Publications by authors named "Christian V Stevens"

123 Publications

Learning Molecular Representations for Thermochemistry Prediction of Cyclic Hydrocarbons and Oxygenates.

J Phys Chem A 2021 Jun 3;125(23):5166-5179. Epub 2021 Jun 3.

Laboratory for Chemical Technology, Department of Materials, Textiles and Chemical Engineering, Ghent University, Technologiepark 125, 9052 Gent, Belgium.

Accurate thermochemistry estimation of polycyclic molecules is crucial for kinetic modeling of chemical processes that use renewable and alternative feedstocks. In kinetic model generators, molecular properties are estimated rapidly with group additivity, but this method is known to have limitations for polycyclic structures. This issue has been resolved in our work by combining a geometry-based molecular representation with a deep neural network trained on data. Each molecule is transformed into a probabilistic vector from its interatomic distances, bond angles, and dihedral angles. The model is tested on a small experimental dataset (200 molecules) from the literature, a new medium-sized set (4000 molecules) with both open-shell and closed-shell species, calculated at the CBS-QB3 level with empirical corrections, and a large G4MP2-level QM9-based dataset (40 000 molecules). Heat capacities between 298.15 and 2500 K are calculated in the medium set with an average deviation of about 1.5 J mol K and the standard entropy at 298.15 K is predicted with an average error below 4 J mol K. The standard enthalpy of formation at 298.15 K has an average out-of-sample error below 4 kJ mol on a QM9 training set size of around 15 000 molecules. By fitting NASA polynomials, the enthalpy of formation at higher temperatures can be calculated with the same accuracy as the standard enthalpy of formation. Uncertainty quantification by means of the ensemble standard deviation is included to indicate when molecules that are on the edge or outside of the application range of the model are evaluated.
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http://dx.doi.org/10.1021/acs.jpca.1c01956DOI Listing
June 2021

Cytosolic delivery of gadolinium via photoporation enables improved in vivo magnetic resonance imaging of cancer cells.

Biomater Sci 2021 Jun 26;9(11):4005-4018. Epub 2021 Apr 26.

Laboratory of General Biochemistry and Physical Pharmacy, Faculty of Pharmaceutical Science, Ghent University, Ottergemsesteenweg 460, 9000 Ghent, Belgium.

Longitudinal in vivo monitoring of transplanted cells is crucial to perform cancer research or to assess the treatment outcome of cell-based therapies. While several bio-imaging techniques can be used, magnetic resonance imaging (MRI) clearly stands out in terms of high spatial resolution and excellent soft-tissue contrast. However, MRI suffers from low sensitivity, requiring cells to be labeled with high concentrations of contrast agents. An interesting option is to label cells with clinically approved gadolinium chelates which generate a hyperintense MR signal. However, spontaneous uptake of the label via pinocytosis results in its endosomal sequestration, leading to quenching of the T-weighted relaxation. To avoid this quenching effect, delivery of gadolinium chelates directly into the cytosol via electroporation or hypotonic cell swelling have been proposed. However, these methods are also accompanied by several drawbacks such as a high cytotoxicity, and changes in gene expression and phenotype. Here, we demonstrate that nanoparticle-sensitized laser induced photoporation forms an attractive alternative to efficiently deliver the contrast agent gadobutrol into the cytosol of both HeLa and SK-OV-3 IP1 cells. After intracellular delivery by photoporation the quenching effect is clearly avoided, leading to a strong increase in the hyperintense T-weighted MR signal. Moreover, when compared to nucleofection as a state-of-the-art electroporation platform, photoporation has much less impact on cell viability, which is extremely important for reliable cell tracking studies. Additional experiments confirm that photoporation does not induce any change in the long-term viability or the migratory capacity of the cells. Finally, we show that gadolinium 'labeled' SK-OV-3 IP1 cells can be imaged in vivo by MRI with high soft-tissue contrast and spatial resolution, revealing indications of potential tumor invasion or angiogenesis.
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http://dx.doi.org/10.1039/d1bm00479dDOI Listing
June 2021

Endocrine disrupting potency and toxicity of novel sophorolipid quaternary ammonium salts.

Ecotoxicology 2021 May 17;30(4):658-666. Epub 2021 Mar 17.

Faculty of Engineering and Architecture, Department of Materials, Textile and Chemical Engineering, Ghent University, Technologiepark 914, B-9052, Ghent-Zwijnaarde, Belgium.

