Biomedical subjects

Ray L Frost

Publications and source records attributed to Ray L Frost.

At least 55 records · Page 3Linked to original sources

PubMed2005

Using Raman spectroscopy to identify mixite minerals.

Raman spectroscopy has been used to identify whether or not a selection of minerals labelled as mixites (formula BiCu6(AsO4)3(OH)6.3H2O) are correctly marked. Of the four samples, two samples are shown to be potentially mixites because of the presence of the characteristic Raman spectra of (AsO4)3- units and (HAsO4)- units, characterised by bands at around 803 and 833 cm(-1). Two of the minerals are shown to be predominantly carbonates. Bands are observed at 3473.9 and 3470.3 cm(-1) for the two mixite samples. Bands observed in the region 880-910 cm(-1) and in the 867-870 cm(-1) region are assigned to the AsO stretching vibrations of (HAsO4)2- and (H2AsO4)- units. Whilst bands at around 803 and 833 cm(-1) are assigned to the stretching vibrations of uncomplexed (AsO4)3- units. Intense bands observed at 473.7 and 475.4 cm(-1) are assigned to the nu4 bending mode of AsO4 units. Bands observed at around 386.5, 395.3 and 423.1 cm(-1) are assigned to the nu2 bending modes of the HAsO4 (434 and 400 cm(-1)) and the AsO4 groups (324 cm(-1)). Raman spectroscopy lends itself to the identification of minerals on host matrices and is especially useful for the identification of mixites.

Arsenates↗

PubMed2005

Raman spectroscopy of halotrichite from Jaroso, Spain.

Raman spectroscopy complimented with infrared ATR spectroscopy has been used to characterise a halotrichite FeSO(4) x Al(2)(SO(4))(3) x 22 H(2)O from The Jaroso Ravine, Aquilas, Spain. Halotrichites form a continuous solid solution series with pickingerite and chemical analysis shows that the jarosite contains 6% Mg(2+). Halotrichite is characterised by four infrared bands at 3569.5, 3485.7, 3371.4 and 3239.0 cm(-1). Using Libowitsky type relationships, hydrogen bond distances of 3.08, 2.876, 2.780 and 2.718 Angstrom were determined. Two intense Raman bands are observed at 987.7 and 984.4 cm(-1) and are assigned to the nu(1) symmetric stretching vibrations of the sulphate bonded to the Fe(2+) and the water units in the structure. Three sulphate bands are observed at 77K at 1000.0, 991.3 and 985.0 cm(-1) suggesting further differentiation of the sulphate units. Raman spectrum of the nu(2) and nu(4) region of halotrichite at 298 K shows two bands at 445.1 and 466.9 cm(-1), and 624.2 and 605.5 cm(-1), respectively, confirming the reduction of symmetry of the sulphate in halotrichite.

Alum Compounds↗

PubMed2005

Raman spectroscopy of newberyite, hannayite and struvite.

The phosphate minerals hannayite, newberyite and struvite have been studied by Raman spectroscopy using a thermal stage. Hannayite and newberyite are characterised by an intense band at around 980cm(-1) assigned to the v(1) symmetric stretching vibration of the HPO(4) units. In contrast the symmetric stretching mode is observed at 942cm(-1) for struvite. The Raman spectra are characterised by multiple v(3) anti-symmetric stretching bands and v(2) and v(4) bending modes indicating strong distortion of the HPO(4) and PO(4) units. Hannayite and newberyite are defined by bands at 3382 and 3350cm(-1) attributed to HOPO(3) vibrations and hannayite and struvite by bands at 2990, 2973 and 2874 assigned to NH(4)(+) bands. Raman spectroscopy has proven most useful for the analysis of these 'cave' minerals where complex paragenetic relationships exist between the minerals.

Magnesium Compounds↗

PubMed2005

Raman spectroscopy of the mineral rhodonite.

