Photoaddition Reaction Research Articles

Ultrafast and Multichannel Generation of the Triplet State in DNA-Intercalated Gilvocarcin V for an Enhanced Photoaddition Reaction.

Gilvocarcin V (GV) is a natural antibiotic exhibiting excellent antitumor activities and remarkably low toxicity in near-ultraviolet or visible light-dependent treatment. Notwithstanding, the [2 + 2] cycloaddition reaction between GV and thymine has been proven to be the key for its function in photodynamic therapy, and crucial mechanistic details about such a reaction are poorly understood. In this study, the electronic relaxation pathways and photoaddition reaction are characterized by femto- to nanosecond time-resolved spectroscopy combined with quantum chemical calculation. Our results reveal that ultrafast intersystem crossing (<3 ps) leads to the population of a local triplet excited state in DNA-intercalated GV. Such a state can further induce the formation of a biradical state, which is identified as the important reactive precursor for photoaddition between GV and thymine. The overall photoaddition quantum efficiency is determined to be 11.57 ± 1.0%. These results are essential to the elucidation of the DNA photoaddition mechanism of C-aryl glycoside-based artificial photocytotoxic agents and could help further development of those medicines.

Reaction-Environment-Dependent Photoaddition Reactions of N-Phenyl Amino Acid Esters Possessing a Silyl Group with Fullerene C60: Selective Formation of Aminomethyl-1,2-dihydrofullerenes vs Fulleropyrrolidines.

The current study investigates SET-promoted photoaddition reactions of the silyl-group-containing N-phenylglycinates and N-phenylalaninates, N-((trimethylsilyl)methyl)-N-phenyl-substituted glycinates and alaninates, respectively, with fullerene C60 to explore how the types of amino acid esters (AAEs) and molecular oxygen affect the photoaddition reaction efficiencies and chemoselectivity of in situ formed radical cations of AAEs. The results showed that under deoxygenated (N2-purged) conditions, photoreactions of N-phenylglycinates with C60 produced aminomethyl-1,2-dihydrofullerenes through the addition of α-amino radicals arising by sequential SET and desilylation processes from initially formed secondary anilines to C60. In oxygenated conditions, photoreactions of N-phenylglycinates with C60, albeit less efficient, took place to form fulleropyrrolidines through a pathway involving 1,3-dipolar cycloaddition of azomethine ylides to C60 assisted by in situ formed 1O2. The same types of photoproducts were observed with N-phenylalaninates, though the reactions were less efficient. The use of methylene blue (MB) as a photosensitizer in the photoreactions under oxygenated conditions was especially effective in enhancing the efficiency of fulleropyrrolidine formation. These results demonstrate that photoaddition reactions of silyl-tether-containing N-phenyl AAEs with C60 can be governed by the reaction conditions and the presence or absence of a photosensitizer employed.

Diastereoselective guest-shape dependent [2+2]-photodimerization of 2-cyclopenten-1-one trapped within a metal-organic framework.

UV-induced [2+2] dimerization of 2-cyclopenten-1-one and 2-methyl-2-cyclopenten-1-one was successfully carried out in a single-crystal-to-single-crystal manner within a porous metal-organic framework. Intermolecular contacts direct the orientation of the α,β-enone molecules within the host channels, which drives the subsequent photoaddition reaction in a facile and diastereoselective fashion, yielding head-to-tail anti dimers only.

Visible-Light-Induced Photoaddition of N-Nitrosoalkylamines to Alkenes: One-Pot Tandem Approach to 1,2-Diamination of Alkenes from Secondary Amines.

The generation of aminium radical cation species from N-nitrosoamines is disclosed for the first time through visible-light excitation at 453 nm. The developed visible-light-promoted photoaddition reaction of N-nitrosoamines to alkenes was combined with the o-NQ-catalyzed aerobic oxidation protocol of amines to telescope the direct handling of harmful N-nitroso compounds, where the desired α-amino oxime derivatives were obtained in a one-pot tandem N-nitrosation and photoaddition sequence.

Hybrid Porous Microparticles Based on a Single Organosilica Cyclophosphazene Precursor.

