Role Of Basicity Research Articles

A Computational Investigation of Unconventional Lone‐Pair Hole Interactions of Group V–VIII Elements

AbstractFor the first time, unconventional lone‐pair (lp) hole interactions were uncovered in chalcogen⋅⋅⋅, halogen⋅⋅⋅, and aerogen⋅⋅⋅Lewis base complexes. An lp‐W‐XYZ⋅⋅⋅B nomenclature was proposed to describe the lp‐hole interaction, where W is the Group V‐VIII element, XYZ are three atoms on the same side of the lp‐hole and B is a Lewis base. Point‐of‐Charge (PoC) approach was adopted to investigate the characteristics of lp‐hole interactions from an electrostatic perspective. Results showed: (i) the occurrence of lp‐holes in the pnicogen‐, chalcogen‐, halogen‐, and aerogen‐containing molecules, (ii) that strength of the lp‐hole interaction increases with increasing negativity of the Lewis basicity, and (iii) the more electronegative XYZ atoms are the lower the favorable interaction energy. The key role of Lewis basicity in orienting the geometrical structure of molecules containing Group V‐VIII elements was reported for the first time.

NiTiFe and NiTiZn LDHs with affinity for hydrogen – Role of the surface basicity

NiTi-based layered double hydroxides modified by isomorphic substitution of nickel by iron or zinc showed appreciable affinity towards hydrogen under ambient conditions. This affinity was correlated to their surface basicity, expressed in terms of CO2 retention capacity (CRC). The latter was assessed through thermal programmed desorption (TPD), and was found to vary almost linearly with the partial negative charge of lattice oxygen (PNCLO). Incorporation of iron or zinc induced a basicity enhancement, which was markedly affected by excessive amount of incorporated iron. This was explained in terms of structure compaction that reduces the amount of accessible basic sites. NiTiFe and NiTiZn LDHs showed almost similar affinity towards hydrogen, which appears to be enhanced by increasing amount of incorporated metal. However, both LDH types displayed thoroughly opposite HRC-CRC correlations presumably due to the different polarizing power of Fe and Zn cations within the LDH frameworks. These findings demonstrate that optimum basicity is an essential requirement for improved affinity towards hydrogen. This basicity can be judiciously tailored through adequate chemical composition for envisaging potential use in hydrogen storage.

All about that base: investigating the role of ligand basicity in pyridyl complexes derived from a copper-Schiff base coordination polymer.

The role of ligand basicity in complex formation has been investigated using monodentate pyridyls or benzimidazole (mP) in combination with a solution-stable species derived form a coordination polymer, [Cu(L)] (where L = 2-(2-hydroxybenzylidene-amino)phenol). The 12 [Cu(L)(mP)n] complexes generated, combined with the {[Cu(L)]2(pP)} complexes from our previous work (where pP is a polypyridyl ligand), allow us to gauge the likelihood of complex formation based on the pKa of the conjugate acid of the pyridyl ligands and Hammett parameter, σ. Above pKa ≈ 4.5, complexes are formed where the only ligands are L2- and mP or pP and the packing interactions are predominantly van der Waals. Below this value, complex formation is unlikely unless there are additional oxygen ligands in the Jahn-Teller axis of the Cu(ii) ion. The structures of two literature [Cu(L)(bP)] complexes, where bP is a chelating bidentate pyridyl ligand are also re-examined to resolve the positional disorder in the [Cu(L)] moiety.

Pt Nanoparticles Supported on Nitrogen-Doped-Carbon-Decorated CeO2 for Base-Free Aerobic Oxidation of 5-Hydroxymethylfurfural.

Currently, the base-free aerobic oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to produce 2,5-furandicarboxylic acid (FDCA) is attracting intense interest due to its prospects for the green, sustainable, and promising production of biomass-based aromatic polymers. Herein, we have developed a new Pt catalyst supported on nitrogen-doped-carbon-decorated CeO2 (NC-CeO2 ) for the aerobic oxidation of HMF in water without the addition of any homogeneous base. It was demonstrated that the small-sized Pt particles could be well dispersed on the surface of the hybrid NC-CeO2 support, and the activity of the supported Pt catalyst depended strongly on the surface structure and properties of the catalysts. The as-fabricated Pt/NC-CeO2 catalyst, with abundant surface defects, enhanced basicity, and favorable electron-deficient metallic Pt species, enabled an almost 100 % yield of FDCA in water with molecular oxygen (0.4 MPa) at 110 °C for 8 h without the addition of any homogeneous base, which is indicative of exceptional catalytic performance. Furthermore, this Pt/NC-CeO2 catalyst also showed good stability and reusability owing to strong metal-support interactions. An understanding of the role of surface structural defects and basicity of the hybrid NC-CeO2 support provides a basis for the rational design of high-performance and stable supported metal catalysts with practical applications in various transformations of biomass-derived compounds.

