- Photocatalytic Degradation of Hexaethylene Glycol
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Abstract: Polyethylene glycol (PEG) photodegradation was studied in water under UV irradiation in the presence of catalytic amount of TiO2 using hexaethylene glycol as a model compound. Full conversion was achieved in 7 h with an average quantum yield around 1%. Formic acid was found to be the main intermediate and was slower to oxidize into CO2 (traces remains after 24 h). The other intermediates [lower PEG, oxidized PEG (formates, aldehydes and acids, acetic acid)] of the photodegradation have also been identified and quantified. A mechanism based on previous literature but also taking into account these new observations is proposed. Graphical Abstract: [Figure not available: see fulltext.].
- Simangoye Ngobissi, Drocilia Ednah,Soufi, Jihène,Vanoye, Laurent,Richard, Dominique
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p. 1608 - 1614
(2017/08/29)
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- Highly efficient synthesis of monodisperse poly(ethylene glycols) and derivatives through macrocyclization of oligo(ethylene glycols)
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A macrocyclic sulfate (MCS)-based approach to monodisperse poly(ethylene glycols) (M-PEGs) and their monofunctionalized derivatives has been developed. Macrocyclization of oligo(ethylene glycols) (OEGs) provides MCS (up to a 62-membered macrocycle) as versatile precursors for a range of monofunctionalized M-PEGs. Through iterative nucleophilic ring-opening reactions of MCS without performing group protection and activation, a series of M-PEGs, including the unprecedented 64-mer (2850Da), can be readily prepared. Synthetic simplicity coupled with versatility of this new strategy may pave the way for broader applications of M-PEGs. Macrocycles make synthesis easier: Convenient macrocyclization of the OEGs provides versatile macrocyclic sulfates. These compounds are cornerstones for both monofunctionalization of OEGs and highly efficient synthesis of monodisperse PEGs and derivatives, including an unprecedented 64-mer.
- Zhang, Hua,Li, Xuefei,Shi, Qiuyan,Li, Yu,Xia, Guiquan,Chen, Long,Yang, Zhigang,Jiang, Zhong-Xing
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p. 3763 - 3767
(2015/03/18)
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- Novel C1-symmetric chiral crown ethers bearing rosin acids groups: Synthesis and enantiomeric recognition for ammonium salts
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Four types of novel C1-symmetric chiral crown ethers including 28-crown-8, 20-crown-6, 17-crown-5 and 14-crown-3 (9a-m) were synthesized and their enantiodiscriminating abilities with protonated primary amines (10-14) were examined by 1H NMR spectroscopy. 20-crown-6 crown ethers exhibited good chiral recognition properties toward these guests and showed different complementarity to some chiral guests, indicating that 20-crown-6 crown ethers could be used as a chiral NMR solvating agent to determine the enantiopurity of these guests. In addition, the binding model and binding site between the hosts and guests were also studied by the computational modeling and experimental calculation.
- Liu, Lu-Zhi,He, Chun-Huan,Yang, Lin,Huang, Yan,Wu, Qiang,Duan, Wen-Gui,Wang, Heng-Shan,Pan, Ying-Ming
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p. 9545 - 9553
(2015/03/05)
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- Valency platform molecules comprising carbamate linkages
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This invention pertains generally to valency molecules, such as valency platform molecules which act as scaffolds to which one or more molecules may be covalently tethered to form a conjugate. More particularly, the present invention pertains to valency platform molecules which comprise a carbamate linkage (i.e., —O—C(=O)—N). In one aspect, the present invention pertains to valency platforms comprising carbamate linkages, which molecules have the structure of any one of Formulae I, II, or III, shown in FIG. 1. In one aspect, the present invention pertains to valency platforms comprising carbamate linkages, which molecules have the structure of any one of Formulae IV, V, or VI, shown in FIG. 8. The present invention also pertains to methods of preparing such valency platform molecules, conjugates comprising such valency platform molecules, and methods of preparing such conjugates.
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- Intramolecular End-to-End Reactions of Photoactive Terminal Groups Linked by Poly(oxyethylene) Chains
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The triplet-sensitized photochemical reaction using a series of poly(oxyethylene) chains with a pair of photoactive terminal groups, dibenzazepine (DBA) chromophores (DBA-COCH2CH2(OCH2CH2)nOCH2CH2CO-DBA, n=0-10) was examined.The photoirradiation of bichromophoric compounds caused either intra- or intermolecular reactions.These reactions were kinetically analyzed by two different methods: the measurement of deactivation processes of the reaction intermediates (excited triplet state of DBA) by nanosecond laser photolysis and the quantitative analysis of the reaction products by GPC.The intramolecular deactivation rate constant, kintra, showed a remarkable chain-length dependence; the maximum kintra value appeared at n=5 and it was found to be 5.9X104 s-1.On the other hand, the intramolecular cyclization rate also depends on the chain length; the maximum quantum yield, φintrad, was given at n=7 (φintrad=0.51).The chain length for the maximum cyclization yield shifted slightly to the longer region than that for the maximum kintra value due to the restriction of the terminal structure (anti-configuration).The results obtained for this reaction system are compared with those obtained for the previously reported polymethylene system and the effect of chain flexibility on the intramolecular ring-closure reaction is discussed.
