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Search for "quenching" in Full Text gives 395 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions

  • Stanislav V. Lozovskiy,
  • Alexander Yu. Ivanov,
  • Olesya V. Khoroshilova and
  • Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2018, 14, 2897–2906, doi:10.3762/bjoc.14.268

Graphical Abstract
  • , D2SO4), (arysulfonyl)allenes (ArSO2–CR1=C=CR2R3) and (arylsulfinyl)allenes (ArSO–CR1=C=CR2R3) undergo cyclization into the corresponding stable 1,2-oxathiolium ions, which were studied by means of NMR and DFT calculations. Quenching of solutions of these cations with low nucleophilic media, aqueous HCl
  • followed by aqueous quenching of the reaction mixture are shown in Table 3. These reactions resulted in the formation of three different products, Z-3a, Z-4a and 5a, depending on the reaction conditions. At room temperature in CF3SO3H or H2SO4 for a short time, 10 min or 1 h, respectively, butadiene Z-3a
  • strongly depends on the nucleophilicity of the quenching medium. Under the conditions of low nucleophilic work-up with aqueous HCl (Table 3, entry 4), the deprotonation takes place leading to butadiene Z-3a. The predominant formation of the Z-isomer of 3a may reveal that cation Ba undergoes deprotonation
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Published 22 Nov 2018

Targeting the Pseudomonas quinolone signal quorum sensing system for the discovery of novel anti-infective pathoblockers

  • Christian Schütz and
  • Martin Empting

Beilstein J. Org. Chem. 2018, 14, 2627–2645, doi:10.3762/bjoc.14.241

Graphical Abstract
  • . aeruginosa quorum quenching assays was observed [56]. This highlights a notable issue when addressing intracellular targets of this Gram-negative bacterium, as permeating the outer and inner membrane while escaping efflux and enzymatic deactivation may represent a true challenge. The elucidation of the
  • pocket next to T265. This also indicates that the quorum quenching activity of 36 depends on slight conformational changes. The L1 loop main chain and a rotation of the T265 side chain are hypothesized to be important for antagonistic/inverse agonistic functionality of PqsR-targeting QSIs. More recently
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Published 15 Oct 2018

Transition metal-free oxidative and deoxygenative C–H/C–Li cross-couplings of 2H-imidazole 1-oxides with carboranyl lithium as an efficient synthetic approach to azaheterocyclic carboranes

  • Lidia A. Smyshliaeva,
  • Mikhail V. Varaksin,
  • Pavel A. Slepukhin,
  • Oleg N. Chupakhin and
  • Valery N. Charushin

Beilstein J. Org. Chem. 2018, 14, 2618–2626, doi:10.3762/bjoc.14.240

Graphical Abstract
  • effects of various factors (type of acylating agents, exposure time for which the reaction mass is kept after mixing 2H-imidazole N-oxide 1 with carboranyllithium 2 and quenching with an acylating agent, as well as the temperature regime, at which the deoxygenative agent is added) have been studied. The
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Published 12 Oct 2018

Pathoblockers or antivirulence drugs as a new option for the treatment of bacterial infections

  • Matthew B. Calvert,
  • Varsha R. Jumde and
  • Alexander Titz

Beilstein J. Org. Chem. 2018, 14, 2607–2617, doi:10.3762/bjoc.14.239

Graphical Abstract
  • significantly reduced. In some cases, however, resistance has already been observed (e.g., through increased expression of efflux pumps to circumvent quorum quenching), with the likelihood of the appearance of resistance mechanisms seemingly dependent upon the importance of the targeted virulence factor to the
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Published 11 Oct 2018

Learning from B12 enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

  • Keishiro Tahara,
  • Ling Pan,
  • Toshikazu Ono and
  • Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

Graphical Abstract
  • with the report by Yoon et al. in which light irradiation to Ru(bpy)32+ resulted in rapid decomposition during the photocatalytic reaction [113]. It was remarkable that a significantly high turnover number based on 1 (10,880) was obtained in the prolonged reaction with Irdfppy. Quenching experiments
  • with time-resolved photoluminescence spectroscopy revealed that the oxidative quenching of the excited state of Irdfppy favorably proceeds over the reductive quenching mechanism. The combination of 1 and Irdfppy offers the best choice for the dechlorination of DDT among our light-driven systems in
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Published 02 Oct 2018

