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Results for “Pyridine”

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Novel selenylated imidazo[1,2-a]pyridines for breast cancer chemotherapy: Inhibition of cell proliferation by Akt-mediated regulation, DNA cleavage and apoptosis

A novel series of selenylated imidazo[1,2-a]pyridines were designed and synthesized with a view to a promising activity against breast cancer cell. The compounds, 7-methyl-3-(naphthalene-1-ylselanyl)-2-phenylimidazo[1,2-a]pyridine, named IP-Se-05, and 3-((2-methoxyphenyl)selanyl)-7-methyl-2-phenylimidazo[1,2-a]pyridine, named IP-Se-06, showed high cytotoxicity for MCF-7 cells (IC{sub 50} = 26.0 μM and 12.5 μM, respectively). Both the compounds inhibited the cell proliferation and caused decrease in the number of cells in the G2/M phase of cell cycle. IP-Se-05 and IP-Se-06 were also evaluated for effects on CT-DNA and DNA of MCF-7 cells. The compounds intercalated into CT-DNA and both treatments caused cleavage of DNA in cells. In addition, the compounds induced cell death by apoptosis. However, the presence of (2-methoxyphenyl) selenyl moiety at the imidazo[1,2-a]pyridine (IP-Se-06) appears to have a better antitumor effect with higher cytotoxicity at a lower concentration and caused less necrosis. Overall, the current study established IP-Se-06 more than IP-Se-05 as a potential prototype compound to be employed as an antiproliferative agent for the treatment of breast cancer.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Photoinduced Electron Transfer from ZrOCo Binuclear Light Absorber to Pyridine Elucidated by Transient Optical and Infrared Spectroscopy

All-inorganic heterobinculear units can be excited to a metal-to-metal charge transfer (MMCT) state by visible and ultraviolet light and form the core of multicomponent artificial photosystems that rely on conjugated molecular wires to transmit electrons and holes across ultrathin silica separation membranes to catalytic sites. To understand electron transfer from a heterobinuclear unit to an organic molecule, model systems consisting of pyridine interacting with Zr IV OCo II or Tisup>IV OCo II sites on silica nanoparticles were assembled and spectroscopically characterized. Transient optical absorption spectroscopy combined with infrared analysis revealed that visible light excitation of assemblies in which pyridine interacts with the Zr center of the ZrOCo unit results in sub-10 ns separation by electron transfer to the organic moiety. Rapid-scan FT-IR spectroscopy supported by density functional theory confirmed the identity of the pyridine radical anion charge-separated state. This state shows a lifetime of 220 (±60) ms prior to complete recovery of the initial state, suggesting spin crossover along the electron transfer path. No hole transfer from excited Zr IV OCo II → Zr III OCo III to pyridine is observed. The rectifying charge transfer behavior is an important design aspect for developing efficient artificial photosystems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Pyridine Catalysis of Anhydride Hydrolysis within Carbodiimide‐Driven Reaction Networks

Carbodiimide-fueled reaction networks offer a versatile platform for nonequilibrium chemical systems. Typically, the carbodiimide converts a carboxylic acid to its anhydride, called “activation,” which subsequently undergoes hydrolysis, called “deactivation.” Here, we investigate pyridines with variable nucleophilicity as catalysts to control deactivation (pyridine, 4-methylpyridine, 4-methoxypyridine, and 4-dimethylaminopyridine). Reactions have been monitored by NMR spectroscopy. Although this reaction network is simple, determination of well-defined rate constants from kinetic modeling is challenging because of correlation between the parameters. This issue can be addressed by analyzing the anhydride hydrolysis independently. The rate of attack of the pyridines on the anhydride follows expected nucleophilicity trends, although this is offset by increased protonation of more-nucleophilic pyridines at typical pH's. The optimized parameters can be used to model the full carbodiimide-driven process, although the presence of the common carbodiimide EDC has unanticipated effects on the anhydride hydrolysis rate. The results offer context for controlling carbodiimide-fueled reaction networks through the choice of suitable catalysts and pH.

