bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemical Investigations of Tau Protein Phosphorylations and Interactions with Pin1
Authors: Martić Sanela , Beheshti Samaneh , Kraatz Heinz‐Bernhard , Litchfield David W. 
Published: September 2012

AbstractPhosphorylation of Tau by the protein kinase GSK‐3β was monitored by electrochemical impedance spectroscopy of immobilized Tau on gold surfaces. As a result of Tau phosphorylation, the film resistance decreases significantly due to conformational changes and reorganization of the immobilized phosphorylated Tau (pTau) protein, which in turn enables the interactions of pTau with the peptidyl‐prolyl cis/trans isomerase, Pin1. Interactions are specific to phospho‐Ser (pSer) and phospho‐Thr (pThr) residues of pTau. Impedance changes occurred as a function of pTauPin1 interactions and are related to the amount of Pin1 bound, which resulted in an increase of the charge‐transfer resistance, RCT. Our results clearly indicate that the isomerase Pin1 interacts favorably with pSer/pThr‐Pro residues in Tau, but does not bind non‐phosphorylated Tau or phospho‐Tyr residues in Tau films. Our study demonstrates the utility of electrochemical impedance studies to probe protein modifications and biomolecular interactions.
Ligand‐Incorporation Site in 5‐Methylcytosine‐Detection Probe Modulating the Site of Osmium Complexation with the Target DNA
Authors: Sugizaki Kaori , Nakamura Akiko , Yanagisawa Hiroyuki , Okamoto Akimitsu 
Published: September 2012

AbstractICON Probes, short DNA strands containing an adenine linked to a bipyridine ligand, formed an interstrand cross‐link with 5‐methylcytosine located opposite the modified adenine in the presence of an osmium oxidant. The location of a bipyridine‐tethered adenine in the probes varied the selectivity of the reactive base. An ICON probe where the modified adenine was located at the probe center showed a 5‐methylcytosine‐selective osmium complexation, whereas an ICON probe with the modified adenine at the strand end exhibited high reactivity towards thymine as well as 5‐methylcytosine. The modulation of reactive bases by the incorporation of a bipyridine‐tethered adenine site made facilitates design of ICON probes for the fluorometric detection of 5‐methylcytosine.
A Dynamic C‐Terminal Segment in the Mycobacterium tuberculosis Mn/Fe R2lox Protein Can Adopt a Helical Structure with Possible Functional Consequences
Authors: Andersson Charlotta S. , Berthold Catrine L. , Högbom Martin 
Published: September 2012

AbstractMycobacterium tuberculosis R2‐like ligand‐binding oxidase (MtR2lox) belongs to a recently discovered group of proteins that are homologous to the ribonucleotide reductase R2 proteins. MtR2lox carries a heterodinuclear Mn/Fe cofactor and, unlike R2 proteins, a large ligand‐binding cavity. A unique tyrosine‐valine cross link is also found in the vicinity of the active site. To date, all known structures of R2 and R2lox proteins show a disordered C‐terminal segment. Here, we present two new crystal forms of MtR2lox, revealing an ordered helical C‐terminal. The ability of alternating between an ordered and disordered state agrees well with bioinformatic analysis of the protein sequence. Interestingly, ordering of the C‐terminal helix shields a large positively charged patch on the protein surface, potentially used for interaction with other cellular components. We hypothesize that the dynamic C‐terminal segment may be involved in control of protein function in vivo.
A Synthetic Pathway for an Unsymmetrical N5O2 Heptadentate Ligand and Its Heterodinuclear Iron(III)Zinc(II) Complex: A Biomimetic Model for the Purple Acid Phosphatases
Authors: Xavier Fernando R. , Bortoluzzi Adailton J. , Neves Ademir 
Published: September 2012

