Current Organic Chemistry - Volume 17, Issue 1, 2013

In recent years, microcapsules have found diverse applications in many areas of science and technology. The inherent advantages of microcapsules, such as small size, high surface area, large inner volume, selectivity, and tunability, have led to applications for tailored microcapsules as drug delivery vehicles, microreactors, catalyst supports, and encapsulants. This review provides an overview of the commonly used techniques for the fabrication of novel microcapsules and emerging applications for these elegant materials. The basic concepts and major issues with respect to the preparation strategies and applications are briefly introduced, and examples from several outstanding research programs are highlighted. This paper provides a comprehensive review of the cutting-edge research activities on microcapsules.

Microencapsulation is a technique devoted to entrapping core material inside one or more polymeric coatings. Cyclodextrins (CDs) and its various derivatives are used as functional building blocks because of their unique physical properties. As well CDs possess, the ability to form well-defined host/guest inclusion complexes with lipophilic guests in aqueous solution or polar organic solvents. This review covers literature over the past decade concerning the design of microcapsules containing CDs and their physiochemical properties. Various applications of CD-based microcapsules are anticipated due to their unique surface functionalization, specific morphology, and the occurrence of a complex tertiary structure. The following themes will be addressed in this review: i) the development of CD-based microcapsules, ii) the physiochemical properties of CD-based microcapsules, and iii) the complexation thermodynamics between CDs and target molecules will be examined due to the limited availability of research corresponding to microcapsule results.

The applications of polysulfone (PSf) microcapsules have been increasing in the last years. The main reason for using PSf as a capsule shell is due to the high chemical and physical stability that this material possesses. In addition, it is a well-known polymer, broadly used by industries and moreover, it is a non-toxic and biocompatible functional material that may be employed for medical and biological applications. Polysulfone microcapsules preparation may be carried out easily by phase inversion precipitation technique that is a well-established technique in which capsule formation takes place in few seconds. Phase inversion precipitation allows obtaining different polymer shapes, it does not produce toxic products and it does not require high temperatures. The present review collects and describes several investigations focused on the use of PSf as polymer system for microencapsulation and its applications.

Miniemulsion is a promising technology to prepare capsules taking advantage of its droplet nucleation and absence of molecular net diffusion between droplets. The versatile shell materials of capsules can be obtained via a normal free radical polymerization, controlled/ living radical polymerization, anionic polymerization, polyaddition, polycondensation of organic and inorganic precursors or coordination polymerization in miniemulsion. This review will concentrate on the preparation of capsules in miniemulsion via different formation mechanisms, including phase separation of polymers, interfacial reactions, and Ouzo effect.

Combination of the advantages of the surface-initiated atom transfer radical polymerization (SI-ATRP) and template-based techniques, the SI-ATRP from colloidal templates approach could be applied to fabricate the controllable-structured polymeric nanocapsules. The different crosslinking techniques, such as chemical crosslinking, ultraviolet (UV)-induced photo-crosslinking, and one-pot surface- initiated atom transfer radical crosslinking copolymerization (SI-ATRCP), for the controllable-structured crosslinked polymeric nanocapsules based on the SI-ATRP from colloidal templates strategy were reviewed. The controlling and tailoring on the size, crosslinking degree, and the surface properties of the polymeric nanocapsules was emphasized. And the stimuli-responsive properties and application in controlled release were also mentioned.

Colloidal Microcapsules (MCs) are hollow micron/sub-micron size spherical constructs composed of nanoparticle-based shells. Recent years have witnessed various strategies towards the fabrication of stable colloidal MCs since they find applications in many areas of material and biological sciences e.g. drug delivery, encapsulation and microreactors. The inherent instability of nanoparticles (NPs) at the interface due to thermal disorder makes it difficult to obtain stable colloidal MCs composed of nanoparticles. Stable microcapsules can be obtained by stitching together the nanoparticles at the liquid-liquid interface by either covalent or non-covalent interactions. This review article highlights the critical role of the organic ligand shell on the surface of nanoparticles in fabricating stable colloidal MCs.

An ideal drug must be absolutely inert in normal conditions, providing release of active compounds only in diseased areas. Nanoengineered polymeric capsules have required features. We describe here basic methods for the fabrication of such containers and give some particular examples of their use when the drug release is triggered by the presence of the disease itself or by the soft external action, with no side effects on the adjacent tissues.

Electric Field Assisted Capillarity (EFAC) is a novel manufacturing technique that allows for the one-step fabrication of enclosed microstructures, such as microchannels and microcapsules. After a brief review of current micro-encapsulation techniques, this paper presents a list of potential applications for this technology; what is currently known about its mechanisms and avenues for further research

This work deals with the catalytic conversion of alcohols to aldehydes using a new support-nanocatalyst system consisting of chromium trioxide supported on nanostructured hydroxyapatite (Cr-NHAP). The oxidation reaction was carried out on a series of substituted benzylic alcohols under solvent-free microwave irradiation conditions. The obtained results showed high selectivity and high yield that was found to depend on the nature, the electronegativity and the position (para or meta) of the substituent on the aromatic cycle of the reagent.

Ionic liquids are often used together with dichloromethane in different reactions. This combination can be problematic because the use of ionic liquids with a carboxylic acid as an anion and dichloromethane can lead to the formation of methylene diesters. The reaction of trioctylmethylammonium benzoate with dichloromethane was studied, where the ionic liquid acted as reactant, solvent and catalyst. The molecular structure of methylene dibenzoate was determined by X-ray crystallography.

This paper reports a comparative study on the influence of solvent systems on its structure, properties and electromechanical behavior of cellulose electro-active paper. Three types of solvent systems, namely N,N’-dimethylacetamide (DMAc)/LiCl, Trifluoroacetic acid (TFA) and 1-butyl-3-methylimidazolium chloride (BMICL) were studied to dissolve cellulose. Regenerated cellulose from DMAc/LiCl showed the best thermal and tensile properties whereas cellulose regenerated from BMICL exhibited high bending deformation with poor thermal and tensile properties, which might be due to the entrapped residual ionic liquid upon regeneration process. The cellulose regenerated with TFA showed the lowest thermal stability and tensile strength. Details of fabrication and characterization of regenerated cellulose films from three solvent systems are explained.