PubMed Journal Database | Journal of the American Chemical Society 
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Showing PubMed Articles 1–25 of 5,800+ from Journal of the American Chemical Society
Alkyl vinyl ethers and isobutylene oxide were concurrently copolymerized through cationic vinyl-addition and ring-opening using B(C6F5)3 as a catalyst. NMR analyses and acid hydrolysis of the products demonstrated that copolymerization successfully proceeded through crossover reactions between vinyl and cyclic monomers to yield multiblock-like copolymers. Appropriate catalyst and monomer combinations with suitable reactivities were key for copolymerization.
Nanoemulsion contrast agents with sub-picomolar sensitivity for xenon NMR.
A new type of contrast agent for Xe NMR based on surfactant-stabilized perfluorocarbon-in-water nanoemulsions has been produced. The contrast agent uses dissolved hyperpolarized xenon gas as a non-perturbing reporting medium as xenon freely exchanges between aqueous solution and the perfluorocarbon interior of the droplets, which are spectroscopically distinguishable and allow for chemical exchange saturation transfer (CEST) detection of the agent. Nanoemulsions with droplet diameters between 160 nm and 310...
The Structural and Energetic Basis of Carbohydrate-Aromatic Packing Interactions in Proteins.
Carbohydrate-aromatic interactions mediate many biological processes. However, the structure-energy relationships underpinning direct carbohydrate-aromatic packing in aqueous solution have been difficult to assess experimentally and remain elusive. Here, we determine the structures and folding energetics of chemically synthesized glycoproteins to quantify the contributions of the hydrophobic effect and CH-π interactions to carbohydrate-aromatic packing interactions in proteins. We find that the hydrophobic...
Despite the high structural symmetry of cofactor arrangement and protein environment, light-induced electron transfer in photosynthetic reaction centers (RCs) of the purple bacterium Rhodobacter (R.) sphaeroides runs selectively over one of the two branches of cofactors. The origin of this functional symmetry break is debated since several decades. Recently, a crucial role of the substituents has been proposed by theoretical studies [H. Yamasaki, Y. Takano, H. Nakamura (2008) J. Phys. Chem. B 112, 13923-139...
With the aim of achieving surface-mediated enantioselective adsorption, the self-assembly of chiral oligo(p-phenylenevinylene) (OPV3T) with nucleosides is investigated at the liquid/solid interface by means of scanning tunneling microscopy and molecular modeling. OPV3T enantiomers form mirror related hexameric rosette patterns. The DNA nucleoside, thymidine, does not self-assemble into stable adlayers but coadsorbs with OPV3T on the surface, leading to a pattern transformation of OPV3T from rosettes to dime...
Manganese-containing MFI-type Mn-ZSM-5 zeolite was synthesized by a facile one-step hydrothermal method using tetrapropylammonium hydroxide (TPAOH) and manganese(III)-acetylacetonate as organic template and manganese salts, respectively. A highly crystalline MFI zeolite structure was formed under pH = 11 in 2 days, without the need for additional alkali metal cations. Direct evidence of the incorporation of Mn in the zeolite framework sites was observed by performing structure parameter refinements, support...
Real-Time Observation of Crystal Evaporation in a Metal Phosphate at High Temperature.
A number of experimental studies on crystal growth have been performed in connection with a variety of crystalline systems ranging from simple oxides to complex organic compounds. In contrast, little is known regarding how crystals evaporate. By using a combination of real-time high-resolution electron microscopy at high temperature, image simulations, and density functional theory calculations, we demonstrate the evaporation of metal-phosphate nanocrystals with flat surfaces at atomic resolution. In situ i...
Understanding the freezing of salt solutions near solid surfaces is important in many scientific fields. Here we use sum frequency generation (SFG) spectroscopy to study the freezing of a NaCl solution next to a sapphire substrate. During cooling we observe two transitions. The first corresponds to segregation of concentrated brine next to the sapphire surface as we cool the system down to the region where ice and brine phases coexist. At this transition, the intensity of the ice-like peak decreases, sugges...
Template Control over Dimerization and Guest Selectivity of Interpenetrated Coordination Cages.
