Stimuli-responsive polyguanidino-oxanorbornene membrane transporters as multicomponent sensors in complex matrices

Anion-Controlled Synthesis of Novel Guanidine-Substituted Oxanorbornanes

The cycloaddition of simple alkyl-substituted guanidine derivatives is an interesting approach toward polycyclic superbases and guanidine-based organocatalysts. Due to the high nucleophilicity of guanidines, an aza-Michael reaction with dienophiles is more common and presents a huge obstacle in achieving the desired synthetic goal. Our preliminary investigations indicated that the proton could act as a suitable protecting group to regulate the directionality of the reaction. To investigate the role of the protonation state and type of anion, the reactivity of furfuryl guanidines with dimethyl acetylenedicarboxylate was explored. Furfuryl guanidines showed a strong reaction dependence on the nucleophilicity of the counterion and the structure of guanidine. While the reaction of DMAD with the guanidinium halides provided products of an aza-Michael addition, Diels-Alder cycloaddition occurred if non-nucleophilic hexafluorophosphate salts were used. Depending on the structure and the reaction conditions, oxanorbornadiene products underwent subsequent intramolecular cyclization. A tendency toward intramolecular cyclization was interpreted in terms of the pK_a of different positions of the guanidine functionality in oxanorbornadienes. New polycyclic guanidines had a slightly decreased pK_a in acetonitrile and well-defined geometry suitable for the buildup of selective sensors.

Enzyme assays with supramolecular chemosensors - the label-free approach

Enzyme activity measurements are essential for many research areas, e.g., for the identification of inhibitors in drug discovery, in bioengineering of enzyme mutants for biotechnological applications, or in bioanalytical chemistry as parts of biosensors. In particular in high-throughput screening (HTS), sensitive optical detection is most preferred and numerous absorption and fluorescence spectroscopy-based enzyme assays have been developed, which most frequently require time-consuming fluorescent labelling that may interfere with biological recognition. The use of supramolecular chemosensors, which can specifically signal analytes with fluorescence-based read-out methods, affords an attractive and label-free alternative to more established enzyme assays. We provide herein a comprehensive review that summarizes the current state-of-the-art of supramolecular enzyme assays ranging from early examples with covalent chemosensors to the most recent applications of supramolecular tandem enzyme assays, which utilize common and often commercially available combinations of macrocyclic host molecules (e.g. cyclodextrins, calixarenes, and cucurbiturils) and fluorescent dyes as self-assembled reporter pairs for assaying enzyme activity.

A mixed chirality α-helix in a stapled bicyclic and a linear antimicrobial peptide revealed by X-ray crystallography

The peptide α-helix is right-handed when containing amino acids with l-chirality, and left-handed with d-chirality, however mixed chirality peptides generally do not form α-helices unless a helix inducer such as the non-natural residue amino-isobutyric acid is used. Herein we report the first X-ray crystal structures of mixed chirality α-helices in short peptides comprising only natural residues as the example of a stapled bicyclic and a linear membrane disruptive amphiphilic antimicrobial peptide (AMP) containing seven l- and four d-residues, as complexes of fucosylated analogs with the bacterial lectin LecB. The mixed chirality α-helices are superimposable onto the homochiral α-helices and form under similar conditions as shown by CD spectra and MD simulations but non-hemolytic and resistant to proteolysis. The observation of a mixed chirality α-helix with only natural residues in the protein environment of LecB suggests a vast unexplored territory of α-helical mixed chirality sequences and their possible use for optimizing bioactive α-helical peptides.

We report the first X-ray crystal structures of mixed chirality α-helices comprising only natural residues as the example of bicyclic and linear membrane disruptive amphiphilic antimicrobial peptides containing seven l- and four d-residues.

