Epoxidation-alcoholysis of cyclic enol ethers catalyzed by Ti(OiPr)4 or Venturello's peroxophosphotungstate complex

Venturello's peroxophosphotungstate compound and Ti(O(i)Pr)(4) were successfully used as catalysts for the epoxidation-alcoholysis of various dihydropyrans and dihydrofuran using H(2)O(2) as the oxidant. Different alcohols can be used as solvents and nucleophiles, resulting in hydroxy ether products with varying alkoxy groups. The Venturello compound can also be used as catalyst in a biphasic conversion of dihydropyran, in which long chain alcohols or fatty acids are incorporated in the hydroxy ether products with high yield and (stereo)selectivity.     

Long electron spin memory times in gallium arsenide

Extremely long electron spin memory times in GaAs are reported. It was established by the optical orientation method that the spin relaxation time of electrons localized at shallow donors in n-type gallium arsenide (N _d ?N _A ≈10¹⁴ cm^?3) is 290±30 ns at a temperature of 4.2 K. The exchange interaction of quasi-free electrons and electrons at donors suppresses the main spin-loss channel for electrons localized at donors—spin relaxation due to the hyperfine interaction with lattice nuclei.     

Nanoporous metal organic framework materials for hydrogen storage

Hydrogen is expected to play an important role in future transportation as a promising alternative clean energy source to carbon-based fuels.One of the key challenges to commercialize hydrogen energy is to develop appropriate onboard hydrogen storage systems,capable of charging and discharging large quantities of hydrogen with fast enough kinetics to meet commercial requirements.Metal organic framework (MOF) is a new type of inorganic and organic hybrid nanoporous particulate materials.Its diverse networks can enhance hydrogen storage through tuning the structure and property of MOFs.The MOF materials so far developed adsorb hydrogen through weak disperston interactions,which allow significant quantity of hydrogen to be stored at cryogenic temperatures with fast kinetics.Novel MOFs are being developed to strengthen the interactions between hydrogen and MOFs in order to store hydrogen under ambient conditions.This review surveys the development of such candidate materials,their performance and future research needs.     

Selective optical control of electron spin coherence in singly charged GaAs-Al0.3Ga0.7As quantum dots

Coherent transient excitation of the spin ground states in singly charged quantum dots creates optically coupled and decoupled states of the electron spin. We demonstrate selective excitation from the spin ground states to the trion state through phase sensitive control of the spin coherence via these three states, leading to partial rotations of the spin vector. This progress lays the ground work for achieving complete ultrafast spin rotations.