bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cascade Reactions: A Driving Force in Akuammiline Alkaloid Total Synthesis
Authors: Smith Joel M. , Moreno Jesus , Boal Ben W. , Garg Neil K. 
Published: October 2014

AbstractThe akuammiline alkaloids are a family of intricate natural products which have received considerable attention from scientists worldwide. Despite the fact that many members of this alkaloid class were discovered over 50 years ago, synthetic chemistry has been unable to address their architectures until recently. This minireview provides a brief overview of the rich history of the akuammiline alkaloids, including their isolation, structural features, biological activity, and proposed biosyntheses. Furthermore, several recently completed total syntheses are discussed in detail. These examples not only serve to highlight modern achievements in alkaloid total synthesis, but also demonstrate how the molecular scaffolds of the akuammilines have provided inspiration for the discovery and implementation of innovative cascade reactions for the rapid assembly of complex structures.
Enantioselective, Protecting‐Group‐Free Total Synthesis of Sarpagine Alkaloids—A Generalized Approach
Authors: Krüger Sebastian , Gaich Tanja 
Published: October 2014

AbstractA generalized synthetic access to sarpagine alkaloids through a joint synthetic sequence has been accomplished. Its applicability is showcased by the enantioselective total syntheses of vellosimine (1), N‐methylvellosimine (3), and 10‐methoxyvellosimine (8). The synthetic sequence is concise (eight steps) from known compound 13, and requires no protecting groups. The indole heterocycle was introduced in the last step. This strategy allows access to sarpagine alkaloids through a shared synthetic route leading to precursor 10, which we term “privileged intermediate”. Starting from this intermediate, all sarpagine alkaloids can be synthesized using phenylhydrazines with different substitution patterns (15–17). Our approach brings about the advantage, that synthesis optimization only needs to be performed once for many natural products. The key features of the synthesis are a [5+2]‐cycloaddition and a ring enlargement.
Synthesis, Structure, and Frequency‐Doubling Effect of Calcium Cyanurate
Authors: Kalmutzki Markus , Ströbele Markus , Wackenhut Frank , Meixner Alfred J. , Meyer H.‐Jürgen 
Published: October 2014

AbstractCalcium cyanurate is synthesized by reacting calcium chloride with potassium cyanate following a solid‐state reaction. The formation of the new compound Ca3(O3C3N3)2 (CCY), which occurs by the cyclotrimerization of cyanate ions, was examined thermoanalytically and the crystal structure was determined by single‐crystal structure analysis. The structure of CCY is closely related to the structure of the well‐known oxoborate β‐BaB2O4 (BBO). Second harmonic generation (SHG) measurements on crystal powders show a higher SHG efficiency for CCY than for BBO by about one order of magnitude.
Polyoxometalate‐Based Entangled Coordination Networks Induced by an Extended Bis(triazole) Ligand
Authors: Hao Xiu‐Li , Ma Yuan‐Yuan , Zhou Wen‐Zhe , Zang Hong‐Ying , Wang Yong‐Hui , Li Yang‐Guang 
Published: October 2014

