Simultaneous formation of ferrite nanocrystals and deposition of thin films via a microwave-assisted nonaqueous sol–gel process

Combination of the surfactant-free nonaqueous sol–gel approach with the microwave technique makes it possible to synthesize Fe₃O₄, CoFe₂O₄, MnFe₂O₄, and NiFe₂O₄ nanoparticles of about 5–6 nm and with high crystallinity and good morphological uniformity. The synthesis involves the reaction of metal acetates or acetylacetonates as precursors with benzyl alcohol at 170 °C under microwave irradiation of 12 min. Immersion of glass substrates in the reaction solution results in the deposition of homogeneous metal ferrite films whose thickness can be adjusted through the precursor concentration. If preformed nickel nanoparticles are used as a type of curved substrate, the ferrite nanoparticles coat the seeds and form core–shell structures. These results extend the microwave-assisted nonaqueous sol–gel approach beyond the simple synthesis of nanoparticles to the preparation of thin films on flat or curved substrates.     

Experimental design applied to spin coating of 2D colloidal crystal masks: a relevant method?

Monolayers of colloidal spheres are used as masks in nanosphere lithography (NSL) for the selective deposition of nanostructured layers. Several methods exist for the formation of self-organized particle monolayers, among which spin coating appears to be very promising. However, a spin coating process is defined by several parameters like several ramps, rotation speeds, and durations. All parameters influence the spreading and drying of the droplet containing the particles. Moreover, scientists are confronted with the formation of numerous defects in spin coated layers, limiting well-ordered areas to a few micrometers squared. So far, empiricism has mainly ruled the world of nanoparticle self-organization by spin coating, and much of the literature is experimentally based. Therefore, the development of experimental protocols to control the ordering of particles is a major goal for further progress in NSL. We applied experimental design to spin coating, to evaluate the efficiency of this method to extract and model the relationships between the experimental parameters and the degree of ordering in the particles monolayers. A set of experiments was generated by the MODDE software and applied to the spin coating of latex suspension (diameter 490 nm). We calculated the ordering by a homemade image analysis tool. The results of partial least squares (PLS) modeling show that the proposed mathematical model only fits data from strictly monolayers but is not predictive for new sets of parameters. We submitted the data to principal component analysis (PCA) that was able to explain 91% of the results when based on strictly monolayered samples. PCA shows that the ordering was positively correlated to the ramp time and negatively correlated to the first rotation speed. We obtain large defect-free domains with the best set of parameters tested in this study. This protocol leads to areas of 200 μm(2), which has never been reported so far.     

α-Scission of sulfonyl radicals: a versatile process for organic synthesis

The reversible addition of aliphatic radicals to sulphur dioxide can be exploited to design a variety of tin-free chain reactions. This brief review summarises some of the possibilities, namely radical allylation, vinylation, alkynylation, and azidation of various substrates.     

Microdroplets: a sea of applications?

The exploitation of microdroplets produced within microfluidic environments has recently emerged as a new and exciting technological platform for applications within the chemical and biological sciences. Interest in microfluidic systems has been stimulated by a range of fundamental features that accompany system miniaturization. Such features include the ability to process and handle small volumes of fluid, improved analytical performance when compared to macroscale analogues, reduced instrumental footprints, low unit cost, facile integration of functional components and the exploitation of atypical fluid dynamics to control molecules in both time and space. Moreover, microfluidic systems that generate and utilize a stream of sub-nanolitre droplets dispersed within an immiscible continuous phase have the added advantage of allowing ultra-high throughput experimentation and being able to mimic conditions similar to that of a single cell (in terms of volume, pH, and salt concentration) thereby compartmentalizing biological and chemical reactions. This review provides an overview of methods for generating, controlling and manipulating droplets. Furthermore, we discuss key fields of use in which such systems may make a significant impact, with particular emphasis on novel applications in the biological and physical sciences.     

