Experimental Correlation between Apparent p and Gelation Propensity in Amphiphilic Hydrogelators Derived from l-Dopa.

We report the gelation propensity of three gelators derived from l-dihydroxyphenylalanine (l-Dopa), where the amino group is derivatized with three different fatty acids (lauric acid, palmitic acid, and azelaic acid). The long aliphatic side chains should introduce additional van der Waals interactions among the molecules, contributing to the self-assembly process. The hydrogels have been prepared with the pH change method, and both the hydrogels and the corresponding aerogels have been analyzed using several techniques.

Smartphone-Based Chemiluminescence Glucose Biosensor Employing a Peroxidase-Mimicking, Guanosine-Based Self-Assembled Hydrogel.

Chemiluminescence is widely used for hydrogen peroxide detection, mainly exploiting the highly sensitive peroxidase-luminol-HO system. Hydrogen peroxide plays an important role in several physiological and pathological processes and is produced by oxidases, thus providing a straightforward way to quantify these enzymes and their substrates. Recently, biomolecular self-assembled materials obtained by guanosine and its derivatives and displaying peroxidase enzyme-like catalytic activity have received great interest for hydrogen peroxide biosensing.

Taurine Stabilizing Effect on Lysozyme.

Taurine is an important organic osmolyte in mammalian cells, and it weakens inflammation and oxidative stress mediated injuries in some diseases. Recently, taurine has been demonstrated to play a therapeutic role against neurodegenerative disorders, although its parallel involvement in several biochemical mechanisms makes not clear taurine specific role in these diseases. Furthermore, the stabilizing effect of this molecule in terms of protein stability is known, but not deeply investigated.

Self-Assembly of Functionalized Lipophilic Guanosines into Cation-Free Stacked Guanine-Quartets.

The hierarchical self-assembly of various lipophilic guanosines exposing either a phenyl or a ferrocenyl group in the C(8) position was investigated. In a solution, all the derivatives were found to self-assemble primarily into isolated guanine (G)-quartets. In spite of the apparent similar bulkiness of the two substituents, most of the derivatives form disordered structures in the solid state, whereas a specific 8-phenyl derivative self-assembles into an unprecedented, cation-free stacked G-quartet architecture.

Reversible Photoisomerization in Thin Surface Films from Azo-Functionalized Guanosine Derivatives.

Two novel azo-functionalized guanosine derivatives were synthesized, and their photoisomerization process was investigated in molecular monolayers at the air-water interface and in the Langmuir-Blodgett (LB) films on solid substrates. Measurements of surface pressure vs area isotherms, surface potential measurements, UV-visible (vis) absorption spectroscopy, Brewster angle microscopy (BAM), and atomic force microscopy (AFM) were performed. Despite not having a typical amphiphilic molecular structure, the derivatives formed stable films on the water surface.

Trehalose Effect on the Aggregation of Model Proteins into Amyloid Fibrils.

Protein aggregation into amyloid fibrils is a phenomenon that attracts attention from a wide and composite part of the scientific community. Indeed, the presence of mature fibrils is associated with several neurodegenerative diseases, and in addition these supramolecular aggregates are considered promising self-assembling nanomaterials. In this framework, investigation on the effect of cosolutes on protein propensity to aggregate into fibrils is receiving growing interest, and new insights on this aspect might represent valuable steps towards comprehension of highly complex biological processes.

Metallo-responsive self-assembly of lipophilic guanines in hydrocarbon solvents: a systematic SAXS structural characterization.

Lipophilic guanines (LipoGs) in aprotic solvents undergo different self-assembly processes based on different H-bonded motifs. Cylindrical nanotubes made by π-π stacked guanine tetramers (G-quadruplexes) and flat, tape-like aggregates (G-ribbons) have been observed depending on the presence of alkali metal ions. To obtain information on the structural properties and stability of these LipoG aggregates, Small-Angle X-ray Scattering (SAXS) experiments have been performed in dodecane, both in the presence and in the absence of potassium ions.

Playing supramolecular dominoes with light: building and breaking a photoreversible G-quadruplex made from guanosine, boric acid and an azobenzene.

Addition of azobenzene-derivative 1 in its E configuration to an aqueous solution containing various guanosine borate esters induces a helical G-quartet based self-organization, stabilized by intercalation of the dye. The process is driven, in a domino fashion, by the initial host-guest interaction between the dye and a specific guanosine borate diester, whose structure can be thus assigned. This inclusion complex templates the formation of G-quartets.

Halloysite nanotubes for efficient loading, stabilization and controlled release of insulin.

Hypothesis: Oral insulin administration is not actually effective due to insulin rapid degradation, inactivation and digestion by proteolytic enzymes which results in low bioavailability. Moreover insulin is poorly permeable and lack of lipophilicity. These limits can be overcome by the loading of protein in some nanostructured carrier such as halloysite nanotubes (HNTs).

