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11.
The intramolecular hydrogen atom abstraction by the nitrogen atom in isolated aliphatic amine radical cations is examined experimentally and with composite high-level ab initio methods of the G3 family. The magnitude of the enthalpy barriers toward H-atom transfer varies with the shape and size of the cyclic transition state and with the degree of substitution at the nitrogen and carbon atoms involved. The lower barriers are found for 1,5- and 1,6-abstraction, for chairlike transition states, for abstraction reactions in ionized primary amines, and for abstraction of H from tertiary carbon atoms. In most cases, the internal energy required for 1,4-, 1,5-, and 1,6-hydrogen atom abstraction to occur is less than that required for gas-phase fragmentation by simple cleavage of C-C bonds, which explains why H-atom transfer can be reversible and result in extensive H/D exchange prior to the fragmentation of many low-energy deuterium labeled ionized amines. The H-atom transfer to nitrogen is exothermic for primary amine radical cations and endothermic for tertiary amines. It gives rise to a variety of distonic radical cations, and these may undergo further isomerization. The heat of formation of the gauche conformers of the gamma-, delta-, and epsilon-distonic isomers is up to 25 kJ mol(-1) lower than that of the corresponding trans forms, which is taken to reflect C-H-N hydrogen bonding between the protonated amino group and the alkyl radical site. 相似文献
12.
Børge Bak Niels A. Kristiansen Henrik Svanholt Arne Holm Steen Rosenkilde 《Chemical physics letters》1981,78(2):301-303
Microwave Spectra of 13CH212C80,78Se and 12CH213C80,78Se (selenoketene) are recorded. B 5-13C-1,2,3-selenadiazole all four species are formed. The 13C scrambling may take place via a three-membered ring, selenirene, but as expected its microwave spectrum was not observed. 相似文献
13.
The change in fluorescence quantum yield for indole as a function of excitation wavelength between 250 and 220 nm is found to vary with the static dielectric constant of various alcohol—water mixtures at 296 K. The supports the intermediacy of a CTTS state in the photoionization process. 相似文献
14.
Soler AM Angell-Petersen E Warloe T Tausjø J Steen HB Moan J Giercksky KE 《Photochemistry and photobiology》2000,71(6):724-729
The aim of this prospective randomized study was to compare the clinical and cosmetic outcome of superficial basal cell carcinomas (BCC), using either laser or broadband halogen light, in photodynamic therapy with topical 5-aminolevulinic acid (ALA). A total of 83 patients with 245 superficial BCC were included in the study. Standard treatment involved 15 min of local pretreatment with 99% dimethylsulfoxide (DMSO) before topical application of 20% ALA with DMSO (2%) and ethylendiaminetetraacetic acid (2%) as cofactors for 3 h before light exposure with either laser or a broadband lamp (BL). A complete response was achieved in 95 lesions (86%) in the laser group and 110 lesions (82%) in the BL group 6 months after treatment. Of these, 80 lesions (84%) in the laser group and 101 lesions (92%) in the lamp group were independently evaluated to have an excellent or good cosmetic post-treatment score. No serious adverse events were reported. This study shows that there is no statistical significant difference in cure the rate (P = 0.49) and the cosmetic outcome (P = 0.075) with topical application of a modified ALA-cream between light exposure from a simple BL with continuous spectrum (570-740 nm) or from a red-light laser (monochromatic 630 nm). Cost and safety are further elements in favor of the BL in this setting. 相似文献
15.
Abstract— The 248 nm laser flash photolysis of myoglobin in various redox states (oxy, met and ferryl) in neutral aqueous solution yielded hydrated electrons with concurrent changes in the visible absorption spectrum of the heme. The results could be ascribed to the photoionization of both the peptide and the heme group, in approximately equal yields. The ionization of met- and ferrylmyoglobin was biphotonic, but that of oxymyoglobin was a mixture of mono- and biphotonic processes. Using appropriate electron and radical scavengers, the changes in the heme absorption could be investigated at times ≥100 ns and were shown to be associated with a +1 increase of the formal oxidation state of the heme. Using this method, the formal iron(V) state of native myoglobin could be spectroscopically characterized for the first time. Its absorption, blue-shifted and less intense relative to the ferryl state, is reminiscent of that of the compound I of peroxidases, which contains a ferryl-oxo (iron[IV]) group and a porphyrin radical cation. On this basis, the same structure is proposed for the formal iron(V) state of native myoglobin. The transition from oxy- to metmyoglo-bin took -5 μs, which may reflect the kinetics of exchange of oxygen with water as ligand. The transitions from the met to the ferryl state, and from ferryl to iron(V) states were faster (∽250 ns), consistent with processes that involve proton or electron movements but no changes in the iron coordination state. 相似文献
16.
17.
