Field Of Molecular Self-assembly Research Articles

Reversing the Trend: Deciphering Self-Assembly of Unconventional Amphiphiles having both Alkyl-chain and PEG.

In the field of molecular self-assembly, the core of an assembly is always made up of hydrophobic moiety like a long alkyl chain, whereas the outer part has always been a hydrophilic moiety such as poly(ethylene glycol) (PEG), or charged species. Hence, reversing the trend to manifest self-assembled structures with a PEG core and a surface consisting of alkyl chains in aqueous system is incredibly challenging. Herein, we architected a unique class of cationic bolaamphiphiles containing low molecular weight PEG and alkyl chains of different lengths. The bolaamphiphiles spontaneously form vesicles without external stimuli. These vesicles are unprecedented because PEG makes up the vesicle core, while the alkyl chains appear on the vesicles' exterior. Hence, this is the first report on an assembly that reverses the usual trend. The vesicle size increases with the increase in alkyl chain-length. To our great surprise, we obtained large micelles for longest alkyl-chain amphiphile, which in turn act as a gemini amphiphile. The shift from a particular bolaamphiphile to gemini amphiphile with the variation of alkyl chain is also unexplored. Therefore, this specific class of self-assembled structure would compound a new paradigm in the fields of molecular self-assembly and supramolecular chemistry.

Tumor Microenvironment Targeting and Responsive Peptide-Based Nanoformulations for Improved Tumor Therapy.

The tumor microenvironment participates in all stages of tumor progression and has emerged as a promising therapeutic target for cancer therapy. Rapid progress in the field of molecular self-assembly using various biologic molecules has resulted in the fabrication of nanoformulations that specifically target and regulate microenvironment components to inhibit tumor growth. This inhibition process is based on differentiating between biophysicochemical cues guiding tumor and normal tissue microenvironments. Peptides and peptide derivatives, owing to their biocompatibility, chemical versatility, bioactivity, environmental sensitivity, and biologic recognition abilities, have been widely used as building blocks to construct multifunctional nanostructures for targeted drug delivery and controlled release. Several groups of peptides have been identified as having the ability to penetrate plasma membranes, regulate the essential signaling pathways of angiogenesis and immune reactions, and recognize key components in the tumor microenvironment (such as vascular systems, stromal cells, and abnormal tumor biophysicochemical features). Thus, using different modules, various functional peptides, and their derivatives can be integrated into nanoformulations specifically targeting the tumor microenvironment with increased selectivity, on-demand response, elevated cellular uptake, and improved tumor therapy. In this review, we introduce several groups of functional peptides and highlight peptide-based nanoformulations that specifically target the tumor microenvironment. We also provide our perspective on the development of smart drug-delivery systems with enhanced therapeutic efficacy.

Photon Upconversion and Molecular Solar Energy Storage by Maximizing the Potential of Molecular Self-Assembly.

The self-assembly of functional molecules into ordered molecular assemblies and the fulfillment of potentials unique to their nanotomesoscopic structures have been one of the central challenges in chemistry. This Feature Article provides an overview of recent progress in the field of molecular self-assembly with the focus on the triplet-triplet annihilation-based photon upconversion (TTA-UC) and supramolecular storage of photon energy. On the basis of the integration of molecular self-assembly and photon energy harvesting, triplet energy migration-based TTA-UC has been achieved in varied molecular systems. Interestingly, some molecular self-assemblies dispersed in solution or organogels revealed oxygen barrier properties, which allowed TTA-UC even under aerated conditions. The elements of molecular self-assembly were also introduced to the field of molecular solar thermal fuel, where reversible photoliquefaction of ionic crystals to ionic liquids was found to double the molecular storage capacity with the simultaneous pursuit of switching ionic conductivity. A future prospect in terms of innovating molecular self-assembly toward molecular systems chemistry is also discussed.

Two-dimensional self-assembly of amphiphilic porphyrins on a dynamically shrinking droplet surface

Developing a new field of molecular self-assembly in the sub-micrometer regime-with precision as high as that used to make discrete nano-sized molecular architectures through molecular design-is a major challenge for supramolecular chemistry. At present, however, there is no effective strategy for controlling the assembling molecules when their quantity is greater than one thousand. Herein, we propose a potential solution by exploiting a novel supramolecular system in conjunction with dynamically shrinking oil droplets, enabling more than a thousand component molecules to organize simultaneously into the form of sub-micrometer-scale ring structures. In our developed system, amphiphilic porphyrins, having potential two-dimensional assembling ability, were compartmentalized into droplets with narrow distributions and molecular numbers. These droplets were subsequently transformed into discrete ring-like structures during the process of solvent removal from the inner organic layer, i.e., shrinking the droplets. Unique self-assembled structures, which are not accessible through conventional supramolecular strategies, can be selectively created depending on the initial stage of the droplet.

Effect of Organochloride Guest Molecules on the Stability of Homo/Hetero Self-Assembled α,γ-Cyclic Peptide Structures: A Computational Study Toward the Control of Nanotube Length

