSS) have been synthesized, and their ... more Copper(II) complexes formed with sulfonated salan ligands (HSS) have been synthesized, and their coordination chemistry has been characterized using pH-potentiometry and spectroscopic methods [UV-vis, electron paramagnetic resonance (EPR), and electron-electron double resonance (ELDOR)-detected NMR (EDNMR)] in aqueous solution. Several bridging moieties between the two salicylamine functions were introduced, e.g., ethyl (HSS), propyl (PrHSS), butyl (BuHSS), cyclohexyl (cis-CyHSS, trans-CyHSS), and diphenyl (dPhHSS). All of the investigated ligands feature excellent copper(II) binding ability via the formation of a (O-,N,N,O-) chelate system. The results indicated that the cyclohexyl moiety significantly enhances the stability of the copper(II) complexes. EPR studies revealed that the arrangement of the coordinated donor atoms is more symmetrical around the copper(II) center and similar for HSS, BuHSS, CyHSS, and dPhHSS, respectively, and a higher rhombicity of the g tensor was detected for PrHSS. The copper(II) complexes of the sulfosalan ligands were isolated in solid form also and showed moderate catalytic activity in the Henry (nitroaldol) reaction of aldehydes and nitromethane. The best yield for nitroaldol production was obtained for copper(II) complexes of PrHSS and BuHSS, although their metal binding ability is moderate compared to that of the cyclohexyl counterparts. However, these complexes possess larger spin density on the nitrogen nuclei than that for the other cases, which alters their catalytic activity.
Inorganic Chemistry, 2021
In recent years Auger electron emitters have been suggested as promising candidates for radiother... more In recent years Auger electron emitters have been suggested as promising candidates for radiotherapy with no side effects in cancer treatment. In this work we report a detailed coordination chemistry study of [Sb(PCTA)] (PCTA: 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid), a macrocyclic aminopolycarboxylate-type complex of antimony(III), whose 119Sb isotope could be a suitable low-energy electron emitter for radiotherapy. The thermodynamic stability of the chelate obtained by pH-potentiometry and UV-vis spectrophotometry is high enough (log K[Sb(PCTA)] = 23.2(1)) to prevent the hydrolysis of the metal ion near physiological pH. The formation of [Sb(PCTA)] is confirmed by NMR and electrospray ionization mass spectrometry measurements in solution; furthermore, the structure of [Sb(PCTA)]·NaCl·3H2O and [Sb(PCTA)]·HCl·3H2O is described by X-ray and density functional theory calculations. Consequently, the [Sb(PCTA)] is the first thermodynamically stable antimony(III) complex bearing polyamino-polycarboxylate macrocyclic platform. Our results demonstrate the potential of rigid (pyclen derivative) ligands as chelators for future applications of Sb(III) in a targeted radiotherapy based on the 119Sb isotope.
Chemical Engineering Research and Design, 2021
Abstract By pursuing the aim of identifying new types of catalysts in the electrolytic production... more Abstract By pursuing the aim of identifying new types of catalysts in the electrolytic production of NaClO3 from NaCl (chlorate process), we report a detailed study on the decomposition of hypochlorous acid accelerated by yttrium(III) chloride (YCl3), yttrium(III) oxide (Y2O3) and telluric acid (Te(OH)6) at 80 °C. The results were compared with those obtained in the uncatalyzed and chromium(VI) catalyzed reactions. In general, the decomposition of HOCl occurs via two competing paths toward the formation of ClO3− or O2. In the case of YCl3, the decomposition proceeds via the oxygen path over the entire studied pH range. Y2O3 slightly catalyzes the chlorate path under acidic conditions, however the noted catalytic effect is probably due to the “self-buffering” of the reaction mixture (Y2O3 suspension). Although, a real catalytic process takes place in the presence of Te(OH)6, a significant pH-effect is also observed which is most likely associated with the acid–base equilibria of telluric acid. pH dependent studies demonstrate that the optimum pH of decomposition is at around 6.7–6.9 in this case. The comparison of the results obtained in the presence of chromium(VI) and Te(OH)6 reveals that the former is a more active catalyst. On the basis of kinetic and stoichiometric results, it is reasonable to assume that Te(OH)6 may be utilized as an alternative catalyst in the chlorate process.
