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The Journal of the American Chemical Society, founded in 1879, is the flagship journal of the American Chemical Society and a highly esteemed journal in the field. This periodical is devoted to the publication of research papers in all fields of chemistry and publishes approximately 13,000 pages of new chemistry a year. Published weekly, JACS provides research crucial to the field of chemistry. The Journal of the American Chemical Society publishes articles, communications to the Editor, book reviews, and computer software reviews.

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American Chemical Society

Publications in this journal

• Aromatic Transition States in Non-Pericyclic Reactions: Anionic 5-Endo Cyclizations are Aborted Sigmatropic Shifts.

  Authors: Kerry Gilmore, Mariappan Manoharan, Judy I-Chia Wu, Paul von Rague' Schleyer, Igor V Alabugin

  Journal of the American Chemical Society.

  The transition states (TS's) of 5-endo-dig and 5-endo-trig anionic ring closures are the first unambiguous examples of non-pericyclic reactions with TS's stabilized by aromaticity. Their 5-center,The transition states (TS's) of 5-endo-dig and 5-endo-trig anionic ring closures are the first unambiguous examples of non-pericyclic reactions with TS's stabilized by aromaticity. Their 5-center, 6-electron in-plane aromaticity is revealed by the diatropic dissected nucleus independent chemical shifts (NICS), -24.1 ppm and -13.7 ppm, respectively, resulting from the delocalization of the lone pair at the nucleophilic center, a sigma CC bond, and an in-plane alkyne (or alkene) π bond. Other seemingly analogous exo and endo cyclization TS's do not have these features. A symmetry-enhanced combination of through-space and through-bond interactions explains the anomalous geometric, energetic, and electronic features of the 5-endo ring closure transition state. Anionic 5-endo cyclizations can be considered to be "aborted" [2,3]-sigmatropic shifts. The connection between anionic cyclizations and sigmatropic shifts offers new possibilities for the design and electronic control of anionic isomerizations.

• Heterogeneous Kinetics of the Carbon Monoxide Association and Dissociation Reaction to Nitrophorin 4 and 7 Coincide with Structural Heterogeneity of the Gate-Loop.

  Authors: Stefania Abbruzzetti, Chunmao He, Hideaki Ogata, Stefano Bruno, Cristiano Viappiani, Markus Knipp

  Journal of the American Chemical Society.

  NO is an important signaling molecule in human tissue. However, the mechanisms by which this molecule is controlled and directed are currently little understood. Nitrophorins (NPs) comprise a groupNO is an important signaling molecule in human tissue. However, the mechanisms by which this molecule is controlled and directed are currently little understood. Nitrophorins (NPs) comprise a group of ferriheme proteins originating from blood-sucking insects that are tailored to protect and deliver NO via coordination to and release from the heme iron. Therefore, the kinetics of the association and dissociation reactions were studied in this work using the ferroheme-CO complexes of NP4, NP4(D30N), and NP7 as isoelectronic models for the ferriheme-NO complexes. The kinetic measurements performed by nanosecond laser-flash-photolysis and stopped-flow are accompanied by resonance Raman and FT-IR spectroscopy to characterize the carbonyl species. Careful analysis of the CO rebinding kinetics reveals that in NP4 and, to a larger extent, NP7 internal gas binding cavities are located, which temporarily trap photodissociated ligands. Moreover, changes in the free energy barriers throughout the rebinding and release pathway upon increase of the pH are surprisingly small in case of NP4. Also in case of NP4, a heterogeneous kinetic trace is obtained at pH 7.5, which corresponds to the presence of two carbonyl species in the heme cavity that are seen in vibrational spectroscopy that are due to the change of the distal pocket polarity. Quantification of the two species from FT-IR spectra allowed the fitting of the kinetic traces as two processes, corresponding to the previously reported open and closed conformation of the A-B and G-H loops. Using the A-B loop mutant NP4(D30N) it was confirmed that the kinetic heterogeneity is controlled by pH through the disruption of the H-bond between Asp30 side-chain and the Leu130 backbone carbonyl. Overall, this first study on the slow phase of the dynamics of diatomic gas molecule interaction with NPs comprises an important experimental contribution for the understanding of the dynamics involved in the binding/release processes of NO/CO in NPs.

