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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Kinetics and Mechanisms of Metal Carbonyls

Ladogana, Santino 05 1900 (has links)
Pulsed laser flash photolysis with both visible and infrared detection has been applied to the study of the displacement of weakly coordinating ligands (Lw) by strongly "trapping" nucleophiles (Ls) containing either an olefinic functionality (Ls = 1-hexene, 1-decene, 1-tetradecene) or nitrogen (Ls = acetonitrile, hydrocinnamonitrile) from the photogenerated 16 electron pentacarbonylchromium (0) intermediate. 5-Chloropent-l-ene (Cl-ol), a potentially bidentate ligand, has been shown to form (ol-Cl) pentacarbonylchromium (0), in which Cl-ol is bonded to Cr via a lone pair on the chlorine, and isomerize to (Cl-ol) pentacarbonylchromium (0), in which Cl-ol is bonded to the olefinic functionality on the submillisecond time scale. This process has been studied in both the infrared and visible region employing both fluorobenzene or n-heptane as the "inert" diluent. Parallel studies employing 1-chlorobutane and 1-hexene were also evaluated and showed great similiarity with the Cl-ol system. The data supported a largely dissociative process with a possibility of a small interchange process involving the H's on the alkyl chain. Studies were also carried out for various Cr(CO)6/arene/Ls systems (arene = various alkyl or halogenated substituted benzenes). The data indicated that for both C6H5R (R=various alkyl chains) or multi-alkyl substituted arenes (i.e. o-xylene, 1,2,3-trimethylbenzene) containing an "unhindered" ring-edge, bonding to the the Cr(CO)5 moiety occurs "edge on" via a partially delocalized center of unsaturation on the ring. The data indicated that both electronic and steric properties of the arenes influence the kinetics, and that an interchange pathway takes place at least, in part, through the alkyl chains on both the arenes and "trapping" nucleophiles. Moreover, halogenated arenes bond through the lone pair on the halogen for both CI- and Br- derivatives but "edge-on" for the fluorinated arenes. Finally, in the case of arene complexes without and "unhindered" ring-edge (i.e., 1,2,3,4,5-pentamethylbenzene) bonding can occur either "edge-on" or through the ring center of the arene or combination of the two. Carbonyl stretching frequencies for the arenes are also indicative of the type of bonding.
52

Syntheses of a New C₂₂H₂₈ Cage Hydrocarbon System and 2,2- Tetramethylene-1 /4-Dibromobutane

Wu, An-hsiang 12 1900 (has links)
(1). An improved method for synthesizing bicyclo (2,2,1) hepta-2,5-diene-7-spiro-1'-cyclopentane (5) has been developed. Thermal reaction of compound (5) with neat iron pentacarbonyl under nitrogen atmosphere affords the corresponding cage dimer (6). Some aspects of the syntheses, spectra, and chemistry of compound (5) and (6) are discussed. (2). A structure isomer of decamethyldodecahedrane (C₃₀H₄₀), molecule (11), is expected to be synthesized via thermal reaction of iron carbonyl complexes with compound (10). An intermediate in this synthesis, 2,2- tetramethylene-1,4-dibromobutane (9) was efficiently synthesized starting from cyclopentanone. Some aspects of the syntheses, spectra, and chemistry of compound (1) to (9) will be discussed.
53

Kinetics and Mechanism of Reactions of Disubstituted Octahedral Metal Carbonyls with Phosphorus Donor Ligands and Germanium Tetraiodide

