Effect Of pH Changes Research Articles

Effect of pH Change on the Microalgae-Based Biogas Upgrading Process

An alternative way to remove CO2 from biogas is the use of photosynthetic microorganisms, such as microalgae. This can be achieved by the operation of an open photobioreactor, connected with a mass transfer column, such as a counterflow column. This technology provides up-graded biogas with high quality. The microalgal uptake of CO2 from the biogas in counterflow columns generates pH changes in microalgae culture. To clarify the potential effect of these dynamic pH conditions in the culture, the effect of pH change on the photosynthetic activity and PSII quantum yield was studied for microalgae Chlorella sorokiniana. Thus, assays were carried out, where the pH drop reported in the counterflow columns was replicated in batch microalgae culture through HCl addition and CO2 injection, moving the culture pH from 7.0 to 5.0 and from 7.0 to 5.8, respectively. Moreover, the effect of light/darkness on photosynthetic activity was tested when the pH decreased. The results obtained in this research showed that the photosynthetic activity decreased for the light conditions when the pH was shifted by HCl addition and CO2 injection. Despite this, the value of the PSII quantum yield remained at 0.6–0.7, which means that the microalgae culture did not suffer a negative effect on the photosynthetic system of cells because a high value of PSII efficiency remained. In the same way, the results indicated that when the pH change was corrected, the photosynthetic activity recovered. Moreover, the apparent affinity constant for dissolved inorganic carbon (KDIC) was 0.9 µM at pH 5 and 112.0 µM at pH 7, which suggests that the preferred carbon source for C.sorokniana is CO2. Finally, all the results obtained indicated that the pH drop in the counter-flow column for biogas upgrading did not cause permanent damage to the photosynthetic system, and the decrease in the photosynthetic activity as a result of the pH drop can be recovered when the pH is corrected.

Long-term differences in fertilisation type change the bacteria:archaea:fungi ratios and reveal a heterogeneous response of the soil microbial ionome in a Haplic Luvisol

Organic farm management through farmyard manure application is associated with soil organic carbon sequestration facilitated by more balanced nutrient stoichiometry of macro- and micronutrients. Quantitative information on micronutrients within the soil microbial biomass is lacking. Using soils from a 40-year old long-term field trial (DOK), we investigated if fertilisation differences (farmyard manure equivalent to 0.7 or 1.4 livestock units per hectare and mineral fertilisation) and farm management (biodynamic, organic, conventional) changed the soil microbial ionome and stoichiometry and if this is related to microbial community shifts. Soil (15% sand, 70% silt and 15% clay) from the top 20 cm was analysed for microbial biomass carbon, nitrogen and phosphorus. Further elements were assessed via an adapted chloroform-fumigation extraction procedure. Abundances of bacteria, archaea, and fungi were determined (qPCR). Farmyard manure increased microbial biomass by approximately two-fold and the contribution of bacteria and archaea by up to approximately five-fold. Microbial biomass phosphorus and magnesium increased with mineral fertilisation (from 7 to 14 μg g−1 soil) and farmyard manure (from 0.5 to 2.7 μg g−1 soil), respectively. The microbial biomass carbon to potassium ratio remained similar, at around 47:1, revealing stoichiometric control. Microbial biomass manganese was reduced from 3.5 to 2.2 μg g−1 soil with lower availability due to raised pH in biodynamic management. The microbial stoichiometry and ionome were mainly affected by nutrient input and soil chemical properties; direct links between microbial (micronutrient-) stoichiometry and microbial community changes cannot be established with certainty due to potential confounding effects of pH changes.

Effect of pH fluctuations on the biodegradability of nanocomposite Mg-alloy in simulated bodily fluids

According to the National Institute of Health, the biodegradability, non-toxic nature, and remarkable natural and mechanical properties of magnesium and its components make them desirable choices for use in the production of supplies for biomedical implantation. Simulated bodily fluid (SBF) is used as a standard electrolyte for in vitro corrosion research. Each SBF module's independent and synergistic corrosion effects are studied in this study. Artificial pH variations increase degradation, according to the results. This experiment examined the Mg corrosion submerged in a SBF solution. The effect of pH changes on the rate of corrosion of Mg immersed in standard SBF solution was investigated. According to the previously published study, the corrosion process of Mg has been confirmed by scanning electron microscopy observations of damaged surface morphology. Because of these investigations, pH 7 was selected as the pH for bodily fluids since it is neutral.