AbstractThe introduction of an extended bridging bis(triazole) ligand, that is, 4,4′‐bis(1,2,4‐triazol‐1‐ ylmethyl)biphenyl (BBPTZ), into the hydrothermal reaction system containing transition metal ions and Keggin‐type polyoxometalates (POMs) led to the isolation of three new organic–inorganic hybrid entangled coordination networks, [CuI2CuII(BBPTZ)6][SiW12O40]⋅12 H2O (1), [Ni(BBPTZ)2(H2O)][H2SiW12O40]⋅11 H2O (2), and [Ni2(BBPTZ)4(H2O)2][SiW12O40]⋅3 H2O (3). All three compounds were characterized by elemental analysis, IR spectroscopy, TG analysis, powder X‐ray diffraction, and single‐crystal X‐ray diffraction. Compound 1 contains a 2‐D POM‐based metal–organic layer entangled with 1‐D ladder‐like metal–organic chains. The adjacent 2‐D networks are parallel to each other, further stacking into a 3‐D supramolecular framework with 1‐D channels. Compound 2 exhibits a 1‐D cantilever‐type loop‐containing chain. The Keggin‐type POMs act as the cantilever groups, leading to the adjacent catilever‐type chains interwaving together to form a 3‐D supramolecular open framework with two types of channels. Compound 3 possesses a 3‐D open framework based on 2‐D metal–organic undulated layer and Keggin‐type POM clusters. Three sets of such frameworks further interpenetrate with each other to form an interesting three‐fold interpenetrating framework. The photocatalytic activities of compounds 1–3 for the decomposition of methylene blue (MB) under UV light have been investigated.
An FITC‐BODIPY FRET Couple: Application to Selective, Ratiometric Detection and Bioimaging of Cysteine
Authors: Ma Dong Hee , Kim Dokyoung , Akisawa Takuya , Lee Kyung‐Ha , Kim Kyong‐Tai , Ahn Kyo Han 
Published: October 2014

AbstractA novel FRET couple of fluorescein is disclosed, and it was readily constructed by conjugating an amino‐BODIPY dye, a new FRET donor, with fluorescein isocyanate. Its potential was demonstrated by a fluorescence sensing system for cysteine, which was prepared by introducing acryloyl groups to the fluorescein moiety. The FRET probe exhibited promising ratiometric response to cysteine with high selectivity and sensitivity in a buffer solution containing acetonitrile at a physiological pH of 7.4, but showed slow reactivity. This slow response was solved by addition of a surfactant, thus allowing ratiometric imaging and determination of the endogenous level of cysteine in cells in HEPES buffer, by confocal fluorescence microscopy. Imaging experiments toward various cells suggested that such aryl acrylate type probes are vulnerable to the ubiquitous esterase activity. For the selected C6 cell line, in which the esterase activity was minimal, the ratiometric quantification of cysteine level was demonstrated. The FRET probe was also applied to determine the level of cysteine in human blood plasma.
Determination of ethanol using permanganate–CdS quantum dot chemiluminescence system
Authors: Abolhasani Jafar , Hassanzadeh Javad 
Published: October 2014

AbstractA novel and highly sensitive chemiluminescence (CL) method for the determination of ethanol was developed based on the CdS quantum dots (QDs)–permanganate system. It was found that KMnO4 could directly oxidize CdS QDs in acidic media resulting in relatively high CL emission. A possible mechanism was proposed for this reaction based on UV/Vis absorption, fluorescence and the generated CL emission spectra. However, it was observed that ethanol had a remarkable inhibition effect on this system. This effect was exploited in the determination of ethanol within the concentration range 12–300 µg/L, with detection at 4.3 µg/L. In order to evaluate the capability of presented method, it was satisfactorily utilized in the determination of alcohol in real samples. Copyright © 2014 John Wiley & Sons, Ltd.
Direct Synthesis of Partially Modified 2′‐O‐Pivaloyloxymethyl RNAs by a Base‐Labile Protecting Group Strategy and their Potential for Prodrug‐Based Gene‐Silencing Applications
Authors: Biscans Annabelle , Bos Maxence , Martin Anthony R. , Ader Nicholas , Sczakiel Georg , Vasseur Jean‐Jacques , Dupouy Christelle , Debart Françoise 
Published: October 2014

