CH2 Symmetric Stretch Research Articles

Molecular Cage Reports on Its Contents: Spectroscopic Signatures of Cryo-Cooled K+- and Ba2+-Benzocryptand Complexes.

UV photofragment spectroscopy and IR-UV double resonance methods are used to determine the structure and spectroscopic responses of a three-dimensional [2.2.2]-benzocryptand cage to the incorporation of a single K+ or Ba2+ imbedded inside it (labeled as K+-BzCrypt, Ba2+-BzCrypt). We studied the isolated ion-cryptand complex under cryo-cooled conditions, brought into the gas phase by nano-electrospray ionization. Incorporation of a phenyl ring in place of the central ethyl group in one of the three N-CH2-CH2-O-CH2-CH2-O-CH2-CH2-N chains provides a UV chromophore whose S0-S1 transition we probe. K+-BzCrypt and Ba2+-BzCrypt have their S0-S1 origin transitions at 35,925 and 36,446 cm-1, respectively, blue-shifted by 174 and 695 cm-1 from that of 1,2-dimethoxybenzene. These origins are used to excite a single conformation of each complex selectively and record their IR spectra using IR-UV dip spectroscopy. The alkyl CH stretch region (2800-3000 cm-1) is surprisingly sensitive to the presence and nature of the encapsulated ion. We carried out an exhaustive conformational search of cage conformations for K+-BzCrypt and Ba2+-BzCrypt, identifying two conformations (A and B) that lie below all others in energy. We extend our local mode anharmonic model of the CH stretch region to these strongly bound ion-cage complexes to predict conformation-specific alkyl CH stretch spectra, obtaining quantitative agreement with experiment for conformer A, the gas-phase global minimum. The large electrostatic effect of the charge on the O- and N-lone pairs affects the local mode frequencies of the CH2 groups adjacent to these atoms. The localized CH2 scissors modes are pushed up in frequency by the adjacent O/N-atoms so that their overtones have little effect on the alkyl CH stretch region. However, the localized CH2 wags are nearly degenerate and strongly coupled to one another, producing an array of delocalized wag normal modes, whose highest frequency members reach up above 1400 cm-1. As such, their overtones mix significantly with the CH stretch modes, most notably involving the CH2 symmetric stretch fundamentals of the central ethyl groups in the all-alkyl chains and the CH stretches adjacent to the N-atoms and antiperiplanar to the nitrogen lone pair.

Distinct Lipid Phenotype of Cancer-Associated Fibroblasts (CAFs) Isolated From Overweight/Obese Endometrial Cancer Patients as Assessed Using Raman Spectroscopy.

Obesity is strongly linked with increased risk and poorer prognosis of endometrial cancer (EC). Cancer-associated fibroblasts (CAFs) are activated fibroblasts that form a large component of the tumor microenvironment and undergo metabolic reprogramming to provide critical metabolites for tumor growth. However, it is still unknown how obesity, characterized by a surplus of free fatty acids drives the modifications of CAFs lipid metabolism which may provide the mechanistic link between obesity and EC progression. The present study aims to evaluate the utility of Raman spectroscopy, an emerging nondestructive analytical tool to detect signature changes in lipid metabolites of CAFs from EC patients with varying body mass index. We established primary cultures of fibroblasts from human EC tissues, and CAFs of overweight/obese and nonobese women using antibody-conjugated magnetic beads isolation. These homogeneous fibroblast cultures expressed fibroblast markers, including α-smooth muscle actin and vimentin. Analysis was made in the Raman spectra region best associated with cancer progression biochemical changes in lipids (600-1800 cm-1 and 2800-3200 cm-1). Direct band analysis and ratiometric analysis were conducted to extract information from the Raman spectrum. Present results demonstrated minor shifts in the CH2 symmetric stretch of lipids at 2879 cm-1 and CH3 asymmetric stretching from protein at 2932 cm-1 in the overweight/obese CAFS compared to nonobese CAFs, indicating increased lipid content and a higher degree of lipid saturation. Principal component analysis showed that CAFs from overweight/obese and nonobese EC patients can be clearly distinguished indicating the capability of Raman spectroscopy to detect changes in biochemical components. Our results suggest Raman spectroscopy supported by chemometric analysis is a reliable technique for characterizing metabolic changes in clinical samples, providing an insight into obesity-driven alteration in CAFs, a critical stromal component during EC tumorigenesis.

