Study of the thermal decomposition of a sepiolite by mid- and near-infrared spectroscopies

Near-infrared (NIR) and mid-infrared (MIR) spectroscopies were used to characterize the hydroxyl groups present in a sepiolite and its calcination products at 250, 500 and 800 °C. Calcining the sepiolite at 250 °C was found to result in its dehydration through the loss of coordination water. Raising the calcination temperature to 500 °C caused the sepiolite structure to fold and hydroxyl groups in octahedral layers to be removed. Finally, calcination at 800 °C resulted in a phase change leading to enstatite, as confirmed by XRD spectroscopy.     

Study of the dynamics of surface molecules by time-resolved sum-frequency generation spectroscopy

Sum-frequency generation (SFG) is a nonlinear laser-spectroscopy technique suitable for analysis of adsorbed molecules. The sub-monolayer sensitivity of SFG spectroscopy enables vibrational spectra to be obtained with high specificity for a variety of molecules on a range of surfaces, including metals, oxides, and semiconductors. The use of ultra-short laser pulses on time-scales of picoseconds also makes time-resolved measurements possible; this can reveal ultrafast transient changes in molecular arrangements. This article reviews recent time-resolved SFG spectroscopy studies revealing site-hopping of adsorbed CO on metal surfaces and the dynamics of energy relaxation at water/metal interfaces. Time-resolved sum frequency generation spectroscopy at surfaces with non-resonant laser pulse irradiation     

Pulsed EPR Dipolar Spectroscopy under the Breakdown of the High-Field Approximation: The High-Spin Iron(III) Case

Pulsed EPR dipolar spectroscopy (PDS) offers several methods for measuring dipolar coupling and thus the distance between electron-spin centers. To date, PDS measurements to metal centers were limited to ions that adhere to the high-field approximation. Here, the PDS methodology is extended to cases where the high-field approximation breaks down on the example of the high-spin Fe³⁺/nitroxide spin-pair. First, the theory developed by Maryasov et al. (Appl. Magn. Reson. 2006 , 30, 683–702) was adapted to derive equations for the dipolar coupling constant, which revealed that the dipolar spectrum does not only depend on the length and orientation of the interspin distance vector with respect to the applied magnetic field but also on its orientation to the effective g-tensor of the Fe³⁺ ion. Then, it is shown on a model system and a heme protein that a PDS method called relaxation-induced dipolar modulation enhancement (RIDME) is well-suited to measuring such spectra and that the experimentally obtained dipolar spectra are in full agreement with the derived equations. Finally, a RIDME data analysis procedure was developed, which facilitates the determination of distance and angular distributions from the RIDME data. Thus, this study enables the application of PDS to for example, the highly relevant class of high-spin Fe³⁺ heme proteins.     

Investigating the Selectivity of Triacontyl Interphases

What causes the shape selectivity of C ₃₀ phases? This question can be answered by combining NMR and fluorescence spectroscopies with HPLC separations at various temperatures. The selectivities depend on the ratio of trans to gauche conformations of the alkyl chains, whose dynamic behavior was characterized with a two-dimensional solid-state NMR spectrum (shown on the right).     

Surface properties of the Ni-Cu-Cr oxide catalyst for dehydrogenative hydrolysis of amines

Catalysts for dehydrogenative hydrolysis of amines, prepared by sorption of copper ions from a solution on a preformed Ni-Cr oxide system, were studied by Auger electron spectroscopy, X-ray photoelectron spectroscopy, and IR spectroscopy of adsorbed CO and NH₃ probe molecules. It was shown that on adsorption copper blocked the chromium ions in the Ni-Cr catalyst with concomitant stabilization as Cu⁺. The incorporation of copper into the Ni-Cr system increased the ability of nickel to reduce water with the formation of oxygen-containing complexes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 288–291, February, 1993.     

Isolation and Spectroscopic Characterization of New Endohedral Fullerenes in the Size Gap of C74 to C76

New alkaline earth metal endohedral fullerenes Sr@C₇₄, Sr@C₇₆‐I, II and Ca@C₇₄, prepared by means of the RF‐method, have been isolated using multistep HPLC. The purity was ascertained by anionic LDI TOF mass spectroscopy, considering the isotopic patterns of the compounds. The influence of the incorporated metal on the electronic structure has been studied by VIS‐NIR and Raman spectroscopy. Photoexcited triplet‐state EPR spectroscopy was used to investigate the structure of these otherwise EPR‐silent fullerenes. Displaying the frequency of the cage vs. encapsulated metal vibrational modes as a function of the square root of the reciprocal masses of the metals clearly separates the M³⁺@C_n^3— and the M²⁺@C_n^2— families. This seems to be a generally applicable tool for monitoring the metal to fullerene charge transfer.     

