Blue, green and red emissive silver nanoclusters formed in organic solvents

Strongly luminescent silver nanoclusters with tunable emission are directly synthesized in organic polar and apolar solvents. We show that an amphiphilic polystyrene-block-poly(methacrylic acid) block copolymer can be universally used as their support medium. A remarkable similarity in spectroscopic properties is observed between these clusters and charge-transfer organic dyes.     

Effect of interphase mixing on a water–organic solvent two-liquid phase microbial system: ethanol fermentation

Ethanol fermentation by Saccharomyces cerevisiae was investigated in broth-organic solvent two-liquid phase systems with and without interphase mixing. The effect of interphase mixing with aliphatic alcohols as polar solvents and with alkanes as apolar solvents was determined from investigations in three distinct systems: a solvent-saturated broth, a solvent-broth dispersion system and a dispersion-free solvent-broth system. Microbial activities, measured as a function of solvent volume and inoculum size, revealed that a dispersed polar solvent caused a longer growth lag time and a slower growth rate. Viability measurements showed that yeast cells were gradually killed in a dodecanol-water dispersion system and not in a dispersion-free one. This process was believed to be initiated and enhanced by cell adhesion to the solvent interface as observed under a microscope. Yeast activity was also measured as a function of an apolar solvent volume and inoculum size. A full fermentative activity was observed in an initially alkanesaturated broth unlike in an intermixed biphasic system. As a result of these investigations, it was concluded firstly that microbial activity in initially solvent-saturated broths with and without contact with a stagnant solvent phase can be different and secondly that the process efficiency of a biphasic bioreactor, unlike that of a chemical reactor, can be hampered by interphase mixing. The yeast activities in the presence of the various alcohols and alkanes were correlated with ‘log P’ values of the solvents. Full activity was observed at log P > 5 and almost none at log P < 4.     

Phase behavior of laundry surfactants in polar solvents

Laundry surfactants are usually mixtures of ionic and nonionic detergents that exhibit a complex phase behavior. Here the ternary phase behavior of an isotropic and a liquid crystalline (LC) surfactant mixture has been examined in water/solvent systems. The size of the LC area in the ternary phase diagram was correlated to solvent parameters including the dielectric constant and the Gordon cohesiveness parameter. The Gordon parameter was found to have a linear relationship with the amount of solvent needed to go from an LC to an isotropic state over a wide range of solvents from polar to apolar. For solvents in which no surfactant aggregation (micellar or inverted micellar) is expected, the size of the LC area is linear with the reciprocal of the dielectric constant of the solvent. On diluting practical detergent liquids with water, a large LC area can be avoided by using solvents with a relatively low dielectric constant and with a relatively low molecular weight. The aggregated state of the surfactant mixtures in the isotropic regions of the phase diagram was studied using the solvatochromic fluorescent probe Nile Red. In the water corner of the phase diagram, the surfactants are aggregated into micelles. In strongly polar solvents, such as glycerol, ethylene glycol, formamide, and ethanolamine, the surfactants are also aggregated into micelles. In somewhat less polar solvents, such as methanol, ethanol, and t-butanol, the surfactant molecules are randomly distributed. In the surfactant-rich corner of the phase diagram of the isotropic mixture, the surfactant forms inverted micelles. An inverted micelle-to-micelle transition could be observed on dilution in ethylene glycol as a discontinuity in the trend of the Nile Red fluorescence maxima.     

Characteristic features of the matrix effect on the stokes shift of fluorescent dye molecules in pure and plasticized polymers

The influence of the chemical structure, composition, and physical properties of polymers [polyacrylates and -methacrylates, poly(vinyl acetate), polystyrene, and polybutadiene] and plasticized polymers [poly(methyl methacrylate) and polystyrene] on the Stokes shift of fluorescent dyes has been investigated. The results indicate that the structure and overall mobility of the polymer matrix as well as the nature of the dopant all together influence the separation of the absorption and emission band of a given fluorescent dye. In general, polar and highly flexible polymers favor the band separation. The effect of both polar and apolar dopants seems to be primarily a plasticization in case of polar polymers, whereas for apolar polymers the plasticizer effect can be neglected and the increased Stokes shift upon addition of polar dopants has to be attributed to particular dopant/dye interactions. These findings open some new routes to improve the efficiency of solar collectors based on fluorescent dyes.     

微扰理论的应用研究(Ⅱ)——水-正丁醇-MX三元体系液液平衡的计算

在本文(Ⅰ)报基础上,应用微扰理论导出了带电离子流体混合物的过量Helmholty自由能计算公式.该公式考虑了体系中溶质—溶剂、溶剂—溶剂和溶质—溶质间所有作用能(包括分子色散能、排斥能、偶极定向能、诱导能、离子静电能、离子偶极能).计算了在25℃下3个加盐混合溶剂体系[H_2O-nC_4H_9OH-MX(NaCl、KCl、KBr)]液液平衡中溶剂的活度系数,并与实验值进行了比较.     

