Theoretical Insight into Complexation Between Cyclocarbons and C60 Fullerene.

This work conducts the comprehensive theoretical study on the non-covalent complexation between cyclocarbons and C60 fullerene for the first time. The binding energy between cyclocarbons and C60 fullerene is significantly stronger than that between two C18 or two C60 fullerenes, indicating a particularly strong affinity. The cyclocarbons and C60 fullerene can spontaneously assemble into complexes in the gas phase at room temperature, and the hydrophobic effect caused by the solvent environment can promote this binding. The binding strength with C60 fullerene increases almost linearly with the increase of cyclocarbon size, and the C34@C60 dimer exhibits a perfect nano-Saturn structure. As the ring size increases, the angle between the two cyclocarbons of the 2:1 trimers formed by cyclocarbons and C60 fullerene gradually decreases. In C60@2C34 trimer, the fullerene is symmetrically surrounded by two cyclocarbons. The results on the trimers formed by cyclocarbon and C60 fullerenes in a 1:2 ratio showed when the cyclocarbon sandwiched between two fullerenes is not quite large, the trimers exhibit an ideal dumbbell-like structure, and the presence of the first fullerene has a significant synergistic effect on the binding of the second one. The cyclocarbon greatly promotes the dimerization of fullerenes, which acted as a "molecular glue".

Metal-Organic Framework on Fullerene (MOFOF) as a Hierarchical Composite by the Integration of Coordination Chemistry and Supramolecular Chemistry.

There is a synergy between coordination chemistry and supramolecular chemistry that has led to the development of innovative hierarchical composites with diverse functionalities. Here, we present a novel approach for the synthesis and characterization of a metal-organic framework on fullerene (MOFOF) composites, achieved through the integration of coordination chemistry and supramolecular chemistry principles. The hierarchical nature of the MOFOF harnesses the inherent properties of metal-organic frameworks and fullerenes. The two-step synthesis procedure involves controlled assembly of fullerenes as tube-like nanostructures (fullerene nanotube: FNT), their surface functionalization, and the on-surface growth of the MOF (in this case, ZIF-67). The method permits the precise tuning of morphology, effective distribution of MOF-on-FNT, and tight compositional control. The materials were comprehensively structurally characterized using electron microscopy, spectroscopic techniques, and other methods to elucidate the unique features and interactions within the MOFOF composites. The main findings reveal that the novel synthesis and characterization of MOFOF composites demonstrate the successful integration of coordination chemistry and supramolecular chemistry for the designing and fabricating of advanced hierarchical composites with tailored properties, including micro- and mesopore channels, interfacial facets, and defect sites. These properties are expected to lead to numerous potential applications such as gas storage and separation, catalysis, sensing, energy storage, and environmental remediation. However, only the capability of acid vapor sensing was tested and is described here.

Progress in Non-Fullerene Acceptors: Evolution from Small to Giant Molecules.

With the rapid development of non-fullerene acceptors (NFAs), the power conversion efficiency (PCE) of organic solar cells (OSCs) is increasing. According to their different chemical structures, NFAs can initially be divided into two categories: small molecule acceptors (SMAs) and polymerized small molecule acceptors (PSMAs). Due to the strong absorption capacity and controllable energy levels, the PCE of devices based on SMAs has approached 20%. Compared with SMAs, PSMAs have advantages in stability and flexibility, and the PCE of PSMA-based devices has exceeded 18%. However, the higher synthesis cost and lower batch repeatability hinder its further development. Recently, the concept of giant molecule acceptors (GMAs) has been proposed. These materials have a clear molecular structure and are considered novel acceptor materials that combine the advantages of SMAs and PSMAs. Currently, the PCE of devices based on GMAs has exceeded 19%. In this review, we will introduce the latest developments in SMAs, PSMAs, and GMAs. Then, the advantages of GMAs and the relationship between their structure and performance will be analyzed. In the end, perspectives on the opportunities and challenges of these materials are provided, which could inspire further development of NFAs for advanced OSCs.

C60 Fullerene Reduces the Level of Liver Damage in Chronic Alcohol Intoxication of Rats.

