scholarly journals Guanine: A Combined Study Using Vibrational Spectroscopy and Theoretical Methods

2012 ◽  
Vol 27 ◽  
pp. 273-292 ◽  
Author(s):  
R. Pedro Lopes ◽  
M. Paula M. Marques ◽  
Rosendo Valero ◽  
John Tomkinson ◽  
Luís A. E. Batista de Carvalho
Keyword(s):  
Vibrational Spectroscopy ◽  
Significant Contribution ◽  
Inelastic Neutron Scattering ◽  
Spectroscopic Characterization ◽  
Inelastic Neutron ◽  
Condensed State ◽  
Purine Base ◽  
Mechanical Methods ◽  
Prevalent Form

The present paper reports a conformational study of solid-state anhydrous guanine, using vibrational spectroscopy techniques—infrared, Raman, and inelastic neutron scattering—coupled to quantum mechanical methods at the DFT level, both for the isolated molecule and the condensed state. In both cases, the 7H-keto-amino tautomer was found to be the prevalent form, contrary to aqueous solutions and hydrated polycrystalline guanine, where the 9H-keto-amino tautomer is the most favoured species. This paper is a significant contribution for the existing spectroscopic characterization of this purine base, by unambiguously assigning its vibrational spectra.

scholarly journals Spectroscopic Characterization of Omeprazole and Its Salts

2017 ◽  
Vol 2017 ◽  
pp. 1-11
Author(s):  
Tomislav Vrbanec ◽  
Primož Šket ◽  
Franci Merzel ◽  
Matej Smrkolj ◽  
Jože Grdadolnik
Keyword(s):  
Vibrational Spectroscopy ◽  
Alkali Metals ◽  
Alkaline Earth ◽  
Active Pharmaceutical Ingredient ◽  
Spectroscopic Characterization ◽  
Infrared And Raman Spectroscopy ◽  
Acid Environment ◽  
Ph Range ◽  
Spectroscopic Tool

During drug development, it is important to have a suitable crystalline form of the active pharmaceutical ingredient (API). Mostly, the basic options originate in the form of free base, acid, or salt. Substances that are stable only within a certain pH range are a challenge for the formulation. For the prazoles, which are known to be sensitive to degradation in an acid environment, the formulation is stabilized with alkaline additives or with the application of API formulated as basic salts. Therefore, preparation and characterization of basic salts are needed to monitor any possible salinization of free molecules. We synthesized salts of omeprazole from the group of alkali metals (Li, Na, and K) and alkaline earth metals (Mg, Ca). The purpose of the presented work is to demonstrate the applicability of vibrational spectroscopy to discriminate between the OMP and OMP-salt molecules. For this reason, the physicochemical properties of 5 salts were probed using infrared and Raman spectroscopy, NMR, TG, DSC, and theoretical calculation of vibrational frequencies. We found out that vibrational spectroscopy serves as an applicable spectroscopic tool which enables an accurate, quick, and nondestructive way to determine the characteristic of OMP and its salts.

scholarly journals Investigations of Hydrocarbon Species on Solid Catalysts by Inelastic Neutron Scattering

2020 ◽  
Author(s):  
Longfei Lin ◽  
Qingqing Mei ◽  
Xue Han ◽  
Stewart F. Parker ◽  
Sihai Yang
Keyword(s):  
Heterogeneous Catalysis ◽  
Neutron Scattering ◽  
Vibrational Spectroscopy ◽  
Inelastic Neutron Scattering ◽  
Inelastic Neutron ◽  
Surface Species ◽  
Catalytic Systems ◽  
Selection Rules ◽  
Solid Catalysts ◽  
Wide Range

Abstract The status of surface species on solid catalysts during heterogeneous catalysis is often mysterious. Investigations of these surface species are crucial to deconvolute the reaction network and design more efficient catalysts. Vibrational spectroscopy is a powerful technique to study the interactions between surface species and the catalysts and infrared (IR) and Raman spectroscopies have been widely applied to study reaction mechanisms in heterogeneous catalysis. However, IR/Raman spectra are difficult to model computationally and important vibrational modes may be IR-, Raman- (or both) inactive due to restrictions by optical selection rules. Inelastic neutron scattering (INS) is another form of vibrational spectroscopy and relies on the scattering of neutrons by the atomic nucleus. A consequence of this is that INS is not subject to any optical selection rules and all vibrations are measurable in principle. INS spectroscopy has been used to investigate surface species on catalysts in a wide range of heterogeneous catalytic reactions. In this mini-review, we focus on applications of INS in two important fields: petrochemical reactions and C1 chemistry. We introduce the basic principles of the INS technique, followed by a discussion of its application in investigating two key catalytic systems: (i) the behaviour of hydrocarbons on metal-oxide and zeolite catalysts and (ii) the formation of hydrocarbonaceous species on methane reforming and Fischer–Tropsch catalysts. The power of INS in studying these important catalytic systems is demonstrated.