Porous organosilica microparticles consisting of silane-derived cyclophosphazene bridges were synthesized by a surfactant-mediated sol-gel process. Starting from the substitution of hexachlorocyclotriphosphazene with allylamine, two different precursors were obtained by anchoring three or six alkoxysilane units, via a thiol-ene photoaddition reaction. In both cases, spherical, microparticles (size average of ca. 1000 nm) with large pores were obtained, confirmed by both, scanning and transmission electron microscopy. Particles synthesized using the partially functionalized precursor containing free vinyl groups were further functionalized with a thiol-containing molecule. While most other reported mesoporous organosilica particles are essentially hybrids with tetraethyl orthosilicate (TEOS), a unique feature of these particles is that structural control is achieved by exclusively using organosilane precursors. This allows an increase in the proportion of the co-components and could springboard these novel phosphorus-containing organosilica microparticles for different areas of technology.

Kinetics of Direct Photoinduced Addition of Carbosilane Thiols with Bulky Groups to Polyallylcarbosilane

The kinetics of the addition of carbosilane thiols of various structures to a hyperbranched polyallylcarbosilane matrix in n-hexane solution under direct photoinitiation is studied. A kinetic scheme that makes it possible to describe the photoaddition reaction at the quantitative level is proposed. The reaction rate constants are determined, and the dependence of the differential quantum yield of the photochemical reaction on the kinetic parameters and the concentration of allyl groups in the polyallylcarbosilane matrix is obtained. The assignment of the absorption bands to the corresponding components of the reaction system is confirmed by the quantum-chemical calculations of transition energies and oscillator strengths of the chromophore groups of thiols and the resulting thioesters. It is shown that the lowest rate of thiol-ene addition is observed for thiol with the smallest length of a polymethylene spacer between sulfur and silicon atoms.

Addition of tryptophan methyl-ester on [60]fullerene: theoretical investigation of the mechanisms of azomethine ylides and fulleropyrrolidine formation.

In this paper, we perform the synthesization of carbon nanoparticles for active principle vectorization, with the suggestion of a reaction mechanism of tryptophan methyl ester addition on [60]fullerene. Firstly, we studied the effect of tryptophan form on its addition reaction on [60]fullerene. So, in order to determine the preferred environment that makes this reaction the most favorable, we considered all tryptophan possible forms in our investigation: the molecular, the zwitterionic, and the dibasic forms. Secondly, we investigate the proposed reaction mechanism of tryptophan methyl ester addition on [60]fullerene using theoretical thermodynamic calculation. Our hypothesis suggests the formation of azomethine ylide molecule in a first step followed by its addition on [60]fullerene in the second step by the photo-addition reaction involving the oxygen in its singlet state. The stability of each reactive intermediate involved in this mechanism is verified thermodynamically. The 12 most stable conformations of azomethine ylide were observed through potential energy surface analysis. They were obtained by a relaxed scan of the four dihedral angles. The calculations were conducted on the optimized geometry of fulleropyrrolidine mono-adduct and the bulk values of its thermodynamic constants were also determined. Infrared spectra observed in 100-4000cm-1 region confirmed our hypothesis suggesting the first step of azomethine ylide formation followed by the second step of azomethine ylide addition on [60]fullerene by ν(Caliphatic-C-N), ν(Caromatic-C-N) and δ(N-H) coupled with ν(C-N) absorption bond. Graphical abstract Optimized geometry of the Fulleropyrrolidine monoaduct molecule.

Catalyst free, visible-light promoted photoaddition reactions between C60 and N-trimethylsilylmethyl-substituted tertiary amines for synthesis of aminomethyl-1,2-dihydrofullerenes

An efficient and benign method for the preparation of aminomethyl-substituted fullerenes has been developed. The process, involving catalyst free, visible-light irradiation of 10% EtOH-toluene solutions containing fullerene C60 and N-trimethylsilylmethyl-substituted amines by using a 20 W compact fluorescent lamp, leads to formation of aminomethyl-substituted fullerene adducts in a highly efficient manner. The photoaddition reaction takes place via a pathway initiated by visible light absorption by C60, followed by SET from the amine to the triplet excited state of C60. Ethanol-promoted desilylation of the resulting a minimum radical then generates the corresponding α-amino radical which couples with the C60 radical anion to form the anion precursor of the fullerene adducts. The new approach using visible-light takes place under mild conditions and it does not require the use of photocatalysts. Thus, the method developed in this effort could broadens the range of functionalized fullerene derivatives that can be readily prepared.

