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The ability to use bio-inspired building-blocks in the assembly of novel supramolecular frameworks is at the forefront of this exciting research field. Herein, we present the first polyproline helix to self-assemble into a reversibly porous, crystalline, supramolecular peptide framework (SPF). This framework is assembled from a short oligoproline, adopting the polyproline II conformation, driven by hydrogen-bonding and dispersion interactions. Thermal activation, guest-induced dynamic porosity and enantioselective guest inclusion have been demonstrated for this novel system. The principles of the self-assembly associated with this SPF will be used as a blueprint allowing for the further development of helical peptide linkers in the rational design of SPFs and metalpeptide frameworks.

To investigate the dynamic stereochemical inversion behavior of pillar[5]arenes (P[5]s) in more detail, we synthesized a series of novel rim-differentiated P[5]s with various substituents and examined their rapid rotations by variable-temperature NMR (203–298 K). These studies revealed for the first time the barrier of “methyl-through-the-annulus” rotation (ΔG‡ = 47.4 kJ·mol–1 in acetone) and indicated that for rim-differentiated P[5]s with two types of alkyl substituents, the smaller rim typically determines the rate of rotation. However, substituents with terminal C=C or C≡C bonds give rise to lower inversion barriers, presumably as a result of attractive π–π interactions in the transition state. Finally, data on a rim-differentiated penta-methyl-penta-propargyl P[5] exhibited the complexity of the overall inversion dynamics.

Herein, we present the first high resolution single crystal structure of an unfunctionalized tetrameric proline in the poly-proline II conformation. This rationally designed oligoproline tetramer, self-assembles to form a permanently porous crys-talline supramolecular peptide framework (SPF). Thermal activation, guest inclusion and thermally induced release of chemical guests have been demonstrated for this novel system. This discovery provides a conclusive insight into the pre-viously ambiguous conformation of short oligoprolines and will allow for the further development of proline-based pep-tide linkers in the rational design of SPFs and metal-peptide frameworks.

[Image: see text] The development of an efficient synthetic route toward rim-differentiated C(5)-symmetric pillar[5]arenes (P[5]s), whose two rims are decorated with different chemical functionalities, opens up successive transformations of this macrocyclic scaffold. This paper describes a gram-scale synthesis of a C(5)-symmetric penta-hydroxy P[5] precursor, and a range of highly efficient reactions that allow functionalizing either rim at will via, e.g., sulfur(VI) fluoride exchange (SuFEx) reactions, esterifications, or Suzuki–Miyaura coupling. Afterward, BBr(3) demethylation activates another rim for similar functionalizations.

A new bimodal fluorescent cationic calix[4]arene (L-1) conjugate has been synthesized in multiple steps and well characterized by NMR and electrospray ionizationmass spectrometry (ESIMS) techniques. L-1 has been investigated for its DNA binding ability by various spectroscopy techniques like absorption, fluorescence, and circular dichroism (CD). The formation of L(1)DNA complex has been confirmed by the gel electrophoresis in the presence of incremental concentration of L-1. To visualize the packing of the plasmid (pBR322), detailed tapping mode atomic force microscopy study has been performed, which revealed blob-like structure of plasmid upon addition of the incremental amount of L-1. Concentration dependent transfection ability of L-1 has been established in MCF-7 cells by confocal microscopy by carrying the red fluorescent protein (RFP) encoded plasmid pCMV-tdTomato-N1 to emit both intrinsic fluorescence of L-1 as well as that from RFP. All this has been possible in the absence of any adjuvant phospholipids (DOPE) that are commonly used as helper. Further transfection efficiency of L-1 has been compared with the commercially available lipofectamine (LTX) in two cancer cell lines, MCF 7 and SH-SY5Y, and found that the L-1 is as efficient as that of LTX. Hence, L-1 is an efficient and effective cargo to transport genetic material into the cells.

