Crystalline Salts Research Articles

Complex Coacervates: From Polyelectrolyte Solutions to Multifunctional Hydrogels for Bioinspired Crystallization

Hydrogels represent multifarious functional materials due to their diverse ranges of applicability and physicochemical properties. The complex coacervation of polyacrylate and calcium ions or polyamines with phosphates has been uncovered to be a fascinating approach to synthesizing of multifunctional physically crosslinked hydrogels. To obtain this wide range of properties, the synthesis pathway is of great importance. For this purpose, we investigated the entire mechanism of calcium/polyacrylate, as well as phosphate/polyamine coacervation, starting from early dynamic ion complexation by the polymers, through the determination of the phase boundary and droplet formation, up to the growth and formation of thermodynamically stable macroscopic coacervate hydrogels. By varying the synthesis procedure, injectable hydrogels, as well as plastic coacervates, are presented, which cover a viscosity range of three orders of magnitude. Furthermore, the high calcium content of the calcium/polyacrylate coacervate (~19 wt.%) enables the usage of those coacervates as an ions reservoir for the formation of amorphous and crystalline calcium-containing salts like calcium carbonates and calcium phosphates. The exceptional properties of the coacervates obtained here, such as thermodynamic stability, viscosity/plasticity, resistance to acids, and adhesive strength, combined with the straightforward synthesis and the character of an ions reservoir, open a promising field of bioinspired composite materials for osteology and dentistry.

Hydrogen production capabilities of lichens micro-ecosystem under extreme salinity, crystalline salt exposure, and simulated Mars-like conditions

This work aims to demonstrate the extremophilic behavior of the lichen Pleurosticta acetabulum at extreme salinities, while maintaining its metabolic capacity to produce hydrogen. Lichen is a special micro-ecosystem that includes mostly a fungus and a green alga or cyanobacterium, as well as a microbiome. The peculiarity of this symbiotic system is its ability to dry out completely and stay inactive to survive harsh conditions. Lichens that had been dehydrated for six months revived quickly when rehydrated, restoring their photosynthetic efficiency and ability to produce hydrogen. The lichen microbiome was crucial for hydrogen production, especially through dark fermentation. The experiments of this work showed that lichen during its exposure to different salinity conditions (0%NaCl – control, 3,5%NaCl – sea salt concentration, 36%NaCl – saturated salt concentration), but also after exposure to crystalline salt (100%NaCl) could maintain the structure and the functionality of its photosynthetic apparatus. This was tested using chlorophyll a fluorescence induction measurements. Based on the results of thermal conductivity gas chromatography (GC-TCD) for the determination of hydrogen production, it was shown that despite being exposed to extreme salinity conditions, lichens maintained its ability to produce hydrogen. The experimental combination of lichen exposure to extreme salinities (up to 100% NaCl), with an extreme atmosphere (100% CO2) and low atmospheric pressure (<10mbar), simulating Mars conditions, highlighted the functional potential of the lichen for survival in a Mars-like environment. This lichen’s ability to withstand extreme conditions and to produce large amounts of hydrogen, makes it a promising candidate for future biotechnological applications, even in challenging environments like Mars, opening new astrobiological and astrobiotechnological perspectives.

Novel Crystalline Salts of 4-Piperidyl- and 4-Pyridylmethylamines Prepared by Catalytic Hydrogenation of 4-Pyridinecarbonitrile: Crystallographic Unit Cells Based on Powder XRD Patterns by Using the DASH Program Package

Structures of some hydrogenated products and intermediates, prepared by a heterogeneous Pd/C or Ru/C catalyst starting from 4-pyridinecarbonitrile (4PN), in water and in the presence of an acidic additive (HCl or H2SO4), were confirmed in various salt forms of 4-piperidylmethylamine (4PIPA) and 4-pyridylmethylamine (4PA). Crystallographic unit cell structure of the completely hydrogenated product salts (4PIPA·H2SO4 and 4PIPA·2HCl) showed a common double-protonated [4PIPA+2H]2+ divalent cation structure, also proved by FT-IR, and that of the 4PA·H2SO4 intermediate salt was also indexed and modeled by means of powder X-ray diffraction, applying the DASH 4.0 software package and crystal coordinates coming from former single-crystal X-ray structure determination. Formations of the anhydrous and hydrated forms of 4PA·0.5H2SO4·xH2O (x = 0 or x = 0.5, hemisulfates) were also studied by powder XRD and FT-IR spectroscopy for comparing these crystal structures.

