L-cysteine In Solution Research Articles

Eliminating the «memory effect» during mass spectrometric determination of mercury

When estimating mercury content by inductively coupled plasma mass spectrometry (ICP-MS), this element adsorbs on the surface of the sample introduction system of the instrument, which creates problems in the determination of trace amounts of mercury. Various methods of cleaning the instrument have been proposed in the literature. Objective: to experimentally compare the effectiveness of trace mercury removal methods proposed in the literature for elemental analysis by ICP-MS and to select the optimal cleaning agent. Methods: Mercury content in solution was determined by the Agilent Technologies 7900 inductively coupled plasma mass spectrometer using 202Hg isotope. Diluted solutions of nitric and hydrochloric acids, solutions of gold chloride, potassium dichromate, thiourea, L-cysteine, potassium bromide, potassium bromate of different concentrations in water and 1% nitric and hydrochloric acids, aqueous solution of ammonium pyrrolidinedithiocarbomate were used as washing agents. Results: The background level of mercury content is achieved by using solutions of copper chloride (5%), thiourea (0.01, 0.1, and 0.5%), L-cysteine (2%), potassium bromide and bromate (0.0005 M) in 1.0% hydrochloric acid solution. The background is lowered by using 3 and 5% HCl, potassium dichromate (60 mg/liter), potassium bromide and bromate (0.01 and 0.05 M) solutions in 1% hydrochloric acid. Application of aqueous solution of ammonium pyrrolidinedithiocarbamate causes sharp degradation of plastic tubes of the sample introduction system. Conclusion: The efficiency of washing agents based on hydrochloric acid is higher than that based on nitric acid and water. The most promising washing agents are bromide-containing solutions and potassium bichromate solution in hydrochloric acid. The optimal way to clean the device is its washing with 0.5 mM potassium bromide solution in 1.0% hydrochloric acid. Its use allows to reduce the background content of mercury and does not complicate the analysis of the content of other elements.

Simultaneous Electrodeposition of Gold Nanoparticles and Electropolymerization of L-Cysteine through Paper-Based Microfluidic Sensor