Synthesis and Properties of Phenothiazine Derivatives. 2. Spectral (ESR and IR) Characteristics of the Radical-cations of the Phenothiazine N-Derivatives

The temperature dependence of the ESR spectra of the radical-cations of the N-derivatives of phenothiazine were studied in the range of 200-393 K (o-xylene). It was established that at temperatures of 323-333 K the nature of the HFS varies from doublet to quartet with approximate intensity ratios of 1:2:2:1, and this transformation is irreversible. A hypothesis explaining the results is proposed. IR spectroscopy was used to confirm the proposed mechanism of localization of the unpaired electron.     

Characterization of the benzene-insoluble fraction of the hydrolyzate of phenyltrimethoxysilanes in the presence of benzyltrimethylammonium hydroxide

The insoluble fraction obtained from the hydrolysis and condensation of (4-dimethylamino-, 2-methyl-, and nonsubstituted)phenyltrimethoxysilanes in the presence of benzyltrimethylammonium hydroxide in benzene was characterized. IR, ¹H NMR, and ²⁹Si NMR suggested that the insoluble fraction was composed of RSi(O )₃, that is, a T³ structure. X-ray diffraction indicated the presence of a long-range ordered structure composed of a mixture of crystals. Raman spectroscopy strongly suggested a cage structure by the presence of a ring-opening vibration assignable to a cubic structure at 475–482 cm⁻¹. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4587–4597, 2004     

Terahertz time-domain and Raman spectroscopy of the sulfur-containing peptide dimers: Low-frequency markers of disulfide bridges

The terahertz time-domain and Raman spectra of sulfur-containing cystein-based peptides in the region of the low-frequency infrared vibrations have been measured at room temperature. The low-frequency bands that can be assigned to the S–S bridges are observed. The vibrational modes found in molecular crystalline materials should be described as phonon modes with strong coupling to the intra molecular vibrations.     

Analyzing the Vibrational Signatures of Thiophenol Adsorbed on Small Gold Clusters by DFT Calculations

Using density functional theory, we calculate the IR and Raman signatures of the thiophenol (TP) molecule adsorbed on gold clusters by mimicking the different types of adsorption sites, and we analyze these signatures by using advanced tools implemented into the pyvib2 program. First, we follow the evolution of the vibrational normal modes from the isolated TP molecule to those of TP adsorbed on different clusters to highlight the influence of the site of adsorption on the vibrational motions. The use of the overlap matrix between the modes enables mode permutations, mode mixings, and mode splittings to be highlighted, all of which depend not only on the adsorption but also on the type of cluster and its symmetry. Second, the IR and Raman signatures were analyzed by using group coupling matrices and atomic contribution patterns based on the Hug decomposition scheme. Key results include 1) the fact that Raman spectroscopy is more sensitive than IR spectroscopy with respect to the nature of the coordination site, 2) an IR criterion that distinguishes between on‐top coordination (onefold coordinated) with respect to the bridge (twofold coordinated) and hexagonal close‐packed hollow site coordination (threefold coordinated), and 3) the best agreement to the experimental Raman spectrum with regard to signatures in the 500 to 1200 cm^?1 region is obtained for bridged, twofold coordination.     

烟碱与人血清蛋白相互作用的光谱研究

在0．1moL／L的磷酸氢二钠-柠檬酸体系中，采用荧光光谱、紫外吸收光谱研究了人血清蛋白与烟碱的相互作用。荧光滴定表明这种相互作用使HSA的内源荧光猝灭。通过猝灭常数、结合常数和结合位点数的计算，证明了这种猝灭为静态猝灭机制。尼古丁和HsA形成1：1稳定复合物；考察不同温度和酸度下的猝灭作用，进一步证实其静态猝灭行为和疏水作用机制。紫外吸收光谱和同步荧光光谱表明，相互作用引起HSA构象变化，而同步荧光光谱提示结合位点更接近于色氨酸。     

The effect of the molecular weight of chitosan nanoparticles and its application on drug delivery

