Molecular tectonics. Porous hydrogen-bonded networks built from derivatives of pentaerythrityl tetraphenyl ether

From CPG to hybrid support: Review on the approaches in nucleic acids synthesis in various media

Solid-phase synthesis is, to date, the preferred method for the manufacture of oligonucleotides, in quantities ranging from a few micrograms for research purposes to several kilograms for therapeutic or commercial use. But for large-scale oligonucleotide manufacture, scaling up and hazardous waste production pose challenges that necessitate the investigation of alternate synthetic techniques. Despite the disadvantages of glass supports, using soluble supports as a substitute presents difficulties because of their high overall yield and complex purification steps. To address these challenges, various independent approaches have been developed; however, other problems such as insufficient cycle efficiency and synthesis of oligonucleotide chains of desired length continue to exist. In this study, we present a review of the current developments, advantages, and difficulties of recently reported alternatives to supports based on controlled pore glass, and discuss the importance of a support choice to resolve issues arising during oligonucleotide synthesis.

Self-Associated 1,8-Naphthalimide as a Selective Fluorescent Chemosensor for Detection of High pH in Aqueous Solutions and Their Hg2+ Contamination

A novel diamino triazine based 1,8-naphthalimide (NI-DAT) has been designed and synthesized. Its photophysical properties have been investigated in different solvents and its sensory capability evaluated. The fluorescence emission of NI-DAT is significantly impacted by the solvent polarity due to its inherent intramolecular charge transfer character. Moreover, the fluorescence emission quenched at higher pH as a result of photo-induced electron transfer (PET) from triazine moiety to 1,8-naphthalimide after cleaving hydrogen bonds in the self-associated dimers. Furthermore, the new chemosensor exhibited a good selectivity and sensitivity towards Hg²⁺ among all the used various cations and anions in the aqueous solution of ethanol (5:1, v/v, pH = 7.2, Tampon buffer). NI-DAT emission at 540 nm was quenched remarkably only by Hg²⁺, even in the presence of other cations or anions as interfering analytes. Job's plot revealed a 2:1 stoichiometric ratio for NI-DAT/Hg²⁺ complex, respectively.

The chemistry of biguanides: from synthetic routes to applications in organic chemistry

In this minireview, we discuss the chemistry of biguanides and their applications in catalysis. We present their super basicity as a consequence of their structure, the most efficient ways to synthesize symmetric and unsymmetric functionalized biguanides, and their applications in organic catalysis as triazine precursors and ligands in organometallic catalysis.

Controlled Growth of Ag Nanocrystals in a H-Bonded Open Framework

A procedure that enabled rational access to the first example of hybrid material made of NPs grown within a H-bonded framework is reported. To avoid competitive reactions with the framework units, the metal precursor was chemically trapped in the porous structure and subsequently photo-reduced to afford the hybrid material Ag@SPA-2, which consists of Ag NPs of nanometric sizes (<15 nm) homogeneously distributed in the crystals of the host material. In a subsequent step, taking advantage of the porous matrix the silver NPs have been transformed in situ to Ag₂ S NP by simple infiltration of H₂ S. The supramolecular network is shown to play an important role in stabilizing the inorganic nanomaterials and thus in controlling their growth.

Porous Hydrogen-Bonded Organic Frameworks

Ordered porous solid-state architectures constructed via non-covalent supramolecular self-assembly have attracted increasing interest due to their unique advantages and potential applications. Porous metal-coordination organic frameworks (MOFs) are generated by the assembly of metal coordination centers and organic linkers. Compared to MOFs, porous hydrogen-bonded organic frameworks (HOFs) are readily purified and recovered via simple recrystallization. However, due to lacking of sufficiently ability to orientate self-aggregation of building motifs in predictable manners, rational design and preparation of porous HOFs are still challenging. Herein, we summarize recent developments about porous HOFs and attempt to gain deeper insights into the design strategies of basic building motifs.

Synthesis, characterization and antitumor activity of novel tetrapodal 1,4-dihydropyridines: p53 induction, cell cycle arrest and low damage effect on normal cells induced by genotoxic factor H2O2

Synthesis of novel tetrakis(2,6-dimethyl-4-phenyl-1,4-dihydropyridinyl)methanes5a–dby acid-catalyzed condensation of the tetrakis-aldehydes6a–dwith eight equivalents of 3-aminobut-2-enenitrile2is reported. Antitumor activities of compounds5a–dwere also investigated.

Cinchona alkaloid-based chiral catalysts act as highly efficient multifunctional organocatalysts for the asymmetric conjugate addition of malonates to nitroolefins

New pentaerythritol tetrabromide-based chiral quaternary ammonium salts acting as organocatalysts (7a and 7b) have been prepared and used as organocatalysts for enantioselective Michael addition reactions between various nitroolefins and Michael donors (malonates) under mild reaction conditions, such as lower concentration of base and catalyst and room temperature, with very good chemical yields (up to 97%) and ee's (up to 99%).

