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1.
Electrochemical and EPR methods have been applied to a study of perimidyl free radicals containing a bulky tert-butyl substituent in the 2-position. A stepwise mechanism is proposed for the dehydrogenation of 1,3-dimethyl-2-tert-butyl-2,3-dihydroperimidine; the mechanism involves formation of a cation-radical from the substrate in the first step. Shielding of the nitrogen atoms seems to be an important factor in increasing the stability of free perimidyl radicals.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 970–972, July, 1986.  相似文献   

2.
Vibrational predissociation spectra of the F(-)(H(2)O) x Ar and F(-)(D(2)O) x Ar complexes are observed over a range of 600 to 3800 cm(-1), which include bands attributed to the fundamentals as well as the first two overtones of the vibrations primarily associated with the shared hydrogen. This information allows us to characterize both the extended potential surface confining the anionic H-bonded hydrogen and the degree to which this motion is coupled to the motions of other atoms in the complex. We analyze these new data with reduced dimensional treatments using explicit potential energy and electric dipole moment surfaces. The often employed one-dimensional treatment with fixed OF distance does not even qualitatively account for the observed isotope dependent level structures, but a simple extension to two dimensions, corresponding to the OF distance and the shared proton position, accurately recovers the observed spectra. The resulting two-dimensional wave functions are used to evaluate the extent of proton transfer in each vibrational level. The main conclusion of this work is that vibrational excitation of the shared proton can be regarded as optically driven, intracluster proton transfer.  相似文献   

3.
Using a distillation method for the separation of18F-fluoride from aqueous18F-solutions obtained after cyclotron irradiation of a water target by means of the16O(3He, p)18F reaction, the radiohalogen could be generated as a highly reactive species for nucleophilic substitution reactions. Thus, with the starting compounds 1,3,4,6-tetra-O-acetyl-2-O-trifluoromethanesulfonyl--D-mannopyranose and 1,2:5,6-di-O-isopropylidene-3-O-trifluoromethanesulfonyl--D-allofuranose18F-2-deoxy-2-fluoro-D-glucose (2-18FDG) and18F-3-deoxy-3-fluoro-D-glucose (3-18FDG) could be synthesized with radiochemical yields of 71.6% and 85.9%, respectively. Including purification by HPLC, the total preparation time was 70 min, yielding the glucose derivatives in a no-carrier-added state. Specific activities coold be calculated to be greater than 103 Ci/mmol.  相似文献   

4.
C2H5ONO was photolyzed with 366 nm radiation at ?48, ?22, ?2.5, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yield of CH3CHO, Φ{CH3CHO}, was measured as a function of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?1a = 0.29 ± 0.03 independent of temperature. The C2H5O radicals can react with NO by two routes The C2H5O radical can also react with O2 via Values of k6/k2 were determined at each temperature. They fit the Arrhenius expression: Log(k6/k2) = ?2.17 ± 0.14 ? (924 ± 94)/2.303 T. For k2 ? 4.4 × 10?11 cm3/s, k6 becomes (3.0 ± 1.0) × 10?13 exp{?(924 ± 94)/T} cm3/s. The reaction scheme also provides k8a/k8 = 0.43 ± 0.13, where   相似文献   

5.
6.
The combinations and disproportionations of the CH3 and 2-propyl (iP) radicals with the 1,1,2-trimethylallyl (TMA) radical have been studied in the gas phase in the temperature interval of 389–451 K and 490–540 K, respectively. For the ratios of the terminal (t) and non-terminal (n) combinations of the CH3 and iP radicals with the TMA radical, values of 1.9±0.1 and 2.84±±0.10 were obtained, respectively. The ratios of the tt and tn and nn to tn combinations of the TMA radical were 1.59 and 0.46, respectively. The disproportionation-combination rations were (CH3 , TMA)=0.022±±0.012 and (iP, TMA)=0.026±0.011.
CH 3 2- (iP) 1,1,2- (TMA) : 389–451 K 490–540 K. (t) (n) TMA 1,9±0,1 2,84±0,10, . tt tn nn tn TMA 1,59 0,46, . (CH 3 , TMA)=0,022±0,012 (iP, TMA)=0,026±0,011.
  相似文献   