AbstractOne major field of interest in bioinorganic chemistry is the design and synthesis of inorganic compounds with low molecular mass, showing structural, spectroscopic, and reactivity properties that mimic enzymes, such as purple acid phosphatases (PAPs). In this study, the unsymmetrical heptadentate ligand 2‐[(4,7‐diisopropyl‐1,4,7‐triazacyclonon‐1‐yl)methyl]‐6‐{[(2‐hydroxybenzyl)(pyridin‐2‐ylmethyl)‐amino]methyl}‐4‐methylphenol (H2L) and its first mixed‐valence complex [FeIIIZnII(L)(μ‐OAc)2]ClO4 (1) were synthesized. Physical and chemical measurements (crystal structure, conductometry, IR and UV/VIS spectroscopy, and electrochemistry) were performed for 1, and these properties are compared with those presented by the kbPAPs active sites. Potentiometric titration studies of 1 have confirmed its acid/base properties that are crucial for the understanding of the phosphodiester and DNA catalytic cleavage in future studies.
Synthesis and AcidBase Properties of an Imidazole‐Containing Nucleotide Analog, 1‐(2′‐Deoxy‐β‐D‐ribofuranosyl)imidazole 5′‐Monophosphate (dImMP2−)
Authors: Megger Nicole , Johannsen Silke , Müller Jens , Sigel Roland K. O. 
Published: September 2012

AbstractDeletion of the substituted pyrimidine ring in purine‐2′‐deoxynucleoside 5′‐monophosphates leads to the artificial nucleotide analog dImMP2−. This analog can be incorporated into DNA to yield, upon addition of Ag+ ions, a molecular wire. Here, we measured the acidity constants of H2(dImMP)± having one proton at N(3) and one at the PO group by potentiometric pH titrations in aqueous solution. The micro acidity constants show that N(3) is somewhat more basic than PO and, consequently, the (H⋅ dImMP)− tautomer with the proton at N(3) dominates to ca. 75%. The calculated micro acidity constants are confirmed by 31P‐ and 1H‐NMR chemical shifts. The assembled data allow many quantitative comparisons, e.g., the N(3)‐protonated and thus positively charged imidazole residue facilitates deprotonation of the P(O)2(OH)− group by 0.3 pK units. Information on the intrinsic site basicities also allows predictions about metal‐ion binding; e.g., Mg2+ and Mn2+ will primarily coordinate to the phosphate group, whereas Ni2+ and Cu2+ will preferably bind to N(3). Macrochelate formation for these metal ions is also predicted. The micro acidity constant for N(3)H+ deprotonation in the (H ⋅ dImMP⋅H)± species (pka 6.46) and the Mn+‐binding properties are of relevance for understanding the behavior of dImMP units present in DNA hairpins and metalated duplexes.
Molecular Evolution, Structure, and Function of Peroxidasins
Authors: Soudi Monika , Zamocky Marcel , Jakopitsch Christa , Furtmüller Paul G. , Obinger Christian 
Published: September 2012

AbstractPeroxidasins represent the subfamily 2 of the peroxidase‐cyclooxygenase superfamily and are closely related to chordata peroxidases (subfamily 1) and peroxinectins (subfamily 3). They are multidomain proteins containing a heme peroxidase domain with high homology to human lactoperoxidase that mediates one‐ and two‐electron oxidation reactions. Additional domains of the secreted and glycosylated metalloproteins are type C‐like immunoglobulin domains, typical leucine‐rich repeats, as well as a von Willebrand factor C module. These are typical motifs of extracellular proteins that mediate protein–protein interactions. We have reconstructed the phylogeny of this new family of oxidoreductases and show the presence of four invertebrate clades as well as one vertebrate clade that includes also two different human representatives. The variability of domain assembly in the various clades was analyzed, as was the occurrence of relevant catalytic residues in the peroxidase domain based on the knowledge of catalysis of the mammalian homologues. Finally, the few reports on expression, localization, enzymatic activity, and physiological roles in the model organisms Drosophila melanogaster, Caenorhabditis elegans, and Homo sapiens are critically reviewed. Roles attributed to peroxidasins include antimicrobial defense, extracellular matrix formation, and consolidation at various developmental stages. Many research questions need to be solved in future, including detailed biochemical/physical studies and elucidation of the three dimensional structure of a model peroxidasin as well as the relation and interplay of the domains and the in vivo functions in various organisms including man.
The Need for Combined Inorganic, Biochemical, and Nutritional Studies of Chromium(III)
Authors: Vincent John B. , Love Sharifa T. 
Published: September 2012

