The stepwise supramolecular organisation of guanosine derivatives

Several supramolecular architectures generated by guanosine derivatives are described. The research started from the fortuitous observation of a lyotropic behavior exhibited by a guanylic nucleotide in water. This observation stimulated extensive research on several natural and lipophilic guanosine derivatives which self-assemble in different architectures (discs, ribbons, helices...), according to their structure and environment. These ordered structures can be used as scaffolds for photo- or electro-active moieties and for the fabrication of molecular electronic devices.     

G-quartets 40 years later: from 5'-GMP to molecular biology and supramolecular chemistry

Molecular self-assembly is central to many processes in both biology and supramolecular chemistry. The G-quartet, a hydrogen-bonded macrocycle formed by cation-templated assembly of guanosine, was first identified in 1962 as the basis for the aggregation of 5'-guanosine monophosphate. We now know that many nucleosides, oligonucleotides, and synthetic derivatives form a rich array of functional G-quartets. The G-quartet surfaces in areas ranging from structural biology and medicinal chemistry to supramolecular chemistry and nanotechnology. This Review integrates and summarizes knowledge gained from these different areas, with emphasis on G-quartet structure, function, and molecular recognition.     

From molecular to macroscopic engineering: shaping hydrogen-bonded organic nanomaterials

The self‐assembly and self‐organization behavior of chromophoric acetylenic scaffolds bearing 2,6‐bis(acetylamino)pyridine ( 1 , 2 ) or uracyl‐type ( 3 – 9 ) terminal groups has been investigated by photophysical and microscopic methods. Systematic absorption and luminescence studies show that 1 and 2 , thanks to a combination of solvophilic/solvophobic forces and π–π stacking interactions, undergo self‐organization in apolar solvents (i.e., cyclohexane) and form spherical nanoparticles, as evidenced by wide‐field optical microscopy, TEM, and AFM analysis. For the longer molecular module, 2 , a more uniform size distribution is found (80–200 nm) compared to 1 (20–1000 nm). Temperature scans in the range 283–353 K show that the self‐organized nanoparticles are reversibly formed and destroyed, being stable at lower temperatures. Molecular modules 1 and 2 were then thoroughly mixed with the complementary triply hydrogen‐bonding units 3 – 9 . Depending on the specific geometrical structure of 3 – 9 , different nanostructures are evidenced by microscopic investigations. Combination of modules 1 or 2 with 3 , which bears only one terminal uracyl unit, leads to the formation of vesicular structures; instead, when 1 is combined with bis‐uracyl derivative 4 or 5 , a structural evolution from nanoparticles to nanowires is observed. The length of the wires obtained by mixing 1 and 4 or 1 and 5 can be controlled by addition of 3 , which prompts transformation of the wires into shorter rods. The replacement of linear system 5 with the related angular modules 6 and 7 enables formation of helical nanostructures, unambiguously evidenced by AFM. Finally, thermally induced self‐assembly was studied in parallel with modules 8 and 9 , in which the uracyl recognition sites are protected with tert‐butyloxycarbonyl (BOC) groups. This strategy allows further control of the self‐assembly/self‐organization process by temperature, since the BOC group is completely removed on heating. Microscopy studies show that the BOC‐protected ditopic modules 8 self‐assemble and self‐organize with 1 into ordered linear nanostructures, whereas BOC‐protected tritopic system 9 gives rise to extended domains of circular nano‐objects in combination with 1 .     

Carboxylate anion diminishes chloride transport through a synthetic, self-assembled transmembrane pore

Six amphiphilic heptapeptides with the structure (C18H37)2NCOCH2OCH2CO-(Gly)3-Pro-(Gly)n-(Glx)-(Gly)m-O(CH2)6CH3, in which Glx represents glutamic acid or its benzyl ester and n+m=2, have been studied. In addition, the glutamate residue in the GGGPGGE sequence was esterified by fluorescent 1-pyrenemethanol. These compounds insert into phospholipid bilayers and form anion-conducting pores. Hill plots based on carboxyfluorescein release indicate that the pores are at least dimeric. Studies that involved ion-selective electrode techniques showed that transport of chloride varied with the position of glutamate within the peptide chain and whether glutamic acid was present as the free acid or its benzyl ester. Chloride transport activity was significantly higher for the glutamate esters than for free carboxylates irrespective of the glutamate position. Activity was highest when the glutamate residue in approximately (Gly)3-Pro-(Xxx)3 approximately was closest to the C terminus of the peptide. A fluorescent pyrene residue was introduced to probe the aggregation state of the amphiphile. The selectivity of the pore for Cl(-) over K+ was maintained even when the carboxylate anion was present within it. Complexation of Cl(-) by the ionophoric peptides was confirmed by negative ion mass spectrometry. Planar bilayer voltage clamp experiments confirmed that pores with more than one conductance state may form in these dynamic, self-assembled pores.     