A new class of biosurfactants, namely quaternary ammonium sophorolipids (SQAS), suitable for pharmaceutical applications, was tested for the evaluation of their (anti)estrogenic and (anti)androgenic potency with the help of YES/YAS assays. Also their toxicity towards yeasts (Saccharomyces cerevisiae) and bacteria (Escherichia coli) was checked. The results achieved for SQAS, which can be regarded as potential micropollutants, were compared with those obtained for two well-known micropollutants diclofenac and 17α-ethinylestradiol subjected to the same testing procedures. This work demonstrated that acetylation of the hydroxyl group of the carbohydrate head of SQAS decreased the toxicity of this class of biosurfactants towards Saccharomyces cerevisiae. Furthermore, it contributed to the decrease of their endocrine disrupting potency. None of the SQAS studied showed clear agonist activity for female or male hormones. SQAS1 and SQAS2 revealed weak antiestrogenic and antiandrogenic potency. All of these properties were weaker, not only to the potency of the appropriate positive control in the antagonists bioassays, but also compared to the potency of other tested compounds, i.e. DCF and EE2. SQAS3 possessed most probably inhibitory activity towards male hormones. Moreover, cytotoxicity of two out of four studied SQAS at the highest concentrations towards the strains of Saccharomyces cerevisiae interfered with the endocrine disruption activity. It would be also worth studying it with the use of another endocrine activity test.
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http://dx.doi.org/10.1007/s10646-021-02378-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8060166PMC
May 2021

Overview of N-Rich Antennae Investigated in Lanthanide-Based Temperature Sensing.

Chemistry 2021 May 16;27(25):7214-7230. Epub 2021 Mar 16.

Department of Green Chemistry and Technology, Ghent University, Ghent, Belgium.

The market share of noncontact temperature sensors is expending due to fast technological and medical evolutions. In the wide variety of noncontact sensors, lanthanide-based temperature sensors stand out. They benefit from high photostability, relatively long decay times and high quantum yields. To circumvent their low molar light absorption, the incorporation of a light-harvesting antenna is required. This Review provides an overview of the nitrogen-rich antennae in lanthanide-based temperature sensors, emitting in the visible light spectrum, and discusses their temperature sensor ability. The N-rich ligands are incorporated in many different platforms. The investigation of different antennae is required to develop temperature sensors with diverse optical properties and to create a diverse offer for the multiple application fields. Molecular probes, consisting of small molecules, are first discussed. Furthermore, the thermometer properties of ratiometric temperature sensors, based on di- and polynuclear complexes, metal-organic frameworks, periodic mesoporous organosilicas and porous organic polymers, are summarized. The antenna mainly determines the application potential of the ratiometric thermometer. It can be observed that molecular probes are operational in the broad physiological range, metal-organic frameworks are generally very useful in the cryogenic region, periodic mesoporous organosilica show temperature dependency in the physiological range, and porous organic polymers are operative in the cryogenic-to-medium temperature range.
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http://dx.doi.org/10.1002/chem.202100007DOI Listing
May 2021

Continuous Flow Synthesis of Metal-NHC Complexes*.

Chemistry 2021 Mar 3;27(18):5653-5657. Epub 2021 Mar 3.

Department of Chemistry and Centre for Sustainable Chemistry, Ghent University, Krijgslaan 281,S-3, 9000, Ghent, Belgium.

The use of weak bases and mild conditions is currently the most sustainable and attractive synthetic approach for the preparation of late-transition metal complexes, some of which are widely used in catalysis, medicinal chemistry and materials science. Herein, the use of cuprate, aurate or palladate species for a continuous flow preparation of Cu , Au and Pd -NHC complexes is reported. All reactions examined proceed under extremely mild conditions and make use of technical grade acetone as solvent. The scalability of the process was exemplified in a multigram-scale synthesis of [Cu(IPr)Cl].
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http://dx.doi.org/10.1002/chem.202100190DOI Listing
March 2021

Quantifying the Likelihood of Structural Models through a Dynamically Enhanced Powder X-Ray Diffraction Protocol.

Angew Chem Int Ed Engl 2021 Apr 8;60(16):8913-8922. Epub 2021 Mar 8.

Center for Molecular Modeling (CMM), Ghent University, Technologiepark 46, 9052, Zwijnaarde, Belgium.

