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Publication Fast synthesis of thiolated Au 25 nanoclusters via protection-deprotection method(2012-09-06) Yuan, X.; Yu, Y.; Yao, Q.; Zhang, Q.; Xie, J.; CHEMICAL & BIOMOLECULAR ENGINEERINGThis letter reports a new synthesis strategy for atomically precise Au nanoclusters (NCs) by using a protection-deprotection method. The key in our synthesis strategy is to introduce a surfactant molecule to protect thiolate-Au I complexes during their reduction. The protecting layer provides a good steric hindrance and controls the formation rate of thiolated Au NCs, which leads to the direct formation of atomically precise Au NCs inside the protecting layer. The protecting layer was then removed from the surface of thiolated Au NCs to bring back the original functional groups on the NCs. The protection-deprotection method is simple and facile and can synthesize high-purity thiolated Au 25 NCs within 10 min. Our synthesis protocol is fairly generic and can be easily extended to prepare Au 25 NCs protected by other thiolate ligands. © 2012 American Chemical Society.Publication Experimental and theoretical investigation on the interaction between palladium nanoparticles and functionalized carbon nanotubes for Heck synthesis(2013-09-01) Sun, W.; Liu, Z.; Jiang, C.; Xue, Y.; Chu, W.; Zhao, X.; CHEMICAL & BIOMOLECULAR ENGINEERINGMulti-walled carbon nanotubes (MWNTs) with different defect density and oxygen-containing groups have been prepared and they were utilized as the carriers of palladium based catalysts for Heck synthesis. The catalytic activity, stability and Pd leaching were investigated. Furthermore, characterization techniques such as Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), High-resolution transmission electron microscope (HRTEM), X-ray diffractometer (XRD) and Density Functional Theory (DFT) simulation were employed to investigate the defects impacts on Pd/MWNTs catalysts. The results showed that Pd/MWNTs catalysts had good and similar activity under air atmosphere; while the Pd/MWNTs catalysts with higher defect density were more stable than that of lower defect density. The characterization results revealed that defects on CNTs carrier effectively suppressed the increase of Pd nanoparticle size. The DFT simulation proved that defects on CNTs promoted the redistribution of electrons, which enhanced the Pd-C interaction. Because the high surface energy of Pd nanoparticles was efficiently decreased, less Pd particle size could be found in the system with MWNTs of higher defects density. Meanwhile, defects played a role of new nucleation center for Pd deposition, which suppressed the increase of Pd particle size. © 2012 Elsevier B.V. All rights reserved.Publication Three-dimensionally ordered porous membranes prepared via self-assembly and reverse micelle formation from well-defined amphiphilic block copolymers(2005-04-12) Fu, G.D.; Kang, E.T.; Neoh, K.G.; CHEMICAL & BIOMOLECULAR ENGINEERINGBlock copolymers of poly(pentafluorostyrene) (PFS) and poly(tert-butyl acrylate) (PtBA), or PFS-b-PtBA copolymers, were synthesized via consecutive atom transfer radical polymerizations (ATRPs). Amphiphilic block copolymers of PFS and poly(acrylic acid) (PFS-b-PAAC copolymers) were prepared via hydrolysis of the corresponding PFS-b-PtBA copolymers. The chemical structure and composition of the PFS-b-PtBA and PFS-b-PAAC block copolymers were studied by nuclear magnetic resonance (NMR) spectroscopy, themogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The amphiphilic PFS-b-PAAC copolymers were cast into porous membranes by phase inversion in aqueous media. The surface and cross-sectional morphology of the PFS-b-PAAC membranes were studied by scanning electron microscopy (SEM). Membranes with well-defined pores of sizes in the micrometer range were obtained as a result of inverse micelle formation. The pH of the aqueous media for phase inversion and the PAAC content in the PFS-b-PAAC copolymers could be used to adjust the pore size of the membranes. © 2005 American Chemical Society.Publication Heat removal from reverse flow reactors used in methane combustion(2005-08) Balaji, S.; Lakshminarayanan, S.; CHEMICAL & BIOMOLECULAR ENGINEERINGThe idea of using Reverse Flow Reactors (RFR) for methane reduction in exhausts has been well elucidated