• Iridium-Catalyzed [2+2+2] Cycloaddition of α,ω-Diynes with Nitriles.

  Authors: Gen Onodera, Yoshihisa Shimizu, Jun-Na Kimura, Junya Kobayashi, Yukiko Ebihara, Kei Kondo, Ken Sakata, Ryo Takeuchi

  Journal of the American Chemical Society.

  [Ir(cod)Cl]2/DPPF or BINAP efficiently catalyzed the cycloaddition of α,ω-diynes with nitriles to give pyridines. The reaction can accommodate a very wide range of nitriles. Both aliphatic and[Ir(cod)Cl]2/DPPF or BINAP efficiently catalyzed the cycloaddition of α,ω-diynes with nitriles to give pyridines. The reaction can accommodate a very wide range of nitriles. Both aliphatic and aromatic nitriles smoothly reacted with α,ω-diynes to give pyridines. 10 Equiv of unactivated aliphatic nitrile were enough to give the product in high yield. Aliphatic nitriles bearing an acetal or amino moiety could be used for the reaction. The highly regioselective cycloaddition of unsymmetrical diyne bearing two different internal alkyne moieties was achieved. The observed regioselectivity could be reasonably explained by considering the different reactivities of the α-position in iridacyclopentadiene. Regioselective cycloaddition was successfully applied to the synthesis of terpyridine and quinquepyridine. This chemistry was extended to a new and efficient synthesis of oligoheteroarenes. Five aromatic or heteroaromatic rings were connected in a single operation. [Ir(cod)Cl]2/chiral diphosphine catalyst can be applied to enantioselective synthesis. Kinetic resolution of the racemic secondary benzyl nitrile catalyzed by [Ir(cod)Cl]2/SEGPHOS gave a central carbon chiral pyridine in 80% ee. The mechanism was analyzed on the basis of the B3LYP level of density functional calculations.

• Reaction of Singlet Oxygen with Tryptophan in Proteins: A Pronounced Effect of the Local Environment on the Reaction Rate.

  Authors: Rasmus Lybech Jensen, Jacob Arnbjerg, Peter R Ogilby

  Journal of the American Chemical Society.

  Singlet molecular oxygen, O2(a1Δg), can influence many processes pertinent to the function of biological systems, including events that result in cell death. Many of these processes involve aSinglet molecular oxygen, O2(a1Δg), can influence many processes pertinent to the function of biological systems, including events that result in cell death. Many of these processes involve a reaction between singlet oxygen and a given amino acid in a protein. As a result, the behavior of that protein can change, either because of a structural alteration and/or a direct modification of an active site. Surprisingly, however, little is known about rate constants for reactions between singlet oxygen and amino acids when the latter are in a protein. In this report, we demonstrate using five separate proteins, each containing only a single tryptophan residue, that the rate constant for singlet oxygen reaction with tryptophan depends significantly on the position of this amino acid in the protein. Most importantly, the reaction rate constant depends not just on the accessibility of the tryptophan residue to oxygen, but also on factors that characterize the local molecular environment of the tryptophan in the protein. The fact that the local protein environment can either appreciably inhibit or accelerate the reaction of singlet oxygen with a given amino acid can have significant ramifications for singlet-oxygen-mediated events that perturb cell function.

• Energetic basis of human telomeric DNA folding into G-quadruplex structures.

  Authors: Matjaž Bončina, Jurij Lah, Iztok Prislan, Gorazd Vesnaver

  Journal of the American Chemical Society.

