Buffers in Education. I. Measuring the pH and the Fundamentals of Buffer Theory

Puferi su važni za mjerenje i održavanje vrijednosti pH koje je ključno u mnogobrojnim svakodnevnim znanstvenim i industrijskim djelatnostima. Stoga, cilj ovoga teksta je razjasniti fizikalno-kemijske parametre na kojima počivaju puferi. Obrađeno je kako se i zašto provodi umjeravanje članka za mjerenje pH. Navedeno je koji se problemi mogu pojaviti tijekom mjerenja pH i kako te probleme riješiti. Rad se bavi primjenom stečenog znanja u nastavi, kao i njihovom provjerom kroz primjere i računske zadatke. Navedenim praktičnim primjerima olakšano je usvajanje temeljnih pojmova vezanih uz pH i pufere. Tako je obrađeno kako pravilno definirati pH, što je Henderson-Hasselbalchova jednadžba i koja su joj ograničenja, kako vizualno provjeriti djelovanje pufera, koja je povezanost Le Chatelirova načela i pufera, o čemu treba voditi računa prilikom mjerenja pH. Među ostalim, navedena je i važnost utjecaja temperature kod umjeravanja pH-članka, mjerenja pH uzorka, ali i iskazivanja vrijednosti pH. Na kraju, navedeno je kako unaprijediti stečena znanja i vještine kroz pitanja povezana s vrijednostima pH i puferima. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.Buffers are of high importance for pH measurement and control, which is crucial in many everyday scientific and industrial activities. The aim of this article was to elucidate the physicochemical parameters of buffers. Explained are the process and background of pH electrode calibration, as are described the problems that may arise in pH measurement, and their solutions. The focus of this article is the application and assessment of this knowledge in education through examples and numerical problems. The practical examples facilitate the learning of basic concepts related to pH and buffers. We clarify the correct definition of pH value, the Henderson-Hasselbalch equation and its limitations, the use of visual indicators with buffers, the connection between Le Chatelier’s principle and buffers, and what is important in pH measurement. A special mention is given to the influence of temperature in pH electrode calibration, pH measurement, and expressing the pH value. Finally, we suggest how to further improve the students’ knowledge and skills through questions on problems related to pH value and buffers. This work is licensed under a Creative Commons Attribution 4.0 International License

Chemistry in Education: Buffers in Education. II. Preparation and Use

U ovom tekstu razmatra se kako odabrati pufer ovisno o svrsi i kako ga pripraviti, pri čemu je navedeno nekoliko načina pripremanja puferskih otopina. Uz naglašeno nužno razumijevanje konstanti disocijacije kiselina, čitateljima se nastoji približiti ispravan način pripremanja željenih puferskih otopina. To se ponajprije odnosi na uzimanje u obzir svih faktora koji mogu utjecati na neki puferski sustav. U tekstu se zato obrađuju važni pojmovi i povezuju s njihovim primjenama u znanstvenom i inženjerskom svijetu. Također, pojašnjava se pojam kapaciteta pufera i njegova uloga, pojam ionske jakosti te na što ona utječe. Navedena su bitna svojstva koja pufer treba imati te kako produljiti trajanje puferskih otopina. Na kraju se može provjeriti što su zapravo puferi te su dani zadatci s ciljem samostalne provjere usvojenosti rješavanja računskih zadataka. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.The text discusses how to choose buffers depending on the purpose, and how to prepare them in several ways. With the necessary understanding of acid dissociation constants and buffer mechanisms, it is meant to give the readers the correct approach when preparing desired buffer solutions by taking into account all factors that may affect the buffer system. Therefore, the text covers important concepts, and links them with their applications in the world of science and engineering. It also explains buffer capacity and its role, as well as the concept of ionic strength and how it affects the pH. At the end, explanations of buffers are summarized and some numerical problems are given to enable self-evaluation of the comprehension of the given subject. This work is licensed under a Creative Commons Attribution 4.0 International License

The extraction efficiency of maceration, UAE and MSPD in the extraction of pyrethrins from Dalmatian pyrethrum