Introduction Using catalytic active modifiers and additives e.g. to improve electron or ion transport in electrochemical sensors usually offers significant benefits by improving sensitivity and selectivity. An elegant way to introduce both is electrodeposition and electropolymerization. Examples are known, where through these methods enhanced catalytic activity, stability, reproducibility, and active surface area could be achieved [1,2]. Paper-based microfluidic electrochemical sensors (μCS) have gained significant attention due to their simplicity, portability, cost-effectiveness, and potential for point-of-care applications. Although electrodeposition of AuNPs and electropolymerization of (L-cysteine) have been widely studied in static voltammetry using glassy carbon electrodes or screen-printed carbon-based electrodes (SPCE), their application by the microfluidic systems has been limited, and based on our knowledge, no report has been done on electrodeposition and electropolymerization through a μCS.In this work, we show the electrodeposition of AuNPs and electropolymerization of (L-cysteine) onto the electrodes of paper-based microfluidic electrochemical sensor, while using the microfluidic channel also for transport of the electrodeposition solution. Experimental The alignment of the component for the μCS device is sketched in Scheme 1. After providing the HAuCl4 and L-cysteine solution through the sponge the electrochemical fabrication and detection are carried out through cyclic voltammetry (CV). AuNPs were electrodeposited and L-cysteine were electropolymerized simultaneously through the μCS by handling a potential window of −1.5 to +2.2 V at a scan rate of 100 mV/s for 10 cycles in a solution of 0.1 M PBS at pH = 5.5 consists of 1.0 mM HAuCl4 and 1.0 mM L-cysteine. Scanning electron microscope (SEM), CV, and electrochemical impedance spectroscopy (EIS) were employed to certify that the AuNPs and poly (L-cysteine) were attached successfully to the working electrode surface. Results and discussion CVs of the platforms were recorded in the redox probe solution consisting of 5.0 mM of [Fe(CN)6]3−/4−. By modifying the platforms by simultaneous electrodeposition of AuNPs and electropolymerization of (L-cysteine) not only did peak currents increase dramatically but also ΔEp were decreased to 17 mV and 13 mV for SPCE/S (ED & EP) and μCS/S (ED & EP), respectively. This decrement behavior indicating the presence of AuNPs, and poly (L-cysteine) enhances the reversible nature of the electrochemical reaction.By comparing the Nyquist plots related to the bare SPCE and μCS it is clear that the Rct value for μCS (46 Ω) is much lower than SPCE (690 Ω) It may be attributed to the 3D and sandwich-like structure of μCS devices. SPCE/S (ED & EP) and μCS/S (ED & EP) present very smaller semicircles with Rct values of 225 Ω and 13 Ω, respectively. This remarkable increase in the current and substantial decrease in resistance of the modified platforms at first confirms which AuNPs and poly (L-cysteine) were successfully achieved onto the WE surface. Interestingly, the simultaneous deposition of AuNPs and poly (L-cysteine) by using μCS shows the lowest Rct and could be a highly interesting sensing electrode.To ensure the performance of both simultaneous electrodeoposition of AuNPs and electropolymerization of (L-cysteine) and μCS in the enhancement of the surface area, accordingly, the calculated A of the SPCE/S (ED & EP) and μCS/S (ED & EP) were estimated to be 0.09 cm2 and 1.14 cm2, respectively. In comparison with the A value of the bare SPCE (0.06 cm2) and μCS, (0.31 cm2) these increases are 1.5 times for the SPCE and 3.6 times for the μCS. Conclusion The μCS/S (ED & EP) offers several core advantages over SPCE/S (ED & EP) in terms of cost, simplicity, and sensitivity. These unique advantages are due to the combined microfluidic configuration, 3D electrode layout, and a unique electrochemical modifier. According to the SEM results, the images corroborated that the simultaneous synthesis of nanocomposite on the working electrode surface is carried out successfully. This strategy can assist as the proper way to boost the surface area of the sensor. We believe our findings would have significant implications in developing other portable, fast, and cost-effective electrochemical detection platforms, such as clinical diagnosis and security inspection. References Mei, Xue, et al. "A novel electrochemical sensor based on gold nanobipyramids and poly-l-cysteine for the sensitive determination of trilobatin." Analyst 148.10 (2023): 2335-2342.Ghanbari, Mohammad Hossein, et al. "Simultaneous electrochemical detection of uric acid and xanthine based on electrodeposited B, N co-doped reduced graphene oxide, gold nanoparticles and electropolymerized poly (L-cysteine) gradually modified electrode platform." Microchemical Journal 175 (2022): 107213.Bard, Allen J., Larry R. Faulkner, and Henry S. White. Electrochemical methods: fundamentals and applications. John Wiley & Sons, 2022. Figure 1

Electrochemical and Spectroscopic Investigations of Bismuth(III) Pharmaceuticals with L-Glutathione

Due to the importance of L-cysteine in the human system, the interaction of metals with this amino acid are worthy of investigation by various methods. In this laboratory1, we have investigated the interaction of bismuth(III) compounds with L-cysteine by both cyclic voltammetry and UV-VIS spectroscopy in an attempt to understand the role of bismuth in treating gastrointestinal maladies.2 The addition of bismuth(III) compounds to solutions of L-cysteine causes a negative potential shift for bismuth(III) reduction as an indication of complex formation between bismuth(III) and L-cysteine. This interaction is also evident by the appearance of a UV-VIS spectroscopic band at 340 nm (Bi-sulfur bond). Even at low pH values (pH 1.0), electrochemical studies show evidence of some kind of interaction even when there is no 340 nm band. These investigations have been conducted at pH 1.00 and 3.00 to simulate conditions in the human stomach and at pH 7.40 MOPS [(3-N-morpholino)propanesulfonic acid] to simulate general physiological conditions, in particular the intestinal tract. Recent work has involved extension of this work to L-glutathione, a tripeptide incorporating L-cysteine, under similar conditions. As might be expected, these interactions are considerably more complicated than those involving L-cysteine. As an example, there is a considerable positive potential shift for the reduction of bismuth(III) citrate in the presence of L-glutathione on the first and second voltammetric sweeps at gold and glassy carbon electrodes. This behavior evidently reflects the rather long (several seconds) time required for the re-formation of the bismuth complex with L-glutathione after its reductive ligand (L-glutathione) loss during bismuth(III) reduction on the first sweep. In addition, there is evidence of a film buildup on the electrode surface as observed by peak current increases during multiple potential sweeps. These observations are planned for inclusion in this symposium presentation.References T. Cheek and D. Peña, J. Electrochem. Soc., 167, 155522 (2020)Li, R. Wang, and H. Sun, Acc. Chem. Res., 52, 216 (2019).

