Self-assembly Of Small Organic Molecules Research Articles

Self-Assembly of Small Organic Molecules into Luminophores for Cancer Theranostic Applications.

Self-assembled biomaterials have been widely explored for real-time fluorescence imaging, imaging-guided surgery, and targeted therapy for tumors, etc. In particular, small molecule-based self-assembly has been established as a reliable strategy for cancer theranostics due to the merits of small-sized molecules, multiple functions, and ease of synthesis and modification. In this review, we first briefly introduce the supramolecular chemistry of small organic molecules in cancer theranostics. Then, we summarize and discuss advanced small molecule-based self-assembly for cancer theranostics based on three types, including peptides, amphiphilic molecules, and aggregation-induced emission luminogens. Finally, we conclude with a perspective on future developments of small molecule-based self-assembled biomaterials integrating diagnosis and therapy for biomedical applications. These applications highlight the opportunities arising from the rational design of small organic molecules with self-assembly properties for precision medicine.

From Oligo(Phenyleneethynylene) Monomers to Supramolecular Helices: The Role of Intermolecular Interactions in Aggregation.

Supramolecular helices that arise from the self-assembly of small organic molecules via non-covalent interactions play an important role in the structure and properties of the corresponding materials. Here we study the supramolecular helical aggregation of oligo(phenyleneethynylene) monomers from a theoretical point of view, always guiding the studies with experimentally available data. In this way, by systematically increasing the number of monomer units, optimized n-mer geometries are obtained along with the corresponding absorption and circular dichroism spectra. For the geometry optimizations we use density functional theory together with the B3LYP-D3 functional and the 6–31G** basis set. For obtaining the spectra we resort to time-dependent density functional theory using the CAM-B3LYP functional and the 3–21G basis set. These combinations of density functional and basis set were selected after systematic convergence studies. The theoretical results are analyzed and compared to the experimentally available spectra, observing a good agreement.

Insight into Intermolecular Charge Transfer Determined by Two Packing Mode Cocrystals

Cocrystal molecules obtained through simple self-assembly of small organic molecules often have unique properties that monomolecular crystals do not have. However, it is not easy to purposefully construct a series of cocrystals with specific functions. Moreover, the structures and dynamics of cocrystals are still riddles on account of the initial stage of cocrystal development. In this work, two electron donors (hexamethylbenzene and 1,3,5-trimethoxybenzene) are selected to govern the degree of charge transfer (CT) between the donor and acceptor (pyromellitic dianhydride), which may help obtain two light-emitting materials. In comparison with the monocomponent crystals, the emitting wavelengths of these cocrystals redshift from the ultraviolet range to visible region. It is worth noting that the intermolecular CT of these cocrystal materials is probed by femtosecond transient absorption (fs-TA) spectrometry. The relationship between the characteristics of emission and the stacking patterns of two specific cocrystals has been explored by fs-TA and density functional theory simulation. This work established the foundation to trace the excited-state evolution channels of the organic cocrystal materials.

Near-infrared BODIPY-paclitaxel conjugates assembling organic nanoparticles for chemotherapy and bioimaging

Self-assembly of organic molecules has attracted more and more attention because of precise molecular structure and multifarious synthesis chemistry. Herein, near-infrared brominated boron-dipyrromethenes (BODIPY) paclitaxel conjugate (BrBDP-2PTX) was synthesized. BrBDP-2PTX could self-assemble into uniform spherical nanoparticles (BrBDP-2PTX NPs) via nanoprecipition method. The obtained nanoparticles showed satisfying stability in aqueous solution and 10% fetal bovine serum (FBS) containing phosphoric acid buffer solution (PBS). Moreover, BrBDP-2PTX NPs could make rapid enzyme response to Proteinase K as evidenced by the obvious changes in size and size distribution. BrBDP-2PTX NPs could be internalized by the HeLa cells and exhibited potent cytotoxicity toward tumor cells (human cervical carcinoma cells and liver hepatocellular carcinoma cells) as revealed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays and live/dead staining. Furthermore, in vivo experiments indicated BrBDP-2PTX NPs could be used as efficient bioimaging agents without causing any systemic toxicity. This work highlights the potential of using self-assembly of small organic molecules to develop functional nanomaterials.

The Metal Effect on Self-Assembling of Oxalamide Gelators Explored by Mass Spectrometry and DFT Calculations.

