Characteristic motion of a camphanic acid disk on water depending on the concentration of Triton X-100

As a simple autonomous motor, the self-motion of a camphanic acid disk on the aqueous phase with a neutral surfactant (Triton X-100) was investigated. Whereas only continuous motion was observed on water, intermittent motion (alternating between motion and rest) was observed upon addition of Triton X-100. Under the experimental conditions that gave intermittent motion, the surface tension of the aqueous phase changed periodically, synchronous with the contact angle around the camphanic acid disk. These characteristics of self-motion are discussed in relation to the surface tension depending on the concentration of camphanic acid with or without Triton X-100 as the driving force of the motion.     

Self-motion of a phenanthroline disk on divalent metal ion aqueous solutions coupled with complex formation

The self-motion of a 1,10-phenanthroline disk on divalent metal ion aqueous solutions was investigated as a simple autonomous motor coupled with complex formation. The characteristic features of motion (continuous and oscillatory motion) and their concentration regions differed among metal ions, and the frequency of oscillatory motion depended on the temperature of the aqueous solution. The nature of the characteristic motion is discussed in relation to the stability constant of complex formation between phenanthroline and a metal ion, and the difference in surface tension between phenanthroline and its metal complex as the driving force.     

Enhancing percutaneous delivery of methotrexate using different types of surfactants

Regarding the potential severe toxicity associated with systemic administration of methotrexate (MTX), a topical formulation might be of greater utility for the treatment of psoriasis and other hyperproliferative skin disorders. One of the presumed reasons for the lack of clinical activity of topical methotrexate in psoriasis is insufficient percutaneous penetration necessary to inhibit epidermal DNA synthesis. The present study was undertaken to prepare a formulation to enhance skin penetration of MTX. For this mean, topical gel formulations were prepared and evaluated for MTX percutaneous absorption using rat skin and standard Franz diffusion cells. For enhancing percutaneous absorption, three surfactants (anionic, cationic and nonionic) were incorporated into formulations with different concentrations. Finally salicylic acid as a keratolytic material was added for more enhancement effect. The results showed that SLS (sodium lauryl sulphate) and alkyl benzyl dimethyl chloride did not show significant enhancement effect on the penetration of MTX. Transcutol was able to enhance transdermal absorption of MTX and the higher enhancement ratio was obtained with 2% (w/w) concentration of transcutol. Addition of salicylic acid increased this ratio. Prepared formulation containing transcutol 2% (w/w) and salicylic acid 6% (w/w) showed higher enhancement property and could be used clinically for local treatment of psoriasis.     

Adsorption of water on zeolites of different types

We have investigated the interaction of water with Na⁺-ion exchanged zeolites of different structures (LTA, FAU, ERI, MOR and MFI) by means of temperature-programmed desorption (TPD). The non-isothermal desorption of water shows, depending on the zeolite type, differently structured desorption profiles. In every case the profiles have, however, two main ranges. Using a regularization method, desorption energy distribution functions have been calculated. The desorption energy distributions between 42–60 kJ mol^?1, which can be attributed to a non-specific interaction of water, show two clearly distinguished energy ranges. The water desorption behaviour of this range correlates with the electronegativity of the zeolites and the average charge of the lattice oxygen atoms calculated by means of the electronegativity equalization method (EEM). The part of the desorption energy distributions in the range of 60–90 kJ mol^?1, reflecting interactions of water with Na⁺ cations, shows two more or less pronounced maxima. In agreement with vibrational spectroscopic studies in the far infrared region, it may be concluded that all samples under study possess at least two different cation sites.     

Effect of surfactants on the stability of thin liquid film flow on a rotating disk

The effect of surfactants on surface instabilities of thin liquid film flow on a rotating disk was studied at different flow rates Q (0.5相似文献   

Interaction of poly(L-glutamic acid) with cationic surfactants carrying different head groups

Three cationic surfactants carrying a common hydrocarbon tail (dodecyl group) interact differently with fully ionized poly(L-glutamic acid)(PGA), depending on the type of their ionic head groups. Decrease of pH occurred in the order; dodecylammonium chloride (DAC) > dodecyldimethylammonium chloride (DDAC) > dodecyltrimethylammonium chloride (DTAC). The-helix of PGA was strongly induced by the addition of DAC and DDAC but weakly by DTAC. The induction was inhibited when NaCl concentration was greater than 0.05 M. In the solid state, proton transfer through hydrogen bonds from ionic heads of DDAC to carboxylate groups of the polypeptide was observed. Distortion of circular dichroism spectra occurred at high mixing ratios of surfactant to polymer, due to the aggregation of-helices, as confirmed by light scattering measurements and infrared absorption spectra.     

