Unilateral NMR study of a XVI century wall painted.

Wall paintings in the XVI century Serra Chapel in the "Chiesa di Nostra Signora del Sacro Cuore" Rome, have been studied using unilateral NMR. In order to map the distribution of moisture content in the wall painted, a large number of Hahn echo measurements, covering large areas of the wall painting were performed. Because the intensity of the Hahn echo is proportional to the amount of moisture in the area under study, the experimental data were transformed into 2D gradient colour maps which allowed an easy visualization of the moisture content of the wall. The state of conservation of the wall painting was monitored using T2 measurements specially with regards to outcropping salt.

The role of water coordination in binary mixtures. A study of two model amphiphilic molecules in aqueous solutions by molecular dynamics and NMR.

Two binary aqueous mixtures which contain the small amphiphilic molecules TMAO (trimethylamine-N-oxide) and TBA (tert-butyl alcohol) have been investigated by molecular dynamics simulations and NMR chemical shift and self-diffusion measurements. TMAO is an osmolyte, while TBA is a monohydrate alcohol. Both possess bulky hydrophobic groups and polar heads, namely, NO in TMAO and OH in TBA. The hydrophilic/hydrophobic content of these isosteric molecules strongly modulates the structure and dynamics of the hydration shell, which is thought to be responsible for the effects observed on proteins and phospholipids. Simulation results, especially on hydrogen-bond networking, spatial correlations, and self-diffusivity, are consistent with NMR data and agree well with previous numerical studies on similar solutions. The methods employed allow the elucidation of the microscopic features of the solutions. For TBA solutions, the hydration shell is found to have a low density and a large spatial spread, and thus, above the molar fraction of 0.03, reduction of hydrophobic hydration drives self-aggregation of the solute. This effect does not take place in TMAO solutions, where the hydration shell is more compact and stable, maintaining its structure over a wider range of solute concentrations.

Fresco paintings studied by unilateral NMR.

Unilateral NMR has been used to monitor the state of conservation of frescoes in the Vasari's house in Florence. The causes of deterioration of ancient frescoes are varied, which result in the detachment and crumbling of the painted film from the supporting plaster and in the outcropping of salts. Unilateral measurements of Hahn echo performed on such frescoes have allowed a perfect identification of the detachment of the painted film from the plaster. The presence of soluble salts on the pictorial film affects the spin-spin relaxation times, T(2). It is then possible using this technique, to characterize the effect of chemical treatments, of cleansing and consolidation procedures using the distribution of T(2) spin-spin relaxation times.

Monitoring degradation in paper: non-invasive analysis by unilateral NMR. Part II.

High quality paper samples have been oxidized with a specific oxidant to reproduce one of the possible causes of the aging of paper. All samples have been characterized by 13C CP-MAS NMR spectroscopy. The artificial aging of paper has been monitored using a standard NMR relaxometer and the results have been compared with the corresponding data obtained using an unilateral NMR relaxometer. Experimental values obtained with both techniques are in agreement, demonstrating that unilateral NMR relaxometric measurements constitute a suitable non-invasive method for assessing the degradation process of cellulose-based materials. The sensitivity of the non-invasive NMR method allows the detection of degradation even at a very early stage. Effects due to the sample volume and to the penetration depth have been investigated.

Degradation of historical paper: nondestructive analysis by the NMR-MOUSE.

The NMR-MOUSE is a mobile sensor for single-sided NMR inspection of organic materials which takes advantage of the principles of magnetic resonance and inside-out-NMR. Historical books dating from the 17th century were measured at different points by positioning the NMR-MOUSE on the paper. Different degrees of paper degradation can be discriminated from the regularized inverse Laplace transform of the envelope of the acquired echo signals. For the first time the degradation of historical paper was characterized entirely nondestructively by NMR. As a contribution to current preservation efforts, NMR shows great promise for future use in damage assessment of historical documents.

Geographical characterization of italian extra virgin olive oils using high-field (1)H NMR spectroscopy.

