Strong Raman Bands Research Articles

Scytonin in gypsum endolithic colonisation: First Raman spectroscopic detection of a new spectral biosignature for terrestrial astrobiological analogues and for exobiological mission database extension

Microbial colonisations of gypsum from Eastern Poland (Badenian, Middle Miocene age) were investigated by Raman microspectrometry with a rarely used excitation 445 nm excitation. Zones of microbial colonisation in selenitic gypsum endolithic outcrops comprise algae and cyanobacteria, which commonly contain the photosynthetic and protective pigments carotenoids, scytonemin and gloeocapsin. Diagnostic bands differing from those of scytonemin have been identified in black colonies in gypsum outcrops at Chotel Czierwony (Poland). Raman spectral signatures of scytonin are reported here for the first time in two endolithic specimens identified by the band wavenumbers predicted from DFT calculations. The strong or medium strong intensity Raman bands observed at 1603, 1585, 1559, 1435, and 1424 cm−1. Other weaker bands were located at 1676 (sh), 1660 (sh), 1649, 1399, 1362, 1342, 1320, 1294, 1272, 1259, and 1052 cm−1. The first observation of the Raman spectrum of scytonin in the cyanobacterial colonisation of gypsum facilitates the inclusion of this new biomolecular signature in the library of unique Raman spectra of biological pigments invaluable for detection of traces of life in frame of the planetary missions.

Structure-Property Correlation in Sodium Borophosphate Glasses Modified with Niobium Oxide

Bulk glasses of the series (100−x)[0.4Na2O-0.2Nb2O5-0.4P2O5]-xB2O3 with x = 0–48 mol% B2O3 were prepared by slow cooling in air. Their glass transition temperature increases within the range of 0–16 mol% B2O3, but further additions of B2O3 result in its decrease. Their structure was investigated by Raman, 11B, and 31P MAS NMR spectroscopy. The relative number of BO4 units decreases with increasing B2O3 content, while the number of BO3 units increases up to 59 % at x = 48. The upfield shift of a broad resonance peak in the 31P MAS NMR spectra is ascribed to an increasing connectedness of the structural network with increasing B2O3 content. Strong Raman band at 916–929 cm−1 shows on the presence of NbO6 octahedra in the structural network of these glasses. With the B2O3 addition, a decrease in DC conductivity is observed, which is attributed to the decrease in the concentration of Na+ ions.

On closed-shell interactions between heavy main-group elements.

A series of di- and polymetal complexes involving closed-shell, heavy main-group atoms and ions shows a selection of special physical properties. These involve short metal-metal contacts, low entropies of formation and, most interestingly, strong Raman bands at low wavenumbers. These results together with the constitution of the coordination compounds, where the majority of electrons are assembled on the highly polarizable metal atoms and ions, experimental results have been interpreted in terms of direct, partial covalent metal-metal bonding. Previous theoretical studies have challenged this view and instead attributed the obvious attractive forces involved to secondary-type of interactions, such as dispersion. This study utilizes a multitude of theoretical tools, such as natural bond order (NBO) and natural energy decomposition analysis (NEDA), non-covalent interaction (NCI) analysis, electron localization functions (ELFs), and atoms-in-molecules (AIM) to characterize the interactions in models comprising closed-shell dimers, as well as experimentally studied ring and cage systems constituting the main reason for the hypotheses on metal-metal interactions. The results show that all experimental results can be attributed to the covalent interactions between the electron-rich, metal centers and the bridging anions in ring and cage coordination compounds of high symmetry, where the experimentally observed effects can be traced to the combination of covalent interactions between the metal centers and the anions along the edges of the ring and cage systems in combination with the cooperative effects generated by the high symmetry of these ring and cage systems.

Utilization of infrared, Raman spectroscopy for structural analysis of alkali boro-germanate glasses

Melt quenching technique was used to prepare (30-x)Li2O–xNa2O–40B2O3–30GeO2 glasses (x = 0, 5, 10, 20 & 30 mol %). The room temperature infrared spectra of the powdered glass samples were recorded in the range of 400–2000cm−1. Raman measurements were performed in the range of 200–2000cm−1 at room temperature. Raman and Infrared spectroscopy was utilized for structural study of this glass system. Specific modes of vibration and peak position were identified from de-convolution of infrared and Raman spectra using Gaussian fitting. Ge–O–Ge bonds’ symmetrical stretching vibrations related to 3 members GeO4 rings were allotted to the IR band of 483 cm−1. The strongest Raman band was allotted to symmetrical stretching vibrations of Ge–O in GeO4 having one non-bridging oxygen with 3 bridging oxygens at 797 cm−1. The observed Raman and IR spectra of various specimens are utilized here to explain the structural characteristics of current glass.

