A rationally designed peptoid for the selective chelation of Zn2+ over Cu2

Boronic Acid-Linked Apo-Zinc Finger Protein for Ubiquitin Delivery in Live Cells

Delivering cargo into live cells has extensive applications in chemistry, biology, and medicine. Cell-penetrating peptides (CPPs) provide an ideal solution for cellular delivery. Enhancing CPPs with additional functional units can improve delivery efficiency. We investigate the conjugation of boronic acid modules to enhance internalization through interactions with cell surface glycans. The aim of this study is to determine whether adding boronic acid can transform a peptide that typically lacks CPP properties into one that functions as a CPP, enabling the delivery of crucial biological cargo like ubiquitin (Ub). The zinc finger protein in its apo state was selected as a "boronate-enabled" CPP. Results indicate that skeletal point mutations and post-synthetic modifications, combined with conjugated benzoboroxole derivatives, enable the apo-ZFP the ability to transport Ub within A549 cells, confirmed through microscopy and flow cytometry. This effective internalization of cargo offers valuable insights for advancing the development of boronic acid-mediated cell-penetrating peptides.

Metal-directed hierarchical superhelices from hybrid peptide foldamers

A superhelix is a three-dimensional arrangement of a helix in which the helix is coiled around a common axis. Here, we are reporting a short 12-helix of α,γ-hybrid peptides terminated by metal binding ligands, self-assembled into a right-handed superhelix around a common axis in the presence of Cd(II) ions. Furthermore, these superhelices are assembled into hierarchical superhelical β-sheet-type structural motifs in single crystals. The results reported here may give new insights to construct advanced self-assembled architectures from peptide foldamers.

Synthesis of Tin Oxide Nanoparticles from E-Waste for Photocatalytic Mixed-Dye Degradation under Sunlight

Electronic waste (e-waste) has become a significant environmental concern worldwide due to the rapid advancement of technology and short product lifecycles. Waste-printed electronic boards (WPCBs) contain valuable metals and semiconductors; among them, tin can be recycled and repurposed for sustainable material production. This study presents a potential ecofriendly methodology for the recovery of tin from WPCBs in the form of tin oxide nanostructured powders. The soldering points in the WPCBs are extracted and dissolved in the dilute HNO3 solution, followed by the formation of metastannic acid, which is subsequently transformed into SnO2 nanoparticles. Different characterization techniques (XRD, XPS, FE-SEM, and TEM) are employed to confirm the morphology and composition of nanoparticles. The prepared SnO2 NPs, having a size range of <50 nm, show excellent photocatalytic degradation of cationic (methylene blue, MB) and anionic (eosin Y, EY) dyes for wastewater treatment. The as-synthesized SnO2 can degrade the mixed dyes (MB+EY) under the illumination of natural sunlight at rate constants of 0.0153 and 0.1103 min-1 for MB and EY, respectively. The positive zeta potential and smaller particle size of the SnO2 NPs possess the extra advantage of the adsorption of anionic over cationic dye, resulting in faster degradation of EY, which is further supported by DFT calculation. The synthesis of SnO2 from waste-printed electronic boards offers a dual benefit: It not only provides a sustainable solution for managing electronic waste but also contributes to the production of useful photocatalysts for wastewater treatment. By converting waste into valuable resources, this approach aligns with the principles of the circular economy and mitigates the environmental impact associated with e-waste disposal.

Aza-BODIPY-based logic gate chemosensors and their applications

Dimethylaniline-substituted aza-BODIPY dyes (DA, DM, DP) were designed and synthesized aiming for ion detection. The Zn2+ recognition ability was found in all compounds and the binding mechanism was possibly via dimethylaniline sites linked to the aza-BODIPY core. Upon Zn2+ addition, the new absorption band and the color change occurred due to the altered charge transfer of the adducts. The custom-made colorimeter was successfully integrated into the dye's application, demonstrating a good linear relationship between resistance values and Zn2+ concentration. The chromophore test strips were fabricated and exhibited distinct color changes upon aqueous Zn2+ exposure. The compound DA also exhibits logical behavior with DA-Zn2+-Cu2+ system. In terms of environmental hazards, the compounds exhibited no adverse effect on Pseudomonas putida at the concentration level of 0.2 mg/mL. These findings indicated that all synthesized aza-BODIPYs might be suitable for chemosensor probes for Zn2+ detection with possibly low environmental risk.

