Neeladri Das

Triptycene based 1,2,3-triazole linked network polymers (TNPs): small gas storage and selective CO2 capture

Herein, facile synthesis and characterization of four triazole linked network polymers (TNPs) in high yields is described. These nitrogen rich polymers are derived using a “click” reaction between 2,6,14-triazido triptycene and various di- or triethynyl comonomers. The TNPs are microporous and exhibit high surface area (SABET up to 1348 m2 g−1). Due to the incorporation of the 1,2,3-triazole motif (a CO2-philic moiety), the TNPs record moderate to high CO2 uptake (up to 4.45 mmol g−1 at 273 K and 1 bar). The TNPs also show very good CO2/N2 (up to 48) and CO2/CH4 (8–9) selectivity. While the highest storage capacity has been registered by TNP4 (CO2 4.45 mmol g−1 at 273 K and 1 bar, CH4 23.8 mg g−1, H2 1.8 wt%), the highest CO2/N2 and CO2/CH4 selectivity is shown by TNP3 which contains additional nitrogen rich building blocks in the form of heteroaromatic pyrazine rings. These results suggest that TNPs are porous materials with potential practical application in gas storage and separation.

Pyrazine-Based Organometallic Complex: Synthesis, Characterization, and Supramolecular Chemistry

The design, synthesis, and characterization of a new pyrazine-based ditopic platinum(II) organometallic complex are reported. The molecular structure of the organoplatinum pyrazine dipod was determined by single-crystal X-ray crystallography. The potential utility of this organometallic ditopic acceptor as a building block in the construction of neutral metallasupramolecular macrocycles containing the pyrazine motif was explored. Pyrazine motifs containing supramolecules were characterized by multinuclear NMR (including (1)H DOSY), mass spectrometry, and elemental analysis. The geometry of each supramolecular framework was optimized by employing the PM6 semiempirical molecular orbital method to predict its shape and size. The ability of the pyrazine-based organoplatinum complex to act as a host for nitroaromatic guest (2,4-dinitrotoluene and PA) molecules was explored by isothermal titration calorimetry (ITC). The binding stoichiometry and thermodynamic parameters of these host-guest complexation reactions were evaluated using ITC. Theoretical calculations were performed to obtain insight into the binding pattern between the organometallic host and nitroaromatic guests. The preferable binding propensity of the binding sites of complex 1 for both nitroaromatics (PA and 2,4-dinitrotoluene) determined by molecular simulation studies corroborates well with the experimental results as obtained by ITC experiments.

Pyrazine Motif Containing Hexagonal Macrocycles: Synthesis, Characterization, and Host–Guest Chemistry with Nitro Aromatics

The synthesis and characterization of cationic two-dimensional metallamacrocycles having a hexagonal shape and cavity are described. Both macrocycles utilize a pyrazine motif containing an organometallic acceptor tecton with platinum(II) centers along with different donor ligands. While one macrocycle is a relatively larger [6 + 6], the other is a relatively smaller [2 + 2] polygon. A unique feature of the smaller ensemble is that it is an irregular polygon in which all six edges are not of equal length. Molecular modeling of these macrocycles confirmed the presence of hexagonal cavities. The ability of these π-electron rich macrocycles to act as potential hosts for relatively electron deficient nitroaromatics (DNT = 2,4-dinitrotoluene and PA = picric acid) has been studied using isothermal titration calorimetry (ITC) as a tool. Molecular dynamics simulation studies were subsequently performed to gain critical insight into the binding interactions between the nitroaromatic guest molecules (PA/DNT) and the ionic macrocycles reported herein.

Triptycene based organosoluble polyamides: synthesis, characterization and study of the effect of chain flexibility on morphology

Synthesis of new triptycene-containing polyamides (TPAs) using 2,6-diaminotriptycene and various aromatic and aliphatic dicarboxylates (Yamazaki–Higashi phosphorylation polyamidation) is described. The effect of the polymer backbone flexibility on the surface morphology of the respective polymer is studied. Polyamides thus prepared are organosoluble and have relatively low solution viscosities (0.18–0.5 dL g−1). TGA indicated that triptycene polyamides containing aliphatic chains are thermally less stable than the wholly aromatic triptycene polyamides. These polyamides may be categorized as self-extinguishing materials. FTIR spectroscopy studies show that hydrogen bonding interactions are weaker in wholly aromatic polyamides (TPA1–TPA3) relative to those in semi-aromatic polyamides (TPA4–TPA6). FE-SEM images of TPAs show that replacement of aromatic dicarboxylates with aliphatic dicarboxylates results in a drastic change in the morphology of the polyamides.

