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

Incorporation of a metal-mediated base pair into an ATP aptamer – using silver(I) ions to modulate aptamer function

  • Marius H. Heddinga and
  • Jens Müller

Beilstein J. Org. Chem. 2020, 16, 2870–2879, doi:10.3762/bjoc.16.236

Graphical Abstract
  • (Figure S2). The fluorescence intensities were normalized according to Inorm = F/F0, wherein F = fluorescence intensity and F0 = fluorescence intensity of the fluorescein-labeled oligonucleotide without any additions. As expected, the oligonucleotide 1af shows the most efficient quenching upon the
  • was expected for the imidazole-free derivative 1af. Nevertheless, the addition of 10 equiv of Ag(I) leads to a slight decrease in the emission. The oligonucleotides 1bf, 1cf, and 1df all show less efficient quenching upon the addition of 1q, which can be attributed to the presence of the destabilizing
  • additional bases of 1q2 should be able to form two more canonical base pairs with the aptamer and therefore compensate for the destabilization caused by the imidazole mismatches. As expected, all fluorophore-labeled aptamers show a more effective quenching upon the addition of 1q2 (Figure S5 in Supporting
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Published 25 Nov 2020

Selective recognition of ATP by multivalent nano-assemblies of bisimidazolium amphiphiles through “turn-on” fluorescence response

  • Rakesh Biswas,
  • Surya Ghosh,
  • Shubhra Kanti Bhaumik and
  • Supratim Banerjee

Beilstein J. Org. Chem. 2020, 16, 2728–2738, doi:10.3762/bjoc.16.223

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  • of anthracene tagged imidazolium receptors responded to ATP through an amplified fluorescence quenching [60]. Based on these results, we wanted to develop similar self-assembled systems which would show a “turn-on” response in the presence of ATP or other phosphate analytes. The current design of
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Published 10 Nov 2020

NMR Spectroscopy of supramolecular chemistry on protein surfaces

  • Peter Bayer,
  • Anja Matena and
  • Christine Beuck

Beilstein J. Org. Chem. 2020, 16, 2505–2522, doi:10.3762/bjoc.16.203

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  • indeed recognize the highly positively charged area on cytochrome c (Cyt c) that binds Cyt c peroxidase. The inhibition of this protein–protein interaction was demonstrated as well using a luminescence quenching assay. The protein surface recognition of two porphyrin ligands bearing carboxylate
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Published 09 Oct 2020

Recent developments in enantioselective photocatalysis

  • Callum Prentice,
  • James Morrisson,
  • Andrew D. Smith and
  • Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

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  • Tung et al. merged photoredox, cobalt, and amine catalysis towards the synthesis of α-functionalised ketones 21 from tetrahydroisoquinolines (THIQs) 22 and ketones 23 (Scheme 3) [28]. The proposed mechanism involves an oxidative quenching cycle using the [CoIII] catalyst to generate [CoII] and [Ru
  • 101 could be generated in an oxidative quenching cycle from THIQs 102 using a ruthenium-based photocatalyst and 1,3-dinitrobenzene (DNB) as a sacrificial oxidant (Scheme 13) [51]. These iminium ions could then be intercepted by a Breslow intermediate 103, formed between aldehydes 104 and the NHC
  • quenching cycle, generating [Ir]•−, which reduces the phthalimide ester 117 to give α-amino radicals 117• after decarboxylation. The CPA then activates the azaarene 118 through protonation and brings the two reactive species together in a hydrogen bonded complex 119, which facilitates radical addition
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Published 29 Sep 2020

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

  • Shakeel Alvi and
  • Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

Graphical Abstract
  • by quenching with Cp*ZrCl3 to furnish the blackish-green solution. Since the complex 124 was found to be unstable in THF-d8, therefore, immediately it was replaced by toluene-d8 which was further replaced by CD2Cl2 to remove THF-d8 completely. Furthermore, they reported the ruthenium sumanene complex
  • followed by quenching the hexaanionic species with selenium powder to afford 159 containing one 1,2-diselenin ring and two selenophene rings. Compound 159 was later subjected to deselenation in the presence of copper nanopowder (80–100 nm grain size) to furnish the expected compound 160 in quantitative
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Published 09 Sep 2020