Anhydrides↗
DOE OSTI2026

The presence of Ru metal modifies the behavior of deuterium bound to pyridinic nitrogen in doped graphene-like materials

We used a combination of x-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) to investigate how the presence of a ruthenium (Ru) metal substrate modifies the N-D bond strength of the pyridinic nitrogen species in nitrogen (N)-doped graphene (Gr) on Ru(0001) compared to metal-free highly-oriented pyrolytic graphite (HOPG) substrate. The N-dopants were introduced through low-energy N+/N2+ irradiation. N is embedded in the carbon materials in two predominant configurations: as graphitic N (GN: N substituted in the hexagonal C lattice) and pyridinic N (PN: substitutional N adjacent to a C vacancy). XPS data showed that upon atomic deuterium (D) exposure at 220 K, the PN peak shifted to a higher binding energy by +1.2 eV for HOPG and +1.0 eV for N-doped graphene on Ru(0001), while the GN peak remained unchanged, indicating that the D atoms bound solely to pyridinic N. 85% of PN sites on HOPG can be saturated with D atoms, whereas only ~30% of pyridinic N sites are able to bind D atoms in N-doped Gr/Ru(0001). Our DFT analysis shows that this difference is due to the coordination of PN to Ru atoms, which necessitates bond cleavage of the N-Ru interaction prior to D atom adsorption. D begins desorbing from N-HOPG at ~573 K and is fully desorbed by ~973 K, whereas desorption from N-doped graphene on Ru(0001) begins at ~290 K, with complete desorption observed at ~700 K, indicating that the Ru metal weakens the N-D bond strength. We also studied a high-surface-area, layered, and porous N-doped carbon material, internally labeled NC900, which was synthesized by pyrolysis of glucose and graphitic carbon nitride (g-C3N4) at 1173 K. D exposure caused a +1.1 eV PN peak shift in NC900, with no change in the GN peak. Moreover, the NC900 exhibited the same desorption behavior as HOPG, demonstrating that well-defined model systems can effectively capture the behavior of more complex N-doped carbon materials.

Alupothe Gedara, Buddhika S.↗
DOE OSTI2017

Electrochemical Reduction of CO 2 Catalyzed by Re(pyridine-oxazoline)(CO) 3 Cl Complexes

In a series of rhenium tricarbonyl complexes coordinated by asymmetric diimine ligands containing a pyridine moiety bound to an oxazoline ring were synthesized, structurally and electrochemically characterized, and screened for CO 2 reduction ability. We reported complexes are of the type Re(N-N)(CO) 3 Cl, with N-N = 2-(pyridin-2-yl)-4,5-dihydrooxazole (1), 5-methyl-2-(pyridin-2-yl)-4,5-dihydrooxazole (2), and 5-phenyl-2-(pyridin-2-yl)-4,5-dihydrooxazole (3). The electrocatalytic reduction of CO 2 by these complexes was observed in a variety of solvents and proceeds more quickly in acetonitrile than in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). The analysis of the catalytic cycle for electrochemical CO 2 reduction by 1 in acetonitrile using density functional theory (DFT) supports the C–O bond cleavage step being the rate-determining step (RDS) (ΔG ‡ = 27.2 kcal mol –1 ). Furthermore, the dependency of the turnover frequencies (TOFs) on the donor number (DN) of the solvent also supports that C–O bond cleavage is the rate-determining step. Moreover, the calculations using explicit solvent molecules indicate that the solvent dependence likely arises from a protonation-first mechanism. Unlike other complexes derived from fac-Re(bpy)(CO) 3 Cl (I; bpy = 2,2'-bipyridine), in which one of the pyridyl moieties in the bpy ligand is replaced by another imine, no catalytic enhancement occurs during the first reduction potential. Remarkably, catalysts 1 and 2 display relative turnover frequencies, (i cat /i p ) 2 , up to 7 times larger than that of I.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Gas phase protonated nicotine is a mixture of pyridine- and pyrrolidine-protonated conformers: implications for its native structure in the nicotinic acetylcholine receptor

