Carboxymethylated polyethylenimine modified magnetic nanoparticles specifically for purification of His‐tagged protein

Employing immobilized metal‐ion affinity chromatography and magnetic separation could ideally provide a useful analytical strategy for purifying His‐tagged protein. In the current study, a facile route was designed to prepare CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ (CMPEI=carboxymethylated polyethyleneimine) magnetic nanoparticles composed of a strong magnetic core of Fe₃O₄ and a Ni²⁺‐immobilized carboxymethylated polyethyleneimine coated outside shell, which was formed by electrostatic interactions between polyanionic electrolyte of carboxymethylated polyethyleneimine and positively charged surface of 3‐(trimethoxysilyl)propylamin modified SiO₂@Fe₃O₄. The resulting CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ composite nanoparticles displayed well‐uniform structure and high magnetic responsiveness. Hexa His‐tagged peptides and purified His‐tagged recombinant retinoid X receptor alpha were chosen as the model samples to evaluate the adsorption, capacity, and reusability of the composite nanoparticles. The results demonstrated the CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ nanoparticles possessed rapid adsorption, large capacity, and good recyclability. The obtained nanoparticles were further used to purify His‐tagged protein in practical environment. It was found that the nanoparticles could selectively capture His‐tagged recombinant retinoid X receptor protein from complex cell lysate. Owing to its easy synthesis, large binding capacity, and good reusability, the prepared CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ magnetic nanoparticles have great potential for application in biotechnological fields.     

Preparation of thermosensitive,calix[4]arene incorporated P(NIPAM‐co‐HBCalix) hydrogel as a reusable adsorbent of nickel(II) ions

A calix‐conjugated thermo‐responsive hydrogel containing 15% tetra(5‐hexenyloxy)‐p‐tert‐butylcalix[4]arene (HBCalix), P(NIPAM‐co‐HBCalix), was used to remove nickel(II) ions from water. Both thermo‐sensitive properties and the Ni²⁺‐adsorption capabilities of the prepared P(NIPAM‐co‐HBCalix) hydrogels are investigated. Introduction of the monomer HBCalix considerably enhanced the adsorption of Ni²⁺ onto the hydrogel by chelation between hexenyloxy groups and metal ion. When HBCalix units capture Ni²⁺ and forms HBCalix/Ni²⁺ host–guest complexes, the lower critical solution temperature of the hydrogel shifts to a higher temperature due to both the repulsion between charged HBCali/Ni²⁺ groups and the osmotic pressure within the hydrogel. Adsorption studies were carried out by varying contact time, counter ion and initial concentration of Ni²⁺. The evaluation of adsorption properties showed that the hydrogel exhibited better correlation with Langmuir isotherm model. P(NIPAM‐co‐HBCalix) could be used repeatedly with little loss in adsorption capacity by simply changing the environmental temperature. This kind of ion‐recognition hydrogel is promising as a novel adsorption material for adsorption and separation of Ni²⁺ ions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2401–2408     

Dual crosslinked pH‐ and temperature‐sensitive hydrogel beads for intestine‐targeted controlled release

Novel drug‐loaded hydrogel beads for intestine‐targeted controlled release were developed by using pH‐ and temperature‐sensitive carboxymethyl chitosan‐graft‐poly(N,N‐diethylacrylamide) (CMCTS‐g‐PDEA) hydrogel as carriers and vitamin B₂ (VB₂) as a model drug. The hydrogel beads were prepared based on Ca²⁺ ionic crosslinking in acidic solution and formed dual crosslinked network structure. The structure of hydrogel and morphology of drug‐loaded beads were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The study about swelling characteristics of hydrogel beads indicated that the beads had obvious pH‐ and temperature‐sensitivity. In vitro release studies of drug‐loaded beads were carried out in pH 1.2 HCl buffer solution and pH 7.4 phosphate buffer solution at 37°C, respectively. The results indicated that the dual crosslinked method could effectively control the drug release rate under gastrointestinal tract (GIT) conditions, which was superior to traditional single crosslinked beads. In addition, the effects of grafting percentage, pH value, and temperature on the release behavior of the VB₂ were investigated. The drug release mechanism of CMCTS‐g‐PDEA drug‐loaded beads was analyzed by Peppa's potential equation. According to this study, the dual crosslinked hydrogel beads based on CMCTS‐g‐PDEA could serve as suitable candidate for drug site‐specific carrier in intestine. Copyright © 2009 John Wiley & Sons, Ltd.     

