Glycol Molecules Research Articles

Pharmacokinetics, excretion, distribution, and metabolism of 60-kDa polyethylene glycol used in BAY 94-9027 in rats and its value for human prediction

The covalent binding of proteins with polyethylene glycol (PEG) molecules is a valuable tool to extend the half-life of many biotherapeutics, including factor VIII (FVIII) products to treat patients with haemophilia A. Although PEG has low toxicity, accumulation of large PEG molecules (>20–30 kDa) with long-term exposure is a potential concern. Thus, it is important to determine whether sufficient excretion processes exist for PEG molecules used in biotherapeutics. BAY 94-9027 is an extended–half-life FVIII product modified through addition of a 60-kDa (branched: dual 30-kDa) PEG molecule. BAY 1025662 is the 60-kDa PEG moiety used for PEGylation of BAY 94-9027. This study investigated the pharmacokinetic (PK) properties, distribution, and excretion of BAY 1025662 in rats in order to predict estimated 60-kDa PEG PK properties in patients. Plasma concentrations in male rats after a single 11-mg/kg intravenous dose of BAY 1025662 (approximating the cumulative PEG-60 exposure in patients during 30 years of BAY 94-9027 treatment) decreased with an initial half-life of 119 h (5 days) in the interval of 114–336 h post administration. Single-dose mass balance studies using radiolabeled BAY 1025662 ([prop-14C]BAY 1025662) showed that 30.4% of radioactivity was excreted within 1 week and 79.1% by Day 168 (primarily in urine). The terminal half-life of radioactivity elimination was approximately 24 days in blood and plasma and was 31–68 days in the majority of other organs up to Day 168. Elimination was nearly complete at the end of the experiment on Day 168; only ~4% of residual radioactivity was present in the animal body. There was no irreversible binding of radioactivity to any tissues and no penetration of the blood-brain barrier. Based on these results, very low steady-state concentrations of 60-kDa PEG were predicted in patients treated with BAY 94-9027, and the validity of these predictions was supported by clinical studies in which almost all 179 patients receiving BAY 94-9027 for prophylaxis had undetectable PEG in plasma for up to >5 years; those with detectable PEG levels demonstrated concentrations within the predicted range. These combined preclinical and clinical observations suggest that excretion processes are in place for high-molecular-weight PEGs such as the PEG-60 moiety used in BAY 94-9027.

INTERFERONS AND EYE DISEASES

The review contains an analysis of the medical use of interferons – a group of signaling protein molecules that have antiviral, antitumor, and immunomodulatory activity – in ophthalmic practice. Interferons have a wide spectrum of action, including antiviral, immunomodulatory, antitumor and other types of activity. This provides a great potential for interferon use in ophthalmology, both in combination and as a first-line therapy for conjunctival papillomatosis, squamous cell neoplasia, conjunctival melanoma, keratitis caused by the herpes simplex virus, uveitis, geographical choriopathy, cystic and diabetic macular edemas, etc. There are considered mechanism of action, dosing regimens, side effects of using interferons and such their solutions as use of newly discovered interferon lambda and interferon pegylation. In contrast to the ubiquitous expression of the IFN-α receptor, IFN-λ receptor is determined mainly in the epithelial cells of the mucous membranes and skin keratinocytes, which provides a more targeted effect of the drugs. Modifying the properties of biologically active substances by combining them with low molecular weight carriers, for example, polyethylene glycol molecules (PEG), leads to a decrease in the therapeutic dose of the drug and an increase in the selectivity of its action due to changes in pharmacokinetic and pharmacodynamic parameters.

Mathematical modeling of direct ethylene glycol fuel cells incorporating the effect of the competitive adsorption

In this work, a one-dimensional mathematical model for a direct ethylene glycol fuel cell using hydrogen peroxide as oxidant is developed. This model considers the ethylene glycol crossover and the competitive adsorption between ethylene glycol molecules and hydroxyl ions at reaction sites, in addition to mass/charge transport and electrochemical reactions. In addition, the complicated co-existence of the hydrogen peroxide reduction reaction, the hydrogen peroxide oxidation reaction, and the oxygen reduction reaction in the cathode is also considered in this model. The mathematical model under the consideration of the above-mentioned physicochemical processes exhibits a good agreement with experimental results. In addition, the effects of various operating and electrode structural parameters on the cell performance are examined, including concentrations of various species, the exchange current densities and the thicknesses of diffusion layer. The numerical results exhibit that the cell performance improves with the increasing concentrations of hydrogen peroxide and sulfuric acid. As for the ethylene glycol and hydroxyl ions, increasing the concentrations makes contribution to higher performance, while the cell performance experiences a degradation at a high current density region due to the remarkable ohmic loss. The model also shows that increasing both the anode and cathode exchange current densities leads to an improved cell performance, which indicates the significance of developing novel catalyst with superior catalytic activity. Moreover, the effect of the structural design parameters of the anode and cathode diffusion layer is also investigated, and the results show that increasing thickness of diffusion layers has a negative effect on the cell performance.

