Search results for "Spectroscopy"
showing 10 items of 10293 documents
Sesterterpenes and macrolide derivatives from the endophytic fungus Aplosporella javeedii.
2020
Abstract Five sesterterpenes (1–5) including two new compounds (1 and 2), as well as a new (6) and a known macrolide (7) were isolated from the endophytic fungus Aplosporella javeedii. The structures of the new compounds were elucidated by analysis of their 1D and 2D NMR and HRMS data as well as by comparison with the literature. Compound 4 and its acetyl derivatives 4a, 4b, 4c which were prepared by acetylation of 4 exhibited moderate cytotoxicity against the mouse lymphoma cell line L5178Y with IC50 values ranging from 6.2 to 12.8 μM, respectively. Moreover, 4a and 4c exhibited also cytotoxicity against human leukemia (Jurkat J16) and lymphoma (Ramos) cell lines. Compound 7 showed strong …
Marine Isonitriles and Their Related Compounds.
2016
Marine isonitriles represent the largest group of natural products carrying the remarkable isocyanide moiety. Together with marine isothiocyanates and formamides, which originate from the same biosynthetic pathways, they offer diverse biological activities and in spite of their exotic nature they may constitute potential lead structures for pharmaceutical development. Among other biological activities, several marine isonitriles show antimalarial, antitubercular, antifouling and antiplasmodial effects. In contrast to terrestrial isonitriles, which are mostly derived from α-amino acids, the vast majority of marine representatives are of terpenoid origin. An overview of all known marine isoni…
Using ATR-FTIR Spectroscopy To Design Active Antimicrobial Food Packaging Structures Based on High Molecular Weight Chitosan Polysaccharide
2007
ATR-FTIR spectroscopy has been used in this study to characterize the molecular mechanisms and kinetic processes that take place when a chitosonium acetate thin coating is put in contact with water solutions, Staphylococcus aureus solutions, microbial nutrient solutions, and with a high water activity TSA hydrogel medium to simulate the effect of direct contact with high moisture foods such as fresh meats, fish, and seafood products or beverages. The results of this work suggest that the biocide carboxylate groups that form when chitosan is cast from acetic acid solutions are being continuously evaporated from the formed film in the form of acetic acid (mechanism I) in the presence of envir…
Influence of synthesis conditions on the performance of chitosan–Heteropolyacid complexes as membranes for low temperature H2–O2 fuel cell
2015
Flat, free-standing chitosan/phosphotungstic acid (PTA) polyelectrolyte membranes were prepared by in-situ ionotropic gelation process at room temperature on porous alumina support firstly impregnated by H3PW12O40. Scanning electron microscopy revealed the formation of compact and homogeneous membranes, whose thickness resulted to be dependent on chitosan concentration and reticulation time. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) evidenced the formation of almost amorphous membrane without appreciable concentration of not protonated NH2 groups and PTA3- ions with preserved Keggin structure. Membranes were tested as proton conductor in low temperature H2-O2 fuel…
Ab initio calculations and vibrational spectroscopy on the phenylenediamine isomers
1998
Molecular orbital calculations at HF and MP2 levels have been performed using the 6-3IG** basis set for full geometry optimization of the phenylenediamine isomers. Our results show that only a transoid conformer is found for o-phenylenediamine, whereas cis and trans conformers exist for m- and p-phenylenediamine. Vibrational normal modes have been also analyzed for the gas phase and in chloroform solution, and compared with experimental data we have obtained using FTIR spectroscopy. © 1998 Elsevier Science B.V.
