We describe in this Minireview the synthesis, properties, and applications of artificial genetic sets built from base pairs that are larger than the natural Watson–Crick architecture. Such designed systems are being explored by several research groups to investigate basic chemical questions regarding the functions of the genetic information storage systems and thus of the origin and evolution of life. For example, is the terrestrial DNA structure the only viable one, or can other architectures function as well? Working outside the constraints of purine–pyrimidine geometry provides more chemical flexibility in design, and the added size confers useful properties such as high binding affinity and helix stability as well as fluorescence. These features are useful for the investigation of fundamental biochemical questions as well as in the development of new biotechnological, biomedical, and nanostructural tools and methods. 相似文献
The repolarization of μ+ in a longitudinal field as a function of field strength has been measured at various temperatures in KCl and KBr single crystals.
The data at room temperature in KCl are essentially in agreement with Ivanteret al. /1/ and Nishiyamaet al. /5/. The obtained quenching curves can be reasonably fitted by assuming that the long lived muonium state, seen directly
in transverse field experiments by Kieflet al. /4/, is preceded by another short lived muonium state with reduced hf-coupling. It is also necessary to allow for electron
spin exchange in the precursor state. The model fits yield the hyperfine frequency of the precursor state, its chemical lifetime
and an electron spin flip rate. It is speculated that the precursor state and the temperature dependence of the fitted parameters
reflect the early history of the μ+ in its terminal spur. 相似文献
Zeitschrift für Physik A Hadrons and nuclei - Using gaseous60CoI2 sources, the velocity distribution of60Ni nuclei afterβ-decay of60Co has been measured by the... 相似文献
Polarized116In nuclei have been produced by capture of polarized thermal neutrons in several In compounds. At temperaturesT below 77 °K and magnetic field strengthsH0 of several kOe, asymmetries of a few percent of the β? decay of the116In ground state could be observed in polycrystalline InP, InAs and InSb, thus indicating the nuclear polarization. Nuclear magnetic resonance signals have been measured with the result for the magnetic moment μi(116In)=2.7723 (10) nm (uncorrected). β? decay asymmetry and spin lattice relaxation timeT1 have been studied as a function ofH0 andT. The effect ofH0 is to decouple the hyperfine interaction caused by the capture-γ recoil process. However,H0 has no influence uponT1, which demonstrates the absence of nuclear relaxation due to paramagnetic impurities.T1 is determined by quadrupolar relaxation. A quadrupole momentQ(116In)=0.09 (2) b was calculated by comparison of the116In relaxation rates with those of the stable115In isotope in the same compounds. Above 30 °K the temperature dependence of 1/T1 agrees with a recent theoretical investigation. Below 30 °K the relaxation rate shows an anomalous behaviour, which can be explained by resonance modes due to recoil lattice defects. 相似文献
Nuclear magnetic resonance of110Ag has been observed in silver halides using the polarized neutron capture,β decay anisotropy method. The magnetic moment was determined asμI(110Ag)=2.7084 (5) nm (uncorrected). 相似文献
Persistent spectral-hole burning was performed in the gamma line of V(4+) in the wide-gap semiconductor 6HSiC. Spectral holes burned at 11 K were stable to temperatures of at least 320 K for several days. The hole-burning mechanism consists of two-step photoionization of V(4+) (self-gated spectral-hole burning). The spectral holes could be erased optically, either by pumping of electrons back from stable traps or, presumably, by a charge-transfer transition from the valence band to the V(5+) ions. 相似文献
Polyamides are very important polymers that find applications from commodities up to the automotive and biomedical sectors, and their impact is continuously growing. The synthesis of structurally significant, chiral, and sustainable polyamides is described via a new, convenient, and solvent‐free anionic polymerization of a biobased ε‐lactam, which is obtained from the renewable terpenoid ketone l ‐menthone in a one‐step synthesis. These polyamides are shown to have outstanding structural and thermal properties, which are thus introduced via the structure and chirality of the natural lactam monomer and which are discussed and compared with those of petroleum‐based, established, and commercial polyamide Nylon‐6. X‐ray data reveal a remarkable degree of crystallinity in these green polymers and emphasize the impact of their structural features on the resulting properties.