Formation Of J-type Aggregates Research Articles

Aryl-Boron-Substituted BODIPYs: Direct Access via Aluminum-Chloride-Mediated Arylation from Arylstannanes and Tuning the Optoelectronic Properties

An efficient procedure is presented for functionalization of BODIPYs at boron with arylstannanes as weak nucleophiles in the presence of aluminum chloride, providing new aryl-boron-substituted BODIPY and aza-BODIPY derivatives of singular importance. Most of these aryl-boron-substituted BODIPYs showed bright emission in the aqueous solution with significant aggregation-induced emission enhancement and high solid-state emission as a result of the restricted rotation of the meso-phenyl group and boron-substituted aryl groups as well as the formation of J-type aggregates.

Bispyrene-Based Self-Assembled Nanomaterials: In Vivo Self-Assembly, Transformation, and Biomedical Effects.

Self-assembled nanomaterials show potential high efficiency as theranostic agents for high-performance imaging and therapy. However, superstructures and properties of preassembled nanomaterials are somewhat compromised under complicated physiological conditions. Given the advantages of the dynamic nature and adaptive behavior of self-assembly systems, we propose an "in vivo self-assembly" strategy for in situ construction of nanomaterials in living objects. For the proof-of-concept study of in vivo self-assembly, we developed a bispyrene (BP) molecule as a multifunctional building block. BP molecules show nonfluorescence in the monomeric state. Quantum-chemical calculations indicate that BP forms twisted intramolecular charge transfer states, which are separated into two orthogonal units, preventing the fluorescence emission. Interestingly, the typical excimeric emission of BP is observed with the formation of J-type aggregates, as confirmed by single-crystal X-ray diffraction. Packing of the BP molecules generates parallel pyrene units that interact with adjacent ones in a slipped face-to-face fashion through intermolecular π-π interactions. BP and/or its amphiphilic derivatives are capable of self-aggregating into nanoparticles (NPs) in aqueous solution because of the hydrophobic and π-π interactions of BP. Upon specific biological stimuli, BP NPs can be transformed into variable self-assembled superstructures. Importantly, the self-assembled BP NPs exhibit turn-on fluorescence signals that can be used to monitor the self-assembly/disassembly process in vitro and in vivo. On the basis of the photophysical properties of BP and its aggregates, we synthesized a series of designed BP derivatives as building blocks for in situ construction of functional nanomaterials for bioimaging and/or therapeutics. We observed several new biomedical effects, e.g., (i) the assembly/aggregation-induced retention (AIR) effect, which shows improved accumulation and retention of bioactive nanomaterials in the regions of interests; (ii) the transformation-induced surface adhesion (TISA) effect, which means the BP NPs transform into nanofibers (NFs) on cell surfaces upon binding with specific receptors, which leads to less uptake of BP NPs by cells via traditional endocytosis pathway; and (iii) transformation of the BP NPs into NFs in the tumor microenvironment, showing high accumulation and long-term retention, revealing the transformation-enhanced accumulation and retention (TEAR) effect. In this Account, we summarize the fluorescence property and emission mechanism of BP building blocks upon aggregation in the biological environment. Moreover, BP-derived compounds used for in vivo self-assembly and transformation are introduced involving modulation strategies. Subsequently, unexpected biomedical effects and applications for theranostics of BP based nanomaterials are discussed. We finally conclude with an outlook toward future developments of BP-based self-assembled nanomaterials.

Synthesis and gelation capability of Fmoc and Boc mono-substituted cyclo(L-Lys-L-Lys)s

Fmoc or Boc mono-substituted cyclo(L-Lys-L-Lys)s were synthesized via the reaction of lysine cyclic dipeptide with Fmoc N-hydroxysuccinimide este(Fmoc-OSu) and di-tert-butyl dicarbonate[(Boc)2O], respectively. The resulted mono-substituted cyclo(L-Lys-L-Lys)s(2―4) by means of test tube inversion method served as organogelators enabled to form stable thermo-reversible organogels in alcoholic, substituted benzene and chlorinated solvents, with the minimum gelation concentration(MGC) in a range of 1%―4%(mass fraction). The transmission electron microscopy(TEM) and scanning electron microscopy(SEM) observations reveal that these gelators self-assembled into 3D nanofiber, nanoribbon or nanotube network structures. The rheological measurement exhibited that the storage modulus of gels is higher than the loss one, and the complex viscosity is reduced linearly with the increasing of scanning frequency. The fluorescence spectrum of compound 2 in 1,2-dichloroethane and benzene demonstrates that the emission peak of Fmoc at 320 nm has red-shifted and the intensity decreases gradually, while the intensity of the emission peak at 460 nm substantially enhances as a function of concentration, indicating the existence of π-π stacking interactions and the formation of J-type aggregates. Meanwhile, compound 4 self-assembled into nanotubes via the stacking of multiple bilayer membranes. Fmoc and Boc disubstituted cyclo(L-Lys-L-Lys)(3) holds the relatively lower MGC values, showing the stronger gelation ability in most selected organic solvents due to the presence of both Fmoc and Boc groups.

