Evaluation of GHK peptide-heparin interactions in multifunctional liposomal covering.

Small biospecific peptides with defined chemical structure and cellular responses are promising alternatives to full-length therapeutic proteins. Identification of these peptides solely or in combination with other bioactive factors and determination of their targets are of substantial interest in current drug delivery research. This study is aimed at the development of new liposomal formulations of ECM-derived GHK peptide known for its multiple regeneration-related activities but poorly recognized cellular targets. In situ association of membranotropic GHK derivative with unilamellar liposomes was performed to prepare GHK-modified liposomes with defined properties. According to DLS, the GHK component on the liposomal surface interacted with heparin in a specific manner compared to other polysaccharides and RGD counterpart, whereas ITC analysis of such interactions was complicated. The results provide a useful tool for screening of bio-interactions of synthetic peptide-presenting liposomes by the DLS technique. They were also employed to produce a multi-functional nanosized GHK-heparin covering for liposomes. The resulting composite liposomes possessed low size dispersity, increased anionic charge, and mechanical rigidity. The heparin component significantly promoted the accumulation of GHK-modified liposomes in 3T3 fibroblasts so that the composite liposomes exhibited the highest cell-penetrating activity. Furthermore, the latter formulation stimulated cell proliferation and strongly inhibited ROS production and GSH depletion under oxidative stress conditions. Together, the results support that cell-surface glycosaminoglycans can be involved in GHK-mediated liposomal delivery, which can be further greatly enhanced by association with heparin. The composite liposomes with GHK-heparin covering can be considered as an advanced GHK-based formulation for therapeutic and cosmeceutical applications.

Ergothioneine in a peptide: Substitution of histidine with 2-thiohistidine in bioactive peptides.

Ergothioneine (EGT) is the betaine of 2-thiohistidine (2-thioHis) and may be the last undiscovered vitamin. EGT cannot be incorporated into a peptide because the α-nitrogen is trimethylated, although this would be advantageous as an EGT-like moiety in a peptide would impart unique antioxidant and metal chelation properties. The amino acid 2-thioHis is an analogue of EGT and can be incorporated into a peptide, although there is only one reported occurrence of this in the literature. A likely reason is the harsh conditions reported for protection of the thione, with similarly harsh conditions used in order to achieve deprotection after synthesis. Here, we report a novel strategy for the incorporation of 2-thioHis into peptides in which we decided to leave the thione unprotected. This decision was based upon the reported low reactivity of EGT with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), a very electrophilic disulfide. This strategy was successful, and we report here the synthesis of 2-thioHis analogues of carnosine (ßAH), GHK-tripeptide, and HGPLGPL. Each of these peptides contain a histidine (His) residue and possesses biological activity. Our results show that substitution of His with 2-thioHis imparts strong antioxidant, radical scavenging, and copper binding properties to the peptide. Notably, we found that the 2-thioHis analogue of GHK-tripeptide was able to completely quench the hydroxyl and ABTS radicals in our assays, and its antioxidant capacity was significantly greater than would be expected based on the antioxidant capacity of free 2-thioHis. Our work makes possible greater future use of 2-thioHis in peptides.

Coassemble dopamine and GHK tripeptide into fluorescent nanoparticles for pH sensing.

Fluorescent nanostructures have been widely applied to biomedical researches and clinical diagnosis such as biolabeling/imaging/sensing and have even acted as therapy reagents. Peptide-based fluorescent nanostructures attract recent interest from biomedical researchers. Inspired by the natural existence of GHK-Cu complex with a growth factor-like effect in human blood, here we have developed a novel approach for designing nanosensors through the co-assembling of two kinds of biomolecules. By making best use of both π-π stacking between carbon rings and the easy-oxidation property of an important transmitter molecule, dopamine (DA), we successfully built up a supersensitive and robust fluorescent pH nanosensor by co-assembling oxidized DA (DAox ) with a tripeptide GHK. The GHK-DAox nanostructures have a quantum yield of 20.82%, which might be the brightest one among all the current co-assembling structures merely through unmodified biomolecules. We envision this approach could open a new avenue for not only hybrid nanostructure construction, but also may inspire the bioengineering of in vivo luminescent probes.

