Synthesis, crystal structures and properties of carbazole-based [6]helicenes fused with an azine ring

• Daria I. Tonkoglazova,
• Anna V. Gulevskaya,
• Konstantin A. Chistyakov and
• Olga I. Askalepova

Beilstein J. Org. Chem. 2021, 17, 11–21, doi:10.3762/bjoc.17.2

• were used as starting materials. To discern the effect of merging an azine moiety within a helical skeleton, the X-ray structures, UV–vis absorption and fluorescence spectra of the helicenes were investigated and compared to that of the parent carbazole-based [6]helicene (7H-phenanthro[3,4-c]carbazole

• ]helicenes 10 only weak fluorescence in the solution under UV irradiation was observed (Table 7, see also Supporting Information File 1, Figures S42–S45). Helicenes 10b and 10c exhibited blue emission with emission peaks at 481 and 440 nm, respectively. Quinoxaline-fused helicene 10a demonstrated a yellow

• ]helicenes 10. Supporting Information Supporting Information File 76: Experimental procedures and analytical data, copies of 1H and 13C NMR spectra of all new compounds, X-ray data for 9c and 10a–c, HPLC spectra of helicenes 10a–c, UV–vis and fluorescence spectra of 10a–c. Acknowledgements The authors

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

• Hisham Qrareya,
• Lorenzo Meazza,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 3008–3014, doi:10.3762/bjoc.16.250

• that the fluorescence is significantly red shifted (about 30 nm) with respect to that of the corresponding diethyl aryl phosphates (see Figure 1 and Figure 2). On the other hand, when focusing on compound 3a, we noticed the presence of two emission bands located at 307 and 360 nm, respectively (see

• Figure 3) and their relative intensity was solvent dependent. Indeed, the band at 360 nm is favored and slightly blue shifted when increasing the proticity of the medium (see the comparison of the fluorescence spectra obtained in methanol and in a methanol/TFE 4:1 mixture, Figure 3). A similar behavior

• selected diaryl- and triaryl phosphates 1 and 3. Supporting Information Supporting Information File 406: Experimental section, fluorescence, and 1H and 13C NMR spectra. Funding H. Q. thanks the Arab American University-Palestine (AAUP) for financial support, and the University of Pavia (Italy) for

Selected peptide-based fluorescent probes for biological applications

• Debabrata Maity

Beilstein J. Org. Chem. 2020, 16, 2971–2982, doi:10.3762/bjoc.16.247

• fluorescence techniques have attracted immense interest. Synthetic peptide-based fluorescent probes are advantageous over protein-based sensors, since they are synthetically accessible, more stable, and can be easily modified in a site-specific manner for selective biological applications. Peptide receptors

• organic fluorophore (reporter) with a specific peptide sequence is the common approach for designing peptide-based fluorescent probes [16]. Fluorophores on peptidic arms perform as reporter during the interaction with biomolecules [17][18]. The interaction with biomolecules will alter the fluorescence

• intensity, lifetime or excitation/emission maxima. The fluorescence turn-on response offers a bright signal against a dark background, which maximizes spatial resolution than the fluorescence turn-off signal [19]. A shift in the absorption/emission spectrum is also advantageous as the changes in ratio of

Naphthalonitriles featuring efficient emission in solution and in the solid state

• Sidharth Thulaseedharan Nair Sailaja,
• Iván Maisuls,
• Jutta Kösters,
• Alexander Hepp,
• Andreas Faust,
• Jens Voskuhl and
• Cristian A. Strassert

Beilstein J. Org. Chem. 2020, 16, 2960–2970, doi:10.3762/bjoc.16.246

• scattering (DLS). The steady-state and time-resolved photoluminescence spectroscopy studies revealed that all the molecules show intense fluorescence both in solution and in the aggregated state. In THF solutions, a blue emission was observed for the unsubstituted (H), methyl- (Me) and tert-butyl- (t-Bu

• -containing substituents such as NMe2 possess more electron-donating ability than the S-based moieties such as SMe. Moreover, it was found that NMe2 showed higher luminescence quantum yields (ΦF) in comparison to SMe, indicating that N-substituted groups could enhance the fluorescence intensity. Therefore

UV resonance Raman spectroscopy of the supramolecular ligand guanidiniocarbonyl indole (GCI) with 244 nm laser excitation

• Tim Holtum,
• Vikas Kumar,
• Daniel Sebena,
• Jens Voskuhl and
• Sebastian Schlücker

