Photochemical synthesis
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Oxidative stress may cause extended tyrosine posttranslational modifications of peptides and proteins. The 3-nitro-L-tyrosine (Nit), which is typically formed, affects protein behavior during neurodegenerative processes, such as Alzheimer's and Parkinson's diseases. Such metabolic products may be conveniently detected at very low concentrations by surface enhanced Raman spectroscopy (SERS). Previously, we have explored the SERS detection of the Nit NO2 bending vibrational bands in a presence of hydrogen chloride (Niederhafner et al., Amino Acids 53:517-532, 2021, ibid). In this article, we describe performance of a new SERS substrate, "pink silver", synthesized photochemically. It provides SERS even without the HCl induction, and the acid further decreases the detection limit about 9 times. Strong SERS bands were observed in the asymmetric (1550-1475 cm-1) and symmetric (1360-1290 cm-1) NO stretching in the NO2 group. The bending vibration was relatively weak, but appeared stronger when HCl was added. The band assignments were supported by density functional theory modeling.
- Klíčová slova
- Nitration, Oxidative stress, Photochemical synthesis, Posttranslational protein modification (PTM), Silver colloids, Surface enhanced Raman spectroscopy (SERS),
- MeSH
- oxid dusičitý MeSH
- peptidy MeSH
- proteiny MeSH
- Ramanova spektroskopie * metody MeSH
- stříbro * chemie MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- oxid dusičitý MeSH
- peptidy MeSH
- proteiny MeSH
- stříbro * MeSH
A photoenolization reaction is shown to be the key reaction step in the preparation of substituted indan-1-ones as convenient precursors for the synthesis of donepezil, a well-known acetylcholinesterase inhibitor. Model 2,5-dialkylphenacyl chlorides, differently substituted in the alpha-carbon position, were found to produce indan-1-ones upon irradiation in non-nucleophilic solvents in high chemical yields via hydrogen chloride release. While direct excitation of 4,5-dimethoxy-2-methylphenacyl chloride led to a complex mixture of photoproducts, photolysis of the corresponding benzoate was found to form 5,6-dimethoxyindan-1-one in 62-72% chemical yields and a relatively low quantum efficiency (Phi approximately 0.02). This compound can then be easily converted to donepezil by standard synthetic steps described in the literature. Isotopic exchange and quenching experiments revealed that the product is obtained by the photoenolization process via the triplet excited state, while minor side-photoproducts originate from the singlet excited state. Irradiation of the reactant in neat acetone, used both as a triplet sensitizer and solvent at the same time, was found to form 5,6-dimethoxyindan-1-one exclusively in high (90%) chemical yield.
- Publikační typ
- časopisecké články MeSH
An electronic excited-state switching strategy has been utilized to control the selectivity of a key photochemical step in the total synthesis of indanorine. The excited-state character of 4,5-dimethoxy-2-methylphenacyl epoxide was changed from an unfavorable (3)π,π* state to a productive (3)n,π* state by a temporary structural modification, resulting in a relatively efficient and high-yielding formation of an indanone derivative. The corresponding structural modification was selected on the basis of quantum chemical calculations prior to the synthesis.
- Publikační typ
- časopisecké články MeSH
A temperature-sensitive photochemical nucleophilic aromatic substitution on 4-nitroanisole by a hydroxide ion in homogeneous solutions, in a two-phase system under phase-transfer catalysis conditions, and in the microwave field is reported. It was found that reaction regioselectivity dramatically changes with temperature in the region of -20 to 196 degrees C. The quantum yield of the 4-methoxyphenol formation was found to be temperature independent, in contrast to that of the 4-nitrophenol formation, suggesting that there is a temperature dependent process occurring after the partitioning between replacement of the nitro group and the methoxy group has taken place. The reaction was also investigated by using quantum chemical calculations. A technique for microwave-assisted photochemical synthesis is proposed as an efficient and practical tool for organic synthesis.