The mineral rhodonite an orthosilicate has been characterised by Raman spectroscopy. The Raman spectra of three rhodonites from Broken Hill, Pachapaqui and Franklin were compared and found to be similar. The spectra are characterised by an intense band at around 1000 cm(-1) assigned to the nu(1) symmetric stretching mode and three bands at 989, 974 and 936 cm(-1) assigned to the nu(3) antisymmetric stretching modes of the SiO(4) units. An intense band at around 667 cm(-1) was assigned to the nu(4) bending mode and showed additional bands exhibiting loss of degeneracy of the SiO(4) units. The low wave number region of rhodonite is complex. A strong band at 421.9 cm(-1) is attributed to the nu(2) bending mode. The spectra of the three rhodonite mineral samples are similar but subtle differences are observed. It is proposed that these differences depend upon the cationic substitution of Mn by Ca and/or Fe(2+) and Mg.

Calcium↗

PubMed2005

Near-infrared spectroscopy of autunites.

NIR spectroscopy has been applied to the study water in the interlayer of the autunite minerals. The spectra of autunites and metaautunites in the first HOH fundamental overtone are different and the spectra of autunites of different origins in the 6000-7500 cm(-1) region are considerably different. A number of conclusions are made based upon the NIR spectra: (a) The spectra of different autunites are different in the NIR spectral region; (b) the spectra of metaautunites show similarity; (c) the spectra of metaautunites are different from that of autunites. NIR spectroscopy provides a method of determination of the structure of water in the interlayer of natural autunites. The implication from the variation in the NIR spectra is that the structural arrangement of water for different autunites is different and is sample dependent. NIR spectroscopy has a wide potential for the study of the autunite minerals.

Aluminum Silicates↗

PubMed2005

Infrared spectroscopy of organoclays synthesized with the surfactant octadecyltrimethylammonium bromide.

Infrared (IR) spectroscopy using a smart endurance single bounce diamond attenuated total reflection (ATR) cell has been used to study the changes in the spectra of the surfactant octadecyltrimethylammonium (ODTMA) bromide upon intercalation into a sodium montmorillonite. The wavenumbers of bands attributed to CH-stretching and CH-bending vibrations, in general, decrease as the concentration of the surfactant measured in terms of the cation exchange capacity (CEC) up to 1.0 CEC. After this point, the bands increase approaching a value the same as that of the surfactant. Significant changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane (SiO) surface of the montmorillonite. Such a concept is supported by changes in the SiO-stretching bands of the montmorillonite siloxane surface.

Bentonite↗

PubMed2005

NIR spectroscopy of selected iron(II) and iron(III) sulphates.

A problem exists when closely related minerals are found in paragenetic relationships. The identification of such minerals cannot be undertaken by normal techniques such as X-ray diffraction. Vibrational spectroscopic techniques may be applicable especially when microtechniques or fibre-optic techniques are used. NIR spectroscopy is one technique, which can be used for the identification of these paragenetically related minerals and has been applied to the study of selected iron(II) and iron(III) sulphates. The near-IR spectral regions may be conveniently divided into four regions: (a) the high wavenumber region>7500 cm(-1), (b) the high wavenumber region between 6400 and 7400 cm(-1) attributed to the first overtone of the fundamental hydroxyl stretching mode, (c) the 5500-6300 cm(-1) region attributed to water combination modes of the hydroxyl fundamentals of water, and (d) the 4000-5500 cm(-1) region attributed to the combination of the stretching and deformation modes of the iron(II) and iron(III) sulphates. The minerals containing iron(II) show a strong, broad band with splitting, around 11,000-8000 cm(-1) attributed to (5)T(2g)-->(5)E(g) transition. This shows the ferrous ion has distorted octahedral coordination in some of these sulphate minerals. For each of these regions, the minerals show distinctive spectra, which enable their identification and characterisation. NIR spectroscopy is a less used technique, which has great application for the study of minerals, particularly minerals that have hydrogen in the structure either as hydroxyl units or as water bonded to the cation as is the case for iron(II) and iron(III) sulphates. The study of minerals on planets is topical and NIR spectroscopy provides a rapid technique for the distinction and identification of iron(II) and iron(III) sulphates minerals.