Beilstein J. Org. Chem. 2020, 16, 2911–2919, doi:10.3762/bjoc.16.240

• strengths. Various spectroscopic techniques can be employed for monitoring these changes. For example, electronic absorption or fluorescence spectroscopy can probe the spectral differences due to the complexation of the supramolecular ligand with a peptide or protein. However, electronic spectroscopies

• Kerr-gate for temporally separating the Raman scattering from the time-delayed fluorescence or in the frequency domain by using shorter excitation wavelengths for blue-shifting the UVRR signal away from the UV-excited autofluorescence. In this study, we have demonstrated the performance of UVRR

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

• mispairs with a reduced ATP affinity. A fluorescence spectroscopy assay and a binding assay with immobilized ATP were used to evaluate the aptamer derivatives. Upon the addition of one Ag(I) ion per mispair, stabilizing Im–Ag(I)–Im base pairs were formed. As a result, the affinity of the aptamer derivative

• observed in the CD spectra, indicating that the formation of the Ag(I)-mediated base pairs as deduced from the melting curves does not influence the overall DNA topology. This is a well-known feature of the Im–Ag(I)–Im base pair [31]. Fluorescence spectroscopy assay In 2003, the ATP/AMP-binding aptamer was

• ’ terminus (Figure 4A and Figure 5). In the absence of AMP, the sequences should form a regular duplex structure, with the fluorescence of the fluorescein being quenched by the DABCYL moiety located nearby. In the presence of AMP and Ag(I), the aptamer should instead form the aptamer:AMP complex, releasing

One-pot multicomponent green Hantzsch synthesis of 1,2-dihydropyridine derivatives with antiproliferative activity

• Giovanna Bosica,
• Kaylie Demanuele,
• José M. Padrón and
• Adrián Puerta

Beilstein J. Org. Chem. 2020, 16, 2862–2869, doi:10.3762/bjoc.16.235

• reported by Cao and collaborators [19]. Catalyst characterization and recyclability The catalyst was analyzed by X-ray fluorescence (XRF) spectroscopy in order to ascertain the PW/Al2O3-support ratio. The mass percentage ratio of tungsten, which is the main component of the catalyst, and aluminium, the

Changed reactivity of secondary hydroxy groups in C8-modified adenosine – lessons learned from silylation

• Jennifer Frommer and
• Sabine Müller

Beilstein J. Org. Chem. 2020, 16, 2854–2861, doi:10.3762/bjoc.16.234

• . Accordingly, the field has developed to a stage that allows custom-design of RNA probes and tools for specific application. For example, investigations of RNA structures by NMR, EPR, or fluorescence spectroscopy require labeling of the RNA molecules with specific reporter groups [2][4][7][8][9][10]. Likewise

Using multiple self-sorting for switching functions in discrete multicomponent systems

• Amit Ghosh and
• Michael Schmittel

Beilstein J. Org. Chem. 2020, 16, 2831–2853, doi:10.3762/bjoc.16.233

• self-sorting protocols. The present mini review will provide an overview over the latest advancements in this field with a focus on reversibly switchable functions in discrete supramolecular systems. Keywords: copper; fluorescence; self-assembly; self-sorting; zinc porphyrin; Introduction Since self

• reversibility was achieved by the addition of the rhodium porphyrin 19 that reversed the system reviving the state SelfSORT-I. Since both self-sorted states exhibited a distinct fluorescence due to the changes at the zinc porphyrin sites, luminescence was used for the selective detection of DABCO in a mixture

• innovative catch–release system with multiple functions combined the ON/OFF-adjustment of silver(I) catalysis and fluorescence monitoring [59]. Actually, the ratiometric luminescence response allowed the exact monitoring of the catalytic activity. In the initial incomplete self-sorting (state SelfSORT-I

Synthesis and investigation of quadruplex-DNA-binding, 9-O-substituted berberine derivatives

• Jonas Becher,
• Daria V. Berdnikova,
• Heiko Ihmels and
• Christopher Stremmel

Beilstein J. Org. Chem. 2020, 16, 2795–2806, doi:10.3762/bjoc.16.230

• experiments. For that purpose, the DNA melting temperature Tm of the dye-labeled oligonucleotides F21T and Fa2T (for sequence see caption of Figure 2) was monitored by fluorescence spectroscopy, as the thermally induced unfolding of the quadruplex disrupts the Förster resonance energy transfer (FRET) between

• the ligands 4a–e on the addition of G4-DNA is the result of a sufficiently tight complexation. As this fluorescence light-up effect depends significantly on the length of the linker chain n, it is also concluded that the ligands with the strongest effect, i.e., 4c and 4d (n = 4 and 5), have a more

