The effect of the linking group on mesogenic properties of three‐ring derivatives of p‐carborane and biphenyl

Four series of mesogenic derivatives of p‐carborane (series A[0] and A[1]) and their benzene analogues (series B[0] and B[1]) with variable linking groups were prepared and investigated for phase behaviour. The data allowed a comparison of the effect of the group on the mesophase stability as a function of the adjacent ring (carborane or benzene), the variable central ring (carborane or benzene), and the presence of an oxygen atom in the terminal chain. The results showed that substitution of carborane for a benzene ring in B[m] depresses the clearing point by 50 K to 208 K and eliminates all smectic behaviour in A[m]. The carborane derivatives A[m] are weakly dependent (effectiveness of : –CH = CHCOO–～–COO–～–CH = CH–>–CH = N–～–CH₂CH₂–>–CONH–), whereas the benzene analogues B[m] are strongly dependent (effectiveness of : –CONH–>–CH = CH–>–CH = N–～–CH = CHCOO–>–COO–>–CH₂CH₂–) on the structure of the linking group . The difference in the effectiveness of the amide group on mesophase stability (ΔT _I = 208 K) has been attributed to the stabilizing intermolecular H‐bonding in B[m], which is prevented in A[m] by steric and electronic effects of the carborane cage on the carbonyl group.     

The cooperative effect of a hydroxyl and carboxyl group on the catalytic ability of novel β-homoproline derivatives on direct asymmetric aldol reactions

Novel β-homoproline derivatives, 2-hydroxy-2-(pyrrolidin-2-yl)acetic acids (R,S)- and (S,S)-1a-d, were synthesized. All of the prepared compounds were used as organocatalysts in the direct asymmetric aldol reaction of 4-nitrobenzaldehyde with several ketones. Among these catalysts, (R)-2-hydroxy-2-((S)-pyrrolidin-2-yl)acetic acid (R,S)-1a showed good catalytic ability in the formation of aldol product 13 (up to 69% ee, 95% yield), which was similar to the results catalyzed by l-proline (71% ee, 96% yield). Relatively low yields and low enantioselectivities were observed in aldol reactions catalyzed by (S,S)-1a, for example, 13 was obtained in 55% yield and 13% ee. The aldol reaction catalyzed by the methyl-protected carboxylic acid 1b and esters 1c,d produced much lower chemical yields and enantioselectivities during the formation of 13. The cooperative effect of the (R)-configured hydroxyl group and the carboxyl group was found to play an important role in inducing enantioselectivity in the aldol reaction. Relatively high diastereoselectivities (anti:syn = 85:15) and enantioselectivity (anti, 83% ee) were observed in the aldol reactions of 4-nitrobenzaldehyde with cyclohexanone, which was catalyzed by (R,S)-1a.     

Reasons for the effect of the amount of electrolyte on the performance of lithium–sulfur cells

As is known, the depth of the electrochemical reduction of sulfur and lithium polysulfides, the reduction rate, and the cycle life of lithium–sulfur cells decrease with the electrolyte content. The present paper studies the reasons for the effect of the amount of electrolyte on the depth of sulfur reduction and the cycle life of lithium–sulfur cells. The main reason for the effect of the amount of electrolyte on the depth of the electrochemical reduction of sulfur was shown to be the generation of solvate complexes of lithium polysulfides. The minimum amount of electrolyte required for complete reduction of sulfur during the discharge of lithium–sulfur cells is determined by the composition of the generated solvate complexes of lithium polysulfides. The solvate numbers of the lithium ion in the solvate complexes of lithium polysulfides generted in sulfolane electrolyte systems were evaluated from the experimental data. An analysis of the results shows that the minimum solvate number of lithium ions in the solvate complexes of lithium polysulfides with sulfolane is 1.     