AbstractAn original and straightforward synthesis of partially modified 2′‐O‐pivaloyloxymethyl‐substituted (PivOM‐substituted) oligoribonucleotides has been achieved. The aim of this 2′‐enzymolabile modification was to enhance nuclease stability of RNA and transmembrane transport. To make these modified RNAs easily available we developed a base‐labile protecting group strategy with standard protections for nucleobases (acyl) and phosphates (cyanoethyl), a Q‐linker and two different acetalester protection groups for 2′‐OH: propionyloxymethyl (PrOM) and PivOM. Interestingly, orthogonal deprotection conditions based on anhydrous butylamine in THF were found to remove propionyloxymethyl groups selectively, while preserving PivOM groups. Duplex stability, circular dichroism studies and nuclease resistance, as well as the ability to inhibit gene expression of modified 2′‐O‐PivOM RNA, were evaluated.
Engineered Pt‐Doped Nanoceria for Oxidase‐Based Bioelectrodes Operating in Oxygen‐Deficient Environments
Authors: Sardesai Naimish P. , Karimi Anahita , Andreescu Silvana 
Published: October 2014

AbstractThe use of Pt‐doped nanoceria as a new catalytic amplification system for first‐generation electrochemical oxidase‐based biosensors is described. The catalytic activity and oxygen‐rich surface of nanoceria, combined with the high conductivity of noble‐metal Pt electrocatalysts, provide enhanced performance characteristics of mediatorless glucose oxidase biosensors for the detection of glucose in oxygen‐deficient environments. The Pt‐doped nanoceria particles act as both an internal oxygen reservoir to satisfy the oxygen requirement for the enzymatic reaction and a catalytic amplification system for the detection of enzymatically generated H2O2. The biosensor allows detection of glucose in anaerobic conditions with a detection limit of 37.4 μM. The proposed strategy can be widely applicable to other oxidase‐based biosensors that require measurements of their substrates in oxygen‐deficient conditions.
The Mtr Pathway of Shewanella oneidensis MR‐1 Couples Substrate Utilization to Current Production in Escherichia coli
Authors: TerAvest Michaela A. , Zajdel Tom J. , Ajo‐Franklin Caroline M. 
Published: October 2014

AbstractThe front cover artwork is provided by the group of Dr. Caroline Ajo‐Franklin at Berkeley Lab, USA. The cover image shows electrogenic E. coli transporting electrical energy, originating from its metabolism, to external metals. Read the full text of the article at 10.1002/celc.201402194.
Coumarin‐3‐Aldehyde as a Scaffold for the Design of Tunable PET‐Modulated Fluorescent Sensors for Neurotransmitters
Authors: Hettie Kenneth S. , Glass Timothy E. 
Published: October 2014

AbstractNeuroSensor 521 (NS521) is a fluorescent sensor for primary‐amine neurotransmitters based on a platform that consists of an aryl moiety appended to position C4 of the coumarin‐3‐aldehyde scaffold. We demonstrate that sensors based on this platform behave as a directly linked donor–acceptor system that operates through an intramolecular acceptor‐excited photoinduced electron transfer (a‐PET) mechanism. To evaluate the PET process, a series of benzene‐ and thiophene‐substituted derivatives were prepared and the photophysical properties, binding affinities, and fluorescence responses toward glutamate, norepinephrine, and dopamine were determined. The calculated energy of the highest occupied molecular orbital (EHOMO) of the pendant aryl substituents, along with oxidation and reduction potential values derived from the calculated molecular orbital energy values of the platform components, allowed for calculation of the fluorescence properties of the benzene sensor series. Interestingly, the thiophene derivatives did not fit the typical PET model, highlighting the limitations of the method. A new sensor, NeuroSensor 539, displayed enhanced photophysical properties aptly suited for biological imaging. NeuroSensor 539 was validated by selectively labeling and imaging norepinephrine in secretory vesicles of live chromaffin cells.
Excimer Formation in a Confined Space: Photophysics of Ladderphanes with Tetraarylethylene Linkers
Authors: Chen Chih‐Hsien , Satyanarayana Kamani , Liu Yi‐Hung , Huang Shou‐Ling , Lim Tsong‐Shin , Luh Tien‐Yau 
Published: October 2014

