scholarly journals UV Spectrophotometric Determination of Thermodynamic Dissociation Constants of Some Aromatic Hydrazones in Acid Media

2019 ◽  
Vol 63 (4) ◽  
Author(s):  
Mirjana Jankulovska ◽  
Ilinka Spirevska ◽  
Vesna Dimova ◽  
Milena Jankulovska
Keyword(s):  
Proton Affinity ◽  
Dissociation Constants ◽  
Uv Spectroscopy ◽  
Sodium Perchlorate ◽  
Atomic Charge ◽  
Protonated Form ◽  
Uv Spectra ◽  
Semiempirical Methods ◽  
Acid Media ◽  
Protonation Site

The spectral behavior of some p-nitro-p-substituted benzoylhydrazones in the perchloric acid media was followed, applying the UV spectroscopy. The position of the absorption maximum in the spectra was defined in acidic media and the electronic transitions were discussed, as well (7<pH<1). The equilibrium between neutral and protonated form was investigated in the ethanol-water (V/V, 1:1) solutions. The observed changes in the UV spectra suggested that protonation process took place in one step. The pH region of protonation ranges between 1.4 and 2.9. Using the changes in the UV spectra which appear as a result of the protonation reaction the stoichiometric dissociation constants were determined numerically (pKBH+ = n·pH + logI) and graphically (intercept of the dependence of logI on pH). Thermodynamic dissociation constants were estimated as an intercept of dependence of pKBH+ on square root of the ionic strength. In order to achieve that, measurements were performed at different ionic strengths: 0.1, 0.25 and 0.5 mol/dm3, adjusted with sodium perchlorate. The obtained thermodynamic pKBH+ values ranged between 2.07 and 2.58. In order to predict proton transfer at a given pH, semiempirical methods AM1 and PM3 were applied. The influence of the substituents present in the p-position of the benzene ring on pKBH+ values of investigated hydrazones was discussed, too. Total energy, binding energy, enthalpy of formation, Gibbs energies of formation, atomic charge and proton affinity values were used to predict protonation site in hydrazone molecule. Furthermore, the stability and the proton affinity of the isomers (E and Z) in which hydrazones exist and their protonated forms were defined.

scholarly journals Spectrophotometric study of the protonation processes of some indole derivatives in sulfuric acid

1999 ◽  
Vol 64 (12) ◽  
pp. 775-787 ◽  
Author(s):  
Blagoja Andonovski ◽  
Goran Stojkovic
Keyword(s):  
Sulfuric Acid ◽  
Carboxylic Acid ◽  
Dissociation Constants ◽  
Uv Spectroscopy ◽  
Spectrophotometric Study ◽  
Protonated Form ◽  
Indole Derivatives ◽  
Acid Media ◽  
Solvent Parameter ◽  
Pka Value

The protonation of 3-methylindole, D-tryptophan, 3-formylindole, 3-acetylindole and indolyl-2-carboxylic acid in sulfuric acid media was studied by UV spectroscopy. The measurement of the absorbance at four selected wavelengths enabled the calculation of the corresponding molar absorptivities. The results were used to calculate the pKa value of the protonated form of the indole derivatives by the Hammett Method. The Hammett postulate (the slope of the plot log [c(BH+)/c(B)]vs. H should be equal to 1) was tested. The dissociation constants and solvent parameter m* were also obtained by applying the Excess Acidity Method. The position of the additional protons in the protonated compounds is discussed.

scholarly journals Comparison of theoretical and experimental investigation of protonation process of some thiones in acid media

2021 ◽  
Vol 62 (1) ◽  
pp. 9-21
Author(s):  
Mirjana Jankulovska ◽  
Vesna Dimova ◽  
Ilinka Spirevska ◽  
Milena Jankulovska
Keyword(s):  
Hydrochloric Acid ◽  
Phosphoric Acid ◽  
Dissociation Constants ◽  
Uv Spectroscopy ◽  
Semiempirical Method ◽  
Mineral Acid ◽  
Acidity Function ◽  
Acid Media ◽  
One Step ◽  
Absorbance Data

