bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Mechanistic Study of the Effects of Antioxidants on the Formation of Malondialdehyde‐Like Products in the Reaction of Hydroxyl Radicals with Deoxyribose
Authors: Rachmilovich‐Calis Sandra , Meyerstein Naomi , Meyerstein Dan 
Published: June 2009

AbstractThe reactions of .OH radicals with deoxyribose, DR, form five different DR. radicals, only one of which is transformed into malondialdehyde (MDA)‐like products. The radiolytic yield of the MDA‐like products increases with the increase in the DR concentration indicating that some of the initially formed “unproductive” radicals react with DR to form the “productive” radicals. The yield of the MDA‐like products also increases with the dose rate delivered to the solution suggesting that the formation of the MDA‐like products involves the reaction of the “productive” radicals with a radical. The addition of ascorbate, AH−, to the solution decreases the yield of the MDA‐like products as expected from the relative rates of the reaction of DR and AH− with .OH radicals. On the other hand the addition of the exogenous thiol, N‐acetylcysteine (NAC), to the solutions decreases the yield of the MDA‐like products considerably more than expected from the rate constants of the reaction with .OH radicals. The addition of the endogenous thiol, glutathione (GSH), to the solutions affects the yield of the MDA‐like products at low concentration less than expected and at “high” concentrations more than expected from the rate constant of the reaction. Addition of low concentration of AH− to solutions containing GSH increases considerably its antioxidant activity whereas addition of small concentrations of AH− to solutions containing NAC has no effect on its antioxidant activity. The results point out that the DR. radicals react differently with NAC and GSH and that the GS. and NAC. radicals react differently with DR, the GS. radical being considerably more active than the NAC. radical. Thus it has to be concluded that the relative activity of antioxidants depends also on the rate constants of many secondary reactions and on the concentrations of all the solutes present in the system.
Reversible Uptake of COS, CS2, and SO2: Ionic Liquids with O‐Alkylxanthate, O‐Alkylthiocarbonyl, and O‐Alkylsulfite Anions
Authors: Heldebrant David J. , Yonker Clement R. , Jessop Philip G. , Phan Lam 
Published: June 2009

AbstractCO2‐binding organic liquids (CO2BOLs) are mixtures of a base (typically an amidine or guanidine) and an alcohol, and have been shown to reversibly capture and release CO2 with low reaction energies and high gravimetric CO2 capacity. We now report the ability of such liquid blends to chemically bind and release other acid gases such as CS2, COS, and SO2 analogously to CO2. These systems bind with sulfur‐containing acid gases to form colored ionic liquids with new O‐alkylxanthate, O‐alkylthiocarbonyl, and O‐alkylsulfite anions. The capture and thermal stripping of each acid gas from these systems and their applicability towards flue gas desulfurization is discussed.
Release of Toxic Gd3+ Ions to Tumour Cells by Vitamin B12 Bioconjugates
Authors: Siega Patrizia , Wuerges Jochen , Arena Francesca , Gianolio Eliana , Fedosov Sergey N. , Dreos Renata , Geremia Silvano , Aime Silvio , Randaccio Lucio 
Published: June 2009

AbstractTwo probes consisting of vitamin B12 (CNCbl) conjugated to Gd chelates by esterification of the ribose 5′‐OH moiety, Gd–DTPA–CNCbl (1; DTPA=diethylenetriamine‐N,N,N′,N′′,N′′‐pentaacetic acid) and Gd–TTHA–CNCbl (2; TTHA=triethylenetetramine‐N,N,N′,N′′,N′′′,N′′′‐hexaacetic acid), have been synthesised and characterised. The crystal structure of a dimeric form of 1, obtained by crystallisation with an excess of GdCl3, has been determined. The kinetics of binding to and dissociation from transcobalamin II show that 1 and 2 maintain high‐affinity binding to the vitamin B12 transport protein. Complex 2 is very stable with respect to Gd3+ release owing to the saturated co‐ordination of the Gd3+ ion by four amino and five carboxylate groups. Hydrolysis of the ester functionality occurs on the time scale of several hours. The lack of saturation and the possible involvement of the ester functionality in co‐ordination result in lower stability of 1 towards hydrolysis and in a considerable release of Gd3+ in vitro. Gd3+ ions released from 1 are avidly taken up by the K562 tumour cells to an extent corresponding to approximately 1010 Gd3+ per cell. The internalisation of toxic Gd3+ ions causes a marked decrease in cell viability as assessed by Trypan blue and WST‐1 tests. On the contrary, the experiments with the more stable 2 did not show any significant cell internalisation of Gd3+ ions and any influence on cell viability. The results point to new avenues of in situ generation of cytotoxic pathways based on the release of toxic Gd3+ ions by vitamin B12 bioconjugates.
From Azides to Nitrogen‐Centered Radicals: Applications of Azide Radical Chemistry to Organic Synthesis
Authors: Minozzi Matteo , Nanni Daniele , Spagnolo Piero 
Published: June 2009