AbstractThe history of biochemical and nutritional studies of the element is unfortunately full of twists and turns, most leading to dead ends. Chromium (Cr), as the trivalent ion, has been proposed to be an essential element, a body mass and muscle development agent, and, in the form of the most popular Cr‐containing nutritional supplement, to be toxic when given orally to mammals. None of these proposals, despite significant attention in the popular media, has proven to be correct. Trivalent chromium has also been proposed as a therapeutic agent to increase insulin sensitivity and affect lipid metabolism, although a molecular mechanism for such actions has not been elucidated. Greater cooperative research interactions between nutritionists, biochemists, and chemists might have avoided the earlier issues in nutritional and biochemical Cr research and is necessary to establish the potential role of Cr as a therapeutic agent at a molecular level.
Synthesis of Glucopyranosyl Schiff Base Zinc(II) Complexes Capable of Interacting with Mononucleotides, and Their DNA‐Cleavage Activities
Authors: Nakai Misaki , Fukuda Hironobu , Yano Shigenobu , Nakabayashi Yasuo 
Published: September 2012

AbstractNew glucopyranosyl Schiff base zinc complexes, [Zn(GlcSal)2] (1; GlcSalH=N‐(2‐deoxy‐β‐D‐glucopyranos‐2‐yl‐salicylaldimine) and [Zn(AcOGlcSal)2] (2; AcOGlcSalH=N‐(2‐deoxy‐β‐D‐1,3,4,6‐tetraacetylglucopyranos‐2‐yl‐salicylaldimine) were synthesized, and characterized by spectral and analytical methods. The interaction between the Zn complexes and mononucleotides was investigated by 1H‐NMR, 31P‐NMR and UV/VIS spectroscopies. Mononucleotides, cytidine 5′‐monophosphate (CMP) and uridyl 5′‐monophosphate (UMP), interacted with these complexes to form a 1 : 1 complex with 1 and a 1 : 2 complex with 2, depending on the presence of the OH group of glucopyranosyl substituents. The DNA‐cleavage activities of 1 and 2 were studied using plasmid DNA (pBR322) in a medium of 5 mM Tris⋅HCl/50 mM NaCl buffer in the presence of H2O2. The DNA‐cleavage activity decreased in the order of 2>1>Zn(OAc)2, indicating the significant promoting effect of the glucopyranosyl Schiff base ligand and the participation of the glucopyranosyl OH groups in the cleavage mechanism. The mechanism of the DNA cleavage by 1 and 2 was investigated by evaluation of the effect of a HO. radical scavenger and a singlet‐oxygen (1O2) quencher under aerobic conditions. The former exhibited little effect, excluding the HO. radical as an active species and supporting the hydrolysis mechanism for the main process of the DNA cleavage. The latter quencher somewhat hindered the cleavage, indicating the partial participation of a 1O2 as a competitive active species in the present system.
X‐Ray Crystal Structure of a Mutant Assimilatory Nitrite Reductase That Shows Sulfite Reductase‐Like Activity
Authors: Nakano Shogo , Takahashi Misa , Sakamoto Atsushi , Morikawa Hiromichi , Katayanagi Katsuo 
Published: September 2012

AbstractAssimilatory nitrite reductase (aNiR) reduces nitrite ions (NO) to ammonium ions (NH), whereas assimilatory sulfite reductase reduces sulfite (SO) to hydrogen sulfide (HS−). Although aNiR can also reduce SO, its activity is much lower than when NO is reduced as the substrate. To increase the SO‐reduction activity of aNiR, we performed a N226K mutation of Nii3, a representative aNiR. The resulting Nii3‐N226K variant could bind non‐native targets, SO, and HCO, in addition to its native target, i.e., NO. We have determined the high‐resolution structure of Nii3‐N226K in its apo‐state and in complex with SO, NO, and HCO. This analysis revealed conformational changes of Lys226 and the adjacent Lys224 upon binding of SO, but not NO. In contrast, HCO binding induced a conformational change at Arg179. After replacing Asn226 with a positively charged Lys, aNiR showed affinity for several anions. A comparison of all ligand‐bound structures for Nii3‐N226K revealed that structural changes in the active site depend on the size of the substrate.
Quinoline‐Based, Glucose‐Pendant Fluorescent Zinc Probes
Authors: Mikata Yuji , Ugai Anna , Yasuda Keiko , Itami Saori , Tamotsu Satoshi , Konno Hideo , Iwatsuki Satoshi 
Published: September 2012

