Interaction Of Pyridine Research Articles

Interaction of pyridine π-bridge-based poly(methacrylate) dyes for the fabrication of dye-sensitized solar cells with the influence of different strength phenothiazine, fluorene and anthracene sensitizers as donor units with new anchoring mode

A simple and low-cost approach for the synthesis of three novel propeller-shaped (D2)–π–A type organic polymer dyes has been developed; a new acceptor and π-bridge (PYN) were used to tune the photoelectric properties: DFT studies.

On the interactions of nitriles and fluoro-substituted pyridines with silicon tetrafluoride: Computations and thin film IR spectroscopy

The nature of the interactions between silicon tetrafluoride and series of nitrogen bases, including nitriles (RCN, with R > CH3), pyridine, and various fluoro-substituted pyridines, has been investigated via quantum-chemical computations, low-temperature IR spectroscopy, and bulk reactivity experiments. Using (primarily) M06 with the 6-311+G(2df,2pd) basis set, we obtained equilibrium structures, binding energies, harmonic frequencies, and N–Si potentials in the gas-phase and in bulk dielectric media for an extensive series of 1:1 molecular complexes, including: C6H5CH2CN–SiF4, CH3CH2CN–SiF4, (CH3)3CCN–SiF4, C5H5N–SiF4, 4-FC5H4N–SiF4, 3,5-C5F2H3N–SiF4, 2,6-C5F2H3N–SiF4 and 3,4,5-C5F3H2N–SiF4. In addition, for the analogous 2:1 complexes of pyridine and 3,5-difluororpyridine, we obtained equilibrium structures, binding energies, and harmonic frequencies. The N–Si distances in the 1:1 nitrile complexes are fairly long, ranging from 2.84 Å to 2.88 Å, and the binding energies range from 4.0 to 4.2 kcal/mol (16.7–17.6 kJ/mol). Also, computations predict extremely anharmonic N–Si potentials, for which the inner portions of the curve are preferentially stabilized in dielectric media, which predict an enhancement of these interactions in condensed-phases. However, we see no evidence of bulk reactivity between C6H5CH2CN, CH3CH2CN, or (CH3)3CCN and SiF4, nor any significant interaction between (CH3)3CCN and SiF4 in low temperature IR spectra of solid, (CH3)3CCN/SiF4 thin films. Conversely, the interactions in four of the five 1:1, pyridine-SiF4 complexes are generally stronger; binding energies range from 5.7 to 9.6 kcal/mol (23.8–40.2 kJ/mol), and correspondingly the N–Si distances are relatively short (2.12–2.25 Å). The exception is 2,6-C5F2H3N–SiF4, for which the binding energy is only 3.6 kcal/mol (15.1 kJ/mol), and the N–Si distance is quite long (3.12 Å). In addition, both pyridine and 3,5-difluororpyridine were found to form stable reaction products with SiF4; but no analogous product was obtained with 2,6-difluororpyridine and SiF4, nor was any significant interaction indicated in low-temperature IR spectra of 2,6-difluororpyridine/SiF4 films. By contrast, low temperature spectra of pyridine/SiF4 and 3,5-difluororpyridine/SiF4 thin films are consistent with the presence of a distinct 2:1 reaction product. Moreover, the observed frequencies agree reasonably well with those predicted for the cis, octahedral coordination isomers of the 2:1 molecular complexes, in which the N–Si bonds are compressed slightly relative to those in the predicted gas-phase structures.

New theoretical insight on the acid sites distribution, their local structures and acid strength of the SAPO‐11 molecular sieve

AbstractONIOM(DFT:PM3) calculations were carried out to investigate and characterize possible acid sites of SAPO‐11 molecular sieve. Two functionals were employed: B3LYP and ωB97X‐D. This last functional includes dispersion effects that are absent in the former. Benzene, pyridine, and ammonia interaction energies as well as the OH stretching frequencies of the POH, SiOH, and bridged Si(OH)Al groups were used to characterize the acid sites. This work shows that the adsorption of benzene on the surface is as strong as the adsorptions inside main channel of SAPO‐11. Pyridine adsorption on the surface is weaker than the one corresponding to the main channel. NH3 molecule interacts strongly with all OH groups or acid sites present in SAPO‐11. Moreover, the results reveal that it is possible to adsorb two NH3 molecules at only one Brønsted site. The adsorption of the second NH3 molecule is energetically favorable mainly due to the hydrogen bond formation between the NH3 molecules. In general the interaction energy increases with the type of functional used, according to the trend ωB97X‐D > B3LYP. The results show that ONIOM methodology seems to be suited to investigate the acid sites in SAPO‐11.