Dinitroxide biradical crystals with polar order

A dinitroxide biradical (dCdO) has the peculiar tendency to crystallize in non-centrosymmetric polar space groups either as a stable dichloromethane solvate or as a pure phase. The molecules arrange with no compensation of their dipolar moment resulting in net macroscopic polar order.

Supramolecular imidazolium frameworks: direct analogues of metal azolate frameworks with charge-inverted node-and-linker structure

Assembly of imidazolium cations with tetrahedral divalent anions leads to supramolecular imidazolium frameworks, molecular analogues of metal azolate frameworks, illustrating a charge-inverted framework design involving cationic linkers and anionic nodes.

Synthesis of Janus compounds for the recognition of G-U mismatched nucleobase pairs

The design and synthesis of two Janus-type heterocycles with the capacity to simultaneously recognize guanine and uracyl in G-U mismatched pairs through complementary hydrogen bond pairing is described. Both compounds were conveniently functionalized with a carboxylic function and efficiently attached to a tripeptide sequence by using solid-phase methodologies. Ligands based on the derivatization of such Janus compounds with a small aminoglycoside, neamine, and its guanidinylated analogue have been synthesized, and their interaction with Tau RNA has been investigated by using several biophysical techniques, including UV-monitored melting curves, fluorescence titration experiments, and (1)H NMR. The overall results indicated that Janus-neamine/guanidinoneamine showed some preference for the +3 mutated RNA sequence associated with the development of some tauopathies, although preliminary NMR studies have not confirmed binding to G-U pairs. Moreover, a good correlation has been found between the RNA binding affinity of such Janus-containing ligands and their ability to stabilize this secondary structure upon complexation.

Bifacial nucleoside as a surrogate for both T and A in duplex DNA

A new functional bifacial nucleoside derived from 7-aminopyrimido[4,5-d]pyrimidine-2,4(1H,3H)-dione, a Janus-type nucleobase, has been synthesized and incorporated into DNA oligonucleotides. The nucleobase, having self-complementary H-bonding faces, mimics both T and A and engages in the corresponding Watson-Crick-like base pairs, forming stable duplexes.

Complex interplay and hierarchy of interactions in two-dimensional supramolecular assemblies

In order to address the interplay of hydrogen bonding, dipolar interactions, and metal coordination, we have investigated the two-dimensional mono- and bicomponent self-assembly of three closely related diaminotriazine-based molecular building blocks and a complementary perylenetetracarboxylic diimide by means of scanning tunneling microscopy. The simplest molecular species, bis-diaminotriazine-benzene, only interacts via hydrogen bonds and forms a unique supramolecular pattern on the Au(111) surface. For the two related molecular species, which exhibit in addition to hydrogen bonding also dipolar interactions and metal coordination, the number of distinct supramolecular structures increases dramatically with the number of possible interaction channels. Deposition together with the complementary perylene species, however, always results in a single well-defined supramolecular arrangement of molecules. A detailed analysis of the observed mono- and bicomponent assemblies allows shedding light on the hierarchy of the competing interactions, with important implications for the fabrication of surface-supported supramolecular networks by design.

A four-armed Schiff base: 6,6',6'',6'''-tetra-meth-oxy-2,2',2'',2'''-[methanetetra-yltetra-kis(methylenenitrilo-methyl-idyne)]tetra-phenol

In the structure of the title compound, C(37)H(40)N(4)O(8), penta-erythrityltetra-mine is bonded to four o-vanillin mol-ecules, forming a four-armed Schiff base mol-ecule. These mol-ecules are connected by inter-molecular C-H⋯O hydrogen bonds. Intramolecular C-H⋯N and O-H⋯N hydrogen bonds are also present.

Janus-AT bases: synthesis, self-assembly, and solid state structures

The high yielding synthesis of heterocycles with defined H-bond accepting and donating capabilities provides for the design of self-assembling structures and specific recognition of biological targets. Herein we report the syntheses and solid-state structures of three self-complementary uracil/thymine derivatives where each presents the standard ADA face inherently complementary to adenine and a synthetically appended DAD face complementary to uracil/thymine. These heterocycles, which have never before been reported or characterized, represent diaminopurine-uracil/thymine hybrids that, in two of the three cases, relate to previously reported heterocyclic hybrids of G and C. All three heterocycles crystallized to afford the first X-ray crystal structures of self-complementary heterocycles capable of ADA-DAD pairing. The potential use in DNA and RNA recognition are briefly discussed.