Synthesis of BiDy composite oxide nanoflakes with good electrochemical properties

Bismuth dysprosium (BiDy) composite oxide nanoflakes with a thickness of about 50 nm were synthesized using a one-step hydrothermal method. Electrodes modified with BiDy composite oxide nanoflakes exhibited a superior electrochemical behavior for detecting l-cysteine using the cyclic voltammetry (CV) method. The impacts of scan rate, electrolyte and concentration of l-cysteine on electrochemical behaviors were investigated. A pair of strong quasi-reversible CV peaks was observed at +0.03 V (cvp1) and −0.69 V (cvp1′) with peak currents of 171.2 and 171.3 μA, respectively, for a BiDy-composite-oxide-nanoflake-modified glassy carbon electrode (GCE) in 0.1 M potassium chloride (KCl) and 2 mM l-cysteine solution. The GCE modified with BiDy composite oxide nanoflakes displayed a broad range of linearity (0.001–2 mM) and a low detection limit (0.29 μM) for l-cysteine. Using a hydrothermal approach as a synthesis technique for nanoflakes, a facile and sensitive electrochemical sensor based on nanoflakes was developed for detecting l-cysteine, making it a promising approach for practical application.

Determination of methylmercury in urine by direct mercury analyzer

Objective: To develop asolvent extraction-direct mercury analyzer method for determination of methylmercury in urine. Methods: After the urinehydrolyzesd by hydrobromic acid, methylmercury was extracted by tolueneand reverse-extracted from L-cysteine solution, it was then detectedbydirect mercuryanalyzer. Results: The linear range was 0.2-50.0 μg/L, and the related coefficient was 0.9999. The relative standard deviations (RSD) within the group were 5.04%-6.64%, and the RSD between the group were 5.65%-8.11 %. The average recovery efficiencies were 85.4%-95.5%. The detection limitation was 0.0482 μg/L and the quantification concentrations was 0.1607 μg/L. Conclusion: The method, which has low detection limit, high sensitivity, easy to operate, is stability for the determination of methylmercury in urine.

Melatonin reduces pink rib discoloration in wounded lettuce midribs

Pink rib discoloration is a physiological disorder resulting in loss of quality and marketability of minimally processed and whole head lettuce (Lactuca sativa L.). Although the biochemistry of pink rib is complex and a comprehensive understanding is lacking, multiple research efforts have focused on inhibiting or reducing pink rib through exogenous application of small molecules such as L-cysteine. In this study, the effects of naturally occurring phytochemicals [serotonin (0.5 or 1 g L−1), naringenin (0.5 g L−1), L-cysteine (0.5 g L−1), and melatonin (1 g L−1)] on pink rib expression were examined in iceberg and Romaine lettuce. The exogenous application of these natural compounds was investigated for reduced pink rib discoloration in lettuce during simulated commercial storage and examined for metabolite and enzymatic activity changes. Immersing wounded midribs for 30 s in serotonin, naringenin, or L-cysteine solutions had no or only a slight inhibitory effect to inhibit pink rib discoloration while those immersed in a melatonin solution had reduced development of pink rib in both iceberg and Romaine lettuces after 5 d at 5 °C. Phenylalanine ammonia lyase (PAL) activity and chlorogenic acid concentration increased upon pink rib discoloration, consistent with previous reports. However, melatonin-treated samples did not result in reduced PAL activity, chlorogenic acid content, or polyphenol oxidase (PPO) activity. Untargeted metabolite analysis showed that melatonin treatment resulted in a global effect on metabolite changes in the wounded lettuce midrib tissue. To compare the severity of pink rib among treatments, pink rib was quantified throughout storage visually and by converting digital images of the lettuce midribs to the L*a*b* color space. The a* component of L*a*b* represents redness versus greenness, thus its values were used to objectively measure pink rib severity. Melatonin was shown to be a promising compound to minimize development of pink rib discoloration at cut surfaces of iceberg and Romaine lettuce during commercial handling and storage.