Discovering the stacking landscape of a pyridine-pyridine system

Extremely extensive calculations of potential energy surfaces for the parallel-displaced configuration of pyridine dimer systems have been carried out using a dispersion-corrected density functional. Instead of focusing on stationary geometries these calculations provide much deeper insight into the “landscape” of the interaction energies of the particular systems—one can learn how the pyridine dimer stability changes along with various geometrical parameters. Other calculations such as natural bond orbital and energy decomposition have also been applied. The interplay of two significant factors, electrostatic forces and electron correlation effects, have been evaluated. The role of π···π interactions in the stacked pyridine systems has also been confirmed, and surprisingly, this happened to be true even for the geometries where the formation of C-H···π interactions might be proposed instead. The combination of many different methods has revealed the complexity of the stacking interactions. Apart from providing a “literal new look” into pyridine interaction patterns another picture has emerged. A stacking interaction in a pyridine dimer system is perceived as a combination of many different sources of the interaction energy, including orbital ones, and this is true for many different geometries.

DFT and TD-DFT study of isomeric 5-(pyridyl)-1,3,4-oxadiazol-2-thiones and 2-methylthio-5-(pyridyl)-1,3,4-oxadiazoles

Internal rotations of pyridine fragment around single bond of isomeric 5-(2′, 3′ and 4′-pyridyl)-1,3,4-oxadiazol-2-thiones and 2-methylthio-5-(2′, 3′ and 4′-pyridyl)-1,3,4-oxadiazoles have been performed by DFT (B3LYP) and MP2 methods with RHF/6-31G(d,p) basis set. It was found that the MP2 barrier height lies a few below than DFT barrier heights for all studied compounds. In the molecule of 2-methylthio-5-(2′-pyridyl)-1,3,4-oxadiazole an anomeric effect detected due to a lone pair-lone pair interaction of pyridine and N4 oxadiazole nitrogen atoms. But it not found in the molecule of 5-(2′-pyridyl)-1,3,4-oxadiazol-2-thione. Furthermore, theoretical UV spectra of the compounds were studied using TD-DFT/6-31G(d,p) method. Theoretical transitions located about 10nm in the long-wavelength region relatively to the experimental bands field. Whereas, the theoretical transitions of 2-methylthio-5-(2′, 3′ and 4′-pyridyl)-1,3,4-oxadiazoles have very good agreement with the position of experimental bands. The longest wavelength band in both of experimental and theoretical spectra of the investigated compounds have been observed for 5-(4′-pyridyl)-1,3,4-oxadiazole-2-thione and 2-methylthio-5-(2′-pyridyl)-1,3,4-oxadiazole. Furthermore, the longest-wavelength experimental band's position are in good agreement with (r2=0.95) the HOMO-LUMO energetic gaps of studied compounds.

The effect of ortho-fluorination on intermolecular interactions of pyridine: Microwave spectrum and structure of the CO2 – 2,6-difluoropyridine weakly bound complex

The weakly bound complex formed from CO2 and 2,6-difluoropyridine (2,6-DFP) has been observed by chirped pulse and conventional cavity Fourier transform microwave spectroscopy. As in the related complexes with pyridine and 3,5-difluoropyridine, the carbon of the CO2 approaches the nitrogen of the heterocycle in the plane of the ring. However, the CO2−2,6-DFP complex is found to differ from the pyridine and 3,5-DFP analogues in several respects. First, the data indicate that the N⋯C weak bond distance is 2.9681(32) Å, a value that is ∼0.17 Å longer than that previously determined for CO2−pyridine (2.798 Å) and 0.14 Å longer than that in CO2−3,5-difluoropyridine (2.825 Å). Second, unlike the pyridine and 3,5-difluoropyridine complexes, the CO2 oxygens in CO2−2,6-DFP do not lie in the plane of the ring, i.e., fluorination of the pyridine in the ortho positions causes the CO2 to rotate 90° out of plane. Moreover, the observed rotational constants indicate that the CO2 moiety undergoes large amplitude vibrational motion with an average bending amplitude of ∼31° off this perpendicular geometry. Third, M06-2X/6-311++G(3df,3pd) and MP2/6-311++G(3df,3pd) calculations both indicate that in the equilibrium configuration, the carbon of the CO2 is displaced from the C2 axis of the 2,6-DFP such that axis forms an angle of 20–23° with the line joining the nitrogen and the CO2 carbon. The current results support the previous conjecture that the anomalously short N⋯C distances in CO2−pyridine and CO2−3,5-difluoropyridine result from secondary attractive interactions between the oxygen atoms and the ortho hydrogens. These interactions are eliminated in the 2,6-DFP system by fluorination in the ortho positions, causing the weak bond distance to increase and the CO2 to rotate out of the plane.

