Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

• Alexander Zika and
• Franziska Gröhn

Beilstein J. Org. Chem. 2021, 17, 166–185, doi:10.3762/bjoc.17.17

• suggests that the changes of the structure depend on the deprotonation of the photoacid due to irradiation and the subsequently higher charged molecule. The last two steps for cycle II are as in cycle I and the size and structure of the assemblies switch back to the starting point. Interestingly, these two

• ), and a photoacid. Ternary assemblies with sizes in the hundred-to-few hundred nanometers range in aqueous solution exhibit a multi-addressable size and shape. The concept exploits the unique property of the photoacid to form a more highly charged molecule and to switch the Flavy molecule in the same

Selected peptide-based fluorescent probes for biological applications

• Debabrata Maity

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

• binding GCP moiety. In between these two arms, a fluorophore (aminonaphthalimide for 4 and diethylaminocoumarin for 5) is linked to a third arm. Compounds 4 and 5 are weakly fluorescent and show significant “switch-on” fluorescence response upon interaction with dsDNA (Figure 5B). Probe 4 shows preference

• (Figure 9). Sensors 10 and 11 switch from an open form to a folded form upon binding to heparin, which give rise to a ratiometric fluorescence signal. Upon the heparin binding, the emission switches from the pyrene monomer to the excimer for 10, and the FRET process is enabled between a naphthalene donor

• peptide shows “switch-on” fluorescence response upon interaction with nucleic acids. Reproduced with permission from [32], Maity et al., “Peptide‐Based Probes with an Artificial Anion‐Binding Motif for Direct Fluorescence “Switch‐On” Detection of Nucleic Acid in Cells”, Chem. – Eur. J. © 2017 Wiley‐VCH

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

• circumvented either by temporally discriminating the Raman signal from the autofluorescence by using an optical switch such as a Kerr gate [18][19], or by using short excitation wavelengths for spectrally separating the UVRR signals from the UV-excited autofluorescence. The latter approach is achieved by

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

• (or removal) of external triggers, allowing to switch the nucleic acid function [8]. For example, DNA can be used in nanotechnology to create mechanically moving systems such as walkers, fueled by the addition of appropriately designed oligonucleotides [9]. Moreover, external triggers can be applied

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

• . An astounding modus operandi of a switchable catalytic system was realized based on information processing. The switchable system actually did not rely on a molecular switch in different toggling states, but on a smart seven-component mixture that reversibly regulated two diverse catalytic ON/OFF

• . Communication between the nanoswitch 21 and the supramolecular assemblies [Cu4(22)2(24)2]4+ or [Cu6(23)2(24)3]6+ was guided by a double self-sorting. (a) The chemical structures and cartoon representations of the switch 25, the decks 26 and 27, and the bipeds 28 and 29. (b) The double self-sorting led to a

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

• for conformational switches but have, to our knowledge, never been used as stimuli-responsive surfactants [13][14]. The compounds would have the benefit of being generally inexpensive due to the high production of glucose. However, going from glucose to a conformational switch often involves time

• surfactant with amphiphilic properties induced by the presence of Zn2+ ions (Figure 1b). In order to synthesize a glucopyranose-based molecular switch, a 2,4- or 3,6-functional group pattern is needed as these positions reside cis on the ring, making them pointing in the same direction of the 1C4

Vicinal difluorination as a C=C surrogate: an analog of piperine with enhanced solubility, photostability, and acetylcholinesterase inhibitory activity

• Yuvixza Lizarme-Salas,
• Alexandra Daryl Ariawan,
• Ranjala Ratnayake,
• Hendrik Luesch,
• Angela Finch and
• Luke Hunter

Beilstein J. Org. Chem. 2020, 16, 2663–2670, doi:10.3762/bjoc.16.216

• motif is sometimes but not always an effective surrogate for E-alkenes suggests that this bioisosteric switch could be exploited more widely in medicinal chemistry as a means of increasing the selectivity of a lead compound towards its desired target. The natural product piperine (1) is the inspiration

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

• Jannis Ludwig,
• Tobias Moje,
• Fynn Röhricht and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2589–2597, doi:10.3762/bjoc.16.210