The infrared (IR) spectra of gas phase protonated nicotine has been measured in the never-before probed N–H “fingerprint region” (3200–3500 cm -1 ). The protonated molecules generated by an electrospray source are thermalized in the first ion trap with water vapor and He gas at a pre-determined temperature prior to being probed by IR spectroscopy in the second ion trap at 4 K. The IR spectra exhibit two N–H stretching bands which are assigned to the pyridine and pyrrolidine protomers with the aid of high-level electronic structure calculations. This finding is in sharp contrast to previous spectroscopic studies that suggested a single population of the pyridine protomer. The relative populations of the two protomers vary by changing the temperature of the thermalizing trap from 180-300 K. The relative conformer populations at 240 K and 300 K are well reproduced by the theoretical calculations, unequivocally determining that gas phase nicotine is a 3 : 2 mixture of both pyridine and pyrrolidine protomers at room temperature. The thermalizing anhydrous vapor does not result in any population change. It rather demonstrates the catalytic role of water in achieving equilibrium between the two protomers. The combination of IR spectroscopy and electronic structure calculations establish the small energy difference between the pyridine and pyrrolidine protomers in nicotine. Finally, one of the gas phase nicotine pyrrolidine protomers has the closest conformational resemblance among all low-lying energy isomers with the X-ray structure of nicotine in the nicotinic acetylcholine receptor (nAChR).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Selectively catalytic activity of metal–organic frameworks depending on the N-position within the pyridine ring of their building blocks

Iron metal–organic frameworks (MOFs) [Fe(L){sub 2}(SCN){sub 2}]{sub ∝} (L1: 4-bpdh=2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene for 1Fe; and L2: 3-bpdh=2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene for 2Fe) were assembled in a MeOH–H{sub 2}O solvent system. 1Fe exhibits a two-dimensional extended-grid network, whereas 2Fe exhibits a stair-like double-chain; the N-position within the pyridine ring of the complexes was observed to regulate the MOF structure as layers or chains. Furthermore, selectively catalytic activity was observed for the layered MOF but not the chain-structured MOF; micro/nanoparticles of the layered MOF were therefore investigated for new potential applications of micro/nano MOFs. - Graphical abstract: Iron metal–organic frameworks (MOFs) [Fe(L){sub 2}(SCN){sub 2}]{sub ∝} (L1: 4-bpdh=2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene for 1Fe; and L2: 3-bpdh=2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene for 2Fe) were assembled in a MeOH–H{sub 2}O solvent system. The N-position within the pyridine ring of the complexes was observed to regulate the MOF structure as layers or chains. Selectively catalytic activity was observed for the layered MOF but not the chain-structured MOF. - Highlights: • Synthesis and structure of metal–organic framework [Fe(L){sub 2}(SCN){sub 2}]{sub ∝}. • Selectively catalytic activity depending on the N-position within the pyridine ring. • The degradation and conversion of methyl orange.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

A coverage dependent study of the adsorption of pyridine on the (111) coinage metal surfaces

Using density functional theory we explore the adsorption of pyridine (NC 5 H 5 ) on Cu, Ag, and Au(111) surfaces. To study the effect of coverage we run calculations on a 3 × 4 (12 atom), 4 × 4 (16 atom), 5 × 4 (20 atom), and 4 × 6 (24 atom) surface. To examine the role of the van der Waals interaction we use the following vdW inclusive functionals: optB86-vdW, optB88-vdW, optPBE-vdW, revPBE-vdW, rPW86-vdW2, SCAN+rVV10 along with the PBE functional. Regardless of functional, metal, and coverage we find the most energetically stable adsorption site to be a vertical site with the pyridine's N atom directly above a metal atom, which contradicts the available experimental literature. Introducing the vdW interaction lowers the energy gap between the most energetically favorable flat and vertical adsorption configurations. Moving to a higher coverage increases the overall interaction of the pyridine molecule with the surface. We also find that the SCAN+rVV10 functional performs similarly to the optB86b-vdW and optB88-vdW functional. Along with the geometric properties of the substrate/adsorbate system, here we report several electronic properties of the substrate/adsorbate system such as charge transfer from the surface to the molecule, change in the surface's work function, and change in d-band of the atoms in the first layer of the substrate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Synthesis and Characterization of Pyridine Dipyrrolide Uranyl Complexes