A predictive method for calculating the solubility of solids in supercritical gases application to apolar mixtures

A thermodynamic method is proposed for calculating the solublities of apolar solids compounds in apolar supercritical gases. The method, analogous to the Hildebrand theory of solids' solubilities in liquid solvents, is mainly based on the application of Scatchard-Hildebrand equation to supercritical fluid mixtures.The derived method is applied to the determination of the ethylene/naphthalene equfiibria at 5 temperatures between 12 and 50°C and over pressure ranges of 50–270 ata. Calculated data are compared with the experimental data by Diepen and Scheffer.Methods for determining the solubility parameters of supercritical gases are discussed. The possibility of extending the proposed theory to polar mixtures of condensed phases in supercritical gases is also indicated.     

Diblock copolymer stabilization of multi-wall carbon nanotubes in organic solvents and their use in composites

A versatile method for the preparation of dispersed nanotubes using polystyrene-b-polyisoprene diblock copolymers in different selective organic solvents is presented. Stable dispersions have been obtained in polar (DMF) and apolar (heptane) media depending on the selectivity of the diblock copolymers. They have been characterized by means of optical microscopy, TEM imaging and dynamic light scattering, showing the first demonstration of multiwall carbon nanotubes (MWCNTs) solutions with in situ characterization of diblock copolymer stabilization. The most effectively stabilized dispersions have been used to make nanotube/polystyrene composites. We find that the coating of the nanotubes by the diblock polymer does not prevent electrical transport, so that the system can exhibit a relatively high surface conductivity above the percolation threshold. The low percolation threshold experimentally determined is presumably due to weak attractive interactions between the nanotubes as the composites are dried.     

Photodegradation of Anthracene and Benzo[a]anthracene in Polar and Apolar Media: New Pathways of Photodegradation

The photochemical reactions of anthracene and benzo[a]anthracene polycyclic aromatic hydrocarbons (PAHs) in polar and apolar solvents (cyclohexane and water/acetonitrile) were studied using spectroscopic and chromatographic techniques. These homogenous photolysis experiments are used as simplified models to compare PAHs photochemistry in water and oil (or oil films). Moreover, these processes were to some extent used as model in literature in order to study those occurring on particulate matter and aerosol surfaces. In both media, new photochemical reaction products were found. Generally, the reaction rate in the polar medium is faster than that in the apolar medium, and the photodegradation quantum yields increase with increasing polarity of the medium. HPLC-absorption/emission analysis confirmed the literature reports that mainly oxygenated photoproducts, such as PAH-hydroxides, were formed. The novelty of this article is that GC-MS data revealed the presence of new photoproducts that have not yet been described. This simplified model system allowed us to characterize the product distribution, thus simplifying the interpretation of the photodegradation mechanism. The identification of new photofragmentation paths, originating by irradiation of primary PAH photoproducts, may suggest an innovative way of remediation triggered by light.     

Evaluation of solubility parameters for nonvolatile branched hydrocarbons by inverse gas chromatography

Flory‐Huggins interaction parameters determined by inverse gas chromatographic (IGC) technique have been used for the estimation of solubility parameters of nonvolatile branched hydrocarbon solvents. A family of isosteric branched hydrocarbons consists of one apolar stationary phase, 19,24‐dioctadecyldotetracontane (C78), and four polar stationary solvents formed by replacing one of the ? CH₃ groups of C78 by ? OH (POH), ? CN (PCN), ? SH (PSH), ? CF₃ (MTF), and two other polar solvents formed by replacing four ? CH₃ groups of C78 with four ? CF₃ (TTF) and ? OCH₃ (TMO) are investigated. The three‐dimensional Hansen solubility parameters of the solvents have been estimated following the approaches of Voelkel and the method of Huang at five different temperatures. In the three components estimated by Voelkel method, the dispersion component is decreasing rapidly, whereas the polar, and hydrogen bonding components of the solubility parameters are increasing with temperature. In the components of solubility parameter estimated by Huang method, the dispersion and hydrogen bonding components are slowly decreasing with temperature, however, the polar components are almost constant with temperature. The components of solubility parameters for different solvents have been discussed in terms of solvent polarity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Processing of single polymer composites using the concept of constrained fibers