Unveiling the anticancer potential: Exploring 4-fluoro benzoic acid and piperazine through spectroscopic, X-ray diffraction, DFT and molecular docking analysis

The crystalline substance formed from piperazine and 4-fluorobenzoic acid (PZ-PFBA) was successfully synthesized. This synthesis involved the transfer of protons between the selected acid and base, resulting in the formation of distinct crystalline salt. The SCXRD analysis conforms the salt crystallized in a monoclinic crystal system with a P 21/c space group and lattice parameters are a = 13.0688(14) Å, b = 8.2686(8) Å, and c = 8.2552(9) Å. Hirshfeld surface analysis, a technique for quantifying molecular interactions, was employed to investigate the prepared crystalline salt. Additionally, the salt was subjected to further examination using FT-IR, 1H NMR, 13C NMR, and SCXRD studies. The crystalline salt has major and established biological actions that inhibit the human lung cancer cell line A549. In vitro, and Insilico anticancer tests show that PZ-PFBA has better efficacy against the human cervical cancer cell line (HeLa) and in bioinformatics analysis. PZ-PFBA demonstrated more efficacy in reducing pathogenic strains compared to its parent reactants.

Optimization of Progressive Freeze Crystallization Process by Response Surface Methodology for the Treatment of Electroplating Wastewater for Copper (II) Sulphate Recovery

&lt;p style="line-height:200%;text-align:justify;text-indent:0cm;text-justify:inter-ideograph;"&gt;&lt;span style="line-height:200%;" lang="EN-US"&gt;For the copper-containing electroplating wastewater generated by a semiconductor company, the recovery of copper salts by progressive freeze crystallization and its process parameters were experimentally optimized and studied.&amp;nbsp;Based on the results of single-factor experiments, according to the principles of Box-Behnken Design experimental design for response surface methodology to investigate the effects of coolant temperature, agitation rate, and freezing time on salt removal and optimize process parameters. The optimization results of the response surface method showed that the optimal conditions were when the coolant temperature was -8°C, the stirring rate was 264 r&lt;/span&gt;&lt;span style="font-family:Symbol;line-height:200%;" lang="EN-US"&gt;×&lt;/span&gt;&lt;span style="line-height:200%;" lang="EN-US"&gt;min&lt;sup&gt;-1&lt;/sup&gt;, and the freezing time was 78 min.&amp;nbsp;Three validation experiments were conducted under optimum conditions, and salt removal was obtained as 60.13 ± 4.10%, which is more in line with the predicted values.&amp;nbsp;Treatment of copper-containing electroplating wastewater using tertiary freezing under response surface optimized experimental conditions.&amp;nbsp;At this time, the total ice rate of the wastewater was about 65.00%, and the conductivity was also concentrated from 2.17&amp;nbsp;mS&lt;/span&gt;&lt;span style="font-family:Symbol;line-height:200%;" lang="EN-US"&gt;×&lt;/span&gt;&lt;span style="line-height:200%;" lang="EN-US"&gt;cm&lt;sup&gt;-1&lt;/sup&gt; of the raw water to 2.99&amp;nbsp;mS&lt;/span&gt;&lt;span style="font-family:Symbol;line-height:200%;" lang="EN-US"&gt;×&lt;/span&gt;&lt;span style="line-height:200%;" lang="EN-US"&gt;cm&lt;sup&gt;-1&lt;/sup&gt; with a total concentration ratio of 1.38.&amp;nbsp;In addition, a higher concentration of concentrated liquid was obtained in the third freezing, while a crystalline salt precipitated from the bottom of the reactor. The precipitate was analyzed mainly as copper sulfate pentahydrate using XRD, XRF, EDS, and other characterization techniques.&lt;/span&gt;&lt;span lang="EN-US"&gt; Theoretical calculations show that pre-cooling of raw wastewater reduces energy consumption by up to 20.40%.&lt;/span&gt;&lt;/p&gt;

