A chemist and biologist talk to each other about caged neurotransmitters

• Graham C.R. Ellis-Davies

Beilstein J. Org. Chem. 2013, 9, 64–73, doi:10.3762/bjoc.9.8

• isolation. Thus, to solve the biological problem provided by the biologist (Hess), a newer caging chromophore [18] had to be synthesized by a chemist (Carpenter). Thus, chemists came to play a crucial role in the caged compound field. Chemistry at the service of biology is not unusual or unique, as the

• nitroindolinyl-caged transmitters [26][27][32][36]. Because of this problem, chemists have resorted to inserting a spacer unit between the caging chromophore and the substrate [7][55][56][57][58][59]. This strategy has been very successful in creating some highly stable caged compounds, but sometimes at the

• of uncaging involves two completely distinct properties [80]. First, we must consider how well a molecule absorbs light, through the molar extinction coefficient, ε. This property measures how effectively a chromophore absorbs photons. Thus, fluorescein (ε = 80,000/M/cm) absorbs light much better

Polar reactions of acyclic conjugated bisallenes

• Reiner Stamm and
• Henning Hopf

Beilstein J. Org. Chem. 2013, 9, 36–48, doi:10.3762/bjoc.9.5

• valuable for structure assignment; they clearly show that the products obtained possess a conjugated triene chromophore. The formation of the monochlorides very likely proceeds via the carbocationic intermediates 49/50 and 52/53 (R = CH3). For the generation of the aromatic isomers of the substrate we

• of a diene chromophore (see Supporting Information File 1). Repeating the bromine addition experiment with the fully substituted bisallene derivative 11 also leads to bromine addition as demonstrated by GC–MS analysis of the raw product mixture, but all attempts to separate at least the major adducts

• importance are its amide bands (3515 and 1679 cm−1) in the IR spectrum and the absorption maximum at 284 nm in the electronic spectrum (triene chromophore). The central double bond of the triene system is trans-configured (3J = 15.2 Hz) [35]. The main product is the β-lactam derivate 71. Since this primary

Acylsulfonamide safety-catch linker: promise and limitations for solid–phase oligosaccharide synthesis

• Jian Yin,
• Steffen Eller,
• Mayeul Collot and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2012, 8, 2067–2071, doi:10.3762/bjoc.8.232

• linker 1 [13][14] (Figure 1) has been developed, which can be readily cleaved from the resin by basic methanolysis. The released chromophore-containing part, such as aromatic benzyl ether protecting groups, facilitates the purification of the synthetic oligosaccharides by HPLC. Final deprotection of the

Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

• up the photolysis of a strongly absorbing chromophore. Here, a thin film of the substrate solution flows down a glass plate or tube in close proximity to the light source. The short path length leads to very efficient irradiation. The downside is that residence time is short and often the solution

A simple and efficient dual optical signaling chemodosimeter for toxic Hg(II)

• Sabir H. Mashraqui,
• Sapna A. Tripathi,
• Sushil S. Ghorpade and
• Smita R. Britto

Beilstein J. Org. Chem. 2012, 8, 1352–1357, doi:10.3762/bjoc.8.155

• ratiometric or switch-on responses even for the paramagnetic metal ions [17][18][19]. The first luminescence chemodosimeter for Hg2+ was developed by Czarnik et al. and was based on the Hg2+-mediated desulfurization of anthracene-thioamide chromophore [20][21]. Following this pioneering report, several other

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

• mechanism, we examined the solvent effects on the chromophore conformation of CDNS by circular dichroism spectroscopy and also on the CDNS-sensitized photoisomerization. Indeed, the ICD intensity was enhanced upon the addition of ethanol to an aqueous solution of CDNS (Figure 2b), which encouraged us to

Partial thioamide scan on the lipopeptaibiotic trichogin GA IV. Effects on folding and bioactivity

• Marta De Zotti,
• Barbara Biondi,
• Cristina Peggion,
• Matteo De Poli,
• Haleh Fathi,
• Simona Oancea,
• Claudio Toniolo and
• Fernando Formaggio

Beilstein J. Org. Chem. 2012, 8, 1161–1171, doi:10.3762/bjoc.8.129

• nm) and near-UV (400–250 nm) CD spectra of the three peptides, recorded in 2,2,2-trifluoroethanol (TFE) solution, are illustrated in Figure 3. In the near-UV region, in which the peptide chromophore is known not to absorb, both ψ[CS-NH]2 and ψ[CS-NH]9 display two well-separated Cotton effects at