Synthetic Method and Oil Displacement Capacity of Nano-MoS2

Nanomaterials can be used to emulsify and reduce the fluid viscosity, reduce pore pressure, and increase injection volume. Therefore, nanomaterials have a great potential in the enhanced oil recovery. However, the current research on nanooil flooding materials mostly focuses on the evaluation of the oil-displacing effect, and the lack of research on the size of the oil-displacing materials for tight oil is obvious. In this work, 1T phase molybdenum disulfide nanosheets were prepared by one-step hydrothermal method, which were further modified with CTAB powders to obtain MoS2-CTAB nanosheet powders. Combined with SEM, TEM, and AFM methods, the nanosheets were optimized based on the appearance and morphology. The stability, wetting reversal, and oil displacement capacity of selected nanosheets were tested. The results show that the best experimental condition to synthesize small-sized molybdenum disulfide is 200°C in the weak acid environment through 12 h. Due to the steric hindrance effect of the CATB molecule, the size and interlayer gap of MoS2 nanosheets increased slightly after modification. The layer gap reaches to 0.7 nm, and the number of stacked layers is 3~4 layers. Strong Raman bands are observed at 137 cm-1, 291 cm-1, and 391 cm-1, which indicates that the synthesized product is 1T MoS2. The modified MoS2 nanosheets in aqueous solution have better dispersion than the unmodified one. After the Zeta test, it was found that the absolute value after modification became lower, indicating that the modification of nano-MoS2 was effective. Moreover, the MoS2-CTAB can complete the wetting reversal within 4 h and make the interfacial tension reach 0.89 mN/m at 0.005 wt%, which greatly reduces the capillary pressure. The enhanced oil recovery effect of MoS2-CTAB nanosheets increased by 85.7% compared with that before modification and 62.5% higher compared with pure surfactant.

Raman imaging reveals in-situ microchemistry of cuticle and epidermis of spruce needles

BackgroundThe cuticle is a protective layer playing an important role in plant defense against biotic and abiotic stresses. So far cuticle structure and chemistry was mainly studied by electron microscopy and chemical extraction. Thus, analysing composition involved sample destruction and the link between chemistry and microstructure remained unclear. In the last decade, Raman imaging showed high potential to link plant anatomical structure with microchemistry and to give insights into orientation of molecules. In this study, we use Raman imaging and polarization experiments to study the native cuticle and epidermal layer of needles of Norway spruce, one of the economically most important trees in Europe. The acquired hyperspectral dataset is the basis to image the chemical heterogeneity using univariate (band integration) as well as multivariate data analysis (cluster analysis and non-negative matrix factorization).ResultsConfocal Raman microscopy probes the cuticle together with the underlying epidermis in the native state and tracks aromatics, lipids, carbohydrates and minerals with a spatial resolution of 300 nm. All three data analysis approaches distinguish a waxy, crystalline layer on top, in which aliphatic chains and coumaric acid are aligned perpendicular to the surface. Also in the lipidic amorphous cuticle beneath, strong signals of coumaric acid and flavonoids are detected. Even the unmixing algorithm results in mixed endmember spectra and confirms that lipids co-locate with aromatics. The underlying epidermal cell walls are devoid of lipids but show strong aromatic Raman bands. Especially the upper periclinal thicker cell wall is impregnated with aromatics. At the interface between epidermis and cuticle Calcium oxalate crystals are detected in a layer-like fashion. Non-negative matrix factorization gives the purest component spectra, thus the best match with reference spectra and by this promotes band assignments and interpretation of the visualized chemical heterogeneity.ConclusionsResults sharpen our view about the cuticle as the outermost layer of plants and highlight the aromatic impregnation throughout. In the future, developmental studies tracking lipid and aromatic pathways might give new insights into cuticle formation and comparative studies might deepen our understanding why some trees and their needle and leaf surfaces are more resistant to biotic and abiotic stresses than others.

