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排序方式: 共有85条查询结果,搜索用时 15 毫秒
1.
A trideaza analog of aminopterin, N-(4[2-(2,4-diamino-6-quinazolinyl)ethyl]benzoyl)-L-glutamic acid, was prepared by a Wittig condensation of 2,4-diaminoquinazoline-6-carboxaldehyde and [P-(N-[1,3-bis(ethoxycarbonyl)propan-1-yl]aminocarbonyl)phenylmethyl]triphenylphosphonium bromide followed by catalytic reduction and mild hydrolysis. This compound was found to have confirmed inhibitory activity against leukemia L1210 in mice. 相似文献
2.
Rosenstein BS Phelps RG Weinstock MA Bernstein JL Gordon ML Rudikoff D Kantor I Shelton R Lebwohl MG 《Photochemistry and photobiology》1999,70(5):798-806
Sun exposure histories were obtained from a series of patients age 35 or younger following diagnosis and removal of a basal cell carcinoma (BCC). The DNA was extracted from tumor biopsy samples derived from BCC of 10 patients who reported that they did not use sunscreens during youth (age 18 or younger) and 10 patients who routinely employed sunscreens during this age period. Exons 5-9 of the p53 gene were then amplified in three fragments from these samples using a nested polymerase chain reaction (PCR) approach and screened for mutations using an RNA heteroduplex assay. All PCR products displaying evidence of a mutation were sequenced. It was found that 6 of the 10 patients who were not routine sunscreen users displayed mutations in these p53 exons. All of the mutations were located at dipyrimidine sites, five of the six were C-->T transitions and one mutation was a tandem double mutation, consistent with a role for solar UVB in BCC formation. In contrast, only one p53 mutation was detected in the group of 10 patients who routinely employed sunscreens during childhood and adolescence. Hence, a significantly (P = 0.029) lower level of p53 mutations was detected in the BCC obtained from sunscreen users compared with tumors derived from nonusers. These findings suggest that the mechanisms involved in the etiology of skin carcinogenesis differ in sunscreen users compared with people who did not routinely employ sunscreens. These data are also indicative of a protective effect associated with sunscreen use against the formation of p53 mutations. It is possible that the patients who were diagnosed with BCC despite their use of sunscreens possessed a genetic susceptibility for skin cancer formation and developed BCC through a p53-independent pathway. Alternatively, solar UVA wavelengths, that were generally not blocked by the suncare products employed by the sunscreen users, may have played a significant role in BCC development through induction of a mutation(s) in an oncogene and/or a tumor suppressor gene, other than p53, for these patients. 相似文献
3.
Diels-Alder reaction of cyclopentadiene and methyl N-carbobenzyloxy-2-iminoacetate generated in situ from methyl 2-chloro-N-carbobenzyloxyglycinate by triethylamine gave the N-carbobenzyloxy unsaturated bicyclic proline ester. This was converted in two steps to 2-azabicylo[2.2.1]heptane-3-carboxylic acid. In contrast to N-carbobenzyloxy-L-proline methyl ester, the corresponding bicyclic proline ester was resistant to hydrolysis catalyzed by carboxypeptidase Y. 相似文献
4.
5.
A one step synthesis of (E)-4-oxo-2-butenoic acid ethyl ester via the reaction of ethyl 2-ethoxy-2-hydroxyacetate and (formylmethylene)triphenylphosphorane is described. The method proceeds in good yield on a molar scale. 相似文献
6.
A. Müller N. Mohan S.J. Cyvin N. Weinstock O. Glemser 《Journal of Molecular Spectroscopy》1976,59(2):161-170
The complete infrared spectrum of gaseous NSCl, including the hitherto unobserved ν3, is reported. A set of force constants for gaseous NSCl consistent with a number of pieces of independent data such as the isotopic shifts (14N32S35Cl, 15N32S35Cl, 14N32S37Cl, 15N32S37Cl, 14N34S35Cl and 15N34S35Cl), centrifugal distortion constants (14N32S35Cl), and the inertia defect (14N32S35Cl) has been computed. Also, the force field of NSF has been redetermined using the vibrational frequencies and the centrifugal distortion constants. 相似文献
7.
8.
Electrocatalysis by polyoxometalate (POM)-monolayer protected gold nanoparticles is herein demonstrated using a newly discovered phenomenon that makes it possible to observe the electrochemistry of dilute aqueous solutions of these colloidal nanostructures. To preserve the integrity of the gold nanoparticles’ electrostatically-stabilized POM-monolayer structures, deposition and drying of the POM-protected metal(0) NPs on the electrode surface must be avoided. Overcoming this constraint, we here show that POM-monolayer protected gold nanoparticles can be induced to reversibly associate with electrode surfaces, resulting in dramatic current amplification and well behaved, quasi-reversible cyclic voltammetric behavior at remarkably small electrolyte concentrations, thus making it possible to investigate electrocatalysis by dilute aqueous solutions of POM-protected gold NPs. 相似文献
9.
Weinstock BA Yang H Hirsche BL Griffiths PR 《Langmuir : the ACS journal of surfaces and colloids》2005,21(9):3915-3920
A novel method for determining the rates of adsorption of gaseous adsorbates on granular adsorbents in the millisecond time regime is described. Mixtures of the adsorbate and nitrogen are passed through a solenoid valve and 100 mg of the adsorbent for periods of (typically) 100 ms. The concentration of the adsorbate passing into a low-volume, long path length gas cell is measured with an ultra-rapid-scanning Fourier transform infrared spectrometer capable of gathering 200 mid-infrared spectra per second with 6-cm(-1) resolution. The pressure of the gas entering the cell is measured simultaneously with a capacitance manometer. A dynamic mathematical model was developed to analyze and describe the results in terms of a Langmuir isotherm. The success of this approach is demonstrated by the estimation of the rate of adsorption of vapor-phase acetaldehyde on aminopropylsilylated granular silica gel. 相似文献
10.
Dr. Yizhan Wang Dr. Manoj Raula Prof. Yifeng Wang Dr. Offer Zeiri Dr. Sourav Chakraborty Gal Gan-Or Eyal Gadot Prof. Ira A. Weinstock 《Angewandte Chemie (International ed. in English)》2017,56(25):7083-7087
The controlled assembly of gold nanoparticles (AuNPs) with the size of quantum dots into predictable structures is extremely challenging as it requires the quantitatively and topologically precise placement of anisotropic domains on their small, approximately spherical surfaces. We herein address this problem by using polyoxometalate leaving groups to transform 2 nm diameter gold cores into reactive building blocks with hydrophilic and hydrophobic surface domains whose relative sizes can be precisely tuned to give dimers, clusters, and larger micelle-like organizations. Using cryo-TEM imaging and 1H DOSY NMR spectroscopy, we then provide an unprecedented “solution-state” picture of how the micelle-like structures respond to hydrophobic guests by encapsulating them within 250 nm diameter vesicles whose walls are comprised of amphiphilic AuNP membranes. These findings provide a versatile new option for transforming very small AuNPs into precisely tailored building blocks for the rational design of functional water-soluble assemblies. 相似文献