Diradicals acting through diamagnetic phenylene vinylene bridges: Raman spectroscopy as a probe to characterize spin delocalization

We present a complete Raman spectroscopic study in two structurally well-defined diradical species of different lengths incorporating oligo p-phenylene vinylene bridges between two polychlorinated triphenylmethyl radical units, a disposition that allows sizeable conjugation between the two radicals through and with the bridge. The spectroscopic data are interpreted and supported by quantum chemical calculations. We focus the attention on the Raman frequency changes, interpretable in terms of: (i) bridge length (conjugation length); (ii) bridge conformational structure; and (iii) electronic coupling between the terminal radical units with the bridge and through the bridge, which could delineate through-bond spin polarization, or spin delocalization. These items are addressed by using the"oligomer approach" in conjunction with pressure and temperature dependent Raman spectroscopic data. In summary, we have attempted to translate the well-known strategy to study the electron (charge) structure of π−conjugated molecules by Raman spectroscopy to the case of electron (spin) interactions via the spin delocalization mechanism.

In-line Monitoring of Precipitation Process using Raman Spectroscopy and ATR-FTIR

Polymorfian jatkuva seuranta saostuksessa on hyödyllistä suunnittelun ja kidetuotteen ominaisuuksien sekä kiteytystä seuraavan jatkoprosessoinnin kannalta. Tässä diplomityössä on tutkittu L-glutamiinihapon kahden (- ja ß) polymorfimuodon liukoisuuden riippuvuutta pH:sta ja lämpötilasta.Tulokseksi saatiin, että kummankin polymorfin liukoisuus kasvoi sekä pH:ta ettälämpötilaa kasvatettaessa. ¿¿muodon liukoisuus oli korkeampi kuin ß-muodon liukoisuus valituilla pH-arvoilla eri lämpötiloissa. Lisäksi seurattiin puolipanostoimisen saostuksen aikana 1-litraisella laboratoriokiteyttimellä muodostuvan kiteisen polymorfiseoksen koostumusta hyödyntäen in-line Raman-spektroskopiaa. Myös liuoksen pH-muutosta seurattiin sekä liuoksen koostumusta ATR FTIR-spektroskopian (Attenuated Total Reflection Fourier Transform Infrared Spectrometer) avulla. Tutkittavina muuttujina olivat mm. sekoitusintensiteetti, sekoitintyyppi, reaktanttien (natriumglutamaatti ja rikkihappo) konsentraatiot sekä syötetyn rikkihapon syöttökohta kiteyttimessä. Työhön sisältyi 36 koetta ja osa kokeista toistettiin tulosten oikeellisuuden tarkistamiseksi. Inline-mittaustulosten verifioimiseksi kidenäytteet analysoitiin myös käyttämällä konfokaali Raman-mikroskooppia. Kidemorfologiaa tutkittiin SEM-kuvien (Scanning Eletronic Microscope) avulla. Työ osoitti, että Raman-spektroskopia on joustava ja luotettava menetelmä saostusprosessin jatkuvaan seurantaan L-glutamiinihapolla. Alhaiset lähtöainepitoisuudet tuottivat pääasiassa ¿¿muotoa, kun taas alhainen sekoitusteho edisti ß-muodon muodostumista. Syöttökohta vaikutti merkittävästi polymorfiaan. Kun rikkihapon syöttökohta oli epäideaalisesti sekoitetulla vyöhykkeellä, nousi ylikylläisyystaso korkeaksi ja päätuote oli tällöin ß-muotoa. 6-lapainen vinolapaturbiini (nousukulma 45o) ja 6-lapainen levyturbiini eivät merkittävästi poikenneet toisistaan muodostuvien polymorfien osalta.

Raman spectroscopy and microspectroscopy of reactive dyes on cotton fibres: analysis and detection limits

A collaborative study on Raman spectroscopy and microspectrophotometry (MSP) was carried out by members of the ENFSI (European Network of Forensic Science Institutes) European Fibres Group (EFG) on different dyed cotton fabrics. The detection limits of the two methods were tested on two cotton sets with a dye concentration ranging from 0.5 to 0.005% (w/w). This survey shows that it is possible to detect the presence of dye in fibres with concentrations below that detectable by the traditional methods of light microscopy and microspectrophotometry (MSP). The MSP detection limit for the dyes used in this study was found to be a concentration of 0.5% (w/w). At this concentration, the fibres appear colourless with light microscopy. Raman spectroscopy clearly shows a higher potential to detect concentrations of dyes as low as 0.05% for the yellow dye RY145 and 0.005% for the blue dye RB221. This detection limit was found to depend both on the chemical composition of the dye itself and on the analytical conditions, particularly the laser wavelength. Furthermore, analysis of binary mixtures of dyes showed that while the minor dye was detected at 1.5% (w/w) (30% of the total dye concentration) using microspectrophotometry, it was detected at a level as low as 0.05% (w/w) (10% of the total dye concentration) using Raman spectroscopy. This work also highlights the importance of a flexible Raman instrument equipped with several lasers at different wavelengths for the analysis of dyed fibres. The operator and the set up of the analytical conditions are also of prime importance in order to obtain high quality spectra. Changing the laser wavelength is important to detect different dyes in a mixture.