AbstractOver the last thirty years organic azides have drawn a great deal of attention as radical traps for carbon‐ and heteroatom‐centered radicals, both in intra‐ and in intermolecular processes. The resulting intermediates (nitrogen‐centered radicals such as triazenyls, aminyls, or even iminyls) can be conveniently employed in the synthesis of a variety of cyclic and acyclic nitrogen‐containing compounds.
Heterogeneous Wheel‐Shaped Cu20‐Polyoxotungstate [Cu20Cl(OH)24(H2O)12(P8W48O184)]25− Catalyst for Solvent‐Free Aerobic Oxidation of n‐Hexadecane
Authors: Chen Lifang , Hu Juncheng , Mal Sib Sankar , Kortz Ulrich , Jaensch Helge , Mathys Georges , Richards Ryan M. 
Published: June 2009

AbstractThe selective oxidation of alkanes as a green process remains a challenging task because partial oxidation is easier to achieve with sacrificial oxidants, such as hydrogen peroxide, alkyl hydroperoxides or iodosylbenzene, than with molecular oxygen or air. Here, we report on a heterogeneous catalyst for n‐hexadecane oxidation comprised of the wheel shaped Cu20‐polyoxotungstate [Cu20Cl(OH)24(H2O)12(P8W48O184)]25− anchored on 3‐aminopropyltriethoxysilane (apts)‐modified SBA‐15. The catalysts were characterized by powder X‐ray diffraction (XRD), N2‐adsorption measurements and Fourier transform infrared reflectance (FT‐IR) spectroscopy. The heterogeneous Cu20‐polyanion system catalyzed the solvent‐free aerobic oxidation of n‐hexadecane to alcohols and ketones by using air as the oxidant under ambient conditions. The catalyst exhibits an exceptionally high turn over frequency (TOF) of 20 000 h−1 at 150 °C and is resistant to poisoning by CS2. Moreover, it can be easily recovered and reused by filtration without loss of its catalytic activity. Possible homogeneous contributions also have been examined and eliminated. Thus, this system can use air as oxidant, which, in combination with its good overall performance and poison tolerance, raises the prospect of this type of heterogeneous catalyst for practical applications.
Modelling the Magnetic Behaviour of Square‐Pyramidal CoII5 Aggregates: Tuning SMM Behaviour through Variations in the Ligand Shell
Authors: Klöwer Frederik , Lan Yanhua , Nehrkorn Joscha , Waldmann Oliver , Anson Christopher E. , Powell Annie K. 
Published: June 2009

AbstractThree new μ4‐bridged CoII5 clusters with similar core motifs have been synthesised with the use of N‐tert‐butyldiethanolamine (tbdeaH2) and pivalic acid (piv): [CoII5(μ4‐N3)(tbdea)2(μ‐piv)4(piv)(CH3CN)2]⋅CH3CN (1), [CoII5(μ4‐Cl)(Cl)(tbdea)2(μ‐piv)4(pivH)2] (2) and [CoII5(μ4‐N3)(Cl)(tbdea)2(μ‐piv)4(pivH)2] (3). Magnetic measurements were performed for all three compounds. It was found that while the chloride‐bridged cluster 2 does not show an out‐of‐phase signal, which excludes single‐molecule magnet (SMM) behaviour, the azide‐bridged compounds 1 and 3 show out‐of‐phase signals as well as frequency dependence of the ac susceptibility, as expected for SMMs. We confirmed that 1 is a SMM with zero‐field quantum tunnelling of the magnetisation at 1.8 K. Compound 3 is likely a SMM with a blocking temperature well below 1.8 K. We established a physical model to fit the χT versus T and M versus B curves of the three compounds to reproduce the observed SMM trend. The analysis showed that small changes in the ligand shell modify not only the magnitude of exchange constants, but also affect the J and g matrices in a non‐trivial way.
High‐Throughput Reaction Optimisation and Activity Screening of Ferrocene‐Based Lewis Acid–Catalyst Complexes by Using Continuous‐Flow Reaction Detection Mass Spectrometry
Authors: Martha Cornelius T. , Heemskerk Anton , Hoogendoorn Jan‐Carel , Elders Niels , Niessen Wilfried M. A. , Orru Romano V. A. , Irth Hubertus 
Published: June 2009

