Equatorial Perturbation Driven Reaction Bifurcation in Non-Heme Iron Complexes for Chlorite Oxidation

Chlorine oxyanions have various applications, such as bleaching and oxidizers in rocket fuels. However, their high solubility in water and long environmental lifetimes have led to ecological concerns, especially regarding drinking water quality. This study focuses on the conversion of chlorite to chlorine dioxide, which is of significant interest as it exhibits superior antimicrobial activity and generates less harmful byproducts for water treatment. Two nonheme iron(II) complexes capable of producing chlorine dioxide from chlorite at room temperature and pH 5.0 are presented. These complexes oxidize chlorite through high-valent iron (IV)-oxo intermediates formed in-situ. The study establishes second-order rate constants for chlorite oxidation and investigates the effects and mechanisms involved by substituting a methyl group in the secondary coordination sphere of the Fe^IV(O)(N4Py) system. By employing kinetic analysis and spectroscopic investigations, the crucial elements for the reaction mechanism in chlorite oxidation are identified. These findings pave the way for future advancements in this field.     

Is the μ‐Oxo‐μ‐Peroxodiiron Intermediate of a Ribonucleotide Reductase Biomimetic a Possible Oxidant of Epoxidation Reactions?

Density functional calculations on a mu-oxo-mu-peroxodiiron complex (1) with a tetrapodal ligand BPP (BPP=N,N-bis(2-pyridylmethyl)-3-aminopropionate) are presented that is a biomimetic of the active site region of ribonucleotide reductase (RNR). We have studied all low-lying electronic states and show that it has close-lying broken-shell singlet and undecaplet (S=0, 5) ground states with essentially two sextet spin iron atoms. In strongly distorted electronic systems in which the two iron atoms have different spin states, the peroxo group moves considerably out of the plane of the mu-oxodiiron group due to orbital rearrangements. The calculated absorption spectra of (1,11)1 are in good agreement with experimental studies on biomimetics and RNR enzyme systems. Moreover, vibrational shifts in the spectrum due to (18)O(2) substitution of the oxygen atoms in the peroxo group follow similar trends as experimental observations. To identify whether the mu-oxo-mu-1,2-peroxodiiron or the mu-oxo-mu-1,1-peroxodiiron complexes are able to epoxidize substrates, we studied the reactivity patterns versus propene. Generally, the reactions are stepwise via radical intermediates and proceed by two-state reactivity patterns on competing singlet and undecaplet spin state surfaces. However, both the mu-oxo-mu-1,2-peroxodiiron and mu-oxo-mu-1,1-peroxodiiron complex are sluggish oxidants with high epoxidation barriers. The epoxidation barriers for the mu-oxo-mu-1,1-peroxodiiron complex are significantly lower than the ones for the mu-oxo-mu-1,2-peroxodiiron complex but still are too high to be considered for catalytic properties. Thus, theory has ruled out two possible peroxodiiron catalysts as oxidants in RNR enzymes and biomimetics and the quest to find the actual oxidant in the enzyme mechanism continues.     

Determination of pharmaceuticals classified as emerging pollutants using capillary electrophoresis with capacitively coupled contactless conductivity detection

A study on the simultaneous separation of 13 pharmaceutical products by capillary electrophoresis with capacitively coupled contactless conductivity detection was presented. The parameters of the background electrolyte, such as pH, organic additives as well as types and concentrations of cyclodextrins (CD) were studied. The optimal separation conditions were achieved with a background electrolyte consisting of 9 mM Tris/5 mM lactic acid at pH 8.0, containing 5% n-propanol, 0.025% gamma-CD, 0.075% hydroxyl-beta-CD and 0.15% dimethyl-beta-CD. Limits of detections ranged from 61 to 1676 microg/L (S/N=3) and the relative standard deviations for migration time and peak area were below 2 and 6%, respectively. This demonstrated the potential of the capillary electrophoresis-capacitively coupled contactless conductivity detection method for biomedical and environmental analysis, as shown in the determination of pharmaceuticals identified as emerging pollutants in water samples.     

