Raman Characterization of Plastics: A DFT Study of Polystyrene.

Plastic materials are ubiquitous and raise concerns about their impact on health and the environment. To address these concerns, it is crucial to characterize the structural, size, and textural properties of plastics throughout their lifecycle from production to degradation. Raman spectroscopy appears as a valuable tool for this purpose, offering speed, robustness, and sensitivity to nanoscale and amorphous particles. In order to be properly used for plastics, the Raman response of reference materials needs to be carefully assessed, with the literature on such assessments being scarce. This study addresses this gap by using theoretical calculations to generate ab initio spectra for polystyrene, a reference material. The aim is to explain the origins of the spectral peaks and their consistency across various compositions and structures using linear ordered polymeric and finite amorphous models. The CRYSTAL package is employed to obtain full Raman spectra based on a careful benchmark of computational settings. While some peaks are present across all spectra and can serve for calibration, others exhibit structure-dependent behavior, enabling polymer identification. We conclude that Raman spectroscopy is a well-suited technique for plastics characterization provided that a careful analysis of signal origin is conducted to fully interpret the spectra and deploy applications.

Special Issue "Theoretical Calculation and Molecular Modeling of Nanomaterials".

The continuous advancement of computational chemistry and the chemical modeling of materials is closely aligned with the ever-evolving computational power and related techniques [...].

On the Origin of Raman Activity in Anatase TiO2 (Nano)Materials: An Ab Initio Investigation of Surface and Size Effects.

Titania-based materials are abundant in technological applications, as well as everyday products; however, many of its structure-property relationships are still unclear. In particular, its surface reactivity on the nanoscale has important consequences for fields such as nanotoxicity or (photo)catalysis. Raman spectroscopy has been used to characterize titania-based (nano)material surfaces, mainly based on empirical peak assignments. In the present work, we address the structural features responsible for the Raman spectra of pure, stoichiometric TiO2 materials from a theoretical characterization. We determine a computational protocol to obtain accurate Raman response in a series of anatase TiO2 models, namely, the bulk and three low-index terminations by periodic ab initio approaches. The origin of the Raman peaks is thoroughly analyzed and the structure-Raman mapping is performed to account for structural distortions, laser and temperature effects, surface orientation, and size. We address the appropriateness of previous experimental use of Raman to quantify the presence of distinct TiO2 terminations, and provide guidelines to exploit the Raman spectrum based on accurate rooted calculations that could be used to characterize a variety of titania systems (e.g., single crystals, commercial catalysts, thin layered materials, facetted nanoparticles, etc.).

A molecular understanding of citrate adsorption on calcium oxalate polyhydrates.

Calcium oxalate precipitation is a common pathological calcification in the human body, whereby crystallite morphology is influenced by the chelating properties of biological ions such as citrate. It has been suggested that citrate could steer oxalate formation towards its dihydrated form and away from the monohydrated form, which was identified as a major cause for disease. To assess the influence of the citrate ion on the resulting calcium oxalate, surface energies were calculated at the dispersion-corrected density functional level of theory for both monohydrated and dihydrated calcium oxalate. Different adsorption geometries were considered by varying the attacking angle of citrate as well as by considering the citrate ion on top of an adsorbed water layer or penetrating the water layer. The obtained results were compared to ab initio molecular dynamics simulations and experimental scanning electron microscope images. A strong preference for citrate adsorption on calcium oxalate dihydrate was observed, suggesting medical applications for the treatment of such pathological calcifications.

Understanding the Reactivity of Supported Late Transition Metals on a Bare Anatase (101) Surface: A Periodic Conceptual DFT Investigation.

The rapidly growing interest for new heterogeneous catalytic systems providing high atomic efficiency along with high stability and reactivity triggered an impressive progress in the field of single-atom catalysis. Nevertheless, unravelling the factors governing the interaction strength between the support and the adsorbed metal atoms remains a major challenge. Based on periodic density functional theory (DFT) calculations, this paper provides insight into the adsorption of single late transition metals on a defect-free anatase surface. The obtained adsorption energies fluctuate, with the exception of Pd, between -3.11 and -3.80 eV and are indicative of a strong interaction. Depending on the considered transition metal, we could attribute the strength of this interaction with the support to i) an electron transfer towards anatase (Ru, Rh, Ni), ii) s-d orbital hybridisation effects (Pt), or iii) a synergistic effect between both factors (Fe, Co, Os, Ir). The driving forces behind the adsorption were also found to be strongly related to Klechkowsky's rule for orbital filling. In contrast, the deviating behaviour of Pd is most likely associated with the lower dissociation enthalpy of the Pd-O bond. Additionally, the reactivity of these systems was evaluated using the Fermi weighted density of states approach. The resulting softness values can be clearly related to the electron configuration of the catalytic systems as well as with the net charge on the transition metal. Finally, these indices were used to construct a model that predicts the adsorption strength of CO on these anatase-supported d-metal atoms. The values obtained from this regression model show, within a 95 % probability interval, a correlation of 84 % with the explicitly calculated CO adsorption energies.