Non-Toxic Ternary Quantum Dots AgInS2 and AgInS2/ZnS: Synthesis and Optical Properties

Colloidal ternary quantum dots of AgInS2 and AgInS2/ZnS were synthesized in water in the presence of mercapto alkyl carboxylic acid. Selective size separation of AIS and AIS/ZnS hydrophilic nanoparticles was performed as well as the ligand exchange by thiolated methoxypolyethylene glycol molecules having an amphiphilic nature. The influence of nanocrystal size, composition and surface molecules on the optical properties of QDs was studied.

Improvement in the Predicted Partitioning of Alcohol and Polyethylene Oxide Groups Between Water and Octanol (logP) in Molecular Dynamics Simulations

Molecular dynamics simulations can be applied to explore the complex liquid phase behavior of lipid-based formulations and the gastrointestinal tract lumen. In order for the results from these simulations to be of value, the manner in which molecules interact with both aqueous and oil phases present needs to be as correct as possible. An existing molecular dynamics force field, GROMOS 53a6, was demonstrated to poorly reproduce the partitioning of straight-chain alcohol and short-chain polyethylene glycol (PEG) molecules between octanol and water phase (logP), with the molecules too hydrophobic. Force field parameters for Lennard-Jones interactions between CH2 and CH3 with water oxygen were adjusted to reproduce the experimental octanol logP, with all other Lennard-Jones and force field parameters left untouched. This parameter set, called 53a6DBW, was subsequently used to recalculate straight-chain alcohol and short-chain PEG molecules, with significant improvement in the values obtained. Simulations of a nonionic surfactant in water, octaethylene glycol monocaprylate, were also performed to observe the aggregation behavior. 53a6DBW demonstrated significant improvements in water interactions with the PEG chains, well hydrating the PEG groups, and allowing the formation of micelles. Further improvements and evaluation of the improved parameter set are ongoing.

Microscopic picture of water-ethylene glycol interaction near a model DNA by computer simulation: Concentration dependence, structure, and localized thermodynamics.

It is known that crowded molecular environment affects the structure, thermodynamics, and dynamics of macromolecules. Most of the previous works on molecular crowding have majorly focused on the behavior of the macromolecule with less emphasis on the behavior of the crowder and water molecules. In the current study, we have precisely focused on the behavior of the crowder, (ethylene glycol (EG)), salt ions, and water in the presence of a DNA with the increase of the EG concentration. We have probed the behavior of water and crowder using molecular dynamics (MD) simulation and by calculating localized thermodynamic properties. Our results show an interesting competition between EG and water molecules to make hydrogen bonds (H-bond) with DNA. Although the total number of H-bonds involving DNA with both EG and water remains essentially same irrespective of the increase in EG concentration, there is a proportional change in the H-bonding pattern between water-water, EG-EG, and EG-water near DNA and in bulk. At low concentrations of EG, the displacement of water molecules near DNA is relatively easy. However, the displacement of water becomes more difficult as the concentration of EG increases. The density of Na+ (Cl-) near DNA increases (decreases) as the concentration of EG is increased. The density of Cl- near Na+ increases with the increase in EG concentration. It was also found that the average free energy per water in the first solvation shell increases with the increase in EG concentration. Putting all these together, a microscopic picture of EG, water, salt interaction in the presence of DNA, as a function of EG concentration, has emerged.

