Lionello Pogliani

Structural and dynamical studies of the relaxation effects induced by proton perturbation during 13C spin-lattice relaxation rate measurements

Abstract An NMR method for determining carbon spin-lattice relaxation rates under three different proton perturbation conditions is proposed. Thymidine is investigated as a model system. Dynamical and structural information is obtained by comparison of the carbon-13 relaxation rates obtained under broad-band pulse and selected pulse conditions with standard spin-lattice relaxation rates.

The sudden character of the sudden polarization effect

Abstract The evolution of the suggested sudden polarization parameter in excited singlet states in one-end pyramidalized ethylene, propylene and butadiene during geometrical relaxation of the double bond was investigated. As the sudden polarization parameter decreases the energy gap grows between the corresponding excited polar states.

Proton magnetic relaxation mechanisms and solution dynamics of L-histidine

Longitudinal and transverse proton relaxation rates have been measured for L-histidine in water solution. From a comparison of the former, measured in the selective and non-selective modes, it was found that the dipolar relaxation mechanism dominates the proton relaxation process. Molecular and internal motions have been quantified on the basis of a ‘jump’ relaxation model. Complex relaxation behaviour has been observed for protons of the histidyl species.

Heteronuclear Overhauser Effects: 2d NMR Measurements of through Space 1H-13C Dipolar Couplings In Solution

Abstract Summary-A 2D NMR study of proton-carbon through space dipolar connectivities has been performed on procaine in DMSO solution. A suitable pulse sequence generated vicinal and geminal heteronuclear Overhauser effects. Long distance dipolar interactions could not be detected due to the low sensitivity of this 2D approach. A combined use of ID and 2D NMR measurements is illustrated for elucidating molecular structures and dynamics by the analysis of heteronuclear through space dipolar interactions.

C-13 spin-relaxation study of some amino acids, their phospho-derivatives and some small peptides

Abstract Carbon C-13 spin-lattice relaxation times, T1, of Serine, Threonine, Phosphoserine and Phosphothreonine have been measured in D2O at neutral pD. Changes in over-all motions under phosphorylation has been detected. Segmental motions are not affected by phosphorylation. With the aid of T1(C-13) values of other amino acids an empirical relationship between NT1 and molecular weights (Mw) is tested that seems valid also for small peptides. Such relationship allows to interpret results from T1 measurements with the aid of a simple spherical model. In the course of a NMR study on amino acids Ser and Thr and their corresponding phospho derivatives, phosphoserine (PSer) and phosphothreonine (PThr) (1,2) the biological significance of which has been recently confirmed (3–5), we detected an influence of the phospho group on the over-all conformation of the side-chain. Aim of the present letter is to investigate by the aid of T1(C-13) relaxation time the possibility of the phospho group to act like an ‘ancho...

Long-Range Coupling Constants and Structure in Cyclic Molecules The Pyrrolidinic Ring of Proline Derivatives

Abstract In this letter we discuss the importance of interproton long-range coupling constant in proline and prolyl-derivatives, as a tool in the analysis of some complex NMR spectra of protons, as well as an aid in the conformational analysis of these compounds.

1H-NMR Relaxation Studies of Glycopeptides: A Dynamic Structural Investigation

The Glycopeptide Man5GlcNAc4Asn (ACCB2) in water solution has been studied by means of 1H NMR relaxation techniques in order to define molecular structure and dynamics. From the analysis of selective and non-selective proton relaxation rates of selected ACCB2 protons, a lack of internal mobility along the polysaccharide chain was observed. The presence of a conformationally well-defined molecular structure for ACCB2 is proposed.

Magnetic resonance reinvestigation of MnII–5′ ATP equilibria in solution

The MnII–5′ ATP system in aqueous solution has been reinvestigated in order to understand the complexation mechanisms. Lineshape e.s.r. analysis, linewidth variation, water-proton nuclear relaxation rates dependent on molar ratios, temperature and pH provide information on dynamics of the metal–nucleotide complex. The combined use of e.s.r. and n.m.r. techniques follows the equilibria between various MnII–5′ ATP inner-and outer-sphere complexes in solution. A chemical equilibrium taking into account the presence of Mn(ATP)x species at high pH and 5′-ATP concentrations is proposed.

C-13 NMR Investigation of Cellobiose in the Presence and Absence of β-Glucosidase

Abstract T1(C-13) NMR measurements of cellobiose in aqueous solutions at pH=5 in the presence and absence of enzyme β-glucosidase detected at T=276°K a fast interaction between cellobiose and the enzyme at C1′α level of the disaccharide molecule. T1(C-13) measurements of equal solutions of cellobiose in the presence and absence of EDTA at the same temperatures suggest also a competitive interaction of cellobiose, at C1′α level, with EDTA complexed with a metal ion. T1 data justify a nearly spherical shape of cellobiose in solution.

Longitudinal relaxation of the quaternary carbons of some phosphine oxides

A detailed analysis of the longitudinal relaxation of the quaternary carbons of the phenyl groups in some diphenylphosphine oxides, and a comparison of the NMR data with X-Ray and theoretical resul...