Structurally characterizing new materials is tremendously challenging, especially when single crystal structures are hardly available which is often the case for covalent organic frameworks. Yet, knowledge of the atomic structure is key to establish structure-function relations and enable functional material design. Herein, a new protocol is proposed to unambiguously predict the structure of poorly crystalline materials through a likelihood ordering based on the X-ray diffraction (XRD) pattern. Key of the procedure is the broad set of structures generated from a limited number of building blocks and topologies, which is submitted to operando structural characterization. The dynamic averaging in the latter accounts for the operando conditions and inherent temporal character of experimental measurements, yielding unparalleled agreement with experimental powder XRD patterns. The proposed concept can hence unquestionably identify the structure of experimentally synthesized materials, a crucial step to design next generation functional materials.
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http://dx.doi.org/10.1002/anie.202017153DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8048908PMC
April 2021

Strongly Reducing (Diarylamino)benzene-Based Covalent Organic Framework for Metal-Free Visible Light Photocatalytic HO Generation.

J Am Chem Soc 2020 Nov 13;142(47):20107-20116. Epub 2020 Nov 13.

COMOC - Center for Ordered Materials, Organometallics and Catalysis, Department of Chemistry, Ghent University, Krijgslaan 281-S3, 9000 Ghent, Belgium.

Photocatalytic reduction of molecular oxygen is a promising route toward sustainable production of hydrogen peroxide (HO). This challenging process requires photoactive semiconductors enabling solar energy driven generation and separation of electrons and holes with high charge transfer kinetics. Covalent organic frameworks (COFs) are an emerging class of photoactive semiconductors, tunable at a molecular level for high charge carrier generation and transfer. Herein, we report two newly designed two-dimensional COFs based on a (diarylamino)benzene linker that form a Kagome () lattice and show strong visible light absorption. Their high crystallinity and large surface areas (up to 1165 m·g) allow efficient charge transfer and diffusion. The diarylamine (donor) unit promotes strong reduction properties, enabling these COFs to efficiently reduce oxygen to form HO. Overall, the use of a metal-free, recyclable photocatalytic system allows efficient photocatalytic solar transformations.
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http://dx.doi.org/10.1021/jacs.0c09684DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7705891PMC
November 2020

Structural and Photophysical Properties of Various Polypyridyl Ligands: A Combined Experimental and Computational Study.

Chemphyschem 2020 11 28;21(22):2489-2505. Epub 2020 Oct 28.

Center for Molecular Modeling (CMM), Ghent University, Technologiepark 46, 9052, Zwijnaarde, Belgium.

Covalent triazine frameworks (CTFs) with polypyridyl ligands are very promising supports to anchor photocatalytic complexes. Herein, we investigate the photophysical properties of a series of ligands which vary by the extent of the aromatic system, the nitrogen content and their topologies to aid in selecting interesting building blocks for CTFs. Interestingly, some linkers have a rotational degree of freedom, allowing both a trans and cis structure, where only the latter allows anchoring. Therefore, the influence of the dihedral angle on the UV-Vis spectrum is studied. The photophysical properties are investigated by a combined computational and experimental study. Theoretically, both static and molecular dynamics simulations are performed to deduce ground- and excited state properties based on density functional theory (DFT) and time-dependent DFT. The position of the main absorption peak shifts towards higher wavelengths for an increased size of the π-system and a higher π-electron deficiency. We found that the position of the main absorption peak among the different ligands studied in this work can amount to 271 nm; which has a significant impact on the photophysical properties of the ligands. This broad range of shifts allows modulation of the electronic structure by varying the ligands and may help in a rational design of efficient photocatalysts.
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http://dx.doi.org/10.1002/cphc.202000592DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7756581PMC
November 2020

Chemical Genetics Approach Identifies Abnormal Inflorescence Meristem 1 as a Putative Target of a Novel Sulfonamide That Protects Catalase2-Deficient against Photorespiratory Stress.

Cells 2020 09 2;9(9). Epub 2020 Sep 2.

VIB Center for Plant Systems Biology, B-9052 Ghent, Belgium.

Alterations of hydrogen peroxide (HO) levels have a profound impact on numerous signaling cascades orchestrating plant growth, development, and stress signaling, including programmed cell death. To expand the repertoire of known molecular mechanisms implicated in HO signaling, we performed a forward chemical screen to identify small molecules that could alleviate the photorespiratory-induced cell death phenotype of mutants lacking HO-scavenging capacity by peroxisomal catalase2. Here, we report the characterization of pakerine, an -sulfamoyl benzamide from the sulfonamide family. Pakerine alleviates the cell death phenotype of mutants exposed to photorespiration-promoting conditions and delays dark-induced senescence in wild-type leaves. By using a combination of transcriptomics, metabolomics, and affinity purification, we identified abnormal inflorescence meristem 1 (AIM1) as a putative protein target of pakerine. AIM1 is a 3-hydroxyacyl-CoA dehydrogenase involved in fatty acid β-oxidation that contributes to jasmonic acid (JA) and salicylic acid (SA) biosynthesis. Whereas intact JA biosynthesis was not required for pakerine bioactivity, our results point toward a role for β-oxidation-dependent SA production in the execution of HO-mediated cell death.
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http://dx.doi.org/10.3390/cells9092026DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7563276PMC
September 2020

N-Rich Porous Polymer with Isolated Tb -Ions Displays Unique Temperature Dependent Behavior through the Absence of Thermal Quenching.

