Cu(II)-Based Nanofibrous Metallogel for Phenoxazinone Synthase-like Activity

Open AccessCCS ChemistryMINI REVIEW1 Mar 2022Multidimensional Mass Spectrometry Assisted Metallo-Supramolecular Chemistry Heng Wang, Chenxing Guo and Xiaopeng Li Heng Wang College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518073 Shenzhen University General Hospital, Shenzhen University Clinical Medical Academy, Shenzhen 518055 , Chenxing Guo College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518073 and Xiaopeng Li *Corresponding author: E-mail Address: [email protected] College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518073 Shenzhen University General Hospital, Shenzhen University Clinical Medical Academy, Shenzhen 518055 https://doi.org/10.31635/ccschem.021.202101408 SectionsAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Metallo-supramolecular chemistry based on the reversible, directional, and predictable noncovalent interaction of metal–ligand coordination has been widely applied in constructing a myriad of two- and three-dimensional supramolecules with sophisticated structures. The development of metallo-supramolecular chemistry highly relies on facile characterization methods. For advancement of structural complexity with desired functions, however, conventional crystallographic and spectroscopic characterizations are limited by crystal growth, sample purity, and severe signal overlaps. With high sensitivity and low requirement for purity, multidimensional mass spectrometry (MS), including electrospray ionization-MS (ESI-MS), tandem MS (MS2), and ion mobility-MS (IM-MS), is emerging as an essential analytical tool for characterization of the chemical compositions, connectivity, stability, shape, and size of metallo-supramolecules, as well as kinetic and thermodynamic features of self-assembly processes. Thus, this review mainly focuses on the recent development of multidimensional MS in metallo-supramolecular characterization and discusses how ESI-MS, MS2, and IM-MS assist the development of metallo-supramolecular chemistry. Download figure Download PowerPoint Introduction Supramolecular self-assembly, inspired by the precise organization of bio-macromolecules in living systems, allows for the spontaneous formation of ordered complexes from a chaos state.1 Among various noncovalent driving forces, metal–ligand coordination plays a vital role in the self-assembly of structurally and functionally sophisticated metallo-supramolecules, benefitting from the high directionality and predictable feature of coordination bonds.2–6 As a result, metallo-supramolecular chemistry has witnessed an explosion in constructing a myriad of artificial supramolecular architectures, including polygons,7–11 knots,12–15 links,16–19 fractals,20–22 as well as Platonic,23–27 Archimedean,28–34 Goldenberg polyhedrons,35,36 and so on. And these complexes show great potentials among different fields, including catalysis,37–46 nano-electronics,47,48 stabilization of air- or water-sensitive molecules,49–51 disease diagnosis and therapy,52–57 and so on. Furthermore, various delicate assembling approaches, inter alia, directional bonding,2 symmetry interactions,58 molecular paneling,59 and sub-components,60 have been developed to assist the exploration of metallo-supramolecular chemistry. Compared to the flourish of self-assembly strategies, however, the lack of efficient characterization methods always limits the investigation of assembled complexes at equilibrium and the kinetic details of self-assembly processes in solution because of the weak interaction and dynamic nature of metallo-supramolecules. Among the conventional characterizations of metallo-supramolecules, single-crystal X-ray diffraction (SC-XRD) is a powerful and direct method that allows for detailed structural information at the atomic level.61 However, it remains a formidable challenge to obtain high-quality single crystals, particularly for metallo-supramolecules with large voids filled by disordered solvent molecules or counterions. In addition, the refinement of the crystal structures for large metallo-supramolecules is difficult because the current crystal refinement approaches were mainly developed for small molecules. Apart from those issues the structural information obtained through SC-XRD in solid phase may not correlate with the study of metallo-supramolecular systems in solution or gas phase. Another well-established characterization method is NMR spectroscopy, whereby various nuclei in metallo-supramolecular systems, such as 1H, 13C, 19F, 31P, and so on can be detected, allowing the chemical environment of these nuclei in metallo-supramolecules to be elucidated.62,63 Through two-dimensional (2D) NMR spectroscopic techniques, for example, 1H–1H correlation spectroscopy (COSY), nuclear Overhauser effect spectroscopy (NOESY), and diffusion ordered spectroscopy (DOSY), diverse structural information about the metallo-supramolecules can be further obtained, including metal–ligand coordinations, geometric distributions of nuclei, and details of the size and shape of assembled architectures. However, the application of NMR is also limited in analyzing samples with low purity, severe overlapping signals, or those containing paramagnetic metal ions. As complementary characterization techniques, various microscopic methods, including atomic force microscopy (AFM), scanning tunneling microscopy (STM), and transmission electron microscopy (TEM), directly image the analytes. AFM and STM, in which tips probe the surface of the target molecules on substrates, reveal the size and shape of an individual molecule64 and distinguish the metal ions by using scanning tunneling spectroscopy (STS).65 However, high image resolution relies on sharp tips, as well as high-quality samples without impurities, severe aggregations, or dissociations of the target supramolecules. TEM uses electrons as the "probe" and can offer atomic resolution of the entire molecular structure assisted by computer-assisted three-dimensional (3D) reconstruction, selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDX) techniques.66 Unfortunately, in addition to the challenges of preparing a high-quality sample, TEM also suffers from the intrinsic instability of metallo-supramolecules under electron beam or during sample preparation. The mass-to-charge ratio (m/z) information of the intact metallo-supramolecular ions obtained by mass spectrometry (MS) measurements in the gas phase enables the determination