Synergistic Effects in the Activity of Nano-Transition-Metal Clusters Pt12 M (M=Ir, Ru or Rh) for NO Dissociation.

The dissociation of environmentally hazardous NO through dissociative adsorption on metallic clusters supported by oxides, is receiving growing attention. Building on previous research on monometallic M13 clusters [The Journal of Physical Chemistry C 2019, 123 (33), 20314-20318], this work considers bimetallic Pt12 M (M=Rh, Ru or Ir) clusters. The adsorption energy and activation energy of NO dissociation on the clusters have been calculated in vacuum using Kohn-Sham DFT, while their trends were rationalized using reactivity indices such as molecular electrostatic potential and global Fermi softness. The results show that doping of the Pt clusters lowered the adsorption energy as well as the activation energy for NO dissociation. Furthermore, reactivity indices were calculated as a first estimate of the performance of the clusters in realistic amorphous silica pores (MCM-41) through ab initio molecular dynamics simulations.

Crystalline structures of L-cysteine and L-cystine: a combined theoretical and experimental characterization.

It is assumed that genetic diseases affecting the metabolism of cysteine and the kidney function lead to two different kinds of pathologies, namely cystinuria and cystinosis whereby generate L-cystine crystals. Recently, the presence of L-cysteine crystal has been underlined in the case of cystinosis. Interestingly, it can be strikingly seen that cystine ([-S-CH2-CH-(NH2)-COOH]2) consists of two cysteine (C3H7NO2S) molecules connected by a disulfide (S-S) bond. Therefore, the study of cystine and cysteine is important for providing a better understanding of cystinuria and cystinosis. In this paper, we elucidate the discrepancy between L-cystine and L-cysteine by investigating the theoretical and experimental infrared spectra (IR), X-ray diffraction (XRD) as well as Raman spectra aiming to obtain a better characterization of abnormal deposits related to these two genetic pathologies.

Towards a predictive model for polymer solubility using the noncovalent interaction index: polyethylene as a case study.

In this work we present the development of a novel, quantitative solubility descriptor based on the non-covalent interaction index. It is presented as a more insightful alternative to Hansen's solubility parameters and the COSMO model to assess and predict polymer solubility in different solvents. To this end, we studied the solvation behaviour as a function of the chain length of a single chain of arguably the most simple polymer, polyethylene, in anisole (solvent) and methanol (poor solvent) via molecular dynamics simulations. It was found that in anisole the solute maximized its interface with the solvent, whereas in methanol the macromolecule formed rod-like structures by folding on itself once the chain length surpassed a certain barrier. We assessed this behaviour - which can be related to solubility - quantitatively and qualitatively via well-known descriptors, namely the solvation free energy, and the solvent accessible surface area. In addition, we propose the non-covalent interaction (NCI) index as a versatile descriptor, providing information on the strength, as well as the nature, of the solute-solvent interactions, the solute's intramolecular interactions and on the solute's conformation, both qualitatively and quantitatively. Finally, as a quantitative measure for solubility, defined in this context as the solute's tendency to maximize its interactions with the solvent, we propose two new NCI-based descriptors: the relative integrated NCI density and the integrated NCI difference. The former represents the quantitative difference in solute-solvent interactions between a fully extended coil and the actual conformation during simulation and the latter the quantitative difference between the intermolecular (solute-solvent) and the intramolecular (in the solute) non-covalent interactions. The easy interpretation and calculation of these novel quantities open up the possibility of fast, reliable and insightful high-throughput screening of different (anti)solvent and solute combinations.

Study on the biological behaviors of CaP coatings with different morphology on carbon/carbon composites.

