Reply to the Comment on¶Low temperature specific heat of blue bronze K0.30MoO3

Eur. Phys. J. B 24, 315 (2001) In our Reply to the Comment [#!1!#] we refute the “straightforward” interpretation of the excess low-temperature specific heat, C_p, contribution we have measured in our study of CDW systems K_0.3MoO₃ and (TaSe₄)₂I [#!2!#] as originating solely from normal phonon modes. The specific sensitivity of the bump in C _p / T ³ at low temperatures to the impurity content is consistent with the increased value of the phason pinning gap while the dispersion of normal phonons remains unaffected. We ascribe at least this part of the anomaly to the phason contribution. As stated in reference [3] that the phonon density of states extracted from neutron scattering measurements is the least reliable in this energy range (<0.5 meV), we conclude that C_p measurements are more accurate for detecting the phason contribution. Received 17 April 2002 Published online 19 July 2002     

Application of ultrasound technique in the synthesis of methanofullerene derivatives

Methanofullerene derivatives C₆₀(CCl₂) (1a), C₆₀(CBr₂) (1b), C₆₀(CI₂) (1c) and C₁₂₁ (2) were synthesized in 55–84% yields by dehalogenation of the corresponding α-polyhalides via sodium hydroxide, magnesium, respectively, followed by the in situ reaction with fullerene under the irradiation of ultrasound in a non-conventional reaction media, ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF₄]. Only single [6,6]-ring junction cycloaddition isomers of the products were detected in the reaction solutions under our conditions. In contrast, low yields of 6–21% were obtained when the same reactions were operated in tetrahydrofuran. All of the products were purified with HPLC and characterized by ¹³C NMR and FAB-MS.     

Theoretical studies of ethylene addition to transition metal compounds with carbene and oxo groups LnM(CH2)(O)

Quantum chemical calculations using density functional theory at the B3LYP level in combination with relativistic effective core potentials for the metals and TZ2P valence basis sets have been carried out for elucidating the reaction pathways of ethylene addition to MeReO₂(CH₂) ( C1 ). The results are compared with our previous studies of ethylene addition to OsO₂(CH₂)₂ ( A1 ) and OsO₃(CH₂) ( B1 ). Significant differences have been found between the ethylene additions to the osmium compounds A1 and B1 and the rhenium compound C1 . Seven pathways for the reaction C1 +C₂H₄ were studied, but only the [2+2]_Re,C addition yielding rhenacyclobutane C5 is an exothermic process with a high activation barrier of 48.9 kcal mol^?1. The lowest activation energy (27.7 kcal mol^?1) is calculated for the [2+2]_Re,C addition, which leads to the isomeric form C5 ′. Two further concerted reactions [3+2]_O,C, [3+2]_O,O, and [2+2]_Re,O and the addition/hydrogen migration of ethylene to one oxo ligand are endothermic processes which have rather high activation barriers (>35 kcal mol^?1). Four isomerization processes of C1 have very large activation energies of >65 kcal mol^?1. The ethylene addition to the osmium compounds A1 and B1 are much more exothermic and have lower activation barriers than the C₂H₄ addition to C1 . Copyright © 2007 John Wiley & Sons, Ltd.     

A miniature tunable TEA CO<Subscript>2</Subscript> laser using isotope <Superscript>13</Superscript>C<Superscript>16</Superscript>O<Subscript>2</Subscript> and <Superscript>12</Superscript>C<Superscript>16</Superscript>O<Subscript>2</Subscript>

A miniature tunable TEA CO₂ laser using isotope ¹³C¹⁶O₂ as the active medium is developed to extend the spectral range of CO₂ lasers for further application. The optimization of the energy parameters of the tunable TEA ¹³C¹⁶O₂ laser and the same laser using ¹²C¹⁶O₂ are studied. When a gas mixture (¹³C¹⁶O₂: N₂: He = 1: 1: 3) at a total pressure of 6.4 × 10⁴ Pa is used, the TEA ¹³C¹⁶O₂ laser of a 45-cm³ active volume obtains 51 emission lines in the [00⁰1–10⁰0] and [00⁰1–02⁰0] bands. The maximum pulse energy of the TEA ¹³C¹⁶O₂ laser is about 357 mJ. The same laser using the conventional gas mixture (¹²C¹⁶O₂: N₂: He = 1: 1: 3) at a pressure of 6.66 × 10⁴ Pa is measured to obtain 69 laser emission lines and the maximum pulse energy of laser radiation is about 409 mJ.     