Mitigation strategy towards stabilizing the Electrochemical Interface under high CO and H2O containing reformate gas feed

Despite the enhanced CO tolerance of the high temperature polymer electrolyte membrane (HT PEMFC) technology, the synergistic effect of CO and steam in the anodic reformate gas feed was proven to result in serious performance reduction and operation instabilities, due to the dynamic disturbance of the electrochemical interface (EI). In this work a mitigation strategy is presented by controlling the hydrophilicity of the catalytic layer in order to achieve the optimum structure of the EI. The thin and continuous film distribution of the phosphoric acid (PA) inside the catalytic layer (CL) without blocking the pores is the main characteristic property that determines the good quality of the EI. As shown, a hydrophilic catalytic layer is preferable, since the acid, being at any hydration level, will be able to spread over the catalytic surface aiming to the formation of a thin and continuous film so as to maximize the extend of the EI without blocking the pores of the catalytic layer. This facilitates the uninterrupted transport of protons and the fast diffusion of the reacting gases. Herein, this was accomplished by modifying the surface properties of the CL through the anchoring of pyridine moieties on the MWCNTs, which plays the role of the Pt catalyst support. The basic pyridine moieties enhance the hydrophilicity of the nanotubes through the acid (PA)-base (pyridine) interaction so that the contact angle between a PA drop and the catalytic layer is very close to zero. The good affinity of the PA with the pyridine based catalytic layer secures the PA thin film distribution and continuity. More importantly it is not affected even at high hydration levels of the PA, when the partial pressure of steam is increased at values>20kPa. Otherwise, on conventional C supports, hydrated PA has the tendency to shrink and create ganglia leading to the disruption of the EI. The pyridine modified catalytic layers approach Pt surface utilization values as high as 80% as compared to 50% utilization measured for the case of conventional Pt/C catalytic layers.

Introducing Supramolecular Interactions into Robust Bis(tetrabromocatecholate) Chelated Manganese(III) Systems and Biomimetic Catalytic Activity

AbstractThis report deals with the syntheses, structures, supramolecular interactions, and biomimetic catalytic activity of three new manganese(III) complexes (1–3) containing the tetrabromocatechol ligand. Three different amines were used, with the goal of introducing their protonated species into the crystal lattice as counter cations for the robust bis(tetrabromocatecholate) chelated manganese(III) anionic species. All these systems present interesting noncovalent interactions in their crystal packing, including hydrogen bonding, halogen bonding, π –stacking and anion–π interactions. The geometrical differences (octahedral vs square pyramidal) have been analyzed by means of DFT studies, revealing that the strong anion–π interaction of pyridine with the complex anion compensates for the absence of one apical methanol molecule in 3. All of the complexes exhibited leveling catalytic activity for aerobic oxidation of 3,5‐di‐tert‐butylcatechol. DFT calculations support the formation of a stable complex‐substrate intermediate through hydrogen bonding, thereby disclosing the origin of catecholase activity of these complex anions.

Multidimensional Large Amplitude Dynamics in the Pyridine-Water Complex.

