Size-selective Pt siderophores based on redox active azo-aromatic ligands

We demonstrate a strategy inspired by natural siderophores for the dissolution of platinum nanoparticles that could enable their size-selective synthesis, toxicological assessment, and the recycling of this precious metal. From the fabrication of electronics to biomedical diagnosis and therapy, PtNPs find increasing use. Mitigating concerns over potential human toxicity and the need to recover precious metal from industrial debris motivates the study of bio-friendly reagents to replace traditional harsh etchants. Herein, we report a family of redox-active siderophore-viz. π-acceptor azo aromatic ligands (L) that spontaneously ionize and chelate Pt atoms selectively from nanoparticles of size ≤6 nm. The reaction produces a monometallic diradical complex, Pt^II(L˙⁻)₂, isolated as a pure crystalline compound. Density functional theory provides fundamental insights on the size dependent PtNP chemical reactivity. The reported findings reveal a generalized platform for designing π-acceptor ligands to adjust the size threshold for dissolution of Pt or other noble metals NPs. Our approach may, for example, be used for the generation of Pt-based therapeutics or for reclamation of Pt nano debris formed in catalytic converters or electronic fabrication industries.

Biofriendly recycling of Pt is enabled by ligands that size-selectively dissolve nanoclusters.     

Effect of axial ligands and macrocyclic structure on redox potentials and electron-transfer mechanisms of SnIV porphyrins

The electrochemical properties of dichloro- and dihydroxo-SnIV porphyrins with three different macrocycles were examined in CH2Cl2 containing 0.1 or 0.2 M tetra-n-butylammonium perchlorate as supporting electrolyte. The investigated compounds are represented as (TPP)SnX2, (P)Sn(X)2, and (PQ)Sn(X)2, where TPP = 5,10,15,20-tetraphenylporphyrin, P = 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin, PQ = 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b']porphyrin, and X = Cl or OH. Each porphyrin can be electroreduced in two one-electron-transfer steps with the half-wave potentials and stability of the eletroreduced compounds being dependent upon the type of coordinated axial ligand and specific macrocyclic structure. All reductions of (TPP)Sn(OH)2, (P)Sn(OH)2, and (PQ)Sn(OH)2 are reversible under the given experimental conditions and lead to the expected porphyrin pi-anion radicals and dianions, which were characterized by thin-layer UV-vis spectroelectrochemistry. This contrasts with what occurs upon the reduction of (PQ)SnCl2, which undergoes a chemical reaction with trace H2O in solution, leading to the formation of (PQ)Sn(OH)2 as well as to a protonated form of the quinoxalinoporphyrin, (PQH)Sn(OH)2, under the application of an applied potential. A protonation of the Q group breaks the conjugation between the fused quinoxaline unit and the porphyrin macrocycle, thus effectively giving a compound whose reduction properties resemble that of the metalloporphyrin in the absence of the fused ring. The electrooxidation of each neutral SnIV porphyrin was also investigated, and the effect of axial ligand and fused quinoxaline ring on the redox potentials and products of electron transfer are discussed.     

New redox active ligands involving a tetrathiafulvalene vinylogue backbone

Two synthetic approaches towards a new bisthiopicoline substituted vinylogous tetrathiafulvalene (TTFV) are described. As evidenced by electrochemistry and ¹H NMR studies, this redox active ligand shows excellent coordinating properties towards Zn²⁺ metal ion.     

New NiIII/II redox systems with pH controlled potentials based on macrocyclic ligands with azacyclam ligands

Replacement of carbon atoms by non-coordinating nitrogen atoms in 14-membered macrocyclic ligands L increased the redox potentials of Ni_III/IIL couples. Compounds of this type are new systems whose redox potentials can be varied by changing the pH of the medium.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 6, pp. 375–378, November–December, 1995.This study was supported by the State Fund for Fundamental Research, Ukraine State Committee on Science and Technology (project 33/52) and in part by the International Science Fund (grant UBG 000).     