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

  • Shahboz Yakubov and
  • Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

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Published 03 Sep 2020

Naphthalene diimide–amino acid conjugates as novel fluorimetric and CD probes for differentiation between ds-DNA and ds-RNA

  • Annike Weißenstein,
  • Myroslav O. Vysotsky,
  • Ivo Piantanida and
  • Frank Würthner

Beilstein J. Org. Chem. 2020, 16, 2032–2045, doi:10.3762/bjoc.16.170

Graphical Abstract
  • . Accordingly, an incubation period of 180 s proved to be sufficient. Generally, the addition of any DNA/RNA resulted in a strong quenching of 3a,b, and 5 emission. However, the emission of reference compound 5 was non-selectively quenched by any DNA/RNA (Figure 5c), whereas solutions of 3a or 3b showed a
  • stronger quenching for GC-DNA and the weaker for AT(U)-polynucleotides (Figure 5a and b). Because guanine is the most electron-rich nucleobase, this behaviour points at a fluorescence quenching mechanism by charge transfer from the electron-rich purine bases to the electron-poor NDI molecular probes
  • -induced emission quenching of acridine or 4,9-diazapyrene derivatives [43]. In order to confirm the fluorimetric data by an independent method, and also to characterise thermodynamic parameters of complex formation, ITC titrations were performed (Figure 6, Supporting Information File 1, Figures S28–S30
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Published 19 Aug 2020

A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates

  • Olusesan K. Koleoso,
  • Matthew Turner,
  • Felix Plasser and
  • Marc C. Kimber

Beilstein J. Org. Chem. 2020, 16, 1983–1990, doi:10.3762/bjoc.16.165

Graphical Abstract
  • each reaction shown in Scheme 4. A tentative mechanism for this transformation is described in Scheme 5a. Excitation of the Ir(III) complex 17 provides *Ir(III) that subsequently undergoes reductive quenching by Et3N, delivering Ir(II) [48]. Single electron transfer from Ir(II) to 18 then generates an
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Published 12 Aug 2020

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

  • Lucas Guillemard and
  • Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

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  • , followed by the insertion of an alkyne into the C–M bond. The key step of the dual catalysis is the reductive quenching of the photoexcited catalyst by Rh(I), a low-valent metal obtained after C–N reductive elimination. Hence, the Rh(III) active catalyst is regenerated and the resulting reduced
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Published 21 Jul 2020

Clickable azide-functionalized bromoarylaldehydes – synthesis and photophysical characterization

  • Dominik Göbel,
  • Marius Friedrich,
  • Enno Lork and
  • Boris J. Nachtsheim

Beilstein J. Org. Chem. 2020, 16, 1683–1692, doi:10.3762/bjoc.16.139

Graphical Abstract
  • ,π*) excited states, owing to the poor orbital overlap, resulting in a decreased spin-orbit coupling. Quenching processes of triplet states, induced by molecular motions, oxygen, or humidity, restrict the versatile application of such organic materials [24]. Thus, low temperatures [25][26][27] or
  • defined up to 8.66 ns for iminium bromide 25, with quantum yields Φ below 1% (see Figure S32, Supporting Information File 1). The absence of any long living triplet species in all fluorene derivatives in solution as well as in the solid-state again indicates undesirable quenching events, induced by the
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Published 14 Jul 2020

Facile synthesis of 7-alkyl-1,2,3,4-tetrahydro-1,8-naphthyridines as arginine mimetics using a Horner–Wadsworth–Emmons-based approach

  • Rhys A. Lippa,
  • John A. Murphy and
  • Tim N. Barrett

Beilstein J. Org. Chem. 2020, 16, 1617–1626, doi:10.3762/bjoc.16.134

Graphical Abstract
  • -1,8-naphthyridine analogues. The investigation initially began using commercially available N-Boc-protected tetrahydro-1,8-naphthyridine 8 [16]. Upon deprotonation and quenching with diethyl chlorophosphate, migration of the Boc group from the nitrogen atom to the exocyclic methyl group was observed
  • would afford phosphonate 12 upon quenching with diethyl chlorophosphate via formation of the dianion. This could then be used in a subsequent Horner–Wadsworth–Emmons reaction to construct the carbon skeleton of amine 6. Upon the addition of a single equivalent of diethyl chlorophosphate, phosphoramidate
  • to account for the deprotonation of the more acidic phosphonate product 7 versus the starting material 13, and potential lithium sequestration by chelation between an oxygen atom of the phosphonate and the nitrogen atom of the unsaturated ring. Monitoring of the deprotonation followed by quenching
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Published 08 Jul 2020

