Predicting ion selectivity in water purification by capacitive deionization: Electric double layer models

Ion-selective water treatment is needed to address emerging problems in an energy- and cost-efficient manner. Capacitive deionization (CDI) is a membraneless water treatment technology, which relies on storing ions in charged electric double layers (EDLs) of micropores. CDI has shown remarkable selectivity, with local density approximations (LDAs) showing some success in guiding selective separations. However, many underlying processes are represented by lumped fitting parameters in LDA models, hindering further progress. Atomistic models help unravel selectivity mechanisms, but are difficult to integrate with cell-level CDI theory. Here, we review and extend LDA models for CDI, highlight a knowledge gap in connecting between LDA and atomistic models for CDI, and emphasize and build upon analogies between micropore EDLs and nanofiltration membranes.     

Phosphino[tris(trimethylsilyl)methyl]Boranes and 2,4‐Bis[tris(trimethylsilyl)methyl]‐1,3,2,4‐diphosphadiboretanes [1]

The reaction of tris(trimethylsilyl)methylboron dihalides (Me₃Si)₃CBX₂ (X = Cl, F) with the lithium phosphides LiPHtBu and LiPHmes leads to the phosphinoboranes (Me₃Si)₃CBX‐(PHR), (Me₃Si)₃CB(PHR)₂ or the 1,3,2,4‐diphosphadiboretanes [(Me₃Si)₃CB(PR)]₂, depending on the ratio of the reagents, the reaction temperature and concentration. High dilution and low temperatures are required for the synthesis of (Me₃Si)₃CB(Hal)PHR ( 1–3 ) in order to prevent the formation of (Me₃Si)₃CB(PHR)₂ ( 4 and 5 ). The latter compounds are best prepared in a two step phosphination from (Me₃Si)₃CBHal₂ and LiPHR. At higher temperatures the four‐membered 1,3,2,4‐diphosphadiboretanes [(Me₃Si)₃CB(PR)]₂ 6 and 7 are the most stable compounds. On the other hand, compounds of type (Me₃Si)₃CB(Hal)PR₂, 8 and 9 , are thermally more stable than the monophosphinoboranes 1 – 3 . Phosphinoboranes of type (Me₃Si)₃CB(PR₂)₂ (R = tBu, mes) could not be prepared. NMR and mass spectral data are in accord with the monomeric nature of compounds 1 to 9 .     

Molecular modeling on recognition of sheared and normal DNA by novel metal complex Λ- and Δ-[Co(phen)2hpip]

Recognition of sheared and normal DNA by a novel metal complex [Co(phen)₂hpip]³⁺ (phen=1,10-phenanthroline, HPIP=2-(2-hydroxyphenyl)imidazole[4,5-f][1,10]phenanethroline) is studied by molecular modeling. Calculating results indicate that, this complex can specifically recognize DNA segment of sequence –MMNNMM– (M means mismatch base pairs and N means normal base pairs). Intercalating from minor groove between the middle normal duplex into the sheared DNA with the depth of 1.2 nm is of preference and enantioselectivity is observed. Comparison on the two DNA structures of optimal conformation and analysis on the interaction between DNA and the two tail ligands of the complex show that, the effect of the two neighboring mismatch duplexes on the structure of the middle normal base pairs and the steric interaction between the mismatch duplexes and the two tail ligands of the complex are the essential reason to the segment specificity. Investigation on the detailed energy terms indicate that, in effecting enantioselectivity, the electrostatic distribution of the complex is in the majority and steric interaction is at the next place. But, steric interaction is surely the only factor determining the intercalating from minor groove.     

