Neutral Form Research Articles

From Gas to Solution: The Changing Neutral Structure of Proline upon Solvation.

Liquid-jet photoelectron spectroscopy (LJ-PES) and electronic-structure theory were employed to investigate the chemical and structural properties of the amino acid l-proline in aqueous solution for its three ionized states (protonated, zwitterionic, and deprotonated). This is the first PES study of this amino acid in its biologically relevant environment. Proline's structure in the aqueous phase under neutral conditions is zwitterionic, distinctly different from the nonionic neutral form in the gas phase. By analyzing the carbon 1s and nitrogen 1s core levels as well as the valence spectra of aqueous-phase proline, we found that the electronic structure is dominated by the protonation state of each constituent molecular site (the carboxyl and amine groups) with small yet noticeable interference across the molecule. The site-specific nature of the core-level spectra enables the probing of individual molecular constituents. The valence photoelectron spectra are more difficult to interpret because of the overlapping signals of proline with the solvent and pH-adjusting agents (HCl and NaOH). Yet, we are able to reveal subtle effects of specific (hydrogen-bonding) interaction with the solvent on the electronic structure. We also demonstrate that the relevant conformational space is much smaller for aqueous-phase proline than for its gas-phase analogue. This study suggests that caution must be taken when comparing photoelectron spectra for gaseous- and aqueous-phase molecules, particularly if those molecules are readily protonated/deprotonated in solution.

Can the pH-dependent adsorption of phenoxyalkanoic herbicides in soils be described with a single equation?

The six phenoxyalkanoic acid herbicides currently used in the European Union have similar molecular structures. Therefore, we assumed the soil components involved in the adsorption mechanisms of these herbicides to be identical. The values of the adsorption distribution coefficient Kd, obtained via batch experiments involving typical Polish Arenosol, Luvisol, and Chernozem profiles with a native pH of 4.2-7.7, were examined using Lasso regression, as well as adsorption on isolated fractions of humic substances, Al2O3, and goethite. The neutral forms of the herbicides were adsorbed on the surface of fulvic acids available to them, covering soil mesopores with a size of > 2.5nm. The models revealed that fulvic acids had a lognormal-like distribution in soil pores. Herbicide anions were adsorbed on the pH-dependent sites of Al oxyhydroxides and on the sites created by the Al+3 species adsorbed on the surface of fulvic acids (both sites were active up to pH 7.5), the sites of humic acids associated with the adsorbed Al3+ species, sites of Fe oxyhydroxides (active at pH < 5), and, to a limited extent, sites of humins. Two models describing the adsorption of phenoxyalkanoic acid herbicides in soils were created. A simpler model was based on humic substance fractions and the variables related to the potential acidity of soils. In the more extensive model, humic substance fractions and Al and Fe oxyhydroxide contents were used as predictors, and, where necessary, the predictors were combined with the modified Henderson-Hasselbalch formula to estimate the activity ranges of pH-dependent sorption sites. The study findings revealed that fulvic and humic acids were the main adsorbents of phenoxyalkanoic herbicides in soils, indicating that transporting of the herbicides with dissolved organic matter is an important mechanism of groundwater and surface water contamination with these chemicals.

Direct capture of the alanine ghost in alanine-doped triglycine sulfate crystals.

In this report, ghostly ultra-trace amounts of alanine in alanine-doped triglycine sulfate crystal were directly observed by solid-state nuclear magnetic resonance, and the presence of two chemical states in the cation form and neutral form in the doped alanine was revealed. As the result, the crystal structure of alanine-doped triglycine sulfate was determined for the first time.

Fluorescence Enhancement of Nonemissive Monodeprotonated Luteolin in a Poly(vinyl alcohol) Film.