Ferric Compounds↗

PubMed2005

Near-infrared spectroscopic study of selected hydrated hydroxylated phosphates.

Near-infrared spectroscopy has been applied to a suite of hydrated hydroxylated phosphate minerals including cacoxenite, hureaulite, planerite, gormanite and wardite. The NIR spectra may be conveniently divided into three regions (a) the first hydroxyl fundamental, (b) the water HOH overtone and (c) the region between 4000 and 4800 cm(-1) where combination bands resulting from the bands in the mid-IR. For each of these regions, the minerals show distinctive spectra which enable their identification and characterisation. NIR spectroscopy is a less used technique which does have great application for the study of minerals, particularly minerals which have hydrogen in the structure either as hydroxyl units or as water bonded to the cation or as zeolitic water as is the case for cacoxenite. The study of minerals on planets is topical and NIR spectroscopy provides a rapid technique for the distinction and identification of minerals.

Hydroxylation↗

PubMed2005

Near-infrared spectroscopy of stitchtite, iowaite, desautelsite and arsenate exchanged takovite and hydrotalcite.

The hydrotalcite minerals stitchtite, iowaite and desautelsite together with the arsenate exchanged takovite and arsenate exchanged hydrotalcite have been studied using near-IR reflectance spectroscopy. Each mineral has its own characteristic NIR spectrum enabling recognition of the particular hydrotalcite. As such the technique has application in the field for the analysis and identification of hydrotalcites. Hydrotalcites have proven useful as an anion exchange material. Takovite and hydrotalcite were used to exchange carbonate anions by arsenate. Three Near-IR spectral regions are identified: (a) the high wavenumber region between 6400 and 7400 cm(-1) attributed to the first overtone of the fundamental hydroxyl stretching mode, (b) the 4800-5400 cm(-1) region attributed to water combination modes of the hydroxyl fundamentals of water, and (c) the 4000-4800 cm(-1) region attributed to the combination of the stretching and deformation modes of the MOH units of the hydrotalcites. NIR spectroscopy enables the separation of the hydroxyl bands of the water and M-OH units for the hydrotalcites. Compared with the NIR spectroscopy of the structural units of the hydrotalcites namely gibbsite and brucite, the bands are broad.

Aluminum Hydroxide↗

PubMed2005

Peisleyite an unusual mixed anion mineral--a vibrational spectroscopic study.

The mineral peisleyite has been studied using a combination of electron microscopy and vibrational spectroscopy. Scanning electron microscope (SEM) photomicrographs reveal that the peisleyite morphology consists of an array of small needle-like crystals of around 1 microm in length with a thickness of less than 0.1 microm. Raman spectroscopy in the hydroxyl stretching region shows an intense band at 3506 cm(-1) assigned to the symmetric stretching mode of the OH units. Four bands are observed at 3564, 3404, 3250 and 3135 cm(-1) in the infrared spectrum. These wavenumbers enable an estimation of the hydrogen bond distances 3.052(5), 2.801(0), 2.705(6) and 2.683(6)A. Two intense Raman bands are observed at 1023 and 989 cm(-1) and are assigned to the SO(4) and PO(4) symmetric stretching modes. Other bands are observed at 1356, 1252, 1235, 1152, 1128, 1098 and 1067 cm(-1). The bands at 1067 cm(-1) is attributed to AlOH deformation vibrations. Bands in the low wavenumber region are assigned to the nu(4) and nu(2) out of plane bending modes of the SO(4) and PO(4) units. Raman spectroscopy is a useful tool in determining the vibrational spectroscopy of mixed hydrated multianion minerals such as peisleyite. Information on such a mineral would be difficult to obtain by other means.

Anions↗

PubMed2005

Raman spectroscopy of likasite at 298 and 77 K.