In this work, we designed and fabricated a CaP composite bio-coating with different surface morphologies on a carbon/carbon (C/C) matrix by means of hybrid supersonic atmospheric plasma spraying (SAPS) and microwave-hydrothermal (MH) technologies. We found that all studied coating materials can support mesenchymal stem cells (MSCs) proliferation with prolonged culture time (3 days and 7 days) in vitro. Furthermore, according to the (Confocal Laser Scanning Microscopy) CLSM results, the MSCs also showed good attachment and different spreading morphologies on SAPS/MH coatings. As such, C/C matrix, the MH treated coatings with needle-like and rod-like microstructures were chosen for further in vivo investigation. Considering the good bonding between host tissue and the studied materials, the in vivo morphology studies confirmed a good histocompatibility for all coating samples, as well as a decreasing expression for inflammatory factors in a physiological environment. The histological results around the implants indicated different cell aggregation and vascularization ability in the local micro-environment. In particular, based on the reduction of the C/C initial surface flaws (e.g. hydrophobicity, biological inertia and easily producing carbon fragments or particles), the MH treated coating with rod-like surface morphology with a specific surface area (~2.33 m2/g) and roughness (~13.80 µm), showed excellent performance as a promising implant in live tissue.

In Search of an Efficient Complexing Agent for Oxalates and Phosphates: A Quantum Chemical Study.

Limiting gastrointestinal oxalate absorption is a promising approach to reduce urinary oxalate excretion in patients with idiopathic and enteric hyperoxaluria. Phosphate binders, that inhibit gastrointestinal absorption of dietary phosphate by the formation of easily excretable insoluble complexes, are commonly used as a treatment for hyperphosphatemia in patients with end-stage renal disease. Several of these commercially available phosphate binders also have affinity for oxalate. In this work, a series of metallic cations (Li+, Na+, Mg2+, Ca2+, Fe2+, Cu2+, Zn2+, Al3+, Fe3+ and La3+) is investigated on their binding affinity to phosphate and oxalate on one side and anionic species that could be used to administer the cationic species to the body on the other, e.g., acetate, carbonate, chloride, citrate, formate, hydroxide and sulphate. Through quantum chemical calculations, the aim is to understand the competition between the different complexes and propose possible new and more efficient phosphate and oxalate binders.

Lanthanum carbonate to control plasma and urinary oxalate level in type 1 primary hyperoxaluria?

INTRODUCTION: The therapy to reduce urinary oxalate excretion in primary hyperoxaluria type 1 is still required. CASE PRESENTATION: A 37-year-old hemodialyzed man suffered from systemic oxalosis secondary to primary hyperoxaluria type 1 exhibited a drastic plasma oxalate decrease from 110 to 22 µmol/L two months after adjunction of lanthanum carbonate to classical treatment (intensive hemodialysis with pyridoxine). A 34-year-old woman with normal kidney function presented 10 years of bilateral kidney stones due to primary hyperoxaluria type 1 [hyperoxaluria (109.2 mg/24 h), plasma oxalate (56.0 µmol/L)]. The oxalate level remained uncontrolled despite of low oxalate-normal calcium diet, pyridoxine and increased water intake though the lanthanum carbonate adjunction resulted in significant decrease in plasma oxalate and oxaluria. CONCLUSION: We report the lanthanum efficacy in reducing circulating and urinary oxalate levels in type 1 primary hyperoxaluria. Possible mechanism of observed falls in oxalate concentration would be a decrease in the intestinal absorption of oxalate.

A novel multinuclear solid-state NMR approach for the characterization of kidney stones.

The spectroscopic study of pathological calcifications (including kidney stones) is extremely rich and helps to improve the understanding of the physical and chemical processes associated with their formation. While Fourier transform infrared (FTIR) imaging and optical/electron microscopies are routine techniques in hospitals, there has been a dearth of solid-state NMR studies introduced into this area of medical research, probably due to the scarcity of this analytical technique in hospital facilities. This work introduces effective multinuclear and multidimensional solid-state NMR methodologies to study the complex chemical and structural properties characterizing kidney stone composition. As a basis for comparison, three hydrates (n=1, 2 and 3) of calcium oxalate are examined along with nine representative kidney stones. The multinuclear magic angle spinning (MAS) NMR approach adopted investigates the 1H, 13C, 31P and 31P nuclei, with the 1H and 13C MAS NMR data able to be readily deconvoluted into the constituent elements associated with the different oxalates and organics present. For the first time, the full interpretation of highly resolved 1H NMR spectra is presented for the three hydrates, based on the structure and local dynamics. The corresponding 31P MAS NMR data indicates the presence of low-level inorganic phosphate species; however, the complexity of these data make the precise identification of the phases difficult to assign. This work provides physicians, urologists and nephrologists with additional avenues of spectroscopic investigation to interrogate this complex medical dilemma that requires real, multitechnique approaches to generate effective outcomes.

Reactivity of Single Transition Metal Atoms on a Hydroxylated Amorphous Silica Surface: A Periodic Conceptual DFT Investigation.