THE EFFECT OF ADDITION GREEN INHIBITOR D-GALACTOSE ON CORROSION RATE OF ALUMINUM ALLOY 5052 IN SULFURIC ACID (H2SO4) MEDIA

Aluminum alloy 5052 (Al 5052) is one of the metals used as a bipolar plate in a Proton Exchange Membrane Fuel Cell (PEMFC) due to has its light mass and being easy to form, and, has high conductivity and resistivity properties. This material is prone to corrosion and current knowledge to protect its surface is currently lacking. The product of PEMFC produces electrical energy, hot steam (313 – 353 K), and water. These conditions have an impact on the degraded bipolar plate caused by the acidic nafion membrane. This increases the risk of corrosion on the cathode side of the bipolar plate. Coating with a green inhibitor using the electrophoretic deposition technique (EPD) is one way to deal with the corrosion that occurs. The analysis method used electrochemical with potentiodynamic polarization techniques, electrochemistry impedance spectroscopy (EIS), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). In this study, green inhibitor D-galactose was used with a concentration of 0.5 – 1.5 g and an, EPD time of 15 – 45 minutes in 0.5 M sulfuric acid (H2SO4) media pH 1-4. Potentiodynamic polarization analysis at the lowest corrosion current value (Icorr) at demonstrates (the inhibitor concentration of 1.5 g with an and EPD time of 45 minutes) resulted corrosion rate of Al5052 before EPD was 0.0075 mmPY while the corrosion rate of Al5052 after EPD was 0.0041 mmPY with (inhibitors efficiency 45.2%). The FTIR spectrum, broad peak appeared in the range of 3000-3600 cm-1, which refers to the formation of hydrogen bonding of hydroxyl group. Methyl group of D-galactose also appear on 2918 cm-1 and 2850 cm-1 which attributed to =CH2 asymmetric stretch and −CH3 symmetric stretch, respectively. Carbonyl group on 1500 – 1700 cm-1 represent C=O bond of amide, and aldehyde. Peak 1097 – 1035 cm-1 which attributed to C-O were connected to the secondary and primary alcohols. The resistance value for Al5052 before and after EPD are 1.2 kΩ/cm2 after and 2.2 kΩ/cm2, respectively. Here we find that the resistance increases with the increasing concentration and time of EPD. The results cross section Al5052 within average 29.8 μm, and morphology with SEM Al5052 before EPD showed pitting corrosion. On the other hand, the image of Al5052 inhibitor coating 1.5 gr with EPD of 45 minutes shows a smooth surface and visible black lumps, suggesting Al5052 is successfully reduced a corrosion rate by the D-galactose. Our simple and robust method inferred a protection route towards a viable and physically stable green inhibitors.

Infrared spectra of complex organic molecules in astronomically relevant ice mixtures

Context. In the near future, high spatial and spectral infrared (IR) data of star-forming regions obtained by the James Webb Space Telescope may reveal new solid-state features of various species, including more intriguing classes of chemical compounds. The identification of complex organic molecules (COMs) in the upcoming data will only be possible when laboratory IR ice spectra of these species under astronomically relevant conditions are available for comparison. For this purpose, systematic series of laboratory measurements are performed, providing high-resolution IR spectra of COMs. Here, spectra of pure methylamine (CH3NH2) and methylamine-containing ices are discussed. Aims. The work is aimed at characterizing the mid-IR (500–4000 cm−1, 20–2.5 μm) spectra of methylamine in pure and mixed ices to provide accurate spectroscopic data of vibrational bands that are most suited to trace this species in interstellar ices. Methods. Fourier transform infrared spectroscopy is used to record spectra of CH3NH2 in the pure form and mixed with H2O, CH4, and NH3, for temperatures ranging from 15 to 160 K. The IR spectra in combination with HeNe laser (632.8 nm) interference data of pure CH3NH2 ice was used to derive the IR band strengths of methylamine in pure and mixed ices. Results. The refractive index of amorphous methylamine ice at 15 K was determined as being 1.30 ± 0.01. Accurate spectroscopic information and band strength values are systematically presented for a large set of methylamine-containing ices and different temperatures. Selected bands are characterized and their use as methylamine tracers is discussed. The selected bands include the following: the CH3 antisymmetric stretch band at 2881.3 cm−1 (3.471 μm), the CH3 symmetric stretch band at 2791.9 cm−1 (3.582 μm), the CH3 antisymmetric deformation bands, at 1455.0 and 1478.6 cm−1 (6.873 and 6.761 μm), the CH3 symmetric deformation band at 1420.3 cm−1 (7.042 μm), and the CH3 rock at 1159.2 cm−1 (8.621 μm). Using the laboratory data recorded in this work and ground-based spectra of ices toward YSOs (Young Stellar Objects), upper-limits for the methylamine ice abundances are derived. In some of these YSOs, the methylamine abundance is less than 4% relative to H2O.

High-resolution infrared spectroscopy of jet cooled CH2Br radicals: The symmetric CH stretch manifold and absence of nuclear spin cooling.