Ionic conductivity of poly[N-(3,6,9-trioxadecyl)-4-vinylpyridinium)] salts with univalent counter-ions in aqueous solutions

In order to determine the counter-anion effect on conductivity of poly[N-(3,6,9-trioxadecyl)-4-vinylpyridinium)] backbone in aqueous solutions, a set of three polyelectrolytes with three different counter-ions: poly[N-(3,6,9-trioxadecyl)-4-vinylpyridinium]bromide P4VP164Br and its chlorate and tosylate derivatives P4VP164ClO₄ and P4VP164Ts respectively, were prepared by spontaneous polymerization of 4-vinylpyridine. This method gives a grafted polyelectrolyte having a positive charge on each pyridinic moiety on the backbone. The conductivities of cationic polyelectrolyte aqueous solution were determined in the concentration range from 10⁻⁴ to 10⁻² M at 25 °C. The variation of the conductivity versus concentration of the investigated system exhibits a typical polyelectrolyte behavior. The polycation mobility was found to be dependent on the counter-anion nature. Thus, the polyelectrolyte conductivity increases with the ion size. This shows that big ions are weakly or not associated to the backbone.In order to confirm this steric hindrance, we have considered the conductivities of these three anions Br⁻, ClO₄⁻ and Ts⁻ in their sodium salts, both alone and in the presence of 3,6,9-trioxadecanol (PEO164) free chains. In the two cases, the conductivities decrease in the order Λ_Br>Λ_ClO4>Λ_Ts.These results suggest that counter-ion mobility is mainly influenced by steric effect PEO164 grafted chains.Values of the conductivity predicted from Manning rod-like polyelectrolyte model were compared with our experimental results.     

Synthese und Konformation einiger Azaspirane mit Alkyl-bzw. Aryl-Sulfonamid-Gruppen

Preferred conformations of some azaspiran systems substituted with large groups at the nitrogen atoms were established by UV absorption spectroscopy. These groups prohibit the inversion at nitrogen, as was deduced from the¹H NMR spectra.

     

The steric and electronic effects of aliphatic fluoroalkyl groups

Ab initio calculations were performed on 18 fluorinated and unfluorinated alcohols at the B3LYP and HF levels with the 6-311G^∗∗ basis set. Molar volumes of the alcohols were computed at each level and averaged to produce a scale of relative size. From this, various isosteric replacements of potential use in drug design were suggested: ethyl by FCH₂CH₂ or HCF₂CH₂, propyl by CF₃CH₂, isopropyl by CF₃(CH₃)CH or (FCH₂)₂CH, isobutyl or t-butyl by (CF₃)₂CH, and 3-methyl-2-butyl by CF₃(CH₃)₂C. Calculation of the charge on oxygen and the Wiberg index of the CO bond allowed an electronegativity scale to be constructed for the fluoroalkyl groups. Electronegativity decreased in the order: (CF₃)₃C>(CF₃)₂CH>C₂F₅CH₂>CF₃CH₂>CH₃(CF₃)₂C>HCF₂CH₂>CF₃(CH₃)CH>(FCH₂)₂CH>FCH₂CH₂>CF₃(CH₃)₂C. This ranking agreed with literature acid dissociation data for the alcohols studied.     

Cerium (IV) ammonium nitrate (CAN)-mediated regioselective synthesis and anticancer activity of 6-substituted 5,8-dimethoxy-1,4-naphthoquinone

6-Substituted 5,8-O-dimethyl-1,4-naphthoquinones (6-DMNQ), the promising anticancer scaffolds, were selectively generated by oxidative demethylation of 2-substituted 1,4,5,8-tetramethoxynaphthalenes with CAN in EtOAc/H₂O in comparatively high yields. An interesting finding was that apart from the reported electron-withdrawing effects of substituents on position 2 of naphthalene ring, regioselective synthesis of 6-DMNQ was largely dependent on the steric effects in CAN-mediated oxidation. The selective cytotoxicities of 6-DMNQ from the in vitro cell-based assays were exhibited between the cancer cells and normal cells. Moreover, most of sulfur-containing 6-DMNQ derivatives displayed better anticancer activities than the corresponding oxygen-containing ones, which could provide an available strategy for the design of 6-DMNQ derivatives as potential anticancer agents.     