Dalmatian pyrethrum (Tanacetum cinerariifolium /Trevir./ Sch. Bip.) synthesizes secondary metabolite pyrethrin, known for its potent insecticidal and repellent activity. The present study was aimed at optimizing the maceration extraction parameters that improve the efficiency of pyrethrin extraction from the dried Dalmatian pyrethrum flower heads. Extraction efficiencies under several conditions were investigated: different solvent types, extraction time, the rotational speed of the stirrer, and the solvent volume. The highest recovery values were obtained with 5 mL of acetone, at the rotational speed of 400 rpm, and the extraction time of three hours. In addition, the extraction efficiency of maceration was compared to that of ultrasound-assisted and matrix solid phase dispersion extraction, both previously optimized for pyrethrin extraction. The extractions were carried out on samples of three natural Dalmatian pyrethrum populations (Krk, Mt. Kozjak, and Senj). Both the total pyrethrin content and the HPLC profile varied between different extraction techniques. Across applied methods, the highest efficiency was observed with matrix solid phase dispersion extraction. Evaluation of the differences between data obtained using different extraction techniques was performed by the Bland-Altman analysis, revealing good agreement between the three methods

The contribution of abiotic elimination processes to the fate of pharmaceuticals in the aquatic environment

Abiotički procesi mogu značajno doprinijeti manjoj postojanosti farmaceutika u površinskim vodama. Sukladno tome, unutar doktorske disertacije istražen je utjecaj abiotičkih procesa na razgradnju farmaceutika hidroksiklorokina i metoklopramida u vodenom okolišu uporabom optimirane i validirane kromatografske metode, HPLC-PDA i HPLC-MS/MS. Ispitana je hidrolitička stabilnost, pri čemu je ustanovljeno kako su oba farmaceutika otporna na hidrolitičku razgradnju. Također, razvijene metode primijenjene su za praćenje fotolitičke razgradnje hidroksiklorokina i metoklopramida pod utjecajem umjetnog Sunčeva zračenja. Ispitana je fotolitička razgradnja u destiliranoj deioniziranoj vodi te prirodnim i sintetskim otpadnim vodama. Rezultati su pokazali kako je izravna fotoliza odgovorna za razgradnju obaju farmaceutika i kako je posebno značajna u slučaju metoklopramida. Neizravna fotoliza značajno je utjecala na vrijeme poluraspada hidroksiklorokina u riječnoj, izvorskoj i morskoj vodi. Značajno različita vremena poluraspada, pod utjecajem ksenonske svjetiljke (500 W m^−2), dobivena su pri različitim vrijednostima pH. Najbrža razgradnja uočena je pri pH = 9 (1/2 = 0,09 h), a najsporija pri pH = 4 (1/2 = 23,1 h). I u slučaju metoklopramida (250 W m^−2) vrijednost pH utjecala je na brzinu razgradnje, ali je vrijeme poluraspada u području pH relevantnom za vode u okolišu bilo kraće od 10 minuta. Ispitivanjem utjecaja sastojaka prirodnih voda (nitrata, huminskih kiselina, klorida, bromida, sulfata, hidrogenkarbonata i željezovih(III) iona), utvrđeno je da nastankom hidroksilnih radikala dolazi do ubrzane razgradnje hidroksiklorokina. Drugi utjecaji, poput djelovanja određenih sastojaka vode kao hvatača radikala i zasjenjenja svjetlosti, manje su izraženi. U slučaju metoklopramida, neizravna fotoliza usporava razgradnju, jer prisutne tvari u prirodnim vodama (huminske kiseline, nitrati i dr.) također apsorbiraju svjetlo. U svim slučajevima kinetika je slijedila reakciju pseudo-prvog reda, osim za fotolitičku razgradnju metoklopramida u morskoj vodi, čija kinetika razgradnje odgovara dvoeksponencijalnoj funkciji (brzini razgradnje u dva stupnja). Sastav matice (velika koncentracija kloridnih iona) uzrokovao je sporiju fotolitičku razgradnju metoklopramida u morskoj vodi. Spektroradiometrijski su određeni kvantni prinosi razgradnje obaju farmaceutika i ovisili su o vrijednosti pH, odnosno udjelu pojedine specije farmaceutika. Kvantni prinosi razgradnje hidroksiklorokina za vrijednosti pH od 4 do 9 iznosili su (2,64 – 453,49) · 10^−4, te za metoklopramid (35,83 – 22,98) · 10^−4 za raspon vrijednosti pH od 4 do 11. Budući da abiotičkim procesima mogu nastati razgradni produkti toksičniji od početnog spoja, ispitana je toksičnost prema bakteriji Vibrio fischeri i genotoksičnost prema Salmonella