Synthesis of new norbornenones with the aminoester group methyl bicyclo [2-2-1] hept 5-ene 7-one 1-amino 2-carboxylates

Amino norbornenonecarboxylates were synthesized from methyl acrylate and amino butadienecarboxylates. This result is equivalent of amino cyclopentadienones Diels-Alder reaction. Amino butadienecarboxylates were prepared by prototropic transposition of the β-allenic aminoesters.     

The Au(n) cluster probe in secondary ion mass spectrometry: influence of the projectile size and energy on the desorption/ionization rate from biomolecular solids

A Au-Si liquid metal ion source which produces Au(n) clusters over a large range of sizes was used to study the dependence of both the molecular ion desorption yield and the damage cross-section on the size (n = 1 to 400) and on the kinetic energy (E = 10 to 500 keV) of the clusters used to bombard bioorganic surfaces. Three pure peptides with molecular masses between 750 and 1200 Da were used without matrix. [M+H](+) and [M+cation](+) ion emission yields were enhanced by as much as three orders of magnitude when bombarding with Au(400) (4+) instead of monatomic Au(+), yet very little damage was induced in the samples. A 100-fold increase in the molecular ion yield was observed when the incident energy of Au(9) (+) was varied from 10 to 180 keV. Values of emission yields and damage cross-sections are presented as a function of cluster size and energy. The possibility to adjust both cluster size and energy, depending on the application, makes the analysis of biomolecules by secondary ion mass spectrometry an extremely powerful and flexible technique, particularly when combined with orthogonal time-of-flight mass spectrometry that then allows fast measurements using small primary ion beam currents.     

Decreasing Subsequences in Permutations and Wilf Equivalence for Involutions

In a recent paper, Backelin, West and Xin describe a map φ^* that recursively replaces all occurrences of the pattern k... 21 in a permutation σ by occurrences of the pattern (k−1)... 21 k. The resulting permutation φ^*(σ) contains no decreasing subsequence of length k. We prove that, rather unexpectedly, the map φ^* commutes with taking the inverse of a permutation. In the BWX paper, the definition of φ^* is actually extended to full rook placements on a Ferrers board (the permutations correspond to square boards), and the construction of the map φ^* is the key step in proving the following result. Let T be a set of patterns starting with the prefix 12... k. Let T′ be the set of patterns obtained by replacing this prefix by k... 21 in every pattern of T. Then for all n, the number of permutations of the symmetric group _n that avoid T equals the number of permutations of _n that avoid T′. Our commutation result, generalized to Ferrers boards, implies that the number of involutions of _n that avoid T is equal to the number of involutions of _n avoiding T′, as recently conjectured by Jaggard. Both authors were partially supported by the European Commission's IHRP Programme, grant HPRN-CT-2001-00272, “Algebraic Combinatorics in Europe”     

Preliminary theoretical study of perfluorodimethyl ether and its protonated form

3-21G RHF calculations on (CF₃)₂O and (CF₃)₂OH⁺ molecules are carried out to assess the changes induced in the molecular properties of ether links in poly (perfluoro ethers) interacting with acid sites at contact surfaces. Geometry of the species, vibrational frequencies, proton affinity, and energetics of the (CF₃)₂OH⁺ fragmentation provide a preliminary basis to understand problems raised by lubricant degradation. © 1993 John Wiley & Sons, Inc.     

Influence of chlorine substitution on the self-assembly of zinc phthalocyanine

The adsorption and ordering of zinc phthalocyanine (ZnPc) and octachloro zinc phthalocyanine (ZnPcCl(8)) on an Ag(111) surface is studied in situ by scanning tunneling microscopy under ultrahigh vacuum. Two-dimensional self-assembled supramolecular domains are observed for these two molecules. We show how substituting chlorine atoms for half of the peripheral hydrogen atoms on ZnPc influences the self-assembly mechanisms. While intermolecular interactions are dominated by van der Waals forces in ZnPc molecular networks, ZnPcCl(8) molecular packing undergoes a sequential phase evolution driven by the creation of C-Cl...H-C hydrogen bonds between adjacent molecules. At the end of this evolution, the final molecular assembly involves all possible hydrogen bonds. Our study also reveals the influence of molecule-substrate interactions through the presence of fault lines generating a stripe structure in the molecular film.     

NMR Study of Water Distribution inside Tomato Cells: Effects of Water Stress

Tomato pericarp tissue was studied by low-field nuclear magnetic resonance (NMR) relaxometry. Two kinds of experiments were performed to investigate the correlation between multi-exponential NMR relaxation and the subcellular compartments. The longitudinal (T ₁) versus transverse (T ₂) relaxation times were first measured on fresh samples and then the transverse relaxation time was measured on samples exposed to water stress. Four signal components were found in all experiments. The results showed that all signal components corresponded to the water in different cell compartments, and that no signal from non-exchangeable protons was present. Moreover, we demonstrated that NMR relaxation is suitable for the continuous monitoring of water rebalancing between subcellular compartments of plant tissues.     

Assessing induced folding of an intrinsically disordered protein by site-directed spin-labeling electron paramagnetic resonance spectroscopy

We used site-directed spin-labeling electron paramagnetic resonance (EPR) spectroscopy to study the induced folding of the intrinsically disordered C-terminal domain of measles virus nucleoprotein (N(TAIL)). Four single-site N(TAIL) mutants (S407C, S488C, L496C, and V517C), located in three conserved regions, were prepared and labeled with a nitroxide paramagnetic probe. We could monitor the gain of rigidity that N(TAIL) undergoes in the presence of either the secondary structure stabilizer 2,2,2-trifluoroethanol (TFE) or one of its physiological partners, namely, the C-terminal domain (XD) of the viral phosphoprotein. The mobility of the spin label grafted at positions 488, 496, and 517 was significantly reduced upon addition of XD, contrary to that of the spin label bound to position 407, which was unaffected. Furthermore, the EPR spectra of spin-labeled S488C and L496C bound to XD in the presence of 30% sucrose are indicative of the formation of an alpha-helix in the proximity of the spin labels. Such an alpha-helix had been already identified by previous biochemical and structural studies. Using TFE we unveiled a previously undetected structural propensity within the N-terminal region of N(TAIL) and showed that its C-terminal region "resists" gaining structure even at high TFE concentrations. Finally, we for the first time showed the reversibility of the induced folding process that N(TAIL) undergoes in the presence of XD. These results highlight the suitability of site-directed spin-labeling EPR spectroscopy to identify protein regions involved in binding and folding events, while providing insights at the residue level.     

MSE-MRI sequence optimisation for measurement of bi- and tri-exponential T2 relaxation in a phantom and fruit

The transverse relaxation signal from vegetal cells can be described by multi-exponential behaviour, reflecting different water compartments. This multi-exponential relaxation is rarely measured by conventional MRI imaging protocols; mono-exponential relaxation times are measured instead, thus limiting information about of the microstructure and water status in vegetal cells. In this study, an optimised multiple spin echo (MSE) MRI sequence was evaluated for assessment of multi-exponential transverse relaxation in fruit tissues. The sequence was designed for the acquisition of a maximum of 512 echoes. Non-selective refocusing RF pulses were used in combination with balanced crusher gradients for elimination of spurious echoes. The study was performed on a bi-compartmental phantom with known T₂ values and on apple and tomato fruit. T₂ decays measured in the phantom and fruit were analysed using bi- and tri-exponential fits, respectively. The MRI results were compared with low field non-spatially resolved NMR measurements performed on the same samples.