Pseudopeptidic Polymers Research Articles

A tunable light scattering device fabricated using pseudopeptide polymer incorporated chiral nematic liquid crystal

PFLC-based tunable light scattering device is fabricated using chiral nematic LC and pseudopeptide polymer.

Uncovering the Optimal Molecular Characteristics of Hydrophobe-Containing Polypeptoids to Induce Liposome or Cell Membrane Fragmentation.

Cellular functions of membrane proteins are strongly coupled to their structures and aggregation states in the cellular membrane. Molecular agents that can induce the fragmentation of lipid membranes are highly sought after as they are potentially useful for extracting membrane proteins in their native lipid environment. Toward this goal, we investigated the fragmentation of synthetic liposome using hydrophobe-containing polypeptoids (HCPs), a class of facially amphiphilic pseudo-peptidic polymers. A series of HCPs with varying chain lengths and hydrophobicities have been designed and synthesized. The effects of polymer molecular characteristics on liposome fragmentation are systemically investigated by a combination of light scattering (SLS/DLS) and transmission electron microscopy (cryo-TEM and negative stained TEM) methods. We demonstrate that HCPs with a sufficient chain length (DPn ≈ 100) and intermediate hydrophobicity (PNDG mol % = 27%) can most effectively induce the fragmentation of liposomes into colloidally stable nanoscale HCP-lipid complexes owing to the high density of local hydrophobic contact between the HCP polymers and lipid membranes. The HCPs can also effectively induce the fragmentation of bacterial lipid-derived liposomes and erythrocyte ghost cells (i.e., empty erythrocytes) to form nanostructures, highlighting the potential of HCPs as novel macromolecular surfactants toward the application of membrane protein extraction.

Pseudopeptidic polymers for modulating electro-optic switching, dielectric and electrical properties of liquid crystal

Herein, we report the stabilization of a nematic liquid crystal using chiral amino acid-based polymers. For the first time, the effect of molecular weight of structurally similar polymers on the physical parameters of polymer-stabilized liquid crystals (PSLCs) is investigated. To obtain PSLCs, three pseudopeptidic bottlebrush polymers of different molecular weights are synthesized from the same monomer using a ring-opening metathesis polymerization (ROMP) reaction. The bottlebrush polymers form self-assembly networks in the LC matrix. The size of the self-assembled network is readily tunable by the systematic variation in the molecular weight of the constituent polymer. The polymer network assembly is characterized by using field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and polarizing optical microscopy (POM). The ion density and diffusion coefficient of two different types of mobile ions are calculated by utilizing experimental dielectric data. The constituent polymer determines the structure of self-assembly network in PSLC and hence, the dielectric, electrical, electro-optic, and optical properties. The PSLCs show significant improvement in the response time (∼21%), dielectric anisotropy (∼40%), conductivity (∼11%), current (5-fold increment at 20 V), and phase transition temperature (PTT) upon variation in the molecular weight of the doped polymer units. This simple method of tuning response time, dielectric anisotropy, conductivity, current, and PTT using polymers of different molecular weights presents several possibilities of fabricating optoelectronic devices.

Comb-like Pseudopeptides Enable Very Rapid and Efficient Intracellular Trehalose Delivery for Enhanced Cryopreservation of Erythrocytes.

Cell cryopreservation plays a key role in the development of reproducible and cost-effective cell-based therapies. Trehalose accumulated in freezing- and desiccation-tolerant organisms in nature has been sought as an attractive nontoxic cryoprotectant. Herein, we report a coincubation method for very rapid and efficient delivery of membrane-impermeable trehalose into ovine erythrocytes through reversible membrane permeabilization using pH-responsive, comb-like pseudopeptides. The pseudopeptidic polymers containing relatively long alkyl side chains were synthesized to mimic membrane-anchoring fusogenic proteins. The intracellular trehalose delivery efficiency was optimized by manipulating the side chain length, degree of substitution, and concentration of the pseudopeptides with different hydrophobic alkyl side chains, the pH, temperature, and time of incubation, as well as the polymer-to-cell ratio and the concentration of extracellular trehalose. Treatment of erythrocytes with the comb-like pseudopeptides for only 15 min yielded an intracellular trehalose concentration of 177.9 ± 8.6 mM, which resulted in 90.3 ± 0.7% survival after freeze-thaw. The very rapid and efficient delivery was found to be attributed to the reversible, pronounced membrane curvature change as a result of strong membrane insertion of the comb-like pseudopeptides. The pseudopeptides can enable efficient intracellular delivery of not only trehalose for improved cell cryopreservation but also other membrane-impermeable cargos.

