Sulfamethazine Molecule Research Articles

MINI REVIEW ON RECENT ADVANCES OF THE ADSORPTION MECHANISM BETWEEN MICROPLASTICS AND EMERGING CONTAMINANTS FOR CONSERVATION OF WATER

Pharmaceuticals and microplastics have long been identified as water pollutants. Pollutants, including pharmaceutical compounds, have been shown to be transported by microplastics (MPs). In this mini-review, adsorption mechanism between microplastics and emerging contaminants were highlighted. Polyethylene is a non-polar, semi-cystalline microplastic with a density of 240 to 244 kg/m3. Besides, Ibuprofen adsorption onto microplastics is pH dependent. Non-polar or neutral compounds that are homogeneous and extremely hydrophobic in nature interact with non-polar and weakly polar plastics such as Polypropylene and Polyethylene. Furthermore, Molecular dynamic (MD) simulation can be employed to study the mechanism of interaction between MPs and contaminants. As a result, some studies show a complex interaction between polyethylene (PE) and certain contaminants, with no significant differences in adsorption energies, but sulfamethazine molecules effectively adsorbed on the MPs surface. In summary, this mini review shed lights on the insights of adsorption mechanism between these compounds.

Revealing the effect of hard carbon structure on the sodium storage behavior by using a model hard carbon precursor

The sodium storage mechanism of hard carbon anodes still remains controversial. It is usually believed that there exists relationship between the plateau capacity and the closed pores of hard carbon. Herein, a sulfamethazine molecule is selected as a model precursor to prepare hard carbon. A molten state occurs during the carbonization process of this precursor, which reduces the formation of open pores. Hard carbon materials exhibiting diverse closed pore structures are synthesized by carbonizing at temperatures ranging from 1100 °C to 1700 °C. The closed pores and plateau capacity exhibit a linear correlation, which is based on their closed pore volume and sodium-ion storage capacities. The hard carbon material prepared at 1500 °C exhibits excellent electrochemical performance, which delivers a high reversible capacity of 292 mAh g−1 with a plateau capacity of 230 mAh g−1 at a current density of 0.05 A g−1, as well as decent cycling stability (83 % capacity retention at 0.1 A g−1 over 200 cycles). The model hard carbon confirms that the plateau capacity is attributed to the storage of sodium ions in the closed pores.

Co-adsorption characteristics of antibiotics with different functional groups and cadmium combined contamination on activated carbon

Due to the diversity of functional groups of antibiotics, antibiotics are easy to complex with metals, thereby changing their migration and transformation behavior. The adsorption/complexation mechanism of three antibiotics co-adsorbed with Cd(Ⅱ) and systematic comparison were studied using Raman, FTIR, XPS and Materials Studio (norfloxacin (NOR), sulfamethazine (SMT) and tetracycline (TC)). We concluded that two NORs complexed with Cd(Ⅱ) through oxygen atoms from carboxylic acid and carbonyl in ketone group to form a six-membered ring chelate. The Cd(II)(NOR±)2+ showed a stronger adsorption coefficient than other forms of NOR, Cd(II)(NOR±)2+, NOR and Cd(Ⅱ) would compete the same permanent charge sites, thus exhibiting an inhibitory effect on NOR adsorption. Contrarily, one SMT molecule complexed with Cd(Ⅱ) through the N atom on pyrimidine ring and the -NH attached to the pyrimidine ring, forming an AC-Cd(Ⅱ)-SMT ternary complex on activated carbon (AC), and Cd(Ⅱ) acted as bridge. The bridging effect of Cd(Ⅱ) and multi-layer adsorption of SMT provided more adsorption sites for SMT, thus promoting the SMT adsorption. There was no complexation between TC and Cd(Ⅱ), and the addition of Cd(Ⅱ) had no significant effect on TC adsorption. The adsorption capacity of AC-Cd(Ⅱ)-SMT complex (107.4 mg·g−1) was stronger than NOR-Cd(Ⅱ) complex (40.2 mg·g−1), and the adsorption capacity of antibiotics was SMT>TC>NOR in all systems. The correlation analysis and molecular orbital calculation further supported the strong effect of complexation between Cd(Ⅱ) and antibiotics with different function groups on the adsorption, and the environmental behavior of system was jointly determined by complex structure and adsorption mechanism.

