Self-organization of dipeptide-grafted polymeric nanoparticles film: A novel method for surface modification

Novel dipeptide-grafted polymeric nanoparticles were prepared by grafting the dipeptide (Gly-Gly) to a block copolymer backbone, comprised of styrene-alt-(maleic anhydride) and styrene. In aqueous solution PSt₁₃₀-b-P(St-alt-MAn)₅₈-g-GlyGly₂₆ formed stable dispersed spherical aggregates of ca. 75 nm. The critical micelle concentration for the dipeptide-grafted block copolymer self-aggregates was 6.3 × 10⁻³ mg mL⁻¹. The zeta-potential of the aggregates was estimated experimentally. The dispersed polymer nanoparticles effectively self-organized to form stable nanoparticle thin films on hydrophobic solid surfaces, such as octadecyltrichlorosilane modified glass (OTS-G). As the ionic strength and temperature of the polymer suspension increased the surface coverage of the nanoparticle film increased and its hydrophobicity (water contact angle) decreased. Significantly less bovine serum albumin (BSA) adsorbed to nanoparticles modified surfaces with compared OTS-G surfaces. Diglycine grafted polymer nanoparticles have the potential to be used as a novel platform to study protein-protein interactions and to control fouling.     

Calcium hydroxylapatite/methylcellulose nanocomposite: Synthesis and properties

Organomineral nanocomposites (OMCs) of calcium hydroxylapatite Ca₁₀(PO₄)₆(OH)₂ (HA) and natural methylcellulose biopolymer [C₆H₇O₂(OH)_{3 ? x} (OCH₃) _x ] _n (MC) were prepared by coprecipitation from aqueous solution in the Ca(OH)₂-H₃PO₄-[C₆H₇O₂(OH)_3?x (OCH₃) _x ] _n -H₂O system under biomimetic conditions (37°C). Synthesis products were identified by X-ray powder diffraction, IR spectroscopy, thermal analysis, scanning and transmission microscopy, and electron diffraction. The compositions and structural features of the OMCs and the crystallographic parameters, sizes, and morphology of HA nanoparticles in the OMCs were determined. The HA nanoparticles in the OMCs were found to interact with MC molecules to form agglomerates with sizes on the order of 150–200 nm.     

Phase diagrams of ionic liquids-based aqueous biphasic systems as a platform for extraction processes

In the past few years, ionic liquid-based aqueous biphasic systems have become the subject of considerable interest as a promising technique for the extraction and purification of several macro/biomolecules. Aiming at developing guidelines for more benign and efficient extraction processes, phase diagrams for aqueous biphasic systems composed of ionic liquids and inorganic/organic salts are here reported. Several combinations of ionic liquid families (imidazolium, pyridinium, phosphonium, quaternary ammonium and cholinium) and salts [potassium phosphate buffer (KH₂PO₄/K₂HPO₄ at pH 7), potassium citrate buffer (C₆H₅K₃O₇/C₆H₈O₇ at pH 5, 6, 7 and 8) and potassium carbonate (K₂CO₃ at pH ∼13)] were evaluated to highlight the influence of the ionic liquid structure (cation core, anion and alkyl chain length), the pH and the salt nature on the formation of aqueous biphasic systems. The binodal curves and respective tie-lines reported for these systems were experimentally determined at (298 ± 1) K. In general, the ability to promote the aqueous biphasic systems formation increases with the pH and alkyl chain length. While the influence of the cation core and anion nature of the ionic liquids on their ability to form aqueous biphasic systems closely correlates with ionic liquids capacity to be hydrated by water, the effect of the different salts depends of the ionic liquid nature and salt valency.     

In situ Synthesis and Lubrication of PbS Nanoparticles in Lamellar Liquid Crystal

The partial phase diagram of the Triton X-100/C₁₀H₂₁OH/H₂O system was determined. PbS nanoparticles were synthesized in solvent layer of Triton X-100/C₁₀H₂₁OH/H₂O lamellar liquid crystal. The size of PbS nanoparticles was about 8 nm and limited by the thickness of the solvent layer. Lubricities of the mixed system of Triton X-100/C₁₀H₂₁OH/H₂O lamellar liquid crystal and PbS nanoparticles were determined. The results showed that the lamellar liquid crystal and the mixed system showed higher load carrying capacity relative to the commercial grease. They are potential lubricants for Al alloy, especially at high load.     