A classic experiment revisited: membrane permeability changes during the action potential.

The ability to understand the relationship between the reversal potential and the membrane potential is a fundamental skill that must be mastered by students studying membrane excitability. To clarify this relationship, we have reframed a classic experiment carried out by Hodgkin and Katz, where we compare graphically the membrane potential at three phases of the action potential (resting potential, action potential peak, and afterhyperpolarization) to reversal potential for K+ (EK), reversal potential for Na (ENa), and membrane potential (Em) (calculated by the Goldman Hodgkin Katz equation) to illustrate that the membrane potential approaches the reversal potential of the ion to which it is most permeable at that instant.

Regenerative and Protective Actions of the GHK-Cu Peptide in the Light of the New Gene Data.

The human peptide GHK (glycyl-l-histidyl-l-lysine) has multiple biological actions, all of which, according to our current knowledge, appear to be health positive. It stimulates blood vessel and nerve outgrowth, increases collagen, elastin, and glycosaminoglycan synthesis, as well as supports the function of dermal fibroblasts. GHK’s ability to improve tissue repair has been demonstrated for skin, lung connective tissue, boney tissue, liver, and stomach lining. GHK has also been found to possess powerful cell protective actions, such as multiple anti-cancer activities and anti-inflammatory actions, lung protection and restoration of chronic obstructive pulmonary disease (COPD) fibroblasts, suppression of molecules thought to accelerate the diseases of aging such as NFκB, anti-anxiety, anti-pain and anti-aggression activities, DNA repair, and activation of cell cleansing via the proteasome system. Recent genetic data may explain such diverse protective and healing actions of one molecule, revealing multiple biochemical pathways regulated by GHK.

Similarities and differences of copper and zinc cations binding to biologically relevant peptides studied by vibrational spectroscopies.

GHK and DAHK are biological peptides that bind both copper and zinc cations. Here we used infrared and Raman spectroscopies to study the coordination modes of both copper and zinc ions, at pH 6.8 and 8.9, correlating the data with the crystal structures that are only available for the copper-bound form. We found that Cu(II) binds to deprotonated backbone (amidate), the N-terminus and Nπ of the histidine side chain, in both GHK and DAHK, at pH 6.8 and 8.9. The data for the coordination of zinc at pH 6.8 points to two conformers including both nitrogens of a histidine residue. At pH 8.9, vibrational spectra of the ZnGHK complexes show that equilibria between monomers, oligomers exist, where deprotonated histidine residues as well as deprotonated amide nitrogen are involved in the coordination. A common feature is found: zinc cations coordinate to Nτ and/or Nπ of the His leading to the formation of GHK and DAHK multimers. In contrast, Cu(II) binds His via Nπ regardless of the peptide, in a pH-independent manner.

Glycyl-l-histidyl-l-lysine prevents copper- and zinc-induced protein aggregation and central nervous system cell death in vitro.

Common features of neurodegenerative diseases are oxidative and inflammatory imbalances as well as the misfolding of proteins. An excess of free metal ions can be pathological and contribute to cell death, but only copper and zinc strongly promote protein aggregation. Herein we demonstrate that the endogenous copper-binding tripeptide glycyl-l-histidyl-l-lysine (GHK) has the ability to bind to and reduce copper redox activity and to prevent copper- and zinc-induced cell death in vitro. In addition, GHK prevents copper- and zinc-induced bovine serum albumin aggregation and reverses aggregation through resolubilizing the protein. We further demonstrate the enhanced toxicity of copper during inflammation and the ability of GHK to attenuate this toxicity. Finally, we investigated the effects of copper on enhancing paraquat toxicity and report a protective effect of GHK. We therefore conclude that GHK has potential as a cytoprotective compound with regard to copper and zinc toxicity, with positive effects on protein solubility and aggregation that warrant further investigation in the treatment of neurodegenerative diseases.

Tripeptides Ghk and GhkCu-modified silver nanoparticles for enhanced antibacterial and wound healing activities.

