Fused-core

Tetracyclines are a family of antibiotics which display a characteristic 4-fused-core ring structure (Figure 1.16). They exhibit broad antimicrobial activity and induce their effect by inhibiting protein synthesis in sensitive microorganisms. Chlortetracycline was the first member of this family to be discovered (in 1948). Penicillin G and streptomycin were the only antibiotics in use at that time, and chlortetracycline was the first antibiotic employed therapeutically that retained its antimicrobial properties upon oral administration. Since then, a number of additional tetracyclines have been discovered (all produced by various strains of Streptomyces), and a variety of semi-synthetic derivatives have also been prepared (Table 1.18). 

During the mechanical loading of the fuse core, small sections more than 2mm long are sometimes not filled with BlkPdr due to malfunction of mechanical parts. These faults are only observed when they interrupt the propagation of the flame when the fuse is ignited. These undetected faults can cause safety problems to workers in the field and also considerable loss of time... 

Fig. 8 HPLC-MS/MS chromatograms for multiclass analysis of illicit drugs obtained by normal bore (a) and fused core (b) columns...

Good efficiency and shorter analysis time are keys of the usefulness of this new technology for the determination of illicit drugs in biological samples [66, 89]. In Fig. 8 we report chromatograms obtained with analytical column and chromatograms obtained with a core shell (or fused core) column. 

It should bs secured by either snueezlng the sides of the fuse gently with thin nllers or hv pounding the ends of the fuse gently with small banner All thet is required Is to crimp the oulekmetch and the fuse core Into firm contact. 

As an alternative to wholly porous sub-2-pm particles, 1.7-pm fused-core particles surrounded by a 0.5-pm porous silica layer with 90 A pores, have emerged. In a comparative study, substantially lower back pressure was reported when the fused-core particles were used. This allowed for columns to be coupled in series, which increased the peak efficiency up to 92,750 plates (164). Wider-pore fused-core particles have an average pore diameter of 160 A. The wider-pore particles are particularly useful for increased sample loading and the rapid separation of peptides using volatile mobile phases (165). 

Salisbury, J.J., Fused-core particles A practical alternative to sub-2 micron particles, J. Chromatogr. Sci., 46(10), 883, 2008. 

Hsieh, Y., Duncan, C.J., and Brisson, J.M., Fused-core silica column high-performance liquid chromatography/tandem mass spectrometric determination of rimonabant in mouse plasma, Anal. Chem., 79(15), 5668, 2007. 

Cunliffe, J.M. and Maloney, T.D., Fused-core particle technology as an alternative to sub-2-microm particles to achieve high separation efficiency with low backpressure, J. Sep. Sci., 30(18), 3104, 2007. 

An important advantage of ULE (Coming) is the possibility to fabricate lightweight blanks because of the low density of 2.21 g.cm 3 of the glass itself (glass ceramics have values between 2.5 and 2,6 g.cm"3) and because of using special machined and fused core structures and bonding techniques [67]. 

It should be mentioned that there is another type of relatively new column that is made from the 2.7-pm fused-core silica particles, bonded with C18 alkyl chains, by fusing a 0.5-pm porous silica layer onto 1.7-pm non-porous silica cores. The selectivity of the fused-core particle columns is very similar to that of certain <2-pm C18 columns and has the advantage of a substantially lower back-pressure at much higher flow rates, which allows rapid separations to be performed even routinely on a conventional LC system without significant loss in efficiency or resolution. The fused-core columns are new to antibiotic analysis and may serve as good alternatives to <2-pm columns in the field. 

Abrahim A, Al-Sayah M, Skrdla P, Bereznitski Y, Chen Y, Wu N, Practical comparison of 2.7 p.m fused-core silica particles and porous sub-2 p.m particles for fast separations in pharmaceutical process development, J. Pharmaceut. Biomed.Anal. 2010 51(1) 131-137. 

Tarm (l/3A ) = 1/9A/. The force at the midpoint of the core CmiA depends on its structure. If the star has a linear core (Fig. 27a), in each of the three sets of arms add up to ffmid = 3parallel bonds (Fig. 27b), c aid in each of the three parallel links would scale ffmid = parallel links in the center of the core. parallel links, tj d has the form... 

Unlike previous researchers, Xue and Agarwal were more interested in the effect of core structure on the shear stability of star-shaped polymers. They synthesized six-arm star poly(methyl methacrylate) (PMMA) bearing either a linear core (A, M = 2,350 kDa) or a fused core (B, M = 2,100 kDa) (Fig. 31) [228,... 

Fig. 31 Star-shaped PMMA polymers bearing (a) a linear core and (b) a fused core in Xue and Agarwal s work [228]...

Fig. 32 (a) Representative size exclusion chromatography traces of samples for star PMMA with a linear core at different number of passes indicated in the legend. The dashed line represents the peak position of the original star molecules and the dotted line represents that of the arms, (b) Peak molecular weight of the degraded star molecules (solid symbols) and arms (open symbols). Square and circular symbols denote fused core and linear core, respectively. (Adopted with permission from Xue et al. [228]. Copyright 2005 American Chemical Society)... 