Solid polymer matrixes can modulate the electronic states of embedded chromophores and have been widely used in flexible optoelectronic and optical materials. Luteolin is one of the most common natural flavonoids, and its neutral and monodeprotonated forms are nonemissive in aqueous solution induced by ultrafast excited-state proton transfer (ESPT) followed by nonradiative relaxation. In this study, we have incorporated luteolin into poly(vinyl alcohol) (PVA) films and studied their fluorescence behaviors. Neutral and one monodeprotonated luteolin coexist in the PVA film. Weak steady-state fluorescence of neutral luteolin peaking at about 440 nm is observed for the first time. In addition, the monodeprotonated luteolin in PVA film exhibits obvious fluorescence peaking at 500 nm, with a fluorescence quantum yield of as high as 0.4 and a fluorescence lifetime of as long as 2.4 ns. Time-dependent density functional theory calculations have determined that the ESPT of neutral luteolin is barrierless but that of monodeprotonated luteolin needs to surmount a barrier, explaining their distinct emission properties. These results indicate the modulation ability of the PVA film in both ground-state deprotonation and ESPT, broadening the application areas of the solid polymer matrix.

Second Generation Zwitterionic Aza‐Diarylethene: Photoreversible CN Bond Formation, Three‐State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization

Diarylethenes are a well‐studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza‐diarylethenes have been developed in which carbon‐carbon bond connections are replaced by carbon‐nitrogen connections. This structural elaboration opens an entire new structure and property space expanding versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza‐diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High‐yielding photoswitching between the neutral open form and a zwitterionic Z isomer is achieved with two different wavelengths of light. The third zwitterionic E isomeric state can be reached up to 87% upon irradiation with a third wavelength. Its high energy content of &gt;10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza‐diarylethenes into interesting candidates for molecular solar thermal energy storage (MOST) applications. The third state further serves as locking state, allowing to toggle light‐responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA), directly harnessing the unleashed chemical reactivity of aza‐diarylethene in materials applications.

Second Generation Zwitterionic Aza-Diarylethene: Photoreversible CN Bond Formation, Three-State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization.

Diarylethenes are a well-studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza-diarylethenes have been developed in which carbon-carbon bond connections are replaced by carbon-nitrogen connections. This structural elaboration opens an entire new structure and property space expanding versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza-diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High-yielding photoswitching between the neutral open form and a zwitterionicZisomer is achieved with two different wavelengths of light. The third zwitterionicEisomeric state can be reached up to 87% upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza-diarylethenes into interesting candidates for molecular solar thermal energystorage (MOST) applications. The third state further serves as locking state, allowing to toggle light-responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA),directly harnessing the unleashed chemical reactivity of aza-diarylethene in materials applications.

Elucidating the Supramolecular Interaction of Positively Supercharged Fluorescent Protein with Anionic Phthalocyanines.

Developing bioinspired materials to convert sunlight into electricity efficiently is paramount for sustainable energy production. Fluorescent proteins are promising candidates as photoactive materials due to their high fluorescence quantum yield and absorption extinction coefficients in aqueous media. However, developing artificial bioinspired photosynthetic systems requires a detailed understanding of molecular interactions and energy transfer mechanisms in the required operating conditions. Here, the supramolecular self-assembly and photophysical properties of fluorescent proteins complexed with organic dyes are investigated in aqueous media. Supercharged mGreenLantern protein, mutated to have a charge of +22, is complexed together with anionic zinc phthalocyanines having 4 or 16 carboxylate groups. The structural characterization reveals a strong electrostatic interaction between the moieties, accompanied by partial conformational distortion of the protein structure, yet without compromising the mGreenLantern chromophore integrity as suggested by the lack of emission features related to the neutral form of the chromophore. The self-assembled biohybrid shows a total quenching of protein fluorescence, in favor of an energy transfer process from the protein to the phthalocyanine, as demonstrated by fluorescence lifetime and ultrafast transient absorption measurements. These results provide insight into the rich photophysics of fluorescent protein-dye complexes, anticipating their applicability as water-based photoactive materials.