High-intensity ultrasound promoted the aldol-type condensation as an alternative mean of synthesizing pyrazines in a Maillard reaction model system of D-glucose-13C6 and L-glycine

This study evaluated how the generation of pyrazines was promoted by high-intensity ultrasound (HIU) in a Maillard reaction (MR) model system of glucose-glycine. Carbohydrate module labeling (CAMOLA) technique was adopted using D-glucose-¹³C₆ to elucidate the carbon skeleton of both intermediate and final MR products (MRPs). In the D-glucose-¹³C₆-glycine HIU-MR model system, the concentration of 11 types of pyrazines was significantly higher than their counterparts in the thermal MR. Results of CAMOLA analysis showed that a significantly lower proportion of [M]⁺ in pyrazines with long-length side chains was observed when compared with the pyrazines generated in thermal MR. This phenomenon may suggest the aldol-type condensation was promoted by the HIU, which is a conversion from pyrazines with short-length side chains to those with long-length side chains involving carbonyl compounds. Furthermore, the analysis of isotopomers distribution in 2,3-dimethyl-quinoxaline as the o-phenylenediamine-derivatized 2,3-butanedione indicated that the increased proportion of [M + 4]⁺ in 2,3-dimethyl-quinoxaline (15.74% ± 0.11%) was attributed to a cleavage of D-glucose-¹³C₆ promoted by the HIU. The above-mentioned findings elucidate that the aldol-type condensation and cleavage of D-glucose contribute to the promoted synthesis of pyrazines. The HIU would generate an extremely high temperature and pressure environment that is favored by the aldol-type condensation as a high-pressure favored reaction. The HIU, therefore, can be further developed as a promising technique to promote flavor generation through the MR.     

Intramolecular Diels–Alder reaction in enyne–allenes: a computational investigation and comparison with the Myers–Saito and Schmittel reactions

The reaction mechanisms as well as substituted effect and solvent effect of the enyne–allenes are investigated by Density Functional Theory (DFT) method and compared with the Myers–Saito and Schmittel reactions. The Myers–Saito reaction of non‐substituted enyne–allenes is kinetically and thermodynamically favored as compared to the Schmittel reaction; while the concerted [4 + 2] cycloaddition is only 1.32 kcal/mol higher than the C₂? C₇ cyclization and more exothermic (Δ_RE = ?69.38 kcal/mol). For R₁ = CH₃ and t‐Bu, the increasing barrier of the C₂? C₇ cyclization is higher than that for the C₂? C₆ cyclization because of the steric effect, so the increased barrier of the [4 + 2] cycloaddition is affected by such substituted electron‐releasing group. Moreover, the strong steric effect of R₁ = t‐Bu would shift the C₂? C₇ cyclization to the [4 + 2] cycloaddition. On the other hand, for R₁ = Ph, NH₂, O^?, NO₂, and CN substituents, the barrier of the C₂? C₆ cyclization would be more diminished than the C₂? C₇ cyclization due to strong mesomeric effect; the reaction path of C₂? C₇ cyclization would also shift to the [4 + 2] cycloaddition. The solvation does not lead to significant changes in the potential‐energy surface of the reaction except for the more polar surrounding solvent such as dimethyl sulfoxide (DMSO), or water. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantum chemical study of the (Z)-2-penten-1-ol (HOCH2–CH = CHCH2CH3) + OH + O2 reactions