The first actinide complexes of the pyridine dipyrrolide (PDP) ligand class, ( Mes PDP Ph )UO 2 (THF) and ( Cl2Ph PDP Ph )UO 2 (THF), are reported as the U VI uranyl adducts of the bulky aryl substituted pincers ( Mes PDP Ph ) 2– and ( Cl2Ph PDP Ph ) 2– (derived from 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine (H 2 Mes PDP Ph , Mes = 2,4,6-trimethylphenyl), and 2,6-bis(5-(2,6-dichlorophenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine (H 2 Cl2Ph PDP Ph , Cl 2 Ph = 2,6-dichlorophenyl), respectively). Following the in situ deprotonation of the proligand with lithium hexamethyldisilazide to generate the corresponding dilithium salts (e.g., Li 2 Ar PDP Ph , Ar = Mes of Cl 2 Ph), salt metathesis with [UO 2 Cl 2 (THF) 2 ] 2 afforded both compounds in moderate yields. The characterization of each species has been undertaken by a combination of solid- and solution-state methods, including combustion analysis, infrared, electronic absorption, and NMR spectroscopies. In both complexes, single-crystal X-ray diffraction has revealed a distorted octahedral geometry in the solid state, enforced by the bite angle of the rigid meridional ( Ar PDP Ph ) 2– pincer ligand. The electrochemical analysis of both compounds by cyclic voltammetry in tetrahydrofuran (THF) reveals rich redox profiles, including events assigned as U VI /U V redox couples. Here, a time-dependent density functional theory study has been performed on ( Mes PDP Ph )UO 2 (THF) and provides insight into the nature of the transitions that comprise its electronic absorption spectrum.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Selective CO 2 Reduction by Bis(bipyridine)cobalt(II) Catalysts: The Role of Pendant Pyridine as a Proton Acceptor

Electrochemical CO 2 reduction reaction (CO 2 RR) catalyzed by molecular earth-abundant metal catalysts is a promising strategy to convert CO 2 into value-added products. One recent trend in this field has been focusing on the rational design of catalysts by incorporating redox-active ligands and modifying the secondary coordination sphere (SCS) to achieve efficient and selective CO 2 RR. Herein, we report a series of Co bis­(bipyridine) catalysts featuring various dangling groups, such as pyridine, tertiary amine, or butyl, in the secondary coordination sphere (Co-PyMe, Co-Py, Co-PrN, and Co-Bu). Efficient, selective electrocatalytic CO 2 RR was achieved by the complexes after the generation of triply reduced intermediate consisting of a Co I center and a dianionic ligand, producing CO as the major product and trace amount of H 2 . Strong correlations with the identity of dangling groups and turnover frequency (TOF) have been observed, in which Co-PyMe displayed the highest TOF (1086 s –1 in MeCN/H 2 O). Mechanistic studies indicated that the acceleration of CO 2 RR with pyridine-functionalized catalysts were derived from the protonation of pyridine dangling groups which participated as weak acids in the H-bonding network with exogenous proton sources, stabilizing CO 2 -bound intermediates and facilitating proton transfer. In addition, precatalytic CO 2 binding and activation at the third reduction (−2.1 V) was revealed by CV and SEC-IR studies. The resultant doubly reduced CO-bound species acted as a trapping state which inhibited CO 2 RR electrocatalysis. Regeneration of active species was accessed via reductive dissociation of CO at a more negative potential. In conclusion, this study highlights the combined effects of redox-active ligands and pyridine/pyridinium as SCS groups on CO 2 RR catalysis and provides design principles for future development of CO 2 RR catalysts utilizing pyridine/pyridiniums as SCS functional groups to fine-tune the catalytic activity.