Heterogeneous photocatalysis in flow chemical reactors

  • Christopher G. Thomson,
  • Ai-Lan Lee and
  • Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

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Published 26 Jun 2020

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

  • Alessandra Del Tito,
  • Havall Othman Abdulla,
  • Davide Ravelli,
  • Stefano Protti and
  • Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123

Graphical Abstract
  • -isocyano-1,1'-biaryls 4.1 have been reported, as summarized in Scheme 4. Along with substrate 4.1, a radical source R–X and a photocatalyst (PC), which is activated upon visible-light irradiation, are usually required. Oxidative quenching of the photoexcited PC* by R–X (path a) affords, upon loss of the
  • the bromoalkanes through an oxidative quenching mechanism [48]. Phenanthridines may be also formed by the initial addition of an electrophilic radical onto isonitriles. Thus, a library of 6-alkylated phenanthridines (5.2a–d in Scheme 5) and other nitrogen-based heterocycles have been prepared from
  • quenching of the excited photocatalyst, in turn triggering the formation of radicals 12.2·a–d. These smoothly underwent radical cyclization to give the corresponding methyl 5,6-dihydrophenanthridine-6-carboxylates and then the desired phenanthridine 6-carboxylates 12.3a–d in good yields. Noteworthy, the
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Published 25 Jun 2020

Synthesis of new fluorescent molecules having an aggregation-induced emission property derived from 4-fluoroisoxazoles

  • Kazuyuki Sato,
  • Akira Kawasaki,
  • Yukiko Karuo,
  • Atsushi Tarui,
  • Kentaro Kawai and
  • Masaaki Omote

Beilstein J. Org. Chem. 2020, 16, 1411–1417, doi:10.3762/bjoc.16.117

Graphical Abstract
  • concentrated solutions by aggregation-caused quenching (ACQ) [8]. On the other hand, there are molecules that exhibit strong emission even in poor solvents or in the solid state. This property is referred to as aggregation-induced emission (AIE) and has attracted much attention in the field of fluorescence
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Published 22 Jun 2020

Distinctive reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines under photoredox conditions

  • Shrikant D. Tambe,
  • Kwan Hong Min,
  • Naeem Iqbal and
  • Eun Jin Cho

Beilstein J. Org. Chem. 2020, 16, 1335–1342, doi:10.3762/bjoc.16.114

Graphical Abstract
  • quenched by single-electron transfer from Cy2NMe, resulting in the generation of the highly reducing [IrII] species and the radical cation A. To validate the reductive quenching pathway, we carried out Stern−Volmer quenching experiments (Figure S1, Supporting Information File 1). The emission intensity of
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Published 18 Jun 2020

[3 + 2] Cycloaddition with photogenerated azomethine ylides in β-cyclodextrin

  • Margareta Sohora,
  • Leo Mandić and
  • Nikola Basarić

Beilstein J. Org. Chem. 2020, 16, 1296–1304, doi:10.3762/bjoc.16.110

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  • and intercepted with AN to yield cycloadducts 7 or 11, respectively. However, the formation of cycloadducts is very inefficient, which may be ascribed to a smaller rate constant for the quenching due to steric hindrance imposed by the bulky cyclohexane or adamantine moiety. Thus, irradiation of 2 gave
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Published 12 Jun 2020

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

  • Stephanie G. E. Amos,
  • Marion Garreau,
  • Luca Buzzetti and
  • Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

