Degree Of Deprotonation Research Articles

TD-DFT calculations and thermal effects on conformers of calmagite in protic solvents varying the degree of protonation.

The main absorption peaks were obtained for 1-(1-hydroxy-4-methyl-2-phenylazo)-2-naphthol-4-sulfonic acid. Generalized gradient approximation, hybrid, semi-empirical, and Coulomb attenuating methods were utilized to compare theoretical electronic transitions and experimental absorption spectra at different pH. The main peaks and shoulders observed in experimental spectra were assigned to its correct conformer. In order to find the most populated conformer, thermal effects on stability calculations were investigated to obtain molar fractions of possible isomers present at room and higher temperature. Theoretical electronic transitions at distinct pH could be obtained varying the protonation a deprotonation degree. It was found that generalized gradient approximation performs very well the first transition peak at neutral pH. For higher pH, all methodologies got a bathochromic shift in agreement with experiment and finally, from these theoretical results, it was obtained that this azo dye is hardly protonated in experiments since results presented here, predict a variation of absorption spectra for all proposed methodologies when the molecule is protonated, which is different to experimental results. Graphical Abstract Calculated electronic transitions of azo and hydrazone tautomers in water implicit solvent (BLYP/6-311G(2d,p) methodology).

Lanthanide ion complexes of deprotonated p-isopropylcalix[n]arenes in dipolar aprotic solvents

The binding of lanthanide(III) cations with p-isopropylcalix[n]arenes (n = 4, 6, 8) after partial deprotonation has been investigated using UV-Vis absorption spectrophotometry. The ease and degree of deprotonation of the calixarenes closely parallels the behaviour of their t-butyl analogues in the same solvents. The conditional stability constants of the praseodymium, europium, ytterbium and yttrium complexes were determined in DMF and in acetonitrile. The effect of water on the stability of lanthanide complexes in DMF was also treated. The results show that the cation binding selectivity, stoichiometry and stability of the complexes depend on various factors such as the degree of condensation (n) and the consequent number of O-donor atoms as well as the nature of the cation solvation. The stability of the Y(III), Pr(III), Eu(III) and Yb(III) complexes in DMF increased in all cases with increase of the ring size. DFT calculations were used to estimate the influence of the solvent on both the acidity and the conformations of the calixarene anions.

Metal complexes of a pentadentate N2O3bis(semicarbazone) Schiff-base. A case study of structure-spectroscopy correlation

Schiff condensation of 2,6-diformyl 4-methylphenol with semicarbazide hydrochloride in 1:2 molar ratio produces the bis(semicarbazone) ligand, herein called H3L. A comprehensive spectroscopic analysis of the compound was performed by 1H and 13C NMR, FTIR and electronic spectroscopies. Assignments to the UV–vis spectrum of H3L were supported by semi-empirical quantum mechanics ZINDO/S calculations. The ligand H3L forms monoclinic crystals in the space group P21/c and its structure is stabilized by classic hydrogen bonds with propanone molecules. It promptly reacts with first row metal ions to produce the following coordination compounds: [Co2(L)(μ-NO3)]·DMF, [Ni2(H2L)(μ-CH3COO)(CH3COO)2]·2H2O, [Cu2(L)(μ-NO3)(H2O)2]·H2O, [Cu2(L)(μ-CH3COO)(H2O)2]·H2O and [Cu2(H2L)(μ-Cl)Cl2]·3H2O, that have different compositions, depending on the degree of deprotonation of the ligand upon coordination. Electronic and EPR spectroscopies as well as effective magnetic moment measurements of the complexes were used in an attempt to better understand their mode of coordination, the microsymmetry around the metal ions and magnetic properties.

Water Contact Angle Dependence with Hydroxyl Functional Groups on Silica Surfaces under CO2 Sequestration Conditions.