Effect of Coating Thickness and Polyethylene Glycol’s Molecular Weight on Diltiazem Hydrochloride Release from Controlled Porosity Osmotic Pump Tablets

The purpose of this research was to design CPOP tablets to achieve controlled delivery of diltiazem hydrochloride (DH) up to 12 hours, which is a water-soluble calcium channel blocker with a short biological half-life. Two batches of osmotic tablet cores were prepared, containing DH with mannitol as an osmotic agent (1: 1.5 ratio). The tablet cores formulation with 10 mm diameter achieved the required technical and mechanical specifications. Direct compression technique was used to prepare the tablet cores which were evaluated in terms of mechanical resistance and uniformity of dosage units, followed by spray film coating using cellulose acetate as a former polymer of the semipermeable membrane and polyethylene glycol (PEG) as a pore forming agent. Several molecular weights of PEG (6000, 1500 and 400) were used and coating thickness levels were obtained. In vitro drug release, morphology of coating surface and the effect of pH change on release rate were investigated. Most of the prepared formulations demonstrated a burst release at the initial stage, which could be controlled by increasing the coating thickness. Formulations with PEG400 as a pore former presented better controlled and less burst release than those containing PEG6000, PEG1500, or a mixture of PEG6000: PEG400 (1: 1), and the pH change did not affect the drug release except in the initial stage.

Electrochemical Behavior and Ultrasensitive, Simple and Effective Voltammetric Determination of Acetaminophen Using Modified Glassy Carbon Electrode Based on 4‐Hydroxyquinoline‐3‐carboxylic Acid

AbstractAn electrochemical oxidation of acetaminophen (ACOP) has been successfully performed by using glassy carbon electrode covered with 4‐hydroxyquinoline‐3‐carboxylic acid (4HQ3CA) to reinforce electrode's feature. To characterize the modified electrode (4HQ3CA/GC), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and Fourier transform infrared spectroscopy (FT‐IR) techniques were used. The finding optimum conditions (supporting electrolyte, pH) and the electrochemical determination studies were performed with differential pulse voltammetry (DPV). It was decided that the supporting electrolyte medium suitable for ACOP determination was Britton‐Robinson (BR) buffer and the effect of pH change on the oxidation peak of ACOP in this media was investigated. The effect of changing scan rate on the oxidation peak of ACOP was examined and this study showed that the oxidation process of ACOP on the 4HQ3CA/GC modified electrode surface was diffusion and adsorption controlled process. A wide concentration range from 0.0025 μM to 141 μM with a limit of detection (LOD) of 5.98×10−10 M (3 s/m) was obtained. This prepared sensor was carried out for the determination of ACOP in pharmaceutical sample.

Unveiling the G4-PAMAM capacity to bind and protect Ang-(1-7) bioactive peptide by molecular dynamics simulations.

Angiotensin-(1-7) re-balance the Renin-Angiotensin system affected during several pathologies, including the new COVID-19; cardiovascular diseases; and cancer. However, one of the limiting factors for its therapeutic use is its short half-life, which might be overcome with the use of dendrimers as nanoprotectors. In this work, we addressed the following issues: (1) the capacity of our computational protocol to reproduce the experimental structural features of the (hydroxyl/amino)-terminated PAMAM dendrimers as well as the Angiotensin-(1-7) peptide; (2) the coupling of Angiotensin-(1-7) to (hydroxyl/amino)-terminated PAMAM dendrimers in order to gain insight into the structural basis of its molecular binding; (3) the capacity of the dendrimers to protect Angiotensin-(1-7); and (4) the effect of pH changes on the peptide binding and covering. Our Molecular-Dynamics/Metadynamics-based computational protocol well modeled the structural experimental features reported in the literature and our double-docking approach was able to provide reasonable initial structures for stable complexes. At neutral pH, PAMAM dendrimers with both terminal types were able to interact stably with 3 Angiotensin-(1-7) peptides through ASP1, TYR4 and PRO7 key amino acids. In general, they bind on the surface in the case of the hydroxyl-terminated compact dendrimer and in the internal zone in the case of the amino-terminated open dendrimer. At acidic pH, PAMAM dendrimers with both terminal groups are still able to interact with peptides either internalized or in its periphery, however, the number of contacts, the percentage of coverage and the number of hydrogen bonds are lesser than at neutral pH, suggesting a state for peptide release. In summary, amino-terminated PAMAM dendrimer showed slightly better features to bind, load and protect Angiotensin-(1-7) peptides.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10822-022-00470-5.

