Naphthalene Diimide-Tetraazacycloalkane Conjugates Are G-Quadruplex-Based HIV-1 Inhibitors with a Dual Mode of Action

Human immunodeficiency virus 1 (HIV-1) therapeutic regimens consist of three or more drugs targeting different steps of the viral life cycle to limit the emergence of viral resistance. In line with the multitargeting strategy, here we conjugated a naphthalene diimide (NDI) moiety with a tetraazacycloalkane to obtain novel naphthalene diimide (NDI)-tetraazacycloalkane conjugates. The NDI inhibits the HIV-1 promoter activity by binding to LTR G-quadruplexes, and the tetraazacycloalkane mimics AMD3100, which blocks HIV entry into cells by interfering with the CXCR4 coreceptor. We synthesized, purified, and tested the metal-free NDI-tetraazacycloalkane conjugate and the two derived metal-organic complexes (MOCs) that incorporate Cu2+ and Zn2+. The NDI-MOCs showed enhanced binding to LTR G4s as assessed by FRET and CD assays in vitro. They also showed enhanced activity in cells where they dose-dependently reduced LTR promoter activity and inhibited viral entry only of the HIV-1 strain that exploited the CXCR4 coreceptor. The time of addition assay confirmed the dual targeting at the different HIV-1 steps. Our results indicate that the NDI-MOC conjugates can simultaneously inhibit viral entry, by targeting the CXCR4 coreceptor, and LTR promoter activity, by stabilizing the LTR G-quadruplexes. The approach of combining multiple targets in a single compound may streamline treatment regimens and improve the overall patient outcomes.

Acid⋅⋅⋅Amide Supramolecular Synthon for Tuning Amino Acid-Based Hydrogels' Properties

Invited for the cover of this issue is the Laboratory of Supramolecular and Bio-Nanomaterials, coordinated by Pierangelo Metrangolo, at the Politecnico di Milano, Italy. The image depicts the co-crystal formed by N-Fmoc-pentafluorophenylalanine and benzamide, which is also involved in the formation of their mixed hydrogels. Read the full text of the article at 10.1002/chem.202301743.

Acid⋅⋅⋅Amide Supramolecular Synthon for Tuning Amino Acid-Based Hydrogels' Properties

Supramolecular hydrogels formed by the self-assembly of N-Fmoc-l-phenylalanine derivatives are gaining relevance for several applications in the materials and biomedical fields. In the challenging attempt to predict or tune their properties, we selected Fmoc-pentafluorophenylalanine (1) as a model efficient gelator, and studied its self-assembly in the presence of benzamide (2), a non-gelator able to form strong hydrogen bonds with the amino acid carboxylic group. Equimolar mixtures of 1 and 2 in organic solvents afforded a 1 : 1 co-crystal thanks to the formation of an acid⋅⋅⋅amide heterodimeric supramolecular synthon. The same synthon occurred in the transparent gels formed by mixing the two components in 1 : 1 ratio in aqueous media, as revealed by structural, spectroscopic, and thermal characterizations performed on both the co-crystal powder and the lyophilized hydrogel. These findings revealed the possibility of modulating the properties of amino acid-based hydrogels by involving the gelator in the formation of a co-crystal. Such a crystal engineering-based approach is shown also to be useful for the time-delayed release of suitable bioactive molecules, when involved as hydrogel coformers.

Particle profiling of EV-lipoprotein mixtures by AFM nanomechanical imaging

The widely overlapping physicochemical properties of lipoproteins (LPs) and extracellular vesicles (EVs) represents one of the main obstacles for the isolation and characterization of these pervasive biogenic lipid nanoparticles. We herein present the application of an atomic force microscopy (AFM)-based quantitative morphometry assay to the rapid nanomechanical screening of mixed LPs and EVs samples. The method can determine the diameter and the mechanical stiffness of hundreds of individual nanometric objects within few hours. The obtained diameters are in quantitative accord with those measured via cryo-electron microscopy (cryo-EM); the assignment of specific nanomechanical readout to each object enables the simultaneous discrimination of co-isolated EVs and LPs even if they have overlapping size distributions. EVs and all classes of LPs are shown to be characterised by specific combinations of diameter and stiffness, thus making it possible to estimate their relative abundance in EV/LP mixed samples in terms of stoichiometric ratio, surface area and volume. As a side finding, we show how the mechanical behaviour of specific LP classes is correlated to distinctive structural features revealed by cryo-EM. The described approach is label-free, single-step and relatively quick to perform. Importantly, it can be used to analyse samples which prove very challenging to assess with several established techniques due to ensemble-averaging, low sensibility to small particles, or both, thus providing a very useful tool for quickly assessing the purity of EV/LP isolates including plasma- and serum-derived preparations.