We have previously shown that the self-assembly of dibenzosuberone-based bis-monodentate pyridyl ligands L(1) with Pd(II) cations leads to the quantitative formation of interpenetrated coordination cages [BF4@Pd4L(1)8]. The BF4(-) anion inside the central cavity serves as a template, causing the outer two pockets to show a tremendous affinity for allosteric binding of two small chloride anions. Here we show that derivatization of the ligand backbone with a bulky aryl substituent allows us to control the dim...
Spotlights on Recent JACS Publications.
Understanding the Mechanisms of Cobalt-Catalyzed Hydrogenation and Dehydrogenation Reactions.
Cobalt(II) alkyl complexes of aliphatic PNP pincer ligands have been synthesized and characterized. The cationic cobalt(II) alkyl complex [(PNHP(Cy))Co(CH2SiMe3)]BAr(F)4 (4) (PNHP(Cy) = bis[(2-dicyclohexylphosphino)ethyl]amine) is an active precatalyst for the hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols. To elucidate the possible involvement of the N-H group on the pincer ligand in the catalysis via a metal-ligand cooperative interaction, the reactivities of 4 and [...
Poly(p-phenylene vinylene) derivatives (PPVs) are one of the most widely investigated p-type polymers in organic electronics. PPVs generally exhibit electron mobilities lower than 10(-4) cm(2) V(-1) s(-1), thus hindering their applications in high-performance polymer field-effect transistors and organic photovoltaics. Herein, we design and synthesize a novel electron-deficient PPV derivative, benzodifurandione-based PPV (BDPPV). This new PPV derivative displays high electron mobilities up to 1.1 cm(2) V(-1)...
Three small molecules named DR3TBDTT, DR3TBDTT-HD and DR3TBD2T with benzo[1,2-b:4,5-b']dithiophene (BDT) unit as the central building block have been designed and synthesized for solution processed bulk-heterojunction solar cells. PCEs of 8.12% (certified 7.61%) and 8.02% under AM 1.5G irradiation (100 mWcm(-2)) have been achieved for DR3TBDTT and DR3TBDTT based photovoltaic devices with PC71BM as acceptor, respectively. The better PCEs are achieved by improving the Jsc without scarifying the high Voc and F...
Building on the known photophysical properties of well-defined copper-carbazolide complexes, we have recently described photoinduced, copper-catalyzed N-arylations and N-alkylations of carbazoles. Until now, there have been no examples of the use of other families of heteroatom nucleophiles in such photoinduced processes. Herein, we report a versatile photoinduced, copper-catalyzed method for coupling aryl thiols with aryl halides wherein a single set of reaction conditions, using inexpensive CuI as a preca...
Toward the Molecular Mechanism(s) by Which EGCG Treatment Remodels Mature Amyloid Fibrils.
Protein misfolding and/or aggregation has been implicated as the cause of several human diseases, such as Alzheimer's and Parkinson's diseases and familial amyloid polyneuropathy. These maladies are referred to as amyloid diseases, named after the cross-β-sheet amyloid fibril aggregates or deposits common to these disorders. Epigallocatechin-3-gallate (EGCG), the principal polyphenol present in green tea, has been shown to be effective at preventing aggregation and is able to remodel amyloid fibrils compri...
The sensitive detection of cancer biomarkers in urine could revolutionize cancer diagnosis and treatment. Such detectors must be inexpensive, easy to interpret, and sensitive. This report describes a bioaffinity matrix of viruses integrated into PEDOT films for electrochemical sensing of prostate-specific membrane antigen (PSMA), a prostate cancer biomarker. High sensitivity to PSMA resulted from synergistic action by two different ligands to PSMA on the same phage particle. One ligand was genetically encod...
Mechanism-Based Triarylphosphine-Ester Probes for Capture of Endogenous RSNOs.
Nitrosothiols (RSNOs) have been proposed as important intermediates in nitric oxide (NO(•)) metabolism, storage, and transport as well as mediators in numerous NO-signaling pathways. RSNO levels are finely regulated, and dysregulation is associated with the etiology of several pathologies. Current methods for RSNO quantification depend on indirect assays that limit their overall specificity and reliability. Recent developments of phosphine-based chemical probes constitute a promising approach for the dire...
