Fourth-generation

Figure 9-6N(b). Fleximax high performance random metal packing available in two sizes and reported by manufacturer to be a fourth generation random packing. Used by permission of Koch Engineering Co., Inc., Bull. KFM-1. 

The class A enzymes have Mx values around 30,000. Their substrate specificities are quite variable and a large number of enzymes have emerged in response to the selective pressure exerted by the sometimes abusive utilization of antibiotics. Some of these new enzymes are variants of previously known enzymes, with only a limited number of mutations (1 4) but a significantly broadened substrate spectrum while others exhibit significantly different sequences. The first category is exemplified by the numerous TEM variants whose activity can be extended to third and fourth generation cephalosporins and the second by the NMCA and SME enzymes which, in contrast to all other SXXK (3-lactamases, hydrolyse carbapenems with high efficiency. Despite these specificity differences, the tertiary structures of all class A (3-lactamases are nearly superimposable. 

Recently, leaders in the pharmaceutical industry have developed a list of desired properties for a fourth generation of SERMs (Table 2). In general, future SERMs must oppose endogenous hormone action in the breast and reproductive system while displaying full estrogenic effects in the cardiovasculature, bone and central nervous systems. Additional criteria are that fourth generation compounds possess superior bioavailability compared with existing SERMs and have... 

Selective Sex Steroid Receptor Modulators. Table 2 Criteria for fourth generation SERMs... 

The reason for the low intrinsic viscosities in solution is that dendrimers exist as tightly packed balls. This is by contrast with linear polymers, which tend to form flexible coils. The effect of this difference is that, whereas polymer solutions tend to be of high viscosity, dendrimer solutions are of very low viscosity. In fact, as dendrimers are prepared, their intrinsic viscosity increases as far as the addition of the fourth monomer unit to growing branches (the so-called fourth generation), but this is the maximum value that the viscosity reaches, and as the side chains grow beyond that, the viscosity decreases. 

Johanson C-E, Shuster CR Cocaine, in Psychopharmacology The Fourth Generation of Progress. Edited by Bloom FE, Kupfer DJ. New York, Raven, 1995, pp 1685— 1697... 

Very interesting antenna systems have been constructed by functionalizing the chain ends of a poly(arylether) convergent dendritic backbone with cou-marin-2 A =435 nm) and its focal point with coumarin-343 X =49Q nm) [33] dendrimer 8 represents the fourth generation. 

An interesting example of core shielding is represented by Pd porphyrins surrounded by polyglutamic dendrons up to the fourth generation (24-26) [57]. In... 

A comparison between two families of dendrimers containing polyfaryl ether) dendrons and either a Zn porphyrin (GnPZn) or a tetraphenylporphyrin (G/JTPPH2) core up to the fourth generation (30 and 31) shows that the core... 

In a recent study, poly(aryl ether) dendritic branches terminated with triethyleneglycol chains were attached to Cgg [66] dendrimer 32 represents the fourth generation. The photophysical properties of these fullerodendrimers have been systematically investigated in three solvents, namely toluene, dichloromethane, and acetonitrile. On increasing dendrimer generation, it has been found that in each solvent (i) the maximum of the fullerene fluorescence band is red-shifted... 

Rotzinger, S, Bourin, M, Akimoto, Y, Coutts, RT and Baker, GB (1999) Metabolism of some second and fourth generation antidepressants iprindole, viloxazine, buproprion, mianserin, maprotiline, trazodone, nefazodone and venlafaxine. Cell. Molec. Neurobiol. 19 427 42. 

Heeger, A. J., Semiconducting and metallic polymers the fourth generation of polymeric materials, Nohel lecture, December 8, 2000. 

Smith, A.B. Ill, Freeze, B.S., Xian, M., Hirose, T. (2005) Total Synthesis of (-l-)-Discodermolide A Highly Convergent Fourth-Generation Approach. Organic Letters, 7, 1825-1828. 

Iberer, G., Hahn, R., and Jungbauer, A., Monoliths as stationary phases for separating biopolymers—fourth-generation chromatography sorbents, LC-GC, 17(11), 998, 1999. 

Combination Regimens Cefazolin or cefuroxime plus Meropenem Third- or fourth-generation... 

Newer antimicrobials have not demonstrated superiority in the prevention of SSI and should be reserved for treatment only. Carbapenems, antipseudomonal penicillins, and third-or fourth-generation cephalosporins are not appropriate antibiotics for surgical prophylaxis. Overuse of these antibiotics may contribute to collateral damage and the development of bacterial resistance. 

Because the progression of infection in neutropenic patients can be rapid, empirical antibiotic therapy should be administered quickly to such patients once fever is documented. Currently, the most commonly used initial antibiotic agent is cefipime, a fourth-generation cephalosporin that has good antipseudomonal coverage as well as adequate coverage against viridans streptococci and pneumococci.23... 

Lin, K. M. Poland, R. E. (1995). Ethnicity, Culture, and Psychopharmacology in Psychopharmacology The Fourth Generation of Progress. New York NY Raven Press. 

Frdchet et al. reported the synthesis of a unimolecular micelle (Fig. 6) generated by a convergent approach starting with 3,5-dihydroxybenzyl alcohol, as the key branched monomer unit [65]. Fourth generation dendrimer 15 with 32 carboxylic acid moieties on the periphery was synthesized and its correspond-... 

Moss and Liao [182,183] reported a metallo-dendrimer built by a convergent strategy. An approach similar to that of Frechet was used to synthesize a fourth generation dendrimer containing 48 peripheral ruthenium atoms. 

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