Synthetic protocols and building blocks for molecular electronics

Simple and readily accessible aryl bromides are useful building blocks for thiol end-capped molecular wires. Thus, 4-bromophenyl tert-butyl sulfide and 1-bromo-4-(methoxymethyl)benzene serve as precursors for a variety of oligo(phenylenevinylene) and oligo(phenyleneethynylene) wires via efficient synthetic transformations as presented in this paper.     

Synthesis of ruthenium acetylides: new building blocks for molecular electronics

Several ruthenium(II) mono(acetylides) trans-[Cl(dppe)₂Ru---(CC)_n---R] (n=1–4; R=SiMe₃, H) and bis(acetylide) trans-[(dppe)₂Ru(---(CC)₂---R)₂] (R=SiMe₃, H) were selectively obtained and could be used as a new set of building blocks for rigid rod-like structures and further assemblies. Especially, the oxidative coupling of trans-[Cl(dppe)₂Ru---(CC)₃---H] with Cu(OAc)₂ led to the formation of the first Ruthenium(II) binuclear species with 12 carbon atoms between the remote metals. This compound shows two reversible redox processes.     

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.     

Tetraimine macrocyclic transition metal complexes as building blocks for molecular devices

The synthetic strategy initiated by Busch and further developed in recent years resulted in an impressive variety of new azamacrocyclic ligand superstructures. In this contribution, we have reviewed papers containing general synthetic strategies, structural and electronic properties and results of electrochemical studies for a long series of neutral and charged macrocyclic tetraimine complexes of transition metals leading to a new type of homo- and heteronuclear[2]catenanes as examples of switchable molecular machines. The whole series consists of neutral and charged mono-, bis- and trismacrocycles and appropriate reference neutral molecules and many of their derivatives. The bismacrocyclic moieties are constructed from simpler tetraazamacrocyclic fragments. When two of them are linked through polymethylene chains, they form face-to-face biscyclidenes—rectangular box-like moieties. They can host some small guest molecules (water, π-electron-donating compounds) and are stabilized by hydrogen bonds with solvent molecules or a shell of neighboring counterions. Neutral thiol derivatives are used as recognition sites of monolayers self-assembled on electrode surfaces to be employed in devices based on donor–acceptor interactions.Our catenanes consist of bismacrocyclic transition metal complexes linked by aliphatic chains and interlocked with a substituted crown ether. We have proved that under external stimuli – electrochemical pulses – the heteronuclear catenane exhibits controlled intramolecular relocation of the crown ether between two positions. The relocation is possible due to π?π interactions between the aromatic fragments of the crown ether and the transition metal (Ni, Cu) coordinating macrocyclic rings.Our model tetraimine complexes of transition metals can also be used to solve the problem of controlling directional relative movement of molecular fragments present in complex supramolecules. On the way to this aim we have synthesized trismacrocyclic derivatives which are now appropriately modified to serve as components of complex catenanes.     

Playing with organic radicals as building blocks for functional molecular materials

The literature has shown numerous contributions on the synthesis and physicochemical properties of persistent organic radicals but there are a lesser number of reports about their use as building blocks for obtaining molecular magnetic materials exhibiting an additional and useful physical property or function. These materials show promise for applications in spintronics as well as bistable memory devices and sensing materials. This critical review provides an up-to-date survey to this new generation of multifunctional magnetic materials. For this, a detailed revision of the most common families of persistent organic radicals-nitroxide, triphenylmethyl, verdazyl, phenalenyl, and dithiadiazolyl-so far reported will be presented, classified into three different sections: materials with magnetic, conducting and optical properties. An additional section reporting switchable materials based on these radicals is presented (257 references).     

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.     

Adamantane-retropeptides, new building blocks for molecular channels

Novel adamantane-oxalamide derivatives, N,N′-bis(1-adamantylglycine methyl ester)oxalamide (meso-1 and rac-1), N,N′-bis(3-aminoadamantane-1-carboxylic acid methyl ester)oxalamide (2) and N,N′-bis(3-aminoadamantane-1-carboxylic acid)oxalamide (3) were prepared and structurally characterized by spectroscopic methods and X-ray analysis. Crystal packing of the structures meso-1 and rac-1 is defined by one-dimensional α-networks of hydrogen-bonded chains. The crystal structures of 2 and 3 are characterized by two-dimensional β-networks of hydrogen bonds. The oxalamide 3 crystallizes as the solvates only. In the crystal structure of 3 the protic solvent participates in hydrogen bonding with the oxalamide moieties. However, in non-protic solvents 3 crystallizes as a solvate but the solvent does not participate in hydrogen bonding. The two-dimensional network of hydrogen bonds connecting molecules of 3 generates channels, which are filled by discrete solvent molecules.     

A renaissance of color: New structures and building blocks for organic electronics

Natural dyes and pigments like indigo and its derivatives valued for their bright colors and photochemical stability has been used since antiquity. Recently, the need for better performing materials in the organic electronics field has inspired a resurgence of these historical molecules and their subsequent transformation into new families of π‐conjugated building blocks used to construct new (macro)molecular semiconductors. This Highlight will explore the renaissance of notable building blocks including diketopyrrolopyrrole, (iso)indigo, benzodipyrrolidone, and benzodifuranone, as well as nonfullerene acceptor structures 9,9′‐bifluorenylidene and quinacridone. In addition, as the organic electronics field continues to evolve, the design of molecules with precise structure and function embodies a new paradigm for the next generation of materials. Representative examples will be described that embrace this new model and point the direction for advanced technologies. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

DNA and microfluidics: building molecular electronics systems

The development of molecular electronics using DNA molecules as the building blocks and using microfluidics to build nanowire arrays is reviewed. Applications of DNA conductivity to build sensors and nanowire arrays, and DNA conjugation with other nanostructures, offers an exciting opportunity to build extremely small analytical devices that are suitable for single-molecule detection and also target screening.     

