Eine neue Methode zum Nachweis und zur Bestimmung von Jod in organischen Substanzen

Ohne Zusammenfassung     

Mononuclear rearrangement of heterocycles in ionic liquids catalyzed by copper(II) salts

The reactivity of E- and Z-phenylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole in the presence of CuCl₂ and Cu(ClO₄)₂·6H₂O has been studied in four imidazolium ionic liquids [bmim][X] (X=BF₄⁻, PF₆⁻, SbF₆⁻ and CF₃SO₃⁻). The reaction may follow different mechanistic patterns, depending on the nature of the ionic liquid anion, accounting for both qualitative and kinetic data. In the presence of CuCl₂, two processes take place at the same time, i.e., the E?Z isomerization and the rearrangement of Z-isomer into the relevant 4-benzoylamino-2,5-diphenyl-1,2,3-triazole. In contrast, in the presence of Cu(ClO₄)₂·6H₂O, the rearrangement occurs only in solution of [bmim][BF₄] and [bmim][CF₃SO₃]. Collected data show that the effect of the ionic liquid on the isomerization and the rearrangement is different. In particular, a higher cross-linking degree seems to favour the triazole, but disfavour the E?Z isomerization.     

Absorption Spectra and Luminescence Properties of Isomeric Platinum (II) and Palladium (II) Complexes containing 1,1′-biphenyldiyl, 2-phenylpyridine,and 2,2′-bijpyridine as ligands

The absorption spectra, luminescence spectra, and luminescence lifetimes of the isomeric [M(bph)(bpy)] and [M(phpy)₂] complexes M = Pt(II) or Pd(II), bph^2? = 1,1′-biphenyl-2,2′-diyl dianion, phpy^? = 2-phenylpyridine-2′-yl anion, and bpy = 2,2′-bipyridine have been investigated and compared with those of [M(bpy)₂]²⁺ complexes and of the free protonated ligands H₂bph, Hbpy⁺, and Hphpy. In the absorption spectra, the region below 320 mm is dominated by ligand-centered (LC) transitions, whereas metal-to-ligand charge transfer (MLCT) transitions are responsible for the bands present in the near UV/VIS region. The MLCT bands move to higher energies on replacing Pt with Pd and in going from [M(bph)(bpy)] to the [M(phpy)₂] isomer. For the mixed-ligand complexes, evidence for both M → bph^2? (at higher energies) and M → bpy bands is found. The structured luminescence observed at 77 K shows lifetimes of 4.0 and 1.1 μs for [Pt(phpy)₂] and [Pt(bph)(bpy)], respectively, and 480 and 250 μs for the analogous Pd complexes. On the basis of the energy and lifetime data, the luminescence of the Pt(II) complexes is assigned to the lowest triplet MLCT excited state, whereas for the Pd complexes the luminescent state is thought to result from a mixture of MLCT and LC triplet levels.     

A second-order perturbation theory route to vibrational averages and transition properties of molecules: general formulation and application to infrared and vibrational circular dichroism spectroscopies

A general formulation to compute anharmonic vibrational averages and transition properties at the second-order of perturbation theory is derived from the Rayleigh-Schro?dinger development. This approach is intended to be applicable to any property expanded as a Taylor series up to the third order with respect to normal coordinates or their associated momenta. The equations are straightforward to implement and can be easily adapted to various properties, as illustrated for the case of electric and magnetic dipole moments. From those, infrared and vibrational circular dichroism spectra can be readily obtained. This fully automatic procedure has been applied to several chiral molecules of small-to-medium sizes and compared to the standard double harmonic approximation and to experimental data.     

Deterministic qubit transfer between orbital and spin angular momentum of single photons

In this work we experimentally implement a deterministic transfer of a generic qubit initially encoded in the orbital angular momentum of a single-photon to its polarization. Such a transfer of quantum information, which is completely reversible, has been implemented adopting an electrically tunable q-plate device and a Sagnac interferometer with a Dove prism. The adopted scheme exhibits high fidelity and low losses.     

A possible 2,1 → 3,1 isomerization mechanism in zirconocene-catalyzed propene polymerization: An application of the density functional theory and combined ONIOM approach

The unimolecular isomerization mechanism from a secondary 2,1 → 3,1 propene unit promoted by the prototype zirconocene system H₂SiCp₂Zr⁺(P) (P = polymeryl chain) has been investigated by using density functional theory calculations (B3LYP) for both gas and solvent phases. The typical route occurring through β-hydrogen elimination to the metal, olefin rotation around the metal center and olefin reinsertion into the metal hydrogen bond has been calculated by using QM/MM calculations with the ONIOM model in the presence of the counterion and compared to the alternative intramolecular reversible formation of a zirconocene allyl dihydrogen complex. Our calculations show that the alternative route remains energetically less accessible, at least for the prototype metallocene system used here.     