7.
8.
[reaction: see text] The radical cascade cyclizations of N-alkenyl-2-aziridinylmethyl radicals to pyrrolizidines and indolizidines were examined using density functional theory (DFT) calculations. A large preference for cyclization to pyrrolizidines was found. These predictions corroborated very well with experimental results, leading to an efficient synthesis of pyrrolizidines. No radical cascade cyclization to indolizidines could be performed in practice as only ring opening of N-alkenyl-2-aziridinylmethyl radicals to N-allyl-N-alkenylamines occurred.  相似文献   

9.
使用高水平的从头算CCSD(T)/aug-cc-pVTZ方法, 经过Counterpoise校正, 计算了He2F-体系的分子间相互作用势能面. 在He2F-体系的相互作用势能面的最小值处, 发现了一个等腰三角形的稳定结构. 在这个结构中, He…F- 距离是 0.334 nm, He…He 的距离是 0.295 nm, ∠HeF-He 为 52.5°. 计算了此稳定结构的频率、相互作用能、二体相互作用能和三体相互作用能. 在CCSD(T)/d-aug-cc-pVTZ水平下, 相互作用能为-1.727 kJ/mol.  相似文献   

10.
The presence of human epidermal growth factor type 2 (HER2) on 20-30% of human breast cancer is a prognostic indicator of more rapid disease progression and a therapeutic indicator for anti-HER2 monoclonal antibodies. Because the literature has demonstrated some discordance between primary and metastatic tumors in the same patient for expression of the HER2 marker, we set out to develop an imaging agent that could be used to assess the marker concentration in vivo in an individual patient. The pharmaceutical company Affibody® AB has optimized the specificity of Affibody® molecules for HER2. Two Affibody® molecules, a 7 kDa and an 8 kDa protein, were designed with a single carboxy terminal cysteine in order to provide a specific location for the purposes of labeling for various types of imaging. We have prepared [18F]FBEM utilizing a coupling reaction between [18F]fluorobenzoic acid and aminoethylmaleimide. We then optimized the conjugation of this radiolabeled maleimide to the free sulfhydryl of cysteine by incubating at pH 7.4 in phosphate buffered saline containing 0.1% sodium ascorbate. An overall uncorrected yield of radiolabeled Affibody® molecule of approximately 10% from [18F]fluoride was achieved in a 2 h synthesis. These conjugated Affibody® molecules were obtained with a specific activity of 2.51 ± 0.92 MBq/μg. Characterization of the product by HPLC-MS supported the conjugation of [18F]FBEM with the Affibody® molecule. The radiolabeled Affibody® molecule retained its binding specificity as demonstrated by successful imaging of xenografts expressing HER2.  相似文献   

11.
CeO2/SiO2粒状除氟剂的制备及其对F-的吸附性能  相似文献   

12.
The generation of 2-indolylacyl radicals from the corresponding phenyl selenoesters, aldehydes, and alpha-keto carboxylic acids and the scope of their participation in intermolecular addition reactions to carbon-carbon double bonds have been studied. Whereas the phenyl selenoester method has provided easy access to a variety of 1,4-dicarbonyl compounds bearing the 2-acylindole moiety, the glyoxylic acid route has been employed for the preparation of 2-indolyl pyridyl ketones.  相似文献   

13.
An interstitial hydroxyl radical (HO*) has been generated in bulk amorphous SiO2 (a-SiO2) loaded with interstitial H2O molecules and exposed to F2 laser light (hnu = 7.9 eV, lambda = 157 nm) at 77 K. F2 laser light dissociates an O-H bond of interstitial H2O into a pair of hydrogen atom (H0) and HO*. The resultant H0 disappears below 150 K, whereas HO* is detectable after thermal annealing at 200 K. The electron paramagnetic resonance (EPR) signal of the interstitial HO* recorded at 77 K is similar to that formed in amorphous ice, indicating that HO* is confined in an orthorhombic field by hydrogen bonding, probably with adjacent H2O molecules, silanol (SiOH) groups, and bridging oxygen atoms in the a-SiO2 network.  相似文献   