Parlez-vous protein?

If you’ve ever learned a language, says Jen Heemstra of Emory University, there are two levels of understanding. First you learn to read text and comprehend it. Then you begin speaking the language and interacting with others. In Heemstra’s lab, she says her team members are even more ambitious: the group is teaching molecules to speak both nucleic acid and protein languages simultaneously (J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.9b09146). (Heemstra partners with C&EN to write a monthly column, Office Hours.) Peptide nucleic acids (PNAs) are artificial polymers that were originally invented in 1991 to be synthetic mimics of DNA. Instead of having a deoxyribose phosphate backbone like DNA, PNA has a pseudopeptide polymer backbone to which nucleobases are linked. The resulting biopolymer is stabler than DNA, yet it can still “speak,” or interact, with complementary RNA or DNA strands. The new innovation in PNA coming from Heemstra’s PhD student

A New Strategy for Intestinal Drug Delivery via pH-Responsive and Membrane-Active Nanogels.

Oral administration of hydrophobic and poorly intestinal epithelium-permeable drugs is a significant challenge. Herein, we report a new strategy to overcome this problem by using novel, pH-responsive, and membrane-active nanogels as drug carriers. Prepared by simple physical cross-linking of amphiphilic pseudopeptidic polymers with pH-controlled membrane-activity, the size and hydrophobicity-hydrophilicity balance of the nanogels could be well-tuned. Furthermore, the amphiphilic nanogels could release hydrophobic payloads and destabilize cell membranes at duodenum and jejunum pH 5.0-6.0, which suggests their great potential for intestinal drug delivery.

A Pseudopeptide Polymer Micelle Used for Asymmetric Catalysis of the Aldol Reaction in Water.

Micelles assembled from amphiphilic molecules have proved to be ideal scaffolds to construct artificial catalysts mimicking enzymatic catalytic behavior. In this paper, we describe the synthesis of amphiphilic poly(2-oxazoline) derivatives with l-prolinamide units in the side chain and their application in asymmetric aldol reactions. Upon dissolution in water, the pseudopeptide polymers self-assembled into particles with different sizes, relying on the copolymer composition and distribution of hydrophilic/hydrophobic segments in the polymer chain. A preliminary study has demonstrated that the catalytic activity of these polymeric organocatalysts are strongly dependent on the aggregated architecture. The micelle-type assemblies can act as nanoreactors to efficiently promote the direct aldolisation of cyclohexanone with aromatic aldehydes in aqueous media, affording anti-aldol products in excellent yields (88–99%) and higher stereoselectivities (90/10 dr, 86% ee) compared to their nonmicellar systems under identical conditions.

Simulation Studies on the Lipid Interaction and Conformation of Novel Drug-Delivery Pseudopeptidic Polymers.

Pseudopeptides based on poly(l-lysine isophthalamide) backbone have emerged as promising drug delivery candidates due to their pH-activated membrane disruption ability. To gain molecular understanding on these novel polymeric species, we have constructed force-field parameters and simulated the behaviors of polymers with and without phenylalanine grafted as side chains under conditions compatible with different pHs. The free energy changes upon polymer permeation through membrane were calculated using the umbrella sampling technique. We show that both polymers with and without grafts interact better with the membrane under conditions compatible with lower pH. The conformational states of the polymers were investigated in water and at a water-membrane interface. On the basis of Markov state modeling results, we propose a possible advantage of the grafted polymer over the ungrafted polymer for membrane rupture because of its quicker conformational rearrangement kinetics.

Membrane-Anchoring, Comb-Like Pseudopeptides for Efficient, pH-Mediated Membrane Destabilization and Intracellular Delivery.

Endosomal release has been identified as a rate-limiting step for intracellular delivery of therapeutic agents, in particular macromolecular drugs. Herein, we report a series of synthetic pH-responsive, membrane-anchoring polymers exhibiting dramatic endosomolytic activity for efficient intracellular delivery. The comb-like pseudopeptidic polymers were synthesized by grafting different amounts of decylamine (NDA), which act as hydrophobic membrane anchors, onto the pendant carboxylic acid groups of a pseudopeptide, poly(l-lysine iso-phthalamide). The effects of the hydrophobic relatively long alkyl side chains on aqueous solution properties, cell membrane destabilization activity, and in-vitro cytotoxicity were investigated. The optimal polymer containing 18 mol % NDA exhibited limited hemolysis at pH 7.4 but induced nearly complete membrane destabilization at endosomal pH within only 20 min. The mechanistic investigation of membrane destabilization suggests the polymer-mediated pore formation. It has been demonstrated that the polymer with hydrophobic side chains displayed a considerable endosomolytic ability to release endocytosed materials into the cytoplasm of various cell lines, which is of critical importance for intracellular drug delivery applications.