Graphical Abstract
  • quenching cycle, PC* acts as a reductant donating an electron to A. This generates the oxidized form of the photocatalyst, PC•+, and a reduced acceptor, A•−. Alternatively, in a reductive quenching cycle, PC* acts as an oxidant promoting an SET oxidation of the electron donor D. This leads to the reduced
  • different redox-active functional groups (Figure 2) [48]. Among them, dihydropyridines (DHPs), silicates, and tetrafluoroborate salts were recently exploited in organophotocatalytic reactions. These functionalities can act as donors in reductive quenching manifolds and release the desired C(sp3) radicals
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Published 29 May 2020

Aryl-substituted acridanes as hosts for TADF-based OLEDs

  • Naveen Masimukku,
  • Dalius Gudeika,
  • Oleksandr Bezvikonnyi,
  • Ihor Syvorotka,
  • Rasa Keruckiene,
  • Dmytro Volyniuk and
  • Juozas V. Grazulevicius

Beilstein J. Org. Chem. 2020, 16, 989–1000, doi:10.3762/bjoc.16.88

Graphical Abstract
  • 6 are relatively small, and their LE emissions are mainly ultraviolet. There was practically no positive solvatochromism observed for the dilute solutions of compounds 3, 5, and 6. Only tails related to CT can be observed in the PL spectra of these compounds. Quenching of internal molecular motion
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Published 13 May 2020

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

  • Rodrigo Costa e Silva,
  • Luely Oliveira da Silva,
  • Aloisio de Andrade Bartolomeu,
  • Timothy John Brocksom and
  • Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

Graphical Abstract
  • catalysts in both oxidative and reductive quenching. The use of porphyrins as a photosensitizer for singlet oxygen generation is presented in the second topic, which was subdivided into two sections: pericyclic reactions and heteroatom oxidations. The first section describes the use of singlet oxygen in
  • photoredox catalysts up to now [10][22]. Remarkably the same system can be applied for both pathways, oxidative and reductive processes, beyond singlet oxygen generation [9][10][23]. Only a few photocatalysts can be applied in both photoredox processes (oxidative and reductive quenching), for example, [Ru
  • this transformation involves the formation of an aryl radical by SET between the diazo compound and the porphyrin in its excited state (Scheme 3). The authors demonstrated that meso-arylated porphyrins can efficiently act by an oxidative quenching. However, issues about why an electron-poor porphyrin
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Published 06 May 2020

A method to determine the correct photocatalyst concentration for photooxidation reactions conducted in continuous flow reactors

  • Clemens R. Horn and
  • Sylvain Gremetz

Beilstein J. Org. Chem. 2020, 16, 871–879, doi:10.3762/bjoc.16.78

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  • reaction conditions (0.5 N citronellol, 1 mL/min,1 mol % catalyst, 2 equiv oxygen, 8 bar, 20 °C, reactor volume: 2.7 mL, solvent: ethanol (B, C, D, E, and F) or dichloromethane (A, G, H, and I)). aThe conversion was determined by GC after quenching with PPh3. bTransmission (in %) of the starting solution
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Published 27 Apr 2020

Aldehydes as powerful initiators for photochemical transformations

  • Maria A. Theodoropoulou,
  • Nikolaos F. Nikitas and
  • Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

Graphical Abstract
  • irradiation, supporting the other two pathways. Also, mechanistic studies by Cui et al. showed that the energy levels of the reactions (1) and (2) in Scheme 5 were closely tied, so distinguishing them is not always trivial [32]. The triplet state quenching of 8 and related compounds, such as aryl ketones, has
  • of an α-hydroxybenzyl radical (11) and a benzoyl radical (10). This upper statement shows the potential of benzaldehyde (8) compared to the related aryl ketones, which are known to be capable of HAT. Until recently, the quenching of the fluorescence of excited benzaldehyde (9) was unreasonably
  • thought to originate from the basicity of the aldehyde. A recent publication though came to empower the statement that the HAT properties of benzaldehyde (8) are responsible for the observed quenching of the fluorescence [34]. Aldehydes as photoinitiators for photochemical polymerizations A number of
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Published 23 Apr 2020

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

  • Mingbing Zhong,
  • Xavier Pannecoucke,
  • Philippe Jubault and
  • Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