Molecular Dynamics Simulations of Metal Ion Binding to the His‐tag Motif

In our previous study, we have observed that the chelation of various metal ions to the His‐tag motifs mostly involves the i and i+2 His residues for Ni²⁺, Cu²⁺, Zn²⁺ and Co²+. In the present study, various 200 ps molecular dynamics simulations were further conducted to investigate the chelating pathway of various metal ions to the His‐tag motif with 6 His residues (His‐tag6) and the binding affinities of these metal binding pockets towards these metal ions. The results indicate that His‐tag6 with the chelated metal ion located in positions His(2,4) or His(3,5) exhibits the strongest affinity for Ni²+ and Cu²+.K⁺ was found to be preferred to chelate in His(1,3) and His(3,5) coordinations. However, Fe³+ was found to have higher affinity towards His(1,3) and His(2,4) binding pockets. Our results also suggest that Ni²⁺ exhibits the highest binding affinity towards His‐tag6 over the other metal ions. Most of the structural variations of the His‐tag6 motif were from the Histidyl side chains during metal ion binding. In addition, there is an inverse linear correlation between the final chelated distance and the charge/volume ratio of metal ion. There is a negative correlation between the metal binding affinity and the averaged potential energy generated from the MD simulations.     

Novel polyamidoamine‐based hydrogel with an innovative molecular architecture as a Co2+‐, Ni2+‐, and Cu2+‐sorbing material: Cyclovoltammetry and extended X‐ray absorption fine structure studies

An amphoteric polyamidoamine (PAA)‐based hydrogel, named INT‐PAA1, with a novel molecular architecture was prepared and studied as a Co²⁺‐, Ni²⁺‐, and Cu²⁺‐sorbing material. This hydrogel was obtained by the synthesis of a PAA in the presence of a second presynthesized PAA carrying many primary amino groups as side substituents, which acted as a macromolecular crosslinking agent. Therefore, it had an intersegmented structure. INT‐PAA1 exhibited a remarkable sorption capacity and sorption rate for Co²⁺, Ni²⁺, and Cu²⁺ that were advantageously in situ monitored by cyclic voltammetry. An extended X‐ray absorption fine structure spectroscopy characterization of the Co²⁺/INT‐PAA1 complex was also performed. The very fast and quantitative metal‐ion uptake, made apparent by an intense coloring of the hydrogel, showed remarkable potential for environmental applications such as heavy‐metal detection, recovery, and elimination. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2316–2327, 2006     

Cobalt(III)‐Mediated Permanent and Stable Immobilization of Histidine‐Tagged Proteins on NTA‐Functionalized Surfaces

We present the cobalt(III)‐mediated interaction between polyhistidine (His)‐tagged proteins and nitrilotriacetic acid (NTA)‐modified surfaces as a general approach for a permanent, oriented, and specific protein immobilization. In this approach, we first form the well‐established Co²⁺‐mediated interaction between NTA and His‐tagged proteins and subsequently oxidize the Co²⁺ center in the complex to Co³⁺. Unlike conventionally used Ni²⁺‐ or Co²⁺‐mediated immobilization, the resulting Co³⁺‐mediated immobilization is resistant toward strong ligands, such as imidazole and ethylenediaminetetraacetic acid (EDTA), and washing off over time because of the high thermodynamic and kinetic stability of the Co³⁺ complex. This immobilization method is compatible with a wide variety of surface coatings, including silane self‐assembled monolayers (SAMs) on glass, thiol SAMs on gold surfaces, and supported lipid bilayers. Furthermore, once the cobalt center has been oxidized, it becomes inert toward reducing agents, specific and unspecific interactions, so that it can be used to orthogonally functionalize surfaces with multiple proteins. Overall, the large number of available His‐tagged proteins and materials with NTA groups make the Co³⁺‐mediated interaction an attractive and widely applicable platform for protein immobilization.     