Evaluation of pH change effects on the HSA folding and its drug binding characteristics, a computational biology investigation.

The binding of therapeutics to human serum albumin (HSA), which is an abundant protein in plasma poses a major challenge in drug discovery. Although HSA has several binding pockets, the binding site I on D2 and binding site II on D3 are the main binding pockets of HSA. To date, a few experiments have been conducted to examine the effects of the potential of hydrogen (pH) changes on HSA attributes. In the present investigation, the effect of acidic (pH7.1) and basic states (pH7.7) on HSA structure and its drug binding potency were examined in comparison with the physiological state (pH 7.4). For this purpose, molecular dynamics (MD), free energy landscape (FEL), principal component analysis (PCA), probability distribution function (PDF), tunnel-cavity investigation, secondary structure analysis, docking study, and free energy investigation were employed to investigate the effect of pH changes on the structural characteristics of HSA at the atomic level. The results obtained from this study revealed the significant effect of pH alterations on the secondary and tertiary structure of HSA. In addition, HSA stability and its drug binding ability can be severely affected following pH changes. Given that pH change frequently occurs in various diseases such as cancer, diabetes, and kidney failure, therefore, pharmaceutical companies should allocate specific consideration to this subject throughout their drug design experiments.

In-situ preparation of lactate-sensing membrane for the noninvasive and wearable analysis of sweat

In the wearable electrochemical biosensors, sensing signal duration is significantly dependent on the long-term stability of functional materials modified on the flexible substrate, the effect of pH changes of sweat on the sensing device and signal fluctuation caused by the bending of sensor. Here, we proposed a wearable biosensor based on the lactate-sensing membrane mainly constituted by Prussian blue (PB), reduced graphene oxide (rGO), Au nanoparticles and lactate oxidase (LOx). Based on the in-situ layer-by-layer spin-coating preparation method, the electrode surface was covered with an extensive and uniform PB/GO membrane with a high stability. After the electro-reduction of GO to rGO and the combination of urchin-like Au particles with sufficient tentacles to LOx, the sensing membrane showed the improved electron transport from the enzyme active center to the electrode. Therefore, the wearable biosensor achieved a high sensitivity of 40.6 μA mM−1 cm−2 in a range of 1–222 μM and a low sensitivity of 1.9 μA mM−1 cm−2 in a wide range of 0.222–25 mM, satisfying the requirement of the typical test. In addition, with the excellent running and mechanical stability, the lactate biosensor was successfully applied on volunteers’ skin for real-time monitoring of perspiration in vivo. The results were comparable with ex vivo measurements achieved by a commercial lactate sensor. The wearable electrochemical biosensor provides a good candidate in the future for the evaluation of human sweat in sports and biomedical fields.