  Recent theoretical studies performed on the folding/unfolding mechanism of the model telomeric human DNA, 5'-AGGGTTAGGGTTAGGGTTAGGG-3' (Tel22), have indicated that in the presence of K(+) ions Tel22Recent theoretical studies performed on the folding/unfolding mechanism of the model telomeric human DNA, 5'-AGGGTTAGGGTTAGGGTTAGGG-3' (Tel22), have indicated that in the presence of K(+) ions Tel22 folds into two hybrid G-quadruplex structures characterized by one double and two reversal TTA loops arranged in a different way. They predicted a new unfolding pathway from the initial mixture of hybrid G-quadruplexes via the corresponding intermediate triplex structures into the final, fully unfolded state. Significantly, no experimental evidence supporting the suggested pathway has been reported. In the current study, we performed a comprehensive global thermodynamic analysis of calorimetric (DSC, ITC) and spectroscopic (CD) data obtained on monitoring the folding/unfolding of Tel22 induced by changes of temperature and K(+) concentration. We show that unfolding of Tel22 may be described as a monomolecular equilibrium three-state process that involves thermodynamically distinguishable folded (F), intermediate (I) and unfolded (U) state. Considering that calorimetric methods cannot distinguish between energetically similar G-quadruplex or triplex conformations predicted by the theoretical model one can conclude that our results represent the first experimental support of the suggested unfolding/folding mechanism of Tel22. This conclusion is confirmed by the fact that the estimated number of K(+) ions released upon each unfolding step in our thermodynamic model agrees well with the corresponding values predicted by the theoretical model and that the observed changes in enthalpy, entropy and heat capacity accompanying the F->I and I->U transitions can be reasonably explained only if the intermediate state I is considered to be a triplex structural conformation.

• Construction of 1,5-Enynes by Stereospecific Pd-Catalyzed Allyl-Propargyl Cross-Couplings.

  Authors: Michael J Ardolino, James P Morken

  Journal of the American Chemical Society.

  The palladium-catalyzed cross-coupling of chiral propargyl acetates and allyl boronates delivers chiral 1,5-enynes with excellent levels of chirality transfer and can be applied across a broad rangeThe palladium-catalyzed cross-coupling of chiral propargyl acetates and allyl boronates delivers chiral 1,5-enynes with excellent levels of chirality transfer and can be applied across a broad range of substrates.

• Aryl and NHC Compounds of Technetium and Rhenium.

  Authors: Elisabeth Oehlke, Shushu Kong, Pawel Arciszewski, Swantje Wiebalck, Ulrich Abram

  Journal of the American Chemical Society.

  Air- and water-stable phenyl complexes with nitridotechnetium(V) cores can be prepared by straightforward procedures. [TcNPh2(Ph3P)2] is formed during the reaction of [TcNCl2(Ph3P)2] with PhLi. TheAir- and water-stable phenyl complexes with nitridotechnetium(V) cores can be prepared by straightforward procedures. [TcNPh2(Ph3P)2] is formed during the reaction of [TcNCl2(Ph3P)2] with PhLi. The analogous NHC compound [TcNPh2(HLPh)2], were HLPh is 1,3,4-triphenyl-1,2,4-triazol-5-ylidene, is available from (NBu4)[TcNCl4] and HLPh or its methoxo-protected form. The latter compound allows the comparison of different Tc-C bonds within one compound. Surprisingly, the Tc chemistry with such NHC's does not resemble that of corresponding Re complexes, where CH activation and orthometallation dominates.

• Modulation of DNA binding by reversible metal-controlled molecular reorganizations of scorpiand-like ligands.

  Authors: Mario Inclán, M Teresa Albelda, Juan Carlos Frias, Salvador Blasco, Carolina Serena, Antonio García-España, Enrique Garcia-Espana, Begoña Verdejo, Maria Luisa Díaz, Claudia Salat-Canela

  Journal of the American Chemical Society.

  DNA interaction with scorpiand aza-macrocycles is achieved through modulation of their binding affinity. Studies performed with different experimental techniques evidenced that pH or metal-drivenDNA interaction with scorpiand aza-macrocycles is achieved through modulation of their binding affinity. Studies performed with different experimental techniques evidenced that pH or metal-driven molecular reorganizations of these ligands, regulate their ability to interact with calf thymus DNA (ctDNA) through an intercalative mode. Interestingly enough, metal-driven molecular reorganizations serve to significantly increase or decrease the biological activity of these compounds.

• Atomic Ensemble and Electronic Effects in Ag-Rich AgPd Nanoalloy Catalysts for Oxygen Reduction in Alkaline Media.

  Authors: Daniel Adam Slanac, William G Hardin, Keith P Johnston, Keith J Stevenson

  Journal of the American Chemical Society.