The pH dependence of dispersion of TiO2 particles in aqueous surfactant solutions

The pH dependence of dispersion of titanium dioxide (TiO₂) particles has been examined in the presence of surfactant molecules in water. Whereas particles were dispersed in water at acid and alkaline regions rather than at neutral region, the dispersion was enhanced at neutral region in an aqueous sodium dodecyl sulfate (SDS) solution and at acid and alkaline regions in an aqueous dodecyldimethylamine oxide (C₁₂DAO) solution. Considering the pH dependence of zeta potential, the adsorption models of surfactant molecules on a particle were estimated on the basis of the modes of hemimicelle and double-layer compression. While the particles that adsorbed Al³⁺ were remarkably dispersed around pH 6, their dispersion does not largely depend on pH in the addition of SDS, indicating the adsorption of SDS molecules to form double-layer compression in the whole pH region. Dynamic light-scattering measurement and electron microscopic observation suggested that the particles were dispersed in water as small flocs.     

Thermotropic mesophases of ionic amphiphiles

In part I of this article the thermotropic mesophases of anhydrous ionic amphiphiles were discussed. In this part the thermotropic mesophases of ionic amphiphiles in aqueous media, as determined by thermal analysis, microscopic studies, X-ray diffraction and other techniques are reviewed. The fatty acids saturated or unsaturated that are found in the above molecules are: Lauric acid (C₁₂H₂₄O₂); myristic acid (C₁₄H₂₈O₂); palmitic acid (C₁₆H₃₂O₂); stearic acid (C₁₈H₃₆O₂); arachic acid (C₂₀H₄₀O₂); behenic acid (C₂₂H₄₄O₂); oleic acid (C₁₈H₃₄O₂).     

胆酸盐与Gemini表面活性剂复合物构建的纳米纤维和囊泡

Gemini表面活性剂(Cs H2s-α,ω-(Me2N+Cm H2m+1Br-)2,m-s-m)与胆汁酸盐(BS)利用静电作用构建超分子复合物,通过改变m-s-m和BS的结构,可以分别得到纳米纤维和囊泡状超分子聚集体.聚集体的形貌、结构和性质分别通过偏光显微镜(POM)、透射电子显微镜(TEM)、场发射扫描电子显微镜(FE-SEM)、X射线粉末衍射(XRD)及其它测试手段进行了表征.研究发现,通过改变m-s-m的烷基链长和间隔基团的长度,以及BS胆甾骨架上羟基的数目和位置,聚集体的形貌会发生明显的变化,聚集体主要依靠静电相互作用,并在疏水作用及氢键的协同作用下形成,本文的结果将有助于更好地理解离子自组装机理,并对超分子聚集体的设计提供新的思路.     

Functional Group Modification and Bonding Characteristics of Ti3C2 MXene-Organic Composites from First-Principles Calculations

The unique physical structure and abundant surface functional groups of MXene make the grafted organic molecules exhibit specific electrical and optical properties. This work reports the results of first-principles calculations to investigate the composite systems formed by different organic molecular monomers, namely acrylic acid (AA), acrylamide (AM), 1-aziridineethanol (1-AD) and glucose, and Ti₃C₂ MXene saturated with different functional groups, namely −OH, −O and −F. The results show that the interaction between organic molecules and the MXene surface depends on the type of functional groups of the organic molecules, while the strength of the interaction is determined by the type of surface functional groups and the number of hydrogen bonds. The bare Ti₃C₂ and Ti₃C₂(OH)₂ can readily form strong chemical and hydrogen bonds with AA and AM molecules, leading to strong adsorption energy and a large amount of charge transfer, while the interaction between organic molecules and MXene saturated by −F or −O groups mainly exhibits physical interactions, accompanied by low adsorption energy and a small amount of charge transfer. This research provides theoretical guidance for the synthesis of high-performance MXene organic composite systems.     