Effect of pH on structural dynamics of HMG-CoA reductase and binding affinity to β-sitosterol

Human 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR; EC 1.1.1.34) catalyzes the conversion of (3S)-hydroxy-3-methylglutaryl-CoA (HMG-CoA) to mevalonic acid, which has been defined as the rate-limiting step in the synthesis of cholesterol and other isoprenoids, thus playing a critical role in cellular cholesterol homeostasis. In this study, the effect of changing pH on the structural dynamics and binding affinity of HMGCR were investigated by molecular dynamics simulation using OpenMM, and molecular docking using Autodock Vina. The results pinpoint pH 8.0 for optimum structural stability/activity of HMGCR, and the insightful relationships between pH, structural dynamics radius of gyration (Rg) or root mean square deviation (RMSD), and binding affinity of HMGCR. This method will be useful to predict the pH for the uncharacterized human proteins, toward biomedical and biotechnological applications Communicated by Ramaswamy H. Sarma

Electrochemical techniques for monitoring the biodegradability of nanocomposite Mg-alloy/HA for repairing bone fracture

Mg and its composites are considered attractive candidates for supplying biomedical implantation. Mg-alloys are gaining popularity for biomedical implant applications, particularly bone regeneration because they have characteristics that are like those of natural bone. Simulated body fluid (SBF) is an electrolyte that is often utilized in vitro corrosion investigations. Using each SBF module individually and in combination, this research evaluates the corrosion effects on the system. pH alterations hasten the degeneration of the organism's pH and it was decided to explore the corrosion of Mg in an SBF. In this study, the effect of pH changes on the corrosion rate of Mg immersed in standard SBF solution was investigated in detail. According to previously published research, the corrosion process of Mg has been substantiated by scanning electron microscopy examinations of damaged surface morphology. In this investigation, pH 7 was determined to be the optimal pH for physiological fluids since it is neutral. To accomplish these aims, researchers examined Mg–2 wt.% Zn–0.5 wt.% Ca (ZC21) alloy pins microstructurally and mechanically, as well as the degradation of the alloy pins and their interactions with the SBF solution. The degradation of bone and its cytocompatibility with other substances. The degradation control of Mg-alloy occurred at a much slower rate than that of Mg alone. Bone cell development on the applied nano alloy is visible on SEM-EDS charts, demonstrating that this alloy is extremely compatible with human bone and that its usage as a stent for bone fracture is highly suggested in this study.

Effect of change in pH, heat and ultrasound pre-treatments on binding interactions between quercetin and whey protein concentrate

The effects of change in pH, heat and ultrasound pre-treatments on the binding mechanism of quercetin (Q) with whey protein concentrate (WPC) were investigated, as well as the antioxidant capacity and stability of Q in the complexes. The main interaction between WPC and Q was hydrophobic and was not affected by pre-treatments. The binding affinity for Q with WPC at pH 7.4 after heating at 80 °C for 30 min, was the strongest, resulting in a WPC-Q complex with a more compact structure, the smallest particle size (184.43 ± 10.47 nm) and the largest ζ-potential (-20.58 ± 0.60 mV). This complex also provided the greatest stabilization of Q, when exposed to 37 °C and light. Complexation of WPC with Q reduced the ABTS radical scavenging capacity of Q, but enhanced its DPPH radical scavenging capacity and reducing power. These findings provide valuable information for optimizing the formation conditions of WPC-Q.

Reversible Adsorption of Polycarboxylates on Silica Fume in High pH, High Ionic Strength Environments for Control of Concrete Fluidity.

Polycarboxylate-based superplasticizers are essential for production of ultrahigh-performance concrete (UHPC), facilitating particle dispersion through electrostatic repulsion and steric hindrance. This study examines for the first time the effect of changes in pH, ionic strength, and charge on the adsorption/desorption behavior of a polycarboxylate-based superplasticizer on silica fume in aqueous chemistries common in low-CO2 UHPC. Data from total organic carbon measurements, Fourier transform infrared and nuclear magnetic resonance spectroscopy, and zeta potential measurements reveal the silica surface chemistry and electrokinetic properties in simulated UHPC. Addition of divalent cations (Ca2+) results in polycarboxylate adsorption on silica fume via (i) adsorption of Ca2+ ions on the silica surface and a negative zeta potential of lower magnitude on the silica surface and (ii) reduction of polycarboxylate anionic charge density due to complexation with Ca2+ ions and counter-ion condensation. Addition of OH– ions results in polycarboxylate desorption via deprotonation of silanol groups and a negative zeta potential of greater magnitude on the silica surface. Simultaneous addition of both Ca2+ and OH– results in rapid polycarboxylate desorption via (i) formation of an electric double layer and negative zeta potential on the silica surface and (ii) an increase in polycarboxylate anionic charge density due to deprotonation of the carboxylate groups in the polymer backbone, complexation with Ca2+ ions, and counter-ion condensation. This provides an explanation for the remarkable fluidizing effect observed upon addition of small amounts (1.0 wt %) of a solid, powdered Ca source to fresh, low-CO2, UHPC, which exhibits significantly higher fresh state pH (>13) than those based on Portland cement (pH 11).

