Self-assembled organic–inorganic magnetic hybrid adsorbent ferrite based on cyclodextrin nanoparticles

• Ângelo M. L. Denadai,
• Frederico B. De Sousa,
• Joel J. Passos,
• Fernando C. Guatimosim,
• Kirla D. Barbosa,
• Ana E. Burgos,
• Fernando Castro de Oliveira,
• Jeann C. da Silva,
• Bernardo R. A. Neves,
• Nelcy D. S. Mohallem and
• Rubén D. Sinisterra

Beilstein J. Org. Chem. 2012, 8, 1867–1876, doi:10.3762/bjoc.8.215

• -Ni/Zn/βCD presented smaller particles and a more homogeneous particle size distribution. Higher porosity for this MHM compared to Fe-Ni/Zn was observed by Brunauer–Emmett–Teller isotherms and positron-annihilation-lifetime spectroscopy. Based on the pKa values, potentiometric titrations demonstrated

• materials was evaluated by Brunauer–Emmett–Teller isotherm (BET) and positron-annihilation-lifetime spectroscopy (PALS). Thus, considering the advanced functional properties achieved by βCD insertion in the inorganic matrix identified by the above experiments and the MHM capability to self-assemble, the

• different morphologies for these two samples. Determination of free volume by PALS The free volume was measured by positron probe through the PALS technique, where the longest component of the positron-lifetime spectrum, τ3 (the o-Ps pick-off lifetime), can be correlated with free volume holes in condensed

Interaction of cyclodextrins with pyrene-modified polyacrylamide in a mixed solvent of water and dimethyl sulfoxide as studied by steady-state fluorescence

• Akihito Hashidzume,
• Yongtai Zheng and
• Akira Harada

Beilstein J. Org. Chem. 2012, 8, 1312–1317, doi:10.3762/bjoc.8.150

• one to construct functional systems that convert photo energy based on molecular recognition. Among aromatic compounds, pyrene is the most examined as a fluorescence probe or label because it shows a relatively high fluorescence quantum yield and a relatively long fluorescence lifetime in both monomer

Cyclodextrin nanosponge-sensitized enantiodifferentiating photoisomerization of cyclooctene and 1,3-cyclooctadiene

• Wenting Liang,
• Cheng Yang,
• Masaki Nishijima,
• Gaku Fukuhara,
• Tadashi Mori,
• Andrea Mele,
• Franca Castiglione,
• Fabrizio Caldera,
• Francesco Trotta and
• Yoshihisa Inoue

Beilstein J. Org. Chem. 2012, 8, 1305–1311, doi:10.3762/bjoc.8.149

• intermolecular interactions, short lifetime and high reactivity of the excited-state substrate are the major causes that prevent efficient asymmetric induction in chiral photochemistry. A supramolecular approach to photochirogenesis provides a convenient and also promising tool to facilitate the excited-state

Enantioselective supramolecular devices in the gas phase. Resorcin[4]arene as a model system

• Caterina Fraschetti,
• Matthias C. Letzel,
• Antonello Filippi,
• Maurizio Speranza and
• Jochen Mattay

Beilstein J. Org. Chem. 2012, 8, 539–550, doi:10.3762/bjoc.8.62

• by several computational supports (molecular dynamics and ab initio optimization). The dynamic point of view is fundamental for supramolecular ionic aggregates, because the synergy of several noncovalent interactions confers a pronounced stability even to very flexible aggregates, and the lifetime of

On the mechanism of action of gated molecular baskets: The synchronicity of the revolving motion of gates and in/out trafficking of guests

• Keith Hermann,
• Stephen Rieth,
• Hashem A. Taha,
• Bao-Yu Wang,
• Christopher M. Hadad and
• Jovica D. Badjić

Beilstein J. Org. Chem. 2012, 8, 90–99, doi:10.3762/bjoc.8.9

• revolving rate of the gates is temperature dependent, thereby governing the lifetime of Ha or Hb nuclei, each residing in a particular chemical environment (τ = 1/krac); the hydrogen nuclei are observed as separate resonances when τ >> 1/Δν(Ha/b) [33]. Accordingly, we performed the classical line-shape

Continuous-flow enantioselective α-aminoxylation of aldehydes catalyzed by a polystyrene-immobilized hydroxyproline

• Xacobe C. Cambeiro,
• Rafael Martín-Rapún,
• Pedro O. Miranda,
• Sonia Sayalero,
• Esther Alza,
• Patricia Llanes and
• Miquel A. Pericàs

Beilstein J. Org. Chem. 2011, 7, 1486–1493, doi:10.3762/bjoc.7.172

• operations other than the reaction itself (washing, drying, storage, etc.) [72]. This frequently leads to a significant extension of the catalyst’s lifetime. In addition, any further processing for the separation of the catalyst from the reaction mixture is no longer needed. The combined effect of these

