Metal Ion-Coordinated Biomolecular Noncovalent Glass with Ceramic-like Mechanics

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Metadata	Details
Publication Date	2024-03-04
Journal	CCS Chemistry
Authors	Shuai Cao, Wei Fan, Rui Chang, Chengqian Yuan, Xuehai Yan
Institutions	University of Chinese Academy of Sciences, Institute of Process Engineering
Citations	24

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLES23 Mar 2024Metal Ion-Coordinated Biomolecular Noncovalent Glass with Ceramic-like Mechanics Shuai Cao, Wei Fan, Rui Chang, Chengqian Yuan and Xuehai Yan Shuai Cao State Key Laboratory of Biochemical Engineering, Key Laboratory of Biopharmaceutical Preparation and Delivery, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049 , Wei Fan State Key Laboratory of Biochemical Engineering, Key Laboratory of Biopharmaceutical Preparation and Delivery, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049 , Rui Chang State Key Laboratory of Biochemical Engineering, Key Laboratory of Biopharmaceutical Preparation and Delivery, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049 , Chengqian Yuan *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory of Biochemical Engineering, Key Laboratory of Biopharmaceutical Preparation and Delivery, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049 and Xuehai Yan *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory of Biochemical Engineering, Key Laboratory of Biopharmaceutical Preparation and Delivery, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049 Center for Mesoscience, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 https://doi.org/10.31635/ccschem.024.202303832 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Glass materials play a vital role in scientific research and engineering applications. Biomolecular noncovalent glasses (BNG), based on amino acids and peptides, have been proposed as the next-generation glass materials to meet the demand of a sustainability and circular economy. However, bulk BNG with remarkable mechanics and tunable photoluminescence are still rare due to the nature of weak noncovalent interactions and oversimplified molecular structures. Herein, we report the design and creation of metal ion-coordinated BNG (MIBNG) based on a simple amino acid derivative and metal ions. The obtained MIBNG exhibit ceramic-like mechanics, including the hardness, elasticity, and wear resistance, that are unattainable by the pure BNG counterpart. Such remarkable mechanics can be attributed to the enhanced noncovalent crosslinking network connectivity of biomolecules within MIBNG resulting from the incorporation of strong metal coordination interaction with hydrogen bonding and aromatic interactions. Moreover, fluorescence emission of MIBNG can be tuned feasibly through precisely modulating the types of metal ions coordinated. This study sheds light on the crucial role of multiple noncovalent interactions in the construction of BNG and advances the exploration and potential applications of BNG-based functional materials with tunable mechanical and optical properties in such fields as electronics and optics. Download figure Download PowerPoint Introduction Glass is a material with an amorphous structure that has a wide range of applications crossing a variety of fields. It is composed of a series of randomly packed atoms or molecules, lacking in long-range ordering.1,2 Its disordered nature endows glass with special physical and chemical properties, such as high transparency, uniform light scattering, and low thermal conductivity.3-5 The structure of glass can be changed and optimized by adjusting its composition and preparation process to achieve a specifuc performance on demand.6,7 There are many methods to prepare glass, including melting-quenching, sol-gel, and vapor deposition methods.8-10 The basic component of traditional inorganic glass is silicate, such as sodium calcium silicate, boron silicate, and aluminum silicate.11 With the progress in technology and changes in demand, innovations in glass materials continues to evolve, resulting in the emergence of new types of functional glass. For example, flexible glass and thin-film glass are gradually being applied in fields such as wearable devices and flexible displays.12,13 Nanostructured glass materials have special optical and magnetic properties, making them a research hotspot in the fields of nanotechnology and biomedicine.14 These developments provide more possibilities and prospects for the research and application of glass materials. Nevertheless, the development of green, ecofriendly and even biodegradable glass materials yet remains a formidable challenge. These are mainly manifested in the following aspects. First, the chemical stability of commonly used glass materials makes it difficult to degrade, leading to potential long-term environmental impacts.15 Second, glass materials cannot be decomposed and recycled through natural