About different types of water in swollen polyelectrolyte multilayers

The review addresses swelling of polyelectrolyte multilayers in water. Different models for the determination of the water content are compared. It is clearly shown that voids under dry conditions present cavities for water which contribute to the water content of the multilayer in the swollen state. This so-called “void water” does not lead to any changes in thickness but in scattering length density during swelling. The “swelling water” leads to both changes in scattering length density and in thickness. Depending on the preparation conditions like the type polymers, polymer charge density, ionic strength and type of salt the ratio of “void water” differs between 1 and 15 vol.% while the amount of “swelling water” is of several ten's of vol.%.     

Adsorption of surfactants on two different hydrates

The interaction between surfactants and hydrates provides insight into the role of surfactants in promoting hydrate formation. This work aims at understanding the adsorption behavior of sodium dodecyl sulfate (SDS) on cyclopentane (CP) hydrates and its derivative surfactant on tetrabutylammonium bromide (TBAB) hydrates. Cyclopentane (CP) is a hydrophobic former whereas tetrabutylammonium bromide (TBAB) is a salt that forms semiclathrate hydrates. The adsorption on these two hydrates was studied by zeta potential and pyrene fluorescence measurements. CP hydrates have a negative surface charge in the absence of SDS, and it decreases to a minimum as the SDS concentration increases from 0 to 0.17 mM. Then, it increases with further increased SDS concentration. The adsorption density of DS (-) on CP hydrates reaches a saturated value at 1.73 mM SDS. The micropolarity parameter of the TBAB hydrate/water interface starts to increase rapidly at 0.17 mM SDS and levels off at 1.73 mM SDS. The presence of Br (-) in TBAB hydrate suspensions could compete with TBADS (from association of DS (-) and TBA (+)) and DS (-) for the adsorption on the hydrate surface, but they have a much stronger affinity for the hydrates than does Br (-). From the fluorescence measurements, it was found that the micropolarity of the hydrate/water interface is mainly dependent on the polarity of hydrate formers.     

Soret effect of nonionic surfactants in water studied by different transient grating setups

We studied the thermal diffusion behavior of the nonionic surfactant solutions C 12E 6/water and C 12E 5/water at different concentrations and temperatures using thermal diffusion forced Rayleigh scattering (TDFRS). Two different types of TDFRS setups have been applied. In the classical TDFRS, we use an argon laser to write the optical grating into the sample by using a small amount of ionic dye to convert the optical grating into a temperature grating. In the other setup, called IR-TDFRS, we use an infrared laser as the writing beam, which utilizes the water absorption band to convert the optical grating into a temperature grating. The measurements by IR-TDFRS show a one-mode signal for all concentrations and temperatures, while the signal in the classical TDFRS consists of two modes for higher temperatures and lower surfactant concentrations (Ning, H.; et al. J. Phys. Chem. B 2006, 110, 10746). We find good agreement between the Soret coefficient determined in the IR-TDFRS and the one derived from the first fast mode in the previous studies. The Soret coefficient of the nonionic solutions is positive and enhanced at the critical point. In general, the Soret coefficient of the micelles tends to increase with temperature. We found that the presence of the second mode observed in the classical TDFRS is related to the addition of the ionic dye, but even with the ionic dye it is not possible to observe a second mode in the IR-TDFRS. The origin of the second mode is discussed in terms of charged micelles and an inhomogenous dye distribution in the temperature gradient.     