Using Diffusion NMR To Characterize Guanosine Self‐Association: Insights into Structure and Mechanism

This paper presents results from a series of pulsed field gradient (PFG) NMR studies on lipophilic guanosine nucleosides that undergo cation‐templated assembly in organic solvents. The use of PFG‐NMR to measure diffusion coefficients for the different aggregates allowed us to observe the influences of cation, solvent and anion on the self‐assembly process. Three case studies are presented. In the first study, diffusion NMR confirmed formation of a hexadecameric G‐quadruplex [G 1 ]₁₆ ? 4 K⁺ ? 4 pic^? in CD₃CN. Furthermore, hexadecamer formation from 5′‐TBDMS‐2′,3′‐isopropylidene G 1 and K⁺ picrate was shown to be a cooperative process in CD₃CN. In the second study, diffusion NMR studies on 5′‐(3,5‐bis(methoxy)benzoyl)‐2′,3′‐isopropylidene G 4 showed that hierarchical self‐association of G₈‐octamers is controlled by the K⁺ cation. Evidence for formation of both discrete G₈‐octamers and G₁₆‐hexadecamers in CD₂Cl₂ was obtained. The position of this octamer–hexadecamer equilibrium was shown to depend on the K⁺ concentration. In the third case, diffusion NMR was used to determine the size of a guanosine self‐assembly where NMR signal integration was ambiguous. Thus, both diffusion NMR and ESI‐MS show that 5′‐O‐acetyl‐2′,3′‐O‐isopropylidene G 7 and Na⁺ picrate form a doubly charged octamer [G 7 ]₈ ? 2 Na⁺ ? 2 pic^? 9 in CD₂Cl₂. The anion's role in stabilizing this particular complex is discussed. In all three cases the information gained from the diffusion NMR technique enabled us to better understand the self‐assembly processes, especially regarding the roles of cation, anion and solvent.     

Functional Liquid‐Crystalline Assemblies: Self‐Organized Soft Materials

In the 21st century, soft materials will become more important as functional materials because of their dynamic nature. Although soft materials are not as highly durable as hard materials, such as metals, ceramics, and engineering plastics, they can respond well to stimuli and the environment. The introduction of order into soft materials induces new dynamic functions. Liquid crystals are ordered soft materials consisting of self‐organized molecules and can potentially be used as new functional materials for electron, ion, or molecular transporting, sensory, catalytic, optical, and bio‐active materials. For this functionalization, unconventional materials design is required. Herein, we describe new approaches to the functionalization of liquid crystals and show how the design of liquid crystals formed by supramolecular assembly and nano‐segregation leads to the formation of a variety of new self‐organized functional materials.     

Metallopolymer–Peptide Hybrid Materials: Synthesis and Self‐Assembly of Functional,Polyferrocenylsilane–Tetrapeptide Conjugates

Conjugates of poly(ferrocenyldimethylsilane) (PFDMS) with Ac‐(GA)₂‐OH, Ac‐A₄‐OH, Ac‐G₄‐OH and Ac‐V₄‐OH have been prepared by reaction of the tetrapeptide units with the amino‐terminated metallopolymer. The number average degree of polymerisation (DP_n) of the PFDMS was approximately 20 and comparable materials with shorter (DP_n≈10) and/or amorphous chains have been prepared by the same procedure. Poly(ferrocenylethylmethylsilane) (PFEMS) was employed for the latter purpose. All conjugates were characterised by GPC, MALDI‐TOF MS, NMR and IR spectroscopy. With the exception of Ac‐V₄‐PFDMS₂₀, all materials exhibited some anti‐parallel β‐sheet structure in the solid state. The self‐assembly of the conjugates was studied in toluene by DLS. The vast majority of the materials, irrespective of peptide sequence or chain crystallinity, afforded fibres consisting of a peptidic core surrounded by a PFS corona. These fibres were found in the form of cross‐linked networks by TEM and AFM. The accessibility of the chemically reducing PFS corona has been demonstrated by the localised formation of silver nanoparticles on the surface of the fibres.     

