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Wang D.,Institute of Chemical and Engineering Sciences, Singapore
IEEE Transactions on Industrial Informatics | Year: 2011

Making on-specification products is a primary goal, and also a challenge in chemical batch process operation. Due to the uncertainty of raw materials and instability of operating conditions, it may not produce the desired on-spec final product. It would be helpful if one can predict the product quality during each operation, so that one can make adjustments to process conditions in order to make on-spec product. This paper addresses the issue of real-time prediction of final product quality during a batch operation. First, a data-driven modeling approach is presented. This multimodel approach uses available process information up to the current points to capture their time-varying relationships with the final product quality during the course of operation, so that the prognosis of product quality can be obtained in real-time. Then, due to its data-driven nature, the focus is given on how to make the models robust in order to eliminate the effect of noise, especially, outliers in the data. A model-based outlier detection method is presented. The proposed approach is applied to a generic chemical batch case study, with its prediction performance being evaluated. © 2011 IEEE.


Richard J.-A.,Institute of Chemical and Engineering Sciences, Singapore
European Journal of Organic Chemistry | Year: 2014

(+)-Hyperforin (1) is a polyprenylated acylphloroglucinol (PPAP) natural product isolated in 1971 from Hypericum perforatum. Also known as St. John's wort, Hypericum perforatum is a popular medicinal plant because of its antidepressant properties. (+)-Hyperforin (1) is the main component of the plant and has attracted the interest of the scientific community since it was identified as the agent responsible for the antidepressant activity. The subsequent discovery that it also displayed a wide range of biological activities triggered the interest of synthetic chemists because of its appealing, compact molecular structure. This microreview presents an overview of the synthetic studies reported so far for the racemic and enantioselective syntheses of (+)-hyperforin (1) and analogues, and attempts to shed light on the intriguing structure-activity relationships (SARs) of the natural product. (+)-Hyperforin is the main component of the medicinal plant Hypericum perforatum. The broad range of its biological activity has attracted the interest of the synthetic community. This microreview summarizes the chemical approaches directed toward the total synthesis of (+)-hyperforin and its analogues. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Juturu V.,Institute of Chemical and Engineering Sciences, Singapore | Wu J.C.,Institute of Chemical and Engineering Sciences, Singapore
Biotechnology Advances | Year: 2012

Enzymatic depolymerization of hemicellulose to monomer sugars needs the synergistic action of multiple enzymes, among them endo-xylanases (EC 3.2.1.8) and β-xylosidases (EC 3.2.1.37) (collectively xylanases) play a vital role in depolymerizing xylan, the major component of hemicellulose. Recent developments in recombinant protein engineering have paved the way for engineering and expressing xylanases in both heterologous and homologous hosts. Functional expression of endo-xylanases has been successful in many hosts including bacteria, yeasts, fungi and plants with yeasts being the most promising expression systems. Functional expression of β-xylosidases is more challenging possibly due to their more complicated structures. The structures of endo-xylanases of glycoside hydrolase families 10 and 11 have been well elucidated. Family F/10 endo-xylanases are composed of a cellulose-binding domain and a catalytic domain connected by a linker peptide with a (β/α)8 fold TIM barrel. Family G/11 endo-xylanases have a β-jelly roll structure and are thought to be able to pass through the pores of hemicellulose network owing to their smaller molecular sizes. The structure of a β-d-xylosidase belonging to family 39 glycoside hydrolase has been elucidated as a tetramer with each monomer being composed of three distinct regions: a catalytic domain of the canonical (β/α)8 - TIM barrel fold, a β-sandwich domain and a small α-helical domain with the enzyme active site that binds to d-xylooligomers being present on the upper side of the barrel. Glycosylation is generally considered as one of the most important post-translational modifications of xylanases, but a few examples showed functional expression of eukaryotic xylanases in bacteria. The optimal ratio of these synergistic enzymes is very important in improving hydrolysis efficiency and reducing enzyme dosage but has hardly been addressed in literature. Xylanases have been used in traditional fields such as food, feed and paper industries for a longer time but more and more attention has been paid to using them in producing sugars and other chemicals from lignocelluloses in recent years. Mining new genes from nature, rational engineering of known genes and directed evolution of these genes are required to get tailor-made xylanases for various industrial applications. © 2011 Elsevier Inc.


