Electrochemical Kinetics of Cyanometalate Complexes in Aqueous Solution at High Pressures

For the aqueous couples Os(CN)63-/4-, Mo(CN)83-/4-, and W(CN)83-/4-, volumes of reaction ΔVAg/AgCl relative to Ag/AgCl/4.0 mol L-1 KCl and volumes of activation ΔVel⧧ for the electrode reactions are reported. Values of ΔVAg/AgCl are consistent with a very small increase in the metal−carbon bond length on reduction in each case, the main component of ΔVAg/AgCl (other than that of the reference electrode) being electrostrictive solvation change. For media in which the cation is 0.5 mol L-1 K+ or (for Mo) Na+, ΔVel⧧ is strongly positive (+9.4 ± 0.7, +7.3 ± 0.7, and +10.8 ± 0.4 cm3 mol-1 for Os(CN)63-/4-, Mo(CN)83-/4-, and W(CN)83-/4-, respectively, at 25 °C), whereas the theoretical expectation for a mechanism involving only the cyanometalate anions is −3 ± 1 cm3 mol-1. For Mo(CN)83-/4- in Et4NCl, however, ΔVel⧧ is −4.2 ± 0.2 cm3 mol-1. In all cases, ΔVel⧧ is just one-half of the corresponding parameter ΔVex⧧ for the homogeneous (bimolecular) self-exchange reaction of the same couple, giving strong confirmation of the “fifty-percent rule” (Fu, Y.; Swaddle, T. W. J. Am. Chem. Soc. 1997, 119, 7137). These and related results are interpreted in terms of a mechanism for both electrode and homogeneous electron-transfer reactions of cyanometalates in which the counterion mediates the electron-transfer process. For alkali metal cations, partial deaquation to permit this mediation results in positive ΔVel⧧ values, whereas for tetraalkylammonium counterions, there are no aqua ligands to be removed and ΔVel⧧ is “normal”

Relationship between Heterogeneous and Homogeneous Kinetics of Electron Transfer between Transition Metal Complexes in Aqueous Solution: Volumes of Activation

Electrochemical rate constants kel and volumes of activation ΔVel⧧ for self-exchange at an electrode of the aqueous couples Co(phen)33+/2+, Co(en)33+/2+, Fe(H2O)63+/2+, Co(diamsar)3+/2+, Co(diamsarH2)3+/2+, Co(sep)3+/2+, Co(ttcn)23+/2+, Fe(phen)33+/2+, Mo(CN)83-/4-, and Fe(CN)63-/4- have been measured by high-pressure AC voltammetry over the range 0.1−200 MPa at 25 °C; the respective values of ΔVel⧧ are −9.1, −8.3, −5.5, −3.5, −3.8, −3.0, −2.8, −1.6, +7.3, and +11 cm3 mol-1. Although the theory of Marcus (Electrochim. Acta 1968, 13, 1005) suggests that ln kel should be linearly related to 1/2 ln kex, where kex is the rate constant of the corresponding homogeneous (bimolecular) self-exchange reaction, ln kel is often sensitive to the nature of the working electrode and the supporting electrolyte and is only weakly correlated with ln kex, with slope ≈0.1. In contrast, ΔVel⧧ = (0.50 ± 0.02)ΔVex⧧, in precise agreement with an extension of Marcus' theory, regardless of the nature of the electrode and the supporting electrolyte. This result implies that electron transfer in these couples occurs adiabatically on direct ion−ion and ion−electrode contact (i.e., within the outer Helmholtz plane), and also that ΔVel⧧ values are predictable in the manner described elsewhere (Can. J. Chem. 1996, 74, 631) for ΔVex⧧. Conversely, where ΔVex⧧ cannot be measured for technical reasons (e.g., where paramagnetism of both reactants precludes NMR measurements of kex), it can be reliably estimated as 2ΔVel⧧

Solvent Dynamics and Pressure Effects in the Kinetics of the Tris(bipyridine)cobalt(III/II) Electrode Reaction in Various Solvents