Extending the Pre-ordered Precursor Reduction strategy to L10 ternary alloys: the case of MnFePt

L10 nanostructured alloys continue to attract a great deal of attention due to their advanced physico-chemical properties arising from the peculiar arrangement of the atoms in the tetragonal unit cell. Efforts have been focused on synthesizing and optimizing L10 3d-5d binary alloys, with the incorporation of a third element to enhance the chemical order degree and/or modulate the physical properties. Among the family members, magnetic L10 MnFePt ternary alloys are of great relevance owing to the possibility to tune the magnetic properties to meet the requirements of many applications including data storage/processing, sensors, catalysis, and biomedicine. In this work, a direct, effective and sustainable strategy, called Pre-ordered Precursor Reduction (PPR), was exploited for the first time to synthesize highly-ordered L10 MnFePt ternary alloy nanoparticles by thermal decomposition in reductive atmosphere of MnxFe1-x(H2O)6PtCl6 crystal salts whose crystallographic structure resembles the specific atomic arrangement of the L10 phase. Despite the higher complexity with respect to the binary system, the peculiar atomic arrangement of the elements in the precursor crystalline salt allows a great control over the structural and magnetic properties. By modulating the process conditions and the initial chemical composition it is possible to finely tune the magnetic properties thus proving the high versatility and efficiency of the PPR approach to synthesize highly ordered L10 ternary alloys with controlled properties.

Use of differential scanning calorimetry as a rapid, effective in-process check method for impurity quantitation of an early clinical batch of Giredestrant (GDC-9545)

Giredestrant (GDC-9545) is a selective estrogen receptor degrader (SERD) that was developed for treatment of ER+/HER2− metastatic breast cancer. An anhydrous crystalline tartrate salt was identified as the solid form suitable for clinical development. An early clinical batch of the active pharmaceutical ingredient (API)/drug substance failed to pass the GMP purity specifications owing to the presence of a substantial amount of high molecular weight impurities (oligomers), as determined by size exclusion chromatography. Several trial rework batches were manufactured using various re-slurry and recrystallization conditions to purge impurities in the drug substance to adhere to purity specifications. Based on the melting point depression of the API in presence of oligomers in these rework batches, a differential scanning calorimetry method was developed to quantify impurity content as a function of melting point onset of the API. This thermal analysis method was used as a surrogate for chromatography as a rapid, effective in-process check method for impurity quantitation to enable the timely release of the final reworked clinical batch. Post release, the % w/w oligomer value determined by calorimetry was in excellent agreement to that obtained by size exclusion chromatography.

Phosphoric acid salts of amino acids as a source of oligopeptides on the early Earth

Because of their unique proton-conductivity, chains of phosphoric acid molecules are excellent proton-transfer catalysts. Here we demonstrate that this property could have been exploited for the prebiotic synthesis of the first oligopeptide sequences on our planet. Our results suggest that drying highly diluted solutions containing amino acids (like glycine, histidine and arginine) and phosphates in comparable concentrations at elevated temperatures (ca. 80 °C) in an acidic environment could lead to the accumulation of amino acid:phosphoric acid crystalline salts. Subsequent heating of these materials at 100 °C for 1–3 days results in the formation of oligoglycines consisting of up to 24 monomeric units, while arginine and histidine form shorter oligomers (up to trimers) only. Overall, our results suggest that combining the catalytic effect of phosphate chains with the crystalline order present in amino acid:phosphoric acid salts represents a viable solution that could be utilized to generate the first oligopeptide sequences in a mild acidic hydrothermal field scenario. Further, we propose that crystallization could help overcoming cyclic oligomer formation that is a generally known bottleneck of prebiotic polymerization processes preventing further chain growth.

