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11.
Chayada Klinchan Yu-Ling Hsu Lee-Chiang Lo Wanchai Pluempanupat Pitak Chuawong 《Tetrahedron letters》2014
Non-hydrolyzable substrate analogs for tRNA-dependent amidotransferase, 2′- or 3′-aspartyl or -glutamyl adenosine, were synthesized from adenosine without protection of the adenine base. The hydroxyl groups of adenosine were selectively protected, followed by a series of oxidation/reductions to alter the stereochemistry. DFT calculations revealed the driving forces for the ketone hydrate formation at C-2′, but not the C-3′ carbon during the oxidation step. Subsequently, triflation and azide replacement yielded azidoadenosines, which were coupled to protected amino acids after deprotection and reduction. After global deprotection, the target substrate analogs were obtained in 2–14% overall yields from adenosine. 相似文献
12.
Rare earth element substituted bismuth ferrites (BiFeO3) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi
x
La1−x
FeO3 (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of
these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz
to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz).
All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature
shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds
to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity
as well as ε′ are found to be maximum for the sample x=0.2 at room temperature. 相似文献
13.
CoFe2O4-BaTiO3 composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases
in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in
the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac
conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric
conversion factor has been studied as a function of magnetic field. 相似文献
14.
Nakanishi W Hayashi S Pitak MB Hursthouse MB Coles SJ 《The journal of physical chemistry. A》2011,115(42):11775-11787
The structure of 2-(2-pyridylimino)-2H-1,2,4-thiadiazolo[2,3-a]pyridine (NSN) indicates that the molecule has a planar geometry with a linear N···S···N linkage, creating a tetracyclic structure of the formal C(2v) symmetry. To clarify the nature of the NSN σ(3c-4e) bonding, together with the related NSeN and NTeN, the dynamic and static behaviors are investigated by applying atoms-in-molecules (AIM) dual functional analysis to both the fully optimized and perturbed structures. The structures were optimized computationally, retaining C(2v) symmetry. All bond critical points are detected as expected and exhibited on both sides of the N···Z···N moiety which supports the formation of NZN σ(3c-4e). It is confirmed that N···S···N is of the covalent nature close to Me(2)S(+)-?-Cl or Me(2)Se(+)-?-Br, whereas N···Se···N and N···Te···N have the (regular) CS nature close to the CT adducts of Me(2)S(-?-Cl)(2) (TBP) and Me(2)Se-?-Br(2) (MC), respectively. An experimental high-resolution charge density determination has been performed on NSN, which thoroughly supports the theoretical results. Very similar results are obtained in the analogous pyrimidyl derivatives for N···S···N, N···Se···N, and N···Te···N. AIM dual functional analysis, as validated by experimental high-resolution charge densities, is thus confirmed to be an excellent method to elucidate the nature of these interactions. 相似文献
15.
Reaction of lanthanide nitrates with (t)Bu(3)PO (=L) lead to the isolation of complexes Ln(NO(3))(3)L(2)·H(2)O·nEtOH (Ln = La (1), Nd(2)), Ln(NO(3))(3)L(2)?·nEtOH (Sm(3), Eu(4)), and Ln(NO(3))(3)L(2) (Dy(5), Er(6), Lu(7)). These have been characterized by elemental analysis, infrared and NMR((1)H, (13)C and (31)P) spectroscopy and single-crystal X-ray diffraction. The structures show L to be positioned on opposite sides of the metal with the nitrates forming an equatorial band. When Ln = Dy, Er, and Lu two distinct molecules are present in the unit cell. A major isomer (70%) has a (P)O-Ln-O(P) angle of less than 180° with one of the nitrate ligands twisted out of the plane of the other nitrates while the lower abundance isomer is more symmetric with the (P)O-Ln-O(P) angle of 180° and the nitrate ligands coplanar giving a hexagonal bipyramidal geometry. These isomers cannot be observed by variable temperature solution (31)P NMR measurements but are clearly seen in the solid-state NMR spectrum of the Lu complex. Variable temperature solid-state NMR indicates that the isomers do not interconvert at temperatures up to 100 °C. Attempts to prepare cationic species [Ln(NO(3))(2)L(3)](+)[PF(6)](-) have not been totally successful and led to the isolation of crystals of Lu(NO(3))(3)L(2) and Tb(NO(3))(3)L(2).CH(3)CN (8). 相似文献
16.
The 6-azabicyclo[3.2.1]octane ring system, prevalent in a range of biologically active molecules, is prepared through a novel semipinacol rearrangement utilizing a cyclic phosphorane or sulfite intermediate. The rearrangement proceeds with exclusive N-acyl group migration of a β-lactam ring and results in carbonyl functionality at the 7- and bridging 8-position of the bicycle. Precursor ring-fused β-lactam diols are prepared through a sequence of 4-exo trig carbamoyl radical cyclization, regioselective dithiocarbamate group elimination, and dihydroxylation. 相似文献
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We present a rare example of a decay mechanism playing a constructive role in quantum information processing. We show how
the state of an atom trapped in a cavity can be teleported to a second atom trapped in a distant cavity by the joint detection
of photon leakage from the cavities. The scheme, which is probabilistic, requires only a single three level atom in a cavity.
We also show how this scheme can be modified to a teleportation with insurance. 相似文献