Bacterial skin infections represent a major healthcare concern that can delay healing and threaten human health. Silver nanoparticles (AgNPs) have been widely used for antimicrobial purposes; however, their high toxicity limits their applications. Therefore, there is an urgent need to develop simple and efficient therapeutic approaches for treating bacterial infections and promoting wound healing. Here, novel tripeptide (Ghk and GhkCu)-modified AgNPs were developed and subsequently evaluated their antibacterial efficacy against four pathogenic bacterial isolates, cytotoxic properties, and therapeutic effects as a topical treatment for infected wounds. Spherical GhkAgNPs and GhkCuAgNPs with average sizes of 45.92 nm and 56.82 nm exhibited potential antibacterial activity, with a MIC concentration of 8 µg/ml against S. aureus and E. coli. Both AgNPs showed superior bactericidal effects against S. aureus, with complete inhibition after 7 days of treatment. Cytotoxicity assays revealed IC50 (half maximal inhibitory concentrations) values ranging from 6.75 to 6.99 µg/ml in L929 cells. GhkAgNPs displayed accelerated cell migration and facilitated healing up to 92% after 12 h. Furthermore, topical applications of GhkAgNPs and GhkCuAgNPs to S. aureus-infected wounds demonstrated enhanced in vivo wound healing efficacy compared to control groups, as evidenced by increased regenerated epidermal thickness, improved collagen deposition, and downregulation of TNF-α expression. Hence concluded that these novel tripeptides Ghk and GhkCu-modified AgNPs exhibited potent antibacterial effects and significantly promoted wound healing properties.

The glycyl-l-histidyl-l-lysine-Cu2+ tripeptide complex attenuates lung inflammation and fibrosis in silicosis by targeting peroxiredoxin 6.

Silicosis is the most common type of pneumoconiosis, having a high incidence in workers chronically exposed to crystalline silica (CS). No specific medication exists for this condition. GHK, a tripeptide naturally occurring in human blood and urine, has antioxidant effects. We aimed to investigate the therapeutic effect of GHK-Cu on silicosis and its potential underlying molecular mechanism. An experimental silicosis mouse model was established to observe the effects of GHK-Cu on lung inflammation and fibrosis. Moreover, the effects of GHK-Cu on the alveolar macrophages (AM) were examined using the RAW264.7 cell line. Its molecular target, peroxiredoxin 6 (PRDX6), has been identified, and GHK-Cu can bind to PRDX6, thus attenuating lung inflammation and fibrosis in silicosis mice without significant systemic toxicity. These effects were partly related to the inhibition of the CS-induced oxidative stress in AM induced by GHK-Cu. Thus, our results suggest that GHK-Cu acts as a potential drug by attenuating alveolar macrophage oxidative stress. This, in turn, attenuates the progression of pulmonary inflammation and fibrosis, which provides a reference for the treatment of silicosis.

Relief of ovalbumin-induced airway remodeling by the glycyl-l-histidyl-l-lysine-Cu2+ tripeptide complex via activation of SIRT1 in airway epithelial cells.

Fixed airflow limitation (FAO), prevalent in patients with severe or difficult-to-treat asthma, is mainly caused by airway remodeling. Airway remodeling is initiated by inflammation and involves subsequent pathological changes. Glycyl-l-histidyl-l-lysine (GHK) is a matrikine with anti-inflammatory and antioxidant effects, naturally existing in human tissue. At present, the GHK level in human plasma and whether it is related to airway remodeling of asthma remain unclear. This study was conducted to determine how GHK is involved in airway remodeling in asthma. Our result showed that the plasma GHK levels of patients with asthma were significantly lower than those of age-matched healthy controls. In asthma patients, plasma GHK levels display a moderate correlation with FEF25-75%, and patients with FAO had significantly lower GHK levels. Ovalbumin-induced mice of asthma model treated with PBS or GHK-Cu (a form of GHK with higher bioavailability) were used to evaluate the effect of exogenous GHK supplement on airway remodeling. GHK-Cu administration alleviated airway remodeling, as reflected by decreased peribronchial collagen deposition and airway mucus secretion, and suppressed epithelial-mesenchymal transition. The therapeutical effect related to decreased TGF-ß1 level. Successively, network pharmacology and the validation data of experiments in vivo and vitro demonstrated that GHK-Cu decreased TGF-ß1 level by increasing SIRT1 expression and activating SIRT1 deacetylation in airway epithelial cells, thereby alleviating airway remodeling. Collectively, decreased plasma GHK levels were related to FAO in asthma patients. Through the direct binding and activation of SIRT1, exogenous GHK-Cu administration alleviated airway remodeling in asthmatic mice.

