Squaric Acids Research Articles

Reversible crosslinking of polybenzimidazole-based organic solvent nanofiltration membranes using difunctional organic acids: Toward sustainable crosslinking approaches

Solvent resistance is a crucial property for achieving organic solvent nanofiltration (OSN) membranes with good separation performance and long lifespan. Polybenzimidazole (PBI) has been widely used for OSN membrane fabrication owing to its excellent mechanical properties, thermal stability, and resistance in various organic solvents. However, pristine PBI membranes show unsatisfactory stability in polar aprotic solvents. To circumvent this issue, extensive research has been conducted on the covalent crosslinking of PBI membranes. Herein, to develop a more sustainable crosslinking strategy, difunctional organic acids — oxalic and squaric acids — were used for the reversible crosslinking of PBI membranes in water at room temperature, affording robust membranes with long-term stability in polar aprotic solvents. An analysis at the molecular level of the difunctional acid crosslinking system based on p K a values and binding energies was presented. The molecular weight cutoff and solvent flux of the PBI membranes crosslinked with oxalic and squaric acids were 779 and 844 g mol −1 and 153.9 and 139.7 L m −2 h −1 bar −1 in N , N -dimethylacetamide at 30 bar, respectively. The crosslinking was successfully reversed under basic conditions, allowing the recovery of the pristine PBI polymer. A sustainability assessment revealed the advantages of the proposed crosslinking system over conventional covalent crosslinking approaches. The solvent-resistant properties of polybenzimidazole membranes are enhanced using a crosslinking approach by employing oxalic and squaric acids as mild organic acid crosslinkers in water under ambient conditions. • OSN membranes formed via mild organic acid crosslinking at ambient conditions in aqueous solutions. • Difunctional organic acids with p K a lower than 5.23 can crosslink polybenzimidazole (PBI) membrane. • Improved membrane stability in NMP, DMSO, DMAc, DMF polar aprotic solvents up to two weeks. • Less hazardous and more sustainable crosslinking approach for OSN membrane fabrication. • Membranes crosslinked with oxalic and squaric acids were recovered as pristine PBI.

Squaric acid as a new chemoselective moiety for mass spectrometry-based metabolomics analysis of amines.

The investigation of microbiome-derived metabolites is important to understand metabolic interactions with their human host. New methodologies for mass spectrometric discovery of undetected metabolites with unknown bioactivity are required. Herein, we introduce squaric acid as a new chemoselective moiety for amine metabolite analysis in human fecal samples.

Thermodynamic, Raman Spectroscopic, and UV-Visible Optical Characterization of the Deltic, Squaric, and Croconic Cyclic Oxocarbon Acids.

A precise and complete thermodynamic, Raman spectroscopic, and ultraviolet-visible (UV-vis) optical characterization of the deltic, squaric, and croconic cyclic oxocarbon acids is obtained using theoretical solid-state methods employing very demanding calculation parameters. The computed fundamental thermodynamic properties include the isobaric specific heat, the entropy, the enthalpy, and the Gibbs free energy as a function of temperature. The calculated specific heats at 298.15 K of the deltic, squaric, and croconic acids are 89.7, 111.2, and 133.2 J mol-1 K-1, respectively, and the corresponding entropies are 98.3, 117.3, and 136.5 J mol-1 K-1. The only value of these properties known from experimental measurements is the specific heat of the squaric acid, which differs from the computed value at 315 K by about 4.9%. The calculated values of the thermodynamic properties are then used to determine the thermodynamic properties of formation of these materials in terms of the elements. As an application of the calculated thermodynamic properties of formation, the Gibbs free energies of reaction and associated reaction constants are evaluated for the reactions of thermal decomposition and complete combustion of the squaric and croconic acids and the reaction of interconversion between them. The only available experimental values of these properties, namely, the enthalpies of combustion of squaric and croconic acids at room temperature, are reproduced theoretically with high accuracy. The Raman spectra of these materials are also computed using density functional perturbation theory. The analysis of the theoretical Raman spectra of these materials points out to significant differences with respect to their usual empirical assignment. Therefore, the Raman spectra of these materials are fully reassigned. Finally, the ultraviolet-visible (UV-vis) optical properties of the deltic, squaric, and croconic acids are computed. The UV-vis absorption spectrum of the croconic acid in the spectral region 225-425 nm and the UV absorption spectrum of the squaric acid in the region 200-350 nm, which had previously been measured experimentally, are well reproduced. The corresponding spectrum for the deltic acid and the reflectivity, optical conductivity, dielectric, refractive index, and loss optical functions of the three materials, which had never been published as far as we know, are reported as a function of the wavelength of incident radiation in the range 200-750 nm. The origin of the peaks in the absorption spectra, which had not been analyzed so far, is unveiled here by examining the interband electronic transitions in these materials.