SET-promoted photoaddition reactions of N-α-trimethylsilylmethyl-N,N-dibenzylamines with fullerene C60. Electronic factors that govern photoaddition efficiencies

Single electron transfer (SET) promoted photoaddition reactions of N-α-trimethylsilylmethyl-N,N-dibenzylamines to fullerene C60 were investigated as part of an effort aimed at developing a general method to prepare various aryl ring containing aminomethylfullerenes and exploring factors that govern photoaddition efficiencies. The results show that the photoaddition reactions take place highly efficiently to form 1,2-adducts. The mechanism for this process involves generation of aminium radicals and C60 anion radical intermediates by a pathway initiated by excited state SET. SET is followed by desilylation of the aminium radicals to produce α-amino radicals that couple with either C60 or its radical anion to form precursors of the 1,2-adducts. The electronic nature of para-substituents on the aryl ring of N-α-trimethylsilylmethyl-N,N-dibenzylamines has a pronounced effect on the efficiency of the photoaddition reaction, with electron donating groups causing a greater than 2-fold enhancement compared to that brought about by electron withdrawing groups.

Effect of phosphate buffer on the complexation and photochemical interaction of riboflavin and caffeine in aqueous solution: A kinetic study

A study of the photodegradation of 5 × 10−5 M riboflavin (RF) in 0.2–1.0 M phosphate buffer in the presence and absence of 2.50 × 10−4 M caffeine at pH 6.0–8.0 has been carried out. RF in phosphate buffer is photodegraded simultaneously by normal photolysis (photoreduction) and photoaddition reactions giving rise to lumichrome (LC) and cyclodehydroriboflavin (CDRF) as the main final products, respectively. RF and its photoproducts, formylmethylflavin (FMF), lumiflavin (LF), LC and CDRF in degraded solution have been determined by a specific multicomponent spectrophotometric method with an accuracy of ±5%. The apparent first-order rate constants for the photodegradation of RF and for the formation of LC and CDRF are 5.47–15.05 × 10−3 min−1, 1.06–8.30 × 10−3 min−1 and 4.31–8.05 × 10−3 min−1, respectively. An increase in phosphate concentration leads to an increase in the rate of formation of CDRF and alters the photodegradation of RF in favor of the photoaddition reaction. This photoaddition reaction is further enhanced in the presence of caffeine which results in a further decrease of the fluorescence of RF in phosphate buffer. Caffeine may facilitate the photoaddition reaction by suppression of the photoreduction pathway of RF.

Expanding the horizon of the thymine isostere biochemistry: unique cyclobutane dimers formed by photoreaction between a thymine and a toluene residue in the dinucleotide framework.

Substituted toluenyl groups are considered as close isosteres of the thymine residue. They can be recognized by DNA polymerases as if they were thymine. These toluene derivatives are generally inert toward radical additions, including the [2+2] photo-cycloadditions, due to the stable structure of the aromatic ring and are usually used as solvents for radical reactions. Surprisingly, after incorporating toluene into the dinucleotide framework, we found that the UV excited thymine residue readily dimerizes with the toluenyl moiety through a [2+2] photo-addition reaction. Furthermore, the reaction site on the toluenyl moiety is not the C5=C6 bond, as commonly observed in cyclobutane pyrimidine dimers, but the C4=C5 or C3=C4 instead. Such a reaction pattern suggests that in the stacked structure, it is one of these bonds, not the C5=C6, that is close to the thymine C5=C6 bond. A similar structural feature is found in DNA duplex with a thymine replaced by a 2,4-difluorotoluene. Our results argue that although the substituted toluenyl moieties closely mimic the size and shape of the thymine residue, their more hydrophobic nature determines that they stack on DNA bases differently from the natural thymine residue and likely cause local conformational changes in duplex DNA.