A cocktail of Cu2+- and Zn2+-peptoid-based chelators can stop ROS formation for Alzheimer's disease therapy

The formation of reactive oxygen species (ROS) in the brain is a major cause of neuropathologic degradation associated with Alzheimer's Disease (AD). It has been suggested that the copper (Cu)-amyloid-β (Aβ) peptide complex can lead to ROS formation in the brain. An external chelator for Cu that can extract Cu from the CuAβ complex should inhibit the formation of ROS, making Cu chelation an excellent therapeutic approach for AD. Such a chelator should possess high selectivity for Cu over zinc (Zn), which is also present within the synaptic cleft. However, such selectivity is generally hard to achieve in one molecule due to the similarities in the binding preferences of these two metal ions. As an alternative to monotherapy (where Cu extraction is performed using a single chelator), herein we describe a variation of combination therapy - a novel cocktail approach, which is based on the co-administration of two structurally different peptidomimetic chelators, aiming to target both Cu2+ and Zn2+ ions simultaneously but independently from each other. Based on rigorous spectroscopic experiments, we demonstrate that our peptidomimetic cocktail allows, for the first time, the complete and immediate inhibition of ROS production by the CuAβ complex in the presence of Zn2+. In addition, we further demonstrate the high stability of the cocktail under simulated physiological conditions and its resistance to proteolytic degradation by trypsin and report the water/n-octanol partition coefficient, initially assessing the blood-brain barrier (BBB) permeability potential of the chelators.

Unravelling the potential of L-carnosine analog-based nano-assemblies as pH-responsive therapeutics in treating glioma: an in vitro perspective

Self-assembled small peptide-based nanoparticles (NPs) constitute a major section of the biomimetic smart NPs owing to their excellent compatibility and minimal adverse effects in the biological system. Here, we have designed a modified L-carnosine dipeptide analog, "Fmoc-β-Ala-L-His-(Trt)-o-methyl formate", which was assembled along with a modified single amino acid, Fmoc-Arg-(Pbf)-OH and zinc ions to form stable and mono-dispersed L-carnosine analog NPs (CaNPs) with inherent anti-cancer properties. Furthermore, the CaNPs demonstrated an average size of ∼200 nm, making them suitable to invade the tumor site by following the enhanced permeability and retention (EPR) effect. Our studies depicted a remarkable cancer cell killing ability of the NPs of ∼82% in C6 glioma cells. Thereafter, cellular investigations were performed in C6 cells to analyze the influence of the NPs on cellular cytoskeleton integrity by using a phalloidin assay and anti-cancer efficacy by using calcein AM/PI, and an apoptosis assay further indicated their anti-cancer effect. Additionally, the NPs negatively impacted the ability of C6 cells to migrate across a premade scratch (∼44% wound closure) demonstrating their tendency to halt cancer cell migration and metastasis. Also, our NPs depicted ∼19.51 ± 0.17% permeability across the bEnd.3 transwell model establishing their BBB penetrability. Collectively, our results could positively implicate the successful anti-cancer potential of the minimalistic, biologically compliant, L-carnosine analog (Ca)-based nanostructures in glioma.

Development of a bisphenol A based chemosensor for Al3+ and its application in cell imaging and plant root imaging

Bisphenol A is a fluorophoric platform that is used to develop chemosensors for various species. Herein, we report a bisphenol A based Schiff-base molecule, 4,4'-(propane-2,2-diyl)bis(2-((E)-((2-hydroxy-5-methylphenyl)imino)methyl)phenol) (Me-H4L), as a selective chemosensor for Al3+. Among the several metal ions, it shows a significant increment in its fluorescence intensity (50 fold) at 535 nm in the presence of Al3+ ions. The enhanced fluorescence was attributed to the CHEFF mechanism and inhibition of CN isomerization. The limit of detection value of Me-H4L for Al3+ was determined to be 9.65 μM. Its quantum yield and lifetime increased considerably in the presence of the cation. Some theoretical calculations were performed to explain the interaction between Al3+ and the probe. Furthermore, Me-H4L was applied in cell imaging studies using animal cells and plant roots.