Synthesis, Characterization and Identification of Mononuclear Transition Metals Complexes 1, 3-Bis-((5-methyl-1H-Imidazol-4-yl) Methyleneamino) Propan-2-ol Ligand

The ligand 1,3-bis-((5-methyl-1H-imidazol-4-yl)methyleneamino)propan-2-ol (H3L) derived from 1,3-diaminopropan-2-ol and 5-methyl-1H-imidazole-4-carbaldehyde has been synthetized and used to prepare five complexes in which the ligand acts in tetradentate fashion. Complexes formulated as [Mn(H3L)(H2O)2].2SCN (1), [(Co(H3L)].2SCN (2), [(Ni(H3L)].2SCN (3), [(Cu(H3L)(NO3)].(NO3).2H2O (4), and [(Zn(H3L)].2SCN (5) were synthesized by mixing an equimolar amount of an methanol solution containing the appropriate nitrate salt and KSCN, in 1:2 ratio, in the case of 1, 2, 3 and 5 and an ethanol solution containing the appropriate ligand H3L. The complex 4 has been synthetized in the absence of KSCN. In all the complexes the ligand acts in its neutral form and in tetradentate fashion, its hydroxy group remaining free and non-deprotonated. The ligand is coordinated to metal ion through two azomethine nitrogen atoms and two pyrazole sp2 nitrogen atoms. The complexes are characterized by elemental analysis, conductance and room temperature magnetic moments measurements, UV–Vis and IR spectroscopic studies. The structure of the copper(II) complex 4 is confirmed by X-ray diffraction. 4 crystallizes in the monoclinic space group P21/c with unit cell dimensions a = 8.5459 (3) Å, b = 10.9177 (3) Å, c = 22.4562 (6) Å, b = 96.954 (3)°, V = 2079.79 (11) Å3, Z = 4, R1 = 0.050 and wR2 = 0.131. The CuII cation in N4O inner is situated in a distorted square pyramidal environment.

Enzymatic synthesis of ω-3 fatty acids-based structured phospholipids: A novel solvent-free preparation approach and its catalytic mechanism

ω-3 fatty acids-based phospholipids (ω-3-PLs) exhibit higher bioavailability within organisms and stability compared to polyunsaturated fatty acids in their neutral forms. In this study, ω-3 fatty acids enriched partial acylglycerols (ω-3-AGs) were produced from hydrolysis of algal oil firstly. The effects of hydrolysis processing parameters such as enzyme type, enzyme loading, oil-water ratio, reaction temperature, and time were evaluated. Subsequently, ω-3-PLs were prepared via interesterification of ω-3-AGs with PLs catalyzed by PLA1. When monoacylglycerols (MAGs) reached 60% in partial acylglycerols, the interesterification reaction showed a marked improvement, leading to the achievement of the optimal final ω-3-PLs content of 38.93%. Using molecular docking techniques to speculate on the catalytic mechanism, the results indicate that MAGs exhibit an affinity of up to −6.33 kcal/mol with PLA1, verifying their critical role in the interesterification process.

Luminescent Mannich bases: Synthesis, crystal structures, and photophysical properties

Three Mannich bases have been obtained starting from 5-bromo-salicylaldehyde: 5-bromo-3-(((2-(dimethylamino)ethyl)(methyl)amino)methyl)-2-hydroxybenzaldehyde (TMEN), 5-bromo-3-((benzyl(methyl)amino)methyl)-2-hydroxybenzal-dehyde (MBA), 5-bromo-3-(ethyl(methyl)amino)methyl)-2-hydroxybenzaldehyde (EMA). The crystal structure of MBA has been solved. The UV-Vis absorption and emission spectra were investigated in different solvents, revealing the presence of several species, the neutral forms, the zwitterionic, the anionic and the cationic (the protonated nitrogen) ones. In order to characterize the last two species, further experiments were performed in the presence of hydrogen extracting and hydrogen donating compounds, sodium fluoride (NaF) and tetra butyl ammonium hydroxide (TBOH) to evidence the anion, and trichloroacetic acid (TCA) for the protonated cation. The experimental results were rationalized by DFT calculations of the potential energy surfaces (PES) of the S0 and S1 states and of the absorption and emission maxima.