Tiara[5]arenes (T[5]s), a new class of five‐fold symmetric oligophenolic macrocycles that are not accessible from the addition of formaldehyde to phenol, were synthesized for the first time. These pillar[5]arene‐derived structures display both unique conformational freedom, differing from that of pillararenes, with a rich blend of solid‐state conformations and excellent host–guest interactions in solution. Finally we show how this novel macrocyclic scaffold can be functionalized in a variety of ways and used as functional crystalline materials to distinguish uniquely between benzene and cyclohexane., I have a tiara! Tiara[5]arenes, a class of five‐fold symmetric oligophenol macrocycles, which is not accessible by direct phenol‐formaldehyde condensation, was synthesized through the metamorphosis of pillar[5]arenes.

A bifunctional calix[4]arene molecule bearing coumarin moiety on the lower rim and thioether moiety on the upper rim (L1), has been synthesized and well characterized by (1)H, (13)C NMR and mass spectrometry. Suitably functionalized coumarin moieties are well suited for selective recognition of various cations and anions. Among the 10 different metal ions studied, only Cu(2+) and Fe(3+) exhibit appreciable changes in the absorption spectra owing to the availability of functional moieties present at both the lower as well as the upper rim of free L1 in acetonitrile solution. To bring better selectivity, we blocked one of these functional moieties by coating on to a surface so that only the other one is exposed to the environment for sensing. Such a study carried out in the present case using the self-assembled monolayer (SAM) of L1 on Au(111) resulted in selective sensing of Cu(2+) over several other metal ions as studied by surface plasmon resonance (SPR). The SAM of L1 on Au(111) was confirmed by different techniques, such as grazing incidence FT-IR, contact angle measurement, cyclic voltammetry and scanning tunneling microscopy. Thus, L1 is proven to be a suitable sensor for Cu(2+) when attached to gold surface.

A phenylene diimine capped conjugate of 1,3-calix[4]arene (L) was synthesized and characterized, and its Mg(2+) complex has been isolated and characterized. The chemo sensing ensemble of Mg(2+) bound L provides distinguishable features of response toward phosphates, viz., HPO4(2-), P2O7(4-), and AMP(2-) (Set A) and H2PO4(-), ATP(2-), and ADP(2-) (Set B). While the Set A shows the formation of ternary complex, the Set B does not exhibit any intermediate complex, but both show the release of Mg(2+) and L at different equivalents. The structures of {L + Mg(2+)} and its phosphate bound ternary complexes have been established by computational calculations, and the corresponding results agree well with the experimental ones. The microscopy studies show an aggregation-disaggregation phenomenon in the presence of different equivalents of phosphates in both of the sets. Using the fluorescence data, an INHIBIT logic gate has been built.

Lower rim amide linked 8-amino quinoline and 8-amino naphthalene moiety 1,3,5-triderivatives of calix[6]arene L1 and L2 have been synthesized and characterized. While the L1 acts as a receptor molecule, the L2 acts as a control molecule. The complexation between L1 and Cu(2+) or Zn(2+) was delineated by the absorption and electrospray ionization (ESI) MS spectra. The binding ability of these molecules toward biologically important metal ions was studied by fluorescence and absorption spectroscopy. The derivative L1 detects Zn(2+) by bringing ratiometric change in the fluorescence signals at 390 and 490 nm, but in the case of Cu(2+), it is only the fluorescence quenching of 390 nm band that is observed, while no new band is observed at 390 nm. The stoichiometry of both the complexes is 1:1 and was confirmed in both the cases by measuring the ESI mass spectra. The isotopic peak pattern observed in the ESI MS confirmed the presence of Zn(2+) or Cu(2+) present in the corresponding complex formed with L1. Among these two ions, the Cu(2+) exhibits higher sensitivity. The density-functional theory (DFT) studies revealed the conformational changes in the arms and also revealed the coordination features in the case of the metal complexes. The arm conformational changes upon Zn(2+) binding were supported by nuclear Overhauser effect spectrometry (NOESY) studies. The stronger binding of Cu(2+) over that of Zn(2+) observed from the absorption study was further supported by the complexational energies computed from the computational data. While the L1 exhibited spherical particles, upon complexation with Cu(2+), it exhibits chain like morphological features in scanning electron microscopy (SEM) but only small aggregates in the case of Zn(2+). Thus, even the microscopy data can differentiate the complex formed between L1 and Cu(2+) from that formed with Zn(2+).