An intramolecular cobalt-peptoid complex as an efficient electrocatalyst for water oxidation at low overpotential

Water electrolysis is the simplest way to produce hydrogen, as a clean renewable fuel. However, the high overpotential and slow kinetics hamper its applicability. Designing efficient and stable electrocatalysts for water oxidation (WO), which is the first and limiting step of the water splitting process, can overcome this limitation. However, the development of such catalysts based on non-precious metal ions is still challenging. Herein we describe a bio-inspired Co(iii)-based complex i.e., a stable and efficient molecular electrocatalyst for WO, constructed from a peptidomimetic oligomer called peptoid - N-substituted glycine oligomer - bearing two binding ligands, terpyridine and bipyridine, and one ethanolic group as a proton shuttler. Upon binding of a cobalt ion, this peptoid forms an intramolecular Co(iii) complex, that acts as an efficient electrocatalyst for homogeneous WO in aqueous phosphate buffer at pH 7 with a high faradaic efficiency of up to 92% at an overpotential of about 430 mV, which is the lowest reported for Co-based homogeneous WO electrocatalysts to date. We demonstrated the high stability of the complex during electrocatalytic WO and that the ethanolic side chain plays a key role in the stability and activity of the complex and also in facilitating water binding, thus mimicking an enzymatic second coordination sphere.

Boronic Acid-Linked Cell-Penetrating Peptide for Protein Delivery

Studying functional protein delivery into live cells is important, ranging from fundamental research to therapeutics. Cell-penetrating peptides (CPPs) are known to deliver proteins with applauded efficacy and have gained importance for applications in protein therapeutics and exploration of versatile cellular mechanisms. The primary aim of the work is to design a CPP as a tool and delivery vehicle for macromolecules, including proteins. In this work, boronic acid-linked cyclic deca arginine (cR10) is reported as an efficient CPP that exhibited 3-fold higher delivery of chemically synthesized ubiquitin (Ub) than pristine cR10-linked Ub, examined with live U2OS cells. As a futuristic plan, an artificial intelligence machine learning-based rationale has been designed and proposed.

Highly selective, sensitive and biocompatible rhodamine-based isomers for Al3+ detection: A comparative study

Selective detection of a metal ion with high selectivity is of great importance to understand its existence and its role in many chemical and biological processes. We report here the synthesis, characterization and Al3+ sensing properties of two rhodamine-based isomers, (E)-2-((2-(allyloxy)benzylidene)amino)ethyl)-3',6'-bis(ethylamine)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one (L-2-oxy) and (E)-2-((4-(allyloxy)benzylidene)amino)ethyl)-3',6'-bis(ethylamine)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one (L-4-oxy). L-2-oxyand L-4-oxy show pink coloration, significant enhancement in absorbance at 530 nm and fluorescence intensity at 553 nm in the presence of Al3+ among several cations. Quantum yield and lifetime of the probes increase in the presence of Al3+. LOD values have been determined as low as ∼1.0 nM for both the isomers. DFT study suggests that the cation induces opening of spirolactam ring resulting in the changes of the rhodamine dyes. Additional reason could be Chelation Enhanced Fluorescence (CHEF) effect due to the subsequent chelation of the metal ion. Between two isomers, L-2-oxy displays better sensing ability towards Al3+ in terms of fluorescence enhancement, limit of detection, lifetime enhancement. Both the probes have been utilized in cell imaging studies using rat skeletal myoblast cell line (L6 cell line).