Bio-adhesive Nanoporous Module: Toward Autonomous Gating

Here we report a bio-adhesive porous organic module (^Glue COF) composed of hexagonally packed 1D nanopores based on a covalent organic framework. The nanopores are densely decorated with guanidinium ion (Gu⁺ ) pendants capable of forming salt bridges with oxyanionic species. ^Glue COF strongly adheres to biopolymers through multivalent salt-bridging interactions with their ubiquitous oxyanionic species. By taking advantage of its strong bio-adhesive nature, we succeeded in creating a gate that possibly opens the nanopores through a selective interaction with a reporter chemical and releases guest molecules. We chose calmodulin (CaM) as a gating component that can stably entrap a loaded guest, sulforhodamine B (SRB), within the nanopores (^CaM COF⊃SRB). CaM is known to change its conformation on binding with Ca²⁺ ions. We confirmed that mixing ^CaM COF⊃SRB with Ca²⁺ resulted in the release of SRB from the nanopores, whereas the use of weakly binding Mg²⁺ ions resulted in a much slower release of SRB.

Stereorandomization as a Method to Probe Peptide Bioactivity

Solid-phase peptide synthesis (SPPS) is usually performed with optically pure building blocks to prepare peptides as single enantiomers. Herein we report that SPPS using racemic amino acids provides stereorandomized (sr) peptides, containing up to billions of different stereoisomers, as well-defined single HPLC peaks, single mass products with high yield, which can be used to investigate peptide bioactivity. To exemplify our method, we show that stereorandomization abolishes the membrane-disruptive effect of α-helical amphiphilic antimicrobial peptides but preserves their antibiofilm effect, implying different mechanisms involving folded versus disordered conformations. For antimicrobial peptide dendrimers by contrast, stereorandomization preserves antibacterial, membrane-disruptive, and antibiofilm effects but reduces hemolysis and cytotoxicity, thereby increasing their therapeutic index. Finally, we identify partially stereorandomized analogues of the last resort cyclic peptide antibiotic polymyxin B with preserved antibacterial activity but lacking membrane-disruptive and lipopolysaccharide-neutralizing activity, pointing to the existence of additional targets.

Stimuli-Responsive Cycloaurated "OFF-ON" Switchable Anion Transporters

Anion transporters have shown potential application as anti-cancer agents that function by disrupting homeostasis and triggering cell death. In this research article we report switchable anion transport by gold complexes of anion transporters that are "switched on" in situ in the presence of the reducing agent GSH by decomplexation of gold. GSH is found in higher concentrations in tumors than in healthy tissue and hence this approach offers a strategy to target these systems to tumors.

Supramolecular Chemistry in the Biomembrane

The combination of supramolecular functional systems with biomolecular chemistry has been a fruitful exercise for decades, leading to a greater understanding of biomolecules and to a great variety of applications, for example, in drug delivery and sensing. Within these developments, the phospholipid bilayer membrane, surrounding live cells, with all its functions has also intrigued supramolecular chemists. Herein, recent efforts from the supramolecular chemistry community to mimic natural functions of lipid membranes, such as sensing, molecular recognition, membrane fusion, signal transduction, and gated transport, are reviewed.

Fluorescence Imaging of Bacterial Killing by Antimicrobial Peptide Dendrimer G3KL

We recently discovered that peptide dendrimers such as G3KL ((KL)₈(KKL)₄(KKL)₂KKL, K = branching l-lysine) exert strong activity against Gram-negative bacteria including Pseudomonas aeruginosa, Acinetobacter baumannii, and Escherichia coli. Herein, we report a detailed mechanistic study using fluorescence labeled analogs bearing fluorescein (G3KL-Fluo) or dansyl (G3KL-Dansyl), which show a similar bioactivity profile as G3KL. Imaging bacterial killing by super-resolution stimulated emission depletion (STED) microscopy, time-lapse imaging, and transmission electron microscopy (TEM) reveals that the dendrimer localizes at the bacterial membrane, induces membrane depolarization and permeabilization, and destroys the outer leaflet and the inner membrane. G3KL accumulates in bacteria against which it is active; however, it only weakly penetrates into eukaryotic cells without inducing significant toxicity. G3KL furthermore binds to lipopolysaccharide (LPS) and inhibits the LPS induced release of TNF-α by macrophages, similarly to polymyxin B. Taken together, these experiments show that G3KL behaves as a potent membrane disruptive antimicrobial peptide.