Functional groups on silica surfaces under CO2 sequestration conditions are complex due to reactions among supercritical CO2, brine and silica. Molecular dynamics simulations have been performed to investigate the effects of hydroxyl functional groups on wettability. It has been found that wettability shows a strong dependence on functional groups on silica surfaces: silanol number density, space distribution, and deprotonation/protonation degree. For neutral silica surfaces with crystalline structure (Q(3), Q(3)/Q(4), Q(4)), as silanol number density decreases, contact angle increases from 33.5° to 146.7° at 10.5 MPa and 318 K. When Q(3) surface changes to an amorphous structure, water contact angle increases 20°. Water contact angle decreases about 12° when 9% of silanol groups on Q(3) surface are deprotonated. When the deprotonation degree increases to 50%, water contact angle decreases to 0. The dependence of wettability on silica surface functional groups was used to analyze contact angle measurement ambiguity in literature. The composition of silica surfaces is complicated under CO2 sequestration conditions, the results found in this study may help to better understand wettability of CO2/brine/silica system.

Instability of Surface-Grafted Weak Polyacid Brushes on Flat Substrates

We study the stability of weak polyacid brush (WPAB) gradients in aqueous media covering a range in grafting density (σ) spanning 0.05–0.5 chains/nm2 using two analogous surface-anchored bromoisobutyrate-based initiators for atom transfer radical polymerization (ATRP) bearing either an ester or amide linker. Variations in dry thickness of ester-based WPABs as a function of time and pH are consistent with WPAB degrafting via linker hydrolysis catalyzed by mechanical tension in the grafted chains. Sources of tension considered include high σ, as well as swelling and electrostatic repulsion associated with increasing degree of deprotonation (α) of repeat units in the WPAB. Normalized thickness of the WPAB decreases by a maximum amount at intermediate σ between ∼0.05−0.15 chains/nm2, implying that contributions to tension by α are counterbalanced by charge regulation in the WPAB at high σ. Amide-based WPABs are more stable up to 264 h incubation, suggesting that commonly used ester-bearing ATRP initiators are...

Study of homo- and heteronuclear complex formation in 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP)—erbium(iii) and HEDP—erbium(iii)—calcium(ii) systems in an aqueous solution

Erbium(iii)—HEDP and erbium(iii)—calcium(ii)—HEDP systems (HEDP is 1-hydroxyethylidene-1,1-diphosphonic acid) have been studied using potentiometry method in association with mathematical modelling. In the erbium(iii)—HEDP system the formation of compexes having various degree of deprotonation of a ligand, 1 : 1 and 2 : 1 monoand dinuclear complexes, as well as mononuclear bis-complexes has been shown. It was found, that heteronuclear complexes generated in erbium(iii)—calcium(ii)—HEDP system, do not coincide neither with calcium nor with erbium forms in composition.

Zero-, one-, two- and three-dimensional coordination polymers based on tetracarboxylic acid: Syntheses, structures, magnetic and luminescent properties

A series of coordination polymers, namely, {[Co(H2ttac)(phen)2]4H2O}n (1), {[Zn(H2ttac)(phen)2]4H2O}n (2), [Cu(H2ttac)(phen)]n (3), [Zn2(ttac)(DMZ)H2O]n (4), and [Cd(ttac)(phen)H2O]n (5)(H4ttac = 4,5-di(3'-carboxylphenyl)-phthalic acid, phen = 1,10-phenanthroline, DMZ = Dimidazole) have been prepared under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, and single crystal X-ray diffraction. Structural analysis reveals that the as-synthesized coordination polymers have different structures, ranging from zero-(1 and 2), one-(3), two-(4) to three-(5) dimensions, which are mainly due to the different metal ions, the degree of deprotonation and coordination modes of the H4ttac ligands. It is worth mentioning that, based on the diversified π–π stacking and/or C–H···π interactions between H4ttac ligands and/or nitrogen-containing auxiliary ligands, 1–4 are assembled form low-dimensional structures into three-dimensional (3D) frameworks. Especially, Jahn-Teller effect occurs in 3 and its magnetic study confirms that it presents antiferromagnetic coupling through the (O2C-Ar-Ar-CO2)2 bridges. Significantly, luminescent emission of 3 displays selective recognition towards L-Arginin. Thermogravimetric (TG) analyses of the coordination polymers have also been investigated.