Chemical Engineering Research and Design, 2021
Abstract By pursuing the aim of identifying new types of catalysts in the electrolytic production... more Abstract By pursuing the aim of identifying new types of catalysts in the electrolytic production of NaClO3 from NaCl (chlorate process), we report a detailed study on the decomposition of hypochlorous acid accelerated by yttrium(III) chloride (YCl3), yttrium(III) oxide (Y2O3) and telluric acid (Te(OH)6) at 80 °C. The results were compared with those obtained in the uncatalyzed and chromium(VI) catalyzed reactions. In general, the decomposition of HOCl occurs via two competing paths toward the formation of ClO3− or O2. In the case of YCl3, the decomposition proceeds via the oxygen path over the entire studied pH range. Y2O3 slightly catalyzes the chlorate path under acidic conditions, however the noted catalytic effect is probably due to the “self-buffering” of the reaction mixture (Y2O3 suspension). Although, a real catalytic process takes place in the presence of Te(OH)6, a significant pH-effect is also observed which is most likely associated with the acid–base equilibria of telluric acid. pH dependent studies demonstrate that the optimum pH of decomposition is at around 6.7–6.9 in this case. The comparison of the results obtained in the presence of chromium(VI) and Te(OH)6 reveals that the former is a more active catalyst. On the basis of kinetic and stoichiometric results, it is reasonable to assume that Te(OH)6 may be utilized as an alternative catalyst in the chlorate process.
We report the Mn(II) complexes with two pyclen-based ligands (pyclen = 3,6,9,15-tetraazabicyclo[9... more We report the Mn(II) complexes with two pyclen-based ligands (pyclen = 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene) functionalized with acetate pendant arms either at positions 3,6 (3,6-PC2A) or 3,9 (3,9-PC2A) of the macrocyclic fragment. The 3,6-PC2A ligand was synthesized in five steps from pyclen-oxalate by protecting one of the secondary amine groups of pyclen using Alloc protecting chemistry. The complex with 3,9-PC2A is characterized by a higher thermodynamic stability (logKMnL = 17.09(2) than the 3,6-PC2A analogue (logKMnL = 15.53(1), 0.15 M NaCl). Both complexes contain a water molecule coordinated to the metal ion, which results in relatively high 1H relaxivities (r1p = 2.72 and 2.91 mM-1 s -1 for the complexes with 3,6- and 3,9-PC2A, respectively, 25 ºC, 0.49 T). The coordinated water molecule displays fast exchange kinetics with the bulk in both cases; the rates (kex 298) are 140106 and 126106 s -1 for [Mn(3,6-PC2A)] and [Mn(3,9- PC2A)], respectively. Th...
Inorganic Chemistry, 2020
Detailed equilibrium, spectroscopic and SOD activity studies are reported on nickel(II) complexes... more Detailed equilibrium, spectroscopic and SOD activity studies are reported on nickel(II) complexes formed with the N-terminally free HHDLPCGVY-NH2 (NiSODHH) and HCDLPHGVY-NH2 (NiSODHC) peptides mimicking the nickel binding loop in NiSOD. In these model peptides, cysteine was incorporated in different positions in order to gain better insight into the role of the cysteine residues in NiSOD. The results are compared with those obtained with the wild-type fragment of NiSOD. The complex formation equilibria of nickel(II) with the two peptides exhibit different features. In the case of NiSODHH, the ligand field of the (NH2,NIm,NIm,S-) donor set is not strong enough to cause spin pairing and an octahedral paramagnetic complex is formed under physiological conditions. In contrast, NiSODHC forms square-planar diamagnetic complex with (NH2,N-,S-,NIm) donors which exhibits remarkable SOD activity. Our results unambiguously prove that the presence of cysteine in the secondary position of the peptide chain is crucial to establish the square-planar geometry in the reduced form of NiSOD, while the distant cysteine affects the redox properties of the Ni(II)/Ni(III) couple. Compared to the model systems, the Ni(II) complex with the wild-type fragment of NiSOD exhibits superior SOD activity. This confirms that both cysteinyl residues are essential in efficient degradation of superoxide ion. The enzyme mimetic complexes are also capable to assist the decomposition of superoxide ion, however, they show considerably smaller catalytic activity due to the absence of one of the cysteine residues.