1H high-field nuclear magnetic resonance (NMR) was used to analyze 216 extra virgin olive oils collected in three years (1996, 1997, and 1998) in different Italian areas in order to evaluate the potential contribution of this technique to the geographical characterization of olive oils. A statistical procedure performed on the intensity of selected NMR peaks has been proposed. Tree clustering analysis of NMR data performed without any a priori hypothesis showed the existence of reliable parameters able to group the olive oils according to the location of olive oil production. Linear discriminant analysis applied to selected NMR parameters of olive oils of the same year of production allowed the grouping of samples according to their geographical origin with only very few errors. Moreover, a satisfactory grouping is reached by combining the NMR data of olive oils from two different years (1996 and 1997). Operating on appropriate sampling, a careful analysis of data yielded the conclusion that the place of olive production could be singled out as a discriminating factor regardless of the cultivars from which the olive oils are derived.

The structure of gellan in dilute aqueous solution.

A full assignment of high-field nmr spectra of gellan was obtained in dilute aqueous solution by performing a series of selective one-dimensional nmr experiments. The observed nuclear Overhauser effects (NOEs) cannot be interpreted assuming that each sugar residue is intrinsically rigid and in a chair conformation. In fact, the rhamnose residue gives strong NOE contacts coherent only with an equilibrium involving both a chair as well as a boat (or a hemiboat) conformation. Molecular dynamic calculations performed on a heptamer with a central rhamnose support the above finding, and show a structure based on a very stiff single chain in which it is present a flipping of the rhamnose residue. At low temperatures (5-20 degrees C) in very dilute solutions (0.018 mg/mL) nmr spectra show a splitting of the resonance due to the methyl group of rhamnose residue, thus confirming the presence of a slow equilibrium among different conformers.

Conformations in solution of the fuscopeptins. Phytotoxic metabolites of Pseudomonas fuscovaginae.

Fuscopeptins are phytotoxic amphiphilic lipodepsipeptides containing 19 amino acid residues. They are produced by the plant pathogenic bacterium Pseudomonas fuscovaginae in two forms, A and B, which differ only in the number of methylene groups in the fatty acid chain. Their covalent structure and biological properties have been reported previously. CD and NMR spectroscopy investigations in solution revealed the absence of identifiable elements of secondary and tertiary structure for these molecules. Fuscopeptin B appears to be completely unstructured in aqueous solution, and has a large molecular flexibility. A dramatic conformational change was observed upon addition of trifluoroethanol. This study reports the complete interpretation of the two-dimensional NMR spectra and the NOE results obtained for fuscopeptin B in water/trifluoroethanol solutions; the signals relative to the peptidic moiety are identical to those observed for fuscopeptin A. The results of this investigation were used to determine the solution structure of fuscopeptin B by computer simulations applying distance geometry and simulated annealing procedures. In water/trifluoroethanol solutions the peptidic region appears to have a partly helical structure. The lactonic ring assumes defined conformations very similar to those already reported for other lipodepsipeptides. The structure for fuscopeptin B in solution is also valid for fuscopeptin A because of the negligible structural difference between the two metabolites.

LC/MS analysis and antioxidative efficiency of Maillard reaction products from a lactose-lysine model system.

Aqueous solutions of lactose and lysine were refluxed for up to 4 h without pH control. Samples were collected every hour, and the reaction was monitored by measuring the pH, the optical density at 420 nm, and the relative antioxidative efficiency (RAE). The greatest change in optical density and antioxidative efficiency occurred for the mixture heated for 4 h. The 4 h solution was separated into three fractions according to the molecular weights of the components and tested for RAE. The high molecular weight fraction was more colored, and it had the highest antioxidative activity. The low molecular weight fraction was separated by high-performance liquid chromatography (HPLC). RAE values were measured for each purified compound. HPLC coupled with diode array and electrospray mass spectrometry allowed a rapid screening of the solutions and a tentative identification of several peaks. Nuclear magnetic resonance analysis allowed the identification of galactosylisomaltol and pyrraline. The resonance assignments for these compounds were revised.

Solution conformation of the Pseudomonas syringae MSU 16H phytotoxic lipodepsipeptide Pseudomycin A determined by computer simulations using distance geometry and molecular dynamics from NMR data.

Pseudomycin A is a cyclic lipodepsinonapeptide phytotoxin produced by a strain of the plant pathogenic bacterium Pseudomonas syringae. Like other members of this family of bacterial metabolites, it is characterised by a fatty acylated cyclic peptide with mixed chirality and lactonic closure. Several biological activities of Pseudomycin A are lower than those found for some of its congeners, a difference which might depend on the diverse number and distribution of charged residues in the peptide moiety. Hence, it was of interest to investigate its conformation in solution. After the complete interpretation of the two-dimensional NMR spectra, NOE data were obtained and the structure was determined by computer simulations, applying distance geometry and molecular dynamics procedures. The conformation of the large ring of Pseudomycin A in solution includes three rigid structural regions interrupted by three short flexible regions that act as hinges. The overall three-dimensional structure of the cyclic moiety is similar to that of previously studied bioactive lipodepsinonapeptides produced by other pseudomonads.