PM3 semiempirical method was used for quantum chemical investigation in order to investigate the electronic properties and to determine the protonation centre in 1,2,4-triazoline-3-thione molecule. Confirmation of protonation center in acid media of investigated compounds was made using the values of atomic charges, as well as, proton affinity values. The results from semiempirical calculations indicated that the protonation center in the thione molecule was the sulphur atom. The behavior of thiones was investigated in mineral acid media using UV spectroscopy. The influence of the strength of the acid and its anion on the protonation process was discussed using three different mineral acids (perchloric, hydrochloric and phosphoric acid) for protonation. The protonation process in perchloric and hydrochloric acid took place in one step, while in phosphoric acid was not finished even when its concentration was to the highest degree. The dissociation constants of protonated forms (pKBH + ) and the solvation parameter m* values were calculated in accordance with "excess acidity" function method (Cox and Yates) using the absorbance data from the experimental and reconstructed spectra (Characteristic Vector Analysis (CVA)). The determined pKBH + values in hydrochloric acid had more negative value than those obtained in perchloric acid media. The pKBH + values were in agreement with the literature data for this class of compounds.

scholarly journals Analysis of acid-base properties of some p-substituted aromatic hydrazones in aqueous perchloric acid by spectrophotometric and semiempirical methods

2014 ◽  
Vol 33 (1) ◽  
pp. 85 ◽  
Author(s):  
Mirjana Stojan Jankulovska ◽  
Ilinka Spirevska
Keyword(s):  
Perchloric Acid ◽  
Dissociation Constants ◽  
Protonated Form ◽  
Heat Of Formation ◽  
Semiempirical Methods ◽  
Acid Base ◽  
Spectrophotometric Methods ◽  
Aqueous Perchloric Acid ◽  
The Stability ◽  
Base Properties

<p>The acid-base properties of some <em>p</em>-substituted aromatic hydrazones were examined in aqueous perchloric acid medim by spectrophotometric methods. The possible site where the proton may take place and the stability of the protonated form was discussed using the values of the total energy, binding energy, heat of formation and proton affinity calculated according to the semiempirical methods AM1 and PM3. Furthermore, the stability of the protonated forms, as well as, the stability of the isomers (<em>E</em> and <em>Z</em>) was discussed. Electronic absorption studies were utilized for determination of the dissociation constants of the protonated form (p<em>K</em><sub>BH</sub><sup>+</sup>), numerically and graphically, at different ionic strength (0.1, 0.25 and 0.5 mol/dm<sup>3</sup>), as well as, thermodynamic dissociation constants.  The influence of the solvent on the appearance of the recorded spectra was compensated by the use of the method of characteristic vector analysis (CVA).</p><p> </p>

scholarly journals DETERMINATION OF THE DISSOCIATION CONSTANTS OF SOME p-SUBSTITUTED AROMATIC HYDRAZONES

2017 ◽  
Vol 32 (1-2) ◽  
Author(s):  
Mirjana Jankulovska ◽  
Ilinka Spirevska ◽  
Katica Cholančeska Ragjenovikj
Keyword(s):  
Ionic Strength ◽  
Room Temperature ◽  
Dissociation Constants ◽  
Aqueous Sodium Hydroxide ◽  
Uv Spectra ◽  
Hydroxyl Group ◽  
Semiempirical Methods ◽  
Dissociation Process ◽  
Neutral Media

A b s t r a c t: The acid-base behavior of five p-substituted aromatic hydrazones has been studied, using UV spectrophotometric method. The influence of the acidity of the medium on the absorption spectra is followed in aqueous sodium hydroxide solutions in pH region from 7 to 14. The measurements are performed at room temperature, and at ionic strength of 0.1, 0.25 and 0.5 mol dm–3. A batochromic shift of the absorption band that appears in neutral media is observed, when pH is up to 7. It suggests that the dissociation process of the amide and hydroxyl group takes place. Deprotonation enthalpies and total energy values are calculated by using the semiempirical methods AM1 and PM3. Using the changes in the UV spectra with pH of the solution, the determination of dissociation constants, pKBH, at three different ionic strengths, as well as, the thermodynamic dissociation constants at zero ionic strength, is performed. In order to obtain more precise results, the calculations are made from the absorbance values at four selected wavelengths. Furthermore, the pKBH values were determined graphically from the intercept of the dependence of logI on pH. The results showed that the numerically calculated pKBH values are identical to those graphically obtained.

scholarly journals Ultraviolet Spectroscopy Used to Fingerprint Five Wild-Grown Edible Mushrooms (Boletaceae) Collected from Yunnan, China

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Yan Li ◽  
Ji Zhang ◽  
Tao Li ◽  
Tianwei Yang ◽  
Yuanzhong Wang ◽  
...  
Keyword(s):  
Cluster Analysis ◽  
Discriminant Analysis ◽  
Hierarchical Cluster Analysis ◽  
Visual Discrimination ◽  
Uv Spectroscopy ◽  
Hierarchical Cluster ◽  
Uv Spectra ◽  
Edible Mushrooms ◽  
Ultraviolet Spectroscopy