Journal of Inorganic Biochemistry, 2020
With the aim of identifying new types of water-soluble catalyst precursors for modification of bi... more With the aim of identifying new types of water-soluble catalyst precursors for modification of biological membranes by homogeneous hydrogenation in aqueous solution and under mild conditions, we have performed detailed equilibrium and spectroscopic characterization of complex formation between nickel(II) or palladium(II) and salan-type ligands sulfonated in their aromatic rings (N,N'-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminoethane (HSS), N,N'-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminopropane (PrHSS) and N,N'-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminobutane (BuHSS)) in the slightly acidic-alkaline pH range. The stability constants of the metal complexes were determined using pH-potentiometry. The catalytic activities of the [Ni(HSS)] and [Pd(HSS)] complexes in hydrogenation and redox isomerization of oct-1-en-3-ol were also studied. The results indicate, that all of the investigated ligands exhibit excellent nickel(II) and palladium(II) binding ability via the formation of (O-,N,N,O-) linked chelate system. Both [Ni(HSS)] and [Pd(HSS)] catalyze the hydrogenation and redox isomerization of oct-1-en-3-ol. [Pd(HSS)] shows excellent activity and the reaction was highly selective to the formation of octan-3-ol. [Ni(HSS)] is also an active and selective catalyst for this hydrogenation reaction and to the best of our knowledge, [Ni(HSS)] is the first nickel(II)-based, hydrolytically stable, water-soluble catalyst bearing sulfonated salan moiety.
ChemPlusChem, 2019
Copper(II) complexes of the N-terminal peptide fragments of tau protein have been studied by pote... more Copper(II) complexes of the N-terminal peptide fragments of tau protein have been studied by potentiometric and various spectroscopic techniques (UV-vis, CD, ESR and ESI-MS). The octapeptide Tau(9-16) (AcÀ EVMEDHAGÀ NH 2) contains the H14 residue of the native protein, while Tau(26-33) (AcÀ QGGYTMHQÀ NH 2) and its mutants Tau(Q26K-Q33K) (AcÀ KGGYTMHKÀ NH 2) and Tau(Q26K-Y29A-Q33K) (AcÀ KGGATMHKÀ NH 2) include the H32 residue. To compare the binding ability of H14 and H32 in a single molecule the decapeptide AcÀ EDHAGTMHQDÀ NH 2 (Tau(12-16)(30-34)) has also been synthesized and studied. The histidyl residue is the primary metal binding site for metal ions in all the peptide models studied. In the case of Tau(9-16) the side chain carboxylate functions enhance the stability of the MÀ N im coordinated complexes compared to Tau(26-33) (logK(CuÀ N im) = 5.04 and 3.78, respectively). Deprotonation and metal ion coordination of amide groups occur around the physiological pH range for copper(II). The formation of the imidazole-and amide-coordinated species changes the metal ion preference and the complexes formed with the peptides containing the H32 residue predominate over those of H14 at physiological pH values (90 %-10 %) and in alkaline samples (96 %-4 %).
Dalton Transactions, 2019
Equilibrium and spectroscopic characterization of zinc(ii) complexes with NiSOD related peptides ... more Equilibrium and spectroscopic characterization of zinc(ii) complexes with NiSOD related peptides highlights the crucial role of terminal amino groups in the enzymatic function.
Inorganic Chemistry, 2019
Detailed equilibrium and spectroscopic characterization of the complex formation processes of the... more Detailed equilibrium and spectroscopic characterization of the complex formation processes of the nickel binding loop in NiSOD and its related fragments is reported in the slightly acidic− alkaline pH range. The N-terminally free and protected nonapeptides HCDLPCGVY-NH 2 (NiSODM 1), HCDLACGVY-NH 2 (Ni-SODM 3), and Ac-HCDLPCGVY-NH 2 (NiSODM 2) and the Nterminally shortened analogues HCDL-NH 2 and HCA-NH 2 were synthesized, and their nickel(II) complexes were studied by potentiometric and several spectroscopic techniques. EPR spectroscopy was also used to assign the coordinating donor sites after the in situ oxidation of nickel(II) complexes. The terminal amino groups are the primary metal binding sites for nickel(II) ion in NiSODM 1 and NiSODM 3 , resulting in the high nickel(II) binding affinity of this peptide via the formation of a square-planar, (NH 2 ,N − ,S − ,S −) or (NH 2 ,N Im N − ,S −) coordinated species in a wide pH range. The latter coordination sphere prevents the formation of the active structure of NiSOD under physiological pH, reflecting the crucial role of proline in nickel(II) binding. In situ oxidation of the Ni(II) complexes yielded Ni(III) transient species in the case of nonapeptides. The square-pyramidal coordination environment with axial imidazole ligation provides the active structure of the oxidized form of NiSOD in the case of N-terminally free peptides. Consequently, these ligands are promising candidates for modeling NiSOD. The acylation of the amino terminus significantly reduces the nickel(II) binding affinity of the nonapeptide, while the oxidation results in coordination isomers.
