Versatile approach toward the self-assembly of heteromultimetallic salen structures

A general route is presented toward the template-directed preparation of self-assembled heteromultimetallic salen structures using noncovalent coordinative metal-ligand interactions. Various higher order assemblies have been studied in detail using a combination of NMR spectroscopy and X-ray crystallography.     

Photoinduced charge separation in three-layer supramolecular nanohybrids: fullerene-porphyrin-SWCNT

Photoinduced charge separation processes of three-layer supramolecular hybrids, fullerene-porphyrin-SWCNT, which are constructed from semiconducting (7,6)- and (6,5)-enriched SWCNTs and self-assembled via π-π interacting long alkyl chain substituted porphyrins (tetrakis(4-dodecyloxyphenyl)porphyrins; abbreviated as MP(alkyl)(4)) (M = Zn and H(2)), to which imidazole functionalized fullerene[60] (C(60)Im) is coordinated, have been investigated in organic solvents. The intermolecular alkyl-π and π-π interactions between the MP(alkyl)(4) and SWCNTs, in addition, coordination between C(60)Im and Zn ion in the porphyrin cavity are visualized using DFT calculations at the B3LYP/3-21G(*) level, predicting donor-acceptor interactions between them in the ground and excited states. The donor-acceptor nanohybrids thus formed are characterized by TEM imaging, steady-state absorption and fluorescence spectra. The time-resolved fluorescence studies of MP(alkyl)(4) in two-layered nanohybrids (MP(alkyl)(4)/SWCNT) revealed efficient quenching of the singlet excited states of MP(alkyl)(4) ((1)MP*(alkyl)(4)) with the rate constants of charge separation (k(CS)) in the range of (1-9) × 10(9) s(-1). A nanosecond transient absorption technique confirmed the electron transfer products, MP˙(+)(alkyl)(4)/SWCNT˙(-) and/or MP˙(-)(alkyl)(4)/SWCNT˙(+) for the two-layer nanohybrids. Upon further coordination of C(60)Im to ZnP, acceleration of charge separation via(1)ZnP* in C(60)Im→ZnP(alkyl)(4)/SWCNT is observed to form C(60)˙(-)Im→ZnP˙(+)(alkyl)(4)/SWCNT and C(60)˙(-)Im→ZnP(alkyl)(4)/SWCNT˙(+) charge separated states as supported by the transient absorption spectra. These characteristic absorptions decay with rate constants due to charge recombination (k(CR)) in the range of (6-10) × 10(6) s(-1), corresponding to the lifetimes of the radical ion-pairs of 100-170 ns. The electron transfer in the nanohybrids has further been utilized for light-to-electricity conversion by the construction of proof-of-concept photoelectrochemical solar cells.     

A facile and expeditious approach for the synthesis of 2-azetidinone derivatives via a multicomponent reaction

Abstract  

New organic reactions allow chemical transformations which were previously unknown. Therefore, new reactions are important contributions to progress in the field of organic synthesis. Herein, we are reporting a simple, one-pot, efficient three-component synthesis of novel 3-chloro-4-[4-(2-oxo-2H-chromen-4-ylmethoxy)phenyl]-1-phenylazetidin-2-one derivatives using 4-(2-oxo-2H-chromen-4-ylmethoxy)benzaldehydes, anilines, and chloroacetyl chloride in the presence of triethyl amine as a catalyst under different conditions. Taking into account environmental and economic considerations, the protocol presented here has the merits of simple operation, convenient work-up, being environmentally benign, and providing good yields. The synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, MS, and elemental analysis.     

Facile fabrication of conducting polymer hydrogels via supramolecular self-assembly

We describe a simple and versatile method to fabricate conducting polymer hydrogels via supramolecular self-assembly between polymers and multivalent cations; the as-prepared hydrogels are potentially applicable in the fields of electrosensors, chemical release and artificial muscles.     