Conformational analysis on protonation and deprotonation of calmagite in protic solvents and its reactivity through Fukui function

In the present work a systematic theoretical study on 1-(1-hydroxy-4-methyl-2-phenylazo)-2-naphthol-4-sulfonic acid was performed. All possible protonation and deprotonation degrees were analyzed. The use of solvents in calculations affect in a direct way the stability of azo and hydrazone tautomers. This is the first systematic theoretical study, from electronic structure point of view, on this widely used azodye. Additionally, local reactivity utilizing the Fukui function was obtained. Interestingly, reactivity of the molecule undergoes no significant changes despite azo–hydrazone tautomerism, since the Fukui functions are not modified in a significant way in both tautomers. It is worth mentioning that results presented here are important in studies about degradation of this kind of azodyes, in studies when calmagite forms complex compounds with metallic and lanthanide atoms or in photoabsorption studies since spectrum depends on protonation and deprotonation degree and on the most stable conformers in the sample.

Complexes of tetramethylensulfonatocalix[4]resorcinarene aggregates with methyl orange: Interactions with guests and driving force of color response

Abstract Here we report on the examination of 12 guests (G1–12) interactions with the aggregates of tetramethylensulfonated tetrapentylcalix[4]resorcinarene ( H ) and the azo-pH-indicator methyl orange (MO). At pH 4.2, addition of 40 and 100 equiv. of the guests to 40:1 H :MO solution resulted in deprotonation of the dye accompanied by UV/Vis spectra changes. Variation of MO deprotonation degree in the presence of G1–12 is discussed in relation to the guest interactions with the aggregated H and competition with the surface-bound MO.

Cyclic Interconversion among Molecular Salts via Neat Grinding and Related Photoluminescence Properties

We report three molecular salts formed by 5-sulfosalicylic acid dihydrate (A·2H2O) and 4,4′-diaminodiphenylmethane (B) in different stoichiometric ratios. The A1B1·H2O, A1B2 and A2B1·H2O molecular salts can be accessed via mechanochemical grinding and from solution. Structural aspects were analyzed using single crystal and X-ray powder diffraction (XRPD). The reversible solid state ionic interconversion between A1B1·H2O, A1B2, and A2B1·H2O upon neat grinding by adding an appropriate amount of A·2H2O or B is described. In the ionic interconversion water molecules are included or excluded upon grinding, which suggests that water plays an important role in the proton transfer. The solid-state fluorescence spectra of A1B1·H2O, A1B2, and A2B1·H2O showed that the three molecular salts exhibit emission features and are red-shifted compared with the starting materials A·2H2O and B. The interparticle (CT) interactions and the degree of anion deprotonation are important in the solid-sate fluorescence of the described molecular salts. The photoluminescence experimental results have been corroborated using time-dependent density functional theory (TD-DFT), which has been shown to provide reasonable results for the excited states of molecules involved in the formation of the molecular salts.

Re6(μ3-Se)8]2+ Core-Containing Cluster Complexes with Isonicotinic Acid: Synthesis, Structural Characterization, and Hydrogen-Bonded Assemblies

Three new complexes of the [Re6(μ3-Se)8]2+ core-containing cluster with isonicotinic acid (INA) were synthesized and characterized by multinuclear NMR (1H and 31P) and high-resolution mass spectrometry. Their molecular and crystal structures were determined by single-crystal X-ray diffraction studies. Unusual degrees of deprotonation of the INA ligand(s) are observed in the crystal structure, possibly due to the activation by the Lewis acidic cluster core. Extensive hydrogen bonding interactions occurring between carboxylate groups of neighboring cluster units as revealed by crystallographic studies lead to the assembly of both linear and zigzag multi-cluster chains in the solid state.

Performance of exchange–correlation functionals on describing ground state geometries and excitations of Alizarin Red S: Effect of complexation and degree of deprotonation

Ground state optimizations and excited state calculations were performed to analyze the possible anionic forms of Alizarin Red S(ulphonated) and its ML2 type metal complexes formed with palladium(II). Six functionals have been tested (B3LYP, M06-2X, M06, BH&HLYP, PBE0, LC-wPBE, and CAM-B3LYP) with two basis sets (6-311+g(d,p) and TZVP). The relative errors of these functionals in reproducing the experimental UV–Vis absorption wavelengths are reported for the energetically lowest lying isomers. It was found that the degree of deprotonation affects several functionals in a systematic way. M06 and CAM-B3LYP xc-functionals gave the best estimates according to the average relative errors. These two functionals were then used to explore the coordination mode (hydroxy–keto or catechol) of the palladium(II) complexes and the effect of (de)protonation.

