Catalyzing methanolysis of alkyl halides in the interior of an amphiphilic molecular basket

A molecular basket with four cholate units assembled on a cone-shaped calix[4]arene assumed reversed micelle-like conformation in 5% methanol/carbon tetrachloride. The inwardly facing hydroxyl groups on the cholates concentrated the polar solvent from the mostly nonpolar mixture. Methanolysis of alkyl halides benefited from the concentrated pocket of methanol if the substrate was capable of entering the basket. Substrates that were too large or too hydrophobic to fit within the basket showed no rate acceleration.     

NMR characterisation of unstable solvent and dihydride complexes generated at low temperature by in-situ UV irradiation

Low temperature in-situ UV irradiation of toluene solutions containing bis(alkene)rhodium complexes and parahydrogen in conjunction with NMR monitoring enables the characterisation of unstable eta 2-solvent complexes and dihydrogen activation products.     

Structural transition to electrolyte-water solvent and changes in the molecular dynamics of water and properties of solutions

A model of concentration transition “ions and complexes in a water structure → ionic and ionicaqueous clusters → polymer structures of salt and crystal hydrate melts” is suggested. The appearance of cluster nanostructures outside the first zone of a waterlike structure is regarded as a general characteristic of solutions. The characteristics of solutions, phase equilibria, and salts of complex composition are interpreted based on this model. Investigation of the complex dielectric constant of electrolytic solutions in the SHF and EHF bands (7–119 GHz) at high concentrations showed that there are two dispersion regions in which the relaxation times differ by a factor of 5–10. Relaxation processes are separated, the numbers of molecules in hydration shells are calculated, and relaxation times are determined for bulky tetrahedral water with hydration shells of ions, for clusters, and for ionicaqueous polymer chains. It is shown that the two structure subsystems of water molecules in concentrated solutions may be described using the limited rotator/generalized diffusion molecular model. Translated fromZhumal Strukturnoi Khimii, Vol. 39, No. 5, pp. 851–863, September–October, 1998.     

Temperature sensitivity trends and multi-stimuli sensitive behavior in amphiphilic oligomers

A series of oligomers, containing oligo(ethylene glycol) (OEG) moieties, with the same composition of amphiphilic functionalities has been designed, synthesized, and characterized on the basis of their temperature-sensitive behavior. The non-covalent amphiphilic aggregates, formed from these molecules, influence their temperature sensitivity. Covalent tethering of the amphiphilic units also has a significant influence on their temperature sensitivity. The lower critical solution temperatures of these oligomers show increasingly sharp transitions with increasing numbers of OEG functional groups, indicating enhanced cooperativity in dehydration of the OEG moieties when they are covalently tethered. These molecules were also engineered to be concurrently sensitive to enzymatic reaction and pH. This possibility was investigated using porcine liver esterase as the enzyme; we show that enzymatic action on the pentamer lowers its temperature sensitivity. The product moiety from the enzymatic reaction also gives the amphiphilic oligomer a pH-dependent temperature sensitivity.     

Application of a multi-dentate amphiphilic compound to transfer silver nanoparticles into an organic solvent

A multi-dentate amphiphilic compound, 3,3'-(dodecylazanediyl)-bis-[N-(2-aminoethyl)propanamide] (12C-2NH2) has been synthesized. The molecular structure was characterized by Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-vis) spectra, nuclear magnetic resonance (NMR) spectra, and fast atom bombardment mass (FAB-MS) spectra. 12C-2NH2 was employed to stabilize silver nanoparticles. Surface properties and stability of silver nanoparticles were controlled by adjusting the 12C-2NH2 to silver (0) molar ratio. 12C-2NH2 was also applied to transfer silver nanoparticles from an aqueous to an organic phase. The transfer efficiency depends on 12C-2NH2 concentration. When 12C-2NH2 to silver (0) molar ratio was 2:1, the highest efficiency of phase transfer to toluene was obtained. These 12C-2NH2 stabilized silver nanoparticles are very stable over a period of four days in toluene.     

Solar UV irradiation and dermal photoaging.