GHK peptide prevents sleep-deprived learning impairment in aging mice.

Sleep deprivation is known to cause memory impairment and is associated with inflammation and cell damage linked to neurodegenerative diseases. GHK (glycyl-L-histidyl-L-lysine) is a naturally occurring tripeptide found in mammalian plasma. GHK has anti-inflammatory activity and can pass through the blood-brain barrier suggesting the potential to prevent neuroinflammation associated with sleep deprivation. In this study, mice were injected with 15 mg/kg GHK per day for five days and sleep deprived on the last two days of treatment. Sleep-deprived mice treated with GHK did not show the acute learning impairment seen in sleep-deprived mice treated with saline. GHK prevented an increase in MCP-1 and nitrotyrosine levels in the hippocampus of sleep-deprived mice suggesting that inflammatory and reactive nitrogen/oxygen species activity could be therapeutic targets for learning impairment associated with short-term sleep deprivation.

Intranasal GHK peptide enhances resilience to cognitive decline in aging mice.

Brain aging and cognitive decline are aspects of growing old. Age-related cognitive impairment entails the early stages of cognitive decline, and is extremely common, affecting millions of older people. Investigation into early cognitive decline as a treatable condition is relevant to a wide range of cognitive impairment conditions, since mild age-related neuropathology increases risk for more severe neuropathology and dementia associated with Alzheimer's Disease. Recent studies suggest that the naturally occurring peptide GHK (glycyl-L-histidyl-L-lysine) in its Cu-bound form, has the potential to treat cognitive decline associated with aging. In order to test this concept, male and female C57BL/6 mice, 20 months of age, were given intranasal GHK-Cu, 15 mg/kg daily, for two months. Results showed that mice treated with intranasal GHK-Cu had an enhanced level of cognitive performance in spatial memory and learning navigation tasks, and expressed decreased neuroinflammatory and axonal damage markers compared to mice treated with intranasal saline. These observations suggest that GHK-Cu can enhance resilience to brain aging, and has translational implications for further testing in both preclinical and clinical studies using an atomizer device for intranasal delivery.

Behavioral and neuropathological features of Alzheimer's disease are attenuated in 5xFAD mice treated with intranasal GHK peptide.

Efforts to find disease modifying treatments for Alzheimer's disease (AD) have met with limited success in part because the focus has been on testing drugs that target a specific pathogenic mechanism. Multiple pathways have been implicated in the pathogenesis of AD. Hence, the probability of more effective treatment for AD is likely increased by using an intervention that targets more than one pathway. The naturally occurring peptide GHK (glycyl-L-histidyl-L-lysine), as a GHK-Cu complex, supports angiogenesis, remodeling, and tissue repair, has anti-inflammatory and antioxidant properties, and has been shown to improve cognitive performance in aging mice. In order to test GHK-Cu as a neurotherapeutic for AD, male and female 5xFAD transgenic mice on the C57BL/6 background at 4 months of age were given 15 mg/kg GHK-Cu intranasally 3 times per week for 3 months until 7 months of age. Results showed that intranasal GHK-Cu treatment delayed cognitive impairment, reduced amyloid plaques, and lowered inflammation levels in the frontal cortex and hippocampus. These observations suggest additional studies are warranted to investigate the potential of GHK-Cu peptide as a promising treatment for AD.

In situ photo-crosslinkable hyaluronic acid-based hydrogel embedded with GHK peptide nanofibers for bioactive wound healing.