Moradi-Araghi, Ahmad 08 1900 (has links)
The kinetics and mechanism of the reactions of (tmpa)W-(CO)^ and (tmen)W(CO)^ (tmpa = N,N,N',N'-tetramethy1-1,3-diaminopropane and tmen = N,N,N1,N1-tetramethylethylenediamine) with four phosphorus donor ligands (triisopropyl phosphite, triphenyl phosphite, triphenylphosphine and "constrained phosphite", 4-methyl-2,6,7-trioxa-l-phosphabicylo[2.2.2]octane) in xylene have been investigated in detail. These reactions were found to take place by the ring-opening of the bidentate ligand in a reversible step which leads to the formation of a five-coordinate intermediate of the type [(h^-tmpa)W(CO)or [(h^-tmen)W(CO). The intermediate then reacts with one molecule of phosphorus ligand, L, to form a six-coordinate intermediate, which can either expel the bidentate ligand and react with another molecule of L leading to the formation of a new disubstituted tungsten tetracarbonyl or go through a ring-reclosure step to form a seven-coordinate activated com-2 2plex or intermediate of the type [(h -tmpa)W(CO)^(L)] or [(h - tmen)W(CO)^(L)] which then regenerates the substrate through the expulstion of the L molecule. This mechanism is consistent with the observed rate behavior in these systems. For the reaction of (tmpa)W(CO)^ with the "constrained phosphite", an intermediate of the type [(h1-tmpa)W(CO)4P(OCH2)3CCH3] was isolated and identified.
54

Ανάπτυξη μιας νέα [sic] φωτομετρικής μεθόδου για τον προσδιορισμό των πρωτεϊνικών καρβονυλομάδων, ως δείκτη της πρωτεϊνικής υπεροξείδωσης των οργανισμών