  The ability to design and characterize uniform, bimetallic alloy nanoparticles, where the less active metal enhances the activity of the more active metal, would be of broad interest in catalysis.The ability to design and characterize uniform, bimetallic alloy nanoparticles, where the less active metal enhances the activity of the more active metal, would be of broad interest in catalysis. Herein, we demonstrate that simultaneous reduction of Ag and Pd precursors provides uniform, Ag-rich AgPd alloy nanoparticles (~5 nm) with high activities for the oxygen reduction reaction (ORR) in alkaline media. The particles are crystalline and uniformly alloyed, as shown by X-ray diffraction and probe corrected scanning transmission electron microscopy. The ORR mass activity per total metal was 60% higher for the AgPd(2) alloy relative to pure Pd. The mass activities were 2.7 and 3.2 times higher for Ag(9)Pd (340 mA/mg(metal)) and Ag(4)Pd (598 mA/mg(metal)), respectively, than those expected for a linear combination of mass activities of Ag (60 mA/mg(Ag)) and Pd (799 mA/mg(Pd)) particles, based on rotating disk voltammetry. Moreover, these synergy factors reached five-fold on a Pd mass basis. For silver-rich alloys (Ag(≥4)Pd), the particle surface is shown to contain single Pd atoms surrounded by Ag from cyclic voltammetry and CO stripping measurements. This morphology is favorable for the high activity through a combination of modified electronic structure, as shown by XPS, and ensemble effects, which facilitate the steps of oxygen bond breaking and desorption for the ORR. This concept of tuning the hetero-atomic interactions on the surface of small nanoparticles with low concentrations of precious metals for high synergy in catalytic activity may be expected to be applicable to a wide variety of nanoalloys.

• Aqueous Multiphase Systems of Polymers and Surfactants Provide Self-Assembling Step-Gradients in Density.

  Authors: Charles R Mace, Ozge Akbulut, Ashok A Kumar, Nathan D Shapiro, Ratmir Derda, Matthew R Patton, George M Whitesides

  Journal of the American Chemical Society.

  This communication demonstrates the generation of over 300 phase-separated systems-ranging from two to six phases-from mixtures of aqueous solutions of polymers and surfactants. These aqueousThis communication demonstrates the generation of over 300 phase-separated systems-ranging from two to six phases-from mixtures of aqueous solutions of polymers and surfactants. These aqueous multiphase systems (MuPSs) form self-assembling, thermodynamically stable, step-gradients in density using a common solvent (water). The steps in density between phases of a MuPS can be very small (∆ρ ~ 0.001 g/cm3), do not change over time, and can be tuned by the addition of co-solutes. We use two sets of similar objects-glass beads and pellets of different formulations of Nylon-to demonstrate the ability of MuPSs to separate mixtures of objects by differences in density. The stable interfaces between phases facilitate the convenient collection of species after separation. These results suggest that the stable, sharp, step-gradients in density provided by MuPSs can enable new classes of fractionations and separations based on density.

• Particle Formation during Oxidation Catalysis with Cp* Iridium complexes.

  Authors: Ulrich Hintermair, Sara M Hashmi, Menachem Elimelech, Robert H Crabtree

  Journal of the American Chemical Society.

  Real-time monitoring of light scattering and UV-Vis profiles of four different Cp*IrIII precursors under various conditions gave insight into nanoparticle formation during oxidation catalysis withReal-time monitoring of light scattering and UV-Vis profiles of four different Cp*IrIII precursors under various conditions gave insight into nanoparticle formation during oxidation catalysis with NaIO4 as primary oxidant. Complexes bearing chelate ligands such as 2,2'-bipyridine, 2-phenylpyridine, or 2-(2'-pyridyl)-2-propanolate were found to be highly resistant towards particle formation, and oxidation catalysis with these compounds is thus believed to be molecular in nature under our conditions. Even with the less stable hydroxo/aqua complex [Cp*2Ir2(µ-OH)3]OH, nanoparticle formation strongly depended on the exact conditions and elapsed time. Test experiments on the isolated particles and comparison of UV-Vis data with light scattering profiles revealed that the formation of a deep purple-blue color (~580 nm) is not indicative of particle formation during oxidation catalysis with molecular iridium precursors as suggested previously.

• Caerulomycins and Collismycins Share a Common Paradigm for 2,2'-Bipyridine Biosynthesis via an Unusual Hybrid Polyketide-Peptide Assembly Logic.

