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Electronic and spatial structures of water-soluble dinitrosyl iron complexes with thiol-containing ligands underlying their ability to act as nitric oxide and nitrosonium ion donors.

Vanin AF, Burbaev DSh - J Biophys (2012)

Bottom Line: Similarly, the {(RS(-))(2)Fe(+)(NO(+))(2)}(+) structure describing the distribution of unpaired electron density in M-DNIC corresponds to the low-spin (S = 1/2) state with a d(7) electron configuration of the iron atom and predominant localization of the unpaired electron on MO(d(z2)) and the square planar structure of M-DNIC.On the other side, the formation of molecular orbitals of M-DNIC including orbitals of the iron atom, thiolate and nitrosyl ligands results in a transfer of electron density from sulfur atoms to the iron atom and nitrosyl ligands.Most probably, the S-nitrosating effect of nitrosyl ligands is a result of weak binding of thiolate ligands to the iron atom under conditions favoring destabilization of M-DNIC.

View Article: PubMed Central - PubMed

Affiliation: N. N. Semyonov Institute of Chemical Physics, Russian Academy of Sciences, Kosygin Street 4, Moscow 119991, Russia.

ABSTRACT
The ability of mononuclear dinitrosyl iron commplexes (M-DNICs) with thiolate ligands to act as NO donors and to trigger S-nitrosation of thiols can be explain only in the paradigm of the model of the [Fe(+)(NO(+))(2)] core ({Fe(NO)(2)}(7) according to the Enemark-Feltham classification). Similarly, the {(RS(-))(2)Fe(+)(NO(+))(2)}(+) structure describing the distribution of unpaired electron density in M-DNIC corresponds to the low-spin (S = 1/2) state with a d(7) electron configuration of the iron atom and predominant localization of the unpaired electron on MO(d(z2)) and the square planar structure of M-DNIC. On the other side, the formation of molecular orbitals of M-DNIC including orbitals of the iron atom, thiolate and nitrosyl ligands results in a transfer of electron density from sulfur atoms to the iron atom and nitrosyl ligands. Under these conditions, the positive charge on the nitrosyl ligands diminishes appreciably, the interaction of the ligands with hydroxyl ions or with thiols slows down and the hydrolysis of nitrosyl ligands and the S-nitrosating effect of the latter are not manifested. Most probably, the S-nitrosating effect of nitrosyl ligands is a result of weak binding of thiolate ligands to the iron atom under conditions favoring destabilization of M-DNIC.

No MeSH data available.


Spectra EPR of 2.03 complex from the solutions of DNIC with cysteine, containing 14NO (a) or 15NO (b), DNIC with mercaptotriazole (c), or DNIC with cysteine containing 57Fe (d). Recordings were made at 77 K (left side) or at ambient temperature (right side). Right side: magnetic field scales are shown separately for EPR signal of DNIC with mercaptotriazole (c) and for EPR signals of DNIC with cysteine containing 14NO, 15NO, or 57Fe (a, b, d).
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fig2: Spectra EPR of 2.03 complex from the solutions of DNIC with cysteine, containing 14NO (a) or 15NO (b), DNIC with mercaptotriazole (c), or DNIC with cysteine containing 57Fe (d). Recordings were made at 77 K (left side) or at ambient temperature (right side). Right side: magnetic field scales are shown separately for EPR signal of DNIC with mercaptotriazole (c) and for EPR signals of DNIC with cysteine containing 14NO, 15NO, or 57Fe (a, b, d).