Quinolines from the cyclocondensation of isatoic anhydride with ethyl acetoacetate: preparation of ethyl 4-hydroxy-2-methylquinoline-3-carboxylate and derivatives

  • Nicholas G. Jentsch,
  • Jared D. Hume,
  • Emily B. Crull,
  • Samer M. Beauti,
  • Amy H. Pham,
  • Julie A. Pigza,
  • Jacques J. Kessl and
  • Matthew G. Donahue

Beilstein J. Org. Chem. 2018, 14, 2529–2536, doi:10.3762/bjoc.14.229

Graphical Abstract
  • quenching with ethyl chlorooxolate furnishing ethyl oxalate 4a in 29–79% yield [12]. This sequence works well with the unsubstituted benzene ring of the series a compounds where R = H. However, to access quinoline 2 with scaffolds such as 4b with halogen substitution in the benzene ring at the 5-, 6-, 7- or
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Published 28 Sep 2018

Synthesis of aryl sulfides via radical–radical cross coupling of electron-rich arenes using visible light photoredox catalysis

  • Amrita Das,
  • Mitasree Maity,
  • Simon Malcherek,
  • Burkhard König and
  • Julia Rehbein

Beilstein J. Org. Chem. 2018, 14, 2520–2528, doi:10.3762/bjoc.14.228

Graphical Abstract
  • disulfide (Figure 3b). Stern–Volmer quenching studies showed that the arene is quenched at a much higher rate than the disulfide (Figure 3c). This indicates that the oxidation of the arene is the key step in the C–H sulfenylation reaction. Anisole does not quench the luminescence of [Ir(dF(CF3)ppy)2(dtbpy
  • (1,3,5-TMB•+) is formed indeed during the quenching process of the catalyst by 1,3,5-TMB (Scheme 5) ns-time-resolved transient absorption spectroscopy was used [50]. To allow for a decomposition of the multicomponent spectra we conducted laser flash photolysis (LFP) experiments on the single components
  • -trimethoxybenzene in CH3CN. (b) Changes in the fluorescence spectra upon the addition of diphenyl disulfide in CH3CN. (c) Stern–Volmer quenching plot of iridium catalyst in the presence of 1,2,4-trimethoxybenzene and diphenyl disulfide. Kq (arene) = 318 ± 2.6 M−1 L and Kq (disulfide) = 36 ± 0.7 M−1 L. Black line
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Published 27 Sep 2018

Calixazulenes: azulene-based calixarene analogues – an overview and recent supramolecular complexation studies

  • Paris E. Georghiou,
  • Shofiur Rahman,
  • Abdullah Alodhayb,
  • Hidetaka Nishimura,
  • Jaehyun Lee,
  • Atsushi Wakamiya and
  • Lawrence T. Scott

Beilstein J. Org. Chem. 2018, 14, 2488–2494, doi:10.3762/bjoc.14.225

Graphical Abstract
  • thermostated dual beam UV–vis spectrophotometer. Addition of microlitre aliquots of DCM solutions of the respective tetraalkylammonium salts (TRAX; where R = Me, Et; n-Bu and X = Cl−, Br−, I− or BF4−) resulted in quenching of the absorption spectra in the 300–700 nm range, with visible isosbestic points at
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Published 25 Sep 2018

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

  • Alex Frichert,
  • Peter G. Jones and
  • Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

Graphical Abstract
  • cyanoformate in the presence of DMPU affording an inconsequential 5.6:1 mixture of diastereomers favoring 10 (3J3H-4H 12.2 Hz vs 4.8 Hz, Scheme 1). The cyclohexadiene system of 11 was formed after deprotonation of 10 (LiHMDS) and quenching with triflic anhydride. All compounds carrying the 1,3-cyclohexadiene
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Published 20 Sep 2018

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

  • Michael K. Bogdos,
  • Emmanuel Pinard and
  • John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

Graphical Abstract
  • classed as a reductive quenching cycle (Figure 4). In a reductive quenching catalytic cycle, a species must act as an oxidant to return the photocatalyst to its native oxidation state. If ET occurs such that the catalyst is oxidised, the cycle is classed as an oxidative quenching cycle (Figure 5). In an
  • oxidative quenching catalytic cycle, a species must act as a reductant to return the photocatalyst to its native oxidation state. The reducing and oxidising species can be the substrate or an additive, since the classification of a catalytic cycle as either reductive or oxidative quenching considers only
  • the reaction is not dependent on the catalytic cycle characterisation – either reductive or oxidative quenching. Net oxidative reactions require the presence of an oxidising agent. The advantage of photoredox net oxidative reactions, compared to conventional oxidation reactions, is that much milder
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Published 03 Aug 2018