The rational design of cell-penetrating peptides for application in delivery systems

Cell penetrating peptides (CPPs) play a crucial role in the transportation of bioactive molecules. Although CPPs have been used widely in various delivery systems, further applications of CPPs are hampered by several drawbacks, such as high toxicity, low delivery efficiency, proteolytic instability and poor specificity. To design CPPs with great cell-penetrating ability, physicochemical properties and safety, researchers have tried to develop new methods to overcome the defects of CPPs. Briefly, (1) the side chain of arginine containing the guanidinium group is essential for the facilitation of cellular uptake; (2) the hydrophobic counterion complex around the guanidinium-rich backbone can "coat" the highly cationic structure with lipophilic moieties and act as an activator; (3) the conformation-constrained strategy was pursued to shield the peptide, thereby impeding access of the proteolytic enzyme; (4) targeting strategies can increase cell-type specificity of CPPs. In this review, the above four aspects were discussed in detail.

Stereoselective pH Responsive Peptide Dendrimers for siRNA Transfection

Transfecting nucleic acids into cells is an essential procedure in biological research usually performed using nonviral transfection reagents. Unfortunately, most transfection reagents have polymeric or undisclosed structures and require nonstandard synthetic procedures. Herein we report peptide dendrimers accessible as pure products from standard building blocks by solid-phase peptide synthesis and acting as nontoxic single component siRNA transfection reagents for a variety of cell lines with equal or better performance than the gold standard lipofectamine L2000. Structure-activity relationships and mechanistic studies illuminate their transfection mechanism in unprecedented detail. Stereoselective dendrimer aggregation via intermolecular β-sheets at neutral pH enables siRNA complexation to form nanoparticles which enter cells by endocytosis. Endosome acidification triggers protonation of amino termini and rearrangement to an α-helical conformation forming smaller dendrimer/siRNA nanoparticles, which escape the endosome and release their siRNA cargo in the cytosol. Two particularly efficient d-enantiomeric dendrimers are proposed as new reference reagents for siRNA transfection.

Peptide-based gene delivery vectors

Gene therapy as a strategy for disease treatment requires safe and efficient gene delivery systems that encapsulate nucleic acids and deliver them to effective sites in the cell.

Non-delaminating Polymer Hydrogel Coatings via C,H-Insertion Crosslinking (CHic) - A Case Study of Poly(oxanorbornenes)

Robust, non-delaminating polymer coatings and hydrogels are needed for technical and biomedical applications. This study focusses on surface-attached poly(oxanorbornene) hydrogels obtained by simultaneous UV-activated crosslinking and surface-immobilization. The synthesis and copolymerization of two oxanorbornene monomers carrying the UV-crosslinkers malonic acid diazoester or benzophenone, which can both undergo UV-triggered C,H-insertion crosslinking (CHic), is presented. The crosslinking efficiency and network stability of hydrogels made from these self-crosslinkable polymers are studied and compared to the properties of poly(oxanorbornene) networks obtained by UV-triggered thiol-ene-reactions involving a low molecular weight crosslinker. Smooth, defect-free, non-delaminating hydrogel coatings were obtained by CHic, not only on laboratory model surfaces but also on a technical product.

Engineering the Aromaticity of Cationic Helical Polypeptides toward "Self-Activated" DNA/siRNA Delivery