CO2 reduction↗
DOE OSTI2022

Surface Chemistry and Heterogeneous Processes in Solar-Driven Pyridine-Catalyzed CO 2 Reduction

The objective of our studies was to advance our fundamental understanding of the surface chemistry and heterogeneous processes that occur in solar-driven pyridine-catalyzed CO 2 reduction. Solar-driven CO 2 reduction to produce fuels offers tremendous promise but commercial deployment is impeded by the lack of suitable catalysts that simultaneously provide high efficiency and product selectivity. Pyridine (C 5 H 5 N) has been reported as an effective, selective co-catalyst in the conversion of CO 2 to methanol (CH 3 OH) in photoelectrochemical cells employing gallium phosphide (GaP) photocathodes. However, despite considerable electrochemical characterization and a large number of theoretical considerations, there are still many fundamental questions about the surface chemistry and heterogeneous processes that are involved in the conversion mechanism. Our research was aimed at investigating the role of the electrode surface and heterogeneous processes in this catalysis. Gaining this fundamental understanding of the origin of pyridine’s effectiveness is important to the continued optimization of solar-driven CO 2 reduction.

10 SYNTHETIC FUELS↗
DOE OSTI2018

Computational Chemistry-Guided Design of Selective Chemoresponsive Liquid Crystals Using Pyridine and Pyrimidine Functional Groups

Computational chemistry-guided designs of chemoresponsive liquid crystals (LCs) with pyridine or pyrimidine groups that bind to metal-cation-functionalized surfaces to provide improved selective responses to targeted vapor species (dimethylmethylphosphonate (DMMP)) over nontargeted species (water) are reported. The LC designs against experiments are tested by synthesizing 4-(4-pentyl-phenyl)-pyridine and 5-(4-pentyl-phenyl)-pyrimidine and quantifying LC responses to DMMP and water. Consistent with the computations, pyridine-containing LCs bind to metal-cation-functionalized surfaces too strongly to permit a response to either DMMP or water whereas pyrimidine-containing LCs undergo a surface-driven orientational transition in response to DMMP without interference from water. The computation predictions are not strongly dependent on assumptions regarding the degree of coordination of the metal ions but are limited in their ability to predict LC responses when using cations with mostly empty d orbitals. Overall, this work identifies a promising new class of chemoresponsive LCs based on pyrimidine that exhibits enhanced tolerance to water, a result that is important because water is a ubiquitous and particularly challenging chemical interferent in chemical sensing strategies based on LCs. The work also provides further evidence of the transformative utility of computational chemistry methods to design LC materials that exhibit selective orientational responses in specific chemical environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Thermodynamic Stability and Site‐Specific Distribution of Graphitic and Pyridinic Nitrogen in Graphene Moiré on Ru(0001)

Abstract Graphene‐like materials are of interest for large‐scale hydrogen storage applications due to their lightweight, durable, and scalable properties. Nitrogen‐doping minimizes kinetic limitations in diffusion and recombination on surfaces, however, the role of graphitic nitrogen (GN) and pyridinic nitrogen (PN) is not well understood. Nitrogen‐doped graphene is synthesized on Ru(0001) using chemical vapor deposition (CVD) of pyridine and ion irradiation. Scanning tunneling microscopy (STM), x‐ray photoelectron spectroscopy (XPS), and density functional theory (DFT) are used to identify the structure, location, and thermodynamic stability of nitrogen species within the graphene moiré. CVD of pyridine results in a low nitrogen concentration (<0.1at%), while the post‐growth nitrogen ion irradiation allows us to increase the concentration further. The concentration of GN and PN is controlled by varying the ion dose and annealing temperature. Comparison of measured and simulated STM images of GN and PN yield an excellent agreement, allowing us to confidently establish that GN is preferentially located near the center of the Atop region, while PN is located in the valley region of the graphene moiré. This report explicitly confirms the site assignments and provides a foundation for the site synthesis and analysis of structural and electronic properties that drive the reactivity of N‐doped graphene.