What is the Effect of Changing pH on Pharmaceuticals’ Sorption?

What is the Effect of Changing pH on Pharmaceuticals’ Sorption?

Evaluation of the effects of newly synthesized metallophthalocyanines on breast cancer cell lines with photodynamic therapy.

In this study, the new phthalonitrile derivative 3-(4-(3-oxobutyl)phenoxy)phthalonitrile (1) and its non-peripheral metallophthalocyanine derivatives [zinc (2), copper (3), cobalt (4), manganese (5), gallium (6), and indium (7)] were synthesized. The newly synthesized phthalocyanines were characterized by standard spectroscopic methods, such as FT-IR, 1H NMR, UV-Vis, fluorescence spectroscopies, and MALDI-TOF spectrometry. Aggregation behaviors of the novel phthalocyanines were investigated by UV-Vis spectroscopy. The effect of pH change on the electronic and emission spectra of the newly synthesized phthalocyanine derivatives was studied in THF media. The electronic spectra of the new zinc (2), copper (3), and cobalt (4) phthalocyanines exhibited bathochromic shifts in acidic pH values due to the presence of monoprotonated forms. Surprisingly, the same effect was not observed for manganese (5) and indium (7) phthalocyanines. On the other hand, gallium (6) showed a slight red-shifted band with the addition of HCl to the medium. Also, it was determined that the synthesized zinc (2) and gallium (6) phthalocyanines had a selective phototoxic effect on the MCF-7 breast cancer cell line compared to the MCF-10A healthy breast cell line. The IC50 values of zinc (2) and gallium (6) phthalocyanines were determined for MCF-7 and MCF-10A cell lines. The IC50 values of MCF-7 for compounds 2 and 6 were found to be 1.721 ± 0.4 μg mL-1 and 7.406 ± 0.32 μg mL-1, respectively. The IC50 values of MCF-10A for phthalocyanines 2 and 6 were found to be 48.90 ± 0.69 μg mL-1 and 14.77 ± 1.09 μg mL-1, respectively. In the LDH (lactate dehydrogenase)-ELISA study, the LDH levels that formed on a cellular basis after the application were measured, and it was observed that the cells were directed towards apoptosis. In addition, it was observed that cancer cells underwent more apoptosis than healthy cells as a result of this application with cell-cycle and dead cell kits performed by flow cytometry. This research shows that non-peripheral substituted gallium and zinc phthalocyanine derivatives (2 and 6) can be suitable photosensitizers for the photodynamic treatment of breast cancers.

Aplikasi Zeolit Alam Aktif Wonosari Sebagai Adsorben Zat Warna Remazol Yellow Fg

Zeolite as an adsorbent has been widely used. Zeolite activation was carried out to increase the absorption. This study aimed to determine the characteristics of the active zeolite and apply it as an adsorbent. The activation process was carried out by adding acid and calcining at 4500C for 6 hours. Remazol Yellow FG is a dye that is widely used in the textile industry. In this study, the adsorption process was carried out on the Remazol Yellow FG solution, then analyzed the effect of changes in pH (5, 6, 7, 8, 9), contact time (30, 60, 90, 120, 150 minutes) and the concentration of Remazol Yellow FG solution ( 50, 100, 150, 200, 250 ppm) on the adsorption of Remazol Yellow FG dye. From the analysis of the sample solution of Remazol Yellow, the values of Ce and qe can be calculated. These values were then used to calculate KL and KF in the Langmuir adsorption isotherm and Freundlich adsorption isotherm models. From the experimental results, it could be seen that as the contact time increased, the adsorption capacity would be greater. However, when the zeolite was already in the saturated phase, the adsorption capacity would tend to decrease. In the Langmuir adsorption isotherm, the KL value was 0.0274 L/mg and in the Freundlich adsorption isotherm model, the KF value was 29.25 L/mg. Remazol Yellow FG adsorption tended to follow the Langmuir adsorption isotherm model with an R2 value of 0.998.

