Determination of the Acid-Base Dissociation Constant of Acid-Degradable Hexamethylenetetramine by Capillary Zone Electrophoresis

Takayanagi, Toshio; Shimakami, Natsumi; Kurashina, Masashi; Mizuguchi, Hitoshi; Yabutani, Tomoki

doi:10.2116/analsci.32.1327

Cited by 10 publications

(6 citation statements)

References 11 publications

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“…HMTA dissolved in DMSO- d 6 at neutral pH shows a singlet at 4.56 ppm (Supporting Figure S16). However, incremental addition of hydrochloric acid to this solution produces a downfield shift of this singlet to 4.83 ppm in line with the reported monoprotic p K aH value for HMTA (4.93), confirming the identity of the final product of MDA 2+ degradation as HMTA-H + . Integration of the relevant 1 H NMR signals confirms the stoichiometric 8:1 ratio of NH 4 + /HMTA-H + expected by the proposed degradation route.…”

Section: Results and Discussionsupporting

confidence: 82%

Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide

et al. 2023

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Formamidinium lead triiodide (FAPbI3) is the leading candidate for single-junction metal–halide perovskite photovoltaics, despite the metastability of this phase. To enhance its ambient-phase stability and produce world-record photovoltaic efficiencies, methylenediammonium dichloride (MDACl2) has been used as an additive in FAPbI3. MDA2+ has been reported as incorporated into the perovskite lattice alongside Cl–. However, the precise function and role of MDA2+ remain uncertain. Here, we grow FAPbI3 single crystals from a solution containing MDACl2 (FAPbI3-M). We demonstrate that FAPbI3-M crystals are stable against transformation to the photoinactive δ-phase for more than one year under ambient conditions. Critically, we reveal that MDA2+ is not the direct cause of the enhanced material stability. Instead, MDA2+ degrades rapidly to produce ammonium and methaniminium, which subsequently oligomerizes to yield hexamethylenetetramine (HMTA). FAPbI3 crystals grown from a solution containing HMTA (FAPbI3-H) replicate the enhanced α-phase stability of FAPbI3-M. However, we further determine that HMTA is unstable in the perovskite precursor solution, where reaction with FA+ is possible, leading instead to the formation of tetrahydrotriazinium (THTZ-H+). By a combination of liquid- and solid-state NMR techniques, we show that THTZ-H+ is selectively incorporated into the bulk of both FAPbI3-M and FAPbI3-H at ∼0.5 mol % and infer that this addition is responsible for the improved α-phase stability.

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Section: Results and Discussionsupporting

confidence: 82%

Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide

et al. 2023

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“…Відомо [2; [16][17][18], що HMTA у водних розчинах (у присутності HCl, H2SO4 [2]; у цитратно-фосфатних буферних системах [16] тощо) схильний до кислотного гідролізу з утворенням формальдегіду і солей амонію: С6H12N4 + 4H3O + + 2H2O [26]. Таким чином, буферна ємність виражається рівнянням:…”

Section: вступunclassified

ФІЗИКО-ХІМІЧНІ ХАРАКТЕРИСТИКИ БУФЕРНОЇ СИСТЕМИ HMTA – HCl – H2O

Khoma¹,

Чеботарьов²,

Снігур³

et al. 2023

J. of Chem. and Tech.

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Досліджено стабільність водних розчинів гексаметилентетраміну (HMTA) без кислотних добавок (HCl, H2SO4, цитратно-фосфатні буферні системи тощо) в області температур 1.0 ÷ 20.0 °С та концентрацій HMTA 0.10 ÷ 1.0 М (pH0 = 7.05 ÷ 8.25) методами спектрофотометрії, прямої рН- та редоксметрії. Оцінено вміст іонів амонію та формальдегіду – кінцевих продуктів гідролізу HMTA. Молярна концентрація іонів амонію складає не більше 5.0 % від загального вмісту HMTA та у кілька разів вища за концентрацію формальдегіду. Показано, що динаміка накопичення іонів амонію та формальдегіду не корелює із ходом потенціометричних кривих. Встановлено, що зі збільшенням концентрації водних розчинів HMTA (0.50 та 1.00 М) підвищується їх гідролітична стійкість. Отримано алгебраїчне рівняння, що описує співвідношення об’ємів розчинів 1.00 М (2.50 М) HMTA та 0.10 М HCl, які необхідні для приготування буферних розчинів із певним значенням pH в області 4.30 ÷ 7.40 (5.00 ÷ 7.50). Запропоновано математичну модель, яка в першому наближенні описує концентраційну залежність буферної ємності розчинів HMTA – HCl – H2O. Показано, що розведення в тисячу разів розчинів, які приготовлені на основі 1.00 М HMTA та 0.10 М HCl (рН0 5.45 та 6.35), а також 2.50 М HMTA та 0.10 М HCl (рН0 5.90) практично не призводить до помітних змін значень рН.

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“…A pK a value of the degradant was also determined [17]. pK a values of acid-degradable pravastatin [18] and hexamethylenetetramine [19] were determined under degraded conditions without any interference from the degraded species. Determination of acid dissociation constants by CE was also successful with alkaline-degradable catecholamines [20], ascorbic acid [21], and flavin derivatives [22].…”

Section: Determination Of Acid Dissociation Constants Under Degrading Conditionsmentioning

confidence: 99%

Development of Novel Analysis and Characterization Methods Utilizing Reaction Dynamics in a Separation Capillary

Takayanagi

2022

Chromatography

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Electrophoretic migration of an analyte in capillary electrophoresis (CE) reflects reaction dynamics of the analyte in solution.In affinity CE, an analyte of interest interacts with a modifier added in the separation buffer in fast equilibrium, and effective electrophoretic mobility of the analyte is contributed from its equilibrium species. Precise measurement of effective electrophoretic mobility allows analyzing the equilibrium. Analysis of equilibria under CE separation possesses several advantages against traditional analyses in homogeneous solution; coexisting substances including impurities and kinetically generated substances are resolved by CE from the equilibrium species of interest. Characteristics of the CE analysis have been applied to analyses of acid-base equilibria of degradable substances and ion-association equilibria in an aqueous solution. Since CE is operated in an open-tubular capillary, it is also suitable for the characterization of carbon nanoclusters such as graphene and carbon nanotube, and measurement of effective electrophoretic mobility helps characterization of nanoclusters. A novel analysis technique of capillary electrophoresis/dynamic frontal analysis (CE/DFA) has also been proposed for the analysis of such reactions as involving equilibria and kinetic reactions. In CE/DFA, kinetically generated product is continuously resolved from the equilibrium species, and a plateau signal would be detected when the reaction rate is constant. Michaelis-Menten constants have successfully been determined through the plateau height by CE/DFA. In this review, analysis and characterization methods utilizing reaction dynamics in a separation capillary are summarized.

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Determination of the Acid-Base Dissociation Constant of Acid-Degradable Hexamethylenetetramine by Capillary Zone Electrophoresis

Cited by 10 publications

References 11 publications

Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide

Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide

ФІЗИКО-ХІМІЧНІ ХАРАКТЕРИСТИКИ БУФЕРНОЇ СИСТЕМИ HMTA – HCl – H2O

Development of Novel Analysis and Characterization Methods Utilizing Reaction Dynamics in a Separation Capillary

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