of the chemical composition of analytes. Furthermore, MS characterization provides higher sensitivity but a lower sample purity requirement than crystallographic analysis and NMR. Such features along with high analytical speed make it possible to monitor the dynamic process of self-assembly before the system in question reaches equilibrium. Thus, MS is emerging as an essential analytical tool for determining structures and monitoring reaction processes. However, traditional MS approaches also suffer from the fragmentation of metallo-supramolecules bound by weak coordination interaction even when a soft ionization method, that is, electrospray ionization (ESI), is applied. Cold-spray ionization (CSI),67 equipped with an ESI source cooled by liquid nitrogen, was used to overcome the problem by lowering the internal energy gained during the ionization. Due to the labile connectivity, matrix-assisted laser desorption/ionization (MALDI) could cause very severe fragmentation and thus is not preferred for the characterization of metallo-supramolecules. In addition to the m/z information obtained from MS, tandem MS (MS2) and ion mobility-MS (IM-MS) can elucidate more detailed information of the analytes. First, as a controllable fragmentation technique, MS2 offers deeper insight into the analytes, such as the information about the stability and connectivity of the structures. Furthermore, as an orthogonal in situ separation method, IM-MS can identify different species with the same m/z; more importantly, it provides structural information in terms of the shape and size of selected ions. During the past two decades, multidimensional MS with the combination of MS, IM-MS, and MS2 has played an important role in the development of metallo-supramolecular chemistry. Here, we discuss how ESI-MS, MS2, and IM-MS can be applied in (1) determining chemical compositions, connectivity, shape, and size of metallo-supramolecules, (2) distinguishing the isomers and by-products present in a dynamic combinatorial library, and (3) investigating kinetic and thermodynamic features of self-assembly processes. More importantly, we anticipate that multidimensional MS would not only act as an analytical method, but also serve as a powerful tool to assist the design of next-generation metallo-supramolecules, and even advance the development of new synthetic strategies. ESI-MS Studies Charged coordination complexes are ideal analytes for ESI-MS studies because of the easy-to-ionize feature of these supramolecules in which the counterions are readily stripped off, especially in polar and volatile solvents. Another advantage of ESI-MS is its intrinsic capability of reducing the signals corresponding to the multiply charged analytes with high molar mass (<104 Da) to the mass range of the conventional mass analyzers, since it only measures the m/z values of these ensembles. Consequently, a series of peaks is usually observed, representing different charge states of the same intact analyte through successive loss of counterions. To minimize the fragmentation during ionization, it is crucial to ionize the fragile analytes under mild conditions, including careful selection of the focusing and ionization voltages, low operation temperature, and fast ion extraction process through increasing source pressure (or a low vacuum).68 Additionally, highly concentrated metallo-supramolecular samples are often required to inhibit the potential entropy-driven dissociation in solution, although the ESI source needs more extensive cleaning after each measurement. Without annoying fragmentation, ESI-MS is suitable for detecting the chemical compositions of the ionic species in the metallo-supramolecular analytes, as well as providing information regarding the following aspects of the self-assembly: (1) fast screening the assembled structures; (2) monitoring the dynamic processes during the self-assembly; and (3) detecting the minor products to guide further design. Acting as a fast-screening characterization approach for the self-assembly Fast screening of the analytes' structural information by ESI-MS does not require extensive purification processes that are otherwise inevitable for NMR measurement and single-crystal growth. In most cases, after simply removing the inorganic salts to reduce ion suppression, the resulting sample solution is ready for direct measurement. With careful control of stoichiometry, the solution containing the self-assembled species can be directly subjected to ESI-MS without any further purification. Additionally, its capability of detecting m/z values enables the characterization of multiple assemblies with different numbers of building blocks, paramagnetic metallo-supramolecular analytes, and host–guest adducts. Therefore, ESI-MS could serve as a complementary or even superior method to perform structural characterization compared to NMR. The first example showcasing the fast screening by ESI-MS is the characterization of different generations of metallo-dendrimers S1/ S2 (Figure 1a) comprised of polyazaaromatic Ru(II) complexes reported by Kirsch-De Mesmaeker et al.69 ESI-MS directly generated clear and simple patterns that allowed the unambiguous determination of the chemical formula, whereas the other spectroscopic characterization just provided nonconclusive data (Figure 1b). Second, in the characterization of metallo-macrocycles reported by Newkome and co-workers,701H NMR gave very similar chemical shifts for the hexagon, octagon, and decagon ( S3- S5) assembled from the Ru(II)-connected bitopic 2,2′:6′,2″-terpyridyl (TPY) subunit L3 (Figure 1c) because of the similar symmetry and chemical environments of the detected protons. In contrast, these analogs with distinct molar mass were unambiguously identified by ESI-MS, where three distinct sets of peaks were detected (Figures 1d and 1e).70 Figure 1 | ESI-MS acting as a fast-screening approach for the preparation of (a and b) metallo-dendrimers comprised of polyazaaromatic Ru(II) complexes S2 and its corresponding ESI-MS spectrum; (c–e) TPY-Ru(II)/Fe(II)-based metallo-hexagon S3, -octagon S4, and -decagon S5 with corresponding 1H NMR spectra and ESI-MS spectra; (f–h) self-assembly of supramolecular fractals S6 based on the metal complexation between a TPY-based ligand and paramagnetic metal ions with corresponding 1H NMR and ESI-MS spectrum of the Co(II) complex (S6-Co). (a and b) Adapted with permission from ref 69. Copyright 1996 American Chemical Society. (c–e) Adapted with permission