How does the integration of amino acids enhance the bonding ability of triazine-based inhibitors with iron surfaces: Insights from SCC-DFTB, COSMO-RS and molecular dynamics simulations

Theoretical investigations into the adsorption of molecules on metal surfaces play a pivotal role in the development of more efficient corrosion inhibitors. This study offers a novel approach by combining Density Functional Tight Binding (DFTB), Molecular Dynamics (MD) simulations, and conductor-like screening model for realistic solvation (COSMO-RS) calculations to comprehensively assess the interaction and diffusion properties of glycine (Gly), 2,2′-azanediyldiacetic acid (IDA), and 5-aminopentanoic acid (5-APA) with two 1,3,5-triazine (Tris) derivatives (Tris-Gly and Tris-IDA) for corrosion protection of carbon steel in acidic medium. The solvation properties of these molecules were evaluated alongside their interaction strength with the Fe(1 1 0) surface, considering both neutral and protonated forms. DFTB simulations revealed a clear trend in interaction energies, following the order: Tris-IDA > Tris-Gly > 5-APA > IDA > Gly. It ranges from −1.191 eV to −1.853 eV, with the highest stability observed for protonated Tris-IDA (−1.853 eV), while neutral Glycine exhibits the lowest interaction energy (−1.263 eV). While these theoretical results diverged slightly from experimental observations, with Tris-Gly outperforming Tris-IDA, this discrepancy was attributed to steric effects and solvent interactions. The DFTB results also indicated strong covalent interactions, particularly involving acetic groups, between the inhibitors’ orbitals and the iron’s 3d orbitals. MD simulations further demonstrated the impact of protonation on inhibitor mobility, with reduced diffusion coefficients due to enhanced electrostatic interactions and hydrogen bonding. COSMO-RS solvation analysis confirmed the strong hydrogen bonding capabilities of these molecules with water. Overall, this study elucidates the mechanisms of corrosion inhibition by integrating multiple simulation techniques, providing key molecular insights that can guide the design of more effective corrosion inhibitors. The findings emphasize the significance of electronic interactions and molecular structure in enhancing inhibitor performance, making this a valuable contribution to corrosion science.

Język niebinarny jako wyzwanie translatorskie na przykładzie polskiego tłumaczenia powieści Bernardine Evaristo pt. Girl, Woman, Other

NON-BINARY LANGUAGE AS A TRANSLATION CHALLENGE. THE CASE OF THE POLISH TRANSLATION OF BERNARDINE EVARISTO’S NOVEL GIRL, WOMAN, OTHER Translating non-binary language has been one of the major challenges for Polish translators in recent years. At present, various strategies are employed to neutralise the binary gender opposition in Polish. Some of them fit into the existing linguistic system, while others are completely innovative. The solutions range from using gender-neutral expressions (e.g. constructions involving the noun osoba ‘a person’ modified by an adjective or participle or the use of impersonal forms) to coining special forms for non-binary persons (e.g. nouns of neuter gender). The aim of this article is to analyse the non-binary language solutions adopted by Aga Zano in her translation of Bernardine Evaristo’s novel Girl, Woman, Other. The study shows that the translator employs a number of linguistic markers of non-binariness, which, in line with her aim, reflects the linguistic reality of our time. In the case of pronouns and verbs referring to the non-binary character of Morgan, the translator uses the neuter gender. She also creates innovative neutral forms of nouns that describe this person.

The effect of perfluoroalkyl chain length and the type of acid group on PFAS adsorption from water