A Virus-Mimicking, Endosomolytic Liposomal System for Efficient, pH-Triggered Intracellular Drug Delivery.

A novel multifunctional liposomal delivery platform has been developed to resemble the structural and functional traits of an influenza virus. Novel pseudopeptides were prepared to mimic the pH-responsive endosomolytic behavior of influenza viral peptides through grafting a hydrophobic amino acid, l-phenylalanine, onto the backbone of a polyamide, poly(l-lysine isophthalamide), at various degrees of substitution. These pseudopeptidic polymers were employed to functionalize the surface of cholesterol-containing liposomes that mimic the viral envelope. By controlling the cholesterol proportion as well as the concentration and amphiphilicity of the pseudopeptides, the entire payload was rapidly released at endosomal pHs, while there was no release at pH 7.4. A pH-triggered, reversible change in liposomal size was observed, and the release mechanism was elucidated. In addition, the virus-mimicking nanostructures efficiently disrupted the erythrocyte membrane at pH 6.5 characteristic of early endosomes, while they showed negligible cytotoxic effects at physiological pH. The efficient intracellular delivery of the widely used anticancer drug doxorubicin (DOX) by the multifunctional liposomes was demonstrated, leading to significantly increased potency against HeLa cancer cells over the DOX-loaded bare liposomes. This novel virus-mimicking liposomal system, with the incorporated synergy of efficient liposomal drug release and efficient endosomal escape, is favorable for efficient intracellular drug delivery.

Pseudopeptide polymer coating for improving biocompatibility and corrosion resistance of 316L stainless steel

The coating formed by electrochemical assembly of hydrolyzed poly(2-methyl-2-oxazoline) and dopamine could improve the migration and proliferation of HUVECs.

Polypeptoid Materials: Current Status and Future Perspectives

Polypeptoids have recently emerged as a subject of scientific interest due to their structural resemblance to existing pseudo-peptidic polymers including poly(α-peptide)s, poly(β-peptide)s, poly(2-oxazoline)s, and poly(N-substituted acrylamide)s. With demonstrated backbone degradability, biocompatibility, and thermal processability, polypeptoids are potentially useful in a variety of biotechnological applications. Before those applications can be realized, it is important to develop their synthesis and understand their fundamental properties. In this Perspective, we will review recent advances in the synthesis and characterization of polypeptoids and their copolymers as well as the development of polypeptoid-based functional and structured materials. We will conclude by discussing the future prospects for this nascent class of pseudo-peptidic polymers.

Synthesis and pH-responsive properties of pseudo-peptides containing hydrophobic amino acid grafts

Pseudo-peptidic polymers have been synthesised by grafting L-valine (PV), L-leucine (PL) and L-phenylalanine (PP) onto the pendant carboxylic acid moieties of a pH-responsive polyamide, poly(L-lysine isophthalamide). The pH-responsive aqueous solution properties of PV-75, PL-75 and PP-75 with a stoichiometric degree of substitution of 75 mol% have been compared with those of the parent poly(L-lysine isophthalamide) using UV-visible and fluorescence spectroscopy. At low concentrations (≤0.1 mg mL−1), the grafted polymers displayed pH-dependent conformation. The pH at the onset of hydrophobic association (pHh) and the pH range over which association occurred varied significantly between the different amino acid grafts. The pHh values of PV-75, PL-75 and PP-75 at 0.025 mg mL−1 were 6.2, 7.0 and 7.2, respectively. Increasing concentration enhanced intermolecular aggregation. A bis-functional Cy5 derivative, incorporated within the backbones of poly(L-lysine isophthalamide) (polyCy5) and PP-75 (PDP-75), was demonstrated to act as a fluorescence reporter on the state of polymer conformation and aggregation. The intracellular trafficking of PDP-75, examined by confocal microscopy, indicates potential applications of the grafted polymers in drug delivery and medical imaging.

Effective Delivery of Antisense Peptide Nucleic Acid Oligomers into Cells by Anthrax "Protective Antigen".