Make use of miniaturization use shorter and above all thinner columns - be careful of possible overloading with the main peak/the matrix - use smaller par-ticles/fused core materials. 

Packing material classical CIS columns (e.g.. Symmetry CIS, SunFire), monolith (e.g., Chromolith Performance and HR), hybrid materials (e.g., XBridge ClS/Shield, Gemini-NX), Fused Core (e.g., Kinetex, Accucore, Ascentis Express), Mixed Mode Phases (e.g., Primesep C, Obehsc N/R). 

Of course, with <2 pm particles and/or 20 mm columns, fused core materials, high throughput columns and Chromolith HR, we have noticed tailing and peak broadening due to the instrumental dead volume, especially with the early peaks - even with modern equipment But for simple separations we can live with the loss of 20-40% efficiency, because whether a peak has a peak width of 3 or 4 s will, due to the narrow peak form and a satisfactory separation, not usually be registered from the user as a disadvantage - and then it is no problem. 

Fig. 4 High-pressure fast gradient separation of natural phenolic antioxidants, (a) Ascentis Express CIS column with fused core 2.7 Jtm CIS particles with a thin porous outer shell (0.5 p.m), 30 X 3.0 mm I.D. at 1.5 ml/min, 53 MPa. (b) Acquity BEH Phenyl column with totally porous particles in 1.7 Jtm particles at 1.5 ml/min, 74 MPa, UV detection, 254 nm. Sample 1, gallic acid 2, protocatechine 3, esculine 4, chlorogenic acid 5, caffeine 6, epicatechine 7, vanilline S, rutine 9, sinapic acid 10, hesper-idine 11,4-hydroxycoumarine 12, morine 13, quercetine 14, 7-hydroxyflavone.

The most recent approach in fast LC methodology for the analysis of pesticide residues in food has been presented. UHPLC, using either sub-2 am particle size column or fused-core column technologies, is becoming a reliable alternative to GC-MS methodologies for the analysis of pesticides, with sub-2 am columns being the most popular ones. 

Recently, another type of stationary phase known as fused-core or core-shell technology came onto the market in 2007 and it provides similar performance to... 

Synthesis of tetrahydroimidazo[2,l-a]isoquinolines is another example of the reaction s utility in a fused core synthesis. Formation of compounds of structure 57 starts with 7-phenyl-5,6,7,8-tetrahydroiso-quinoline (56) amination in either DMA or tetralin in autoclave at 220 C for 18 h, which gives 53 in 41-48% yield, consecutively, although a higher yield is achieved when heating the starting material in DMA in the microwave for 12 h, which gives 58 in a 59% yield. The product is then used to construct the tetrahydroimidazo[2,l-a]isoquinoline framework using chloroacetone or 3-bromobutanone, which affords 58a,b in 46% and 75% yields, respectively... 

Figure 22-17 van Deemter curves Plate height as a function of linear flow rate (mtn/s) for microporous (Hgure 22-18) stationary phase particle diameters of 5A 3-5, and 1.8 icm. as well as superficially porous (or fused-core) particles (Rgure 22-19) with a diameter of 2.7 p.m and a 0.5- i,m porous layer thickness. Measurements for naphthalene eluted from Cu-silica (50 mm long x 4.6 mm diameter) with 60 vol% acetonitrile/40 vol% H,0 at 24 C. (Courtesy MAC-MOO Analytical, Chadds Ford, RA.]... 

Figure 22-19 shows rapid separation of proteins on superficially porous particles (also called fused-core particles), which consist of a 0.25-p.m-thick porous silica layer on a 5-p,m-diameter nonporous silica core. A stationary phase such as C]g is bonded throughout the thin, porous outer layer. Diffusion of solute into a... 

Fused-core Fused-core particle Short diffnsion path Lower back pressure Higher solvent... 

Song, W, Pabbisetty, D., Groeber, E.A., Steenwyk, R.C., Past, D.M. (2009) Comparison of fused-core and conventional particle size columns by LC-MS/MS and UV apphcation to pharmacokinetic study. Journal of Pharmaceutical and Biomedical Analysis, 50,491-500. 

Addressing the allenylpyridine instability problem, Gevorgyan developed the Cu(I)-catalyzed cycloisomerization of conjugated alkynyl imines 317, perfect allene 318 surrogates, as an alternative route for the construction of indolizine and other pyrrole-fused cores 319 (Scheme 9.110) [291-293]. This protocol proved to be very general and efficient for the synthesis of a variety of diversely functionalized C3-substituted heterocycles 319. On the other hand, this approach was not applicable... 

Dysinosin A is a highly oxygenated novel inhibitor of thrombin and factor Vila. Hanessian and co-workers employed a ring-closing metathesis strategy in their preparation of the 6,5-fused core of dysinosin A." Olefin metathesis of 206 and 208 using only 1 mol % of 4 gave quantitative yields... 

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