from ref 70. Copyright 2011 Wiley-VCH. (f–h) Adapted with permission from ref 71. Copyright 2020 American Chemical Society. Download figure Download PowerPoint Metallo-supramolecules containing paramagnetic transition metal ions with unpaired electrons remain a formidable challenge for NMR characterization. In contrast, ESI-MS has no problem characterizing these samples. For example, Shionoya et al.25 constructed a series of metallo-supramolecular octahedra by mixing a tritopic pyridinyl building block with different transition metal ions. ESI-MS spectra of the paramagnetic analytes containing Cu(II), Ni(II), Co(II), and Mn(II) ions clearly showed a dominant set of peaks ascribed to the designed structures; whereas, NMR spectra only displayed broad peaks with limited information.25 Similarly, with the help of ESI-MS characterization, coordination-driven self-assembly based on a TPY-paramagnetic metal ion complex was applied to construct a series of supramolecular fractals reported by Li et al.,71 which not only expanded the library of metal ions for assembling TPY-based architectures but also set up an ideal platform for studying the kinetic and thermodynamic features of these metallo-supramolecules (Figures 1f–1h). When characterizing the paramagnetic Co(II) and Ni(II) cages assembled using the sub-component self-assembly strategy, the reliable ESI-MS method also played a vital role in identifying the formation of target structures.72,73 Investigation of host–guest complexation is an important subfield of metallo-supramolecular chemistry, which is related to the fundamental study of molecular recognition and the potential applications of these metal–organic containers. NMR spectroscopy is extensively applied to provide evidence for the interaction with diagnostic chemical shifts of the protons on guest molecules. However, it cannot always accurately address how many guest molecules are encapsulated in the containers. ESI-MS can properly examine the exact change in mass upon the encapsulation of the guest molecules, thus, providing an accurate m/z value for deducing the number of guest molecules. In a self-assembled M8L6 (M = the metal ion, L = the ligand) cube with porphyrin faces, Nitschke et al.74 described that large guests such as coronene and fullerene can be selectively encapsulated (Figure 2a). Compared with the complicated NMR spectra that only provided a 2:1 ratio of guests in two different environments, ESI-MS spectrum of the coronene-encapsulated cube directly provided the number of the guest molecules via deconvolution of the dominant set of peaks (Figures 2b and 2c). The ESI-MS spectrum also clearly confirmed that the cube allowed for selective encapsulation of C70, C76, C82, and C84 over C60 from the fullerene soot, as evidenced by the absence of any discernible peaks assignable to the C60-encapsulated or guest-free cube. Figure 2 | ESI-MS-based fast screening for studying the guest encapsulation of metallo-supramolecular cages. (a–c) Self-assembly of porphyrin-faced cube S8 for encapsulation of three coronene with corresponding characterization by 1H NMR and ESI-MS; (d and e) a PBI-edged tetrahedron capable of encapsulating two molecules of C60S9 and the corresponding ESI-MS spectrum; (f–h) self-assembly of a metallo-supramolecular peanut S10 for simultaneous encapsulation of one diamantane and two phenanthrenes (S11) with corresponding characterization by 1H NMR and ESI-MS. (a–c) Adapted with permission from ref 74. Copyright 2011 Wiley-VCH. (d and e) Adapted with permission from ref 76. Copyright 2013 American Chemical Society. (f–h) Adapted with permission from ref 83. Copyright 2017 Springer Nature. Download figure Download PowerPoint Thus, ESI-MS is also a feasible and rapid method for qualitatively studying the encapsulation selectivity of a certain metallo-supramolecule with different guests. In another example of selective encapsulation, when mixing a metallo-supramolecular tetragonal prism with a mixture of C60 and its derivatives, the selectivity could be determined qualitatively by comparing the relative abundance of the peaks corresponding to the host–guest complexes containing different guests. Among them, C60 and PCBM-C60 have higher affinity with the host than N-methylpyrrolidine-C60.75 However, it is still challenging to quantitatively determine the selectivity by ESI-MS because of the different ionization efficiency of those complexes, although the host molecules are the same. Ideally, quantitative data could be obtained if the ionization efficiencies of different complexes are calibrated. In addition to encapsulating one fullerene molecule, Würthner et al.76 applied ESI-MS to unequivocally prove the encapsulation of one or two molecules of C60 inside the cavity of perylene-bisimide (PBI) edged tetrahedron S9 (Figures 2d and 2e). Note that the C60 guest does not bear any protons so that it can only be identified by 13C NMR. Although the 13C NMR could confirm the encapsulation of the C60, it was unable to determine the number of guest molecules because conventional 13C NMR does not allow for quantitative analysis as opposed to 1H NMR. Metallo-supramolecular trigonal prisms, wherein C3-symmetrical tritopic pyridyl ligands, linear ditopic pyridyl ligands, and an end-capped Pd(II) moiety served as the base faces, pillars, and vertices, respectively, were found to be an excellent molecular container capable of encapsulating a variety of guest molecules, including, coronene,77 triphenylene,78 pyrene-4,5-dione,79,80 and metal–organic complexes.81,82 More intriguingly, the number of the encapsulated guest molecules can be precisely manipulated via tuning the length of the organic pillars. The accurate number of encapsulated guests could be unambiguously determined by ESI-MS. A more complicated situation was reported by Yoshizawa et al.83 The self-assembled metallo-supramolecular peanut S10 heteroleptically encapsulated two different types of guests, that is, one diamantane and two phenanthrenes, inside its two cavities (Figure 2f). Without an SC-XRD result or clear NMR spectrum (Figure 2g), such an unusual encapsulation was identified by ESI-MS (Figure 2h), where peaks with m/z values of the expected host–guest complex were found. Monitoring the dynamic processes for unveiling self-assembly details Metallo-supramolecules bonded via labile coordination interactions exhibit dynamic features in solution due to the dissociation and reassociation of the weak bonds. Thus, it is hard to investigate