Effect of pH Change on the Electrochemical Behavior of Intermetallic Particles in AA1050 Aluminum

Commercial purity aluminum alloys, such as AA1050 and AA1100, are widely used for infrastructure and battery materials for their high formability, high electrical conductivity, and excellent corrosion resistance. The commercial purity aluminum alloys are known to contain Fe-rich intermetallic particles (IMPs). Although the IMPs are needed to provide the valuable properties, some of the IMPs could turn into an initiation site for pitting under salty environments. Since the Fe-rich IMPs show higher electrode potential than that of the Al-matrix, the IMPs work as a cathodic reaction site. As oxygen reduction reaction proceeds on the IMPs, the pH around the IMPs increases locally. The dissolution of the Al-matrix (often referred as trenching) is caused by the local alkalization, and a trench is formed around the IMPs. Crystallographic pitting is likely to be initiated inside the trench. Although the IMPs have an important role in trenching, the electrochemical behavior of the IMPs during trenching is still unknown. In this study, the dissolution behavior of the IMPs and surrounding Al-matrix was observed in situ using an optical microscopy in order to analyze the morphological change during trenching. The effect of pH change on the electrochemical behavior of the IMPs was analyzed using the bulk IMPs fabricated by arc-melting.

Nanostructure and Molecular-Level Characterization of Aminoalkyl Methacrylate Copolymer and the Impact on Drug Solubilization Ability.

The effects of pH changes and saccharin (SAC) addition on the nanostructure and mobility of the cationic aminoalkyl methacrylate copolymer Eudragit E PO (EUD-E) and its drug solubilization ability were investigated. Small-angle X-ray scattering performed using synchrotron radiation and atomic force microscopy showed that the EUD-E nanostructure, which has a size of approximately several nanometers, changed from a random coil structure at low pH (pH 4.0-5.0) to a partially folded structure at high pH (pH 5.5-6.5). The EUD-E also formed a partially folded structure in a wide pH range of 4.5-6.5 when SAC was present, and the coil-to-globule transition was moderate with pH increase, compared with that when SAC was absent. The equilibrium solubility of the neutral drug naringenin (NAR) was enhanced in the EUD-E solution and further increased as the pH increased. The enlargement of the hydrophobic region of EUD-E in association with the coil-to-globule transition led to efficient solubilization of NAR. The interaction with SAC enhanced the mobility of the EUD-E chains in the hydrophobic region of EUD-E, resulting in changes in the drug-solubilizing ability. 1H high-resolution magic-angle spinning NMR measurements revealed that the solubilized NAR in the partially folded structure of EUD-E showed higher molecular mobility in the presence of SAC than in the absence of SAC. This study highlighted that solution pH and the presence of SAC significantly changed the drug solubilization ability of EUD-E, followed by changes in the EUD-E nanostructure, including its hydrophobic region.

Characterization of the structure and properties of the isolating interfacial layer of oil–water emulsions stabilized by soy hull polysaccharide: Effect of pH changes

The effect of pH on the microstructure and properties of the soy hull polysaccharide interfacial layer was determined. The particle size at pH 2.0 was the largest (36.7 μm), whereas the absolute ζ-potential was the smallest. The protein content was the lowest at pH 2.0 and 9.0 and peaked around pH 4.0–5.0 (77.7%). The ordered secondary protein structure content under low pH conditions was greater than that under high pH conditions and the stability of the interfacial layer was higher at high pH, whereas the emulsion viscosity decreased by two orders of magnitude between pH 2.0 and 9.0. It appears that low pH reduced the thermal stability and increased the apparent viscosity of the emulsion by increasing the structural order of the protein in the interfacial layer. These findings lay the foundation for future work to reveal the key components and characteristic structures of soy hull polysaccharide that affect interfacial stability.