• intense maximum (265 nm) and an extremely weak maximum (320 nm) found in the corresponding region of the UV absorption spectra (not shown) of our peptides in the same solvent. We assign the two bands to the π→π* and n→π* transitions, respectively, of thioamide chromophore [29][30][32][33][34][35][36][40

• ][41][43]. We attribute the overall much less intense CD spectrum of ψ[CS-NH]5 in this region primarily to a thioamide chromophore positioned in this peptide between the two achiral Gly5 and Gly6 residues, i.e., it is significantly far apart from the nearest chiral center (the Leu7 α-carbon). In the

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• , azobenzene and glutamate derivative (MAG) was used as a photochromic agonist of an ionotropic glutamate receptor (iGluR) (Figure 5a) [89][90][91]. The chromophore consists of a terminal maleimide unit, which is associated covalently to the protein via a cysteine residue, a central azobenzene unit and a

Recent advances towards azobenzene-based light-driven real-time information-transmitting materials

• Jaume García-Amorós and
• Dolores Velasco

Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113

• -chromophore and the thermal cis-to-trans isomerisation, the kinetics and mechanism are also discussed as a key point for reaching azoderivatives endowed with fast thermal back-isomerisation kinetics. Keywords: kinetics; light-controlled materials; molecular switches; photochromic switches; push–pull

• similar behaviour: relaxation times of 33 min and 306 ms in toluene and ethanol, respectively [59]. The differential kinetic behaviour detected for azophenols 11–13 in toluene and ethanol clearly evidences that the intermolecular interactions established between both the chromophore and the solvent

Synthesis and anion recognition properties of shape-persistent binaphthyl-containing chiral macrocyclic amides

• Marco Caricato,
• Nerea Jordana Leza,
• Claudia Gargiulli,
• Giuseppe Gattuso,
• Daniele Dondi and
• Dario Pasini

Beilstein J. Org. Chem. 2012, 8, 967–976, doi:10.3762/bjoc.8.109

• (R)-7 [45] were prepared according to literature procedures. THF (Na), CH2Cl2 (CaH2) and CHCl3 (4 Å molecular sieves) were dried before use. Analytical thin-layer chromatography was performed on silica gel, chromophore-loaded, commercially available plates. Flash chromatography was carried out by

Diarylethene-modified nucleotides for switching optical properties in DNA

• Sebastian Barrois and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2012, 8, 905–914, doi:10.3762/bjoc.8.103

• by CD spectroscopy, but not in the case of the spiropyran form. Attempts to attach spiropyrans covalently to DNA are rare [26][27] and include our recent approaches to incorporate synthetically the spiropyran chromophore [28], by either DNA building block 1 [29] or by DNA base modifications 2 and 3

• buffer solutions [31], and (according to our experience) the DNA environment does not efficiently prevent this decomposition. (ii) Moreover, we found out that the spiropyran chromophore in the DNA environment loses its photoswitching abilities [29]. The second alternative, diarylethenes, have been

• linker between the chromophore and DNA base as the point of attachment. The purpose of this conformationally flexible tether is to overcome problems in the enzymatic activity by DNA polymerases in the context of primer-extension (PEX) or PCR studies [35][36][37]. However, the shortest possible linking of

meta-Oligoazobiphenyls – synthesis via site-selective Mills reaction and photochemical properties

• Raphael Reuter and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2012, 8, 877–883, doi:10.3762/bjoc.8.99

• absorption of the whole spectrum is noted due to the additional chromophore in the molecule. Upon irradiation at 356 nm (8 W hand-held UV lamp, at room temperature) all compounds underwent an E→Z isomerization, which can be seen as a decrease of the π–π* and an increase of the n–π* band. In this respect all

Enaminones in a multicomponent synthesis of 4-aryldihydropyridines for potential applications in photoinduced intramolecular electron-transfer systems

• Nouria A. Al-Awadi,
• Maher R. Ibrahim,
• Mohamed H. Elnagdi,
• Elizabeth John and
• Yehia A. Ibrahim

Beilstein J. Org. Chem. 2012, 8, 441–447, doi:10.3762/bjoc.8.50

•  2). This is expected to produce DHP with no substitution at the 2-position and different substituents at the 1-, 3-, 4- and 5-positions. This system contains the characteristic cyclic enaminone chromophore, which is expected to exhibit strong UV absorption with a maximum around 350 nm and extending