• )-porphyrins; photoswitch; record player molecules; spin state; spin switch; Introduction Molecular spin switches operated with visible light in homogeneous solution [1] or on surfaces [2], hold promise for a number of hitherto unprecedented applications such as switchable contrast agents [3][4][5][6][7

• substituents at the pyridine or imidazole part) to increase the Ni–ligand coordination strength. Strong coordination in turn improves the performance of the spin switch, namely the conversion rate to the cis isomer, the conversion rate to the high-spin state, as well as the thermal stability of the high-spin

• state. 4-Substituted pyridines exhibit a distinguished correlation between basicity and coordination strength as axial ligands with Ni-porphyrins [12]. Hence, Hammet σ values might be used to predict and to systematically optimize the performance of the spin switch. In previous studies we have shown

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

• Henrik Hupatz,
• Marius Gaedke,
• Hendrik V. Schröder,
• Julia Beerhues,
• Arto Valkonen,
• Fabian Klautzsch,
• Sebastian Müller,
• Felix Witte,
• Kari Rissanen,
• Biprajit Sarkar and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2020, 16, 2576–2588, doi:10.3762/bjoc.16.209

• and the redox unit, TTFC8 offers the best compromise of sufficiently high binding constants combined with sufficient Coulomb repulsion between the oxidized TTF and the ammonium ion to construct a molecular switch [35]. This trend can directly be translated to the smaller exTTFC7 and TTFC7, which

Leveraging glycomics data in glycoprotein 3D structure validation with Privateer

• Haroldas Bagdonas,
• Daniel Ungar and
• Jon Agirre

Beilstein J. Org. Chem. 2020, 16, 2523–2533, doi:10.3762/bjoc.16.204

• convey significantly more information than what is available through protein synthesis and the expression of the genetic code alone. For example, glycosylation is used as a switch to modulate protein activity [1]; glycosylation plays a crucial part in folding/unfolding pathways of some proteins in cells

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

• shifts for both 1H and 13C nuclei. Methylation of Lys and Arg occurs as posttranslational modification (PTM) of proteins in nature, often used as a switch to regulate protein interactions and thus their function [112][113]. The Crowley lab has used this advantage to study the binding of sulfonatocalix[4

Computational tools for drawing, building and displaying carbohydrates: a visual guide

• Kanhaya Lal,
• Rafael Bermeo and
• Serge Perez

Beilstein J. Org. Chem. 2020, 16, 2448–2468, doi:10.3762/bjoc.16.199

• , Ser or Thr, then structure building is limited by to a set of “rules” (limiting building options to known carbohydrates). These rules may be deactivated with a switch button to draw freely. A list of 13 monosaccharides is deployed, and sequential clicking allows their addition to the existing

• structure and definition of the associated glycosidic bond (the relative sizes of the options available related to their real statistical value for that particular linkage). Upon building some specific motifs, if they are recognised, an option for repeating units appears. Other switch buttons allow the user

Hierarchically assembled helicates as reaction platform – from stoichiometric Diels–Alder reactions to enamine catalysis

• David Van Craen,
• Jenny Begall,
• Johannes Großkurth,
• Leonard Himmel,
• Oliver Linnenberg,
• Elisabeth Isaak and
• Markus Albrecht

Beilstein J. Org. Chem. 2020, 16, 2338–2345, doi:10.3762/bjoc.16.195

• compared to Li[Li3(5)6Ti2] [35][36]. Thus, the higher amount of undesired monomer in solution of Li[Li3(1)3(6)3Ti2] resulted in a partial switch-off of the stereoselectivity. Screening of the dienophile The variation of the dienophile was studied in chloroform using the helicate Li4[(1)3(4)3Ti2]. N

• systems possessing catalytic activity with improved solubility. Formation of hierarchically assembled lithium-bridged titanium(IV) helicates as well as the ligands used for the stereoselective Diels–Alder reaction. Previously reported on/off switch for “remote-controlled” [23][24][25][26][27][28][29][30

Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst

• Jannis Ludwig,
• Julian Helberg,
• Hendrik Zipse and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2119–2126, doi:10.3762/bjoc.16.179