Effect of dispersed phase concentration on gelation and formation of silver nanoparticles in aqueous solutions of l-cysteine and silver nitrite

Effect of dispersed phase concentration on gelation and formation of silver nanoparticles in aqueous solutions of l-cysteine and silver nitrite

Characterization of particles of the dispersed system based on low-concentrated aqueous solutions of L-cysteine and silver acetate

The authors of this work conducting a study of the precursor of reference materials of the zeta potential of particles in dispersed systems. The precursor is based on supramolecular solution of L-cysteine and silver acetate (CSSac). Particles and aggregates of CSSac were studied by dynamic light scattering (DLS), phase analysis of scattered radiation (PALS), inductively coupled plasma mass spectrometry (ICP-MS) and high-resolution transmission electron microscopy (HR-TEM). It was established that the diameter of the potential-determining aggregates of the CSSac is in the range from 20 nm to 100 nm. These aggregates consist of nanoparticles up to 10 nm in diameter.

Case–control study related to the use of L-cysteine in the differential diagnosis of oral halitosis

Oral halitosis is characterized by a foul, unpleasant breath that emanates from the oral cavity due to local or systemic conditions. Approximately 90% of offensive odors are caused by volatile sulfur compounds (VSCs). L-cysteine, used as a test solution to control bad breath, induces the formation of VSCs and serves as a preliminary rinse. The study aim was to investigate the effectiveness of L-cysteine solution in differentiating the origin of oral halitosis using a gas chromatography apparatus. Methods: In total, 37 patients with an average age of 49.56 years were evaluated and divided into two groups: halimetry before the use of L-cysteine (n = 37) and halimetry after the use of L-cysteine (n = 37). Patients over 18 years of age, without severe systemic health impairment or infectious/contagious diseases, and who did not use medicines that influenced their breath were included. Halimetry was performed using the OralCroma™ device. In the halimetry before the use of L-cysteine group, 5.40%, 5.40%, and 64.86% of the patients had high levels of sulfide, methyl mercaptan, and dimethyl sulfide, respectively. After the use of L-cysteine, 48.64%, 8.10%, and 37.84% of the patients had high levels of sulfide, methyl mercaptan, and dimethyl sulfide. In this study, L-cysteine proved to be important for the assessment of oral halitosis and effective in differentiating the origin of oral halitosis; therefore, this compound could be used for the differential diagnosis of oral halitosis origin using the OralChroma™ device.

ANALYSIS OF THE PRODUCTS OF THE L-CYSTEINE REACTION WITH Fe(III) COMPOUNDS IN AN ACIDIC MEDIUM

The interaction of the L-cysteine solution with iron(III) compounds of FeCl3, Fe2(SO4)3, Fe(NO3)3 was studied in an acidic medium (pH 2). It was shown that the reaction proceeded 30 minutes with the formation of L-cystine (21–40%) as the main product. It was found that the L-cysteine reaction with FeCl3 leads to the formation of the L-cysteine sulfinic acid in the solution as a by-product. The products of the L-cysteine reaction
 with Fe(III) compounds were interpreted by IR and NMR spectroscopy.

A hydrophobic layer of amino acid enabling dendrite-free Zn anodes for aqueous zinc-ion batteries

The zincl-cysteine functional layer was constructed byin situetching Zn anode in 1 Ml-cysteine solution. This functional layer not only improves the hydrophobicity and corrosion resistance of zinc anode, but also guides uniform zinc deposition.

Synthesis, predictions of drug-likeness, and pharmacokinetic properties of some chiral thioureas as potent enzyme inhibition agents.