The development of potent yet nontoxic membrane-penetrating materials is in high demand for effective intracellular gene delivery. We have recently developed α-helical polypeptides which afford potent membrane activities to facilitate intracellular DNA delivery via both endocytosis and the nonendocytic "pore formation" mechanism. Endocytosis will cause endosomal entrapment of the DNA cargo, while excessive "pore formation" would cause appreciable cytotoxicity. Additionally, helical polypeptides with stiff, rodlike structure suffer from low siRNA binding affinity. To address such critical issues, we herein incorporated various aromatic domains (benzyl, naphthyl, biphenyl, anthryl, and pyrenyl) into the side-chain terminals of guanidine-rich, helical polypeptides, wherein the flat-rigid shape, π-electronic structures of aromatic motifs "self-activated" the membrane-penetrating capabilities of polypeptides to promote intracellular gene delivery. Benzyl (Bn)- and naphthyl (Naph)-modified polypeptides demonstrated the highest DNA uptake level that outperformed the unmodified polypeptide, P2, by ∼4 fold. More importantly, compared with P2, Bn- and Naph-modified polypeptides allowed more DNA cargos to be internalized via the nonendocytic pathway, which significantly bypassed the endosomal entrapment and accordingly enhanced the transfection efficiency by up to 42 fold, outperforming PEI 25k as the commercial reagent by 3-4 orders of magnitude. The aromatic modification also improved the siRNA condensation capability of polypeptides, achieving notably enhanced gene-silencing efficiency against tumor necrosis factor-α to treat acute hepatic inflammation. Furthermore, we revealed that aromaticity-augmented membrane activity was accompanied by comparable or even significantly reduced "pore formation" capability, thus leading to diminished cytotoxicity at high concentrations. This study therefore provides a promising approach to manipulate the membrane activities and penetration mechanisms of polycations, which overcomes the multiple critical barriers preventing effective and safe gene delivery.

ROMP- and RAFT-Based Guanidinium-Containing Polymers as Scaffolds for Protein Mimic Synthesis

Cell-penetrating peptides are an important class of molecules with promising applications in bioactive cargo delivery. A diverse series of guanidinium-containing polymeric cell-penetrating peptide mimics (CPPMs) with varying backbone chemistries was synthesized and assessed for delivery of both GFP and fluorescently tagged siRNA. Specifically, we examined CPPMs based on norbornene, methacrylate, and styrene backbones to determine how backbone structure impacted internalization of these two cargoes. Either charge content or degree of polymerization was held constant at 20, with diguanidinium norbornene molecules being polymerized to both 10 and 20 repeat units. Generally, homopolymer CPPMs delivered low amounts of siRNA into Jurkat T cells, with no apparent backbone dependence; however, by adding a short hydrophobic methyl methacrylate block to the guanidinium-rich methacrylate polymer, siRNA delivery to nearly the entire cell population was achieved. Protein internalization yielded similar results for most of the CPPMs, though the block polymer was unable to deliver proteins. In contrast, the styrene-based CPPM yielded the highest internalization for GFP (≈40 % of cells affected), showing that indeed backbone chemistry impacts protein delivery, specifically through the incorporation of an aromatic group. These results demonstrate that an understanding of how polymer structure affects cargo-dependent internalization is critical to designing new, more effective CPPMs.

Increased Hydrophobic Block Length of PTDMs Promotes Protein Internalization

The plasma membrane is a major obstacle in the development and use of biomacromolecules for intracellular therapeutic applications. Protein transduction domains (PTDs) have been used to overcome this barrier, but often require covalent conjugation to their cargo and can be time consuming to synthesize. Synthetic monomers can be designed to mimic the amino acid moieties in PTDs, and their resulting polymers provide a well-controlled platform to vary molecular composition for structure-activity relationship studies. In this paper, a series of polyoxanorbornene-based synthetic mimics, inspired by PTDs, with varying cationic and hydrophobic densities, and the nature of the hydrophobic chain and degree of polymerizations were investigated in vitro to determine their ability to non-covalently transport enhanced green fluorescent protein into HeLa cells, Jurkat T cells, and hTERT mesenchymal stem cells. Polymers with high charge density lead to efficient protein delivery. Similarly, the polymers with the highest hydrophobic content and density proved to be the most efficient at internalization. The observed improvements with increased hydrophobic length and content were consistent across all three cell types, suggesting that these architectural relationships are not cell type specific. However, Jurkat T cells showed distinct variation in uptake between polymers than with the other two cell types. These results provide important design parameters for more effective delivery of biomacromolecules for intracellular delivery applications.

