Ratio In Tetrahydrofuran Research Articles

Innovative preparation of polyimide/polysulfone amide (PI/PSA) membrane-pore-like nanofibers with biomimetic penguin feather shaft structure and thermal insulation performances

The white-browed penguin can survive in extreme environments due to its unique feather structure. The feather shafts of penguins are porous, separated by the membrane-pore-like structure made of keratin fiber membranes. The feather branches are densely arranged around the feather shafts. This unique structure provides inspiration for researchers. In this work, we developed a simple method to construct polyimide/polysulfone amide (PI/PSA) membrane-pore-like structure nanofibers resembling penguin feather shafts and studied the effects of different low-boiling point solvents (tetrahydrofuran (THF), ethyl acetate (EA), and acetone (AC)) on the morphology, tensile properties, and thermal insulation properties of PI/PSA membrane-pore-like structure nanofibers. Comprehensive characterization was also performed using scanning electron microscope, total reflection infrared spectrometer, X-ray diffractometer, universal testing machine, thermal conductivity meter, pore size analyzer, thermal gravimetric analyzer, infrared thermal imaging instruments, and thermocouple testing instruments. The results showed that when the mass ratio of THF to N, N-dimethylacetamide (DMAC) was 20/80, the prepared PI/PSA membrane-pore-like structure nanofibers exhibited excellent thermal insulation properties, with a low thermal conductivity of 0.0436 W·m−1·K−1, a breaking strength of 7.72 ± 2.64 MPa, and a breaking elongation of 8.19 ± 4.07 %. The biomimetic membrane-pore-like structure with excellent thermal insulation properties is expected to be applied in various fields, such as heat-protective clothing and architectural coatings in harsh environments.

Role of alkyl chain length on aggregation enhanced two-photon absorption and thermal diffusivity of Carbazole-Barbituric acid D-π-A systems

Aggregation Induced Emission (AIE) luminogens exhibit no or faint emission in dilute solution and are induced to emit when aggregated with restriction of intramolecular motion as the principle mechanism. We investigated the role of hydrophobic interaction in AIE effect by varying the alkyl chain length of Carbazole-Barbituric acid (CBA) D-π-A system. We synthesized six CBA conjugates, studied their photophysical properties and morphological changes upon aggregation by varying water: tetrahydrofuran ratio. We performed thermal lens experiment in all CBA conjugates to understand the variation in radiative and non-radiative decays upon aggregation. Both aggregation and hydrophobic interaction is found to play significant role in tuning thermal diffusivity of CBA conjugates. The knowledge about their energy levels was gained by using DFT in Gaussian 09 program package. Perturbation of energy levels associated with molecular aggregation open up the possibility of such D-π-A system in nonlinear optics. The open aperture Z-scan technique with Nd:YAG laser at 1064 nm was utilized to measure the change in two-photon absorption (TPA) coefficient at different stages of aggregation and as a function of alkyl chain lengths. We observed an aggregation enhanced TPA and could tune the TPA in aqueous solution by changing the alkyl chain length. Experimentally observed TPA coefficient showed the same trend as obtained in DFT calculation for hyperpolarizability. Furthermore, for practical utility we fabricated CBA conjugate doped PMMA thin films for low threshold optical limiting applications.

Synthesis of ultra-stretchable thermoelectric nanofibrous membrane based on wet-electrospun Polyurethane/MWCNTs composites