Anilinopyridine–metal complexes for the selective chromogenic sensing of cyanide anion

Abstract

Probe 1, which contains an anilinopyridine chromophore and an aza-oxa macrocyclic subunit, presented an absorption band centered at 340 nm in acetonitrile. Addition of Fe(III), Cr(III) and Hg(II) induced the growth of a new absorption band at 430 nm (with color change from colorless to yellow), whereas in the presence of Cu(II), Zn(II) and Pb(II), less marked changes were observed. The color changes observed upon addition of Fe(III), Cr(III) and Hg(II) were ascribed to the formation of 1:1 stoichiometry complexes with probe 1. Coordination of Fe(III), Cr(III) and Hg(II) with the pyridine fragment of 1 induced an enhancement of the charge transfer character accompanied with a marked bathochromic shift that was reflected in a color change from colorless to yellow. The strength of the interaction between probe 1 and Fe(III) cation was modulated upon interaction with anions. Of all the anions tested, only cyanide was able to induce the bleaching of the yellow 1·Fe(III) complex solution. This bleaching was ascribed to the formation of 1·Fe(III)-CN complex that restored, to some extent, the optical features of the free probe allowing the chromogenic sensing of cyanide. Besides, 1·Fe(III) complex was used to detect cyanide in acetonitrile-water 90:10 v/v mixtures with good recoveries.     

The effect of activated fillers on the properties of styrene–acrylic adhesives

Results of kaolin modification by thermal activation, sonication and 3% solution of acetic acid are considered. It is shown that the introduction of thermally activated kaolin to compositions based on styrene–acrylic filming agents increases the adhesion characteristics by 1.25–1.4 times (for steel and cement–sand surfaces) and cohesive strength by 1.5–2 times.     

The effect of gypsum on the hydration of alite–belite–ferrite phase system

Journal of Thermal Analysis and Calorimetry - Thermal analysis is a very effective method for the study of the hydration process of cement. This paper focuses on the interactions between the...     

Quinoxalinone–benzimidazole rearrangement: an efficient strategy for the synthesis of structurally diverse quinoline derivatives with benzimidazole moieties

A novel and efficient procedure for the synthesis of structurally diverse benzimidazolylquinolines has been realized through a new acid-catalyzed quinoxalinone–benzimidazole rearrangement of the spiro-quinoxalinone derivatives formed in situ from the reaction of 3-(2-aminophenyl)quinoxalin-2(1Н)-ones and different ketones.     

The disarming effect of the 4,6-acetal group on glycoside reactivity: torsional or electronic?

An evaluation of whether the well-known deactivating effect of a 4,6-acetal protection group on glycosyl transfer is caused by torsional or an electronic effect from fixation of the 6-OH in the tg conformation was made. Two conformationally locked probe molecules, 2,4-dinitrophenyl 4,8-anhydro-7-deoxy-2,3,6-tri-O-methyl-beta-D-glycero-D-gluco-octopyranoside (18R) and the L-glycero-D-gluco isomer (18S), were prepared, and their rate of hydrolysis was compared to that of the flexible 2,4-dinitrophenyl 2,3,4,6-tetra-O-methyl-beta-D-glucopyranoside (21) and the locked 2,4-dinitrophenyl 4,6-O-methylidene-2,3-di-O-methyl-beta-D-glucopyranoside (26). The rate of hydrolysis at pH 6.5 was 21 > 18R > 18S > 26, which showed that the deactivating effect of the 4,6-methylene group is partially torsional and partially electronic. A comparison of the rate of acidic hydrolysis of the corresponding methyl alpha-glycosides likewise showed that the probe molecules 17S and 17R hydrolyzed significantly slower than methyl tetra-O-methyl-glucoside 19, confirming a deactivating effect of locking the saccharide in the (4)C(1) conformation. The experiments showed that the hydroxymethyl rotamers deactivate the rate of glycoside hydrolysis in the order tg > gt > gg.     

8-AminoBODIPYs: cyanines or hemicyanines? The effect of the coplanarity of the amino group on their optical properties

The role of the amino group twisting ability in the BODIPY photophysics for nonsterically hindered and constrained molecular structures was studied. When a coplanar disposition of the amino and the BODIPY core is feasible, a hemicyanine-like delocalized π-system gives rise to novel blue and efficient BODIPY laser dyes. The key role of such rotamer is confirmed by newly synthesized derivatives where the amino and the BODIPY core are electronically decoupled by steric repulsions.     