Aqueous pyridine plays an important role in a variety of catalytic processes aimed at harnessing solar energy. In this work, the pyridine-water interaction is studied by microwave spectroscopy and density functional theory calculations. Water forms a hydrogen bond to the nitrogen with the oxygen tilted slightly toward either of the ortho-hydrogens of the pyridine, and a tunneling motion involving in-plane rocking of the water interconverts the resulting equivalent structures. A pair of tunneling states with severely perturbed rotational spectra is identified and their energy separation, ΔE, is inferred from the perturbations and confirmed by direct measurement. Curiously, values of ΔE are 10404.45 and 13566.94 MHz for the H2O and D2O complexes, respectively, revealing an inverted isotope effect upon deuteration. Small splittings in some transitions suggest an additional internal motion making this complex an interesting challenge for theoretical treatments of large amplitude motion. The results underscore the significant effect of the ortho-hydrogens on the intermolecular interaction of pyridine.

A DFT study of volatile organic compounds adsorption on transition metal deposited graphene

Recently, elevated global emission of volatile organic compounds (VOCs) was associated to the acceleration and increasing severity of climate change worldwide. In this work, we investigated the performance of VOCs removal via modified carbon-based adsorbent using density functional theory. Here, four transition metals (TMs) including Pd, Pt, Ag, and Au were deposited onto single-vacancy defective graphene (SDG) surface to increase the adsorption efficiency. Five prototypical VOCs including benzene, furan, pyrrole, pyridine, and thiophene were used to study the adsorption capability of metal-deposited graphene adsorbent. Calculation results revealed that Pd, Pt, Au, and Ag atoms and nanoclusters bind strongly onto the SDG surface. In this study, benzene, furan and pyrrole bind in the π-interaction mode using delocalized π-electron in aromatic ring, while pyridine and thiophene favor X- interaction mode, donating lone pair electron from heteroatom. In terms of adsorption, pyridine VOC adsorption strengths to the TM-cluster doped SDG surfaces are Pt4 (−2.11eV)>Pd4 (−2.05eV)>Ag4 (−1.53eV)>Au4 (−1.87eV). Our findings indicate that TM-doped SDG is a suitable adsorbent material for VOC removal. In addition, partial density of states analysis suggests that benzene, furan, and pyrrole interactions with TM cluster are based on p-orbitals of carbon atoms, while pyridine and thiophene interactions are facilitated by hybridized sp2-orbitals of heteroatoms. This work provides a key insight into the fundamentals of VOCs adsorption on carbon-based adsorbent.

Phenylmethylene as intermediate in acid-catalyzed oxidation of styrene epoxide

The absorption spectrum of iminium ylide (λmax = 450 nm) has been registered under the conditions of acid-catalyzed consumption of styrene epoxide under the influence of p-toluenesulfonic acid (MeCN, ButOH (90 vol.%) + chlorobenzene (10 vol.%), 343 K) in the presence of pyridine. The spectrum coincides with the spectrum of the ylide product of the interaction of pyridine with phenylcarbene of phenylmethylene formed in the conventional flash-photolytic preparation of carbene from diazo derivative. The result confirms the earlier assumption on the formation of the particles of carbene nature reacting with oxygen in the epoxy-acid system. In the absence of O2 these particles destruct introduced hydroperoxides. The spectra of corresponding carbonyl oxide (λmax ≈ 408, 400 nm) in the presence and absence of pyridine were recorded in acetonitrile.

Interaction of Pyridine and Water with the Reconstructed Surfaces of GaP(111) and CdTe(111) Photoelectrodes: Implications for CO2 Reduction

Pyridine (Py) is an effective cocatalyst during the photoelectrochemical reduction of CO2 to methanol over GaP, CdTe, and CuInS2 semiconductor surfaces. Identifying the role Py plays in the catalytic reduction mechanism is essential for optimizing the design of such photocatalytic processes. The Py-enhanced mechanism, however, is under considerable debate. Recent studies suggest that the semiconductor surface itself participates in a heterogeneous mechanism, and for this reason a detailed understanding of the interaction between Py and the surface is required. Additionally, surface reconstructions occurring during operation alter the nature of adsorption sites available for interaction with the solution, therefore impacting the performance of the electrode. To address this issue, we report a density functional theory investigation of the stability of GaP(111) and CdTe(111) surface reconstructions, as well as adsorption trends of intermediate species across sites created by such reconstructions. We also de...