the kinetic processes by traditional characterization techniques in solution. Nevertheless, in an ESI-MS measurement, each complex ion is a separated species in gas phase. Therefore, the dynamic process is "frozen" to display the kinetic instead of thermodynamic feature of the system. As one type of dynamic process, ligand exchange involves the disassociation of a ligand from the assembled supramolecule and subsequent replacement by another ligand. Such a process is related to the coordination bond strength and the activation energies during the exchange processes. If the time scales of such dynamic exchanges are comparable for MS measurement, one should be able to study the exchange process of two kinds of pre-assembled supramolecules with distinct molar masses of ligands by MS. Once the exchange occurs, the m/z values corresponding to each possible re-assembled species as well as the initial ensembles would be different, all of which can be specifically recorded by ESI-MS measurement. For example, Fujita et al.84 reported the studies of ligand exchange between two M12L24 spheres via mixing two topologically identical spheres bearing different length of alkyl chains (–OC3H7 vs –OC6H13) and then monitoring under time-dependent ESI-MS (Figures 3a and 3b). Due to the difference in mass, all the peaks corresponding to the initial two spheres and the exchanged ones were easily identified in the spectra. Time-dependent measurements revealed a quite remarkable kinetic stability of the spheres regarding ligand exchange. The half-time for the first ligand exchange was measured to be approximately 20 days. After evaluating the ionization efficiency of two spherical supramolecules, the estimated kinetic ligand exchange rate was found to be 2 × 10−2 M−1·s−1, which is far less than the exchange rate between a free ligand with a sphere (half-time of 23 min). Therefore, the ESI-MS studies semi-quantitatively revealed that the fully closed framework slowed down the dynamic exchange processes through a cooperative effect.84 A similar method was also utilized to carefully study the dynamic nature of metallo-polygons assembled from organoplatinum motifs and pyridyl ligands with 1H/2D isotope labeling.85 In addition to the quantitative determination of the ligand exchange rates, further understanding about the kinetic processes in coordination-driven self-assembly was provided by time-dependent ESI-MS, which showed the ligand exchange rate highly depended on the experimental conditions such as temperature, solvent, and counterions. Figure 3 | ESI-MS of ligand exchange. (a) Ligand exchange between two structurally identical spheres (Pd12L724 and Pd12L824) with different alkyl chain lengths (-n-C3H7 vs -n-C6H13), and (b) the time-dependent ESI-MS spectra; (c) self-assembly of four types of supramolecular snowflakes (S12–S15) with different lengths of the ligands, and time-dependent ESI-MS spectra of the mixture of and (a and b) Adapted with permission from ref Copyright American Chemical Society. and e) with permission from ref Copyright Wiley-VCH. with permission from ref Copyright 2017 American Chemical Society. Download figure Download PowerPoint In addition to the pyridyl ESI-MS also provided insight into the ligand exchange processes of metallo-supramolecular systems based on analyzing the peaks to the complexes in ESI-MS it was revealed that the exchange processes a certain of to the size and shape of the ligand via the of the structure when the Through a time-dependent ESI-MS measurement, such a was estimated in the metallo-supramolecular snowflakes with different length of ligand The exchange rate was found to directly correlate with that is, the the the ligand exchange. When = the exchange equilibrium = required for whereas = in no exchange (Figures Furthermore, the ligand exchange rate was also found to correlate with the coordination metal ion in TPY-based To quantitatively these exchange rates, different metal ions (M = were applied. of these metal ions was used to two structures with the same molecular size and shape but different molar After mixing the of pre-assembled supramolecules, time-dependent ESI-MS was utilized to the relative abundance of each After the ionization efficiency of these supramolecules, ESI-MS data provided exchange of these metallo-supramolecules at with a of Mn(II) Co(II), whereas the and fractals were found to be to the ligand exchange. The exchange rate of fractals was determined to be × M−1·s−1, which is higher than that of fractals × Monitoring the in the self-assembly processes is also a kinetic investigation that can be carefully by ESI-MS. When using NMR to monitor the complexation of ligands with or Ni(II) shifts of the peaks were observed, the of an before the formation of However, the limited information provided by NMR spectra not elucidate the ESI-MS was then used to the and the that is, linear by the m/z value of the intact Thus, ESI-MS can reveal the reaction via monitoring the Such capability was also used in monitoring the formation of a supramolecular wherein ligand and self-assembly were in a The time-dependent the of the coordination and processes (Figures and Figure | (a) The formation of supramolecular via a ligand and self-assembly (b) time-dependent ESI-MS monitoring the (b) Adapted with permission from ref Copyright American Chemical Society. Download figure Download PowerPoint With m/z values of the more details about the self-assembly processes could be allowing for deeper understanding of the assembling For in the of ligands with ions to and an with metal ion in the ligand with instead of was through ESI-MS by increasing ligand or metal Such an that the complexation to the A similar of complexation was also in other systems by ESI-MS, its ESI-MS of the species during the formation of prism with a ligand revealed the of the The ESI spectra the of self-assembly and showed the formation of the base with a Such a the design of a building block with two types of two distinct geometric that is, as base and respectively, allowing for the self-assembly of a structures to further design With the reliable m/z ESI-MS can identify the desired before other and characterization. For based on the directional an tritopic ligand was designed to metallo-supramolecules by coordination with or to the assembled could be or Unfortunately, NMR characterization because of the Nevertheless, ESI-MS provided evidence for the formation of a which the of the ligand to the of the complex for structural on