The drive to develop maximal atom-efficient catalysts coupled to the continuous striving for more sustainable reactions has led to an ever-increasing interest in single-atom catalysis. Based on a periodic conceptual density functional theory (cDFT) approach, fundamental insights into the reactivity and adsorption of single late transition metal atoms supported on a fully hydroxylated amorphous silica surface have been acquired. In particular, this investigation revealed that the influence of van der Waals dispersion forces is especially significant for a silver (98 %) or gold (78 %) atom, whereas the oxophilicity of the Group 8-10 transition metals plays a major role in the interaction strength of these atoms on the irreducible SiO2 support. The adsorption energies for the less-electronegative row 4 elements (Fe, Co, Ni) ranged from -1.40 to -1.92 eV, whereas for the heavier row 5 and 6 metals, with the exception of Pd, these values are between -2.20 and -2.92 eV. The deviating behavior of Pd can be attributed to a fully filled d-shell and, hence, the absence of the hybridization effects. Through a systematic analysis of cDFT descriptors determined by using three different theoretical schemes, the Fermi weighted density of states approach was identified as the most suitable for describing the reactivity of the studied systems. The main advantage of this scheme is the fact that it is not influenced by fictitious Coulomb interactions between successive, charged reciprocal cells. Moreover, the contribution of the energy levels to the reactivity is simultaneously scaled based on their position relative to the Fermi level. Finally, the obtained Fermi weighted density of states reactivity trends show a good agreement with the chemical characteristics of the investigated metal atoms as well as the experimental data.

Effect of sprayed techniques on the surface microstructure and in vitro behavior of nano-HAp coatings.

Supersonic atmospheric plasma spray (SAPS) technique is a classical method which is employed to coat the carbon/carbon (C/C) composites by nano-hydroxyapatite (HAp) powders to decrease the biologically inert, hydrophobic drawbacks of substrate surfaces. In recent years, profiting from the promoting of energy conservation and environmental protection, more emphasis was placed on industrial manufacturing to simplify the experimental steps. This paper aims to study the preparation of nano-HAp coatings by suspension plasma spray (SPS) instead of the original SAPS technique. A denser, more uniform and less defective coating is successfully fabricated on C/C substrate using SPS technique. More important, fewer surface flaws in SPS coating could be observed by scanning electron microscopy (SEM) which shows that the large drawbacks of the coating have disappeared during spraying process. Meanwhile, except for HAp, phase compositions of the SPS coating appear with slight calcium oxide (CaO, 0.8%) and tricalcium phosphate (TCP, 30.7%), and then all CaO as well as TCP phases transform into dicalcium phosphate anhydrous (DCPA, 60.6%) after microwave-hydrothermal (MH) treatment. Thermal analysis (TG/DSC) reveals that SPS coating (97.51%) has a higher thermal stability than that of the SAPS coating (82.37%). Also, in comparison, the SPS coating after MH treatment (SPS-MH coating) exhibits better thermal properties (92.76%). In addition, compared to the SAPS and SPS coatings, due to the more flaw reduction and phase transformation, SPS-MH coating shows a better biological properties according to the surface microstructure in simulation body fluid (SBF) solution and cell spreading area on coating. The highest corrosion resistance with the current density of 3.9798 × 10-7 A/cm2 and a potential of 0.0419 V is achieved for SPS-MH coating.

Unravelling phosphate adsorption on hydrous ferric oxide surfaces at the molecular level.

The thorough understanding of the adsorption mechanism of phosphate on hydrous ferric oxides is necessary to deal with the environmental issues related to high phosphate concentrations in soils and open water. In this work, we consider three different adsorption geometries (monodentate and bidentate chemisorption and physisorption) and calculate the adsorption geometries and related adsorption energies at optPBE-vdW level. Using the Maxwell-Boltzmann distribution, it is estimated that about 83% of the phosphate molecules is in a monodentate chemisorption configuration, while 17% is physisorbed. Furthermore, theoretical infra-red spectra are obtained and compared to equivalent experimental spectra, supporting the conclusion that mainly monodentate chemisorption and physisorption occur. Most interestingly, a weighed infra-red spectrum is then calculated, using the weights from the Maxwell-Boltzmann distribution, showing a very good comparison with the experimental spectra.

Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry.

For a few years now, quantum chemical modeling of materials has experienced a tremendousboost due to the increasing computational power [...].

Design and Synthesis of Gold-Gadolinium-Core-Shell Nanoparticles as Contrast Agent: a Smart Way to Future Nanomaterials for Nanomedicine Applications.

