1,721,273 research outputs found
Applicazioni dell'HR-MAS NMR all'analisi di campioni vegetali
No full textSono stati presentati a un workshop sulle applicazioni HR-MAS NMR al Politecnico di Milano i risultati preliminari ottenuti su campioni di limone, cedro e crocus sativus
Ex-vivo HR-MAS NMR contribution to the diagnosis of brain tumours
No full textSome results on the role of HR-MAS NMR in the study of brain tumors, both in animal model and in humans, were presented. The changes in tissue metaboloma were deeple investigated through 1H and 13C NMR and statistics
Characterization of a low-sulfated chondroitin sulfate from the body of Viviparus ater (mollusca gastropoda). Modification of its structure by lead pollution.
No full textA chondroitin sulfate was purified from the body of Viviparus ater (Mollusca gastropoda) and analyzed for molecular mass, constituent disaccharides, and structure by H-1 NMR and H-1 2D NMR. A quite unique glycosaminoglycan species was isolated having a high molecular mass (greater than 45,000) and low charge density, about 0.60, due to the presence of 42% non-sulfated disaccharide, 5% 6-sulfated disaccharide, 48% 4-sulfated disaccharide, and 5% 4,6-disulfated disaccharide. Specimens of Mollusca were also submitted to lead exposure for different times, and the effect on chondroitin sulfate structure was studied. After 96 h treatment a strong decrease in chondroitin sulfate content was observed with a significant modification of its structure producing a more desulfated polymer, in particular in position 4 of the galactosamine unit. Simultaneously, the amount of unsaturated non-sulfated disaccharide increased with an overall decrease of the charge density
Caratterizzazione di politiofeni con tecniche in "inverse detection"
No full textSono state spiegate le strategie alla base della caratterizzazione dei politiofeni con tecniche in "inverse detection"
HMQC and HMBC Experiments: Useful Tools for the Assignment of the Regiochemistry of Poly(3-Hexylthiophene) through the Unambiguous Characterization of Relative Configurational Diads and Triads
No full textHMQC and HMBC inverse-detection experiments were used for the assignment of the regiochemistry of Poly(3-Hexylthiophene), through the unambiguous characterization of relative configurational diads and triads
Conformational Preferences of 1,2-Diphenyl Derivatives of 1,1,2,2-Tetrachloroethane with Ortho Substituents: a 1H DNMR 1D and 2D Study
No full textThe conformational preferences of 1,2-diphenyl derivatives of 1,1,2,2-tetrachloroethane with ortho substituents were studied through dynamic NMR, carrying out 1D and 2D NMR experiment at variable temperature
Analisi Conformazionale in Soluzione di 1,2-Diaril Derivati del Tetracloroetano tramite Risonanza Magnetica Nucleare a Temperatura Variabile
No full textE' presentato uno studio NMR a temperatura variabile condotto su tetracloroetani. Vengono determinate le barriere alla rotazione attorno al legame centrale Csp3-Csp3 e a quelli C-sp3-Csp2
Inverse detection applied to the 1H and 13C assignment and to the regiochemical characterization of beta-substituted alpha,alpha' coupled oligo- and polythiophenes
No full textbeta-Substituted alpha-alpha'-coupled oligo- (OTs) and polythiophenes (PTs) are materials currently investigated for their potential applications in optical and electronic devices. beta-Substituents modify both processability and electronic properties with respect to the unsubstituted analogues and these modifications are function not only of the type of substituents but also of their relative positions. When two beta-substituted thiophenes are alpha-alpha' coupled three regiochemically different bithiophenes can be obtained from the three different possible coupling paths: head-to-head, head-to-tail and tail-to-tail. The number of regioisomers enhances in longer oligomers, whereas the interpretation of 1-H and 13-C of PTs is usually based on a four configurational triad model. When the complete 1-H and 13-C assignment and the regiochemical characterisation of OTs and PTs are required, 1-H and 13-C inverse detection proves to be a very powerful tool of investigation. Heteronuclear inverse-detected correlations over one and more bonds are studied and the proton and carbon assignments are often contextual. One-bond correlations are utilised to distinguish between alpha and beta(C,H) pairs, thanks to the different values of alpha and beta 1J(H,C) coupling constantsof thiophene. As far as PTs are concerned, the absence of alpha(C,H) pairs confirms that only alpha,alpha' coupling occurred. Intra-residue correlations over two or three bonds are found running experiments with diffferent evolution delays. When long evolution delays are employed inter-residue correlations are also detected. These last correlations are extremely useful in establishing the thiophene backbone connectivities. Similarly, the association of each beta-substituent to the corresponding ring is found through long-range correlations