Spontaneous vesicle formation of mixtures of double-chain cationic surfactants with a different counterion

Aggregate formation of a didodecyldimethylammonium bromide (DDAB) and didodecyldimethylammonium chloride (DDAC) mixture in aqueous solution was investigated. The concentration vs composition diagram of aggregate formation was constructed by analyzing the surface tension, turbidity, and electrical conductivity data. The cryogenic transmission electron microscopy was applied to several representative points in the diagram and provided information of the morphology of aggregates. The sequence of monomer (m) - m + small aggregate (A) - m + A + vesicle (V) - m + V was concluded with increasing total concentration of surfactants at all mixing ratios. The compositions of counterions in A and V were estimated on the basis of thermodynamic consideration and examined from the viewpoint of asymmetry of constituents and uneven distribution between outer and inner monolayers of a vesicle bilayer. Vesicle surfaces were suggested to abound in chloride ions compared to bulk solution, which is opposite to spherical micelle surfaces.     

Mixed monolayers of Gemini surfactants and stearic acid at the air/water interface

The properties of mixed monolayers composed of the cationic Gemini surfactant ([C(18)H(37)(CH(3))(2)N(+)(CH(2))(3)N(+)(CH(3))(2)C(18)H(37)],2Br(+), abbreviated as 18-3-18,2Br(-1)) and stearic acid (SA) at the air/water interface were investigated by using a Langmuir film balance. The excess areas at the different mixed monolayer compositions were obtained and used to evaluate the miscibility and nonideality of mixing. Due to the electrostatic attractive interactions between 18-3-18,2Br(-1) and SA, the excess areas indicated negative deviations from ideal mixing. Moreover, 18-3-18,2Br(-1) and SA were miscible at the air/water interface, as was confirmed by atomic force microscopy (AFM) images of the LB films transferred onto mica substrates. The attenuated total reflectance (ATR) infrared spectra showed that SA in the mixed monolayers was ionized completely at a composition X(SA)=0.67 and formed a "cationic-anionic surfactant," i.e., the carboxylate, with 18-3-18,2Br(-1) owing to the electrostatic interaction between the head groups.     

Effect of water hardness on the interaction of cationic dye with anionic surfactants

ABSTRACT

The effect of water hardness causing ions on the critical micelle concentration (cmc) of surfactants was studied using conductivity measurement. Spectrophotometric and conductometric studies of dye and surfactant interaction under the influence of water hardness causing ions were also investigated. It was found that with increasing hardness in water, cmc of the surfactants tends to decrease. The change in the colour of the solution was observed as the degree of hardness increases. Hardness of water can consider as a major contributor of fading or change in colour during washing and cleaning of dyed material. Dye in a surfactant solution containing varying amount of hardness causing ions undergoes a blue shift in the visible region and red shift in ultraviolet region. The comparison between sodium dodecylsulphate (SDS) and saponin natural surfactant showed that turbidity was observed only in the aqueous solution of SDS in the presence of very hard water.     

Photocleavage studies of fluorescent amino acid conjugates bearing different types of linkages

The synthesis and photochemistry of 3-oxo-3H-benzopyran derivatives linked through ester, anhydride, urethane and carbonate bonds to representative l-amino acids, at the amino and carboxylic acid groups at the main chain or the hydroxyl group at the side chain, were carried out. The stability to photolysis of the resulting conjugates was studied at different wavelengths of irradiation (254, 300 and 350 nm), the anhydride and ester linkages being the most sensitive in the studied conditions.     

Comparative study of different types of graphenes as electrocatalysts for ascorbic acid

A comparative study regarding the electrocatalytic activity of graphene oxide (GO), chemically-reduced graphene oxide (crGO) and graphene produced by direct liquid exfoliation (dG) is presented. Sensors were developed by modifying glassy carbon (GC) electrodes with GO, crGO and dG and ascorbic acid was used as a pilot analyte. GC/GO electrodes offer substantially lower oxidation overpotential, up to 350 mV, compared with GC/crGO, GC/dG and unmodified GC electrodes. In addition, the different carbon-to-oxygen atomic ratios in GO, as it occurs depending on the synthetic route, were found to have a remarkable effect on the performance of the sensors. Reduction of GO was achieved by immersing the modified electrodes into a stirred solution of NaBH₄ for 10 min at room temperature. This process was used alternatively of the time consuming and laborious process of hydrazine, and its effectiveness was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. Analytical utility of the sensors is demonstrated.     