The volume of activation ΔVel⧧ for the Co(bpy)33+/2+ electrode reaction in aqueous NaCl (0.2 mol L-1) is −8.6 ± 0.4 cm3 mol-1 at 25.0 °C, as expected on theoretical grounds and by analogy with Co(en)33+/2+ and Co(phen)33+/2+, and neither the rate constant kel at various pressures nor ΔVel⧧ correlate with the corresponding mean diffusion coefficients D for the couple and the diffusional activation volume ΔVdiff⧧, respectively. In organic solvents, however, ΔVel⧧ is strongly positive (9.1 ± 0.3, 10.2 ± 0.7, and 12.2 ± 0.9 cm3 mol-1 for CH3CN, acetone, and propylene carbonate, respectively, with 0.2 mol L-1 [(C4H9)4N]ClO4 at 25 °C) and correlates with ΔVdiff⧧, while kel correlates with D. These results support the proposition of Murray et al. (J. Am. Chem. Soc. 1996, 118, 1743; 1997, 119, 10249) that solvent dynamics control the rate of the Co(bpy)33+/2+ electrode reaction in organic solvents. In aqueous solution at near-ambient temperatures, solvent dynamical influences would not be revealed by pressure effects, but in any event the aqueous Co(bpy)33+/2+ electrode reaction appears to be mechanistically different from the nonaqueous cases. For the reduction of Co(bpy)33+ with Co(sep)2+ in homogeneous aqueous solution, the rate constant is lower, and the volume of activation more negative, than can be accommodated by extended Marcus theory, suggesting nonadiabatic behavior. These observations are consistent with the view that, although the self-exchange and electrode reactions are generally adiabatic, cross reactions involving CoIII/II couples (and presumably others) become increasingly nonadiabatic as the driving potential is increased

Volumes of Activation for Electron Transfer in Low-Spin/Low-Spin Cationic Couples in Aqueous Solution

Volumes of reaction ΔVAg/AgCl (vs Ag/AgCl/4.0 mol L-1 KCl) and of activation ΔVel⧧ for the electrode reactions of the aqueous Co(azacapten)3+/2+, Ru(en)33+/2+, and Co(tacn)23+/2+ couples have been measured by high-pressure cyclic and AC voltammetry. For the low-spin/low-spin Co(azacapten)3+/2+ couple, ΔVel⧧ = −3.3 ± 0.4 cm3 mol-1, whereas high-pressure NMR measurements gave a volume of activation ΔVex⧧ for the self-exchange reaction of −6.5 ± 0.5 cm3 mol-1, in accordance with the “fifty-percent rule” (J. Am. Chem. Soc. 1997, 119, 7137) and with the prediction of an adaptation of the Marcus theory of intermolecular electron-transfer kinetics (Can. J. Chem. 1996, 74, 631). For the Ru(en)33+/2+ self-exchange reaction, ΔVex⧧ was estimated indirectly as −15.1 ± 1.7 cm3 mol-1 from the Co(phen)33+/Ru(en)32+ cross reaction (ΔV12⧧ = −12.9 ± 0.5 cm3 mol-1), for which the rate constant k12 was consistent with the Marcus cross relation. For the Fe(H2O)63+/Ru(en)32+ cross reaction (ΔV12⧧ = −18.3 ± 1.2 cm3 mol-1), k12 was slower than predicted from the Marcus cross relation, and consequently the estimated ΔVex⧧ for Ru(en)33+/2+ (−18.9 ± 2 cm3 mol-1) may be less reliable. For the Ru(en)33+/2+ electrode reaction, ΔVel⧧ = −7.5 ± 0.4 cm3 mol-1, again in accordance with the fifty-percent rule and, conversely, authenticating the estimated ΔVex⧧. The ΔVex⧧ estimates for Ru(en)33+/2+, however, are some 10 cm3 mol-1 more negative than can be accommodated by the adapted Marcus theory. For the low-spin/high-spin couple Co(tacn)23+/2+, ΔVel⧧ (−5.9 ± 0.9 cm3 mol-1) is intermediate between values expected for CoIII/II clathrochelates and low-spin/high-spin tris(bidentate) chelates, although ΔVAg/AgCl places this couple within the latter group

Image_2_Antifungal, Plant Growth-Promoting, and Genomic Properties of an Endophytic Actinobacterium Streptomyces sp. NEAU-S7GS2.TIF