A versatile hydrogel was developed for enhancing bioactive wound healing by introducing the amphiphilic GHK peptide (GHK-C16) into a photo-crosslinkable tyramine-modified hyaluronic acid (HA-Ty). GHK-C16 self-assembled into GHK nanofibers (GHK NF) in HA-Ty solution, which underwent in situ gelation after the wound area was filled with precursor solution. Blue light irradiation (460-490 nm), with riboflavin phosphate as a photoinitiator, was used to trigger crosslinking, which enhanced the stability of the highly degradable hyaluronic acid and enabled sustained release of the nanostructured GHK derivatives. The hydrogels provided a microenvironment that promoted the proliferation of dermal fibroblasts and the activation of cytokines, leading to reduced inflammation and increased collagen expression during wound healing. The complexation of Cu2+ into GHK nanofibers resulted in superior wound healing capabilities compared with non-lipidated GHK peptide with a comparable level of growth factor (EGF). Additionally, nanostructured Cu-GHK improved angiogenesis through vascular endothelial growth factor (VEGF) activation, which exerted a synergistic therapeutic effect. Furthermore, in vivo wound healing experiments revealed that the Cu-GHK NF/HA-Ty hydrogel accelerated wound healing through densely packed remodeled collagen in the dermis and promoting the growth of denser fibroblasts. HA-Ty hydrogels incorporating GHK NF also possessed improved mechanical properties and a faster wound healing rate, making them suitable for advanced bioactive wound healing applications. STATEMENT OF SIGNIFICANCE: By combining photo-crosslinkable tyramine-modified hyaluronic acid with self-assembled Cu-GHK-C16 peptide nanofibers (Cu-GHK NF), the Cu-GHK NF/HA-Ty hydrogel offers remarkable advantages over conventional non-structured Cu-GHK for wound healing. It enhances cell proliferation, migration, and collagen remodeling-critical factors in tissue regeneration. The incorporation of GHK nanofibers complexed with copper ions imparts potent anti-inflammatory effects, promoting cytokine activation and angiogenesis during wound healing. The Cu-GHK NF/hydrogel's unique properties, including in situ photo-crosslinking, ensure high customization and potency in tissue regeneration, providing a cost-effective alternative to growth factors. In vivo experiments further validate its efficacy, demonstrating significant wound closure, collagen remodeling, and increased fibroblast density. Overall, the Cu-GHK NF/HA-Ty hydrogel represents an advanced therapeutic option for wound healing applications.

Glycyl-L-histidyl-L-lysine-Cu2+ attenuates cigarette smoke-induced pulmonary emphysema and inflammation by reducing oxidative stress pathway.

Background: Chronic obstructive pulmonary disease (COPD) is a common respiratory disorder manifested as chronic airway inflammation and persistent airflow limitation with the essential mechanism as inflammatory response and oxidative stress induced by toxic exposures such as cigarette smoke (CS). Glycyl-L-histidyl-L-lysine (GHK) is a nontoxic tripeptide involved in the process of healing and regeneration as a natural product. With the combination of Cu(II), glycyl-L-histidyl-L-lysine-Cu2+ (GHK-Cu) improves antioxidative and anti-inflammatory bioavailability, and they might offer potential therapeutic properties for COPD. Thus, the present study aimed to identify the potential effects of GHK-Cu on emphysema induced by cigarette smoke. Methods: In the in vivo experiment, C57BL/6J mice were exposed to CS for 12 weeks to induce pulmonary emphysema. GHK-Cu was injected intraperitoneally at doses of 0.2, 2 and 20 µg/g/day in 100 µl of saline on alternative days from the 1st day after CS exposure. The effects of GHK-Cu on the morphology of CS-induced emphysema, the inflammatory response and oxidative stress were evaluated. The antioxidative effect of GHK-Cu on human alveolar epithelial A549 cells was assessed in vitro. Results: GHK-Cu treatment attenuated the CS-induced emphysematous changes and partially reversed the matrix metalloprotein -9 (MMP-9)/tissue inhibitor of metalloproteinases-1 (TIMP-1) imbalance in the lung tissue. GHK-Cu reduced the inflammation and oxidation by decreasing the expression of inflammatory cytokines (IL-1ß and TNF-α) in the bronchoalveolar lavage and the enzymatic activity of MPO and MDA in the lung homogenate while restoring the T-AOC and GSH content. Furthermore, administration of GHK-Cu reversed the increase in NF-κB expression induced by CS and increased the Nrf2 level, as an antioxidant defense component, in mice with chronic CS exposure. In CSE-exposed human alveolar epithelial A549 cells, GHK-Cu also inhibited oxidative stress by suppressing MDA levels and restoring T-AOC and GSH levels, which were modulated by upregulating Nrf2 expression. Conclusion: GHK-Cu treatment attenuated CS-induced emphysema by anti-inflammation by downregulating NF-κB and antioxidation via upregulation of the Nrf2/Keap1 in lung tissues.