Cell Penetrating Peptides: Classification, Mechanisms, Methods of Study, and Applications

Cell-penetrating peptides (CPPs) encompass a class of peptides that possess the remarkable ability to cross cell membranes and deliver various types of cargoes, including drugs, nucleic acids, and proteins, into cells. For this reason, CPPs are largely investigated in drug delivery applications in the context of many diseases, such as cancer, diabetes, and genetic disorders. While sharing this functionality and some common structural features, such as a high content of positively charged amino acids, CPPs represent an extremely diverse group of elements, which can differentiate under many aspects. In this review, we summarize the most common characteristics of CPPs, introduce their main distinctive features, mechanistic aspects that drive their function, and outline the most widely used techniques for their structural and functional studies. We highlight current gaps and future perspectives in this field, which have the potential to significantly impact the future field of drug delivery and therapeutics.

Computation meets experiment: identification of highly efficient fibrillating peptides

Self-assembling peptides are of huge interest for biological, medical and nanotechnological applications. The enormous chemical variety that is available from the 20 amino acids offers potentially unlimited peptide sequences, but it is currently an issue to predict their supramolecular behavior in a reliable and cheap way. Herein we report a computational method to screen and forecast the aqueous self-assembly propensity of amyloidogenic pentapeptides. This method was found also as an interesting tool to predict peptide crystallinity, which may be of interest for the development of peptide based drugs.

Membrane-Sensing Peptides for Extracellular Vesicle Analysis

Analytical platforms for small extracellular vesicle (sEV) high-throughput analysis are highly desirable. These bionanoparticles present fairly distinctive lipid membrane features including high curvature, lipid-packing defects, and a relative abundance in lipids. sEV membrane could be considered as a "universal" marker, complementary or alternative to traditional surface-associated proteins. Here, we describe the use of membrane-sensing peptides as a new, highly efficient ligand to directly integrate sEV capturing and analysis on a microarray platform.

Hybrid Peptide-Agarose Hydrogels for 3D Immunoassays

Recent advances in biosensing analytical platforms have brought relevant outcomes for novel diagnostic and therapy-oriented applications. In this context, 3D droplet microarrays, where hydrogels are used as matrices to stably entrap biomolecules onto analytical surfaces, potentially provide relevant advantages over conventional 2D assays, such as increased loading capacity, lower nonspecific binding, and enhanced signal-to-noise ratio. Here, we describe a hybrid hydrogel composed of a self-assembling peptide and commercial agarose (AG) as a suitable matrix for 3D microarray bioassays. The hybrid hydrogel is printable and self-adhesive and allows analyte diffusion. As a showcase example, we describe its application in a diagnostic immunoassay for the detection of SARS-CoV-2 infection.

Epitope Mapping on Microarrays Highlights a Sequence on the N Protein with Strong Immune Response in SARS-CoV-2 Patients

In SARS-CoV-2 pandemic scenario, the identification of rapid methods to detect antibodies against coronavirus has been a wide and urgent issue. Epitope mapping on peptide microarrays is a rapid way to identify sequences with a high immunoreactivity. The process begins with a proteome-wide screening, based on immune affinity; the use of a high-density microarray is followed by a validation phase, where a restricted panel of probes is tested using peptide microarrays; peptide sequences are immobilized through a click-based strategy.COVID-19-positive sera are tested and immuno-domains regions are identified on SARS-CoV-2 spike (S), nucleocapsid (N) protein, and Orf1ab polyprotein. An epitope on N protein (region 155-171) provided good diagnostic performance in discriminating COVID-19-positive vs. healthy individuals. Using this sequence, 92% sensitivity and 100% specificity are reached for IgG detection in COVID-19 samples, and no cross-reactivity with common cold coronaviruses is detected. Overall, epitope 155-171 from N protein represents a promising candidate for further development and rapid implementation in serological tests.