Αργυροπούλου, Βασιλική 12 September 2014 (has links)
Το οξειδωτικό στρες είναι μια κατάσταση στην οποία βρίσκονται τα κύτταρα όταν σε αυτά οι αντιοξειδωτική άμυνα υπερκεράζεται έναντι των οξειδωτικών εκθέσεων των κυττάρων και χαρακτηρίζεται από την εμφάνιση ελευθέρων ριζών οι οποίες στη συνέχεια προκαλούν καταστροφές στα βιομόρια του κυττάρου (λιπίδια, νουκλεϊκά οξέα, πρωτεΐνες). Το οξειδωτικό στρες φαίνεται να εμπλέκεται στους μηχανισμούς τόσο φυσιολογικών (διαφοροποίηση, γήρανση), όσο και παθολογικών καταστάσεων (νευροεκφυλιστικές παθήσεις). Σε περίπτωση έντονου οξειδωτικού στρες εξαιτίας φυσιολογικών ή παθολογικών ερεθισμάτων στα κύτταρα επέρχονται βλάβες σε μόρια, όπως οι πρωτεΐνες. Ως εκ τούτου η ακριβής ποσοτικοποίηση της πρωτεϊνικής υπεροξείδωσης με μεθόδους που εξειδικευμένα ποσοτικοποιούν συγκεκριμένες αλλαγές, όπως τη δημιουργία των πρωτεϊνικών καρβονυλομάδων, είναι χρήσιμες για την εκτίμηση της έκτασης της βλάβης. Οι καρβονυλομάδες δημιουργούνται σε συγκεκριμένα αμινοξέα των πρωτεϊνών (λυσίνη, αργινίνη, προλίνη και θρεονίνη [1]), ύστερα από έκθεση των κυττάρων/οργανισμών σε συνθήκες υψηλού οξειδωτικού στρες. Για την ποσοτικοποίησή τους, η κλασική φωτομετρική μέθοδος, που στηρίζεται στην αντίδραση των καρβονυλομάδων με το αντιδραστήριο 2,4,-dinitrophenylhydrazine (DNPH) παρουσιάζει αρκετά μειονεκτήματα. Τα βασικότερα είναι: (1) η μη φωτομετρική διάκριση της προκύπτουσας υδραζόνης από το ελεύθερο DNPH, σε συνδυασμό με την απομόνωσή του μέσω πρωτεϊνικής καταβύθισης και αναποτελεσματικού πλυσίματος του πρωτεϊνικού ιζήματος για την απομάκρυνση του μη ειδικά συνδεδεμένου DNPH στην πρωτεΐνη, και (2) η υδρόλυση του δεσμού της υδραζόνης σε όξινο pH. Ως εκ τούτου, η κλασική μέθοδος του DNPH παρουσιάζει προβλήματα επαναληψιμότητας και ακρίβειας. H παρούσα μεταπτυχιακή διατριβή στοχεύει στην ανάπτυξη μιας νέας ευαίσθητης και απλής μεθοδολογίας με βάση το αντιδραστήριο DNPH για την ποσοτικοποίηση των πρωτεϊνικών καρβονυλίων σε δείγματα ιστών, η οποία θα αντιμετωπίζει τα προαναφερθέντα μειονεκτήματα της κλασικής φωτομετρικής μεθόδου. Τα αποτελέσματα της διατριβής έχουν ευρεία βιολογική σημασία εξαιτίας του ότι η νέα μέθοδος (αλκαλική DNPH μέθοδος) μπορεί να εφαρμοστεί σε ένα μεγάλο εύρος βιολογικών δειγμάτων, κάνοντας τις πρωτεϊνικές καρβονυλομάδες έναν αξιόπιστο δείκτη του οξειδωτικού στρες. / Oxidative stress is a condition where the cells are characterized by low antioxidant defense, which leads to the generation of oxygen/nitrogen free radicals that damage the central molecules of the cell (lipids, nucleic acids, proteins). Oxidative stress is involved in both physiological (e.g. differentiation, aging) and pathological conditions (e.g. neurodegenerative diseases). In case of severe oxidative stress due to physiological or pathological parameters in the cells, proteins and other macromolecules are damaged. Therefore, the accurate quantification of protein peroxidation with assays for specific oxidative modifications such as protein carbonyls is very important for the evaluation of the extent of damage. Carbonyl groups are formed in certain amino acids of proteins (lysine, arginine, proline, and threonine residues [1]), following the exposure of cells/organisms to high oxidative stress conditions. For their quantification, the standard photometric method, based on the reaction of carbonyl groups with the reagent 2,4,-dinitrophenylhydrazine (DNPH) presents several disadvantages. The main disadvantages are: (1) the non-photometric differentiation of the protein-DNPH hydrazone from free DNPH, coupled with its isolation via protein precipitation and ineffective washing of the protein precipitate to remove non-specifically bound DNPH to the protein, and (2) the hydrolysis of the hydrazone bond at acidic pH. Therefore, the standard DNPH assay cannot be used accurately. The present study aims to develop a novel sensitive and simple DNPH-based methodology for the quantification of the protein carbonyls in tissue samples, which overcomes all the aforementioned disadvantages. The findings presented here are very important because the new assay (alkaline DNPH assay) is applicable to a wide spectrum of biological samples, making protein carbonyls a very reliable marker of oxidative stress.
55

Μια νέα φθορισμομετρική μέθοδος ποσοτικοποίησης των καρβονυλομάδων στις πρωτεΐνες, ως δείκτη οξειδωτικού στρες των οργανισμών