苯甲醛衍生物的结构与其半波电位关系的研究

以半经验分子轨道方法计算苯甲醛衍生物的分子结构参数，以多元线性回归方法研究了苯甲醛衍生物的半波电位与其分子结构参数间的关系。研究发现，在所选择的２３个分子结构参数中，基态双中心总能量（ＥＴ（ｔｗｏ）、电离势（Ｉｐ）及分子的生成热（Ｈｆ）与其半波电位有较好的相关性。其回归方程为：ｙ＝－５．４２３２＋０．５４７７８Ｉｐ－３．３３１＊１０＾－３Ｅｔ（ｔｗｏ）－１．６７０＊１０＾－３Ｈｆ（ｒＲＣ＝０．９２     

Synthesis, structure and redox potentials of biologically active ferrocenylalkyl azoles

The syntheses, structures, electrochemical properties of the series of ferrocenylalkyl azoles, FcAlkAz, as well as the antitumor activity of ferrocenylmethyl benzimidazole (8) have been studied. Above mentioned compounds were investigated by the method of cyclic voltametry. All of them exhibited a reversible one-electron oxidation-reduction wave owing to the ferrocene-ferrocenium redox couple with a positive shift (0.50-0.65 V) compared with that of ferrocene (0.42 V). The X-ray determination of molecular structures of 1-(ferrocenylmethyl)imidazole (4), 1-(ferrocenylbenzyl)imidazole (7) and 1-(ferrocenylmethyl)bezimidazole (8) was carried out. Compound 4 with imidazolyl substituent was found to be present in N-protonated form. Antitumor activity of 1-(ferrocenylmethyl)benzimidazole (8) against some solid tumor models such as adenocarcinoma 755 (Ca755), melanoma B16 (B16) and Lewis lung carcinoma was studied. The antitumor activity of compound 8 was compared with cisplatin effectiveness against some experimental tumor systems.     

Tetrathiafulvalene based phosphino-oxazolines: a new family of redox active chiral ligands

Reaction of the lithium salt of EDT-TTF-2-(4-methyl)oxazoline with chloro-diphenylphosphine afforded the novel redox active chiral chelating ligands, EDT-TTF-phosphino-oxazolines, for which a palladium (II) dichloride complex was synthesized and structurally characterized.     

Tetrathiafulvalene hydrazone: efficient synthon for the synthesis of novel bidentate redox active ligands

The synthesis and the ability of TTF-hydrazone to act as a versatile precursor for the design of electroactive ligands are reported together with the chelating ability of these ligands through their M(CO)₄ complexes, (M = Mo, W).     

Modulation of redox potential in electron transfer proteins: effects of complex formation on the active site microenvironment of cytochrome b5

The reduction potential of cytochrome b5 is modulated via the formation of a complex with polylysine at the electrode surface (Rivera et al., Biochemistry, 1998, 37, 1485). This modulation is thought to originate from the neutralization of a solvent exposed heme propionate and from dehydration of the complex interface. Although direct evidence demonstrating that neutralization of the charge on the heme propionate contributes to the modulation of the redox potential of cytochrome b5 has been obtained, evidence demonstrating that water exclusion from the complex interface plays a similar role has not been conclusive. Herein we report the preparation of the V45I/V61I double mutant of rat liver outer mitochondrial membrane (OM) cytochrome b5. This mutant has been engineered with the aim of restricting water accessibility to the exposed heme edge of cytochrome b5. The X-ray crystal structure of the V45I/V61I mutant revealed that the side chain of Ile at positions 45 and 61 restricts water accessibility to the interior of the heme cavity and protects a large section of the heme edge from the aqueous environment. Electrochemical studies performed with the V45I/V61I mutant of cytochrome b5, and with a derivative in which the heme propionates have been converted into the corresponding dimethyl ester groups, clearly demonstrate that dehydration of the heme edge contributes to the modulation of the reduction potential of cytochrome b5. In fact, these studies showed that exclusion of water from the complex interface exerts an effect (approximately 40 mV shift) that is comparable, if not larger, than the one originating from neutralization of the charge on the solvent exposed heme propionate (approximately 30 mV shift).     

Synthesis and electrochemical studies of tetrathiafulvalene derivatives (TTFs) as redox active ligands

A simple route for synthesis of new tetrathiafulvalene dimethyl ester (TTF‐DME) is reported. The tetrathifulvalene dimethylester (TTF‐DME) has been prepared by introducing an ester coordination function as a bifunctional new donor. The redox behavior of the TTF‐DME was investigated in comparison to the well‐known dibenzotetrathiafulvene (DB‐TTF) by cyclic voltammetry. A two‐electron redox behavior was observed as a two waves.     