Syntheses, structures, and stabilities of aliphatic and aromatic fluorous iodine(I) and iodine(III) compounds: the role of iodine Lewis basicity.

The title molecules are sought in connection with various synthetic applications. The aliphatic fluorous alcohols RfnCH2OH (Rfn = CF3(CF2)n–1; n = 11, 13, 15) are converted to the triflates RfnCH2OTf (Tf2O, pyridine; 22–61%) and then to RfnCH2I (NaI, acetone; 58–69%). Subsequent reactions with NaOCl/HCl give iodine(III) dichlorides RfnCH2ICl2 (n = 11, 13; 33–81%), which slowly evolve Cl2. The ethereal fluorous alcohols CF3CF2CF2O(CF(CF3)CF2O)xCF(CF3)CH2OH (x = 2–5) are similarly converted to triflates and then to iodides, but efforts to generate the corresponding dichlorides fail. Substrates lacking a methylene group, RfnI, are also inert, but additions of TMSCl to bis(trifluoroacetates) RfnI(OCOCF3)2 appear to generate RfnICl2, which rapidly evolve Cl2. The aromatic fluorous iodides 1,3-Rf6C6H4I, 1,4-Rf6C6H4I, and 1,3-Rf10C6H4I are prepared from the corresponding diiodides, copper, and RfnI (110–130 °C, 50–60%), and afford quite stable RfnC6H4ICl2 species upon reaction with NaOCl/HCl (80–89%). Iodinations of 1,3-(Rf6)2C6H4 and 1,3-(Rf8CH2CH2)2C6H4 (NIS or I2/H5IO6) give 1,3,5-(Rf6)2C6H3I and 1,2,4-(Rf8CH2CH2)2C6H3I (77–93%). The former, the crystal structure of which is determined, reacts with Cl2 to give a 75:25 ArICl2/ArI mixture, but partial Cl2 evolution occurs upon work-up. The latter gives the easily isolated dichloride 1,2,4-(Rf8CH2CH2)2C6H3ICl2 (89%). The relative thermodynamic ease of dichlorination of these and other iodine(I) compounds is probed by DFT calculations.

A green approach to the synthesis of a nano catalyst and the role of basicity, calcination, catalytic activity and aging in the green synthesis of 2-aryl bezimidazoles, benzothiazoles and benzoxazoles

A green synthesis of hydrotalcite (a double layered catalyst) by a grinding method using Al/Mg molar ratios of 1.0–3.0 at room temperature is described.

On the Solubility of Ferrocene in Nonaqueous Solvents

The solubility of ferrocene in various organic solvents is important because of its application in chemical process and its role as a standard electrochemical probe in nonaqueous systems. A multilinear quantitative structure property relationship (QSPR) model based on theoretical descriptors and a new linear solvation energy relationship (LSER) model based on empirical scales of solvents are suggested for Ostwald solubility coefficient of ferrocene in 35 organic solvents. The constructed models were validated using different statistical approaches such as internal validation and external test set. In addition to excellent external prediction ability, QSPR and LSER models covered 94 and 92% of cross-validated variance, respectively. The proposed models confirmed the role of polar interactions and basicity of solvents during the solvation of ferrocene in organic phase.

On the role of a direct interaction between protein ions and solvent additives during protein supercharging by electrospray ionization mass spectrometry.

The addition of certain reagents during the electrospray ionization mass spectrometry of proteins can shift the protein ion signal charge-state distributions (CSDs) to higher average charge states, a phenomenon known as 'supercharging'. The role of reagent gas-phase basicity (GB) during this process was investigated in both the negative and positive ion modes. Reagents with known or calculated GBs were added individually in equimolar amounts to protein solutions which were subsequently electrosprayed for mass spectrometry analysis. Shifts in the CSDs of the protein ion signals were monitored and related to the reagents' GBs. Trends for this data were evaluated for possible insights into a supercharging mechanism involving the direct interaction between supercharging reagent and protein ion. Reagent GB was confirmed to be directly related to the amount of supercharging observed in the negative ion mode. Supercharging in the positive ion mode, on the other hand, showed a maximal trend. Interestingly, a loss of signal and supercharging efficacy was observed for reagents with GBs intermediate within the investigated range, between ~800 and ~840 kJ mol(-1), at the 100 mM concentration used in the present study. The possibility of a direct interaction model for supercharging in the negative and positive ion modes dependent on the GBs of the protein ions and reagents is discussed. In the positive ion mode, supercharging appears to depend on the stability of a proton bridge formed between the reagent and a highly charged protein ion.