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.     

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.     

A comparison of potential molecular wires as components for molecular electronics

The field of electronics using single-molecule components has recently received much attention as a possible new design concept for the continued miniturisation of electronics. Molecular wires are the conceptually simplest components of such electronic systems and several different compound types have been used to produce molecular wires. Examples of some of the most promising families of molecular wires are presented, namely conjugated hydrocarbons, carbon nanotubes, porphyrin oligomers and DNA. Discussion centres around their potential use in functioning electronic architectures in terms of their electronic properties, ease and controllability of synthesis and potential for self-assembly.     

Towards a quantum chemical software package utilizing transferable fragments as molecular building blocks

Computer programs have been developed or are under development for the IBM personal computer that enable their users to get information on atomic charges, electrostatic potentials, conformational and other properties of molecular systems containing H, C, N, O, F, Si, P, S, or Cl atoms. The zero-order wavefunction is constructed of strictly localized molecular orbitals with fixed atomic orbital coefficients. The wave function can be refined by optimizing these coefficients, i.e., considering inductive effects via a coupled set of 2 × 2 secular equations within the CNDO /2 approximation. Delocalization and exchange effects are accounted for by expanding the wavefunction on a basis of the aforementioned strictly localized orbitals, instead of conventional atomic orbitals, and solving the corresponding SCF equations. Our method has been applied to the study of large systems. We calculated the electrostatic field of the complex of β-trypsin and basic pancreatic trypsin inhibitor and it has been found that strong field regions more or less coincide with hydration sites. A further potential application of protein electrostatic fields is in NMR spectroscopy. We found a linear correlation between C^αH or backbone NH proton chemical shifts and the protein field at the site of the corresponding proton. At last, we propose a simple method to mimic the bulk around atomic clusters modeling crystalline and amorphous silicon. Based on this method we found a linear correlation between atomic net charges and bond angle distortions in silicon clusters with 35 atoms.     

Tetrameric molecular bowl assembled from glycoluril building blocks

Glycoluril derivative--whose bulky Ph-C[triple bond]C- substituents prevent formation of H-bonded tapes--undergoes solvent dependent assembly in the crystal; a tetrameric molecular bowl is formed by R(24) H-bonding interactions from CH(2)Cl(2) whereas DMF results in H-bond dimerization followed by oligomerization via C-H...pi interactions.     

From small building blocks to complex molecular architecture

[reaction: see text] We describe a synthesis of a dendrimer-like amphiphile containing a flat rigid core and 12 hydrophobic and hydrophilic arms. We employ a modular approach based on stepwise protection chemistry starting from simple building blocks. The key feature of this approach is the absence of a polymerization step, which makes it applicable for linear monofunctionalized precursors of any kind. This strategy also allows for precise control of the number of arms and ensures their alternating arrangement.     

Halogeno(triazolyl)zinc complexes as molecular building blocks for metal–organic frameworks

The isomorphous title complexes, dichlorido[4‐(3,5‐dimethyl‐4H‐1,2,4‐triazol‐4‐yl)benzoic acid‐κN¹]zinc(II) dihydrate, [ZnCl₂(C₁₁H₁₁N₃O₂)₂]·2H₂O, and dibromido[4‐(3,5‐dimethyl‐4H‐1,2,4‐triazol‐4‐yl)benzoic acid‐κN¹]zinc(II) dihydrate, [ZnBr₂(C₁₁H₁₁N₃O₂)₂]·2H₂O, were synthesized and crystallized by slow evaporation of the solvent from a solution of the ligand and either zinc chloride or zinc bromide, respectively, in water/ethanol. The Zn^II ions occupy twofold axes in the noncentrosymmetric orthorhombic space group Fdd2. The metal ion is approximately tetrahedrally coordinated by two monodentate triazole groups of the ligands and additionally by two halide ions. The water molecules incorporate the complexes into a three‐dimensional framework made up by hydrogen bonds. Furthermore, each complex possesses two hydrogen‐bond‐donor sites represented by the carboxy groups and two acceptor sites at the noncoordinating N atoms of the triazoles.     

New building blocks for the assembly of sequence selective molecular zippers

Synthetic H-bonded molecular zippers contain no sequence information that can be used to engineer the selective binding interactions characteristic of biopolymers; reversing the sense of the amide bonds in the two binding partners generates a new orthogonal recognition motif and the mutually complementary binding partners form complexes an order of magnitude more stable than the corresponding mismatch complexes.     

Transition-metal-doped aluminum hydrides as building blocks for supramolecular assemblies

Density functional theory calculations were carried out to characterize a series of transition-metal-doped aluminum hydrides, forming TMAl(n)H(2n) and TMAl(n)H(2n+1) (TM = Sc, Ti, V; n = 3,4), in either charged or neutral form. A new electron-counting rule for these clusters was formulated as PSEN (paired skeleton electron number) = 4n, which can characterize both closed-shell and open-shell clusters. On the basis of this electron-counting rule, the superatomic clusters such as TiAl(4)H(9) and TiAl(3)H(6) were identified and can be used to assemble supramolecular structures. Electronic structure analysis showed that three-centered TM-H-Al bonds largely contributed to the structural stability. Also, the spin state of a wide range of clusters in their ground state can be predicted by the electron-counting rule.