• the groove or loops has a direct influence on the strength and mode of the terminal π-stacking of the berberine unit. The tighter binding with better fitting of the side chain to the binding site is further supported by the observation that both ICD and the fluorescence light-up effect are the

Easy access to a carbohydrate-based template for stimuli-responsive surfactants

• Thomas Holmstrøm,
• Daniel Raydan and
• Christian Marcus Pedersen

Beilstein J. Org. Chem. 2020, 16, 2788–2794, doi:10.3762/bjoc.16.229

• metal-binding event. This study was carried out by having pyrene fluorophores attached to the two non-chelating positions, giving rise to excimer fluorescence when the distance between them was decreased due to the ring flip [12]. Carbohydrates with gluco stereochemistry have also been used as templates

Encrypting messages with artificial bacterial receptors

• Pragati Kishore Prasad,
• Naama Lahav-Mankovski,
• Leila Motiei and
• David Margulies

Beilstein J. Org. Chem. 2020, 16, 2749–2756, doi:10.3762/bjoc.16.225

• receptors is described. We show that the binding of DNA-based artificial receptors to E. coli expressing His-tagged outer membrane protein C (His-OmpC) induces a Förster resonance energy transfer (FRET) between the dyes, which results in the generation of a unique fluorescence fingerprint. Because the

• cell decreases over time. This occurs because each bacterium continuously divides, which forces the synthetic receptors to split between the two daughter cells (Figure 2A). The manifestation of this phenomenon was experimentally validated [2] by observing a decrease in the fluorescence generated by the

• security systems that can generate (pseudo) random fluorescence patterns [4][5][6]. Originally, the pattern-generating probes (or ID-probes [24]) were designed to detect multiple different analytes and their combinations [24][25][26]. In a later stage, we showed that the unique emission fingerprints

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

• 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

• compact arrangement of the stacked pyrene chromophores and this restriction of internal motion might have resulted in a higher excimer intensity [71]. In order to see whether the presence of other phosphate analytes interfered in ATP detection, fluorescence enhancements of PBIm12 (75 µM), for only ATP (50

• fluorescence experiments applying the time correlated single photon counting (TCSPC) method. 1H and 13C NMR were performed on Jeol 400 MHz and Bruker 500 MHz spectrometers. Mass spectra were recorded in a Bruker mass spectrometer. SEM images was recorded by using the instrument CARL ZEISS (model SUPRA 55VP

Enzyme-instructed morphological transition of the supramolecular assemblies of branched peptides

• Dongsik Yang,
• Hongjian He and
• Bing Xu

Beilstein J. Org. Chem. 2020, 16, 2709–2718, doi:10.3762/bjoc.16.221

• and 4 h. While the control cells (without adding 1 or 2) showed little fluorescence, the cells treated with RPE and 1 or 2 started to show many red fluorescent puncta inside the cells after 2 h. The puncta remained inside the cells at 4 h and showed little change (Figure 6). These results indicate

Optical detection of di- and triphosphate anions with mixed monolayer-protected gold nanoparticles containing zinc(II)–dipicolylamine complexes

• Lena Reinke,
• Julia Bartl,
• Marcus Koch and
• Stefan Kubik

Beilstein J. Org. Chem. 2020, 16, 2687–2700, doi:10.3762/bjoc.16.219

• sensing [1][2][3][4][5][6]. The analyte can be detected by relying on the enhancement of the Raman scattering intensity, if it is bound close to the gold surface (surface enhanced Raman scattering, SERS), for example, or by the release from the metal surface of a chromophore the fluorescence of which is

Synthesis and characterization of S,N-heterotetracenes

• Astrid Vogt,
• Florian Henne,
• Christoph Wetzel,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2020, 16, 2636–2644, doi:10.3762/bjoc.16.214

• (Table 1). Fluorescence quantum yields were far below 1% except for hexacene 22, which showed a very moderate value of 1.9%. This result is in line with the series of S,N-heteroacenes where noticeable fluorescence started with heptacene SN7 (ϕem = 19%) reaching 93% for the longest tridecamer SN13 [17][37

• ', and SN4''. UV–vis absorption spectra of TTA, Hex-SN4 9, Pr-SN4'' 33 and fluorescence spectrum of 33 in THF at rt (left) and corresponding cyclic voltammograms in dichloromethane/tetrabutylammonium hexafluorophosphate (0.1 M), 100 mV/s (right). Energy diagram of the frontier molecular orbitals of

Water-soluble host–guest complexes between fullerenes and a sugar-functionalized tribenzotriquinacene assembling to microspheres