Calixarenes, along with cyclodextrins (viz. β-CD) and crown ethers, are the most commonly studied macrocyclic compounds. These bucket shaped molecules have gained tremendous importance for having both hydrophilic and hydrophobic compartments together in the same species. The primary target of this review is to give the readers of various disciplines an updated overview of the recent advancements of the conjugates of calixarenes with respect to their nano chemistry in understanding the nanoscience of these supramolecular systems. Calixarenes now compete with cyclodextrins and calixresorcinols. Thus it is important to look into the current advancement in the literature to draw appropriate comparisons and to provide appropriate designs for their nano science aspects. This review is expected to provide all this. The review covers over 113 conjugates of calixarenes published in 106 references that include contributions from our research group. All the conjugates and their nanoscience aspects were depicted through 63 figures and two schemes. The characterization of these nano systems has been carried out by a variety of techniques that includes spectroscopy and microscopy. The advancement of the conjugates of calixarenes in the nanoworld can be considered as one of the most recent encroachment in the calixarene chemistry and is expected to come out as a major thrust research area in near future.

A triazolium-anthracenyl calix[4]arene conjugate (L) was synthesized by methylating the precursor triazole derivative and then characterized. The potential of the cationic L to differentiate nucleoside triphosphates (NTPs) from their mono- and diphosphates was demonstrated. Due to its unique combination of arms with the calix-platform, a fluorescence enhancement was observed for L with all the NTPs, whereas there is no report with such enhancement being exhibited in case of all the NTPs. This has been supported by the aggregation of L observed from microscopy. Selectivity of L towards NTPs over other phosphates was a result of specific weak interactions, namely, ion-ion, hydrogen bonding and π⋅⋅⋅π, present in the 1:2 complex of L and NTPs (based on ESI MS), which were absent in their congener-phosphates as delineated by NMR and computational studies. Thus, L stands as a unique receptor for NTPs.

The glyco-conjugate, LS, its Hg2+ complex, and the LO were synthesized and characterized in their solid state by FTIR, diffuse reflectance, and powder XRD. The mercury complex shows dumbbell-like microstructures as a result of the metal ion-induced aggregation of the glyco-conjugate as studied based on scanning electron microscopy. The aggregation was also supported by atomic force microscopy. The Hg2+ was detected on LS-coated silica gel sheets by switch-on fluorescence, wherein, the enhancement in the fluorescence intensity varies linearly with the added Hg2+ in the concentration range 5–60 μM. The concentration-dependent variation was also detected on silica gel sheets by viewing their colour under 365 nm light. Hg2+ was detected by the LS-coated silica gel sheets by switch-on fluorescence even in the presence of blood serum. Thus, this method is extendable for the detection and quantification of Hg2+ present in blood and or in biological fluids using disposable silica gel sheets. The sensing of Hg2+ in HEPES buffer solution is well demonstrated in this paper using various techniques, such as fluorescence, absorption, visual color, ESI MS, and 1H NMR. In the buffer medium, the LS exhibit selective chromogenic as well as fluorogenic properties towards Hg2+ by showing ∼75-fold higher fluorescence emission intensity and the studies were further extended to show that none of the 13 ions studied compete for Hg2+. A minimum detection limit of 25 ± 4 ppb was shown by LS for Hg2+ in the buffer. All the experimental studies carried out support the formation of 2 : 1 complex between LS and Hg2+. At higher mole ratios of Hg2+, the same yields the oxo-product, viz., LO. The structure of the 2 : 1 complex was modeled by DFT using B3LYP/LANL2DZ.