The skin is increasingly exposed to ambient UV-irradiation thus increasing risks for photooxidative damage with long-term detrimental effects like photoaging, characterized by wrinkles, loss of skin tone and resilience. Photoaged skin displays alterations in the cellular component and extracellular matrix with accumulation of disorganized elastin and its microfibrillar component fibrillin in the deep dermis and a severe loss of interstitial collagens, the major structural proteins of the dermal connective tissue. The unifying pathogenic agents for these changes are UV-generated reactive oxygen species (ROS) which deplete and damage non-enzymatic and enzymatic antioxidant defense systems of the skin. As well as causing permanent genetic changes, ROS activate cytoplasmic signal transduction pathways in resident fibroblasts that are related to growth, differentiation, senescence and connective tissue degradation. This review focuses on the role of UV-induced ROS in the photodamage of the skin resulting in clinical and biochemical characteristics of photoaging. In addition, the relationship of photoaging to intrinsic aging of the skin will be briefly discussed. A decrease in the overall ROS load by efficient sunscreens or other protective agents may represent promising strategies to prevent or at least minimize ROS-induced photoaging.     

Effects of low molecular weight photosensitizer and UV irradiation on gas permeability and selectivity of polyimide membrane

A polyimide membrane, 6FDA–TMPD, was prepared from 5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis-1,3-isobenzofurandione (6FDA), and 2,4,6-trimethyl-1,3-phenylenediamine (TMPD). The effect of ultraviolet irradiation (UV irradiation) using a high-pressure mercury lamp on the gas transport properties of the 6FDA–TMPD membrane and membranes containing a photosensitizer was explored. Comparison between UV treatment and thermal treatment was also examined. The gas selectivities in all membranes were increased due to the irradiation. Especially in the H₂/N₂ and H₂/CH₄ separations, the selectivities effectively increased without a significant reduction in the H₂ permeability. These increases were considerable in the membrane having no photosensitizer which was expected to be an initiator for the cross-linking reaction. There was little effect of cross-linking, which was formed by the irradiation, on the gas permeation properties. Photosensitizers prevented drastic change in the membrane morphologies due to the irradiation.     

An amphiphilic approach to nanocrystal quantum dot-titania nanocomposites

The addition of octylamine-modified poly(acrylic acid) to nanocrystal quantum dots (NQDs) results in robust, alcohol-soluble nanoparticles that can be readily incorporated into titania matrices without large changes in photoluminescence quantum yields. This approach relies on the amphiphilic nature of the polymer to create an NQD-polymer complex in which the alkyl chains interact with the hydrophobic part of the NQD, leaving the polar carboxylic acid groups on the periphery. This procedure is applicable to hydrophobically capped NQDs of a variety of shapes and compositions, making it a truly generalized route to nanocrystal-titania nanocomposites.     

Structural and morphological changes during UV irradiation of the trans-planar form of syndiotactic polypropylene

Syndiotactic polypropylene films, obtained in the trans-planar mesophase, were exposed to accelerated weathering in a UV device at 45 °C for increasing times. A different series of films, characterized by the same structural organization, was annealed at 45 °C for the same times, to discern the thermal effects from those due to UV irradiation. The influence of UV irradiation and thermal treatments on the structural changes in terms of phase composition, crystallite sizes, and chain conformations was studied. Diffractometric and thermal analyses show that UV radiation causes a strong increase of helical crystallinity (189% with respect to the initial value), leaving the trans-planar mesophase unchanged. The mesophase domains have a higher rigidity and hinder the oxygen diffusion slowing down the photooxidative degradation.The chain scission in the amorphous phase produces a higher mobility, allowing crystallization. The crystallinity also increases in the thermally treated samples, but the increase is limited to the first 48 h and reaches about 89% of the initial value. Both in the thermally treated and UV irradiated samples the crystallite coherence length perpendicular to the 200 planes increases with time. The amorphous chains do crystallize at the beginning near the already formed crystals, thus increasing their dimensions. The carbonyl index shows an induction period of 48 h, before a rapid increase which apparently is inversely proportional to the percentage of mesomorphic and crystalline phases of the irradiated samples, indicating that the photooxidative reactions took place mainly in the amorphous region. A comparison with data already published on the photooxidative behavior of samples crystallized in form I shows that the presence of compact domains in trans-planar mesophase led to an increase in the induction period and to a greater stability of the material in the first 150 h of UV treatment.     