Electrospinning is a versatile method used to create nanofiber membranes with surface-to-volume ratios much higher than those achievable with other film fabrication methods. This technique allows the control of nanofiber morphology, including diameter, shape, and orientation. Such nanostructuring can enhance the thermoelectric performance of composite materials due to quantum confinement and filtering effects. However, the thermoelectric efficiency of a typical electrospun composite is limited due to the insulating nature of the polymer matrix. Therefore, many researchers have combined electrospinning with other techniques or post-treatments to accomplish higher thermoelectric performance. In this study, a new strategy to prepare a stretchable thermoelectric nanofibrous membrane is proposed. The ternary composite of Thermoplastic Polyurethane (TPU)/Multi Wall Carbon Nanotubes (MWCNTs)/Poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT: PSS) is obtained by electrospinning of TPU/MWCNTs solution in coagulation bath of PEDOT: PSS water dispersion. The nonsolvent-induced phase separation (NISP) phenomenon, and consequently, the formation of CNTs/PEDOT: PSS/CNTs electrically-conductive chains, were controlled by tuning the concentrations from binary solvents. The optimal value of the Power Factor, 4.28 μW m⁻1 K⁻2, was obtained for 0.12% MWCNTs and a 1:4 ratio of Tetrahydrofuran (THF) to N, N-Dimethylformamide (DMF) in the binary solvent. The sample exhibits a high value of electrical conductivity of 85 S m⁻1 and shows a strain range of 190 %. This study demonstrates the significant potential of the wet-spinning method for producing wearable and sustainable thermoelectric devices, offering an alternative to conventional devices that raise concerns regarding resource scarcity and environmental impact.

Structure and Dynamics of the Electrical Double Layer during the Rapid Alternating Polarity Electro-Synthesis

Conventional electrochemical organic synthesis uses direct current (DC) condition, where the electrode polarity is not changed during the operation. Unlike DC, alternating current (AC) introduces two more tunable parameters into the potential or current profile: frequency and waveform, allowing new possibilities for modulating reaction efficiency and selectivity. Several very recent AC electrosynthesis examples have shown that the AC can lead to enhanced chemoselectivity that cannot be reproduced by their DC counterparts1–3. For instance, Hayashi et al. presented a highly selective and easily scalable Birch-type reduction of heteroarenes by rapid alternating polarity (rAP) waveform3. AC voltage transforms the reaction kinetics presumably by affecting the mass transfer of reactive species both in the bulk solution and the electrical double layers (EDL). However, the mechanistic origin of the unique reactivity in AC electrosynthesis is underexplored. Molecular-level details are still in lack to possibly guide the rational design of AC reaction parameters.In this study, we have chosen the rAP heteroarene reduction as the example system and employed classical molecular dynamics (MD) simulations to reveal the liquid structure and dynamics in bulk and interfacial electrolyte. To capture the electrode-electrolyte interfaces, a slab-geometry simulation cell was used, where a 10 nm thick liquid electrolyte is sandwiched between two oppositely charged graphene surfaces. The multicomponent electrolyte was composed of ethanol and tetrahydrofuran (THF) as the co-solvent, [(CH3)4N]+[(BF4)]- as the salt, and a heteroarene substrate. Based on the charge distribution function statistics, the EDL layer was about 1 nm thick, so if any of the oxygen atom in the ethanol or THF is within 6 Å to the electrode surface, they are considered to be within the EDL. Under both AC and DC, the ethanol to THF ratio was higher than that in the bulk electrolyte due to stronger ion-ethanol attraction. The EDL structure responded to electric field polarity change at different time scales. First, the molecule orientation would flip also within the picosecond time scale after the polarity switch. By tracking the number of molecules in the EDL, we have found that the compositional fluctuation in the EDL converges in about 40 ps. Although it is the ion migration that gets directly affected by the alternating electric field, diffusion of charge-neutral molecules was also found to be accelerated under AC, according to the higher mean squared displacement calculated from the movement of all molecules of each species in the simulation box. This accelerated diffusion spans a larger length and longer time scales. A multi-scale model is proposed to describe both reaction kinetics and liquid structure dynamics simultaneously.

Effects of diesel-ethanol-THF blend fuel on the performance and exhaust emissions on a heavy-duty diesel engine