A highly directional fourfold hydrogen-bonding motif for supramolecular structures through self-assembly of fullerodendrimers

Supramolecular dendrimers resulting from the dimerization of fullerene-functionalized dendrons through a quadruple hydrogen-bonding motif were prepared. The synthetic strategy is based on the esterification of a tert-butoxycarbonyl (Boc)-protected 2-ureido-4-[1H]pyrimidinone precursor possessing an alcohol function with fullerodendrons bearing a carboxylic acid unit at the focal point. Subsequent acidic treatment to cleave the protecting group and reaction of the resulting amine with octylisocyanate affords the targeted compounds. As demonstrated by the results of MALDI-TOF mass spectrometry and 1H NMR spectroscopy, both of the 2-ureido-4-[1H]pyrimidinone derivatives form self-assembled dimers spontaneously through hydrogen-bonding interactions, thus leading to supramolecular structures containing two or ten fullerene moieties.     

Construction of functionalized metallosupramolecular tetragonal prisms via multicomponent coordination-driven self-assembly

A new approach for the construction of functionalized metallosupramolecular tetragonal prisms via multicomponent, coordination-driven, template-free self-assembly is described. The combination of tetra-(4-pyridylphenyl)ethylene, a 90° Pt(II) acceptor, and ditopic bipyridine or carboxylate ligands functionalized with hydroxyl or amine groups, hydrophobic alkyl chains, or electrochemically active ferrocene, yields a suite of seven self-assembled tetragonal prisms under mild conditions. These three-dimensional metallosupramolecules were characterized by multinuclear NMR ((31)P and (1)H) and mass spectrometry. Their shapes and sizes were established using Merck Molecular Force Field (MMFF) simulations. In addition, their approximate sizes were further supported by pulsed-field-gradient spin-echo (PGSE) NMR experiments.     

MXene: A two-dimensional material in selective water separation via pervaporation

MXene, well-identified as Ti₃C₂T_X, belongs to the family of two-dimensional (2D) materials, which have been currently explored in various applications. Very recently, such materials have been pointed out as potential nanomaterials for advanced solute separations when introduced in membranes, such as ion separation, gas separation, nanofiltration, chiral molecular separation, and solvent separation. This latter separation, generally named Pervaporation (PV), is identified as a highly selective technology for water separations. To date, few pieces of research have been released but providing interesting insights into several solvent (including water) separations. Hence, this brief review aims to analyze and discuss the latest advances for utilizing MXenes for PV membranes. Particular emphasis has been devoted to the relevant outcomes in the field, along with the strategies followed by researchers to tailor membranes. Based on the current findings, the perspectives in the field are also stated.     

An in situ protonation-activated supramolecular self-assembly for selective suppression of tumor growth

An in situ supramolecular self-assembly in the subcellular organelles could provide a new strategy to treat diseases. Herein, we report a protonation-activated in situ supramolecular self-assembly system in the lysosomes, which could destabilize the lysosome membrane, resulting in the selective suppression of cancer cells. In this system, pyridyl-functionalized tetraphenylethylene (TPE-Py) was protonated in the lysosomes of A549 lung cancer cells to form octahedron-like structures with cucurbit[8]uril (CB[8]), which impaired the integrity of the lysosome membrane, resulting in selective suppression of cancer cells. Moreover, its anticancer efficiency was also systematically evaluated in vivo, triggering the apoptosis of tumor tissues with ignorable effects on normal organs. Overall, the protonation-activated self-assembly in the lysosomes based on the host–guest complexation would provide a method for novel anti-cancer systems.

A protonation-activated supramolecular self-assembly through host–guest interaction was successfully constructed in lysosomes, which could selectively suppress the tumor growth.     

