Density Functional Study of Crystalline Analogs of Polycarbonates

Montanari, B.; Ballone, Pietro; Jones, R.

doi:10.1021/ma980770j

Cited by 16 publications

(36 citation statements)

References 34 publications

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“…Since the main dipolar group in BPA-PC is the carbonyl one, this assignment would justify the marked asymmetry of the dielectric c-relaxation, presenting the loss maximum in the high frequency side. The identification of the isolated component with the motions of the carbonyl group would also be supported by the comparison of the activation energy value obtained (29.5 kJ mol À1 ) with those reported in the literature [7,9,11] for the processes assigned to the carbonyl motion (around 30 kJ mol À1 ) and with that obtained from calculations on analogous of polycarbonates (36 kJ mol À1 ) [12]. Nevertheless, other molecular mechanism could be responsible for such relaxation component.…”

Section: Discussionsupporting

confidence: 77%

Effect of cold-drawing on the secondary dielectric relaxation of bisphenol-A polycarbonate

Mitxelena¹,

Colmenero²,

Alegría³

2005

Journal of Non-Crystalline Solids

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Section: Discussionsupporting

confidence: 77%

Effect of cold-drawing on the secondary dielectric relaxation of bisphenol-A polycarbonate

Mitxelena¹,

Colmenero²,

Alegría³

2005

Journal of Non-Crystalline Solids

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“…The corresponding N-C 6 -C 7 -N 4 dihedral angle of ca. 120° found in penicillins (38), for example, would therefore be only accessible to 1 after surmounting an energy barrier of several kilocalories (39). We have previously reported that the X = NH analogues of 1 , where the barrier would be even higher, are not substrates or inhibitors of the P99 β-lactamase or of the structurally similar Streptomyces R61 DD-peptidase (24).…”

Section: Resultsmentioning

confidence: 99%

Kinetics and Mechanism of Inhibition of a Serine β-Lactamase by O-Aryloxycarbonyl Hydroxamates

Pelto

Pratt

2008

Biochemistry

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The class C serine β-lactamase of Enterobacter cloacae P99 is irreversibly inhibited by Oaryloxycarbonyl hydroxamates. A series of these new inhibitors has been prepared to investigate the kinetics and mechanism of the inactivation reaction. A pH-rate profile for the reaction indicated that the reactive form of the inhibitor is neutral rather than anionic. The reaction rate is enhanced by electron-withdrawing aryloxy substituents and by hydrophobic substitution on both aryloxy and hydroxamate groups. Kinetics studies show that the rates of loss of the two possible leaving groups, aryloxide and hydroxamate are essentially the same as the rate of enzyme inactivation. Nucleophilic trapping experiments prove, however, that the aryloxide is the first to leave. It is likely, therefore, that the rate-determining step of inactivation is the initial acylation reaction, most likely of the active site serine, yielding a hydroxamoyl-enzyme intermediate. This then partitions between hydrolysis and aminolysis by Lys 315, the latter to form an inactive, cross-linked active site. A previously described crystal structure of the inactivated enzyme shows a carbamate cross-link of Ser 64 and Lys 315. Structure-activity studies of the reported compounds suggest that they do not react at the enzyme active site in the same way as normal substrates. In particular, it appears that the initial acylation by these compounds does not involve the oxyanion hole, an unprecedented departure from known and presumed reactivity. Molecular modeling suggests that an alternative oxyanion hole may have been recruited, consisting of the side chain functional groups of Tyr 150 and Lys 315. Such an alternative mode of reaction may lead to the design of novel inhibitors.For decades now, β-lactams have been one of our most effective weapons against bacterial infections (1). These drugs, although still the first line of attack in many clinical situations, have been compromised to a considerable degree by bacterial resistance to them (2). Among various sources of resistance that have arisen in bacteria, the most generally troublesome is the production of β-lactamases. These enzymes very effectively catalyze the hydrolysis and thus destruction of β-lactams before they can reach their cellular targets (3).The threat posed by β-lactamases to the efficacy of β-lactam antibiotics has been tackled by pharmaceutical companies in several ways. One approach that has been quite successful to date is that of including a β-lactamase inhibitor with a β-lactam antibiotic in combination therapies. For many years now, such combinations, using the now-classical β-lactamase inhibitors clavulanic acid, sulbactam and tazobactam, have been used to advantage (4). Since these inhibitors are themselves β-lactams, however, it is perhaps not surprising to find that certain β-lactamase mutants are capable of hydrolyzing them quite effectively. Such mutants have †

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“…1. This polymer has been extensively studied with both first-principles methods [4][5][6] and coarse-grained molecular dynamics simulations. 7 To understand the nature of adhesion it is necessary to consider processes which occur at different time, length, and temperature scales and therefore a multiscale study is desirable.…”

Section: Introductionmentioning

confidence: 99%

Polymer adhesion: First-principles calculations of the adsorption of organic molecules onto Si surfaces

Johnston

Nieminen

2007

Phys. Rev. B

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The structures and energetics of organic molecules adsorbed onto clean and H-passivated Si͑001͒-͑2 ϫ 1͒ surfaces have been calculated using density functional theory. For benzene adsorbed on the clean Si surface the tight-bridge structure was found to be stable and the butterfly structure metastable. Both carbonic acid, H 2 CO 3 , and propane, C 3 H 8 , dissociate on contact with the surface. Passivation of the Si surface with H atoms has a dramatic effect on the surface properties. The passivated surface is very inert and the binding energy of all the molecules is very weak.

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Density Functional Study of Crystalline Analogs of Polycarbonates

Cited by 16 publications

References 34 publications

Effect of cold-drawing on the secondary dielectric relaxation of bisphenol-A polycarbonate

Effect of cold-drawing on the secondary dielectric relaxation of bisphenol-A polycarbonate

Kinetics and Mechanism of Inhibition of a Serine β-Lactamase by O-Aryloxycarbonyl Hydroxamates

Polymer adhesion: First-principles calculations of the adsorption of organic molecules onto Si surfaces

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