Harvesting of shear piezoelectricity in a molded multicomponent crystal disc

Biomolecular piezoelectrics, such as amino acids and peptides, exhibit significant shear piezoelectric responses in single crystal form. However, naturally occurring longitudinal piezoelectricity is rare and, when present, is dampened due to the multi-directional self-assembly in polycrystalline device layers. Here we utilise cocrystallisation to engineer a multicomponent crystalline salt hydrate of S(+)Mandelic Acid and LLysine, S-Mand•L-Lys•5H2O (1). This material exhibits a predicted single crystal longitudinal piezoelectric response of d33 = 3.5 pC/N. In polycrystalline form, 1 grows as an assembly of plates which increases the measured longitudinal piezoelectricity to 11 pC/N in its macroscopic solid-state. This is due to contributions from the shear piezoelectric response d36 = 10.8 pC/N, originating from the presence of plates oriented at acute angles relative to the surface. The brittleness of the crystals (E = 37 GPa) is overcome by reinforcing the substrate-free piezoelectric disc with a thin polymer coating to prevent flaking. Structural analysis confirms that the triclinic structure of 1 gives rise to this increased response due to the relative orientations of individual crystallites. Confined crystallisation of this multi-component form with a plate-like morphology, results in macroscopic self-assembly of an amino acid cocrystal that allows for the harvesting of higher shear piezoelectricity, but in a facile longitudinal configuration.

A new crystalline daidzein-piperazine salt with enhanced solubility, permeability, and bioavailability.

To overcome the poor solubility, permeability, and bioavailability of the plant isoflavone daidzein (DAI), a novel salt of DAI with anhydrous piperazine (PIP) was obtained based on cocrystallization strategy. The new salt DAI-PIP was characterized by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared (FT-IR) spectroscopy, and optical microscopy. The results showed that the maximum apparent solubility (Smax) of DAI-PIP increased by 7.27-fold and 1000-fold compared to DAI in pH 6.8 buffer and water, respectively. The peak apparent permeability coefficient (P app ) of DAI-PIP in the Caco-2 cell model was 30.57 ± 1.08 × 10-6cm/s, which was 34.08% higher than that of DAI. Additionally, compared to DAI, the maximum plasma concentration (Cmax) value of DAI-PIP in beagle dogs was approximately 4.3 times higher, and the area under the concentration-time curve (AUC0-24) was approximately 2.4 times higher. This study provides a new strategy to enhance the dissolution performance and bioavailability of flavonoid drugs, laying a foundation for expanding their clinical applications.

Enantiospecific crystallisation behaviour of malic acid in mechanochemical reactions with vinpocetine

We report an intriguing example of enantioselectivity in the formation of new multicomponent crystalline solid containing vinpocetine and malic acid. Several experimental data sets confirmed that the multicomponent system presents a clear enantiospecific crystallisation behaviour both in the solid-state and in solution: only the system consisting of vinpocetine and L-malic acid produces a free-flowing solid consisting of a new crystalline form, while the experiments with D-malic acid produced an amorphous and often deliquescent material. The new vinpocetine-L-malic system crystallizes in the monoclinic space group of P21 and in a 1:1 molar ratio, where the two molecules are linked through intermolecular hydrogen bonds in the asymmetric unit. The vinpocetine-DL-malic system was partially crystalline (with also traces of unreacted vinpocetine) with diffraction peaks corresponding to those of vinpocetine-L-malic acid. Solid-state NMR experiments revealed strong ionic interactions in all the three systems. However, while vinpocetine-L-malic acid system was a pure and crystalline phase, the other two systems persistently showed the presence of unreacted vinpocetine. This resulted in a significant worsening of the dissolution profile with respect to the pure vinpocetine-L-malic crystalline salt, whose dissolution kinetics appeared superior.

Salt hydrates as a source to form co-amorphous systems when prepared in the absence of water: Hydrogen bond analysis

Pharmaceutical multi-component solid forms, including salts, co-crystals and co-amorphous systems (COAMs), are used to modify the physicochemical and pharmaco-kinetic properties of these drugs. Gefitinib and two co-formers, bumetanide and furosemide, form salt hydrates in the presence of water and COAMs in the absence of water using solvent evaporation method. Molecular dynamic simulation and isolated water analysis reveal that water molecules play a multi-faceted role in stabilizing the crystalline salt hydrate systems by reducing the total energy of the system, establishing hydrogen bonds, and maintaining the crystalline 3D structures. Salt hydrates are also formed in the presence of water using liquid-assisted grinding. In the absence of water, intermolecular interactions between Gefitinib and co-formers facilitate the formation of COAMs during ball milling and quench cooling, i.e., in the absence of water. These findings provide valuable insights to the formation of salt hydrates and COAMs by controlling the presence of water.