Dalton Trans., 2017
The N-terminally free but C-terminally amidated peptides Pen-SSACS-NH2 and CSSA-Pen-S-NH2 contain... more The N-terminally free but C-terminally amidated peptides Pen-SSACS-NH2 and CSSA-Pen-S-NH2 containing L-penicillamine (Pen) in the sequence have been synthesized and their nickel(II), zinc(II) and cadmium(II) complexes were studied by potentiometric...
Coordination Chemistry Reviews, 2016
Abstract Numerous studies have demonstrated the high metal binding capacity and selectivity of pe... more Abstract Numerous studies have demonstrated the high metal binding capacity and selectivity of peptide molecules. The terminal amino group, deprotonated amide nitrogens, and various side chain donor functions are the most common metal binding sites in these complexes. Imidazole-N donors of histidyl residues are especially important for complex formation because their complexes exhibit outstanding thermodynamic stability and high structural variation. Complex formation reactions with simple oligopeptides containing one histidyl residue have already been clarified satisfactorily and the results have been reviewed. However, the coordination chemistry of multihistidine peptides is understood less well, although the relevant molecules have major biological significance. These systems include peptide fragments of prion protein, amyloid-β and various copper(II) or zinc(II) transporter proteins. Recently, much data have been reported about these complexes and the most important results are summarized in this review. The second part of this review describes complex formation by peptides that contain another strongly coordinating side chain (e.g., carboxylates of Asp and Glu, and thiolates of Cys residues) in addition to the histidyl sites.
New J. Chem., 2016
Hexapeptides containing separate histidyl and cysteinyl residues have outstanding metal binding a... more Hexapeptides containing separate histidyl and cysteinyl residues have outstanding metal binding ability but the binding sites of peptides reveal a significant specificity.
New J. Chem., 2015
The novel synthesized cysteine peptides form stable zinc(ii) and cadmium(ii) complexes; the speci... more The novel synthesized cysteine peptides form stable zinc(ii) and cadmium(ii) complexes; the specific sequence makes possible metal induced amide deprotonation.
Recent Highlights II, 2022
New Journal of Chemistry, 2022
Cysteine containing ligands with free amino- and amidated C-termini were studied and their nickel... more Cysteine containing ligands with free amino- and amidated C-termini were studied and their nickel(II), zinc(II) and cadmium(II) complexes were described in the aspect of their thermodynamic stability and structure, including...
Inorganic Chemistry Frontiers, 2022
Cu(ii) complexes formed with cross-bridged pentaazamacrocycle ligands exhibit high stability and ... more Cu(ii) complexes formed with cross-bridged pentaazamacrocycle ligands exhibit high stability and appropriate inertness, as well as fast complex formation auguring a bright future for this ligand family in radiotheranostic applications.
Chemistry – A European Journal, 2020
Detailed equilibrium, spectroscopica nd superoxide dismutase (SOD) activity studies are reported ... more Detailed equilibrium, spectroscopica nd superoxide dismutase (SOD) activity studies are reported on an ickel complex formed with an ew metallopeptide bearing two nickel binding loops of NiSOD. The metallopeptide exhibits unique nickel binding ability and the binuclear complex is a major speciesw ith 2 (NH 2 ,N amide ,S À ,S À)d onor set even in an equimolar solution of the metal ion and the ligand. Nickel(III) species were generated by oxidizing the Ni II complexes with KO 2 and the coordination modes were identified by EPR spectroscopy.T he binuclear complex formed with the binding motifs exhibits superior SOD activity,i nt his respect it is an excellent model of the native NiSOD enzyme.Adetailed kinetic model is postulated that incorporates spontaneous decomposition of the superoxide ion, the dismutation cycle and fast redox degradationo ft he binuclear complex. The latter process leads to the elimination of the SOD activity.A unique feature of this system is that the Ni III form of the catalyst rapidlya ccumulates in the dismutation cycle and simultaneously the Ni II form becomes am inor species.