Direct laser absorption of a slit supersonic discharge expansion provides the first high-resolution spectroscopic results on the symmetric CH stretch excitation (ν1) of the bromomethyl (CH2Br) radical in the ground electronic state. Narrowband (<1 MHz) mid-infrared radiation is produced by difference-frequency generation of two visible laser beams, with the open shell halohydrocarbon radical generated by electron dissociative attachment of CH2Br2 in a discharge and rapidly cooled to Trot = 18 ± 1 K in the subsequent slit-jet supersonic expansion. A rovibrational structure in the radical spectrum is fully resolved, as well as additional splittings due to spin-rotation effects and 79Br/81Br isotopologues in natural abundance. Spectroscopic constants and band origins are determined by fitting the transition frequencies to a non-rigid Watson Hamiltonian, yielding results consistent with a vibrationally averaged planar radical and an unpaired electron in the out-of-plane pπ orbital. Additionally, extensive satellite band structure from a vibrational hot band is observed and analyzed. The hot band data is compared to CFOUR/VPT2 (CCSD(T)cc-pVQZ) ab initio anharmonic predictions of the vibration rotation alpha matrix, which permits unambiguous assignment to CH2 symmetric-stretch excitation built on the singly excited CH2 out-of-plane bending mode (ν1 + ν4 ← ν4). Longitudinal cooling of the Doppler width in the slit-jet expansion geometry also reveals partially resolved hyperfine structure on transitions out of the lowest angular momentum states in excellent agreement with predictions based on microwave studies. High level ab initio MOLPRO calculations [CCSD(T)-f12b/VnZ-f12 (n = 3, 4, CBS)] are also performed with explicitly correlated f12 electron methods for the out-of-plane CH2 bending mode over the halogen series CH2X (X = F, Cl, Br, I), which clearly reveals a non-planar geometry for X = F (with a ΔE ≈ 0.3 kcal/mol barrier) and yet planar equilibrium geometries for X = Cl, Br, and I. Finally, a detailed Boltzmann analysis of the transition intensities provides support for negligible collisional equilibration of the entangled H atom nuclear spin states on the few hundred microsecond time scale and high collision densities of a slit supersonic expansion.

Optimization and characterization of n-hexane extracts of arabica coffee ground (Coffea arabica L.) fromgayo plateau as source of natural antioxidant

Arabica coffee is a major commodity crop in the Gayo Plateau, Aceh Province. Utilization of coffee in the area only as a raw material for making coffee drinks and produce waste that is not utilized. The aim of this study is optimization and characterization of n-hexane extract of Arabica Gayo coffee ground (Coffeaarabica L.) as a source of natural antioxidant. The extraction process used soxhlet method with n-hexane solvent. Characterization of arabica coffee ground oil consist ofanalysis of functional group using FTIR, component analysis using GC-MS and antioxidant analysis using DPPH method. The optimum time of the soxhletprocess of Arabica coffee is 180 minutes with rendement of 9,54%, analysis of functional group shows CH2 asymmetric stretch at 2922 cm−1, CH2 symmetric stretch at 2853 cm−1, C=O asymmetric stretch at 1741 cm−1, CH2 bending at 1458 cm−1, C-CH3 vibration at 1159 cm−1 and CH vibration at 718 cm−1. The main component of Arabica Gayo coffee ground oil is 1,2-benzenedicarboxylic acid, bis(2-ethylhexyl) ester with an area of 18.09%, antioxidant activitiy of Arabica Gayo coffee ground oil is very weak with IC50 value = 1222,31 ppm.

Orientational Analysis of Monolayers at Low Surface Concentrations Due to an Increased Signal-to-Noise Ratio (S/N) Using Broadband Sum Frequency Generation Vibrational Spectroscopy.

Sum frequency generation (SFG) * Equal contributors. spectroscopy was used to deduce the orientation of the terminal methyl (CH3) group of self-assembled monolayers (SAMs) at the air-solid and air-liquid interfaces at surface concentrations as low as 1% protonated molecules in the presence of 99% deuterated molecules. The SFG spectra of octadecanethiol (ODT) and deuterated octadecanethiol (d37 ODT) SAMs on gold were used for analysis at the air-solid interface. However, the eicosanoic acid (EA) and deuterated EA (d39 EA) SAMs on the water were analyzed at the air-liquid interface. The tilt angle of the terminal CH3 group was estimated to be ∼39 ° for a SAM of 1% ODT : 99% d37 ODT, whereas the tilt angle of the terminal CH3 group of the 1% EA : 99% d39 EA monolayer was estimated to be ∼32 °. The reliability of the orientational analysis at low concentrations was validated by testing the sensitivity of the SFG spectroscopy. A signal-to-noise (S/N) ratio of ∼60 and ∼45 was obtained for the CH3 symmetric stretch (SS) of 1% ODT : 99% d37 ODT and 1% EA : 99% d39 EA, respectively. The estimated increase in S/N ratio values, as a measure of the sensitivity of the SFG spectroscopy, verified the capacity to acquire the SFG spectra at low concentrations of interfacial molecules under ambient conditions. Overall, the orientational analysis of CH3 SS vibrational mode was feasible at low concentrations of protonated molecules due to increased S/N ratio. In support, the improved S/N ratio on varying incident power density of the visible beam was also experimentally demonstrated.