Addendum: anomalous mechanical behavior of the deltic, squaric and croconic cyclic oxocarbon acids

The mechanical properties of the deltic, squaric, and croconic acids were determined in a previous work by using rigorous theoretical solid-state methods based in Density Functional Theory using plane waves and pseudopotentials using a high-quality setup. These three materials were shown to display small negative Poisson ratios (NPR). Croconic acid was also shown to exhibit the phenomenon of negative linear compressibility (NLC) for applied pressures larger than ∼0.4 GPa directed along the direction of minimum Poisson ratio. The main purpose of this communication is to show that the croconic acid also exhibits the NLC phenomenon when submitted to isotropic pressures. The a lattice parameter of croconic acid increases for applied isotropic pressures in the range from 0.41 GPa to 0.46 GPa. The computed compressibility along a direction at the pressure of P = 0.44 GPa is ka = −79.7 TPa−1.

Anomalous mechanical behavior of the deltic, squaric and croconic cyclic oxocarbon acids

The structural and mechanical properties of the deltic, squaric and croconic cyclic oxocarbon acids were obtained using theoretical solid-state methods based in Density Functional Theory employing very demanding calculation parameters in order to yield realistic theoretical descriptions of these materials. The computed lattice parameters, bond distances, angles, and x-ray powder diffraction patterns of these materials were in excellent agreement with their experimental counterparts. The crystal structures of these materials were found to be mechanically stable since the calculated stiffness tensors satisfy the Born mechanical stability conditions. Furthermore, the values of the bulk modulus and their pressure derivatives, shear and Young moduli, Poisson ratio, ductility and hardness indices, as well as mechanical anisotropy measures of these materials were reported. A complete review of the literature concerning the negative Poisson ratio and negative linear compressibility phenomena is given together with the theoretical study of the mechanical behavior of cyclic oxocarbon acid materials. The deltic, squaric, and croconic acids in the solid state are highly anisotropic materials characterized by low hardness and relatively low bulk moduli. The three materials display small negative Poisson ratios. The croconic acid displays the phenomenon of negative linear compressibility for applied pressures larger than ∼0.4 GPa directed along the direction of minimum Poisson ratio and undergoes a pressure induced phase transition at applied pressures larger than ∼1.0 GPa.

LiFePO4/C ultra-thin nano-flakes with ultra-high rate capability and ultra-long cycling life for lithium ion batteries

LiFePO4/C ultra-thin nanoflakes have been synthesized via evaporative self-assembly induced by squaric acid and successfully applied for cathode materials in full cell. The morphologies and structures were characterized by X-ray diffractometer, scanning electron microscopy and transmission electron microscopy. Some LiFePO4/C nanoparticles about 40–80 nm in diameter are connected by LiFePO4/C ultra-thin nano-flakes which are constructed by squaric acids, other LiFePO4 nanoparticles are embedded in the ultra-thin carbon nanoflakes. LiFePO4/C ultra-thin nano-flakes deliver a initial discharge capacity of 164 mAh g−1 at 0.2C rate and 92 mAh g−1 at 50 C rate. Its capacity retention is still 96% at 10 C rate after 1000 cycles. The unique LiFePO4/C ultra-thin nano-flakes can effectively increase the contact between electrode and electrolyte, improve the electronic and ionic conductivity and promote the transportations for lithium ions.