The liver is the main organ responsible for the metabolism of ethanol, which suffers significantly as a result of tissue damage due to oxidative stress. It is known that C60 fullerenes are able to efficiently capture and inactivate reactive oxygen species in in vivo and in vitro systems. Therefore, the purpose of this study is to determine whether water-soluble C60 fullerene reduces the level of pathological process development in the liver of rats induced by chronic alcohol intoxication for 3, 6, and 9 months, depending on the daily dose (oral administration; 0.5, 1, and 2 mg/kg) of C60 fullerene throughout the experiment. In this context, the morphology of the C60 fullerene nanoparticles in aqueous solution was studied using atomic force microscopy. Such biochemical parameters of experimental animal blood as ALT (alanine aminotransferase), AST (aspartate aminotransferase), GGT (gamma-glutamyl transferase) and ALP (alkaline phosphatase) enzyme activities, CDT (carbohydrate-deficient transferrin) level, values of pro-antioxidant balance indicators (concentrations of H2O2 (hydrogen peroxide) and GSH (reduced glutathione), activities of CAT (catalase), SOD (superoxide dismutase) and GPx (selenium-dependent glutathione peroxidase)), and pathohistological and morphometric features of liver damage were analyzed. The most significant positive change in the studied biochemical parameters (up to 29 ± 2% relative to the control), as markers of liver damage, was recorded at the combined administration of alcohol (40% ethanol in drinking water) and water-soluble C60 fullerenes in the optimal dose of 1 mg/kg, which was confirmed by small histopathological changes in the liver of rats. The obtained results prove the prospective use of C60 fullerenes as powerful antioxidants for the mitigation of pathological conditions of the liver arising under prolonged alcohol intoxication.

Exohedral Diels-Alder Reactivity of Endohedral Metallofullerene C36.

Understanding the exohedral reactivity of metallofullerenes is crucial for its application in various fields. By systematically controlling the trapped species inside the fullerene its reactivity can be tamed. In this work we report the preferential position of 3d metal atoms inside the C36 cage and their effect on exohedral reactivity in comparison with the neutral and the dianionic cage. The Diels-Alder (DA) reaction between butadiene and all non-equivalent [5-5], [6-5] and [6-6] C-C bonds on the fullerene cage was considered for the analysis, by using density functional theory at the S12g/TZ2P level including COSMO solvation model to elucidate the complete mechanistic pathways. Our results indicate that the preferential position of the metal ion is at the position close to the upper hexagon, and that the general trend in the reactivity of bonds follows the order [5-5] > [6-5] > [6-6]. Moreover, the encapsulation of metal atoms further enhances the reactivity of these bonds, by distorting the system and delocalizing the LUMOs all over the cage.

Metabolite responses of cucumber on copper toxicity in presence of fullerene C60 derivatives.

Copper (Cu) toxicity in crops is a result of excessive release of Cu into environment. Little is known about mitigation of Cu toxicity through the application of carbon-based nanomaterials including water-soluble fullerene C60 derivatives. Two derivatives of fullerene were examined: polyhydroxylated C60 (fullerenol) and arginine C60 derivative. In order to study the response of Cu-stressed plants (Cucumis sativus L.) to these nanomaterials, metabolomics analysis by gas chromatography-mass spectrometry (GC-MS) was performed. Excess Cu (15 µM) caused substantial increase in xylem sap Cu, retarded dry biomass and leaf chlorosis of hydroponically grown cucumber. In Cu-stressed leaves, metabolomes was disturbed towards suppression metabolism of nitrogen (N) compounds and activation metabolism of hexoses. Also, upregulation of some metabolites involving in antioxidant defense system, such as ascorbic acid, tocopherol and ferulic acid, was occurred in Cu-stressed leaves. Hydroponically added fullerene adducts decreased the xylem sap Cu and alleviated Cu toxicity with effectiveness has been most pronounced for arginine C60 derivative. Metabolic responses of plants subjected to high Cu with fullerene derivatives were opposite to that observed under Cu alone. Fatty acids up-regulation (linolenic acid) and antioxidant molecules (tocopherol) down-regulation might indicate that arginine C60 adduct can alleviate Cu induced oxidative stress. Although fullerenol slightly improved cucumber growth, its effect on metabolic state of Cu-stressed plants was not statistically significant. We suggest that tested fullerene C60 adducts have a potential to prevent Cu toxicity in plants through a mechanism associated with their capability to restrict xylem transport of Cu from roots to shoot, and to maintain antioxidative properties of plants.