Nevirapine quantification in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry. Application to bioequivalence study

A rapid, sensitive and specific method to quantify nevirapine in human plasma using dibenzepine as the internal standard (IS) was developed and validated. The method employed a liquid-liquid extraction. The analyte and the IS were chromatographed on a C(18) analytical column, (150 x 4.6 mm i.d. 4 microm) and analyzed by tandem mass spectrometry in the multiple reaction monitoring mode. The method had a chromatographic run time of 5.0 min and a linear calibration curve over the range 10-5000 ng ml(-1) (r(2) > 0.9970). The between-run precision, based on the relative standard deviation for replicate quality controls was 1.3% (30 ng ml(-1)), 2.8% (300 ng ml(-1)) and 3.6% (3000 ng ml(-1)). The between-run accuracy was 4.0, 7.0 and 6.2% for the above-mentioned concentrations, respectively. This method was employed in a bioequivalence study of two nevirapine tablet formulations (Nevirapina from Far-Manguinhos, Brazil, as a test formulation, and Viramune from Boehringer Ingelheim do Brasil Química e Farmacêutica, as a reference formulation) in 25 healthy volunteers of both sexes who received a single 200 mg dose of each formulation. The study was conducted using an open, randomized, two-period crossover design with a 3 week washout interval. The 90% confidence interval (CI) of the individual ratio geometric mean for Nevirapina/Viramune was 96.4-104.5% for AUC((0-last)), 91.4-105.1% for AUC((0-infinity)) and 95.3-111.6% for C(max) (AUC = area under the curve; C(max) = peak plasma concentration). Since both 90% CI for AUC((0-last)) and AUC((0-infinity)) and C(max) were included in the 80-125% interval proposed by the US Food and Drug Administration, Nevirapina was considered bioequivalent to Viramune according to both the rate and extent of absorption.     

Nitration versus nitrosation chemistry of menthofuran: remarkable fragmentation and dimerization pathways and expeditious entry into dehydromenthofurolactone

The reaction chemistry of menthofuran (1), a toxic furan terpenoid from various mint oils, with nitric acid and nitrous acid has been investigated. Treatment of 1 with nitric acid afforded a 1:1 mixture of the bisfuran derivatives 5 and 6, resulting from the unexpected cleavage of the furan into two carbonyl fragments (3-methylcyclohexanone and hydroxyacetone) and their subsequent trapping by unreacted 1. Under conditions of high dilution, the nitrofuran derivative 7 was formed instead as the major reaction product. During investigation of this chemistry, it was found that oxidation of 1 with DDQ led to the important fragrant monoterpenoid 4 [dehydromenthofurolactone (anhydro Woodward-Eastman lactone)] in 44% yield. Exposure of 1 to nitrite ions at pH 3 afforded a completely different type of products, encompassing the known lactone 14, the lactam 15, and the remarkable dimer 16, bearing a N-hydroxy-2-pyrrolinone moiety linked to a nitrooximinofuran unit by an oxygen bridge. By using a combined spectroscopic and DFT approach, the constitution and configuration of 16 could be determined. These results fill a gap in the chemistry of furan compounds and describe routes to menthofuran-derived scaffolds of potential synthetic and biomedical relevance.     

Conformational characterization of lanthanide(III)-DOTA complexes by ab initio investigation in vacuo and in aqueous solution

The conformational behavior of four [Ln(DOTA)(H(2)O)](-) systems (Ln = La, Gd, Ho, and Lu) has been characterized by means of ab initio calculations performed in vacuo and in aqueous solution, the latter by using the polarizable continuum model (PCM). Calculated molecular geometries and conformational energies of the [Ln(DOTA)(H(2)O)](-) systems, and interconversion mechanisms, barriers, and (13)C NMR spectra of the [Lu(DOTA)](-) complex are compared with experimental values. For each system, geometry optimizations, performed in vacuo and in solution at the HF/3-21G level and using a 46+4f(n) core electron effective core potential (ECP) for lanthanides, provide two minima corresponding to a square antiprismatic (A) and an inverted antiprismatic (IA) coordination geometry. All the systems are nonacoordinated, with the exception of the IA isomer of the Lu complex that, from in solution calculations, is octacoordinated, in agreement with experimental data. On comparing the in vacuo relative free energies calculated at different theory levels it can be seen that the nonacoordinated species dominates at the beginning of the lanthanide series while the octacoordinated one does so at the end. Furthermore, on passing along the series the IA isomer becomes less and less favored with respect to A and for the Lu complex a stabilization of the IAisomer is observed in solution (but not in vacuo), in agreement with the experimental data. Investigation of the A<-->IA isomerization process in the [Lu(DOTA)](-) system provides two different interconversion mechanisms: a single-step process, involving the simultaneous rotation of the acetate arms, and a multistep path, involving the inversion of the cyclen cycle configuration. While in vacuo the energy barrier for the acetate arm rotation is higher than that involved in the ring inversion (23.1 and 13.1 kcal mol(-)(1) at the B3LYP/6-311G level, respectively), in solution the two mechanisms present comparable barriers (14.7 and 13.5 kcal mol(-)(1)), in fairly good agreement with the experimental values. The NMR shielding constants for the two isomers of the [Lu(DOTA)](-) complex have been calculated by means of the ab initio GIAO and CSGT methods, and using a 46-core-electron ECP for Lu. The calculated (13)C NMR chemical shifts are in close agreement with the experimental values (rms 3.3 ppm, at the HF/6-311G level) and confirm the structural assignment of the two isomers based on experimental NMR spectra in solution. The results demonstrate that our computational approach is able to predict several physicochemical properties of lanthanide complexes, allowing a better characterization of this class of compounds for their application as contrast agents in medical magnetic resonance imaging (MRI).