Structural Effect on Electrochemical Performance of 4,4’-Biphenyldicarboxylate Soduim Salts As an Anode for Na-Ion Batteries

Sodium ion batteries have recently gained recognition as a promising candidate for next-generation battery systems on the basis of their potential cost advantages due to the natural abundance of Na resources [1-6]. In this presentation, we first introduce the crystal structures and electrochemical performance of 4,4’-biphenyldicarboxylate sodium salts as an anode for Na-ion batteries. The structural modification of 4,4’-biphenyldicarboxylate sodium salts showing different degree of deprotonation and the coordination of a water molecule are deliberately accomplished through various precipitation and solvothermal methods. This results in the formation of three different crystal structures even though they are composed of the same organic (bpdc) and inorganic (Na+) building blocks.The crystal structures are determined by single-crystal X-ray diffraction, and the powder X-ray diffraction patterns showed the good agreement with the corresponding simulated patterns. This indicates that the phase pure powders have the same crystal structure as the single crystals.The level of deprotonation in 4,4’-biphenyldicarboxylate sodium salts affected not only electrochemical performance but also reaction mechanisms. The fully deprotonated 4,4’-biphenyldicarboxylate disodium salt (Na2bpdc) exhibited promising electrochemical performance including reversible capacity of 220 mA h g-1 at ca. 0.5 V vs. Na/Na+, negligible capacity fading over 150 cycles, and excellent rate performance delivering about 100 mA h g-1 even at a 20C rate, which is better than monosodium 4,4’-biphenyldicarboxylate (NaHbpdc) that is partially deprotonated. This better rate performance of Na2bpdc salts is definitely attributed to the smaller particle size (short diffusion length) of that compared to NaHbpdc. However, even the dehydrated disodium 4,4’-biphenyldicarboxylate monohydrate (h-Na2bpdc) having similar size to NaHbpdc exhibited better rate performance than NaHbpdc. This means that the rate performance is affected by the degree of deprotonation in 4,4’-biphenyldicarboxylate sodium salts. Carboxylic group causes the large amount of electrolyte decomposition to form thick solid electrolyte interphase (SEI) layers, resulting in the increase of polarization due to large charge-transfer resistance.Also, the de/sodiaiton of Na2bpdc salts proceeds in a two-phase reaction, regardless of the degree of deprotonation. However, unlike the fully deprotonated showing reversible phase transition during sodiation and desodiation, the partially deprotonated exhibited irreversible phase transition during cyclings. It seems to be attributed to the partial phase transition of NaHbpdc to Na2bpdc due to the ion-exchange between Na+ and H+.

Predicting the pKa and stability of organic acids and bases at an oil-water interface.

We have used density functional theory and the implicit solvent model, COSMO-RS, to investigate how the acidity constant, pKa, of organic acids and bases adsorbed at the organic compound-aqueous solution interface changes, compared to its value in the aqueous phase. The pKa determine the surface charge density of the molecules that accumulate at the fluid-fluid interface. We have estimated the pKa by comparing the stability of the protonated and unprotonated forms of a series of molecules in the bulk aqueous solution and at an interface where parts of each molecule reside in the hydrophobic phase and the rest remains in the hydrophilic phase. We found that the pKa for acids is shifted by ∼1 pH unit to higher values compared to the bulk water pKa, whereas they are shifted to lower values by a similar amount for bases. Because this pKa shift is similar in magnitude for each of the molecules studied, we propose that the pKa for molecules at a water-organic compound interface can easily be predicted by adding a small shift to the aqueous pKa. This shift is general and correlates with the functional group. We also found that the relative composition of molecules at the fluid-fluid interface is not the same as in the bulk. For example, species such as carboxylic acids are enriched at the interface, where they can dominate surface properties, even when they are a modest component in the bulk fluid. For high surface concentrations of carboxylic acid groups at an interface, such as a self-assembled monolayer, we have demonstrated that the pKa depends on the degree of deprotonation through direct hydrogen bonding between protonated and deprotonated acidic headgroups.

