Mechanistic consequences of composition in acid catalysis by polyoxometalate keggin clusters

The kinetics and mechanism of ether and alkanol cleavage reactions on Br?nsted acid catalysts based on polyoxometalate (POM) clusters are described in terms of the identity and dynamics of elementary steps and the stability of the transition states involved. Measured rates and theoretical calculations show that the energies of cationic transition states and intermediates depend on the properties of reactants (proton affinity), POM clusters (deprotonation enthalpy), and ion-pairs in transition states or intermediates (stabilization energy). Rate equations and elementary steps were similar for dehydration of alkanols (2-propanol, 1- and 2-butanol, tert-butanol) and cleavage of sec-butyl-methyl ether on POM clusters with different central atoms (P, Si, Co, Al). Dehydration rates depend on the rate constant for elimination from adsorbed alkanols or ethers and on the equilibrium constant for the formation of unreactive reactant dimers. Elimination involves E1 pathways and late carbenium-ion transition states. This is consistent with small kinetic isotope effects for all deuterated alkanols, with strong effects of substituents on elimination rates, and with the similar alkene stereoselectivities measured for alkanol dehydration, ether cleavage, and alkene double-bond isomerization. n-Donor reactants (alkanols, ethers) and products (water) inhibit dehydration rates by forming stable dimers that do not undergo elimination; their stability is consistent with theoretical estimates, with the dynamics of homogeneous analogues, and with the structure and proton affinity of the n-donors. Elimination rate constants increased with increasing valence of the central POM atom, because of a concurrent decrease in deprotonation enthalpies (DPE), which leads to more stable anionic clusters and ion-pairs at transition states. The DPE of POM clusters influences catalytic rates less than the proton affinity of the alkene-like organic moiety at the late carbenium-ion-type transition states involved. These different sensitivities reflect the fact that weaker acids typically form anionic clusters with a higher charge density at the transition state; these clusters stabilize cationic fragments more effectively than those of stronger acids, which form more stable conjugate bases with lower charge densities. These compensation effects are ubiquitous in acid chemistry and also evident for mineral acids. The stabilization energy and the concomitant charge density and distribution in the anion, but not the acid strength (DPE), determine the kinetic tolerance of n-donors and the selectivity of reactions catalyzed by Br?nsted acids.     

Correlation,verification and prediction of vapour–liquid equilibria using equation of state with association term: II. Alcohols + non-aliphatic hydrocarbons

An equation of state with association term was used to correlate all available binary VLE data sets for mixtures of alkanols with non-aliphatic hydrocarbons. The self association of alkanols was described using a uniform set of parameters. The cross association between alkanols and aromatic compounds was taken into account. The verification of the VLE data for mixtures of alkanols and non-aliphatic hydrocarbons is described and recommended data are given.The method of prediction of the VLE in the investigated mixtures is described. The recommended data were compared with the results of the prediction.     

Novel functional copolymers based on glycidyl methacrylate: Synthesis,characterization, and polymerization kinetics

A new methacrylate monomer 2-(4-nitrophenyl)-2-oxoethyl-2-methacrylate (NFM) was synthesized and its radical copolymerization with glycidyl methacrylate (GMA) was studied in 1,4-dioxane solution at 65°C using 2,2′-azobisisobutyronitrile as an initiator. The synthesized monomer and copolymers were characterized by FTIR, ¹H and ¹³C-NMR spectroscopy. The analysis of reactivity ratios revealed that NFM is less reactive than GMA, and copolymers formed are statistically in nature. Thermogravimetric analysis of the polymers reveals that the thermal stability of the copolymers increases with an increasing in the mole fraction of NFM in the copolymers. Glass transition temperatures of the copolymers decreased with an increasing of NFM molar fraction in copolymers. In addition, according to the results obtained from the contact angle and zeta potential measurements the hydrophobic character of the polymer decreases (it means surface free energy increases) and its zeta potential becomes more negative with increase of NFM ratio in the copolymer. Polymers with carbonyl functional groups have been particularly interesting because of their use as photoresists.     