• Si-Yuan Liu,
• Xin-Rui Wang,
• Man-Ping Li,
• Wen-Rong Xu and
• Dietmar Kuck

Beilstein J. Org. Chem. 2020, 16, 2551–2561, doi:10.3762/bjoc.16.207

• -fullerene in co-organic solvents and aqueous solution was investigated by fluorescence spectroscopy and ultraviolet-visible spectroscopy. The association stoichiometry of the complexes TBTQ-(OG)6 with C60 and TBTQ-(OG)6 with C70 was found to be 1:1 with binding constants of Ka = (1.50 ± 0.10) × 105 M−1 and

• order to investigate the host–guest relationship between TBTQ-(OG)6 and fullerenes, fluorescence titration experiments were performed in toluene/DMSO 1:1 (v/v), in which both the host and the guest components could be dissolved, instead of in water. As shown in Figure 2, the spectrum of TBTQ-(OG)6

• concentration of the fullerenes C60 and C70 increase, the emission is significantly quenched, indicating the photoinduced energy transfer from TBTQ-(OG)6 to the fullerenes [47][48]. Molar ratio plots (see Figure S16, Supporting Information File 1) on the basis of the fluorescence titration experiments suggested

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

• the lines and decreases the signal intensities even more. In addition, the stabilization of the 14-3-3 peptide interaction in the presence of the ligand was confirmed by biochemical assays such as isothermal titration calorimetry (ITC) and fluorescence anisotropy. On a quest for modulators of 14-3-3

• fluorescence screening, yielding less false positive hits due to ligand aggregation or auto-fluorescence, while at the same time identifying the ligand binding site. Specific amino acid labeling For larger and intrinsically disordered proteins (IDPs), signal overlap in 1H,15N-HSQC/TROSY-HSQC spectra becomes a

• for measuring binding affinities, such as isothermal titration calorimetry (ITC) or fluorescence anisotropy/polarization, are only able to provide an averaged KD. Outlook In the last two decades, additional NMR methods have been developed to extend the size limits of NMR spectroscopy to very large

Synthesis of 1,4-benzothiazinones from acylpyruvic acids or furan-2,3-diones and o-aminothiophenol

• Ekaterina E. Stepanova,
• Maksim V. Dmitriev and
• Andrey N. Maslivets

Beilstein J. Org. Chem. 2020, 16, 2322–2331, doi:10.3762/bjoc.16.193

• studies on biological activity, chemosensors, and fluorescence, were developed via the reaction of furan-2,3-diones or acylpyruvic acids in the presence of carbodiimides with o-aminothiophenols. The target enaminones were formed together with pharmaceutically interesting 2-hydroxy-2H-1,4-benzothiazin-3(4H

• potential Cu2+ chemosensors [14], and their BF2 chelates, as multicolor fluorescence complexes, some of which exhibited aggregation-induced emission (AIE) properties [15]. In addition, enaminones I and II proved themselves to be versatile and available building blocks for the synthesis of various

• fused to 1,4-benzothiazin-2-one moieties, which may be interesting for studies on biological activity, chemosensors, and fluorescence. The first approach is based on the reaction of furan-2,3-diones 5 with o-aminothiophenols 1 in acetonitrile. This approach gave less side products, but the yields of

Chan–Evans–Lam N1-(het)arylation and N1-alkеnylation of 4-fluoroalkylpyrimidin-2(1H)-ones

• Viktor M. Tkachuk,
• Oleh O. Lukianov,
• Mykhailo V. Vovk,
• Isabelle Gillaizeau and
• Volodymyr A. Sukach

Beilstein J. Org. Chem. 2020, 16, 2304–2313, doi:10.3762/bjoc.16.191

• pyrimidin-2(1H)-ones 5a–e exhibit fluorescence properties with emission of λmax = 490–532 nm in CH2Cl2 solution. In order to analyze the effect exerted on the Chan–Evans–Lam arylation by 4-, 5-, and 6-substituents on the pyrimidine ring and also aiming at the further functionalization of pyrimidin-2(1H)-one

Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties

• Anka Utama Putra,
• Deniz Çakmaz,
• Nurgül Seferoğlu,
• Alberto Barsella and
• Zeynel Seferoğlu

Beilstein J. Org. Chem. 2020, 16, 2282–2296, doi:10.3762/bjoc.16.189

• ][12][13][14]. Among dyestuffs classes, the push-pull fluorescent dyes are renowned to own such special behaviors. The push-pull dyes generate higher charge delocalization upon excitation, thus enhance both polarizability and fluorescence emission [12][13][14][18]. The charge delocalization upon