Emergence of Elastic Properties in a Minimalist Resilin-Derived Heptapeptide upon Bromination

Bromination is herein exploited to promote the emergence of elastic behavior in a short peptide-SDSYGAP-derived from resilin, a rubber-like protein exerting its role in the jumping and flight systems of insects. Elastic and resilient hydrogels are obtained, which also show self-healing behavior, thanks to the promoted non-covalent interactions that limit deformations and contribute to the structural recovery of the peptide-based hydrogel. In particular, halogen bonds may stabilize the β-sheet organization working as non-covalent cross-links between nearby peptide strands. Importantly, the unmodified peptide (i.e., wild type) does not show such properties. Thus, SDSY(3,5-Br)GAP is a novel minimalist peptide elastomer.

Composite Peptide-Agarose Hydrogels for Robust and High-Sensitivity 3D Immunoassays

Canonical immunoassays rely on highly sensitive and specific capturing of circulating biomarkers by interacting biomolecular baits. In this frame, bioprobe immobilization in spatially discrete three-dimensional (3D) spots onto analytical surfaces by hydrogel encapsulation was shown to provide relevant advantages over conventional two-dimensional (2D) platforms. Yet, the broad application of 3D systems is still hampered by hurdles in matching their straightforward fabrication with optimal functional properties. Herein, we report on a composite hydrogel obtained by combining a self-assembling peptide (namely, Q3 peptide) with low-temperature gelling agarose that is proved to have simple and robust application in the fabrication of microdroplet arrays, overcoming hurdles and limitations commonly associated with 3D hydrogel assays. We demonstrate the real-case scenario feasibility of our 3D system in the profiling of Covid-19 patients' serum IgG immunoreactivity, which showed remarkably improved signal-to-noise ratio over canonical assays in the 2D format and exquisite specificity. Overall, the new two-component hydrogel widens the perspectives of hydrogel-based arrays and represents a step forward towards their routine use in analytical practices.

Solid-Phase Synthesis of Gly-Ψ[CH(CF3)NH]-Peptides

The solid-phase synthesis of Gly-Ψ[CH(CF₃)NH]-peptides is presented. In order to achieve this goal, the synthesis of Gly-Ψ[CH(CF₃)NH]-dipeptides having the C-terminus unprotected, the N-terminus protected as Fmoc- or Teoc-, and possibly side chain functionalities protected with acid-labile protecting groups has been developed. A selected small library of six peptidomimetics, encompassing analogues of biological relevant peptides, have been obtained in high purity.

SARS-CoV-2 Epitope Mapping on Microarrays Highlights Strong Immune-Response to N Protein Region

A workflow for rapid SARS-CoV-2 epitope discovery on peptide microarrays is herein reported. The process started with a proteome-wide screening of immunoreactivity based on the use of a high-density microarray followed by a refinement and validation phase on a restricted panel of probes using microarrays with tailored peptide immobilization through a click-based strategy. Progressively larger, independent cohorts of Covid-19 positive sera were tested in the refinement processes, leading to the identification of immunodominant regions on SARS-CoV-2 spike (S), nucleocapsid (N) protein and Orf1ab polyprotein. A summary study testing 50 serum samples highlighted an epitope of the N protein (region 155-71) providing good diagnostic performance in discriminating Covid-19 positive vs. healthy individuals. Using this epitope, 92% sensitivity and 100% specificity were reached for IgG detection in Covid-19 samples, and no cross-reactivity with common cold coronaviruses was detected. Likewise, IgM immunoreactivity in samples collected within the first month after symptoms onset showed discrimination ability. Overall, epitope 155-171 from N protein represents a promising candidate for further development and rapid implementation in serological tests.