Human pathogenic Cryptosporidium species bioanalytical detection method with single oocyst detection capability

A bioanalytical detection method for specific detection of viable human pathogenic Cryptosporidium species, C. parvum, C. hominis, and C. meleagridis is described. Oocysts were isolated from water samples via immunomagnetic separation, and mRNA was extracted with oligo-dT magnetic beads, amplified using nucleic acid sequence-based amplification (NASBA), and then detected in a nucleic acid hybridization lateral flow assay. The amplified target sequence employed was hsp70 mRNA, production of which is stimulated via a brief heat shock. The described method was capable of detecting one oocyst in 10 μL using flow-cytometer-counted samples. Only viable oocysts were detected, as confirmed using 4′,6-diamidino-2-phenylindole and propidium iodide (DAPI/PI) staining. The detection system was challenged by detecting oocysts in the presence of large numbers of common waterborne microorganisms and packed pellet material filtered from environmental water samples. When the method was compared with EPA Method 1622 for C. parvum detection, highly comparable results were obtained. Since the described detection system yields unambiguous results within 4.5 h, it is an ideal method for monitoring the safety of drinking water.     

The Mahler measure of parametrizable polynomials

Our aim is to explain instances in which the value of the logarithmic Mahler measure m(P) of a polynomial P∈Z[x,y] can be written in an unexpectedly neat manner. To this end we examine polynomials defining rational curves, which allows their zero-locus to be parametrized via x=f(t), y=g(t) for f,g∈C(t). As an illustration of this phenomenon, we prove the equality

     

The effect and influence of cis-ligands on the electronic and oxidizing properties of nonheme oxoiron biomimetics. A density functional study

Density functional theory studies on the nature of the cis effect and cis influence of ligands on oxoiron nonheme complexes have been performed. A detailed analysis of the electronic and oxidizing properties of [Fe(IV)O(TPA)L](+) with L = F(-), Cl(-), and Br(-) and TPA = tris-(2-pyridylmethyl)amine are presented and compared with [Fe(IV)O(TPA)NCCH(3)](2+). The calculations show that the electronic cis effect is determined by favorable orbital overlap between first-row elements with the metal, which are missing between the metal and second- and third-row elements. As a consequence, the metal 3d block is split into a one-below-two set of orbitals with L = Cl(-) and Br(-), and the HOMO/LUMO energy gap is widened with respect to the system with L = F(-). However, this larger HOMO/LUMO gap does not lead to large differences in electron affinities of the complexes. Moreover, a quantum mechanical analysis of the binding of the ligand shows that it is built up from a large electric field effect of the ligand on the oxoiron species and a much smaller quantum mechanical effect due to orbital overlap. These contributions are of similar strength for the three tested halogen cis ligands and result in similar reactivity patterns with substrates. The calculations show that [Fe(IV)O(TPA)L](+) with L = F(-), Cl(-), and Br(-) have closely lying triplet and quintet spin states, but only the quintet spin state is reactive with substrates. Therefore, the efficiency of the oxidant will be determined by the triplet-quintet spin state crossing of the reaction. The reaction of styrene with a doubly charged reactant, that is, [Fe(V)O(TPA)L](2+) with L = F(-), Cl(-), and Br(-) or [Fe(V)O(TPA)NCCH(3)](3+), leads to an initial electron transfer from the substrate to the metal followed by a highly exothermic epoxidation mechanism. These reactivity differences are mainly determined by the overall charge of the system rather than the nature of the cis ligand.     

Unique intermolecular reaction of simple porphyrins at a metal surface gives covalent nanostructures

Deposition of a porphyrin onto metallic copper followed by heating leads to an unprecedented type of linking of the molecules giving a mixture of covalent multiporphyrin nanostructures at the surface.     

Deracemization of unnatural amino acid: homoalanine using D-amino acid oxidase and ω-transaminase

A deracemization method was developed to generate optically pure L-homoalanine from racemic homoalanine using D-amino acid oxidase and ω-transaminase. A whole cell reaction using a biphasic system converted 500 mM racemic homoalanine to 485 mM L-homoalanine (>99% ee).