• macroporous resins. We accordingly expected that the catalyst immobilized on such a more heavily cross-linked resin, such as 1b, would retain an important level of activity while having less of a tendency for structural collapse under the flow conditions, and that, as a consequence, the useful lifetime of the

Efficient and selective chemical transformations under flow conditions: The combination of supported catalysts and supercritical fluids

• M. Isabel Burguete,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2011, 7, 1347–1359, doi:10.3762/bjoc.7.159

• processes. Furthermore, the catalyst lifetime can, in many cases, be dramatically improved under supercritical conditions, owing to reduced coking [69][70]. The selective monoprotection of 1,n-terminal diols is a characteristic example of how mono-substituted ethers can be selectively prepared versus the

Triple-channel microreactor for biphasic gas–liquid reactions: Photosensitized oxygenations

• Ram Awatar Maurya,
• Chan Pil Park and
• Dong-Pyo Kim

Beilstein J. Org. Chem. 2011, 7, 1158–1163, doi:10.3762/bjoc.7.134

• from long reaction times due to restricted spatial illumination. In addition, the short lifetime of singlet oxygen in solutions, the low interfacial area between the oxygen and the reaction solution, and the long molecular diffusion distances significantly reduce the reaction efficiency. In this

Fine-tuning alkyne cycloadditions: Insights into photochemistry responsible for the double-strand DNA cleavage via structural perturbations in diaryl alkyne conjugates

• Wang-Yong Yang,
• Samantha A. Marrone,
• Nalisha Minors,
• Diego A. R. Zorio and
• Igor V. Alabugin

Beilstein J. Org. Chem. 2011, 7, 813–823, doi:10.3762/bjoc.7.93

• of the reaction mixture. This observation suggests that the ISC to the triplet state with m-acetamidyl acetylene 4 is more efficient than with p-acetamidyl acetylene 3, the lifetime of the triplet of 4 is longer than that of 3, or the triple state of 4 is more electrophilic than the triplet state of

• potentially lead to a stronger pH-dependency on the photochemistry of the respective lysine conjugate, which is controlled by the protonation-gated intramolecular electron transfer from the α-amino group [25]. Interestingly, the meta-isomer has a noticeably longer singlet lifetime than the other two isomers

• (Figure 8c). Only glycerol at pH 6 and glycerol and DMSO at pH 8 showed ~10% of protection. Little effect was observed for NaN3, suggesting that the formation of singlet oxygen via triplet energy transfer is inefficient, possibly because of a short triplet lifetime and fast intramolecular photocyclization

A comparative study of the Au-catalyzed cyclization of hydroxy-substituted allylic alcohols and ethers

• Berenger Biannic,
• Thomas Ghebreghiorgis and
• Aaron Aponick

Beilstein J. Org. Chem. 2011, 7, 802–807, doi:10.3762/bjoc.7.91

• , these data do not provide sufficient details to compare accurately between different classes of substrates. We also sought to gain more insight into how fast the reaction proceeds and to be able to comment on catalyst lifetime. To be consistent, we chose to study the simple system shown in Scheme 2 and

Intraannular photoreactions in pseudo-geminally substituted [2.2]paracyclophanes

• Henning Hopf,
• Vitaly Raev and
• Peter G. Jones

Beilstein J. Org. Chem. 2011, 7, 658–667, doi:10.3762/bjoc.7.78

• diradical intermediate of type 17, its lifetime is evidently too short to allow ring-expansion as depicted in Scheme 7. Whether this process might be induced thermally (vinylcyclopropane→cyclopentene rearrangement; [23]) is an open question. Conclusion Although the detailed mechanisms of the

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• intersystem crossing by the heavy-atom effect, and thus decreases the singlet excited-state lifetime of the arene. Mattay considered this as direct proof that the addition of benzene to 1,3-dioxoles takes place primarily via the singlet excited-state of benzene. Ferree et al. had earlier provided evidence

Fluorometric recognition of both dihydrogen phosphate and iodide by a new flexible anthracene linked benzimidazolium-based receptor

• Kumaresh Ghosh and
• Debasis Kar

Beilstein J. Org. Chem. 2011, 7, 254–264, doi:10.3762/bjoc.7.34

• %), τ2 = 7.76 ns (87.78%). The faster decay component (3.42 ns) is due to the anthracene moiety [47] and the relatively stable component with longer lifetime (7.76 ns) is attributed to the benzimidazolium motif of 1. However, in the presence of 1 equiv of H2PO4−, the lifetime of both the components

• marginally decreases (Table 2). In the presence of 2 equiv of H2PO4−, the lifetime of the anthracene component increases without showing any marked change in the pre-exponential factor. This was also true for the benzimidazolium component. Figure 13 shows the decay profiles. The change in the lifetimes of