Mapping Optimal Charge Density and Length of ROMP-Based PTDMs for siRNA Internalization

A fundamental understanding of how polymer structure impacts internalization and delivery of biologically relevant cargoes, particularly small interfering ribonucleic acid (siRNA), is of critical importance to the successful design of improved delivery reagents. Herein we report the use of ring-opening metathesis polymerization (ROMP) methods to synthesize two series of guanidinium-rich protein transduction domain mimics (PTDMs): one based on an imide scaffold that contains one guanidinium moiety per repeat unit, and another based on a diester scaffold that contains two guanidinium moieties per repeat unit. By varying both the degree of polymerization and, in effect, the relative number of cationic charges in each PTDM, the performances of the two ROMP backbones for siRNA internalization were evaluated and compared. Internalization of fluorescently labeled siRNA into Jurkat T cells demonstrated that fluorescein isothiocyanate (FITC)-siRNA internalization had a charge content dependence, with PTDMs containing approximately 40 to 60 cationic charges facilitating the most internalization. Despite this charge content dependence, the imide scaffold yielded much lower viabilities in Jurkat T cells than the corresponding diester PTDMs with similar numbers of cationic charges, suggesting that the diester scaffold is preferred for siRNA internalization and delivery applications. These developments will not only improve our understanding of the structural factors necessary for optimal siRNA internalization, but will also guide the future development of optimized PTDMs for siRNA internalization and delivery.

Efficient Mini-Transporter for Cytosolic Protein Delivery

An efficient method to deliver active proteins into cytosol is highly desirable to advance protein-based therapeutics. Arginine-rich cell-penetrating peptides (RPPs) have been intensively studied for intracellular protein delivery, and their applications require further improvement on delivery efficiency, serum stability, and cytotoxicity. Designing synthetic analogs of RPPs provides an alternative way to achieve efficient cytosolic protein delivery. Herein we report the design and synthesis of a dendritic small molecule TG6, which is composed of one rigid planar core and four flexible arms with one guanidinium on each arm. Protein structure and function are well preserved in the TG6-protein conjugates, which are readily internalized into cytosol. Our study demonstrates that TG6 is a serum-stable and low-toxic molecular transporter delivering both small cargoes and large active proteins efficiently into cytosol.

Anionic Lipid Content Presents a Barrier to the Activity of ROMP-Based Synthetic Mimics of Protein Transduction Domains (PTDMs)

Many biophysical studies of protein transduction domains (PTDs) and their synthetic mimics (PTDMs) focus on the interaction between the polycationic PTD(M) and anionic phospholipid surfaces. Most, but not all, of these studies suggest that these cation-anion interactions are vital for membrane activity. In this study, the effect of anionic lipid content on PTDM performance was examined for three ring-opening metathesis (ROMP)-based PTDMs with varying hydrophobicity. Using a series of dye-loaded vesicles with gradually increasing anionic lipid content, we saw that increased anionic lipid content inhibited dye release caused by these PTDMs. This result is the opposite of what was found in studies with poly- and oligo-arginine. While the effect is reduced for more hydrophobic PTDMs, it is observable even with the most hydrophobic PTDMs of our test panel. Additional experiments included dynamic light scattering and zeta potential measurements to measure size as a function of vesicle surface charge in the presence of increasing PTDM concentration and surface plasmon resonance spectroscopy to quantify binding between PTDMs and surface-bound lipid layers with varying anion content. The results from these measurements suggested that PTDM hydrophobicity, not cation-anion interactions, is the main driving force of the interaction between our PTDMs and the model membranes investigated. This suggests a model of interaction where surface association and membrane insertion are driven by PTDM hydrophobicity, while anionic lipid content serves primarily to "pin" the PTDM to the membrane surface and limit insertion.

Optimal Hydrophobicity in Ring-Opening Metathesis Polymerization-Based Protein Mimics Required for siRNA Internalization