Theoretical Studies on the Interaction of Ruthenium Sensitizers and Redox Couple in Different Deprotonation Situations

We report a DFT study of interaction between the Ru complex sensitizer [Ru(dcbpy)2(NCS)2: dcbpy = 4,4'-dicarboxy-2,2'-bipyridyl] (N3) and iodide ion under the influence of different deprotonation situations. There are two kinds of interaction mechanisms: iodide ion interacts with metal-center Ru atom or carboxyl, derived from the natural charge distribution analysis. The calculation indicated that there were several stable intermedium forms in different deprotonation degree. The stability of these intermedium forms would be perturbed gradually while the number of eliminated protons increased. It can be predicted that in the initial period of absorption and injection as well as the dissolve process where the deprotonation was demanded, the dye will not attacked by the iodide ion in solution extensively. Additionally, dye with more carboxyls will reduce the activity of redox reaction and more obstacles are required to be overcome before or during the redox reaction. The comparison of natural charge between isolate N3 and N3 with iodide ion intermedium (N3I(-)) showed the iodide ion attacking made the charge contribute on N3 molecule more negative, nevertheless the N3I(-) still has ability to attract another iodide ion. The attacking of iodide ion will also influence the electronic transition and absorption properties through the analysis of the frontier molecular orbitals and the densities of states. The results reported in this paper give us the guidance to carry out the further investigations about the dye regeneration process.

A Versatile Dinucleating Ligand Containing Sulfonamide Groups

Copper, iron, and gallium coordination chemistries of the new pentadentate bis-sulfonamide ligand 2,6-bis(N-2-pyridylmethylsulfonamido)-4-methylphenol (psmpH3) were investigated. PsmpH3 is capable of varying degrees of deprotonation, and notably, complexes containing the fully trideprotonated ligand can be prepared in aqueous solutions using only divalent metal ions. Two of the copper(II) complexes, [Cu2(psmp)(OH)] and [Cu2(psmp)(OAc)2](-), demonstrate the anticipated 1:2 ligand/metal stoichiometry and show that the dimetallic binding site created for exogenous ligands possesses high inherent flexibility since additional one- and three-atom bridging ligands bridge the two copper(II) ions in each complex, respectively. This gives rise to a difference of 0.4 Å in the Cu···Cu distances. Complexes with 2:3 and 2:1 ligand/metal stoichiometries for the divalent and trivalent metal ions, respectively, were observed in [Cu3(psmp)2(H2O)] and [M(psmpH)(psmpH2)], where M = Ga(III), Fe(III). The deprotonated tridentate N-2-pyridylsulfonylmethylphenolato moieties chelate the metal ions in a meridional fashion, whereas in [Cu3(psmp)2(H2O)] the rare μ2-N-sulfonamido bridging coordination mode is observed. In the bis-ligand mononuclear complexes, one picolyl arm of each ligand is protonated and uncoordinated. Magnetic susceptibility measurements on the doubly and triply bridged dicopper(II) complexes indicate strong and medium strength antiferromagnetic coupling interactions, with J = 234 cm(-1) and 115 cm(-1) for [Cu2(psmp)(OH)] and [Cu2(psmp)(OAc)2](-), respectively (in HHDvV =...+JS1S2 convention). The trinuclear [Cu3(psmp)2(H2O)], in which the central copper ion is linked to two flanking copper atoms by two μ2-N-sulfonamido bridges and two phenoxide bridges shows an overall magnetic behavior of antiferromagnetic coupling. This is corroborated computationally by broken-symmetry density functional theory, which for isotropic modeling of the coupling predicts an antiferromagnetic coupling strength of J = 70.5 cm(-1).

A Light and pH Dual-Stimuli-Responsive Block Copolymer Synthesized by Copper(0)-Mediated Living Radical Polymerization: Solvatochromic, Isomerization, and “Schizophrenic” Behaviors