Αργυροπούλου, Βασιλική 14 September 2014 (has links)
Το οξειδωτικό στρες είναι μια κατάσταση στην οποία βρίσκονται τα κύτταρα όταν σε αυτά η αντιοξειδωτική άμυνα υπερκεράζεται έναντι των οξειδωτικών εκθέσεων των κυττάρων και χαρακτηρίζεται από την εμφάνιση ελευθέρων ριζών οι οποίες στη συνέχεια προκαλούν καταστροφές στα βιομόρια του κυττάρου (λιπίδια, νουκλεϊκά οξέα, πρωτεΐνες). Το οξειδωτικό στρες φαίνεται να εμπλέκεται στους μηχανισμούς τόσο φυσιολογικών (διαφοροποίηση, γήρανση), όσο και παθολογικών καταστάσεων (νευροεκφυλιστικές παθήσεις). Σε περίπτωση έντονου οξειδωτικού στρες εξαιτίας φυσιολογικών ή παθολογικών ερεθισμάτων στα κύτταρα επέρχονται βλάβες σε μόρια, όπως οι πρωτεΐνες. Ως εκ τούτου η ακριβής ποσοτικοποίηση της πρωτεϊνικής υπεροξείδωσης με μεθόδους που εξειδικευμένα ποσοτικοποιούν συγκεκριμένες αλλαγές, όπως τη δημιουργία των πρωτεϊνικών καρβονυλομάδων, είναι χρήσιμες για την εκτίμηση της έκτασης της βλάβης. Οι καρβονυλομάδες υπερισχύουν ποσοτικά ως προϊόντα οξείδωσης των πρωτεϊνών και δημιουργούνται σε συγκεκριμένα αμινοξέα των πρωτεϊνών (λυσίνη, αργινίνη, προλίνη και θρεονίνη [1]) ύστερα από έκθεση των κυττάρων/οργανισμών σε συνθήκες υψηλού οξειδωτικού στρες. Για την ποσοτικοποίησή τους, η κλασική φθορισμομετρική μέθοδος, που στηρίζεται στην αντίδραση των καρβονυλομάδων με το αντιδραστήριο fluorescein-5-thiosemicarbazide (FTC) παρουσιάζει αρκετά μειονεκτήματα. Τα βασικότερα είναι: (1) η μη φθορισμομετρική διάκριση της προκύπτουσας υδραζόνης από το ελεύθερο FTC, σε συνδυασμό με την απομόνωσή του μέσω πρωτεϊνικής καταβύθισης και αναποτελεσματικού πλυσίματος του πρωτεϊνικού ιζήματος για την απομάκρυνση του μη ειδικά συνδεδεμένου FTC στην πρωτεΐνη, και (2) η υδρόλυση του δεσμού της υδραζόνης σε σύντομο χρονικό διάστημα. Ως εκ τούτου, η κλασική φθορισμομετρική μέθοδος του FTC παρουσιάζει προβλήματα επαναληψιμότητας και ακρίβειας. H παρούσα μεταπτυχιακή διατριβή στοχεύει στην ανάπτυξη μιας νέας ευαίσθητης και απλής φθορισμομετρικής μεθοδολογίας με βάση ένα νέο αντιδραστήριο, το Rhodamine B Hydrazine (RBH) για την ποσοτικοποίηση των πρωτεϊνικών καρβονυλίων σε δείγματα ιστών, η οποία θα αντιμετωπίζει τα προαναφερθέντα μειονεκτήματα της κλασικής φθορισμομετρικής μεθόδου και επιπλέον θα στοχεύει σε μεγαλύτερη ευαισθησία (λιγότερη ποσότητα πρωτεΐνης). Τα αποτελέσματα της διατριβής έχουν ευρεία βιολογική σημασία εξαιτίας του ότι η νέα μέθοδος (φθορισμομετρική RBH μέθοδος) μπορεί να εφαρμοστεί σε ένα μεγάλο εύρος βιολογικών δειγμάτων, κάνοντας τις πρωτεϊνικές καρβονυλομάδες έναν αξιόπιστο δείκτη του οξειδωτικού στρες. / Oxidative stress is a condition where the cells are characterized by low antioxidant defense, which leads to the generation of oxygen/nitrogen free radicals that damage the central molecules of the cell (lipids, nucleic acids, proteins). Oxidative stress is involved in both physiological (e.g. differentiation, aging) and pathological conditions (e.g. neurodegenerative diseases). In case of severe oxidative stress due to physiological or pathological parameters in the cells, proteins and other macromolecules are damaged. Therefore, the accurate quantification of protein peroxidation with assays for specific oxidative modifications such as protein carbonyls is very important for the evaluation of the extent of damage. Carbonyl groups are quantitatively the major type of oxidative modification of proteins, and are formed in certain amino acids of proteins (lysine, arginine, proline, and threonine residues [1]), following the exposure of cells/organisms to high oxidative stress conditions. For their quantification, the standard fluorometric method, based on the reaction of carbonyl groups with the reagent fluorescein-5-thiosemicarbazide (FTC) presents several disadvantages. The main disadvantages are: (1) the non-fluorometric differentiation of the protein-FTC hydrazone from free FTC, coupled with its isolation via protein precipitation and ineffective washing of the protein precipitate to remove non-specifically bound FTC to the protein, and (2) the hydrolysis of the hydrazone bond at acidic pH. Therefore, the standard FTC assay cannot be used accurately. The present study aims to develop a novel sensitive and simple fluorometric assay based on a novel reagent, Rhodamine B Hydrazine (RBH), for the quantification of protein carbonyls in tissue samples, which overcomes all the aforementioned disadvantages. The findings presented here are very important because the new assay (fluorometric RBH assay) is applicable to a wide spectrum of biological samples, making protein carbonyls a very reliable marker of oxidative stress.
56