14.
Acetylperoxy radicals were produced by the flash photolysis of chlorine in the presence of acetaldehyde and oxygen. By adding various concentrations of nitrogen dioxide, the rate constant for the reaction producing PAN was measured to be k4 (153 Torr) = (2.29 ± 0.05) × 109 L/mol s. The effect of pressure has been studied over the range 76–612 Torr and the data fitted to a fall-off curve with k 4 ° = 1.85 × 1013 L2/mol2 s. and k = 3.67 × 109 L/mol s. With a calculated value of the dissociation constant, k ?4 ° = 268 L/mol s and of the equilibrium constant, K4 = 1.04 × 1012 L/mol, the expected strong collision value for k 4 ° is 2.79 × 1014 L2/mol2 s. The ultraviolet absorption spectrum of PAN has been characterized in the range 205–260 nm.  相似文献   

15.
Regioselectivity of the nucleophilic ring opening of N-benzoyl (Bz) and N-benzyloxycarbonyl (Cbz) activated 2-methylaziridines with anhydrous tetramethylammonium fluoride, anhydrous hydrogen fluoride, and 19F or [18F]-labelled potassium cryptand fluoride ([K222][18/19F]) were investigated. Whereas all reactions with rigorously anhydrous N(CH3)4F did not ring-open the aziridines, reactions with anhydrous HF exclusively yielded the 2-fluoropropanamine derivatives. Reactions of Bz-protected and Cbz-protected 2-methylaziridine with [K222][18/19F] yielded the 2-fluoropropanamine and 1-fluoro-2-propanamine derivatives as the major products, respectively, and represents the first example of regiocontrol during ring opening of aziridines with [18F]-fluoride.  相似文献   

16.
i-C4H9ONO was photolyzed with 366-nm radiation at ?8, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yield of i-C3H7CHO, Φ{i-C3H7CHO}, was measured as a function of reaction of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?1 = 0.24 ± 0.02 independent of temperature. The i-C4H9O radicals can react with NO by two routes The i-C4H9O radical can decompose via or react with O2 via Values of k4/k2 ? k4b/k2 were determined to be (2.8 ± 0.6) × 1014, (1.7 ± 0.2) × 1015, and (3.5 ± 1.3) × 1015 molec/cm3 at 23 55, and 88°C, respectively, at 150-torr total pressure of N2. Values of k6/k2 were determined from ?8 to 120°C. They fit the Arrhenius expression: For k2 ? 4.4 × 1011 cm3/s, k6 becomes (3.2 ± 2.0) × 10?13 exp{?(836 ± 159)/T} cm3/s. The reaction scheme also provides k4b/k6 = 3.59 × 1018 and 5.17 × 1018 molec/cm3 at 55 and 88°C, respectively, and k8b/k8 = 0.66 ± 0.12 independent of temperature, where   相似文献   

17.
The rate constant for the reaction CH3O2 + NO2 → (products) has been measured directly by flash photolysis and kinetic spectroscopy. At room temperature and at total pressures between 53 and 580 Torr, k3 = (9.2 ± 0.4) × 108 liter/mole sec so that the rate of formation of the probable primary product peroxymethyl nitrate (CH3O2NO2) may be significant in urban atmospheres.  相似文献   

18.
Hyperfine sublevel correlation (HYSCORE) spectroscopy has been used to study the tyrosyl radicals in Photosystem II and bovine liver catalase. The HYSCORE data allow a complete resolution of all the 1H hyperfine tensors of these radicals. The present work shows that the proper analysis of the HYSCORE data allows the complete assignment of the 1H-hyperfine tensors in tyrosine radicals and this offers an alternative experimental tool relative to ENDOR.  相似文献   

19.
Quantum mechanical calculations were used to determine the structure and energetics of peroxy radicals (P1 and P2) and alkoxy radicals (A1-A3) formed in the atmospheric degradation of 2-methyl-3-buten-2-ol. At the level of theory employed (B3LYP/6-31G(d,p)) low energy conformers were identified with zero, one, or two hydrogen bonds. The beta C-C scission (decomposition) reactions are computed to occur with low barriers, and the 1,5 H-shift (isomerization) reaction of A2 is computed to be of negligible importance. Scission 2 of A2 is computed to be about 93% of the fate of A2, with the balance being scission 1. The new BB1K functional of Truhlar was employed to investigate activation barriers for single intramolecular H-atom transfers across the OH...O* hydrogen bonds, but the barriers to these reactions appear to be too high for these reactions to be important. Extensive searches for transition states for simultaneous double intramolecular H-atom transfer across OH...OH...O* hydrogen bond pairs were unsuccessful.  相似文献   

20.
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