AbstractQuinoline‐based tetradentate ligands with glucose pendants, N,N′‐bis[2‐(β‐d‐glucopyranosyloxy)ethyl]‐N,N′‐bis[(6‐methoxyquinolin‐2‐yl)methyl]ethylenediamine (N,N′‐6‐MeOBQBGEN) and its N,N‐counterpart, N,N‐6‐MeOBQBGEN, have been prepared, and their fluorescence‐spectral changes upon Zn binding were investigated. Upon excitation at 336 nm, N,N′‐6‐MeOBQBGEN showed weak fluorescence (ϕ≈ 0.016) in HEPES buffer (HEPES 50 mM, KCl 100 mM, pH 7.5). In the presence of Zn, N,N′‐6‐MeOBQBGEN exhibited a significant increase in fluorescence (ϕ=0.096) at 414 nm. The fluorescence enhancement is specific for Zn and Cd (ICd/IZn of 50% at 414 nm). On the other hand, N,N‐6‐MeOBQBGEN exhibited a smaller fluorescence enhancement upon Zn complexation (ϕ=0.043, λex=334 nm, λem=407 nm) compared with N,N′‐6‐MeOBQBGEN. Fluorescence microscopic analysis using PC‐12 rat adrenal cells revealed that N,N′‐6‐MeOBQBGEN exhibits a 1.8‐fold higher fluorescence‐signal response to Zn ion concentration compared with sugar‐depleted compound 2 (N,N′‐bis[(6‐methoxyquinolin‐2‐yl)methyl]ethylenediamine), due to its enhanced uptake into cells due to the targeting ability of the attached carbohydrates.
Group‐10 Metal Complexes of Biological Molecules and Related Ligands: Structural and Functional Properties
Authors: Shimazaki Yuichi , Yamauchi Osamu 
Published: September 2012

AbstractThe complexes of group‐10 metals, Ni, Pd, and Pt, with biological molecules and related ligands have been attracting increasing attention in recent years due to their reactivities and functions, such as catalysts and drugs, and their biological relevance. The well‐defined structures and kinetic inertness especially of Pt complexes have been used as the sites for weak interactions with other molecules. The Ni complexes have been reported as models not only for Ni enzymes but also for other metalloenzyme active sites for deeper understanding of the reactivities such as oxygen activations and detailed electronic structures. Pd Complexes are widely known for their catalytic activities in conversions of various organic molecules including useful biological molecules, such as SuzukiMiyaura cross‐coupling, while Pt complexes have been intensively studied for their antitumor activities. We focus in this review on our recent results on weak interactions and reactivities of the group‐10 metal complexes with biological molecules and related compounds, and discuss their structural features and some new properties pointing to functional possibilities.
Coordination of Thiosemicarbazones and Bis(thiosemicarbazones) to Bismuth(III) as a Strategy for the Design of Metal‐Based Antibacterial Agents
Authors: Lessa Josane A. , Reis Débora C. , Da Silva Jeferson G. , Paradizzi Lúcia T. , da Silva Nayane F. , de Fátima A. Carvalho Mariany , Siqueira Sarah A. , Beraldo Heloisa 
Published: September 2012