typhimurium uporabom SOS/umu-c testa. Oba farmaceutika, kao i njihovi fotolitički produkti nisu toksični, prema navedenim testnim vrstama. Iznimka su smjese fotolitičkih produkata hidroksiklorokina za koje je 30 minutni test pokazao inhibiciju luminiscencije bakterije Vibrio fischeri (do 27 %). Nadalje, identificirano je nekoliko, do sada nepoznatih, razgradnih produkata za oba farmaceutika te su predloženi putovi razgradnje. Razgradni produkti nastali su kao rezultat hidroksilacije aromatskog prstena i dealkilacije na bočnom amino-ogranku. U slučaju metoklopramida uočeno je i fotodekloriranje, a u morskoj vodi i nukleofilna supstitucija atoma klora bromom. Na temelju provedenih istraživanja može se zaključiti kako fotoliza može značajno doprinijeti razgradnji obaju farmaceutika u okolišu.Abiotic processes can contribute considerably to degradation routes of pharmaceuticals in the environment. This doctoral thesis explores the role of abiotic processes in the degradation of hydroxychloroquine and metoclopramide in natural aquatic environments. Development and validation of appropriate chromatographic methods for their detection, as well as tests confirming their hydrolytic stability were performed. The developed chromatographic methods (HPLC-PDA and HPLC-MS/MS) were used to monitor the photolytic degradation of hydroxychloroquine and metoclopramide in different water matrices (distilled deionised water, natural waterbodies and different samples of synthetic wastewater) under the effect of simulated solar radiation. The results showed that direct photolysis is responsible for the degradation of both pharmaceuticals, showing a larger contribution for metoclopramide. Indirect photolytic degradation of hydroxychloroquine in rivers, water springs, and seawater significantly affects its half-life. Largely different half-lives under the influence of a Xe lamp (500 W m^−2) were obtained for different pH values, commonly found in the aquatic environment. The fastest degradation was observed at pH = 9 (1/2 = 0.09 h) and the slowest at pH = 4 (1/2 = 23.1 h). In the case of metoclopramide at 250 W m^−2, the pH also affected the rate of degradation, but the half-life for pH = 9 was less than 10 min. Examination of the influence of natural water constituents (nitrates, humic acids, chlorides, bromides, sulfates, bicarbonates, and ferric(III) ions) showed that the formation of hydroxyl radicals increases degradation of hydroxychloroquine. For this compound, radical-scavenging properties and light screening effects due to these matrix constituents are less pronounced. In the case of metoclopramide, indirect photolysis decreased degradation due to the presence of light absorptive substances. In all cases, the kinetics followed a pseudo-first-order character, except for the photolytic degradation of metoclopramide in seawater in which the degradation kinetics corresponded to a two-stages function. Slower degradation of metoclopramide in seawater was observed due to the presence of chloride and bromide ions. Quantum yields were determined using spectroradiometer for both pharmaceuticals, and values depended on the proportion of each compound in the mixture. Quantum yields of hydroxychloroquine were (2,64 ̶ 453,49) · 10^−4 in the range of pH from 4 to 9, and quantum yields of metoclopramide (35,83 ̶ 22,98) · 10^−4 for pH range from 4 to 11. Since degradation products could potentially be more toxic than the original compounds, toxicity to Vibrio fischeri and genotoxicity to Salmonella typhimurium with SOS/umu-c test were examined. Only the photolytic products of hydroxychloroquine presented acute toxicity, with inhibition of Vibrio fischeri luminescence (up to 27%) being observed for a 30 minutes test. Furthermore, several degradation products for both pharmaceuticals were identified and degradation pathways were proposed. The degradation products were the result of hydroxylation of the aromatic ring and dealkylation on the amino-side chain. In the case of metoclopramide, photodechlorination was also observed, and in seawater and nucleophilic substitution of chlorine atoms by bromine. Based on this research, it can be concluded that the contribution of photolysis to both pharmaceuticals is crucial for their respective environmental degradation routes