Nanoparticulate drug delivery systems offer several advantages over conventional forms of dosing, with polymer nanoparticles prepared from biomaterials being good candidates for use in drug delivery. We selected fluorouracil (5FU) as a model drug because it has been suggested that chitosan might prevent the side effects induced by 5FU. We have exploited the complexation between oppositely charged macromolecules to develop a safe and efficient method of preparation of chitosan bead formulations for use as drug delivery systems. In this study, we examined the effect that the molecular weight of chitosan had on the resulting nanoparticles' properties; the initial concentration of chitosan was held constant, but its molecular weight was decreased through the action of NaNO₂. FTIR spectroscopy suggested that no structural change occurred during the depolymerization process. The diameters of the nanoparticles—determined using dynamic light scattering and TEM techniques—decreased as the value of the viscosity of molecular weight (Mv) of chitosan decreased. In addition, we prepared fluorouracil-loaded chitosan nanoparticles and characterized them using NMR spectroscopy. The encapsulation efficiency increased as the value of Mv of chitosan decreased. The particles produced using 55-kDa chitosan had a mean diameter of 70.6 nm and a 66% drug loading.     

PELDOR Spectroscopy Distance Fingerprinting of the Octameric Outer‐Membrane Protein Wza from Escherichia coli.

Distance fingerprinting : Pulsed electron–electron double resonance spectroscopy (PELDOR) is applied to the octameric membrane protein complex Wza of E. coli. The data yielded a detailed distance fingerprint of its periplasmic region that compares favorably to the crystal structure. These results provide the foundation to study conformation changes from interaction with partner proteins.

     

Role of the solvent on the stability of cycloserine under ESI‐MS conditions

The effects of methanol (M) and acetonitrile (A) on the stability of cycloserine (1) have been studied. InfraRed Multiphoton PhotoDissociation (IRMPD) spectroscopy of the ionic species from electrospray ionization tandem mass spectrometry (ESI‐MS) of 1/M and 1/A solutions points to extensive dimerization of 1 to cis‐3,6‐bis(aminooxymethyl)‐2,5‐piperidinedione (2), while the same process is not observed in the ESI‐MS of 1/M solutions. 1D and 2D nuclear magnetic resonance experiments confirmed these findings by showing that partial dimerization of 1 actually takes place at room temperature in acetonitrile even before ESI‐MS analysis. Comparison of nuclear magnetic resonance and IRMPD spectroscopic data from the same 1/A solution suggests that dimerization of cycloserine is enhanced in the ESI source. Copyright © 2014 John Wiley & Sons, Ltd.     

Geometrical Evolution and Formation of the Photoproduct in the Cycloreversion Reaction of a Diarylethene Derivative Probed by Vibrational Spectroscopy

The geometrical evolution of the reactant and formation of the photoproduct in the cycloreversion reaction of a diarylethene derivative were probed using time-resolved absorption spectroscopies in the visible to near-infrared and mid-infrared regions. The time-domain vibrational data in the visible region show that the initially formed Franck-Condon state is geometrically relaxed into the minimum in the excited state potential energy surface, concomitantly with the low-frequency coherent vibrations. Theoretical calculations indicate that the nuclear displacement in this coherent vibration is nearly parallel to that in the geometrical relaxation. Time-resolved mid-infrared spectroscopy directly detected the formation of the open-ring isomer with the same time constant as the decrease of the closed-ring isomer in the excited state minimum. This observation reveals that no detectable intermediate, in which the population is accumulated, is present between the excited closed-ring isomer and the open-ring isomer in the ground state.     

Two-Dimensional Solid-State NMR Spectroscopy: New Possibilities for the Investigation of the Structure and Dynamics of Solid Polymers [New Analytical Methods (38)]

NMR spectroscopy is an effective method not only for examining liquid samples but also for characterizing molecular sturcture, order and dynamics in amorphous and ordered solids. Recent developments in the area of solid-state NMR spectroscopy span from model-dependent studies of conventional one-dimensional spectra to the more definitive two-dimensional (2D) spectra which provide more specific information. For example, with 2D-NMR spectroscopy it is possible to determine the orientational distribution functions of molecular segments in drawn polymers and to distinguish different mechanisms of complex molecular motions. Following an introduction to basic NMR spectroscopy, an overview of the current state-of-the-art of 2D methods in solid-state NMR spectroscopy is presented and demonstrated with selected examples.