processes, further increasing their environmental burden.16 In addition, the production of glass materials often uses a large amount of energy and raw materials, leading to resource waste and environmental pollution.17 Biomolecular noncovalent glasses (BNG) based on amino acids and peptides have attracted much attention, due to their biocompatibility, biodegradability, and recyclability compared to commercial glass and plastic materials currently used.18,19 However, supramolecular materials connected by noncovalent interactions usually suffer from weak strength and mechanical stability.20-24 The mechanical properties of these materials are usually limited due to their weak noncovalent interactions. Therefore, further improving the performance of BNG and expanding their potential for applications remains an important research topic. Similarly, we enrich the functionality of existing glass materials by adding and doping other components to change the properties of the glass, resulting in specific functions and applications.25 For example, a coating of indium tin oxide can make glass conductive and suitable for optoelectronic devices or sensor applications.26 Adding rare earth ions, such as europium ions (Eu3+), to glass can achieve fluorescence effects, giving glass the characteristics of a fluorescent material.27 By adding antibacterial agents such as silver nanoparticles, glass can be endowed with antibacterial ability.28 This flexibility from the integration of functional components allows glass to be widely used in various fields such as electronics, optics, medicine, and so on.29,30 Inspired by the glass materials coordinated with other components, we successfully prepared a series of metal ion-coordinated BNG (MIBNG) through the introduction of metal coordination. A simple amino acid derivative, N-fluorene methoxycarbonyl-l-leucine (Fmoc-Leu-OH, abbreviated as Fml), was selected as one typical model building block, which coordinates with metal ions through carboxyl and carbonyl groups. The cooperation of multiple noncovalent interactions drives the formation and stabilization of MIBNG. The mechanics of MIBNG has been improved compared to the pristine BNG. The introduction of metal coordination interactions endows MIBNG with ceramic-like mechanics, including hardness, wear resistance, and elasticity that are difficult to achieve by the pure BNG counterpart. Moreover, by modulating the types of rare earth ions coordinated, precise regulation on the fluorescence of MIBNG was achieved. This study provides an effective strategy to fabricate multifunctional MIBNG with flexible mechanical and optical properties that holds broad application prospects in fields such as smart optics. Experimental Methods Materials Potassium hydroxide (KOH) was sourced from Beijing Chemical Co. Ltd. (Beijing, China), extra dry methanol was provided by Energy Chemical (Shanghai, China), and Fmoc-Leu-OH (referred to as Fml) was obtained from Energy Chemical. Anhydrous cobalt sulfate, anhydrous copper sulfate, and anhydrous zinc sulfate were supplied by Macklin (Shanghai, China). Lanthanum chloride heptahydrate, cerium chloride heptahydrate, europium chloride hexahydrate, terbium chloride hexahydrate, and lutetium chloride hexahydrate were all procured from the manufacturer, Energy Chemical. Synthesis of MIBNG KOH was dissolved in extra dry methanol at a concentration of 0.1 M. Subsequently, Fml was dissolved in the extra dry methanol solution containing KOH at a concentration of 100 mg mL−1. Once complete dissolution was achieved, taking the solution and dissolving the sulfate at the concentration of 0.0204 M allowed Fml molecules to fully interact with metal ions. The mixture was thoroughly blended to form a precursor solution. This precursor solution was then subjected to centrifugation in a high-speed centrifuge at 10,000 revolutions per minute (rpm) for 5 min. Following centrifugation, the supernatant was heated to 80 °C using a heat-collecting constant-temperature magnetic stirring tank to produce a viscous fluid. The resulting viscous fluid was further heated to 160 °C using a heated magnetic stirrer, then melted, cooled, and quenched at room temperature, thereby forming MIBNG. Characterizations Glass transition and melting temperature analysis Thermogravimetric analyzer combined with a differential scanning calorimeter (TGA-DSC) analyses were performed on all specimens using a TGA/DSC 3+ series instrument from Mettler Toledo (Greifensee, Zurich, Switzerland), and a DSC 1 instrument, also from Mettler Toledo. Before testing, two empty platinum crucibles with loose lids were used for baseline adjustments. One platinum crucible was filled with glass powders, while the other remained empty as a control. Using the TGA/DSC 3+ series instrument, the specimens underwent heating from room temperature to 773.15 K to determine Tm and Td. With the DSC 1 instrument, samples were subjected to controlled heating and cooling