Enhanced degradation mechanism of sulfamethazine by vacuum ultraviolet/persulfate

Vacuum ultraviolet/ persulfate (VUV/PS) has been a prospective method for antibiotics removal, however, the enhanced degradation mechanism is still unclear. This study compared the sulfamethazine (SMT) degradation by VUV/PS and ultraviolet/persulfate (UV/PS) processes using a photoreaction system. Results showed that the SMT degradation rate and PS activation rate by VUV/PS was 1.36 times and 1.39 times those of the conventional UV/PS process under the same dosage of PS, respectively. VUV/PS also achieved a high SMT mineralization. SO4•− and HO• played important roles in the degradation of SMT by both processes, while the role of •O2− was little. SMT concentration changed the distributions of 185 nm and 254 nm photons absorbed by solution components and altered the initiated photolysis reaction. Both processes had faster degradation rates at low initial SMT concentrations and the optimum reaction condition was at solution pH of 5. The inhibited level of the SMT degradation in both processes by four anions was in the following order: NO3−> Cl−> HCO3−>SO42. VUV/PS process was also more efficient than UV/PS for degrading environmental (200 μg/L) and high (5 mg/L) concentration of SMT from three kinds of typical water matrices (tap, river and lake water). Finally, ten photoproducts of SMT degradation by VUV (or UV) were identified, which were mainly the oxidized products of C-N, -NH2 and S-C on SMT molecules, and four degradation pathways were proposed. Overall, these findings could provide useful insights into the application of VUV/PS in efficient antibiotics removal from water.

Tuning band structure of graphitic carbon nitride for efficient degradation of sulfamethazine: Atmospheric condition and theoretical calculation

Numerous approaches have been used to modify graphitic carbon nitride (g-C 3 N 4 ) for improving its photocatalytic activity. In this study, we demonstrated a facial post-calcination method for modified graphitic carbon nitride (g-C 3 N 4 -Ar/Air) to direct tuning band structure, i.e. , bandgap and positions of conduction band (CB)/valence band (VB), through the control of atmospheric condition without involving any additional elements or metals or semiconductors. The synthesized g-C 3 N 4 -Ar/Air could efficiently degrade sulfamethazine (SMT) under simulated solar light, i.e. , 99.0% removal of SMT with rate constant k 1 = 2.696 h −1 within 1.5 h (4.9 times than pristine g-C 3 N 4 ). Material characterizations indicated that the damaged/partial-collapsed structure and decreased nanosheet-interlayer distance for g-C 3 N 4 -Ar/Air resulted in the shift of band structure due to the denser stacking of pristine g-C 3 N 4 through oxidative exfoliation and planarization by air calcination. In addition, the bandgap of g-C 3 N 4 -Ar/Air was slightly shrunk from 2.82 eV (pristine g-C 3 N 4 ) to 2.79 eV, and the CB was significantly upshifted from −0.44 eV (pristine g-C 3 N 4 ) to −0.81 eV, suggesting the powerful ability for donating the electrons for O 2 to form • O 2 − . Fukui index ( f – ) based on theoretical calculation indicated that the sites of SMT molecule with high values, i.e. , N9, C4 and C6, preferred to be attacked by • O 2 − and • OH, which is confirmed by the intermediates’ analysis. The tuning method for graphitic carbon nitride provides a simple approach to regulate the charge carrier lifetime then facilitate the utilization efficiency of solar light, which exhibits great potential in efficient removal of emerging organic contaminants from wastewater. Modified graphitic carbon nitride (g-C3N4-Ar/Air) was synthesized via a facial post-calcination method and exhibited efficiently photocatalytic activity for SMT removal due to the tune of band structure.