A series of porphyrin-based ionic complexes were prepared through the reaction of two porphyrin precursors, 5,10,15,20-tetrakis(4-(2-pyridyl)phenyl)porphyrin H2TPhPyP (1) and trans-dihydroxo [5,10,15,20-tetrakis(4-(2-pyridyl)phenyl)porphyrinato]tin(IV) Sn(OH)2TPhPyP (2), with various acids (HCl, HNO3, CF3COOH, H2SO4, H2CO3, and H3PO4). The complexes were characterized via elemental analysis, 1H nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet (UV)-visible spectroscopy, fluorescence spectroscopy, and field-emission scanning electron microscopy (FE-SEM). Each compound exhibited different results for UV-visible, fluorescence, FT-IR, and FE-SEM studies depending on the counter anions. The complexes possessed different self-assembled nanostructures based on electronic interactions between the cations of compounds 1 and 2 with different counter anions. These aggregated species are stabilized by electrostatic forces and the π-π stacking interactions between the two porphyrin rings, in which the counter anions play an important bridging role. The counter anions also play an important role in controlling the morphology and photocatalytic properties of the as-developed materials. The complexes were then used for the photocatalytic degradation of the malachite green (MG) dye in aqueous media under visible light irradiation for up to 70 min. A morphology-dependent photocatalytic degradation of the MG dye was observed for all the ionic complexes, with efficiencies ranging from 50% to 95%.