Molecules, 2021
N-oxides of N-heteroaromatic compounds find widespread applications in various fields of chemistr... more N-oxides of N-heteroaromatic compounds find widespread applications in various fields of chemistry. Although the strictly planar aromatic structure of 1,10-phenanthroline (phen) is expected to induce unique features of the corresponding N-oxides, so far the potential of these compounds has not been explored. In fact, appropriate procedure has not been reported for synthesizing these derivatives of phen. Now, we provide a straightforward method for the synthesis of a series of mono-N-oxides of 1,10-phenanthrolines. The parent compounds were oxidized by a green oxidant, peroxomonosulfate ion in acidic aqueous solution. The products were obtained in high quality and at good to excellent yields. A systematic study reveals a clear-cut correlation between the basicity of the compounds and the electronic effects of the substituents on the aromatic ring. The UV spectra of these compounds were predicted by DFT calculations at the TD-DFT/TPSSh/def2-TZVP level of theory.
Inorganic Chemistry, 2021
Copper(II) complexes formed with sulfonated salan ligands (HSS) have been synthesized, and their ... more Copper(II) complexes formed with sulfonated salan ligands (HSS) have been synthesized, and their coordination chemistry has been characterized using pH-potentiometry and spectroscopic methods [UV-vis, electron paramagnetic resonance (EPR), and electron-electron double resonance (ELDOR)-detected NMR (EDNMR)] in aqueous solution. Several bridging moieties between the two salicylamine functions were introduced, e.g., ethyl (HSS), propyl (PrHSS), butyl (BuHSS), cyclohexyl (cis-CyHSS, trans-CyHSS), and diphenyl (dPhHSS). All of the investigated ligands feature excellent copper(II) binding ability via the formation of a (O-,N,N,O-) chelate system. The results indicated that the cyclohexyl moiety significantly enhances the stability of the copper(II) complexes. EPR studies revealed that the arrangement of the coordinated donor atoms is more symmetrical around the copper(II) center and similar for HSS, BuHSS, CyHSS, and dPhHSS, respectively, and a higher rhombicity of the g tensor was detected for PrHSS. The copper(II) complexes of the sulfosalan ligands were isolated in solid form also and showed moderate catalytic activity in the Henry (nitroaldol) reaction of aldehydes and nitromethane. The best yield for nitroaldol production was obtained for copper(II) complexes of PrHSS and BuHSS, although their metal binding ability is moderate compared to that of the cyclohexyl counterparts. However, these complexes possess larger spin density on the nitrogen nuclei than that for the other cases, which alters their catalytic activity.
Inorganic Chemistry, 2021
In recent years Auger electron emitters have been suggested as promising candidates for radiother... more In recent years Auger electron emitters have been suggested as promising candidates for radiotherapy with no side effects in cancer treatment. In this work we report a detailed coordination chemistry study of [Sb(PCTA)] (PCTA: 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid), a macrocyclic aminopolycarboxylate-type complex of antimony(III), whose 119Sb isotope could be a suitable low-energy electron emitter for radiotherapy. The thermodynamic stability of the chelate obtained by pH-potentiometry and UV-vis spectrophotometry is high enough (log K[Sb(PCTA)] = 23.2(1)) to prevent the hydrolysis of the metal ion near physiological pH. The formation of [Sb(PCTA)] is confirmed by NMR and electrospray ionization mass spectrometry measurements in solution; furthermore, the structure of [Sb(PCTA)]·NaCl·3H2O and [Sb(PCTA)]·HCl·3H2O is described by X-ray and density functional theory calculations. Consequently, the [Sb(PCTA)] is the first thermodynamically stable antimony(III) complex bearing polyamino-polycarboxylate macrocyclic platform. Our results demonstrate the potential of rigid (pyclen derivative) ligands as chelators for future applications of Sb(III) in a targeted radiotherapy based on the 119Sb isotope.