A lipophilic "fully-anti" dodecamer from a (5'S)-5',8-cyclo-2'-deoxyguanosine.

The self-assembly of a lipophilic derivative of (5'S)-5',8-cyclo-2'-deoxyguanosine, a mutagenic product formed by hydroxyl radical attack against DNA, has been investigated. This derivative forms, with high fidelity, a dodecameric complex composed of three stacked G-quartets in the presence of strontium picrate. This is the first example of a fully-anti lipophilic G-quadruplex.

In-peptide synthesis of di-oxazolidinone and dehydroamino acid-oxazolidinone motifs as β-turn inducers.

Small and easy-to-do mimetics of β-turns are of great interest to interfere with protein-protein recognition events mediated by β-turn recognition motifs. We propose a straightforward procedure for constraining the conformation of tetrapeptides lacking a pre-formed scaffold. According to the stereochemistry array, N-Ts tetrapeptides including Thr or PhSer (phenylserine) at the positions 2 or 3 gave rise in a single step to the sequences Oxd(2)-Oxd(3) or ΔAbu(2)-Oxd(3) (Oxd, oxazolidin-2-one; ΔAbu, 2,3-dehydro-2-aminobutyric).

Control of the helical chirality of enantiopure sulfinyl (Z)-azobenzene-based photoswitches.

A new class of enantiopure ortho,ortho-disubstituted azobenzene photoswitches has been synthesized from (S)-2-(p-tolylsulfinyl)benzoquinone and arylhydrazines. The sulfoxide acts as a unidirectional controller of the helical chirality that arises in the Z isomer after photoisomerization. Highly congested E-azobenzenes 5 c showed two atropisomeric diastereoconformers in the solid state that converged upon irradiation into a unique Z isomer with defined helicity (M), as evident in the X-ray structure.

1,2-Di(phenylethynyl)ethenes with axially chiral, 2,2'-bridged 1,1'-binaphthyl substituents: potent cholesteric liquid-crystal inducers.

Axially chiral, 3,5-dihydro-4H-dinaphtho[2,1-c:1',2'-e]azepine (dinaphthazepine) and 1,1'-binaphthyl-2,2'-disulfonimide (dinaphthosulfonimide) moieties were rigidly connected via N-p-phenylene linkers to photochemically (E)/(Z)-isomerisable 1,2-diethynylethene scaffolds. The chemical stability of the resulting systems was found to be critically related to the other substituents on the central π-conjugated scaffold. High helical twisting power (HTP), up to 315 μm(-1), for the induction of a cholesteric liquid-crystalline phase through doping of a nematic phase was measured, resulting from the introduction of the chiral, mesogenic 1,1'-binaphthyl motifs.

The interplay of configuration and conformation in helical perylenequinones: Insights from chirality induction in liquid crystals and calculations.

The chirality transfer in liquid crystals induced by two helical perylenequinones (namely, the natural compounds cercosporin and phleichrome) was investigated by integrating measurements of helical twisting power with a conformational analysis by DFT calculations and with the prediction of their twisting ability by the surface-chirality method. The two quasi-enantiomeric derivatives induce oppositely handed cholesteric phases when introduced as dopants in nematic solvents. We evaluated the role of the different conformations of the chiral hydroxyalkyl side chains in determining the helical twisting power: They were found to affect the strength of the chirality transfer, although the handedness of the induced cholesteric phase is essentially determined by the axial chirality (helicity) of the core of the perylenequinones.

Central-to-axial chirality transfer revealed by liquid crystals: a combined experimental and computational approach for the determination of absolute configuration of carboxylic acids with an α chirality centre.

The conversion into 6,7-dihydro-5H-dibenz[c,e]azepine (DAZ) N-protected amides is a viable route for the determination of the absolute configuration of chiral 2-substituted carboxylic acids. The biphenyl moiety of DAZ, besides being a probe of chirality for the electronic circular dichroism (ECD) spectroscopy, makes these systems suitable for configuration assignment by exploiting the chirality amplification which occurs in nematic liquid crystals. To assess the reliability of the liquid crystal method in detecting the absolute stereochemistry of chiral amides bound to a biphenyl group, we measured the helical twisting power of a series of DAZ-N-protected amides and compared these data with the results obtained from ECD measurements.

Identifying guanosine self assembly at natural isotopic abundance by high-resolution 1H and 13C solid-state NMR spectroscopy.

By means of the (1)H chemical shifts and the proton-proton proximities as identified in (1)H double-quantum (DQ) combined rotation and multiple-pulse spectroscopy (CRAMPS) solid-state NMR correlation spectra, ribbon-like and quartet-like self-assembly can be identified for guanosine derivatives without isotopic labeling for which it was not possible to obtain single crystals suitable for diffraction. Specifically, characteristic spectral fingerprints are observed for dG(C10)(2) and dG(C3)(2) derivatives, for which quartet-like and ribbon-like self-assembly has been unambiguously identified by (15)N refocused INADEQUATE spectra in a previous study of (15)N-labeled derivatives (Pham, T. N.

