Self-association of caffeine in aqueous solution: an FT-IR study

1990 ◽  
Vol 68 (8) ◽  
pp. 1293-1299 ◽  
Author(s):  
Michael Falk ◽  
Manuel Gil ◽  
Nerea Iza
Keyword(s):  
Infrared Spectroscopy ◽  
Molar Absorptivity ◽  
Polymer Model ◽  
Infrared Band ◽  
Caffeine Concentration ◽  
Spectral Changes ◽  
Ft Ir ◽  
Self Association ◽  
Association Equilibria ◽  
Ir Study

Spectra of caffeine in D2O solution (0.003 to 0.129 M) were studied by Fourier-transform infrared spectroscopy. Spectral changes in the carbonyl stretching region were interpreted in terms of the self-association equilibria resulting from the stacking of caffeine molecules. Absence of isosbestic points indicated the occurrence of more than two spectroscopically distinct caffeine species. A simple monomer–dimer–polymer model was employed, in which the successive equilibria are governed by two association constants, Kd for the formation of dimers and Kp for the formation of trimers and larger polymers. The value Kd = 158.1 L mol−1 was taken from a recent ultraviolet study by Iza etal. and the value Kp = 27 L mol−1 was derived from the analysis of infrared band profiles sharpened by Fourier self-deconvolution. From these values of Kd and Kp, the weight fractions of monomers, dimers, and polymers were calculated for every caffeine concentration and their individual molar absorptivity spectra were derived. In agreement with the earlier work of Maevsky and Sukhorukov, it was found that stacking association causes shifts of both C=O stretching fundamentals to higher wavenumbers. The monomer-dimer shifts are smaller than the dimer-polymer shifts. Analogous shifts were observed for the stacking self-association of 1,3-dimethyluracil in D2O. The shifts to higher wavenumbers are probably caused by the diminished hydrogen bonding of water to C=O groups of the stacked bases. Keywords: caffeine, self association, infrared spectroscopy, base stacking.

scholarly journals Application of attenuated total reflection infrared spectroscopy in the study ofPeruphasma schulteidefensive secretion

2007 ◽  
Vol 21 (3) ◽  
pp. 169-176 ◽  
Author(s):  
Michael P. Mcleod ◽  
Aaron T. Dossey ◽  
M. Khalique Ahmed
Keyword(s):  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Natural Product ◽  
Short Communication ◽  
Defensive Secretion ◽  
Structural Characteristics ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Ft Ir ◽  
Ir Study

In this short communication, we present the first Fourier Transform Infrared Absorbance (FT-IR) study of peruphasmal; a defensive secretion fromPeruphasma schultei. The spectral data collected are representative of the natural product structure proposed by Dossey et al. This study demonstrates the viability of FT-IR as another tool in the physical and biological chemist's repertoire for use in determining important structural characteristics from minute amounts of available sample.

FT-IR study of N-tertiobutoxycarbonylproline-N′-methylamide self-association in carbon tetrachloride and influence of the solvent on the conformation

1992 ◽  
Vol 270 ◽  
pp. 217-227 ◽  
Author(s):  
J. Parmentier ◽  
K. De Wael ◽  
Th. Zeegers-Huyskens
Keyword(s):  
Carbon Tetrachloride ◽  
Ft Ir ◽  
Self Association ◽  
Ir Study

FT-IR Study of the Proton Acceptor Ability of Ethylacetamidoacetate. Self-Association and Interaction with Proton Donors

1993 ◽  
Vol 26 (10) ◽  
pp. 1939-1951 ◽  
Author(s):  
K. De Wael ◽  
Th. Zeegers-Huyskens
Keyword(s):  
Proton Acceptor ◽  
Proton Donors ◽  
Ft Ir ◽  
Self Association ◽  
Ir Study

An FT-ir study of cis study of trans-dichlorodiammineplatinum(II) bound to inosine-5′-monophosphate

1984 ◽  
Vol 62 (8) ◽  
pp. 1429-1440 ◽  
Author(s):  
H. A. Tajmir-Riahi ◽  
T. Theophanides
Keyword(s):  
Trans Isomer ◽  
Platinum Complexes ◽  
Disodium Salt ◽  
Spectral Changes ◽  
Ir Studies ◽  
Stretching Vibration ◽  
Ft Ir ◽  
Purine Ring ◽  
Ir Study ◽  
Cis And Trans