cycles. In Upscan 1, the platinum crucible containing the powders were heated from room temperature (T0) to a temperature (T1) exceeding Tm but below Td. Subsequently, quenching from T1 to a temperature (T2) lower than T0 occurred, followed by an isothermal hold at T1 for 5 min. In Upscan 2, the product was reheated from T2 to a temperature (T3) proximate to Tm, and Tg was recorded. To ensure sample uniformity, the platinum crucible was filled to less than 50% of its capacity. The heating and cooling rates were set at 10 K min−1. Throughout the measurements, samples were shielded with a nitrogen atmosphere. XRD measurement X-ray powder diffraction (XRD) analyses were conducted with a Rigaku SmartLab diffractometer (Rigaku, Tokyo, Japan), equipped with a 9 kW power source, utilizing a Cu filter and Cu Kα1 radiation (λ = 1.5406 Å) from Japan. Data collection involved scanning in the 2θ range from 10° to 40° at a rate of 10° min−1, with a 0.01 increment step. The specimens were carefully affixed to pristine silicon substrates. Polarized optical microscopy analysis Cross-polarized optical microscope (POM) was conducted using a BX53 polarized microscope system (Olympus, Tokyo, Japan). A 1.5 mg glass powder sample was carefully placed on a 30.0 mm diameter and 1.0 mm thick glass slide. The powder was subjected to controlled heating and cooling processes to achieve the vitreous state, and polarized microscopy images were subsequently acquired. Scanning electron microscope measurement This study involved the examination and observation of the surface morphology, texture, structure, and elemental composition of the samples using a Hitachi S-4800 II electron scanning microscope (Hitachi, Tokyo, Japan). The procedures involved attaching the glass powder specimen to conductive tape, gold-coating the sample for 2 min using a gold-sputtering apparatus, and examining the gold-coated sample with the scanning electron microscope (SEM) at an operational voltage of 10 kV to obtain surface morphology details. High-resolution electrospray ionization mass spectrometry measurement High-resolution electrospray ionization mass spectrometry (HR-ESI-MS) was performed using an Agilent Technologies (Santa Clara, California, USA) quadrupole time-of-flight (Q-TOF) mass spectrometer (model 6540) with electrospray ionization. Fourier transform infrared measurement Fourier transform infrared (FT-IR) spectra were acquired using a VERTEX 70v infrared spectrophotometer (Bruker, Karlsruhe, Baden-Württemberg, Germany). Each spectrum was generated through the accumulation of 32 scans over the spectral range from 4000 to 400 cm−1. Raman spectroscopy In-situ Raman spectroscopy was performed with the Renishaw RM 1000 micro-Raman system (Renishaw, London, UK), based in England. A 1200 line mm−1 grating was used for spectral acquisition in a backscattering geometry. The excitation wavelength was 532 nm, covering the range of 50-3500 cm−1. Specimens were directly placed under the microscope without any prior treatment, and data were subsequently collected. UV-vis absorption measurement Absorption spectra were acquired using a Lambda 1050+ spectrophotometer (Perkin Elmer, Waltham, Massachusetts, USA). The glass samples, approximately 2 mm in thickness, were oriented perpendicularly to the incident beam. Fluorescence spectroscopy Solid sample fluorescence spectra were obtained using an RF-6000 spectrofluorometer (Shimadzu, Kyoto, Japan). A 150-W Xenon arc lamp, supplied by Ushio Inc. (Tokyo, Japan), served as the light source. Scanning was conducted at a rate of 2000 nm min−1, with an excitation bandwidth of 1.5 nm and an emission light bandwidth of 1.0 nm. The specimens were placed on clean, flat quartz substrates. Nanoindentation The Young’s modulus and hardness of the glass samples were determined using a G200 instrument equipped (Keysight, Santa Rosa, California, USA) with a three-sided pyramidal (Berkovich) diamond indenter tip, capable of penetrating up to 500 nm. The sample size for determining the Young’s modulus and hardness was approximately 10 mm in length, 8 mm in width, and 0.8 mm in thickness. The specimens were encased in epoxy resin and progressively polished with progressively finer diamond suspensions. Nanoindentation tests were performed under dynamic displacement control, maintaining a constant strain rate of 0.05 s−1 over four cycles. Results and Discussion Initially, our focus was on preparing a viscous fluid containing metal ions and amino acids because the viscous fluid, similar to supercooled liquid, serves as a precursor for glass formation. In a standard procedure, Fml and metal ion salts were codissolved in methanol. The solvent was then evaporated at a temperature below the decomposition temperature (Td) of Fml to yield a viscous fluid. The thermal decomposition process of Fml powder was determined using a TGA-DSC. Fml clearly exhibited Tm at 429.1 K and Td at 530.9 K ( Supporting Information Figure S1). The