The contribution of abiotic elimination processes to the fate of pharmaceuticals in the aquatic environment

Abiotički procesi mogu značajno doprinijeti manjoj postojanosti farmaceutika u površinskim vodama. Sukladno tome, unutar doktorske disertacije istražen je utjecaj abiotičkih procesa na razgradnju farmaceutika hidroksiklorokina i metoklopramida u vodenom okolišu uporabom optimirane i validirane kromatografske metode, HPLC-PDA i HPLC-MS/MS. Ispitana je hidrolitička stabilnost, pri čemu je ustanovljeno kako su oba farmaceutika otporna na hidrolitičku razgradnju. Također, razvijene metode primijenjene su za praćenje fotolitičke razgradnje hidroksiklorokina i metoklopramida pod utjecajem umjetnog Sunčeva zračenja. Ispitana je fotolitička razgradnja u destiliranoj deioniziranoj vodi te prirodnim i sintetskim otpadnim vodama. Rezultati su pokazali kako je izravna fotoliza odgovorna za razgradnju obaju farmaceutika i kako je posebno značajna u slučaju metoklopramida. Neizravna fotoliza značajno je utjecala na vrijeme poluraspada hidroksiklorokina u riječnoj, izvorskoj i morskoj vodi. Značajno različita vremena poluraspada, pod utjecajem ksenonske svjetiljke (500 W m^−2), dobivena su pri različitim vrijednostima pH. Najbrža razgradnja uočena je pri pH = 9 (1/2 = 0,09 h), a najsporija pri pH = 4 (1/2 = 23,1 h). I u slučaju metoklopramida (250 W m^−2) vrijednost pH utjecala je na brzinu razgradnje, ali je vrijeme poluraspada u području pH relevantnom za vode u okolišu bilo kraće od 10 minuta. Ispitivanjem utjecaja sastojaka prirodnih voda (nitrata, huminskih kiselina, klorida, bromida, sulfata, hidrogenkarbonata i željezovih(III) iona), utvrđeno je da nastankom hidroksilnih radikala dolazi do ubrzane razgradnje hidroksiklorokina. Drugi utjecaji, poput djelovanja određenih sastojaka vode kao hvatača radikala i zasjenjenja svjetlosti, manje su izraženi. U slučaju metoklopramida, neizravna fotoliza usporava razgradnju, jer prisutne tvari u prirodnim vodama (huminske kiseline, nitrati i dr.) također apsorbiraju svjetlo. U svim slučajevima kinetika je slijedila reakciju pseudo-prvog reda, osim za fotolitičku razgradnju metoklopramida u morskoj vodi, čija kinetika razgradnje odgovara dvoeksponencijalnoj funkciji (brzini razgradnje u dva stupnja). Sastav matice (velika koncentracija kloridnih iona) uzrokovao je sporiju fotolitičku razgradnju metoklopramida u morskoj vodi. Spektroradiometrijski su određeni kvantni prinosi razgradnje obaju farmaceutika i ovisili su o vrijednosti pH, odnosno udjelu pojedine specije farmaceutika. Kvantni prinosi razgradnje hidroksiklorokina za vrijednosti pH od 4 do 9 iznosili su (2,64 – 453,49) · 10^−4, te za metoklopramid (35,83 – 22,98) · 10^−4 za raspon vrijednosti pH od 4 do 11. Budući da abiotičkim procesima mogu nastati razgradni produkti toksičniji od početnog spoja, ispitana je toksičnost prema bakteriji Vibrio fischeri i genotoksičnost prema Salmonella typhimurium uporabom SOS/umu-c testa. Oba farmaceutika, kao i njihovi fotolitički produkti nisu toksični, prema navedenim testnim vrstama. Iznimka su smjese fotolitičkih produkata hidroksiklorokina za koje je 30 minutni test pokazao inhibiciju luminiscencije bakterije Vibrio fischeri (do 27 %). Nadalje, identificirano je nekoliko, do sada nepoznatih, razgradnih produkata za oba farmaceutika te su predloženi putovi razgradnje. Razgradni produkti nastali su kao rezultat hidroksilacije aromatskog prstena i dealkilacije na bočnom amino-ogranku. U slučaju metoklopramida uočeno je i fotodekloriranje, a u morskoj vodi i nukleofilna supstitucija atoma klora bromom. Na temelju provedenih istraživanja može se zaključiti kako fotoliza može značajno doprinijeti razgradnji obaju farmaceutika u okolišu.Abiotic processes can contribute considerably to degradation routes of pharmaceuticals in the environment. This doctoral thesis explores the role of abiotic processes in the degradation of hydroxychloroquine and metoclopramide in natural aquatic environments. Development and validation of appropriate chromatographic methods for their detection, as well as tests confirming their hydrolytic stability were performed. The developed chromatographic methods (HPLC-PDA and HPLC-MS/MS) were used to monitor the photolytic degradation of hydroxychloroquine and metoclopramide in different water matrices (distilled deionised water, natural waterbodies and different samples of synthetic wastewater) under the effect of simulated solar radiation. The results showed that direct photolysis is responsible for the degradation of both pharmaceuticals, showing a larger contribution for metoclopramide. Indirect photolytic degradation of hydroxychloroquine in rivers, water springs, and seawater significantly affects its half-life. Largely different half-lives under the influence of a Xe lamp (500 W m^−2) were obtained for different pH values, commonly found in the aquatic environment. The fastest degradation was observed at pH = 9 (1/2 = 0.09 h) and the slowest at pH = 4 (1/2 = 23.1 h). In the case of metoclopramide at 250 W m^−2, the pH also affected the rate of degradation, but the half-life for pH = 9 was less than 10 min. Examination of the influence of natural water constituents (nitrates, humic acids, chlorides, bromides, sulfates, bicarbonates, and ferric(III) ions) showed that the formation of hydroxyl radicals increases degradation of hydroxychloroquine. For this compound, radical-scavenging properties and light screening effects due to these matrix constituents are less pronounced. In the case of metoclopramide, indirect photolysis decreased degradation due to the presence of light absorptive substances. In all cases, the kinetics followed a pseudo-first-order character, except for the photolytic degradation of metoclopramide in seawater in which the degradation kinetics corresponded to a two-stages function. Slower degradation of metoclopramide in seawater was observed due to the presence of chloride and bromide ions. Quantum yields were determined using spectroradiometer for both pharmaceuticals, and values depended on the proportion of each compound in the mixture. Quantum yields of hydroxychloroquine were (2,64 ̶ 453,49) · 10^−4 in the range of pH from 4 to 9, and quantum yields of metoclopramide (35,83 ̶ 22,98) · 10^−4 for pH range from 4 to 11. Since degradation products could potentially be more toxic than the original compounds, toxicity to Vibrio fischeri and genotoxicity to Salmonella typhimurium with SOS/umu-c test were examined. Only the photolytic products of hydroxychloroquine presented acute toxicity, with inhibition of Vibrio fischeri luminescence (up to 27%) being observed for a 30 minutes test. Furthermore, several degradation products for both pharmaceuticals were identified and degradation pathways were proposed. The degradation products were the result of hydroxylation of the aromatic ring and dealkylation on the amino-side chain. In the case of metoclopramide, photodechlorination was also observed, and in seawater and nucleophilic substitution of chlorine atoms by bromine. Based on this research, it can be concluded that the contribution of photolysis to both pharmaceuticals is crucial for their respective environmental degradation routes

