Biocatalytic approaches toward the synthesis of both enantiomers of trans-cyclopentane-1,2-diamine

[reaction: see text] A lipase-catalyzed double monoaminolysis of dimethyl malonate by (+/-)-trans-cyclopentane-1,2-diamine allows the sequential resolution of the latter compound, affording an enantiopure bis(amidoester), which is subsequently transformed into an optically active polyamine. As an alternative, both enantiomers of the diamine can be obtained from enantiopure (+)- or (-)-2-aminocyclopentanol, prepared by enzymatic resolution.     

Monitoring the atmospheric stability by using radon concentration measurements: A study in a Central Italy site

Summary Meteorological and radon concentration data referring to a measurement campaign carried out in Urbino, Central Italy, are reported and discussed. This study presents a method allowing monitoring of the vertical atmospheric stability using continuous measurements of radon gas near ground. In particular radon evidences the presence of temperature inversion such as the formation of the nocturnal stable layer and gives information on the vertical turbulence and the motion of air masses. This technique is very useful in describing the temporal evolution of the pollutants in the atmosphere.     

Electrocatalytic effect of iron sulfates on oxygen reduction. Influence of the solvation sphere of the mediator

The redox catalysis of oxygen reduction was performed on a platinum rotating disk electrode. The Fe(III)/Fe(II)/H₂SO₄ system at different pH's was used as a MEDIATOR. The catalytic effect of mediator was directly related to the solvation sphere of Fe(III) and Fe(II). Only the redox couple FeHSO ₄ ²⁺ /FeHSO ₄ ⁺ (pH<0) showed a catalytic effect on oxygen reduction.     

Structure elucidation and 3D solution conformation of the antibiotic enduracidin determined by NMR spectroscopy and molecular dynamics

Enduracidin and ramoplanin belong to the large family of cyclodepsipeptide antibiotics, highly effective against Gram-positive bacteria. The primary and 3D solution structure of ramoplanin is already well known, and the primary structure of enduracidin has been determined by a combination of chemical and NMR spectroscopic methods. Both antibiotics share a similar peptide core of 17 amino acids and differ mainly in the length of the acyl chain and the presence of two D-mannose moieties in ramoplanin. Based on the high sequence homology with ramoplanin, the structure in solution of enduracidin is modeled as a cyclic peptide. The tertiary structure thus obtained was refined through molecular dynamics (MD) simulation, in which the interatomic NOE-derived distance restraints were imposed. MD simulations yielded a family of representative 3D structures (RMSD = 0.89), which highlighted a backbone geometry similar to that of ramoplanin in its beta-hairpin arrangement. In contrast, enduracidin displays a different arrangement of the side-chain and of the residues forming the hydrophobic core.     

Adiabatic squeezing of molecular wave packets by laser pulses

Strong pulse sequences can be used to control the position and width of the molecular wave packet. In this paper we propose a new scheme to maximally compress the wave packet in a quasistatic way by freezing it at a peculiar adiabatic potential shaped by two laser pulses. The dynamic principles of the scheme and the characteristic effect of the different control parameters are presented and analyzed. We use two different molecular models, electronic potentials modeled by harmonic oscillators, with the same force constants, and the Na(2) dimer, to show the typical yield that can be obtained in compressing the initial (minimum width) molecular wave function.     

H-N HMBC as a valuable tool for the identification and characterization of nitrones

¹H-¹⁵N HMBC has been evaluated as an efficient and high-speed method to determine ¹⁵N chemical shifts for nitrones, which can be used to identify aromatic nitrones and to extract structural information by comparison with reference data. Substituent effects have been measured on C and N aryl groups separately, showing up the influence of electronic effects on C-aryl groups rather than N-aryl groups on the ¹⁵N chemical shifts. Steric effects are remarkable in the case of C-aryl-N-alkyl nitrones. Depending on N or C substitution, chemical shift changes in such an additive way that it is possible to predict chemical shifts for unknown nitrones.     

Asymmetric synthesis of 2H-azirines derived from phosphine oxides using solid-supported amines. Ring opening of azirines with carboxylic acids

A simple and efficient asymmetric synthesis of 2H-azirine-2-phosphine oxides 3 is described. The key step is a solid-phase bound achiral or chiral amine-mediated Neber reaction of beta-ketoxime tosylates derived from phosphine oxides 1. Reaction of 2H-azirines 3 and 11 with carboxylic acids 4 gives phosphorylated ketamides 5 and 12. Ring closure of ketamides 5 and 12 with triphenylphosphine and hexachloroethane in the presence of triethylamine leads to the formation of phosphorylated oxazoles 8 and 13.     

Synthesis of pyrazine-phosphonates and -phosphine oxides from 2H-azirines or oximes

[reaction: see text] Tetrasubstituted pyrazines containing two phosphonate groups 2 in positions 2 and 5 and trisubstituted pyrazines containing a phosphonate 5 or a phosphine oxide group 7 in position 2 are obtained by thermal treatment of 2H-azirine-2-phosphonates 1 and -phosphine oxides 6. These pyrazines can also be prepared from beta-ketoxime tosylates 9 and 10 or from oxime derived from phosphine oxide 11.     

Quantitative determination of formic acid in apple juices by H NMR spectrometry

A quantitative determination method of formic acid in apple juices is proposed by means of the proton nuclear magnetic resonance (¹H NMR) technique. Formic acid gives a singlet signal at the 8.2-8.4 ppm interval of the spectrum, and its area is used to determine the concentration of the acid. 1,3,5-Benzenetricarboxylic acid is added to the juice as an internal standard. Since the chemical shift of both species varies with the pH, ascorbic acid is also added to adjust it at 2.74 and to avoid the overlapping of the signals. Recoveries between 95 and 109% are obtained when the standard addition method is applied to the juices of five different cider apple varieties. The coefficient of variation obtained is 3.9% for intra-day repeatability (n = 5), and 4.6% for inter-day repeatability (n = 10). The limit of detection is 1.49 mg/l, calculated from “3S_y/x + intercept”. The described method is direct and no previous derivatization is needed.     

On the additivity of basis set effects in some simple fluorine containing systems

The reactions F + H₂ → HF + H, HF → H + F, F → F⁺ + e^? and F + e^? → F^? were used as simple test cases to assess the additivity of basis set effects on reaction energetics computed at the MP4 level. The 6-31G and 6-311G basis sets were augmented with 1, 2, and 3 sets of polarization functions, higher angular momentum polarization functions, and diffuse functions (27 basis sets from 6-31Gd, p) to 6-31 ++ G(3df, 3pd) and likewise for the 6-311G series). For both series substantial nonadditivity was found between diffuse functions on the heavy atom and multiple polarization functions (e.g., 6-31 + G(3d, 3p) vs. 6-31 + G(d, p) and 6-31G(3d, 3p)). For the 6-311G series there is an extra nonadditivity between d functions on hydrogen and multiple polarization functions. Provided that these interactions are taken into account, the remaining basis set effects are additive to within ±0.5 kcal/mol for the reactions considered. Large basis set MP4 calculations can also be estimated to within ±0.5 kcal/mol using MP2 calculations, est. E_MP4(6-31 ++ G(3df, 3pd)) ≈ E_MP4(6-31G(d, p)) + E_MP2(6-31 ++ G(3df, 3pd)) – E_MP2(6-31G(d, p)) or E_MP4(6-31 + G(d, p) + E_MP2(6-31 ++ G(3df, 3pd)) – E_MP2(6-31 + G(d, p)) and likewise for the 6-311G series.