AbstractComplexes [Bi(2Fo4Ph)Cl2] (1), [Bi(2Ac4Ph)Cl2] (2), [Bi(2Bz4Ph)Cl2] (3), [Bi(H2Gy3DH)Cl3] (4), [Bi(H2Gy4Et)(OH)2Cl] (5), and [Bi(H2Gy4Ph)Cl3] (6) were prepared with pyridine‐2‐carbaldehyde 4‐phenylthiosemicarbazone (H2Fo4Ph), 1‐(pyridin‐2‐yl)ethanone 4‐phenylthiosemicarbazone (H2Ac4Ph), phenyl(pyridin‐2‐yl)methanone 4‐phenylthiosemicarbazone (H2Bz4Ph), as well as with glyoxaldehyde bis(thiosemicarbazone) (H2Gy4DH) and its 4‐Et (H2Gy4Et) and 4‐Ph (H2Gy4Ph) derivatives. The complexes exhibited antibacterial activities against Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, and Pseudomonas aeruginosa. Coordination to BiIII proved to be an effective strategy to increase the antibacterial activity of the thiosemicarbazones and bis(thiosemicarbazones).
Mono(maleonitriledithiolene)molybdenum(IV) and Bis(μ‐sulfido)‐Bridged Dimolybdenum(V) Complexes with MoS Moiety
Authors: Bose Moumita , Moula Golam , Sarkar Sabyasachi 
Published: September 2012

AbstractMono(maleonitriledithiolene)sulfidomolybdenum(IV) complex, [MoS(S4)(mnt)]2− (2; mnt=maleonitriledithiolene) was synthesized by the substitution reaction of a tetrasulfido ligand of the known [MoS(S4)2]2− (1) upon reaction with one or even excess equivalent of Na2(mnt) in aqueous MeCN solution in air. Surprisingly, 2 undergoes dimerization on treatment with alkyl halide such as MeI and PhCH2Br to form bis(μ‐sulfido)dimolybdenum(V) species, [{MoS(mnt)}2(μ‐S)2]2− (3). These complexes have been characterized by IR, UV/VIS spectroscopy, cyclic voltammetry, elemental analysis, and by X‐ray crystal‐structure analysis. Differences in the relative stability and electrochemical behavior of 1, 2, and 3 have been correlated with theoretical calculations at DFT level.
Organometallic Ruthenium and Osmium Compounds of Pyridin‐2‐ and ‐4‐ones as Potential Anticancer Agents
Authors: Henke Helena , Kandioller Wolfgang , Hanif Muhammad , Keppler Bernhard K. , Hartinger Christian G. 
Published: September 2012

AbstractOrganometallic RuII compounds are among the most widely studied anticancer agents. Functionalizing metal centers with biomolecule‐derived ligands has been shown to be a promising strategy to improve the antiproliferative activity of metal‐based chemotherapeutics. Herein, the synthesis of a series of novel 3‐hydroxypyridin‐2‐one‐derived ligands and their MII(η6‐p‐cymene) half‐sandwich complexes (M=Ru, Os) is described. The compounds were characterized by 1D‐ and 2D‐NMR spectroscopy, and elemental analysis.
Diamminetetrakis(carboxylato)platinum(IV) Complexes – Synthesis, Characterization, and Cytotoxicity
Authors: Hoffmeister Björn R. , Adib‐Razavi Mahsa S. , Jakupec Michael A. , Galanski Mathea Sophia , Keppler Bernhard K. 
Published: September 2012

AbstractA series of eight novel diamminetetrakis(carboxylato)platinum(IV) complexes was synthesized and characterized by multinuclear 1H‐, 13C‐, 15N‐, and 195Pt‐NMR spectroscopy. Their antiproliferative potency was evaluated in three human cancer cell lines representing ovarian (CH1), lung (A549), and colon carcinoma (SW480). In cisplatin‐sensitive CH1 cancer cells, cytotoxicity was found in the low micromolar range, whereas, in inherently cisplatin‐resistant A549 and SW480 cells, the activity was very low or negligible. Astonishingly, raise in lipophilicity of the complexes, as found in the case of cisplatin analogs, did not result in a significant enhancement of the cytotoxic effect.
Binding of Divalent Metal Ions to Calcium‐Free Peroxidase: Thermodynamic and Kinetic Studies
Authors: Nazari Kohdadad , Kelay Vahid , Mahmoudi Ali , Hashemianzadeh Seyed Majid 
Published: September 2012