High-resolution sub-Doppler infrared spectroscopy of atmospherically relevant Criegee precursor CH2I radicals: CH2 stretch vibrations and "charge-sloshing" dynamics.

The combination of a pulsed supersonic slit-discharge source and single-mode difference frequency direct absorption infrared spectroscopy permit first high resolution infrared study of the iodomethyl (CH2I) radical, with the CH2I radical species generated in a slit jet Ne/He discharge and cooled to 16 K in the supersonic expansion. Dual laser beam detection and collisional collimation in the slit expansion yield sub-Doppler linewidths (60 MHz), an absolute frequency calibration of 13 MHz, and absorbance sensitivities within a factor of two of the shot-noise limit. Fully rovibrationally resolved direct absorption spectra of the CH2 symmetric stretch mode (ν2) are obtained and fitted to a Watson asymmetric top Hamiltonian with electron spin-rotation coupling, providing precision rotational constants and spin-rotation tensor elements for the vibrationally excited state. Analysis of the asymmetric top rotational constants confirms a vibrationally averaged planar geometry in both the ground- and first-excited vibrational levels. Sub-Doppler resolution permits additional nuclear spin hyperfine structures to be observed, with splittings in excellent agreement with microwave measurements on the ground state. Spectroscopic data on CH2I facilitate systematic comparison with previous studies of halogen-substituted methyl radicals, with the periodic trends strongly correlated with the electronegativity of the halogen atom. Interestingly, we do not observe any asymmetric CH2 stretch transitions, despite S/N ≈ 25:1 on strongest lines in the corresponding symmetric CH2 stretch manifold. This dramatic reversal of the more typical 3:1 antisymmetric/symmetric CH2 stretch intensity ratio signals a vibrational transition moment poorly described by simple "bond-dipole" models. Instead, the data suggest that this anomalous intensity ratio arises from "charge sloshing" dynamics in the highly polar carbon-iodine bond, as supported by ab initio electron differential density plots and indeed consistent with observations in other halomethyl radicals and protonated cluster ions.

Modeling the CH Stretch/Torsion/Rotation Couplings in Methyl Peroxy (CH3OO).

The manifestations of CH stretch/torsion/rotation coupling in the region of the CH stretch fundamentals are explored in the CH3OO radical. Following our earlier study of the fundamental in the totally symmetric CH stretch (the ν2 fundamental), this work focuses on the other two CH stretch fundamentals, ν1 and ν9, which would be degenerate in the absence of a barrier in the potential along the methyl torsion coordinate. The simplest model, which assumes a decoupling of the CH stretch vibrations from the torsion, fails to reproduce several important features of the spectrum. Specifically, the absence of a strong peak around the origin of the ν1 fundamental and broadening of the strong peak near the origin in the observed spectrum of the ν9 fundamental are not captured by this model. The origins of these features are explored through two more sophisticated treatments of the torsion/CH stretch couplings. In the first, a four-dimensional potential based on the three CH stretches and the torsion is developed and shown to reproduce both of these features. On the basis of the results of these calculations, the calculated parameters are adjusted to simulate the recorded spectrum. To further explore the torsion/CH stretch couplings in CH3OO, a 9-state model Hamiltonian is developed and discussed. The implications of various types of couplings on the observed energy level patterns are also discussed.

In-situ Monitoring System Equipped with FT-IR and QMS and Thermal Decomposition of Zr(NCH3C2H5)4 Precursor

