Determination of vinyl orientation of mouse neuroglobin by 2D nuclear Overhauser spectroscopy

1H NMR has been used to determine the 2-,4-vinyl orientation of heme active site from oxidized mouse neuroglobin (mNgb).The NOEs between 3-methyl and Hα, Hβ of 2-vinyl, together with the NOEs between 5-methyl and Hα, Hβ of 4-vinyl, allowed the unambiguous determination of trans and cis orientations for the 2- and 4-vinyl groups in the mNgb, respectively.     

Terahertz time-domain spectroscopy of some pentoses

1 Introduction Terahertz time-domain spectroscopy (THz-TDS) is a new spectral technique based on femto-second laser technology developed since the 1980s[1]. Terahertz (THz) waves lie between the infrared and microwave bands in the electromagnetic spectrum covering the frequency range from 100 GHz to 10 THz. Despite great scientific interest, the THz frequency range re- mains one of the least tapped regions of the electro- magnetic spectrum because there are neither conven- ient high-power…     

Negative ion photoelectron spectroscopy of N2O− and (N2O)−2

We have recorded the photoelectron spectra of the gas phase negative ions N₂O⁻ and (N₂O)₂⁻ both of which were prepared in a nozzle ion source. The shift between the maxima of the two spectra is interpreted in terms of the dissociation energy of the dimer ion.     

The X2Σ+ state of LiCa studied by Fourier-transform spectroscopy

The paper reports on a successful observation of high resolution Fourier transform spectra of LiCa. The fine structure of the ground state was observed and attributed to effective spin-rotation interaction. The experimental observations are described by two models using potential energy curves. One of them takes into account the fine structure splitting by means of effective constants, the other by means of a R dependent function γ(R), built in the radial Schr?dinger equation. Ab initio calculations were performed for γ(R) which comes close to the experimental function.     

2DIR spectroscopy of human amylin fibrils reflects stable β-sheet structure

The aggregation of human amylin to form amyloid contributes to islet β-cell dysfunction in type 2 diabetes. Studies of amyloid formation have been hindered by the low structural resolution or relatively modest time resolution of standard methods. Two-dimensional infrared (2DIR) spectroscopy, with its sensitivity to protein secondary structures and its intrinsic fast time resolution, is capable of capturing structural changes during the aggregation process. Moreover, isotope labeling enables the measurement of residue-specific information. The diagonal line widths of 2DIR spectra contain information about dynamics and structural heterogeneity of the system. We illustrate the power of a combined atomistic molecular dynamics simulation and theoretical and experimental 2DIR approach by analyzing the variation in diagonal line widths of individual amide I modes in a series of labeled samples of amylin amyloid fibrils. The theoretical and experimental 2DIR line widths suggest a "W" pattern, as a function of residue number. We show that large line widths result from substantial structural disorder and that this pattern is indicative of the stable secondary structure of the two β-sheet regions. This work provides a protocol for bridging MD simulation and 2DIR experiments for future aggregation studies.     

Negative ion photoelectron spectroscopy of teo−

We have recorded the photoelectron spectrum of Te0⁻ using a hot-cathode discharge ion source and a negative ion photoelectron spectrometer. The adiabatic electron affinity of TeO is determined to be 1.697±0.022 eV. The negative ion parameters determined in this work are: (w_e″(TeO⁻) = 690 ± 80 cm⁻¹, r_e″(TeO⁻) = 1.884 ± 0.028 Å. and D_o     

Submillimeter-wave and far-infrared spectroscopy of high-J transitions of the ground and ν2 = 1 states of ammonia

Complete and reliable knowledge of the ammonia spectrum is needed to enable the analysis and interpretation of astrophysical and planetary observations. Ammonia has been observed in the interstellar medium up to J=18 and more highly excited transitions are expected to appear in hot exoplanets and brown dwarfs. As a result, there is considerable interest in observing and assigning the high J (rovibrational) spectrum. In this work, numerous spectroscopic techniques were employed to study its high J transitions in the ground and ν(2)=1 states. Measurements were carried out using a frequency multiplied submillimeter spectrometer at Jet Propulsion Laboratory (JPL), a tunable far-infrared spectrometer at University of Toyama, and a high-resolution Bruker IFS 125 Fourier transform spectrometer (FTS) at Synchrotron SOLEIL. Highly excited ammonia was created with a radiofrequency discharge and a dc discharge, which allowed assignments of transitions with J up to 35. One hundred and seventy seven ground state and ν(2)=1 inversion transitions were observed with microwave accuracy in the 0.3-4.7 THz region. Of these, 125 were observed for the first time, including 26 ΔK=3 transitions. Over 2000 far-infrared transitions were assigned to the ground state and ν(2)=1 inversion bands as well as the ν(2) fundamental band. Of these, 1912 were assigned using the FTS data for the first time, including 222 ΔK=3 transitions. The accuracy of these measurements has been estimated to be 0.0003-0.0006?cm(-1). A reduced root mean square error of 0.9 was obtained for a global fit of the ground and ν(2)=1 states, which includes the lines assigned in this work and all previously available microwave, terahertz, far-infrared, and mid-infrared data. The new measurements and predictions reported here will support the analyses of astronomical observations by high-resolution spectroscopy telescopes such as Herschel, SOFIA, and ALMA. The comprehensive experimental rovibrational energy levels reported here will permit further refinement of the potential energy surface to improve ammonia ab initio calculations and facilitate assignment of new high-resolution spectra of hot ammonia.     