ABSTRACT

The mechanism and products of the reaction of (Z)-2-penten-1-ol [(Z)-PO21] with OH radical in the presence of O₂ have been elucidated by using high-level quantum chemical methods CCSD(T)/6-311+G(d,p)//BH&;HLYP/6-311++G(d,p). The calculations clearly indicate that addition channels contribute maximum to the total reaction and H-abstraction channels can be neglected at temperatures of 220–500 K. The rate constant for the reaction of OH radical with (Z)-PO21 at 298 K is computed to be 1.22 × 10^?10 cm³ molecule^?1 s^?1, which is in stronger agreement with the previously reported experimental values. The kinetic data obtained over the temperature range 220?500 K are used to derive an non-Arrhenius expression: k = 3.69 × 10^?13 × exp(1763.7/T) cm³ molecule^?1 s^?1. For the reaction of (Z)-PO21with OH radical in the presence of O₂, the major primary reaction products found in this study are propanal [CH₃CH₂C(O)H] and glycolaldehyde [HOCH₂C(O)H], whereas formaldehyde [HC(O)H], 2-hydroxybutanal [CH₃CH₂CH(OH)C(O)H] and the epoxide P18 are anticipated to be minor products. The calculated results are consistent with the recent experimental observations.     

Towards an Inhalative 13C Breath Test Method

Abstract

Customary ¹³CO₂ breath tests—and also ¹⁵N urine tests—always start with an oral administration of a test substrate. The test person swallows a stable isotope labelled diagnostic agent. This technique has been used to study several pathophysiological changes in gastrointestinal organs. However, to study pathophysiological changes of the bronchial and lung epithelium, the inhalative administration of a stable isotope labelled agent appeared more suitable to us. [1-¹³C]Hexadecanol and [1-¹³C]glucose were chosen. Inhaled [1-¹³C]hexadecanol did not yield ¹³CO₂ in the exhaled air, but [1-¹³C]glucose did. To study the practicability of the [1-¹³C]glucose method and the reproducibility of the results, 18 inhalation tests were performed with healthy subjects. In 6 self-tests, the optimum inhalative dose of [¹³C]glucose was determined to be 205 mg. Using the APS aerosol provocation system with the nebulizer ‘Medic Aid’ (Erich Jaeger Würzburg), a 25% aqueous solution was inhaled. Then, breath samples were collected at 15 min. intervals and analysed for ¹³CO₂. 75–120min after the end of inhalation a well-reproducible maximum δ¹³C value of 6‰ over baseline (DOB) was detected for 12 healthy probands.

Speculating that the pulmonary resorption of the [¹³C]glucose is the rate-limiting step of elimination, decompensations in the epithelium ought to be reflected in changed [1-¹³C]glucose resorption rates and changed ¹³CO₂ output.

Therefore, we speculate that the inhalation of suitable ¹³C-labelled substrates will pave the way for a new group of ¹³CO₂ breath tests aiding investigations of specific pathophysiological changes in the pulmonary tract, such as inflammations of certain sections and decompensations of cell functions.     

Molecular insight into structures of monocationic and dicationic ionic liquids in mica slits

Structures of ionic liquids (ILs) 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)azanide ([C₁₀mim][TFSA]) and 1-decyl-dimethylimidazolium bis(trifluoromethanesulfonyl)azanide ([C₁₀(mim)₂](TFSA)₂) in different-sized mica slits have been investigated using molecular dynamics simulations. Ion density and angular distributions for monocationic IL [C₁₀mim][TFSA] were analysed to elucidate the IL structures under different surface charges and especially their changes in the direction perpendicular to the surfaces. [C₁₀mim][TFSA] formes in bilayers, compatible with existing models of ILs with long alkyl chains. For dicationic IL [C₁₀(mim)₂](TFSA)₂, cations adjacent to the mica surface tend to stay parallel to the surface with both positively charged rings absorbed. While near the centre of the slit, dications show the weak tendency of orientation distribution, more random than [C₁₀mim]⁺ ions. Structures of [C₁₀(mim)₂](TFSA)₂ cannot be described by bilayer models. Additionally, the in-plane arrangement of [C₁₀mim][TFSA] is more ordered when K⁺ ions completely neutralise the negative charge of the mica surface, and [C₁₀mim]⁺ ions tend to be located in hexagonal mica lattices with two aluminium atoms in replacement of silicon atoms. [TFSA]^? ions are constrained by the neighbouring K⁺ ions absorbed onto mica lattices.     