Metal‐Ion‐Mediated Tuning of Duplex DNA Binding by Bis(2‐(2‐pyridyl)‐1H‐benzimidazole)

Studies of double‐stranded‐DNA binding have been performed with three isomeric bis(2‐(n‐pyridyl)‐1H‐benzimidazole)s (n=2, 3, 4). Like the well‐known Hoechst 33258, which is a bisbenzimidazole compound, these three isomers bind to the minor groove of duplex DNA. DNA binding by the three isomers was investigated in the presence of the divalent metal ions Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺. Ligand–DNA interactions were probed with fluorescence and circular dichroism spectroscopy. These studies revealed that the binding of the 2‐pyridyl derivative to DNA is dramatically reduced in the presence of Co²⁺, Ni²⁺, and Cu²⁺ ions and is abolished completely at a ligand/metal‐cation ratio of 1:1. Control experiments done with the isomeric 3‐ and 4‐pyridyl derivatives showed that their binding to DNA is unaffected by the aforementioned transition‐metal ions. The ability of 2‐(2‐pyridyl)benzimidazole to chelate metal ions and the conformational changes of the ligand associated with ion chelation probably led to such unusual binding results for the ortho isomer. The addition of ethylenediaminetetraacetic acid (EDTA) reversed the effects completely.     

Efficient fabrication of high‐capacity immobilized metal ion affinity chromatographic media: The role of the dextran‐grafting process and its manipulation

Novel high‐capacity Ni²⁺ immobilized metal ion affinity chromatographic media were prepared through the dextran‐grafting process. Dextran was grafted to an allyl‐activated agarose‐based matrix followed by functionalization for the immobilized metal ion affinity chromatographic media. With elaborate regulation of the allylation degree, dextran was completely or partly grafted to agarose microspheres, namely, completely dextran‐grafted agarose microspheres and partly dextran‐grafted ones, respectively. Confocal laser scanning microscope results demonstrated that a good adjustment of dextran‐grafting degree was achieved, and dextran was distributed uniformly in whole completely dextran‐grafted microspheres, while just distributed around the outside of the partly dextran‐grafted ones. Flow hydrodynamic properties were improved greatly after the dextran‐grafting process, and the flow velocity increased by about 30% compared with that of a commercial chromatographic medium (Ni Sepharose FF). A significant improvement of protein binding performance was also achieved by the dextran‐grafting process, and partly dextran‐grafted Ni²⁺ chelating medium had a maximum binding capacity for His‐tagged lactate dehydrogenase about 2.5 times higher than that of Ni Sepharose FF. The results indicated that this novel chromatographic medium is promising for applications in high‐efficiency and large‐scale protein purification.     

Electrochemical Signal‐triggered Release of Biomolecules Functionalized with His‐tag Units

His‐tagged molecular species, a ferrocene derivative and Protein A, were immobilized on electrode surfaces (Au and graphite) through formation of a chelated complex in the presence of Cu²⁺ cations used as bridging units. The complex was cleaved and the attached molecules were released from the electrode surface by applying reductive potential to the electrodes resulting in Cu²⁺ reduction, thus decomposing the chelate complex. The molecule release process was followed by cyclic voltammetry in case of the ferrocene derivative. His‐tagged Protein A was additionally labeled with a fluorescent tag and its release was followed by fluorescence measurements in the solution and by impedance spectroscopy at the electrode. The studied release of the His‐tagged redox species and biomolecules was considered as a new generic approach to the signal‐controlled molecule release applicable in various biotechnological and biomedical applications.     