A "schizophrenic" block copolymer (poly[1'-(2-methacryloxyethyl)-3',3'-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2'-indoline)]-b-poly(acrylic acid) (PSPMA-b-PAA)) was synthesized by sequential copper(0)-mediated living radical polymerization (Cu(0)-mediated LRP) at 30 °C in an oxygen-tolerant system followed by hydrolysis of the resulting polymer. The solvatechromic behaviors of the PSPMA10-b-poly(t-butyl acrylate)40 (PSPMA10-b-PtBA40) and PSPMA10-b-PAA40 block copolymers in organic solvents were investigated by UV-vis spectroscopy. The PSPMA10-b-PtBA40 stabilizes the nonpolar photoisomer and is not sensitive to the polarity of the solvent, while the PSPMA10-b-PAA40 stabilizes the planar zwitterionic form without irradiation. Furthermore, light-induced isomerization of spiropyran (Sp) moieties from Sp to merocyanine (Mc) was demonstrated. Finally, the "schizophrenic" micellization behavior of as-prepared copolymer in aqueous solution regulated by light and pH stimuli was vividly demonstrated, and the reversibility of micellization processes performed in this study was also examined. The large compound micelles can bring out a gradually extended and even transformed conformation with increasing deprotonation degree at pH > pKa.

Compositional effects on Si–OH bond length in hydrous silicates with implications for trends in the SiOH acidity

Theoretical calculations of the structure and Brønsted acidity of SiOH groups in silica clusters have never addressed the question if these vary with the degree of SiOH deprotonation. In this connection, a statistical analysis is presented of Si–OH bond lengths in crystalline hydrogen silicates with well-determined structures with a special emphasis placed on effects of the silicate composition. It is found that among hydrogen silicates of large cations with low charges the Si–OH bonds are always longer than terminal Si–O bonds in the same anion and correlate in length with the anionic charge per tetrahedron. The findings are explained by steric limitations on charge balancing at oxygen atoms by hydrogen bonds and/or cations. It is suggested that similar limitations and imbalances may underlie the well-known trends in the Brønsted acidity of silicic acids and silicas in aqueous media: decreased acidity with increased SiOH deprotonation and increased acidity with increased tetrahedra connectivity.

Direct visualization of the interfacial position of colloidal particles and their assemblies.

A method for direct visualization of the position of nanoscale colloidal particles at air-water interfaces is presented. After assembling hard (polystyrene, poly(methyl methacrylate), silica) or soft core-shell gold-hydrogel composite (Au@PNiPAAm) colloids at the air-water interface, butylcyanoacrylate is introduced to the interface via the gas phase. Upon contact with water, an anionic polymerization reaction of the monomer is initiated and a film of poly(butylcyanoacrylate) (PBCA) is generated, entrapping the colloids at their equilibrium position at the interface. We apply this method to investigate the formation of complex, binary assembly structures directly at the interface, to visualize soft, nanoscale hydrogel colloids in the swollen state, and to visualize and quantify the equilibrium position of individual micro- and nanoscale colloids at the air-water interface depending of the amount of charge present on the particle surface. We find that the degree of deprotonation of the carboxyl group shifts the air-water contact angle, which is further confirmed by colloidal probe atomic force microscopy. Remarkably, the contact angles determined for individual colloidal particles feature a significant distribution that greatly exceeds errors attributable to the size distribution of the colloids. This finding underlines the importance of accessing soft matter on an individual particle level.

Discovery of New Calcium Etidronates Employing Ultrasound Adapted High-Throughput Methods

The formation of calcium etidronates was investigated employing high-throughput ultrasonic synthesis. In the study of the system CaCl2/H2O3P-C(OH)(CH3)-PO3H2/H2O/KOH three new crystalline products were obtained in dependence of the deprotonation degree of the bisphosphonic acid HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, H2O3P-C(OH)(CH3)-PO3H2) and the sonication time. In a large region of the parameter space and at short reaction times [Ca(HO3P-C(OH)(CH3)-PO3H)(H2O)]·2.5H2O (1) forms. At higher pH [KCa(HO3P-C(OH)(CH3)-PO3)(H2O)]·H2O (2) containing the asymmetrically deprotonated HO3P-C(OH)(CH3)-PO33– ion and [K2Ca(O3P-C(OH)(CH3)-PO3)(H2O)6] (3) with the fully deprotonated ligand are obtained. The crystal structures of 1 and 2 were solved and refined from X-ray powder diffraction data. The thermal decomposition of the compounds was investigated. If exposed to moderate temperatures 1.5 water molecules per formula unit are removed from the crystal structure of 1 and the pseudopolymorphic compound [Ca(H...