- Ashikaga, Kazuo,Ito, Shinzaburo,Yamamoto, Masahide,Nishijima, Yasunori
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p. 2443 - 2450
(2007/10/02)
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- A NOVEL, UNEQUIVOCAL SYNTHESIS OF POLYETHYLENE GLYCOLS
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Unequivocal synthesis of polyethyleneglycols is presented.The key step for this synthesis is the selective monobenzylation of oligoethyleneglycols by the phase transfer catalysis technique.
- Coudert, Gerard,Mpassi, Michel,Guillaumet, Gerald,Selve, Claude
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- Molecular Design of Crown Ethers. 1. Effects of Methylene Chain Length: 15- to 17-Crown-5 and 18- to 22-Crown-6
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The ring-enlarged crown ethers, 16- and 17-crown-5 and 19- to 22-crown-6, were synthesized and their cation-binding abilities were evaluated by solvent extraction of aqueous alkali metal picrates.The cation-binding abilities of less symmetrical crown ethers, 3a-e and 4a,b, were generally lower than those of the common symmetrical crown ethers 15-crown-5 (5a) and 18-crown-6 (5b), for which the less symmetrical arrangement of the donor oxygen atoms must be responsible.Compared with 18-crown-6 (5b), the ring-extended crown ethers, 3d, 3e, and 4b, showed a significant shift in cation selectivity, probably due to the enlarged cavity size.The thermodynamic parameters for the extraction of sodium and potassium picrates with 3a, 3c, and 5a,b were calculated from the change of the extraction equilibrium constants (Kex) between 10-25 deg C.The stability of the cation-crown ether complexes was shown to be governed in general by the enthalpy change.However, a significant contribution of the entropy factor was found in unfavorable size combinations of K+ with 3a and Na+ with 3c.
- Ouchi, Mikio,Inoue, Yoshihisa,Kanzaki, Takashi,Hakushi, Tadao
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p. 1408 - 1412
(2007/10/02)
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- The Influence of Cation Binding on the Kinetics of the Hydrolysis of Crown Ether Acetals
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The rate of hydrogen ion-catalysed hydrolysis of crown ether acetals in 60:40 (v/v) dioxan-water is found to be strongly decreased by the addition of alkali and alkaline earth metal chlorides having cations of appropriate size to be complexed by the substrate ring.The compounds studied are the monoacetals CH3CH(OCH2CH2)xO with x=1-8.The dependence of the initial rate of formation of acetaldehyde on metal-ion concentration is expressed in terms of (i) the equilibrium constant for complex formation, (ii) the influence of the bound cation on the rate constant, and (iii) an electrolyte effect.A curve-fitting procedure is used to derive the parameters governing the first two of these effects.The equilibrium constants are large and cannot be evaluated with any precision, but a fair estimate of the influence of the guest cation on the rate can be obtained.This effect is explicable by the electrostatic repulsion between the cationic charges of the metal ion and the proton added to the acetal in the first step of the hydrolysis.The size of the effect requires the values of the effective relative permittivity of the space between the charges to be close to that of the bulk solvent.
- Baker, David S.,Gold, Victor,Sghibartz, Cristian M.
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p. 1121 - 1128
(2007/10/02)
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- The Synthesis of Adrenaline Crown Ethers
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The syntheses of adrenaline-15-crown-5 and adrenaline-18-crown-6 starting from acetovanillone are reported, together with the properties of these compounds.Alkali and alkaline-earth metal complexes of these ligands have been prepared.A method of separating crown ethers based on their preferential complexation of barium is discussed.
- Fenton, David E.,Parkin, Donald,Newton, Roger F.
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p. 449 - 454
(2007/10/02)
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- MACROHETEROCYCLES. VIII. SYNTHESIS AND COMPLEXING ABILITY OF TRICARBONYL ANALOGS OF CROWN ETHERS
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The respective dicarboxylic acids were obtained by the reaction of glycolic, β-phenyllactic, and thioglycolic acids with diglycolic anhydride.Thirteen new macrocyclic esters were obtained by the reaction of the chlorides of these acids with polyethylene glycols under the conditions of high dilution.The stability constants of the complexes of these compounds with potassium and sodium cations in alcohol were determined by a polarographic method.It was established that certain crown ether triones exhibit appresiable sodium/potassium selectivity.
- Bogat-skii, A. V.,Luk'yanenko, N. G.,Popkov, Yu. A.,Zakharov, K. S.,Varava, V. M.
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p. 938 - 943
(2007/10/02)
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- Membrane transport systems. I. Synthesis and characterization of carriers for a proton driven alkali metal cation pump
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The synthesis of a series of macrocyclic polyethers (crown ethers) of interest as carriers for the countertransport of metal ions and protons across artificial membranes is described.Thallium mediated cyclization of oligoethyleneglycol diiodides with (+)-N,N,N',N'-tetramethyltartaramide gave 15-crown-5 and 18-crown-6 diamides which were converted, via the diacids and anhydrides, to crown ether monoamides bearing long chain alkyl groups (octyl, tetradecyl, and octadecyl).The alkali metal salts and complexes of these carriers are soluble in nonpolar solvents and alkali metal ions are extracted from aqueous solutions into chloroform solutions of the carriers.Acidity constants and stability constants for complex formation in methanol/water (90:10 v/v) solutions have been determined using a combination of ion selective electrode and pH-metric techniques.Deprotonation of the ligand carboxylic acid group results not only in more stable complexes but also more selective complexation.Implications for membrane transport are discussed.
- Frederick, Laurel A.,Fyles, Thomas M.,Gurprasad, Narine P.,Whitfield, Dennis M.
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p. 1724 - 1733
(2007/10/02)
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