• frontier molecular orbitals of the dyes are shown in Figure S92 in Supporting Information File 1. Solvatochromic studies on emissions were also done to gain insights into the photophysical behavior of the new push-pull dyes bearing free amino and azomethine groups. Therefore, the fluorescence spectra of

• all dyes 3–7 and 8–12 were recorded in the same solvents of various polarities that were used in the UV–vis studies, and the results are summarized in Table 1 and Table S1 (Supporting Information File 1). All dyes showed fluorescence properties and there was no direct correlation of the increase of

The B & B approach: Ball-milling conjugation of dextran with phenylboronic acid (PBA)-functionalized BODIPY

• Patrizia Andreozzi,
• Lorenza Tamberi,
• Elisamaria Tasca,
• Gina Elena Giacomazzo,
• Marta Martinez,
• Mirko Severi,
• Marco Marradi,
• Stefano Cicchi,
• Sergio Moya,
• Giacomo Biagiotti and
• Barbara Richichi

Beilstein J. Org. Chem. 2020, 16, 2272–2281, doi:10.3762/bjoc.16.188

• solution-based synthetic route. PBA-BODIPY dextran assembles into nanoparticles of around 200 nm by hydrophobic interactions. The resulting PBA-BODIPY dextran nanoparticles retain an apolar interior as proved by pyrene fluorescence, suitable for the encapsulation of hydrophobic drugs with high

• shoulder at shorter wavelength (λabs = 364 nm) is typical for a symmetric dye. Normalized fluorescence spectra of conjugate Dex-1b were recorded at two different excitation wavelengths (λexc = 380 and 460 nm) and they are shown in Figure 3B and Figure S2 (Supporting Information File 1). The maximum

• assemblies of the conjugate Dex-1b a simple experiment with pyrene was conducted. It is well known that the fluorescence spectrum of pyrene is very sensitive to the polarity of the environment [37]. Indeed, the ratio (I1/I3) between the first (I1 = 372 nm) and the third bands (I3 = 383 nm) in the emission

Tools for generating and analyzing glycan microarray data

• Akul Y. Mehta,
• Jamie Heimburg-Molinaro and
• Richard D. Cummings

Beilstein J. Org. Chem. 2020, 16, 2260–2271, doi:10.3762/bjoc.16.187

• microarray scanner (for example, Genepix 4400A). Microarray scanners are fluorescence scanners which utilize laser technology, such that the excitation wavelength is generated by specific lasers. Commonly used laser wavelengths are 488 nm, 532 nm, 594 nm and 635 nm, which match with usual fluorophore labels

• the slide. Thus, high-resolution images (2.5–10 μm/pixel) yield adequate data points for glycan microarray spots to provide lower standard deviations between replicate spots. The fluorescence intensity of the spots can be fine-tuned by controlling the laser power (also called LP) and the

• photomultiplier tube gain (also called PMT Gain). The image produced is saved as a TIFF image, usually with headers which describe the scanner settings used to acquire the image, and the intensity at each pixel is saved as the relative fluorescence units (RFU) for those scan settings. Spot alignment and data

Naphthalene diimide bis-guanidinio-carbonyl-pyrrole as a pH-switchable threading DNA intercalator

• Poulami Jana,
• Filip Šupljika,
• Carsten Schmuck and
• Ivo Piantanida

Beilstein J. Org. Chem. 2020, 16, 2201–2211, doi:10.3762/bjoc.16.185

• the DNA/RNA conjugate NDI-GCP2 showed also aggregation along the ds-polynucleotide and AFM and DLS demonstrated that NDI-GCP2 has pronounced ds-DNA condensation ability. Keywords: AFM; circular dichroism; DNA/RNA recognition; fluorescence; guanidinio-carbonyl-pyrrole; naphthalene diimide

• monitoring, fluorescence is still the most popular method [8][9][10][11]. However, many new techniques or established ones with increased sensitivity are constantly improved or developed to report complementary to fluorescence. For instance, circular dichroism (CD) spectropolarimetry, highly sensitive to

• chiral properties of the DNA or RNA helical structures [12][13], could also take advantage of induced CD spectrum (ICD) in the visible spectrum range of small achiral dyes, which they show only upon binding to DNA/RNA [14]. Moreover, with recent advances in fluorescence emission-based polarisation

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

• cleavage reactions [80] and 1,5-HAT [81] and iii) the excited state of the simple organic molecule target can possess an ultrashort lifetime [82] that precludes photochemistry in favor of photophysical or nonradiative deactivation, e.g., fluorescence or internal conversion (IC). Instead of direct UV