Raman spectroscopy at 298 and 77K has been used to study the structure of likasite, a naturally occurring basic copper(II) nitrate of formula Cu3NO3(OH)5.2H2O. An intense sharp band is observed at 3522 cm(-1) at 298 K which splits into two bands at 3522 and 3505 cm(-1) at 77 K and is assigned to the OH stretching mode. The two OH stretching bands at 3522 and 3505 provide estimates of the hydrogen bond distances of these units as 2.9315 and 2.9028 angstroms. The significance of this result is that equivalent OH units in the 298 K spectrum become two non-equivalent OH units at 77 K suggesting a structural change by cooling to liquid nitrogen temperature. A number of broad bands are observed in the 298 K spectrum at 3452, 3338, 3281 and 3040 cm(-1) assigned to H2O stretching vibrations with estimates of the hydrogen bond distances of 2.8231, 2.7639, 2.7358 and 2.6436 angstroms. Three sharp bands are observed at 77 K at 1052, 1050 and 1048 cm(-1) attributed to the nu1 symmetric stretching mode of the NO3 units. Only a single band at 1050 cm(-1) is observed at 298 K, suggesting the non-equivalence of the NO3 units at 77 K, confirming structural changes in likasite by cooling to 77 K.

Chemistry, Physical↗

PubMed2005

Raman spectroscopy of synthetic and natural iowaite.

The chemistry of a magnesium based hydrotalcite known as iowaite Mg6Fe2Cl2(OH)16.4H2O has been studied using Raman spectroscopy. Iowaite has chloride as the counter anion in the interlayer. The formula of synthetic iowaite was found to be Mg5.78Fe2.09(Cl,(CO3)0.5)(OH)16.4H2O. Oxidation of natural iowaite results in the formation of Mg4FeO(Cl,CO3) (OH)8.4H2O. X-ray diffraction (XRD) shows that the iowaite is a layered structure with a d(001) spacing of 8.0 angtsroms. For synthetic iowaite three Raman bands at 1376, 1194 and 1084 cm(-1) are attributed to CO3 stretching vibrations. These bands are not observed for the natural iowaite but are observed when the natural iowaite is exposed to air. The Raman spectrum of natural iowaite shows three bands at 708, 690 and 620 cm(-1) and upon exposure to air, two broad bands are found at 710 and 648 cm(-1). The Raman spectrum of synthetic iowaite has a very broad band at 712 cm(-1). The Raman spectrum of natural iowaite shows an intense band at 527 cm(-1). The air oxidized iowaite shows two bands at 547 and 484 cm(-1) attributed to the (CO3)(2-)nu2 bending mode. Raman spectroscopy has proven most useful for the study of the chemistry of iowaite and chemical changes induced in natural iowaite upon exposure to air.

Air↗

PubMed2005

Near-infrared spectroscopy of torbernites and metatorbernites.

A suite of torbernites and metatorbernites have been analysed by near-infrared spectroscopy. The spectra of torbernites and metatorbernites in the first HOH fundamental overtone are different and the spectra of torbernites of different origins in the 6000-7500 cm(-1) region vary. NIR spectroscopy provides a method of studying the hydration of cations in the interlayer of torbernite. NIR spectroscopy shows that the spectra of torbernites from different origins in the water HOH first fundamental overtone and combination regions are different. This difference implies the hydration of cations is different for torbernite minerals. The structural arrangement of the water molecules in the interlayer is sample dependent. The NIR spectra of metatorbernites are different from that of torbernites and a similarity of the spectra of metatorbernites suggests that the water structure in metatorbernites is similar.

Cations↗

PubMed2005

Raman and infrared spectroscopy of selected vanadates.