large gap between Tm and Td provides the possibility to obtain stable viscous fluid coordinated with metal ions. Subsequent heating and quenching of this viscous liquid led to the formation of MIBNG (Figure 1a and Supporting Information Figure S2). The pristine Fml glass and MIBNG coordinated with different metal ions (e.g., Fml-Co, Fml-Cu, and Fml-Zn glasses) are displayed in Figure 1b. Figure 1 | Preparation and characterization of MIBNG. (a) Schematic diagram of the preparation process of MIBNG. (b) Appearance of different Fml glass MIBNG beads. (c) XRD patterns of Fml glass and MIBNG. (d) Bright (top) and polarized field (bottom) optical images of Fml glass and MIBNG. (e) DSC curves of Fml glass and MIBNG. (f) Optical transmittance of Fml glass and MIBNG. (g) SEM images of Fml glass and MIBNG. Download figure Download PowerPoint To ascertain the amorphous structure of MIBNG, we conducted XRD tests. The results revealed distinct diffraction peaks in the XRD pattern of Fml powder ( Supporting Information Figure S3), signifying its crystalline nature. However, XRD patterns of the glass samples displayed no discernible peaks, indicating the disordered atomic and molecular arrangement of MIBNG (Figure 1c). According to the Bragg equation,31 the spacing corresponding to the broad peak around 22° is nearly 0.40 nm, which can be ascribed to the local aromatic interactions between Fmoc rings.32 Subsequently, POM was employed to identify the crystalline and glassy samples (Figure 1d). The MIBNG displayed no detectable anisotropic birefringence, indicating their isotropic and amorphous characteristics. In contrast, the Fml powder exhibited strong optical anisotropy, suggesting the presence of an orientationally organized structure within the Fml powder ( Supporting Information Figure S4). Glass transition temperature (Tg) refers to the temperature range at which a material shifts from a rigid, glassy state to a pliable, rubbery state.33 This parameter is important in the realm of glassy materials, as it governs their characteristics across a range of temperatures and is associated with its practical utility in assessing material stability, processability, and suitability for various applications.34 Consequently, the investigation of Tg holds both theoretical and practical significance. To elucidate their glass transition properties, DSC measurement was employed to analyze the heat flow characteristics of Fml glass and MIBNG. The presence of distinct endothermic peaks in the second upscan of the DSC curves for these glasses (Figure 1e) indicated the occurrence of glass transitions at their respective temperatures. The Tg and heat capacity change (ΔCp) values for Fml glass and Fml-Co/Fml-Cu/Fml-Zn MIBNG were determined to be 310.4 K (ΔCp = 0.581 J g−1 K−1), 314.4 K (ΔCp = 0.549 J g−1 K−1), 315.4 K (ΔCp = 0.496 J g−1 K−1), and 313.0 K (ΔCp = 0.419 J g−1 K−1), respectively. The Tg/Tm ratios for the four samples were calculated to be 0.72, 0.73, 0.74, and 0.73, respectively, following the Kauzmann “2/3” law.35,36 Moreover, the similar values signified that the introduction of metal ions had little influence on the glass-forming ability of viscous liquid consisting of amino acids. Moreover, ΔCp exhibited a negative correlation with the degree of network connectivity and topological constraints.37 When compared to pristine Fml glass, the ΔCp of MIBNG decreased, suggesting an increase in network connectivity. Furthermore, the higher Tg values determined on the DSC curve indicated stronger noncovalent interactions and more stable noncovalent crosslinking network structure within MIBNG.38 DSC analysis of MIBNGs demonstrated that Tg values varied with the type of metal ions coordinated. This variation may be attributed to the difference in the coordination abilities of different metal ions with Fml. Moreover, compared to the glass obtained by direct melting-quenching of Fml powder, the glass obtained by methanol solvent evaporation method had a higher glass transition temperature ( Supporting Information Figure S5), indicating that the presence of methanol during glass formation endowed the glass with a more compact molecular arrangement and stronger intermolecular interactions. In the context of rapid quenching, a liquid can avoid crystallization and remain in a metastable supercooled state until it reaches the glass transition, resulting in a significant increase in viscosity during subsequent cooling.39 The second DSC upscans of Fml-Cu glass, measured at varying heating rates, demonstrated that with the increase in quenching rate ( Supporting Information Figure S6a), the Tg value also increased. This indicates that fast quenching rates are beneficial for the formation of MIBNG with a high Tg. Such a dependence can be understood by the fact that rapid quenching rates exceed the speed at which the system deviates for structural adjustments. This results in the occurrence of the glass transition at higher