Infrared studies of fluoroalcohol-base complexes in the gas phase,carbon tetrachloride solutions and argon matrices

Hydrogen bonded complexes of fluoroalcohols with oxygen-containing bases like dimethyl ether and alkanols have been investigated in argon matrices, in CCl₄ solutions and in the gas phase. The increase of the proton donor capacities with succesive substitution of fluorine atoms into the alkyl group of alcohols is indicated by a strong increase of the shift Δν of the OH stretching frequency in the complexes. For alkanols as acceptors, an increase of Δν is observed along the series CH₃OH, CH₃CH₂OH, (CH₃)₂CHOH, and (CH₃)₃CHOH. The frequency shifts Δν increase as one passes from the gas phase to CCl₄ solutions and argon matrices.     

Biocatalytic nylon nanofibrous membranes

Nylon-6 nanofibrous membranes (NFM) have been prepared, characterized and used to build-up electrochemical biosensing devices. The assembly and the functioning of biocatalytic NFM are described in connection with the physical and the covalent immobilization of glucose oxidase for the detection of glucose. Effects of the enzyme loading, the mediator, the pH, the surface acidity and the kinetic of the catalysis have been thoroughly investigated. The results show that NFM allow the binding of proteins without the need for the hydrolysis step, in contrast to the nylon film. Furthermore, the high surface-to-volume ratio of the NFM allow superior loading of the enzyme with respect to thin film technology. The immobilization step does not affect the permeability of the coating to the mediator used. These results give evidence that NFM are a promising and inexpensive coating for a novel electrochemical transducer.     

Fabrication and invitro evaluation of electrospun gum ghatti-polyvinyl alcohol polymeric blend green nanofibre mat (GG-PVA NFM) as a novel material for polymeric scaffolds in wound healing

The present research is mainly based on the fabrication of biodegradable nanofiber mats (NFM) through the process of electrospinning using a novel combination of Gum Ghatti (GG) and Poly vinyl alcohol (PVA). The prepared NFM was crosslinked (CL-1) using Glutaraldeyde-HCl vapours and was characterized for its tensile strength along other analytical characterizations using FTIR, TGA, DSC and XRD. The mechanical strength of the NFM was found to be sufficiently high than in comparison to noncrosslinked sample and PVA NFM. The internal architecture of the CL-1 by use of atomic force microscopy (AFM) revealed that there was very well formed crosslinks suitable for drug loading as well as cell proliferation. The wound healing properties of the CL-1 in mice animal model indicated the healing within 5 days as compared to the control wound. Moreover, the sample was also analysed for its ability as polymeric scaffold and no toxicity was found onto the locally applied tissue on histological investigations.     

Laponite–Gelatin Nanofibrous Microsphere Promoting Human Dental Follicle Stem Cells Attachment and Osteogenic Differentiation for Noninvasive Stem Cell Transplantation

Nanofibrous microspheres (NFM) are emerging as prominent next-generation biomimetic injectable scaffold system for stem cell delivery and different tissue regeneration where nanofibrous topography facilitates ECM-like stem cells niches. Addition of osteogenic bioactive nanosilicate platelets within NFM can provide osteoconductive cues to facilitate matrix mediated osteogenic differentiation of stem cells and enhance the efficiency of bone tissue regeneration. In this study, gelatin nanofibrous microspheres are prepared containing fluoride-doped laponite XL21 (LP) using the emulsion mediated thermal induce phase separation (TIPS) technique. Systematic studies are performed to understand the effect of physicochemical properties of biomimicking NFM alone and with different concentrations of LP on human dental follicle stem cells (hDFSCs), their cellular attachment, proliferation, and osteogenic differentiation. The study highlights the effect of LP nanosilicate with biomimicking nanofibrous injectable scaffold system aiding in enhancing stem cell differentiation under normal physiological conditions compared to NFM without LP. The laponite–NFM shows suitability as excellent injectable biomaterials system for stem cell attachment, proliferation and osteogenic differentiation for stem cell transplantation and bone tissue regeneration.     