The concept of “overheating” is one of the known methods for manufacturing single polymer composites. This concept is validated on two categories of semi‐crystalline polymers: the drawable, apolar (i.e., isotactic polypropylene [iPP], ultra‐high molecular weight polyethylene [UHMWPE]) and the less drawable, polar ones (i.e., polyethyleneterephalate [PET] and polyamides [PA]). The interchain interactions in apolar polymers are relatively weak and therefore a high degree of drawability can be obtained. Polar polymers on the other hand have relative strong interchain interactions, they are therefore less drawable. A shift higher than 20°C of the melting temperature can be obtained in case of highly extended iPP (draw ratios >14). Ultra‐drawn PE shows only 10°C overheating upon constraining and this is mainly due to the change in chain mobility for PE in the hexagonal phase. In case of PET and PA6, only draw ratios of 4 could be reached; however, temperature shifts of about 10°C for constrained fibers compared to unconstrained fibers could be measured. A proof of principle of the potential of the constraining concept for the manufacturing of single polymer composites is obtained by the preparation of single fiber model composites. The effect of the post‐drawing conditions on overheating is examined in details on the example of iPP. It is concluded that both post‐drawing temperature and ultimate draw ratio have a significant influence on the degree of overheating. POLYM. COMPOS., 26:114–120, 2005. © 2004 Society of Plastics Engineers     

Underexposed polar residues and protein stabilization

Increasing protein stability is interesting for practical reasons and because it tests our understanding of protein energetics. We explore here the feasibility of stabilizing proteins by replacing underexposed polar residues by apolar ones of similar size and shape. We have compared the stability of wild-type apoflavodoxin with that of a few carefully selected mutants carrying Y → F, Q → L, T → V or K → M replacements. Although a clear inverse correlation between native solvent exposures of replaced polar residues and stability of mutants is observed, most mutations fail to stabilize the protein. The promising exceptions are the two Q → L mutations tested, which characteristically combine the greatest reduction in polar burial with the greatest increase in apolar burial relative to wild type. Analysis of published stability data corresponding to a variety of mutant proteins confirms that, unlike Y → F or T → V replacements, Q → L mutations tend to be stabilizing, and it suggests that N → L mutations might be stabilizing as well. On the other hand, we show that the stability changes associated to the apoflavodoxin mutations can be rationalized in terms of differential polar and apolar burials upon folding plus a generic destabilizing penalty term. Simple equations combining these contributions predict stability changes in a large data set of 113 mutants (Y → F, Q → L or T → V) similarly well as more complex algorithms available on the Internet.     

Adhesion of anionic surfactants to polymer surfaces and low-energy materials

To study the adhesion of the anionic surfactant sodium dodecyl sulfate (SDS) to various materials, a schematic molecular model of SDS was used which optimally correlates with its critical micelle concentration (c.m.c.) values under various conditions. Using the surface tension components and parameters of (a) the SDS apolar and polar moieties and (b) the polymeric surfaces of cellulose and nylon, the energy of adhesion of SDS to these polymeric surfaces as well as to a typical low-energy material (greasy dirt) in the guise of hexadecane was determined. It could be quantitatively shown (using a surface-thermodynamic approach) that SDS, in water, adheres more strongly to the low-energy (greasy dirt) compounds than to the polymeric materials. The c.m.c. of SDS was derived directly from the surface tension components and parameters of its apolar and polar moieties, and the ζ potential of its polar heads. The c.m.c. values obtained using this model correlate well with the published c.m.c. values obtained experimentally at different ionic strengths.     

Use of the combined Lifshitz–van der Waals and Lewis acid–base approaches in determining the apolar and polar contributions to surface and interfacial tensions and free energies

Recently, a number of authors have been rearranging the various combinations and permutations of the different apolar and polar liquids with which contact angles can be measured on polar surfaces and in so doing have arrived at bizarre results. The rational order and procedures to be followed in the determination of the apolar and polar surface tension properties of polar materials, according to the van Oss-Chaudhury-Good components and parameters of the approach, are reiterated.     

AOT-磷脂反胶团体系萃取蛋白质的研究

研究了PC/AOT和PE/AOT混合体系在有机溶剂中形成反胶团的性质及其萃取蛋白质的性能,并解决了反胶团萃取中有磷脂存在时的蛋白质浓度的分析问题.研究结果表明,在AOT体系中加入磷脂能使胶团尺寸变大,且加入PE能提高血红蛋白和枯草杆菌a—淀粉酶的萃取率,加入PC则常使萃取性能变差.因此,在反胶团萃取蛋白质时,影响萃取的主要因素不仅是胶团的大小,还有胶团与蛋白质之间的相互作用.     