Widespread use of per- and polyfluoroalkyl substances (PFAS) poses significant ecological and health risks due to their non-degradability in the environment and consequent bioaccumulation in humans. In this work, we carried out a systematic computational study to unravel the effect of perfluorinated carbon chain length and the type of acid head group on the adsorption mechanism of PFAS from water. We considered the adsorption of perfluoroalkyl carboxylic acids (PFCA) and perfluoroalkyl sulfonic acids (PFSA) with chain lengths of three to eight perfluorinated carbons in hydrophobic all-silica zeolite Beta. Molecular dynamics (MD) simulations coupled with enhanced sampling calculations showed that adsorption free energies of both PFCA and PFSA decreased with increasing number of perfluorinated carbons. Calculated free energies further showed that PFCA and PFSA, which are anions in water, must overcome substantially large interfacial energy barriers to be adsorbed in hydrophobic pores. Subsequent ab initio MD simulations revealed that PFCA and PFSA gain a proton at the water–zeolite interface and are eventually adsorbed in neutral form. Breakdown of guest–host interaction energies into hydrophobic and polar components showed that hydrophobic interactions dominate PFCA adsorption whereas polar interactions are dominant in PFSA adsorption. This is due to sulfonic acid giving rise to stronger electrostatic interactions and the rearrangement of the electron density distribution in the perfluorinated carbon chain, which render the hydrophobic interactions relatively weaker. Our study reveals that a combination of adsorbents that provide optimized hydrophobic and polar interactions should be used for the capture of diverse PFAS from water.

Gossypol derivate as a green anti-corrosion agent in the aqueous phase of crude oil.

Keeping recruitment of green and cost-effective solutions for environmental challenges in view, the current work was designed to solve the problems related to metal corrosion in the aqueous phases of crude oil in chemical industries. Green materials can play an important role in protecting metals from this corrosion. Hence, the green anti-corrosion material based upon gossypol derivate is suggested to solve the above problems. The electrochemical characteristics were appraised by cyclic voltammetry, electrochemical impedance spectroscopy, potentiodynamic polarization, and electrochemical noise methods. The thermodynamics were studied by gravimetric analyses. The surface morphology was scrutinized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Density functional theory and molecular dynamic simulations were exploited in theoretical analyses. The gossypol derivate is green, non-toxic, more efficient, non-volatile, and chemically stable anti-corrosion material for gas and oil industries. Carbon steel corrosion simulated in aqueous phases of crude oil (NaCl solutions (1.0M) saturated with H2S and CO2) was maximally prohibited by forming a protective layer of binaphthalene. Its protection degree is 96.71% (at 100.0mg/L/0.107mM). The gossypol ring is a suitable core for preparing the next modification materials to protect against corrosion. The rigid adsorption progressed mainly via hydroxyl functional moieties. Compared to the inhibition behavior of the neutral form of gossypol, the optimized protonated form causes a greater inhibition.

Production and Antibacterial Activity of Atypical Siderophore from Pseudomonas sp. QCS59 Recovered from Harpachene schimperi.

Among sixty-eight pseudomonads, isolate QCS59 from the rhizosphere of H. schimperi was selected based on its siderophore level. Production was optimal in Kings B supplemented with 2% peptone and 0.5% fructose at pH 6.5 and 25 °C for 72 h. Additionally, the threshold potential of iron was found at a concentration of 10 µM. After purification, the acidified siderophore presented a maximum absorption peak of 360 nm, while the neutral form presented a maximum of 414 nm, confirming its pyoverdine (PVD) nature. Furthermore, a major peak appeared at a retention time (RT) of 27.5 min during RP-HPLC, confirming its homogeneity. Interestingly, it demonstrated effective antibacterial activity, especially against Escherichia coli ATCC 8739, with a minimum inhibitory concentration (MIC) of 6.3 µg/mL and a minimum bactericidal concentration (MBC) of 12.5 µg/mL. At ½ the MIC value, it inhibited 82.1% of well-established biofilms of Salmonella enterica. There was an increase in malondialdehyde (MDA) and antioxidative enzymes, especially catalase (CAT) in the treated bacteria because of the peroxidation of membrane lipids and oxidative stress, respectively. SEM proved cellular lysis and surface malformation in most of the treated bacteria. This study concludes that QCS59 siderophore is a promising antibacterial candidate for treating wastewater bacteria and skin pathogens.