Modelling molecular weight changes induced in polydimethylsiloxane by gamma and electron beam irradiation

A commercial linear polydimethylsiloxane (PDMS) was subject to gamma irradiation under vacuum and in air, as well as to accelerated electron beam radiolysis (EB). All irradiation treatments were done at room temperature. The molecular weight changes induced by the radiation processes have been investigated using size exclusion chromatography (SEC) with refraction index (RI) and multi angle laser light scattering (MALLS) detectors to obtain the number and weight average molecular weights of the irradiated samples.

The analysis of the data indicates that crosslinking reactions predominated over scission reactions in all cases. Gamma irradiation under vacuum was the most efficient process within the analyzed dose range, reaching the gel point earlier. Irradiation in the presence of oxygen induces oxidative effects, both in gamma and EB irradiations. A previously developed mathematical model of the irradiation process that accounts for simultaneous scission and crosslinking and allows for both H and Y crosslinks fitted well the measured molecular weight data.     

Photodegradation of polyglycidol in aqueous solutions exposed to UV irradiation

The photodegradation of polyglycidol in aqueous solution with UV wavelength of 254 nm was investigated. The experiments were carried out in air at a constant temperature and the photodegradation of polyglycidol (PGl) was compared to that of poly(ethylene oxide) (PEO), the most widely studied polyether. Size exclusion chromatography with multiangle light scattering detection (SEC-MALLS) was used to measure the changes in the molar masses and molar mass dispersities of polymers during degradation. The molar mass of PGl decreased dramatically during the first period of UV irradiation and then gradually approached a limiting value of 17,000 g/mol, regardless of the initial polymer concentration. PEO was less sensitive to UV irradiation than polyglycidol however, both polymers degrade mainly via chain scission. The degradation of PGl and PEO leads to acidification of their water solution. The photooxidation products were analyzed by FTIR and NMR spectroscopy and the spectrophotometric results revealed that the irradiation of the polymers led to the formation of carbonyl groups in the macromolecular chains. A mechanism accounting for the main routes of PGl photooxidation is proposed.     

Biomolecular and amphiphilic films probed by surface sensitive X-ray and neutron scattering

In this review article we discuss the thin film analytical techniques of interface sensitive X-ray and neutron scattering applied to aligned stacks of amphiphilic bilayers, in particular phospholipid membranes in the fluid L phase. We briefly discuss how the structure, composition, fluctuations and interactions in lipid or synthetic membranes can be studied by modern surface sensitive scattering techniques, using X-rays or neutrons as a probe. These techniques offer an in-situ approach to study lipid bilayer systems in different environments over length scales extending from micrometer to nanometer, both with and without additional membrane-active molecules such as amphiphilic peptides or membrane proteins.     

Influence of multiwall carbon nanotubes on morphological and structural changes during UV irradiation of syndiotactic polypropylene films

The effect of UV irradiation on the morphology and structure of syndiotactic polypropylene (sPP) is investigated both for pure films and those filled with multiwall carbon nanotubes (MWCNTs). UV treatment causes a structural reorganization of pure sPP films. It seems that the incorporation of MWCNTs has a strong stabilizing effect, with nanotubes acting as a limiter of the UV‐induced chain breakage, especially when a good dispersion of carbon nanotubes in the polymer is achieved. The incorporation of MWCNTs introduces a high concentration of defects in the crystal structure of sPP, which limits the UV‐induced growth of crystallites, and prevents the development and propagation of cracks caused by UV irradiation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

An EPR study on wastewater disinfection by peracetic acid,hydrogen peroxide and UV irradiation

EPR spectroscopy was applied to obtain qualitative and quantitative information on the radicals produced in disinfection processes of wastewater for agricultural reuse. The DEPMPO spin trap was employed to detect hydroxyl and carbon-centered short living radicals in two different peracetic acid solutions and a hydrogen peroxide solution used for water disinfection either in the absence or in the presence of UV-C irradiation. Moreover, three different kinds of water (wastewater, demineralized water, distilled water) were analysed in order to assess the contribution of Fenton reactions to the radical production. The spectroscopic results were discussed in relation to the efficiency of the different oxidizing agents and UV irradiation in wastewater disinfection evaluated as Escherichia Coli, Faecal and Total Coliforms inactivation.     