Solubilization and acidic and receptor properties of calix[4]resorcinarenes in aqueous solutions of oxyethylated dodecanol Brij-35

Solubilization of calix [4]resorcinarenes (Cn) with a varied length of hydrophobic substituents (R =Me, Pr, C₅H₁₁, C₇H₁₅, C₉H₁₉, and C₁₁H₂₃) in aqueous solutions of oxyethylated dodecanol Brij-35 was studied by the solubility method and 1D and 2D ¹H NMR spectroscopy. The solubilization of Cn in micellar solutions of Brij-35 is caused by the formation of mixed Cn-Brij-35 aggregates and is weakened substantially with the elongation of R. It was shown by pH-metry and 1D ¹H NMR spectroscopy that the receptor properties of the Cn anions toward the tetramethylammonium cations in the mixed aggregates differ substantially from those for the monomeric molecules in aqueous-organic and aqueous solutions. In particular, the binding of the tetramethylammonium cations does not result in screening of their N-Me fragments with the cyclophane cavity of the receptor.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 376–382, February, 2005.     

Facile synthesis of calcium carbonate with an absolutely pure crystal form using 1-butyl-3-methylimidazolium dodecyl sulfate as the modifier

Calcium carbonate (CaCO₃) nanocrystals with controllable polymorph and morphology have been successfully synthesized with the aid of an effective control agent, a halogen-free, low-cost ionic liquid surfactant, 1-butyl-3-methylimidazolium dodecylsulfate ([C₄mim][C₁₂SO₄]) in a supersaturated aqueous solution. For the first time, facile preparation of pure lens-like vaterite, sheet-like calcite, and peanut-like aragonite was all achieved in the [C₄mim][C₁₂SO₄] aqueous solution through changing the concentration, temperature, and initial pH value and adding magnesium ions. Washed by water and ethanol, all the aggregates were free of [C₄mim][C₁₂SO₄] and can be stable at least 1 month in air. The crystal form of the aggregates changed from pure calcite to pure vaterite at room temperature only through increasing [C₄mim][C₁₂SO₄] concentration. Formation of the ordered CaCO₃ structures is mainly ascribed to the aggregation of the primary nanoparticles whose formation mechanism is related to the change of supersaturation. This study can provide a facile and environment-friendly method to fabricate CaCO₃ crystal aggregates with various morphologies and polymorphs and can be used for large-scale industrial production and biomimetic synthesis.     

Effect of additives on the surface active and morphological features of 1-octyl-3-methylimidazolium halide aggregates in aqueous media

The influence of two salts as additives namely sodium chloride and sodium sulphate and a nonelectrolyte, 2-butoxyethanol on surface chemical and aggregation characteristics of ionic liquids (IL) of 1-octyl-3-methylimidazolium chloride, [C₈mim][Cl], 1-octyl-3-methylimidazolium bromide, [C₈mim][Br], and 1-octyl-3-methylimidazolium iodide, [C₈mim][I] in aqueous media were monitored through surface tension and small angle neutron scattering measurements. The addition of salts drastically decreased the critical aggregation concentration (CAC) and increased the area per adsorbed IL molecule. The co-ions of salts modify the surface of IL molecules and aggregates through various interactions such as charge neutralization, specific interactions and dehydration The results obtained by analyzing the SANS curves in the whole Q range showed that the oblate ellipsoidal shape of the aggregates of ionic liquids is un-altered upon the addition of additives. However the additives facilitate the growth of the aggregates in to microstructures with cubic packing at high salt concentrations.     

Spectrophotometric Study of the Interaction of β‐Cyclodextrin with Hydroxamic acids

Cyclodextrins have attracted considerable interest because of their ability to form stable inclusion complexes with a wide variety of inorganic and organic guest molecules. In the present communication, binding constant of β‐cyclodextrin and a series of substituted benzohydroxamic acids (X‐C₆H₄CON(OH)H), X=H, 4‐NO₂, 4‐Me 4‐OMe, and 2‐OH and N‐phenylbenzohydroxamic acid (C₆H₅CON(OH)C₆H₅) were determined at 27°C spectrophotometrically. In all the cases the formation of 1:1 host‐guest complex was established. The addition of β‐CD results in an increase in the absorbance intensity but does not cause a shift in λ_max. The values of binding constants are in good agreement with in those determined from kinetic and pH metric techniques.     

