Adrenaline recognition in water

Host molecule 1 displays a high affinity in water towards catecholamines and especially related structures such as beta-blockers with extended aromatic pi-faces (up to 7x10(3) M(-1) for each single complexation step or 5x10(7) M(-2) for both steps). The amphiphilic structural design leads to an extensive self-association of host molecules through their aromatic flanks. Above a cmc (critical micelle concentration) of 3x10(-4) M, host 1 forms micelles that produce a favorable microenvironment for hydrophobic interactions with the included guest molecules. Electrostatic attraction of the ammonium alcohol by the phosphonate anions is thus combined with hydrophobic contributions between the aromatic moieties. Ionic hydrogen bonds with polar OH or NH groups of the guest enforce the non-covalent interactions, and finally lead to increased specificity. Both its affinity and its selectivity towards adrenergic receptor substrates are greatly enhanced if the receptor molecule 1 is transferred from water into a lipid monolayer. Catecholamines and beta-blockers lead to drastically different effects at concentrations approaching the micromolar regime. Especially beta-blockers with minute structural changes can be easily distinguished from each other. In both cases, extensive hydrophobic interactions with a self-associated and/or self-organized microenvironment are largely responsible for the observed high efficiency and specificity.     

Treating singularities present in the Sutcliffe-Tennyson vibrational Hamiltonian in orthogonal internal coordinates

Two methods are developed, when solving the related time-independent Schrodinger equation (TISE), to cope with the singular terms of the vibrational kinetic energy operator of a triatomic molecule given in orthogonal internal coordinates. The first method provides a mathematically correct treatment of all singular terms. The vibrational eigenfunctions are approximated by linear combinations of functions of a three-dimensional nondirect-product basis, where basis functions are formed by coupling Bessel-DVR functions, where DVR stands for discrete variable representation, depending on distance-type coordinates and Legendre polynomials depending on angle bending. In the second method one of the singular terms related to a distance-type coordinate, deemed to be unimportant for spectroscopic applications, is given no special treatment. Here the basis set is obtained by taking the direct product of a one-dimensional DVR basis with a two-dimensional nondirect-product basis, the latter formed by coupling Bessel-DVR functions and Legendre polynomials. With the basis functions defined, matrix representations of the TISE are set up and solved numerically to obtain the vibrational energy levels of H3+. The numerical calculations show that the first method treating all singularities is computationally inefficient, while the second method treating properly only the singularities having physical importance is quite efficient.     

Determination of nonylphenol and octylphenol in paper by microwave-assisted extraction coupled to headspace solid-phase microextraction and gas chromatography-mass spectrometry

A novel and simple method for the determination of active endocrine disrupter compounds (octylphenol OP, and nonylphenol NP) in paper using microwave-assisted extraction (MAE) and headspace solid-phase microextraction, coupled with gas chromatography-mass spectrometry has been developed. Parameters affecting the efficiency in the MAE process such as exposure time and extraction solvent were studied in order to determine operating conditions. The optimised method was linear over the range studied (1.25-125 microg kg(-1) for OP and 9.50-950 microg kg(-1) for NP) and showed good level of precision, with a RSD lower than 10% and detection limits at 0.10 and 4.56 microg kg(-1) for OP and NP, respectively. The results obtained from six different types of paper revealed the presence of the target compounds in all samples analysed, at levels ranging between 3 and 211 microg kg(-1).     

An algorithm for determining dynamically defined reaction paths (DDRP)

Summary A numerically stable and well-parallelizable curve variational algorithm is described for determining tangent curves of vector fields between two given stationary points. In particular, the method is suitable for finding reaction paths and saddle points on potential energy hypersurfaces (PHS). The stability of the procedure is illustrated by an artificial mathematical function, showing phases of following the reaction on the PHS.Dedicated to Professor Zoltán G. Szabó, the great teacher and scientist in reaction kinetics and in many other fields of physical chemistry, on his 84th birthday.     

Strong 1,4-P-O intramolecular interactions as a source of conformational preferences in alpha-stabilized phosphorus ylides

For the first time, the existence of a strong intramolecular 1,4-interaction between the phosphorus atom and the oxygen atom in alpha-keto-stabilized ylides has been demonstrated by means of theoretical calculations. This interaction has a notable influence on the conformational preferences and rotational barriers of alpha-stabilized phosphorus ylides and bis-ylides.     