Quantitative analysis on the impact factors of salt weathering for sandstone grottoes along Silk Road, China

A large number of exquisite sandstone grottoes remaining along the Silk Road in Northwest China suffer from severe salt damage due to the vulnerability of the sandstone materials used and long-term continuous fluctuation of environmental conditions. Exploring the mechanism of salt weathering is crucial for the conservation of these grottoes. This study aims to quantitatively analyze the damage potential and the main impact factors of salt weathering in 14 grottoes along the Silk Road that were selected and investigated by using visual evaluation, salt analysis including thermodynamic modeling, and a comprehensive evaluation based on the entropy weight method. The results indicate that salt weathering of the sandstone grottoes is primarily characterized by efflorescences, peeling, and powdering. The overall salt content within the weathering layer typically exceeds a threshold of 1 %. Within the semi-arid area, the humidity fluctuations critical for significant volume changes in crystalline salts fall within the ranges 46–76 % and 16–30 %. In the semi-humid area, these ranges are 58–90 %, 42–50 %, and 16–30 %. A total of 14 salts can precipitate in the study area with NaCl, NaNO3, KNO3, Na2SO4·xH2O and several double salts occuring most frequently. Generally, the damage degree of sandstones grottoes in the semi-humid area is more serious than that in the semi-arid area. Through a comparison of visual inspection and more comprehensive quantitative evaluation, it has been confirmed that the salt damage is primarily influenced by the factors salt content, salt type, and environmental conditions. Furthermore, the order of influence for each factor on salt weathering can be ranked as follows: salt content > salt type > environmental conditions. This study quantitatively reveals the impact of various factors on salt weathering and proposes a method to evaluate the salt damage potential, which is of great significance for the preventive conservation of sandstone grottoes.

Plasma electron spectroscopy in short glow discharge for registration of vapors and decomposition products of crystalline salts

Plasma electron spectroscopy in short glow discharge for registration of vapors and decomposition products of crystalline salts

Magnetic Bistability in the Crystaline Fullerene Radical Salt

Comprehensive SummaryCompounds with magnetic bistability is highly attractive for the construction of switches, thermal sensors, information‐storage media and memory devices. Herein, we report a crystalline fullerene radical anion salt [Na(THF)5]C60 (1), obtained by the reduction of C60 with Na in solution, which exhibits magnetic bistability accompanied with one magnetostructural transition, giving low temperature (LT), high temperature (HT) phases and a metastable phase. Fullerene radical anions (C60•‐) in the structure were found arranged into a three‐dimensional close‐packed honeycomb subnetwork with hollow channels occupied by complex cations [Na(THF)5]+ as spacers. The magnetic bistability is attributed to structural transitions as the LT−IT phase transition was associated with the orientational disorder of fullerene anions and the distortion of the complex cations [Na(THF)5]+ in the 3D packing of fullerene anions.

Research on the Multifactor Synergistic Corrosion of N80 and P110 Steel Tubing in Shale Gas Wells in Sichuan Basin