Chen D.Y.-K.,Seoul National University | Pouwer R.H.,Griffith University | Richard J.-A.,Institute of Chemical and Engineering Sciences, Singapore
Chemical Society Reviews | Year: 2012

In this tutorial review, recent advances in the synthesis of cyclopropane-containing natural products are discussed, highlighting the application of novel synthetic methodologies and innovative synthetic strategies in the construction of highly functionalized cyclopropanes. The examples showcased herein aim to inspire students and practitioners of organic synthesis to seek further advances in the chemical synthesis of cyclopropanes, both in the context of target-oriented syntheses and method developments. © 2012 The Royal Society of Chemistry.


Richard J.-A.,Institute of Chemical and Engineering Sciences, Singapore | Pouwer R.H.,Institute of Chemical and Engineering Sciences, Singapore | Chen D.Y.-K.,Seoul National University
Angewandte Chemie - International Edition | Year: 2012

With their fascinating biological profiles and stunningly complex molecular architectures, the polycyclic polyprenylated acylphloroglucinols (PPAPs) have long provided a fertile playing field for synthetic organic chemists. In particular, the recent advent of innovative synthetic methods and strategies together with C-C bond-forming reactions and asymmetric catalysis have revitalized this field tremendously. Consequently, PPAP targets which once seemed beyond reach have now been synthesized. This Review aims to highlight the recent achievements in the total synthesis of PPAPs, as well as notable methods developed for the construction of the bicyclo[3.3.1] core of these chemically and biologically intriguing molecules. Recently completed total syntheses and the ingenious synthetic approaches developed for the construction of the biologically significant polycyclic polyprenylated acylphloroglucinols (PPAPs) are presented in this Review. The state-of-the-art synthetic methods and strategies, current limitations, as well as the outlook for this field are highlighted. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Khoo H.H.,Institute of Chemical and Engineering Sciences, Singapore
Renewable and Sustainable Energy Reviews | Year: 2015

A review of 55 pretreatment and bio-conversion methods for the production of lignocellulose-ethanol was carried out. Bio-conversion studies include enzymatic fermentation, simultaneous saccharification and fermentation, process modelling, supply chain simulations, Life Cycle Assessment and other experimental studies. A new sustainability indicator labeled Land Footprint, from farm-to-fuel, was introduced. The Land Footprint (LF) results are projected for bio-ethanol derived from stover and switchgrass from U.S., sugarcane bagasse from Brazil and India, and rice husk and straw from China and India. In order to produce 1 million L bio-ethanol, bagasse and rice straw are observed to have the highest potential to be sustainable resources that demand the least amount of agricultural land. The Land Footprints for both countries are 85 ha-yr for bagasse-ethanol and 80 ha-yr for China rice straw-ethanol. The Land Footprints per 1 million bio-ethanol from switchgrass and stover in the U.S. are 140 ha-yr and 366 ha-yr, respectively. Utilizing stover as a feedstock, an estimated LF of 14.7 million ha-yr is required to satisfy up to 50% of U.S.'s year 2022 bio-ethanol mandate. The more efficient switchgrass-ethanol would require 4.4-6.6 million ha-yr agricultural land to meet 40-60% of bio-ethanol demands for year 2022. As the most productive crop per hectare of land, sugarcane bagasse require about 2.4 million ha-yr land to supply sufficient amount of bagasse to meet up to 60% of bio-ethanol national demands. © 2015 Elsevier Ltd. All rights reserved.