Raman and infrared spectroscopy has been used to study the structure of selected vanadates including pascoite, huemulite, barnesite, hewettite, metahewettite, hummerite. Pascoite, rauvite and huemulite are examples of simple salts involving the decavanadates anion (V10O28)6-. Decavanadate consists of four distinct VO6 units which are reflected in Raman bands at the higher wavenumbers. The Raman spectra of these minerals are characterised by two intense bands at 991 and 965 cm(-1). Four pascoite Raman bands are observed at 991, 965, 958 and 905 cm(-1) and originate from four distinct VO6 sites. The other minerals namely barnesite, hewettite, metahewettite and hummerite have similar layered structures to the decavanadates but are based upon (V5O14)3- units. Barnesite is characterised by a single Raman band at 1010 cm(-1), whilst hummerite has Raman bands at 999 and 962 cm(-1). The absence of four distinct bands indicates the overlap of the vibrational modes from two of the VO6 sites. Metarossite is characterised by a strong band at 953 cm(-1). These bands are assigned to nu1 symmetric stretching modes of (V6O16)2- units and terminal VO3 units. In the infrared spectra of these minerals, bands are observed in the 837-860 cm(-1) and in the 803-833 cm(-1) region. In some of the Raman spectra bands are observed for pascoite, hummerite and metahewettite in similar positions. These bands are assigned to nu3 antisymmetric stretching of (V10O28)6- units or (V5O14)3- units. Because of the complexity of the spectra in the low wavenumber region assignment of bands is difficult. Bands are observed in the 404-458 cm(-1) region and are assigned to the nu2 bending modes of (V10O28)6- units or (V5O14)3- units. Raman bands are observed in the 530-620 cm(-1) region and are assigned to the nu4 bending modes of (V10O28)6- units or (V5O14)3- units. The Raman spectra of the vanadates in the low wavenumber region are complex with multiple overlapping bands which are probably due to VO subunits and MO bonds.

Minerals↗

PubMed2005

Spectroscopic characterization of chromite from the Moa-Baracoa Ophiolitic Massif, Cuba.

The Cuban chromites with a spinel structure, FeCr2O4 have been studied using optical absorption and EPR spectroscopy. The spectral features in the electronic spectra are used to map the octahedral and tetrahedral co-ordinated cations. Bands due Cr3+ and Fe3+ ions could be distinguished from UV-vis spectrum. Chromite spectrum shows two spin allowed bands at 17,390 and 23,810 cm(-1) due to Cr3+ in octahedral field and they are assigned to 4A2g(F) --> 4T2g(F) and 4A2g(F) --> 4T1g(F) transitions. This is in conformity with the broad resonance of Cr3+ observed from EPR spectrum at g = 1.903 and a weak signal at g = 3.861 confirms Fe3+ impurity in the mineral. Bands of Fe3+ ion in the optical spectrum at 13,700, 18,870 and 28,570 cm(-1) are attributed to 6A1g(S) --> 4T1g(G), 6A1g(S) --> 4T2g(G) and 6A1g(S) --> 4T2g(P) transitions, respectively. Near-IR reflectance spectroscopy has been used effectively to show intense absorption bands caused by electronic spin allowed d-d transitions of Fe2+ in tetrahedral symmetry, in the region 5000-4000 cm(-1). The high frequency region (7500-6500 cm(-1)) is attributed to the overtones of hydroxyl stretching modes. Correlation between Raman spectral features and mineral chemistry are used to interpret the Raman data. The Raman spectrum of chromite shows three bands in the CrO stretching region at 730, 560 and 445 cm(-1). The most intense peak at 730 cm(-1) is identified as symmetric stretching vibrational mode, A1g(nu1) and the other two minor peaks at 560 and 445 cm(-1) are assigned to F2g(nu4) and E(g)(nu2) modes, respectively. Cation substitution in chromite results various changes both in Raman and IR spectra. In the low-wavenumber region of Raman spectrum a significant band at 250 cm(-1) with a component at 218 cm(-1) is attributed F2g(nu3) mode. The minor peaks at 195, 175, 160 cm(-1) might be due to E(g) and F2g symmetries. Broadening of the peak of A1g mode and shifting of the peak to higher wavenumber observed as a result of increasing the proportion of Al3+O6. The presence of water in the mineral shows bands in the IR spectrum at 3550, 3425, 3295, 1630 and 1455 cm(-1). The vibrational spectrum of chromite gives raise to four frequencies at 985, 770, 710 and 650 cm(-1). The first two frequencies nu1 and nu2 are related to the lattice vibrations of octahedral groups. Due to the influence of tetrahedral bivalent cation, vibrational interactions occur between nu3 and nu4 and hence the low frequency bands, nu3 and nu4 correspond to complex vibrations involving both octahedral and tetrahedral cations simultaneously. Cr3+ in Cuban natural chromites has highest CFSE (20,868 cm(-1)) when compared to other oxide minerals.