Explanation of the Formation of Complexes between Representatives of Oxazolidinones and HDAS-β-CD Using Molecular Modeling as a Complementary Technique to cEKC and NMR.

Molecular modeling (MM) results for tedizolid and radezolid with heptakis-(2,3-diacetyl-6-sulfo)-β-cyclodextrin (HDAS-β-CD) are presented and compared with the results previously obtained for linezolid and sutezolid. The mechanism of interaction of chiral oxazolidinone ligands belonging to a new class of antibacterial agents, such as linezolid, tedizolid, radezolid, and sutezolid, with HDAS-β-CD based on capillary electrokinetic chromatography (cEKC), nuclear magnetic resonance (NMR) spectroscopy, and MM methods was described. Principles of chiral separation of oxazolidinone analogues using charged single isomer derivatives of cyclodextrin by the cEKC method were presented, including the selection of the optimal chiral selector and separation conditions, complex stoichiometry, and binding constants, which provided a comprehensive basis for MM studies. In turn, NMR provided, where possible, direct information on the geometry of the inclusion complexes and also provided the necessary structural information to validate the MM calculations. Consequently, MM contributed to the understanding of the structure of diastereomeric complexes, the thermodynamics of complexation, and the visualization of their structures. The most probable mean geometries of the studied supramolecular complexes and their dynamics (geometry changes over time) were determined by molecular dynamics methods. Oxazolidinone ligands have been shown to complex mainly the inner part of cyclodextrin, while the external binding is less privileged, which is consistent with the conclusions of the NMR studies. Enthalpy values of binding of complexes were calculated using long-term molecular dynamics in explicit water as well as using molecular mechanics, the Poisson–Boltzmann or generalized Born, and surface area continuum solvation (MM/PBSA and MM/GBSA) methods. Computational methods predicted the effect of changes in pH and composition of the solution on the strength and complexation process, and it adapted the conditions selected as optimal during the cEKC study. By changing the dielectric constant in the MM/PBSA and MM/GBSA calculations, the effect of changing the solution to methanol/acetonitrile was investigated. A fairly successful attempt was made to predict the chiral separation of the oxazolidinones using the modified cyclodextrin by computational methods.

PH Changes Have a Profound Effect on Gene Expression, Hydrolytic Enzyme Production, and Dimorphism in Saccharomycopsis fibuligera.

Saccharomycopsis fibuligera is an amylolytic yeast that plays an important role within nuruk (a traditional Korean fermentation starter) used for the production of makgeolli (Korean rice wine), which is characterized by high acidity. However, the effect of pH change (neutral to acidic) on the yeast cell to hyphal transition and carbohydrate-hydrolyzing enzyme activities for S. fibuligera has not been investigated yet. In this study, S. fibuligera strains were cultured under the different pH conditions, and the effect on the enzyme production and gene expression were investigated. An acidic pH induced a hyphal transition from yeast cell of S. fibuligera KPH12 and the hybrid strain KJJ81. In addition, both strains showed a gradual decrease in the ability to degrade starch and cellulose as the pH went down. Furthermore, a transcriptome analysis demonstrated that the pH decline caused global expression changes in genes, which were classified into five clusters. Among the differentially expressed genes (DEGs) under acidic pH, the downregulated genes were involved in protein synthesis, carbon metabolism, and RIM101 and cAMP-PKA signaling transduction pathways for the yeast-hyphal transition. A decrease in pH induced a dimorphic lifestyle switch from yeast cell formation to hyphal growth in S. fibuligera and caused a decrease in carbohydrate hydrolyzing enzyme production, as well as marked changes in the expression of genes related to enzyme production and pH adaptation. This study will help to elucidate the mechanism of adaptation of S. fibuligera to acidification that occur during the fermentation process of makgeolli using nuruk.