Syntheses of α‐Amino Squaric Acids Using an Aminomalonate Equivalent Bearing a Squaryl Group.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access the actual ChemInform Abstract, please click on HTML or PDF.

Syntheses of α-Amino Squaric Acids Using an Aminomalonate Equivalent Bearing a Squaryl Group

The synthesis of an amino acid analogue bearing a squaryl group as a carboxylic acid surrogate (sq-AA; 2) has been developed. Aminomalonate equivalent 6 was used as a nucleophilic synthon whose alkylation or conjugate addition reaction followed by deprotection and decarboxylation reaction gave sq-AAs.

Synthesis of Novel Amino Squaric Acids via Addition of Dianion Enolates Derived from N‐Boc Amino Acid Esters.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The Novel Functional Chromophores Based on Squarylium Dyes

Squarylium or squaraine dyes are derived from 1,2-dihydroxycyclobuten-3,4-dione, otherwise known as squaric acids. They are two principal types: the 1,2-bisdonorsubstituted derivatives, and the 1,3-bisdonorsubstituted derivatives. The former are essentially merocyanines and have no distinctive properties, whereas the latter represent a unique type of chromophore, which is neither a merocyanines nor cyanine and has exceptional light absorption characteristics. They also have many functional applications based on their special properties. Thus it was the objective of this research project to synthesize a range of 1,3-squarylium dyes of widely differing structural types, and to investigate their light absorption and fluorescence properties in general, and the color change properties of appropriate examples in particular. Also in this study, the various pHinduced colour change processes were examined.

Synthesis of novel amino squaric acids via addition of dianion enolates derived from N-Boc amino acid esters

Novel α-amino squaric acid analogs were synthesized by initial addition reaction of a dianion enolate generated from N-Boc amino acid tert-butyl ester to squaric acid diisopropyl ester, and subsequent decarboxylation of the resulting carboxylic acid moiety.

Squaric acids: a new motif for designing inhibitors of protein tyrosine phosphatases.

[structure: see text] Protein tyrosine phosphatases (PTPases) are important targets in medicinal chemistry. These enzymes play a role in a number of human diseases, including type II diabetes and infection by Yersinia pestis, the causative agent of bubonic plague. Derivatives of squaric acids such as 2-aryl-1-hydroxycyclobut-1-ene-3,4-diones represent a new class of monoanionic inhibitors for PTPases.

Interanionic (-)O-H...O(-) interactions: a solid-state and computational study of the ring and chain motifs.

The (-)O-H...O(-) interaction formed by the anions HCO3-, HCO4, HC4O4 and HC5O5- (HA-), obtained upon monodeprotonation of the corresponding carbonic, oxalic, squaric and croconic acids (H2A), has been investigated theoretically and experimentally. The ring (RING) and chain (CHAIN) hydrogen bond motifs established between these anions have been analysed in terms of geometry and energy and their occurrence in crystalline salts investigated by searching the Cambridge Structural Database (CSD) and the Inorganic Chemistry Structural Database (ICSD). It has been shown that hydrogen carbonates form RINGs, with the notable exception of NaHCO3, while only CHAINs are known for hydrogen oxalates. Hydrogen squarates and hydrogen croconates can form both RINGs and CHAINs. The structures of Rb- and Cs- hydrogen croconates, which present the two alternative motifs, have been discussed together with that of the hydrated salt NaHC5O5.H2O. The relationship between RING and CHAIN has been examined in the light of ab initio calculations. A rigorous quantum chemical study of the nature of the interanionic (-)O-H...O(-) interaction in both vacuum and condensed phase has shown that the interaction energy is dominated by the electrostatic component which becomes attractive at short O...O distances (less than 2.5 A) if the net ionic charge on the anion is delocalised away from the -OH group. It has been demonstrated that the RING motif is slightly metastable with respect to dissociation in the gas phase, but becomes stable in the crystal owing to the influence of the Madelung field. However, the CHAIN motif is unstable both in the gas phase and in the crystal. It is argued that interanionic (-)O-H...O(-) interactions ought to be regarded as stabilising bonding interactions rather than proper intermolecular hydrogen bonds because the RING and CHAIN aggregates are not energetically stable on an absolute scale of bonding energy (i.e., in the absence of counterions). The presence of very short non-hydrogen-bridged O...O contacts resulting from charge compression of polyatomic anions bridged by alkali cations is also discussed.