Synthesis and characterization of a colloidal novel folic acid?C??-cyclodextrin conjugate for targeted drug delivery

A novel folic acid?C??-cyclodextrin (??-CD) conjugate was synthesized and preliminarily characterized by ¹H NMR, ESI-MS, and MALDI-MS. ¹H NMR shows the presence of ??- and ??-conjugates which are generated by ??-CD linkage in turn with both carboxylic functions of folic acid. Moreover ROESY evidences supramolecular interactions between the benzene ring of the folic acid and the ??-CD cavity. DOSY suggests that ethylenediamine derived ??-CD?Cfolic acid forms a colloidal dispersion difficult to purify from free folic acid. An analysis of self-diffusion coefficient (D_s) of the three species (??-, ??-conjugates, and free folic acid) and relaxation times (T₁ and T₂) is reported to tentatively explain the colloidal behaviour of the new species in an aqueous solution.     

Removal of 17β-estradiol by powdered activated carbon—Microfiltraion hybrid process: The effect of PAC deposition on membrane surface

The removal of 17β-estradiol (E2) was investigated in a powdered activated carbon-submerged microfiltration (PAC-MF) hybrid system to better understand the effect on the system performance of PAC deposition on the membrane. A series of experiments were carried out under various operating conditions. Although the rejection or adsorption of E2 by MF membrane itself was almost negligible, the concentration of E2 in the permeate was always lower than it was in the reactor. This is because E2 was further removed as it passed through the PAC layer deposited on the membrane. As the E2 removal efficiency by the deposited PAC was lower than that by the PAC in the bulk phase, the overall E2 removal was largely dependent on the fraction of the deposited PAC on the membrane which were influenced by operating parameters such as permeate flux, hydraulic retention time (HRT) and mixing intensity in a PAC-MF system. The effect of these parameters on the overall E2 removal rate were also determined quantitatively using model equations developed in this study.     

Slow relaxation mode in mixtures of water and organic molecules: supramolecular structures or nanobubbles?

Aqueous solutions of tetrahydrofuran, ethanol, urea, and alpha-cyclodextrin were studied by a combination of static and dynamic laser light scattering (LLS). In textbooks, these small organic molecules are soluble in water so that there should be no observable large structures or density fluctuation in either static or dynamic LLS. However, a slow mode has been consistently observed in these aqueous solutions in dynamic LLS. Such a slow mode was previously attributed to some large complexes or supramolecular structures formed between water and these small organic molecules. Our current study reveals that it is actually due to the existence of small bubbles ( approximately 100 nm in diameter) formed inside these solutions. Our direct evidence comes from the fact that it can be removed by repeated filtration and regenerated by air injection. Our results also indicate that the formation of such nanobubbles in small organic molecule aqueous solutions is a universal phenomenon. Such formed nanobubbles are rather stable. The measurement of isothermal compressibility confirms the existence of a low density microphase, presumably nanobubbles, in these aqueous solutions. Using a proposed structural model, that is, each bubble is stabilized by small organic molecules adsorbed at the gas/water interface, we have, for the first time, estimated the pressure inside these nanobubbles.     

Development of a scalable palladium-catalyzed α-arylation process for the synthesis of a CGRP antagonist

The Pd-catalyzed α-arylation of cycloheptapyridyl ketone is a key complexity-building step in the synthesis of BMS-846372, a CGRP antagonist. A first-generation process utilized Pd(OAc)₂/P^tBu₃·HBF₄ catalyst system with a strong base NaO^tBu. Although this process was demonstrated on multi-kilo scale, the harsh conditions led to non-selective metal catalyzed processes, which generated several operational, quality, and throughput issues. By acquiring detailed knowledge around several important process parameters, we were able to design an efficient and scalable second-generation α-arylation process using a Pd(OAc)₂/RuPhos catalyst system with the weaker base, K₃PO₄ in tert-amyl alcohol. This new weak base process was high yielding, efficient, and superior in several respects compared to the strong base process. The strategy behind the reaction and isolation development and the process considerations important to scaling a catalytic reaction from laboratory to manufacturing scale will be discussed.     