  Authors: Xudong Qu, Bo Pang, Zhicong Zhang, Ming Chen, Zhuhua Wu, Qunfei Zhao, Qinglin Zhang, Yinyan Wang, Yun Liu, Wen Liu

  Journal of the American Chemical Society.

  Caerulomycins (CAEs) and collismycins (COLs), mainly differing in sulfur decoration, are two groups of structurally similar natural products containing a 2,2'-bipyridine (2,2'-BP) core, derivativesCaerulomycins (CAEs) and collismycins (COLs), mainly differing in sulfur decoration, are two groups of structurally similar natural products containing a 2,2'-bipyridine (2,2'-BP) core, derivatives of which have widely been used in chemistry. The biosynthetic pathways of CAEs and COLs remain elusive. Herein, cloning of the CAE biosynthetic gene cluster allowed us to mine a highly conserved gene cluster encoding COL biosynthesis in a Streptomyces strain, which was previously unknown as a 2,2'-BP producer. In vitro and in vivo investigations into the biosynthesis revealed that both of CAEs and COLs share a common paradigm, featuring an atypical hybrid polyketide synthase/non-ribosomal peptide synthetase system that programs the 2,2'-BP formation. This likely involves an unusual intramolecular cyclization-rearrangement, and the difference in processing the sulfhydryl group derived from a same precursor cysteine drives the bio-synthetic route towards CAEs and COLs, respectively.

• Nanoscale Molecular Traps and Dams for Ultrafast Protein Enrichment in High-Conductivity Buffers.

  Authors: Kuo-Tang Liao, Chia-Fu Chou

  Journal of the American Chemical Society.

  We report a new approach, molecular dam, to enhance mass transport for protein enrichment in nanofluidic channels by nanoscale electrodeless dielectrophoresis under physiological buffer conditions.We report a new approach, molecular dam, to enhance mass transport for protein enrichment in nanofluidic channels by nanoscale electrodeless dielectrophoresis under physiological buffer conditions. Dielectric nanoconstrictions down to 30 nm embedded in nanofluidic devices serve as field-focusing lenses capable of magnifying the applied field to 10(5)-fold when combined with a micro- to nanofluidic step interface. With this strong field and the associated field gradient at the nanoconstrictions, proteins are enriched by the molecular damming effect faster than the trapping effect, to >10(5)-fold in 20 s, orders of magnitude faster than most reported methods. Our study opens further possibilities of using nanoscale molecular dams in miniaturized sensing platforms for rapid and sensitive protein analysis and biomarker discovery, with potential applications in precipitation studies and protein crystallization and possible extensions to small-molecules enrichment or screening.

• Directional Cyclooligomers via Alkyne Metathesis.

  Authors: Scott William Sisco, Jeffrey S Moore

  Journal of the American Chemical Society.

  Macrocyclic oligomers possessing a directional-defining ester linkage were synthesized via metathesis of the non-directional alkyne functional group. Alkyne metathesis is expected to scramble theMacrocyclic oligomers possessing a directional-defining ester linkage were synthesized via metathesis of the non-directional alkyne functional group. Alkyne metathesis is expected to scramble the relative orientation of adjacent ester groups, potentially leading to a complex mixture of macrocyclic products. We wondered if a narrow product distribution was achievable with proper choice of the building block structure. Here we show that the shape of the building block determines whether the macrocyclic products are directionally uniform or scrambled. Specifically, two isomeric arylene-ethynylene polyesters afforded significantly different product distributions upon being subjected to depolymerization-macrocyclization. These results underscore the importance of learning how building block shape and geometry affects the macrocyclization energy landscape.

• Polycyclic π-Electron System with a Boron at Its Center.

  Authors: Shohei Saito, Kyohei Matsuo, Shigehiro Yamaguchi

  Journal of the American Chemical Society.