Complications in the Castagnoli-Cushman reaction: An unusual course of reaction between cyclic anhydrides and sterically hindered indolenines

Attempted reaction of indolenines (which represent rather sterically hindered cyclic imines) with a series of dicarboxylic acid anhydrides yielded no expected product, the Castagnoli-Cushman lactam. Instead, products presumably formed via N-acyliminium species trapping by a carboxylate anion. Among them, hydrolytically labile 2:2 adducts of an indolenine and a cyclic anhydride, containing a 16-membered cyclic core, are particularly intriguing. This result contradicts the recently reported successful Castagnoli-Cushman reaction of indolenines with homophthalic anhydride suggesting a mechanistic switch in the course of the reaction.     

1,3-Migration of Trimethylsilyl Group from Carbon to Oxygen in Highly Sterically Hindered Silanol of the Type (Me 3 Si) 3 CSi(C 6 H 4 Me- p )MeOH and Reaction of the Related Iodide with Iodine Monochloride and Iodine Monobromide

The silanol (Me 3 Si) 3 CSi(C 6 H 4 Me- p )MeOH has been shown to isomerize to (Me 3 Si) 2 CHSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ) when it was kept at room temperature for 10 h in 0.2 M NaOMe/MeOH. Corresponding isomerizations of the above silanol (to give (Me 3 Si) 2 CHSi(C 6 H 4 Me- p ) (Me)(OSiMe 3 )) are complete after 26 h under reflux in pyridine. The reaction involve 1,3-migration from carbon to oxygen within a silanolate ion to give a carbanion, which rapidly acquires a proton from the solvent. Treatment of (Me 3 Si) 3 CSi(C 6 H 4 Me- p )MeOH with MeLi in Et 2 O/THF give, by the same rearrangement, the organolithium reagent (Me 3 Si) 2 CLiSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ) which on treatment with Me 2 SiHCl gives (Me 3 Si) 2 C(SiMe 2 H)Si(C 6 H 4 Me- p )(Me)(OSiMe 3 ) and (Me 3 Si) 2 CHSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ). When the experiment was repeated, but with Me 3 SiCl in place of Me 2 SiHCl, it gives exclusively (Me 3 Si) 2 CHSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ). Treatment of the organolithium reagent (Me 3 Si) 2 CLiSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ) with Mel gives exclusively (Me 3 Si) 2 CMeSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ). The related iodide (Me 3 Si) 3 CSi(C 6 H 4 Me- p )Mel reacts with ICI and IBr to give rearranged (Me 3 Si) 2 C(SiMe 2 X)Si(C 6 H 4 Me- p )Me 2 and unrearranged products (Me 3 Si) 3 CSi(C 6 H 4 Me- p )MeX, (X = Cl, Br) respectively. The rearranged bromide (Me 3 Si) 2 C(SiMe 2 Br)Si(C 6 H 4 Me- p )Me 2 reacts with a range of silver [I] salts AgY (Y = OOCCH 3 , SO 4 2 m ) and Mercury [II] salt HgY 2 (Y = OOCCH 3 , SO 4 2 m ) in glacial CH 3 COOH to give the corresponding species (Me 3 Si) 2 C(SiMe 2 OOCCH 3 )Si(C 6 H 4 Me- p )Me 2 . The reaction of the bromide with AgBF 4 in MeOH or i -PrOH give the corresponding rearranged products (Me 3 Si) 2 C(SiMe 2 Y)Si(C 6 H 4 Me- p )Me 2 (Y = --OMe, --OPr i ).     

烯烃聚合催化剂的研究进展

获得高性能聚烯烃材料是化学家们不断的追求。烯烃聚合催化剂的结构对其催化性能有重要影响,而聚烯烃的改性则能够改善聚合物实际应用中表面形貌、本体性能中存在的缺陷,如通过改性可增加聚合物韧性、降低聚合物表面的摩擦系数或提升表面能等。 本文系统总结了金属烯烃聚合催化剂研究进展,包括Ziegler-Natta催化剂、茂金属催化剂、非茂金属催化剂的结构及调控策略,探讨了位阻效应、双金属协同效应以及其他效应对催化效果的影响。