Light olefins (c&) can be converted to a mixture of higher molecular weight olefins via a sequence of acid-catalyzed-shape-selective polymerization and isomerization reactions over the ZSM-5 zeolite catalyst. T h e composition and molecular weight of the product are very dependent on reaction temperature and pressure through both thermodynamic and kinetic constraints. Distillate-range olefins having an almost petrochemical-type structure with high-quality fuel properties are produced a t relatively high pressure (30-100-bar) and lower temperature (200-300 "C) conditions. At lower pressure and higher temperature, lower molecular weight products are formed, including aromatics and saturates from olefin condensation and hydrogen-transfer reactions.

Using the zeolite ZSM-5, new technology has been developed for catalytically oligomerizing light olefins (C, to C, ) to gasoline (C, to C,,,) and diesel (C,o to C2J range product. This reaction produces product constrained by both the shape selectivity of the zeolite catalyst and the thermodynamics governing the oligomerization reaction. S. SCOPEMany refinery and synthetic fuel processes produce effect shape selectivity has on product chemistry and large amounts of light C,/C, olefins which can then b e to determine what effects thermodynamics have on catalytically oligomerized to gasoline-or diesel-range constraining molecular weight. The relationship of products. A new development in this area is the use of these effects to commercial oligomerization technolshape-selective zeolite catalysts. This reaction has ogy is also discussed. been studied over ZSM-5 catalyst to determine what CONCLUSIONS AND SIGNIFICANCEThe reaction of light olefins over ZSM-5 catalyst was product molecular weight is shown up to -625 K to be found to proceed sequentially by reaction to discrete governed by the kinetics of the reaction, dependent on oligomers, followed by cracking and copolymerization. temperature, pressure, and space velocity. Above The shape of the product molecules is governed pri--625 K equilibrium constraints become important and marily by the pore structure of zeolite catalyst. The limit the molecular weight of the product. ExperimentalIn general, all experiments were conducted in high-pressure pilot-plant reactors capable of operating up to approximately 18,000 kPa. The reactors used were enclosed in either a three-or four-zone furnace with an isothermal zone, holding from 10 to 100 cm' of catalyst. Reactor pressure was maintained by a gas phase backpressure control valve, while liquid depressurization was by liquid level control on a high-pressure phase separator. Product analysis was by both gas chromatography and mass spectrometry.

Metabolic engineering of N-linked oligosaccharide biosynthesis to produce novel glycoforms or glycoform distributions of a recombinant glycoprotein can potentially lead to an improved therapeutic performance of the glycoprotein product. A mathematical model for the initial stages of this process, up to the first galactosylation of an oligosaccharide, was previously developed by Umana and Bailey (1997) (UB1997). Building on this work, an extended model is developed to include further galactosylation, fucosylation, extension of antennae by N-acetyllactosamine repeats, and sialylation. This allows many more structural features to be predicted. A number of simplifying assumptions are also relaxed to incorporate more variables for the control of glycoforms. The full model generates 7565 oligosaccharide structures in a network of 22,871 reactions. Methods for solving the model for the complete product distribution and adjusting the parameters to match experimental data are also developed. A basal set of kinetic parameters for the enzyme-catalyzed reactions acting on free oligosaccharide substrates is obtained from the previous model and existing literature. Enzyme activities are adjusted to match experimental glycoform distributions for Chinese Hamster Ovary (CHO). The model is then used to predict the effect of increasing expression of a target glycoprotein on the product glycoform distribution and evaluate appropriate metabolic engineering strategies to return the glycoform profile to its original distribution pattern. This model may find significant utility in the future to predict glycosylation patterns and direct glycoengineering projects to optimize glycoform distributions.

Effective representation and characterization of biosynthetic pathways of glycosylation can be facilitated by mathematical modeling. This paper describes the expansion of a previously developed detailed model for N-linked glycosylation with the further application of the model to analyze MALDI-TOF mass spectra of human N-glycans in terms of underlying cellular enzyme activities. The glycosylation reaction network is automatically generated by the model, based on the reaction specificities of the glycosylation enzymes. The use of a molecular mass cutoff and a network pruning method typically limits the model size to about 10,000 glycan structures. This allows prediction of the complete glycan profile and its abundances for any set of assumed enzyme concentrations and reaction rate parameters. A synthetic mass spectrum from model-calculated glycan profiles is obtained and enzyme concentrations are adjusted to bring the theoretically calculated mass spectrum into agreement with experiment. The result of this process is a complete characterization of a measured glycan mass spectrum containing hundreds of masses in terms of the activities of 19 enzymes. In addition, a complete annotation of the mass spectrum in terms of glycan structure is produced, including the proportions of isomers within each peak. The method was applied to mass spectrometric data of normal human monocytes and monocytic leukemia (THP1) cells to derive glycosyltransferase activity changes underlying the differences in glycan structure between the normal and diseased cells. Model predictions could lead to a better understanding of the changes associated with disease states, identification of disease-associated biomarkers, and bioengineered glycan modifications.