Insight into heterogeneous catalytic degradation of sulfamethazine by peroxymonosulfate activated with CuCo2O4 derived from bimetallic oxalate

CuCo2O4 was synthesized via the calcination of a copper-cobalt bimetallic oxalate precursor and was used as a heterogeneous catalyst of peroxymonosulfate (PMS) for the degradation of sulfamethazine (SMZ). The results demonstrated that the CuCo2O4 had higher catalytic activity than the monometallic CuO and Co3O4. The degradation efficiency of SMZ (50 mg/L) by PMS (1 mmol/L) activated with CuCo2O4 (0.1 g/L) was above 98% within 30 min at initial pH 5. Electron paramagnetic resonance (EPR) and radical quenching experiments proved that both sulfate radicals (SO4−) and singlet oxygen (1O2) were responsible for the efficient removal of SMZ, especially 1O2. The superoxide radicals (O2−) produced from the reaction improved the generation of SO4− and 1O2. Cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS) and hydrogen temperature- programmed reduction (H2-TPR) investigations revealed that the synergy of Cu and Co species in PMS activation resulted from higher electroconductibility, more electron transfer, and better redox potential of the CuCo2O4. The synergy between the Co(III)/Co(II) and the Cu(II)/Cu(I) couples enhanced the turnover frequency (TOF) of CuCo2O4. The possible degradation pathways are further proposed according to the identification of the SMZ degradation products and the theoretical calculations of the frontier electron densities (FEDs) of the SMZ molecule.

Thermodynamic analysis and preferential solvation of sulfamethazine in acetonitrile + water cosolvent mixtures

This paper presents the solubility of sulfamethazine (SMT) in the acetonitrile (MeCN) + water (W) cosolvent system at nine temperatures. From the solubility experimental data, the thermodynamic functions of solution, mixing, and transfers are calculated and analyzed using the Perlovich graphical method. On the other hand, an enthalpy−entropy compensation analysis is performed and the preferential solvation parameters are calculated using the Kirkwood-Buff (IKBI) inverse integral method. The result of the performed calculations indicates that the SMT solution process is endothermic with entropic favor, where the addition of MeCN has a positive cosolvent effect between pure water and the mixture with w1 = 0.90. As for the preferential solvation, the SMT molecule is preferentially surrounded by water in water- and MeCN-rich mixtures, and in intermediate mixtures, the SMT molecule tends to be surrounded by MeCN.

Encapsulation of sulfamethazine by native and randomly methylated β-cyclodextrins: The role of the dipole properties of guests.

Sulfonamides are preventive and therapeutic agents for certain infections caused by gram-positive and gram-negative microorganisms. In this work the interactions of sulfamethazine, a representative of sulfonamide antibiotics, with two β-cyclodextrin derivatives were investigated at different pH. Results show formation of stable sulfamethazine - β-cyclodextrin complexes and reflect importance of the competition of the hydrogen bonding and electrostatic interactions. The complex geometry formed is affected by the orientation of the pH-dependent dipole moment of sulfamethazine molecule and prolonged prior the sulfamethazine molecule enters into the β-cyclodextrin's cavity. Functionalization of the β-cyclodextrin molecule doesn't affect considerably the complex stabilities, therefore the native β-cyclodextrin molecule looks the simplest and most effective inclusion host to design selective and sensitive tool for sulfamethazine sensing.

MOF-derived three-dimensional flower-like FeCu@C composite as an efficient Fenton-like catalyst for sulfamethazine degradation