(Liquid + liquid) equilibrium for binary systems of N-formylmorpholine with alkanes

(Liquid + liquid) equilibrium (LLE) data were determined for four binary systems containing N-formylmorpholine (NFM) and alkanes (3-methylpentane, heptane, nonane, and 2,2,4-trimethylpentane) over the temperature range from around 300 K to near 420 K using a set of newly designed equilibrium equipment. The compositions of both light and heavy phases were analyzed by gas chromatography. The mutual solubility increased as the temperature increased for all these systems. The binary (liquid + liquid) equilibrium data were correlated by the NRTL and UNIQUAC equations with temperature-dependent parameters. Both models correlate the experimental results well. Furthermore, the UNIFAC (Do) group contribution model was used to correlate and estimate the LLE data for NFM containing systems. Two methods of group division for NFM were used. NFM is treated as a single group: NFM group (method I) or divided into two groups: CHO and C₄H₈NO (method II), respectively. The group interaction parameters for CH₂–NFM, or CH₂–CHO and CH₂–C₄H₈NO were fitted from the experimental LLE data. The UNIFAC (Do) model correlates the experimental data well. In addition, in order to develop UNIFAC (Do) group contribution model to estimate the LLE data of (NFM + cycloalkane) systems, some literature LLE data were used. The group interaction parameters for c-CH₂–NFM, c-CH₂–CHO and c-CH₂–C₄H₈NO were correlated. Then these group interaction parameters were used to estimate the phase equilibrium data of binary systems in the literature by the UNIFAC (Do) model. The results showed that the estimated values are in good agreement with the literature data. In contrast, the method I is better than the method II. This shows that treating NFM as a single NFM group is more reasonable, and the fitted parameters are satisfactory for designing the aromatic recovery process with NFM as solvent.     

Self-assembly of alkanols on Au(111) surfaces

Self-assembled monolayers (SAMs) of alkanols (1-C(N)H(2N+1)OH) with varying carbon-chain lengths (N = 10-30) have been systematically studied by means of scanning tunneling microscopy (STM) at the interfaces between alkanol solutions (or liquids) and Au(111) surfaces. The carbon skeletons were found to lie flat on the surfaces. This orientation is consistent with SAMs of alkanols on highly oriented pyrolytic graphite (HOPG) and MoS2 surfaces, and also with alkanes on reconstructed Au(111) surfaces. This result differs from a prior report, which claimed that 1-decanol molecules (N = 10) stood on their ends with the OH polar groups facing the gold substrate. Compared to alkanes, the replacement of one terminal CH3 group with an OH group introduces new bonding features for alkanols owing to the feasibility of forming hydrogen bonds. While SAMs of long-chain alkanols (N > 18) resemble those of alkanes, in which the aliphatic chains make a greater contribution, hydrogen bonding plays a more important role in the formation of SAMs of short-chain alkanols. Thus, in addition to the titled lamellar structure, a herringbone-like structure, seldom seen in SAMs of alkanes, is dominant in alkanol SAMs for values of N < 18. The odd-even effect present in alkane SAMs is also present in alkanol SAMs. Thus, the odd N alkanols (alkanols with an odd number of carbon atoms) adopt perpendicular lamellar structures owing to the favorable interactions of the CH3 terminal groups, similar to the result observed for odd alkanes. In contrast to alkanes on Au(111) surfaces, for which no SAMs on an unreconstructed gold substrate were observed, alkanols are capable of forming SAMs on either the reconstructed or the unreconstructed gold surfaces. Structural models for the packing of alkanol molecules on Au(111) surfaces have been proposed, which successfully explain these experimental observations.     

Viscosity of the systems m-xylene, +1-propanol, +2-propanol, +1-butanol, +t-butanol

Viscosities, η, of the systems, m-xylene, +1-propanol, +2-propanol, +1-butanol and +t-butanol have been measured for the whole range of composition at 303.15, 308.15, 313.15, 318.15 and 323.15?K. The variation of viscosities has been plotted against mole fraction of alkanols. Viscosities have been found to increase slowly up to a considerable concentration of alkanols, followed by a rapid rise of viscosities at higher concentrations. The slow rise of viscosity is attributed to dissociation of alkanols in m-xylene, while the rapid rise of viscosity is ascribed to self-association of alkanols. Excess viscosities, η^E, have been plotted as a function of mole fraction of alkanols. The curves show negative values for the whole range of composition, with minima occurring in alkanol-rich region.?η?and η^E have been fitted to appropriate polynomial equations. The study shows the effect of branching and chain length of alkanols on?η?and η^E.     