in the past. However, there are intricacies in such operations to maintain the ignited state of the reactor along with maintaining low outlet concentrations of methane. This is especially true under rich feed conditions where combustion reactions liberate more heat leading to possible catalyst deactivation. Under favourable conditions, it is possible to continuously extract heat from the RFR system-this is a viable way of maintaining acceptable thermal conditions in the reactor and consequently retaining catalyst activity. This paper elaborates upon the optimal amount of heat that can be removed from the system without losing the sustainability while preventing overheating of the catalyst bed. A simple event based control strategy is implemented for switching the inlet and outlet ports (flow reversal). Issues relating to the operation of reverse flow reactors with side feeding and the possibility of extraction of useful heat from such systems are also discussed. Methane combustion reaction and a continuous two dimensional heterogeneous model of the reactor have been employed in this study.Publication Negotiation-based approach for order acceptance in a multiplant specialty chemical manufacturing enterprise(2011-05-04) Behdani, B.; Adhitya, A.; Lukszo, Z.; Srinivasan, R.; CHEMICAL & BIOMOLECULAR ENGINEERINGOrder acceptance under uncertainty is a challenging problem in supply chain management, especially in make-to-order plants, such as in a specialty chemical manufacturing enterprise. In this work, we consider the effect of rush orders and design a negotiation-based policy for order acceptance. Rush orders pose a complex challenge primarily because the different actors involved (customer and enterprise) have different interests and asymmetric information. In addition, the interaction involves uncertainties both in the short- and long-term. To capture the rich complexity of the problem and provide a conceptual basis for developing agent-based models for such negotiation situation, this paper presents a general framework for negotiation and illustrates it using the customer-enterprise rush order due date negotiation case. On the basis of this framework, an agent-based model is developed. Various experiments are conducted to evaluate the effect of due date negotiation on profit and long-term customer behavior. © 2011 American Chemical Society.Publication Carbon molecular sieve membranes derived from pseudo-interpenetrating polymer networks for gas separation and carbon capture(2011-05) Low, B.T.; Chung, T.S.; NUS NANOSCIENCE & NANOTECH INITIATIVE; CHEMICAL & BIOMOLECULAR ENGINEERINGThe design of polyimide-based pseudo-interpenetrating polymer networks (IPNs) is proposed to tailor the molecular structure of polymeric precursors for fabricating carbon molecular sieve membranes (CMSMs). To demonstrate the feasibility of this concept, pseudo-IPNs comprising of poly(2,3,5,6-phenylene-2, 2′-bis(3,4-carboxylphenyl)hexafluoropropane) diimide (6FDA-TMPDA) and 2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone (azide) are used to fabricate CMSMs. The gas transport properties of CMSMs are dependent on the azide loading and heat treatment temperature. During the pyrolysis, two competing processes of pore evolution from the released gases and molecular transformation are occurring simultaneously. The creation of pores determines the structural morphology of the CMSM at a low pyrolysis temperature of 550 °C while the molecular rearrangement is the governing factor for carbonization at an elevated temperature of 800 °C. The CMSMs prepared at 550 °C display good CO2/N2 separation performance. The 6FDA-TMPDA/azide (90-10) CMSM pyrolyzed at 550 °C shows a CO2 permeability of 9290 ± 170 Barrer and an ideal CO2/N2 selectivity of 26.0 ± 0.8. CMSMs with high CO2/CH4 selectivity can be fabricated by carbonization at 800 °C. The 6FDA-TMPDA/azide (70-30) CMSM prepared at 800 °C has a CO2 permeability of 280 ± 7.0 Barrer and CO2/CH4 selectivity of 164 ± 6.0. The CMSMs derived from polyimide/azide pseudo-IPNs exhibit potential use in pre- and post-combustion CO2 capture. © 2011 Elsevier Ltd. All rights reserved.Publication Asymmetric trans-dihydroxylation of cyclic olefins by enzymatic or chemo-enzymatic sequential epoxidation and hydrolysis in one-pot(2011-09) Xu, Y.; Li, A.; Jia, X.; Li, Z.; CHEMICAL & BIOMOLECULAR ENGINEERINGNovel and efficient one-pot enzymatic and chemo-enzymatic synthetic methods are developed for the asymmetric trans-dihydroxylations of cyclic olefins 1a and 1bvia sequential epoxidation and hydrolysis. The Novozym 435 ®-mediated epoxidation of cyclohexene 1a and subsequent hydrolysis of the intermediate cyclohexene oxide 2a with resting cells of Sphingomonas sp. HXN-200 in one-pot gave (1R,2R)-cyclohexane diol 3a in 84% ee and 95% conversion. trans-Dihydroxylation of N-benzyloxycarbonyl 3-pyrroline 1b with the same enzymatic system gave the corresponding (3R,4R)-N- benzyloxycarbonyl-3,4-dihydroxy-pyrrolidine 3b in 93% ee and 94% conversion. In the one-pot chemo-enzymatic system, epoxidation of N-benzyloxycarbonyl 3-pyrroline 1b by m-CPBA and subsequent hydrolysis of epoxide intermediate 2b with resting cells of Sphingomonas sp. HXN-200 gave the trans-diol (3R,4R)-3b in 92% ee and 94-97% conversion. While the trans-dihydroxylation of cyclohexene 1a to (1R,2R)-cyclohexane diol 3a is reported for the first time, the trans-dihydroxylation of N-benzyloxycarbonyl 3-pyrroline 1b to (3R,4R)-3b with such an enzymatic or chemo-enzymatic system afforded a much higher product concentration than the same reaction with the system using a microorganism containing the two necessary enzymes. The developed one-pot enzymatic and chemo-enzymatic systems for the asymmetric trans-dihydroxylation of olefins are new, easy to prepare, adjust and operate, are high yielding, complementary to Sharpless asymmetric dihydroxylation and particularly useful for the asymmetric synthesis of cyclic trans-diols. © 2011 The Royal Society of Chemistry.Publication Light-Induced Self-Escape of Spherical Nucleic Acid from Endo/Lysosome for Efficient Non-Cationic Gene Delivery(WILEY-V C H VERLAG GMBH, 2020) Shi, Leilei; Wu, Wenbo; Duan, Yukun; Xu, Li; Xu, Yingying; Hou, Lidan; Meng, Xiangjun; Zhu, Xinyuan; Liu, Bin; Prof Bin Liu; MATERIALS SCIENCE AND ENGINEERING; CHEMICAL & BIOMOLECULAR ENGINEERINGDeveloping non-cationic gene carriers and achieving efficient endo/lysosome escape of functional nucleic acids in cytosol are two major challenges faced by the field of gene delivery. Herein, we demonstrate the concept of self-escape spherical nucleic acid (SNA) to achieve light controlled non-cationic gene delivery with sufficient endo/lysosome escape capacity. In this system, Bcl-2 antisense oligonucleotides (OSAs) were conjugated onto the surface of aggregation-induced emission (AIE) photosensitizer (PS) nanoparticles to form core–shell SNA. Once the SNAs were taken up by tumor cells, and upon light irradiation, the accumulative O produced by the AIE PSs ruptured the lysosome structure to promote OSA escape. Prominent in vitro and in vivo results revealed that the AIE-based core–shell SNA could downregulate the anti-apoptosis protein (Bcl-2) and induce tumor cell apoptosis without any transfection reagent. 1 2Publication Fabrication and characterizations of a novel drug delivery device liposomes-in-microsphere (LIM)(2004-09) Feng, S.-S.; Ruan, G.; Li, Q.-T.; CHEMICAL & BIOMOLECULAR ENGINEERINGIn the present work, we developed a novel drug delivery system, liposomes-in-microsphere (LIM) of biodegradable polymers, which is conceived from a combination of the polymer- and the lipid-based delivery systems and can thus integrate the advantages and avoid the drawbacks of the two systems. Liposomes were encapsulated into microspheres of biodegradable polymers by the solvent extraction/evaporation process to form LIMs. The integrity of the liposomes was preserved by modifying the microencapsulation process and coating the liposomes with chitosan. We demonstrated by scanning electron microscopy, laser light scattering and fluorescence spectroscopy that the particle size and surface morphology of the polymeric microspheres did not change significantly with the liposomes encapsulated, the liposomes remained intact within the polymeric matrix of the microspheres, and the encapsulated liposomes could be released from the microspheres in a controlled manner at a nearly constant release rate after an initial off-release period. Decreasing the particle size of liposomes and increasing the pore size of the polymeric matrix shortened the initial off-release period and increased the liposome release rate. In conclusion, a novel drug delivery system, liposomes-in-microsphere, was successfully developed and characterized. The liposome release kinetics could be controlled by the composition and fabrication parameters of the liposomes and polymeric microspheres. Such a novel controlled release system may have potential to be applied for drug delivery and gene therapy. © 2003 Elsevier Ltd. All rights reserved.Publication In silico metabolic model of rhodococcus erythropolis to study and improve desulfurization(2011) Aggarwal, S.; Karimi, I.A.; Lee, D.