Ab initio and density functional theory studies of the structure, gas‐phase acidity and aromaticity of tetraselenosquaric acid

AbstractResults of ab initio self‐consistent‐field (SCF) and density functional theory (DFT) calculations of the gas‐phase structure, acidity (free energy of deprotonation, ΔG*) and aromaticity of tetraselenosquaric acid (3, 4‐diselenyl‐3‐cyclobutene‐1,2‐diselenone, H2 C4 Se4)are reported. The global minimum found on the potential energy surface of tetraselenosquaric acid presents a planar conformation. The ZZ isomer was found to have the lowest energy among the three planar conformers and the ZZ and ZE isomers are very dose in energy. The optimized geometric parameters exhibit a bond length equalization relative to reference compounds, cyclobutanediselenone, and cyclobutanediselenol. The computed aromatic stabilization energy (ASE) by homodesmotic reaction is ‐77.4 (MP2(fu)/6–311+G** /RHF/6 ‐ 311 + G** ) and ‐ 54.8 kJ/mol (B3LYP/6 ‐ 311 + G** //B3LYP/6 ‐311 + G**). The aromaticity of tetraselenosquaric acid is indicated by the calculated diamagnetic susceptibility exaltation (A) ‐19.13 (CSGT(IGAIM)‐RHF/6–311 + G**// RHF/6–311 + G** and ‐32.91 (4π·10−6 m−3/mol)(CSGT(I‐GAIM)‐B3LYP/6 ‐ 311 + G* * //B3LYP/6 ‐ 311 + G**). Thus, tetraselenosquaric acid fulfils the geometric, energetic and magnetic criteria of aromaticity. The calculated gas‐phase acidity is ΔG1*(298k) = 1257.7 and ΔG*2 (298k) = 1617.1 kJ/mol. Hence, tetraselenosquaric acid is the strongest acid among the three squaric acids (3, 4‐dihydroxy‐3‐cyclobutene‐1, 2‐dione, H2 C4 3,4‐dithiohydroxy‐3‐cyclobutene‐1,2‐dithione, H2C4 S4, 3, 4‐diselenyl‐3‐cyclobutene‐1,2‐diselenone, H2C4Se4).

A theoretical study of aromaticity in squaramide and oxocarbons

A systematic estimation of aromaticity in oxocarbon acids, their dianions, squaramide and its complex with the ammonium cation have been studied using structural and magnetic criteria. Results based on Nucleus Independent Chemical Shift (NICS) predict that deltic and squaric acids and their dianions are aromatic, while croconic and rhodizonic acids and their dianions are non-aromatic. Squaramide is less aromatic than its complex with the ammonium cation. Therefore, the gain in aromaticity in the squaramide ring is a possible explanation for the remarkable hydrogen bond acceptor character of squaramide.

Cyclobutene-1,2-diones. A Theoretical and Spectroscopic Study

The properties of substituted cyclobutene-1,2-diones 1 are examined by the use of (17)O NMR spectroscopy and theoretical calculations and compared to those of cyclopropenones 2 and other models. Cyclobutene-1,2-diones have less negative charge per oxygen compared to cyclopropenones, and electron donation by substituents enhances the negative charge on oxygen. Calculated (17)O chemical shifts reproduce the measured trends. The dianions of squaric and deltic acids are highly stabilized by negative charge delocalization to the oxygens.