Chemical Engineering Research and Design, 2021
Abstract By pursuing the aim of identifying new types of catalysts in the electrolytic production... more Abstract By pursuing the aim of identifying new types of catalysts in the electrolytic production of NaClO3 from NaCl (chlorate process), we report a detailed study on the decomposition of hypochlorous acid accelerated by yttrium(III) chloride (YCl3), yttrium(III) oxide (Y2O3) and telluric acid (Te(OH)6) at 80 °C. The results were compared with those obtained in the uncatalyzed and chromium(VI) catalyzed reactions. In general, the decomposition of HOCl occurs via two competing paths toward the formation of ClO3− or O2. In the case of YCl3, the decomposition proceeds via the oxygen path over the entire studied pH range. Y2O3 slightly catalyzes the chlorate path under acidic conditions, however the noted catalytic effect is probably due to the “self-buffering” of the reaction mixture (Y2O3 suspension). Although, a real catalytic process takes place in the presence of Te(OH)6, a significant pH-effect is also observed which is most likely associated with the acid–base equilibria of telluric acid. pH dependent studies demonstrate that the optimum pH of decomposition is at around 6.7–6.9 in this case. The comparison of the results obtained in the presence of chromium(VI) and Te(OH)6 reveals that the former is a more active catalyst. On the basis of kinetic and stoichiometric results, it is reasonable to assume that Te(OH)6 may be utilized as an alternative catalyst in the chlorate process.
Chemical Engineering Research and Design, 2021
Abstract By pursuing the aim of identifying new types of catalysts in the electrolytic production... more Abstract By pursuing the aim of identifying new types of catalysts in the electrolytic production of NaClO3 from NaCl (chlorate process), we report a detailed study on the decomposition of hypochlorous acid accelerated by yttrium(III) chloride (YCl3), yttrium(III) oxide (Y2O3) and telluric acid (Te(OH)6) at 80 °C. The results were compared with those obtained in the uncatalyzed and chromium(VI) catalyzed reactions. In general, the decomposition of HOCl occurs via two competing paths toward the formation of ClO3− or O2. In the case of YCl3, the decomposition proceeds via the oxygen path over the entire studied pH range. Y2O3 slightly catalyzes the chlorate path under acidic conditions, however the noted catalytic effect is probably due to the “self-buffering” of the reaction mixture (Y2O3 suspension). Although, a real catalytic process takes place in the presence of Te(OH)6, a significant pH-effect is also observed which is most likely associated with the acid–base equilibria of telluric acid. pH dependent studies demonstrate that the optimum pH of decomposition is at around 6.7–6.9 in this case. The comparison of the results obtained in the presence of chromium(VI) and Te(OH)6 reveals that the former is a more active catalyst. On the basis of kinetic and stoichiometric results, it is reasonable to assume that Te(OH)6 may be utilized as an alternative catalyst in the chlorate process.
We report the Mn(II) complexes with two pyclen-based ligands (pyclen = 3,6,9,15-tetraazabicyclo[9... more We report the Mn(II) complexes with two pyclen-based ligands (pyclen = 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene) functionalized with acetate pendant arms either at positions 3,6 (3,6-PC2A) or 3,9 (3,9-PC2A) of the macrocyclic fragment. The 3,6-PC2A ligand was synthesized in five steps from pyclen-oxalate by protecting one of the secondary amine groups of pyclen using Alloc protecting chemistry. The complex with 3,9-PC2A is characterized by a higher thermodynamic stability (logKMnL = 17.09(2) than the 3,6-PC2A analogue (logKMnL = 15.53(1), 0.15 M NaCl). Both complexes contain a water molecule coordinated to the metal ion, which results in relatively high 1H relaxivities (r1p = 2.72 and 2.91 mM-1 s -1 for the complexes with 3,6- and 3,9-PC2A, respectively, 25 ºC, 0.49 T). The coordinated water molecule displays fast exchange kinetics with the bulk in both cases; the rates (kex 298) are 140106 and 126106 s -1 for [Mn(3,6-PC2A)] and [Mn(3,9- PC2A)], respectively. Th...