Gedara, Buddhika S. A. [Physical and Computational↗
DOE OSTI2023

Pyridine-containing substrate analogs are restricted from accessing the human cytochrome P450 8B1 active site by tryptophan 281

The human oxysterol 12α-hydroxylase cytochrome P450 8B1 (CYP8B1) is a validated drug target for both type 2 diabetes and nonalcoholic fatty liver disease, but effective selective inhibitors are not yet available. Herein, steroidal substrate-mimicking compounds with a pyridine ring appended to the C12 site of metabolism were designed as inhibitors, synthesized, and evaluated in terms of their functional and structural interactions with CYP8B1. While the pyridine nitrogen was intended to coordinate the CYP8B1 active site heme iron, none of these compounds elicited shifts in the CYP8B1 Soret absorbance consistent with this type of interaction. However, when CYP8B1 was cocrystallized with the pyridine-containing compound with the 3-keto-Δ4 steroid backbone most similar to the endogenous substrate, it was apparent that this ligand was bound in a channel leading to the active site, instead of near the heme iron. Inspection of this structure suggested that tryptophan 281 directly above the heme might restrict active site binding of potential inhibitors with this design. This hypothesis was supported when a CYP8B1 W281F mutation did allow all three compounds to coordinate the heme iron as designed. These results indicated that the design of next-generation CYP8B1 inhibitors should be compatible with the low-ceiling tryptophan immediately above the heme iron.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

A trigold carbide cation stabilized as a labile pyridine adduct

Auration of trimethylsilyldiazomethane by an (N-heterocyclic carbene)gold alkoxide affords a stable (silyldiazoalkyl)gold complex. The reaction of this species with a gold(I) fluoride, more efficient in the presence of an added gold cation equivalent, results in auration, desilylation, and N 2 loss. The putative trigold carbide cation was isolated as its pyridine adduct, a stable N-(triauromethyl)pyridinium ion. Reaction of the cationic pyridine adduct with carbon monoxide breaks the C—N bond, forming the stable trigold ketenylidene cation. Finally, DFT studies suggest substantial negative charge at the bridging carbon in the methylpyridinium analogue and in two possible intermediates, the trigold carbide cation and the pyridine adduct of a neutral digold carbide.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Mass Spectrometric Characterization of an Acid-Labile Adduct Formed with 2-Amino-1-methyl-6-phenylimidazo[4,5- b ]pyridine and Albumin in Humans

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a carcinogenic heterocyclic aromatic amine formed during the high-temperature cooking of meats. The cytochrome P450-mediated N-hydroxylation of the exocyclic amine group of PhIP produces 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-$b$]pyridine, an electrophilic metabolite that forms adducts with DNA and proteins. Previous studies conducted by our laboratory showed that the reaction of N-oxidized PhIP metabolites with human albumin in vitro primarily occurs at the Cys 34 residue, to produce an acid-labile linked sulfinamide adduct. On the basis of these findings, we developed a sensitive ultraperformance liquid chromatography–mass spectrometry method to measure acid-labile albumin–PhIP adducts in human volunteers administered a dietary-relevant dose of 14 C-labeled PhIP [Dingley, K. H., et al. (1999) Cancer Epidemiol., Biomarkers Prev. 8, 507–512]. Mild acid treatment of albumin (0.1 N HCl, 37 °C for 1 h) or proteolytic digestion with Pronase [50 mM ammonium bicarbonate buffer (pH 8.5) at 37 °C for 18 h] released similar amounts of covalently bound PhIP, which was characterized by multistage scanning and quantified by Orbitrap mass spectrometry. The amount of [ 14 C]PhIP recovered by acid treatment of albumin 24 h following dosing accounted for 7.2–21.3% of the [ 14 C]PhIP bound to albumin based on accelerator mass spectrometry measurements. 2-Amino-1-methyl-6-(5-hydroxy)phenylimidazo[4,5-b]pyridine, a hydrolysis product of the Cys 34 S–N linked sulfenamide adduct of PhIP, was not detected in either acid-treated or protease-treated samples. These findings suggest that a portion of the PhIP bound to albumin in vivo probably occurs as an acid-labile sulfinamide adduct formed at the Cys 34 residue.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Interrogating the Lewis Acidity of Metal Sites in Beta Zeolites with 15 N Pyridine Adsorption Coupled with MAS NMR Spectroscopy