Exploring the role of polymer structure for the internalization of biologically relevant cargo, specifically siRNA, is of critical importance to the development of improved delivery reagents. Herein, we report guanidinium-rich protein transduction domain mimics (PTDMs) based on a ring-opening metathesis polymerization scaffold containing tunable hydrophobic moieties that promote siRNA internalization. Structure-activity relationships using Jurkat T cells and HeLa cells were explored to determine how the length of the hydrophobic block and the hydrophobic side chain compositions of these PTDMs impacted siRNA internalization. To explore the hydrophobic block length, two different series of diblock copolymers were synthesized: one series with symmetric block lengths and one with asymmetric block lengths. At similar cationic block lengths, asymmetric and symmetric PTDMs promoted siRNA internalization in the same percentages of the cell population regardless of the hydrophobic block length; however, with 20 repeat units of cationic charge, the asymmetric block length had greater siRNA internalization, highlighting the nontrivial relationships between hydrophobicity and overall cationic charge. To further probe how the hydrophobic side chains impacted siRNA internalization, an additional series of asymmetric PTDMs was synthesized that featured a fixed hydrophobic block length of five repeat units that contained either dimethyl (dMe), methyl phenyl (MePh), or diphenyl (dPh) side chains and varied cationic block lengths. This series was further expanded to incorporate hydrophobic blocks consisting of diethyl (dEt), diisobutyl (diBu), and dicyclohexyl (dCy) based repeat units to better define the hydrophobic window for which our PTDMs had optimal activity. High-performance liquid chromatography retention times quantified the relative hydrophobicities of the noncationic building blocks. PTDMs containing the MePh, diBu, and dPh hydrophobic blocks were shown to have superior siRNA internalization capabilities compared to their more and less hydrophobic counterparts, demonstrating a critical window of relative hydrophobicity for optimal internalization. This better understanding of how hydrophobicity impacts PTDM-induced internalization efficiencies will help guide the development of future delivery reagents.

Boronic Acid-Appended Molecular Glues for ATP-Responsive Activity Modulation of Enzymes

Water-soluble linear polymers GumBAn (m/n = 18/6, 12/12, and 6/18) with multiple guanidinium ion (Gu(+)) and boronic acid (BA) pendants in their side chains were synthesized as ATP-responsive modulators for enzyme activity. GumBAn polymers strongly bind to the phosphate ion (PO4(-)) and 1,2-diol units of ATP via the Gu(+) and BA pendants, respectively. As only the Gu(+) pendants can be used for proteins, GumBAn is able to modulate the activity of enzymes in response to ATP. As a proof-of-concept study, we demonstrated that trypsin (Trp) can be deactivated by hybridization with GumBAn. However, upon addition of ATP, Trp was liberated to retrieve its hydrolytic activity due to a higher preference of GumBAn toward ATP than Trp. This event occurred in a much lower range of [ATP] than reported examples. Under cellular conditions, the hydrolytic activity of Trp was likewise modulated.

Relating structure and internalization for ROMP-based protein mimics

Elucidating the predominant cellular entry mechanism for protein transduction domains (PTDs) and their synthetic mimics (PTDMs) is a complicated problem that continues to be a significant source of debate in the literature. The PTDMs reported here provide a well-controlled platform to vary molecular composition for structure activity relationship studies to further our understanding of PTDs, their non-covalent association with cargo, and their cellular internalization pathways. Specifically, several guanidine rich homopolymers, along with an amphiphilic block copolymer were used to investigate the relationship between structure and internalization activity in HeLa cells, both alone and non-covalently complexed with EGFP by flow cytometery and confocal imaging. The findings indicate that while changing the amount of positive charge on our PTDMs does not seem to affect the endosomal uptake, the presence of hydrophobicity appears to be a critical factor for the polymers to enter cells either alone, or with associated cargo.

Length-Dependent Formation of Transmembrane Pores by 310-Helical α-Aminoisobutyric Acid Foldamers

The synthetic biology toolbox lacks extendable and conformationally controllable yet easy-to-synthesize building blocks that are long enough to span membranes. To meet this need, an iterative synthesis of α-aminoisobutyric acid (Aib) oligomers was used to create a library of homologous rigid-rod 3₁₀-helical foldamers, which have incrementally increasing lengths and functionalizable N- and C-termini. This library was used to probe the inter-relationship of foldamer length, self-association strength, and ionophoric ability, which is poorly understood. Although foldamer self-association in nonpolar chloroform increased with length, with a ∼14-fold increase in dimerization constant from Aib₆ to Aib₁₁, ionophoric activity in bilayers showed a stronger length dependence, with the observed rate constant for Aib₁₁ ∼70-fold greater than that of Aib₆. The strongest ionophoric activity was observed for foldamers with >10 Aib residues, which have end-to-end distances greater than the hydrophobic width of the bilayers used (∼2.8 nm); X-ray crystallography showed that Aib₁₁ is 2.93 nm long. These studies suggest that being long enough to span the membrane is more important for good ionophoric activity than strong self-association in the bilayer. Planar bilayer conductance measurements showed that Aib₁₁ and Aib₁₃, but not Aib₇, could form pores. This pore-forming behavior is strong evidence that Aib_m (m ≥ 10) building blocks can span bilayers.