AbstractCommunication between chromophores is vital for both natural and non‐natural photophysical processes. Spatial confinements offer unique conditions to scrutinize such interactions. Polynorbornene‐ and polycyclobutene‐based ladderphanes are ideal model compounds in which all tetraarylethylene (TAE) linkers are aligned coherently. The spans for each of the monomeric units in these ladderphanes are 4.5–5.5 Å. Monomers do not exhibit emission, because bond rotation in TAE can quench the excited‐state energy. However, polymers emit at 493 nm (Φ=0.015) with large Stokes shift under ambient conditions and exhibit dual emission at 450 and 493 nm at 150 K. When the temperature is lowered, the emission intensity at 450 nm increases, whereas that at 493 nm decreases. At 100 K, both monomers and polymers emit only at 450 nm. This shorter‐wavelength emission arises from the intrinsic emission of TAE chromophore, and the emission at 493 nm could be attributed to the excimer emission in the confined space of ladderphanes. The fast kinetics suggest diffusion‐controlled formation of the excimer.
Bispidines for Dual Imaging
Authors: Stephan Holger , Walther Martin , Fähnemann Silke , Ceroni Paola , Molloy Jennifer K. , Bergamini Giacomo , Heisig Fabian , Müller Christa E. , Kraus Werner , Comba Peter 
Published: October 2014

AbstractThe efficient transformation of the hexadentate bispidinol 1 into carbamate derivatives yields functional bispidines enabling convenient functionalization for targeted imaging. The BODIPY‐substituted bispidine 3 combines a coordination site for metal ions, such as radioactive 64CuII, with a fluorescent unit. Product 3 was thoroughly characterized by standard analytical methods, single crystal X‐ray diffraction, radiolabeling, and photophysical analysis. The luminescence of ligand 3 was found to be strongly dependent on metal ion coordination: CuII quenches the BODIPY fluorescence, whereas NiII and ZnII ions do not affect it. It follows that, in imaging applications with the positron emitter 64CuII, residues of its origin from enriched 64Ni and the decay products 64NiII and 64ZnII, efficiently restore the fluorescence of the ligand. This allows for monitoring of the emitted radiation as well as the fluorescence signal. The stability of the 64CuII3 complex is investigated by transmetalation experiments with ZnII and NiII, using fluorescence and radioactivity detection, and the results confirm the high stability of 64CuII3. In addition, metal complexes of ligand 3 with the lanthanide ions TbIII, EuIII, and NdIII are shown to exhibit emission of the BODIPY ligand and the lanthanide ion, thus enabling dual emission detection.
Enhanced Ethylene Photodegradation Performance of g‐C3N4–Ag3PO4 Composites with Direct Z‐Scheme Configuration
Authors: Chen Xuxing , Huang Xintang , Yi Zhiguo 
Published: October 2014

AbstractPhotocatalytic oxidation of ethylene continues to be a challenge at the frontier of chemistry. In a previous report, a simple Ag3PO4 semiconductor material was shown to have strong photooxidative properties and efficiently oxidised water and decomposed organics in aqueous solution under visible‐light illumination. Herein, its effects on the photo‐oxidation of gaseous C2H4 were investigated by fabricating graphitic C3N4–Ag3PO4 composite semiconductors with direct Z‐scheme configuration. It was found that both the ethylene photo‐oxidative activity and the stability of Ag3PO4 are considerably improved by fabrication of Z‐scheme composites. Moreover, stable C2H4 photo‐oxidation activity could be obtained by treating the composite at 450 °C for 3 h after long‐term operation. From the point of view of environmental pollutant cleanup, the present technique avoids the side reaction of oxidising water and will be valuable for further investigations on both Ag3PO4 and CH degradation.
Aliphatic Organoimido Derivatives of Polyoxometalates Containing a Bioactive Ligand
Authors: She Shan , Bian Shengtai , Hao Jian , Zhang Jiangwei , Zhang Jin , Wei Yongge 
Published: October 2014