Cycloaddition of 2′-azidoethyl glycosides to fullerene[C60] under ultrasonic irradiation

The reactions of fullerene[C₆₀] with 2′-azidoethyl 2,3,4,6-tetra-O-acetyl-α-d-mannopyranoside (2a) and 2′-azidoethyl 2,3,4,6-tetra-O-acetyl-β-d-galactopyranoside (2b) under ultrasonic irradiation cause the cycloaddition of 2′-azidoethyl glycosides to fullerene[C₆₀] and lead to d-glycosyl fullerene[C₆₀] derivatives 3a and 3b, respectively. The glycosyl fullerene[C₆₀] derivatives were characterized by ¹H and ¹³C NMR, UV–vis, FAB-MS, FT-IR spectra and were a 1:1 glycoside fullerene [C₆₀]-adduct.     

Measuring the solubility of benzoic acid in room temperature ionic liquids using chronoamperometric techniques

The electrochemical reduction of benzoic acid (BZA) has been studied at platinum micro‐electrodes (10 and 2 µm diameters) in acetonitrile (MeCN) and six room temperature ionic liquids (RTILs): [C₂mim][NTf₂], [C₄mim][NTf₂], [C₄mpyrr][NTf₂], [C₄mim][BF₄], [C₄mim][NO₃] and [C₄mim][PF₆] (where [C_nmim]⁺ = 1‐alkyl‐3‐methylimidazolium, [NTf₂]^? = bis(trifluoromethylsulphonyl)imide, [C₄mpyrr]⁺ = N‐butyl‐N‐methylpyrrolidinium, [BF₄]^? = tetrafluoroborate, [NO₃]^? = nitrate and [PF₆]^? = hexafluorophosphate). Based on the theoretical fitting to experimental chronoamperometric transients in [C₄mpyrr][NTf₂] and MeCN at several concentrations and on different size electrodes, it is suggested that a fast chemical step preceeds the electron transfer step in a CE mechanism (given below) in both RTILs and MeCN, leading to the appearance of a simple one‐electron transfer mechanism. The six RTIL solvents and MeCN were saturated with BZA, and potential‐step chronoamperometry revealed diffusion coefficients of 170, 4.6, 3.2, 2.7, 1.8, 0.26 and 0.96 × 10^?11 m² s^?1 and solubilities of 850, 75, 78, 74, 220, 2850 and 48 mM in MeCN and the six ionic liquids, respectively, at 298 K. The high solubility of BZA in [C₄mim][NO₃] may suggest a strong interaction of the dissolved proton with the nitrate anion. Although there are relatively few literature reports of solubilities of organic solutes in RTILs at present, these results suggest the need for further studies on the solubilities of organic species (particularly acids) in RTILs, because of the contrasting interaction of dissolved species with the RTIL ions. Chronoamperometry is suggested as a convenient methodology for this purpose. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and Optical Properties of 1-Alkyl-3-Methylimidazolium Lauryl Sulfate Ionic Liquids

We report the synthesis of a new series of imidazolium-based halogen-free ionic liquids 1-alkyl-3-methylimidazolium lauryl sulfates. By reacting 1-methylimidazole (MIM) with butyl, hexyl, octyl, and decyl bromides and exchanging bromide ion with lauryl sulfate anion, a series of ionic liquids [RMIM][C₁₂H₂₅OSO₃] were produced. The high purity of these ionic liquids was verified with ¹H-NMR, ¹³C-NMR, FT-IR and mass spectrometry (MS), demonstrating the effectiveness of this synthetic approach. Solubility test of these ionic liquids showed that they are soluble in most organic solvents except nonpolar solvents such as hexane and cyclohexane. The optical properties of [BMIM]Br and [BMIM][C₁₂H₂₅OSO₃], where B refers to butyl, were examined. Both ionic liquids absorbed light in the UV region, yet essentially no absorption was recorded beyond 450 nm. Furthermore, both ionic liquids showed excitation wavelength-dependent fluorescence behavior. As an example, with an excitation wavelength of 360 nm, [BMIM][C₁₂H₂₅OSO₃] showed an emission band maximum at 447 nm. Increasing the excitation wavelength to 440 nm, the emission band maximum was shifted to ∼500 nm.     