INTRODUCTION: The development of biopolymers for the synthesis of Gd(III) nanoparticles, as therapeutics, could play a key role in nanomedicine. Biocompatible polymers are not only used for complex monovalent biomolecules, but also for the realization of multivalent active targeting materials as diagnostic and/or therapeutic hybrid nanoparticles. In this article, it was reported for the first time, a novel synthesis of Gd(III)-biopolymer-Au(III) complex, acting as a key ingredient of core-shell gold nanoparticles (Gd(@AuNPs). MATERIAL AND METHODS: The physical and chemical evaluation was carried out by spectroscopic analytical techniques (Raman spectroscopy, UV-visible and TEM). The theoretical characterization by DFT (density functional theory) analysis was carried out under specific conditions to investigate the interaction between the Au and the Gd precursors, during the first nucleation step. Magnetic features with relaxivity measurements at 7T were also performed as well as cytotoxicity studies on hepatocyte cell lines for biocompatibility studies. The in vivo detailed dynamic biodistribution studies in mice to characterize the potential applications for biology as MRI contrast agents were then achieved. RESULTS: Physical-chemical evaluation confirms the successful design and reaction supposed. Viabilities of TIB-75 (hepatocytes) cells were evaluated using Alamar blue cytotoxic tests with increasing concentrations of nanoparticles. In vivo biodistribution studies were then accomplished to assess the kinetic behavior of the nanoparticles in mice and characterize their stealthiness property after intravenous injection. CONCLUSION: We demonstrated that Gd@AuNPs have some advantages to display hepatocytes in the liver. Particularly, these nanoconjugates give a good cellular uptake of several quantities of Gd@NPs into cells, while preserving a T1 contrast inside cells that provide a robust in vivo detection using T1-weighted MR images. These results will strengthen the role of gadolinium as complex to gold in order to tune Gd(@AuNPs) as an innovative diagnostic agent in the field of nanomedicine.

Understanding the Role of Rutile TiO2 Surface Orientation on Molecular Hydrogen Activation.

Titanium oxide (TiO2) has been widely used in many fields, such as photocatalysis, photovoltaics, catalysis, and sensors, where its interaction with molecular H2 with TiO2 surface plays an important role. However, the activation of hydrogen over rutile TiO2 surfaces has not been systematically studied regarding the surface termination dependence. In this work, we use density functional theory (PBE+U) to identify the pathways for two processes: the heterolytic dissociation of H2 as a hydride-proton pair, and the subsequent H transfer from Ti to near O accompanied by reduction of the Ti sites. Four stoichiometric surface orientations were considered: (001), (100), (110), and (101). The lowest activation barriers are found for hydrogen dissociation on (001) and (110), with energies of 0.56 eV and 0.50 eV, respectively. The highest activation barriers are found on (100) and (101), with energies of 1.08 eV and 0.79 eV, respectively. For hydrogen transfer from Ti to near O, the activation barriers are higher (from 1.40 to 1.86 eV). Our results indicate that the dissociation step is kinetically more favorable than the H transfer process, although the latter is thermodynamically more favorable. We discuss the implications in the stability of the hydride-proton pair, and provide structures, electronic structure, vibrational analysis, and temperature effects to characterize the reactivity of the four TiO2 orientations.

Dibenzyl Disulfide Adsorption on Cationic Exchanged Faujasites: A DFT Study.

Although dibenzyl disulfide (DBDS) is used as a mineral oil stabilizer, its presence in electrical transformer oil is associated as one of the major causes of copper corrosion and subsequent formation of copper sulfide. In order to prevent these undesirable processes, MY zeolites (with M = Li, Na, K, Cs, Cu or Ag) are proposed to adsorb molecularly DBDS. In this study, different MY zeolites are investigated at the DFT+D level in order to assess their ability in DBDS adsorption. It was found that CsY, AgY and CuY exhibit the best compromise between high interaction energies and limited S-S bond activation, thus emerging as optimal adsorbents for DBDS.

Porphyrins Conjugated with Peripheral Thiolato Gold(I) Complexes for Enhanced Photodynamic Therapy.

Porphyrins fused to imidazolium salts across two neighboring ß-pyrrolic positions were used as N-heterocyclic carbene (NHC) precursors to anchor AuI -Cl complexes at their periphery. Synthesis of several thiolato-AuI complexes was then achieved by substituting chloride for thiolates. Photodynamic properties of these complexes were investigated: the data obtained show that the Au-S bonds could be cleaved upon irradiation. The proposed mechanism to explain the release of thiolate moiety involves the S atom oxidation by singlet oxygen generated in the course of irradiation. In view of photodynamic therapy (PDT) applications, these porphyrins fused to NHC-AuI complexes were tested as photosensitizers to kill MCF-7 breast cancer cells. Results show the important role played by the ancillary ligands (chloride versus thiolates) on the photodynamic effect.