Christian D. Buch Steen H. Hansen Dmitri Mitcov Camilla M. Tram Gary S. Nichol Euan K. Brechin Stergios Piligkos 《Chemical science》2021,12(20):6983
Heterolanthanide complexes are difficult to synthesize owing to the similar chemistry of the lanthanide ions. Consequently, very few purely heterolanthanide complexes have been synthesized. This is despite the fact that such complexes hold interesting optical and magnetic properties. To fine-tune these properties, it is important that one can choose complexes with any given combination of lanthanides. Herein we report a synthetic procedure which yields pure heterodinuclear lanthanide cryptates LnLn*LX3 (X = NO3− or OTf−) based on the cryptand H3L = N[(CH2)2N CH–R–CH N–(CH2)2]3N (R = m-C6H2OH-2-Me-5). In the synthesis the choice of counter ion and solvent proves crucial in controlling the Ln–Ln* composition. Choosing the optimal solvent and counter ion afford pure heterodinuclear complexes with any given combination of Gd(iii)–Lu(iii) including Y(iii). To demonstrate the versatility of the synthesis all dinuclear combinations of Y(iii), Gd(iii), Yb(iii) and Lu(iii) were synthesized resulting in 10 novel complexes of the form LnLn*L(OTf)3 with LnLn* = YbGd 1, YbY 2, YbLu 3, YbYb 4, LuGd 5, LuY 6, LuLu 7, YGd 8, YY 9 and GdGd 10. Through the use of 1H, 13C NMR and mass spectrometry the heterodinuclear nature of YbGd, YbY, YbLu, LuGd, LuY and YGd was confirmed. Crystal structures of LnLn*L(NO3)3 reveal short Ln–Ln distances of ∼3.5 Å. Using SQUID magnetometry the exchange coupling between the lanthanide ions was found to be anti-ferromagnetic for GdGd and YbYb while ferromagnetic for YbGd.We present a synthetic strategy to prepare the first heterodinuclear lanthanide(iii) cryptate complexes. The cryptate design ensures that the complexes are stable in solution for days. The exchange coupling in YbYb, GdGd and YbGd is investigated. 相似文献
18.
DFT calculations have been carried out for 2-, 3- and 4-methoxybenzyl alcohol radical cations (1+, 3+ and 4+, respectively) and the α-methyl derivatives 2+ and 5+ using the UB3LYP/6-31G(d) method. The theoretical results have been compared with the experimental rate constants for deprotonation of 1+-5+ under acidic and basic conditions. In acidic solution, the decay of 1+-5+ proceeds by cleavage of the C-H bond, while in the presence of −OH all the radical cations undergo deprotonation from the α-OH group. This pH-dependent change in mechanism has been interpreted qualitatively in terms of simple frontier molecular orbital theory. The −OH induced α-O-H deprotonation is consistent with a charge controlled reaction, whereas the C-H deprotonation, observed when the base is H2O, appears to be affected by frontier orbital interactions. 相似文献
19.
PRIMARY DNA DAMAGE, HPRT MUTATION AND CELL INACTIVATION PHOTOINDUCED WITH VARIOUS SENSITIZERS IN V79 CELLS 总被引:1,自引:0,他引:1
Barbara B. Noodt Egil Kvam Harald B. Steen Johan Moan 《Photochemistry and photobiology》1993,58(4):541-547
DNA strand breaks and hypoxanthine guanine phosphoribosyl transferase (HPRT) mutants were measured in parallel in photochemically treated (PCT) cells and compared at the same level of cell survival. Chinese hamster fibroblasts (V79 cells) were either incubated with the lipophilic dyes tetra(3—hydroxyphenyl)porphyrin (3THPP) and Photofrin II (PII), the anionic dye meso -tetra(4—sulfonatophenyl)porphine (TPPS4 ) or the cationic dye meso -tetra( N -methyl-4-pyridyl)porphine ( p -TMPyPH2 before light exposure. In the cells, the lipophilic dyes were localized in membranes, including the nuclear membrane, while the hydrophilic dyes were taken up primarily into spots in the cytoplasm. In addition, the hydrophilic TPPS4 was distributed homogeneously throughout the whole cytoplasm and nucleoplasm. According to the HPRT mutation test, the mutagenicity of light doses survived by 10% of the cells was a factor of six higher in the presence of 3THPP than of PII, whereas for X-rays it was a factor of three higher than for PCT with 3THPP. Light exposure in the presence of the hydrophilic dyes TPPS4 and p -TMPyPH2 was not significantly mutagenic. There was no correlation between the induced rates of HPRT mutants and of DNA strand breaks. Thus, TPPS4 was the most efficient sensitizer with regard to DNA strand breaks when compared at the same level of cell survival, followed by 3THPP, PII and p -TMPyPH2 . Hence, the rate of DNA strand breaks cannot be used to predict the mutagenicity of PCT. 相似文献
20.
Gerard de Leeuw John S. Field Raymond J. Haines Beth McCulloch Elsie Meintjies Christiaan Monberg Gillian M. Olivier Praveen Ramdial Clifford N. Sampson Beate Sigwarth Nick D. Steen Kandasamy G. Moodley 《Journal of organometallic chemistry》1984,275(1):99-111
Reaction of [Fe2(CO)9] with a half molar amount of R2PYPR2 (Y = CH2, R = Ph, Me, OMe or OPri; Y = N(Et), R = OPh, OMe or OCH2; Y = N(Me), R = OPri or OEt) leads to the ready formation of a product which on irradiation with ultraviolet light rapidly decarbonylates to the heptacarbonyl derivative [Fe2(μ-CO)(CO)6{μ-R2PYPR2}]. Treatment of the latter with a slight excess of the appropriate ligand results, under photochemical conditions, in the formation of the dinuclear pentacarbonyl complex [Fe2(μ-CO)(C))4{μ-R2PYPR2}2] but under thermal conditions in the formation of the mononuclear species [Fe(CO)3{R2PYPR2}]. Reaction of [Ru3(CO)12] with an equimolar amount of (RO)2PN(R′)P(OR)2 (R′ = Me, R = Pri or Et; R′ = Et, R = Ph or Me) under either thermal or photochemical conditions produces [Ru3(CO)10{μ-(RO)2PN(OR)2}] which reacts further with excess (RO)2PN(R′)P(OR)2 on irradiation with ultraviolet light to afford the dinuclear compound [Ru2(μ-CO)(CO4{μ-(RO)2PN(R′)P(OR)2}2]. The molecular structure of [Ru2(μ-CO)(CO)4{μ-(MeO)2PN(Et)P(OMe)2}2], which has been determined by X-ray crystallography, is described. 相似文献