Colloidal Stability of Aqueous Suspensions of Polymer-Coated Iron Oxide Nanorods: Implications for Biomedical Applications

Iron oxide nanorods are considered to be very promising platforms for biomedical applications, such as magnetic hyperthermia, magnetic resonance imaging, or immunoassays based on magnetooptical effects. However, their efficient colloidal stabilization is challenging, and colloidal aggregation could lead to the total loss of their performance. This work is focused on the synthesis and colloidal stabilization of iron oxide nanorods of an average length and diameter, L × d = 31 × 6 nm, synthesized by the hydrolysis of iron(III) salt, followed by reduction of the obtained akaganeite to iron oxide in a microwave reactor. Synthesized nanorods exhibited a weak ferrimagnetic behavior with remnant magnetization MR ∼ 3 emu/g and saturation magnetization MS ∼ 13 emu/g. The nanorods were dispersed in water after adsorption on their surface of three different polymers: linear bisphosphonate–poly(ethylene glycol) (PEG) molecules (denoted as OPT), polymethacrylate backbone/PEG side chains comb polymer (denoted as PCP; w...

Ethylene glycol solution-induced DNA conformational transitions**Project supported by the National Natural Science Foundation of China (Grant Nos. 11635003, 11025524, and 11161130520), the National Basic Research Program of China (Grant No. 2010CB832903), and the European Commissions 7th Framework Programme (FP7-PEOPLE-2010-IRSES) (Grant No. 269131).

We study the properties of the ethylene glycol solutions and the conformational transitions of DNA segment in the ethylene glycol solutions by molecular dynamics simulations based on GROMACS. The hydrogen network structures of water–water and ethylene glycol–water are reinforced by ethylene glycol molecules when the concentrations of the solutions increase from 0% to 80%. As illustrated by the results, conformation of the double-stranded DNA in ethylene glycol solutions, although more compact, is similar to the structure of DNA in the aqueous solutions. In contrast, the DNA structure is an A–B hybrid state in the ethanol/water mixed solution. A fraying of terminal base-pairs is observed for the terminal cytosine. The ethylene glycol molecules preferentially form a ring structure around the phosphate groups to influence DNA conformation by hydrogen interactions, while water molecules tend to reside in the grooves. The repulsion between the negatively charged phosphate groups is screened by ethylene glycol molecules, preventing the repulsion from unwinding and extending the helix and thus making the conformation of DNA more compact.

Highly Efficient Copper Sulfide-Based Near-Infrared Photothermal Agents: Exploring the Limits of Macroscopic Heat Conversion.

Among the foreseeable therapeutic approaches at the cellular level, nanoplatform-driven photothermal therapy is a thriving tool for the selective eradication of malignant tissues with minimal side effects to healthy ones. Hence, chemically versatile, near-infrared absorbing plasmonic nanoparticles are distinctly appealing and most sought after as efficient photothermal agents. In this work, a straightforward method to synthesize monodisperse PEGylated copper sulfide nanoparticles of pure covellite (CuS) phase, featuring strong localized surface plasmonic resonance absorption in the near-infrared and flexible surface chemistry, imparted by monomethyl ether polyethylene glycol molecules, is developed and optimized. These nanoparticles show a remarkable photothermal heat conversion efficiency (HCE) of 71.4%, which is among the highest for CuS systems and rivals that of plasmonic noble metal nanostructures. Moreover, through critical evaluation and mathematical modeling of the material's properties and measurement methodology, it is assessed that the calculated HCE values drastically depend on experimental conditions such as wavelength-dependent solvent absorption properties, sol concentration, and optical path. These findings are of paramount relevance to the photothermal community, since they call for a standardization of the procedure for the evaluation of the HCE of proposed photothermal agents, in order to make the reported values universally and reliably comparable.

PEGylated Gold Nanoparticles with Interesting Plasmonic Properties Synthesized Using an Original, Rapid, and Easy-to-Implement Procedure

In this letter, we report a new, one-step, rapid, and easy-to-implement method for the synthesis of PEGylated gold nanoparticles (PEG-AuNPs) having a narrow size distribution and very interesting plasmonic properties. Unmodified polyethylene glycol molecules with a molecular weight of 1000 g/mole (PEG1000) have been employed as reducing and capping agents for the synthesis of spherical gold nanoparticles having an average diameter of 35 nm, within a few minutes. The novelty of the herein proposed synthesis method consists in the fact that the synthesis takes place inside of a sealed bottle flask containing aqueous solutions of PEG1000, tetrachloroauric(III) acid (HAuCl4), and NaOH, placed in the center of a microwave oven, capable to provide a very uniform temperature environment. It turned out that, during the very short synthesis procedure (2 minutes), PEG 1000 suffers an oxidative transformation in such a manner that its terminal alcohol groups (-CH2-OH) are transformed in carboxylate ones (-COO−). The as-synthesized PEG-AuNPs possess very interesting plasmonic properties allowing the detection of different molecules by means of SER spectroscopy performed either in liquid droplets or on solid spots. As a consequence of their unique plasmonic properties, the SER spectra acquired using this new class of nanoparticles on different molecules of interest (methylene blue, rhodamine 6G, doxorubicin, and 5-fluorouracil) are highly reproducible, making them ideal candidates for further use as SERS substrates.