A detailed understanding of the genetic basis of inherited and acquired hematologic diseases has emerged during recent decades, encouraging efforts to develop genetically targeted reagents as both experimental tools and novel therapeutics. Peptide nucleic acid (PNA), a DNA mimic in which the phosphate deoxyribose backbone of DNA has been replaced by a pseudopeptide polymer, first described in 1991, has attracted particular interest as a gene-targeting reagent, since it is highly stable and binds to complementary RNA and DNA with high affinity and specificity. However, because PNA oligomers resist cellular uptake, their development as tools for modifying gene expression in whole animal studies or as potential therapeutic agents has been limited. To explore the possibility that the transmembrane "transport" domains of microbial toxin proteins might serve as vehicles for cellular delivery of PNA, we studied the ability of recombinant Anthrax "protective antigen" (PA), the non-toxic component of Anthrax toxin that mediates cell binding and delivery, to transport antisense PNA oligomers effectively into cells. For these studies, we first generated CHO-K1 cell lines (CHO-Luc654) that had been engineered by stable transfection to express a modified luciferase gene (Luc-βIVS2-654) interrupted by a mutant β-globin intron-2 with an aberrant splice site that could be blocked by antisense PNA, thereby inducing luciferase expression as an indicator of antisense activity (ref. Sazani & Kole, J Clin Invest 112:481, 2003). We then synthesized PNA oligomers with poly-lysine tails and 18-mer nucleobase sequences antisense to a region of Luc-βIVS2-654 pre-mRNA flanking the aberrant IVS2-654 splice site. As anticipated from prior reports (Nucleic Acids Res 29:3965, 2001), antisense PNA-(Lys)8 oligomers demonstrated detectable sequence-specific activity in inducing luciferase expression in CHO-Luc654 cells when incubated with the cells for 48–72 hrs at micromolar concentrations. However, this activity was greatly and significantly amplified when CHO-Luc654 cells were incubated with antisense PNA-(Lys)8 together with Anthrax PA (0.3–1.0 μg/mL), which had no effects on the cells by itself, such that antisense activity could be detected at PNA concentrations as low as 30 nM. Antisense PNA-(Lys)8 (300 nM), with but not without Anthrax PA (0.3 μg/mL), was also found by rtPCR to induce correctly spliced β-globin transcripts in cultured erythroid progenitor cells obtained from a patient with β-thalassemia [genotype, IVS2-654(βo/βE), kindly provided to us by Dr. Edmond Ma, Queen Mary Hospital, Univ. of Hong Kong]. These studies provide proof-of-principle evidence that the transmembrane transport function of microbial toxins (e.g. Anthrax PA) can be harnessed to deliver antisense PNA oligomers effectively into cells. Since microbial toxin proteins can be molecularly engineered to achieve cell selective binding (as exemplified by the IL2-diphtheria fusion toxin, ONTAK®), our findings support the possibility that novel therapeutic agents, based on PNA oligomer constructs and modified microbial toxin proteins, can be developed that combine both genetic targeting and cell selectivity.

The peptide nucleic acids (PNAs): a new generation of probes for genetic and cytogenetic analyses

Peptide nucleic acids (PNAs) are synthetic homologs of nucleic acids in which the phosphate–sugar polynucleotide backbone is replaced by a flexible pseudo-peptide polymer to which the nucleobases are linked. This structure gives PNAs the capacity to hybridize with high affinity and specificity to complementary sequences of DNA and RNA, and also confers remarkable resistance to DNAses and proteinases. The unique physico-chemical characteristics of PNAs have led to the development of a wide range of biological assays. Several exciting new applications of PNA technology have been published recently in genetics and cytogenetics. Also, PNA-based hybridization technology is developing rapidly within the field of in situ fluorescence hybridization, pointing out the great potential of PNA probes for chromosomal investigations.

The peptide nucleic acids (PNAs), powerful tools for molecular genetics and cytogenetics.

Peptide nucleic acids (PNAs) are synthetic mimics of DNA in which the deoxyribose phosphate backbone is replaced by a pseudo-peptide polymer to which the nucleobases are linked. PNAs hybridize with complementary DNAs or RNAs with remarkably high affinity and specificity, essentially because of their uncharged and flexible polyamide backbone. The unique physico-chemical properties of PNAs have led to the development of a variety of research assays, and over the last few years, the use of PNAs has proven their powerful usefulness in molecular biology procedures and diagnostic assays. The more recent applications of PNA involve their use as molecular hybridization probes. Thus, several sensitive and robust PNA-dependent methods have been designed for developing antigene and anticancer drugs, modulating PCR reactions, detecting genomic mutation or labelling chromosomes in situ.