• studies of DHPs containing the enaminocarboxylate chromophore with suitable substituents in the 4-position [7][8]. The DHP products reported in the present synthesis allow an easy method for a wide range of DHP derivatives having this expected characteristic of a photoinduced intramolecular electron

Liquid-crystalline nanoparticles: Hybrid design and mesophase structures

• Gareth L. Nealon,
• Romain Greget,
• Cristina Dominguez,
• Zsuzsanna T. Nagy,
• Daniel Guillon,
• Jean-Louis Gallani and
• Bertrand Donnio

Beilstein J. Org. Chem. 2012, 8, 349–370, doi:10.3762/bjoc.8.39

• to emphasise the wider applicability of this approach to nanohybrid science. Fundamental studies into the photochemical activity of lipophilic azobenzene- and stilbene thiols (10, Figure 12) on Au NPs surfaces were reported [66], which indicated a chromophore-to-NP distance dependence of the

Imidazole as a parent π-conjugated backbone in charge-transfer chromophores

• Jiří Kulhánek and
• Filip Bureš

Beilstein J. Org. Chem. 2012, 8, 25–49, doi:10.3762/bjoc.8.4

• diimidazoles, benzimidazoles, bis(benzimidazoles), imidazole-4,5-dicarbonitriles, and imidazole-derived chromophores chemically bound to a polymer chain. Keywords: charge transfer; chromophore; conjugation; donor–acceptor system; imidazole; Introduction Over the past three decades, great progress has been

• devices, etc [1][2][3]. A typical one-component organic D-π-A chromophore consists of a π-conjugated system end-capped with strong electron donors D (e.g. NR2 or OR groups) and strong electron acceptors A (e.g. NO2 or CN groups). This D-π-A arrangement assures efficient intramolecular charge transfer (ICT

• solvents, and should be available in reasonable quantities. Hence, various five- and six-membered heterocycles were utilized as suitable π-conjugated chromophore backbones. Moreover, heteroatoms may act as auxiliary donors or acceptors and improve the overall polarizability of the chromophore. In this

One-pot four-component synthesis of pyrimidyl and pyrazolyl substituted azulenes by glyoxylation–decarbonylative alkynylation–cyclocondensation sequences

• Charlotte F. Gers,
• Julia Rosellen,
• Eugen Merkul and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2011, 7, 1173–1181, doi:10.3762/bjoc.7.136

• in a wide range of cosmetic formulations [30]. In addition, numerous azulene derivatives display appealing properties for material [31][32][33] and pharmaceutical sciences [34][35][36][37][38]. Furthermore, the use of the azulene moiety as part of a protecting group chromophore in carbohydrate

Microphotochemistry: 4,4'-Dimethoxybenzophenone mediated photodecarboxylation reactions involving phthalimides

• Oksana Shvydkiv,
• Kieran Nolan and
• Michael Oelgemöller

Beilstein J. Org. Chem. 2011, 7, 1055–1063, doi:10.3762/bjoc.7.121

• enable extensive penetration of light even at high chromophore concentrations. In addition, products are removed from the irradiated area thus preventing light-induced follow-up reactions or decompositions [17][18][19]. Recently, a number of photoreactions in microreactors have therefore been described

A novel high-yield synthesis of aminoacyl p-nitroanilines and aminoacyl 7-amino-4-methylcoumarins: Important synthons for the synthesis of chromogenic/fluorogenic protease substrates

• Xinghua Wu,
• Yu Chen,
• Herve Aloysius and
• Longqin Hu

Beilstein J. Org. Chem. 2011, 7, 1030–1035, doi:10.3762/bjoc.7.117

• acid/peptide conjugates liberates the free chromophore or fluorophore, allowing the convenient determination of the rate of enzyme catalysis with a UV or fluorescence spectrophotometer. p-Nitroaniline (pNA) is one of the most commonly used chromogenic reagents. The synthesis of peptide-pNAs usually

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

• transformation does not require H-atom abstraction from an external H-atom source such as CHD and DNA, and thus the DNA-damaging ability of this chromophore is not expected to be significant. Photophysics and kinetics of photoinduced electron transfer The fluorescence quenching by triethylamine (Et3N) was

• . A similar trend has been previously observed for the lifetimes of m-substituted enediynes [63]. The absorption spectra of all four acetylenes are shown in Figure 6. The core Ph-TFP-acetylene (Ph-TFP) chromophore without the amide group has no significant absorption at >320 nm. The lowest absorptions