Nowadays, wild-grown edible mushrooms which are natural, nutritious, and healthy get more and more popular by large consumers. In this paper, UV spectra of different Boletaceae mushrooms with the aid of partial least squares discriminant analysis (PLS-DA) and hierarchical cluster analysis (HCA) were shown to be a practical and rapid method for discrimination purpose. The specimens of Boletus edulis, Boletus ferrugineus, Boletus tomentipes, Leccinum rugosiceps, and Xerocomus sp. were described based on the UV spectra. From the results, all the specimens were characterized by strong absorption at the wavelengths of 274 and 284 nm and showed the shoulder at 296 nm. However, changes could be seen in the peak heights at the same wavelength for different samples. After analyzing by chemometrics, visual discrimination among samples was presented and the relationships among them were also obtained. This study showed that UV spectroscopy combined with chemometrics methods could be used successfully as a simple and effective approach for characterization of these five wild-grown edible mushrooms at species and genus levels. Meanwhile, this rapid and simple methodology could also provide reference for the discrimination of edible mushrooms.

Substituent effects on polarographic reduction of some photographic color intermediates

1976 ◽  
Vol 54 (8) ◽  
pp. 1205-1210 ◽  
Author(s):  
Ahmad S. Shawali ◽  
Bahgat E. El-Anadouli
Keyword(s):  
Dissociation Constants ◽  
Substituent Effects ◽  
Protonated Form ◽  
Acid Dissociation ◽  
Polarographic Reduction ◽  
Substituent Constant ◽  
Acid Dissociation Constants ◽  
Controlled Potential Electrolysis ◽  
Half Wave ◽  
Controlled Potential

Polarographic reduction of two series of benzoylacetanilides has been investigated in 40% (by volume) ethanolic Britton–Robinson buffers. One series (A) contains substituents on the anilide moiety, and the second (B) has substituents on both the anilide and benzoyl moieties. Polarographic controlled-potential electrolysis data indicate that the electroactive species in both series is the protonated form (ArCOCH2CONHAr′)H+. The reduction half-wave potentials of anilides of series A were found to be independent of the nature of the substituent, whereas those of series B show a good linear relationship when plotted vs. the σ substituent constant of the substituent on the benzoyl moiety (ρ = 0.284, r = 0.995). Values of the acid dissociation constants of the keto (K1) and enol (K2) tautomers of the anilides of series A were calculated; unlike their E1/2 values, the pK1 data show a linear correlation with the Hammett substituent constant, σ. The pK2 values show, however, little variation with σ.

Ab Initio-Rechnungen zur Protonenaffinität unverzweigter primärer aliphatischer Amine / Ab Initio-Calculations on the Protonaffinity of Unbranched Primary Aliphatic Amines

1984 ◽  
Vol 39 (6) ◽  
pp. 593-595
Author(s):  
Eberhard Heyne ◽  
Gerhard Raabe ◽  
Jörg Fleischhauer
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Proton Affinity ◽  
Positive Charge ◽  
Semiempirical Calculations ◽  
Aliphatic Amines ◽  
Semiempirical Methods ◽  
Satisfactory Correlation ◽  
Primary Aliphatic Amines

Recently we reported the results of semiempirical calculations (MNDO, MINDO/3) which led us to the conclusion, that the proton-affinity of molecules R-NH2 (R = H, CH3, C2H5, n-C3H7 and n-C4H9) is determined by the ability of the groups R to carry positive charge in the corresponding cations R-NH3+. We did extend our investigations concerning the protonaffinities of primary aliphatic amines including NH3 and performed ab initio calculations with an STO-3G basis. The results qualitatively parallel those obtained by the semiempirical methods mentioned above. In contrast to the semiempirical results we found that there is a satisfactory correlation between the Mulliken-charges of the nitrogen-atoms and of the NH2-groups and the experimental protonaffinities if NH3 is excluded.

scholarly journals Exploring Abundance and Isotope Anomalies in CP Stars with the HST/GHRS: High Resolution UV Spectroscopy of χ Lupi

1993 ◽  
Vol 138 ◽  
pp. 42-59 ◽  
Author(s):  
David S. Leckrone ◽  
Glenn M. Wahlgren ◽  
Sveneric G. Johansson ◽  
Saul J. Adelman
Keyword(s):  
High Resolution ◽  
Uv Spectroscopy ◽  
Uv Spectra ◽  
Heavy Elements