Chemical Perturbation of Oncogenic Protein Folding: from the Prediction of Locally Unstable Structures to the Design of Disruptors of Hsp90-Client Interactions

Protein folding quality control in cells requires the activity of a class of proteins known as molecular chaperones. Heat shock protein-90 (Hsp90), a multidomain ATP driven molecular machine, is a prime representative of this family of proteins. Interactions between Hsp90, its co-chaperones, and client proteins have been shown to be important in facilitating the correct folding and activation of clients. Hsp90 levels and functions are elevated in tumor cells. Here, we computationally predict the regions on the native structures of clients c-Abl, c-Src, Cdk4, B-Raf and Glucocorticoid Receptor, that have the highest probability of undergoing local unfolding, despite being ordered in their native structures. Such regions represent potential ideal interaction points with the Hsp90-system. We synthesize mimics spanning these regions and confirm their interaction with partners of the Hsp90 complex (Hsp90, Cdc37 and Aha1) by Nuclear Magnetic Resonance (NMR). Designed mimics selectively disrupt the association of their respective clients with the Hsp90 machinery, leaving unrelated clients unperturbed and causing apoptosis in cancer cells. Overall, selective targeting of Hsp90 protein-protein interactions is achieved without causing indiscriminate degradation of all clients, setting the stage for the development of therapeutics based on specific chaperone:client perturbation.

Organic Cages as Building Blocks for Mechanically Interlocked Molecules: Towards Molecular Machines

The research on systems able to perform controllable motions under external stimuli arises great interest in the scientific community. Over the years, a library of innovative devices has been produced, classified in different categories according to the molecular or supramolecular level of motion. This minireview aims to highlight some representative studies, in which organic cages are used as building blocks for mechanically interlocked molecules, and in which intramolecular motions are triggered by external input. However, the application of organic cages in the construction of molecular machines is hardly achieved. A good compromise must actually be reached, between flexibility and rigidity of the cage's framework for an effective control of the intra- and/or intermolecular motion in the final mechanical device. Our final goal is to stimulate researchers' curiosity towards cage-like molecules, so that they take on the challenge of converting a cage into a molecular machine.

Membrane-binding peptides for extracellular vesicles on-chip analysis

Small extracellular vesicles (sEVs) present fairly distinctive lipid membrane features in the extracellular environment. These include high curvature, lipid-packing defects and a relative abundance in lipids such as phosphatidylserine and ceramide. sEV membrane could be then considered as a "universal" marker, alternative or complementary to traditional, characteristic, surface-associated proteins. Here, we introduce the use of membrane-sensing peptides as new, highly efficient ligands to directly integrate sEV capturing and analysis on a microarray platform. Samples were analysed by label-free, single-particle counting and sizing, and by fluorescence co-localisation immune staining with fluorescent anti-CD9/anti-CD63/anti-CD81 antibodies. Peptides performed as selective yet general sEV baits and showed a binding capacity higher than anti-tetraspanins antibodies. Insights into surface chemistry for optimal peptide performances are also discussed, as capturing efficiency is strictly bound to probes surface orientation effects. We anticipate that this new class of ligands, also due to the versatility and limited costs of synthetic peptides, may greatly enrich the molecular toolbox for EV analysis.

Towards Building Blocks for Supramolecular Architectures Based on Azacryptates

In this work, we report the synthesis of a new bis(tris(2-aminoethyl)amine) azacryptand L with triphenyl spacers. The binding properties of its dicopper complex for aromatic dicarboxylate anions (as TBA salts) were investigated, with the aim to obtain potential building blocks for supramolecular structures like rotaxanes and pseudo-rotaxanes. As expected, UV-Vis and emission studies of [Cu₂L]⁴⁺ in water/acetonitrile mixture (pH = 7) showed a high affinity for biphenyl-4,4′-dicarboxylate (dfc²⁻), with a binding constant of 5.46 log units, due to the best match of the anion bite with the Cu(II)-Cu(II) distance in the cage’s cavity. Compared to other similar bistren cages, the difference of the affinity of [Cu₂L]⁴⁺ for the tested anions was not so pronounced: conformational changes of L seem to promote a good interaction with both long (e.g., dfc²⁻) and short anions (e.g., terephthalate). The good affinity of [Cu₂L]⁴⁺ for these dicarboxylates, together with hydrophobic interactions within the cage’s cavity, may promote the self-assembly of a stable 1:1 complex in water mixture. These results represent a good starting point for the application of these molecular systems as building units for the design of new supramolecular architectures based on non-covalent interactions, which could be of interest in all fields related to supramolecular devices.