A series of chiral thioureas (1 - 17) were synthesized from and tested for their anticholinesterase, tyrosinase, and urease enzyme inhibitor activities. Various phenylisothiocyanates were added to solution of l-cysteine in methanol: water (1 : 1 v/v) at room temperature and stirred for 24 h. The precipitated solid was recrystallized from n-butanol. Pure compounds were characterized by NMR (1H and 13C), FTIR, and CHNS. Tertiary amine containing N-(4-(diethylamino)phenyl)-N'-(2-mercapto-carboxyethanyl)thiourea 17, N-(4-(dimethylamino)phenyl)-N'-(2-mercapto-carboxyethanyl)thiourea 16 and trimethoxy containing N-(3,4,5-trimethoxyphenyl)-N'-(2-mercapto-carboxyethanyl)thiourea 14 were more active than galantamine against AChE and BChE enzymes. In tyrosinase enzyme inhibition activity, compound 14, 10, 12, 6, 13, and 11 exhibited higher tyrosinase inhibitory activity showing IC50 values of 1.1 ± 0.1, 1.5 ± 0.3, 1.6 ± 0.6, 1.9 ± 0.5, 2.2 ± 0.9 and 2.9 ± 0.2 mM, respectively. In urease enzyme inhibition activity assay, 17 showed higher activity. This work demonstrates the pharmacological significance of chiral thiourea derivatives synthesized from l-cysteine and shows their potential. There is a need to perform more in vitro and in vivo biological activities followed by clinical trials to bring such thiourea to the market.

Antimicrobial Preparations Based on L-Cysteine, Silver Acetate, and PHMG-HC for Impregnation of Chemical Fibers and Textiles

Hydrogels prepared from L-cysteine, silver acetate, and polyhexamethyleneguanidine hydrochloride (PHMG-HC) were used in rheological, structural, and antibacterial studies. Aqueous solutions of Lcysteine and silver acetate were found to be very miscible with aqueous solutions of PHMG-HC to form transparent hydrogels. A model for the three-dimensional structure of the gel network was proposed. The hydrogel exhibited high antimicrobial activity against test cultures of pathogenic and conditionally pathogenic microorganisms.

Cysteine challenge test as a novel diagnostic tool to distinguish oral halitosis.

The cysteine challenge test is often used to check the H2 S production capacity of the mouth. Patients with oral halitosis group (n = 305) or non-oral halitosis group (n = 191) and healthy individuals (control group, n = 102) were compared with each other to identify any possible relationship between initial and cysteine-induced oral H2 S concentrations. The medical records of 598 participants were reviewed retrospectively. Oral H2 S concentrations before (pre-CR) and after cysteine rinse (post-CR) with 5 mL of 20 mmol L-cysteine solution for 30 s were compared. Pre-CR H2 S concentrations were >0.8 ppm in 75.1% of oral group patients but less than <0.8 ppm in 87.3% of the non-oral group and 86.9% of controls. After cysteine rinse, oral H2 S concentrations exceeded 12 ppm in 72% of the oral halitosis patients but were lower in 88% of non-oral group and 99% of controls. Whilst post-CR/pre-CR ratio was >12 in 74.5% of the oral group, it was <12 in 81.7% of the non-oral group and 83.4% of controls. Cysteine challenge test can be used as a diagnostic tool to identify an individual's tendency to produce oral malodor, not only to quantify momentary halitosis level.

Гелеобразование в низкоконцентрированных растворах глицирама и аминокислот в присутствии нитрата серебра

Research relevance: low molecular weight supramolecular hydrogels are unique objects that can solve many pressing problems in medicine, food industry and other sectors of the national economy. Research objectives: in recent past, it was discovered that low-concentration solutions of L-cysteine and silver nitrate (CSN) can form, when electrolyte solutions are added to hydrogels. We were faced with the task of obtaining hydrogels from dilute solutions of glycyram (GC) by adding CSN, since GC, due to its poor solubility, has low bioavailability. Materials and research methods: using the method of isomolar series, a comparative study of the formation of hydrogels by dilute GC solutions with the addition of CSN and GCP was carried out. It has been found that most durable hydrogels were obtained using CSN. Thus, GC hydrogels were obtained at a concentration of 10−3 M after adding CSN and GCP, which have a supramolecular character and combine the properties of GC, amino acids, and silver ions. Research results: glycyram hydrogels were obtained at its concentration equal to 10−3 M by mixing it with silver amino acids L-cysteine (CSN) and L-glutamic acid (GCP) solutions in same low concentrations. Conclusions: hydrogels with glycyram form silver solutions of those amino acids that are capable of giving frame structures at a ratio of amino acid: silver nitrate of 1.25.