Regulation of gel formation, hierarchical structures, rheological behavior, and surface wettability via the linker of molecule center on bis(cholesteric) derivatives supramolecular self-assembly systems

We report the Fourier transform infrared (FTIR)–Raman spectroscopy study of spinel Li–Fe–Ti–O oxides viz., LiFeTiO4 and Li2FeTiO4 in order to probe structural details such as type of bonding networks viz., octahedral and tetrahedral, and type of different atomic bonds present in those materials. Both the samples were prepared through solid-state reaction route prior to high-energy ball-milling. All the phases prepared through solid-state reaction and ball-milled were probed using X-ray diffraction, field emission scanning electron microscopy, and FTIR–Raman spectroscopy. X-ray diffraction study indicates spinel phase formation with Fd3m space group symmetry for both LiFeTiO4 and Li2FeTiO4. However, pure phase of Li2FeTiO4 was not achieved in these preparation routes, rather mixed phases of Li2FeTiO4 and Fe2TiO4 were achieved. Field emission scanning electron microscopy (FESEM) analysis indicated porous microstructure for LiFeTiO4 while more agglomerated microstructure for Li2FeTiO4. Ball-milling reduces the grain size partly for both the samples. FTIR–Raman spectroscopy indicates the presence of LiO4 tetrahedral, LiO6 and TiO6 octahedral in the spinel network. Presence of Li–Li–O type bonding was also indicated from spectroscopy analysis. Existence of Fe2TiO4 phase with Li2FeTiO4 was also identified from both FTIR and Raman spectrum. Effect of ball-milling on the spectrum has been exhibited by broadening and peak shifting the FTIR–Raman spectrum, arising from the enhanced lattice strain and structural disorder.

Protein Conformation in Amorphous Solids by FTIR and by Hydrogen/Deuterium Exchange with Mass Spectrometry

In this paper, carbon nanotubes were characterized by several characterization methods such as FESEM (field emission scanning electron microscopy), Raman spectroscopy and fourier transform infrared (FTIR) spectroscopy. FESEM is used to characterize the morphology of carbon nanotubes, the structural is characterize by raman spectroscopy and bonding characteristic is determine by FTIR. The morphology of CNTs is found to be multiwall carbon nanotubes with diameter around 30-50 nm. D-peak was observed at 1341 Cm-1 and G-peak at 1575 Cm-1 based on raman spectroscopy result. The chemical bonding observed at range 2400 - 400 from FTIR spectra. These CNTs will be used for in vitro study in future.

Rhodanine‐chitosan (RC) hydrogel is examined as a novel antioxidant for acrylonitrile‐butadiene rubber (NBR) composites. RC is added to NBR with different proportions (1, 2 phr) and compared to the commercial 2,2,4‐trimethyl‐1,2‐dihydroquinoline polymer (TMQ) antioxidant. Physico‐mechanical properties including tensile strength, elongation, and modulus are also studied. It is found that NBR composite containing 2 phr of RC has the most favorable mechanical properties. The formed composites were subjected to thermo‐oxidative aging at 90°C for 1, 3, and 5 days. It is noticed that NBR composite containing 2 phr of RC is the most resistant to aging. Swelling properties and crosslink density are also determined. Composite containing 2 phr of RC has also higher crosslink density than the other prepared composites. The formed NBR composites containing both TMQ and RC are characterized by Fourier transforms infrared (FTIR), thermogravimetric analysis (TGA), and field emission scanning electron microscope (FESEM). The effect of aging on chemical structure of the composite and on surface morphology are also studied. It is found that the chemical structure of the composites containing 2 phr of RC is not affected by aging. Highlights Rhodanine‐chitosan (RC) is assessed as a new antioxidant for acrylonitrile‐butadiene rubber (NBR). RC is incorporated into NBR at two different concentrations: 1 and 2 phr. Mechanical, thermo‐oxidative aging, and swelling properties are evaluated. Thermal stability, Fourier transforms infrared and field emission scanning electron microscope are studied. Vulcanizates with 2 phr of RC show the most superior properties.