A stapled chromogranin A-derived peptide is a potent dual ligand for integrins αvβ6 and αvβ8

Combining 2D STD-NMR, computation, biochemical assays and click-chemistry, we have identified a chromogranin-A derived compound (5) that has high affinity and bi-selectivity for αvβ6 and αvβ8 integrins and is stable in microsomal preparations. 5 is suitable for nanoparticle functionalization and delivery to cancer cells, holding promise for diagnostic and/or therapeutic applications.

Clickable cellulosic surfaces for peptide-based bioassays

The use of peptides in paper-based analytics is a highly appealing field, yet it suffers from severe limitations. This is mostly due to the loss of effective target recognition properties of this relatively small probes upon nonspecific adsorption onto cellulose substrates. Here we address this issue by introducing a simple polymer-based strategy to obtain clickable cellulose surfaces, that we exploited for the chemoselective bioconjugation of peptide bioprobes. Our method largely outperformed standard adsorption-based immobilization strategy in a challenging, real case immunoassay, namely the diagnostic discrimination of Zika + individuals from healthy controls. Of note, the clickable polymeric coating not only allows efficient peptides bioconjugation, but it provides favorable anti-fouling properties to the cellulosic support. We envisage our strategy to broaden the repertoire of cellulosic materials manipulation and promote a renewed interest in peptide-based paper bioassays.

A self-assembling peptide hydrogel for ultrarapid 3D bioassays

Biosensing analytical platforms rely on the intimate structure-function relationship of immobilized probes. In this context, hydrogels are appealing semi-wet systems to locally confine biomolecules while preserving their structural integrity and function. Yet, limitations imposed by biomolecule diffusion rates or fabrication difficulties still hamper their broad application. Here, using a self-assembling peptide, a printable and self-adhesive hydrogel was obtained and applied to fabricate arrays of localized bio-functional 3D microenvironments on analytical interfaces. This soft matrix represents a robust and versatile material, allowing fast and selective tuning of analyte diffusion, which is exploited here to run in-gel immunoassays under solution-like conditions in an unprecedented (<10 min) time frame. The developed material overcomes major limitations associated with hydrogels for bioassays, widening the prospects for easy fabrication of multifunctional bio-interfaces for high-throughput, molecular recognition assays.

A Catalytic and Selective Scissoring Molecular Tool for Quadruplex Nucleic Acids

A copper complex embedded in the structure of a water-soluble naphthalene diimide has been designed to bind and cleave G-quadruplex DNA. We describe the properties of this ligand, including its catalytic activity in the generation of ROS. FRET melting, CD, NMR, gel sequencing, and mass spectrometry experiments highlight a unique and unexpected selectivity in cleaving G-quadruplex sequences. This selectivity relies both on the binding affinity and structural features of the targeted G-quadruplexes.

A halogen bond-donor amino acid for organocatalysis in water

Herein we report a halogen bond-donor amino acid, 4-iodotetrafluorophenylalanine, which behaves as a catalyst for the aqueous synthesis of bis-(heterocyclic)methanes. We also provide experimental evidence that halogen bonding is a plausible explanation for the observed catalytic effect.

Enhancing Antibody Serodiagnosis Using a Controlled Peptide Coimmobilization Strategy

Antigen immunoreactivity is often determined by surface regions defined by the 3D juxtapositions of amino acids stretches that are not continuous in the linear sequence. As such, mimicking an antigen immunoreactivity by means of putative linear peptide epitopes for diagnostic purposes is not trivial. Here we present a straightforward and robust method to extend the reach of immune-diagnostic probes design by copresenting peptides belonging to the same antigenic surface. In this case study focused on a computationally predicted Zika virus NS1 protein putative antigenic region, we reached a diagnostic confidence by the oriented and spatially controlled coimmobilization of peptide sequences found adjacent within the protein fold, that cooperatively interacted to provide enhanced immunoreactivity with respect to single linear epitopes. Through our method, we were able to differentiate Zika infected individuals from healthy controls. Remarkably, our strategy fits well with the requirements to build high-throughput screening platforms of linear and mixed peptide libraries, and it could possibly facilitate the rapid identification of conformational immunoreactive regions.