The contribution of abiotic elimination processes to the fate of pharmaceuticals in the aquatic environment

Abiotički procesi mogu značajno doprinijeti manjoj postojanosti farmaceutika u površinskim vodama. Sukladno tome, unutar doktorske disertacije istražen je utjecaj abiotičkih procesa na razgradnju farmaceutika hidroksiklorokina i metoklopramida u vodenom okolišu uporabom optimirane i validirane kromatografske metode, HPLC-PDA i HPLC-MS/MS. Ispitana je hidrolitička stabilnost, pri čemu je ustanovljeno kako su oba farmaceutika otporna na hidrolitičku razgradnju. Također, razvijene metode primijenjene su za praćenje fotolitičke razgradnje hidroksiklorokina i metoklopramida pod utjecajem umjetnog Sunčeva zračenja. Ispitana je fotolitička razgradnja u destiliranoj deioniziranoj vodi te prirodnim i sintetskim otpadnim vodama. Rezultati su pokazali kako je izravna fotoliza odgovorna za razgradnju obaju farmaceutika i kako je posebno značajna u slučaju metoklopramida. Neizravna fotoliza značajno je utjecala na vrijeme poluraspada hidroksiklorokina u riječnoj, izvorskoj i morskoj vodi. Značajno različita vremena poluraspada, pod utjecajem ksenonske svjetiljke (500 W m^−2), dobivena su pri različitim vrijednostima pH. Najbrža razgradnja uočena je pri pH = 9 (1/2 = 0,09 h), a najsporija pri pH = 4 (1/2 = 23,1 h). I u slučaju metoklopramida (250 W m^−2) vrijednost pH utjecala je na brzinu razgradnje, ali je vrijeme poluraspada u području pH relevantnom za vode u okolišu bilo kraće od 10 minuta. Ispitivanjem utjecaja sastojaka prirodnih voda (nitrata, huminskih kiselina, klorida, bromida, sulfata, hidrogenkarbonata i željezovih(III) iona), utvrđeno je da nastankom hidroksilnih radikala dolazi do ubrzane razgradnje hidroksiklorokina. Drugi utjecaji, poput djelovanja određenih sastojaka vode kao hvatača radikala i zasjenjenja svjetlosti, manje su izraženi. U slučaju metoklopramida, neizravna fotoliza usporava razgradnju, jer prisutne tvari u prirodnim vodama (huminske kiseline, nitrati i dr.) također apsorbiraju svjetlo. U svim slučajevima kinetika je slijedila reakciju pseudo-prvog reda, osim za fotolitičku razgradnju metoklopramida u morskoj vodi, čija kinetika razgradnje odgovara dvoeksponencijalnoj funkciji (brzini razgradnje u dva stupnja). Sastav matice (velika koncentracija kloridnih iona) uzrokovao je sporiju fotolitičku razgradnju metoklopramida u morskoj vodi. Spektroradiometrijski su određeni kvantni prinosi razgradnje obaju farmaceutika i ovisili su o vrijednosti pH, odnosno udjelu pojedine specije farmaceutika. Kvantni prinosi razgradnje hidroksiklorokina za vrijednosti pH od 4 do 9 iznosili su (2,64 – 453,49) · 10^−4, te za metoklopramid (35,83 – 22,98) · 10^−4 za raspon vrijednosti pH od 4 do 11. Budući da abiotičkim procesima mogu nastati razgradni produkti toksičniji od početnog spoja, ispitana je toksičnost prema bakteriji Vibrio fischeri i genotoksičnost prema Salmonella typhimurium uporabom SOS/umu-c testa. Oba farmaceutika, kao i njihovi fotolitički produkti nisu toksični, prema navedenim testnim vrstama. Iznimka su smjese fotolitičkih produkata hidroksiklorokina za koje je 30 minutni test pokazao inhibiciju luminiscencije bakterije Vibrio fischeri (do 27 %). Nadalje, identificirano je nekoliko, do sada nepoznatih, razgradnih produkata za oba farmaceutika te su predloženi putovi razgradnje. Razgradni produkti nastali su kao rezultat hidroksilacije aromatskog prstena i dealkilacije na bočnom amino-ogranku. U slučaju metoklopramida uočeno je i fotodekloriranje, a u morskoj vodi i nukleofilna supstitucija atoma klora bromom. Na temelju provedenih