Synthesis, conformational studies, vibrational spectra and thermal properties, of new 1,4-(phenylenebis(methylene) bis(methyl-imidazolium) ionic liquids

Three new substituted dicationic ionic liquids (DILs) based on biphenylenedimethylene linked bis-1-methylimidazolium ionic liquids [bis-(PhCH2MIm)+], combined with three anions, namely dichloride [Cl]2, di (hexafluorophosphate) [PF6−]2 and di(bis(trifluoromethylsulfonyl)Imide) [(CF3SO2)2N−]2 were synthesized. The three synthesized dicationic ionic liquids were characterized by Nuclear Magnetic Resonance and Fourier transform infrared (FTIR) and Raman spectroscopy in the region 4000–600 cm−1 and 4000–45 cm−1, respectively. A complete vibrational assignments have been performed; the biphenylene linkage spacer is confirmed by the presence of strong Raman band at 1616 cm−1 related to the C=C vibration in all our investigated DILs. Moreover, a conformational investigation of the cation was performed by means of DFT calculations using the 6 31G∗∗ basis set and the B3LYP theory. The comparison of the computed and experimental Raman spectra further corroborate the structure of the cation. Finally, the thermal stability of the DILs was investigated by TGA and DTA measurements. The DILs with Cl−, PF6− and [(CF3SO2)2N−] anions decompose at 252, 323 and 420 °C, respectively.

BaGeO3: A Mid-IR Transparent Crystal with Superstrong Raman Response.

Stimulated Raman scattering processes based on Raman crystals offer a simple and effective method to generate mid-IR lasers. However, currently available mid-IR Raman crystals are extremely scarce. Herein, a new type of mid-IR Raman crystal, BaGeO3, is reported. It crystallizes in the monoclinic space group C2/c with Ba2+ cations and [Ge3O9]6- rings as basic building units and features high transparency from 2.5 to 5.5 μm and a Raman response larger than that of diamond. The BaGeO3 crystal has 45 IR-active modes (22Au + 23Bu) and 42 Raman-active modes (20Ag + 22Bg). The wide mid-IR transparent window is attributed to the low phonon energy of the second-order IR-active Au ⊗ Bg mode. The strongest Raman band, located at 799 cm-1, arises from the symmetrically stretching vibration of the [Ge3O9]6- extra-ring Ge-O bonds. The findings provide new insights into the crystallographic and Raman spectroscopic characteristics of high-performance mid-IR Raman crystals.

Pyrene Coating Transition Metal Disulfides as Protection from Photooxidation and Environmental Aging.

Environmental degradation of transition metal disulfides (TMDs) is a key stumbling block in a range of applications. We show that a simple one-pot non-covalent pyrene coating process protects TMDs from both photoinduced oxidation and environmental aging. Pyrene is immobilized non-covalently on the basal plane of exfoliated MoS2 and WS2. The optical properties of TMD/pyrene are assessed via electronic absorption and fluorescence emission spectroscopy. High-resolution scanning transmission electron microscopy coupled with electron energy loss spectroscopy confirms extensive pyrene surface coverage, with density functional theory calculations suggesting a strongly bound stable parallel-stacked pyrene coverage of ~2–3 layers on the TMD surfaces. Raman spectroscopy of exfoliated TMDs while irradiating at 0.9 mW/4 μm2 under ambient conditions shows new and strong Raman bands due to oxidized states of Mo and W. Yet remarkably, under the same exposure conditions TMD/pyrene remain unperturbed. The current findings demonstrate that pyrene physisorbed on MoS2 and WS2 acts as an environmental barrier, preventing oxidative surface reactions in the TMDs catalyzed by moisture, air, and assisted by laser irradiation. Raman spectroscopy confirms that the hybrid materials stored under ambient conditions for two years remained structurally unaltered, corroborating the beneficial role of pyrene for not only hindering oxidation but also inhibiting aging.