An investigation of the lowest reaction pathway of propene + BCl3 decomposition in chemical vapor deposition process

The lowest reaction pathway or one of the favored possible paths in the CVD process of preparing boron carbides with BCl₃-C₃H₆(propene)-H₂ precursors was searched theoretically, which involves 95 transition states and 103 intermediates. The geometries of the species were optimized by employing the B3PW91/6-311G(d,p) method. The transition states as well as their linked intermediates were confirmed with frequency and the intrinsic reaction coordinates analyses. The energy barriers and the reaction energies were evaluated with the accurate model chemistry method at G3(MP2) level after a non-dynamical electronic correlation detection. The heat capacities and entropies were obtained with statistical thermodynamics, and the heat capacities were fitted into analytical equations. The Gibbs free energies at 298.15 K for all of the reaction steps were reported. The energies at any temperature could be derived classically by using the analytical heat capacities. All the possible elementary reactions, including both direct decomposition and the radical attacking dissociations, for each reaction step were examined, and the one with the lowest energy or energy barrier was further studied in the next step. It was found that there are 19 reaction steps in the lowest path to produce the final BC₃ cluster including two steps of initializing the reaction chain of producing H and Cl radicals. The highest energy in the lowest reaction pathway is 215.1 kJ/mol at 298.15 K and that for 1,200 K is 275.1 kJ/mol. The results are comparable with the most recent experimental observation of the apparent activation energy 208.7 kJ/mol.     

Exploiting the divalent nature of isonitriles: a novel Pictet–Spengler amidination process

An isocyanide-based multicomponent reaction (IMCR) utilized for the rapid assembly of novel, biologically relevant dihydropyrrolo[1,2-a]quinoxalines-amidines is herein presented. Starting from 1-(2-aminophenyl)pyrroles, aldehydes, and isonitriles, the target heterocyclic scaffold is assembled in a one-pot, operationally friendly process. With three points of diversity and formation of three chemical bonds in one step, this strategy proves to be very general. Novel, mild methodology for the generation of amidines from secondary amine anilines and isonitriles is also introduced.     

Proposition for the acylation mechanism of serine proteases: A one-step process?

This work proposes a very detailed ab initio study of the hypothesis for a one-step serine protease acylation process with one water molecule acting as the main catalyst reactant. For the 11 increasing complexity models considered, the minimum and transition state conformations for the reaction are determined by full geometry optimizations at the ab initio self-consistent field (SCF ) levels within several basis sets, from MINI-1 to 6-31G, and, for the smallest complexes, at the post-SCF MP2 level within the 6-31G** basis set. The related thermodynamical quantities are calculated for all the conformations. The influence of the oxyanion hole stabilizer and of the dyad His57-Asp102 is quantified and a very good agreement is obtained with point mutagenesis. The activation barrier is found in the range 15–18 kcal/mol. © 1996 John Wiley & Sons, Inc.     

A structural two-ring version of a tubular stack ofβ-rings in crystals of a cyclic D,L-hexapeptide

An X-ray analysis of single crystals (from MeOH) of cyclo(-D-Leu-L-MeLeu-D-Leu-L-MeLeu-D-Leu-L-MeLeu-) has been carried out. The analysis reveals that the molecules of the cyclopeptide occur in the crystals with two slightly different, almost hexagonal backbone conformations of the -type, and that pairs of molecules with the same conformation interact through their nonmethylated face, forming dimeric units (units A and B) with six interannular H-bonds. This kind of pairing reproduces well that expected for a two-ring element in a stack of antiparalle-rings. The X-ray analysis has also revealed the presence in the A units of two water molecules, each at one of two equivalent sites located on the 3-fold axis of the units and equidistant from the center of gravity, and the presence in the B units of one water molecule at the center of the units. This provides experimental support for the idea that stacks of-rings can serve as molecular channels.     

Does a fluorinated Lewis acid catalyst change the molecular mechanism of the decomposition process of nitroethyl carboxylates?

The molecular mechanism of the decomposition reaction of nitroethyl benzoates catalyzed by Lewis acids based on boron element—BH₃ and BF₃—was studied using density functional theory methods. These reactions take place much faster than the uncatalyzed process. However, the presence of fluorinated Lewis acids has a unique influence on the molecular mechanism. In the case of BF₃, a change from a one-step mechanism to a two-step one involving a zwitterionic intermediate is observed.     

Can colloidal particles flocculate at two energy minima simultaneously in a quiescent medium?

The effect of electrostatic repulsion forces on the gravity-induced flocculation of non-Brownian particles in a quiescent medium is analyzed, and the phenomenon that colloidal particles can simultaneously flocculate at both the primary minimum and the secondary minimum of the total interaction curve of DLVO theory is proved. A narrow strip region describing this "combined" flocculation behavior exists on the stability diagram, and the concept of a limiting trajectory can be applied to explain this interesting result.     