Design of Robust Thermal and Anion Dual-Responsive Membranes with Switchable Response Temperature

In this study, poly(ionic liquids/ N-isopropylacrylamide) (PIL/NIPAM) modified poly(ether sulfone) microporous membranes were prepared using a pore-filling method. Due to the anion-sensitive wettability of the PIL and the thermal-sensitive phase transformation of PNIPAM, the permeability of the modified membranes showed robust anion and thermal dual-responsive behaviors. In addition, the response temperature of the membranes could be adjusted precisely from 30 to 55 °C by anion exchange, which was attributed to the cooperative interaction of the PIL and PNIPAM. The switchable response temperature and the dual-responsive performances of the membranes were demonstrated by measuring the water fluxes under various conditions. The results indicated that the membrane permeabilities increased when exchanging the counteranions (CAs) from hydrophilic to hydrophobic ones; the thermal response behaviors were also obvious, and the sensitivity increased when increasing the hydrophobicity of the CA (the fluxes could be adjusted from 0 to 3800 mL/m2 mmHgh by controlling the temperature and CAs). At last, filtration tests were designed with the membranes, and the results indicated that by controlling the temperature and/or CA species, three different poly(ethylene glycol) molecules could be easily separated according to their molecule sizes in a single step.

Fast-Response Flexible Photochromic Gels for Self-Erasing Rewritable Media and Colorimetric Oxygen Indicator Applications

Photoreversible color switching that can change colors with fast response and high stability is urgently desired in color-on-demand applications. Yet, developing such materials has long been a significant challenge. In this work, a strategy based on the integration of TiO2 nanoparticle (NP) photocatalytic color switching of redox dyes and poly(vinyl alcohol) gel matrix could produce robust and flexible photochromic gels (FPGs) that exhibit fast light-responsive time and high photoreversible stability. Benefited by the soft network structures and monomeric form of redox dyes in the FPG maintained by poly(vinyl alcohol) and ethylene glycol molecules, as well as enhanced photoreductive activity of TiO2 NPs modified by both surface ligands and oxygen vacancies, the FPG exhibits long photoreversible switching cycles (≥50 times), decoloration in a short period of less than 8 s upon UV illumination, and recoloration in 16 min in ambient air and rapidly in 140 s upon near-infrared light illumination. Consequently, the excellent photoreversible color switching of the FPGs is highly applicable as both self-erasing rewritable media and colorimetric oxygen indicators. We believe that the current systems represent a big step forward toward practical applications, such as time-sensitive information storage, colorimetric oxygen sensor, and potentially many other technologies.

Multi-Layer Filters: Adsorption and Filtration Mechanisms for Improved Separation.

Filters made of cellulose fiber and perlite particles were prepared using a wet laying papermaking technique. Polyamide-amine-epichlorohydrin (PAE) was added to provide wet strength. Filters were prepared at two different total basis weights of 200 and 400 grams per square meter (gsm). Single and multi-layered filters were structured for each total basis weights. The effect of total basis weights and multi-layered structure on methylene blue adsorption and silicon dioxide (SiO2) particle filtration was investigated. Methylene blue adsorption was performed in two modes: constant pressure and constant flow rate. In both operation modes, the adsorption capacity of multi-layered filters was significantly higher (16–100%) than for single-layer filters at the same overall weight. The effect of layer separation was also characterized using polypropylene separators and tested under constant flow rate operation. Separators provided more effective methylene blue adsorption by generating a well-distributed flow. Filtration performance was quantified with 0.5 μm silicon dioxide particles under constant pressure conditions; this is to mimic bacteria rejection. Filtration capability of SiO2 particles was reduced slightly (12%) with decreasing individual filter layer thickness regardless of the multi-layered structure. Filtering polyethylene glycol (PEG) molecules with two different molecular weights was performed; however, no rejection was recorded. The filter internal pore structure was visualized by 3D-X ray computed tomography and the void fraction was quantified. 400 gsm single layer presented areas of low fiber density forming pores, while the pore volume decreased for thinner filter layers.