Inosine-5′-monophosphate disodium salt (5′-IMPNa2) reacts with cis-dichlorodiammineplatinum(II) (cis-DDP) and its trans-isomer (trans-DDP) to give complexes of the type cis- and trans-Pt(NH3)2(IMPNa2)nCl2•xH2O, n = 1 or 2 and Pt(IMPNa2)nCl2•xH2O, where n = 1, 2, or 3 and x = 0–6. In the 1:2 platinum complexes the nucleotide binds only to the N7-atom of the purine ring system, while in the 1:1 metal complexes there is indication for Pt–carbonyl interaction (bridging or chelation) in addition to the N7-bonding at neutral pH values with cis-DDP.Solution FT-ir studies (H2O and D2O) showed that the 1:1 species formed with cis-DDP at neutral pH's behaved differently from those with trans-DDP. The carbonyl stretching vibration of the free base at 1685 cm−1 (H2O) and 1670 cm−1 (D2O) exhibited marked spectral changes in intensity, shifting, and shape upon complexation, whereas the reaction with the trans-isomer produced only slight perturbations in the above region.

FT-IR Study of the Imidization Process of Photosensitive Polyimide PMDA/ODA

1998 ◽  
Vol 52 (7) ◽  
pp. 985-989 ◽  
Author(s):  
W. S. Li ◽  
Z. X. Shen ◽  
J. Z. Zheng ◽  
S. H. Tang
Keyword(s):  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
High Temperature ◽  
Film Thickness ◽  
Cure Process ◽  
Cure Reaction ◽  
Ft Ir ◽  
Lower Temperature ◽  
Ir Study

Fourier transform infrared spectroscopy (FT-IR) was used to study the cure reaction process of an ester-type photosensitive polyimide, PMDA/ODA films coated on silicon wafer substrates. In the in situ high-temperature FT-IR study carried out in vacuum, all the characteristic peaks of imide and the crosslinkable group were observed to decrease gradually with an increase in temperature. The completion of the imidization reaction is at ∼270 °C. Our result shows that the ester-type photosensitive polyimide can be cured at a much lower temperature than previously reported. The imide peak δas(C, C > NC) at 588 cm−1 was used to follow the imidization process, and the result agrees well with that obtained by using another imide peak v(C–N–C) at 1378 cm−1. The film shrinks by one third during the cure process, and the temperature dependence of the film thickness shows excellent agreement with the “imidization degree”.

Reaction of Nitrogen Oxides with Black Carbon: An FT-IR Study

1988 ◽  
Vol 42 (4) ◽  
pp. 674-680 ◽  
Author(s):  
D. M. Smith ◽  
W. F. Welch ◽  
S. M. Graham ◽  
A. R. Chughtai ◽  
Brian G. Wicke ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Black Carbon ◽  
Oxides Of Nitrogen ◽  
Surface Species ◽  
Qualitative And Quantitative ◽  
Quantitative Studies ◽  
Ft Ir ◽  
Ir Study

Qualitative and quantitative studies of the reaction of black carbon with the oxides of nitrogen, including NO, NO2/N2O4, N2O, and N2O3, have been carried out with the use of Fourier transform infrared spectroscopy (FT-IR). The active reactant is shown to be NO2, whether it acts as a disproportionation product or as an impurity in the gas under study. FT-IR spectra of the surface species identify them as resulting from reaction of carbon with NO2. For paraffin candle soot which was exposed simultaneously to oxygen atoms, and nitric oxide at 298 K, the surface species also are due to NO2, formed by oxidative adsorption of NO on the soot surface.

FT-IR study of self-association of some hydroperoxides

2004 ◽  
Vol 700 (1-3) ◽  
pp. 73-79 ◽  
Author(s):  
A.B. Remizov ◽  
D.I. Kamalova ◽  
R.A. Skochilov ◽  
I.A. Suvorova ◽  
N.N. Batyrshin ◽  
...  
Keyword(s):  
Ft Ir ◽  
Self Association ◽  
Ir Study

Milk acetone determination by the photometrical method after microdiffusion and via FT infra-red spectroscopy

2011 ◽  
Vol 28 (1) ◽  
pp. 33-48 ◽  
Author(s):  
Oto Hanuš ◽  
Václava Genčurová ◽  
Yunhai Zhang ◽  
Pavel Hering ◽  
Jaroslav Kopecký ◽  
...  
Keyword(s):  
Infrared Spectroscopy ◽  
Indirect Method ◽  
Geometric Mean ◽  
Mid Infrared ◽  
Subclinical Ketosis ◽  
Infra Red ◽  
Variation Range ◽  
Ft Ir ◽  
Infrared Method ◽  
Photometrical Method