Graphical Abstract
  • , probably due to their intrinsic reduction potential. Interestingly, the bromide substrate derived from menthol was readily reduced in an excellent 74% isolated yield. The authors conducted some mechanistic studies (including cyclic voltammetry and Stern–Volmer quenching experiments, for instance), and
  • the reaction mechanism and suggested the following one: First, the excited in situ-formed copper complex reduced the NHP ester, as demonstrated by the Stern–Volmer quenching experiment. The formed radical anion collapsed into the corresponding alkyl radical and the phthalimide anion. Then, the
  • oxidative quenching. First, the excited [Cu(I)]* species was oxidized in the presence of iodine, furnishing a [Cu(II)] complex. Then, an oxidation of the diarylamine occurred, generating the N-centered radical cation, which undergoes an intramolecular cyclization. A final oxidation of the aryl radical
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Published 23 Mar 2020

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

  • Kaj M. van Vliet,
  • Nicole S. van Leeuwen,
  • Albert M. Brouwer and
  • Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

Graphical Abstract
  • solvents did not lead to any significant increase of the yield or selectivity (Table 1, entries 5–9). The reduction of catalyst loading resulted in a lower yield and a lower selectivity for the acid compound 3 (Table 1, entries 10–14). The products indicate an oxidative quenching of the photoredox catalyst
  • the formation of the cation of the photoredox catalyst, we believe that after oxidative quenching the catalyst is not fully reduced back to the neutral complex, accumulates in solution and as a result precipitates as chloride salt (with Cl− stemming from the substrate). We assume that the same happens
  • product was not formed at all. Addition of [Ag]PF6 to remove the chloride and solubilize the oxidized photocatalyst also did not lead to any product formation. [Ag]PF6 is poorly soluble in benzene and the Ag+ ion is likely to act as an oxidizing agent quenching the excited state of the photocatalyst
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Published 16 Mar 2020

Architecture and synthesis of P,N-heterocyclic phosphine ligands

  • Wisdom A. Munzeiwa,
  • Bernard Omondi and
  • Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

Graphical Abstract
  • to obtain cyclopropyl intermediate 45. The latter was converted into compound 46 by reaction with lithium diphenylphosphide in dry THF. Finally, the desired ligand 47 was obtained after quenching the intermediate compound 46 with a saturated solution of ammonium chloride. Ligand 47 was investigated
  • magnesium-containing triazoles 66 which, upon quenching with ammonium chloride, afforded the triazoles 67. Lithiation followed by coupling with the appropriate chlorophosphines resulted in the desired 1,5-disubstitued triazolylphosphine ligands 68. The procedure could be performed in one pot by directly
  • quenching the metalated triazole 66 with chlorophosphine. However, a separation of the triazole before phosphorylation makes purification of the final ligand easier [74]. The direct ortho-metalation of pyridyltriazole 69 and subsequent reaction with chlorophosphines gave the isomeric ligands 71 and 72 in
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Published 12 Mar 2020

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

  • Panagiotis S. Gritzapis,
  • Panayiotis C. Varras,
  • Nikolaos-Panagiotis Andreou,
  • Katerina R. Katsani,
  • Konstantinos Dafnopoulos,
  • George Psomas,
  • Zisis V. Peitsinis,
  • Alexandros E. Koumbis and
  • Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

Graphical Abstract
  • conditions (λexcitation = 540 nm at room temperature). Thus, the quenching observed in an EB–DNA solution upon addition of the compounds 11 and 12 may reveal their competition to EB for the DNA-intercalation sites as monitored by fluorescence emission spectroscopy with λexcitation = 540 nm. A significant
  • quenching of the EB–DNA fluorescence (up to 68.5% of the initial fluorescence for compound 12 (Figure 4) was found in the presence of the compounds. The as-observed quenching (which is in good agreement (R = 0.99) with the linear Stern–Volmer equation [72]) may be attributed to the competition of compounds
  • (up to the value of r = 0.35) [11]. EB-displacement studies The ability of compounds 11 and 12 to displace EB from its DNA–EB conjugate was investigated by fluorescence emission spectroscopy. The Stern–Volmer constant (KSV, in M−1) was used to evaluate the quenching efficiency for each compound
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Published 09 Mar 2020
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