Ultraviolet photoelectron spectroscopy of the hydrogen bonded heterodimer H2S⋯HCl

The HeI photoelectron spectrum of the hydrogen bonded hetero-dimer H₂S⋯HCl shows two vertical ionization energies at 10.91 and 12.16 eV. Ab initio MO calculations reveal that these features are due to the sulphur and chlorine lone pair ionizations respectively. Results show that while the ground ionic state is repulsive the first excited ionic state is strongly bound. The photoelectron spectrum of the diethyl sulphide⋯HCl complex is similar to that of H₂S⋯HCl     

Intracavity laser spectroscopy of the HfCl molecule. Analysis of rotational structure of new bands of the 2Δ-X2Δ electronic transition

Electron absorption spectrum of the HfCl molecule was studied in the 550–800 nm region using intracavity laser spectroscopy. HfCl molecules were obtained using the passage of an impulse electric discharge through a mixture of HfCl₄ and He vapors. A cuvette with the mixture of gases was placed in a dyelaser resonator cavity. The spectra were registered using diffraction spectrograph (resolution capability 240000). The high sensitivity of the intracavity method made it possible to detect in the HfCl spectrum new bands with a resolved rotational structure. Rotational analyses of the given bands were performed and the molecular constants were determined.     

High-resolution Fourier transform infrared absorption spectroscopy of the ν6 band of c-C3H2

The gas-phase high-resolution absorption spectrum of the ν(6) band of cyclopropenylidene (c-C(3)H(2)) has been observed using a Fourier transform infrared spectrometer for the first time. The molecule has been produced by microwave discharge in an allene (3.3 Pa) and Ar (4.0 Pa) mixture inside a side arm glass tube. The observed spectrum shows a pattern of c-type ro-vibrational transitions in which the Q-branch lines strongly and distinctly stand out in the spectrum. A combined least-squares analysis of the observed 216 ro-vibrational transitions together with 28 millimeter-wave rotational transitions from the previous study has resulted in an accurate determination of the molecular constants in the ν(6) state. The band center is found to be at 776.11622(13) cm(-1) with one standard deviation in parentheses, which is 2.3% lower than the matrix isolation value. The intensity ratio I(3)(ν(3))/I(6)(ν(6)) obtained from the observed ν(3) and ν(6) bands, 1.90(9), is somewhat lower than the ratio estimated from ab initio (2.4-2.6) and DFT (2.8) calculations.     

Photoelectron spectroscopy of (CO2)n(H2O) m − clusters

Photoelectron spectra of (CO₂)_nH₂O^? (2≤n≤8) and (CO₂)_n(H₂O) ₂ ^? (1≤n≤2) were measured at the photon energy of 3.49 eV. The spectra show unresolved broad features, which are approximated by Gaussians. The vertical detachment energies (VDEs) were determined as a function of the cluster size. For (CO₂)_nH₂O^?, the VDE-n plots exhibit a sharp discontinuity between n=3 and 4; the VDE value is ≈3.5 eV at n=3, while it drops down abruptly to 2.59 eV at n=4. This discontinuity in VDE is ascribed to "core switching" at n=4; a C₂O ₄ ^? dimer anion forms the core of (CO₂)_nH₂O^? for n≤3, while a monomer CO ₂ ^? is the core for n≥4. The (CO₂)₂(H₂O) ₂ ^? ion has a VDE of 2.33 eV, indicating the presence of a CO ₂ ^? monomer core in the binary clusters containing two H₂O molecules.     

Intraconfigurational absorption spectroscopy of ReCl2−6 in various A2MCl6 host crystals

Low-temperature absorption and excitation spectra for Re⁴⁺ in distorted substitutional sites in K₂SnCl₆, [N(CH₃)₄]₂SnCl₆, [N(C₂H₅)₄]₂SnCl₆, [N(C₃H₇)₄]₂SnCl₆, and K₂SnBr₆ as well as in pure K₂ReCl₆ are discussed in comparison with the absorption spectra of Re⁴⁺ in cubic K₂PtCl₆, Cs₂ZrCl₆, and (NH₄)₂SnCl₆. Our data indicate that the effects of lowered symmetry are in general small and that the spectra can be interpreted in a manner paralleling earlier studies of Re⁴⁺ in cubic environments. Effects of reduced host symmetry appear to be smaller for this Kramers' ion than was previously noted for Os⁴⁺, a d⁴ system, but about equivalent to those noted for Ir⁴⁺, a d⁵ system, in the same host crystals. Origin shifts do not vary monotonically with cation size but do parallel results seen in Ir⁴⁺. In the N(C₂H₅)⁺₄ and N(C₃H₇)⁺₄ containing host crystals a significant splitting was found that correlated to two substitutional sites with parallel vibronic patterns. Low-symmetry splitting of U′_g states tended, on the contrary, to yield two sets of vibronic side bands with different intensity patterns which is an aid to assignment of the electronic state component.     