The application of ethanol in diesel engines is limited for the poor solubility. Tetrahydrofuran (THF) as a promising biofuel can improve the solubility. In this study, the effects of THF and ethanol on combustion and emissions were investigated on a six-cylinder heavy-duty diesel engine. In terms of test fuels, the volume ratio of THF was 5%, and ethanol ratio was 0%, 10%, and 30%, respectively. Results show that the combustion characteristics are nearly the same in both fuels with and without THF addition in diesel. With the increase of ethanol, the ignition delay prolongs, the peak heat release rate raises and brake thermal efficiency increases. The delay of the combustion phase at a low load is more obvious than a high load. The addition of THF or 30% ethanol increases NOx emissions, while the addition of 10% ethanol reduces NOx emissions at low load. Also, the addition of THF or ethanol decreases soot emissions significantly, but HC and CO emissions increase significantly at low loads. In the World Harmonized Stationary Cycle test cycle of Euro VI regulation (the speeds contain 998, 1137, 1276, 1415, and 1694 rpm and the loads cover the idle to full load), compared with diesel fuel, the addition of 10% and 30% ethanol makes BTE decrease by 1.7% and 0.8%, NOx emissions increase by 16.2% and 22.6%, soot emissions decrease by 39.2% and 77.3%, HC emissions increase by 6.9% and 39.3%, and CO emissions decrease by 13% and increase by 43.5%, respectively.

Fabrication of new ordered mesoporous carbons from petroleum pitch by triblock copolymer direct templating method

A highly ordered mesoporous carbon nanocage (OMC) direct synthesis method is introduced in this article. Petroleum pitch is chosen as a hydrophobic carbon precursor, tetrahydrofuran (THF) is used as solvent, the triblock copolymer F127 as structure directing agent, while the liquid crystal templating (LCT) is used as the templating mechanism, and the OMC was obtained via a one-step nanocasting method. Experimental results showed that the introduction of proper amounts of petroleum pitch and THF ratio does not hamper the synthetic process of the structure of OMC, thus a uniform carbon composite is finally formed. It was found that the as-prepared nanoporous carbon has a three-dimensional 7.5 nm-sized carbon nanocage network. Such a uniform mesoporous carbon material exhibits a high Brunauer–Emmett–Teller (BET) surface area (446.9 m2 g− 1) and a total pore volume (0.6 cm3 g− 1).

Syntheses, silylation, characterization, and antimicrobial and antifertility activities of organoboron derivatives of some bioactive monofunctional bidentate semicarbazones

Some new mononuclear organoboron derivatives of the type PhBL1–5(OH) (1a–1e) were synthesized by the reaction of PhB(OH)2 and LH (LH = OC(NH2)NH:NC(CH3)4C6H4R, where R = H (L1H); CH3(L2H); OCH3(L3H); Cl (L4H); Br (L5H)) in 1:1 molar ratio in refluxing tetrahydrofuran (THF). This was followed by the reactions of PhBL1–5(OH) with NH(SiMe3)2 in 2:1 molar ratio in THF to yield new heterodinuclear derivatives of the type PhBL1–5(OSiMe3) (2a–2e). All these newly synthesized complexes were characterized using elemental analyses and their probable structure was proposed on the basis of infrared, 1H NMR, 13C NMR, 11B NMR and 29Si NMR spectral data and mass spectrometry. Semicarbazone ligands and their corresponding mono‐ and heterodinuclear boron derivatives were screened against pathogenic bacteria (E. coli and P. aeruginosa) and fungi (A. niger and P. peniculosum) to examine their antimicrobial activities. Representative compounds of each series of mono‐ and heterodinuclear boron derivatives and a ligand were screened for their antifertility activity on male adult Wistar rats.

Impact of electrospinning process parameters on the measured current and fiber diameter

In this article, polycaprolactone (PCL) nanofibres were processed by electrospinning using a 3:1 ratio of tetrahydrofuran to methanol as solvent. The solvent choice was motivated by the possibility of greener alternatives to the halogenated compounds most often used for electrospinning. The morphologies and fiber diameters resulting from the electrospinning of PCL solutions at room temperature under various conditions are presented in this article. The material morphology was characterized using scanning electron microscopy and a measuring software. The process was optimized for smaller fibers with a narrower fiber diameter distribution by studying parameters such as polymer concentration, applied voltage, the tip to collector distance (TCD), and the solution flow rate. A comparison analysis was used to separate the current resulting from whipping and that resulting from spraying at high voltage. The fiber diameters obtained under various processing conditions were effectively modeled using the terminal jet theory, referenced in several works. Process parameters were optimal for a 20% PCL concentration spun at a flow rate of 0.5 mL/h, with a TCD of 15 cm and an applied voltage of 8 kV. Fibers spun under these conditions displayed diameters of 546 ± 173 nm. POLYM. ENG. SCI., 55:2576–2582, 2015. © 2015 Society of Plastics Engineers