(+)-Camphor Derivative Induced Asymmetric [2 + 2] Photoaddition Reaction

An efficient approach to construct an enantiomerically pure cyclobutane skeleton by means of the chiral auxiliary induced [2 + 2] photoaddition reactions has been described. This asymmetric photoreaction exhibited high diastereoselectivity and provided the photoadducts in excellent yields.

Ab initio Calculation for Photochemistry of Psoralen Derivatives

Psoralens (Ps) are a class of heterocyclic aromatic compounds that have been extensively utilized in the photochemotherapy of skin disorders such as psoriasis and vitiligo, cutaneous T-cell lymphoma. On exposure to ultraviolet light, especially in the range of 320-400 nm, psoralens form chemical crosslinks to the DNA bases in the three steps. The first step is intercalation of psoralen between to adjacent base-pairs. The second step is formation of monoadduct; that is one psoralen molecule photo-react with one strand of DNA. The third step is the cross-linking of the same psoralen molecule to the other strand of DNA, thus covalently linking the two strand of a double stranded DNA. Psoralens have two photochemical reaction sites, 3,4pyrone double bond and 12,13-furan double bond, both of which are engaged in cross-linking of DNA bases. The formation of interstrand cross-linking through C4-cycloaddition of 3,4and 12,13-double bonds to the 5,6-double bond of the pyrimidine bases, especially thymine, in DNA has been correlated with the biological effects of photoexcited psoralens. Binding of Ps to DNA is generally the consequence of two successive events (1) intercalation into DNA between the base pairs; and (2) photocycloaddition reaction of 3,4Pyrone double bond and/or 12,13-furan double bond with 5,6-double bond of thymine. Although several photoproducts of purine bases from direct and photosensitized irradiation of purines are known, the photoaddition reaction between the excited psoralens and purine bases are not well understood. In the present paper, we report that the formation of interstrand cross-linking through C4-cycloaddition of 3,4and 12,13-double bonds to the 5,6-double bond of the pyrimidine bases, especially thymine, in DNA is calculated by the ab initio method. The molecular geometries are optimized at HF levels of theory with the 6-31G basis set by using the Gaussian 03 program. The 6-31G optimizations of the final structures are done to include the effect of electron correlation and the basis set with polarization function. The photosensitization activity of psoralens is generally correlated to their photoreactivity with pyrimidine bases in DNA. The cross-linkage is caused by the formation of cyclobutane adducts, which are produced by photoreactions of the psoralen 3,4-pyrone and 12,13-furan double bonds to two pyrimidine bases. The association energies for photocycloadduct (ΔE) are obtained by subtracting the sum of the energies of the 5MOP and two thymine from the energy of the full optimized photocycloadduct.

Effect of divalent anions on photodegradation kinetics and pathways of riboflavin in aqueous solution

The present investigation is based on a study of the effect of buffer and non-buffer divalent anions (phosphate, sulphate, tartrate, succinate, malonate) on the kinetics, product distribution and photodegradation pathways of riboflavin (RF) at pH 6.0–8.0. RF solutions (5 × 10 −5 M) were photodegraded in the presence of divalent anions (0.2–1.0 M) using a visible light source and the photoproducts, cyclodehydroriboflavin (CDRF), formylmethylflavin (FMF), lumichrome (LC) and lumiflavin (LF) were assayed by a specific multicomponent spectrophotometric method. RF degradation in the presence of divalent anions follows parallel first-order kinetics to give CDRF and LC as the final products through photoaddition and photoreduction reactions, respectively. The divalent anion-catalysed CDRF formation is affected in the order: phosphate > sulphate > tartrate > succinate > malonate, showing maximum activity of the anions around pH 7. The divalent anions cause deviation of the photoreduction pathway in favour of the photoaddition pathway to form CDRF. The first- and second-order rate constants for the reactions involved in the photodegradation of RF have been determined and the rate–pH profiles and pathway relationships discussed. The catalytic activity of the divalent anions appears to be a function of the relative strength and chemical reactivity of the RF–divalent anion complex acting as a mediator in the photoaddition reaction.