Chemistry 2020 Dec 14;26(67):15596-15604. Epub 2020 Oct 14.

Department of Green Chemistry and Technology, Ghent University, Campus Coupure, Coupure Links 653, 9000, Ghent, Belgium.

The challenge of measuring fast moving or small scale samples is based on the absence of contact between sample and sensor. Grafting lanthanides onto hybrid materials arises as one of the most promising accurate techniques to obtain noninvasive thermometers. In this work, a novel bipyridine based porous organic polymer (bpyDAT POP) was investigated as temperature sensor after grafting with Eu(acac) and Tb(acac) complexes. The bpyDAT POP successfully showed temperature-dependent behavior in the 10-310 K range, proving the potential of amorphous, porous organic frameworks. We observed unique temperature dependent behavior. More intriguingly, instead of the standard observed change in emission as a result of a change in temperature for both Eu and Tb , the emission spectrum of Tb remained constant. This work provides framework- and energy-based explanations for the observed phenomenon. The conjugation in the bpyDAT POP framework is interrupted, creating energetically isolated Tb environments. Energy transfer from Tb to Eu is therefore absent, nor energy back transfer from Tb to bpyDAT POP ligand (i.e. no thermal quenching) is detected.
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http://dx.doi.org/10.1002/chem.202002009DOI Listing
December 2020

Self-assembly of Tween 80 micelles as nanocargos for oregano and trans-cinnamaldehyde plant-derived compounds.

Food Chem 2020 Oct 5;327:126970. Epub 2020 May 5.

Particle and Interfacial Technology Group (PaInT), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, Gent 9000, Belgium.

The self-assembly of Tween 80 (T80) micelles loaded with plant-based oregano essential oil (OR) and trans-cinnamaldehyde (TCA) was studied. The effect of different factors, including the surfactant to oil ratio, the presence of sodium chloride, thermal treatment, and dilution on their formation and physicochemical stability was evaluated. The creation of nano-cargos was confirmed by TEM. The self-associated structures had z-average droplet diameters of 92 to 337 nm without any energy input. Whereas addition of 10% (w/v) NaCl prevented the formation of oregano essential oil nano-assemblies of T80, swollen micelles containing TCA were successfully produced. Moreover, the OR or TCA loaded-micelles had only a slight droplet size variation upon thermal treatment. Ultimately, their antibacterial activity analysis against some food pathogens revealed that the encapsulation of OR and TCA within micelles crucially improved their antibacterial activity. These straightforward and cost-effective designed systems can be applicable in different products, including foods and agrochemicals.
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http://dx.doi.org/10.1016/j.foodchem.2020.126970DOI Listing
October 2020

Single-molecule lamellar hydrogels from bolaform microbial glucolipids.

Soft Matter 2020 Mar;16(10):2528-2539

Sorbonne Université, Centre National de la Recherche Scientifique, Laboratoire de Chimie de la Matière Condensée de Paris, LCMCP, F-75005 Paris, France.

Lipid lamellar hydrogels are rare soft fluids composed of a phospholipid lamellar phase instead of fibrillar networks. The mechanical properties of these materials are controlled by defects, induced by local accumulation of a polymer or surfactant in a classical lipid bilayer. Herein we report a new class of lipid lamellar hydrogels composed of one single bolaform glycosylated lipid obtained by fermentation. The lipid is self-organized into flat interdigitated membranes, stabilized by electrostatic repulsive forces and stacked in micrometer-sized lamellar domains. The defects in the membranes and the interconnection of the lamellar domains are responsible, from the nano- to the micrometer scales, for the elastic properties of the hydrogels. The lamellar structure is probed by combining small angle X-ray and neutron scattering (SAXS, SANS), the defect-rich lamellar domains are visualized by polarized light microscopy while the elastic properties are studied by oscillatory rheology. The latter show that both storage G' and loss G'' moduli scale as a weak power-law of the frequency, that can be fitted with fractional rheology models. The hydrogels possess rheo-thinning properties with second-scale recovery. We also show that ionic strength is not only necessary, as one could expect, to control the interactions in the lamellar phase but, most importantly, it directly controls the elastic properties of the lamellar gels.
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http://dx.doi.org/10.1039/c9sm02158bDOI Listing
March 2020

Techno-economic evaluation of a biorefinery applying food waste for sophorolipid production - A case study for Hong Kong.