Influence of fullerene content on the properties of polyurethane resins: A study of rheology and thermal characteristics.

The effect of different contents of fullerene on the properties of polyurethane resins (PUs), including rheology and thermal properties, was investigated. Polyurethane resins were prepared through polyaddition reactions using different isocyanate monomers such as isophorone diisocyanate (IPDI), methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), and different polyols, such as poly(oxytetramethylene) glycol (PTMG), the triol trade name FA-703, and polypropylene glycols (PPG), at an NCO/OH ratio 0.94 and a temperature of 100 °C. IR spectroscopy was used to control the polymerization of PUs through the shifting of NCO peaks. The results showed that the rheology and thermal properties of the prepared PU resins depend on the type of isocyanates and fullerene used. Based on the type of isocyanates, the PU resin prepared by MDI has the highest viscosity and thermal stability compared to the other isocyanates investigated. On the other hand, the PU resins prepared by IPDI mixed with fullerene had the highest viscosity and thermal stability. However, the initial decomposition temperature (T onset) of the PUs decreased with the addition of fullerene without affecting the maximum decomposition temperature (PDT max) of the PU resin.

Suppressed Defects by Functional Thermally Cross-Linked Fullerene for High-Efficiency Tin-Lead Perovskite Solar Cells.

Mixed tin-lead (Sn-Pb) perovskites have attracted the attention of the community due to their narrow bandgap, ideal for photovoltaic applications, especially tandem solar cells. However, the oxidation and rapid crystallization of Sn2+ and the interfacial traps hinder their development. Here, cross-linkable [6,6]-phenyl-C61-butyric styryl dendron ester (C-PCBSD) is introduced during the quenching step of perovskite thin film processing to suppress the generation of surface defects at the electron transport layer interface and improve the bulk crystallinity. The C-PCBSD has strong coordination ability with Sn2+ and Pb2+ perovskite precursors, which retards the crystallization process, suppresses the oxidation of Sn2+, and improves the perovskite bulk and surface crystallinity, yielding films with reduced nonradiative recombination and enhanced interface charge extraction. Besides, the C-PCBSD network deposited on the perovskite surface displays superior hydrophobicity and oxygen resistance. Consequently, the devices with C-PCBSD obtain PCEs of up to 23.4% and retained 97% of initial efficiency after 2000 h of storage in a N2 atmosphere.

С60 fullerene protective effect against the rat muscle soleus trauma.

Muscle trauma is one of the most common body injuries. Severe consequences of muscle trauma are ischemic injuries of the extremities. It is known that the intensification of free radical processes takes place in almost most acute diseases and conditions, including muscle trauma. C60 fullerene (C60) with powerful antioxidant properties can be considered a potential nanoagent for developing an effective therapy for skeletal muscle trauma. Here the water-soluble C60 was prepared and its structural organization has been studied by the atomic force microscopy and dynamic light scattering techniques. The selective biomechanical parameters of muscle soleus contraction and biochemical indicators of blood in rats were evaluated after intramuscular injection of C60 1 h before the muscle trauma initiation. Analysis of the force muscle response after C60 injection (1 mg kg-1 dose) showed its protective effect against ischemia and mechanical injury at the level of 30 ± 2 % and 17 ± 1 %, accordingly, relative to the pathology group. Analysis of biomechanical parameters that are responsible for correcting precise positioning confirmed the effectiveness of C60 at a level of more than 50 ± 3 % relative to the pathology group. Moreover, a decrease in the biochemical indicators of blood by about 33 ± 2 % and 10 ± 1 % in ischemia and mechanical injury, correspondingly, relative to the pathology group occurs. The results obtained demonstrate the ability of C60 to correct the functional activity of damaged skeletal muscle.

A regulatory compliant short-term oral toxicity study of soluble [60]fullerenes in rats.