AbstractOptimising synthetic conversions and assessing catalyst performance is a tedious and laborious endeavour. Herein, we present an automated alternative to the commonly applied sequential approaches that are used to increase catalyst discovery process efficiencies by increasing the number of entities that can be tested. This new approach combines conversion of the reactants and determination of product formation into a single comprehensive reaction detection system that can be operated with minimal catalyst and reactant consumption. With this approach, rudimentary reaction conditions can be quickly optimised and the same system can then be used to screen for the optimal homogenous catalyst in a selected solution‐phase synthetic conversion. The system, which is composed of standard HPLC components, can be used to screen catalyst libraries at a repetition rate of five minutes and can be run unsupervised. The sensitive mass spectrometric detection that is implemented in the reaction detection methodology can be used for the simultaneous monitoring of reactants, catalysts and product ions. In the experiments, the three‐component reaction that gives a substituted 2‐imidazoline was optimised. Afterwards, the same method was used to assess a library of ferrocene‐based Lewis acid catalysts for performance in the aforementioned conversion in six different solvents. We demonstrate the feasibility of using this methodology to directly compare the performance results obtained in different solvents by calibrating the solvent‐specific MS responses.
Large Di‐ and Heptafullerene Polyelectrolytes Composed of C60 Building Blocks Having a Highly Symmetrical Hexakisaddition Pattern
Authors: Witte Patrick , Hörmann Frank , Hirsch Andreas 
Published: June 2009

AbstractWe report here on the synthesis of three new prototypes (types I–III) of very large fullerene‐based polyelectrolytes which can carry up to 60 charges on their periphery. All fullerene moieties incorporated in these macromolecular structures have an octahedral hexakisaddition pattern. Dumbbell‐shaped icosacarboxylate 5 (type I), which can accumulate up to twenty negative charges, is very soluble in methanol as well as in neutral and basic water. On the other hand, Janus dumbbell 13 (type II) contains both positively and negatively chargeable fullerene building blocks and is very soluble in acidic and basic media. However, in the region of the isoelectric point at pH 6.0–6.5 it precipitates as a pale orange solid due to pronounced intermolecular Coulomb interactions. Giant heptafullerene 15 (type III) can store up to 60 positive charges in its periphery and is the largest molecular polyelectrolyte with defined three‐dimensional structure.
Synthesis and Orthogonal Functionalization of [60]Fullerene e,e,e‐Trisadducts with Two Spherically Defined Addend Zones
Authors: Beuerle Florian , Hirsch Andreas 
Published: June 2009

Abstracte,e,e‐Trisadducts 13 and 15 have been prepared by a highly regioselective threefold cyclopropanation of tripodal malonates 10 and 12 with C60. The yield and regioselectivity depend on the length and structure of the tethers that connect the malonate units to the focal benzene core of 13–15. As a consequence of the template‐directed synthesis, all e,e,e‐trisadducts were formed as in/out isomers exclusively and contain two spherically well‐defined addend zones with equatorial and polar orientation, respectively. By variation of the outer malonate termini of the tethers, selective functionalization of the equatorial addend zone could be achieved, thus leading to fine‐tuning of intermolecular interactions, such as solubility or aggregation phenomena. After removal of the focal benzene moiety in 14 and 15, selective functionalization of the polar addend zone could be achieved. Strong intramolecular hydrogen‐bonding networks of the polar substituents in the polar addend zone could be observed by 1H NMR spectroscopic analysis. By orthogonal functionalization of both addend zones, fullerene derivatives 44–48 could be synthesized as one single in/out isomer, thus greatly enhancing the potential of e,e,e‐trisadducts as building blocks in supramolecular architectures.
Polydiacetylene‐Based Colorimetric Self‐Assembled Vesicular Receptors for Biological Phosphate Ion Recognition
Authors: Jose D. Amilan , Stadlbauer Stefan , König Burkhard 
Published: June 2009