Facile Green Synthesis of Reduced Graphene Oxide in L-cysteine Solution and its Structural, Morphological, Optical and Thermal Characteristics

The current research reports a cost-effective, efficient ad green reducing agent (L-cysteine) to reduce the graphene oxide (GO) for large-scale reduced graphene oxide (rGO) synthesis. Fabrication of rGO was performed by the reduction of GO using different concentrations from L-cysteine. Synthesis of rGO was noticed by change in color of GO solution from brown to black. For additional confirmation, the structural, morphological, optical and thermal properties of synthesized rGO were analyzed using powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), energy dispersive X-ray Spectroscopy (EDX) atomic force microscopy (AFM), thermogravimetric analysis (TGA) and ultraviolet-visible spectrophotometer (UV-Vis). The XRD, FTIR and EDS results showed the oxygen-containing groups such as hydroxyl, carbonyl, and epoxy. The UV-Vis spectrum for GO exhibited an absorbance peak at 233 nm which undergoes a red shift of the absorbance peak to 265, 273 and 278 nm due to reduction of GO to rGO using 5, 8 and 10 mg/L of L-cysteine respectively. XRD patterns demonstrated the disappearance of the characteristics peak of GO (11.1) and reinforced this appearance of peak around ~26, indicating the efficient reduction of GO and restoration of graphene sp2 hybridized structure. Furthermore, FTIR spectroscopy showed the gradual disappearance of band at 1745 cm-1 assigned to GO as L-cysteine concentration was increased. The thermal stability of the GO was much lower than those of all the rGO powders where the increased concentration of L-cysteine resulted in enhanced more thermal stability and higher C/O ratio in rGO. The SEM images confirmed the successful structurally exfoliation of two dimensional rGO sheets and showed the folded, curled and flake-like morphology of the graphene nanosheets.

Facile Synthesis of L-Cysteine Functionalized Graphene Quantum Dots as a Bioimaging and Photosensitive Agent.

Nowadays, a larger number of aggressive and corrosive chemical reagents as well as toxic solvents are used to achieve structural modification and cleaning of the final products. These lead to the production of residual, waste chemicals, which are often reactive, cancerogenic, and toxic to the environment. This study shows a new approach to the modification of graphene quantum dots (GQDs) using gamma irradiation where the usage of reagents was avoided. We achieved the incorporation of S and N atoms in the GQD structure by selecting an aqueous solution of L-cysteine as an irradiation medium. GQDs were exposed to gamma-irradiation at doses of 25, 50 and 200 kGy. After irradiation, the optical, structural, and morphological properties, as well as the possibility of their use as an agent in bioimaging and photodynamic therapy, were studied. We measured an enhanced quantum yield of photoluminescence with the highest dose of 25 kGy (21.60%). Both S- and N-functional groups were detected in all gamma-irradiated GQDs: amino, amide, thiol, and thione. Spin trap electron paramagnetic resonance showed that GQDs irradiated with 25 kGy can generate singlet oxygen upon illumination. Bioimaging on HeLa cells showed the best visibility for cells treated with GQDs irradiated with 25 kGy, while cytotoxicity was not detected after treatment of HeLa cells with gamma-irradiated GQDs.

