"Pocket dendrimers" as nanoscale receptors for bimolecular guest accommodation

Macrocyclic Receptors for Identification and Selective Binding of Substrates of Different Nature

Molecular recognition of host/guest molecules represents the basis of many biological processes and phenomena. Enzymatic catalysis and inhibition, immunological response, reproduction of genetic information, biological regulatory functions, the effects of drugs, and ion transfer-all these processes include the stage of structure recognition during complexation. The goal of this review is to solicit and publish the latest advances in the design and sensing and binding abilities of porphyrin-based heterotopic receptors with well-defined geometries, the recognition ability of which is realized due to ionic, H-bridge, charge transfer, hydrophobic, and hydrophilic interactions. The dissection of the considered low-energy processes at the molecular scale expands our capabilities in the development of effective systems for controlled recognition, selective delivery, and prolonged release of substrates of different natures (including drugs) to their sites of functioning.

Molecular Recognition of Imidazole Derivatives by Co(III)-Porphyrinsin Phosphate Buffer (pH = 7.4) and Cetylpyridinium Chloride Containing Solutions

Bymeans of spectrophotometric titration and NMR spectroscopy, the selective binding ability ofthe Co(III)-5,15-bis-(3-hydroxyphenyl)-10,20-bis-(4-sulfophenyl)porphyrin (Со(III)Р1) andCo(III)-5,15-bis-(2-hydroxyphenyl)-10,20-bis-(4-sulfophenyl)porphyrin (Со(III)Р2) towards imidazole derivatives of various nature (imidazole (L1), metronidazole (L2), and histamine (L3)) in phosphate buffer (pH 7.4) has been studied. It was found that in the case of L2, L3 the binding of the "first" ligand molecule by porphyrinatesCo(III)P1 and Co(III)P2 occurs with the formation of complexes with two binding sites (donor-acceptor bond at the center and hydrogen bond at the periphery of the macrocycle), while the "second" ligand molecule is added to the metalloporphyrin only due to the formation of the donor-acceptor bond at the macrocycle coordination center. The formation of stable complexes with two binding sites has been confirmed by density functional theory method (DFT) quantum chemical calculations and two-dimensional NMR experiments. It was shown that among the studied porphyrinates, Co(III)P2 is more selective towards to L1-L3 ligands, and localization of cobalt porphyrinates in cetylpyridinium chloride (CPC) micelles does not prevent the studied imidazole derivatives reversible binding. The obtained materials can be used to develop effective receptors for recognition, delivery, and prolonged release of drug compounds to the sites of their functioning. Considering that cetylpyridinium chloride is a widely used cationic biocide as a disinfectant, the designed materials may also prove to be effective antimicrobial agents.

Inhibition of Ligand Binding Ability of Three Porphyrins by an Organic Effector

A stimulus-responsive receptor 1 was designed and prepared to control the ligand-binding ability of three active sites, two zinc tetraphenylporphyrin units (P1) and one zinc diethynyldiphenylporphyrin unit (P2), with one effector molecule 2. Bulky hexarylbenzene units were incorporated as shielding panels in the middle of the flexible side arms of 1. Spectroscopic titrations indicated that a stable supramolecular complex 1⋅2 (K_1⋅2 =6.7×10⁶  m^-1 ) was produced by the cooperative formation of multiple hydrogen and coordination bonds. As a result, the binding of a ligand to P1 was inhibited by 2 in a competitive manner. Additionally, the formation of 1⋅2 brought about conformational restriction of the side arms to cover both faces of P2 with the shielding panels. The binding constant of 4-phenylpyridine with P2 in 1⋅2 decreased to 8.9 % of that in 1. Namely, the ligand-binding ability of P2 was inhibited according to an allosteric mechanism.

The study of electron transfer reactions in a dendrimeric assembly: proper utilization of dendrimer fluorescence

Sensing applications of dendrimers: trapping of explosive nitroaromatic compounds within the dendrimer-cage followed by efficient quenching of its fluorescence.