Possibility of thermal analysis of different types of bonding of water in minerals

Various types of water bonding were studied. e.g. water bound by occlusion, by adsorption, by capillary condensation, by chemisorption and as a solid solution, zeolitic water, interlayer water, crystal water and structural water bound in form of hydroxil groups. The differentiation of these various types of bonding is rather difficult, for on heating water is evolved at various temperatures and in rather wide temperature domains which overlap to different extents. Efforts were made to improve the detection by applying the quasi-isothermal quasi-isobaric measuring technique.

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Zusammenfassung Es wurden verschiedene Bindungstypen von Wasser untersucht. Wasser kann unter anderem durch Einschlüsse, Adsorption. Kapillarkondensation, Chemisorption und in Form von Mischkristallen, zeolitisch, schichteingebettetem und Kristallwasser sowie als OH-Form gebunden sein. Die Untersuchung dieser zahlreichen Bindungstypen ist äußerst schwierig, da die Wasserabgabe bei verschiedenen Temperaturen geschieht und die ziemlich breiten Temperaturintervalle mehr oder weniger überlappen. Mittels quasiisothermen und quasiisobaren Meßtechniken wurde versucht, die Möglichkeit der Bestimmung zu verbessern.

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Sorption-photometric determination of anionic surfactants in water

The adsorption of Crystal Violet, anionic surfactants, and their ion associates on nonionic hydrophobic polymer adsorbent Amberlite XAD-16 was studied. A procedure for the sorption-photometric determination of anionic surfactants in water was developed with a detection limit of 0.001–0.003 mg/L at a sample volume of 50 mL.     

Size-dependent interaction of silica nanoparticles with different surfactants in aqueous solution

The size-dependent interaction of anionic silica nanoparticles with ionic (anionic and cationic) and nonionic surfactants has been studied using small-angle neutron scattering (SANS). The surfactants used are anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethyl ammonium bromide (DTAB), and nonionic decaoxyethylene n-dodecylether (C(12)E(10)). The measurements have been carried out for three different sizes of silica nanoparticles (8, 16, and 26 nm) at fixed concentrations (1 wt % each) of nanoparticles and surfactants. It is found that irrespective of the size of the nanoparticles there is no significant interaction evolved between like-charged nanoparticles and the SDS micelles leading to any structural changes. However, the strong attraction of oppositely charged DTAB micelles with silica nanoparticles results in the aggregation of nanoparticles. The number of micelles mediating the nanoparticle aggregation increases with the size of the nanoparticle. The aggregates are characterized by fractal structure where the fractal dimension is found to be constant (D ≈ 2.3) independent of the size of the nanoparticles and consistent with diffusion-limited-aggregation-type fractal morphology in these systems. In the case of nonionic surfactant C(12)E(10), micelles interact with the individual silica nanoparticles. The number of adsorbed micelles per nanoparticle increases drastically whereas the percentage of adsorbed micelles on nanoparticles decreases with the increase in the size of the nanoparticles.     

Nucleic acid microarrays created in the double-spiral format on a circular microfluidic disk

A microfluidic microarray that is created in the double spiral format has produced a greater density of probes than in our previous report. Using this double-spiral format together with centrifugal pumping for liquid delivery, 384 x 384 hybridization assays have been performed on one circular disk at one time, at the intersections between the spiral channels and spiral probe lines. Each sample was introduced into each inlet reservoir leading to 4 spiral channels and was analyzed independently, and so the hybridization results were self-corrected among the 4 spiral channels. In this work, fast microarray hybridizations have been successfully achieved by using both complementary oligonucleotides as well as PCR products prepared from plant fungal pathogen cultures.     

不同结构型熊果酸衍生物在抗肿瘤方面的研究进展

熊果酸是一种植物中常见的五环三萜类活性产物,具有广谱且显著的的抗肿瘤活性,但是较差的水溶性限制了其作为抗癌药物的应用。因此,对熊果酸的结构母核进行适当的修饰,引入特殊的药效基团,以改善其临床应用的局限性,成为了当前人们研究的热点。本综述总结了近10年来报道的具有抗肿瘤活性的熊果酸的各种合成衍生物,以探究不同基团修饰对抗肿瘤活性的影响,为研究熊果酸抗肿瘤方面的构效关系提供参考。