[2.2.2]Paracyclophane as a receptor for the cesium cation in the gas phase

By using electrospray ionisation mass spectrometry, it was proven experimentally that the cesium cation (Cs⁺) forms with [2.2.2]paracyclophane (C₂₄H₂₄) the cationic complex [Cs(C₂₄H₂₄)]⁺. Further, applying quantum chemical calculations, the most probable structure of the [Cs(C₂₄H₂₄)]⁺ complex was derived. In the resulting complex with a symmetry very close to C₃, the ‘central’ cation Cs⁺, fully located in the cavity of the parent [2.2.2]paracyclophane ligand, is bound to all three benzene rings of [2.2.2]paracyclophane via cation–π interaction. Finally, the interaction energy, E(int), of the considered cation–π complex [Cs(C₂₄H₂₄)]⁺ was found to be ?73.2 kJ/mol, confirming the formation of this fascinating complex species as well. This means that [2.2.2]paracyclophane can be considered as a receptor for the Cs⁺ cation in the gas phase.     

The pressure-dependence of the dimerization of 1,3-butadiene: Experimental and theoretical volumes of activation and reaction

Abstract

The volume of activation found for the [4+2]-Diels-Alder cyclodimerization of 1,3-butadiene leading to 4-vinylcyclohexene turned out to be substantially lower than that found for the competing [2+2]-cyclodimerization leading to trans-divinylcyclobutane (ΔΔ₀ ^#= ?12cm³mol^?1). The [4+2]-cyclodimerization of Z, Z-1,4-dideuterio-l,3-butadiene shows only 3 % loss of stereochemistry at 1 bar and <1 % at 6.8–8.0 kbar. These findings show good evidence for a stereospecific pericylic Diels-Alder mechanism competing with a small amount of nonstereospecific stepwise reaction which is almost completely suppressed at high pressure. The volumes of activation and reaction for the various dimerization pathways of 1,3-butadiene are calculated by a Monte-Carlo computer simulation. The good agreeement between experimental and simulated data confirms the hypothesis that configurational effects (e.g. different packing of cyclic and acyclic states) are important for the explanation of activation and reaction volumes.     

New pyrazolino and pyrrolidino[60]fullerenes: the introduction of the hydrazone moiety for the formation of metal complexes

The [3 + 2] cycloaddition reaction of C₆₀ with pyridine‐derived hydrazones (acting as dipolar reagents) was successfully conducted resulting in fullerene derivatives 5a , 5b . The compounds were characterized by means of NMR, UV–Vis spectroscopy, and X‐ray crystallography. The electrochemical behavior was also investigated. The fulleropyrazoline 5a exhibits anodically shifted reduction potentials of about 100 mV when compared with those for C₆₀, whereas 5b exhibits cathodic shifts relative to pristine C₆₀. The complexation reaction of 5b with metallic ions (Zn²⁺, Cd²⁺, and Fe²⁺) was achieved. Job and Benesi–Hildebrand analysis confirmed the formation of complexes with a molar ratio of 1:1 and binding constants between 2.26 × 10⁵ and 1.59 × 10⁵ M^?1. Electrochemistry of these complexes showed a marked influence of the metal ion on the reduction potentials. Copyright © 2016 John Wiley & Sons, Ltd.     