Mentions: The results of analysis of EPR signals of M-DNIC with thiol-containing ligands [4, 8, 9, 15, 16, 50, 51] (Figure 2) are in good agreement with our hypothetical mechanism of formation, composition, and distribution of unpaired electron density in these complexes. First, according to EPR data in the presence of hyperfine structure (HFS) components water-soluble M-DNIC with thiol-containing ligands generate symmetric EPR signals with narrow (0.08–0.15 mT) components at ambient temperature and anisotropic signals with easily resolvable components at g⊥ and g// at 77 K [8–10, 15, 16, 50, 51] suggesting their low-spin (S = 1/2)d7 configuration [16, 50–52]. Second, the high value of hyperfine splitting in doublet HFS from the 57Fe nucleus (1.25 mT) incorporated into M-DNIC (Figure 2(d, right side)) is explicitly suggestive of predominant localization of unpaired electron density on the iron atom, that is, is fully consistent with the hypothetical structure and mechanism of synthesis of these DNIC. Third, the low level of hyperfine splitting in quintet HFS (0.15 mT) characteristic of EPR signals of DNIC with mercaptotriazole (Figure 2(c, right side)) during interaction of unpaired electron density with nitrogen nucleus of nitrosyl ligands (<0.3% of the maximum level). This corresponds to the ionized (NO+) state of nitrosyl ligands into which these ligands are transformed in the course of M-DNIC synthesis (Scheme 1). Moreover, the quintet origin of HFS points unambiguously to identity of both nitrosyl ligands in DNIC. Fourth, additional evidence for the presence of two nitrosyl and two thiol ligands in DNIC with cysteine or glutathione can be derived from the analysis of a hyperfine 13-component structure (HFS) characteristic of narrow EPR signals recorded for these DNIC at ambient temperature (g = 2.03) (Figure 2(a, right side)). This HFS is formed upon interaction of the unpaired electron with two nitrogen nuclei (14N, nuclear spin I = 1, triplet HFS from each nucleus) and four methylene group protons (I = 1/2, doublet HFS from each proton) in two nitrosyl and two cysteine ligands, respectively. After substitution of 14 N for 15 N (I = 1/2, doublet HFS from each nucleus) in nitrosyl ligands, the total number of HFS components decreases to 9 (Figure 2(b, right side)). The low (0.15 and 0.07 mT) level of hyperfine splitting on N nuclei and protons suggests that the negligible amount of unpaired electron density is localized on both nitrosyl and thiol ligands in DNIC with glutathione or cysteine ligands. This finding suggests that in these DNIC nitrosyl ligands also exist in the ionized (NO+) state (Scheme 1).


Electronic and spatial structures of water-soluble dinitrosyl iron complexes with thiol-containing ligands underlying their ability to act as nitric oxide and nitrosonium ion donors.

Vanin AF, Burbaev DSh - J Biophys (2012)

Spectra EPR of 2.03 complex from the solutions of DNIC with cysteine, containing 14NO (a) or 15NO (b), DNIC with mercaptotriazole (c), or DNIC with cysteine containing 57Fe (d). Recordings were made at 77 K (left side) or at ambient temperature (right side). Right side: magnetic field scales are shown separately for EPR signal of DNIC with mercaptotriazole (c) and for EPR signals of DNIC with cysteine containing 14NO, 15NO, or 57Fe (a, b, d).
© Copyright Policy - open-access
Related In: Results  -  Collection