Andymcdonaldite (Fe3+2Te6+O6), a new ferric iron tellurate with inverse trirutile structure from the Detroit district, Juab County, Utah

ABSTRACT Andymcdonaldite is a new ferric-iron-tellurate mineral that occurs within Au-, Te-, and Bi-rich jasperoid at the Wildcat prospect in the Detroit district, Juab County, Utah. The mineral has a yellow-brown to brownish-black color, occurs as extremely cryptocrystalline (11–25 nm) material in thin films and breccia matrix fillings, and is associated with gold (native), tellurium (native), beyerite, clinobisvanite, and a variety of tellurium oxysalt minerals that include carlfriesite, eckhardite, frankhawthorneite, khinite, mcalpineite, paratellurite, tellurite, tlapallite, and xocolatlite. This is the first known natural occurrence of a phase with an ordered (tetragonal) inverse trirutile structure (A3+2B6+O6) which has many synthetic representatives. The B site in andymcdonaldite is occupied by Te and the A site is dominated by Fe with up to approximately 14 mole% substitution by other cations. An empirical formula of (Fe1.74Cu0.12Mn0.06Al0.05Mg0.05)Σ2.02Te1.01O6 was obtained from electron microprobe analyses. Powder X-ray diffraction data, Raman spectra, and unit-cell dimensions for andymcdonaldite strongly resemble those for the synthetic analogue, Fe3+2Te6+O6. The strongest X-ray diffraction lines are [dobsÅ(Iobs)(hkl)]: 4.14(27)(101), 3.28(100)(110), 2.54(71)(103), 1.71(72)(213), and 1.37(39)(303,116). The strongest Raman bands are at 748, 643, and 417 cm–1. The space group is P42/mnm and the cell dimensions are a 4.622–4.630 Å, c 9.077–9.087 Å, and V = 193.94–194.80 Å3 (Z = 2).

Synthesis of ETS-10-like vanadosilicates using 2,6-dimethylpiperidinium cation derivatives as organic templates

Systematic vanadosilicate syntheses were performed using derivatives of 2,6-dimethylpiperidine as organic structure-directing agents (SDAs). Physicochemical analyses of the vanadosilicate materials obtained were carried out by X-ray diffraction (XRD), Raman spectroscopy, infrared (IR) spectroscopy, UV–visible (UV–Vis) spectroscopy, and solid-state NMR spectroscopy (29Si and 51V MAS NMR). The experimental results indicated that the presence of the organic templates had different effects on the final phases of the synthesized vanadosilicates. The XRD results showed that 1,1,2,6-tetramethylpiperidinium (SDA 1) favored synthesis of the known AM-6 vanadosilicates, isostructural to the ETS-10 titanosilicate, while the other organic templates 1,1-diethyl-2,6-dimethylpiperidinium (SDA 2), 6,10-dimethyl-5-azoniaspiro[4.5]decane (SDA 3), and 1,5-dimethyl-6-azoniaspiro[5.5]undecane (SDA 4) directed the formation of vanadosilicates with different phases, such as EVS-10. Strong Raman bands at 870 and 1035 cm−1 indicated vibrational modes associated with the highly symmetric vanadia octahedra. Chemical shifts at −96 ppm (29Si MAS NMR), −610, and −570 ppm (51V MAS NMR) provided further evidence of the incorporation of vanadium into the structures of the vanadosilicates prepared using these novel derivatives of 2,6-dimethylpiperidinium cations as SDAs.

Calculational Raman spectra investigation of nitrogen-hyperdoped silicon formed in different conditions

The Raman spectra difference of the N-hyperdoped silicon prepared under different conditions is due to the different dominant configurations of N in silicon. The separate substitutional N atoms in silicon show several strong Raman peaks which can be also observed in the chalcogen-hyperdoped silicon. The configuration with separate substitutional and interstitial N atoms displays a strong and broad Raman band at 480 cm−1, which is in accordance with our experiment. The introduction of the vacancies may lead to the disappearance or appearance of the Raman peaks, which depends on the dominant configurations of the N atoms. For the compound of interstitial N atoms and vacancies, the calculational Raman spectrum is similar to that of the NF3-prepared silicon and N2-prepared silicon with a lower laser power.