Chirality transfer across length-scales in nematic liquid crystals: fundamentals and applications.

When a chiral dopant is dissolved in an achiral liquid crystal medium, the whole sample organizes into a helical structure with a characteristic length-scale of the order of microns. The relation between chirality at these quite different length-scales can be rationalized by a relatively simple model, which retains the relevant factors coming into play: the molecular shape of the chiral dopant, which controls the chirality of short range intermolecular interactions, and the elastic properties of the nematic environment, which control the restoring torques opposing distortion of the director. In this tutorial review the relation between molecular and phase chirality will be reviewed and several applications of the chiral doping of nematic LCs will be discussed.

Nanopatterning the surface with ordered supramolecular architectures of N(9)-alkylated guanines: STM reveals.

STM study of the self-assembly at the solid-liquid interface of substituted guanines exposing in the N(9)-position alkyl side chains with different lengths revealed the formation of distinct crystalline nanopatterns.

A non-empirical chromophoric interpretation of CD spectra of DNA G-quadruplex structures.

G-quadruplex DNA (G4-DNA) structures are four-stranded helical DNA (or RNA) structures, comprising stacks of G-tetrads, which are the outcome of planar association of four guanines in a cyclic Hoogsteen hydrogen-bonding arrangement. In the last decade the number of publications where CD spectroscopy has been used to study G4-DNAs, is extremely high. However, with very few exceptions, these investigations use an empirical interpretation of CD spectra.

Solvent-induced switching between two supramolecular assemblies of a guanosine-terthiophene conjugate.

We report here our findings on a lipophilic guanosine derivative armed with a terthiophene unit that undergoes a pronounced variation of its supramolecular organisation by changing the polarity of the solvent. In chloroform the guanosine derivative, templated by alkali metal ions, assembles via H-bonding in G-quartet based D(4)-symmetric octamers; the polar guanine bases are located into the inner part of the assembly and act as a scaffold for the terthienyl pendants. On the other hand, in the more polar (and H-bond competing) acetonitrile, different aggregates are observed in which the terthiophene chains are pi-pi stacked in a helicoidal (left-handed) arrangement in the central core, and the guanine bases (free from hydrogen bonding) are located at the periphery and exposed to the solvent.

Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives.

The addition of a chiral non-racemic dopant to a nematic liquid crystal (LC) has the effect of transferring the molecular chirality to the phase organization and a chiral nematic phase is formed. This molecular chirality amplification in the LC provides a unique possibility for investigating the relationship between molecular structure, intermolecular interactions, and mesoscale organization. It is known that axially chiral or helical-shaped molecules with reduced conformational disorder are good candidates for high helical twisting power derivatives.

N-arylated 3,5-dihydro-4H-dinaphtho[2,1-c:1',2'-e]azepines: axially chiral donors with high helical twisting powers for nonplanar push-pull chromophores.

Axially chiral, N-arylated 3,5-dihydro-4H-dinaphtho[2,1-c:1',2'-e]azepines have been prepared by short synthetic protocols from enantiopure 1,1'-bi(2,2'-naphthol) (BINOL) and anilines. Alkynes substituted with two N-phenyldinaphthazepine donors readily undergo a formal [2+2] cycloaddition, followed by retro-electrocyclization, with tetracyanoethene (TCNE) to yield donor-substituted 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs) featuring intense intramolecular charge-transfer (CT) interactions. A dicyanovinyl derivative substituted with one N-phenyldinaphthazepine donor was obtained by a "one-pot" oxidation/Knoevenagel condensation from the corresponding propargylic alcohol.

Self-assembled hexadecanitroxide.

A radical-armed guanosine derivative shows drastic magnetic changes by addition (removal) of alkali metal cations corresponding to the reversible assembly (disassembly). In the presence of templating metal ions, the assembly is formed by 8 molecules and 16 open-shell moieties confined in a sphere with a diameter of ca. 30 A.

Guanosine hydrogen-bonded scaffolds: a new way to control the bottom-up realisation of well-defined nanoarchitectures.

Over the last two decades, guanosine-related molecules have been of interest in different areas, ranging from structural biology to medicinal chemistry, supramolecular chemistry and nanotechnology. The guanine base is a multiple hydrogen-bonding unit, capable also of binding to cations, and fits very well with contemporary studies in supramolecular chemistry, self-assembly and non-covalent synthesis. This Concepts article, after reviewing on the diversification of self-organised assemblies from guanosine-based low-molecular-weight molecules, will mainly focus on the use of guanine moiety as a potential scaffold for designing functional materials of tailored physical properties.