Mixed iron cobalt carbonyl sulphides

Two new mixed iron cobalt carbonyl sulphide clusters HFe₂(CO)₉S and Fe₂Co(CO)₈(NO)S have been prepared and characterized. The hydride complex undergoes acidic dissociation in polar solvents and the resulting anion was isolated as (Et₄N)[Fe₂Co(CO)₉S]. An efficient high pressure synthesis has been found for H₂Fe₃(CO)₉S.     

Structural and energetic aspects of the protonation of phenol,catechol, resorcinol,and hydroquinone

The various protonated forms of phenol (1), catechol (2), resorcinol (3), and hydroquinone (4) were explored by ab initio quantum chemical calculations at the MP2/6-31G(d) and B3LYP/6-31G(d) levels. Proton affinities (PA) of 1-4 were calculated by the combined G2(MP2,SVP) method, and their gas-phase basicities were estimated after calculation of the change in entropy on protonation. These theoretical data were compared with the corresponding experimental values determined in a high-pressure mass spectrometer. This comparison confirmed that phenols are essentially carbon bases and that protonation generally occurs in a position para to the hydroxyl group. Resorcinol is the most effective base (PA = 856 kJ mol-1) due to the participation of both oxygen atoms in the stabilization of the protonated form. Since protonation is accompanied by a freezing of the two internal rotations, a significant decrease in entropy is observed. The basicity of catechol (PA = 823 kJ mol-1) is due to the existence of an intramolecular hydrogen bond, which is strengthened upon protonation. The lower basicity of hydroquinone (PA = 808 kJ mol-1) is a consequence of the fact that protonation necessarily occurs in a position ortho to the hydroxyl group. When the previously published data are reconsidered and a corrected protonation entropy is used, a proton affinity value of 820 kJ mol-1 is obtained for phenol.     

Peroxide derivatives of molybdenum(VI) in neutral and alkaline media

Summary The peroxidation of molybdenum(VI) was investigated in neutral and alkaline media. The stability constants of the peroxo complexes were determined by spectrophotometric measurement as (9.12±0.67)×10^–7, (2.68±0.17) ×10⁵, (1.26±0.06)×10⁶ and (1.58±0.02) for the 11, 21 (yellow), 31 and 41 (red) species. The diperoxomolybdate disproportionates into the tetraperoxo derivative when treated with alkali. Formation of the tetraperoxo complex was found to be pH dependent according to a curve, with maximum at pH 10. Acidification of tetraperoxomolybdate solution results in the regeneration of hydrogen peroxide and the diperoxo complex is reformed.     

Some diels—alder reactions of η1-bonded cyclopentadienylmetal compounds

Bis(cyclopentadienyl)mercury readily undergoes Diels—Alder reactions with RCCR (R = CO₂Me or CF₃), CF₃CFCFCF₃, CF₃CFCF₂, (CF₃)₂CC(CN)₂, C₂(CN)₄ and Ph$\text{NCONNC}$O to give stable adducts characterised by¹H, ¹⁹F and ¹³C NMR, spectroscopy. Similar reactions of CF₃CCCF₃ and CF₃CFCFCF₃ with the cyclopentadiene derivatives Me₃MC₅H₅ and (Me₃M)₂C₅H₄ (M = Si, Sn) are also described.     

Therapeutic monitoring of imipramine and desipramine by micellar liquid chromatography with direct injection and electrochemical detection

A micellar liquid chromatographic (MLC) procedure was developed for the clinical monitoring of imipramine and its active metabolite, desipramine. The determination of these highly hydrophobic substances was carried out after direct injection of the serum samples using a mobile phase composed of 0.15 m SDS--6% (v/v) pentanol buffered at pH 7, pumped at 1.5 mL/min into a C(18) column (250 x 4.6 mm), and electrochemical detection at 650 mV. Using this MLC method, calibration was linear (r > 0.995) and the limits of detection (ng/mL) were 0.34 and 0.24 for imipramine and desipramine, respectively. Repeatabilities and intermediate precision were tested at three different concentrations in the calibration range and a CV (%) below 2.2 was obtained. In this MLC procedure, the serum is determined without treatment, thus allowing repeated serial injections without changes in retention factors, and reducing the time and consumables required to carry out the pretreatment process. The assay method can be applied to the routine determination of serum imipramine and its metabolite in therapeutic drug monitoring.