What is NMR Spectroscopy? A Preliminary Insight into NMR Spectroscopy
No full textNuclear Magnetic Resonance (NMR) is a very powerful tool for the structure determination of biomolecules and natural compounds, for the study of tissue extracts or intact tissues, and for the obtainment of detailed three-dimensional maps of the human body and organs. In the field of biomedicine, the two areas of NMR are represented by Magnetic Resonance Imaging (MRI) and by the multi-branched Magnetic Resonance Spectroscopy (MRS), where MRS is the acronym utilised in place of NMR. MRI uses the strong signal from water protons (1H) to provide detailed anatomical maps and has proven to be an indispensable tool for both researchers and clinicians, but its specificity in defining the pathology is limited to only some diseases. NMR spectroscopy in its one- and two-dimensional version can be utilised to detect and assign the resonances observed in in-vitro extracts and ex-vivo biopsy samples, helping in disentangling the complex spectral pattern due to signal overlapping. This represent the first step in the individuation of the NMR biochemical markers representative of the healthy or pathological state of the tissue or organ. The results can then utilised at diagnostic and prognostic level in in-vitro and rx-vivo analyses. They also provide the rationale basis for the interpretation of in-vivo MRS studies
9-Methyladenine complexes of platinum(II) stabilized by trimethylphosphine: Use of N-15 nuclear magnetic resonance spectroscopy to assign the coordination site
No full textThe new 9-methyladenine (made) complexes cis-[Pt(PMe(3))(2)(made)(2)][NO3](2) and cis-[{Pt(PMe(3))(2)(made - H)}(2)][NO3](2) have been prepared and characterized. They are formed by treating stoichiometric amounts of the nucleobase with an aqueous solution of cis-[Pt(PMe(3))(2)(NO3)(2)] at autogenous and neutral pH, respectively. A detailed multinuclear (H-1, P-31, Pt-195, C-13 and N-15 at natural abundance) NMR investigation in (CD3)(2)SO indicated that in the mononuclear complex the adenine ligands are N(1)-co-ordinated and that rotation around the metal-nitrogen bonds is slow on the NMR time-scale leading to the presence of two conformers with a relative abundance of ca. 2 : 1. In the dinuclear complex the NH2-deprotonated adenine acts as a bridging ligand through the N(1) and N(6) atoms. The sites of metal binding are clearly evidenced in the N-15 NMR spectra by the remarkable shifts shown by the co-ordinated nitrogens (60 ppm upfield for the endocyclic atom and 25 ppm downfield for the exocyclic one, with respect to the unco-ordinated nucleobase) and their coupling with the P-31 nucleus of the ligand in mutual trans position ((2)J(NP) ca. 60 Hz).The new 9-methyladenine (made) complexes cis-[Pt(PMe3)2(made)2][NO3] 2 and cis-[{Pt(PMe3)2(made - H)}2][NO3]2 have been prepared and characterized. They are formed by treating stoichiometric amounts of the nucleobase with an aqueous solution of cis-[Pt(PMe3)2(NO3)2] at autogenous and neutral pH, respectively. A detailed multinuclear (1H, 31P, 195Pt, 13C and 15N at natural abundance) NMR investigation in (CD3)2SO indicated that in the mononuclear complex the adenine ligands are N(1)-co-ordinated and that rotation around the metal-nitrogen bonds is slow on the NMR time-scale leading to the presence of two conformers with a relative abundance of ca. 2:1. In the dinuclear complex the NH2-deprotonated adenine acts as a bridging ligand through the N(1) and N(6) atoms. The sites of metal binding are clearly evidenced in the 15N NMR spectra by the remarkable shifts shown by the co-ordinated nitrogens (60 ppm upfield for the endocyclic atom and 25 ppm downfield for the exocyclic one, with respect to the unco-ordinated nucleobase) and their coupling with the 31P nucleus of the ligand in mutual trans position (2JNP ca. 60 Hz)
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