Rational design of boron-dipyrromethene (BODIPY) reporter dyes for cucurbit[7]uril

  • Mohammad A. Alnajjar,
  • Jürgen Bartelmeß,
  • Robert Hein,
  • Pichandi Ashokkumar,
  • Mohamed Nilam,
  • Werner M. Nau,
  • Knut Rurack and
  • Andreas Hennig

Beilstein J. Org. Chem. 2018, 14, 1961–1971, doi:10.3762/bjoc.14.171

Graphical Abstract
  • quenching by photoinduced electron transfer (PET), whereas the protonated form was brightly fluorescent [31]. We report herein the synthesis and photophysical characterization of BODIPY derivatives with an aniline substituent in the meso-position to which different anchor groups have been attached, and we
  • used polymer microparticles with surface-bound CB7 [66] and added them to a solution containing a mixture of 5 and 1-(aminomethyl)adamantane (AMADA). The latter was added to reduce the surface group density of the dye and prevent undesired self-quenching at high surface concentrations of the
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Published 30 Jul 2018

Assessing the possibilities of designing a unified multistep continuous flow synthesis platform

  • Mrityunjay K. Sharma,
  • Roopashri B. Acharya,
  • Chinmay A. Shukla and
  • Amol A. Kulkarni

Beilstein J. Org. Chem. 2018, 14, 1917–1936, doi:10.3762/bjoc.14.166

Graphical Abstract
  • tanks (T1–T8) with an agitator and a jacket for maintaining the temperature. The intermediate storage tanks can be used for multiple purposes viz. preheating/precooling any reaction intermediate, mixing reagents, quenching the reaction, dilution, crystallization, reaction and can be operated in batch or
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Published 26 Jul 2018

Synthesis of 9-arylalkynyl- and 9-aryl-substituted benzo[b]quinolizinium derivatives by Palladium-mediated cross-coupling reactions

  • Siva Sankar Murthy Bandaru,
  • Darinka Dzubiel,
  • Heiko Ihmels,
  • Mohebodin Karbasiyoun,
  • Mohamed M. A. Mahmoud and
  • Carola Schulzke

Beilstein J. Org. Chem. 2018, 14, 1871–1884, doi:10.3762/bjoc.14.161

Graphical Abstract
  • of 22AG to derivatives 2b and 2c could be used to deduce the binding constant Kb (Figure S2, Table 3). The addition of ct DNA to the derivative 2a led to quenching of the emission intensity (Figure 8A). In contrast, a light-up effect with a factor of 3 was observed upon the addition of ct DNA to
  • ][65][66]. The effect of the donor substituent on the emission quenching was supported by the strong increase of the emission quantum yield of 2c upon protonation of the amino group, that is, by the transformation of the donor to an acceptor substituent (Figure 5) [34]. Considering the water solubility
  • a hypochromic effect and red shift of the absorption bands as well as emission quenching or enhancement upon addition of the nucleic acid. Moreover, the binding constants Kb, as determined from the resulting binding isotherms, are in the same range (Kb = 2.0–22 × 104 M−1, Table 3) of known DNA
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Published 23 Jul 2018

Strong binding and fluorescence sensing of bisphosphonates by guanidinium-modified calix[5]arene

  • Jie Gao,
  • Zhe Zheng,
  • Lin Shi,
  • Si-Qi Wu,
  • Hongwei Sun and
  • Dong-Sheng Guo

Beilstein J. Org. Chem. 2018, 14, 1840–1845, doi:10.3762/bjoc.14.157

Graphical Abstract
  • , we employed fluorescein (Fl) as the reporter dye according to our previously published result [26]. Fl of high brightness is strongly encapsulated into the GC5A cavity (Ka = 5.0 × 106 M−1), accompanied with a drastic complexation-induced fluorescence quenching (Ifree/Ibound = 37). Taken together
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Published 19 Jul 2018

Synthesis of new tricyclic 5,6-dihydro-4H-benzo[b][1,2,4]triazolo[1,5-d][1,4]diazepine derivatives by [3+ + 2]-cycloaddition/rearrangement reactions