Pd(II)-Catalyzed ortho- or meta-C-H Olefination of Phenol Derivatives.
A combination of weakly coordinating auxiliaries and ligand acceleration allows for the development of both ortho- and meta-selective C-H olefination of phenol derivatives. These reactions demonstrate the feasibility of directing C-H functionalizations when functional groups are distal to target C-H bonds. The meta-C-H functionalization of electron-rich phenol derivatives is unprecedented and orthogonal to previous electrophilic substitution of phenols in terms of regioselectivity. These methods are also ap...
Reaction of 1 with B(C6F5)3 under 1 bar of CO2 led to the instantaneous formation of the frustrated Lewis pair (FLP)-type species [ReHBr(NO)(PR3)2(η(2)-O═C═O-B(C6F5)3)] (2, R = iPr a, Cy b) possessing two cis-phosphines and OCO2-coordinated B(C6F5)3 groups as verified by NMR spectroscopy and supported by DFT calculations. The attachment of B(C6F5)3 in 2a,b establishes cooperative CO2 activation via the Re-H/B(C6F5)3 Lewis pair, with the Re-H bond playing the role of a Lewis base. The Re(I) η(1)-format...
Interfacial and perimeter sites have been known for their high activity in various reactions on supported gold nanoparticles. We find that the higher activity of interfacial sites in Au13/TiO2(110) toward methanol decomposition originates from charge-transfer-induced Coulomb interaction among the gold, reactant, and reducible TiO2 support, brought about through the formation of an ionic O-Au bond between gold and methoxy in such sites, which turns the participating perimeter gold atom cationic. A direct res...
Fungal secondary metabolites (SMs) are an important source of medically valuable compounds. Genome projects have revealed that fungi have many SM biosynthetic gene clusters that are not normally expressed. To access these potentially valuable, cryptic clusters, we have developed a heterologous expression system in Aspergillus nidulans . We have developed an efficient system for amplifying genes from a target fungus, placing them under control of a regulatable promoter, transferring them into A. nidulans , a...
Mechanism-based design of a photoactivatable firefly luciferase.
We developed a photoactivatable firefly luciferase (pfLuc) whose activation can be controlled by light. A photocaged Lys analogue was site-specifically incorporated into fLuc to replace its key catalytic Lys residue, Lys529, rendering fLuc inactive until light-triggered removal of the caging group. This photoinduced gain of luminescence provides a facile approach for assessing the photolysis efficiency of this valuable photosensitive Lys analogue within the context of its carrier protein in vitro and in liv...
Structure and flexibility of nanoscale protein cages designed by symmetric self-assembly.
Designing protein molecules that self-assemble into complex architectures is an outstanding goal in the area of nanobiotechnology. One design strategy for doing this involves genetically fusing together two natural proteins, each of which is known to form a simple oligomer on its own (e.g., a dimer or trimer). If two such components can be fused in a geometrically predefined configuration, that designed subunit can, in principle, assemble into highly symmetric architectures. Initial experiments showed that...
Protein scaffold-activated protein trans-splicing in Mammalian cells.
Conditional protein splicing is a powerful biotechnological tool that can be used to rapidly and post-translationally control the activity of a given protein. Here we demonstrate a novel conditional splicing system in which a genetically encoded protein scaffold induces the splicing and activation of an enzyme in mammalian cells. In this system the protein scaffold binds to two inactive split intein/enzyme extein protein fragments leading to intein fragment complementation, splicing, and activation of the f...
The redox homeostasis between peroxynitrite and glutathione is closely associated with the physiological and pathological processes, e.g. vascular tissue prolonged relaxation and smooth muscle preparations, attenuation hepatic necrosis, and activation matrix metalloproteinase-2. We report a near-infrared fluorescent probe based on heptamethine cyanine, which integrates with telluroenzyme mimics for monitoring the changes of ONOO(-)/GSH levels in cells and in vivo. The probe can reversibly respond to ONOO(-)...