Diseases caused by Sclerotinia sclerotiorum have caused severe losses of many economically important crops worldwide. Due to the long-term persistence of sclerotia in soil and the production of air-borne ascospores, synthetic fungicides play limited roles in controlling the diseases. The application of antagonistic microorganisms can effectively reduce the number of sclerotia and eventually eradicate S. sclerotiorum from soil, and therefore considerable interest has been focused on biological control. Streptomyces sp. NEAU-S7GS2 was isolated from the root of Glycine max and its rhizosphere soil. It showed significant inhibitory activity against the mycelial growth of S. sclerotiorum (99.1%) and completely inhibited sclerotia germination. Compared to the control, in the pot experiment the application of NEAU-S7GS2 not only demonstrated excellent potential to control sclerotinia stem rot of soybean with 77 and 38% decrease in disease incidence and disease index, respectively, but could promote the growth of soybean. The light microscopy and scanning electron microscopy showed that co-culture of NEAU-S7GS2 with S. sclerotiorum on potato dextrose agar could lead to contorted and fragmented mycelia of S. sclerotiorum, which was associated with the secretion of hydrolytic glucanase and cellulase and the production of active secondary metabolites by NEAU-S7GS2. The plant growth promoting activity of NEAU-S7GS2 was related to the solubilization of inorganic phosphate, and production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase and indole acetic acid (IAA). To further explore the plant growth promoting and antifungal mechanisms, the complete genome of strain NEAU-S7GS2 was sequenced. Several genes associated with ammonia assimilation, phosphate solubilization and IAA synthesis, together with genes encoding ACC deaminase, glucanase and α-amylase, were identified. AntiSMASH analysis led to the identification of four gene clusters responsible for the biosynthesis of siderophores including desferrioxamine B and enterobactin. Moreover, the biosynthetic gene clusters of lydicamycins, phenazines, and a glycosylated polyol macrolide showing 88% gene similarity to PM100117/PM100118 were identified. These results suggested that strain NEAU-S7GS2 may be a potential biocontrol agent and biofertilizer used in agriculture.</p

Image_1_Antifungal, Plant Growth-Promoting, and Genomic Properties of an Endophytic Actinobacterium Streptomyces sp. NEAU-S7GS2.TIF

Diseases caused by Sclerotinia sclerotiorum have caused severe losses of many economically important crops worldwide. Due to the long-term persistence of sclerotia in soil and the production of air-borne ascospores, synthetic fungicides play limited roles in controlling the diseases. The application of antagonistic microorganisms can effectively reduce the number of sclerotia and eventually eradicate S. sclerotiorum from soil, and therefore considerable interest has been focused on biological control. Streptomyces sp. NEAU-S7GS2 was isolated from the root of Glycine max and its rhizosphere soil. It showed significant inhibitory activity against the mycelial growth of S. sclerotiorum (99.1%) and completely inhibited sclerotia germination. Compared to the control, in the pot experiment the application of NEAU-S7GS2 not only demonstrated excellent potential to control sclerotinia stem rot of soybean with 77 and 38% decrease in disease incidence and disease index, respectively, but could promote the growth of soybean. The light microscopy and scanning electron microscopy showed that co-culture of NEAU-S7GS2 with S. sclerotiorum on potato dextrose agar could lead to contorted and fragmented mycelia of S. sclerotiorum, which was associated with the secretion of hydrolytic glucanase and cellulase and the production of active secondary metabolites by NEAU-S7GS2. The plant growth promoting activity of NEAU-S7GS2 was related to the solubilization of inorganic phosphate, and production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase and indole acetic acid (IAA). To further explore the plant growth promoting and antifungal mechanisms, the complete genome of strain NEAU-S7GS2 was sequenced. Several genes associated with ammonia assimilation, phosphate solubilization and IAA synthesis, together with genes encoding ACC deaminase, glucanase and α-amylase, were identified. AntiSMASH analysis led to the identification of four gene clusters responsible for the biosynthesis of siderophores including desferrioxamine B and enterobactin. Moreover, the biosynthetic gene clusters of lydicamycins, phenazines, and a glycosylated polyol macrolide showing 88% gene similarity to PM100117/PM100118 were identified. These results suggested that strain NEAU-S7GS2 may be a potential biocontrol agent and biofertilizer used in agriculture.</p

Table_1_Antifungal, Plant Growth-Promoting, and Genomic Properties of an Endophytic Actinobacterium Streptomyces sp. NEAU-S7GS2.DOCX