Monomer conversion of composite dental resins photoactivated by a halogen lamp and a LED: a FT-Raman spectroscopy study

Eighteen circular blocks of resins cured either by a LED or a halogen lamp (20, 40 and 60 s), had their top (T) and bottom (B) surfaces studied using a FT-Raman spectrometer. Systematic changes in the intensity of the methacrylate C=C stretching mode at 1638 cm-1 as a function of exposure duration were observed. The calculated degree of conversion (DC) ranged from 45.0% (B) to 52.0% (T) and from 49.0% (B) to 55.0% (T) for the LED and halogen lamp, respectively. LED and halogen light produced similar DC values with 40 and 60 s of irradiation.

Quantification of the bond-angle dispersion by Raman spectroscopy and the strain energy of amorphous silicon

A thorough critical analysis of the theoretical relationships between the bond-angle dispersion in a-Si, Δθ, and the width of the transverse optical Raman peak, Γ, is presented. It is shown that the discrepancies between them are drastically reduced when unified definitions for Δθ and Γ are used. This reduced dispersion in the predicted values of Δθ together with the broad agreement with the scarce direct determinations of Δθ is then used to analyze the strain energy in partially relaxed pure a-Si. It is concluded that defect annihilation does not contribute appreciably to the reduction of the a-Si energy during structural relaxation. In contrast, it can account for half of the crystallization energy, which can be as low as 7 kJ/mol in defect-free a-Si

Quantification of the bond-angle dispersion by Raman spectroscopy and the strain energy of amorphous silicon

A thorough critical analysis of the theoretical relationships between the bond-angle dispersion in a-Si, Δθ, and the width of the transverse optical Raman peak, Γ, is presented. It is shown that the discrepancies between them are drastically reduced when unified definitions for Δθ and Γ are used. This reduced dispersion in the predicted values of Δθ together with the broad agreement with the scarce direct determinations of Δθ is then used to analyze the strain energy in partially relaxed pure a-Si. It is concluded that defect annihilation does not contribute appreciably to the reduction of the a-Si energy during structural relaxation. In contrast, it can account for half of the crystallization energy, which can be as low as 7 kJ/mol in defect-free a-Si

Use of in situ FT-Raman spectroscopy to study the kinetics of the transformation of carbamazepine polymorphs

The solid-state transformation of carbamazepine from form III to form I was examined by Fourier Transform Raman spectroscopy. Using a novel environmental chamber, the isothermal conversion was monitored in situ at 130◦C, 138◦C, 140◦C and 150◦C. The rate of transformation was monitored by taking the relative intensities of peaks arising from two C H bending modes; this approach minimised errors due to thermal artefacts and variations in power intensities or scattering efficiencies from the samples in which crystal habit changed from a characteristic prism morphology (form III) to whiskers (form I). The solid-state transformation at the different temperatures was fitted to various solid-state kinetic models of which four gave good fits, thus indicating the complexity of the process which is known to occur via a solid–gas–solid mechanism. Arrhenius plots from the kinetic models yielded activation energies from 344 kJ mol−1 to 368 kJ mol−1 for the transformation. The study demonstrates the value of a rapid in situ analysis of drug polymorphic type which can be of value for at-line in-process control.

Quantitative analysis of mannitol polymorphs: FT-Raman spectroscopy

Mannitol is a polymorphic excipient which is usually used in pharmaceutical products as the beta form, although other polymorphs (alpha and delta) are common contaminants. Binary mixtures containing beta and delta mannitol were prepared to quantify the concentration of the beta form using FT-Raman spectroscopy. Spectral regions characteristic of each form were selected and peak intensity ratios of beta peaks to delta peaks were calculated. Using these ratios, a correlation curve was established which was then validated by analysing further samples of known composition. The results indicate that levels down to 2% beta could be quantified using this novel, non-destructive approach. Potential errors associated with quantitative studies using FT-Raman spectroscopy were also researched. The principal source of variability arose from inhomogeneities on mixing of the samples; a significant reduction of these errors was observed by reducing and controlling the particle size range. The results show that FT-Raman spectroscopy can be used to rapidly and accurately quantitate polymorphic mixtures.