Kaposi's Sarcoma Complicating Immunosuppressive Therapy for Angioimmunoblastic Lymphadenopathy with Dysproteinemia

Cutaneous and visceral dissemination of Kaposi's sarcoma (KS) occurred in a patient with angioimmunoblastic lymphadenopathy with dysproteinemia (AILD) who had been treated with combination chemotherapy. Three other cases of KS complicating immunosuppressive therapy of AILD have been reported in the literature, and there is evidence to indicate that AILD displays features which are known to predispose to KS. Like in other subjects with profound immunodeficiency (e.g. in young homosexual men), in our patient KS pursued an unusually aggressive course, with involvement of lymph nodes and internal organs as well as the skin. It is concluded that the risk of developing severe KS is a further reason to avoid aggressive combination chemotherapy in patients with AILD, particularly in those of Jewish or Mediterranean ancestry. Even the use of corticosteroids should be reduced to a minimum to avoid immunosuppression, and a conservative approach to treatment seems advisable.

Immunological Reactivity of Serum Ferritin in Patients with Malignancy

Serum ferritin has been suggested as a tumor marker in the diagnosis of certain malignancies and for following the activity or dissemination of the malignant process. Since neoplastic tissues generally contain more acidic isoferritins than their normal tissue counterparts, it has also been suggested that the specific assay of such isoferritins in serum may be of particular value in the diagnosis of malignancy. In this work, we have evaluated ferritin concentration in the serum of normal subjects and patients with acute nonlymphocytic leukemia, Hodgkin's disease, breast cancer and lung cancer by simultaneously using three different immunoassays: an immunoradiometric assay based on polyclonal antibodies against human liver (basic, L-subunit rich) ferritin, a radioimmunoassay based on polyclonad antibodies against HeLa cell (acidic, H-subunit rich) ferritin, and an immunoradiometric assay based on the monoclonal antibody 2A4 raised against human heart (acidic, H-subunit rich) ferritin. Most of the patients studied had increased values for liver-type ferritin in the absence of increased iron stores. Binding of serum ferritin to concanavalin A did not prove to be useful in distinguishing a tumor-specific basic isoferritin. The HeLa ferritin assay was found to be less specific than the heart ferritin assay in the detection of acidic isoferritins, and did not provide any advantage over the liver assay in detecting the increased levels of serum ferritin associated with malignant disease. Heart-type ferritin was found in one-fifth of normal sera and 64% of sera from patients with malignancy. Values were very low compared with those for basic ferritin, ranging from less than 0.1 to 17% of total serum ferritin (geometric mean value 1.3%) in patients with malignancy. These findings indicate that at present there is little application for serum ferritin immunoassays based on antibodies to HeLa cell or heart ferritin in the diagnosis or monitoring of malignant disease. This seems to be due to the presence in human serum of biding factors which are responsible for the rapid clearance of acidic isoferritins from the circulation. The serum concentration of basic ferritin, however, can be useful in the diagnosis and management of some malignancies, and it is possible that studies on cell isoferritins can be important in biologic monitoring of neoplastic disorders. It should also be noted that the increased levels of serum ferritin found in patients with malignancy can exert adverse effects on the host immune response and perhaps an inhibitory effect on hematopoiesis.

G-quadruplex fluorescence sensing by core-extended naphthalene diimides

BACKGROUND

Fluorescent sensing of G-quadruplex nucleic acids (G4s) is an effective strategy to elucidate their role in vitro and in vivo. Small molecule ligands have often been exploited, producing an emission light up upon binding. Naphthalene diimides (NDIs), although potent G4 binders exhibiting red-NIR fluorophores, have only been marginally exploited, as they are usually quenched upon binding. Contrary, aggregating core-extended naphthalene diimides (c_ex-NDIs) proved to be effective probes.

METHODS

We prepared a library of eighteen c_ex-NDIs by organic synthesis, characterising their aggregation-dependent absorption and emission properties. Absorption and emission titrations, fluorescent intercalator displacement assay (FID) and circular dichroism (CD) analysis were performed to elucidate their behavior as G4 fluorescent sensors, selectivity and binding mode.

RESULTS

c_ex-NDIs aggregate under aqueous solvents and as a result, their fluorescence is mostly quenched under physiological conditions. Upon G4 binding, they disaggregate into binding monomers, producing a fluorescent light-up with anti-parallel and hybrid G4s. Contrary, with parallel G4s a light-off was recorded. For the formers a groove-like interaction was inferred by ICD signals, while for the latter an end-stacking interaction mode was hypothesized by G4-FID data.