Inorganic Chemistry, 2020
Detailed equilibrium, spectroscopic and SOD activity studies are reported on nickel(II) complexes... more Detailed equilibrium, spectroscopic and SOD activity studies are reported on nickel(II) complexes formed with the N-terminally free HHDLPCGVY-NH2 (NiSODHH) and HCDLPHGVY-NH2 (NiSODHC) peptides mimicking the nickel binding loop in NiSOD. In these model peptides, cysteine was incorporated in different positions in order to gain better insight into the role of the cysteine residues in NiSOD. The results are compared with those obtained with the wild-type fragment of NiSOD. The complex formation equilibria of nickel(II) with the two peptides exhibit different features. In the case of NiSODHH, the ligand field of the (NH2,NIm,NIm,S-) donor set is not strong enough to cause spin pairing and an octahedral paramagnetic complex is formed under physiological conditions. In contrast, NiSODHC forms square-planar diamagnetic complex with (NH2,N-,S-,NIm) donors which exhibits remarkable SOD activity. Our results unambiguously prove that the presence of cysteine in the secondary position of the peptide chain is crucial to establish the square-planar geometry in the reduced form of NiSOD, while the distant cysteine affects the redox properties of the Ni(II)/Ni(III) couple. Compared to the model systems, the Ni(II) complex with the wild-type fragment of NiSOD exhibits superior SOD activity. This confirms that both cysteinyl residues are essential in efficient degradation of superoxide ion. The enzyme mimetic complexes are also capable to assist the decomposition of superoxide ion, however, they show considerably smaller catalytic activity due to the absence of one of the cysteine residues.
Journal of Inorganic Biochemistry, 2020
With the aim of identifying new types of water-soluble catalyst precursors for modification of bi... more With the aim of identifying new types of water-soluble catalyst precursors for modification of biological membranes by homogeneous hydrogenation in aqueous solution and under mild conditions, we have performed detailed equilibrium and spectroscopic characterization of complex formation between nickel(II) or palladium(II) and salan-type ligands sulfonated in their aromatic rings (N,N'-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminoethane (HSS), N,N'-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminopropane (PrHSS) and N,N'-bis(2-hydroxy-5-sulfonatobenzyl)-1,4-diaminobutane (BuHSS)) in the slightly acidic-alkaline pH range. The stability constants of the metal complexes were determined using pH-potentiometry. The catalytic activities of the [Ni(HSS)] and [Pd(HSS)] complexes in hydrogenation and redox isomerization of oct-1-en-3-ol were also studied. The results indicate, that all of the investigated ligands exhibit excellent nickel(II) and palladium(II) binding ability via the formation of (O-,N,N,O-) linked chelate system. Both [Ni(HSS)] and [Pd(HSS)] catalyze the hydrogenation and redox isomerization of oct-1-en-3-ol. [Pd(HSS)] shows excellent activity and the reaction was highly selective to the formation of octan-3-ol. [Ni(HSS)] is also an active and selective catalyst for this hydrogenation reaction and to the best of our knowledge, [Ni(HSS)] is the first nickel(II)-based, hydrolytically stable, water-soluble catalyst bearing sulfonated salan moiety.
ChemPlusChem, 2019
Copper(II) complexes of the N-terminal peptide fragments of tau protein have been studied by pote... more Copper(II) complexes of the N-terminal peptide fragments of tau protein have been studied by potentiometric and various spectroscopic techniques (UV-vis, CD, ESR and ESI-MS). The octapeptide Tau(9-16) (AcÀ EVMEDHAGÀ NH 2) contains the H14 residue of the native protein, while Tau(26-33) (AcÀ QGGYTMHQÀ NH 2) and its mutants Tau(Q26K-Q33K) (AcÀ KGGYTMHKÀ NH 2) and Tau(Q26K-Y29A-Q33K) (AcÀ KGGATMHKÀ NH 2) include the H32 residue. To compare the binding ability of H14 and H32 in a single molecule the decapeptide AcÀ EDHAGTMHQDÀ NH 2 (Tau(12-16)(30-34)) has also been synthesized and studied. The histidyl residue is the primary metal binding site for metal ions in all the peptide models studied. In the case of Tau(9-16) the side chain carboxylate functions enhance the stability of the MÀ N im coordinated complexes compared to Tau(26-33) (logK(CuÀ N im) = 5.04 and 3.78, respectively). Deprotonation and metal ion coordination of amide groups occur around the physiological pH range for copper(II). The formation of the imidazole-and amide-coordinated species changes the metal ion preference and the complexes formed with the peptides containing the H32 residue predominate over those of H14 at physiological pH values (90 %-10 %) and in alkaline samples (96 %-4 %).