In this paper, a novel three-dimensional flower-like Fenton-like catalyst with iron-copper bimetallic NPs within the mesoporous carbon shell (FeCu@C) was successfully prepared through a simple pyrolysis of a [Fe,Cu]-BDC precursor and applied for catalytic degradation of sulfamethazine (SMT) in the presence of H2O2. The FeCu@C catalyst showed a 100% SMT removal within 90 min and a 72.3% total organic carbon (TOC) conversion within 240 min under the conditions of 20 mg L−1 SMT, 0.25 g L−1 FeCu@C, 1.5 mM H2O2, and initial solution pH 3.0. Combined with the characterization results, we proposed that the unique structure and composition of FeCu@C enable the catalyst to exhibit outstanding adsorption capability and catalytic performance in SMT degradation by H2O2 activation. The porous flower-like carbon matrix not only favors the rapid diffusion of reactants towards the internal bimetallic nanoparticles (NPs), but also offers specific adsorption for the enrichment of SMT molecules from bulk solution through π − π interaction. In addition, the iron and copper species existing in the inner bimetallic NPs are available active sites for a Fenton reaction, and a possible synergistic effect between them could facilitate the generation of additional OH radicals to enhance SMT degradation. Moreover, the accumulation (i.e. adsorption) of SMT molecules on the surface of FeCu@C could increase their contact probability with the OH radicals generated from H2O2 decomposition, further enhancing the reaction efficiency. With its high-magnetization properties, FeCu@C can be magnetically recovered and reused in SMT degradation. Furthermore, the possible reaction mechanism of the FeCu@C/H2O2 system and SMT degradation pathways were also tentatively proposed.

Graphene modified anatase/titanate nanosheets with enhanced photocatalytic activity for efficient degradation of sulfamethazine under simulated solar light

Graphene modified anatase/titanate nanosheets (G/A/TNS) synthesized through hydrothermal treatment were used for solar-light-driven photocatalytic degradation of a typical pharmaceutically active compound, sulfamethazine (SMT). The optimal material was synthesized with 0.5 wt% of graphene loading (G/A/TNS-0.5), which could efficiently degrade 96.1% of SMT at 4 h. G/A/TNS-0.5 showed enhanced photocatalytic activity compared with the neat anatase and unmodified anatase/titanate nanosheets (A/TNS). UV–vis diffuse reflection spectra indicated that G/A/TNS-0.5 had a lower energy band gap (Eg) of 2.8 eV than A/TNS (3.1 eV). The grafted graphene acted as an electron transfer mediator after photoexcitation, resulting in inhibition on rapid recombination of electron-hole pairs. More importantly, architecture of graphene and titanate nanosheets both with two-dimensional structures greatly facilitated the photoexcited electron transfer. •OH and 1O2 were the primary reactive oxygen species (ROS) to SMT degradation. Fukui index (f-) derived from density functional theory (DFT) calculation predicted the active sites on SMT molecule, and then SMT degradation pathway was proposed by means of intermediates identification and theoretical calculation. Furthermore, G/A/TNS-0.5 could be well reused and 90.5% of SMT was also degraded after five runs. The developed new photocatalysts show great potential for degradation of emerging organic contaminants through photocatalysis under solar light.

An investigation on the corrosion behavior of the epoxy coating embedded with mesoporous silica nanocontainer loaded by sulfamethazine inhibitor

In this study, mesoporous silica served as the host for an eco-friendly corrosion inhibitor. This material could adsorb and release corrosion inhibitor in different aqueous media. A composite coating was prepared by embedding 1 wt. % mesoporous silica loaded with sulfamethazine (MSInh) as the corrosion inhibitor into the epoxy film to protect mild steel as substrate. Anti-corrosion properties of the solution containing MSInh and corrosion protection function of composite coating were assessed by electrochemical impedance spectroscopy. Results showed the higher corrosion protection of epoxy/mesoporous silica loaded with inhibitor (MSInh) in NaCl solution for one month of immersion in comparison with epoxy/mesoporous silica and epoxy coatings. Charge transfer resistance of epoxy, epoxy/MS, and epoxy/MSInh after 30 days of immersion estimated 6, 15, and 80 kΩ cm2, respectively. The results revealed the higher corrosion resistance of epoxy/MSInh which confirmed the barrier effect of mesoporous silica against corrosive species and corrosion inhibiting effect of the released sulfamethazine molecules.