istraživanja može se zaključiti kako fotoliza može značajno doprinijeti razgradnji obaju farmaceutika u okolišu.Abiotic processes can contribute considerably to degradation routes of pharmaceuticals in the environment. This doctoral thesis explores the role of abiotic processes in the degradation of hydroxychloroquine and metoclopramide in natural aquatic environments. Development and validation of appropriate chromatographic methods for their detection, as well as tests confirming their hydrolytic stability were performed. The developed chromatographic methods (HPLC-PDA and HPLC-MS/MS) were used to monitor the photolytic degradation of hydroxychloroquine and metoclopramide in different water matrices (distilled deionised water, natural waterbodies and different samples of synthetic wastewater) under the effect of simulated solar radiation. The results showed that direct photolysis is responsible for the degradation of both pharmaceuticals, showing a larger contribution for metoclopramide. Indirect photolytic degradation of hydroxychloroquine in rivers, water springs, and seawater significantly affects its half-life. Largely different half-lives under the influence of a Xe lamp (500 W m^−2) were obtained for different pH values, commonly found in the aquatic environment. The fastest degradation was observed at pH = 9 (1/2 = 0.09 h) and the slowest at pH = 4 (1/2 = 23.1 h). In the case of metoclopramide at 250 W m^−2, the pH also affected the rate of degradation, but the half-life for pH = 9 was less than 10 min. Examination of the influence of natural water constituents (nitrates, humic acids, chlorides, bromides, sulfates, bicarbonates, and ferric(III) ions) showed that the formation of hydroxyl radicals increases degradation of hydroxychloroquine. For this compound, radical-scavenging properties and light screening effects due to these matrix constituents are less pronounced. In the case of metoclopramide, indirect photolysis decreased degradation due to the presence of light absorptive substances. In all cases, the kinetics followed a pseudo-first-order character, except for the photolytic degradation of metoclopramide in seawater in which the degradation kinetics corresponded to a two-stages function. Slower degradation of metoclopramide in seawater was observed due to the presence of chloride and bromide ions. Quantum yields were determined using spectroradiometer for both pharmaceuticals, and values depended on the proportion of each compound in the mixture. Quantum yields of hydroxychloroquine were (2,64 ̶ 453,49) · 10^−4 in the range of pH from 4 to 9, and quantum yields of metoclopramide (35,83 ̶ 22,98) · 10^−4 for pH range from 4 to 11. Since degradation products could potentially be more toxic than the original compounds, toxicity to Vibrio fischeri and genotoxicity to Salmonella typhimurium with SOS/umu-c test were examined. Only the photolytic products of hydroxychloroquine presented acute toxicity, with inhibition of Vibrio fischeri luminescence (up to 27%) being observed for a 30 minutes test. Furthermore, several degradation products for both pharmaceuticals were identified and degradation pathways were proposed. The degradation products were the result of hydroxylation of the aromatic ring and dealkylation on the amino-side chain. In the case of metoclopramide, photodechlorination was also observed, and in seawater and nucleophilic substitution of chlorine atoms by bromine. Based on this research, it can be concluded that the contribution of photolysis to both pharmaceuticals is crucial for their respective environmental degradation routes

