170,145 research outputs found
Metallocalix[n]arenes in catalysis: A 13-year update
No full textAside from their applications in the fields of ion extraction, gas storage and molecular sensors, calixarenes have been extensively employed as ligands for metal complexation. Moreover, metallocalix[n]arenes have shown interesting catalytic activity in a plethora of reactions proving, in many cases, superior to other systems bearing different ligand scaffolds. In this review, we summarize the latest advances (post-2008) in the field, categorizing the complexes by metal center
Use of titanium complexes bearing diphenolate or calix[n]arene ligands in α-olefin polymerization and the ROP of cyclic esters
No full textIn this review, we discuss the use of titanium complexes bearing either bridged diphenolate or calix[n]arene (n = 4, 6, 8) ligation, in the formation of plastics from α-olefins or via the ring opening polymerization (ROP) of cyclic esters. The syntheses, molecular structures and catalytic behaviour of these systems are discussed, as well as where possible, the properties of the resultant polymers
Synthesis of Biodegradable Polymers: A Review on the Use of Schiff-Base Metal Complexes as Catalysts for the Ring Opening Polymerization (ROP) of Cyclic Esters
No full textThis review describes the recent advances (from 2008 onwards) in the use of Schiff-base metal complexes as catalysts for the ring opening polymerization (ROP) of cyclic esters. The synthesis and structure of the metal complexes, as well as all aspects concerning the polymerization process and the characteristics of the polymers formed, will be discussed
Benefits of the chelate effect: Preparation of an unsymmetrical ansa-bis(imido)molybdenum complex containing a seven-membered chelate ring
No full textSiemeling U, Turk T, Schoeller W, Redshaw C, Gibson VC. Benefits of the chelate effect: Preparation of an unsymmetrical ansa-bis(imido)molybdenum complex containing a seven-membered chelate ring. INORGANIC CHEMISTRY. 1998;37(18):4738-4739
Synthesis and structures of mono- and di-nuclear aluminium and zinc complexes bearing α-diimine and related ligands, and their use in the ring opening polymerization of cyclic esters
No full textA series of organoaluminium imino-amido complexes of the type {[ArNC(Me2)C(Me)NAr]AlMe2} (Ar = 2,6-iPr2C6H3 (1), Ar = 2,6-Et2C6H3 (2); Ar = 2,6-Me2C6H3 (3) have been prepared via reaction of AlR3 and the respective α-diimine. Similar reaction of the bis(α-diimine) [ArNC(Me)C(Me)N-]2 (Ar = 2,6-iPr2C6H3) with AlMe3 afforded the bimetallic complex [ArN-C(Me)2C(Me)NAlMe2]2 (4), whilst reaction of the acetyl-imino compound [OC(Me)C(Me)NAr] (Ar = 2,6-Et2C6H3) with AlMe3 afforded the bimetallic complex {[OCMe2CH(Me)NAr]AlMe2}2 (5). In related organozinc chemistry, we have isolated {[ArNC(Me)(Et)C(Me)NAr]ZnEt} (Ar = 2,6-iPr2C6H3, 6) and the trinuclear complex {[ArNC(Me)COCHCO(Me)C(Me)NAr][OCH(Me)C(Me)NAr](ZnEt)3} (Ar = 2,6-iPr2C6H3, 7) from reactions of ZnEt2 with ArNC(Me)C(Me)NAr or [OC(Me)C(Me)NAr], respectively. Reaction of the bis(α-diimine), LiPr-N2-ArCH2Ar-N2, derived from 4,4′-methylenebis(2,6-diisopropylaniline), with ZnCl2 affords [LiPr-N2-ArCH2Ar-N2(ZnCl2)2] (8). The molecular structures of complexes 1-8 are reported. Preliminary results of the ability of 1-8, along with the previously reported metal-metal bonded complex {[ArNC(Me)C(Me)NAr]Al(THF)}2 (9), to act as catalysts for the ring opening polymerization (ROP) of the cyclic esters ϵ-caprolactone (ϵ-CL), δ-valerolactone (δ-VL) and rac-lactide (r-LA) are presented. For ϵ-CL and δ-VL, best results were obtained using the metal-metal bonded complex 9. For r-LA, the Al-based systems exhibited moderate activity affording only liquid oligomers, whilst the Zn-based systems performed better affording at 80 °C isotactic PLA with Mnca. 10 kDa with conversions of up to 66%. The co-polymerization of ϵ-CL with δ-VL was also examined, and differing preferences were noted for monomer incorporation
Lithofacies variations within the Wessex Formation and their influence on coastal stability
No full textRare-earth metal complexes derived from the acids Ph2C(X)CO2H (X= OH, NH2): Structural and ring opening polymerization (ROP) studies.
No full textTreatment of Ln(NO3)3.6H2O (Ln = La, Ce) with an equimolar amount of 2,2’-diphenylglycine (DpgH) in ethanol afforded the corresponding hexacoordinated complexes (DpgH±)3Ln(NO3)3.H2O (DpgH± = zwitterionic 2,2’-diphenylglycine, Ln = La (1), Ce (2)). The spectroscopic and structural features of these compounds have been investigated. Similar reactions with the related benzilic acid (BenzH2) were unsuccessful. The catalytic behaviour of 1 and 2 in the homo- and copolymerization of epsilon-caprolactone (epsilon-CL) and rac-lactide (r-LA) has been investigated herein. In the case of epsilon-CL, the two complexes exhibited comparable activity, allowing for complete monomer conversion under aerobic and solvent-free conditions at 150 °C in 24 h. With respect to the ROP of r-LA, 1 was found to be completely inactive, while only 8% conversion was achieved in the presence of 2. Liquid oligomers were isolated during epsilon-CL/r-LA co-polymerization in the presence of both complexes. The catalytic activity of the pre-ligands DpgH and BenzH2 (i.e. metal-free) was also examined. Interestingly, only BenzH2 was found to be active, although it required a higher catalyst loading and the presence of benzyl alcohol as co-activator
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Comparative assessment of marine weathering of ROP-derived biopolymers against conventional plastics
No full textBio-based plastics were designed to replace single-use plastics and to cause less post-consumer environmental damage. This paper assesses the weathering of four bio-based polymers created by ring opening polymerization (ROP) promoted by a previously reported Ti-based catalyst, to detect any problems before production was scaled up. Samples were aged in seawater to identify degradation products and monitor structural changes. Surfaces evidenced degradation and a range of leaching products was observed. Aside from compounds used in the preparation of the plastics (i.e. residual monomers and benzyl alcohol), the degradation products included carboxylic acids (often found in plastic leachate), oxacyclohexadecan-2-one (potentially toxic to aquatic life) and triphenylmethane (potential carcinogen). Overall, there were fewer structural changes in the fossil fuel based polymer (PS) and in the commercially available bio-based plastic studied for comparison purposes than the lab based bio-based polymers
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