Aluminum↗

PubMed2005

Near-infrared spectroscopy to uranyl arsenates of the autunite and metaautunite group.

A suite of uranyl arsenates have been analysed by near-infrared spectroscopy (NIR). The NIR spectra of zeunerite and metazeunerite in the first HOH fundamental overtone are different and the spectra of uranyl arsenates of different origins in the 6000-7500 cm(-1) region are different. NIR spectroscopy provides a method of determination of the hydration of uranyl arsenates and has implications for the structure of water in the interlayer. Such a conclusion is also supported by the water OH stretching region where considerable differences are observed. NIR is an excellent technique for the study of the autunite minerals and may be used to distinguish between different autunite phases such as the partially dehydrated autunites for example zeunerite and metazeunerite.

Arsenates↗

PubMed2005

Raman spectroscopic study of the hydrotalcite desautelsite Mg6Mn2CO3(OH)16 x 4H2O.

The structure of the hydrotalcite desautelsite Mg6Mn2CO3(OH)16.4H2O has been studied by a combination of Raman and infrared spectroscopy. Three intense Raman bands are observed at 1086, 1062 and 1055 cm(-1). A model based upon the observation of three CO3 stretching vibrations is presented. The CO3 anion may be (a) non-hydrogen bonded, (b) hydrogen bonded to the interlayer water and (c) hydrogen bonded to the brucite-like hydroxyl surface. Two intense bands at 3646 and 3608 cm(-1) are attributed to MgOH and MnOH stretching vibrations. Infrared bands at 3476, 3333, 3165 and 2991 cm(-1) are assigned to water stretching bands. Raman spectroscopy has proven a powerful tool for the study of hydrotalcite minerals.

Aluminum Hydroxide↗

PubMed2005

A Raman spectroscopic study of the uranyl sulphate mineral johannite.

Raman spectroscopy at 298 and 77K has been used to study the secondary uranyl mineral johannite of formula (Cu(UO2)2(SO4)2(OH)2 x 8H2O). Four Raman bands are observed at 3593, 3523, 3387 and 3234cm(-1) and four infrared bands at 3589, 3518, 3389 and 3205cm(-1). The first two bands are assigned to OH- units (hydroxyls) and the second two bands to water units. Estimations of the hydrogen bond distances for these four bands are 3.35, 2.92, 2.79 and 2.70 A. A sharp intense band at 1042 cm(-1) is attributed to the (SO4)2- symmetric stretching vibration and the three Raman bands at 1147, 1100 and 1090cm(-1) to the (SO4)2- anti-symmetric stretching vibrations. The nu2 bending modes were at 469, 425 and 388 cm(-1) at 77K confirming the reduction in symmetry of the (SO4)2- units. At 77K two bands at 811 and 786 cm(-1) are attributed to the nu1 symmetric stretching modes of the (UO2)2+ units suggesting the non-equivalence of the UO bonds in the (UO2)2+ units. The band at 786cm(-1), however, may be related to water molecules libration modes. In the 77K Raman spectrum, bands are observed at 306, 282, 231 and 210cm(-1) with other low intensity bands found at 191, 170 and 149cm(-1). The two bands at 282 and 210 cm(-1) are attributed to the doubly degenerate nu2 bending vibration of the (UO2)2+ units. Raman spectroscopy can contribute significant knowledge in the study of uranyl minerals because of better band separation with significantly narrower bands, avoiding the complex spectral profiles as observed with infrared spectroscopy.

Hydrogen Bonding↗