Solution processed films and nanobelts of substituted zinc phthalocyanine as room temperature ppb level Cl2 sensors

Room temperature Cl2 sensing characteristics of highly selective spin coated Zn (II) 1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (ZnPc(OBu)8) film and self-assembled nanobelts (NBs) have been studied in the concentration range of 5–1500ppb. UV–Visible absorption spectroscopic studies indicate the formation of J-type aggregates in case of ZnPc(OBu)8 film and H-type aggregates in NBs. The electrical conductance of NBs is found to be 60% more than ZnPc(OBu)8 film. For 1500ppb of Cl2, the response of ZnPc(OBu)8 film and NBs is 522% and 655% with a response time of 25s and 15s, respectively. The detection limit of ZnPc film is lowered from 50ppb to 5ppb by making butoxy substitution. X-ray photoelectron spectroscopic studies reveal that absorption sites predominantly are the central metal ions of ZnPc(OBu)8 molecules. The results obtained are compared with Cl2 sensing characteristics of unsubstituted ZnPc film to show the effect of butoxy substitution and NBs formation.

Synthesis and Self Assembling Properties of Rod-Like, 2-Ureido-4-pyrimidinone-Based Main Chain Supramolecular Dendronized Polymers

A series of G1−G3 supramolecular dendronized polymers 6 bearing dimeric 2-ureido-4-pyrimidinone (UPy) units on the main chain and aliphatic hydrocarbon dendrons as side chain appendages was prepared. Because of the high crystallinity and poor solubility of such rigid rod polymers, only the G3 dendron could confer the resulting polymer 6 (n = 3) with enough solubility to enable its characterization and property studies. It was found that the nature of the dendrons play an important role on the UPy binding strength, solubility and self-assembly properties. The reversible nature of the polymerization process was demonstrated in different solvent systems by viscosity studies. A double logarithmic plot of the specific viscosity against concentration revealed a deflection point at 26 mM in CHCl3 at 26 and 40 °C. Below this critical concentration a straight line with a slope of 1.5 was obtained, while a slope of 4.0−4.2 was secured above this concentration. The data suggested that the associative interaction between the di-UPy monomer 5 (n = 3) increased nonlinearly with increasing monomer concentration. While the above investigations confirmed that these were main chain supramolecular dendronized polymers, UV−vis spectroscopic study revealed a large bathochromic shift (32 nm) with increasing polymer concentration in CHCl3. This finding was consistent with the formation of J-type aggregates via stair-case stacking between interchain UPy rings. SEM morphological study also confirmed that the resulting polymers appeared as fibrous superbundles with a very high aspect ratio. A model was purposed to rationalize how such bundles could be assembled from the di-UPy dendritic macromonomer 5 via intrachain hydrogen bonding and interchain stacking interactions.

Spectroscopic Investigation of Mixed LB Films of Benzo(k)fluoranthene

This communication reports the spectroscopic studies of nonamphiphilic benzo(k)fluoranthene, abbreviated as BFL, when incorporated into Langmuir-Blodgett (LB) films mixed with stearic acid (SA). The surface pressure versus area per molecule isotherms of BFL mixed with SA at different mole fractions reveals that the area per molecule decreases with increasing mole fractions of BFL. The area per molecule versus mole fraction shows that there is positive deviation of the experimental data to the idealized one. This indicates formation of aggregation of BFL molecules in the mixed LB films with SA. Formation of J-type aggregates has been confirmed by the absorption spectroscopic study. Aggregation of BFL molecules giving rise to excimeric emission has been demonstrated by the fluorescence spectroscopic study. Changing the mole fraction and number of layers as well as the pressure of lifting can precisely control the order of aggregation. This has been reported in detail.

Spectroscopic and Biochemical Characterisation of Self-Aggregates Formed by Antitumor Drugs of the Camptothecin Family: Their Possible Role In the Unique Mode of Drug Action

We describe the effect strongly influencing the biological activity of some camptothecin (CPT) drugs, the inhibitors of DNA topoisomerase I (topo I), namely, the formation of J-type aggregates in an aqueous buffer solution. These aggregates were built up under certain dilution conditions of the stock DMSO solutions of 20- S-camptothecin (20( S)CPT), 10,11-methylenedioxy-CPT (10,11-CPT) and 7-ethyl-10-hydroxy-CPT (SN38). The aggregates were found to be stereospecific, not being detectable for the 20( R)-stereoisomer of CPT. They were formed by the stacking interaction between quinoline rings of CPT chromophores with the inverse position of the nitrogen atoms. The aggregates were stable at acidic and neutral pHs, but dissociated at basic pHs. Self-aggregation prevented hydrolysis of the lactone ring at neutral pHs, thus preserving the drugs in a biologically active form. Addition of BSA did not induce either disaggregation or hydrolysis of the lactone ring, whereas the monomeric form of the drugs was shown to undergo rapid conversion to an inactive carboxylate form in the presence of human serum albumin [5]. The drugs did not form the aggregates in the presence of topo I. Moreover, rapid dissociation of the aggregates was observed if a self-aggregated drug solution was added to topo I alone or to the DNA-topo I cleavage assay. Neither DNA alone nor oligonucleotides derived from the sequences of the CPT-enhanced or topo I-induced cleavage sites in SV40 plasmid DNA induces changes in the aggregation state of the drugs. These observations are indicative of interaction between the aggregates and topo I. The aggregates were found to penetrate within the cells with much higher efficiency than a monomeric form of the drugs. Cellular uptake of aggregated and nonaggregated species correlated well with cytotoxic effects produced by the drug. In this manner, CPT’s self-aggregation should be regarded as a favourable phenomenon producing species with a more stable biologically active structure of the lactone ring and exhibiting enhanced cellular uptake levels relative to the monomeric forms of medications.