Designed Metal-Containing Peptoid Membranes as Enzyme Mimetics for Catalytic Organophosphate Degradation

The detoxification of lethal organophosphate (OP) residues in the environment is crucial to prevent human exposure and protect modern society. Despite serving as excellent catalysts for OP degradation, natural enzymes require costly preparation and readily deactivate upon exposure to environmental conditions. Herein, we designed and prepared a series of phosphotriesterase mimics based on stable, self-assembled peptoid membranes to overcome these limitations of the enzymes and effectively catalyze the hydrolysis of dimethyl p-nitrophenyl phosphate (DMNP)─a nerve agent simulant. By covalently attaching metal-binding ligands to peptoid N-termini, we attained enzyme mimetics in the form of surface-functionalized crystalline nanomembranes. These nanomembranes display a precisely controlled arrangement of coordinated metal ions, which resemble the active sites found in phosphotriesterases to promote DMNP hydrolysis. Moreover, using these highly programmable peptoid nanomembranes allows for tuning the local chemical environment of the coordinated metal ion to achieve enhanced hydrolysis activity. Among the crystalline membranes that are active for DMNP degradation, those assembled from peptoids containing bis-quinoline ligands with an adjacent phenyl side chain showed the highest hydrolytic activity with a 219-fold rate acceleration over the background, demonstrating the important role of the hydrophobic environment in proximity to the active sites. Furthermore, these membranes exhibited remarkable stability and were able to retain their catalytic activity after heating to 60 °C and after multiple uses. This work provides insights into the principal features to construct a new class of biomimetic materials with high catalytic efficiency, cost-effectiveness, and reusability applied in nerve agent detoxification.

The First Cu(I)-Peptoid Complex: Enabling Metal Ion Stability and Selectivity via Backbone Helicity

Stabilization of Cu(I) is ubiquitous within native copper proteins. Understanding how to stabilize Cu(I) within synthetic biomimetic systems is therefore desired towards biological applications. Peptoids are an important class of peptodomimetics, that can bind metal ions and stabilize them in their high oxidation state. Thus, to date, they were not used for Cu(I) binding. Here we show how the helical peptoid hexamer, having two 2,2'-bipyridine (Bipy) groups that face the same side of the helix, forms the intramolecular air stable Cu(I) complex. Further study of the binding site by rigorous spectroscopic techniques suggests that Cu(I) is tetracoordinated, binding to only three N atoms from the Bipy ligands and to the N-terminus of the peptoid's backbone. A set of control peptoids and experiments indicates that the Cu(I) stability and selectivity are dictated by the intramolecular binding, forced by the helicity of the peptoid, which can be defined as the second coordination sphere of the metal center.

Mobile zinc as a modulator of sensory perception

Mobile zinc is an abundant transition metal ion in the central nervous system, with pools of divalent zinc accumulating in regions of the brain engaged in sensory perception and memory formation. Here, we present essential tools that we developed to interrogate the role(s) of mobile zinc in these processes. Most important are (a) fluorescent sensors that report the presence of mobile zinc and (b) fast, Zn-selective chelating agents for measuring zinc flux in animal tissue and live animals. The results of our studies, conducted in collaboration with neuroscientist experts, are presented for sensory organs involved in hearing, smell, vision, and learning and memory. A general principle emerging from these studies is that the function of mobile zinc in all cases appears to be downregulation of the amplitude of the response following overstimulation of the respective sensory organs. Possible consequences affecting human behavior are presented for future investigations in collaboration with interested behavioral scientists.

Design of a Flexible, Zn-Selective Protein Scaffold that Displays Anti-Irving-Williams Behavior