Raman spectroscopic vibrational analysis of the complex iron sulfates clairite, metavoltine, and voltaite from the burning coal dump Anna I, Alsdorf, Germany

AbstractVibrational spectroscopy has been used to characterize the three uncommon complex iron sulfates clairite, (NH4)2Fe3(SO4)4(OH)3 3H2O, metavoltine, Na6K2Fe2+Fe3+6(SO4)12O2·18H2O, and voltaite, K2Fe2+5Fe3+3Al(SO4)12 18H2O. The investigated specimens were formed at the burning coal dump Anna I (Alsdorf, Germany) due to alteration processes connected with the subsurface thermal activity. It is found that all three minerals display complex Raman spectra with an extensive proliferation of bands attributed to the sulfate vibrational modes. Both clairite and metavoltine show extraordinary strong Raman bands in the low‐wavenumber region, which can be attributed to the FeO stretching modes. Clairite and metavoltine show a very similar spectral shape; it can be concluded that both minerals can exhibit a similar crystal structure. In comparison, voltaite represents a different structural type; therefore, a distinct Raman spectrum is observed.

Assignment of the electronic transition of phenothiazine radical cation in the visible region– a resonance Raman spectroscopy and theoretical calculation investigation

Phenothiazine (PTZ) derivatives represent an important class of molecules, being studied in a number of fields of chemical and pharmaceutical research. The interesting chemical and biological properties of PTZs are considered to be related to their relative stable radical cations, whose formation and reactivity have been extensively studied. In this work, the radical cation of phenothiazine (PTZ+) was generated by the reaction with the mordenite solid acid, an environment in which this species is stabilized. The most intense electronic transition of PTZ+ is located at 516 nm. In order to characterize the electronic and molecular structure of this radical species, a resonance Raman and theoretical calculations of the structure, PTZ+ vibrational frequencies and electronic spectrum were calculated employing DFT B3LYP/6-31G(d,p) and TDDFT methods. In the ground state, PTZ+ is planar, in contrast to the folded structure of neutral PTZ. The strong Raman band at 476 cm−1 was assigned to a CSC bending mode. The reason for its preferential enhancement was investigated using TDDFT, in order to obtain the molecular orbitals involved in the electronic transition at 516 nm. The TDDFT calculations show that this transition is from SOMO-1 and SOMO-2, both double occupied molecular orbitals, localized at the aromatic rings and goes toward SOMO (single occupied molecular orbital). This SOMO has contributions of sulphur and nitrogen atomic orbitals, but with predominance of sulphur atomic orbitals, which are absent in SOMO-1 and SOMO-2. The predominance of sulphur atomic orbitals in the SOMO explains the preferential resonance Raman enhancement of a CSC vibrational mode.

Understanding the infrared and Raman spectra of ganoderic acid A: An experimental and DFT study.

Ganoderic Acids (GAs) are the major medicinal compounds in Ganoderma lucidum used as traditional Chinese medicine since ancient times. Ganoderic acid A (GAA) is the first discovered ganoderic acids reported in the literature, which is also one of most abundant triterpenoids of Ganoderma lucidum. Especially, GAA has been extensively investigated in recent decades for its positive medicinal activities. However, the vibrational properties of GAs have rarely been studied or reported. In this work, we focused on the typical GAA and studied the infrared (IR) and Raman spectra based on both experiments and DFT calculations. As such, we could not only achieve the assignments of the vibrational modes, but also from the IR and Raman spectra, we found that the spectral region from 1500 cm-1 to 1800 cm-1 is particularly useful for distinguishing different types of GAs. In addition, its dehydrogenated derivative ganoderenic acid A (GOA) was also studied, which could be identified due to its spectral feature of strong IR and Raman bands around 1620 cm-1. This work therefore may facilitate the application of IR and Raman spectroscopies in the inspection and quality control of Ganoderma lucidum.

New Insights into Quinine-DNA Binding Using Raman Spectroscopy and Molecular Dynamics Simulations.

Quinine's ability to bind DNA and potentially inhibit transcription and translation has been examined as a mode of action for its antimalarial activity. UV absorption and fluorescence-based studies have lacked the chemical specificity to develop an unambiguous molecular-level picture of the binding interaction. To address this, we use Raman spectroscopy and molecular dynamics (MD) to investigate quinine-DNA interactions. We demonstrate that quinine's strongest Raman band in the fingerprint region, which derives from a symmetric stretching mode of the quinoline ring, is highly sensitive to the local chemical environment and pH. The frequency shifts observed for this mode in solvents of varying polarity can be explained in terms of the Stark effect using a simple Onsager solvation model, indicating that the vibration reports on the local electrostatic environment. However, specific chemical interactions between the quinoline ring and its environment, such as hydrogen bonding and π-stacking, perturb the frequency of this mode in a more complicated but predictable manner. We use this vibration as a spectroscopic probe to investigate the binding interaction between quinine and DNA. We find that, when the quinoline ring is protonated, quinine weakly intercalates into DNA by forming π-stacking interactions with the base pairs. The Raman spectra indicate that quinine can intercalate into DNA with a ratio reaching up to roughly one molecule per 25 base pairs. Our results are confirmed by MD simulations, which also show that the quinoline ring adopts a t-shaped π-stacking geometry with the DNA base pairs, whereas the quinuclidine head group weakly interacts with the phosphate backbone in the minor groove. We expect that the spectral correlations determined here will enable future studies to probe quinine's antimalarial activities, such as disrupting hemozoin biocrystallization, which is hypothesized to be, among other things, one of its primary modes of action against Plasmodium parasites.