Milk acetone determination by the photometrical method after microdiffusion and via FT infra-red spectroscopyMilk acetone (AC) and betahydroxybutyrate (BHB) are important indicators of the energy metabolism of cows (ketosis occurrence) and an effective method for their determination, with reliable results, is of great importance. The goal of this work was to investigate the infrared method MIR-FT in terms of its calibration for milk AC and to develop a usable procedure. The microdiffusion photometric (485 nm; Spekol 11) method was used with salicylaldehyde as a reference (Re) and mid infrared spectroscopy FT (MIR-FT: Lactoscope FT-IR, Delta; MilkoScan FT 6000, M-Sc) as an indirect method. The acetone addition to milk had no recovery using MIR-FT (Delta). The reference AC set must have acceptable statistics for good MIR-FT calibration (M-Sc) and they were: 10.1 ± 9.74 at a geometric mean of 7.26 mg l-1, and a variation range from 1.98 to 33.66 mg l-1. The AC correlation between Re and MIR-FT (Delta) was low at 0.32 (P>0.05 but the Log AC relationship between Re and MIR-FT (M-Sc) was markedly better at 0.80 (P<0.01). The conversion of >10 mg l-1 as an AC subclinical ketosis limit could be > -0.80 (feedback 0.158 mmol l-1 = 9.25 mg l-1) and > -1.66. This could be important for ketosis monitoring (using M-Sc).

scholarly journals Quantification and Classification of Diclofenac Sodium Content in Dispersed Commercially Available Tablets by Attenuated Total Reflection Infrared Spectroscopy and Multivariate Data Analysis

2021 ◽  
Vol 14 (5) ◽  
pp. 440
Author(s):  
Eirini Siozou ◽  
Vasilios Sakkas ◽  
Nikolaos Kourkoumelis
Keyword(s):  
Infrared Spectroscopy ◽  
Low Cost ◽  
Diclofenac Sodium ◽  
Reference Method ◽  
Sodium Content ◽  
Attenuated Total Reflection ◽  
Accuracy And Precision ◽  
Significant Difference ◽  
Ft Ir

A new methodology, based on Fourier transform infrared spectroscopy equipped with an attenuated total reflectance accessory (ATR FT-IR), was developed for the determination of diclofenac sodium (DS) in dispersed commercially available tablets using chemometric tools such as partial least squares (PLS) coupled with discriminant analysis (PLS-DA). The results of PLS-DA depicted a perfect classification of the tablets into three different groups based on their DS concentrations, while the developed model with PLS had a sufficiently low root mean square error (RMSE) for the prediction of the samples’ concentration (~5%) and therefore can be practically used for any tablet with an unknown concentration of DS. Comparison with ultraviolet/visible (UV/Vis) spectrophotometry as the reference method revealed no significant difference between the two methods. The proposed methodology exhibited satisfactory results in terms of both accuracy and precision while being rapid, simple and of low cost.

scholarly journals Changes of Pd Oxidation State in Pd/Al2O3 Catalysts Using Modulated Excitation DRIFTS

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 116
Author(s):  
Gian Luca Chiarello ◽  
Ye Lu ◽  
Miren Agote-Arán ◽  
Riccardo Pellegrini ◽  
Davide Ferri
Keyword(s):  
Particle Size ◽  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Oxidation State ◽  
Diffuse Reflectance ◽  
X Ray ◽  
Spectral Changes ◽  
Diffuse Reflectance Infrared ◽  
X Ray Absorption ◽  
Reversible Reduction

Infrared spectroscopy is typically not used to establish the oxidation state of metal-based catalysts. In this work, we show that the baseline of spectra collected in diffuse reflectance mode of a series of Pd/Al2O3 samples of increasing Pd content varies significantly and reversibly under alternate pulses of CO or H2 and O2. Moreover, these baseline changes are proportional to the Pd content in Pd/Al2O3 samples exhibiting comparable Pd particle size. Similar measurements by X-ray absorption spectroscopy on a different 2 wt.% Pd/Al2O3 confirm that the baseline changes reflect the reversible reduction-oxidation of Pd. Hence, we demonstrate that changes in oxidation state of metal-based catalysts can be determined using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and that this behavior is part of the spectral changes that are returned by experiments under operando conditions.

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