Photoinduced Intramolecular Addition of 3-Acyl-2-haloindoles to Alkenes

1,2-Fused indoles and pyrroles were prepared via an efficient intramolecular photoaddition reaction of 1-(omega-alkenyl)-2-haloindole-3-carbaldehydes and 1-(omega-alkenyl)-2-chloropyrrole-3-carbaldehydes. The presence of an acyl group was necessary for the photocyclization reactions. The halogen-atom-retained exo- and endo-cyclization products were generally produced with results similar to those of an atom-transfer cyclization reaction. In contrast, unsaturated cyclization products were obtained in the photoreaction of substrates having methyl groups on the vinyl group.

Photooxidation and reproduction of pentacene derivatives substituted by aromatic groups

Pentacene derivatives substituted by aromatic groups at the 6,13-positions were prepared and investigated for their electronic properties and the photoaddition reaction with oxygen. The pentacene derivatives substituted by 2-thienyl and phenyl groups reacted with oxygen in solution under light and afforded their endoperoxides. These first-order kinetic constants were evaluated to be 1.5×10 −3 s −1 and 2.7×10 −3 s −1. The pentacene derivative with pentafluorophenyl groups was relatively stable in solution. The thermolysis and photolysis of the endoperoxide with 2-thienyl groups in solution afforded the pentacene derivative with yields of 30 and 44%, respectively. In addition, UV irradiation (254 nm) of the thin film of the endoperoxide was studied, which indicated the reproduction of the pentacene derivative.

3He NMR as a Sensitive Probe of Fullerene Reactivity: [2 + 2] Photocycloaddition of 3-Methyl-2-cyclohexenone to C70

The [2 + 2] photoadditions of 3-methyl-2-cyclohexenone to C70 and 3He@C70 have been studied by a combination of HPLC chromatography and FAB-MS, as well as IR and 1H and 3He NMR spectroscopies. The total yield of the mixture of monoadducts was 55% (67% on the basis of the recovered C70). The use of 3He NMR was especially powerful in determining the regioselectivity of the photoaddition reaction of enone to C70. Results of the 3He NMR experiments conducted on the product mixture implicate the two [6,6] bonds closest to the poles of the fullerene (C1-C2 and C5-C6) in the photoaddition process. This reaction mode is analogous to that of most thermal addition reactions to C70. Separation and characterization of the product mixture shows that eight distinct monoadducts are formed in the photoaddition, namely, the four diastereomeric adducts to the C1-C2 and C5-C6 bonds of the C70 cage, each consisting of cis- and trans-fused isomers in a ratio of 2:3. The major mode of photoaddition, accounting for 65% of the product mixture, involves addition to the C1-C2 bond of the ovoid fullerene. Mechanistic implications of these findings are discussed.

Photoaddition of thienocoumarin derivatives to DNA: stoichiometry and kinetics of binding

Photoreaction of the 6,9-dimethyl-4-methoxymethyl-2 H-thieno[3,2-g]-1-benzopyran-2-one (compound I) and 4-acetoxymethyl-6,9-dimethyl-2 H-thieno[3,2-g]-1-benzopyran-2-one (compound II) to DNA was studied. The quantitative evaluation of the photobound molecules was performed by means of inductively coupled plasma atomic emission spectrometry (ICP-AES), exploiting the presence of the sulphur atom inside the tricyclic chromophore. The concurrent estimation of the phosphorus atom, present exclusively in the macromolecule, allowed possible intercalation sites to be identified and their involvement in the photoaddition reaction to be determined. The development of a kinetic model made it possible to discriminate and evaluate the single kinetic events that constitute the overall photoaddition process of I and II to DNA.

Photochemistry of the Nitrogen‐Thiocarbonyl Systems. Part 40. Intermolecular Photoaddition Reaction of Benzenecarbothioamide with γ,δ‐Unsaturated Ketones: A Novel Formation of Cycloalkane‐Fused Pyridine Derivatives by Photoinduced Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Intermolecular Photoaddition Reaction of Benzenecarbothioamide with g,d- Unsaturated Ketones: A Novel Formation of Cycloalkane-fused Pyridine Deriva- tives by Photoinduced Reaction

Irradiation of benzenecarbothioamide with 2-(2-alkenyl)-cycloalkanone in benzene gives cycloalkane-fused pyridine derivatives in moderate yields.