Size dependent effect of new organometallic triptycene tectons on the dimensions of self-assembled macrocycles

The design, synthesis and characterization of two new triptycene-containing ditopic Pt(II) organometallic complexes is being reported. These complexes comprise of two peripheral bis(trans-trialkylphosphine)platinum units either directly σ-bonded to the central triptycene moiety or connected via a bridging ethynyl spacer linkage. The potential utility of these organometallic complexes as ditopic acceptor building blocks for the construction of neutral metallasupramolecular macrocycles containing the triptycene motif is explored. Triptycene motif containing supramolecules were characterized using multinuclear NMR (including 1H DOSY), mass spectrometry (MALDI-TOF-MS) and elemental analyses. While the self-assembly of a longer acceptor linker with a terephthalate group results in the formation of a [3 + 3] self-assembled macrocycle, the use of a relatively shorter acceptor linker yields the corresponding [2 + 2] supramolecular framework. The shapes and dimensions of these supramolecular structures were also predicted by geometry optimization using PM6 semiempirical molecular orbital methods and the results corroborate well with the experimental observations. These two self-assembled macrocycles are unique examples of triptycene-based neutral “platinamacrocycles” reported in the literature to date. An investigation as to how the shape and size of the resulting discrete supramolecular framework is affected upon changing the length and rigidity of the triptycene-based acceptor linkers is discussed.

Pyrazine-based donor tectons: synthesis, self-assembly and characterization

Two new supramolecular building blocks derived from pyrazine are introduced. These molecules, having pendant pyridine units covalently linked to central pyrazine ring, are structurally rigid with pre-defined bite angles. Therefore they can act as donor tectons in design of supramolecular hexagons using coordination driven self-assembly protocol. Multinuclear NMR (including 1H DOSY) and mass spectrometry have been utilized to confirm the purity and stoichiometry of these self assembled hexagonal ensembles. PM6 molecular modeling studies corroborate their hexagonal shape and nanoscalar dimensions.

Synthesis, characterization and DNA interaction studies of new triptycene derivatives

Summary A facile and efficient synthesis of a new series of triptycene-based tripods is being reported. Using 2,6,14- or 2,7,14-triaminotriptycenes as synthons, the corresponding triazidotriptycenes were prepared in high yield. Additionally, we report the transformation of 2,6,14- or 2,7,14-triaminotriptycenes to the corresponding ethynyl-substituted triptycenes via their tribromo derivatives. Subsequently, derivatization of ethynyl-substituted triptycenes was studied to yield the respective propiolic acid and ethynylphosphine derivatives. Characterization of the newly functionalized triptycene derivatives and their regioisomers were carried out using FTIR and multinuclear NMR spectroscopy, mass spectrometry, and elemental analyses techniques. The study of the interaction of these trisubstituted triptycenes with various forms of DNA revealed interesting dependency on the functional groups of the triptycene core to initiate damage or conformational changes in DNA.

Binding and interaction of di- and tri-substituted organometallic triptycene palladium complexes with DNA

Abstract Two triptycene-based ligands with pendant bromophenyl units have been prepared. These triptycene derivatives have been used as synthons for the synthesis of di and tri nuclear palladium complexes. The organic molecules and their corresponding organometallic complexes have been fully characterized using nuclear magnetic resonance (NMR), infrared (IR) spectroscopy and mass spectrometry. The mode of binding and effect of the complexes on pUC19 plasmid, calf thymus DNA and oligomer duplex DNA have been investigated by a host of analytical methods. The complexes brought about unwinding of supercoiled plasmid and the unwinding angle was found to be related to the binding affinity of the complexes with DNA, where both these parameters were guided by the structure of the complexes. Concentration-dependent inhibition of endonuclease activity of SspI and BamHI by the complexes indicates preference for G/C sequence for binding to DNA. However, neither the complexes did not introduce any cleavage at abasic site in oligomer duplex DNA, nor they created linear form of the plasmid upon co-incubation with the DNA samples. The interactions of the complexes with DNA were found to be strongly guided by the structure of the complexes, where intercalation as well as groove binding was observed, without inflicting any damage to the DNA. The mode of interaction of the complexes with DNA was further confirmed by isothermal calorimetry.Graphical abstract

Self-Assembly of a [1+1] Ionic Hexagonal Macrocycle and its Antiproliferative Activity

A unique irregular hexagon was self-assembled using an organic donor clip (bearing terminal pyridyl units) and a complementary organometallic acceptor clip. The resulting metallamacrocycle was characterized by multinuclear NMR, mass spectrometry, and elemental analyses. Molecular modeling confirmed hexagonal shaped cavity for this metallamacrocycle which is a unique example of a discrete hexagonal framework self-assembled from only two building blocks. Cytotoxicity of the Pt-based acceptor tecton and the self-assembled PtII-based macrocycle was evaluated using three cancer cell lines and results were compared with cisplatin. Results confirmed a positive effect of the metallamacrocycle formation on cell growth inhibition.

Zinc-mediated diastereoselective assembly of a trinuclear circular helicate

Coordination of a triptycene-based ditopic Schiff base ligand (H2L) with Zn2+ leads to the formation of a novel trinuclear circular species. A combination of 1H NMR spectroscopy, infrared spectroscopy, mass spectrometry and elemental analysis allow the unambiguous characterization of H2L and Zn3L3·8H2O. DFT molecular modelling has been used to study the possible isomers of the cyclic trinuclear Zn(II) complex that results from the combination of conformational and optical isomers of the ligand. A NOESY experiment demonstrated that in the trinuclear circular zinc(II) helicate the three isomers of the ligand have an anti configuration of N,O-donor domains and an s-cis configuration of their imine bonds. Besides, a UV-VIS absorption and fluorescence emission study of H2L and Zn3L3·8H2O has been performed.