Development of UV LED Hydrogel Formulation Based on Polyacrylamide Hydrogel

Recent trends show that the UV LED light source can greatly reduce environmental effect without compromising performance as compared to conventional UV mercury-based lamp (UV Hg) system. In this study, the possibility of using UV LED technology for photopolymerization of polyacrylamide (PAAm) hydrogels is presented. This has strongly drives the needs for suitable water-soluble photoinitiator formulation. Specifically, the photoinitiator must possess characteristic wavelength within UV LED range as UV LED emits monochromatic light sources only (365 nm or 385 nm). Here, the commercially available photoinitiator Oligo [2-hydroxy-2-methyl-1-[4-(1-methylvinyl) phenyl] propanone] (Chivacure 300) was chosen. However, Chivacure 300 has limited solubility in water. Hence, addition of tetrahydrofuran (THF) at various ratios was required. The results demonstrated that 9.5:0.5 ratio of water/THF was the minimum ratio needed for the solubility of Chivacure 300. After the synthesis of PAAm hydrogels, almost complete conversion of hydrogels was achieved (> 80 %). The highest conversion was achieved with formulation of Chivacure 300 in 9.5:0.5 ratio of water/THF. At this ratio, the hydrogels obtained were transparent. With increasing ratio of THF in water, the appearance of hydrogels gradually changed to cloudy. Indeed, UV LED technology can be used to polymerize PAAm hydrogels with comparably high conversion to conventional UV Hg system.

Synthesis and Structure of Potassium and Barium Complexes With Diphenylphosphinothioicamido Ligand Containing Ba-S Direct Bonds

GRAPHICAL ABSTRACT

Enhancing concentration of oxygen by polysulfone membrane for environmental applications

For the purpose of using membranes from polysulfone (PSF) for oxygen enrichment, the membranes were prepared by dry/wet method. This method was involved in evaporation step in the air followed by an immersion into a water bath. Then a thin top layer of the asymmetric membrane was formed in the evaporation step. There are three experimental parameters that influce the formation of membrane including polymer concentration, evaporation time, and the ratio of tetrahydrofuran (THF)/N-methylpyrrolidone (NMP) were studied. From experiments, some results of polysulfone membrane formed by dry/wet method showed high selectivity coefficient of 1,53 at 0,1 MPa pressure with the flow of oxygen through the membrane of 0,310ml/s.

Synthesis and Characterization of Salalen Lanthanide Complexes and Their Application in the Polymerization of rac-Lactide

A series of neutral lanthanide complexes supported by ONNO Salalen-type ligands were synthesized, and their catalytic activity for the polymerization of rac-lactide (rac-LA) was explored. The amine elimination reactions of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 with the ONNO Salalen-type ligand L1H2 (L1 = (2-O-C6H2-But2-3,5)CH═NCH2CH2N(Me)CH2(2-O-C6H2-But2-3,5)) in a 1:1 molar ratio in tetrahydrofuran (THF) gave the neutral lanthanide amides L1Ln[N(SiMe3)2](THF) (Ln = Y (1), Sm (2), Nd (3)). Reaction of the lanthanide amides with benzyl alcohol produces the dimeric lanthanide alkoxo complex (L1LnOCH2Ph)2 (Ln = Y (4), Sm (5)) in high isolated yield. Y[N(SiMe3)2]3(μ-Cl)Li(THF)3 reacted with the Salalen-type ligand L2H2 (L2 = (2-O-C6H2-But2-3,5)CH═NCH2CH2N(Me)CH2{2-O-C6H2-(CPhMe2)2-3,5}) in a 1:l molar ratio in THF also gave the desired yttrium amide, but this complex could not be separated because of its very good solubility even in n-pentane. The proton exchange reactions of L1H2 and L2H2 with (C5H5)3Ln(THF) in a 1:1 molar ratio in THF and then with 1 equiv of benzyl alcohol gave the desired lanthanide alkoxides [L1Ln(OCH2Ph)]2 (Ln = Y (4), Sm (5), Yb (6)) and [L2Y(OCH2Ph)]2 (7), respectively. Complexes 1–7 were well characterized by elemental analyses, IR spectra, X-ray single-crystal structure determination, and NMR spectroscopy in the case of complexes 1, 4, and 7. Complexes 1–3 are isostructural and have a solvated monomeric structure. The coordination geometry around the lanthanide atom can be best described as a distorted trigonal bipyramid. Complexes 4–7 are dimeric species in the solid state. They all contain a Ln2O2 core bridging through the oxygen atoms of the two OCH2Ph groups. Each of the lanthanide atoms is also six-coordinated to form a distorted octahedron. It was found that all the complexes are efficient initiators for the ring-opening polymerization of rac-LA, giving PLA with good heterotacticity (Pr up to 0.85). The observed order of increase in activity is in agreement with the order of the ionic radii, whereas the stereoselectivity is in reverse order. The steric bulkiness of the substituents on the phenol ring has no obvious impact on the rate and stereocontrolability of the polymerizations. The Ln–O species resulted in more controllable polymerization than the corresponding Ln–N species, and complex 4 can initiate rac-LA polymerization in a controlled manner.