Spectroscopic characterization of actinide materials

MRS Bulletin ◽  
2010 ◽  
Vol 35 (11) ◽  
pp. 889-895 ◽  
Author(s):  
R. Caciuffo ◽  
E. C. Buck ◽  
D. L. Clark ◽  
G. van der Laan
Keyword(s):  
Electronic Structure ◽  
Degrees Of Freedom ◽  
Inelastic Neutron Scattering ◽  
Occupation Number ◽  
Spectroscopic Characterization ◽  
Inelastic Neutron ◽  
Spectroscopic Techniques ◽  
Magnetic Fluctuations ◽  
Electronic Density ◽  
X Ray

Advanced spectroscopic techniques provide new and unique tools for unraveling the nature of the electronic structure of actinide materials. Inelastic neutron scattering experiments, which address temporal aspects of lattice and magnetic fluctuations, probe electromagnetic multipole interactions and the coupling between electronic and vibrational degrees of freedom. Nuclear magnetic resonance clearly demonstrates different magnetic ground states at low temperature. Photoemission spectroscopy provides information on the occupied part of the electronic density of states and has been used to investigate the momentum-resolved electronic structure and the topology of the Fermi surface in a variety of actinide compounds. Furthermore, x-ray absorption and electron energy-loss spectroscopy have been used to probe the relativistic nature, occupation number, and degree of localization of 5f electrons across the actinide series. More recently, element- and edge-specific resonant and non-resonant inelastic x-ray scattering experiments have provided the opportunity of measuring elementary electronic excitations with higher resolution than traditional absorption techniques. Here, we will discuss results from these spectroscopic techniques and what they tell us of the electronic and magnetic properties of selected actinide materials.

scholarly journals Vibrational spectroscopy of metal methanesulfonates: M = Na, Cs, Cu, Ag, Cd

2018 ◽  
Vol 5 (4) ◽  
pp. 171574 ◽  
Author(s):  
Stewart F. Parker ◽  
Lisha Zhong
Keyword(s):  
Density Functional Theory ◽  
Vibrational Spectroscopy ◽  
Spectroscopic Data ◽  
Density Functional ◽  
Inelastic Neutron Scattering ◽  
Inelastic Neutron ◽  
Functional Theory ◽  
Methyl Group ◽  
Transition Energies ◽  
Mode Of Coordination

In this work, we have used a combination of vibrational spectroscopy (infrared, Raman and inelastic neutron scattering) and periodic density functional theory to investigate six metal methanesulfonate compounds that exhibit four different modes of complexation of the methanesulfonate ion: ionic, monodentate, bidentate and pentadentate. We found that the transition energies of the modes associated with the methyl group (C–H stretches and deformations, methyl rock and torsion) are essentially independent of the mode of coordination. The SO 3 modes in the Raman spectra also show little variation. In the infrared spectra, there is a clear distinction between ionic (i.e. not coordinated) and coordinated forms of the methanesulfonate ion. This is manifested as a splitting of the asymmetric S–O stretch modes of the SO 3 moiety. Unfortunately, no further differentiation between the various modes of coordination: unidentate, bidentate etc … is possible with the compounds examined. While it is likely that such a distinction could be made, this will require a much larger dataset of compounds for which both structural and spectroscopic data are available than that available here.

Vibrational spectroscopy of superconducting K3C60 by inelastic neutron scattering

Nature ◽  
1991 ◽  
Vol 354 (6353) ◽  
pp. 462-463 ◽  
Author(s):  
Kosmas Prassides ◽  
John Tomkinson ◽  
Christos Christides ◽  
Matthew J. Rosseinsky ◽  
D. W. Murphy ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Vibrational Spectroscopy ◽  
Inelastic Neutron Scattering ◽  
Inelastic Neutron
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