Ni2+ Ion Effect of Conformations on Single‐, Double‐ and Three‐Stranded Homopolynucleotides Containing Adenine and Uracil

Differential UV and visible spectroscopy and thermal denaturation were used to study the interaction of Ni²⁺ ions with adenosine 5′‐monophosphate (AMP), uridine 5′‐monophosphate (UMP), single‐stranded polyadenylic acid (polyA) and polyuridylic (polyU), double‐stranded polyA/polyU (AU) and three‐stranded polyA/2 polyU (A2U). The coil → helix transition observed in polyA, AU and A2U at room temperature is induced by Ni²⁺ binding to the oxygen atoms of the phosphate groups which belong to the disordered single‐stranded parts of the polynucleotides. Ni²⁺ ions coordinate with bases only in individual AMP and single‐stranded polyA. This coordination causes disordering of the helical parts of the strands. The disordered single strands form thermally stable compact particles with effective radii of ˜100 Å. Diagrams of the phase equilibrium between single‐, double‐ and three‐stranded conformations as a function of temperature and Ni²⁺ concentration have been obtained. The melting ranges of A2U and AU differ considerably, mainly due to different enthalpies of their helix–coil transitions. The behaviour of the transition parameters in the presence of Ni²⁺ ions agrees with the data obtained from the theory of equilibrium binding. The constants of the Ni²⁺ binding to AU and A2U are found. The effect of Ni²⁺ ions upon the thermal stability of AU and A2U is connected mainly with their different binding to multi‐stranded helices and polyU. The end of melting of the double‐stranded AU formed due to the A2U → AU + U transition has the character of a second‐order phase transition.     

Transition‐Metal‐Ion‐Mediated Polymerization of Dopamine: Mussel‐Inspired Approach for the Facile Synthesis of Robust Transition‐Metal Nanoparticle–Graphene Hybrids

Inspired by the high transition‐metal‐ion content in mussel glues, and the cross‐linking and mechanical reinforcement effects of some transition‐metal ions in mussel threads, high concentrations of nickel(II), cobalt(II), and manganese(II) ions have been purposely introduced into the reaction system for dopamine polymerization. Kinetics studies were conducted for the Ni²⁺–dopamine system to investigate the polymerization mechanism. The results show that the Ni²⁺ ions could accelerate the assembly of dopamine oligomers in the polymerization process. Spectroscopic and electron microscopic studies reveal that the Ni²⁺ ions are chelated with polydopamine (PDA) units, forming homogeneous Ni²⁺–PDA complexes. This facile one‐pot approach is utilized to construct transition‐metal‐ion–PDA complex thin coatings on graphene oxide, which can be carbonized to produce robust hybrid nanosheets with well‐dispersed metallic nickel/metallic cobalt/manganese(II) oxide nanoparticles embedded in PDA‐derived thin graphitic carbon layers. The nickel–graphene hybrid prepared by using this approach shows good catalytic properties and recyclability for the reduction of p ‐ nitrophenol.     

Properties of a 2,3‐Butanediol Dehydrogenase from Taiwanofungus camphorata

2,3‐Butanediol dehydrogenase (Bdh) plays important roles in reduction of acetoin to 2,3‐butanediol, an important platform chemical with many industrial applications. Here, a TcBdh cDNA (1348 bp, GenBank accession JF896462) encoding a putative Bdh was cloned from Taiwanofungus camphorata. The deduced amino acid sequence is similar to the Bdhs from other species. A 3‐D structural model of TcBdh has been constructed based on the known structure of Pseudomonas putida formaldehyde dehydrogenase (PpFdh, PDB code 1KOL). To characterize the TcBdh protein, the coding region was subcloned into an expression vector pYEX‐S1 and transformed into Saccharomyces cerevisiae. The recombinant His6‐tagged TcBdh was expressed and purified by Ni²⁺‐nitrilotriacetic acid Sepharose. The purified enzyme showed a single band of 49 kDa on 12% sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. The Michaelis constant (K_M) value of the recombinant enzyme for acetoin was 8.5 mM. The enzyme’s optical pH was 6. The thermal inactivation of the enzyme showed a half‐life of 5.3 min at 45 °C.     