Acrylic acid monomer in a viscous supporting nylon solution was polymerized and fabricated simultaneously via an electrospinning process. This novel polymerization method defines the fiber morphology as a network of interconnected mats. This network consists of smaller poly(acrylic acid) (PAA) fibers, approximately 19 nm in diameter, and larger nylon 6 fibers, approximately 75 nm in diameter. These two different fibers are separated by extraction of PAA from the fibrous mat in water and differentiation of field-emission scanning electron microscopy (FESEM) images of the same mat using before and after extraction of PAA. The structure of the extracted PAA was confirmed by 1H NMR and Fourier transform infrared (FT-IR) analysis. The observed modification to conventional electrospun mats is due to the presence of an extra phase-separated PAA produced by the electrospinning polymerization process. Finally, fiber morphologies and hybrid property were characterized via FT-IR, FESEM, thermogravimetric analysis, and X-ray diffraction. Similarly extracted samples and synthesis PAA were characterized in FT-IR and 1H NMR spectroscopy.

Hydroxyapatite (HAp) is prepared synthetically by three different routes—wet chemical coprecipitation, sol–gel, and solution combustion routes. Different characterizations of the powders obtained from different routes were done for comparative analysis. The as-prepared powders were calcined between 600 and 1300 °C and studied for phase stability using X-ray diffraction (XRD). The thermal analysis and Fourier transform infrared (FTIR) spectroscopy analysis were also studied. The calcined powders were observed for microstructural changes at different temperatures using field emission scanning electron microscope (FESEM). The powders were then pressed to form pellets for analyzing the different sintering behavior such as dilatometry, bulk density, and apparent porosity. The sintered pellets were also examined under FESEM. It was observed that the HAp obtained from coprecipitation route (HCop) achieved the highest bulk density as well as hardest among all. Bioactivity test was also done for HCop samples for 7, 14, 21, and 28 days and observed under FESEM.

In this paper, novel microgels containing nano-SiO2 were prepared by in situ copolymerization using nano-SiO2 particles as a reinforcing agent, nanosilica functional monomer (silane-modified nano-SiO2) as a structure and morphology director, acrylamide (AAm) as a monomer, acrylic acid (AAc) as a comonomer, potassium persulfate (KPS) as a polymerization initiator, and N,N′-methylene bis (acrylamide) (MBA) as a crosslinker. In addition, a conventional copolymeric hydrogel based on poly (acrylamide/acrylic acid) was synthesized by solution polymerization. The microgel samples, hydrogel and nanoparticles were characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). A FESEM micrograph of copolymeric hydrogel showed the high porosity and 3D interconnected microstructure. Furthermore, FESEM results demonstrated that when nano-SiO2 particles were used in the AAm/AAc copolymerization process, the microstructure and morphology of product changed from porous hydrogel to a nanocomposite microgel with cauliflower-like morphology. According to FESEM images, the copolymerization of AAm and AAc monomers with a nanosilica functional monomer or polymerizable nanosilica particle as a seed led to a microgel with core–shell structure and morphology. These results demonstrated that the polymerizable vinyl group on nano-SiO2 particles have controlled the copolymerization and the product morphology. FTIR analysis showed that the copolymeric chains of polyacrylamide (PAAm) and poly (acrylic acid) (PAAc) were chemically bonded to the surfaces of the nano-SiO2 particles and silane-modified nano-SiO2. The particulate character of microgel samples and the existence of long distance among aggregations of particles led to rapid swelling and increasing of porosity and therefore increasing of degree of swelling.