Selective metal binding is a key requirement not only for the functions of natural metalloproteins but also for the potential applications of artificial metalloproteins in heterogeneous environments such as cells and environmental samples. The selection of transition-metal ions through protein design can, in principle, be achieved through the appropriate choice and the precise positioning of amino acids that comprise the primary metal coordination sphere. However, this task is made difficult by the intrinsic flexibility of proteins and the fact that protein design approaches generally lack the sub-Å precision required for the steric selection of metal ions. We recently introduced a flexible/probabilistic protein design strategy (MASCoT) that allows metal ions to search for optimal coordination geometry within a flexible, yet covalently constrained dimer interface. In an earlier proof-of-principle study, we used MASCoT to generate an artificial metalloprotein dimer, (AB)₂, which selectively bound Co^II and Ni^II over Cu^II (as well as other first-row transition-metal ions) through the imposition of a rigid octahedral coordination geometry, thus countering the Irving-Williams trend. In this study, we set out to redesign (AB)₂ to examine the applicability of MASCoT to the selective binding of other metal ions. We report here the design and characterization of a new flexible protein dimer, B₂, which displays Zn^II selectivity over all other tested metal ions including Cu^II both in vitro and in cellulo. Selective, anti-Irving-Williams Zn^II binding by B₂ is achieved through the formation of a unique trinuclear Zn coordination motif in which His and Glu residues are rigidly placed in a tetrahedral geometry. These results highlight the utility of protein flexibility in the design and discovery of selective binding motifs.

Amide bond hydrolysis of peptoids

Incorporating a chiral non-coordinating substitution at the N-terminal end within peptoids facilitates regio-selective amide bond hydrolysis mediated by a transition metal ion and/or an acidic buffer as evident by X-ray crystallographic analysis, supported by ESI-MS. This opens up a new direction for peptidomimetic compounds towards future application in chemistry, biology and medicine.

Roles of Metal Ions in Foldamers and Other Conformationally Flexible Supramolecular Systems

Conformational control is a key prerequisite for much molecular function. As chemists seek to create complex molecules that have applications beyond the academic laboratory, correct spatial positioning is critical. This is particularly true of flexible systems. Conformationally flexible molecules show potential because they resemble in many cases naturally occurring analogues such as the secondary structures found in proteins and peptides such as α-helices and β-sheets. One of the ways in which conformation can be controlled in these molecules is through interaction with or coordination to metal ions. This review explores how secondary structure (i.e., controlled local conformation) in foldamers and other conformationally flexible systems can be enforced or modified through coordination to metal ions. We hope to provide examples that illustrate the power of metal ions to influence this structure toward multiple different outcomes.

A rhodamine based dual chemosensor for Al3+ and Hg2+: Application in the construction of advanced logic gates

A rhodamine-based compound (RBO), which has been constructed from the reaction between N-(rhodamine-6G)lactam-ethylenediamine and 2,1,3-benzoxadiazole-4-carbaldehyde, is reported here as a selective chemosensor for both Al³⁺ and Hg²⁺ ions in 10 mM HEPES buffer in water:ethanol (1:9, pH = 7.4). Absorption intensity of RBO increases considerably at 528 nm with these cations. It shows fluorescence enhancement at 550 nm by 1140- and 524-fold in the presence of Al³⁺ and Hg²⁺, respectively. LOD has been determined as 6.54 and 16.0 nM for Al³⁺ and Hg²⁺, respectively. Quantum yield and lifetime of RBO enhances with these metal ions. Fluorescence intensity of Al-probe complex or Hg-probe complex is quenched in the presence of fluoride or sulfide ion, respectively, opening a path for the construction logic gates. DFT analysis has been used to understand the spectral transitions. We have constructed a systematic development from single to five inputs complex circuit, and for the first time a time dependent five input complex logic circuit is reported herein.

A Water-Soluble Peptoid Chelator that Can Remove Cu2+ from Amyloid-β Peptides and Stop the Formation of Reactive Oxygen Species Associated with Alzheimer's Disease

Cu bound to amyloid-β (Aβ) peptides can act as a catalyst for the formation of reactive oxygen species (ROS), leading to neuropathologic degradation associated with Alzheimer's disease (AD). An excellent therapeutic approach is to use a chelator that can selectively remove Cu from Cu-Aβ. This chelator should compete with Zn²⁺ ions (Zn) that are present in the synaptic cleft while forming a nontoxic Cu complex. Herein we describe P3, a water-soluble peptidomimetic chelator that selectively removes Cu²⁺ from Cu-Aβ in the presence of Zn and prevent the formation of ROS even in a reductive environment. We demonstrate, based on extensive spectroscopic analysis, that although P3 extracts Zn from Cu,Zn-Aβ faster than it removes Cu, the formed Zn complexes are kinetic products that further dissociate, while CuP3 is formed as an exclusive stable thermodynamic product. Our unique findings, combined with the bioavailability of peptoids, make P3 an excellent drug candidate in the context of AD.