Syntheses and structures of lanthanide borohydrides supported by a bridged bis(amidinate) ligand and their high activity for controlled polymerization of ε-caprolactone, l-lactide and rac-lactide

Metathesis reaction of LLnCl(THF)(2) [L = (Me(3)SiNC(C(6)H(5))N)(2)(CH(2))(3)] with NaBH(4) in a 1 : 1.5 molar ratio in THF (THF = tetrahydrofuran) at 60 °C afforded the monoborohydride LLn(BH(4))(DME) [Ln = Y (1), Nd (2), Sm(3) and Yb(4)] crystallized from DME solution (DME = dimethoxyethane). Crystal structure analyses revealed 1-4 are monomers, in which each metal is ligated by one L ligand, one η(3)-BH(4) group and one DME molecule in a trigonal bipyramid geometry. Complexes 1-4 were found to be very active single-site initiators for the controlled ring opening polymerization of ε-caprolactone (ε-CL) and L-lactide (L-LA) as judged by relatively narrow molecular weight distributions (M(w)/M(n): 1.34-1.50) and experimental values M(n)(exp) were in good agreement with theoretic values M(n)(theo). The highest activity and the best control over the molecular weight for both monomers were found for the system with 2. These monoborohydride complexes can also initiate the ring opening polymerization of rac-LA to gave heterotactically enriched polyLA with Pr (heterotactic enrichment) values in a range of 0.69-0.85 depending on the lanthanide metals and the most effective heterotactic enrichment (Pr) was found for 1 (Pr = 0.85). Moreover, complex 1 initiated the polymerization of rac-LA in a living fashion.

Dispersion and Preparation of Polyurethane/Carbon Nanotubes Composites

In the paper, the polyurethane/carbon nanotubes composites were prepared by solution-blending method. The polyurethane dissolution, carbon nanotubes dispersion agent, dispersion method and preparation of composites were analyzed. The results showed that the tetrahydrofuran and N-N-dimethylfomamide could used as the dissolution of polyurethane. The dissolution is most even with the ratio of tetrahydrofuran and N-N-dimethylfomamide of 1:1, and 1g polyurethane grains were resolved with 20ml solutions about 72 h. The N-N-dimethylfomamide was used as dispersion agent of carbon nanotubes by ultrasonic dispersion about 2h. The producing process of polyurethane/carbon nanotubes composites was successively heating, drying, and solidifing in the air, so the smooth surface could be received. The results indicated that the dispersion effect from good to poor is ultrasonic dispersion, magnetic dispersion and machining dispersion. With extension in time and increasing disperse frequency, the dispersion effect is better and better. But it also presented that the carbon nanotubes were reunited by magnetic and ultrasonic dispersion after the certainly scattered time, their best dispersion time were respectively two hours and one and a half hours.