Adsorption of pyridine from aqueous solutions by polymeric adsorbents MN 200 and MN 500. Part 1: Adsorption performance and PFG-NMR studies

The removal of pyridine from aqueous solutions was carried out using Macronet polymeric adsorbents MN 200 and MN 500. The optimal pyridine uptakes were in approximately neutral solutions as a result of optimal effect of π-π hydrophobic and attractive electrostatic interactions between pyridine and the adsorbents. These adsorbents showed superior pyridine uptake capacities than some apatite and activated carbons in isotherm studies. Thermodynamic analysis showed that pyridine adsorption is exothermic on MN 200 and endothermic on MN 500, implying that the adsorption on MN 500 is an activated process, which is attributed to the presence of sulfonic acid groups. Pseudo-first and second order rate models were used to fit the adsorption kinetics for the adsorbents. Translational dynamics of guest molecules within the porous polymers was analysed by PFG-NMR diffusion technique and the diffusion behaviour was characterised by two distinctive diffusion regions. PFG-NMR derived self-diffusion coefficients of pyridine in MN 500 were much slower than the expected diffusion coefficients based on a purely geometrical confinement effect, which suggests the interaction of pyridine with the sulfonic acid groups on MN 500 and their stronger effect on diffusivity also enhances the adsorption performance of this adsorbent. These studies reveal new insights into adsorption properties of pyridine in porous polymers in relation to the structural and surface properties probed by PFG-NMR and account for the effectiveness of these adsorbents in the treatment of waste water containing the aromatic N-heterocyclic compound.

Densities, viscosities and refractive indices of binary mixtures containing methyl ethyl ketone. Friction theory. New UNIFAC-VISCO and ASOG-VISCO parameter determination

In this paper densities, viscosities and refractive indices of four binary mixtures containing methyl ethyl ketone, at atmospheric pressure and in the temperature range from 288.15 K to 333.15 K are reported. From experimental measurements excess molar volumes, viscosity deviations and refractive index deviations are calculated and fitted to the Redlich–Kister equation. For the analysis of molecular interactions present in the mixtures, molar excess Gibbs free energies of activation of viscous flow are also calculated and fitted to the Redlich–Kister polynomial equation. Experimental viscosity data are modeled by friction theory, predictive UNIFAC-VISCO and ASOG-VISCO models and correlative Teja-Rice, Grunberg–Nissan, McAlister, Eyring-UNIQUAC and Eyring-NRTL models. The new CO–CH2O and CO–pyridine interaction parameters are determined for their application in the UNIFAC-VISCO and ASOG-VISCO models.

Nature of the N–Pd Interaction in Nitrogen-Doped Carbon Nanotube Catalysts

In this work, the geometric and electronic structure of N species in N-doped carbon nanotubes (NCNTs) is derived by X-ray photoemission (XPS) and absorption spectroscopy (NEXAFS) of the N 1s core excitation. Substitutional N species in pyridine-like configuration and another form of N with higher thermal stability are found in NCNTs. The structural configuration of the high thermally stable N species, in the literature often referred to as graphitic N, is assessed in this work by a combined theoretical and experimental study as a 3-fold substitutional N species in an NCNT basic structural unit (BSU). Furthermore, the nature of the interaction of those N species with a Pd metal center immobilized onto NCNTs is of σ-type donation from the filled π-orbital of the N atom to the empty d-orbital of the Pd atom and a π back-donation from the filled Pd atomic d-orbital to the π* antibonding orbital of the N atom. We have found that the interaction of pyridine N with Pd is characterized by a charge transfer typical of a covalent chemical bond with partial ionic character, consistent with the chemical shift observed in the Pd 3d core level of divalent Pd. Graphitic N sites interact with Pd by a covalent bond without any charge redistribution. In this case, the electronic state of the Pd corresponds to metallic Pd nanoparticles electronically modified by the interaction with the support. The catalytic reactivity of these samples in hydrogenation, CO oxidation, and oxygen reduction reaction (ORR) allowed clarifying some aspects of the metal carbon support interaction in catalysis.