AbstractSelf‐assembled vesicular polydiacetylene (PDA) particles with embedded metal complex receptor sites have been prepared. The particles respond to the presence of ATP and PPi (pyrophosphate) in buffered aqueous solution by visible changes of their color and emission properties. Blue PDA vesicles of uniform size of about 200 nm were obtained upon UV irradiation from mono‐ and dinuclear zinc(II)–cyclen and iminodiacetato copper [CuII–IDA] modified diacetylenes, embedded in amphiphilic diacetylene monomers. Addition of ATP and PPi to the PDA vesicle solution induces a color change from blue to red observable by the naked eye. The binding of ATP and PPi changes the emission intensity. Other anions such as ADP, AMP, H2PO4−, CH3COO−, F−, Cl−, Br− and I−, failed to induce any spectral changes. The zinc(II)–cyclen nanoparticles are useful for the facile detection of PPi and ATP in millimolar concentrations in neutral aqueous solutions, while CuII–IDA modified vesicular PDA receptors are able to selectively discriminate between ATP and PPi.
Solvent‐Enhanced Diastereo‐ and Regioselectivity in the PdII‐Catalyzed Synthesis of Six‐ and Eight‐Membered Heterocycles via cis‐Aminopalladation
Authors: Balázs Árpád , Hetényi Anasztázia , Szakonyi Zsolt , Sillanpää Reijo , Fülöp Ferenc 
Published: June 2009

AbstractThe PdII‐catalyzed intramolecular oxidative cyclization of tosyl‐protected cis‐ and trans‐N‐allyl‐2‐aminocyclohexanecarboxamides was examined, and efficient syntheses of cyclohexane‐fused pyrimidin‐4‐ones and 1,5‐diazocin‐6‐ones were developed. In the course of the research, a marked solvent effect was observed on both the regio‐ and diastereoselectivity. Additionally, a novel PdII‐mediated domino oxidation, oxidative amination reaction was discovered. Our experimental and theoretical findings suggest that the reactions proceed via a cis‐aminopalladation mechanism.
Stereochemistry of Compounds with Coordination Number Ten
Authors: Ruiz‐Martínez Antonio , Alvarez Santiago 
Published: June 2009

AbstractThe stereochemistry of ten‐coordinate rare‐earth and transition‐metal compounds is studied from the point of view of continuous shape measures (CShM) and derived tools. A total of 19 ideal ten‐vertex polyhedra belonging to 12 different symmetry point groups have been considered, from which nine are retained for the description of the stereochemistries of all studied compounds. The structures of the coordination spheres are analyzed by families, according to the denticity and topology of the ligands. Some ligand topologies are seen to consistently favor usually neglected ideal polyhedra, such as the capped trigonal cupola.
Is Cyclopropane Really the σ‐Aromatic Paradigm?
Authors: Wu Wei , Ma Ben , I‐Chia Wu Judy , Schleyer Paul von Ragué , Mo Yirong 
Published: June 2009

AbstractDewar proposed the σ‐aromaticity concept to explain the seemingly anomalous energetic and magnetic behavior of cyclopropane in 1979. While a detailed, but indirect energetic evaluation in 1986 raised doubts—“There is no need to involve ‘σ‐aromaticity’,”—other analyses, also indirect, resulted in wide‐ranging estimates of the σ‐aromatic stabilization energy. Moreover, the aromatic character of “in‐plane”, “double”, and cyclically delocalized σ‐electron systems now seems well established in many types of molecules. Nevertheless, the most recent analysis of the magnetic properties of cyclopropane (S. Pelloni, P. Lazzeretti, R. Zanasi, J. Phys. Chem. A 2007, 111, 8163–8169) challenged the existence of an induced σ‐ring current, and provided alternative explanations for the abnormal magnetic behavior. Likewise, the present study, which evaluates the σ‐aromatic stabilization of cyclopropane directly for the first time, fails to find evidence for a significant energetic effect. According to ab initio valence bond (VB) computations at the VBSCF/cc‐PVTZ level, the σ‐aromatic stabilization energy of cyclopropane is, at most, 3.5 kcal mol−1 relative to propane, and is close to zero when n‐butane is used as reference. Trisilacyclopropane also has very little σ‐aromatic stabilization, compared to Si3H8 (6.3 kcal mol−1) and Si4H10 (4.2 kcal mol−1). Alternative interpretations of the energetic behavior of cyclopropane (and of cyclobutane, as well as their silicon counterparts) are supported.
Electron‐Transfer Kinetics of Microperoxidase‐11 Covalently Immobilised onto the Surface of Multi‐Walled Carbon Nanotubes by Reactive Landing of Mass‐Selected Ions
Authors: Mazzei Franco , Favero Gabriele , Frasconi Marco , Tata Alessandra , Pepi Federico 
Published: June 2009