Study of micropores accessibility in coals and activated carbon using immersion heats with C1–C4 alkanols

Two natural coals and a sample of activated carbon were studied with respect to micropores accessibility for C1–C4 alkanols using immersion calorimetry. From the immersion enthalpies, micropores volumes were calculated according to the Stoeckli–Kraehenbuehl (SK) equation, and obtained values were compared with the surface characteristics of gas adsorption measurements. Validity of the SK equation was found to be problematic for natural coals giving micropores volumes up to three times exceeding those of the CO₂ adsorption measurements. Reason for such discrepancy is discussed, with specific interactions between coals and alkanols likewise marked swelling of coals in the presence of alkanols being recognised as possible explanation. A drop in immersion heats with branched butanols was generally observed, enabling at least semi-quantitative evaluation of the abundance of micropores with diameters below ca. 0.7 nm that are inaccessible for tert-butanol.

     

Densities of solutions of four fluoroalcohols in water

Densities of aqueous solutions of four fluoroalcohols have been measured. Apparent and partial molar volumes of the alcoholic components and the excess volumes of mixing have been calculated, and are compared with the corresponding results for alkanols. A linear correlation exists between the volumes and heat capacities of transfer of alcohols from the pure liquids to aqueous solution at infinite dilution. The lines differ for alkanols and fluoroalcohols. Solute-solvent interactions involving fluoroalcohols and water and involving alkanols and water have a different influence on the structural organization of water molecules adjacent to the alcohol solute.     

Aggregation and clouding behavior of aqueous solution of EO-PO block copolymer in presence of n-alkanols

The aqueous solution behavior of an ethylene oxide-propylene oxide triblock copolymer Pluronic^® P123 [(EO)₂₀(PO)₇₀(EO)₂₀] was investigated in the presence of various n-alkanols (C₁-C₆) by cloud-point, viscosity, dynamic light scattering (DLS) and spectroscopic (FTIR, NMR) measurements. For lower alkanols (methanol, ethanol and 1-propanol), the cloud-points (CPs) increased with increase in alkanol concentration. The reverse effect was found for higher alkanols (C₄-C₆) where both the CPs and critical micelle temperatures (CMTs) decreased with increase in concentration. This behavior is explained in terms of a co-operative association of higher alkanols and block copolymers by replacing water molecules in the PPO core and inducing micellar growth in aqueous P123 solution. Lower alkanols are likely to be good solvents for both PEO and PPO blocks and the effect on PPO blocks predominates indicating an increase in CP and CMT with increase in alkanol concentration.     

Gas chromatographic retention indices for C6 alkanols on OV-101 and Carbowax 20M capillary columns

Summary Gas chromatographic retention indices for 16 C₆ alkanols measured on capillary columns coated with OV-101 methylsilicone and Carbowax 20M propylethyleneglycol liquid phases at 80° and 90°C were determined. The respective standard deviation values were 0.5 and 0.8 i.u. The correlation between the retention indices measured on non-polar and polar stationary phases and the boiling points of the alkanols was studied.     

N-甲酰吗啉作为芳烃萃取剂的萃取原理探究

N-甲酰吗啉作为芳烃的优良萃取剂,在国内已被十几家粗苯加氢企业使用。N-甲酰吗啉对芳烃具有较高的溶解度和选择性,但若控制不当效果仍然不够理想。本文从机理上对N-甲酰吗啉萃取过程给出解释以此来指导实际生产显的尤为重要。     

Influence of CTAB/alkanol/cyclohexane w/o microemulsions on the basic hydrolysis of crystal violet

The basic hydrolysis of crystal violet has been studied in w/o microemulsions of the CTAB/alkanols/cyclohexane system (alkanols: 1-butanol and 1-hexanol). The reaction can be considered to occur in the water phase of the droplets and from the rate constant the apparent dielectric constant of the water phase was determined. The cyclohexane incorporation in the system produces a decrease in the effective dielectric constant of the water phase and in the specific conductivity.     