• + ion. Light of 435 nm (violet) isomerizes the ligand back to the trans configuration, which decoordinates for steric reasons. This so-called record player design has been used previously to switch the spin state of Ni2+ between singlet and triplet. We now use the coordination/decoordination process to

• switch the catalytic activity of the dimethylaminopyridine (DMAP) unit. DMAP is a known catalyst in the nitroaldol (Henry) reaction. Upon coordination to the Ni2+ ion, the basicity of the pyridine lone pair is attenuated and hence the catalytic activity is reduced. Decoordination restores the catalytic

• activity. The rate constants in the two switching states differ by a factor of 2.2, and the catalytic switching is reversible. Keywords: catalysis; Ni(II)-porphyrins; nucleophilic catalyst; photoswitch; record player molecules; spin switch; Introduction Photoswitchable catalysis has been realized

Design, synthesis and application of carbazole macrocycles in anion sensors

• Alo Rüütel,
• Ville Yrjänä,
• Sandip A. Kadam,
• Indrek Saar,
• Mihkel Ilisson,
• Astrid Darnell,
• Kristjan Haav,
• Tõiv Haljasorg,
• Lauri Toom,
• Johan Bobacka and
• Ivo Leito

Beilstein J. Org. Chem. 2020, 16, 1901–1914, doi:10.3762/bjoc.16.157

• possibility was investigated after the production of the first macrocycles bearing tert-butyl substituents, we decided to not switch substituents. The formation of macrocycles from 8 was achieved following two different synthetic strategies. For receptors MC003–MC010, amide bond formation was carried out

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• the regiochemistry for terminal alkynes, affording the products substituted at the β-position. This regiochemistry switch might be regarded as the Holy Grail in Pauson–Khand chemistry. The synthetic potential of this methodology was demonstrated by the formal total synthesis of α-cuparenone [74][75

Models of necessity

• Timothy Clark and
• Martin G. Hicks

Beilstein J. Org. Chem. 2020, 16, 1649–1661, doi:10.3762/bjoc.16.137

• it is necessary to switch to the molecular-orbital picture to treat, for instance, the Woodward–Hoffmann rules [29]. Similarly, an extended version of the Lewis model exists alongside the molecular-orbital picture in inorganic chemistry. Is this not a solution to the problems described above

• ontologies [11] or personal paradigms [76] of chemists are assembled from available models and switch happily between them. Consider, for instance, the alternative Woodward–Hoffmann [29] and Dewar–Zimmerman [80][81] rules for electrocyclic reactions. They can be used interchangeably and both give correct

• chemist who uses predominantly the Lewis bonding picture or an inorganic chemist rooted in the VSEPR model switch quite happily to qualitative molecular-orbital arguments to explain electrocyclic reactions or the structure of ferrocene, even in teaching. In contrast, cheminformatics will need to adopt a

Development of fluorinated benzils and bisbenzils as room-temperature phosphorescent molecules

• Shigeyuki Yamada,
• Takuya Higashida,
• Yizhou Wang,
• Masato Morita,
• Takuya Hosokai,
• Kaveendra Maduwantha,
• Kaveenga Rasika Koswattage and
• Tsutomu Konno

Beilstein J. Org. Chem. 2020, 16, 1154–1162, doi:10.3762/bjoc.16.102

• deactivation process from the lowest singlet (S1) excited state to the ground (S0) state [9]. Interestingly, for such π-conjugated molecules, suitable structural modifications can switch the radiative S1→S0 process to another radiative deactivation process from the triplet (T1) excited state to S0 via an S1→T1

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• excellent E:Z ratios within the resulting alkenes. This methodology could be applied to a wide variety of compounds, including those containing heterocycles (176–178). In a later study [67], they found that by changing ligands, a dramatic switch in the selectivity could be induced in silyl additions to

Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo

• Alexander Sailer,
• Franziska Ermer,
• Yvonne Kraus,
• Rebekkah Bingham,
• Ferdinand H. Lutter,
• Julia Ahlfeld and
• Oliver Thorn-Seshold