- Publikační typ
- časopisecké články MeSH
Stilbene derivatives are well-recognised substructures of molecular switches based on photochemically and/or thermally induced (E)/(Z) isomerisation. We combined a stilbene motif with two benzimidazolium arms to prepare new sorts of supramolecular building blocks and examined their binding properties towards cucurbit[n]urils (n=7, 8) and cyclodextrins (β-CD, γ-CD) in water. Based on the 1 H NMR data and molecular dynamics simulations, we found that two distinct complexes with different stoichiometry, i. e., guest@β-CD and guest@β-CD2 , coexist in equilibrium in a water solution of the (Z)-stilbene-based guests. We also demonstrated that the bis(benzimidazolio)stilbene guests can be transformed from the (E) into the (Z) form via UV irradiation and back via thermal treatment in DMSO.
- Klíčová slova
- cucurbit[n]uril, cyclodextrins, host-guest systems, molecular devices, stilbene switch,
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The study of the temperature-sensitive photochemical release of a carboxylic acid from 2,5-dimethylphenacyl ester is reported. Quantum yields of the benzoate ester degradation in benzene increased from 0.22 at room temperature to 0.28 at 50 degrees C whereas a more significant increase (nearly by a factor of 3) was observed in methanol and ethanol, reaching a high reaction efficiency (0.25) typically found in non-polar solvents. The reaction proceeds predominantly via the triplet pathway and the E-photoenol in the whole temperature range in methanol solution. A higher quantum efficiency in heated methanol is explained by enhancing the E-photoenol population. This picture was partially confirmed by the quantum chemical calculations. The 2,5-dimethylphenacyl chromophore is proposed as an efficient photoremovable protecting group for carboxylic acids in solutions under conventional or microwave-assisted heating for applications in organic synthesis, such as the solid-phase synthesis.
- MeSH
- časové faktory MeSH
- chemické modely MeSH
- estery chemie MeSH
- fotochemie MeSH
- magnetická rezonanční spektroskopie MeSH
- methanol chemie MeSH
- mikrovlny MeSH
- organická chemie metody MeSH
- spektrofotometrie MeSH
- světlo * MeSH
- teplota * MeSH
- ultrafialové záření MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- estery MeSH
- methanol MeSH
Recent ground-based observations of Venus have detected a single spectral feature consistent with phosphine (PH3) in the middle atmosphere, a gas which has been suggested as a biosignature on rocky planets. The presence of PH3 in the oxidized atmosphere of Venus has not yet been explained by any abiotic process. However, state-of-the-art experimental and theoretical research published in previous works demonstrated a photochemical origin of another potential biosignature-the hydride methane-from carbon dioxide over acidic mineral surfaces on Mars. The production of methane includes formation of the HC · O radical. Our density functional theory (DFT) calculations predict an energetically plausible reaction network leading to PH3, involving either HC · O or H· radicals. We suggest that, similarly to the photochemical formation of methane over acidic minerals already discussed for Mars, the origin of PH3 in Venus' atmosphere could be explained by radical chemistry starting with the reaction of ·PO with HC·O, the latter being produced by reduction of CO2 over acidic dust in upper atmospheric layers of Venus by ultraviolet radiation. HPO, H2P·O, and H3P·OH have been identified as key intermediate species in our model pathway for phosphine synthesis.
- Klíčová slova
- Density functional theory, Phosphine, Photochemistry, Quantum mechanical calculations, Venus,
- MeSH
- atmosféra MeSH
- fosfiny * MeSH
- fotochemické procesy MeSH
- methan MeSH
- mimozemské prostředí MeSH
- ultrafialové záření MeSH
- Venuše * MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- fosfiny * MeSH
- methan MeSH
- phosphine MeSH Prohlížeč
The oxidative photocyclization of aromatic Schiff bases was investigated as a potential method for synthesis of phenanthridine derivatives, biologically active compounds with medical applications. Although it is possible to prepare the desired phenanthridines using such an approach, the reaction has to be performed in the presence of acid and TEMPO to increase reaction rate and yield. The reaction kinetics was studied on a series of substituted imines covering the range from electron-withdrawing to electron-donating substituents. It was found that imines with electron-withdrawing substituents react one order of magnitude faster than imines bearing electron-donating groups. The 1H NMR monitoring of the reaction course showed that a significant part of the Z isomer in the reaction is transformed into E isomer which is more prone to photocyclization. The portion of the Z isomer transformed showed a linear correlation to the Hammett substituent constants. The reaction scope was expanded towards synthesis of larger aromatic systems, namely to the synthesis of strained aromatic systems, e.g., helicenes. In this respect, it was found that the scope of oxidative photocyclization of aromatic imines is limited to the formation of no more than five ortho-fused aromatic rings.