Near-infrared study of the interaction of pyridine with acid-treated montmorillonite

The effect of acid treatment of montmorillonite on the creation of acid sites was investigated by near infrared (NIR) spectroscopy using pyridine as a probe molecule. Na-form of SAz-1 montmorillonite was treated in HCl for 2–8h. Gradual decrease of the intensities of the bands related to structural OH groups reflected the release of the octahedral atoms from Na-SAz upon protons attack. A new band near 7315cm−1 due to SiOH overtone confirmed the formation of protonated silica. After exposure of the Na-SAz to pyridine vapors the intensity of the (ν+δ)H2O band diminished indicating the partial replacement of water molecules by pyridine. Disappearance of the SiOH band in the spectra of acid-treated samples revealed that silanol groups as weak Brønsted acid sites formed H-bonds with pyridine-nitrogen. After pyridine adsorption, its CH overtone band (2νCH) appeared near 6000cm−1. For examining the strength of the pyridine bonding, samples were heated up to 230°C. The re-appearance of the 7315cm−1 band and decreased intensity of the 2νCH overtone confirmed the release of the H-bonded pyridine molecules. Almost complete loss of pyridine band was observed for Na-SAz-py and for the 8h treated sample heated above 170°C, while a well-resolved 2νCH band, but shifted to higher wavenumbers, was still present in the spectra of the samples dissolved in HCl for 2 and 4h. Partly leached acid-montmorillonite provided protons for generation of pyridinium cations. The bands at 6096 and 6065cm−1 observed in the spectra of SAz-2h-py and SAz-4h-py heated at 230°C were assigned to the C–H vibrations of pyridinium cations. The results showed that NIR spectroscopy can distinguish between different pyridine species on montmorillonite surface.

C–H/O interactions of nucleic bases with a water molecule: a crystallographic and quantum chemical study

The C–H/O interactions of nucleic bases are substantially stronger than the C–H/O interactions of benzene and pyridine. These results can be very important for molecular recognition of DNA and RNA.

Conductometric Studies of Charge Transfer Complexes Interaction of Amino Pyridine with π- Acceptors

Charge Transfer Complexes of Amino Pyridine derivatives as donor with the organic π- Acceptors, maleic anhydride,-nitroso--naphthol ,p-chloroaniline ,picric acid ,anthraquinone and p- bromoaniline in polar solvent have been determined . The study was performed in three different polar solvents namely N,N-dimethylformamide (DMF), acetonitrile (ACN) and dimethylsulfoxide (DMSO). The stoichiometric ratios of these complexes were found to vary from (1: 1) to (1: 1.5) (acceptor - donor) depending on the system solvent used and the (ασM) values has been examined . The distribution profiles of the various pyridine derivatives species and organic -acceptors formed, are obtained.

Influence of supramolecular structures in crystals on parallel stacking interactions between pyridine molecules

Parallel stacking interactions between pyridines in crystal structures and the influence of hydrogen bonding and supramolecular structures in crystals on the geometries of interactions were studied by analyzing data from the Cambridge Structural Database (CSD). In the CSD 66 contacts of pyridines have a parallel orientation of molecules and most of these pyridines simultaneously form hydrogen bonds (44 contacts). The geometries of stacked pyridines observed in crystal structures were compared with the geometries obtained by calculations and explained by supramolecular structures in crystals. The results show that the mean perpendicular distance (R) between pyridine rings with (3.48 Å) and without hydrogen bonds (3.62 Å) is larger than that calculated, because of the influence of supramolecular structures in crystals. The pyridines with hydrogen bonds show a pronounced preference for offsets of 1.25-1.75 Å, close to the position of the calculated minimum (1.80 Å). However, stacking interactions of pyridines without hydrogen bonds do not adopt values at or close to that of the calculated offset. This is because stacking interactions of pyridines without hydrogen bonds are less strong, and they are more susceptible to the influence of supramolecular structures in crystals. These results show that hydrogen bonding and supramolecular structures have an important influence on the geometries of stacked pyridines in crystals.

Special features of the interaction of pyridine and quinoline derivatives, and related compounds with triphenylphosphine

Using pyridine, quinoline, and related compounds as examples, it has been shown that their interaction with triphenylphosphine occurs via different pathways. Reaction of triphenylphosphine with N-vinylisonicotinic acid chloride leads to the mixture of 1,2-bis(triphenylphosphoniumchlorido)ethane and 4-carboxy-2-(triphenylphosphoniumchloridoethyl)pyridine. In the case of α-(N-2-carboxyquinolinylbromido)-β-bromopropionic acid, the reaction with triphenylphosphine proceeds via phosphine attack on the oxygen atom with elimination of quinaldinic acid, and subsequent nucleophilic substitution with the formation of 3-(triphenylphosphoniumbromido) propionic acid bromide.