Beilstein J. Org. Chem. 2020, 16, 125–134, doi:10.3762/bjoc.16.14

• colchicine per se, aiming at compounds where one isomer would be almost biologically inactive such that light can be used to effect a photoisomerisation-based switch-on/switch-off of bioactivity. The end-to-end distance of the HTI scaffold is significantly longer than that in either the biaryl colchicine or

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion

• Sarah Kölsch,
• Heiko Ihmels,
• Jochen Mattay,
• Norbert Sewald and
• Brian O. Patrick

Beilstein J. Org. Chem. 2020, 16, 111–124, doi:10.3762/bjoc.16.13

• the intercalating monomers upon irradiation at 315 nm in the presence of DNA. As a result, it is possible to switch between these two ligands and likewise between two different binding modes by irradiation with different excitation wavelengths. Keywords: azoniahetarenes; DNA ligands

• intrinsic toxicity of the employed drugs [11][12][13]. As a result, there is an urgent need for DNA-targeting chemotherapeutic reagents that can be activated with an external stimulus only at the desired point of action. In this context, light offers several distinct advantages to switch on the activity of

• an otherwise inactive substrate (prodrug) because light is noninvasive, traceless, and easy to apply, and it enables local and temporal control [14]. To this end, photochromic systems appear to be highly attractive as a basis for photocontrollable substrates because they allow to switch the

Photocontrolled DNA minor groove interactions of imidazole/pyrrole polyamides

• Sabrina Müller,
• Jannik Paulus,
• Jochen Mattay,
• Heiko Ihmels,
• Veronica I. Dodero and
• Norbert Sewald

Beilstein J. Org. Chem. 2020, 16, 60–70, doi:10.3762/bjoc.16.8

• (Py/Im) and TA (Hp/Py). However, N-methylhydroxypyrrole (Hp) is neither easy to synthesize nor sufficiently stable. In practice, therefore, Py/Py is used to address both AT and TA. Along this line, it is attractive to incorporate a molecular switch for the selective activation of an initially inactive

• switch in binding activity [29][30]. Importantly, it was demonstrated that the DNA binding was highly dependent on the linker length between the azobenzene and the distamycin moiety. Results and Discussion Here, we report on the design, synthesis, and characterization of photoswitchable minor groove

Light-controllable dithienylethene-modified cyclic peptides: photoswitching the in vivo toxicity in zebrafish embryos

• Sergii Afonin,
• Oleg Babii,
• Aline Reuter,
• Volker Middel,
• Masanari Takamiya,
• Uwe Strähle,
• Igor V. Komarov and
• Anne S. Ulrich

Beilstein J. Org. Chem. 2020, 16, 39–49, doi:10.3762/bjoc.16.6

• ) was recorded, and then in situ illumination (“photoactivation”) was applied to switch into the ring-open photoform and obtain the respective LD50(opened) values (see Figure 2 for the study design and the killing curves). Each time, 12–15 or 18–20 zebrafish embryos at 3 dpf were treated by applying the

Photoreversible stretching of a BAPTA chelator marshalling Ca²⁺-binding in aqueous media

• Aurélien Ducrot,
• Arnaud Tron,
• Robin Bofinger,
• Ingrid Sanz Beguer,
• Jean-Luc Pozzo and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2019, 15, 2801–2811, doi:10.3762/bjoc.15.273

• ions and switch between complexes of different molecularity, albeit largely in organic solvents [32]. Azobenzene is generally considered relatively resistant to fatigue and has been employed to evoke changes in different biological systems, including ion channels based on changes of properties between

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• azoarenes have been ortho-substitution of the benzene ring(s) or replacement of one of the benzenes for a pyrazole (to give arylazopyrazole switches). Here we study the combination of such high-performance features within a single switch architecture. Through computational analysis and experimental

• demonstrate slow thermal Z–E relaxation and the potential to switch with red light, while the o-fluoro compounds reported by Hecht and co-workers [13][14] offer excellent two-way isomerization with visible light and the longest thermal half-life reported for an azobenzene molecule (≈700 days at 25 °C) to date

• that it is indeed possible to combinatorially integrate two high performing azo switch fragments to discover switches with very long thermal half-lives (i.e., months to years). We sought to further explain the trends observed through theoretical analysis of the minimum-energy geometries and noncovalent