AbstractWe are using the HST/GHRS in a long-term program to obtain UV spectra of unprecedented resolution and precision for bright, ultra-sharp-lined Bp (HgMn) stars and comparable normal stars. To date we have doubled the number of heavy elements for which abundances may be estimated in χ Lupi, and have obtained the first observations of Hg III lines with which to test diffusion scenarios for its extreme Hg isotope anomaly.

scholarly journals Exploring the Photodynamic Properties of Two Antiproliferative Benzodiazopyrrole Derivatives

2020 ◽  
Vol 21 (4) ◽  
pp. 1246 ◽  
Author(s):  
Concetta Imperatore ◽  
Mohammadhassan Valadan ◽  
Luciana Tartaglione ◽  
Marco Persico ◽  
Anna Ramunno ◽  
...  
Keyword(s):  
High Resolution Mass Spectrometry ◽  
Light Emitting Diode ◽  
Uv Spectroscopy ◽  
Ionic Species ◽  
Uv Spectra ◽  
Solution Ph ◽  
Null Cell ◽  
Degree Of Ionization ◽  
Promising Therapeutic Approach ◽  
Led Irradiation

The identification of molecules whose biological activity can be properly modulated by light is a promising therapeutic approach aimed to improve drug selectivity and efficacy on the molecular target and to limit the side effects compared to traditional drugs. Recently, two photo-switchable diastereomeric benzodiazopyrrole derivatives 1RR and 1RS have been reported as microtubules targeting agents (MTAs) on human colorectal carcinoma p53 null cell line (HCT 116 p53-/-). Their IC50 was enhanced upon Light Emitting Diode (LED) irradiation at 435 nm and was related to their cis form. Here we have investigated the photo-responsive behavior of the acid derivatives of 1RR and 1RS, namely, d1RR and d1RS, in phosphate buffer solutions at different pH. The comparison of the UV spectra, acquired before and after LED irradiation, indicated that the trans→cis conversion of d1RR and d1RS is affected by the degree of ionization. The apparent rate constants were calculated from the kinetic data by means of fast UV spectroscopy and the conformers of the putative ionic species present in solution (pH range: 5.7–8.0) were modelled. Taken together, our experimental and theoretical results suggest that the photo-conversions of trans d1RR/d1RS into the corresponding cis forms and the thermal decay of cis d1RR/d1RS are dependent on the presence of diazonium form of d1RR/d1RS. Finally, a photo-reaction was detected only for d1RR after prolonged LED irradiation in acidic medium, and the resulting product was characterized by means of Liquid Chromatography coupled to High resolution Mass Spectrometry (LC-HRMS) and Nuclear Magnetic Resonance (NMR) spectroscopy.

Determination of Seawater Salinity by Ultraviolet Spectroscopic Measurements

1997 ◽  
Vol 51 (9) ◽  
pp. 1294-1302 ◽  
Author(s):  
Vito Di Noto ◽  
Mauro Mecozzi
Keyword(s):  
Organic Matter ◽  
Uv Spectroscopy ◽  
Sample Pretreatment ◽  
Uv Spectra ◽  
Linear Calibration ◽  
Synthetic Seawater ◽  
Seawater Salinity ◽  
Seawater Samples ◽  
Nitrate Species

A method for the determination of seawater salinity by ultraviolet (UV) spectroscopy is proposed. The effects of single salt concentrations and of salinity on UV absorption in the 190–250-nm range were investigated. These studies revealed that the absorption spectrum of a solution with a given salinity is due mainly, in order, to KBr >MgCl 2>NaCl. The influence of the temperature and salt concentration on UV spectra was studied by using synthetic seawater samples with the salinities ranging from 1 to 50 parts per thousand (%). Results showed that, in the absence of interferences, the most sensitive and reliable conditions for measuring the salinity are at 212 nm and at temperatures in the range of 25–30 °C. Under these conditions this method shows quite linear calibration curves and allows us to perform salinity determinations in seawater solutions at concentrations as low as 4%. Moreover, it requires no sample pretreatment and offers a precision of 0.20%. The proposed method is very simple and rapid for laboratory and on-board analysis. Finally, the interference of organic matter, nitrite, and nitrate species with the salinity determinations was investigated. These studies show that organic matter does not interfere at concentrations of carbon lower than 1 mg/L and at 210 nm. Interferences due to NO− x species can be ignored if these species are dissolved in solution at concentrations lower than ≈0.2 mg/L and the analyses are carried out at wavelengths lower than 212 nm.

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