Solution conformation of the Pseudomonas syringae pv. syringae phytotoxic lipodepsipeptide syringopeptin 25-A. Two-dimensional NMR, distance geometry and molecular dynamics.

Syringopeptin 25-A is a phytotoxic amphiphilic lipodepsipeptide containing 25 amino acid residues, produced by some isolates of the plant pathogenic bacterium Pseudomonas syringae pv. syringae. Previous papers have reported its covalent structure and some of its biological properties. Attention has now been directed to define its conformation in solution, a structural feature regarded as important for understanding its possible role in the bacterial colonization of host plants, and its toxic action on the plant cell. Here we report the stereochemistry of its amino acid components, the complete interpretation of the two-dimensional NMR spectra and NOE data, and finally the structure obtained by computer simulations applying distance geometry and molecular dynamics procedures. The conformation of syringopeptin 25-A in aqueous solution includes three different structural regions interrupted by rigid 2,3-dehydro-2-aminobutyric acid residues: a loop from residue 2 to 6, a helicoidal zone from 8 to 15, and the lactone ring from 18 to 25. The three-dimensional structure of the lactone moiety is very similar to that of two previously studied bioactive lipodepsinonapeptides. Preliminary circular dichroism evidence of conformational variations in solution of trifluoroethanol, which stimulates a membrane-like environment, are also reported.

Solution conformation of a pectic acid fragment by 1H-NMR and molecular dynamics.

1H-NMR and molecular dynamics simulations in vacuo and in water of (1-->4)-alpha-D-galacturono-disaccharide were performed. The results of the molecular dynamics simulations showed that the molecule fluctuates between two conformations characterized by different values of torsion angles around the glycosidic linkage and two different intramolecular hydrogen bonds. When these conformations are extrapolated to a regular polymeric structure, they generate pectic acid compatible with a 2(1)- or a right-handed 3(1)-helix.

Fusapyrone and deoxyfusapyrone, two antifungal alpha-pyrones from Fusarium semitectum.

A strain of Fusarium semitectum Berk. & Rav. from maize stalk rot in southern Italy produced bioactive metabolites when cultured on autoclaved rice kernels at room temperature for 4 weeks. The organic extracts of fungal culture showed a strong antibiotic activity towards Geotrichum candidum in disk diffusion assays, but they were not toxic to Artemia salina larvae. Two antifungal metabolites were isolated and characterized by chemical and spectroscopic methods as two 3-substituted-4-hydroxy-6-alkyl-2-pyrones, in particular, the 3-(4-deoxy-beta-xylo-hexopyranosyl)-4-hydroxy-6-[2-hydroxy-7-hydroxymeth yl- 1,1,5,9,11-pentamethyl-3,5,8-heptadecatrienyl]-2H-pyran-2-one and its 6-[2-hydroxy-1,1,5,7,9,11-hexamethyl] analog, which were named fusapyrone and deoxyfusapyrone, respectively.

Proton spin lattice relaxation in aromatic polymers.

The most striking requirement for the NMR imaging of an object is that this object should be made with components having different NMR parameters. In most cases these parameters are due to the presence of a fluid and to its mobility, thus measurable parameters are proton signal intensity contrasted in T1 or T2. From the glass transition temperature Tg, by decreasing the temperature, all nonaromatic polymers as well as any well degassed polymers, show a continuous increase of their proton spin-lattice relaxation, which at low temperature is usually larger than 10-20 sec. However, due to O2 molecules selectively adsorbed on aromatic rings, non-degassed aromatic polymers show a marked shortening of the proton spin-lattice relaxation. This effect is maximal at rather low temperature, where T1 can be shorter than 1 msec, and in many known cases shorter than 500 msec. Since the amount of sorbed-O2 is a function of the chemical nature of the polymer, the type of crystallinity (polymorphism of semicrystalline polymers), the crystalline-amorphous ratio, and so on, a careful study of T1 relaxation as a function of the temperature can define optimal conditions for T1 contrast. Examples regarding polymorphism in syndiotactic polystyrene, butadiene-styrene block copolymers and blends, and poly(phenylene) oxide, will be discussed.