Thirty-eight years after its discovery, the safety of [60]fullerene (C60), the most abundant fullerene with many potential applications, particularly in oxidative stress-related medicine, remains controversial. This is mainly due to the alleged dangers of C60 nanomaterial, which are regularly supported by some publications. While several academic studies have confirmed the safety of C60 in various experimental models, it is well known that C60 aggregates can carry toxic elements. Meanwhile, countless websites offer C60-oily solutions to consumers, without any regulatory consideration. Therefore, an officially certified toxicity study is urgently needed to avoid any public health problems. In this context, we report on the first certified short-term oral toxicity study of soluble C60, designed according to the guidelines of the Organization for Economic Cooperation and Development, with a deviation in the duration (2 weeks instead of 4 weeks) accepted by the U.S. Food and Drug Administration. The results of this study, conducted in an independent accredited European Laboratory, clearly show that C60 in soluble form (0.8 mg/ml of extra virgin olive oil), administered at the highest possible dose of 3.8 mg/kg body weight/day, did not cause any adverse effects in rats after 14 days of daily oral administration. This report should settle the debate on the acute oral toxicity of C60 and pave the way for further preclinical studies. The study is accompanied by a comprehensive report that includes documentation of the raw data.

Single-Crystal Cage Framework with High Selectivity and Reversibility in Fullerene Binding.

Host-guest chemistry, a pivotal branch of supramolecular chemistry, plays an essential role in understanding and constructing complex structures through non-covalent interactions. Organic molecular cages, characterized by their intrinsic confined cavities, can selectively bind a variety of guest molecules. Their host-guest chemistry has been well studied in the solution phase, and several attempts have been made to encode well-defined molecular architectures into solid-state polymeric materials. However, only limited studies have explored their potential in the solid state, where their lack of robustness and less ordered networks significantly hinder practical applications. Herein, we report the synthesis of a single-crystal cage framework and a systematic study of its host-guest chemistry, spanning from the solution state to the solid state. Our studies reveal that the host-guest interactions inherent to the cage are successfully maintained in the solid-state polymeric material. Furthermore, the framework's robustness allows for the guest molecules (fullerene) to be released triggered by an organic acid (trifluoracetic acid), with subsequent regeneration of the framework through an organic base (triethylamine) treatment. Our findings represent the first synthesis of a robust, single-crystal cage framework exhibiting highly selective and reversible host-guest chemistry, thus showing great potential towards molecular separation application.

Ultrafast Electron-Transfer Via Hybrid States at Perovskite/Fullerene Interface.

Interfacial charge-transfer between perovskite and charge-transport layers plays a key role in determining performance of perovskite solar cells. The conventional viewpoint emphases the necessity of favorable energy-level alignment of the two components. In recent reports, efficient electron-transfer is observed from perovskite to fullerene-based electron-transport layers even when there are unfavorable energy-level alignments, but the mechanism is still unclear. Here, using an ultrafast in situ two-photon photoelectron spectroscopy, real-time observations of electron-transfer processes at CsPbI3/C60 interface in both temporal and energetic dimensions are reported. Due to strong electronic coupling, a large amount of interfacial hybrid states is generated at the interfaces, aiding fast photoinduced electron-transfer in ≈124 fs. This process is further verified by nonadiabatic molecular dynamics simulations and transient absorption experiments. The short timescale explains why electron-transfer can overcome unfavorable energy-level alignments, providing a guideline for device design.

Silvery fullerene in Ag102 nanosaucer.

Despite the discovery of a series of fullerenes and a handful of noncarbon clusters with the typical topology of I h-C60, the smallest fullerene with a large degree of curvature, C20, and its other-element counterparts are difficult to isolate experimentally. In coinage metal nanoclusters (NCs), the first all-gold fullerene, Au32, was discovered after a long-lasting pursuit, but the isolation of similar silvery fullerene structures is still challenging. Herein, we report a flying saucer-shaped 102-nuclei silver NC (Ag102) with a silvery fullerene kernel of Ag32, which is embraced by a robust cyclic anionic passivation layer of (KPO4)10. This Ag32 kernel can be viewed as a non-centered icosahedron Ag12 encaged into a dodecahedron Ag20, forming the silvery fullerene of Ag12@Ag20. The anionic layer (KPO4)10 is located at the interlayer between the Ag32 kernel and Ag70 shell, passivating the Ag32 silvery fullerene and templating the Ag70 shell. The t BuPhS- and CF3COO- ligands on the silver shell show a regioselective arrangement with the 60 t BuPhS- ligands as expanders covering the upper and lower of the flying saucer and 10 CF3COO- as terminators neatly encircling the edges of the structure. In addition, Ag102 shows excellent photothermal conversion efficiency (η) from the visible to near-infrared region (η = 67.1% ± 0.9% at 450 nm, 60.9% ± 0.9% at 660 nm and 50.2% ± 0.5% at 808 nm), rendering it a promising material for photothermal converters and potential application in remote laser ignition. This work not only captures silver kernels with the topology of the smallest fullerene C20, but also provides a pathway for incorporating alkali metal (M) into coinage metal NCs via M-oxoanions.