temperatures, leading to a higher Tg.40 There are significant variations in the relaxation behavior of as the glass transition, with dynamic properties rapid or changes in to temperature The provides a to these glass-forming exhibit between and analysis of these was by existing data from of glass-forming inorganic materials, and glass-forming Fml-Cu glass as an Its value was determined to be ( Supporting Information Figure suggesting the to form Moreover, its Tg and values Fml-Cu glass within the range of glasses ( Supporting Information Figure similar to glasses such as UV-vis spectra of Fml glass and MIBNG were to determine their optical transmittance (Figure The pure Fml glass exhibited approximately at a wavelength of nm, indicating high However, was a in transmittance the introduction of metal ions. the transmittance of all the MIBNG within the range of nm these glass samples still compared to glass and The enhanced light transmittance can be attributed to the and flat surface structure of these as by the of and in the SEM of the sample (Figure of the elemental data revealed the presence of metal on the of MIBNG samples, the introduction of metal ions the glasses ( Supporting Information Figure To the intermolecular interactions to the formation and stabilization of MIBNG, and UV-vis absorption spectra of MIBNG with pristine Fml powder and glass were and For the crystalline Fml powder, the peak at and were to the and (Figure and Supporting Information Figure The peaks at and were attributed to the of in carboxyl while the one around to the in the Fmoc The peak at from the The presence of these peaks indicates hydrogen arrangement within Fml the pristine Fml and MIBNG these peaks suggesting the of multiple within such Similarly, the Raman spectra of the glass samples also to that of the Fml sample ( Supporting Information Figure the formation of glass, the peak of two with one and while that of These results the of hydrogen and within the crystalline Fml powder and of hydrogen in glasses the introduction of metal ions, the at for the spectrum of Fml glass to while that at to (Figure These changes the of the hydrogen bonding interaction of which was further by the of the II from to In contrast, the peaks at and in Fml glass to and in MIBNG respectively, suggesting the enhanced hydrogen bonding interaction of within MIBNG. the of and electrospray ionization mass spectra of MIBNG demonstrated the presence of metal coordination interactions (Figure and Supporting Information Figure Figure 2 | of the formation and stabilization of MIBNG. spectra of MIBNG with pristine Fml powder and glass. (c) spectra of MIBNG. (d) Raman spectra of MIBNG with pristine Fml powder and glass. (e) Schematic the multiple noncovalent interaction within MIBNG glass. Download figure Download PowerPoint Furthermore, we the Raman in the range of from the of aromatic of pristine Fml powder and glass with MIBNG (Figure and Supporting Information Figure The peak at and peaks at and indicated the aromatic within the Fml In contrast, the and of the Raman peak at the of multiple aromatic within the Fml glass and MIBNG. The of peaks at and indicated the of which is further by the of the at nm in the UV-vis absorption spectra of Fml and MIBNG glasses ( Supporting Information Figure the introduction of strong metal coordination interactions the hydrogen bonding interactions between Fml molecules and enhanced the and disordered aromatic interactions between Fmoc of these noncovalent interactions the formation and of the amorphous glass structure (Figure we the introduction of metal ions can the mechanical properties of MIBNG through the Figure the curves of pristine Fml glass and MIBNG. the the displacement of pristine Fml glass is than that of MIBNG signifying higher displacement in the This is due to the enhanced intermolecular interactions by the introduction of metal coordination interactions within MIBNG. Figure | properties of MIBNG. (a) The curve of MIBNG. (b) Young’s modulus and hardness of MIBNG. of (c) and rate (d) in MIBNG and traditional materials, including and and and The rate of is Download figure Download PowerPoint The Young’s modulus and hardness of MIBNG were determined based on the The results revealed variations in the and hardness properties these four glass samples (Figure In of Fml glass exhibited the Young’s modulus and hardness, and respectively, followed by Fml-Zn glass with values of and Fml-Cu glass with and and glass with the values at and The Young’s modulus and hardness of sample exceed of that and values of MIBNG can be tuned by the types of metal ions coordinated and are higher compared to of pristine Fml glass, that the incorporation of metal ions the mechanics of MIBNG. In to and the value a vital for assessing the to yield A analysis of between MIBNG and traditional materials, including

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DOI: https://doi.org/10.31635/ccschem.024.202303832