The effect of ligand basicity on the thermal stability of heterodinuclear NiII–ZnII complexes

Four complexes of the nuclear structure Ni^II–Zn^II were prepared with bis-N,N′-(salicylidene)-1,3-propanediamine (LH₂), bis-N,N′-(salicylidene)-2,2′-dimethyl-1,3-propanediamine (LDMH₂) and the reduced derivatives of these Schiff bases, bis-N,N′-(2-hydroxybenzyl)-1,3-propanediamine (L^HH₂), bis-N,N′-(2-hydroxybenzyl)-2,2′-dimethyl-1,3-propanediamine (LDM^HH₂). The complexes were characterized using IR spectroscopy, elemental analysis and thermogravimetric methods. The stoichiometry of the complex molecules were found to be NiL·ZnCl₂·(DMF)₂, NiLDM·ZnCl₂·(DMF)₂, NiL^H·ZnCl₂·(DMF)₂ and NiLDM^H·ZnCl₂·(DMF)₂. The molecular models of the complexes prepared with the reduced Schiff bases were determined according to the X-ray diffraction method. It is seen that in these complexes Ni(II) is in octahedral and Zn(II) is in tetrahedral coordination sphere. Ni(II) ion is coordinated between two nitrogen and two oxygen donors of the ligand and oxygen donors of the two DMF molecules. Zn(II) ion on the other hand is coordinated between two oxygen of the organic ligand forming two μ bonds. It also coordinates two Cl ions. The thermogravimetric analysis showed that the complex NiLDM^H·ZnCl₂·(DMF)₂ containing methyl groups is more stable than the other complex NiL^H·ZnCl₂·(DMF)₂ containing reduced Schiff base. The coordinative DMF molecules in NiLDM^H·ZnCl₂·(DMF)₂ were thermally cleaved. However, the cleavage of DMF molecules NiL^H·ZnCl₂·(DMF)₂ resulted in the thermal degradation of the complex. In order to explain the TG data of the ligands were titrated in non-aqueous medium and their basicity strengths were determined. It was found that the basicity of the ligands containing two methyl groups were stronger. It is understood that the two methyl groups increase the negative charge density on nitrogen causing an increase in complex stability.     

The effect of sintering conditions on the properties of WC–10wt%Co PIM compacts

The powder injection molding (PIM) process has an advantage of near net shaping of homogeneous micro structure and density at the complicate form. This study was investigated for microstructure and mechanical properties of WC–10%Co insert tool alloy fabricated by PIM process. The WC–10%Co feedstock mixed with wax binder was fabricated by two blade mixer. After WC–10%Co feedstocks were injection molded, debinding process was carried by two-steps methods with solvent extraction and thermal debinding. The binder was eliminated with normal hexane for 12 h at 50 °C by solvent extraction, and subsequently thermal debinding was examined for 1 h at the temperature 900 °C. After debinding process, the specimens were sintered at vacuum or N₂/H₂ mixed gas atmosphere at 1380 °C. The microstructure and phase were observed by FE-SEM. In the case of sintered at 1380 °C in vacuum atmosphere, the hardness was 1600 Hv, and the relative density of WC–10%Co was 92.5%. The density of WC–10%Co sintered at 1380 °C in mixed gas atmosphere was 87.5% and the hardness was lower than 1400 Hv. Residual carbon contents of sintered at vacuum and mixed gas atmosphere were 5.4 wt%.     

Synthesis of bi- and tervalent ligands of galectins,derivatives of β-lactosylamine,with the amino group in the terminal position of the spacer

A method for the synthesis of glycoclusters by N-alkylation of N-glycyl-β-lactosylamine with N-chloroacetyl derivatives of β-lactosylamine and N,N’-iminodiacetyldilactosylamine has been developed. The glycoclusters obtained with two and three lactosylamine residues with the amino group in the spacer were found to be suitable for further conjugation with carboxy-containing physiologically active compounds. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 647–651, March, 2008.     

Fabrication of the ZnO/NiO p–n junction foam for the enhanced sensing performance

P-Type NiO foam with rough nanostructured surface was prepared by the surface treatment of Ni foam,and then it was decorated with n-type ZnO nanopyramids to construct a 3D p–n junction foam. The p–n junction foam was used for electrochemical detection of dopamine and the sensing performance was improved significantly compared with the single NiO and ZnO. High sensitivity(171 mμA/mmol/L), fast response(2 s), excellent selectivity and stability were achieved. It was attributed to the introduction of numerous p–n junction interfaces, the interfacial potential barrier played as a tuning factor for the electrochemical determination of dopamine. The results demonstrated it would be an important way to improve the biosensing performance by introducing the p–n junction interfaces.     