Bio-instructive materials on-demand - combinatorial chemistry of peptoids, foldamers, and beyond

Combinatorial chemistry allows for the rapid synthesis of large compound libraries for high throughput screenings in biology, medicinal chemistry, or materials science. Especially compounds from a highly modular design are interesting for the proper investigation of structure-to-activity relationships. Permutations of building blocks result in many similar but unique compounds. The influence of certain structural features on the entire structure can then be monitored and serve as a starting point for the rational design of potent molecules for various applications. Peptoids, a highly diverse class of bioinspired oligomers, suit perfectly for combinatorial chemistry. Their straightforward synthesis on a solid support using repetitive reaction steps ensures easy handling and high throughput. Applying this modular approach, peptoids are readily accessible, and their interchangeable side-chains allow for various structures. Thus, peptoids can easily be tuned in their solubility, their spatial structure, and, consequently, their applicability in various fields of research. Since their discovery, peptoids have been applied as antimicrobial agents, artificial membranes, molecular transporters, and much more. Studying their three-dimensional structure, various foldamers with fascinating, unique properties were discovered. This non-comprehensive review will state the most interesting discoveries made over the past years and arouse curiosity about what may come.

Dual Control of Peptide Conformation with Light and Metal Coordination

The design of a stimuli-responsive peptide whose conformation is controlled by wavelength-specific light and metal coordination is described. The peptide adopts a defined tertiary structure and its conformation can be modulated between an α-helical coiled coil and β-sheet. The peptide is designed with a hydrophobic interface to induce coiled coil formation and is based on a recently described strategy to obtain switchable helix dimers. Herein, we endowed the helix dimer with 8-hydroxyquinoline (HQ) groups to achieve metal coordination and shift to a β-sheet structure. It was found that the conformational shift only occurs upon introduction of Zn²⁺ ; other metal ions (Cu²⁺ , Fe³⁺ , Co²⁺ , Mg² , and Ni²⁺ ) do not offer switching likely due to non-specific metal-peptide coordination. A control peptide lacking the metal-coordinating residues does not show conformational switching with Zn²⁺ supporting the role of this metal in stabilizing the β-sheet conformation in a defined manner.

Sequence-function relationship within water-soluble Peptoid Chelators for Cu2

Chelation of Cu²⁺ by synthetic molecules is an emerging therapeutic approach for treating several illnesses in human body such as Wilson disease, cancer and more. Among synthetic metal chelators, those based on peptoids - N-substituted glycine oligomers - are advantageous due to their structural similarity to peptides, ease of synthesis on solid support and versatile controlled sequences. Tuning peptoid sequences, via systematically changing at least one side chain, can facilitate and control their function. Along these lines, this work aims to explore the role of the non-coordinating side chain within peptoid chelators in order to understand the factors that control the selectivity of these chelators to Cu²⁺ in water medium. To this aim, a set of peptoid trimers having a pyridine group at the acetylated N-terminal, a 2,2'-bipyridine group at the second position and a non-coordinating group at the C-terminus, where the latter is systematically varied between aromatic, aliphatic, chiral or non-chiral, were investigated as selective chelators for Cu²⁺. The effect of the position of the non-coordinating group on the selectivity of the peptoid to Cu²⁺ was also tested. Based on extensive spectroscopic data, we found that the choice of the non-coordinating group along with its position dramatically influences the selectivity of the peptoids to Cu²⁺. We showed that peptoids having bulky chiral groups at the C-terminus enable high selectivity to Cu²⁺. We further demonstrated the ability of one of the selective chelators to remove Cu²⁺ from the natural copper binding protein metallothionein in HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) buffer medium.