Accomplishing High-Performance Organic Solar Sub-Modules (≈55 cm2) with >16% Efficiency by Controlling the Aggregation of an Engineered Non-Fullerene Acceptor.

The fabrication of environmentally benign, solvent-processed, efficient, organic photovoltaic sub-modules remains challenging due to the rapid aggregation of the current high performance non-fullerene acceptors (NFAs). In this regard, design of new NFAs capable of achieving optimal aggregation in large-area organic photovoltaic modules has not been realized. Here, an NFA named BTA-HD-Rh is synthesized with longer (hexyl-decyl) side chains that exhibit good solubility and optimal aggregation. Interestingly, integrating a minute amount of new NFA (BTA-HD-Rh) into the PM6:L8-BO system enables the improved solubility in halogen-free solvents (o-xylene:carbon disulfide (O-XY:CS2)) with controlled aggregation is found. Then solar sub-modules are fabricated at ambient condition (temperature at 25 ± 3 °C and humidity: 30-45%). Ultimately, the champion 55 cm2 sub-modules achieve exciting efficiency of >16% in O-XY:CS2 solvents, which is the highest PCE reported for sub-modules. Notably, the highest efficiency of BTA-HD-Rh doped PM6:L8-BO is very well correlated with high miscibility with low Flory-Huggins parameter (0.372), well-defined nanoscale morphology, and high charge transport. This study demonstrates that a careful choice of side chain engineering for an NFA offers fascinating features that control the overall aggregation of active layer, which results in superior sub-module performance with environmental-friendly solvents.

Chalcogen-Bond-Assisted Formation of the N→C Dative Bonds in the Complexes between Chalcogenadiazoles/Chalcogenatriazoles and Fullerene C60.

The existence of the N→C dative bonds in the complexes between N-containing molecules and fullerenes have been verified both theoretically and experimentally. However, finding stable N→C dative bonds is still a highly challenging task. In this work, we investigated computationally the N→C dative bonds in the complexes formed by fullerene C60 with 1,2,5-chalcogenadiazoles, 2,1,3-benzochalcogenadiazoles, and 1,2,4,5-chalcogenatriazoles, respectively. It was found that the N→C dative bonds are formed along with the formation of the N-Ch···C (Ch = S, Se, Te) chalcogen bonds. In the gas phase, from S-containing complexes through Se-containing complexes to Te-containing complexes, the intrinsic interaction energies become more and more negative, which indicates that the N-Ch···C chalcogen bonds can facilitate the formation of the N→C dative bonds. The intrinsic interaction energies are compensated by the large deformation energy of fullerene C60. The total interaction energies of Te-containing complexes are negative, while both total interaction energies of the S-containing complexes and Se-containing complexes are positive. This means that the N→C dative bonds in the Te-containing complexes are more easily observed in experiments in comparison with those in the S-containing complexes and Se-containing complexes. This study provides a new theoretical perspective on the experimental observation of the N→C dative bonds in complexes involving fullerenes. Further, the formation of stable N→C dative bonds in the complexes involving fullerenes can significantly change the properties of fullerenes, which will greatly simulate and expand the application range of fullerenes.

The Preparation of a Low-Cost, Structurally Simple Triboelectric Nanogenerator Based on Fullerene Carbon Soot-Doped Polydimethylsiloxane Composite Film.

Triboelectric nanogenerators (TENGs) have emerged as viable micro power sources for an array of applications. Since their inception in 2012, TENGs have been the subject of significant advancements in terms of structural design and the development of friction materials. Despite these advancements, the complexity of their structural designs and the use of costly friction materials hinder their practical application. This study introduces a simplified TENG model utilizing an economical composite film of fullerene carbon soot (FS)-doped polydimethylsiloxane (PDMS) (FS-TENG). It confirms the FS-TENG's ability to convert mechanical energy into electrical energy, as demonstrated through experimental validation. The generated electricity by the FS-TENG can power devices such as light-emitting diodes (LEDs), digital watches, kitchen timers, and sports stopwatches, highlighting its efficiency. This research enhances the development of TENGs featuring low-cost, streamlined structures for sustainable and autonomous energy sensing applications.