Ethynyl benziodoxolones: functional terminators for cell-penetrating poly(disulfide)s

Hypervalent iodine terminators are introduced to secure synthetic access to doubly-labeled cell-penetrating poly(disulfide)s.

Trimodal Control of Ion-Transport Activity on Cyclo-oligo-(1→6)-β-D-glucosamine-Based Artificial Ion-Transport Systems

Cyclo-oligo-(1→6)-β-D-glucosamines functionalized with hydrophobic tails are reported as a new class of transmembrane ion-transport system. These macrocycles with hydrophilic cavities were introduced as an alternative to cyclodextrins, which are supramolecular systems with hydrophobic cavities. The transport activities of these glycoconjugates were manipulated by altering the oligomericity of the macrocycles, as well as the length and number of attached tails. Hydrophobic tails of 3 different sizes were synthesized and coupled with each glucosamine scaffold through the amide linkage to obtain 18 derivatives. The ion-transport activity increased from di- to tetrameric glucosamine macrocycles, but decreased further when flexible pentameric glucosamine was introduced. The ion-transport activity also increased with increasing length of attached linkers. For a fixed length of linkers, the transport activity decreased when the number of such tails was reduced. All glycoconjugates displayed a uniform anion-selectivity sequence: Cl(-) >Br(-) >I(-) . From theoretical studies, hydrogen bonding between the macrocycle backbone and the anion bridged through water molecules was observed.

Development of Guanidinium-Rich Protein Mimics for Efficient siRNA Delivery into Human T Cells

RNA interference is gaining attention as a means to explore new molecular pathways and for its potential as a therapeutic; however, its application in immortal and primary T cells is limited due to challenges with efficient delivery in these cell types. Herein, we report the development of guanidinium-rich protein transduction domain mimics (PTDMs) based on a ring-opening metathesis polymerization scaffold that delivers siRNA into Jurkat T cells and human peripheral blood mononuclear cells (hPBMCs). Homopolymer and block copolymer PTDMs with varying numbers of guanidinium moieties were designed and tested to assess the effect cationic charge content and the addition of a segregated, hydrophobic block had on siRNA internalization and delivery. Internalization of fluorescently labeled siRNA into Jurkat T cells illustrates that the optimal cationic charge content, 40 charges per polymer, leads to higher efficiencies, with block copolymers outperforming their homopolymer counterparts. PTDMs also outperformed commercial reagents commonly used for siRNA delivery applications. Select PTDM candidates were further screened to assess the role the PTDM structure has on the delivery of biologically active siRNA into primary cells. Specifically, siRNA to hNOTCH1 was delivered to hPBMCs enabling 50-80% knockdown efficiencies, with longer PTDMs showing improved protein reduction. By evaluating the PTDM design parameters for siRNA delivery, more efficient PTDMs were discovered that improved delivery and gene (NOTCH) knockdown in T cells. Given the robust delivery of siRNA by these novel PTDMs, their development should aid in the exploration of T cell molecular pathways leading eventually to new therapeutics.

Development of protein mimics for intracellular delivery

Designing delivery agents for therapeutics is an ongoing challenge. As treatments and desired cargoes become more complex, the need for improved delivery vehicles becomes critical. Excellent delivery vehicles must ensure the stability of the cargo, maintain the cargo's solubility, and promote efficient delivery and release. In order to address these issues, many research groups have looked to nature for design inspiration. Proteins, such as HIV-1 trans-activator of transcription (TAT) and Antennapedia homeodomain protein, are capable of crossing cellular membranes. However, due to the complexities of their structures, they are synthetically challenging to reproduce in the laboratory setting. Being able to incorporate the key features of these proteins that enable cell entry into simpler scaffolds opens up a wide range of opportunities for the development of new delivery reagents with improved performance. This review charts the development of protein mimics based on cell-penetrating peptides (CPPs) and how structure-activity relationships (SARs) with these molecules and their protein counterparts ultimately led to the use of polymeric scaffolds. These scaffolds deviate from the normal peptide backbone, allowing for simpler, synthetic procedures to make carriers and tune chemical compositions for application specific needs. Successful design of polymeric protein mimics would allow researchers to further understand the key features in proteins and peptides necessary for efficient delivery and to design the next generation of more efficient delivery reagents.

