Browsing by Subject "Carbon monoxide"

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Open Access
FTIR spectroscopic study on nickel(II)-exchanged sulfated alumina: nature of the active sites in the catalytic oligomerization of ethene
(Springer, 2002) Davydov, A. A.; Kantcheva, M.; Chepotko, M. L.
The nature of the active sites in nickel(II)-exchanged sulfated alumina in the reaction of ethene oligomerization has been studied by means of FTIR spectroscopy of adsorbed CO. It has been established that isolated nickel(I) species are the active sites in this process. These sites are formed by a reduction process, in which protonic centers are involved. The latter are due to the presence of covalently-bonded sulfate ions on the catalyst surface.
Open Access
FTIR study of low-temperature CO adsorption on Mn-ZSM-5 and MnY zeolites. Effect of the zeolite matrix on the formation of Mn2+(CO)x geminal species
(Elsevier, 2002-08) Hadjiivanov, K.; Ivanova, E.; Kantcheva, M.; Ciftlikli, E. Z.; Klissurski, D.; Dimitrov, L.; Knözinger, H.
Adsorption of CO on Mn-ZSM-5 zeolite at 85 K results in formation of physically adsorbed CO, several kinds of H-bonded CO and Mn2+ (CO)(x) geminal species (2202 cm(-1)). Decreasing the coverage during evacuation results in disappearance of the physically adsorbed CO and the H-bonded forms and in conversion of the dicarbonyls to linear Mn2+-CO Species (2214 cm(-1)). The latter are quite stable at 85 K. Coadsorption (CO)-C-12 and (CO)-C-13 reveals that the CO molecules in the geminal polycarbonyls behave as independent oscillators. In contrast, CO adsorption at 85 K on MnNaY zeolite only leads to formation of linear Mn2+-CO species (2210 cm-1) and mono- and di-carbonyls associated with residual sodium cations. The results are interpreted as evidence that site-specified geminal carbonyls are formed with cations possessing an ionic radius bigger than a critical value. This value is different for different positions in various zeolites and is bigger for cations in S-II positions in Y zeolites than is the case of cations in a ZSM-5 matrix. (C) 2002 Elsevier Science B.V. All rights reserved.
Open Access
The spontaneous hemin release form Lumbricus terrestris hemoglobin
(1997) Smith, M.L.; Paul J.; Ohlsson P.I.; Paul, K.G.
The slow, spontaneous release of hemin from earthworm, Lumbricus terrestris, hemoglobin has been studied under mild conditions in the presence of excess apomyoglobin. This important protein is surprisingly unstable. The reaction is best described as hemin released from the globin into water, followed by quick engulfment by apomyoglobin. The energetics of this reaction are compared with those of other types of hemoglobins. Anomalously low activation energy and enthalpy are counterbalanced by a negative entropy. These values reflect significant low frequency protein motion and dynamics of earthworm hemoglobin and may also indicate an open structure distal to the heme. This is also supported by the infrared spectrum of the carbonyl hemoprotein, which indicates several types of distal interactions with the bound CO. The reported low heme to polypeptide ratio for this protein may be due to facile heme and hemin release by the circulating protein.