ZrO2 have been widely used as dielectric layers in metal–insulator–metal and metal-oxide-semiconductor capacitors, charge trapping layers in non-volatile flash memory devices, and insulating layers in resistive switching memory devices owing to their high dielectric constant and good insulating property. For application in the aforementioned semiconductor devices, the ZrO2 films have been prepared on semiconductor or metal substrate by an atomic layer deposition (ALD) method. In the ALD process, the film grows through a unique surface reaction between the vaporized precursor and reactant, since both reagents are alternately supplied onto each substrate surface. The choice of proper metal precursor is very crucial for a successful ALD process. The main requirements of metal precursors are high vapor pressure at its supplying temperature, no self-decomposition at the process temperature, and an aggressive reaction with the ligands on the surface. Generally, the chemical qualities of metal precursor kept at high temperature should not be degraded with time elapse to maintain the constant qualities of the grown films. However, studies on time dependent quality variation or quality monitoring of precursor have been little reported. In this work, the time-dependent thermal stability and chemical properties of Zr precursor, (CpZr(N(CH3)2)3, have been monitored and investigated using FT-IR, TGA, DSC and NMR analysis with time variation. The influence of metal precursor on material and chemical properties of grown ZrO2 films with time elapse also analyzed with growth rate, XPS, AES. Finally, electrical properties of metal-oxide-semiconductor capacitors with ALD-ZrO2 film have been also analyzed using C-V and J-V measurements.Liquid CpZr(N(CH3)2)3 shows a high vapor pressure and is evaporated smoothly less than 1% residue between 150℃ and 200℃. After precursor boiling at high temperatures of 80-120℃ for 4 weeks, TG, NMR, and FT-IR analyses were performed. It is observed that there is little variation and peak transition, meaning the stable thermal properties of precursor with time elapse. For example, in FT-IR measurement, the peaks are detected such as CH3 symmetric stretch, N-CH3 symmetric stretch, CH3 deformation, CH3 vibration, and NC2 symmetric stretch. Each relative amount ratio of each peaks is constant with time elapse.The precursor of CpZr(N(CH3)2)3 was supplied into ALD chamber at 40°C and ZrO2 films were atomic-layer-deposited at 300°C with H2O. The compositional analyses of ALD-ZrO2 were performed with elapsed time. ALD-ZrO2 thin films show no transition of peaks of Zr 3d and O 1s and no variation of area ratio each peak with time-elapsed precursor.To measure electrical properties of ZrO2 film, metal-ZrO2-Si capacitors were fabricated and C-V and J-V analyses were performed. The electrical properties were traced for 8 weeks without serious change of their characteristics of CET and leakage current density.

High resolution spectroscopy of jet cooled phenyl radical: The ν1 and ν2 a1 symmetry C-H stretching modes.

A series of CH stretch modes in phenyl radical (C6H5) has been investigated via high resolution infrared spectroscopy at sub-Doppler resolution (∼60 MHz) in a supersonic discharge slit jet expansion. Two fundamental vibrations of a1 symmetry, ν1 and ν2, are observed and rotationally analyzed for the first time, corresponding to in-phase and out-of-phase symmetric CH stretch excitation at the ortho/meta/para and ortho/para C atoms with respect to the radical center. The ν1 and ν2 band origins are determined to be 3073.968 50(8) cm(-1) and 3062.264 80(7) cm(-1), respectively, which both agree within 5 cm(-1) with theoretical anharmonic scaling predictions based on density functional B3LYP/6-311g++(3df,3dp) calculations. Integrated band strengths for each of the CH stretch bands are analyzed, with the relative intensities agreeing remarkably well with theoretical predictions. Frequency comparison with previous low resolution Ar-matrix spectroscopy [A. V. Friderichsen et al., J. Am. Chem. Soc. 123, 1977 (2001)] reveals a nearly uniform Δν ≈ + 10-12 cm(-1) blue shift between gas phase and Ar matrix values for ν1 and ν2. This differs substantially from the much smaller red shift (Δν ≈ - 1 cm(-1)) reported for the ν19 mode, and suggests a simple physical model in terms of vibrational mode symmetry and crowding due to the matrix environment. Finally, the infrared phenyl spectra are well described by a simple asymmetric rigid rotor Hamiltonian and show no evidence for spectral congestion due to intramolecular vibrational coupling, which bodes well for high resolution studies of other ring radicals and polycyclic aromatic hydrocarbons. In summary, the combination of slit jet discharge methods with high resolution infrared lasers enables spectroscopic investigation of even highly reactive combustion and interstellar radical intermediates under gas phase, jet-cooled (Trot ≈ 11 K) conditions.