Diseases caused by Sclerotinia sclerotiorum have caused severe losses of many economically important crops worldwide. Due to the long-term persistence of sclerotia in soil and the production of air-borne ascospores, synthetic fungicides play limited roles in controlling the diseases. The application of antagonistic microorganisms can effectively reduce the number of sclerotia and eventually eradicate S. sclerotiorum from soil, and therefore considerable interest has been focused on biological control. Streptomyces sp. NEAU-S7GS2 was isolated from the root of Glycine max and its rhizosphere soil. It showed significant inhibitory activity against the mycelial growth of S. sclerotiorum (99.1%) and completely inhibited sclerotia germination. Compared to the control, in the pot experiment the application of NEAU-S7GS2 not only demonstrated excellent potential to control sclerotinia stem rot of soybean with 77 and 38% decrease in disease incidence and disease index, respectively, but could promote the growth of soybean. The light microscopy and scanning electron microscopy showed that co-culture of NEAU-S7GS2 with S. sclerotiorum on potato dextrose agar could lead to contorted and fragmented mycelia of S. sclerotiorum, which was associated with the secretion of hydrolytic glucanase and cellulase and the production of active secondary metabolites by NEAU-S7GS2. The plant growth promoting activity of NEAU-S7GS2 was related to the solubilization of inorganic phosphate, and production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase and indole acetic acid (IAA). To further explore the plant growth promoting and antifungal mechanisms, the complete genome of strain NEAU-S7GS2 was sequenced. Several genes associated with ammonia assimilation, phosphate solubilization and IAA synthesis, together with genes encoding ACC deaminase, glucanase and α-amylase, were identified. AntiSMASH analysis led to the identification of four gene clusters responsible for the biosynthesis of siderophores including desferrioxamine B and enterobactin. Moreover, the biosynthetic gene clusters of lydicamycins, phenazines, and a glycosylated polyol macrolide showing 88% gene similarity to PM100117/PM100118 were identified. These results suggested that strain NEAU-S7GS2 may be a potential biocontrol agent and biofertilizer used in agriculture.</p

Table_2_Antifungal, Plant Growth-Promoting, and Genomic Properties of an Endophytic Actinobacterium Streptomyces sp. NEAU-S7GS2.docx

Diseases caused by Sclerotinia sclerotiorum have caused severe losses of many economically important crops worldwide. Due to the long-term persistence of sclerotia in soil and the production of air-borne ascospores, synthetic fungicides play limited roles in controlling the diseases. The application of antagonistic microorganisms can effectively reduce the number of sclerotia and eventually eradicate S. sclerotiorum from soil, and therefore considerable interest has been focused on biological control. Streptomyces sp. NEAU-S7GS2 was isolated from the root of Glycine max and its rhizosphere soil. It showed significant inhibitory activity against the mycelial growth of S. sclerotiorum (99.1%) and completely inhibited sclerotia germination. Compared to the control, in the pot experiment the application of NEAU-S7GS2 not only demonstrated excellent potential to control sclerotinia stem rot of soybean with 77 and 38% decrease in disease incidence and disease index, respectively, but could promote the growth of soybean. The light microscopy and scanning electron microscopy showed that co-culture of NEAU-S7GS2 with S. sclerotiorum on potato dextrose agar could lead to contorted and fragmented mycelia of S. sclerotiorum, which was associated with the secretion of hydrolytic glucanase and cellulase and the production of active secondary metabolites by NEAU-S7GS2. The plant growth promoting activity of NEAU-S7GS2 was related to the solubilization of inorganic phosphate, and production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase and indole acetic acid (IAA). To further explore the plant growth promoting and antifungal mechanisms, the complete genome of strain NEAU-S7GS2 was sequenced. Several genes associated with ammonia assimilation, phosphate solubilization and IAA synthesis, together with genes encoding ACC deaminase, glucanase and α-amylase, were identified. AntiSMASH analysis led to the identification of four gene clusters responsible for the biosynthesis of siderophores including desferrioxamine B and enterobactin. Moreover, the biosynthetic gene clusters of lydicamycins, phenazines, and a glycosylated polyol macrolide showing 88% gene similarity to PM100117/PM100118 were identified. These results suggested that strain NEAU-S7GS2 may be a potential biocontrol agent and biofertilizer used in agriculture.</p

Image_4_Antifungal, Plant Growth-Promoting, and Genomic Properties of an Endophytic Actinobacterium Streptomyces sp. NEAU-S7GS2.TIF