Synthesis and spectroscopic investigations (IR, NMR and Mössbauer) of tin(IV) and organotin(IV) derivatives of bis(pyrazol-1-yl) alkanes: X-ray cryst…
1995
A series of 1:1 adducts of the type [(L)R(n)SnX(4-n)] . zH(2)O (L = bis(4-methylpyrazol-1-yl)methane (L(4)), bis(3,4,5-trimethylpyrazol-1-yl)methane (L(T)), 1,2-bis(pyrazol-1-yl)ethane (L(A)) or 1,2-bis(3,5-dimethylpyrazol-1-yl)ethane (L(B)); R = Me, Et, Bu or Ph; X = I, Br or Cl; n = 0, 1 or 2; z = 1, 1.5 or 2), and the likely polynuclear [(L(A))(5)(SnCl4)(4)] . (H2O)(5) and [(L(B))(2)(SnCl4)(3)] . 1/2[Et(2)O] have been characterized in the solid state and in solution by analyses, spectral (IR, Mossbauer, and H-1, C-13 and Sn-119 NMR) data and conductivity measurements. When L(T) reacts with SnCl4, cleavage of a carbon (sp(3))-nitrogen bond was observed and the adduct [(3,4,5-trimethylpyra…
Synthesis and electrochemical study of a new doubly-metallated compound with the ferrocene-labelled phosphine PPh2(C5H4)Fe(C5H5)
1993
Abstract Direct reaction of the metalled compound Rh 2 (μ 2 -O 2 CCH 3 ) 3 [μ 2 -(C 6 H 4 ) PPh 2 ]·(H 2 O) 2 with PPh 2 Fc [Fc = (C 5 H 4 )Fe(C 5 H 5 )] in chloroform solution yields the corresponding mono-adduct Rh 2 (O 2 CCH 3 ) 3 [(C 6 H 4 )PPh 2 ]·(PPh 2 Fc) ( 1 ), which has been characterized by 31 P NMR spectroscopy. Photochemical irradiation of 1 in chloroform gives the compound Rh 2 (μ-O 2 CCH 3 ) 2 (η 2 -O 2 CCH 3 )[μ 2 -(C 6 H 4 )PPh 2 ][PPh 2 Fc]·(H 2 O) ( 2 ) in practically quantitative yield. Compound 2 , by thermal treatment in chloroform solution, yields cleanly the doubly-metallated compound Rh 2 (μ 2 -O 2 CCH 3 ) 2 [μ 2 -(C 6 H 4 )PPhFc][μ 2 -(C 6 H 4 )PPh 2 ]·(H 2 O) 2 ( …
Supramolecular PEG-co-oligo(p-benzamide)s prepared on a peptide synthesizer.
2007
An automated synthesis protocol has been developed for the preparation of oligo(p-benzamide)s on solid support using a commercial peptide synthesizer employing a variation of standard Fmoc chemistry. Bis(trichloromethyl carbonate) in NMP was used to activate the aromatic carboxylic acids for acylation of secondary aromatic amines on solid support. N-Protected hepta(p-benzamide) was automatically prepared on solid support and manually converted to a solid supported block co-oligomer by attaching a poly(ethylene glycol) chain. Cleavage from the support could be achieved with minimal loss of the p-methoxybenzyl N-protective group. While the N-protected block co-oligomer was molecularly dissolv…
Tautomeric preferences of phthalones and related compounds
2007
Abstract Multinuclear magnetic resonance and IR spectra prove that although 2-(diacylmethyl)pyridines and 2-(diacylmethyl)quinolines are β-diketones, their proton transfer product present in chloroform solution is not ketoenol but enaminone (earlier opinions were contradictory). Quinoline derivatives are less zwitterionic by character than the respective pyridyl congeners. The β-diketone form itself may also be rarely present in the solution. X-ray data show that 2-(2(1H)-pyridinylidene)-1H-indene-1,3(2H)-dione, i.e., enaminone tautomer of 2-(pyridin-2-yl)-2H-indene-1,3-dione, is also the only form present in crystal. Ab initio calculations show that the enaminone is usually more stable tha…
(1Z,3Z)-3-[Quinolin-2(1H)-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol: An unexpected most stable tautomer of 1,3-bis(quinolin-2-yl)acetone
2009
Abstract 1 H, 13 C and 15 N NMR spectra reveal that CDCl 3 solution of 1,3-bis(quinolin-2-yl)acetone contains only ( 1Z , 3Z )-3-[quinolin-2(1 H )-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol. The proton transfer takes place between two basic centers of the molecule, which means that the process is an identity reaction by character. The situation is completely different from that detected in chloroform solution of 1,3-bis(pyridin-2-yl)acetone where three different tautomers are in equilibrium with each other. Although the proton transfers in both ( 1Z , 3Z )-3-[quinolin-2(1 H )-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol and ( 1Z , 3Z )-3-hydroxy-1-[quinolin-2(1 H )-ylidene-4-quinolin-2-yl]but-3-e…