Reactive oxygen species formation in thiols solution mediated by pyrogenic carbon under aerobic conditions

Previous studies have demonstrated that pyrogenic carbon can mediate the reductive degradation of pollutants in solutions containing reducing reagents under anaerobic conditions. However, few studies have investigated oxidative species formation and pollutants transformation directly mediated by pyrogenic carbon under aerobic conditions. In this study, we found that activated carbon (AC) can not only mediate reductive hexachloroethane degradation in the absence of O2 but also mediate the oxidation of As(III) and sulfanilamide in L-Cysteine (Cys, a naturally abundant thiol compound) solution under aerobic conditions. Electron paramagnetic resonance and quenching studies indicated that O2•−, H2O2 and •OH was formed in Cys/AC system under aerobic conditions. High O2 content favored the formation of •OH, indicating that O2 participated in •OH production. In addition, an increase in AC concentration and specific surface area led to increased formation of •OH, and other pyrogenic carbon materials such as biochar and graphite were also found capable of mediating the formation of •OH. This study demonstrates that pyrogenic carbon could mediate •OH formation in solutions containing reductive reagents under aerobic conditions, which provides a new perspective for studying the behavior of pyrogenic carbon in the environment and its role in biogeochemical processes.

Efficacy of Arabic Coffee and Black Tea in Reducing Halitosis: A Randomized, Double-Blind, Controlled, Crossover Clinical Trial.

The aim of the study was to objectively evaluate the short-term effect of Arabic coffee and black tea on oral halitosis. This study was a single-center, randomized, double-blind, placebo-controlled, crossover clinical trial on 17 healthy individuals. During the initial visit, pre-treatment breath samples were collected from each subject and analyzed using portable gas chromatography (OralChroma™). Four interventions were evaluated, with Arabic coffee and black tea as the test intervention tools, mouthwash containing a solution (0.05% chlorhexidine, 0.05% cetylpyridinium chloride, and 0.14% zinc lactate (CHX-CPC-Zn)) as a positive control, and drinking water as a negative control. Halitosis was induced by rinsing with 10 mL solution of L-cysteine for 30 s. Twenty minutes later, a breath sample was taken to record the baseline volatile sulfur compounds (VSC) levels (T0). Then, the participants were asked to rinse with 10 mL of a randomly-assigned solution for 30 s. Sixty minutes later, another breath sample was recorded (T1). Finally, after 120 min, the final breath sample was recorded (T2). It was found that rinsing with Arabic coffee decreased the level of H2S both in the first hour (T1) and the second hour (T2). The reduction was significantly greater at T1 (p = 0.017). There was a similar result after the volunteers rinsed with black tea. At T2, Arabic coffee showed a substantially greater reduction in H2S (p < 0.001). On the contrary, using CHX-CPC-Zn showed a significant and continuous decrease in H2S values in the breath throughout the experiment (p < 0.001). Water showed no significant impact on the level of VSC (p = 0.71). This study demonstrates that black tea and Arabic coffee had inhibitory effects on halitosis that was greater in the first hour and was not sustained over a long period. Additionally, Arabic coffee had a greater inhibitory effect on halitosis than black tea.

Development and creation of zeta potential reference material of the particles in a liquid medium

A comprehensive study to develop and create standard samples of the zeta potential unit of particles in a liquid in accordance with the requirements of GOST ISO 13099-2-2016 in the range of measured values from minus 150 mV to plus 150 mV was carried out. The existing standard samples of zeta potential in Russia and the world have been investigated; the analysis of the applicability of the starting materials and components for the creation of new standard samples has done. Samples based on modified polystyrene latex microspheres, bovine serum albumin and supramolecular systems based on aqueous solutions of L-cysteine, N-acetylcysteine, and silver acetate were considered as promising standard samples of the zeta potential of particles. All studies were carried out on equipment from the State Primary Standard of Dispersed Parameters of Aerosols, Suspensions and Powder Materials GET 163-2020 using the method of electrophoretic light scattering and measuring the pH value. It was found that polystyrene latex microspheres do not correspond to the requirements of the work in terms of developing a set of standard samples. Samples based on suspensions of bovine serum albumin do not correspond to the requirements of GOST ISO 13099-2-2016. Supramolecular systems based on aqueous solutions of L-cysteine, N-acetylcysteine, and silver acetate were proposed as standard samples. Such systems are characterized by the ability to modify the initial potential-determining layer of particles without changing their aggregate stability. Studies of the long-term stability of the developed standard samples of the zeta-potential unit of particles in a liquid have been carried out.