Molecular structure of 3-O-(3,6-anhydro-alpha-D-galactopyranosyl)-beta-D-galactopyranose (neocarrabiose) in the solid state and in solution: an investigation by X-ray crystallography, n.m.r. spectroscopy, and molecular mechanics calculations.

The crystal structure of neocarrabiose monohydrate, 3-O-(3,6-anhydro-alpha-D-galactopyranosyl)-beta-D-galactopyranose (C12H20O10.H2O) belongs to the monoclinic space group P2(1), and has a unit cell of dimensions a = 6.351(1), b = 7.675(2), c = 15.096(8) A, and beta = 91.11(1) degree. The reducing unit is in the 4C1 conformation, the non-reducing residue is 1C4, with the 3,6-anhydro bridge in an E conformation, and HO-6 is in a gauche-trans conformation. The orientation about the (1----3) linkage is defined by phi = 94.5 degrees and psi = 141.9 degrees. There is an intramolecular hydrogen bond (O-5'...O-2 = 2.777A). The conformation of the pyranose rings in solution, derived from 3JH.H values, were not significantly different from those in the crystal, but the 3,6-anhydro bridge assumed a half-chair conformation. All these features have been rationalised through molecular modelling and computation of potential energy surfaces.

Unique structure of glycopeptide from alpha-fetoprotein produced in human hepatoma cell line, as determined by 1H-nuclear magnetic resonance spectroscopy.

Determination of alpha-fetoprotein is used in diagnosis of tumors and neural tube defects. A good reliable source of alpha-fetoprotein would be an obvious advantage to the preparation of diagnostic reagents and their standardization. We have recently developed a method for the production of alpha-fetoprotein from a human hepatoma cell line. This method, which is suitable for scaling up, allowed us to produce 40 g of alpha-fetoprotein from culture supernatant liquid through a simple purification procedure. We have previously shown this protein to be identical to alpha-fetoprotein produced from other sources. However, because the presence of different glycoforms has been reported in alpha-fetoprotein preparations, both from human sources and from other species, it was important to establish the type and extent of glycosylation of alpha-fetoprotein prepared by our method. By using 1H-NMR spectroscopy we were able to establish that our product contains a single N-linked biantennary, fully sialylated complex-type oligosaccharide, typical of human hepatomas.

Binding of inositol hexakisphosphate to the oxygenated derivative of dromedary (Camelus dromedarius) and human hemoglobin: 31P-NMR study.

Binding of inositol hexakisphosphate (IHP) to the oxygenated derivative of dromedary (Camelus dromedarius) and human hemoglobin (Hb) was investigated by 31P-NMR. The results obtained show that dromedary Hb binds, with different affinity, two IHP molecules per tetramer at distinct sites, while human Hb binds only one IHP molecule per tetramer.

Structure-activity relationships in 4-deoxypyrido[1',2'-1,2]imidazo[5,4-c]rifamycin SV derivatives.

New 4-deoxyhalogenopyrido[1',2'-1,2]imidazo[5,4-c]rifamycin SV derivatives (V-VIII) have been prepared as an extention of a program which led to the synthesis of analogous pyrido- and alkylpyrido compounds (I-IV) displaying a low level of g.i. absorption. The new compounds give comparatively much lower ED50 p.o./s.c. ratios showing a recovery in the extent of oral absorption. XPS, N.M.R., and HPLC data rationalize this activity in hydrophilicity due to the electron-withdrawing inductive effect of the halogen atoms bound to the pyridoimidazo system. This effect is exerted in particular on the negatively charged N(2'), and is the opposite as that exerted by the alkyl groups present in (I-III).

Chemical modifications of the aliphatic bridge of ansamycins. Synthesis and activity of 25-deacetoxy-25-epi-hydroxyrifamycin S.

Rifamycins are supposed to bind to, and inhibit the bacterial DNA-dependent RNA polymerase (DDRP) by the formation of hydrogen bonds through O (1), O (2), O (9), O (10). Therefore, with the aim of increasing the intrinsic activity of rifamycin S (1), the 25-deacetoxy-25-epi-hydroxyrifamycin S (8), was synthesized, which displays an additional hydroxyl available for the inhibiting interaction with the bacterial enzyme. The configuration and conformation of the new compound were as expected, but the biological evaluation did not confirm the hypothesis.