-Y.; CHEMICAL & BIOMOLECULAR ENGINEERINGThe increasingly stringent rules for ultra-low-sulfur fuels have inspired efforts to improve existing desulfurization techniques and develop new, efficient, and more economical methods. Hydrodesulfurization, the prevalent method for desulfurization, is a chemical process that is energy-intensive, expensive, and incapable of desulfurizing certain recalcitrant sulfur compounds such as benzothiophene, dibenzothiophene (DBT), and their derivatives present in fossil fuels. Studies aimed at evolving new methods of desulfurization have recognized biodesulfurization as a potential alternative. Biodesulfurization involves the use of either enzymes or whole cells for reducing sulfur content of the fossil fuels. It is advantageous, as it can proceed under ambient conditions, does not involve the loss of calorific value, and is relatively economical. Rhodococcus erythropolis IGTS8 was isolated as the first microorganism that can specifically desulfurize polyaromatic sulfur heterocycles (PASHs) such as DBT and its derivatives via the 4S pathway. Over the last two decades, several strains of Rhodococcus have been studied for their desulfurization ability. The desulfurization rates obtained in a biodesulfurization process using naturally occurring bacterial cultures are too low for commercialization. Despite numerous efforts for increased specific desulfurization activity with various manipulations at the genetic level, desirable desulfurization rates are yet to be attained. The complex interactions among the various metabolic pathways and associated reactions largely determine the metabolic fluxes within an organism and hence its cellular activities and phenotypes (here, desulfurization activity). However, most studies have targeted the 4S pathway exclusively, and a holistic systems study of various intracellular activities has not been reported. Therefore, it is critical to study the desulfurizing characteristics of R. erythropolis by considering its interactions and dependence on the other parts of its metabolism. This work represents the very first stoichiometric model of R. erythropolis to study its intracellular metabolic processing of various sulfur compounds. It consists of the sulfur metabolic pathway along with the other biochemical pathways such as central metabolism, amino acids biosynthetic pathways, etc. It describes the dependence of the flux through sulfur metabolism on factors such as the supply of reducing equivalents and demand for sulfur containing precursor metabolites. It has been successfully validated using the experimental data available in literature. The model predicts biomass growth close to the experimental values with the measured DBT uptake rates used as inputs. Moreover, it shows the effects of alternate sulfur sources (i.e., sulfate and DBT) on the growth rates which are in close agreement with the experimental observations. Based on the model findings, we have been able to propose an alternate hypothesis for the effect of sulfate on desulfurizing activity. Successful predictions on the suitability of carbon sources by the model have led us to determine the effectiveness of additional carbon sources and other medium components for achieving higher in silico desulfurizing activity and growth of this biocatalyst. The determination and comparison of the fluxes through other host functions provide insights into the relative influence of the various enzymatic activities on the extent of desulfurization exhibited by R. erythropolis. The analysis of the metabolic network has also enabled us to identify the various metabolic engineering approaches such as gene(s) knockouts, over expression of certain gene(s), etc. that may be instrumental in enhancing the desulfurization activity of R. erythropolis effectively.