Bioresour Technol 2020 May 27;303:122852. Epub 2020 Jan 27.

School of Energy and Environment, City University of Hong Kong, Kowloon, Hong Kong. Electronic address:

This study evaluates the techno-economic feasibility of sophorolipid (SL) production process that co-utilizes food waste, glucose and oleic acid as substrates. Two variables are considered in terms of (a) Plant construction: Purchasing equipment either from the US or Mainland China and (b) Production: to produce SL crystals (about 97% active) or a concentrated SL liquid/syrup (about 78% active). Hence, four scenarios are generated: Scenario I: equipment made in the USA + SL crystals; Scenario II: equipment made in the USA + SL syrup; Scenario III: equipment made in China + SL crystals; Scenario IV: equipment made in China + SL syrup. It is found that all scenarios are economically feasible and Scenario I has the highest net profit. Scenario III has the highest internal rate of return, net present value and the shortest payback period at a 7% discount rate. Finally, comparison of food waste-related techno-economic studies was conducted.
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http://dx.doi.org/10.1016/j.biortech.2020.122852DOI Listing
May 2020

Molecular priming as an approach to induce tolerance against abiotic and oxidative stresses in crop plants.

Biotechnol Adv 2020 May - Jun;40:107503. Epub 2019 Dec 31.

Department of Molecular Stress Physiology, Center of Plant Systems Biology and Biotechnology, Plovdiv 4000, Bulgaria; Department of Plant Physiology and Molecular Biology, University of Plovdiv, Plovdiv 4000, Bulgaria. Electronic address:

Abiotic stresses, including drought, salinity, extreme temperature, and pollutants, are the main cause of crop losses worldwide. Novel climate-adapted crops and stress tolerance-enhancing compounds are increasingly needed to counteract the negative effects of unfavorable stressful environments. A number of natural products and synthetic chemicals can protect model and crop plants against abiotic stresses through induction of molecular and physiological defense mechanisms, a process known as molecular priming. In addition to their stress-protective effect, some of these compounds can also stimulate plant growth. Here, we provide an overview of the known physiological and molecular mechanisms that induce molecular priming, together with a survey of the approaches aimed to discover and functionally study new stress-alleviating chemicals.
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http://dx.doi.org/10.1016/j.biotechadv.2019.107503DOI Listing
May 2020

Optical Properties of Isolated and Covalent Organic Framework-Embedded Ruthenium Complexes.

J Phys Chem A 2019 Aug 1;123(32):6854-6867. Epub 2019 Aug 1.

Center for Molecular Modeling (CMM) , Ghent University , Technologiepark 46 , 9052 Zwijnaarde , Belgium.

Heterogenization of RuL complexes on a support with proper anchor points provides a route toward design of green catalysts. In this paper, Ru(II) polypyridyl complexes are investigated with the aim to unravel the influence on the photocatalytic properties of varying nitrogen content in the ligands and of embedding the complex in a triazine-based covalent organic framework. To provide fundamental insight into the electronic mechanisms underlying this behavior, a computational study is performed. Both the ground and excited state properties of isolated and anchored ruthenium complexes are theoretically investigated by means of density functional theory and time-dependent density functional theory. Varying the ligands among 2,2'-bipyridine, 2,2'-bipyrimidine, and 2,2'-bipyrazine allows us to tune to a certain extent the optical gaps and the metal to ligand charge transfer excitations. Heterogenization of the complex within a CTF support has a significant effect on the nature and energy of the electronic transitions. The allowed transitions are significantly red-shifted toward the near IR region and involve transitions from states localized on the CTF toward ligands attached to the ruthenium. The study shows how variations in ligands and anchoring on proper supports allows us to increase the range of wavelengths that may be exploited for photocatalysis.
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http://dx.doi.org/10.1021/acs.jpca.9b05216DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6698874PMC
August 2019

Fundamental Study on the Salt Tolerance of Oregano Essential Oil-in-Water Nanoemulsions Containing Tween 80.

Langmuir 2019 08 26;35(32):10572-10581. Epub 2019 Jul 26.

Nematology Research Unit, Department of Biology , Ghent University , K.L. Ledeganckstraat 35 , 9000 Gent , Belgium.