We present here a molecular dynamics study on peptide nanotubes composed of cis-3-aminocyclohexanecarboxylic acid-(γ-Ach) or cis-3-aminocyclopentanecarboxylic acid (γ-Acp)-based α,γ-cyclohexapeptides and also on those formed by heterodimeric pairs from a combination of the two aforementioned peptides (γ-Ach/Acp), which is the first time that a self-assembling cyclic peptide nanotube composed of heteromeric units is investigated. The main advantage of these types of nanotube is that they have a partially hydrophobic inner cavity, a property that makes them very exciting alternatives to classical nanotubes. In an effort to analyze the fine details of these ensembles, we investigated the dynamical behavior of model dimeric structures that mimic the fundamental repeating structural motif of longer nanotubes. Despite the structural analogy of the β-sheet interaction, our results suggest that extrapolation of the information obtained from those “capped” dimers to nanotube properties has some limitations because several significant differences have been found between the two systems. This finding is not only relevant for α,γ-cyclic peptide nanotubes but also shows that special care should also be taken when considering other related peptide nanotubes in which N-methylated dimers are used to obtain information about the stability and formation of the nanotubes. The structural and dynamical behavior of dimers and nanotubes in nonpolar (chloroform) and polar protic solvents (water) has been analyzed using state-of-the-art theoretical methods. A marked destabilizing effect on the structure was observed in aqueous solution for all systems studied, suggesting that most of the water molecules that compete for the hydrogen bonds are those that occupy the internal cavity. We show that the introduction of organochloride molecules within the dimers and nanotubes is stabilized in water, and this property opens the door to a large number of possible future applications that are an important challenge in the field of molecular self-assembly, such as in drug delivery processes to control nanotube length by means of appropriate guests. A precise control of the nanotube length can be envisaged from the MD simulations of the encapsulation of 1,2-bis[2-(2,2,2-trichloroethoxy)ethoxy]ethane inside its inner cavity, opening a very interesting possibility in this area.

An ab initio insight into the Cu(111)-mediated Ullmann reaction

The coupling process of phenyl radicals-the important intermediates in the prototypal Ullmann reaction-on Cu(111) is addressed using density functional theory. Consistent with experiments, we prove that the fragments interact attractively already at relatively large distances. An intermediate state involving a "popping-out" surface atom is reached through a non-trivial surface diffusion path. The overall process of coupling to the final biphenyl state (with a barrier of 0.38 eV) is governed by a subtle electronic mechanism that reminds the concepts postulated by Hoffmann about the alignment of molecular frontier orbitals with the metallic Fermi level. Our results can be applied to more complex surface processes in the field of molecular self-assembly.

Nanostructured molecular surfaces: advances in investigation and patterning tools

This feature article is aimed to showcase advanced soft and radiationless nanotools for the morphological characterization and for the preparation/modification of molecular surfaces, namely solid supported ultrathin films not exceeding 1–2 molecular layers. As to the characterization, the development of dynamic scanning force microscopy in attractive regime is presented as an important progress at least as far as it concerns imaging of nanoscale features of molecular surfaces with minimal probe–sample physical interaction. To date, this tool has been applied only by a few groups in spite of its larger resolution and image quality than the conventional scanning probe methods. As to the preparation/modification, the realization of ultrathin nanoscale patterns is reviewed by highlighting at first some recent approaches in the field of molecular self-assembly on solid substrates including the possibility to induce order under both equilibrium and non-equilibrium conditions. Secondly, the area of nanoscale man-made fabrication is featured by choosing some of those techniques of urgent need (high resolution, low cost, potentially of simple use) like scanning probe lithographies and nanodispensing tools.

Distance dependence of electron transfer rates in bilayers of a ferrocene Langmuir-Blodgett monolayer and a self-assembled monolayer on gold

Bilayers consisting of a self-assembled alkanethiol monolayer of variable chain length and Langmuir-Blodgett monolayers of 16-ferrocenylhexadecanoic acid were fabricated on Au electrodes. The hydrophobic ferrocene groups reside at the monolayer-monolayer interface and are variably spaced from the underlying electrode. Interfacial electron transfer rates k” for ferrocene electron transfer across the alkanethiol spacer monolayer were measured cyclic voltammetrically. The rates were found to fall off exponentially with increasing alkanethiol chain length, giving a decay constant of -0.96 per methylene. The electron transfer rate with a dodecanethiol spacer layer (k” = 12 s-l), which involves a non-bonded donor-acceptor couple, is almost 2 orders of magnitude lower than those for the analogous ferrocenes chemically bound on Au through alkane thiols of similar bond length. The higher rate in the latter may be attributed to a through-bond mechanism, as opposed to the former in which there exists a single “break” in the chemical bond network. The results have their implications on the electron transfer studies of biological systems. We have sought to probe long-distance interfacial electron transfer’ (ET) by using designed electrochemical interfaces based on self-assembled monolayer2 (SAM) and LangmuirBlodgett (LB) films.3 In particular, we have fabricated on gold surfaces bilayer structures composed of an inner spacer monolayer of long-chain alkanethiols (CnH2,+1SH, n 2 10) and an outer electroactive LB monolayer, with electrochemically reactive head groups (ferrocene) positioned at the monolayermonolayer interface (Scheme la). The distance dependence of the heterogeneous ET rate constants can be investigated by varying the alkanethiol chain length. Furthermore, a comparison of these rates with those obtained at gold electrodes modified with ferrocene-terminated alkanethiol monolayers2c.f (Scheme lb) can address the question of the relative efficiency of “through-bond” versus “through-space’’ ET pathways. This is one of the key issues currently under investigation4 in the field of long range electron transfer, a reaction that is ubiquitous in biological systems and is involved in such important processes as oxidative phosphorylation and photosynthesis. In a biological electron transfer reaction, the electron donor and acceptor are separated by polypeptides organized into defined threedimensional structures mostly through noncovalent interactions such as hydrogen bonds and van der Waals contacts. The modulation of these noncovalent interactions on the overall electron tunneling efficiency through the polypeptide matrix is therefore well worth investigating. Experimental measurements5 as well as theoretical calculations6 have been carried out using metal-derivatized proteins and physiological protein-protein complexes to examine the effect of biological medium on electron transfer kinetics, although the ability to control the structural details of these systems has not been achieved yet. With the rapid advancement in the field of molecular selfassembly, we are now in a position to fabricate highly ordered monomolecular and multilayer films on solid surfaces with molecular level control over the structures and employ them in