Old materials with new tricks: multifunctional open-framework materials

The literature on open-framework materials has shown numerous examples of porous solids with additional structural, chemical, or physical properties. These materials show promise for applications ranging from sensing, catalysis and separation to multifunctional materials. This critical review provides an up-to-date survey to this new generation of multifunctional open-framework solids. For this, a detailed revision of the different examples so far reported will be presented, classified into five different sections: magnetic, chiral, conducting, optical, and labile open-frameworks for sensing applications. (413 references.)

N-salicylideneanilines: tautomers for formation of hydrogen-bonded capsules, clefts, and chains

[structure: see text] The synthesis, characterization, and solid-state structures of new salicylaldimines are reported. Bis(N-salicylideneaniline)s (BSANs) and tris(N-salicylideneaniline)s (TSANs) are sterically encumbered compounds featuring a central six-membered ring in the keto-enamine tautomer. When extended with additional functional groups, these molecules may form hydrogen-bonded capsules, clefts, and extended structures. A TSAN with N-(t)()BOC-o-phenylenediamine groups has been structurally investigated. The complementary hydrogen-bonding motif in this molecule leads it to form dimers in solution and in the solid state. A BSAN with N-(t)()BOC-o-phenylenediamine substituents forms a hydrogen-bonded cleft in solution but forms an extended hydrogen-bonded ladder assembly of cofacial dimers in the solid state. When N-(t)()BOC-1,8-naphthalenediamine was utilized to extend the cleft, an unusual perimidine structure was obtained with the central core in the enol tautomer. In addition, ab initio calculations have been used to support the assignment of the keto-enamine or enol-imine tautomers of the BSANs and TSANs and to predict tautomerization in related BSANs and TSANs.

Synthesis of a Nonavalent Mannoside Glycodendrimer Based on Pentaerythritol

A nonavalent glycodendrimer bearing terminal alpha-d-mannopyranoside units has been synthesized with a convergent approach. Terminal trivalent mannoside dendrons bearing p-halophenyl ethers were prepared by glycosylation of pentaerythritol derivatives having three 2-hydroxyethyl ether substituents. Two efficient routes were developed for the synthesis of the pentaerythritol-based core (17), which has three terminal propargyl ethers. Conditions were found under which the triple Sonogashira coupling reaction of the dendron and the tri-O-propargyl ether (17) proceeded efficiently. The product was deprotected and it and precursors were fully characterized by NMR spectroscopy and FT-ICR mass spectrometry.

A unique example of a high symmetry three- and four-connected hydrogen bonded 3D-network

We present a three- and four-connected 3D-net based on 4-aminopyridine coordinated to Ag(I) and hydrogen bonded to nitrate with the unusual, high symmetry, topology (8(3))(8(6))2-tfa.

Mechanochemical preparation of molecular and supramolecular organometallic materials and coordination networks

This Dalton Perspective deals with solvent-free reactions taking place within solids or between solids or involving a solid and a vapour. The focus is on reactions involving organometallic and coordination compounds and occurring via reassembling of non-covalent bonding, e.g. hydrogen bonds, and/or formation of ligand-metal coordination bonds. It is argued that reactions activated by mechanical mixing of solid reactants as well as those obtained by exposing a crystalline solid to a vapour can be exploited to "make crystals", which is the quintessence of crystal engineering. It is demonstrated through a number of examples that solvent-free methods, such as co-grinding, kneading, milling of molecular solids, or reactions of solid with vapours represent viable alternative, when not unique, routes for the preparation of novel molecular and supramolecular solids as well as for the preparation of polymorphic or solvate modifications of a same species. The structural characterization of the products requires the preparation of single crystals suitable for X-ray diffraction, a goal often achieved by seeding.

Dendrimers Based on [1,3,5]-Triazines

A comprehensive and chronological account of dendrimers based on [1,3,5]-triazines is provided. Synthetic strategies to install the triazine through cycloaddition, cyclotrimerization, and nucleophilic aromatic substitution of cyanuric chloride are discussed. Motivations and applications of these architectures are surveyed, including the preparation of supra-molecular assemblies in the solution and solid states and their use in medicines, advanced materials, and separations when anchored to solid supports.

A practical guide to arylbiguanides — Synthesis and structural characterization

Monohydrochloride salts of diverse 1-arylbiguanides and 1,5-diarylbiguanides were synthesized by the reaction of anilinium chlorides with dicyandiamide or sodium dicyanamide, and the biguanidinium chlorides were converted into the corresponding biguanides by deprotonation with methanolic NaOCH3. The resulting biguanides and their salts were fully characterized by spectroscopic methods, and the structures of representative compounds were determined by X-ray crystallography.Key words: biguanide, biguanidinium, synthesis, structure, hydrogen bonds, noncovalent interactions, supramolecular chemistry.