Mimicking nature: Self-strengthening properties in a dental adhesive

Chemical and enzymatic hydrolysis provoke a cascade of events that undermine methacrylate-based adhesives and the bond formed at the tooth/composite interface. Infiltration of noxious agents, e.g. enzymes, bacteria, and so forth, into the spaces created by the defective bond will ultimately lead to failure of the composite restoration. This paper reports a novel, synthetic resin that provides enhanced hydrolytic stability as a result of intrinsic reinforcement of the polymer network. The behavior of this novel resin, which contains γ-methacryloxyproyl trimethoxysilane (MPS) as its Si-based compound, is reminiscent of self-strengthening properties found in nature. The efforts in this paper are focused on two essential aspects: the visible-light irradiation induced (photoacid-induced) sol–gel reaction and the mechanism leading to intrinsic self-strengthening. The FTIR band at 2840cm−1 corresponding to CH3 symmetric stretch in –Si–O–CH3 was used to evaluate the sol–gel reaction. Results from the real-time FTIR indicated that the newly developed resin showed a limited sol–gel reaction (<5%) during visible-light irradiation, but after 48h dark storage, the reaction was over 65%. The condensation of methoxysilane mainly occurred under wet conditions. The storage moduli and glass transition temperature of the copolymers increased in wet conditions with the increasing MPS content. The cumulative amounts of leached species decreased significantly when the MPS-containing adhesive was used. The results suggest that the polymethacrylate-based network, which formed first as a result of free radical initiated polymerization, retarded the photoacid-induced sol–gel reaction. The sol–gel reaction provided a persistent, intrinsic reinforcement of the polymer network in both neutral and acidic conditions. This behavior led to enhanced mechanical properties of the dental adhesives under conditions that simulate the wet, oral environment. Statement of SignificanceA self-strengthening dental adhesive system was developed through a dual curing process, which involves the free radical photopolymerization followed by slow hydrolysis and condensation (photoacid-induced sol–gel reaction) of alkoxylsilane groups. The concept of “living” photoacid-induced sol–gel reaction with visible-light irradiation was confirmed in the polymer. The sol–gel reaction was retarded by the polymethacrylate network, which was generated first; the network extended the life and retained the activity of silanol groups. The self-strengthening behavior was evaluated by monitoring the mechanical properties of the hybrid copolymers under wet conditions. The present research demonstrates the sol–gel reaction in highly crosslinked network as a potentially powerful strategy to prolong the functional lifetime of engineered biomaterials in wet environments.

Photophoretic trapping-Raman spectroscopy for single pollens and fungal spores trapped in air

Photophoretic trapping-Raman spectroscopy (PTRS) is a new technique for measuring Raman spectra of particles that are held in air using photophoretic forces. It was initially demonstrated with Raman spectra of strongly-absorbing carbon nanoparticles (Pan et al. [44] (Opt Express 2012)). In the present paper we report the first demonstration of the use of PTRS to measure Raman spectra of absorbing and weakly-absorbing bioaerosol particles (pollens and spores). Raman spectra of three pollens and one smut spore in a size range of 6.2–41.8µm illuminated at 488nm are shown. Quality spectra were obtained in the Raman shift range of 1600–3400cm−1 in this exploratory study. Distinguishable Raman scattering signals with one or a few clear Raman peaks for all four aerosol particles were observed within the wavenumber region 2940–3030cm−1. Peaks in this region are consistent with previous reports of Raman peaks in the 1600–3400cm−1 range for pollens and spores excited at 514nm measured by a conventional Raman spectrometer. Noise in the spectra, the fluorescence background, and the weak Raman signals in most of the 1600–3400cm−1 region make some of the spectral features barely discernable or not discernable for these bioaerosols except the strong signal within 2940–3030cm−1. Up to five bands are identified in the three pollens and only two bands appear in the fungal spore, but this may be because the fungal spore is so much smaller than any of the pollens. The fungal spore signal relative to the air-nitrogen Raman band is approximately 10 times smaller than that ratio for the pollens. The five bands are tentatively assigned to the CH2 symmetric stretch at 2948cm−1, CH2 Fermi resonance stretch at 2970cm−1, CH3 symmetric stretch at 2990cm−1, CH3 out-of-plane end asymmetric stretch at 3010cm−1, and unsaturated =CH stretch at 3028cm−1. The two dominant bands of the up-to-five Raman bands in the 2940–3030cm−1 region have a consistent band spacing of 25cm−1 in all four aerosols. Finally we discuss improvements to the PTRS that should provide a system which can trap a higher fraction of particle types and obtain Raman spectra over a larger range (e.g., 200–3600cm−1) than those achieved here.

Correction to “High-Resolution Rovibrational Spectroscopy of Jet-Cooled Phenyl Radical: The ν19 Out-of-Phase Symmetric CH Stretch”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to “High-Resolution Rovibrational Spectroscopy of Jet-Cooled Phenyl Radical: The ν19 Out-of-Phase Symmetric CH Stretch”Grant T. Buckingham, Chih-Hsuan Chang, and David J. Nesbitt*Cite this: J. Phys. Chem. A 2014, 118, 23, 4232Publication Date (Web):May 28, 2014Publication History Published online28 May 2014Published inissue 12 June 2014https://doi.org/10.1021/jp505197zCopyright © 2014 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views221Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (103 KB) Get e-Alerts Get e-Alerts

Ground State Conformational Preferences and CH Stretch–Bend Coupling in a Model Alkoxy Chain: 1,2-Diphenoxyethane