Understanding the role of ethylene glycol in a remarkable catalyst-free Strecker reaction of a-CF3 ketoimine: A theoretical study

Density functional theory (DFT) calculations have been performed to understand the role of Ethylene Glycol (EG) in a remarkable catalyst-free Strecker reaction of α-CF3 ketoimine. The fluorine hydrogen bonds involved in titled reaction have been studied. To find the suitable calculation methods for the weak CF⋯H interaction, we chose seventeen density functionals and MP2 method for calculation of the structures of three typical CF⋯H hydrogen-bonded systems. Their structures were computed and compared with the available experimental data. The results show that the M05-2X and M06-2X functionals are better than the other methods. Based on these facts, the interactions between the α-CF3 ketoimine and EG were investigated at the M06-2X/6-31G(d,p) level. And the results indicate the presence of strong CF⋯HO hydrogen bond in the complexes between α-CF3 ketoimine and solvent EG. Moreover, we also studied the reaction mechanism of the titled reaction with or without the assistance of EG at the M06-2X/6-31G(d,p) level. The results show that the two possible pathways without the aid of EG have very high free energy barriers and the reaction can't proceed, which is consistent with the experiment fact. However, with the assistance of EG, the reaction activation free energy barrier can decrease greatly. For the two-EGs model with two EG molecules, the reaction free energy barrier decreases from 47.5 kcal mol−1 to 24.7 kcal mol−1. The two EGs play an important role to stabilize the transition state and decrease the activation barrier greatly. The present theoretical calculations imply the role of solvent EG in the titled interesting catalyst-free Strecker reaction of α-CF3 ketoimine. Our theoretical calculations provide a satisfactory explanation for the experiment.

Effect of PEI surface modification with PEG on cytotoxicity and transfection efficiency

Polyethylenimine (PEI) is a cationic polymer with high transfection efficiency as non-viral gene delivery agent that exhibits promising features for gene therapy applications due to its cationic charge and thus favourable DNA-condensing abilities; however, its high cytotoxicity restricts its application. The cellular toxicity of PEI molecules depends on their structure, molecular weight and surface charge density. To improve the properties of branched 25 kDa PEI as a non-viral gene delivery agent, this polymer was conjugated to polyethylene glycol (PEG) molecules at three different molar ratios of 10, 20 and 30. The degree of PEG grafting was determined by 2, 4, 6-trinitrobenzene sulphonic acid assay. The effects of various PEGylation degrees on cellular toxicity and transfection ability of PEI polymer were assessed on BT-474 and MCF-10A cell lines. Compared to unmodified PEI, PEG-grafted PEI copolymers demonstrated reduced cytotoxicity, particularly at higher PEG grafting ratios. Among different PEG-grafted PEIs, the PEG-PEI copolymer which grafted to PEG at a molar ratio of 10:1 had the highest transfection efficiency in both cell lines. The findings of this Letter showed that these PEG-grafted PEI copolymers have desirable gene transfection efficiency and favourable biocompatibility for gene delivery.

Fluorescence techniques can reveal cell wall organization and predict saccharification in pretreated wood biomass

The conversion of cell wall biomass to sugar for fermentation to ethanol requires chemical or physical pretreatments to disrupt the recalcitrant plant cell walls and to make the cellulose accessible to cellulolytic enzymes. Multiscale study of biomass deconstruction gives access to key insights into the cell wall and lignin changes induced by pretreatment. Few studies have compared the effect of pretreatment of different biomass species on the cell wall accessibility.Considering representative softwood (pine) and hardwood (poplar) biomass, we studied the impact of two pretreatments on enzymatic saccharification and cell wall structure and accessibility. Lignin fluorescence properties were investigated by measuring fluorescence lifetime in addition to chemical analysis, and the accessibility of biomass was assessed using fluorescent probes consisting of rhodamine labeled polyethylene glycol (PEG) molecules ranging from 10 to 40 kDa. Hot water treatment and chlorite delignification altered chemical structure and fluorescence lifetime, which was positively correlated with glucose conversion and negatively correlated with lignin and β-O-4′ contents. Imaging distribution of the probes indicated that chlorite pretreatment resulted in a more uniform distribution of probe in the cell wall compared to hot water treatment. The interaction between cell wall and fluorescent PEG probes was evaluated using Förster Resonance Energy Transfer (FRET) and fluorescence microscopy. The FRET efficiency showed a high negative correlation with the probe size and was greatly increased by chlorite delignification, reflecting increased accessibility to the probe and interaction. Thus the accessibility and interactions of small probes in pretreated biomass could be a relevant indicator of potential for saccharification, whereas fluorescence lifetime provides a new criteria for assessing relevant cell wall structural modifications related to enzymatic conversion of lignocellulosic biomass.