On the relationship between the basicity of a surface and its ability to catalyze transesterification in liquid and gas phases: the case of MgO.

Gas or liquid phase transesterification reactions are used in the field of biomass valorization to transform some platform molecules into valuable products. Basic heterogeneous catalysts are often claimed for these applications but the role of basicity in the reaction mechanism depending on the operating conditions is still under debate. In order to compare the catalyst properties necessary to perform a transesterification reaction both in liquid and gas phases, ethyl acetate and methanol, which can be easily processed both in these two phases, were chosen as reactants. The catalyst studied is MgO, known for its basic properties and its ability to perform the reaction. By means of appropriate thermal treatments, different kinds of MgO surfaces, with different coverages of natural adsorbates (carbonates and hydroxyls groups), can be prepared and characterized by means of CO2 adsorption followed by IR spectroscopy and hept-1-ene isomerization model reaction. New results on the basicity of the natural MgO surface (covered by carbonate and hydroxyl groups) are first given and discussed. The catalytic behavior in the transesterification reaction is then determined as a function of the adsorbate coverage. It is shown that the transesterification activity in the liquid phase is directly correlated with the kinetic basicity of the surface in agreement with the mechanism already proposed in the literature. On the reverse, no direct correlation with the basicity of the surface was established with the transesterification activity in the gas phase. A very high activity, in the gas phase, was observed and discussed for the natural surface pre-treated at 623 K. Preliminary DFT modeling of ester adsorption and methanol adsorption capacity determination were performed to investigate plausible reaction routes.

Role of basicity and the catalytic activity of KOH loaded MgO and hydrotalcite as catalysts for the efficient synthesis of 1-[(2-benzothiazolylamino)arylmethyl]-2-naphthalenols

Novel KOH-loaded MgO and hydrotalcite as basic catalysts have been synthesized and were characterized by XRD, SEM and their basicity.

Role of basicity, calcinations, catalytic activity and recyclability of hydrotalcite in eco-friendly synthesis of coumarin derivatives

An efficient and simple protocol is described for synthesis of coumarin derivatives using Mg–Al-CO3 and Ca–Al-CO3 hydrotalcite as an environmental friendly and reusable heterogeneous catalyst under solvent free conditions. The catalysts were characterized by Hammett titration, SEM and XRD data. Present study revealed that catalytic activity and basicity depend on compositions of hydrotalcite. The calcined hydrotalcite with an Mg/Al of 3:1 derived from calcinations at 750K was found to be suitable catalyst that gives the highest basicity and the best catalytic activity for this reaction. Catalyst allows short reaction time, high catalytic activity, easy to work up and is reusable. Step economy, atom efficiency and solvent free conditions are some important salient features of this protocol.

Using Catalytic and Surface-Enhanced Raman Spectroscopy-Active Gold Nanoshells to Understand the Role of Basicity in Glycerol Oxidation

The origin of oxidation activity of gold catalysts has been a subject of great interest, particularly with the discovery of selective glycerol oxidation under water-phase alkaline conditions, for which neither small gold nanoparticles nor a catalyst support is necessary for activity. Little is known about the interactions among the catalyst surface, reactant, and hydroxyl species, which have never been examined spectroscopically because of a lack of developed in situ methods. In this work, we studied the room-temperature, water-phase reaction of glycerol oxidation using gold nanoshells (Au NSs), in which the gold substrate was active for surface-enhanced Raman spectroscopy (SERS) and catalysis. Analysis of glycerol solutions at high pH values and with oxygen content indicated that glycerol and glycerolate species did not bind directly to the catalyst surface in the absence of oxygen. However, glycerate surface species formed very rapidly when oxygen was present, suggesting an Eley–Rideal-type reaction mechanism with O2 (and/or O2-activated OH–) as the adsorbed species. SERS analysis of carbon monoxide chemisorption on Au NSs indicated that higher pH values progressively weakened the C–O bond as the Au negative charge increased. The importance of high alkalinity to Au-catalyzed alcohol oxidation may result from both the activation of glycerol via deprotonation and the weakening of the adsorbed O2 double bond via induced Au negative charge.