1,2-Diphenoxyethane (C6H5-O-CH2-CH2-O-C6H5, DPOE) is a flexible bichromophore in which the two phenyl rings are separated from one another by an -O-CH2-CH2-O- chain with five flexible dihedral angles about which hindered rotation can occur. As such, it is a phenyl capped analog of dimethoxyethane (DMOE), which has served as a model compound for development of force fields for polyethylene glycol (PEG). The ground state conformational energy landscape of DPOE is explored using a combination of single-conformation spectroscopy of the jet-cooled molecule and calculations of the conformational minima and transition states. In the experimental UV spectrum, ultraviolet hole-burning establishes the presence of just two conformations with significant population in the supersonic jet expansion. Fluorescence dip infrared (FDIR) spectroscopy is used to record infrared spectra of the two conformers in the alkyl CH stretch, CH bend, and CO stretch regions. When compared with harmonic vibrational frequency calculations, the two isomers are determined to be of C2h and C2 symmetry, and labeled ttt and tgt to denote the three central dihedrals as trans or gauche. Infrared population transfer spectroscopy is used to determine fractional abundances for the two conformers (f(ttt) = 0.53 ± 0.01; f(tgt) = 0.47 ± 0.01). Relaxed potential energy curves along the three nonequivalent dihedral angles are used to map out the shape of the potential energy landscape that leads to these preferences. The Fermi resonance in the alkyl CH stretch spectrum is successfully modeled using a recently developed methodology [Buchanan et al., J. Chem. Phys. 2013, 138, 064308] employing a reduced dimension Hamiltonian. The scissor overtones couple to the CH2 symmetric stretch and only indirectly to the asymmetric stretch through symmetric stretch/asymmetric stretch coupling. The presence of the oxygen atoms in the chain shifts the CH scissor overtones to higher frequencies than in pure alkyl chains, qualitatively changing the spectral consequences of the Fermi resonance, with the scissor overtones now appearing as the highest frequency bands in the spectrum. The spectra are contrasted with those in 1,2-diphenylethane, a close analog with a very different appearance to its CH stretch spectrum, in which the scissor overtones appear as the lowest frequency bands.

High-Resolution Direct-Absorption Spectroscopy of Hydroxymethyl Radical in the CH Symmetric Stretching Region

High-resolution, fully rotationally resolved direct absorption spectra of hydroxymethyl radical, CH2OH, are presented in the infrared CH stretching region. As a result of low rotational temperatures and sub-Doppler linewidths obtained in the slit supersonic expansion, the Ka = 0 ← 0 band of the symmetric CH stretch for CH2OH has been unambiguously identified and analyzed. By way of chemical confirmation, hydroxymethyl radical is generated via two different slit jet discharge syntheses: (i) direct dissociation of CH3OH to form CH2OH and (ii) dissociation of Cl2 followed by the radical H atom extraction reaction Cl + CH3OH → HCl + CH2OH. The identified transitions are fit to a Watson A-reduced symmetric top Hamiltonian to yield first precision experimental values for the ground state rotational constants as well as improved values for the symmetric stretch rotational constants and vibrational band origin. The results both complement and substantially improve upon spectral efforts via previous double resonance ionization detected infrared methods by Feng et al. [J. Phys. Chem. A, 2004, 108, 7093], as well as offer high-resolution predictions for laboratory and astronomical detection of hydroxymethyl radical in the millimeter-wave region.

Methanol Perturbing Modeling Cell Membranes Investigated using Linear and Nonlinear Vibrational Spectroscopy

Cell membranes play a crucial role in many biological functions of cells. A small change in the composition of cell membranes can strongly influence the functions of membrane-associated proteins, such as ion and water channels, and thus mediate the chemical and physical balance in cells. Such composition change could originate from the introduction of short-chain alcohols, or other anesthetics into membranes. In this work, we have applied sum frequency generation vibrational spectroscopy (SFG-VS), supplemented by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), to investigate interaction between methanol and 1,2-dimyristoyl-d54-sn-glycero-3-phosphocholine (d54-DMPC) lipid bilayers. Lipid's hydrocarbon interior is deuterated while its head group is hydrogenated. At the same time, CH3 symmetric stretch from methanol and lipid head amine group has different frequency, thus we can distinguish the behaviors of methanol, lipid head amine group, and lipid hydrocarbon interior. Based on the spectral feature of the bending mode of the water molecules replaced by methanol, we determined that the methanol molecules are intercalated into the region between amine and phosphate groups at the lipid hydrophilic head. The dipole of CH3 groups of methanol and lipid head, and the water O-H all adopt the same orientation directions. The introduction of methanol into the lipid hydrophilic head group can strongly perturb the entire length of the alkyl chains, resulting that the signals of CD2 and CD3 groups from both leaflets can not cancel each other.