Optical,structural characterization and dielectric relaxation of [C2H5NH3]2ZnCl4 compound

ABSTRACT

The new organic-inorganic compound [C₂H₅NH₃]₂ZnCl₄ has been grown by the slow evaporation at room temperature. The zero-dimensional (0-D) structure for this compound was determined by the single X-ray diffraction. It crystallizes at room temperature in the non-centrosymmetric space group Pna2₁ and consists of ethylammonium cations [C₂H₅NH₃]⁺ and [ZnCl₄]^2? tetrahedra anions. That is interconnected by means of hydrogen bonding contacts N-H···Cl. The molecular geometry and vibrational frequencies of [ZnCl₄]^2? and [C₂H₅NH₃]⁺ in the ground state was calculated using density functional method (B3LYP) with 6–31G(d) and 6–311G (d,p) basis set. The optimized geometric bond lengths and bond angles, obtained by using B3LYP/6–311G (d,p), show the best agreement with the experimental data. The optical absorbance was measured in order to deduce the absorption coefficient α, optical band gap E_g. The optical band gap is determined by extrapolating the plotted graph of (αhυ)^1/2 vs. (hυ). The large value of indirect optical band gap energy indicates the insulating nature of this material. Moreover, the extinction coefficient, refractive index and the dielectric permittivity of [C₂H₅NH₃]₂ZnCl₄ compound were calculated and the results are discussed. The evolution of the dielectric loss as a function of frequency revealed a distribution of relaxation times, probably ascribed to the reorientational dynamics of alkyl chains in this compound, and then analyzed with the Cole–Cole formalism.     

Study of alkyl chain length dependent characteristics of imidazolium based ionic liquids [CnMIM]+[TFSA]− by Brillouin and dielectric loss spectroscopy

This study examined the acoustic phonon mode of ionic liquids consisting of 1-alkyl-3-methyl-imidazolium family (C_nMIM) cations with n values ranging from 2 to 10 and bis(trifluoromethylsulfonyl)amide (TFSA) anion in the temperature range from 300 K to 100 K. [C_nMIM]⁺[TFSA]^? showed depolarized (VH) components of Brillouin peaks at temperatures below the glass transition temperature when n is larger than 4. On the other hand, in the case of ionic liquids with different anions, such as [C₄MIM]⁺[BF₄]^?, [C₄MIM]⁺[PF₆]^? and [C₈MIM]⁺[BF₄]^?, the VH component of Brillouin peaks was not observed in the temperature range investigated. The dielectric loss spectra showed that the temperature dependence of alkyl chain domain relaxation of all ionic liquids followed the Arrhenius law and showed an increase in activation energy at the temperature where the VH component of Brillouin peak appeared. These results suggest that the observed depolarized component of Brillouin peak might originate from uniquely induced polarization in the 2nd domain composed of head groups of cations and anions.     

Vibrational Analysis of Coherent Anti-Stokes Resonance Raman Spectra from Bacteriorhodopsin Containing Isotopically Substituted Retinal Chromophores

Vibrational spectra recorded by coherent anti-Stokes resonance Raman scattering (CARS) from bacteriorhodopsin (BR) samples containing isotopically substituted (²H and ¹³C) retinal chromophores were measured using high repetition rate, low-power, picosecond pulsed excitation (λ₁=580 nm and λ_s=640±3 nm). These picosecond resonance CARS (PR/CARS) data were analyzed via third-order susceptibility relationships [χ ^{( 3 )} ] to obtain band origins, bandwidths, relative intensities, and electronic phase factors assignable to all significant vibrational Raman features in the 1490–1700 cm⁻¹ wavenumber region (the ethylenic stretching and C = N–H rocking or Schiff base modes). Isotopic substitution selectively places ²H at C₁₅, ¹³C singly at the C₁₀ position and at the C₁₄ position, and ¹³C simultaneously in positions of C₁₄ and C₁₅. Each isotopic BR sample was examined not only in H₂O, but also in D₂O, which places a ²H at the Schiff base nitrogen of the retinal. In addition, PR/CARS data were recorded from each isotopic BR sample following either light adaptation [i.e. the BR sample contained a single retinal isomer (all- trans , 15- anti or BR-570)] or dark adaptation [i.e. the BR sample contained a mixture of comparable amounts of retinal isomers (BR-570 and 13- cis , 15- syn or BR-548)]. Excellent agreement was found between the vibrational features observed by PR/CARS and those obtained from spontaneous resonance Raman measurements from the same isotopically substituted BR pigments. Several new vibrational features were also found from the PR/CARS data. Vibrational Raman data from three of the isotopic BR samples in D₂O are reported for the first time.     