Synthesis and characterization of highly luminescent EuOF nanoceramics by using prepared Eu(FOD)3 nanoparticles via sublimation method as precursor

A poly(pyrrolyl methane) (Poly[pyrrole-2, 5-diyl(4-methoxybenzylidane)], PPDMOBA)/multiwalled carbon nanotubes (MWNTs) composites are fabricated by in situ chemical polycondensation of pyrrole and 4-methoxybenzaldehyde on MWNTs. The structure, morphology, thermal stability and electrical property of the resulting composites are investigated via fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and a four-probe method. The electrochemical performance of the composites is determined in a three-electrode system using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. FTIR, FESEM and TEM confirm that the composites have been successfully prepared, and PPDMOBA is uniformly dispersed in MWNTs. Electrical conductivity of PPDMOBA/MWNTs composites is 1.39 S cm-1, which is significantly larger than that of pristine PPDMOBA. The specific capacitance and charge transfer resistance of the composites is 56 F g-1 (1 mA cm-2) and 0.3Ω, respectively.

During the last few decade, magnetite/hydroxyapatite nanoparticles have attracted much attention for its potential applications in the field of medicine and controlled drug delivery. In the present work, we have intended and synthesized, magnetite/hydroxyapatite nanoparticles by wet-chemical precipitation route. The thermal decomposition of the prepared sample was carried out by Thermogravimetric and Differential Scanning Calorimetry (TG/DSC) analysis upto 1000 °C, it showed that the sample was stable up to 919.2 °C. The phase formation, functional groups, morphology and magnetic property of as-prepared and annealed samples were characterized using X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), micro Raman, Field Emission Scanning Electron Microscopy (FE-SEM), Transmission electron microscopy (TEM) and vibrating-sample magnetometer (VSM). By adopting Scherer method detailed structural analysis like the crystallite size, strain, dislocation density, lattice parameter, unit cell volume, surface area and fraction of crystallinity were calculated for as-prepared and annealed HAP samples. The average crystallite size of the as-prepared, annealed at 700 °C, 800 °C and 900 °C are 39, 46, 51 and 65 nm, respectively. The dislocation density, strain and surface area were decreased. FT-IR and Raman spectra showed both as-prepared and annealed samples possessed the characteristic bands of HAP. FE-SEM and TEM images depicted and confirmed the morphological characteristics of HAP. The VSM analysis confirmed that both as-prepared and annealed samples of HAP are in diamagnetic nature. The dielectric constant of as-prepared and annealed samples decreased with increase in annealing temperature whereas the conductivity increases with increase in frequency. The antibacterial property of apatite samples depending on the types of bacterial strains and also activity changed with the crystallite size.

Silver-particle-incorporated polyurethane films were evaluated for antimicrobial activity towards two different bacteria: Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Distributed silver particles sourced from silver nitrate, silver lactate and preformed silver nanoparticles were mixed with polyurethane (PU) and variously characterized by field emission scanning electron microscopy (FESEM), fourier transform infra-red (FTIR) spectroscopy, X-ray diffraction (XRD) and contact angle measurement. Antibacterial activity against E.coli was confirmed for films loaded with 10% (w/w) AgNO3, 1% and 10% (w/w) Ag lactate and preformed Ag nanoparticles. All were active against S. aureus, but Ag nanoparticles loaded with PU had a minor effect. The apparent antibacterial performance of Ag lactate-loaded PU is better than other Ag ion-loaded films, revealed from the zone of inhibition study. The better performance of silver lactate-loaded PU was the likely result of a porous PU structure. FESEM and FTIR indicated direct interaction of silver with the PU backbone, and XRD patterns confirmed that face-centred cubic-type silver, representative of Ag metal, was present. Young’s modulus, tensile strength and the hardness of silver containing PU films were not adversely affected and possibly marginally increased with silver incorporation. Dynamic mechanical analysis (DMA) indicated greater thermal stability.

A piperazine-linked robust N-rich covalent organic polymer (COP), SMCOP-1, was synthesized by a catalyst-free method and characterized by Fourier transform infrared (FTIR), 13C CP/MAS, X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (PXRD). This polymeric material can work as an efficient platform for removing toxic Hg2+ from wastewater. This system showed >97% Hg2+ removal, as confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES), with a maximum uptake capacity of 1329 mg g–1. Hg2+ incorporation inside SMCOP-1 was confirmed by XPS, energy-dispersive spectrometry (EDS), and elemental mapping of field emission scanning electron microscopy (FE-SEM). The high Hg2+ removal capacity of SMCOP-1 can be attributed to the strong noncovalent interaction between the Hg2+ ion and the binding sites of the covalent organic polymer, as suggested by density functional theory (DFT) calculations, noncovalent interaction (NCI) analysis, and the electrostatic potential (ESP) map. The material’s recyclability was studied for up to four consecutive cycles, and it was observed that it retained a high removal capacity without any change in the structure and morphology, as confirmed by FTIR and FE-SEM.