  We now disclose a new planarized triaryl-borane, in which the tri-coordinated boron atom is embedded into a fully-fused polycyclic π-conjugated skeleton. The compound shows a high stability towardsWe now disclose a new planarized triaryl-borane, in which the tri-coordinated boron atom is embedded into a fully-fused polycyclic π-conjugated skeleton. The compound shows a high stability towards oxygen, water, and silica gel, despite the absence of steric protection around the boron atom. Reflecting the electron-donating character of the π skeleton and the electron-accepting character of the boron atom, this compound shows broad absorption bands that cover the entire visible region and a fluorescence in the visible-near IR region. In addition, this compound shows a dramatic property change upon formation of a tetra-coordinated borate, such as thermochromic behavior in the presence of pyridine.

• Conjugated Microporous Polymers as Molecular Sensing Devices: Microporous Architecture Enables Rapid Response and Enhances Sensitivity in Fluorescence-On and Fluorescence-Off Sensing.

  Authors: Xiaoming Liu, Yanhong Xu, Donglin Jiang

  Journal of the American Chemical Society.

  Conjugated polymers are attractive materials for the detection of chemicals because of their remarkable π-conjugation and photoluminescence properties. In this article, we report a new strategy forConjugated polymers are attractive materials for the detection of chemicals because of their remarkable π-conjugation and photoluminescence properties. In this article, we report a new strategy for the construction of molecular detection systems with conjugated microporous polymers (CMPs). The condensation of a trimer-fused carbazole derivative (TCB) leads to the synthesis of conjugated microporous polymers (TCB-CMP) that exhibit blue luminescence and possess large surface areas. Compared with a linear polymer analogue, TCB-CMP showed enhanced detection sensitivity and allowed for the rapid detection of arenes upon exposure to their vapor. TCB-CMP displayed prominent fluorescence enhancement in the presence of electron-rich arene vapor and drastic fluorescence quenching in the presence of electron-deficient arene vapor, and could be reused without a loss of sensitivity and responsiveness. These characteristics were attributed to the microporous conjugated network of the material. Specifically, the micropores absorb arene molecules into the confined space of the polymer, the skeleton possesses a large surface area and provides a broad interface for arenes, and the net-work architecture facilitates exciton migration over the framework. These structure features function cooperatively, enhancing the signaling activity of TCB-CMP in fluorescence-on and fluores-cence-off detection.

• Correction to single-molecule dynamics of lysozyme processing distinguishes linear and cross-linked peptidoglycan substrates.

  Authors: Yongki Choi, Issa S Moody, Patrick C Sims, Steven R Hunt, Brad L Corso, David E Seitz, Larry C Blaszczak, Philip G Collins, Gregory A Weiss

  Journal of the American Chemical Society. 134(19):8286.

• Discovery and Characterization of a Group of Fungal Polycyclic Polyketide Prenyltransferases.

  Authors: Yit-Heng Chooi, Peng Wang, Jinxu Fang, Yanran Li, Katherine Wu, Pin Wang, Yi Tang

  Journal of the American Chemical Society.

  The prenyltransferase (PTase) gene vrtC was proposed to be involved in viridicatumtoxin (1) biosynthesis in Penicillium aethiopicum. Targeted gene deletion and reconstitution of recombinant VrtCThe prenyltransferase (PTase) gene vrtC was proposed to be involved in viridicatumtoxin (1) biosynthesis in Penicillium aethiopicum. Targeted gene deletion and reconstitution of recombinant VrtC activity in vitro established that VrtC is a gera-nyl transferase that catalyzes a regiospecific Friedel-Crafts alkylation of the naphthacenedione carboxamide intermediate 2 at carbon 6 with geranyl diphosphate (GPP). VrtC can function in the absence of divalent ions and can utilize similar naphthacenedione substrates, such as the acetyl-primed TAN-1612 (4). Genome mining using the VrtC protein sequence leads to the identification of a homologous group of PTase genes in the genomes of human and animal-associated fungi. Three enzymes encoded by this new subgroup of PTase genes from Neosartorya fischeri, Microsporum canis and Trichophyton tonsuran were shown to be able to catalyze transfer of dimethylallyl to several tetracyclic naphthacenedione substrates in vitro. In total, seven C5- or C10-prenylated naphthacenedione compounds were generated. The regioselectivity of these new polycyclic PTases (pcPTases) was confirmed by characterization of product 9 obtained by biotransformation of 4 in Escherichia coli expressing the N. fischeri pcPTase gene. The discovery of this new subgroup of PTases extends our enzymatic tools for modifying polycyclic compounds and enables genome mining of new prenylated polyketides.