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fig2: Spectra EPR of 2.03 complex from the solutions of DNIC with cysteine, containing 14NO (a) or 15NO (b), DNIC with mercaptotriazole (c), or DNIC with cysteine containing 57Fe (d). Recordings were made at 77 K (left side) or at ambient temperature (right side). Right side: magnetic field scales are shown separately for EPR signal of DNIC with mercaptotriazole (c) and for EPR signals of DNIC with cysteine containing 14NO, 15NO, or 57Fe (a, b, d).
Mentions: The results of analysis of EPR signals of M-DNIC with thiol-containing ligands [4, 8, 9, 15, 16, 50, 51] (Figure 2) are in good agreement with our hypothetical mechanism of formation, composition, and distribution of unpaired electron density in these complexes. First, according to EPR data in the presence of hyperfine structure (HFS) components water-soluble M-DNIC with thiol-containing ligands generate symmetric EPR signals with narrow (0.08–0.15 mT) components at ambient temperature and anisotropic signals with easily resolvable components at g⊥ and g// at 77 K [8–10, 15, 16, 50, 51] suggesting their low-spin (S = 1/2)d7 configuration [16, 50–52]. Second, the high value of hyperfine splitting in doublet HFS from the 57Fe nucleus (1.25 mT) incorporated into M-DNIC (Figure 2(d, right side)) is explicitly suggestive of predominant localization of unpaired electron density on the iron atom, that is, is fully consistent with the hypothetical structure and mechanism of synthesis of these DNIC. Third, the low level of hyperfine splitting in quintet HFS (0.15 mT) characteristic of EPR signals of DNIC with mercaptotriazole (Figure 2(c, right side)) during interaction of unpaired electron density with nitrogen nucleus of nitrosyl ligands (<0.3% of the maximum level). This corresponds to the ionized (NO+) state of nitrosyl ligands into which these ligands are transformed in the course of M-DNIC synthesis (Scheme 1). Moreover, the quintet origin of HFS points unambiguously to identity of both nitrosyl ligands in DNIC. Fourth, additional evidence for the presence of two nitrosyl and two thiol ligands in DNIC with cysteine or glutathione can be derived from the analysis of a hyperfine 13-component structure (HFS) characteristic of narrow EPR signals recorded for these DNIC at ambient temperature (g = 2.03) (Figure 2(a, right side)). This HFS is formed upon interaction of the unpaired electron with two nitrogen nuclei (14N, nuclear spin I = 1, triplet HFS from each nucleus) and four methylene group protons (I = 1/2, doublet HFS from each proton) in two nitrosyl and two cysteine ligands, respectively. After substitution of 14 N for 15 N (I = 1/2, doublet HFS from each nucleus) in nitrosyl ligands, the total number of HFS components decreases to 9 (Figure 2(b, right side)). The low (0.15 and 0.07 mT) level of hyperfine splitting on N nuclei and protons suggests that the negligible amount of unpaired electron density is localized on both nitrosyl and thiol ligands in DNIC with glutathione or cysteine ligands. This finding suggests that in these DNIC nitrosyl ligands also exist in the ionized (NO+) state (Scheme 1).

Bottom Line: Similarly, the {(RS(-))(2)Fe(+)(NO(+))(2)}(+) structure describing the distribution of unpaired electron density in M-DNIC corresponds to the low-spin (S = 1/2) state with a d(7) electron configuration of the iron atom and predominant localization of the unpaired electron on MO(d(z2)) and the square planar structure of M-DNIC.On the other side, the formation of molecular orbitals of M-DNIC including orbitals of the iron atom, thiolate and nitrosyl ligands results in a transfer of electron density from sulfur atoms to the iron atom and nitrosyl ligands.Most probably, the S-nitrosating effect of nitrosyl ligands is a result of weak binding of thiolate ligands to the iron atom under conditions favoring destabilization of M-DNIC.

View Article: PubMed Central - PubMed

Affiliation: N. N. Semyonov Institute of Chemical Physics, Russian Academy of Sciences, Kosygin Street 4, Moscow 119991, Russia.

ABSTRACT
The ability of mononuclear dinitrosyl iron commplexes (M-DNICs) with thiolate ligands to act as NO donors and to trigger S-nitrosation of thiols can be explain only in the paradigm of the model of the [Fe(+)(NO(+))(2)] core ({Fe(NO)(2)}(7) according to the Enemark-Feltham classification). Similarly, the {(RS(-))(2)Fe(+)(NO(+))(2)}(+) structure describing the distribution of unpaired electron density in M-DNIC corresponds to the low-spin (S = 1/2) state with a d(7) electron configuration of the iron atom and predominant localization of the unpaired electron on MO(d(z2)) and the square planar structure of M-DNIC. On the other side, the formation of molecular orbitals of M-DNIC including orbitals of the iron atom, thiolate and nitrosyl ligands results in a transfer of electron density from sulfur atoms to the iron atom and nitrosyl ligands. Under these conditions, the positive charge on the nitrosyl ligands diminishes appreciably, the interaction of the ligands with hydroxyl ions or with thiols slows down and the hydrolysis of nitrosyl ligands and the S-nitrosating effect of the latter are not manifested. Most probably, the S-nitrosating effect of nitrosyl ligands is a result of weak binding of thiolate ligands to the iron atom under conditions favoring destabilization of M-DNIC.

No MeSH data available.