Controlled self-assembly of a pyrene-based bolaamphiphile by acetate ions: from nanodisks to nanofibers by fluorescence enhancement

In this paper, a pyrene moiety is incorporated into a bolaamphiphile to form a novel molecule denoted PRB. Above the critical micelle concentration, PRB forms nanodisks in the aqueous solution. The addition of acetate ions induces a morphological change in self-assembled aggregates, which convert into nanofibers with a diameter of several nanometers. More interestingly, along with the morphological change, the fluorescence of the assemblies was enhanced concomitantly, which can be attributed to the binding effect of acetate ions on pyridinium head groups of PRB.

Design of aromatic-containing cell-penetrating peptide mimics with structurally modified π electronics

Cell-penetrating peptides (CPPs) and their synthetic mimics (CPPMs) represent a class of molecules that facilitate the intracellular delivery of various cargo. Previous studies indicated that the presence of aromatic functionalities improved CPPM activity. Given that aromatic functionalities play prominent roles in membrane biology and participate in various π interactions, we explored whether these interactions could be optimized for improved CPPM activity. CPPMs were synthesized by ring-opening metathesis polymerization by using monomers that contained aromatic rings substituted with electron-donating and electron-withdrawing groups and covered an electrostatic potential range from -29.69 to +15.57 kcal mol(-1) . These groups altered the quadrupole moments of the aromatic systems and were used to test if such structural modifications changed CPPM activity. CPPMs were added to dye-loaded vesicles and the release of carboxyfluorescein was monitored as a function of polymer concentration. Changes in the effective polymer concentration to release 50% of the dye (effective concentration, EC50 ) were monitored. Results from this assay showed that the strength of the electron-donating and electron-withdrawing groups incorporated in the CPPMs did not alter polymer EC50 values or activity. This suggests that other design parameters may have a stronger impact on CPPM activity. In addition, these results indicate that a wide range of aromatic groups can be incorporated without negatively impacting polymer activity.

Applications of halogen bonding in solution

Halogen bonding is the noncovalent interaction where the halogen atom acts as an electrophile towards Lewis bases. Known for more than 200 years, only recently it has attracted interest in the context of solution-phase applications, especially during the last decade which was marked by the introduction of multitopic systems. In addition, the small yet rich collection of halogen-bond donor moieties that appeared in this period is shown to be versatile enough as to be applied in virtually any solvent system. This review covers the applications of halogen bonding in solution during the past ten years in a semi-comprehensive way. Emphasis is made on molecular recognition, catalytic applications and anion binding and transport. Medicinal applications are addressed as well with key examples. Focussing on the major differences observed for halogen bonding, as compared to the ubiquitous hydrogen bonding, it aims to contribute to the design of future solution-phase applications.

Protein delivery with cell-penetrating poly(disulfide)s

The combination of cell-penetrating poly(disulfide)s with biotin–streptavidin biotechnology affords a general method for the delivery of proteins into cells.

Homopolymer bifunctionalization through sequential thiol–epoxy and esterification reactions: an optimization, quantification, and structural elucidation study

In this study, we probe various aspects of a post-polymerization double-modification strategy involving sequential thiol–epoxy and esterification reactions for the preparation of dual-functional homopolymers.

Single-nucleotide-resolution DNA differentiation by pattern generation in lipid bilayer membranes

Pattern generation/recognition in lipid bilayers is introduced for the differentiation of anionic biological relevant polymers. The amplification of the polymer differences during transport events allows the straightforward identification of a wide range collection of anionic polymers. The introduced approach displays excellent resolution even for single mutations in short single-stranded oligonuclotides.