Ring‐opening polymerization of ε‐caprolactone using perfluoroalkanesulfonates and perfluoroalkanesulfonimides as organic catalysts

AbstractWe examined ring‐opening polymerizations (ROPs) of ε‐caprolactone in toluene at 25–50 °C catalyzed by perfluoroalkanesulfonates and perfluoroalkanesulfonimides as organic catalysts. The ROPs proceeded quickly using these super Brönsted acids as catalysts. We synthesized poly(ε‐caprolactone)s (Mn = 4.8 × 103–13.5 × 103) with low polydispersity (Mw/Mn = 1.10–1.48). These strong Brönsted acids catalyzed living polymerizations of ε‐caprolactone. After polymerization, Nf2NH was recovered and reused. To survey solvents, CHCl3 and tetrahydrofuran (THF) were used instead of toluene as solvents for polymerization. When THF was used as a solvent, not only ε‐caprolactone, but also THF was polymerized and incorporated into the polymer chain (incorporated THF ratio; 6–10%). We investigated the reaction kinetics and activation thermodynamics of the organic catalysts. The activation energy and the activation enthalpy values for the ROPs of ε‐caprolactone using the catalyst having electron‐withdrawing ligand were smaller, but the activation entropy value is more negative. Moreover, the ranked values of the activation enthalpy for the reaction well parallel the polarity of solvents. The ranked values of the activation free energies well parallel those of the times required for polymerization completion. Our findings indicate that the super Brönsted acids are excellent catalysts for rapid ROP of ε‐caprolactone: they are more active than N, N‐dimethylaminopyridine (DMAP) or stannous (II) 2‐ethylhexanoate [Sn(Oct)2]. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Electrospun Cellulose Nitrate Nanofibers

Cellulose nitrate nonwoven mats of submicron-sized fibers (100-1200 nm in diameter) were obtained by electrospinning cellulose nitrate solutions. Two solvent systems were evaluated. A 70:30 (wt) ratio of ethanol to acetone and a 60:40 (wt) ratio of tetrahydrofuran (THF) to N,N-dimethylformamide (DMF) were studied. The effects of the two solvent systems, and type two different collectors; void gap, and steel drum coated with polyvinylidene dichloride (PVDC), were investigated. The PVDC layer applied to the rotating drum aided in fiber harvesting. Electron microscopy (FESEM and ESEM) studies of as-spun fibers revealed that the morphology of cellulose nitrate fibers depended on the collector type and solution viscosity. When a rotating steel drum was employed a random morphology was observed, while the void gap collector produced aligned fiber mats. Increases in viscosity lead to larger diameter fibers.

Long-Chain Ketimine Synthesis in a Gold−Thallium Polymer

The heteropolynuclear complex [Tl{Au(C6Cl5)2}]n reacts with sterically demanding diamines as tetramethylenediamine (TMDA), 2,2′-(ethylenedioxy)bis(ethylamine) (NOON), or triethylenetetramine (trien) in 1:1 molar ratio in tetrahydrofuran (THF), leading to products of stoichiometry [Tl{Au(C6Cl5)2}(L)]n (L = TMDA (1), NOON (2), or trien (3)) or [Tl2{Au(C6Cl5)2}2(L)]n (L = trien (4)) when the solvent used is toluene. Addition of acetylacetone to the diamine complexes in 1:1 molar ratio generates [Tl{Au(C6Cl5)2}{O═C(CH3)CHC(CH3)NH(CH2)4NH2}]n (5) and in 1:2 molar ratio [Tl{Au(C6Cl5)2}(Lx)]n (Lx = {O═C(CH3)CHC(CH3)NHCH2CH2}2 (6), {O═C(CH3)CHC(CH3)NHCH2CH2OCH2}2 (7)). When the molar ratio is 1:2, with the exception of 3, all these complexes display luminescence in the solid state at room temperature and at 77 K. The origin of the luminescence could be assigned to a delocalizated exciton along the heterometallic chain formed by Au···Tl interactions. In addition, a red shift is observed when the temperature decreases, which is attributed to the shortening of the Au−Tl distance at lower temperatures. The emissive properties of solutions of 5−7 and [Tl{Au(C6Cl5)2}]n in THF were studied after adding increasing amounts of different metal ions (Zn2+, Cd2+, Hg2+, Pb2+, Cu2+, Al3+, Ni2+, Ag+, Mn2+, Bi3+) and anions (F−, Cl−, Br−, I−, H2PO4−, ClO4−, Bz−, Ac−, HSO4−, NO3−). Interestingly, an enhancement of the fluorescence emission intensity was observed for the complexes considered only upon addition of Br−, Cl−, and Ac−.

