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N-heterocyclic carbenes(NHCs) have garnered the attention of material scientists and chemists for their tunable electronic properties. NHCs anchored to surfaces have attractive features and may provide new applications that traditional self-assembled monolayers (SAMs) have yet to be employed. In-fact, NHCs have been utilized to functionalize surfaces to tune reactivity and/or selectivity. However, the underlying mechanisms to control the surface-adsorbate interaction is still in its infancy, especially for SAAs. Herein we utilize periodic non-local density functional theory (DFT) calculations to better understand how changing the NHC backbone influences the bonding between the surface and the adsorbate with the end goal to utilize a relatively new mechanism to store hydrogen. 

N-heterocyclic carbenes (NHCs) have grown in popularity in recent years due to their superior surface stability on metal nanoparticles and surfaces. This stability is often characterized experimentally by studying the σ-donation and π-backbonding as measured through NHC-selenium adduct NMR and the Huynh Electronic Parameter (HEP), respectively. However, recent work with NHCs on metal clusters suggests that the ligands can adopt a variety of orientations on the surface. Thus, the surface may have a pronounced impact on the σ-donation and π-backbonding observed for these NHCs. In this work, we aim to determine how well these experimental characterizations compare to trends observed via bond decomposition analysis. 

Computational chemistry is no longer seen as just an academic exercise. Researchers in academia and industry are now aware of the benefits associated with theoretical predictions of molecules. However, there is a skills-gap associated with teaching/learning the basics and the applications of computational chemistry. Herein, we describe the development and utilization of several quantum chemical exercises for educational purposes. 

We have predicted acid dissociation constants (pKa), octanol-water partition coefficients (KOW), and DPMC lipid membrane-water partition coefficients (Klipid-w) of 150 different 8-carbon containing poly-/per-fluoroalkyl carboxylic acids (C8-PFCAs) utilizing COMSO-RS theory. Different trends associated with functionalization, degree of fluorination, degree of saturation, degree of chlorination, and branching are discussed based upon the predicted values for the partition coefficients. In general, functionalization closest to the carboxylic head group had the greatest impact on the value of the predicted physicochemical properties. 

Per-and polyfluoroalkyl substances (PFAS) are a class of contaminants of emerging concern frequently used in products like aqueous firefighting foams and non-stick coatings due to their stability and surfactant-like qualities. The lack of analytical standards for many emerging PFAS have severely limited our ability to comprehensively identify unknown PFAS contaminants in the environment, especially those that occur as isomers. Annotation of small molecules and identification of unknowns based only on elemental composition and mass fragmentation patterns remain major challenges in nontarget analysis employing liquid chromatography with high-resolution mass spectrometry (LC-HRMS). In this study, chromatographic retention factors (k) and mass spectral fragmentation patterns of 32 known PFAS were determined using our optimized parameters in LC-HRMS. The same method was then used to analyze previously unidentified PFAS in actual environmental samples. Using characteristic ions observed in the MS fragmentation of PFAS, the most probable isomeric structures of the detected PFAS were predicted. To increase confidence in the predicted molecular structure, Density Functional Theory and Conductor-like Screening Model for Realistic Solvents (COSMO-RS) calculations were used to predict physicochemical properties of different constitutional isomers. The DFT calculations facilitated geometric optimization, determination of polarizability, and calculation of the chemical potential the isomers. COSMO-RS uses the chemical potential to predict thermodynamic properties of molecules such as pKa, solubility, and Kow. These properties were then used to make a multi-variable linear regression to predict k values. The model was trained using 32 known PFAS. The properties used were log Kow of the neutral and anion species of the PFAS, and their polarizability. The model was specific enough to predict significantly different k values of unknown compounds with similar structures, which facilitated assignment of isomeric structures of PFAS. 