Cycloaromatization of 1,4-pentadiynes: a viable possibility?

[structure: see text] The effects of several mostly sigma-withdrawing, pi-donating substituents X on the hitherto unknown Bergman-like cyclizations of 3-substituted 1,4-pentadiynes were studied at the BLYP/6-311+G//BLYP/6-31G level of theory. As the cyclization with X = OH(+) has the lowest barrier and is about thermoneutral, we predict that the title reaction is viable, for instance, through activation of derivatives with X = O with Lewis acids.     

The migration of styrene butadiene latex during the drying of coating suspensions: when and how does migration of colloidal particles occur?

Surface elemental compositions of model latex clay coatings on an impervious substrate consolidated under various conditions were measured using the XPS technique, in order to clarify when and how colloidal latex particles migrate to the surface during drying. Under similar drying conditions, surface carbon content decreased with the addition of a water-soluble polymer to the coating colors, while remaining virtually unchanged for coatings of different coat weights made with a given color, indicating that surface carbon content variation is mainly caused by migration of latex rather than of water-soluble polymer. The results also showed that for coatings made with a given suspension, surface carbon content decreased with increasing delay time between coating and heating. For coatings frozen during consolidation and dried by sublimation, surface carbon content increased with increasing drying time before freezing. These results suggest that for the model coatings studied, latex migration mainly occurs after coating application before capillary formation during the initial drying stage when coatings are in the liquid phase, contradicting both the conventional capillary transport and boundary wall migration mechanisms. An alternative mechanism which attributes latex migration to surface trapping effect and to higher Brownian mobility of the smaller latex particles compared with pigment appears to provide a systematically consistent explanation to those phenomena. The new particle migration mechanism implies that segregation of colloidal particles is a ubiquitous phenomenon that would occur not only during the drying of paper coatings but also during consolidation of colloidal films containing particles of different sizes. This is of great importance in the control of surface compositions of nanocomposite coatings.     

Interaction of graphene with antipsychotic drugs: Is there any charge transfer process?

Antipsychotics represent an effective therapy for schizophrenia (a chronic mental disorder). Their benefits are related to the interaction of the drugs with dopamine D2 receptor (D2R). Antipsychotics are classified as agonists or antagonists. One of the working hypotheses is that there is a charge transfer process between the drugs and the receptors, which is different for agonists and antagonists. To have more insight into the nature of the interaction of these molecules and the differences between agonists and antagonists, we analyze the interaction of graphene with three molecules: dopamine, pramipexole (an agonist of dopamine), and risperidone (an antagonist of dopamine). The idea is to use graphene as a simple model to analyze the charge transfer process of these three drugs. Optimized structures, atomic charges, and Density of States results indicate that global charges of dopamine and pramipexole are similar, while for risperidone, it is more than double. Pramipexole is an agonist, and the charge transfer process is similar to that of dopamine. Risperidone is an antagonist, and the charge transfer process is different from dopamine. The charge transfer is more significant with risperidone than with dopamine, and this could be related to the mechanism of action. This is in agreement with the working hypotheses that establish that it is possible to distinguish between agonists and antagonists since they have different capacity to transfer charge.     

Alignment of liquid crystals induced by a photopolymerized self‐assembled film

An alignment film derived from a photopolymerized self‐assembled film may be used to orient nematic liquid crystals after irradiating the film with linearly polarized UV (LPUV). A photosensitive cationic amphiphile was first synthesized containing two double bonds and which could be polymerized by UV. A layer‐by‐layer self‐assembled multilayer film was next prepared in an aqueous solution of the cationic amphiphile and poly(sodium 4‐styrenesulphonate); the UV‐Vis spectra showed that each layer of the LBL multilayer film was uniform. When the film was irradiated by LPUV, the photosensitive double bonds underwent [2+2] cycloaddition along the vector direction of LPUV. The polarized UV‐Vis absorption spectra also provided evidence that the film was anisotropic, i.e. the photopolymerization was along a certain direction. The anisotropic film was used as an alignment layer for nematic liquid crystals, and observations under a polarizing microscope indicated that the alignment of the liquid crystals was good, as expected, and that the orientation direction of the liquid crystals was always perpendicular to the electric vector of the irradiating LPUV.