• Thermodynamics of Zn2+ Binding to Cys2His2 and Cys2HisCys Zinc Fingers and a Cys4 Transcription Factor Site.

  Authors: Anne M Rich, Elisa Bombarda, Austin D Schenk, Paul E Lee, Elizabeth H Cox, Anne M Spuches, Lynn D Hudson, Bruno Kieffer, Dean E Wilcox

  Journal of the American Chemical Society.

  The thermodynamics of Zn2+ binding to three peptides corresponding to naturally occurring Zn-binding sequences in transcription factors have been quantified with isothermal titration calorimetryThe thermodynamics of Zn2+ binding to three peptides corresponding to naturally occurring Zn-binding sequences in transcription factors have been quantified with isothermal titration calorimetry (ITC). These peptides, the third zinc finger of Sp1 (Sp1-3), the second zinc finger of myelin transcription factor 1 (MyT1-2) and the second Zn-binding sequence of the DNA-binding domain of glucocorticoid receptor (GR-2), bind Zn2+ with Cys2His2, Cys2HisCys and Cys4 coordination, respectively. CD confirms that Sp1-3 and MyT1-2 have considerable and negligible Zn-stabilized secondary structure, respectively, and indicate only a small amount for GR-2. The pKa's of the Sp1-3 cysteines and histidines were determined by NMR and used to estimate the number of protons displaced by Zn2+ at pH 7.4. ITC was also used to determine this number and the two methods agree. Subtraction of buffer contributions to the calorimetric data reveal that all three peptides have a similar affinity for Zn2+, which has equal enthalpy and entropy components for Sp1-3 but is more enthalpically disfavored and entropically favored with increasing Cys ligands. The resulting enthalpy-entropy compensation originates from the Zn-Cys coordination, as subtraction of the cysteine deprotonation enthalpy results in a similar Zn2+ binding enthalpy for all three peptides and the binding entropy tracks with the number of displaced protons. Metal and protein components of the binding enthalpy and entropy have been estimated. While dominated by Zn2+ coordination to the cysteines and histidines, other residues in the sequence affect the protein contributions that modulate the stability of these motifs.

• Bis(allyl)zinc Revisited: Sigma versus Pi Bonding of Allyl Coordination.

  Authors: Crispin Lichtenberg, Julien Engel, Thomas Paul Spaniol, Ulli Englert, Gerhard Raabe, Jun Okuda

  Journal of the American Chemical Society.

  The re-investigation of two allyl zinc compounds, parent bis(allyl)zinc [Zn(C3H5)2] (1) and 2-methallyl chloro zinc [Zn(C4H7)Cl] (2), revealed two new coordination modes in the solid state for theThe re-investigation of two allyl zinc compounds, parent bis(allyl)zinc [Zn(C3H5)2] (1) and 2-methallyl chloro zinc [Zn(C4H7)Cl] (2), revealed two new coordination modes in the solid state for the allyl ligand, viz cis- and trans-μ2-η1:η1. These results call for modification of the conventional interpretation of zinc‒allyl interactions. Computational results indicate that the classical η3-bonding mode of the allyl ligand is not favored in zinc compounds. A rare case of a zinc‒olefin interaction in the dimer of [Zn(η1-C3H5)(OC(C3H5)Ph2)] was found in the mono-insertion product of 1 with benzophenone.

• Multifluorescently Traceable Nanoparticle by a Single-Wavelength Excitation with Color-Related Drug Release Performance.

  Authors: Deli Lu, Juying Lei, Lingzhi Wang, Jinlong Zhang

  Journal of the American Chemical Society.

  Monodisperse and nanometer-sized periodic mesoporous organosilicas co-doped with fluorescence resonance energy transfer cascades composed of triple fluorophores at various ratios were prepared. TheseMonodisperse and nanometer-sized periodic mesoporous organosilicas co-doped with fluorescence resonance energy transfer cascades composed of triple fluorophores at various ratios were prepared. These nanoparticles exhibit mul-tifluorescent emissions by a single-wavelength excitation and were designed for the application as multichannelly traceable drug carriers. Different from the hydrophilic framework of in-organic mesoporous silica and hydrophobic framework of mesoporous carbon, these multifluorescent nanoparticles have intrinsically different and finely tunable pore surface polarities governed by the type and amount of fluorophore inside the framework. When applied as drug carriers, they can achieve synchronous or asynchronous release of different drugs by sim-ply choosing different colored nanoparticles. These colorful mesoporous composites with finely tunable color-related drug release performance provide a strong barcoding system for the potential applications of fluorescent nanoparticles in effective screening of drugs and therapeutic protocols for diseases.