  • Lin-bo Luan,
  • Zi-jie Song,
  • Zhi-ming Li and
  • Quan-rui Wang

Beilstein J. Org. Chem. 2018, 14, 1826–1833, doi:10.3762/bjoc.14.155

Graphical Abstract
  • proceeded as expected under the usual reaction conditions and the desired products 13 were obtained after quenching with H2O at 0 °C. As can be seen from Scheme 4, both aliphatic and aromatic nitriles worked similarly. In light of the experimental achievements and preceding theoretical work, we rationalized
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Published 18 Jul 2018

Synthesis and photophysical studies of a multivalent photoreactive RuII-calix[4]arene complex bearing RGD-containing cyclopentapeptides

  • Sofia Kajouj,
  • Lionel Marcelis,
  • Alice Mattiuzzi,
  • Adrien Grassin,
  • Damien Dufour,
  • Pierre Van Antwerpen,
  • Didier Boturyn,
  • Eric Defrancq,
  • Mathieu Surin,
  • Julien De Winter,
  • Pascal Gerbaux,
  • Ivan Jabin and
  • Cécile Moucheron

Beilstein J. Org. Chem. 2018, 14, 1758–1768, doi:10.3762/bjoc.14.150

Graphical Abstract
  • + complex onto the calixarene platform does not induce any modification of the photophysical properties of the complex. In order to rule out any intramolecular quenching processes, control experiments were realized with the complex grafted onto the unmodified calixarene (conjugate 7) in the presence of free
  • cyclic pentapeptide units c-[RGDfK] 8 (see Supporting Information File 1). No modification of the luminescence by intermolecular quenching was observed, confirming the absence of internal quenching in the conjugate 9. Photoreactivity of RuII-calixarene conjugate 9 The photoreactivity of Ru-TAP complexes
  • excited state lifetime of conjugate 9 as function of the concentration of guanosine monophosphate (GMP, Figure 4). Stern–Volmer analyses indicate that a dynamic quenching is occurring, with a quenching rate close to the diffusion limit (kQ = 5.6 108 M−1s−1 in intensity and kQ = 5.3 108 M−1s−1 in lifetime
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Published 16 Jul 2018

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

  • Cristina Cebrián and
  • Matteo Mauro

Beilstein J. Org. Chem. 2018, 14, 1459–1481, doi:10.3762/bjoc.14.124

Graphical Abstract
  • distortion and access to quenching channels to some extent. On the other hand, the appearance of new low-lying excited states associated to the π molecular orbitals typically results into efficient emission due to their larger radiative decay rates [25]. Though limited in the 1980s by their sensitive
  • , thus raising the energy of quenching d–d states while lowering emissive MLCT and LC excited states. Alternatively, the use of N-deprotonable azole units has also been largely explored due to the fact that it can exert similar effects to ppy-like ligands [16]. Nevertheless, easier deprotonation of the N
  • the energetic destabilization of quenching MC states [45][46]. Complexes based on C^N^N ligands Following the seminal work of von Zelewski [47][48] on platinum(II) complexes bearing C-deprotonated 2-phenylpyridines (C^N), the development of tridentate analogues has received a great deal of attention
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Published 18 Jun 2018

London dispersion as important factor for the stabilization of (Z)-azobenzenes in the presence of hydrogen bonding

  • Andreas H. Heindl,
  • Raffael C. Wende and
  • Hermann A. Wegner

Beilstein J. Org. Chem. 2018, 14, 1238–1243, doi:10.3762/bjoc.14.106

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  • equiv) and NEt3 (65 µL, 0.44 mmol, 2.2 equiv) in THF (2 mL), pivaloyl chloride (54.4 µL, 0.437 mmol, 2.20 equiv) in THF (0.5 mL) was added dropwise at 0 °C. Then, the reaction was allowed to warm to rt while stirring for 2 h. After quenching with sat. aq. NH4Cl solution (5 mL), the aqueous phase was
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Published 29 May 2018

Investigations of alkynylbenziodoxole derivatives for radical alkynylations in photoredox catalysis