The effect of heavy metals on the anthracene–Me-β-cyclodextrin host–guest inclusion complexes

Anthracene was used to form an inclusion complex with methylated-β-cyclodextrin (Me-β-CD) in water. In aqueous Me-β-CD solution, typical fluorescence emission of anthracene was observed. Benesi–Hildebrand's method was used to obtain the stoichiometry of the anthracene–Me-β-CD complex. The Stern–Volmer quenching constants, K_sv, and fluorescence quantum yields were calculated according to changes in the fluorescence emission intensity of anthracene–Me-β-CD inclusion complexes by adding various amounts of Pb²⁺ and Cd²⁺ salts in water. The K_sv values and fluorescence quantum yields indicate that Pb²⁺ salts quench the anthracene–Me-β-CD inclusion complexes more efficiently than Cd²⁺ salts.     

Promotion of the oxygen evolution performance of Ni–Fe layered hydroxides via the introduction of a proton-transfer mediator anion

Developing efficient catalysts with high durability and activity for the oxygen evolution reaction(OER)is imperative for sustainable energy conversion technologies,including hydrogen generation and CO₂ reduction,as well as other electrochemical energy storage systems.To this end,a comprehensive understanding of the mechanism for the water oxidation reaction is vital.Herein,a surfactant,nonafluoro-1-butanesulfonate(FBS),was introduced into Ni-Fe layered double hydroxide(Ni Fe-FBS/CFP)via electrochemical deposition on the surface of a carbon fiber paper(CFP)substrate.The as-prepared Ni Fe-FBS/CFP electrode exhibited excellent catalytic activities for OER compared to the Ni-Fe layered double hydroxide based electrode(Ni Fe-LDH/CFP),an excellent stability of 15 h,and an ultralow Tafel slope of 25.8 m V dec-1.Furthermore,by combining the results of p H-dependent kinetics investigations,chemical probing,proton inventory studies,and isotopic and atom-protontransfer measurements,it was observed that a proton-transfer process controls the reaction rates of both the Ni Fe-LDH and Ni Fe-FBS catalysts,and the residual sulfonate groups serve as proton transfer mediator to accelerate the proton transfer rate.     

The effect of β-cyclodextrin on the properties of cetyltrimethylammonium bromide micelles

The effect of ß-cyclodextrin (ß-CD) on cetyltrimethylammonium bromide (CTAB) micellar properties was studied by the determination of the diffusion coefficient, D. When the CTAB micelles have a spherical structure, D firstly increased and then remained unchanged, while the micellar aggregation number, N, decreased with the addition of ß-CD. When the CTAB concentration was less than the first critical micellar concentration, CTAB molecules could be included into ß-CD cavities with the molar ratio of CTAB to ß-CD being about 1:1. However, when the CTAB concentration was higher than the first critical micellar concentration, mixed spherical micelles were formed with the molar ratio of CTAB to ß-CD being 9:1.     

Cooperative effect of Fe and Ti species over Fe–Ti–Ox catalysts on the catalytic hydrolysis performance of hydrogen cyanide

FeO_x, TiO₂, and Fe–Ti–O_x catalysts were synthesized and used in the catalytic hydrolysis of hydrogen cyanide (HCN). Nearly 100% HCN conversion was achieved at 250 °C over the Fe–Ti–O_x catalyst. TiO₂ rutile was detected over TiO₂, but not over Fe–Ti–O_x, which suggested that the interaction between Fe and Ti species could inhibit the TiO₂ phase transition. Furthermore, the interaction between Fe and Ti species over Fe–Ti–O_x could promote the selectivity of NH₃ and CO. The mechanism of hydrolysis of HCN over FeO_x, TiO₂, and Fe–Ti–O_x can be given as follows: HCN + H₂O → methanamide → ammonium formate → formic acid → H₂O + CO.