Lactic and Acetic Acids in Sour Beers Promote Corrosion During Aluminum Beverage Can Storage

Newer sour beers are often packaged in aluminum cans, but the compatibility of sour beer and its major acids (lactic, acetic) with cans is unclear. In an initial study, commercial sour beers were packaged in cans containing one of four different liners (bisphenol A (BPA) epoxy, two BPA–non-intent (BPA-NI) epoxy, and acrylic). Corrosion, as measured by dissolved aluminum and visual degradation of the liner, was positively correlated with concentrations of lactic acid, acetic acid, and decreased pH value. After 48 wk, aluminum concentrations up to 58 mg/L were observed in one sour beer, or nearly 100-fold greater than typical dissolved aluminum concentrations in non-sour beers. Liner type did not affect corrosion. In a subsequent model sour beer study with two acrylic liners and one BPA-NI liner, molecular SO2 positively correlated with corrosion, but only at concentrations 5-fold higher than the maximum expected in sour beers. Other added components (chloride, copper, ethanol) did not affect corrosion. Addition of acetic, lactic, and phosphoric acid in varying equinormal combinations to a non-sour beer demonstrated that acetic and lactic acids (average dissolved aluminum = 2.54 mg/L following storage) promote corrosion more than phosphoric acid (average dissolved aluminum = 0.47 mg/L). Titratable acidity (TA) correlated well with corrosion, with increased dissolved aluminum observed at TA > 6 g/L as lactic acid equivalents. Organic acid corrosivity was hypothesized to relate to the proportion of acid in its neutral form, and thus these findings are relevant to producers of other beverages with high levels of organic acids.

Immobilised artificial membrane liquid chromatography vs liposome electrokinetic capillary chromatography: Suitability in drug/bio membrane partitioning studies and effectiveness in the assessment of the passage of drugs through the respiratory mucosa

This study pioneers a comparison of the application of biomimetic techniques, immobilised artificial membrane liquid chromatography (IAM LC) and liposome electrokinetic capillary chromatography (LEKC), for the prediction of pulmonary drug permeability. The pulmonary absorption profiles of 26 structurally unrelated drug-like molecules were evaluated using their IAM hydrophobicity index (CHI IAM) measured in IAM LC, and the logarithm of distribution constants (log KLEKC) derived from the LEKC experiments. Lipophilicity (phospholipids) parameters obtained from IAM LC and most LEKC analyses were linearly related to the n-octanol/water partitioning coefficients of the neutral forms (i.e., log Po/w values) to a moderate extent. However, the relationship with distribution coefficients at the experimental pH (7.4) (i.e., log D7.4) were weaker overall for IAM LC data and sigmoidal for some liposome compositions (phosphatidyl choline (PC): phosphatidyl inositol (PI) 85:15 mol% and 90:10 mol%) and concentrations (4 mM) in LEKC. This suggests that phospholipid partitioning supports both hydrophobic and electrostatic interactions occurring between ionised drugs and charged phospholipid moieties. The latter interactions are original when compared to those taking place in the more established n-octanol/water partitioning systems.A stronger correlation (R2 > 0.65) was identified between the LEKC retention parameters, and the experimental apparent lung permeability (i.e., log Papp values) as opposed to the values obtained by IAM LC. Therefore, LEKC offers unprecedented advantages over IAM LC in simulating cell membrane partitioning processes in the pulmonary delivery of drugs. Although LEKC has the advantage of more effectively simulating the electrostatic and hydrophobic forces in drug/pulmonary membrane interactions in vitro, the technique is unsuitable for analysing highly hydrophilic neutral or anionic compounds at the experimental pH. Conversely, IAM LC is useful for analysing compounds spanning a wider range of lipophilicity. Its simpler and more robust implementation, and propensity for high-throughput automation make it a favourable choice for researchers in drug development and pharmacological studies.

Antimalarial analysis of pharmaceutical formulations and biological samples by capillary electrophoresis: the state of the art and applications.