• hydroxyl radical scavengers, glycerol and DMSO, protected DNA from the cleavage by 33 and 26%, respectively, whereas NaN3 showed ~43% protection. The large protecting effect of NaN3, the singlet oxygen scavenger, is consistent with the efficient photoaddition reaction of its chromophore via triplet

Novel carbazole–pyridine copolymers by an economical method: synthesis, spectroscopic and thermochemical studies

• Aamer Saeed,
• Madiha Irfan and
• Shahid Ameen Samra

Beilstein J. Org. Chem. 2011, 7, 638–647, doi:10.3762/bjoc.7.75

• is due to the optical transition attributed to the presence of the auxochromic OH group, which increases the conjugation length [31] and becomes part of extended chromophore. This effect is absent in the other compounds. The photoluminescence spectra of the polymer solutions of series P1 and P2 in

Stereogenic boron in 2-amino-1,1-diphenylethanol-based boronate–imine and amine complexes

• Sebastian Schlecht,
• Walter Frank and
• Manfred Braun

Beilstein J. Org. Chem. 2011, 7, 615–621, doi:10.3762/bjoc.7.72

• = 395 nm, typical for the imine chromophore, as observed for other boronate–imine complexes. The imine 7 also served for the preparation of the boronate–amine complex 10. For this purpose, it was reduced [22] with cyanoborohydride in methanol in the presence of hydrochloric acid to give the salt of the

• 10 in 63% isolated yield. The lack of any absorption at wavelengths higher than 350 nm indicated the absence of the imine chromophore. Here again the formation of the complex can be deduced from the 11B NMR shift of 5.5 ppm [21]. Suitable crystals of compound 10·CH3OH were obtained from methanol

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

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

• enthalpy of the radical ion pair formation, ΔEexcit = excitation energy of the chromophore, ΔEcoul = coulomb interaction energy of the radical ions and = half wave potential of donor and acceptor. If electron transfer pathways dominate, substitution reactions are found to prevail. However, if the electron

Photoinduced electron-transfer chemistry of the bielectrophoric N-phthaloyl derivatives of the amino acids tyrosine, histidine and tryptophan

• Axel G. Griesbeck,
• Jörg Neudörfl and
• Alan de Kiff

Beilstein J. Org. Chem. 2011, 7, 518–524, doi:10.3762/bjoc.7.60

• +, electronically excited phthalimides are potent electron acceptors [2]. The rich photochemistry of this chromophore has recently been reviewed [3][4]. Intramolecular hydrogen abstraction is an archetype process for electronically excited carbonyl groups (Norrish type II reaction). The 1,4-biradicals formed by γ

Supramolecular FRET photocyclodimerization of anthracenecarboxylate with naphthalene-capped γ-cyclodextrin

• Qian Wang,
• Cheng Yang,
• Gaku Fukuhara,
• Tadashi Mori,
• Yu Liu and
• Yoshihisa Inoue

Beilstein J. Org. Chem. 2011, 7, 290–297, doi:10.3762/bjoc.7.38

• of 7, where the included naphthalene chromophores are arranged in a right-handed screw [24]. As can be seen from Figure 3, naphthalene-capped γ-CD 6 gave only weak induced circular dichroism signals at the 1La and 1Bb bands of the naphthalene chromophore, the intensity of which was not concentration

• examination revealed that the FRET from the excited naphthalene on CD rim to AC included in the CD cavity is operative upon excitation of the naphthalene chromophore at 296 nm. Circular dichroism spectral studies revealed that the two AC molecules are arranged in a right-handed screw sense in the CD cavity

Effects of anion complexation on the photoreactivity of bisureido- and bisthioureido-substituted dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 278–289, doi:10.3762/bjoc.7.37

• auxiliary strategy was developed by Scheffer et al. which allows to influence the stereoselectivity of solid-state photoreactions by chiral counter ions [34]. This is accomplished by providing the chromophore under investigation with a carboxylic acid functionality and then by attaching a chiral

• latter in solution. For that purpose the dibenzobarrelene chromophore was functionalized with ureido or thioureido substituents, since these functionalities are strong hydrogen bonding donors, which may associate with (chiral) anions [38][39]. Moreover, the versatile use of urea and thiourea derivatives

• the dibenzobarrelene unit, by comparison with the absorption of the resembling dibenzobarrelene derivative 1d [45]. This observation indicates that the complexation of the chloride anion has no significant influence on the dibenzobarrelene chromophore, but rather on the trifluoromethyl-substituted