Inorganic—Organic Hybrid 18—Molybdodiphosphate Nanoparticles Bullk—modified Carbon Paste Electrode and Its Electrocatalysis

A kind of inorganic‐organic hybrid 18‐molybdodiphosphate nanoparticles ([(C₄H₉)₄N]₆P₂Mo₁₈Q₆₂·4H₂O) was firstly used as a bulk‐modifier to fabricate a three‐dimensional chemically modified carbon paste electrode (CPE) by direct mixing. The electrochemical behavior of the solid nanoparticles dispersed in the CPE in acidic aqueous solution was characterized by cyclic and square‐wave voltammetry. The hybrid 18‐molybdodiphosphate nanoparticles bulk‐modified CPE (MNP‐CPE) displayed a high electrocatalytic activity towards the reduction of nitrite, bromate and hydrogen peroxide. The remarkable advantages of the MNP‐CPE over the traditional polyoxometalates‐modified electrodes are their excellent reproducibility of surface‐renewal and high stability owing to the insolubility of the hybrid 18‐molybdodiphosphate nanoparticles.     

Helical Folding Competing with Unfolded Aggregation in Phenylene Ethynylene Foldamers

The folding and aggregation behavior of a pair of oligo(phenylene ethynylene) (OPE) foldamers are investigated by means of UV/Vis absorption and circular dichroism spectroscopy. With identical OPE backbones, two foldamers, 1 with alkyl side groups and 2 with triethylene glycol side chains, manifest similar helical conformations in solutions in n‐hexane and methanol, respectively. However, disparate and competing folding and aggregation processes are observed in alternative solvents. In cyclohexane, oligomer 1 initially adopts the helical conformation, but the self‐aggregation of unfolded chains, as a minor component, gradually drives the folding–unfolding transition eventually to the unfolded aggregate state completely. In contrast, in aqueous solution (CH₃OH/H₂O) both folded and unfolded oligomer 2 appear to undergo self‐association; aggregates of the folded chains are thermodynamically more stable. In solutions with a high H₂O content, self‐aggregation among unfolded oligomers is kinetically favored; these oligomers very slowly transform into aggregates of helical structures with greater thermodynamic stability. The folded–unfolded conformational switch thus takes place with the free (nonaggregated) molecules, and the very slow folding transition is due to the low concentration of molecularly dispersed oligomers.     

The reaction of the hydroxyl radical with acetylene

The reaction of OH with acetylene was studied in a discharge flow system at room temperature. OH was generated by the reaction of atomic hydrogen with NO₂ and was monitored throughout the reaction using ESR spectroscopy. Mass-spectrometric analysis of the reaction products yielded the following results: (1) less than 3 molecules of OH were consumed, and less than 2 molecules of H₂O were formed for every molecule of acetylene that reacted; (2) CO was identified as the major carbon-containing product; (3) NO, formed in the generation of OH, reacted with a reaction intermediate to give among other products N₂O. These observations placed severe limitations on the choice of a reaction mechanism. A mechanism containing the reaction OH + C₂H₂ → HC₂O + H₂ better accounted for the experimental results than one involving the abstraction reaction OH + C₂H₂ → C₂H + H₂O. The rate constant for the initial reaction was measured as 1.9 ± 0.6 × 10^?13 cm³ molecule^?1 sec^?1.     

The geometry and electronic structure of the ionic defect in a chain of water molecules between a donor and an acceptor

Quantum chemical calculations of the molecular complexes (NH₃)₃Zn²⁺...(H₂O)_n3...NH₃ (C_n, n=11, 16, 21, and 30) that model the proton donor-aqueous chain-acceptor channel in biological molecules were performed. Periodicity of O-H bond lengths in water chains and charges of the H atoms of H-bonds observed earlier were discussed. In C_n complexes, the geometry and electronic structure of the ionic defect in the aqueous chain with an excess proton were studied. The distributions of O-H bond lengths and charges on H-bond H atoms in the region of the ionic defect obtained in ab initio (B3LYP/6-31+G^**) and semiempirical (PM3) calculations are compared. The influence of aqueous chain extension, the position of the protonated water molecule, and the mobility of water molecules in the chain on the structure of the ionic defect was analyzed.     

