Influence of the Lanthanide Ion and Solution Conditions on Formation of Lanthanide Wells–Dawson Polyoxotungstates

Lanthanide complexes of polyoxometalates, including the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand, have been pioneered by Michael T. Pope, to whom this paper is dedicated. Examination of the solid-state and solution behavior of lanthanide complexes of the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand are reported here to identify trends that will facilitate rational synthesis of hybrid organic lanthanide polyoxometalate complexes. Therefore, combining our data with that obtained by Pope and others a number of trends come into view. It is clear that there are two structural types for the 1:1 or 2:2 [Ln(H₂O)_X(α₂-P₂W₁₇O₆₁)]₂ ¹⁴⁻ species. The early lanthanides show a “cap to cap” structure that allows the Ln ion to be 9 coordinate and accommodates the longer bond lengths. The mid-late lanthanides show a “cap to belt” structure that allows the lanthanides to be 8 coordinate; this structural type is appropriate for the shorter bond lengths of the later lanthanides. The 1:1⇌1:2 equilibrium, that was observed by Pope for the Ce(III) analog is prevalent for the early- mid lanthanides. This equilibrium is slightly dependent on pH; however, cations have a major influence on this equilibrium. Larger, poorly hydrated cations appear to favor the 1:2 species for the early to mid lanthanides. Cations do not appear to influence the equilibrium for the later lanthanides; for all counterions, the 1:1 species was stable with no trace of the 1:2 species. Stability constants, K1 and K2, for the early to mid lanthanides were measured in this study by a competitive method and compared well with other published stability constant determinations. We suggest that the stability constants are not only dependent on the strength of interaction of the Ln with the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand, but are also significantly influenced by the medium. The medium may bias the equilibria of the early-mid lanthanides and later lanthanides. The log K₁/log K₂ ratios are very close, suggesting that it is difficult to separate the 1:1 and 1:2 Ln: α₂-P₂W₁₇O₆₁ ¹⁰⁻ species.Electronic Supplementary Material Supplementary material for this article is available at and is accessible for authorized users.This paper is dedicated to Professor Michael T. Pope in honor of his substantial and sustained contributions to polyoxometalate chemistry and his inspiration to scientists working in the field.     

Asymmetric Henry reaction catalyzed by C2-symmetric tridentate bis(oxazoline) and bis(thiazoline) complexes: metal-controlled reversal of enantioselectivity

[reaction: see text] C(2)-symmetric tridentate bis(oxazoline) and bis(thiazoline) ligands with a diphenylamine backbone have been investigated in the catalytic asymmetric Henry reaction of alpha-keto esters with different Lewis acids. Their Cu(OTf)(2) complexes furnished S enantiomers, while Et(2)Zn complexes afforded R enantiomers, both of them with higher enantioselectivities (up to 85% ee). Reversal of enantioselectivity in asymmetric Henry reactions was achieved with the same chiral ligand by changing the Lewis acid center from Cu(II) to Zn(II). The results show that the NH group in C(2)-symmetric tridentate chiral ligands plays a very important role in controlling both the yields and enantiofacial selectivity of the Henry products.     

Fluorescence decay and quenching of pyrene labeled on sulfonate polyelectrolytes in salt-free aqueous solutions

Fluorescence decay and quenching of pyrene labels on copolymers of 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and N,N-dimethylacrylamide were observed in dilute salt-free aqueous solutions as a function of the mole fraction F_AMPS of AMPS from 0 to 0.896. Monoexponential decay was found for the samples of F_AMPS<0.35 and biexponential decay for the samples of F_AMPS>0.35. The fast decay component is 80%, and the averaged lifetime 〈τ〉 and lifetime τ₁ of the fast decay is decreased with increasing F_AMPS. Quenching efficiency of Cu²⁺, I⁻, CH₃NO₂, and dinitrobenzene to the pyrene label was investigated in the framework of Stern-Volmer plot. With increasing F_AMPS the quenching efficiency of Cu²⁺ is increased while that of I⁻ decreased. For the neutral quenchers, the quenching rate constant k_q increases when F_AMPS<0.449 then decreases, showing a decline of accessibility to the pyrene label. These results were interpreted consistently with the counterion condensation concept, where condensed counterions caused the polyelectrolyte chains to aggregate. The existence of less-polar “temporal aggregated domain” in highly charged polyelectrolytes appears to lead to the slower decay and lower accessibility of the pyrene labels.     

One-Pot Formation of Carbonates from the Reactions of Carbonyl Compounds with Samarium Diiodide and Methyl Chloroformate

Treatment of carbonyl compounds with SmI₂ and methyl chloroformate in the presence of molecular sieves provides the cyclic carbonates or biscarbonates of pinacols. This one-pot reaction proceeds rapidly even with aliphatic ketones. The stereochemistry obtained by this procedure is different from that of conventional pinacolic couplings.     