Synthesis of transition‐metal‐ion‐selective poly(N‐isopropylacrylamide) hydrogels by the incorporation of an Aza crown ether

A functionalized cyclam was synthesized by the attachment of a polymerizable acryloyl group to one of the four nitrogens on the cyclam molecule. The polymerization of the functionalized cyclam was performed with N‐isopropylacrylamide and N,N′‐methylene bisacrylamide, and the gels obtained were studied in the presence of different transition‐metal‐ion solutions. There was a drastic difference in the phase‐transition temperature (T_c) of the poly(N‐isopropylacrylamide) (PNIPAAm)/cyclam gel in comparison with the pure PNIPAAm gel. For the described system, a T_c shift of 15 °C was obtained. The presence of functionalized cyclam increased the hydrophilicity and T_c of the aforementioned polymer gels in deionized water (at pH 6) because of the presence of protonated amino moieties. The PNIPAAm/cyclam gels showed a dependence of the swelling behavior on pH. T_c of the pure PNIPAAm gel was weakly influenced by the presence of any transition‐metal ions, such as Cu²⁺, Ni²⁺, Zn²⁺, and Mn²⁺. The addition of Cu²⁺ or Ni²⁺ to the PNIPAAm/cyclam gel reduced T_c of the polymer gel, and a shift of approximately 12 °C was observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1594–1602, 2003     

Insight into the Complexation Mode of Bis(nitrilotriacetic acid) (NTA) Ligands with Ni2+ Involved in the Labeling of Histidine‐Tagged Proteins

According to literature reports and our own findings, the binding of new Ni²⁺‐preloaded bis(nitrilotriacetic acid) (NTA) ligands with polyhistidine‐tagged proteins has been found to be accompanied by a one‐ to two‐order‐of‐magnitude increase in affinity, compared to the binding of a single Ni²⁺‐preloaded NTA moiety. In spite of the introduction of a second NTA chelating group, a cooperative effect that is less than the theoretical maximum has been observed. Herein, we present a rational explanation for the observed stability of the ternary complex involving the postulated bis‐NTA–(Ni²⁺)₂ species and multivalent polyhistidine tags. We have found that prior to the formation of the ternary complex, the Ni²⁺‐preloading step of bis‐NTA ligands does not form the expected bis‐NTA–(Ni²⁺)₂ exclusively. Instead of the major formation of bis‐NTA–(Ni²⁺)₂ species, it appears that cyclic discrete 1:1 and 2:2 entities are predominantly formed. It is proposed that these species interact upon ring‐opening with multivalent histidine tags. The occurrence of this phenomena accounts for the overall one‐ to two‐order‐of‐magnitude increase in affinity of ternary complexes involving bis‐NTA ligands.     

Synthesis and self‐assembly of novel amphiphilic copolymers poly(lactic acid)‐block‐poly(ascorbyl acrylate)