Two-fold addition reaction of silylene to C60: structural and electronic properties of a bis-adduct.

The addition reaction of C60 with silylene 1, a silicon analog of carbene, yielded the corresponding bis-adduct 3. The structure of 3 was determined by single-crystal X-ray structure analysis, representing the first example of a crystal structure of a silirane (silacyclopropane) derivative of fullerenes. Electrochemical measurements confirmed that the redox potentials of 3 are shifted cathodically compared to those of the parent mono-adduct 2. Density functional theory (DFT) calculations provided the basis for the electronic properties of compound 3.

Synthesis of indano[60]fullerene thioketone and its application in organic solar cells.

Evaporable indano[60]fullerene ketone (FIDO) was converted to indano[60]fullerene thioketone (FIDS) in high yield by using Lawesson's reagent. Three compounds with different substituents in para position were successfully converted to the corresponding thioketones, showing that the reaction tolerates compounds with electron-donating and electron-withdrawing substituents. Computational studies with density functional theory revealed the unique vibrations of the thioketone group in FIDS. The molecular structure of FIDS was confirmed by single-crystal X-ray analysis. Bulk heterojunction organic solar cells using three evaporable fullerene derivatives (FIDO, FIDS, C60) as electron-acceptors were compared, and the open-circuit voltage with FIDS was 0.16 V higher than that with C60.

Novel Sprayable Antioxidative Dressing Based on Fullerene and Curdlan for Accelerating Chronic Wound Healing.

The effective treatment of chronic wounds represents a critical global medical challenge demanding urgent attention. Persistent inflammation, driven by an excess of reactive oxygen radicals, sets in motion a detrimental cycle leading to chronic wounds and impeding the natural healing process. This study develops a sprayable wound dressing by covalently grafting amino fullerene to carboxymethylated curdlan (CMC-C). This novel dressing exhibits excellent biocompatibility, antioxidant, and reactive oxygen species scavenging properties. Furthermore, it demonstrates a targeted affinity for HEK-a cells, efficiently reducing the inflammatory response while promoting cell proliferation and migration in vitro. Moreover, the animal experiment investigations reveal that CMC-C significantly accelerates chronic wounds healing by regulating the inflammatory process, promoting collagen deposition, and improving vascularization. These results demonstrate the potential of the sprayable dressing (CMC-C) in curing the healing of chronic wounds through the modulation of the inflammatory microenvironment. Overall, the sprayable hydrogel dressing based on water-soluble derivative of fullerene and curdlan emerges as a potential approach for clinical applications in the treatment of chronic wounds.

Electrosynthesis of an Improbable Directly Bonded Phosphorene-Fullerene Heterodimensional Hybrid toward Boosted Photocatalytic Hydrogen Evolution.

Phosphorene and fullerene are representative two-dimensional (2D) and zero-dimensional (0D) nanomaterials respectively, constructing their heterodimensional hybrid not only complements their physiochemical properties but also extends their applications via synergistic interactions. This is however challenging because of their diversities in dimension and chemical reactivity, and theoretical studies predicted that it is improbable to directly bond C60 onto the surface of phosphorene due to their strong repulsion. Here, we develop a facile electrosynthesis method to synthesize the first phosphorene-fullerene hybrid featuring fullerene surface bonding via P-C bonds. Few-layer black phosphorus nanosheets (BPNSs) obtained from electrochemical exfoliation react with C602- dianion prepared by electroreduction of C60, fulfilling formation of the "improbable" phosphorene-fullerene hybrid (BPNS-s-C60). Theoretical results reveal that the energy barrier for formation of [BPNS-s-C60]2- intermediate is significantly decreased by 1.88 eV, followed by an oxidization reaction to generate neutral BPNS-s-C60 hybrid. Surface bonding of C60 molecules not only improves significantly the ambient stability of BPNSs, but also boosts dramatically the visible light and near-infrared (NIR) photocatalytic hydrogen evolution rates, reaching 1466 and 1039 µmol h-1 g-1 respectively, which are both the highest values among all reported BP-based metal-free photocatalysts.