微波溶样肉桂基荧光酮和表面活性剂连续荧光测定葡萄酒中铁和钴

观察到肉桂基荧光酮(略作CF)在pH≈8与Fc(Ⅲ)配位后荧光增强,CPB的加入使荧光更强,络合物与试剂荧光强度之比F_(FeR)/F_R随0～0.01μg/ml Fe(Ⅲ)线性变化,λ_(ex)=410nm,λ_(ex)=480nm;而CF在pH≈10与Co(Ⅲ)配位后荧光却减弱,乳化剂OP存在时使试剂荧光增强,若以荧光熄灭Co(Ⅲ)灵敏度便提高,试剂与络合物荧光强度之比F_R/F_(CoR)对0～0.016 μg/ml Co(Ⅲ)呈直线关系,λ_(ex)=300nm,L_(em)=352nm。控制化学条件和激发、发射波长,可不经分离测定葡萄酒(微波溶样)中铁和钴。     

Electrochemical determination of 6-mercaptopurine at silver microdisk electrodes

The electrochemical behaviour of 6-mercaptopurine (6-MP) at a microdisk electrode is investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicate that 6-MP can be strongly adsorbed on the surface of the static mercury drop electrode (SMDE) and reacts with Ag+ ions which are produced at positive potentials. 6-MP yields a well-defined cathodic stripping signal during the negative scan at about -0.812 V (vs. SCE) in pH 9.0 phosphate buffer solution. The electrode has hence been used for the determination of 6-MP by differential pulse voltammetry (DPV). The linear range is between 2.0x10(-7) and 5.0x10(-5) mol/l, with the calculated detection limit (S/N=3) of 8.0x10(-8) mol/l. The relative standard deviation is 3.0% for eight successive determinations of 4.0x10(-5) mol/l 6-MP. The determination of 6-MP in tablets has also been carried out and satisfactory results have been obtained.     

β-环糊精诱导室温燐光法测定痕量苊的研究——以环氧溴丙烷作重原子微扰剂

环糊精诱导室温燐光法(CD-RTP)中的重原子微扰剂,文献报道仅限于1,2-二溴乙烷(DBE)和1,2-二溴丙烷(DBP)。本文首次发现了一种新的微扰剂——环氧溴丙烷(EBH)应用于β-CD-RTP 法测定痕量苊。详细比较了 EBH 和 DBP 的重原子效应,结果表明,二者性能类似,而 EBH 较 DBP 的实验条件宽容。     

Synthesis of benzo-fused 1-azabicyclo[m.n.0]alkanes via the Schmidt reaction: a formal synthesis of gephyrotoxin

The intramolecular capture of benzocyclobutyl, benzocyclopentyl, and benzocyclohexyl carbocations 7 by azides produces spirocyclic aminodiazonium ions 8, which undergo 1,2-C-to-N rearrangement with loss of dinitrogen to produce benzo-fused iminium ions resulting from either aryl (9) or alkyl (10) migration to the electron-deficient nitrogen atom. Reduction of the iminium ions affords regioisomeric benzo-fused 1-azabicyclo[m.n.0]alkanes, e.g., benzopyrrolizidines, benzoindolizidines, benzoquinolizidines, or perhydrobenzo[f]pyrrolo[1,2-a]azepines in two regioisomeric versions, anilines (e.g., 11-14) and benzylic amines (e.g., 15-18), the result of aryl and alkyl migrations, respectively. Generally, aryl migration is preferred, despite modeling that shows that the lowest energy aminodiazonium ions are those where the departing dinitrogen is preferentially antiperiplanar to the migrating alkyl group rather than the aryl group. The utility of this methodology was illustrated by a formal synthesis of the alkaloid gephyrotoxin 4. A dependence on the efficiency and regioselectivity of the Schmidt reaction upon subtle changes in the structure of the cation precursor was observed, necessitating the exploration of a variety of substrates. Fortunately, these materials were easily made. Ultimately, the azido-alkene 81 bearing a 2-bromoethyl side-chain was useful for the Schmidt reaction, producing the known benzo-fused indolizidine 49, which had been transformed by Ito et al. into gephyrotoxin 4. The synthesis of 49 required nine steps (five purifications) from commercially available 4-methoxy-1-indanone 60 and proceeded in 22% overall yield.     

Evaluation of Eigenvalues by Successive Variations

A successive variation method was studied and tested on the hydrogen molecular ion H₂⁺. Results show that it takes less computational time than conventional method. It was also found that ground state wavefunction of H₂⁺ can be well approximated by the linear combination of the simplest Gaussian orbitals e^?I(T-a)3     

Black fungus derived aerogel with double faced properties

Black fungus aerogel (BFA) exhibited interesting double-faced properties. Weexplored the diverse properties of each side of the black fungus in three aspects:water contact angle measurements, liquid selective absorption capacity and air pollutant adsorption abilities.