Tailoring the stability/aggregation of one-dimensional TiO2(B)/titanate nanowires using surfactants

The increased utilization of one-dimensional (1D) TiO2 and titanate nanowires (TNWs) in various applications was the motivation behind studying their stability in this work, given that stability greatly influences both the success of the application and the environmental impact. Due to their high abundance in aqueous environments and their rich technological applicability, surfactants are among the most interesting compounds used for tailoring the stability.The aim of this paper is to determine the influence of surfactant molecular structure on TNW stability/aggregation behavior in water and aqueous NaBr solution by dynamic and electrophoretic light scattering. To accomplish this, two structurally different quaternary ammonium surfactants (monomeric DTAB and the corresponding dimeric 12-2-12) at monomer and micellar concentrations were used to investigate TNW stability in water and NaBr. It was shown that TNWs are relatively stable in Milli-Q water. However, the addition of NaBr induces aggregation, especially as the TNW mass concentration increases. DTAB and 12-2-12 adsorb on TNW surfaces as a result of the superposition of favorable electrostatic and hydrophobic interactions. As expected, the interaction of TNWs with 12-2-12 was stronger than with DTAB, due to the presence of two positively charged head groups and two hydrophobic tails. As a consequence of the higher adsorption of 12-2-12, TNWs remained stable in both media, while DTAB showed an opposite behavior.In order to gain more insight into changes in the surface properties after surfactant adsorption on the TNW surface, a surface complexation model was employed. With this first attempt to quantify the contribution of the surfactant structure on the adsorption equilibrium according to the observed differences in the intrinsic log K values, it was shown that 12-2-12 interacts more strongly with TNWs than DTAB. The modelling results enable a better understanding of the interaction between TNWs and surfactants as well as the prediction of the conditions that can promote stabilization or aggregation