A kinetic and mechanistic study of the thermal decomposition of copper(II) mellitate

The thermal decomposition of copper(II) mellitate proceeds to completion between 470 and 530 K C 6(CO 2) 6Cu 3 → 5.5CO 2+0.03CO+[Cu 3C 6.5O 1.0] by two distinct rate processes. The first is acceleratory and fits the power law (α 1 2 = kt) to fractional reaction (α) = 0.45, during which the copper is extensively reduced (Cu 2+ → Cu +); the activation energy is 155±7 kJ mol −1. The second reaction is strongly deceleratory, being expressed by the third order equation; the activation energy is 200±15 kJ mol −1. Textural changes during reactions have been characterized by scanning electron microscope examinations. The salt does not show evidence of melting. The present work extends a previous investigation of the same reactant. Results here are discussed in the context of similar studies of copper(II) salts of other organic acids; all give evidence of stepwise cation reduction (Cu 2+ → Cu + → Cu 0) during the two consecutive reactions. It is concluded that, unlike other reactants in this comparison, the second step is not decomposition of copper(I) mellitate but involves a range of condensed aromatic anions. A short comparative survey is given of studies of the thermal decompositions of copper(II) salts of formic, oxalic, malonic, maleic, fumaric, squaric and mellitic acids.

Stable carbocations. 287. Carbon-13 NMR and ab initio/IGLO study of protonated oxocarbons, poly-O-protonated squaric, croconic, and rhodizonic acids, their aromatic nature, and preparation and study of tetrahydroxy- and diaminodihydroxyethene dications

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStable carbocations. 287. Carbon-13 NMR and ab initio/IGLO study of protonated oxocarbons, poly-O-protonated squaric, croconic, and rhodizonic acids, their aromatic nature, and preparation and study of tetrahydroxy- and diaminodihydroxyethene dicationsGeorge A. Olah, Joseph Bausch, Golam Rasul, Helmut George, and G. K. Surya PrakashCite this: J. Am. Chem. Soc. 1993, 115, 18, 8060–8065Publication Date (Print):September 1, 1993Publication History Published online1 May 2002Published inissue 1 September 1993https://doi.org/10.1021/ja00071a018RIGHTS & PERMISSIONSArticle Views237Altmetric-Citations14LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (553 KB) Get e-Alerts Get e-Alerts

Interactions of squaric and croconic acids with [PtL 4] 2+ complexes (L = NH 3, L 2 = ethylenediamine): oxidative properties of oxocarbon acids and crystal structure determinations

Squaric (H 2Sq) and croconic (H 2Croc) acid (H 2A) react with [PtL 4] 2+ (L = ammonia or L 2 = ethylenediamine) to yield complexes formulating as [PtL 4](HA) 2. The crystal structure of the complexes [Pt(en) 2](HSq) 2 and [Pt(en) 2](HCroc) 2 have been determined using X-ray diffraction techniques. Oxidation of platinum occurred in the course of the same reaction and complexes of [PtL 4Cl 2]A were obtained. The X-ray determination of the structure of [Pt(NH 3) 4Cl 2]Sq is reported. Electrochemical measurements have been performed in the solid state to support the results obtained during the oxidation process.

ChemInform Abstract: A Theoretical Study of Electronic Structures and Vibrational Frequencies of Deltic and Squaric Acids, CnOnH2 (n = 3 and 4).

Abstract Deltic and square acids, C n O n H 2 ( n = 3 and 4) have been studied by ab initio SCF calculations employing a split-valence 4-31G basis set. The geometries of the three different rotamers have been optimized by the force method. IR frequencies were determined from the ab initio harmonic force field. The dipole moment, quadrupole moment and electric field gradient for oxygen have been calculated. A new molecular arrangement in the crystal of deltic acid is proposed.