Results 1 - 10 of 2187
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[en] The experimental CO stretching frequencies in the 1:1 adducts between (C5H5-nRn)3U and CO range from 1976 cm-1 in (C5H4SiMe3)3U(CO) to 1900 cm-1 in (C5HMe4)3U(CO). The origin of the large difference between the stretching frequencies in free (2143 cm-1) and coordinated CO and the large effect the substituents on the cyclopentadienyl ligands play in the difference is explored by DFT calculations with a small core effective core potential in which 32 electrons on uranium are explicitly treated. The results of these calculations, along with a NBO analysis, show that a sigma-bond is formed between CO and an empty sigma-orbital on the Cp(prime)3U fragment composed of f sigma and d sigma parentage orbitals. The backbonding interaction, which results in lowering the CO stretching frequency, does not originate from non-bonding metal-based orbitals but from the filled ligand-based orbitals of pi-symmetry that are used for bonding in the Cp(prime)3U fragment. This model, which is different from the backbonding model used in the d-transition metal complexes, rationalizes the large substituent effect in the 5f-metal complexes.
[en] The photocycloaddition reaction of 4',5'-dihydropsoralen with thymine was carried out in solution and in the frozen state. A major photoadduct was isolated and characterized by elemental analysis and physical methods. The photoadduct was proven to be the 1:1 C4-cycloaddition product, an analogue of furocoumarine-DNA biadduct, with the stereochemistry of anti-head-to-head formed through 2+2 addition reaction between the pyrone double bond of 4',5'-dihydropsoralen and 5,6-double bond of thymine. (author)
[en] Background: Acrylamide-induced immunotoxicity and allergic dermatitis have been reported in animal experiments and clinical reports, respectively. However, epidemiological evidence from the general population is limited. Objectives: The purpose of the present study was to estimate the associations between acrylamide exposure and allergy-related outcomes in the general US population. Methods: A total of 6982 subjects were selected from the National Health and Nutrition Examination Survey 2005–2006 (NHANES). Internal exposure was measured by the hemoglobin adducts of acrylamide (HbAA) and its metabolite glycidamide (HbGA). Allergy-related outcomes including asthma, hay fever, allergy, itchy rash, sneeze, wheeze and eczema were obtained by self-administered questionnaires. Allergic sensitization was assessed by the total immunoglobulin E (IgE) levels. The associations of HbAA and HbGA quartiles with allergy-related outcomes were calculated using logistic regression models with multivariable adjustments. Analyses were additionally stratified according to age, gender and serum cotinine levels. Results: When setting quartile 1 of HbAA as reference, the odds ratios (ORs) [95% confidence intervals (CIs)] of quartile 2 to 4 for eczema were 1.18 (0.79–1.76), 1.14 (0.73–1.78) and 1.58 (1.14–2.18), respectively (ptrend = 0.002). Individuals at the highest quartile of HbGA had significantly elevated likelihoods of itchy rash (OR = 1.37, 95% CI = 1.02–1.83, ptrend = 0.032) and eczema (OR = 1.45, 95% CI = 1.06–1.97, ptrend = 0.044). The stratification analyses indicated various results in different subgroups. Conclusions: This study indicated significant associations between HbAA and HbGA levels and the likelihoods of allergy-related outcomes in the general US population, depending on age, gender and smoke exposure status. These findings suggested potential public health concerns for the widespread exposure to acrylamide. - Highlights: • Health effects of acrylamide and glycidamide on allergy-related outcomes were assessed in the general US population. • Elevated HbAA levels are associated with increased likelihoods of eczema. • Elevated HbGA levels are associated with increased likelihoods of itchy rash and eczema. • Associations between HbAA and HbGA levels and allergy-related outcomes varied by age, gender and serum cotinine levels. - Levels of HbAA and HbGA are significantly associated with allergy-related outcomes in the general US population.
[en] Highly chemo- and regioselective reaction of hydroxybenzenes with α,β-unsaturated compounds in acidic ionic liquid l-butyl-3-methylimidazolium hydrogen sulphate ([BMIM]HSO4) was reported for the first time. A series of oxa-Michael adducts and Friedel-Crafts alkylated products were synthesized with good yields. The acidic ionic liquid could be easily recycled for at least 5 times with only minor loss in activity
[en] Convenient synthetic method for 4-arylethylpyrazoles and 4-styrylpyrazoles was developed using α-alkenyl-α,β-enones readily accessed from the Morita-Baylis-Hillman reaction. For the synthesis of 4-arylethyl-pyrazole, the reactions with arylhydrazines needed to be carried out in o-dichlorobenzene under N2 balloon atmosphere. On the other hand, 4-styrylpyrazoles required the reactions in ethanol under O2 balloon atmosphere
[en] A new synthetic method for dimethyl 2,3-dihydrobenzo[b]oxepine-2,4-dicarboxylates and methyl 2-(2- carbomethoxybenzo[b]furan-3-yl)propanoates by an intramolecular conjugate displacement reaction or an SN2 reaction of acetates of Morita-Baylis-Hillman adducts of methyl (2-formylphenoxy)acetates has been described
[en] The addition of various nucleophiles to enantiomerically pure (p-methoxyphenyl)-[1'(R)-α-methylbenzyl] aziridin-2(R)-ylmethylene]amine was successful in highly stereoselective manner to give 2-aminomethylaziridine in the presence of BF_3·OEt_2. Commercial success to produce both enantiomers of aziridine-2-carboxylates in optically pure forms prompts us to extend their synthetic utilities for the preparation of enantiopure nitrogen containing molecules. In last few years we have studied with chiral aziridine-2-carboxylates to provide enantiomerically pure α- or β-amino ester and their derivatives. Synthetic study has been extended to construct diamine compounds based on the reaction with the substrate, aziridinyl-2-carboxaldimine. Recently we successfully prepared aminomethylaziridine and 4,5-disubstitued imidazolidin-2-ones by the addition of organomagnesium reagents to aziridinyl-2-carboxaldimine. The additions of alkyl- and arylmagnesium reagents to the chiral [1'(R)-α-methylbenzyl]aziridine-2(R)-carboxaldimine were highly stereoselective in most cases with chelation controlled transition states. The subsequent treatment of theses adducts with triphosgen and NaH afforded enantiopure 5-alkyl- or 5-aryl-4-chloromethylimidazolidin-2-ones
[en] Covalent binding of carcinogen to nucleic acids is believed to be an essential component of the carcinogenic process, so it is desirable to have highly sensitive and specific methods for detecting such adducts in cells and tissues exposed to known and suspected carcinogens. A radioimmunoassay is here described capable of detecting nanogram amounts of DNA adducts resulting from the covalent binding of the carcinogen N-2-acetylaminofluorene and its activated N-acetoxy derivative. (author)