This study provides fundamental information about the influence of salt on the physicochemical stability of oregano essential oil (EO) and its main components incorporated in a nanoemulsion delivery system containing Tween 80 (T80) emulsifier. The emulsion stability was found to be strongly correlated with the lipid phase composition and the type of salts. The oregano essential oil nanoemulsions remained stable for several weeks in the absence of salts. Moreover, they were insensitive to tetrabutylammonium bromide, whereas similar to carvacrol emulsions, they exhibited a rapid phase separation and oiling-off in the presence of sodium chloride. On the other hand, high oleic sunflower oil (HOSO) and -cymene emulsions remained stable in the presence of NaCl. Addition of 70 and 80% HOSO to the lipid phase of oregano EO and carvacrol, respectively, was found to be sufficient for the formation of emulsions with a high stability to 1.7 M NaCl. Hereby, the morphology of the oregano EO emulsions after 30 days of storage in the presence of NaCl was visualized using a transmission electron microscope. The determination of the surface load and area per surfactant molecule by interfacial tension (IFT) measurements and quartz crystal microbalance with dissipation revealed the dehydration of the polyoxyethylene groups of T80 in the presence of salt. The thickness of the T80 adsorbed layer onto solid hydrophobic and hydrophilic surfaces was significantly lower ( < 0.05) in the presence of sodium chloride. It is hypothesized that a combination of Ostwald ripening and coalescence due to an IFT increase and dehydration was responsible for the instability of the emulsions containing the more polar oregano EO and carvacrol in the presence of salt. The results obtained in this study could be useful for the formulation of essential oil nanoemulsions in the presence of salts applicable in food, pharmaceutical, and personal care products.
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http://dx.doi.org/10.1021/acs.langmuir.9b01620DOI Listing
August 2019

Fruity flavors from waste: A novel process to upgrade crude glycerol to ethyl valerate.

Bioresour Technol 2019 Oct 28;289:121574. Epub 2019 May 28.

Center for Microbiology Ecology and Technology (CMET), Ghent University, Coupure Links 653, 9000 Ghent, Belgium(2); CAPTURE, Belgium(3).

Valeric acid and its ester derivatives are chemical compounds with a high industrial interest. Here we report a new approach to produce them from crude glycerol, by combining propionic acid fermentation with chain elongation. Propionic acid was produced by Propionibacterium acidipropionici (8.49 ± 1.40 g·L). In the subsequent mixed population chain elongation, valeric acid was the dominant product (5.3 ± 0.69 g·L) of the chain elongation process. Residual glycerol negatively impacted the selectivity of mixed culture chain elongation towards valeric acid, whereas this was unaffected when Clostridium kluyveri was used as bio-catalyst. Valeric acid could be selectively isolated and upgraded to ethyl valerate by using dodecane as extractant and medium for esterification, whereas shorter-chain carboxylic acids could be recovered by using a 10 wt% solution of trioctylphosphine oxide (TOPO) in dodecane. Overall, our work shows that the combined fermentation, electrochemistry and homogeneous catalysis enables fine chemical production from side streams.
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http://dx.doi.org/10.1016/j.biortech.2019.121574DOI Listing
October 2019

Electrophilic Bromination in Flow: A Safe and Sustainable Alternative to the Use of Molecular Bromine in Batch.

Molecules 2019 Jun 4;24(11). Epub 2019 Jun 4.

SynBioC research Group, Department of Green Chemistry and Technology, Ghent University, Coupure Links 653, 9000 Ghent, Belgium.

Bromination reactions are crucial in today's chemical industry since the versatility of the formed organobromides makes them suitable building blocks for numerous syntheses. However, the use of the toxic and highly reactive molecular bromine (Br) makes these brominations very challenging and hazardous. We describe here a safe and straightforward protocol for bromination in continuous flow. The hazardous Br or KOBr is generated in situ by reacting an oxidant (NaOCl) with HBr or KBr, respectively, which is directly coupled to the bromination reaction and a quench of residual bromine. This protocol was demonstrated by polybrominating both alkenes and aromatic substrates in a wide variety of solvents, with yields ranging from 78% to 99%. The protocol can easily be adapted for the bromination of other substrates in an academic and industrial environment.
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http://dx.doi.org/10.3390/molecules24112116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6600453PMC
June 2019

Lipid-Based Quaternary Ammonium Sophorolipid Amphiphiles with Antimicrobial and Transfection Activities.

ChemSusChem 2019 Aug 1;12(15):3642-3653. Epub 2019 Jul 1.

SynBioC, Department of Green Chemistry and Technology, Ghent University, Coupure Links 653, 9000, Ghent, Belgium.

