Solvent Effects on the Dissociation Constants of Hydroxyflavones in Organic–Water Mixtures. Determination of the Thermodynamic pKa Values by UV–Visible Spectroscopy and DFT Calculations

2013 ◽  
Vol 58 (6) ◽  
pp. 1706-1716 ◽  
Author(s):  
Yamina A. Dávila ◽  
Matias I. Sancho ◽  
María C. Almandoz ◽  
Sonia E. Blanco
Keyword(s):  
Dft Calculations ◽  
Solvent Effects ◽  
Dissociation Constants ◽  
Visible Spectroscopy ◽  
Pka Values ◽  
Uv Visible

Determination of Tannin in Coffee Pulp Using Experimental and Theoritical Approches

2017 ◽  
Vol 751 ◽  
pp. 683-688
Author(s):  
Waleepan Rakitikul
Keyword(s):  
Electronic Structure ◽  
Dft Calculations ◽  
Structure Calculation ◽  
Electronic Structure Calculation ◽  
Visible Spectroscopy ◽  
Coffee Pulp ◽  
Soil Nutrition ◽  
Uv Visible ◽  
Homo Lumo

Currently, Doi Chaang village is the biggest area producing coffee in Thailand. Throughout seed to cup the pulp must be removed from coffee cherry after harvesting and left as waste. Tannin is one of various composition in coffee pulp which is affected by soil nutrition and pH. In this study, we have characterized the amount of tanin in coffee pulp using UV-Visible spectroscopy and electronic structure calculation. The results showed that coffee pulp consist of 5.68% tannin . It was determined to condense tannin form. Moreover, the pH of soil after treated with modified coffee pulp with water, Ca(OH)2, Na2S2O5, 2% Ca(OH)2, and 2% Na2S2O5 is higher than that with non-modified case. Likewise, DFT calculations predicted the structure of tannin with smaller HOMO-LUMO gap in the condense tannin.

The use of UV-visible spectroscopy for the determination of hydrophobic interactions between neuropeptides and membrane model systems

Biopolymers ◽  
1992 ◽  
Vol 32 (8) ◽  
pp. 1061-1064 ◽  
Author(s):  
John K. Young ◽  
William H. Graham ◽  
Debbie J. Beard ◽  
Rickey P. Hicks
Keyword(s):  
Hydrophobic Interactions ◽  
Model Systems ◽  
Membrane Model ◽  
Visible Spectroscopy ◽  
Uv Visible

Determination of dissociation constants of p-hydroxybenzophenone in aqueous organic mixtures – Solvent effects

2008 ◽  
Vol 86 (5) ◽  
pp. 462-469 ◽  
Author(s):  
M I Sancho ◽  
A H Jubert ◽  
S E Blanco ◽  
F H Ferretti ◽  
E A Castro
Keyword(s):  
Solvent Effects ◽  
Dissociation Constants ◽  
Reaction Medium ◽  
Reversed Phase ◽  
Glass Electrode ◽  
Molecular Structures ◽  
Acid Dissociation ◽  
Acidity Constant ◽  
Pka Values ◽  
Solvent Water

The apparent acidity constant of p-hydroxybenzophenone, which is a practically insoluble drug in water but of great pharmaceutical interest, was determined by reversed-phase high-performance liquid chromatography in organic solvent – water mixtures (acetonitrile–water, ethanol–water, and methanol–water), varying the reaction medium permittivity in the interval 56 to 70, at constant ionic strength (0.050) and temperature (30 °C). A combined glass electrode calibrated with aqueous standard buffers was used to obtain pH readings based on the concentration scale (swpH). The pKa values from chromatographic data were obtained using the Hardcastle–Jano equation. Moreover, excellent linear relationships between the pKa values and solvation properties of the reaction medium (relative permittivity and Acity) were used to derive acid dissociation constants in aqueous solution. It has been concluded that the pKa values extrapolated from such solvent–water mixtures are consistent with each other and with previously reported measurements. In addition, the molecular structures of all the chemical species involved in the acid–base dissociation equilibrium studied were calculated with a B3LYP/6–311++G(d,p) method that makes use of the polarizable continuum model (PCM). Taking into account the theoretical pKa values, the conclusions obtained match our experimental determinations.Key words: solvent effects, p-hydroxybenzophenone, acidity constant, solvation parameters, structure, DFT calculation.