CONCLUSIONS

c_ex-NDIs G4 sensing mechanism works via a induced disaggregation. The emission response depends on the G4 topology, which dictates the prevailing -groove or end-stacking- binding mode.

GENERAL SIGNIFICANCE

This study highlights the potential of c_ex-NDIs as G4 fluorescent probes. Besides being readily synthesized and conveniently emitting above 600nm, they light-up upon binding to anti-parallel and hybrid G4, complementing a number of other probes' selectivity for the parallel topology. This article is part of a Special Issue entitled "G-quadruplex" Guest Editor: Dr. Concetta Giancola and Dr. Daniela Montesarchio.

The interaction of Mozobil™ with carboxylates

Mozobil(™) (1,1'-[1,4-phenylenebis(methylene)]bis[1,4,8,11-tetraazacyclotetradecane], 1, also known as JM3100 and AMD 3100) is a specific antagonist of the chemokine coreceptor CXCR4 and favours the mobilisation from the bone marrow of stem cells, which can be used for autologous transplantation. It is believed that the interaction, of both hydrogen bonding and electrostatic nature, involves a partly protonated form of Mozobil(™), LHn(n+) and the COO(-) groups of Asp(171) and Asp(262) residues protruding from the walls of the pocket of the membrane protein CXCR4. We have investigated, through potentiometric titrations in 0.1 M NaNO3 at 25 °C, the interaction equilibria between 1 (L) and linear dicarboxylates A(2-). These studies have demonstrated that the main equilibrium takes place: LH5(5+) + A(2-)⇄ [LH5···A](3+), and that the most stable [LH5···A](3+) complex forms for A(2-) = diphenyl-4,4'-dicarboxylate, whose length matches that of LH5(5+). (1)H NMR titration experiments have shown that in the 7-10 pH interval, LH3(3+), LH2(2+) and LH(+) forms establish π-π interactions with diphenyl-4,4'-dicarboxylate, according to a topological arrangement which excludes the formation of H-bonds. It is finally suggested that, in the pocket of the CXCR4 membrane protein, Mozobil(™) operates as a pentammonium cation, which establishes with carboxylate groups of Asp(171) and Asp(262) strong interactions of hydrogen bonding and electrostatic nature.

Novel hydrogen- and halogen-bonding anion receptors based on 3-iodopyridinium units

Iodopyridinium-based tripodal receptors strongly bind anionic species in their bowl-shaped cavity through the synergistic effect of hydrogen- and halogen-bonding interactions.

Chloride-binding in organic–water mixtures: the powerful synergy of C–H donor groups within a bowl-shaped cavity

2,3,4,5-Tetrafluorobenzyl and imidazolium groups within an open-chain receptor allow for the effective binding of chloride in organic–water solution.

A bistren cryptand with a remote thioether function: Cu(ii) complexation in solution and on the surface of gold nanostars

A di-copper(ii) complex is formed in a bis-tren cage featuring a thioether function, capable of grafting on a monolayer of gold nanostars.

Bistren cryptands and cryptates: versatile receptors for anion inclusion and recognition in water

Bistren cryptands can be easily synthesised through the Schiff base condensation of two molecules of tren and three molecules of a dialdehyde, followed by hydrogenation of the six C=N double bonds to give octamine cages, whose ellipsoidal cavity can be varied at will, by choosing the appropriate dialdehyde, in order to include substrates of varying sizes and shapes. Bistrens can operate as effective anion receptors in two ways: (i) in their protonated form, providing six secondary ammonium groups capable of establishing hydrogen bonding interactions with the anion; (ii) as dicopper(II) cryptates, in which the two coordinatively unsaturated metal centres can be bridged by an ambidentate anion. Representative examples of the two approaches, as well as the design of an anion molecular dispenser, in which a dicopper(II) bistren cryptate acts as a bottle will be illustrated.

Fluorescent sensing of 99Tc pertechnetate in water

The fluorescent cage senses pertechnetate in water at μM concentration, opening perspectives to detect the pollutant without radioanalytical instrumentation.

Mixing the spacers in azacryptands: effects on halide recognition

Replacement of just one spacer in dicopper cryptates drastically alters the cavity's shape, thus affecting halide recognition.