A new sorbent for europium nitrate extraction: phosphonic acid grafted on polystyrene resin

A new chelating polymeric sorbent has been developed using polystyrene resin grafted with phosphonic acid. After characterization by FTIR and elementary analysis, the new resin has been investigated in liquid–solid extraction of europium(III). The results indicated that phosphonic resin could adsorb Eu(III) ion effectively from aqueous solution. The adsorption was strongly dependent on pH of the medium with enhanced adsorption as the pH value of 6.5. The influence of other analytical parameters including contact time, amount of resin, metal ion concentration, and ionic strength were investigated. The maximum uptake capacity of Eu(III) ions was 122.6 mg/g grafted resin at ambient temperature, at an initial pH value of 6.50. The overall adsorption process was best described by pseudo first-order kinetic. When Freundlich and Langmuir isotherms were tested, the latter had a better fit with the experimental data. Furthermore, Eu(III) could be eluted by using 1.0 mol/L H₂SO₄ solution and the grafted resin could be regenerated and reused.     

Synthesis of Ti(OH)OF ⋅ 0.66 H2O in Imidazolium-based Ionic Liquids

The influence of the cation of imidazolium-derived ionic liquids (ILs) on a low-temperature solution-based synthesis of hexagonal tungsten bronze (HTB) type Ti(OH)OF ⋅ 0.66 H₂O and bronze-type TiO₂(B) is investigated. The IL (C_xmim BF₄) acts as solvent and also as reaction partner with respect to the decomposition of [BF₄]⁻, releasing F⁻. In the present study, the chain length of the alkyl chain side groups attached to the imidazolium ring was varied (C₂mim BF₄ to C₁₀mim BF₄), and the obtained solids were analyzed by Powder X-Ray diffraction (PXRD) followed by Rietveld refinement. As a main finding these analyses indicate a transformation of Ti(OH)OF ⋅ 0.66 H₂O into TiO₂(B), and upon prolonged reaction time finally also into anatase TiO₂. Rietveld analysis suggests that when using ILs with longer alkyl chains, the conversion of Ti(OH)OF ⋅ 0.66 H₂O is slower compared to syntheses performed with smaller alkyl chains. Hence, Ti(OH)OF ⋅ 0.66 H₂O appears to be metastable and is stabilized by long-chain ILs serving as surfactant attached to the crystallites’ surface. In this view, the ILs shield the nanoparticles and thus slow down the conversion into the more stable compounds. This confirms previous findings that ILs act as both, solvent and reaction medium in this reaction, thus enabling the synthesis of peculiar Ti-oxides.     

Ferrocene­carboxyl­ic acid–1,4‐di­aza­bi­cyclo­[2.2.2]­octane (2/1): sheets built from O—H⃛N and C—H⃛O hydrogen bonds

In the title compound, 2[Fe(C₅H₅)(C₆H₅O₂)]·C₆H₁₂N₂, the molecular components are linked into finite three‐component aggregates by strong O—H?N hydrogen bonds [O?N 2.578 (4) and 2.604 (5) Å; O—H?N 170 (5) and 174 (6)°]; these aggregates are further linked by C—H?O hydrogen bonds [C?O 3.327 (5)–3.401 (5) Å; C—H?O 149–157°] into continuous sheets in the form of (6,3) nets.     

Structural and Infrared Spectroscopic Study on Solvation of Acetylene by Protonated Water Molecules

The effect of solvation on the conformation of acetylene has been studied by adding one water molecule at a time. Quantum chemical calculations of the H⁺(C₂H₂)(H₂O)_n (n=1-5) clusters indicate that the H₂O molecules prefer to form the OH…π interaction rather than the CH…O interaction. This solvation motif is different from that of neutral (C₂H₂)(H₂O)_n (n=1-4) clusters, in which the H₂O molecules prefer to form the CH…O and OH…C H-bonds. For the H⁺(C₂H₂)(H₂O)_n cationic clusters, the first solvation shell consists of one ring structure with two OH…π H-bonds and three water molecules, which is completed at n=4. Simulated infrared spectra reveal that vibrational frequencies of OH…π H-bonded O-H stretching afford a sensitive probe for exploring the solvation of acetylene by protonated water molecules. Infrared spectra of the H⁺(C₂H₂)(H₂O)_n(n=1-5) clusters could be readily measured by the infrared photodissociation technique and thus provide useful information for the understanding of solvation processes.