Transesterification of Glycerol to Glycerol Carbonate Using KF/Al2O3 Catalyst: The Role of Support and Basicity

Glycerol carbonate was synthesized by transesterification of glycerol with dimethyl carbonate using KF supported catalyst. KF was impregnated on various oxides and non-oxide supports like Al2O3, SiO2, ZnO, ZrO2, H-beta, and carbon to study the influence of the support on the catalytic performance. The preparation procedure of supported KF catalysts was modified to remove weakly adsorbed KF from the catalyst surface. The generation of basic sites by KF depends upon the extent of KF interaction with the support. KF/Al2O3 catalyst with optimized amount of 3.8 mmol KF, gave the highest activity with 95.8 % glycerol conversion and almost 100 % selectivity for glycerol carbonate. It was truly heterogeneous without any leaching of active sites and also showed good reusability. The catalyst exhibited better performance when compared to conventional solid base catalysts such as MgO, CaO and hydrotalcite.

Tuning copper(ii) ion selectivity: the role of basicity, size of the chelating ring and orientation of coordinating atoms

Incorporation of the triazolyl moiety modulates the basicity and effective size of the chelating ring, changes the stoichiometry in complex formation and thereby imparts Cu(2+) ion selectivity.

Role of calcinations and basicity of hydrotalcite as catalyst for environmental benign novel synthesis of 4H-pyrimido[2,1-b][1,3]benzothiazole derivatives of curcumin

A simple, efficient and step-economy synthesis to afford the library of 4H-pyrimido[2,1-b][1,3]benzothiazole derivatives of curcumin (4a–4h) from readily available substrates curcumin (potential biological molecule), 2-amino benzothiazole (biological active) and substituted aromatic aldehydes using novel heterogeneous calcined Mg-Al-CO3 hydrotalcite under solvent free conditions is described. The calcined hydrotalcite with an Mg/Al ratio of 3:1 derived from calcinations at 750 K was found to be a suitable catalyst that gives the highest basicity and the best catalytic activity for this reaction. The catalysts were characterized with XRD and SEM and Hammett titration method. This protocol has several advantages such as easy to work up, high activity of catalyst and reusability.

Hydrogenolysis of glycerol over Cu0.4/Zn5.6−xMgxAl2O8.6 catalysts: The role of basicity and hydrogen spillover

A series of Cu0.4/Zn5.6−xMgxAl2O8.6 catalysts with different Zn/Mg ratios were prepared and used in hydrogenolysis of glycerol in aqueous solution. This reaction proceeded more easily and efficiently over Cu0.4/Zn0.6Mg5.0Al2O8.6 than Cu0.4/Mg5.6Al2O8.6 and Cu0.4/Zn5.6Al2O8.6. The selectivity of 1,2-propanediol is higher than 98.6% in all experiments over Cu0.4/Zn0.6Mg5.0Al2O8.6, and the activity of surface Cu atoms reached 26.6h−1 at 200°C. The structure, morphology, acidity (basicity), and adsorption ability of glycerol/hydrogen for these catalysts were characterized and discussed. It was concluded that the conversion of glycerol depended strongly on the basicity of these Cu-based catalysts and hydrogen spillover also enhanced its performance.

Electrolysis of Molten Iron Oxide with an Iridium Anode: The Role of Electrolyte Basicity

Molten oxide electrolysis (MOE) is a carbon-free, electrochemical technique to decompose a metal oxide directly into liquid metal and oxygen gas. From an environmental perspective what makes MOE attractive is its ability to extract metal without generating greenhouse gases. Hence, an inert anode capable of sustained oxygen evolution is a critical enabling component for the technology. To this end, iridium has been evaluated in ironmaking cells operated with two different electrolytes. The basicity of the electrolyte has been found to have a dramatic effect on the stability of the iridium anode. The rate of iridium loss in an acidic melt with high silica content has been measured to be much less than that in a basic melt with high calcia content.

Solvatochromic, acid–base features and time effect of some azo dyes derived from 1,3-benzothiazol-2-ylacetonitrile: Experimental and semiempirical investigations

The solvatochromism and other spectroscopic properties of seven azo dyes were studied, with a particular respect to the role of the solvent basicity, and interpreted with the aid of experimental findings and semiempirical data. The electronic absorption spectra of the dyes examined in different solvents combined with theoretical calculations showed that most of the investigated compounds coexist in the hydrazone and/or azo-enamine-common anion equilibrium or in the solely anionic form depending upon the nature of the solvent employed. These interesting features open up possibilities for the use of these compounds in analytical chemistry as acid–base indicators. Furthermore, both of intermolecular and intramolecular charge transfer equilibria have been reflected by experimental absorption spectra of compounds 4 and 5. The enthalpies of formation predicted at PM6 (COSMO) and PM6/CI (COSMO) for the ground (S 0) and excited (S 1) states, respectively have been successfully used for the explanation of the observed bathchromic shift in non-polar solvents. The effect of time on the longer wavelength visible band of compound 7 has been thoroughly investigated.