Gels formed by self-assembly of small organic molecules are of wide interest as dynamic soft materials with numerous possible applications, especially in terms of nanotechnology for functional and responsive biomaterials, biosensors, and nanowires. Four bis-oxalamides were chosen to show if electrospray ionization mass spectrometry (ESI-MS) could be used as a prediction of a good gelator and also to shed light on the gelation processes. By inspecting the gelation of several solvent, we showed that bis(amino acid)oxalamide 1 proved to be the most efficient, also being able of forming the largest observable assemblies in the gas phase. The formation of singly charged assemblies holding from one up to six monomer units is the outcome of the strong intermolecular H-bonds, particularly among terminal carboxyl groups. The variation of solvents from polar aprotic towards polar protic did not have any significant effects on the size of the assemblies. The addition of a salt such as NaOAc or Mg(OAc)2, depending on the concentration, altered the assembling. Computational analysis at the DFT level aided in the interpretation of the observed trends and revealed that individual gelator molecules spontaneously assemble to higher aggregates, but the presence of the Na+ cation disrupts any gelator organization since it becomes significantly more favorable for gelator molecules to bind Na+ cations up to the 3:1 ratio than to self-assemble, being fully in line with experimental observations reported here. Graphical Abstract ᅟ.

Molecular-Oriented Self-Assembly of Small Organic Molecules into Uniform Microspheres

Self-assembly of small organic π-conjugated molecules into micro- and nanostructures has drawn much attention because of their wide applications in miniature optoelectronic devices. Many efforts have been focused on the controlled fabrication of organic micro/nanostructures, which are determined by various factors including kinetic and thermodynamic process but still remain poorly understood. In our research, two π-conjugated molecules of (E)-3-(4-(diphenylamino)phenyl)-1-(4-fluoro-2-hydroxyphenyl)prop-2-en-1-one (DFHP) and (E)-3-(4-(bis(4-methoxyphenyl)amino)phenyl)-1-(4-fluoro-2-hydroxyphenyl)prop-2-en-1-one (DFPHP) with a small difference of substituent groups were designed and synthesized. By the solution-exchange method, DFHP are self-assembled into amorphous microspheres while DFPHP tend to grow into crystalline rhombic microcrystals. The head of DFHP organic molecules can form hydrogen bonds with ethanol molecules and the tail of DFHP dissolves in the dichloromethane (DCM) phase, which exhibits amp...

Chromogenic Tubular Polydiacetylenes from Topochemical Polymerization of Self-Assembled Macrocyclic Diacetylenes

Tubular materials formed by self-assembly of small organic molecules find great utility in chemical and material science. Conventional tubular structures often lack stability because noncovalent molecular interactions are responsible for their conformational integrities. Herein we report the development of covalently linked chromogenic organic nanotubes which are prepared by using topochemical polymerization of self-assembled macrocyclic diacetylenes (MCDAs). Crystal structures of five MCDAs having different diameters were elucidated, and four of these substances were transformed to tubular polydiacetylenes (PDA) by UV-induced polymerization. Surprisingly, MCDA-1 was found to self-assemble in stacks with a tilt angle of 62.1°, which significantly deviates from the optimal value for polymerization of 45°. This observation suggests that geometric parameters derived using linear diacetylene (DA) models might not be strictly applicable to polymerization of MCDA systems. Blue-phase PDAs obtained by polymerizat...

A Free-Standing Self-Assembled Tubular Conjugated Polymer Sensor

Tubular materials created by self-assembly of small organic molecules have gained great attention recently. Fabrication of tubular structures that have precise dimensions by using conventional self-assembly approaches is extremely challenging. Herein we describe fabrication of a free-standing tubular polydiacetylene (PDA) sensor based on the meniscus-guided self-assembly and polymerization of diacetylene (DA) monomers. The free-standing single PDA tube can be utilized as an unprecedented microcapillary-based sensor system, which requires only a minimum amount (70–140 nL) of an analyte solution. We have observed 4 orders of magnitude more sensitive to analytes than is a conventional PDA sensor when a biotin-functionalized PDA tube is exposed to streptavidin. The microcapillary-based analytical method developed in this study should find great utility not only for PDA sensors but also for other free-standing wire sensor systems.

Bis-naphthalimides bridged by electron acceptors: optical and self-assembly characteristics

The self-assembly of small organic molecules into molecular stacks plays a vital role in the construction of stable supramolecular structures.

Self-assembly of Natural and Unnatural Nucleobases at Surfaces and Interfaces.

The self-assembly of small organic molecules interacting via non-covalent forces is a viable approach towards the construction of highly ordered nanostructured materials. Among various molecular components, natural and unnatural nucleobases can undergo non-covalent self-association to form supramolecular architectures with ad hoc structural motifs. Such structures, when decorated with appropriate electrically/optically active units, can be used as scaffolds to locate such units in pre-determined positions in 2D on a surface, thereby paving the way towards a wide range of applications, e.g., in optoelectronics. This review discusses some of the basic concepts of the supramolecular engineering of natural and unnatural nucleobases and derivatives thereof as well as self-assembly processes on conductive solid substrates, as investigated by scanning tunnelling microscopy in ultra-high vacuum and at the solid/liquid interface. By unravelling the structure and dynamics of these self-assembled architectures with a sub-nanometer resolution, a greater control over the formation of increasingly sophisticated functional systems is achieved. The ability to understand and predict how nucleobases interact, both among themselves as well as with other molecules, is extremely important, since it provides access to ever more complex DNA- and RNA-based nanostructures and nanomaterials as key components in nanomechanical devices.