Vibrational spectra, structure, theoretical calculations of 3-Fluoro-4-Hydroxybenzaldehyde: With evidence of hydrogen bonding

Fourier-Transform Laser Raman (3500-100 cm−1) and FT-IR (4000-400 cm−1) spectral measurements have been made for the solid 3-Fluoro-4-Hydroxybenzaldehyde. Geometry optimization and frequency calculations performed at two levels namely, RHF/6-31G* and B3LYP/6-31G* have yielded Cs symmetry with energies of −517.1388109 hartrees and −520.0240034 hartrees. A detailed interpretation of infrared and Raman spectra aided by the PEDs (potential energy distributions) for the computed frequencies has been reported. The PES scan yielded four distinct conformers out of which the most stable conformer is that with the orientation of CO of aldehyde group with respect to the hydroxyl group and fluorine in the cis form. The Fluorine substitution is seen to affect its structure and charge distributions in its vicinity as is seen by the NBO analysis and mulliken charges distribution.A broad IR band near 3130 cm−1, due to OH stretch shows evidence of hydrogen bonding. The aldehydic CH vibration predicted at 2801 cm−1 is observed at 2750 cm−1. Downshifting of the aldehydic CO stretch vibration predicted at 1725 cm−1 to an intense IR band at 1670 cm−1; increase in the frequency of in-plane bending vibration of OH as a shoulder absorption band at 1290 cm−1 from its predicted mode 1243 cm−1 are all further indications of OH⋯O bonding. Dimerization for the most stable conformer has been evaluated by B3LYP/6-31G* level. The dimer spectrum is seen to agree fairly well with the observed spectra. CF stretching vibration predicted at 1235 cm−1 is seen to couple with ring bending vibrations and is assigned to a strong Raman band at 1259 cm−1. The optimized structure and harmonic frequencies computed at B3LYP/6-31G* level are in good agreement with the experimental values.

Low frequency vibrational spectra and the nature of metal-oxygen bond of alkaline earth metal acetylacetonates

Theoretical quantum chemistry calculations were used to assign the observed vibrational band frequencies of Be, Mg, Ca, Sr, and Ba acetylacetonates complexes. Density functional theory (DFT) calculations have been carried out at the B3LYP level, using LanL2DZ, def2SVP, and mixed, GenECP, (def2SVP for metal ions and 6-311++G** for all other atoms) basis sets. The B3LYP level, with mixed basis sets, was utilized for calculations of vibrational frequencies, IR intensity, and Raman activity. Analysis of the vibrational spectra indicates that there are several bands which could almost be assigned mainly to the metal-oxygen vibrations. The strongest Raman band in this region could be used as a measure of the stability of the complex.The effects of central metal on the bond orders and charge distributions in alkaline earth metal acetylacetonates were studied by the Natural Bond Orbital (NBO) method for fully optimized compounds. Optimization were performed at the B3LYP/6-311++G** level for the lighter alkaline earth metal complexes (Be, Mg, and Ca acetylacetonates) while the B3LYP level, using LanL2DZ (extrabasis, d and f on oxygen and metal atoms), def2SVP and mixed (def2SVP on metal ions and 6-311++G** for all other atoms) basis sets for all understudy complexes. Calculations indicate that the covalence nature of metal-oxygen bonds considerably decreases from Be to Ba complexes. The nature of metal-oxygen bond was further studied by using Atoms In Molecules (AIM) analysis. The topological parameters, Wiberg bond orders, natural charges of O and metal ions, and also some vibrational band frequencies were correlated with the stability constants of understudy complexes.