In this study, a novel type of amphiphilic block copolymers poly(lactic acid)‐block‐poly(ascorbyl acrylate) (PLA‐block‐PAAA) with biodegradable poly(lactic acid) as hydrophobic block and poly(ascorbyl acrylate) (PAAA) as hydrophilic block was successfully developed by a combination of ring‐opening polymerization and atom transfer radical polymerization, followed by hydrogenation under normal pressure. The chemical structures of the desired copolymers were characterized by ¹H NMR and gel permeation chromatography. The thermal physical properties and crystallinity were investigated by thermogravimetric analysis, differential scanning calorimetry, and wide angle X‐ray diffraction, respectively. Their self‐assembly behavior was monitored by fluorescence‐probe technique and turbidity change using UV–vis spectrometer, and the morphology and size of the nanocarriers via self‐assembly were detected by cryo‐transmission electron microscopy and dynamic light scattering. These polymeric micelles with PAAA shell extending into the aqueous solution have potential abilities to act as promising nanovehicles for targeting drug delivery. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Syntheses,structures of N‐(substituted)‐2‐aza‐[3]‐ferrocenophanes and their application as redox sensor for Cu2+ ion

Rigid N‐(substituted)‐2‐aza‐[3]‐ferrocenophanes L1 and L2 were easily synthesized from 1,1 ‐dicarboxyaldehydeferrocene and the corresponding amines. Ligands L1 and L2 were characterized by ¹H NMR, ¹³C NMR and single‐crystal X‐ray crystallography. The coordination abilities of L1 and L2 with metal ions such as Cu²⁺, Mg²⁺, Ni²⁺, Zn²⁺, Pb²⁺ and Cd²⁺ were evaluated by cyclic voltammetry. The electrochemical shift (ΔE_1/2) of 125 mV was observed in the presence of Cu²⁺ ion, while no significant shift of the Fc/Fc + couple was observed when Mg²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Cd²⁺ metal ions were added to the solution of L1 in the mixture of MeOH and H₂O. Moreover, the extent of the anodic shift of redox potentials was approximately equal to that induced by Cu²⁺ alone when a mixture of Cu²⁺, Mg²⁺, Ni²⁺, Zn²⁺, Pb²⁺ and Cd²⁺ was added to a solution of L1. Ligand L1 was proved to selectively sense Cu²⁺ in the presence of large, excessive first‐row transition and late‐transition metal cations. The coordination model was proposed from the results of controlled experiments and quantum calculations. Copyright © 2012 John Wiley & Sons, Ltd.     

Quercetin 2,4‐Dioxygenase Activates Dioxygen in a Side‐On O2–Ni Complex

Quercetin 2,4‐dioxygenase (quercetinase) from Streptomyces uses nickel as the active‐site cofactor to catalyze oxidative cleavage of the flavonol quercetin. How this unusual active‐site metal supports catalysis and O₂ activation is under debate. We present crystal structures of Ni‐quercetinase in three different states, thus providing direct insight into how quercetin and O₂ are activated at the Ni²⁺ ion. The Ni²⁺ ion is coordinated by three histidine residues and a glutamate residue (E⁷⁶) in all three states. Upon binding, quercetin replaces one water ligand at Ni and is stabilized by a short hydrogen bond through E⁷⁶, the carboxylate group of which rotates by 90°. This conformational change weakens the interaction between Ni and the remaining water ligand, thereby preparing a coordination site at Ni to bind O₂. O₂ binds side‐on to the Ni²⁺ ion and is perpendicular to the C2?C3 and C3?C4 bonds of quercetin, which are cleaved in the following reaction steps.     

Studies on the nuclease activity and interactions of the mixed‐polypyridyl [Ni2(1,3‐tpbd)(diimine)2(H2O)2]4+ complexes with thioredoxin reductase