Avaliação de carbonilas na atmosfera interior e exterior de salas de aula de escolas públicas / Evaluation of carbonyls indoor and outdoor the atmosphere of public classrooms

Márcio de Mello Gomes 24 March 2014 (has links)
Compostos carbonílicos representam uma das principais classes de poluentes atmosféricos e são frequentemente reportados em estudos de poluição atmosférica de interiores. São emitidos para a atmosfera a partir de uma variedade de fontes naturais e antropogênicas. Em projeto empreendido em 2011 pela Secretaria de Estado de Educação do Estado do Rio de Janeiro,foi implementada a climatização em todas as salas de aula de todas as escolas da rede pública estadual. A escala de exposição de ocupantes à climatização, em salas de aula, não apresenta precedentes em nosso estado e representa uma tendência de todo o país. Como é um projeto recente, não há dados a respeito da qualidade do ar interior nesses ambientes e, portanto, das consequências na saúde dos ocupantes. Os procedimentos foram baseados na metodologia TO-11A da U.S.EPA. A técnica de amostragem foi por via seca com reação química, empregando-se cartuchos de sílica revestidos de octadecil (SiO2-C18) impregnados com 2,4-dinitrofenilhidrazina. As carbonilas foram analisados através de Cromatografia Líquida de Alta Eficiência com detecção por UV. Foram encontradas concentrações de formaldeído na faixa de 3,59 a 26,62 μg m-3 (interior) e 0,74 a 23,47 μg m-3 (exterior), acetaldeído na faixa de 0,19 a 259,47 μg m-3 (interior) e 1,19 a 127,51 μg m-3 (exterior), acetona+acroleína na faixa de 0,00 a 48,45 μg m-3 (interior) e 0,00 a 37,00 μg m-3 (exterior). Os valores encontrados geralmente não ultrapassaram os limites determinados por organismos internacionais / Carbonyl compounds represent one of most important classes of atmospheric pollutants and are frequently reported in indoor atmospheric pollution studies. Are emitted for atmosphere from a wide variety of natural and anthropogenic sources. In a project undertaken in 2011 by State Department of Education of Rio de Janeiro, all classrooms were acclimatized in all public schools statewide. The exposure scale of occupants to closed acclimatized classrooms has no precedent in our state and represents a trend throughout the country. As it is a recent project, there are no data regarding the indoor air quality in these environments and, therefore, the consequences on the health of occupants. The procedures were based on the TO-11A U.S.EPA methodology. The sampling technique is dry chemical reaction, using silica coated with octadecyl cartridges impregnated with 2,4-dinitrophenylhydrazine.Carbonyls were analyzed by High Performance Liquid Chromatography wit UV detection. Formaldehyde concentrations were found in range of 3.59 to 26.62 μg m-3 (indoor) and 0.74 to 23.47 μg m-3 (outdoor), acetaldehyde in range of 0.19 to 259.47 μg m-3 (indoor) and 1.19 to 127.51 μg m-3 (outdoor), acetone+ acrolein range of 0.00 to 48.45 μg m-3 (indoor) and 0.00 to 37.00 μg m-3 (outdoor). The values found generally did not exceed the limits set by international organizations
57