Transformation of antimicrobial agent sulfamethazine by peroxymonosulfate: Radical vs. nonradical mechanisms

Peroxymonosulfate (PMS) is increasingly used as an oxidant for in situ remediation of organic contaminants in soil and groundwater. In this study we demonstrated that sulfamethazine (SMZ) could be transformed by PMS in the absence of any activators. Such transformation was ascribed to the oxidation by PMS per se, rather than free radicals (SO4− or HO), superoxide (O2−), or singlet oxygen (1O2). The aniline moiety of SMZ molecule was the reactive site for PMS oxidation, leading to the formation of nitrated products. This nitration pathway in fact played a significant role in the removal of SMZ in activated PMS oxidation processes. For instance, it contributed 26% of the total SMZ transformation, while SO4− contributed the other 74% during the removal of SMZ, in Co(II)/PMS oxidation process with initial PMS and Co(II) concentrations of 1.0 mM and 0.1 μM, respectively. Similar nitration reaction also occurred to other sulfonamide antibiotics bearing an aniline moiety upon the reaction with PMS. Since nitrated sulfonamide antibiotics appear more persistent than the parent compounds and may cause other environmental problems, such a pathway should not be desired. Therefore, PMS might not be an ideal oxidant for the treatment of sulfonamide antibiotics and other compounds having aniline moieties, especially in subsurface remediation practices where efficient activation of PMS represents a major challenge.

Scalable preparation of hierarchical porous carbon from lignin for highly efficient adsorptive removal of sulfamethazine antibiotic

In order to efficiently remove sulfamethazine (SMZ) antibiotic from wastewater, in this work, we first described a facile and scalable synthesis of hierarchical porous carbon using industrial by-product sodium lignosulfonate (SLS) as raw source and potassium hydroxide as inorganic template and chemical activator, by a self-templating and in-situ activation method. The Lignin-derived hierarchical porous carbon obtained at an optimal mass ratio of SLS and alkali of 1:3 (LHPC-3) exhibited a largest specific surface area of 2235m2g−1 and pore volume of 1.512cm3g−1. LHPC-3 possessed a very high saturated monolayer adsorption capacity of 854.7mgg−1 at 288K. The pseudo-second-order rate model described the adsorption kinetics data. It was found that this carbon could be also effective in the high salt environment. Physical adsorption played in an important role in the process of capture SMZ molecules from water. This hierarchical porous carbon had good stability and regeneration property, providing the possibility for the practice application. We gave a novel, simple and effective technique to obtain high-performance hierarchical porous carbon for various use, especially for wastewater treatment.

Insight into the Role of Hydrogen Bonding in the Molecular Self-Assembly Process of Sulfamethazine Solvates

The new solid forms screening of sulfamethazine was conducted in 16 kinds of different pure solvents. Four new sulfamethazine solvates were reported for the first time, and three crystal structures of solvates were successfully determined from single-crystal X-ray diffraction data. The results showed that sulfamethazine solvate formation directly depended on the solvents used in the experiments. The solvent properties were used to evaluate the effects of solvent on solvate formation. It was found that the H-bond acceptor ability of the solvent was the main factor that governed the solvate formation. The H-bonded motifs in the structures of solvates have been fully characterized. The results revealed that sulfamethazine solvate formation was mainly driven by molecular self-assembly through hydrogen bonding between solvent and solute molecules. Meanwhile, the crystal structures results also showed that the sulfamethazine molecule had flexible conformation. Furthermore, the principles of different sulfamethazine molecules packing in different crystal structures were discussed from the view of molecular intermolecular interactions and the molecular conformation.

Roles of phytoplankton- and macrophyte-derived dissolved organic matter in sulfamethazine adsorption on goethite