• Correction to Three-Coordinate and Four-Coordinate Cobalt Hydride Complexes That React with Dinitrogen.

  Authors: Keying Ding, William W Brennessel, Patrick L Holland

  Journal of the American Chemical Society.

• Non-HPLC Rapid Separation of Metallofullerenes and Empty Cages with TiCl(4) Lewis Acid.

  Authors: Kazuhiko Akiyama, Tatsuyuki Hamano, Yusuke Nakanishi, Erina Takeuchi, Shoko Noda, Zhiyong Wang, Shiro Kubuki, Hisanori Shinohara

  Journal of the American Chemical Society.

  Rapid and efficient separation/purification of pure metallofullerenes M(x)@C(n) (M = metal; x = 1,2; n >70) and carbide metallofullerenes of the type M(y)C(2)@C(n-2) (y = 2,3,4; n-2 >68) has beenRapid and efficient separation/purification of pure metallofullerenes M(x)@C(n) (M = metal; x = 1,2; n >70) and carbide metallofullerenes of the type M(y)C(2)@C(n-2) (y = 2,3,4; n-2 >68) has been reported. The present method utilizes rapid and almost perfect preferential formation of TiCl(4) (generally known as a Lewis acid) - ,metallofullerene complexes, which easily decompose to provide pure metallofullerene powders by a simple water treatment. The present method enables one to separate the metallofullerenes up to > 99 % purity within 10 minutes without using any type of high-performance liquid chromatography (HPLC). It is found that the oxidation potentials of the metallofullerenes are crutial factors for the efficient purification of metallofullerenes. The current separation/purification technique may open a brand new era for inducing further applications and commercialization of endohedral metallofullerenes.

• Synthesis of Functional Polyolefins Using Cationic Bisphosphine Monoxide-Palladium Complexes.

  Authors: Brad P Carrow, Kyoko Nozaki

  Journal of the American Chemical Society.

  The copolymerization of ethylene with polar vinyl monomers, such as vinyl acetate, acrylonitrile, vinyl ethers, and allyl monomers, was accomplished using cationic palladium complexes ligated by aThe copolymerization of ethylene with polar vinyl monomers, such as vinyl acetate, acrylonitrile, vinyl ethers, and allyl monomers, was accomplished using cationic palladium complexes ligated by a bisphosphine monoxide (BPMO). The copolymers formed by these catalysts have highly linear microstructures and a random distribution of polar functional groups throughout the polymer chain. Our data demonstrate that cationic palladium complexes can exhibit good activity for polymerizations of polar monomers, in contrast to cationic α-diimine palladium complexes (Brookhart-type) that are not applicable to industrially relevant polar monomers beyond acrylates. Additionally, the studies reported here point out that phosphine-sulfonate ligated palladium complexes are no longer the singular family of catalysts that can promote the reaction of ethylene with many polar vinyl monomers to form linear functional polyolefins.

• Hole transfer in LNA and 5-Me-2'-deoxyzebularine modified DNA.

  Authors: Kiyohiko Kawai, Mitsuo Hayashi, Tetsuro Majima

  Journal of the American Chemical Society.

  We report the measurement of hole-transfer rate constants (kht) in locked nucleic acid (LNA) and 5-Me-2'-deoxyzebularine (B)-modified DNA. LNA modification, which makes DNA more rigid, caused aWe report the measurement of hole-transfer rate constants (kht) in locked nucleic acid (LNA) and 5-Me-2'-deoxyzebularine (B)-modified DNA. LNA modification, which makes DNA more rigid, caused a decrease of more than two orders of magnitude in kht, whereas B modification, which increases DNA flexibility, increased kht by more than 20-fold. The present results clearly showed that hole-transfer- efficiency in DNA can be increased by increasing DNA flexibility.

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