Search results for "IR spectroscopy"

Impact of the ΔPhe configuration on the Boc-Gly-ΔPhe-NHMe conformation: experiment and theory

2019

Conformational propensities of N-t-butoxycarbonyl-glycine-(E/Z)-dehydrophenylalanine N′-methylamides (Boc-Gly-(E/Z)-ΔPhe-NHMe) in chloroform were investigated by NMR and IR techniques. The low-temperature crystal structure of the E isomer was determined by single crystal X-ray diffraction and the experimental data were elaborated by theoretical calculations using DFT (B3LYP, M06-2X) and MP2 approaches. The β-turn tendencies for both isomers were determined in the gas phase and in the presence of solvent. The obtained results reveal that the configuration of ΔPhe residue significantly affects the conformations of the studied dehydropeptides. The tendency to adopt β-turn conformations is sign…

Stereoelectronic Properties of N-acetyl-α,β-dehydroamino acid N′-methylamides

1998

α,β-Dehydroamino acids are useful peptide modifiers. However, their stereoelectronic properties still remain insufficiently recognized. Based on FTIR experiments in the range of νs(N-H), AI, AII and νs(Cα=Cβ) and ab initio calculations with B3LYP/6-31G*, we studied the solution conformational preferences and the amide electron density perturbation of Ac-ΔXaa-NHMe, where ΔXaa = ΔAla, (E)-ΔAbu, (Z)-ΔAbu, (Z)-ΔLeu, (Z)-ΔPhe and ΔVal. Each of these dehydroamides adopts a C5 structure, which in Ac-ΔAla-NHMe is fully extended and accompanied by the strong C5 hydrogen bond. Interaction with bond Cα=Cβ lessens the amidic resonance within the flanking amide groups. The N-terminal C=O bond is noticea…

Spectroscopic markers of the T-R quaternary transition in human hemoglobin

2004

n questo lavoro, usiamo un protocollo sol-gel per intrappolare e confrontare gli stati quaternari R e T di entrambi i deossigenati (deossiHb) ederivati ​​di ossido di carbonio (HbCO) dell'emoglobina umana. La banda di assorbimento ottico del vicino infrarosso III e lo stretching di CO a infrarossibanda sono utilizzati per rilevare l'effetto della struttura quaternaria sulle proprietà spettrali di deoxyHb e HbCO; confronto con mioglobinaconsente una valutazione dei contributi terziari e quaternari ai turni di banda misurati. La RXLa transizione T è indicata per causare un bluspostamento della banda III di ~ 35 cm?1per deoxyHb e uno spostamento rosso della banda di allungamento CO di soli ~ 0…

Estudio del biodeterioro en resinas alquídicas usadas como aglutinante en pinturas modernas mediante espectroscopía FTIR y pirólisis-cromatografía de…

2008

Evaluation of the alteration produced by microbiological attack on alkyd resins has been carried out by FTIR spectroscopy and Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS). The latter included the online derivatisation of alkyd resins using hexamethyldisilazane during pyrolysis. Specimens consisting of thin films of resins formed on glass slides were used. Analyses performed on the specimens in which different genera of bacteria and fungi were inoculated and allowed to grow, indicate that the attack of microorganisms encourages the scissioning of the polymeric resins and the appearance of short-chain fatty acids. IR bands ascribed to carboxylic acids appearing in samples from in…

Photocatalytic degradation of nitrophenols in aqueous titanium dioxide dispersion

1991

Abstract The results are reported of an investigation into the photodegradation of nitrophenol isomers carried out in aqueous titania (anatase) dispersions under various experimental conditions. We investigated the influence of various parameters on the photodegradation rate, such as the concentrations of the catalyst, dissolved oxygen and organic compound, and the presence of various anions in the dispersion. A plausible explanation is proposed for the influence of these parameters, both mechanistic and kinetic factors being accounted for. Gas chromatography and mass spectrometry were used as analytical methods in order to determine intermediate products. Spectroscopic methods (UV-vis and …

Synthesis, structural, and thermal characterization of a new binuclear copper(II) chelate complex bearing an amine-hardener for epoxy resins

2016

A new di(μ-carbonato)bis[aqua(diethylenetriamine)copper(II)] hexahydrate complex, [{Cu(NH(C2H4NH2)2)(H2O)(μ-CO3)}2]⋅6H2O (1), was synthesized by direct interaction of malachite with diethylenetriamine (dien). The crystals of 1 were characterized by X-ray powder diffraction and IR spectra, as well as structurally characterized. Compound 1 consists of [{Cu(dien)(H2O)(μ-CO3)}2] discrete units whose CO32– anions play the role of bridging ligands combining two Cu(II) chelate cores into a centrosymmetric dimer. The elongated octahedral environment of Cu2+ consists of three nitrogens of dien and an oxygen from CO32– at the base of the bipyramid; the two apical positions of such polyhedron are occu…

The influence of weathering processes on labile and stable organic matter in Mediterranean volcanic soils

2008

The relationship and mechanisms among weathering processes, cation fluxes, clay mineralogy, organic matter composition and stability were studied in soils developing on basaltic material in southern Italy (Sicily). The soils were transitions between Phaeozems and Vertisols. Intense losses of the elements Na, Ca and Mg were measured indicating that weathering has occurred over a long period of time. The main weathering processes followed the sequence: amphibole, mica, volcanic glass or if ash was the primary source→smectite→interstratified smectite–kaolinite→kaolinite. Kaolinite formation was strongly related to high Al, Mg and Na losses. The good correlation between oxyhydroxides and kaolin…

Infrared Spectroscopy In Urolithiasis In Children

2014

New Alternative in the Methodology of Extraction and Dyeing with Active Molecules Derived from Vegetal Sources

2016

Abstract The general objective of this study refers to the identification of a sustainable and physical methodology of extraction of active compounds, envisaging the preservation of the high purity active natural dye molecule from nut shell (juglone), even under the conditions of an extraction performed in a mixt solvent medium (water-ethanol). The second major objective of the study consists of the application of these above mentioned dyes onto natural and synthetic substrates, thus making a correlation between their colour attributes and the fibrous composition of the substrates they are applied on. The motivation of this research was given by the identification of an improved extraction …

Can copper(II) mediate Hoogsteen base-pairing in a left-handed DNA duplex? A pulse EPR study

2010

Pulse EPR spectroscopy is sued to investigate possible structural features of the copper(II) ion coordinated to poly(dG-dC) poly(dG-dC) in a frozen aqueous solution, and the structural change of the polynucleotide induced by the presence of the metal ion. Two different copper species were identified and their geometry explained by a molecular model. According to this model, one species is exclusively coordinated to a single guanine with the N7 nitrogen atom forming a coordinative bond with the copper. In the other species, a guanine and a cytosine form a ternary complex together with the copper ion. A copper crosslink between the N7 of guanine and N3 of cytosine is proposed as the most prob…