Positive ion — negative ion coincidence spectroscopy of O2 and H2 using synchrotron radiation

Kinetic studies of the reactions of neutral lead clusters with NO₂, NO and O₂ were performed at 300 K. Reaction with NO₂ is rapid, with the observed second-order rate constants for most clusters being between 0.2 and 5 × 10^?11 cm³/s. There is a general trend of increasing rate with cluster size, although a few clusters display unusually high or low rates compared to ones of neighboring size. The reactions with NO are considerably slower by factors ranging from about 5 to 10. Reaction products are observed by laser ionization at 193 and 222 nm in conjunction with time-of-flight mass spectrometry. At lower fluence, the association products Pb _x (NO₂)⁺ and Pb _x (NO₂) ₂ ⁺ are observed in the case of reactions with NO₂. At higher laser fluence, Pb _x ⁺ and Pb _x O _x ^?1+ dominate the mass spectra of Pb _x reactions with NO₂, showing that the products fragment to more stable oxides. No reaction with oxygen was observed for any cluster, setting upper limits on the rates of 5 × 10^?14 cm³/s.     

An investigation of the effect of microwave treatment on the structure and unfolding pathways of β-lactoglobulin using FTIR spectroscopy with the application of two-dimensional correlation spectroscopy (2D-COS)

Microwave treatment of β-lactoglobulin (β-Lg) in D₂O solution under various conditions was monitored by Fourier transform mid infrared (mid-FTIR) spectroscopy. At sub-ambient temperatures, no microwave-induced changes in the conformation of the protein were detected. Microwave heating of the β-Lg solutions to temperatures in the range of 40–60 °C resulted in a marked increase in the rate of hydrogen–deuterium (H–D) exchange as compared to conventional heating at the same temperature. At heating temperatures in the range of 70–90 °C, the microwave-heated solutions exhibited more extensive protein aggregation than conventionally heated solutions. Application of two-dimensional (2D) correlation analysis to the Fourier self-deconvolved FTIR spectra recorded as a function of number of cycles of microwave or conventional heating revealed that the unfolding pathway of β-Lg was different in these two temperature ranges (40–60 °C versus 70–90 °C) but was similar in both microwave – treated and conventionally heated samples. Nevertheless, within the temperature range of 70–90 °C microwave treatment accelerated the unfolding of β-lactoglobulin.     

Infrared diode laser spectroscopy of the ν2(2+ ← 1−) band of H3O+

Rotational lines in the ν₂ = 2⁺ ← 1⁻ “hot” band of the inversion mode of the oxonium (H₃O⁺) ion have been recorded by diode laser absorption spectroscopy. The ion was generated in low pressure gas discharges and detected using both velocity modulation and modulated hollow cathode techniques. Analysis of the spectra using a simple oblate symmetric top model has allowed the rotational parameters describing the 2⁺ inversion state to be determined for the first time. The band origin lies at 521.4383(52) cm⁻¹. These data will be useful in refining the oxonium ion inversion potential function and should aid in the analysis of other bands involving or perturbed by the 2⁺ level.     

Raman spectroscopy in the near infrared – a most capable method of vibrational spectroscopy

Raman spectroscopy has enjoyed a dramatic improvement during the last years: The interference by the fluorescence of impurities is virtually eliminated, the sample preparation is considerably easier as for infrared spectroscopy and many applications in routine analytics, quality control and process control in various branches of industry are now possible. It is shown that the up-to-date near-infrared Raman spectrometers now meet most demands for a modern analytical instrument concerning applicability, analytical information and convenience. It can be anticipated that Raman spectroscopy will catch up infrared spectroscopy, the current workhorse of vibrational spectroscopy.     

Imaging secondary structure of individual amyloid fibrils of a β2-microglobulin fragment using near-field infrared spectroscopy

Amyloid fibril diseases are characterized by the abnormal production of aggregated proteins and are associated with many types of neuro- and physically degenerative diseases. X-ray diffraction techniques, solid-state magic-angle spinning NMR spectroscopy, circular dichroism (CD) spectroscopy, and transmission electron microscopy studies have been utilized to detect and examine the chemical, electronic, material, and structural properties of amyloid fibrils at up to angstrom spatial resolution. However, X-ray diffraction studies require crystals of the fibril to be analyzed, while other techniques can only probe the bulk solution or solid samples. In the work reported here, apertureless near-field scanning infrared microscopy (ANSIM) was used to probe the secondary structure of individual amyloid fibrils made from an in vitro solution. Simultaneous topographic and infrared images of individual amyloid fibrils synthesized from the #21-31 peptide fragment of β(2)-microglobulin were acquired. Using this technique, IR spectra of the amyloid fibrils were obtained with a spatial resolution of less than 30 nm. It is observed that the experimental scattered field spectrum correlates strongly with that calculated using the far-field absorption spectrum. The near-field images of the amyloid fibrils exhibit much lower scattering of the IR radiation at approximately 1630 cm(-1). In addition, the near-field images also indicate that composition and/or structural variations among individual amyloid fibrils were present.