Ene–yne cross-metathesis with ruthenium carbene catalysts

• Cédric Fischmeister and
• Christian Bruneau

Beilstein J. Org. Chem. 2011, 7, 156–166, doi:10.3762/bjoc.7.22

• . On the other hand, no improvement of stereoselectivity was obtained under these experimental conditions. It was shown that ethylene increased the lifetime of the Fischer carbene intermediate. Moreover, its role might consist in supporting the methylene transfer, thereby enhancing catalyst turnover

Heavy atom effects in the Paternò–Büchi reaction of pyrimidine derivatives with 4,4’-disubstituted benzophenones

• Feng-Feng Kong,
• Jian-Bo Wang and
• Qin-Hua Song

Beilstein J. Org. Chem. 2011, 7, 113–118, doi:10.3762/bjoc.7.16

• triplet excited state is very fast, 1011 s−1 for benzophenones, and not affected by heavy atoms, but the ISC process of triplet benzophenones to singlet ground state would be accelerated, reducing lifetime of triplet benzophenones. Finally, triplet benzophenones with a short lifetime would give rise to a

Miniemulsion polymerization as a versatile tool for the synthesis of functionalized polymers

• Daniel Crespy and
• Katharina Landfester

Beilstein J. Org. Chem. 2010, 6, 1132–1148, doi:10.3762/bjoc.6.130

• particles displayed an excitation lifetime 17 times longer than pyrene dissolved in THF. Metal-catalyzed polymerizations At the end of the last century, many groups focused their research on the production of polyolefins in aqueous media. Ethylene as one of the most industrially relevant monomers was

Solvent-free phase-vanishing reactions with PTFE (Teflon^®) as a phase screen

• Kevin Pels and
• Veljko Dragojlovic

Beilstein J. Org. Chem. 2009, 5, No. 75, doi:10.3762/bjoc.5.75

• (C6F14), has a high global warming potential (GWP ~10,000) and atmospheric lifetime of 3200 years [17]. In addition, some solvents, reagents and reaction products are partially soluble in FC-72 [13][14][15][16][18], which limits our ability to either reuse or recycle it. Ryu and Curran have reported

Gold film- catalysed benzannulation by Microwave- Assisted, Continuous Flow Organic Synthesis (MACOS)

• Gjergji Shore,
• Michael Tsimerman and
• Michael G. Organ

Beilstein J. Org. Chem. 2009, 5, No. 35, doi:10.3762/bjoc.5.35

• lifetime and durability of the film under the optimized reaction conditions was examined. The transformation in Table 2, entry a was followed over the course of 2 h; reaction performance is optimal at the beginning and slowly, but steadily erodes. Visibly, the film darkens over time, which we attribute to

From discovery to production: Scale- out of continuous flow meso reactors

• Peter Styring and
• Ana I. R. Parracho

Beilstein J. Org. Chem. 2009, 5, No. 29, doi:10.3762/bjoc.5.29

• catalyst was detected over the course of the cycles and ICP-ES studies showed the nickel content in the resin was the same as when the catalyst was initially prepared. An important point of concern when using heterogeneous catalyst is its lifetime, particularly for industrial and pharmaceutical

• carried out in a parallel channel meso reactor at a flow rate of 95 ml h−1. Kumada reaction carried out in a parallel channel meso reactor over a 31-hour period at a flow rate of 95 ml h−1 to show catalyst stability and lifetime. Kumada reaction carried out in a parallel channel meso reactor at a flow

The development and evaluation of a continuous flow process for the lipase- mediated oxidation of alkenes

• Charlotte Wiles,
• Marcus J. Hammond and
• Paul Watts

Beilstein J. Org. Chem. 2009, 5, No. 27, doi:10.3762/bjoc.5.27

• activity, again illustrating that careful dosage of H2O2 (2) increased the operational lifetime of the biocatalyst. The authors also noted that the presence of EtOH and urea resulted in moderate deactivation of the enzyme. In 2006, Olivo and co-workers [21] reported an environmentally benign method for

• synthetically useful alkenes, whilst increasing the biocatalyst’s lifetime. With this in mind, our initial investigation into the development of a continuous process for the synthesis of epoxides focussed on the incorporation of immobilised Candida antarctica lipase B, Novozym® 435 (4), into a flow reactor and

Reversible intramolecular photocycloaddition of a bis(9-anthrylbutadienyl)paracyclophane – an inverse photochromic system. (Photoactive cyclophanes 5)

• Henning Hopf,
• Christian Beck,
• Jean-Pierre Desvergne,
• Henri Bouas-Laurent,
• Peter G. Jones and
• Ludger Ernst

Beilstein J. Org. Chem. 2009, 5, No. 20, doi:10.3762/bjoc.5.20

• complete extinction (see Supporting Information p S2). The dissociation kinetics were found to be first order with a half-life of ca 3.8 h. This suggests a much longer lifetime at ambient temperature, as observed experimentally. 4 Structure of the photoproduct Preparative irradiation of a solution of 2 in