Phytoplankton-derived dissolved organic matter (PDOM) and macrophyte-derived dissolved organic matter (MDOM) exist ubiquitously in eutrophic freshwater lakes. To understand the heterogeneous roles of individual fluorescent DOM components in the adsorption of antibiotics onto sediment minerals, the adsorptive fractionation of DOM on goethite (α–FeOOH) and its interaction with sulfamethazine (SMT) were investigated using fluorescence excitation-emission matrix combined with parallel factor analysis (EEM–PARAFAC). The affinity sequence for goethite of the 4 fluorescent PARAFAC components followed the order of: tryptophan- > tyrosine- > long emission wavelength (LEW) humic- > and short emission wavelength (SEW) humic-like component. This sequence indicated the preferential adsorption of protein-like substances. Meanwhile, tyrosine-like components can strongly form complexes with SMT with a large binding constant, followed by tryptophan- and SEW humic-like components. However, LEW humic-like component did not effectively react with SMT. The main mechanism of fluorescence quenching between DOM and SMT was static quenching. The result indicated that protein-like substances in DOM were favorable to SMT adsorption by acting as a bridge to form complexes with both goethite surface and SMT molecules, whereas humic-like substances played secondary roles in the DOM–goethite–SMT ternary system. Due to its higher content of protein-like substances, PDOM improved the SMT adsorption on goethite more than MDOM. Therefore, the abundant DOM released from phytoplankton and macrophytes affected the transport of antibiotics to sediments and might eventually change their bioavailability and toxicity to organisms.

Kinetic and mechanistic investigations of the degradation of sulfamethazine in heat-activated persulfate oxidation process

Sulfamethazine (SMZ) is widely used in livestock feeding and aquaculture as an antibiotic agent and growth promoter. Widespread occurrence of SMZ in surface water, groundwater, soil and sediment has been reported. In this study, degradation of SMZ by heat-activated persulfate (PS) oxidation was investigated in aqueous solution. Experimental results demonstrated that SMZ degradation followed pseudo-first-order reaction kinetics. The pseudo-first-order rate constant (kobs) was increased markedly with increasing concentration of PS and temperature. Radical scavenging tests revealed that the predominant oxidizing species was SO4− with HO playing a less important role. Aniline moiety in SMZ molecule was confirmed to be the reactive site for SO4− attack by comparison with substructural analogs. Nontarget natural water constituents affected SMZ removal significantly, e.g., Cl− and HCO3− improved the degradation while fulvic acid reduced it. Reaction products were enriched by solid phase extraction (SPE) and analyzed by liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI–MS/MS). 6 products derived from sulfonamide SN bond cleavage, aniline moiety oxidation and Smiles-type rearrangement were identified, and transformation pathways of SMZ oxidation were proposed. Results reveal that heat-activated PS oxidation could be an efficient approach for remediation of water contaminated by SMZ and related sulfonamides.

The role of reactive oxygen species in sulfamethazine degradation using UV-based technologies and products identification

• Photo-oxidation processes were compared in terms of sulfamethazine loss rates. • Photolysis and photosensitization were investigated in photo-oxidation processes. • Contribution of photosensitization and reactive oxygen species was investigated. • The cleavage of C S and N S bonds from sulfamethazine was proposed. • Hydroxylated aromatic compounds were detected in the H 2 O 2 /UV system. Sulfamethazine (SMT) is an emerging pollutant continuously delivered into water bodies that has attracted growing attention due to its recalcitrant behavior in the environment. Although UV-based technologies have been investigated for the treatment of both water and wastewater containing SMT, photosensitization of the target compound is not usually examined during photo-induced oxidation processes. It is not our intention to propose processes for water treatment, only to understand the phenomena induced by the interactions between UV radiation and pollutant molecule. In this way, the photo-initiated and photo-induced oxidation processes are compared in terms of changes in SMT degradation rates and photoproducts formed. A tubular photochemical reactor with a concentric low pressure mercury vapor lamp emitting at 254 nm was used and SMT concentrations were determined by ultra-fast liquid chromatography analysis. Hydrogen peroxide consumption was monitored spectrophotometrically and the photoproducts were analyzed by LCMS-IT-TOF. To characterize samples we used three spectroscopic methods based on: (1) UV–Vis absorption; (2) excitation-emission matrix (EEM) fluorescence; and (3) phosphorescence. Our results suggest that photolysis and photosensitization played an important role in sulfamethazine degradation during irradiation at 254 nm. The reaction with singlet oxygen and radical species promotes sulfamethazine degradation during a photosensitized process occurring simultaneously with direct photolysis. The photo-initiated oxidation process was advantageous over the photo-induced oxidation in terms of SMT degradation rates, achieving concentration below the detection limit after 47 min of irradiation. Compounds originated from the cleavage of the C S and N S bonds of the SMT molecule were detected as common transformation products during photo-initiated and photo-induced oxidation processes, whereas a degradation product resulting from the electrophilic addition of hydroxyl radicals to the aromatic ring was detected for the H 2 O 2 /UV system. The high efficiency of the photo-initiated oxidation process on the photodegradation of the recalcitrant sulfamethazine was verified, suggesting the formation of acidic subproducts probably from the oxidative cleavage of hydroxylated aromatic rings.