AbstractA series of aliphatic organoimido derivatives of hexamolybdate based on amantadine, namely (nBu4N)2[Mo6O18(NC10H15)] (1), (nBu4N)2 {cis‐[Mo6O17(NC10H15)2]} (2), (nBu4N)2{trans‐[Mo6O17(NC10H15)2]} (3), and (nBu4N)2[Mo6O16(NC10H15)3] (4), was synthesized in reasonable yield by dehydration with N,N′‐dicyclohexylcarbodiimide (DCC). They were characterized by IR and UV/Vis spectroscopy, elemental analysis, ESI mass spectrometry, and single‐crystal X‐ray structure analysis. The spectral and structural similarities and differences between monosubstituted, cis‐disubstituted, and trans‐disubstituted organoimido derivatives were elucidated and may provide guidance for related work on organoimido‐functionalized Lindqvist‐type polyoxometalates. In addition, trans‐disubstituted and polysubstituted derivatives containing aliphatic organoimido ligands have not yet been reported, and the crystal structure of the trans isomer may lead us to a deeper understanding of disubstituted derivatives. Furthermore, proliferation and morphology of MCF‐7 cells were studied with compound 1. The present results show that the DCC‐dehydrating protocol could be an efficient approach to covalently graft bioactive ligands such as amantadine onto POMs and enhance their application in clinical cancer treatment.
Total Synthesis of Aignopsanes, A Class of Sesquiterpenes: (+)‐Aignopsanoic Acid A, (−)‐Methyl Aignopsanoate A, and (−)‐Isoaignopsanoic A
Authors: Bürki Cédric , Bonjoch Josep , Bradshaw Ben , Villa Giorgio , Renaud Philippe 
Published: October 2014

AbstractA general strategy for the synthesis of aignopsanes, a new family of sesquiterpene natural products of marine origin, is presented. The total synthesis of (+)‐aignopsanoic acid A (1), (−)‐methyl aignopsanoate A (2), and (−)‐isoaignopsanoic A (3) has been achieved and their absolute configuration confirmed. (+)‐Microcionin‐1 (4), a structurally related furanosesquiterpene isolated in both enantiomeric forms from marine sponges, was also synthesized and its absolute configuration established in an unambiguous way. Interestingly, we report that (+)‐microcionin‐1 (4), can be converted by a simple oxidation process to aignopsanoic acid A (1). This transformation supports the hypothesis that (+)‐microcionin‐1 (4) may be an intermediate in the biosynthesis of aignopsanes.
Straightforward Synthesis of 1,2‐Dicyanoalkanes from Nitroalkenes and Silyl Cyanide Mediated by Tetrabutylammonium Fluoride
Authors: Kiyokawa Kensuke , Nagata Takaya , Hayakawa Junpei , Minakata Satoshi 
Published: October 2014

AbstractA straightforward synthesis of 1,2‐dicyanoalkanes by reacting nitroalkenes with trimethylsilyl cyanide in the presence of tetrabutylammonium fluoride is described. The reaction proceeds through a tandem double Michael addition under mild conditions. Employing the hypervalent silicate generated from trimethylsilyl cyanide and tetrabutylammonium fluoride is essential for achieving this transformation. Mechanistic studies suggest that a small amount of water included in the reaction media plays a key role. This protocol is applicable to various types of substrates including electron‐rich and electron‐deficient aromatic nitroalkenes, and aliphatic nitroalkenes. Moreover, vinyl sulfones were found to be good alternatives, particularly for electron‐deficient nitroalkenes. The broad substrate scope and functional group tolerance of the reaction makes this approach a practical method for the synthesis of valuable 1,2‐dicyanoalkanes.
N‐Heterocyclic Carbene Formation Induced Fluorescent and Colorimetric Sensing of Fluoride Using Perimidinium Derivatives
Authors: Zhang Dawei , Yang Haiqiang , Martinez Alexandre , Jamieson Kelsey , Dutasta Jean‐Pierre , Gao Guohua 
Published: October 2014