cellmlmanip and chaste_codegen: automatic CellML to C++ code generation with fixes for singularities and automatically generated Jacobians.

Hundreds of different mathematical models have been proposed for describing electrophysiology of various cell types. These models are quite complex (nonlinear systems of typically tens of ODEs and sometimes hundreds of parameters) and software packages such as the Cancer, Heart and Soft Tissue Environment (Chaste) C++ library have been designed to run simulations with these models in isolation or coupled to form a tissue simulation. The complexity of many of these models makes sharing and translating them to new simulation environments difficult. CellML is an XML format that offers a widely-adopted solution to this problem. This paper specifically describes the capabilities of two new Python tools: the cellmlmanip library for reading and manipulating CellML models; and chaste_codegen, a CellML to C++ converter. These tools provide a Python 3 replacement for a previous Python 2 tool (called PyCML) and they also provide additional new features that this paper describes. Most notably, they can generate analytic Jacobians without the use of proprietary software, and also find singularities occurring in equations and automatically generate and apply linear approximations to prevent numerical problems at these points.

[Antibacterial mechanism of Brevinin-2GHk, an antimicrobial peptide from Fejervarya limnocharis skin].

OBJECTIVE: To investigate the secondary structure, physicochemical properties and antibacterial activity of Brevinin- 2GHk (BR2GK), an antimicrobial peptide from frog skin, and explore its antibacterial mechanism. METHODS: BR2GK was synthesized, purified with high performance liquid chromatography (HPLC) and identified using mass spectrometry. Circular dichroism was used to determine the secondary structure and physicochemical properties of BR2GK. Two-fold dilution method was used to determine the antibacterial activity of BR2GK, and its antibacterial mechanism was explored using laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). The hemolytic activity of BR2GK was analyzed in red blood cells. Isothermal titration calorimetry (ITC) and surface plasmon resonance imaging (SPRi) were employed to detect the binding of BR2GK to lipopolysaccharide (LPS), and the antioxidant activity of BR2GK was evaluated using biochemical kits. RESULTS: The synthesized BR2GK, with a purity exceeding 95% after purification, had the basic characteristics of cationic antimicrobial peptides. BR2GK consisted mainly of α-helical structure in SDS solution and exhibited a broad-spectrum antibacterial activity. Antibacterial activity assay showed that BR2GK had inhibitory and killing activity against a variety of strains with a minimum inhibitory concentration (MIC) of 2.76 µmol/L against Staphylococcus aureus. Observation with LSCM and SEM showed that BR2GK at an active concentration caused bacterial cell membrane damage, cell swelling, contraction, deformation, and massive exudation of intracellular contents without causing hemolysis. ITC showed that the binding affinity KD of BR2GK to LPS was 18.2±0.8 µmol/L. The antioxidant test showed that BR2GK was capable of effectively scavenging NO, ABTS and DPPH. CONCLUSION: BR2GK, as a broad-spectrum antibacterial peptide with also a strong antioxidant capacity, does not cause hemolysis and is capable of binding to LPS. BR2GK has an important value for future design and synthesis of antimicrobial peptides with stronger antibacterial activity and lower cytotoxicity.

Enhanced angiogenic effects of RGD, GHK peptides and copper (II) compositions in synthetic cryogel ECM model.