Twelve new quaternary ammonium sophorolipids with long alkyl chains on the nitrogen atom were synthesized starting from oleic and petroselinic acid-based sophorolipids. These novel derivatives were evaluated for their antimicrobial activity against selected Gram-negative and Gram-positive bacteria and their transfection efficacies on three different eukaryotic cell lines in vitro as good activities were demonstrated for previously synthesized derivatives. Self-assembly properties were also evaluated. All compounds proved to possess antimicrobial and transfection properties, and trends could be observed based on the length of the nitrogen substituent and the total length of the sophorolipid tail. Moreover, all long-chain quaternary ammonium sophorolipids form micelles, which proved to be a prerequisite to induce antimicrobial activity and transfection capacity. These results are promising for future healthcare applications of long-chained quaternary ammonium sophorolipids.
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http://dx.doi.org/10.1002/cssc.201900721DOI Listing
August 2019

Use of (modified) natural adsorbents for arsenic remediation: A review.

Sci Total Environ 2019 Aug 19;676:706-720. Epub 2019 Apr 19.

Department of Green Chemistry and Technology, Ghent University (UGent), Coupure Links 653, 9000 Ghent, Belgium.

Arsenic (As) is a ubiquitous element found in the atmosphere, soils and rocks, natural waters and organisms. It is one of the most toxic elements and has been classified as a human carcinogen (group I). Arsenic contamination in the groundwater has been observed in >70 countries, like Bangladesh, India, West Bengal, Myanmar, Pakistan, Vietnam, Nepal, Cambodia, United States and China. About 200 million people are being exposed to excessive As through consumption of contaminated drinking water. Therefore, developing affordable and efficient techniques to remove As from drinking water is critical to protect human health. The currently available technologies include coagulation-flocculation, adsorption, ion exchange, electrochemical conversion and membrane technologies. However, most of the aforementioned treatment techniques require high initial and maintenance costs, and skilled manpower on top of that. Nowadays, adsorption has been accepted as a suitable removal technology, particularly for developing regions, because of its simple operation, potential for regeneration, and little toxic sludge generation. Processes based on the use of natural, locally available adsorbents are considered to be more accessible for developing countries, have a lower investment cost and a lower environmental impact (CO emission). To increase their performance, these materials may be chemically modified. Hence, this review paper presents progress of adsorption technologies for remediation of As contaminated water using chemically modified natural materials.
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http://dx.doi.org/10.1016/j.scitotenv.2019.04.237DOI Listing
August 2019

Asymmetrical, Symmetrical, Divalent, and Y-Shaped (Bola)amphiphiles: The Relationship between the Molecular Structure and Self-Assembly in Amino Derivatives of Sophorolipid Biosurfactants.

J Phys Chem B 2019 05 19;123(17):3841-3858. Epub 2019 Apr 19.

Laboratory for Chemical Technology (LCT), Department of Materials, Textiles and Chemical Engineering , Ghent University , Technologiepark 125 , 9052 Ghent , Belgium.

Conventional head-chain but also more exotic divalent, Gemini, or bolaform amphiphiles have in common well-defined hydrophilic and hydrophobic blocks with often a predictable self-assembly behavior. However, new categories of amphiphiles, such as microbial biosurfactants, challenge such conventional understanding because of the poorly defined boundaries between the hydrophilic and hydrophobic portions. Microbial glycolipids, such as sophorolipids, rhamnolipids, or cellobioselipids, interesting biodegradable, nontoxic, alternatives to synthetic surfactants, all represent interesting examples of atypical amphiphiles with partially predictable self-assembly properties. However, their limited molecular diversity strongly limits their application potential. For this reason, we used them as ready-made platform to prepare a whole class of new derivatives. In particular, a broad range of amino derivatives of sophorolipid biosurfactant was recently prepared with the goal of producing biobased antimicrobial and transfection agents, of which the efficiency strongly depends on their molecular structure and unpredictable self-assembly behavior. The new compounds contain a set of asymmetrical and symmetrical bolaamphiphiles, the latter with three or four hydrophilic centers, divalent amphiphiles with asymmetric polar headgroups and even Y-shaped amphiphiles, bearing two sophorose groups connected to one nitrogen atom. In this contribution, we employ small-angle X-ray scattering to establish a relationship between their peculiar molecular structures and the self-assembly properties in water. We find that all divalent and Y-shaped compounds form micelles, of which the hydrophilic shell is composed of a bulky sophorose-C ( x = 8,11)-amine moiety, with aggregation numbers between 30 and 100. On the contrary, most symmetrical and asymmetrical bolaamphiphiles display poor self-assembly properties, generally showing aggregation numbers below 20, especially in the presence of either short spacers or large spacers containing hydrophilic centers.
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http://dx.doi.org/10.1021/acs.jpcb.9b01013DOI Listing
May 2019

Design and visualization of second-generation cyanoisoindole-based fluorescent strigolactone analogs.