Polydopamine encapsulation of fluorescent nanodiamonds for biomedical applications.

Fluorescent nanodiamonds (FNDs) are promising bio-imaging probes compared with other fluorescent nanomaterials such as quantum dots, dye-doped nanoparticles, and metallic nanoclusters, due to their remarkable optical properties and excellent biocompatibility. Nevertheless, they are prone to aggregation in physiological salt solutions, and modifying their surface to conjugate biologically active agents remains challenging. Here, inspired by the adhesive protein of marine mussels, we demonstrate encapsulation of FNDs within a polydopamine (PDA) shell. These PDA surfaces are readily modified via Michael addition or Schiff base reactions with molecules presenting thiol or nitrogen derivatives. We describe modification of PDA shells by thiol terminated poly(ethylene glycol) (PEG-SH) molecules to enhance colloidal stability and biocompatibility of FNDs. We demonstrate their use as fluorescent probes for cell imaging; we find that PEGylated FNDs are taken up by HeLa cells and mouse bone marrow-derived dendritic cells and exhibit reduced nonspecific membrane adhesion. Furthermore, we demonstrate functionalization with biotin-PEG-SH and perform long-term high-resolution single-molecule fluorescence based tracking measurements of FNDs tethered via streptavidin to individual biotinylated DNA molecules. Our robust polydopamine encapsulation and functionalization strategy presents a facile route to develop FNDs as multifunctional labels, drug delivery vehicles, and targeting agents for biomedical applications.

Accurate quantification of hydration number for polyethylene glycol molecules**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474325 and 11290161) and the Knowledge Innovation Project of Chinese Academy of Sciences on Water Science Research (Grant No. KJZD-EW-M03).

Hydration water can even decide the physicochemical properties of hydrated organic molecules. However, by far the most important hydration number for organic molecules, in particular polyethylene glycol which we are concerned with here, usually suffers from a large discrepancy. Here, we provide a scheme for accurate and unambiguous quantification of the hydration number based on the universal water-content dependence of glass transition temperature for aqueous solutions, testified by experimental results for polyethylene glycol molecules of a molar weight ranging from 200 to 20000. Moreover, we also clarify the fundamental misunderstanding lying in the definition and quantification of hydration water for PEG molecules in the literature, therein the hydration number for PEG in water-rich solutions has been determined at a critical concentration, across which the properties of the solution display obviously distinct water-content dependence.

On the Solvation Behavior of Graphene Oxide in Ethylene Glycol/Water Mixtures.

The self-association and solvation pattern of graphene oxide (GO) in water, ethylene glycol (EG), and their mixtures were analyzed by means of UV/Vis spectrophotometry. A careful analysis of the absorbance dependencies vs. the GO concentration shows that self-association of the GO sheets in EG occurs at higher concentration compared to that in water. It was established that depending on the mixed solvent composition, two different types of the GO solvates are formed. The results of quantum chemical calculations allow one to suggest that in the water-rich compositions, the GO oxygen-containing groups are in direct contact with water molecules while in the glycol-rich media the EG molecules fully substitute water in the GO's first solvation layer.

Crystal structure of secretory abundant heat soluble protein 4 from one of the toughest “water bears” micro‐animals Ramazzottius Varieornatus

Though anhydrobiotic tardigrades (micro‐animals also known as water bears) possess many genes of secretory abundant heat soluble (SAHS) proteins unique to Tardigrada, their functions are unknown. A previous crystallographic study revealed that a SAHS protein (RvSAHS1) from one of the toughest tardigrades, Ramazzottius varieornatus, has a β‐barrel architecture similar to fatty acid binding proteins (FABPs) and two putative ligand binding sites (LBS1 and LBS2) where fatty acids can bind. However, some SAHS proteins such as RvSAHS4 have different sets of amino acid residues at LBS1 and LBS2, implying that they prefer other ligands and have different functions. Here RvSAHS4 was crystallized and analyzed under a condition similar to that for RvSAHS1. There was no electron density corresponding to a fatty acid at LBS1 of RvSAHS4, where a putative fatty acid was observed in RvSAHS1. Instead, LBS2 of RvSAHS4, which was composed of uncharged residues, captured a putative polyethylene glycol molecule. These results suggest that RvSAHS4 mainly uses LBS2 for the binding of uncharged molecules.