- Klíčová slova
- Schiff bases, azahelicenes, imines, phenanthridines, photocyclization,
- MeSH
- cykloadiční reakce metody MeSH
- fenantridiny chemická syntéza MeSH
- fotochemické oxidanty chemie MeSH
- fotochemické procesy MeSH
- oxidace-redukce MeSH
- Schiffovy báze chemie MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- fenantridiny MeSH
- fotochemické oxidanty MeSH
- Schiffovy báze MeSH
Herein, we report on surprisingly efficient photochemical vapor generation (PVG) of Ru, Re, and especially Ir, achieved from very dilute HCOOH media employing a thin-film flow-through photoreactor operated in flow injection mode. In the absence of added metal ion sensitizers, efficiencies near 20% for Ir and approximately 0.06% for Ru and Re occur in a narrow range of HCOOH concentrations (around 0.01 M), significantly higher than previously reported from conventionally optimized HCOOH concentrations (1-20 M). A substantial enhancement in efficiency, to around 9 and 1.5%, could be realized for Ru and Re, respectively, when 0.005 M HCOONa served as the PVG medium. The addition of metal ion sensitizers (particularly Cd2+ and Co2+) to 0.01 M HCOOH significantly enhanced PVG efficiencies to 17, 2.2, and 81% for Ru, Re, and Ir, respectively. Possible mechanistic aspects occurring in dilute HCOOH media are discussed, wherein this phenomenon is attributed to the action of 185 nm radiation available in the thin-film flow-through photoreactor. An extended study of PVG of Fe, Co, Ni, As, Se, Mo, Rh, Te, W, and Bi from both dilute HCOOH and CH3COOH was undertaken, and several elements for which a similar phenomenon appears were identified (i.e., Co, As, Se, Te, and Bi). Although use of dilute HCOOH media is attractive for practical analytical applications employing PVG, it is less tolerant toward dissolved gases and interferents in the liquid phase due to the likely lower concentrations of free radicals and aquated electrons required for analyte ion reduction and product synthesis.
- Publikační typ
- časopisecké články MeSH
Previous research has identified ribose aminooxazoline as a potential intermediate in the prebiotic synthesis of the pyrimidine nucleotides with remarkable properties. It crystallizes spontaneously from reaction mixtures, with an enhanced enantiomeric excess if initially enantioenriched, which suggests that reservoirs of this compound might have accumulated on the early Earth in an optically pure form. Ribose aminooxazoline can be converted efficiently into α-ribocytidine by way of 2,2'-anhydroribocytidine, although anomerization to β-ribocytidine by ultraviolet irradiation is extremely inefficient. Our previous work demonstrated the synthesis of pyrimidine β-ribonucleotides, but at the cost of ignoring ribose aminooxazoline, using arabinose aminooxazoline instead. Here we describe a long-sought route through ribose aminooxazoline to the pyrimidine β-ribonucleosides and their phosphate derivatives that involves an extraordinarily efficient photoanomerization of α-2-thioribocytidine. In addition to the canonical nucleosides, our synthesis accesses β-2-thioribouridine, a modified nucleoside found in transfer RNA that enables both faster and more-accurate nucleic acid template-copying chemistry.
- MeSH
- evoluce chemická * MeSH
- fosfáty chemická syntéza chemie MeSH
- fotochemické procesy * MeSH
- molekulární konformace MeSH
- oxazoly chemie MeSH
- pyrimidiny chemická syntéza chemie MeSH
- ribonukleosidy chemická syntéza chemie MeSH
- ribosa chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- fosfáty MeSH
- oxazoly MeSH
- pyrimidine MeSH Prohlížeč
- pyrimidiny MeSH
- ribonukleosidy MeSH
- ribosa MeSH