两亲性分子聚集体的相变及其协同性

两亲性分子聚集体是一类重要的软物质,它们有着丰富而复杂的相行为.本文主要从两个方面综述了作者所在的研究组在两亲性分子聚集体相变研究方面的工作进展.(1)磷脂相关体系相变热力学:归纳了多种小分子(二甲基亚砜、甘油、海藻糖、尿素等)对于磷脂体系相行为的调控,比较并讨论了固醇类分子和葡萄糖神经酰胺分子诱导磷脂分子形成液态有序相的能力,还介绍了计算机模拟磷脂相行为的工作进展.(2)两亲性分子聚集体相变的协同性:先介绍了相变协同性(即分子头部、尾部、界面等基团在相变过程中的一致性)问题的提出,然后通过双十八烷基二甲基溴化铵分子和硬脂酰溶血卵磷脂两个体系的研究实例,说明两亲性分子聚集体相变过程中存在着头尾不一致的现象.对这个问题的研究,将为我们打开挑战相态转变的一系列重大问题(如相变动力学、相态多型性、相态稳定性以及相变可逆性等)的新窗口.     

Polyaddition of p-benzenedithiol to p-diethynylbenzene in solid state under UV irradiation

A novel polyaddition of p-benzenedithiol (BDT) to p-diethynylbenzene (DEB) was studied in solid state under UV or γ-ray irradiation at 25–99°C. Thin layer crystals of the 1:1 mixture of BDT and DEB mounted on a glass plate were prepared by a sublimation of an equimolar amount of the mixture of BDT and DEB at 45–80°C under a reduced pressure of nitrogen. The thin layer crystal of the 1:1 mixture of BDT and DEB and that of polymers exhibited almost similar and high crystalline diffraction patterns on x-ray diagraph. Consequently, the polyaddition in the solid state was a topotactic reaction controlled by the crystal lattice of the 1:1 mixture of BDT and DEB. The arrangement of both compounds in the thin layer crystal of the 1:1 mixture of BDT and DEB is seemingly quite ordered induced by a molecular interaction between BDT and DEB, and this is supported on the basis of the broad absorption at 340–450 nm by the diffuse reflectance spectrum taken with the thin layer crystal of the 1:1 mixture of BDT and DEB. The melting point of the 1:1 mixture of BDT and DEB was 90–94°C. However, the polyaddition at 87°C proceeded in a molten state perhaps due to heat evolved in the polyaddition. In the solid state polyaddition M _n of polymers obtained was 3–4 × 10³, whereas in the molten state polyaddition the crystallinity of polymers remarkably decreased, and M _n increased several times.     

Surface and bulk properties of two anionic amphiphilic penicillins in a selective solvent

The surface physicochemical properties of two anionic penicillins-cloxacillin and dicloxacillin-in mixed ethanol-water solvent were investigated by surface tension and dynamic light scattering (DLS). The data were analyzed according to the treatment of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to study the stability of the systems. The aim of the study is to obtain information about the effects of ethanol on the surface activity, bulk properties, and aggregate stability of these amphiphilic drugs, keeping in mind that both penicillins have the same counterion, and the difference in their structures is only a Cl atom in the phenyl ring that makes dicloxacillin more hydrophobic. The surface tension data show a minimum area per molecule increment with ethanol concentration that is related to the variation of the dielectric constant with the alcohol. Dicloxacillin has lower values of the standard Gibbs energies of adsorption than does cloxacillin, which gives this drug a more marked escaping tendency from the aqueous environment to the air-water monolayer. DLS data was fitted to an exponential function for cloxacillin at any drug or alcohol concentration in the range of concentrations studied that indicates that the system can be modeled as an ergodic system of dilute diffusing monodisperse particles. Dicloxacillin DLS data at an ethanol concentration of 5% (v/v) had to be fitted at a sum of an exponential and a stretched exponential function, which indicates that, besides the drug aggregates, a small population of penicillin clusters with longer relaxation times is present. The stability curves predicted by the DLVO theory, for both penicillins, indicate the predominance of electrostatic repulsion, leading to a stable system over the drug-ethanol concentration range studied, but the height of the reduced pair interaction potential energy barrier decreases with ethanol concentration, thus it is expected to undergo a transition from a stable dispersion to a coagulated one.