Malaria is a serious public health problem, being an endemic disease in 84 countries, mainly in Africa. This review explores the application of capillary electrophoresis (CE) techniques for analyzing antimalarial drugs, highlighting methods from 2000 to 2023 for the analysis of pharmaceutical formulations and human biological samples. The versatility, selectivity, high efficiency, cost-effectiveness, and high analytical frequency of CE techniques have become attractive choices for pharmaceutical analysis, focusing on quality control and impurity analysis applications. The evolution of achiral and chiral electromigration methods has been described based on the features of each mode of separation: capillary zone electrophoresis (CZE), micellar electrokinetic chromatography, microemulsion electrokinetic chromatography, and capillary electrochromatography. As expected, CZE is reported in most articles owing to its compatibility with drug properties and separation mode. However, it is necessary to perform other separation modes for a few drugs that are present in neutral form. After exhaustive research using different databases and statistical analyses, 27 articles using CE techniques for antimalarial drug analysis were found and are mentioned in this review.

Photophysical Response of Propranolol in Biomimetic Micellar Media of Alkyltrimethylammonium Bromide Surfactants: Effect of pH and Alkyl Chain Length.

The photophysical behavior of a β-blocker drug propranolol (PPL) in micellar environments, formed by alkyltrimethylammonium bromide surfactants viz.; Cetyltrimethylammonium bromide (CTAB), Tetradecyltrimethylammonium bromide (TTAB), and Dodecyltrimethylammonium bromide (DTAB), has been investigated through fluorescence and UV-visible spectroscopic techniques at pH levels of 3.5, 7.4, and 10.4. The impact of pH on the critical micelle concentration (cmc) and micropolarity of micelles were assessed using pyrene as a photophysical probe. The cmc values were found to be lower at pH 10.4 compared to pH 7.4 and pH 3.5. Fluorescence emission intensities of PPL at 323nm, 338nm, and 352nm were significantly influenced by pH, hydrophobic alkyl chain length of surfactants, and their concentrations. Quenching experiments with Cetylpyridinium chloride (CpCl) indicated the localization of charged and uncharged forms of PPL within micelles, with quenching constant (Ksv) values dependent on alkyl chain length and pH. At pH < pKa, PPL is positioned near the Stern layer, whereas at pH 10.4, its naphthalene moiety resides near the hydrophobic micellar core. UV spectroscopy showed that the charged form of PPL interacted with micelles only above cmc, while the neutral form interacted even below the cmc. Density Functional Theory (DFT) reveals the HOMO of the surfactants to be localized on the hydrocarbon chains, and the LUMO localized around the quaternary ammonium unit. Upon complexation with PPL, both HOMO and LUMO shifted to the drug, thereby decreasing energy levels. The findings are explained based on weak noncovalent interactions, further supported and analyzed through Reduced Density Gradient (RDG) and Noncovalent Interaction (NCI) methods, confirming synergistic non-covalent interactions in surfactant-PPL complexes.

Proton Transfer Kinetics in Histidine Side Chains Determined by pH-Dependent Multi-Nuclear NMR Relaxation.

Histidine is a key amino-acid residue in proteins with unique properties engendered by its imidazole side chain that can exist in three different states: two different neutral tautomeric forms and a protonated, positively charged one with a pKa value close to physiological pH. Commonly, two or all three states coexist and interchange rapidly, enabling histidine to act as both donor and acceptor of hydrogen bonds, coordinate metal ions, and engage in acid/base catalysis. Understanding the exchange dynamics among the three states is critical for assessing histidine's mechanistic role in catalysis, where the rate of proton exchange and interconversion among tautomers might be rate limiting for turnover. Here, we determine the exchange kinetics of histidine residues with pKa values representative of the accessible range from 5 to 9 by measuring pH-dependent 15N, 13C, and 1H transverse relaxation rate constants for 5 nuclei in each imidazole. Proton exchange between the imidazole and the solvent is mediated by hydronium ions at acidic and neutral pH, whereas hydroxide mediated exchange becomes the dominant mechanism at basic pH. Proton transfer is very fast and reaches the diffusion limit for pKa values near neutral pH. We identify a direct pathway between the two tautomeric forms, likely mediated by a bridging water molecule or, in the case of high pH, hydroxide ion. For histidines with pKa 7, we determine all rate constants (lifetimes) involving protonation over the entire pH range. Our approach should enable critical insights into enzymatic acid/base catalyzed reactions involving histidines in proteins.