Supramolecular hydrogels made of basic biological building blocks.

As a consequence of the self-assembly of small organic molecules in water, supramolecular hydrogels are evolving from serendipitous events during organic synthesis to become a new type of materials that hold promise for applications in biomedicine. In this Focus Review, we describe recent advances in the use of basic biological building blocks for creating molecules that act as hydrogelators and the potential applications of the corresponding hydrogels. After introducing the concept of supramolecular hydrogels and defining the scope of this review, we briefly describe the methods for making and characterizing supramolecular hydrogels. We then discuss representative hydrogelators according to the categories of their building blocks, such as amino acids, nucleobases, and saccharides, and highlight the applications of the hydrogels when necessary. Finally, we offer our perspective and outlook on this fast-growing field at the interface of organic chemistry, materials, biology, and medicine. By providing a snapshot for chemists, engineers, and medical scientists, we hope that this Focus Review will contribute to the development of multidisciplinary research on supramolecular hydrogels for a wide range of applications in different fields.

LT-STM studies on substrate-dependent self-assembly of small organic molecules

Low temperature scanning tunnelling microscopy is widely used to image and manipulate individual atoms and molecules on surfaces, as well as to investigate surface molecular processes such as diffusion, desorption, and configuration switching, at the atomic scale. The aim of this contribution is to highlight our recent progress in understanding the interface between small organic molecules and different substrates, focusing on two model systems: copper hexadecafluorophthalocyanine (F16CuPc) on HOPG, Ag(1 1 1), Bi/Ag(1 1 1), and copper(II) phthalocyanine (CuPc) on perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) and C60 pre-covered surfaces. The influence of the underlying substrates on the molecular packing is discussed.

Peptoids at the 7th Summit: Toward macromolecular systems engineering

Methods for facile synthesis of extraordinarily diverse peptide-like oligomers have placed peptoids at the center of a broad and vibrant area of foldamer science and technology. The 7th Peptoid Summit offered a perspective on the current state of peptoid science and technology and on prospects for engineering supramolecular assemblies that rival the complexity of biomolecular systems. Methods for engineering biomolecular systems based on DNA and protein are advancing rapidly, building a technology platform for engineering increasingly large and complex self-assembled nanosystems. A comparative review of the physical basis for DNA, protein, and peptoid engineering indicates that the characteristics of peptoids suit them for a strong role in developing self-assembled nanosystems. Physical parallels between peptoids and proteins indicate that peptoid engineering, like protein engineering, will require specialized software to support design. Access to novel side-chain functionality will enable peptoid designers to exploit novel binding interactions, including many that have been discovered and exploited in crystal engineering, a field that has extensively explored the self-assembly of small organic molecules to form well-ordered structures. Developments in DNA, protein, and inorganic nanotechnologies are converging to provide a technology platform for the design and fabrication of complex, functional, atomically precise nanosystems. Peptoid-based foldamer technologies, can contribute to this convergence, expanding the scope of the emerging field of atomically precise macromolecular nanosystems.

Polymer-Induced Self-Assembly of Small Organic Molecules into Ultralong Microbelts with Electronic Conductivity

The principle of polymer-controlled crystallization of inorganic materials has been successfully transferred to functional aromatic organic dyes, in this instance 3,4,9,10-perylenetetracarboxylic acid potassium salt (PTCAPS), after its single-crystal structure was determined. The cationic double hydrophilic block copolymer poly(ethylene glycol)-block-branched-poly(ethyleneimine) (PEG-b-PEI) was used as the polymer additive to modify the crystallization of PTCAPS. Ultralong hierarchically structured PTCAPS microbelts with constant width and thickness of each individual belt have been fabricated. The belts are a mesocrystalline assembly of primary nanoparticles with high-energy anionic {001} faces stabilized by polymer complexation. Polarization microscopy, X-ray diffraction, optical absorption spectra, and fluorescence spectra indicate the favorable orientation of the 1D microbelts in the close-stacking direction and reveal a specific 1D superstructure fluorescence. Electrical conductivity measurements performed on a single nanobelt disclose in the doped state a remarkably high electronic conductivity and further demonstrate extended, wirelike pi-pi interactions along the [020] long axis of the belts. Together with the very large length of the belts and their organic-organic hybrid nanostructure, this makes these organic wires potentially interesting for the field of nano-/micro-optoelectronics.