Cyclodextrin-functionalised gold nanoparticles via streptavidin: a supramolecular approach

Biofunctionalised nanoparticles (NPs) have received increased attention both for their potential use as drug carriers and imaging agents and for their applications in medical diagnostics. Functionalised gold nanoparticles (AuNPs) bring together their unique electronic and optical properties (including strong plasmon absorption bands and enhanced light scattering) with the specific capabilities of the functionalising biological molecule. Cyclodextrins (CDs) have been used to functionalise NPs with different approaches. CDs are able to protect from physical, chemical and enzymatic degradation drugs that are included in their cavity. In this study, we report on a new supramolecular approach for the fabrication of CD-functionalised AuNPs. Particularly, we synthesised streptavidin (SA)-coated NPs modified with biotinylated β- and γ-CD, in order to exploit the interaction with SA.     

A facile and specific approach to new liquid chromatography adsorbents obtained by ionic self-assembly

A new ionic-liquid monomer, 1-vinyl-3-octadecylimidazolium bromide ([C(18)VIm]Br), was prepared and polymerized on porous silica particles by means of a surface-initiated radical chain-transfer reaction. Further modification for functionalization was performed through the exchange of counteranions from bromide to methyl orange (MO). Two new silica-poly(octadecylimidazolium) (Sil-PImC(18)) hybrid materials (Sil-PImC(18)-Br and Sil-PImC(18)-MO) were synthesized and characterized by elemental analysis, thermogravimetric analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and solid-state (13)C CP/MAS NMR spectroscopy. Sil-PImC(18)-MO presented ultra-high shape selectivity for constrained isomers of polycyclic aromatic hydrocarbons (PAHs) both in reversed- and normal-phase HPLC when used as the stationary phase. Fundamental aspects of the molecular shape selectivity were evaluated by using Standard Reference Material (SRM) 869b; the column selectivity test mixture for liquid chromatography. The impact of this phase was also demonstrated by the separation of SRM 1647e (16 priority pollutant PAHs) and several steroid isomers. Enhanced selectivity could be explained by the highly oriented arrangement between the octadecylimidazolium chain and a rigid segment of MO. These findings may open a new window of research for the design of materials used in chromatographic supports, solid extraction, catalysis, and electrolytes by simple modifications of the counterions in the poly(ionic liquid) analogous phase.     

A facile and green synthetic approach toward fabrication of starch-stabilized magnetite nanoparticles

A facile and green synthetic approach for fabrication of starch-stabilized magnetite nanoparticles was implemented at moderate temperature. This synthesis involved the use of iron salts, potato starch,sodium hydroxide and deionized water as iron precursors, stabilizer, reducing agent and solvent respectively. The nanoparticles(NPs) were characterized by UV-vis, PXRD, HR-TEM, FESEM, EDX, VSM and FT-IR spectroscopy. The ultrasonic assisted co-precipitation technique provides well formation of highly distributed starch/Fe_3O_4-NPs. Based on UV–vis analysis, the sample showed the characteristic of surface plasmon resonance in the presence of Fe_3O_4-NPs. The PXRD pattern depicted the characteristic of the cubic lattice structure of Fe_3O_4-NPs. HR-TEM analysis showed the good dispersion of NPs with a mean diameter and standard deviation of 10.68 4.207 nm. The d spacing measured from the lattice images were found to be around 0.30 nm and 0.52 nm attributed to the Fe3O4 and starch, respectively. FESEM analysis confirmed the formation of spherical starch/Fe_3O_4-NPs with the emission of elements of C, O and Fe by EDX analysis. The magnetic properties illustrated by VSM analysis indicated that the as synthesized sample has a saturation magnetization and coercivity of 5.30 emu/g and 22.898 G respectively.Additionally, the FTIR analysis confirmed the binding of starch with Fe_3O_4-NPs. This method was cost effective, facile and eco-friendly alternative for preparation of NPs.     

"Umpolung" photoinduced charge separation in an anion-bound supramolecular complex

A new supramolecular system, consisting of an expanded porphyrin, cyclo[8]pyrrole (C8) and a pyrene carboxylate (Py) is capable not only of electron transfer upon photoexcitation, but results in "umpolung" or a reversal of the predicted charge-separation behavior in that the higher energy radical ion pair, C8.+-Py.- (2.58 eV) is formed as opposed to C8.--Py.+ (1.31 eV). This observation is rationalized in terms of the latter radical ion pair, C8.--Py.+ being in the Marcus inverted region. Transient absorption spectral studies reveal a charge-separated lifetime of 300 micros, which decays to the triplet state of cyclo[8]pyrrole, also an exceedingly long-lived species. The novel features of this noncovalent dyad highlight the potential utility of anion binding in the construction of supramolecular electron transfer systems.     