Synthetic oligopeptides are a promising alternative to natural full-length growth factors and extracellular matrix (ECM) proteins in tissue regeneration and therapeutic angiogenesis applications. In this work, angiogenic properties of dual and triple compositions containing RGD, GHK peptides and copper (II) ions (Cu2+) were for the first time studied. To reveal specific in vitro effects of these compositions in three-dimensional scaffold, adamantyl group bearing peptides, namely Ada-Ahx-GGRGD (1) and Ada-Ahx-GGGHK (2), were effectively immobilized in bioinert pHEMA macroporous cryogel via host-guest ß-cyclodextrin-adamantane interaction. The cryogels were additionally functionalized with Cu2+ via the formation of GHK-Cu complex. Angiogenic responses of HUVECs grown within the cryogel ECM model were analyzed. The results demonstrate that the combination of RGD with GHK and further with Cu2+ dramatically increases cell proliferation, differentiation, and production of a series of angiogenesis related cytokines and growth factors. Furthermore, the level of glutathione, a key cellular antioxidant and redox regulator, was altered in relation to the angiogenic effects. These results are of particular interest for establishing the role of multiple peptide signals on regeneration related processes and for developing improved tissue engineering materials.

Efficient Ternary Polymer Solar Cells with Tunable Crystallinity and Phase Separation of Active Layers via Incorporating GHK-Cu.

The crystallinity of a nonfullerene small-molecule acceptor plays an important function in the bimolecular recombination and carrier transfer of polymer solar cells (PSCs). However, because of the competition between the donor (PBDB-T) and acceptor (ITIC) in processes of phase separation and crystallization, the PBDB-T preferentially forms a crystalline network, which limits the molecular diffusion of ITIC and leads to the weak crystallinity of ITIC, eventually restricting the photoelectric conversion efficiency (PCE) of PSCs. Therefore, in our work, a small-molecule biomaterial, Gly-His-Lys-Cu (SMBM GHK-Cu), is incorporated into binary PBDB-T:ITIC to construct a PBDB-T:ITIC:GHK-Cu ternary system. The addition of GHK-Cu increases ITIC crystallinity and promotes the formation in continuous single-phase domains of PBDB-T and ITIC, which creates an optimized bicontinuous network path to increase and balance charge transmission in PSCs. Meanwhile, GHK-Cu makes energy transfer from GHK-Cu to PBDB-T appreciably efficient, improving the photon capture and exciton-generation rate of PBDB-T. Moreover, it can form a complementary absorption spectrum with PBDB-T and ITIC, which enhances the PCE of ternary devices. Excitingly, the PCE of PSC-based PBDB-T:ITIC is enhanced from 10.28% to 12.07% via incorporating 0.1 wt % GHK-Cu into PBDB-T:ITIC, in which the enhanced open voltage (VOC) is 0.92 V, the short-circuit current (JSC) is 17.87 mA/cm2, and the fill factor (FF) is 73.4%. Meanwhile, the PCE of PSC-based PM6:Y6 is also enhanced from 15.21% for a binary PSC to 17.11% for ternary PSC-based PM6:Y6:0.1 wt % GHK-Cu. This work shows that the cheap and environmentally friendly GHK-Cu has great potential for application in tuning the crystallinity and phase separation of the active layer.

The copper(II)-binding tripeptide GHK, a valuable crystallization and phasing tag for macromolecular crystallography.

The growth of diffraction-quality crystals and experimental phasing remain two of the main bottlenecks in protein crystallography. Here, the high-affinity copper(II)-binding tripeptide GHK was fused to the N-terminus of a GFP variant and an MBP-FG peptide fusion. The GHK tag promoted crystallization, with various residues (His, Asp, His/Pro) from symmetry molecules completing the copper(II) square-pyramidal coordination sphere. Rapid structure determination by copper SAD phasing could be achieved, even at a very low Bijvoet ratio or after significant radiation damage. When collecting highly redundant data at a wavelength close to the copper absorption edge, residual S-atom positions could also be located in log-likelihood-gradient maps and used to improve the phases. The GHK copper SAD method provides a convenient way of both crystallizing and phasing macromolecular structures, and will complement the current trend towards native sulfur SAD and MR-SAD phasing.