锌酞菁类染料的氧化还原电位研究

金属酞菁染料对红光及近红外光有强吸收,并且具有半导体的性能。由于它具有性质稳定,合成方便等特点,这类染料在传统的染料、颜料工业中有着重要的地位;近年来在太阳能的利用,氧化还原反应的光敏化等方面引起了人们很大的注意。由于一般的金属酞菁染料的溶解度很差,常使它们的应用受到限制。为此,我们合成了一系列在环上带有各种取代基的锌酞菁染料(ZnPcR),以改善其溶解度,并对它们的氧化还原电位和分子结构与轨道能级之间的关系进行了研究。     

Use of pyrazolyl ligands for the formation of a bimetallic cobalt-ruthenium complex

A straightforward route to Ru(pyz)₂(Hpyz)₄ (Hpyz = pyrazole) has been developed. This has been found to react readily with a modified Co(pyrazolylborate)Cl complex in the presence of triethylamine as an HCl acceptor to yield a bimetallic cobalt-ruthenium complex, in which the two metals are each six-coordinate, and bridged by three pyrazolyl anions. Both species have been characterized structurally, as has a modified Co(pyrazolylborate)₂ complex.     

Reactions of biological oxidants with selenourea: formation of redox active nanoselenium

Reactions of biological oxidizing agents, such as hydroxyl radicals ((*)OH), singlet oxygen ((1)O(2)), hydrogen peroxide (H(2)O(2)), and peroxynitrite (ONOO(-)) with selenourea were studied. The kinetics of the reactions was followed using time-resolved techniques, and the bimolecular rate constants were determined. In all these reactions, under aerated conditions, elemental red selenium was produced as one of the reaction products. The average size of the selenium particles could be controlled and stabilized in the range of 20-100 nm with the addition of bovine serum albumin (BSA) or sodium dodecyl sulfate (SDS). The particles were characterized by dynamic light scattering studies (DLS), which revealed that the size and distribution of the particles depended mainly on the amount of selenourea undergoing oxidation. Other factors such as the nature of the oxidant and the concentration of the stabilizer also are important in stabilizing the particles. Nanoselenium-reduced ABTS(*-) to colorless ABTS(2-) (ABTS = 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) and oxidized dichlorodihydrofluoresecein diacetate (DCFA) to fluorescent dichlorofluorescein (DCF) indicating its ability to participate in redox and free radical reactions. The reactivity of selenium nanoparticles with these systems varied linearly with the surface area of the particles. The studies demonstrate that selenourea undergoes oxidation with both one-electron and two-electron oxidants to produce elemental selenium, which, on stabilization to nanometer size, exhibits size-dependent redox activity.     

Experimental and theoretical prediction of the redox potentials of noradrenaline and its supramolecular complex with glycine

The redox reaction of N-protonated noradrenalin (NA) is a two-proton-two-electron reaction in aqueous solution. NA can be oxidated to N-protonated noradrenalin quinone (NAquinone). The standard electrode potential (E⁰) value of NA/NAquinone couples is obtained experimentally with cyclic voltammetry (CV) and theoretically with two methods at B3LYP/6-311++G(d, p) level. The theoretical E⁰ value of NA/NAquinone couples is in good agreement with experimental ones and close to each other. Glycine (Gly) can form hydrogen bonds with NA in physiological environment. The E⁰ values of NA–Gly/NAquinone–Gly couples are predicted experimentally and theoretically. Hydrogen bond interaction weakens the electrondonation abilities of NA.     

Mutual influence of metals and ligands in the complex formation of oxo anions of d-elements with chelating ligands

The complex-formation processes between ions of d-elements having multiple M=O bonds with bidentate monoanions, mainly 1,1-ditiolates, are considered. The data of ESR spectroscopy and X-ray diffration analysis for this type of complexes are analyzed. Owing to the strongtrans-effect of the M=O group, M-ligand valence bonds are not formed in thetrans-position to the M=O group, and only donor-acceptor M-ligand bonds are realized. The valence M-ligand bonds can arise only in the equatorial plane, incis-positions with thespect to the multiple M=O bond. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1471–1480, August, 1998.