Avaliação de carbonilas na atmosfera interior e exterior de salas de aula de escolas públicas / Evaluation of carbonyls indoor and outdoor the atmosphere of public classrooms

Márcio de Mello Gomes 24 March 2014 (has links)
Compostos carbonílicos representam uma das principais classes de poluentes atmosféricos e são frequentemente reportados em estudos de poluição atmosférica de interiores. São emitidos para a atmosfera a partir de uma variedade de fontes naturais e antropogênicas. Em projeto empreendido em 2011 pela Secretaria de Estado de Educação do Estado do Rio de Janeiro,foi implementada a climatização em todas as salas de aula de todas as escolas da rede pública estadual. A escala de exposição de ocupantes à climatização, em salas de aula, não apresenta precedentes em nosso estado e representa uma tendência de todo o país. Como é um projeto recente, não há dados a respeito da qualidade do ar interior nesses ambientes e, portanto, das consequências na saúde dos ocupantes. Os procedimentos foram baseados na metodologia TO-11A da U.S.EPA. A técnica de amostragem foi por via seca com reação química, empregando-se cartuchos de sílica revestidos de octadecil (SiO2-C18) impregnados com 2,4-dinitrofenilhidrazina. As carbonilas foram analisados através de Cromatografia Líquida de Alta Eficiência com detecção por UV. Foram encontradas concentrações de formaldeído na faixa de 3,59 a 26,62 μg m-3 (interior) e 0,74 a 23,47 μg m-3 (exterior), acetaldeído na faixa de 0,19 a 259,47 μg m-3 (interior) e 1,19 a 127,51 μg m-3 (exterior), acetona+acroleína na faixa de 0,00 a 48,45 μg m-3 (interior) e 0,00 a 37,00 μg m-3 (exterior). Os valores encontrados geralmente não ultrapassaram os limites determinados por organismos internacionais / Carbonyl compounds represent one of most important classes of atmospheric pollutants and are frequently reported in indoor atmospheric pollution studies. Are emitted for atmosphere from a wide variety of natural and anthropogenic sources. In a project undertaken in 2011 by State Department of Education of Rio de Janeiro, all classrooms were acclimatized in all public schools statewide. The exposure scale of occupants to closed acclimatized classrooms has no precedent in our state and represents a trend throughout the country. As it is a recent project, there are no data regarding the indoor air quality in these environments and, therefore, the consequences on the health of occupants. The procedures were based on the TO-11A U.S.EPA methodology. The sampling technique is dry chemical reaction, using silica coated with octadecyl cartridges impregnated with 2,4-dinitrophenylhydrazine.Carbonyls were analyzed by High Performance Liquid Chromatography wit UV detection. Formaldehyde concentrations were found in range of 3.59 to 26.62 μg m-3 (indoor) and 0.74 to 23.47 μg m-3 (outdoor), acetaldehyde in range of 0.19 to 259.47 μg m-3 (indoor) and 1.19 to 127.51 μg m-3 (outdoor), acetone+ acrolein range of 0.00 to 48.45 μg m-3 (indoor) and 0.00 to 37.00 μg m-3 (outdoor). The values found generally did not exceed the limits set by international organizations
58

Atmospheric measurements of a series of volatiles organic compounds / Mesures atmosphériques d'une série de composés organiques volatils

