Water stable! Radiochemists have recently discovered silicon chemistry as a tool for the introduction of 18F into biomolecules for positron emission tomography (PET) imaging. 18F‐labeled PET tracers must be stable towards defluorination under physiological conditions. Here, a theoretical model of organofluorosilane hydrolysis is developed that correlates with the experimentally determined hydrolytic half‐lives and allows estimation of the stability of newly designed compounds (see scheme).
Highly efficient Michael addition reactions of malonates to nitroalkenes catalyzed by novel chiral thioureas derived from optically pure BINOL and amino acids are reported. Various trans-nitroalkenes reacted with malonates affording the desired products in up to 95% yield with excellent enantioselectivities (up to 97% ee). 相似文献
Particle swarm optimization (PSO) algorithm has been developing rapidly and many results have been reported. PSO algorithm has shown some important advantages by providing high speed of convergence in specific problems, but it has a tendency to get stuck in a near optimal solution and one may find it difficult to improve solution accuracy by fine tuning. This paper presents a dynamic global and local combined particle swarm optimization (DGLCPSO) algorithm to improve the performance of original PSO, in which all particles dynamically share the best information of the local particle, global particle and group particles. It is tested with a set of eight benchmark functions with different dimensions and compared with original PSO. Experimental results indicate that the DGLCPSO algorithm improves the search performance on the benchmark functions significantly, and shows the effectiveness of the algorithm to solve optimization problems. 相似文献
Reactions of VO2(acac) (Hacac = acetylacetone) and 2,6‐Di(hydroxymethyl)‐4‐methylphenol (H3L) in different organic solvents give rise to two pseudopolymorphs of a new dinuclear oxovanadium(V) compound, [Et3NH]2[V2O4(HL)2] ( 1 ) and [Et3NH]2[V2O4(HL)2]·H2O ( 2 ). The compounds have been synthesized and characterized by elemental analyses, IR spectra and single‐crystal X‐ray diffraction. X‐ray diffraction analyses reveal that 1 and 2 have different weak interactions and display remarkably distinct hydrogen‐bonded networks. 相似文献
The cycloaddition mechanism of the reaction between singlet dimethyl germylidene and formaldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated with CCSD (T)//MP2/6-31G* method. From the potential energy profile, we predict that the cycloaddition reaction between singlet dimethyl germylidene and formaldehyde has two dominant reaction pathways. First dominant reaction pathway consists of three steps: (1) the two reactants (R1, R2) firstly form an intermediate INT1a through a barrier-free exothermic reaction of 43.0 kJ/mol; (2) INT1a then isomerizes to a four-membered ring compound P1 via a transition state TS1a with an energy barrier of 24.5 kJ/mol; (3) P1 further reacts with formaldehyde(R2) to form a germanic heterocyclic compound INT3, which is also a barrier-free exothermic reaction of 52.7 kJ/mol; Second dominant reaction pathway is as following: (1) the two reactants (R1, R2) firstly form a planar four-membered ring intermediate INT1b through a barrier-free exothermic reaction of 50.8 kJ/mol; (2) INT1b then isomerizes to a twist four-membered ring intermediate INT1.1b via a transition state TS1b with an energy barrier of 4.3 kJ/mol; (3) INT1.1b further reacts with formaldehyde(R2) to form an intermediate INT4, which is also a barrier-free exothermic reaction of 46.9 kJ/mol; (4) INT4 isomerizes to a germanic bis-heterocyclic product P4 via a transition state TS4 with an energy barrier of 54.1 kJ/mol. 相似文献
Assembly of 5-sulfosalicylic acid (H3L) and d10 transition metal ions (CdII, AgI) with the neutral N-donor ligands produces five new complexes: [Cd2(HL)2(4,4′-bipy)3]n·2nH2O (1), {[Cd2(μ2-HCO2)2(4,4′-bipy)2(H2O)4][Cd(HL)2(4,4′-bipy)(H2O)2]}n (2), {[Cd(4,4′-bipy)(H2O)4][HL]·H2O}n (3), [Cd(HL)(dpp)2(H2O)]n·4nH2O (4), {[Ag(4,4′-bipy)][Hhbs]}n (5) (4,4′-bipy=4,4′-bipyridine, dpp=1,3-di(pyridin-4-yl)propane, H2hbs=4-hydroxybenzenesulfonic acid, the decarboxylation product of H3L). Complex 1 adopts a 5-connected 3D bilayer topology. Complex 2 has the herring-bone and ladder chain, which are extended to a 3D network via hydrogen bonding. In 3–4 complexes, 3 is a 3D supermolecular structure formed by polymeric chains and 2D network of HL2−, while 4 gives the double-stranded chains. In 5, ladder arrays are stacked with the 2D networks of Hhbs− anions in an –ABAB– sequence. Complexes 1–4 display green luminescences in solid state at room temperature, while emission spectra of 3 and 4 show obvious blue-shifts at low temperature. 相似文献
The nucleation process of iron‐exchanged zeolite Fe‐ZSM‐5, from the assembly of distorted tetrahedrally coordinated iron species and silicate rings in the precursor to the final Fe‐ZSM‐5 crystals, as well as variations in the coordination environment of iron, were studied by UV resonance Raman spectroscopy and complementary techniques.