Synergistic catalytic degradation of antibiotic sulfamethazine in a heterogeneous sonophotolytic goethite/oxalate Fenton-like system

A novel heterogeneous sonophotolytic goethite/oxalate Fenton-like (SP-FL) system was developed in this study. Compared to the corresponding photochemical Fenton-like (P-FL) system and sonochemical Fenton-like system (S-FL) system, it was found that the SP-FL system could achieve synergistic degradation of antibiotic sulfamethazine (SMZ). A synergy factor of 2.2 based on pseudo-first-order degradation rate constant (kobs) was observed, along with great improvements in organic mineralization and wastewater detoxification. Examining the evolution of dissolved iron species and reactive oxygen species (H2O2 and OH) in the three systems revealed that the SMZ degradation strongly relied on the “in-situ” photochemical generation of H2O2 and fast regeneration of dissolved Fe(II) species. Identification of the organic intermediates and released inorganic ions suggested that the cleavage of SN bond in the SMZ molecule was dominant under OH attacking. The important synergistic role of ultrasound (US) in promoting SMZ degradation was proposed. Herein US could affect the system at multi-folds: (1) accelerating the goethite-chelating dissolution by reducing mass transfer barriers, (2) enhancing the radical reactions in the bulk solution with sonochemical cavitation effect, and (3) possible direct hydrolysis of amine intermediates inside the cavitation bubbles.

4-Amino-N-(4,6-dimethylpyrimidin-2-yl)benzenesulfonamide–2-nitrobenzoic acid (1/1)

In the asymmetric unit of the title co-crystal, C12H14N4O2S·C7H5NO4, the sulfamethazine and 2-nitro­benzoic acid mol­ecules form a heterodimer through inter­molecular amide–carb­oxy­lic acid N—H⋯O and carb­oxy­lic acid–pyrimidine O—H⋯N hydrogen-bond pairs, giving a cyclic motif [graph set R 2 2(8)]. The dihedral angle between the two aromatic ring systems in the sulfamethazine mol­ecule is 88.96 (18)° and the nitro group of the acid is 50% rotationally disordered. Secondary aniline N—H⋯Osulfone hydrogen-bonding associations give a two-dimensional structure lying parallel to the ab plane.

A 2:1 sulfamethazine–theophylline cocrystal exhibiting two tautomers of sulfamethazine

In the title cocrystal, 4-amino-N-(4,6-dimethylpyrimidin-2-yl)benzenesulfonamide-4-amino-N-(4,6-dimethyl-1,2-dihydropyrimidin-2-ylidene)benzenesulfonamide-1,3-dimethyl-7H-purine-2,6-dione (1/1/1), C(7)H(8)N(4)O(2)·2C(12)H(14)N(4)O(2)S, two sulfamethazine molecules cocrystallize with a single molecule of theophylline. Each molecule of sulfamethazine forms a hydrogen-bonded ribbon along the b axis crosslinked by further hydrogen bonding. The two sulfamethazine molecules exhibit a hydrogen-shift isomerization so that the crystal structure contains both tautomeric forms. Calculation of their relative energies showed that the tautomer protonated at the chain N atom is considerably more stable than the one where an N atom in the aromatic ring is protonated. The latter, here observed for the first time, is stabilized through strong intermolecular interactions with the theophylline molecules.