Determination of pKa of felodipine using UV–Visible spectroscopy

2013 ◽  
Vol 115 ◽  
pp. 887-890 ◽  
Author(s):  
M.M. Pandey ◽  
A. Jaipal ◽  
A. Kumar ◽  
R. Malik ◽  
S.Y. Charde
Keyword(s):  
Visible Spectroscopy ◽  
Uv Visible

scholarly journals An Acylhydrazone-Based Fluorescent Sensor for Sequential Recognition of Al3+ and H2PO4−

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6392
Author(s):  
Donghwan Choe ◽  
Cheal Kim
Keyword(s):  
Fluorescence Quenching ◽  
Dft Calculations ◽  
1H Nmr ◽  
Fluorescent Sensor ◽  
Visible Spectroscopy ◽  
Nmr Titration ◽  
Esi Ms ◽  
1H Nmr Titration ◽  
Uv Visible ◽  
Sequential Recognition

A novel acylhydrazone-based fluorescent sensor NATB was designed and synthesized for consecutive sensing of Al3+ and H2PO4−. NATB displayed fluorometric sensing to Al3+ and could sequentially detect H2PO4− by fluorescence quenching. The limits of detection for Al3+ and H2PO4− were determined to be 0.83 and 1.7 μM, respectively. The binding ratios of NATB to Al3+ and NATB-Al3+ to H2PO4− were found to be 1:1. The sequential recognition of Al3+ and H2PO4− by NATB could be repeated consecutively. In addition, the practicality of NATB was confirmed with the application of test strips. The sensing mechanisms of Al3+ and H2PO4− by NATB were investigated through fluorescence and UV–Visible spectroscopy, Job plot, ESI-MS, 1H NMR titration, and DFT calculations.

Determination of Rate Constants in Second-Order Kinetics Using UV-Visible Spectroscopy

2001 ◽  
Vol 55 (1) ◽  
pp. 77-83 ◽  
Author(s):  
Sabina Bijlsma ◽  
Hans F. M. Boelens ◽  
Age K. Smilde
Keyword(s):  
Rate Constants ◽  
Second Order ◽  
Visible Spectroscopy ◽  
Uv Visible

scholarly journals DEVELOPMENT AND VALIDATION OF UV-SPECTROPHOTOMETRIC METHODS FOR DETERMINATION OF GEMCITABINE HYDROCHLORIDE IN BULK AND POLYMERIC NANOPARTICLES

2017 ◽  
Vol 9 (5) ◽  
pp. 60 ◽  
Author(s):  
Taranjit Kaur ◽  
Sukhjinder Kaur ◽  
Parminderjit Kaur
Keyword(s):  
Polymeric Nanoparticles ◽  
Visible Spectroscopy ◽  
International Conference ◽  
Spectrophotometric Methods ◽  
Gemcitabine Hydrochloride ◽  
Double Beam ◽  
Uv Visible ◽  
Formulation Analysis ◽  
Development And Validation

Objective: The objective of the present work was to develop and validate a novel, specific, precise and reliable method for estimation of gemcitabine hydrochloride in bulk and polymeric nanoparticles using UV-visible spectroscopy method.Methods: The UV-Visible spectrophotometric determination was performed with double beam Systronics UV-visible spectrophotometer; model UV-2201 (India). The proposed methods were validated for various parameters like linearity, precision, accuracy, robustness, ruggedness, detection, quantification limits, and formulation analysis as per international conference on harmonization (ICH) guidelines.Results: The method was based on measurement of absorbance at wavelength maxima i.e. 267.2 nm, λmax of the drug in distilled water, phosphate buffer pH 6.8 and 7.4. The method obeyed Beer Lambert’s law in the concentration range of 5-30 µg/ml andR2-value was found to be 0.999. Moreover, the % drug recovered from polymeric nanoparticles was found to be 97.97%.Conclusion: According to results, the currently developed method shows compliance with acceptance criteria with Q2 (R1) and international conference on harmonization (2005) guidelines, because the % RSD was found to be less than 2%. The developed method was simple, accurate and précised.

Charge-Transfer Complexes Between Iodine and Substituted Thioureas: Determination of Thermodynamic and Spectroscopic Properties

1996 ◽  
Vol 51 (1-2) ◽  
pp. 116-122 ◽  
Author(s):  
Cornelia Fooken ◽  
Wolfram Baumann
Keyword(s):  
Equilibrium Constants ◽  
Spectroscopic Properties ◽  
Critical Discussion ◽  
Charge Transfer Complexes ◽  
Published Data ◽  
Visible Spectroscopy ◽  
Dichloromethane Solution ◽  
Uv Visible ◽  
Iodine Complexes

Abstract 15 iodine complexes with substituted thioureas were investigated in dichloromethane solution by UV-visible spectroscopy, and their equilibrium constants, reaction enthalpies and molar absorption coefficients were determined. The influence of the substituents on the properties of the charge-trans-fer complexes is examined. A critical discussion of previously published data is given, where comparable data are available.

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