阴离子聚合体系活性种聚合活性的探讨

讨论了非极性和极性溶剂中有机锂活性种的活性，指出添加少量极性添加剂或在极性溶剂中，由于溶剂化作用，有机锂活性种的聚合活性有所降低。     

Colloidal stability of halloysite clay nanotubes

The colloidal stability of halloysite clay nanotubes dispersion is reviewed showing the strategy and the mechanism to obtain stable systems in water and apolar solvents. The selective modification of halloysite inner/outer surfaces can be achieved by exploiting electrostatic interactions. The adsorption of anionic surfactants onto the halloysite cavity allows generating inorganic cylindrical micelles that can be separated from the solvent. On the other hand, the functionalization of halloysite shell by positively charged surfactants drives to obtain stable water-in-oil emulsions. The interactions with ionic and nonionic polymers alters the dispersability of halloysite due to electrostatic and steric effects that are strongly dependent on the nanoarchitecture of the hybrid systems.Modified nanotubes by selective interactions lead to the formation of colloidal systems with tuneable surface properties and controlled colloidal stability adjusted to the solvent polarity. These dispersions are perspectives nanocarriers for substances such as antioxidants, biocides, drugs and corrosion inhibitors, to be released in response to external stimuli.     

溶剂对氧化苯乙烯液相重排制备苯乙醛反应的影响

以HZSM-5分子筛为催化剂,探讨了不同极性的溶剂对氧化苯乙烯液相催化重排制备苯乙醛反应的影响。结果表明,极性最强的DMF溶剂易吸附在分子筛表面,导致催化剂失活,使反应不能进行;极性稍弱的甲醇、乙醇和丙酮溶剂,加快了重排反应的速率,但易与苯乙醛反应生成副产物;弱极性和非极性溶剂性质稳定,能有效抑制催化剂积碳失活,其中1,2-二氯乙烷是氧化苯乙烯液相重排反应最适宜的溶剂。     

Preferential solvation of pomalidomide,an anticancer compound,in some binary mixed solvents at 298.15 K

Preferential solvation of pomalidomide (PMD) was explored in dimethyl sulfoxide (DMSO)-dimethylformamide (DMF), DMSO-tetrahydrofuran (THF), DMSO-methanol (MeOH), DMSO-isopropanol, DMSO-water, water-DMF, water-THF, water-MeOH, and water-isopropanol binary mixed solvents at 298.15 K. Bosch-Rose model was utilized to determine the electronic transition energies (E_T) and other preferential solvation parameters, describing solute-solute and solute-solvent interactions. We found that λ_max situation shifted with dielectric constant of the pure solvents meaningfully. According to the obtained results, E_T enhanced and λ_max shifted to the lower wavelengths as the percentage of DMSO decreased in the binary mixtures, remarking the important role of DMSO for stabilizing the excited state (π^*) of PMD chromophore via efficient intermolecular solute-solvent interactions. In addition, the aqueous binary systems showed an optimum point for the E_T values as the percentage of water changed in the solutions. The local mole fraction of the solvents in the cybotactic region was also estimated to describe the specific and non-specific interactions in the systems.     

Spectroscopic and thermal characterization of the swelling behavior of nafion membranes in mixtures of water and methanol

The spectroscopic and thermal properties of swollen Nafion membranes in methanol aqueous mixtures were investigated to understand the behavior of commercial electrolytes in the presence of polar solvents. Several differences were observed in the absorption processes depending on the composition of the solvent. Deconvolution methods were applied to study specific contributions of solvents and polymer groups based on Fourier transform infrared spectroscopy and thermogravimetric analysis. The results evidence compositional effects on the interactions between solvents and Nafion. A major influence of the nonpolar domains (hydrophobic regions) in the absorption of methanol together with a reduction of the interactions with sulfonate groups was observed. Such changes are accompanied by a modification of the cluster morphology of the equilibrated membranes evaluated by differential scanning calorimetry. These findings can be useful to improve the knowledge on Nafion's microstructure in the presence of polar solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

离子液体在药物晶体工程中的应用

近年来，使用离子液体替代传统溶剂参与调节结晶过程中的各种相互作用以获得新颖的晶体结构是药物晶体工程的研究前沿。研究人员在离子液体体系中得到了使用传统溶剂无法制得的药物晶型或晶习并进行了相应机理的初步探索。针对离子液体在药物晶体工程中的应用，本文从离子液体的组成和性质及其在药物增溶、药物晶型及晶习的调控和药物共晶及盐的制备几方面展开，首次综述了相关研究成果并基于红外光谱、分子动力学模拟等手段从相互作用的角度对机理进行分析，其中氢键和范德华力相互作用起到了重要影响。最后针对该领域现存的问题如离子液体的选择处于盲筛阶段，相应机理研究缺乏和应用范围不广泛，指出建立系统的离子液体选择标准和深入研究机理是未来的主要研究方向。