Dalton Transactions, 2019
Equilibrium and spectroscopic characterization of zinc(ii) complexes with NiSOD related peptides ... more Equilibrium and spectroscopic characterization of zinc(ii) complexes with NiSOD related peptides highlights the crucial role of terminal amino groups in the enzymatic function.
Inorganic Chemistry, 2019
Detailed equilibrium and spectroscopic characterization of the complex formation processes of the... more Detailed equilibrium and spectroscopic characterization of the complex formation processes of the nickel binding loop in NiSOD and its related fragments is reported in the slightly acidic− alkaline pH range. The N-terminally free and protected nonapeptides HCDLPCGVY-NH 2 (NiSODM 1), HCDLACGVY-NH 2 (Ni-SODM 3), and Ac-HCDLPCGVY-NH 2 (NiSODM 2) and the Nterminally shortened analogues HCDL-NH 2 and HCA-NH 2 were synthesized, and their nickel(II) complexes were studied by potentiometric and several spectroscopic techniques. EPR spectroscopy was also used to assign the coordinating donor sites after the in situ oxidation of nickel(II) complexes. The terminal amino groups are the primary metal binding sites for nickel(II) ion in NiSODM 1 and NiSODM 3 , resulting in the high nickel(II) binding affinity of this peptide via the formation of a square-planar, (NH 2 ,N − ,S − ,S −) or (NH 2 ,N Im N − ,S −) coordinated species in a wide pH range. The latter coordination sphere prevents the formation of the active structure of NiSOD under physiological pH, reflecting the crucial role of proline in nickel(II) binding. In situ oxidation of the Ni(II) complexes yielded Ni(III) transient species in the case of nonapeptides. The square-pyramidal coordination environment with axial imidazole ligation provides the active structure of the oxidized form of NiSOD in the case of N-terminally free peptides. Consequently, these ligands are promising candidates for modeling NiSOD. The acylation of the amino terminus significantly reduces the nickel(II) binding affinity of the nonapeptide, while the oxidation results in coordination isomers.
Dalton Trans., 2017
The N-terminally free but C-terminally amidated peptides Pen-SSACS-NH2 and CSSA-Pen-S-NH2 contain... more The N-terminally free but C-terminally amidated peptides Pen-SSACS-NH2 and CSSA-Pen-S-NH2 containing L-penicillamine (Pen) in the sequence have been synthesized and their nickel(II), zinc(II) and cadmium(II) complexes were studied by potentiometric...
Coordination Chemistry Reviews, 2016
Abstract Numerous studies have demonstrated the high metal binding capacity and selectivity of pe... more Abstract Numerous studies have demonstrated the high metal binding capacity and selectivity of peptide molecules. The terminal amino group, deprotonated amide nitrogens, and various side chain donor functions are the most common metal binding sites in these complexes. Imidazole-N donors of histidyl residues are especially important for complex formation because their complexes exhibit outstanding thermodynamic stability and high structural variation. Complex formation reactions with simple oligopeptides containing one histidyl residue have already been clarified satisfactorily and the results have been reviewed. However, the coordination chemistry of multihistidine peptides is understood less well, although the relevant molecules have major biological significance. These systems include peptide fragments of prion protein, amyloid-β and various copper(II) or zinc(II) transporter proteins. Recently, much data have been reported about these complexes and the most important results are summarized in this review. The second part of this review describes complex formation by peptides that contain another strongly coordinating side chain (e.g., carboxylates of Asp and Glu, and thiolates of Cys residues) in addition to the histidyl sites.
New J. Chem., 2016
Hexapeptides containing separate histidyl and cysteinyl residues have outstanding metal binding a... more Hexapeptides containing separate histidyl and cysteinyl residues have outstanding metal binding ability but the binding sites of peptides reveal a significant specificity.
New J. Chem., 2015
The novel synthesized cysteine peptides form stable zinc(ii) and cadmium(ii) complexes; the speci... more The novel synthesized cysteine peptides form stable zinc(ii) and cadmium(ii) complexes; the specific sequence makes possible metal induced amide deprotonation.