We aimed to investigate the corrosion patterns and the main controlling factors of N80 steel and P110 steel tubing under different sections. Conducting weight loss corrosion experiments for 168 h using high-temperature and high-pressure autoclaves to simulate the corrosion behavior of two types of casing materials, N80 steel and P110 steel, in different well sections under specific conditions of CO2 content, chloride ion concentration, temperature, pressure, and sulfate-reducing bacteria population in highly mineralized formation water. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were used to analyze the corrosion products, surface morphology, and elemental composition of the two steel pipes. Additionally, 3D microscopy was employed to observe the morphology and measure the dimensions of localized corrosion pits. Under different well sections, the corrosion products formed on N80 steel and P110 steel mainly consist of FeCO3, and crystalline salts of chlorides present in the solution medium. Under low-water-cut conditions, narrow and deep corrosion defects were observed, while narrow and shallow corrosion defects were found under high-water-cut conditions. In the upper wellbore section, both steel pipes exhibited dispersed and thin corrosion product films that suffered from rupture and detachment, resulting in severe localized corrosion. In the middle wellbore section, the corrosion product film on N80 steel comprised irregularly arranged polygonal grains, some of which exhibited significant gaps, leading to extremely severe corrosion. For P110 steel, the corrosion product film was also dispersed and thin, with extensive detachment and extremely severe corrosion. In the lower wellbore section, both steel pipes were covered with a dense layer of grains, with smaller gaps between them, effectively protecting the metal matrix from corrosion. Consequently, the corrosion rate decreased compared to the middle section but still exhibited severe corrosion. In low-water-cut conditions, attention should be given to the risk of column safety due to corrosion from condensate water and CO2, as well as the size of narrow and deep corrosion defects in the middle wellbore section. In high-water-cut conditions, it is recommended to use corrosion inhibitors in combination while focusing on SRB bacteria corrosion in the upper wellbore section, condensate water in the middle section, CO2 content and chloride ion coupling in the lower section, and the size of narrow and shallow corrosion defects causing column safety risks.

Spectroscopic analysis, quantum computational, and molecular docking investigations on the crystalline salt of 4-phenyl sulfanyl butanoic acid and piperazine with enhanced cytotoxic activity

In this investigation, the target crystalline salt was synthesized by combining 4-phenyl sulfanyl butanoic acid (PSBA) and piperazine (PZ). The process encompassed experimental methodologies, such as Powder X-ray Diffraction (PXRD),Single Crystal X-ray Diffraction (SCXRD), Nuclear Magnetic Resonance (NMR), Infrared Spectroscopy (IR),Thermogravimetric Analysis and Differential Scanning Colorimetry (TGA-DSC), as well as theoretical analyses of the synthesized compound.The crystalline salt was successfully synthesized via the solvent evaporation method at room temperature.PZ-PSBA has an orthorhombic crystal system with space group Pbca and unit cell parameters a = 7.4357(10)Å, b = 9.4853(12)Å, c = 34.299(5), and α=β=γ=90°. We employed the B3LYP functional with 6–311++G (d, p) as a basis set to geometrically optimize the molecular structure using Density Functional Theory (DFT).The synthesized material inhibits the human colon cancer cell line HT-29, the human lung adenocarcinoma cell line A549, and the human gastric cancer cell line MKN45, with substantial biological effects that have been demonstrated to be effective. According to in vitro and in sillico anticancer studies, PZ-PSBA has better activity against the human cervical cancer cell line (HeLa) and in bioinformatics analysis. PZ-PSBA suppressed pathogenic strains better than its parent chemical and can thus be suggested for the treatment of bacterial infections.

Supramolecular Solid Complexes between Bis-pyridinium-4-oxime and Distinctive Cyanoiron Platforms.

The structural features and optical properties of supramolecular cyanoiron salts containing bis-pyridinium-4-oxime Toxogonin® (TOXO) as an electron acceptor are presented. The properties of the new TOXO-based cyanoiron materials were probed by employing two cyanoiron platforms: hexacyanoferrate(II), [Fe(CN)6]4- (HCF); and nitroprusside, [Fe(CN)5(NO)]2- (NP). Two water-insoluble inter-ionic donor-acceptor phases were characterized: the as-prepared microcrystalline reddish-brown (TOXO)2[Fe(CN)6]·8H2O (1a) with a medium-responsive, hydrochromic character; and the dark violet crystalline (TOXO)2[Fe(CN)6]·3.5H2O (1cr). Complex 1a, upon external stimulation, transforms to the violet anhydrous phase (TOXO)2[Fe(CN)6] (1b), which upon water uptake transforms back to 1a. Using the NP platform resulted in the water-insoluble crystalline salt TOXO[Fe(CN)5(NO)]·2H2O (2). The structures of 1cr and 2, solved by single-crystal X-ray diffraction, along with a comparative spectroscopic (UV-vis-NIR diffuse reflectance, IR, solid-state MAS-NMR, Mössbauer), thermal, powder X-ray diffraction, and microscopic analysis (SEM, TEM) of the isolated materials, provided insight for the supramolecular binding, electron-accepting, and H-bonding capabilities of TOXO in the self-assembly of these functionalized materials.