AbstractThermodynamics of binding of divalent metal ions including Ca2+, Mg2+, Ba2+, and Cd2+ to Ca‐free horseradish peroxidase (HRP) enzyme was investigated using UV/VIS spectrophotometry and molecular‐mechanic (MM) calculations. According to the obtained binding and thermodynamic parameters, trend of the relative binding affinities of these divalent metal cations was found to be: Ca2+>Cd2+>Mg2+>Ba2+. Binding analysis based on Scatchard and Hill models showed positive cooperativity effect between the two distal and proximal binding sites. Furthermore, kinetics of binding and reconstitution process was examined (using relaxation‐time method) for binding of Ca2+ (as the typical metal ion) to Ca‐free HRP, which was found a second‐order type having a two‐step mechanism involving fast formation of Ca‐free HRP/1 Ca2+ as the kinetic intermediate in step 1. Finally, by means of MM calculations, the comparative stability energies were evaluated for binding of M2+ metal cations to Ca‐free HRP. Based on MM calculations, preferential binding of Ca2+ ion was occurred on distal and proximal binding sites of Ca‐free HRP associated with higher stability energies (Etotal). Indeed, among the divalent metal ions, Ca2+ with the highest binding affinity (maximum value of Kbin and minimum value of ΔG), maximum value of exothermic binding enthalpy, and stability energies stabilizes the HRP structure along with an optimized catalytic activity.
Density Functional Study on UV/VIS Spectra of Copper‐Protein Active Sites: The Effect of Mutations
Authors: Swart Marcel , Johansson Mikael P. 
Published: September 2012

AbstractUV/VIS Electron excitation spectra have been computed for large, realistic model systems of the blue copper protein family. Fully quantum‐chemical calculations at the density‐functional theory level employing polarized triple‐ζ basis sets have been performed on systems of over 120 atoms, without symmetry. Different mutants, with the ligating methionine of the wild type Cu center exchanged for histidine (M121 H) and glutamine (M121Q), have been investigated in order to obtain insight about how the influence of the exact surrounding milieu of the Cu‐atom affects the computed spectrum. With sufficiently large model sizes, inclusion of the environment by using continuum solvation models do not change the spectra significantly. More direct and rigorous treatments are needed to reliably assess the effect of the surrounding protein on the electronic structure of the active sites.
Efficient Room‐Temperature O‐Silylation of Alcohols Using a SBA‐15‐Supported Cobalt(II) Nanocatalyst
Authors: Rajabi Fatemeh , Luque Rafael , Serrano‐Ruiz Juan Carlos 
Published: September 2012

AbstractThe O‐silylation of OH groups of alcohols and phenols with hexamethyldisilazane (HMDS) was achieved in high‐to‐excellent yields using catalytic quantities of a SBA‐15‐supported cobalt(II) nanocatalyst (typically 0.5 mol‐%) at room temperature and under solvent‐free conditions. Furthermore, the heterogeneous catalyst showed an excellent durability and can be conveniently reused by filtration for at least twelve times without any noticeable loss of activity.
The [(Cp)M(CO)3] (M=Re, 99mTc) Building Block for Imaging Agents and Bioinorganic Probes: Perspectives and Limitations
Authors: Can Daniel , Peindy N'Dongo Harmel W. , Spingler Bernhard , Schmutz Paul , Raposinho Paula , Santos Isabel , Alberto Roger 
Published: September 2012

AbstractStarting from asymmetric Thiele's acid derivatives, two different imaging probes [99mTc(CO)3(CpR)] (R=potential targeting vector) are generated simultaneously in one‐pot and from one substrate. This extends the previously introduced labeling strategy of metal‐mediated retro‐DielsAlder reaction with HCp‐R dimers. We demonstrate that chemically active functionalities such as hydroxamic acids are not following this labeling strategy. Adopting the principle of replacing phenyl rings by [Re(CO)3(Cp)] entities, potent histone deacetylase (HDAC)‐inhibiting Re analogs of suberoylanlilide hydroxamic acid (SAHA; N‐hydroxy‐N′‐phenyloctanediamide) were synthesized and characterized. Cytotoxic evaluation on different tumor cell lines revealed low IC50 values [μM] for these compounds, comparable to their purely organic congeners.