On the self-association of the normal alcohols and the glass transition in alcohol-alcohol solutions

The glass-transition temperature (T_g) in mutual binary mixtures of the primary alkanols from methanol throughn-octanol has been measured as a function of composition. For mixtures of the alkanols heavier than ethanol,T _g is found to be a linear function of the number-average molecular length. Methanol and ethanol mixtures show higherT _g values than indicated by this relation. These results are found to be consistent with association of the heavier alkanols into chains of very great length in the supercooled liquid, while ethanol and methanol must form networks with a moderate degree of crosslinking between chains.     

Recent Progress in Fabrication of Electrospun Nanofiber Membranes for Developing Physiological In Vitro Organ/Tissue Models

Nanofiber membranes (NFMs), which have an extracellular matrix-mimicking structure and unique physical properties, have garnered great attention as biomimetic materials for developing physiologically relevant in vitro organ/tissue models. Recent progress in NFM fabrication techniques immensely contributes to the development of NFM-based cell culture platforms for constructing physiological organ/tissue models. However, despite the significance of the NFM fabrication technique, an in-depth discussion of the fabrication technique and its future aspect is insufficient. This review provides an overview of the current state-of-the-art of NFM fabrication techniques from electrospinning techniques to postprocessing techniques for the fabrication of various types of NFM-based cell culture platforms. Moreover, the advantages of the NFM-based culture platforms in the construction of organ/tissue models are discussed especially for tissue barrier models, spheroids/organoids, and biomimetic organ/tissue constructs. Finally, the review concludes with perspectives on challenges and future directions for fabrication and utilization of NFMs.     

Electrospun Nanofiber Membranes from 1,8-Naphthimide-Based Polymer/Poly(vinyl alcohol) for pH Fluorescence Sensing

Accurately and sensitively sensing and monitoring the pH in the environment is a key fundamental issue for human health. Nanomaterial and nanotechnology combined with fluorescent materials can be emerged as excellent possible methods to develop high-performance sensing membranes and help monitor pH. Herein, a series of fluorescent nanofiber membranes (NFMs) containing poly-1,8-naphthimide derivative-3-[dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]azaniumyl]propane-1-sulfonate (PNI-SBMA) are fabricated by electrospinning the solution of PNI-SBMA blended with poly(vinyl alcohol) (PVA). The surfactant-like functionalities in side chains of PNI-SBMA endow the NFMs with outstanding hydrophilicity, and the naphthimide derivatives are sensitive to pH by photoinduced electron transfer effect, which contribute to highly efficient pH fluorescence sensing applications of NFMs. Specifically, the PNI-SBMA/PVA NFM with a ratio of 1:9 (NFM2) shows high sensitivity and good cyclability to pH. This work demonstrates an effective strategy to realize a fluorescent sensor NFM that has a fast and sensitive response to pH, which will benefit its application of pH sensor monitoring in the water treatment process.     

Interfacial composition, structural parameters and thermodynamic properties of water-in-oil microemulsions

The formation and structural characteristics of water-in-oil microemulsions comprising hexadecylpyridinium chloride (CPC), alkanols (C₄–C₆) and alkanes (C₅, C₈–C₁₀) have been investigated by the method of dilution. The compositions of the surfactant and the cosurfactant in the interfacial region (interphase) of the microemulsion droplets have been determined. The thermodynamics of transfer of the cosurfactants (alkanols) from the continuous oil (alkane) phase to the interface have been evaluated from dilution measurements at different temperatures. The structural parameters, radii of the droplet and the waterpool, aggregation numbers of CPC and the alkanols in the interphase of a droplet, and the nanoparticle density of solution have been estimated assuming monodispersity of the droplets. The thermodynamics and structural parameters have been examined in terms of the chain lengths of the alkanols and alkanes. Received: 12 September 2000 Accepted: 27 October 2000