Jiang, Zhaohui 20 May 2014 (has links)
Les composes carbonyles et BTEX (benzène, toluène, éthylbenzène et xylène) sont deux groupes importants de composés organiques volatils (COV) présents dans l'atmosphère. Ils ont une contribution significative à la formation d'oxydants tels que l'ozone, PAN et d'autres photo-oxydants dans la troposphère. En outre, ils ont des effets néfastes sur la santé humaine. Dans ce travail, les concentrations atmosphériques de carbonyles et d’hydrocarbures aromatiques ont été mesurées et quantifiées en utilisant des techniques HPLC et GC-MS sur un site de mesure semi-urbain à Orléans (ICARE, France), de juin 2010 à août 2011. D’autres mesures ont été conduites à Pékin (CAS-RCEES, Chine) du 6 au 28 Juin 2013 en utilisant les mêmes techniques expérimentales. Les résultats obtenus dans ces deux sites sont présentés, comparés et discutés. / Carbonyls and BTEX (benzene, toluene, ethyl-benzene and xylene) are two important groups of Volatile Organic Compounds (VOCs) present in the atmosphere. They have a significant contribution to the formation of oxidants such as ozone, PAN and other photooxidants in the troposphere. In addition, they have adverse effects on human health. In this work, atmospheric concentrations of carbonyls and aromatic hydrocarbons were measured and quantified using GC-MS and HPLC techniques at a semi-urban site in Orleans (ICARE, France), from June 2010 to August 2011. Urban ambient air sampling was also performed in 6-28th June 2013 in Beijing (RCEES-CAS, China). It has been conducted in order to compare the measured concentrations of the investigated species in two different sites using the same analytical techniques. All results are presented and discussed.
59

Kinetics Studies of Substituted Tungsten Carbonyl Complexes

Wang, I-Hsiung, 1950- 08 1900 (has links)
Thermal reactions and flash photolysis are used to study the olefin bond-migration promoted by tungsten carbonyls. Substitution of piperidine (pip) by 2- allylphenyldiphenylphosphine (adpp) in the cis-(pip)(η^1- adpp)W(CO)-4 complex was investigated, and no olefin bond-migration was observed. This suggests that a vacant coordinated site adjacent to the coordinated olefin is an essential requirement for olefin bond rearrangement. The rates of olefin attack on the photogenerated coordinatively unsaturated species, cis-[(CB)(η^1-ol- P)W(CO)-4] (CB = chlorobenzene, p-ol = Ph-2P(CH-2)-3CH=CH-2; n = 1-4) were measured. Kinetics data obtained both in pure CB and in CB/cyclohexane mixtures support a dissociative mechanism in which the W-CB bond is broken in the transition state. In contrast to results observed in studies of other related systems, no olefin bond-migration is noted. This observation is attributed to P-W coordination at all stages of the reaction, which precludes formation of a reactive intermediate containing a vacant coordination site adjacent to a P-ol bond.
60

Profiling of Low-Molecular-Weight Carbonyls and Protein Modifications in Flavored Milk

Wölk, Michele, Schröter, Theres, Hoffmann, Ralf, Milkovska-Stamenova, Sanja 13 April 2023 (has links)
Thermal treatments of dairy products favor oxidations, Maillard reactions, and the formation of sugar or lipid oxidation products. Additives including flavorings might enhance these reactions or even induce further reactions. Here we aimed to characterize protein modifications in four flavored milk drinks using samples along the production chain—raw milk, pasteurization, mixing with flavorings, heat treatment, and the commercial product. Therefore, milk samples were analyzed using a bottom up proteomics approach and a combination of data-independent (MSE) and data-dependent acquisition methods (DDA). Twenty-one small carbonylated lipids were identified by shotgun lipidomics triggering 13 protein modifications. Additionally, two Amadori products, 12 advanced glycation end products (AGEs), and 12 oxidation-related modifications were targeted at the protein level. The most common modifications were lactosylation, formylation, and carboxymethylation. The numbers and distribution of modification sites present in raw milk remained stable after pasteurization and mixing with flavorings, while the final heat treatment significantly increased lactosylation and hexosylation in qualitative and quantitative terms. The processing steps did not significantly affect the numbers of AGE-modified, oxidized/carbonylated, and lipid-carbonylated sites in proteins.

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