Influence of the Membrane Composition of Retinal Photoreceptors on the Reversible Binding of a Neuronal Calcium Sensor Protein (NCS), Recoverin : A Solid-State NMR and FTIR Study

NCS proteins consist of 4 domains called EF-Hand, which are 2 α-helices joined by a loop with a highly conserved sequence. Binding of calcium ions by this loop induces important conformational changes in the protein. Most of the NCS also have a N-terminal sequence recognized by N-myristoyl transferase which is responsible for the acylation of the proteins. At low calcium concentration, the myristoyl group is sequestered into a hydrophobic cavity. The binding of 1 to 4 Ca2+ leads to the extrusion of the myristoyl (known as the calcium myristoyl switch) and the exposure of many hydrophobic residues allowing the protein to go from a cytosolic form to a membrane bound form. This property has an important biological function in the visual phototransduction cascade. In fact, the absorption of a photon by the visual pigment rhodopsin leads to an important decrease of calcium level in photoreceptors and recoverin, one of the NCS family, plays a key role in the recovery phase of visual excitation by inhibiting rhodopsin kinase at high calcium level. An interesting fact is that the membrane composition of the photoreceptor rod outer segments is known to be very different from that of other membranes, with more than 60% of the lipids being polyinsaturated. We have determined in the present study how the membrane composition affects the reversible membrane binding of recoverin. More specifically, 31P solid-state NMR and 2H solid-state NMR have been used to get information respectively about the lipid polar head groups and the recoverin myristoyl group. FTIR was also used to study the structure of recoverin (amide I’ band) and the lipid acyl chains (CH2 symmetric stretch band).

Micro-Raman Spectroscopy and Univariate Analysis for Monitoring Disease Follow-Up

Micro-Raman spectroscopy is a very promising tool for medical applications, thanks to its sensitivity to subtle changes in the chemical and structural characteristics of biological specimens. To fully exploit these promises, building a method of data analysis properly suited for the case under study is crucial. Here, a linear or univariate approach using a R2 determination coefficient is proposed for discriminating Raman spectra even with small differences. The validity of the proposed approach has been tested using Raman spectra of high purity glucose solutions collected in the 600 to 1,600 cm−1 region and also from solutions with two known solutes at different concentrations. After this validation step, the proposed analysis has been applied to Raman spectra from oral human tissues affected by Pemphigus Vulgaris (PV), a rare life-threatening autoimmune disease, for monitoring disease follow-up. Raman spectra have been obtained in the wavenumber regions from 1,050 to 1,700 cm−1 and 2,700 to 3,200 cm−1 from tissues of patients at different stages of pathology (active PV, under therapy and PV in remission stage) as confirmed by histopathological and immunofluorescence analysis. Differences in the spectra depending on tissue illness stage have been detected at 1,150–1,250 cm−1 (amide III) and 1,420–1,450 cm−1 (CH3 deformation) regions and around 1,650 cm−1 (amide I) and 2,930 cm−1 (CH3 symmetric stretch). The analysis of tissue Raman spectra by the proposed univariate method has allowed us to effectively differentiate tissues at different stages of pathology.

IR and FTMW-IR Spectroscopy and Vibrational Relaxation Pathways in the CH Stretch Region of CH3OH and CH3OD

Infrared spectra of jet-cooled CH(3)OD and CH(3)OH in the CH stretch region are observed by coherence-converted population transfer Fourier transform microwave-infrared (CCPT-FTMW-IR) spectroscopy (E torsional species only) and by slit-jet single resonance spectroscopy (both A and E torsional species, CH(3)OH only). Twagirayezu et al. reported the analysis of ν(3) symmetric CH stretch region (2750-2900 cm(-1); Twagirayezu et al. J. Phys. Chem. A 2010, 114, 6818), and the present work addresses the more complicated higher frequency region (2900-3020 cm(-1)) containing the two asymmetric CH stretches (ν(2) and ν(9)). The additional complications include a higher density of coupled states, more extensive mixing, and evidence for Coriolis as well as anharmonic coupling. The overall observed spectra contain 17 interacting vibrational bands for CH(3)OD and 28 for CH(3)OH. The sign and magnitude of the torsional tunneling splittings are deduced for three CH stretch fundamentals (ν(3), ν(2), ν(9)) of both molecules and are compared to a model calculation and to ab initio theory. The number and distribution of observed vibrational bands indicate that the CH stretch bright states couple first to doorway states that are binary combinations of bending modes. In the parts of the spectrum where doorway states are present, the observed density of coupled states is comparable to the total density of vibrational states in the molecule, but where there are no doorway states, only the CH stretch fundamentals are observed. Above 2900 cm(-1), the available doorway states are CH bending states, but below, the doorway states also involve OH bending. A time-dependent interpretation of the present FTMW-IR spectra indicates a fast (∼200 fs) initial decay of the bright state followed by a second, slower redistribution (about 1-3 ps). The qualitative agreement of the present data with the time-dependent experiments of Iwaki and Dlott provides further support for the similarity of the fastest vibrational relaxation processes in the liquid and gas phases.