Theoretical Study on the Role of Surface Basicity and Lewis Acidity on the Etherification of Glycerol over Alkaline Earth Metal Oxides

Alkaline earth metal oxides (MO) are catalytically active in the etherification of glycerol. Density Functional Theory (DFT) calculations have been used to examine the reactivity of glycerol with MO surfaces with M=Mg, Ca, Sr or Ba. More specifically, the optimum glycerol adsorption mode and the strength of glycerol interaction with regular MO (001) surfaces and a stepped CaO surface have been investigated and involves the interaction with acid-base surface sites. The basicity of lattice oxygen atoms is correlated with the adsorption energy: BaO (-3.02 eV) > SrO (-2.85 eV) > CaO (-2.05 eV) > MgO (-1.35 eV). The interactions have an exothermic character, that is, the more basic the alkaline earth metal oxide, the more exothermic is the adsorption process and the higher the dissociation extent. Thus, the dissociation of glycerol increases in the order: MgO (not dissociated) < CaO (partially dissociated < SrO (partially dissociated) < BaO (completely dissociated). The presence of defects is found to play a key role in the mechanism: glycerol interaction with a stepped CaO surface presents the highest adsorption energy (-3.78 eV), and the molecule is found to dissociate at the step. The calculated structural parameters are found to be in good agreement with experimental data on catalyst reactivity. Moreover, the earlier postulated reaction mechanism, which also involves the additional involvement of Lewis acid sites proved to be feasible for CaO and SrO regular surfaces, and for the stepped CaO surface. It was found that for these oxides one of the most favored adsorption modes involves a non-dissociative adsorption of one hydroxyl group of glycerol, which as a result becomes a better leaving group. Therefore, theoretical evidence was found for the possible direct involvement of Lewis acid sites in the catalytic etherification of bio-derived alcohols, such as glycerol, as it is anticipated that these observations can be extended to sugar alcohols as well.

The pKBHX Database: Toward a Better Understanding of Hydrogen-Bond Basicity for Medicinal Chemists

The hydrogen bond (HB) is one of the fundamental noncovalent interactions between a drug molecule and its local environment. For drug molecules, this local environment may be a biological target, a biological off-target, aqueous solution, a lipid membrane, or even a crystalline solid. Consequently, hydrogen bonding impacts a wide range of molecular properties critical to drug design including potency, selectivity, and permeability and solubility. Despite its importance, it is the authors’ experience that in general the medicinal chemistry community has a poor intuition for the relative basicity (i.e., strengths) of hydrogen-bond acceptors. In an attempt to assess the relative hydrogen-bond basicities of functional groups, it is common practice to resort to a simple correlation with pKBH, 8 which is generally incorrect and holds true only for closely related compounds in a series (i.e., a family dependent relationship). There is also a tendency to view hydrogen-bond acceptors as atomic sites and to consider them equivalent while disregarding the effects of organic functions and substituents that define the local molecular environment. This is evident in the lack of consideration for exploring hydrogen-bond basicity as an SAR parameter, as is commonly done to establish preferred steric, polar, basic, and acidic moieties. This poor intuition may partly stem from the lack of experimentally observable physical properties that are directly attributed to relative hydrogen-bondbasicities.Furthermore, despite thewell-known role of hydrogen bonds in protein-ligand interactions and the fact that hydrogen bonds are qualitatively well understood, it is generally admitted that quantitative data are needed. In the second section of this paper we review hydrogenbond basicity scales in general and introduce the pKBHX scale with a brief thermodynamic discussion on the treatment of polyfunctional compounds. In section 3 we discuss the effects of a medium more polar than the definition solvent CCl4 and changes in the reference HB donor on the pKBHX scale. In section 4, we present the pKBHX database and describe the fields of each entry,which correspond to threemain categories of data: HBA identification, thermodynamic, and spectroscopic. In section 5 we show that the pKBHX scale of HB basicity differs considerably from the pKBH scale of proton transfer basicity. This is important formedicinal chemistswho have a good knowledge of Broensted proton basicity scales and incorrectly consider HB basicity and proton basicity scales as equivalent. Section 6 reviews the hydrogen-bond basicities of functional groups relevant to medicinal chemistry while considering factors that modulate these values. Section 7 extends this medicinal chemistry discussion by providing examples of the role of hydrogen-bond basicity in properties of interest for drug design and briefly reviews computational approaches for addressing hydrogen bonding.