含有二十分子水簇的金属—水二维网的构成

以醋酸铜、1,10-邻菲啰啉和顺丁烯二酸在去离子水和乙醇的混合溶液中反应得到了配合物单晶[Cd(phen)2(male)(H2O)]·9.5H2O (1) (phen＝1,10－邻菲啰啉; H2male＝顺丁烯二酸)。采用元素分析、红外光谱和热重分析对化合物进行了表征。用X－射线单晶衍射分析了晶体结构,结果表明：在化合物１中存在着由二十分子水簇构成的结构新颖的一维水链。一维水链和[Cd(phen)2(male)(H2O)]依靠氢键作用构成了独特的包含金属－水网的二维结构。     

An “Ingredients” Approach to Functional Self‐Synthesizing Materials: A Metal‐Ion‐Selective,Multi‐Responsive,Self‐Assembled Hydrogel

New methodology for making novel materials is highly desirable. Here, an “ingredients” approach to functional self‐assembled hydrogels was developed. By designing a building block to contain the right ingredients, a multi‐responsive, self‐assembled hydrogel was obtained through a process of template‐induced self‐synthesis in a dynamic combinatorial library. The system can be switched between gel and solution by light, redox reactions, pH, temperature, mechanical energy and sequestration or addition of Mg^II salt.     

Multicomponent Supramolecular Systems: Self‐Organization in Coordination‐Driven Self‐Assembly

The self‐organization of multicomponent supramolecular systems involving a variety of two‐dimensional (2 D) polygons and three‐dimensional (3 D) cages is presented. Nine self‐organizing systems, SS₁ – SS₉ , have been studied. Each involves the simultaneous mixing of organoplatinum acceptors and pyridyl donors of varying geometry and their selective self‐assembly into three to four specific 2 D (rectangular, triangular, and rhomboid) and/or 3 D (triangular prism and distorted and nondistorted trigonal bipyramidal) supramolecules. The formation of these discrete structures is characterized using NMR spectroscopy and electrospray ionization mass spectrometry (ESI‐MS). In all cases, the self‐organization process is directed by: 1) the geometric information encoded within the molecular subunits and 2) a thermodynamically driven dynamic self‐correction process. The result is the selective self‐assembly of multiple discrete products from a randomly formed complex. The influence of key experimental variables ‐ temperature and solvent ‐ on the self‐correction process and the fidelity of the resulting self‐organization systems is also described.     

Confinement Effect of Organic Nanotubes Toward Green Fluorescent Protein (GFP) Depending on the Inner Diameter Size

Transportation, release behavior, and stability of a green fluorescent protein (GFP, 3×4 nm) in self‐assembled organic nanotubes with three different inner diameters (10, 20, and 80 nm) have been studied in terms of novel nanocontainers. Selective immobilization of a fluorescent acceptor dye on the inner surface enabled us to not only visualize the transportation of GFP in the nanochannels but to also detect release of the encapsulated GFP to the bulk solution in real time, based on fluorescence resonance energy transfer (FRET). Obtained diffusion constants and release rates of GFP markedly decreased as the inner diameter of the nanotubes was decreased. An endo‐sensing procedure also clarified the dependence of the thermal and chemical stabilities of the GFP on the inner diameters. The GFP encapsulated in the 10 nm nanochannel showed strong resistance to heat and to a denaturant. On the other hand, the 20 nm nanochannel accelerated the denaturation of the encapsulated GFP compared with the rate of denaturation of the free GFP in bulk and the encapsulated GFP in the 80 nm nanochannels. The confinement effect based on rational fitting of the inner diameter to the size of GFP allowed us to store it stably and without denaturation under high temperatures and high denaturant concentrations.