Monitoring the penetration enhancer dimethyl sulfoxide in human stratum corneum in vivo by confocal raman spectroscopy

The stratum corneum (SC) barrier typically consists of layers of corneocytes embedded in a lipid continuum that regulates barrier function. The lipid domain containing ceramides, cholesterol, and free fatty acids provides the major pathway for most drugs permeating across SC. Penetration enhancers diminish the SC barrier function. The classic enhancer is dimethyl sulfoxide (DMSO). Its mechanisms of action remain unclear, although DMSO disrupts lipid organisation and may displace protein-bound water. Here we use confocal Raman spectroscopy to probe molecular interactions between a finite (depleting) dose of DMSO and SC, as functions of depth and time, providing novel information about residence time and location of DMSO in human SC in vivo

Determination of orientations of aromatic groups in self-assembled peptide fibrils by polarised Raman spectroscopy

In this paper we describe a novel combination of Raman spectroscopy, isotope editing and X-ray scattering as a powerful approach to give detailed structural information on aromatic side chains in peptide fibrils. The orientation of the tyrosine residues in fibrils of the peptide YTIAALLSPYS with respect to the fibril axis has been determined from a combination of polarised Raman spectroscopy and X-ray diffraction measurements. The Raman intensity of selected tyrosine bands collected at different polarisation geometries is related to the values and orientation of the Raman tensor for those specific vibrations. Using published Raman tensor values we solved the relevant expressions for both of the two tyrosine residues present in this peptide. Ring deuteration in one of the two tyrosine side chains allowed for the calculation to be performed individually for both, by virtue of the isotopic shift that eliminates band overlapping. Sample disorder was taken into account by obtaining the distribution of orientations of the samples from X-ray diffraction experiments. The results provide previously unavailable details about the molecular conformation of this peptide, and demonstrate the value of this approach for the study of amyloid fibrils.

New insights into the compressibility and high-pressure stability of Ni(CN)2: a combined study of neutron diffraction, Raman spectroscopy, and inelastic neutron scattering

Nickel cyanide is a layered material showing markedly anisotropic behaviour. High-pressure neutron diffraction measurements show that at pressures up to 20.1 kbar, compressibility is much higher in the direction perpendicular to the layers, c, than in the plane of the strongly chemically bonded metal-cyanide sheets. Detailed examination of the behaviour of the tetragonal lattice parameters, a and c, as a function of pressure reveal regions in which large changes in slope occur, for example, in c(P) at 1 kbar. The experimental pressure dependence of the volume data is fitted to a bulk modulus, B0, of 1050 (20) kbar over the pressure range 0–1 kbar, and to 124 (2) kbar over the range 1–20.1 kbar. Raman spectroscopy measurements yield additional information on how the structure and bonding in the Ni(CN)2 layers change with pressure and show that a phase change occurs at about 1 kbar. The new high-pressure phase, (Phase PII), has ordered cyanide groups with sheets of D4h symmetry containing Ni(CN)4 and Ni(NC)4 groups. The Raman spectrum of phase PII closely resembles that of the related layered compound, Cu1/2Ni1/2(CN)2, which has previously been shown to contain ordered C≡N groups. The phase change, PI to PII, is also observed in inelastic neutron scattering studies which show significant changes occurring in the phonon spectra as the pressure is raised from 0.3 to 1.5 kbar. These changes reflect the large reduction in the interlayer spacing which occurs as Phase PI transforms to Phase PII and the consequent increase in difficulty for out-of-plane atomic motions. Unlike other cyanide materials e.g. Zn(CN)2 and Ag3Co(CN)6, which show an amorphization and/or a decomposition at much lower pressures (~100 kbar), Ni(CN)2 can be recovered after pressurising to 200 kbar, albeit in a more ordered form.

Raman spectroscopy analysis of structural photoinduced changes in GeS(2) + Ga(2)O(3) thin films

Photoexpansion and photobleaching effects have been observed in amorphous GeS(2) + Ga(2)O(3) (GGSO) thin films, when their surfaces were exposed to UV light. The photoinduced changes on the surface of the samples are indications that the structure has been changed as a result of photoexcitation. In this paper, micro-Raman, energy dispersive X-ray analysis (EDX) and backscattering electrons (BSE) microscopy were the techniques used to identify the origin of these effects. Raman spectra revealed that these phenomena are a consequence of the Ge-S bonds` breakdown and the formation of new Ge-O bonds, with an increase of the modes associated with Ge-O-Ge bonds and mixed oxysulphide tetrahedral units (S-Ge-O). The chemical composition measured by EDX and BSE microscopy images indicated that the irradiated area is oxygen rich. So, the present paper provides fundamental insights into the influence of the oxygen within the glass matrix on the considered photoinduced effects. (C) 2010 Elsevier B.V. All rights reserved.