Synthesis of Rare-Earth Metal Amides Bearing an Imidazolidine-Bridged Bis(phenolato) Ligand and Their Application in the Polymerization ofl-Lactide

A series of neutral rare-earth metal amides supported by an imidazolidine-bridged bis(phenolato) ligand were synthesized, and their catalytic activity for the polymerization of l-lactide was explored. The amine elimination reactions of Ln[N(TMS)(2)](3)(mu-Cl)Li(THF)(3) with H(2)[ONNO] {H(2)[ONNO] = 1,4-bis(2-hydroxy-3,5-di-tert-butyl-benzyl)-imidazolidine} in a 1:1 molar ratio in tetrahydrofuran (THF) gave the neutral rare-earth metal amides [ONNO]Ln[N(TMS)(2)](THF) [Ln = La (1), Pr (2), Nd (3), Sm (4), Yb (5), and Y (6)] in high isolated yields. All of these complexes are fully characterized. X-ray structural determination revealed that complexes 1-6 are isostructural and have a solvated monomeric structure. The coordination geometry around each of the rare-earth metal atoms can be best described as a distorted trigonal bipyramid. It was found that complexes 1-6 are efficient initiators for the ring-opening polymerization of l-lactide, and the ionic radii of the central metals have a significant effect on the catalytic activity. A further study revealed that these rare-earth metal amides can initiate l-lactide polymerization in a controlled manner in the presence of 1 equiv of isopropyl alcohol.

Synthesis, Reactivity, and Characterization of Sodium and Rare-Earth Metal Complexes Bearing a Dianionic N-Aryloxo-Functionalized β-Ketoiminate Ligand

The synthesis and reactivity of a series of sodium and rare-earth metal complexes stabilized by a dianionic N-aryloxo-functionalized beta-ketoiminate ligand were presented. The reaction of acetylacetone with 1 equiv of 2-amino-4-methylphenol in absolute ethanol gave the compound 4-(2-hydroxy-5-methylphenyl)imino-2-pentanone (LH2, 1) in high yield. Compound 1 reacted with excess NaH to afford the novel sodium cluster [LNa2(THF)2]4 (2) in good isolated yield. Structure determination revealed that complex 2 has the 22-vertex cage structure. Reactions of complex 2 with anhydrous LnCl3 in a 1:4 molar ratio, after workup, gave the desired lanthanide chlorides [LLnCl(DME)]2 [Ln = Y (3), Yb (4), Tb (5)] as dimers. A further study revealed that complexes 3-5 are inert for chlorine substitution reactions. (ArO)3Ln(THF) (ArO = 2,6-Bu(t)2-4-MeC6H2O) reacted with compound 1 in a 1:1 molar ratio in tetrahydrofuran (THF), after workup, to give the desired rare-earth metal aryloxides as dimers [LLn(OAr)(THF)]2 [Ln = Nd (6), Sm (7), Yb (8), Y (9)] in high isolated yields. All of these complexes are well characterized, and the definitive molecular structures of complexes 2 and 4-6 were determined. It was found that complexes 6-9 can be used as efficient initiators for L-lactide polymerization, and the ionic radii of the central metals have a significant effect on the catalytic activity.

Spectrophotometric measurement of carotenes, xanthophylls, and chlorophylls in extracts from plant seeds

The method of spectrophotometric measurement of carotenoid and chlorophyll content in extracts from plant seeds was modified. The pigments were extracted with a mixture of petroleum ether (PE) and tetrahydrofuran (THF) (PE to THF ratio 4: 1). Equations for calculations of β-carotene, lutein, chlorophyll a and b content in PE: THF mixture were obtained using specific absorption coefficients of solutions of particular pigments. It was shown that subtraction of chlorophyll contribution from the absorption spectrum of seed extracts yields spectra, which could be used in some cases for calculation of carotene and xanthophyll contents.