Nanosize precursors as building blocks for monodispersed colloids

It is shown that many monodispersed colloid particles, precipitated in homogeneous solutions, are formed by aggregation of nanosize subunits. A model is described that specifies conditions which may yield such spherical particles of narrow size distribution by interactions of precursor singlets. A good agreement was achieved for size selection of gold and cadmium sulfide dispersions. It is illustrated that particles of other shapes may also formed by the aggregation mechanism, and the challenges facing attempts to quantify such processes are pointed out. Finally, examples are given of consequences caused by particles being composed of nanosubunits. The text was submitted by the author in English.     

Stoichiometric zirconium oxide cations as potential building blocks for cluster assembled catalysts

Employing guided-ion-beam mass spectrometry, we identified a series of positively charged stoichiometric zirconium oxide clusters that exhibit enhanced activity and selectivity for three oxidation reactions of widespread chemical importance. Density functional theory calculations reveal that these clusters all contain the same active site consisting of a radical oxygen center with an elongated zirconium-oxygen bond. Calculated energy profiles demonstrate that each oxidation reaction is highly favorable energetically and involves easily surmountable barriers. Furthermore, the active stoichiometric clusters may be regenerated by reacting oxygen-deficient clusters with a strong oxidizer. This indicates that these species may promote multiple cycles of oxidation reactions and, therefore, exhibit true catalytic behavior. The stoichiometric clusters, having structures that resemble specific sites in bulk zirconia, are promising candidates for potential incorporation into a cluster assembled catalyst material.     

Polysaccharides as building blocks for nanotherapeutics

The use of polysaccharides as building blocks in the development of nano-sized drug delivery systems is rapidly growing. This can be attributed to the outstanding virtues of polysaccharides such as biocompatibility, biodegradability, low toxicity and low cost. In addition, the variety of physicochemical properties and the ease of chemical modifications enable the preparation of a wide array of nanoparticles. This tutorial review describes the properties of common polysaccharides, the main mechanisms for polysaccharide based-nanoparticles preparation, and provides examples from the conceptual design towards pre-clinical and clinical applications.     

Carbohydrates as building blocks of privileged ligands

“Privileged ligands” are chiral auxiliaries of wide applicability in asymmetric catalysis. In the previous decades, their effective three-dimensional structures have often been reproduced by using building blocks from a “chiral pool”, such as the carbohydrates. This strategy has provided unique ligand moieties which combine the performance of “privileged ligands” with increased flexibility and accessibility. This review gives an overview of the research within this field, giving emphasis to the best results obtained with each ligand type.     

Extended structure design with simple molybdenum oxide building blocks and urea as a directing agent

We report here a simple one-pot directed synthesis of an oxomolybdate urea composite in which elementary molybdenum oxide building blocks are linked together with the aid of urea. This type of directed material design resulted in large rod-like crystals of an inorganic-organic hybrid extended structure of {MoO 3(NH 2-CO-NH 2)} infinity consisting of right- and left-handed helical units. In the crystal structure urea acts both as a glue that links the inorganic molybdenum units into a helix and as a supramolecular linker for the stabilization of the crystal structure as a whole. This type of molecular topology resulted in an unexpectedly high thermal stability.     

Silica-supported vanadium oxide nanoparticles as efficient heterogeneous catalyst for hydrolysis of sucrose

The reaction kinetics of the hydrolysis of sucrose by solid catalysts was investigated using polarimetry. In this research work the V₂O₅/SiO₂ was selected as appropriate catalyst. This catalyst was prepared by impregnation method. At the optimizing conditions the activation parameters have been evaluated using the Arrhenius and Eyring plots. The structure and particle size of catalyst has been studied with the use of XRD.     

Approaches to primary tert-alkyl amines as building blocks

Primary tert-alkyl amines include analogues of amantadine, a fragment commonly linked to pharmacophoric groups to enhance biological activity. The preparation of primary tert-alkyl amines is considered to be a difficult problem. Four synthetic procedures, some of which have been previously reported for the synthesis of amines with primary (RCH₂NH₂) or secondary (RR'CHNH₂) alkyl and/or aryl groups, were tested for the synthesis of primary tert-alkyl amines (RR′R″CNH₂) in aliphatic series including adamantane adducts. These procedures included the formation and reduction of tert-alkyl azides, the Ritter reaction in standard and modified conditions, the addition of organometallic reagents to N-tert-butyl sulfinyl ketimines and one-pot reactions between nitriles and organometallic reagents in the presence of a Lewis acid, Τi(iPrO)₄ or CeCl_3. These synthetic routes are unexplored for primary tert-alkyl amines. Studies on the synthetic routes for primary tert-alkyl amines are currently lacking. The reaction conditions and substrate limitations were studied for each procedure, with the first procedure being the most general and applicable also for compounds bearing bulky adducts.     

Acyclic oligopyrroles as building blocks of supramolecular assemblies

The supramolecular chemistry of acyclic oligopyrrole derivatives mainly reported by the author’s group in the last four years has been summarized in this review. The author has demonstrated the “first step” to construct the new materials and concepts based on the new molecular systems consisting of pyrrole rings, which form the complexes, assemblies, and organized structures, by using noncovalent interactions such as metal coordination, hydrogen bonding, and π–π interaction. Acyclic π-conjugated oligopyrroles have exhibited not only host–guest binding behaviors in solutions but also the formation of, for example, (i) metal coordination polymers to give emissive colloidal spheres, (ii) solid-state assemblies of acyclic π-conjugated anion receptors and their anion complexes, (iii) anion-responsive supramolecular gels from the receptors with aliphatic chains, and (iv) solvent-assisted organized structures like vesicles derived from amphiphilic anion receptors.     