AbstractIn this study, two perimidinium derivatives (1 and 2) were designed, synthesized, and developed as efficient fluorescent and colorimetric chemodosisensors for F− in DMSO or more competitive media (DMSO containing 10 % water). In the presence of F−, the yellow and non‐fluorescent solution of 1/2 became colourless and exhibited strong blue fluorescence. This unique spectroscopic behaviour of 1/2 towards F− was attributed to the formation of N‐heterocyclic carbene deprotonated by F−, which immediately reacted with water to give a colourless and fluorescent carbinol. Interestingly, it was found that this carbinol intermediate was unstable and further underwent a redox disproportionation to generate two other optically changed compounds. All the proposed mechanisms for the sensing process have been carefully confirmed by experiments.
Strength by Joining Methods: Combining Synthesis with NMR, IR, and Vibrational Circular Dichroism Spectroscopy for the Determination of the Relative Configuration in Hemicalide
Authors: De Gussem Ewoud , Herrebout Wouter , Specklin Simon , Meyer Christophe , Cossy Janine , Bultinck Patrick 
Published: October 2014

AbstractThe relative configuration of a key subunit of hemicalide, a recently isolated, highly bioactive marine natural product having potent antiproliferative activity against a panel of human cancer cell lines, was assigned by combining stereocontrolled synthesis of model substrates with NMR, IR, and vibrational circular dichroism (VCD) spectroscopy. The assignment of the absolute configuration of asymmetric carbon center C42 in two structurally complex epimeric substructures containing six stereocenters by VCD analysis illustrates the power and reliability of combining methods.
Foldamers to Nanotubes: Influence of Amino Acid Side Chains in the Hierarchical Assembly of α,γ4‐Hybrid Peptide Helices
Authors: Jadhav Sandip V. , Misra Rajkumar , Gopi Hosahudya N. 
Published: October 2014

AbstractSupramolecular assembly of various artificially folded 12‐helical architectures composed of γ4‐Val, γ4‐Leu and γ4‐Phe residues is investigated. In contrast to the 12‐helices composed of γ4‐Val and γ4‐Leu residues, the helices with γ4‐Phe residues displayed unique elongated nanotubular architectures. The elongated nanotube assembly was further explored as a template for biomineralization of silver ions to silver nanowires. A comparative study using an analogous α‐peptide helix reveals the importance of the spatial arrangement of aromatic side chains along the helical cylinder in a 12‐helix. These results suggested that the proteolytically and structurally stable α,γ4‐hybrid peptide 12‐helices may serve as a new generation of potential templates in the design of functional biomaterials.
Long‐Lived States of Magnetically Equivalent Spins Populated by Dissolution‐DNP and Revealed by Enzymatic Reactions
Authors: Bornet Aurélien , Ji Xiao , Mammoli Daniele , Vuichoud Basile , Milani Jonas , Bodenhausen Geoffrey , Jannin Sami 
Published: October 2014

AbstractHyperpolarization by dissolution dynamic nuclear polarization (D‐DNP) offers a way of enhancing NMR signals by up to five orders of magnitude in metabolites and other small molecules. Nevertheless, the lifetime of hyperpolarization is inexorably limited, as it decays toward thermal equilibrium with the nuclear spin‐lattice relaxation time. This lifetime can be extended by storing the hyperpolarization in the form of long‐lived states (LLS) that are immune to most dominant relaxation mechanisms. Levitt and co‐workers have shown how LLS can be prepared for a pair of inequivalent spins by D‐DNP. Here, we demonstrate that this approach can also be applied to magnetically equivalent pairs of spins such as the two protons of fumarate, which can have very long LLS lifetimes. As in the case of para‐hydrogen, these hyperpolarized equivalent LLS (HELLS) are not magnetically active. However, a chemical reaction such as the enzymatic conversion of fumarate into malate can break the magnetic equivalence and reveal intense NMR signals.