Eight anhydrous organic salt forms of 2-amino-4,6-dimethoxypyrimidine and organic acids: Preparation, structure, characterizations, synthons diversity, and hirshfeld surface analysis

The intricate part of the non-covalent associates in numerous realms covering from chemistry, biology, catalysis, material science, to medicinal chemistry inspires a continuous motivation towards the discovery of new synthons that stabilize the supramolecular systems. In this work the co-crystallization between 2-amino-4,6-dimethoxypyrimidine (admpym) and eight organic acids resulted in the manufacturing of eight new crystalline salts, which were further fully characterized via the single crystal X-ray diffraction (SCXRD), spectroscopic (FT-IR) and elemental analysis methods. Their melting points were also measured. All the fabricated salts exhibited the identical stoichiometry regarding the number of the acidic unit and the admpym, namely with the 1:1 ratio at the monacids and 2 : 1 ratio in the diacids.Among the eight crystals, the H-shift from the acid to pyrimidine ring N atom has occurred, yet the NH2 group was not protonated ever. In all the crystals, the respective molecular fragments are permanently tethered to each other via the energetic H-bonds as the Npyrimidinium-Ophenolate/carboxylate type. The various weaker intermolecular linkages, embodying CH···O/CH3···O, CH···CH, CH3···N, CH···Br, CH3···CH, CH3···Cl, Cl···O, CH···π/CH3···π, C···π, O···π and π···π also contributed to the stabilization of the crystal structures in the respective conglomerates. The percentage contribution of the significant non-covalent contacts were calculated via the Hirshfeld surface analysis. The R22(8) graph was enclosed in all the systems when an acid pairs with an admpym. The job ensures that there engender both principle contact modes between the admpym and the acids, which appear in the relative higher frequency, linear heterotetramer (LHT), and cyclic heterotetramer (CHT). LHT is dominant as it appears in 5 cases, CHT in 2 ones, with the rest one structure building a rare heterodimer. The heterotrimer (HT) was never occurred here.

Experimental study of sulfate crystallization damage to glutenite rock in the Maijishan Grottoes

Salt crystallization is one of the most important factors causing weathering in grottoes. Cumulative crystallization of salts causes damage such as flaking and peeling of the rocks and accelerates the weathering processes of the grottoes. The accumulated crystalline salts cause spalling, skinning and other damage and accelerate the weathering process of the grotto rock body. It is necessary to study the existing glutenite rock grottoes. This paper took the glutenite rock of the Maijishan Grottoes as a case study, and Na2SO4 or MgSO4 solutions were applied to glutenite rock specimens subjected to different deterioration cycles. The crystallization patterns of the two different salts and their damage to the glutenite rock were analyzed and studied, the mechanism for salt crystallization damage to the glutenite rock was explored, and the crystallization pressures of the two salts in the glutenite rock were derived with theoretical calculations. The results showed that both Na2SO4 and MgSO4 crystallization damaged the glutenite rock, and the former different sulfate solutions changed at different rates, and the changes in the wave caused faster damage than the latter. The physical indices of the rock samples in the velocities and tensile strengths were consistent. Na2SO4 was mainly accumulated on the surface of the specimen and damaged the glutenite rock centripetally via pulverization and exfoliation. MgSO4 mainly crystallized inside the glutenite rock, which created internal fissures and reduced the strength of the rock. The theoretical maximum crystallization pressures of Na2SO4 and MgSO4 in the glutenite rock specimens reached 33.00 MPa and 9.94 MPa, respectively. This study provides a theoretical basis for studies of salt crystallization in glutenite rock grottoes and provides a method for protecting the stones in cultural heritage sites against weathering.