Here, the Lewis acidity of isolated framework metal sites in Beta zeolites was characterized with 15 N isotopically labeled pyridine adsorption coupled with magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The 15 N chemical shift of adsorbed pyridine was found to scale with the acid character of both Lewis (Ti, Hf, Zr, Nb, Ta, and Sn) and Brønsted (B, Ga, and Al) acidic heteroatoms. The 15 N chemical shift showed a linear correlation with Mulliken electronegativity of the metal center in the order Ti < Hf < Zr < Nb < Ta < Sn < H + . Theoretical calculations using density functional theory (DFT) showed a strong correlation between experimental 15 N chemical shift and the calculated metal–nitrogen bond dissociation energy, and revealed the importance of active site reorganization when determining adsorption strength. The relationships found between 15 N pyridine chemical shift and intrinsic chemical descriptors of metal framework sites complement adsorption equilibrium data and provide a robust method to characterize, and ultimately optimize, metal-reactant binding and activation for Lewis acid zeolites. Direct 15 N MAS NMR detection protocols applied to the Lewis acid–base adducts allowed the differentiation and quantification of framework metal sites in the presence of extraframework oxides, including highly quadrupolar nuclei that are not amenable for quantification with conventional NMR methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Core Level Shifts of Hydrogenated Pyridinic and Pyrrolic Nitrogen in the Nitrogen-Containing Graphene-Based Electrocatalysts: In-Plane vs Edge Defects

A combination of N 1s X-ray photoelectron spectroscopy (XPS) and first principles calculations of nitrogen-containing model electrocatalysts was used to elucidate the nature of the nitrogen defects that contribute to the binding energy (BE) range of the N 1s XPS spectra of these materials above ~400 eV. Experimental core level shifts were obtained for a set of model materials, namely N-doped carbon nanospheres, Fe–N–carbon nanospheres, polypyrrole, polypyridine, and pyridinium chloride, and were compared to the shifts calculated using density functional theory. The results confirm that the broad peak positioned at ~400.7 eV in the N 1s XPS spectra of N-containing catalysts, which is typically assigned to pyrrolic nitrogen, contains contributions from other hydrogenated nitrogen species such as hydrogenated pyridinic functionalities. Namely, N 1s BEs of hydrogenated pyridinic-N and pyrrolic-N were calculated as 400.6 and 400.7 eV, respectively, using the Perdew–Burke–Ernzerhof exchange-correlation functional. A special emphasis was placed on the study of the differences in the XPS imprint of N-containing defects that are situated in the plane and on the edges of the graphene sheet. Density functional theory calculations for BEs of the N 1s of in-plane and edge defects show that hydrogenated N defects are more sensitive to the change in the chemical environment in the carbon matrix than the non-hydrogenated N defects. In conclusion, calculations also show that edge-hydrogenated pyridinic-N and pyrrolic-N defects only contribute to the N 1s XPS peak located at ~400.7 eV if the graphene edges are oxygenated or terminated with bare carbon atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