Three new nickel(II) complexes formulated as [Ni₂(1,3‐tpbd)(diimine)₂(H₂O)₂]⁴⁺ [1,3‐tpbd = N,N,N′,N′‐tetrakis(2‐pyridylmethyl)benzene‐1,3‐diamine, where diimine is an N,N‐donor heterocyclic base like 1,10‐phenanthroline (phen),2,2′‐bipyridine (bpy), 4,5‐diazafluoren‐9‐one (dafo)], have been synthesized and structurally characterized by X‐ray crystallography: [Ni₂(1,3‐tpbd)(phen)₂(H₂O)₂]⁴⁺ (1), [Ni₂(1,3‐tpbd)(bpy)₂(H₂O)₂]⁴⁺(2) and [Ni₂(1,3‐tpbd)(dafo)₂(H₂O)₂]⁴⁺ (3). Single‐crystal diffraction reveals that the metal atoms in the complexes are all in a distorted octahedral geometry and in a trans arrangement around 1,3‐tpbd ligand. The interactions of the three complexes with calf thymus DNA (CT‐DNA) have been investigated by UV absorption, fluorescence spectroscopy, circular dichroism and viscosity. The apparent binding constant (K_app) values are calculated to be 1.91 × 10⁵ m ^?1 for 1, 1.18 × 10⁵ m ^?1 for 2, and 1.35 × 10⁵ m ^?1 for 3, following the order 1 > 3 > 2. The higher DNA binding affinity of 1 is due to the involvement in partial insertion of the phen ring between the DNA base pairs. A decrease in relative viscosities of DNA upon binding to 1–3 is consistent with the DNA binding affinities. These complexes efficiently display oxidative cleavage of supercoiled DNA in the presence of H₂O₂ (250 µ m ), with 3 exhibiting the highest nuclease activity. The rate constants for the conversion of supercoiled to nicked DNA are 5.28 × 10^?5 s^?1 (for 1), 6.67 × 10^?5 s^?1 (for 2) and 1.39 × 10^?4 s^?1 (for 3), also indicating that complex 3 shows higher catalytic activity than 1 and 2. Here the nuclease activity is not readily correlated to binding affinity. The inhibitory effect of complexes 1–3 on thioredoxin reductase has also been examined. The IC₅₀ values are calculated to be 26.54 ± 0.57, 31.03 ± 3.33 and 8.69 ± 2.54 µ m , respectively, showing a more marked inhibitory effect on thioredoxin reductase by complex 3 than the other two complexes. Copyright © 2012 John Wiley & Sons, Ltd.     

EPR Spectroscopy of 4, 4′‐Bis(tert‐butyl)‐2, 2′‐bipyridine‐1, 2‐dithiolatocuprates(II) in Host Lattices with Different Coordination Geometries

A series of new heteroleptic MN₂S₂ transition metal complexes with M = Cu²⁺ for EPR measurements and as diamagnetic hosts Ni²⁺, Zn²⁺, and Pd²⁺ were synthesized and characterized. The ligands are N₂ = 4, 4′‐bis(tert‐butyl)‐2, 2′‐bipyridine (tBu₂bpy) and S₂ =1, 2‐dithiooxalate, (dto), 1, 2‐dithiosquarate, (dtsq), maleonitrile‐1, 2‐dithiolate, or 1, 2‐dicyanoethene‐1, 2‐dithiolate, (mnt). The Cu^II complexes were studied by EPR in solution and as powders, diamagnetically diluted in the isostructural planar [Ni^II(tBu₂bpy)(S₂)] or[Pd^II(tBu₂bpy)(S₂)] as well as in tetrahedrally coordinated[Zn^II(tBu₂bpy)(S₂)] host structures to put steric stress on the coordination geometry of the central CuN₂S₂ unit. The spin density contributions for different geometries calculated from experimental parameters are compared with the electronic situation in the frontier orbital, namely in the semi‐occupied molecular orbital (SOMO) of the copper complex, derived from quantum chemical calculations on different levels (EHT and DFT). One of the hosts, [Ni^II(tBu₂bpy)(mnt)], is characterized by X‐ray structure analysis to prove the coordination geometry. The complex crystallizes in a square‐planar coordination mode in the monoclinic space group P2₁/a with Z = 4 and the unit cell parameters a = 10.4508(10) Å, b = 18.266(2) Å, c = 12.6566(12) Å, β = 112.095(7)°. Oxidation and reductions potentials of one of the host complexes, [Ni(tBu₂bpy)(mnt)], were obtained by cyclovoltammetric measurements.