  • Yue Pan,
  • Kunfang Jia,
  • Yali Chen and
  • Yiyun Chen

Beilstein J. Org. Chem. 2018, 14, 1215–1221, doi:10.3762/bjoc.14.103

Graphical Abstract
  • benziodoxole have opposite effects for the radical alkynylation, we first conducted the fluorescence quenching experiments of tolylacetylenic benziodoxole derivatives 3a–f and found none of them oxidatively quenched the photoexcited Ru(bpy)32+* complex (see Supporting Information File 1, Scheme S1). We next
  • oxidative quenching step by benziodoxole radical (step 2), the electron-donating substituents on BI’-alkynes are both beneficial, while the electron-withdrawing substituents have opposite effects. Conclusion In conclusion, we have developed and investigated novel alkynylbenziodoxole derivatives as radical
  • isolated yields. Mechanistic investigations of alkynylbenziodoxole for radical acceptor and oxidative quenching reactivity. Yields are isolated yields. N/P = not performed. The role of alkynylbenziodoxole derivatives for radical alkynylation in photoredox catalysis. Supporting Information Supporting
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Published 28 May 2018

One hundred years of benzotropone chemistry

  • Arif Dastan,
  • Haydar Kilic and
  • Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

Graphical Abstract
  • ), subsequent quenching by the addition of methanol, yielded dihydro derivative 103 (Scheme 18). In 1978, in order to examine heteroatomic influences on the possible generation of 9C–10π homoaromatic dianions, Paquette’s group described the synthesis and reducibility of benzo-fused-homo-2-methoxyazocines from
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Published 23 May 2018

Polysubstituted ferrocenes as tunable redox mediators

  • Sven D. Waniek,
  • Jan Klett,
  • Christoph Förster and
  • Katja Heinze

Beilstein J. Org. Chem. 2018, 14, 1004–1015, doi:10.3762/bjoc.14.86

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  • application as redox mediator (Scheme 2) [55][56]. Ferrocenyl esters 1–4 are synthetically accessible via the acids of 1 [45][46], 2 [57], 3 and 4 [54] in a direct selective metalation of ferrocene [54][57][58][59][60], quenching with carbon dioxide, followed by esterification [45][46][47][48][54]. The 1,1
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Published 07 May 2018

Volatiles from three genome sequenced fungi from the genus Aspergillus

  • Jeroen S. Dickschat,
  • Ersin Celik and
  • Nelson L. Brock

Beilstein J. Org. Chem. 2018, 14, 900–910, doi:10.3762/bjoc.14.77

Graphical Abstract
  • quenching of cation J with water (box in Scheme 2), suggesting that this enzyme is responsible for the biosynthesis of 15 in A. fischeri. Therefore, the enzyme XP_001265719 is likely responsible for the biosynthesis of 19 and its byproducts. The biosynthetic origin of the observed traces of monoterpenes is
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Published 24 Apr 2018

Investigating radical cation chain processes in the electrocatalytic Diels–Alder reaction

  • Yasushi Imada,
  • Yohei Okada and
  • Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 642–647, doi:10.3762/bjoc.14.51

Graphical Abstract
  • luminescence quenching experiments [19]. With such an understanding in hand, radical ion chain processes could be further optimized to realize greener transformations. We have been developing anodic cycloadditions [20][21][22][23][24][25] enabled by lithium perchlorate/nitromethane electrolyte solution [26
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Published 16 Mar 2018

Continuous multistep synthesis of 2-(azidomethyl)oxazoles

  • Thaís A. Rossa,
  • Nícolas S. Suveges,
  • Marcus M. Sá,
  • David Cantillo and
  • C. Oliver Kappe

Beilstein J. Org. Chem. 2018, 14, 506–514, doi:10.3762/bjoc.14.36

Graphical Abstract
  • through a continuous addition of reagent streams, quenching, liquid–liquid extraction, or even filtration stages, thus avoiding the handling of unstable intermediates [35][36][37]. In this article we present an integrated continuous-flow procedure for the preparation of 2-(azidomethyl)oxazoles 7 starting
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Published 23 Feb 2018

Carbohydrate inhibitors of cholera toxin

  • Vajinder Kumar and
  • W. Bruce Turnbull

Beilstein J. Org. Chem. 2018, 14, 484–498, doi:10.3762/bjoc.14.34

Graphical Abstract
  • tryptophan fluorescence quenching assay to show that octavalent lactose-based dendrimer 34 (Figure 16) had a Kd value of 33 µM as compared to monovalent lactose derivative having a Kd value of 18,000 µM [51]. Hence, compound 34 displayed 545 fold more potency per lactose unit than monovalent lactose. In
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Published 21 Feb 2018
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