SERS Spectroscopy and DFT Studies of Thionine and its Derivatives Adsorbed on Silver Colloids: Which N Atom is Used for Coordination of a Phenothiazine‐Based Natural Dye to Electron‐Deficient Metal Surface?

A Surface‐enhanced Raman scattering (SERS) investigation has been carried out for thionine and its derivatives, well known blue‐based dyes sharing the phenothiazine core. The thionine SERS spectrum is similar to its Raman spectrum. This suggests that the strong Raman bands mostly arising from in‐plane ring modes are also enhanced on metal surface. Several originally weak Raman bands arising from the CNC moiety or H atoms on the thiazine N side also largely strengthen in the SERS spectrum. Density functional theory results for the plausible coordinated structures of thionine and the silver adatom reveal that coordination via the thiazine N atom to Ag+ leads to the most stable structure, and its calculated spectrum also best reproduces the SERS spectrum. The thionine derivatives show surprisingly analogous spectra, reflecting that the derivatives coordinate in a similar fashion to the metal surface. The high preference of the thiazine N atom for coordination is traced to the positive charge on the S atom.

Raman Imaging for LiCoO2 Composite Positive Electrodes in All-Solid-State Lithium Batteries to Investigate State-of-Charge Distributions

All-solid-state batteries show higher safety with low risk of leakage and explosion because of nonflammable inorganic solid electrolytes, which are alternative to conventional organic liquid electrolytes. Bulk-type all-solid-state batteries are constructed by pressing positive and negative electrode layers and a solid electrolyte layer at room temperature. The batteries are capable of having high energy density by adding large amounts of active materials into composite electrodes, which are composed of solid electrolyte particles and active material particles. We have investigated electrochemical performances of bulk-type all-solid-state cells using a LiCoO2 composite positive electrode and a Li2S-P2S5 solid electrolyte.1 Composite positive electrodes have many solid-solid interfaces, and electrochemical reactions at the interfaces have not been studied well. Inhomogeneous reaction may occur in the composite electrodes when solid-solid contact areas are insufficient. To improve cell performance, investigation of state-of-charge (SOC) distributions in the electrodes and fabrication of electrodes showing uniform reaction distributions are important. Raman spectroscopy is a suitable technique for investigating SOC of active materials because Raman spectra are sensitive to the structural changes of active materials during charge-discharge tests. Moreover, Raman mapping technique enables us to obtain SOC distribution maps of composite electrodes. In this study, Raman mapping was carried out for charged and discharged LiCoO2 composite positive electrodes in all-solid-state cells to investigate SOC distributions. A 75Li2S·25P2S5 (mol%) glass and indium foil were used as a solid electrolyte and a negative electrode, respectively. A composite positive electrode was prepared by mixing LiCoO2 particles and 75Li2S·25P2S5 glass particles with 80:20 in weight ratio. All-solid-state cells were charged and discharged with a cut-off voltage of 2.6-4.2 V (vs. Li+/Li) at 25oC under a current density of 0.064 mA cm-2. Raman mapping was conducted for surface parts of composite positive electrodes prepared by an Ar ion-milling technique. There are two strong Raman bands at 486 and 596 cm-1, originating from the E g and A 1g modes corresponding to O-Co-O bending and Co-O stretching, respectively.2 Those peaks of E g and A 1g modes shifted to 470 cm-1 and 582 cm-1 respectively, when the cell was charged to 4.2 V (vs. Li+/Li) and returned to original peak positions after the discharging process. To evaluate SOC of the composite positive electrode, A 1g peak positions were investigated in detail. The mapping image showed that charge-discharge reactions did not proceed uniformly, and inhomogeneous reaction distributions existed at the areas of insufficient contacts between LiCoO2 particles and solid electrolyte particles.3 To achieve uniform electrochemical reactions, a composite positive electrode having sufficient interfaces between LiCoO2 and solid electrolyte particles should be prepared. To increase contact points between them, a composite positive electrode with solid electrolytes with a smaller particle size was fabricated. Raman mapping images of the charged and discharged electrodes suggest that uniform electrochemical reactions are achieved. It is noteworthy that the use of smaller solid electrolyte particles is effective way to obtain uniform reaction distributions for composite positive electrodes in all-solid-state lithium batteries. Acknowledgement This research was financially supported by JST, ALCA-SPRING.