AbstractControlled deposition of biological molecules on nanostructured materials is a basic step towards the realisation of biochip components. In this study we report the investigation of the first covalent immobilisation of mass‐selected redox protein on a carboxyl‐functionalised multi‐walled carbon nanotube (MWCNT) electrode surface by means of ion soft landing. The immobilised protein maintains its biochemical properties, displaying an excellent electrochemical behaviour on the electrode surface. The deposition of mass‐selected ions is influenced by several factors, including the charge state and the collision energy of the projectile ions. To elucidate the mechanism involved in the protein reactive landing onto the MWCNT surface, the data obtained from cyclic voltammetry experiments were modelled according to the Marcus theory. The proposed method opens up the way to the development of a new generation of biocomponents with potential use in biosensors, diagnostics, biofuel cells and bioactive films.
Synthesis and Antimalarial Properties of Streptocyanine Dyes
Authors: Maether Marie‐Pierre , Desoubzdanne Denis , Izquierdo Albert , Guieu Valérie , Maturano Marie , André‐Barrès Christiane , Valentin Alexis , Jullian Valérie , Chevalley Séverine , Maynadier Marjorie , Vial Henri , Payrastre Corinne 
Published: June 2009

AbstractSeveral streptocyanine dyes were synthesized that contain polymethine chains of varying length. Their in vitro antimalarial activities were evaluated against the virulent P. falciparum parasite. In addition to the influence of polymethine chain length, the effects of structural modifications at nitrogen end groups, para substitution of the phenyl groups, and counter‐anions were studied. The most potent antimalarial activities were found for heptacarbon chain streptocyanines, with an IC50 value of 60 nM. Interestingly, most of the compounds were less cytotoxic toward the mammalian cells tested. The best selective toxicity profiles were found for pentacarbon chain streptocyanines, which have a good in vitro specificity index.
Screening for the Drug–Phospholipid Interaction: Correlation to Phospholipidosis
Authors: Alakoskela Juha‐Matti , Vitovič Pavol , Kinnunen Paavo K. J. 
Published: June 2009

AbstractPhospholipid bilayers represent a complex, anisotropic environment fundamentally different from bulk oil or octanol, for instance. Even “simple” drug association to phospholipid bilayers can only be fully understood if the slab‐of‐hydrocarbon approach is abandoned and the complex, anisotropic properties of lipid bilayers reflecting the chemical structures and organization of the constituent phospholipids are considered. The interactions of drugs with phospholipids are important in various processes, such as drug absorption, tissue distribution, and subcellular distribution. In addition, drug–lipid interactions may lead to changes in lipid‐dependent protein activities, and further, to functional and morphological changes in cells, a prominent example being the phospholipidosis (PLD) induced by cationic amphiphilic drugs. Herein we briefly review drug–lipid interactions in general and the significance of these interactions in PLD in particular. We also focus on a potential causal connection between drug‐induced PLD and steatohepatitis, which is induced by some cationic amphiphilic drugs.
Stereoselective HDAC Inhibition from Cysteine‐Derived Zinc‐Binding Groups
Authors: Butler Kyle V. , He Rong , McLaughlin Kathryn , Vistoli Giulio , Langley Brett , Kozikowski Alan P. 
Published: June 2009

AbstractA series of small‐molecule histone deacetylase (HDAC) inhibitors, which feature zinc binding groups derived from cysteine, were synthesized. These inhibitors were tested against multiple HDAC isoforms, and the most potent, compound 10, was determined to have IC50 values below 1 μM. The compounds were also tested in a cellular assay of oxidative stress‐induced neurodegeneration. Many of the inhibitors gave near‐complete protection against cell death at 10 μM without the neurotoxicity seen with hydroxamic acid‐based inhibitors, and were far more neuroprotective than HDAC inhibitors currently in clinical trials. Both enantiomers of cysteine were used in the synthesis of a variety of novel zinc‐binding groups (ZBGs). Derivatives of L‐cysteine were active in the HDAC inhibition assays, while the derivatives of D‐cysteine were inactive. Notably, the finding that both the D‐ and L‐cysteine derivatives were active in the neuroprotection assays suggests that multiple mechanisms are working to protect the neurons from cell death. Molecular modeling was employed to investigate the differences in inhibitory activity between the HDAC inhibitors generated from the two enantiomeric forms of cysteine.