Nontarget analysis using liquid chromatography–high resolution mass spectrometry (LC–HRMS) is a valuable approach in characterizing for contaminants of emerging concern (CECs) in the environment. However, identification of these analytes can be quite costly or taxing without proper analytical standards. To circumvent this problem we utilize Quantitative structure-retention relationships (QSRR) models to predict elution order and retention times. Properties calculated from density functional theory (DFT) and the conductor-like screening model for real solvents (COSMO-RS) theory are used to produce our QSRR models, which can be calculated for virtually any analyte. We show that this methodology has been successful in identification of per- /poly-fluoroalkyl substances (PFAS) and other contaminants. Nontarget analysis using liquid chromatography– high resolution mass spectrometry (LC–HRMS) is a valuable approach in characterizing for contaminants of emerging concern (CECs) in the environment. However, identification of these analytes can be quite costly or taxing without proper analytical standards. To circumvent this problem we utilize Quantitative structureretention relationships (QSRR) models to predict elution order and retention times. Properties calculated from density functional theory (DFT) and the conductor-like screening model for real solvents (COSMO-RS) theory are used to produce our QSRR models, which can be calculated for virtually any analyte. We show that this methodology has been 

https://doi.org/10.1021/scimeetings.0c05786 

The exceptionally π-basic metal fragments {MoTp(NO)(DMAP)} and {WTp(NO)(PMe3)} (Tp = tris(pyrazolyl)borate; DMAP = 4-(N,N-dimethylamino)pyridine) form thermally stable η2-coordinated complexes with a variety of electron-deficient arenes. The tolerance of substituted arenes with fluorine-containing electron withdrawing groups (EWG; −F, −CF3, −SF5) is examined for both the molybdenum and tungsten systems. When the EWG contains a π bond (nitriles, aldehydes, ketones, ester), η2 coordination occurs predominantly on the nonaromatic functional group. However, complexation of the tungsten complex with trimethyl orthobenzoate (PhC(OMe)3) followed by hydrolysis allows access to an η2-coordinated arene with an ester substituent. In general, the tungsten system tolerates sulfur-based withdrawing groups well (e.g., PhSO2Ph, MeSO2Ph), and the integration of multiple electron-withdrawing groups on a benzene ring further enhances the π-back-bonding interaction between the metal and aromatic ligand. While the molybdenum system did not form stable η2-arene complexes with the sulfones or ortho esters, it was capable of forming rare examples of stable η2-coordinated arene complexes with a range of fluorinated benzenes (e.g., fluorobenzene, difluorobenzenes). In contrast to what has been observed for the tungsten system, these complexes formed without interference of C–H or C–F insertion. 

Paleoanthropological and geological field research at Galili, Afar Regional State, Ethiopia was reinitiated in 2016. The site has been established as encompassing sediments ranging between 2.5-4.5± Ma and includes early Australopithecus and perhaps Ardipithecus. While preliminary paleoenvironmental analyses have suggested open woodland to bushland-woodland and shrubland, we present here additional evidence of the diet and functional anatomy of the Early Pliocene bovids from Galili. Fossil bovids have been recognized as a crucial tool in understanding ancient environments and serve as an important ecological indicator. Establishing the habitats of Galili is important for both understanding the environment in which the fauna, including hominins, resided and providing comparison to other contemporaneous sites. Taxonomic identification and metric analyses were performed on bovid teeth (n=93) from the 3.9-4.4 Ma Shabeley Laag and Dhidinley members to reconstruct the paleoenvironment. The sample was dominated by Reduncini, a riparian-associated tribe, and Tragelaphini, a browsing-associated tribe. Hypsodonty index was calculated for each tribe and results suggest the most abundant bovid taxa trend towards the brachydont category. Only three tribes: Alcelaphini, Antilopini, and Hippotragini fell within the mesodont category, and no tribes had hypsodont indices. Mesowear analysis of the sample indicated high occlusal relief and rounded cusp shapes were most common. Taken together, our results indicate a trend in bovid diet towards mixed feeding and browsing at Galili.