Molecular recognition: from solution science to nano/materials technology

In the 25 years since its Nobel Prize in chemistry, supramolecular chemistry based on molecular recognition has been paid much attention in scientific and technological fields. Nanotechnology and the related areas seek breakthrough methods of nanofabrication based on rational organization through assembly of constituent molecules. Advanced biochemistry, medical applications, and environmental and energy technologies also depend on the importance of specific interactions between molecules. In those current fields, molecular recognition is now being re-evaluated. In this review, we re-examine current trends in molecular recognition from the viewpoint of the surrounding media, that is (i) the solution phase for development of basic science and molecular design advances; (ii) at nano/materials interfaces for emerging technologies and applications. The first section of this review includes molecular recognition frontiers, receptor design based on combinatorial approaches, organic capsule receptors, metallo-capsule receptors, helical receptors, dendrimer receptors, and the future design of receptor architectures. The following section summarizes topics related to molecular recognition at interfaces including fundamentals of molecular recognition, sensing and detection, structure formation, molecular machines, molecular recognition involving polymers and related materials, and molecular recognition processes in nanostructured materials.

Carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles in central nervous systems-regenerative medicine: effects on neuron/glial cell viability and internalization efficiency

The applicability of CMCht/PAMAM dendrimer nanoparticles for CNS applications was investigated. AFM and TEM observations revealed that the nanoparticles possessed a nanosphere-like shape with a size from 22.0 to 30.7 nm. The nanoparticles could be bound to fluorescent-probe FITC for tracing purposes. Post-natal hippocampal neurons and cortical glial cells were both able to internalize the FITC-labeled CMCht/PAMAM dendrimer nanoparticles with high efficiency. The percentage of positive cells internalizing the nanoparticles varied, reaching a peak after 48 h of incubation. Further experiments for periods up to 7 d revealed that the periodical addition of FITC-labelled CMCht/PAMAM dendrimer nanoparticles was needed to maintain the overall percentage of cells internalizing them. Finally, it was also observed that cell viability was not significantly affected by the incubation of dendrimer nanoparticles.

Synthesis and photoluminescence study of di-dendron dendrimers derived from mono-Boc-protected ethylenediamine cores

This work is focused on the synthesis and optical properties of cone-shaped structural feature di-dendron polyamidoamine dendrimers up to the third generation with mono-Boc-protected ethylenediamine (EDA) as a core. Strong UV absorbance spectra and fluorescence spectra from di-dendron dendrimers with different terminal groups (-NH(2), -COOCH(3)) were studied under different conditions by varying experimental parameters such as concentration and pH. The optical density and fluorescence intensities increased when di-dendron dendrimers generation number increased from 0.5 to 3.0. It was confirmed that the concentration of di-dendron dendrimers plays an important role in fluorescence intensity. The increase in fluorescence intensity was linear in low concentration regions, but the intensity increased slowly in high concentration regions. The results also showed a rapid increase in fluorescence intensity at low pH. The formation of a fluorescence-emitting moiety had a close relationship to protonated tertiary amine groups in di-dendron dendrimers derived from mono-Boc-protected EDA cores. Furthermore, the formation of fluorescent chemical species was irreversible.

Cooperativity and tunable excited state deactivation: modular self-assembly of depsipeptide dendrons on a Hamilton receptor modified porphyrin platform

A series of novel supramolecular architectures were built around a tin tetraphenyl porphyrin platform 6--functionalized by a 2-fold 1-ethyl-3-3-(3-dimethylaminopropyl)carbodiimide (EDC) promoted condensation reaction--and chiral depsipeptide dendrons of different generations 1-4. Here, implementation of a Hamilton receptor provided the necessary means to keep the constituents together via strong hydrogen bonding. Characterization of all architectures has been performed, including 4 which is the fourth generation, on the basis of NMR and photophysical methods. In particular, several titration experiments were conducted suggesting positive cooperativity, an assessment that is based on association constants that tend to be higher for the second binding step than for the first step. Importantly, molecular modeling calculations reveal a significant deaggregation of the intermolecular network of 6 during the course of the first binding step. As a consequence, an improved accessibility of the second Hamilton receptor unit in 6 emerges and, in turn, facilitates the higher association constants. The features of the equilibrium, that is, the dynamic exchange of depsipeptide dendrons 1-4 with fullerene 5, was tested in photophysical reference experiments. These steady-state and time-resolved measurements showed the tunable excited-state deactivations of these complexes upon photoexcitation.