The role of metal cation in electron-induced dissociation of tryptophan

The fragmentation of tryptophan (Trp) – metal complexes [Trp+M]⁺, where M = Cs, K, Na, Li and Ag, induced by 22 eV energy electrons was compared to [Trp+H]⁺. Additional insights were obtained through the study of collision-induced dissociation (CID) of [Trp+M]⁺ and through deuterium labelling. The electron-induced dissociation (EID) of [Trp+M]⁺ resulted in the formation of radical cations via the following pathways: (i) loss of M to form Trp^+?, (ii) loss of an H atom to form [(Trp-H)+M]^+?, and (iii) bond homolysis to form C₂H₄NO₂M^+?. Deuterium labelling suggests that H atom loss can occur from heteroatom and/or C–H positions. Other types of fragment ions observed include: C₉H₇NM⁺, C₉H₈N⁺, M⁺, C₂H₃NO₂M⁺, CO₂M⁺, C₁₀H₁₁N₂M⁺, C₁₀H₉NOM⁺. Formation of C₂H₄NO₂M^+? and C₉H₇NM⁺ cations suggests that the metal interacts with both the backbone and aromatic side chain, thus implicating π-interactions for all M. CID of [Trp+M]⁺ resulted in: loss of metal cation (for M = Cs and K); successive loss of NH₃ and CO as the dominant channel for M = Na, Li and Ag; formation of C₂H₃NO₂M⁺. Preliminary DFT calculations were carried out on [Trp+Na]⁺ and [(Trp-H)+Na]^+? which reveal that: the most stable conformation involves chelation by the backbone together with a $\pi $ -interaction with the indole side chain; loss of H atom from $\alpha $ -CH of the side chain is thermodynamically favoured over losses from other positions, with the resultant radical cation maintaining a (N, O, ring) chelated structure which is stabilized by conjugation.     

Low temperature magnetic ordering of a series of structurally characterized chloroferrates

Iron-57 Mössbauer spectroscopic results for a new series of related chloroferrate salts of complex ammonium cations are presented. In particular, spectra of materials based on FeCl ₄ ^– , FeCl ₅ ^2– , FeCl ₆ ^– , [FeCl₅(H₂O)]^2–, and [FeCl₅(CH₃OH)]^2– anions are discussed relative to the systematics of their isomer shifts, coordination numbers, and low temperature 3D critical ordering temperatures. The following specific systems have been studied by Mössbauer spectroscopy and definitively characterized by single-crystal X-ray analysis: [CH₃NH ₃ ⁺ ]₄[FeCl₆]^3–[Cl^–](A), [Me₂N(-CH₂CH₂)₂NMe ₂ ⁺ ][FeCl ₅ ^2– ] (B), [H₃NCH₂CH₂NH ₃ ²⁺ ][FeCl₅·H₂O^2–], (C), and [NH₃(CH₂)₆NH ₃ ²⁺ ]₄[(FeCl ₆ ^3– )(FeCl ₄ ^– )ClCl ₄ ^– ] (D). The spectral data for these complexes are considered in the light of results of previous studies for systems such as [K₂FeCl₅·H₂O], [Co(NH₃)₆][FeCl₆], diamethyltriethylenediammoniumpentachloroferrate (E), and the related [FeCl₅·CH₃OH]^2– salt (F). The critical 3D ordering temperatures are 1.45, 6.80, 3.45, and 1.22K forA, B, C, andD, respectively.