Crown ethers as building blocks for carbohydrate receptors

[STRUCTURE: SEE TEXT] Acyclic receptors containing neutral hydrogen bonding sites, such as amino-pyridine groups and a crown unit, perform effective recognition of neutral sugar molecules through multiple interactions. Receptor 1 has been shown to be a particularly effective and highly selective receptor for beta-glucopyranoside.     

Viruses as building blocks for materials and devices

From the viewpoint of a materials scientist, viruses can be regarded as organic nanoparticles. They are composed of a small number of different (bio)polymers: proteins and nucleic acids. Many viruses are enveloped in a lipid membrane and all viruses do not have a metabolism of their own, but rather use the metabolic machinery of a living cell for their replication. Their surface carries specific tools designed to cross the barriers of their host cells. The size and shape of viruses, and the number and nature of the functional groups on their surface, is precisely defined. As such, viruses are commonly used in materials science as scaffolds for covalently linked surface modifications. A particular quality of viruses is that they can be tailored by directed evolution by taking advantage of their inbuilt colocalization of geno- and phenotypes. The powerful techniques developed by life sciences are becoming the basis of engineering approaches towards nanomaterials, opening a wide range of applications far beyond biology and medicine.     

Macromonomers as well-defined building blocks in macromolecular engineering

The present work compares the efficiency of different polymerization methods to design well-defined comb-shaped structures based on macro monomers. Anionic polymerization remains the method of choice and allows the control of polymerization degree of the main chain and the length of the grafts. The presence of an active chain end on the backbone enabled the synthesis of a new type of hyperbranched polymers by reaction with appropriate low molar multifunctional compounds. Free radical polymerization is less efficient for the controlled homopolymerization of macromonomers but less sensitive to the presence of impurities. It requires in most cases long fractionation procedures to access well defined comb-shaped fractions characterized by high molar masses. The controlled free radical polymerization constitutes an interesting alternative. The homopolymerization of macromonomers with late transition metal catalysts was also examined and comb-shaped polymers characterized by a syndiotactic backbone and atactic grafts could be obtained.     

Organosilatrane building blocks

Phenylsilatrane analogues containing reactive amino, bromo, boronic ester, and alkynyl functional groups for coupling reactions have been prepared. Pinacol boronic ester and ethynyl analogues were synthesized from 4-bromophenylsilatrane by palladium catalyzed reactions. The silatrane functional group was shown to be stable during the palladium catalysis procedures and silica-gel purification, making the molecules amenable to further synthetic manipulation. The described phenylsilatranes are useful building blocks for forming more complex organosilatrane species.     

Dicarboxylate-bridged ruthenium complexes as building blocks for molecular nanostructures

Ruthenium complexes with bridging dicarboxylate ligands were combined with 1,2-di-4-pyridylethylene (dpe), 2,4,6-tri-4-pyridyltriazine (4-tpt), or 2,4,6-tri-3-pyridyltriazine (3-tpt) to give a tetranuclear rectangle or hexanuclear coordination cages. The cages display a trigonal-prismatic geometry, as evidenced by single-crystal X-ray crystallography. The 4-tpt-based cages are able to encapsulate polyaromatic molecules such as pyrene, triphenylene, or coronene, whereas the 3-tpt-based cages were found to be incompetent hosts for these guests.     

Amphiphilic building blocks as head groups in linear polymers

Starting with asymmetric A,A′-carbonate couplers A1–A4 via substitution reaction with primary amines at low temperatures (0–25 °C) followed by addition reaction with primary amines at higher temperatures (60–80 °C), bis(functional) compounds with a free hydroxyl group were prepared. These compounds were used: (i) as initiators for ring-opening polymerization of ε-caprolactone; (ii) as substrate for the preparation of an ATRP initiator for MMA polymerization; (iii) as substrate for the preparation of an activated carbonate for grafting of an amine end-functionalized linear polymer (Jeffamine® M1000). Via modifications (i)–(iii), amphiphilic end-functionalized poly(ε-caprolactone)s, poly(methyl methacrylate)s, and polyethers were prepared, respectively.     

Heterobinuclear complexes as building blocks in designing extended structures

The heterobinuclear complex [CuPrL(NO(3))(3)] has been used as a building block for the construction of a two-dimensional coordination polymer with the formula [CuPrL(NO(3)(2)(IN)], 1 (L(2-) = the dianion of the compartmental Schiff-base ligand obtained from the 2:1 condensation of 3-methoxysalicylaldehyde with 1,3-propanediamine; IN(-) = the isonicotinate ion). The heterobinuclear units, [CuPrL(NO(3))(2)](+), are connected through the unsymmetrical exo-bidentate ligands, IN(-), leading to a unique extended structure. Crystal data for compound 1: FW, 790.94; monoclinic, space group P2(1)/n, a = 11.2837(3) A, b = 14.7785(4) A, c = 16.9745(4) A, beta = 100.427(1) degrees; V = 2783.86(12) A(3); Z = 4; R1 = 0.0210, wR2 = 0.0562 [I > 2sigma(I)].