Ding H.,Institute of Chemical and Engineering Sciences, Singapore | Chen D.Y.-K.,Institute of Chemical and Engineering Sciences, Singapore
Angewandte Chemie - International Edition | Year: 2011

A core challenge: The asymmetric formal syntheses of the title compounds have been accomplished. By using a modular approach, phenolic tosylamide 1 was synthesized through palladium cross-couplings (blue bonds), and its participation in a hypervalent iodine mediated oxidative coupling reaction (red bonds) enabled the construction of the challenging heterocyclic core of (-)-phalarine. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Thomas G.L.,Institute of Chemical and Engineering Sciences, Singapore | Johannes C.W.,Institute of Chemical and Engineering Sciences, Singapore
Current Opinion in Chemical Biology | Year: 2011

There is a paucity of chemical matter suitably poised for effective drug development. Improving the quality and efficiency of research early on in the drug discovery process has been a long standing objective for the drug industry and improvements to the accessibility and quality of compound screening decks might have a significant and positive impact. In the absence of specific molecular information that can be modeled and used predicatively we are far from identifying which small molecules are most relevant to emerging biological targets such as protein-protein interactions. Natural products have been historically successful as an entry point for drug discovery and recently screening libraries are being synthesized to emulate natural product like features. © 2011.


Zhang X.,Institute of Chemical and Engineering Sciences, Singapore
Electrochimica Acta | Year: 2011

This work investigates the heat generation characteristics of a cylindrical lithium-ion battery. The battery consists of the graphite, LiPF6 of the propylene carbonate/ethylene carbonate/dimethyl carbonate (PC/EC/DMC) solution, and spinal as anode, electrolyte and cathode, respectively. The coupled electrochemical-thermal model is developed with full consideration of electrolyte transport properties as functions of temperature and Li ion concentration. A truly conservative finite volume numerical method is employed for the spatial discretization of the model equations. Three types of heat generation sources including the ohmic heat, the active polarization heat and the reaction heat are quantitatively analyzed for the battery discharge process. The ohmic heat is found to be the largest contribution with around 54% in the total heat generation. About 30% of the total heat generation in average is ascribed to the electrochemical reaction. The active polarization contributes the least comparing to the ohmic heat and reactions heat. The results also show that the Li ion concentration and its gradient in electrolyte are the main factors giving the effect on the heat generations of active polarization and electrolyte electric resistance. The raised temperature in the battery discharge is positive related with the thickness of both separator and electrodes. © 2010 Elsevier Ltd. All rights reserved.


Chew W.,Institute of Chemical and Engineering Sciences, Singapore
Journal of Raman Spectroscopy | Year: 2011

A methodology of multivariate chemometric techniques based on the information-theoretic approach was applied for elucidating chemical reaction information from a Raman data array Rm × v that arises from in situ reaction monitoring. This reaction-induced dynamic dataset R m × v can be contaminated by random cosmic ray spikes found in the midst of characteristic spectral variations associated with the disappearance or emergence of Raman active reactants, intermediates and products. Such spurious cosmic spikes were identified and removed using a novel and fast numerical approach based on maximum and minimum spectral entropy principles while preserving the genuine reaction-induced spectral variations. Subsequently, the band-target entropy minimization (BTEM) algorithm, a minimum spectral entropy based self-modeling curve resolution technique, was applied to recover the pure component spectra of Raman active chemical species. Information gain through the chemometric analyses was calculated using information entropies with base 2 logarithm. This sequence of information-theoretic chemometric analyses (or transinformations) was successfully tested on the reaction spectral data obtained from alcoholysis of acetic anhydride, which contains four Raman active chemical species. It is envisioned that this series of multivariate statistical analyses will be useful in chemical reaction studies and process analytical technology (PAT) applications that utilize in situ Raman spectroscopy to monitor transient dynamic changes in chemical concentrations, and also in Raman microscopy/imaging data containing spatial variations. © 2010 John Wiley & Sons, Ltd.

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