A novel supramolecular graft copolymer via cucurbit[8]uril-based complexation and its self-assembly

A novel supramolecular graft copolymer（SGP） composed of viologen-containing copolymer（P（DMA-co-diEV）） as the main chain and Np ended PNIPAM（Np-PN1PAm） as the grafts is prepared（DMA:N,N- dimethylacryamide,diEV:ethylviologen dimer,Np:naphthalene,PNIPAM:poly（N-isopropylacrylamide））. The grafting is based on the triple complexation among a host of cucurbit[8]uril（CB[8]）and two guests of diEV and Np,which is characterized by UV-vis spectra and ITC.Temperature sensitive property of PNIPAm moiety allows SGP to self-assemble into non-covalently connected micelle（NCCM） at high temperature. The micelles are sensitive to reducing agents,for example Na₂S₂O₃,which breaks the current inclusion complex pair and induces aggregation.     

A facile approach to the synthesis of 5,7-disubstituted indoles via a highly selective lithium-bromine exchange of 5,7-dibromoindoles

A general approach to the synthesis of 5,7-disubstituted indoles has been developed based upon a highly selective lithium-bromine exchange reaction at the 7-position when 1-alkyl-5,7-dibromoindoles were treated with t-BuLi in ether. The resulting 5-bromo-7-lithiated indoles could react with various electrophiles to afford 5-bromo-7-substituted indoles (6) upon work-up. Without isolation of 6, the intermediates thus obtained could be exposed to a second lithium-bromine exchange reaction in a one-pot procedure and further reacted with various electrophiles to afford 5,7-disubstituted indoles (1).     

Functional, hierarchically structured poly(diacetylene)s via supramolecular self-assembly

The supramolecular self-assembly of macromonomers may serve as a first step to prepare well-defined, highly functionalized, hierarchically structured, conjugated polymers. Functional diacetylene macromonomers equipped with an oligopeptide segment designed to promote self-assembly into parallel beta-sheet type structures and a polydisperse, aliphatic coil segment to prevent global ordering give rise to supramolecular polymers with a tubular double-helical quarternary structure in organic solution. These supramolecular polymers may then be converted into the corresponding poly(diacetylene)s by UV irradiation under retention of their hierarchical structure.     

Efficient and facile formation of two-component nanoparticles via aromatic moiety directed self-assembly

Here we present a two-component self-assembling system employing the interaction of aromatic groups (Fmoc) to construct nanoparticles. Spherical particles of around 70 nm were formed spontaneously by a simple trigonal Fmoc-conjugate, which were then stabilized by Fmoc-dipeptides at physiological pH in aqueous solution. These novel particles, being well-tolerated by cells, capable of encapsulating hydrophobic compounds, and readily decorated by short peptides, are promising carriers for drug delivery.     

Solution and solid state studies of a triangle-square equilibrium: anion-induced selective crystallization in supramolecular self-assembly

We report that an equilibrium mixture of triangular and square supramolecular species results when the flexible, ditopic donor unit, trans-bis(4-pyridyl)ethylene, is reacted with the ditopic acceptor unit, cis-(Me(3)P)(2)Pt(OTf)(2), in a one-to-one ratio. Both products are characterized in solution, by way of multinuclear NMR, and in the solid state, via X-ray crystallography. The effects of water and anions, cobalticarborane versus triflate, on the equilibrium are probed. The selective crystallization of either of the two species can be accomplished via the appropriate choice of solvents and ratio of anions present in the system. The dominant species in solution is not always consistent with the most prevalent species in the solid state.