Diseases caused by Sclerotinia sclerotiorum have caused severe losses of many economically important crops worldwide. Due to the long-term persistence of sclerotia in soil and the production of air-borne ascospores, synthetic fungicides play limited roles in controlling the diseases. The application of antagonistic microorganisms can effectively reduce the number of sclerotia and eventually eradicate S. sclerotiorum from soil, and therefore considerable interest has been focused on biological control. Streptomyces sp. NEAU-S7GS2 was isolated from the root of Glycine max and its rhizosphere soil. It showed significant inhibitory activity against the mycelial growth of S. sclerotiorum (99.1%) and completely inhibited sclerotia germination. Compared to the control, in the pot experiment the application of NEAU-S7GS2 not only demonstrated excellent potential to control sclerotinia stem rot of soybean with 77 and 38% decrease in disease incidence and disease index, respectively, but could promote the growth of soybean. The light microscopy and scanning electron microscopy showed that co-culture of NEAU-S7GS2 with S. sclerotiorum on potato dextrose agar could lead to contorted and fragmented mycelia of S. sclerotiorum, which was associated with the secretion of hydrolytic glucanase and cellulase and the production of active secondary metabolites by NEAU-S7GS2. The plant growth promoting activity of NEAU-S7GS2 was related to the solubilization of inorganic phosphate, and production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase and indole acetic acid (IAA). To further explore the plant growth promoting and antifungal mechanisms, the complete genome of strain NEAU-S7GS2 was sequenced. Several genes associated with ammonia assimilation, phosphate solubilization and IAA synthesis, together with genes encoding ACC deaminase, glucanase and α-amylase, were identified. AntiSMASH analysis led to the identification of four gene clusters responsible for the biosynthesis of siderophores including desferrioxamine B and enterobactin. Moreover, the biosynthetic gene clusters of lydicamycins, phenazines, and a glycosylated polyol macrolide showing 88% gene similarity to PM100117/PM100118 were identified. These results suggested that strain NEAU-S7GS2 may be a potential biocontrol agent and biofertilizer used in agriculture.</p

Image_3_Antifungal, Plant Growth-Promoting, and Genomic Properties of an Endophytic Actinobacterium Streptomyces sp. NEAU-S7GS2.TIF

Diseases caused by Sclerotinia sclerotiorum have caused severe losses of many economically important crops worldwide. Due to the long-term persistence of sclerotia in soil and the production of air-borne ascospores, synthetic fungicides play limited roles in controlling the diseases. The application of antagonistic microorganisms can effectively reduce the number of sclerotia and eventually eradicate S. sclerotiorum from soil, and therefore considerable interest has been focused on biological control. Streptomyces sp. NEAU-S7GS2 was isolated from the root of Glycine max and its rhizosphere soil. It showed significant inhibitory activity against the mycelial growth of S. sclerotiorum (99.1%) and completely inhibited sclerotia germination. Compared to the control, in the pot experiment the application of NEAU-S7GS2 not only demonstrated excellent potential to control sclerotinia stem rot of soybean with 77 and 38% decrease in disease incidence and disease index, respectively, but could promote the growth of soybean. The light microscopy and scanning electron microscopy showed that co-culture of NEAU-S7GS2 with S. sclerotiorum on potato dextrose agar could lead to contorted and fragmented mycelia of S. sclerotiorum, which was associated with the secretion of hydrolytic glucanase and cellulase and the production of active secondary metabolites by NEAU-S7GS2. The plant growth promoting activity of NEAU-S7GS2 was related to the solubilization of inorganic phosphate, and production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase and indole acetic acid (IAA). To further explore the plant growth promoting and antifungal mechanisms, the complete genome of strain NEAU-S7GS2 was sequenced. Several genes associated with ammonia assimilation, phosphate solubilization and IAA synthesis, together with genes encoding ACC deaminase, glucanase and α-amylase, were identified. AntiSMASH analysis led to the identification of four gene clusters responsible for the biosynthesis of siderophores including desferrioxamine B and enterobactin. Moreover, the biosynthetic gene clusters of lydicamycins, phenazines, and a glycosylated polyol macrolide showing 88% gene similarity to PM100117/PM100118 were identified. These results suggested that strain NEAU-S7GS2 may be a potential biocontrol agent and biofertilizer used in agriculture.</p