Plant J 2019 04 12;98(1):165-180. Epub 2019 Feb 12.

SynBioC Research Group, Department of Green Chemistry and Technology, Campus Coupure, Ghent University, Coupure Links 653, 9000, Ghent, Belgium.

Strigolactones (SLs) are a family of terpenoid allelochemicals that were recognized as plant hormones only a decade ago. They influence a myriad of both above- and below-ground developmental processes, and are an important survival strategy for plants in nutrient-deprived soils. A rapidly emerging approach to gain knowledge on hormone signaling is the use of traceable analogs. A unique class of labeled SL analogs was constructed, in which the original tricyclic lactone moiety of natural SLs is replaced by a fluorescent cyanoisoindole ring system. Biological evaluation as parasitic seed germination stimulant and hypocotyl elongation repressor proved the potency of the cyanoisoindole strigolactone analogs (CISAs) to be comparable to the commonly accepted standard GR24. Additionally, via a SMXL6 protein degradation assay, we provided molecular evidence that the compounds elicit SL-like responses through the natural signaling cascade. All CISAs were shown to exhibit fluorescent properties, and the high quantum yield and Stokes shift of the pyrroloindole derivative CISA-7 also enabled in vivo visualization in plants. In contrast to the previously reported fluorescent analogs, CISA-7 displays a large similarity in shape and structure with natural SLs, which renders the analog a promising tracer to investigate the spatiotemporal distribution of SLs in plants and fungi.
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http://dx.doi.org/10.1111/tpj.14197DOI Listing
April 2019

Domino reaction of a gold catalyzed 5-endo-dig cyclization and a [3,3]-sigmatropic rearrangement towards polysubstituted pyrazoles.

Org Biomol Chem 2018 12;16(48):9359-9363

Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Campus Coupure, Coupure Links 653, B-9000 Ghent, Belgium.

Pyrazoles are important heterocyclic compounds with a broad range of biological activities. A new procedure toward tri- or tetrasubstituted pyrazoles has been developed, via a one-pot gold catalyzed synthesis from hydrazines with alkynyl aldehydes or ketones. The reaction proceeds through consecutive hydrazone formation, 5-endo-dig cyclization and an aza-Claisen rearrangement resulting in the desired polysubstitued pyrazoles.
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http://dx.doi.org/10.1039/c8ob02807aDOI Listing
December 2018

Recovering Actives in Multi-Antitarget and Target Design of Analogs of the Myosin II Inhibitor Blebbistatin.

Front Chem 2018 24;6:179. Epub 2018 May 24.

Department of Molecular Technology, Institute of Chemistry, University of Tartu Tartu, Estonia.

In multitarget drug design, it is critical to identify active and inactive compounds against a variety of targets and antitargets. Multitarget strategies thus test the limits of available technology, be that in screening large databases of compounds vs. a large number of targets, or in using methods for understanding and reliably predicting these pharmacological outcomes. In this paper, we have evaluated the potential of several approaches to predict the target, antitarget and physicochemical profile of ()-blebbistatin, the best-known myosin II ATPase inhibitor, and a series of analogs thereof. Standard and augmented structure-based design techniques could not recover the observed activity profiles. A ligand-based method using molecular fingerprints was, however, able to select actives for myosin II inhibition. Using further ligand- and structure-based methods, we also evaluated toxicity through androgen receptor binding, affinity for an array of antitargets and the ADME profile (including assay-interfering compounds) of the series. In conclusion, in the search for ()-blebbistatin analogs, the dissimilarity distance of molecular fingerprints to known actives and the computed antitarget and physicochemical profile of the molecules can be used for compound design for molecules with potential as tools for modulating myosin II and motility-related diseases.
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http://dx.doi.org/10.3389/fchem.2018.00179DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5976736PMC
May 2018

Atom- and Mass-economical Continuous Flow Production of 3-Chloropropionyl Chloride and its Subsequent Amidation.

Chemistry 2018 Aug 13;24(45):11779-11784. Epub 2018 Jul 13.

Department of Green Chemistry and Technology, Ghent University, Coupure Links 653, 9000, Ghent, Belgium.

3-Chloropropionyl chloride is a chemically versatile building block with applications in the field of adhesives, pharmaceuticals, herbicides and fungicides. Its current production entails problems concerning safety, prolonged reaction times and the use of excessive amounts of chlorinating reagents. We developed a continuous flow procedure for acid chloride formation from acrylic acid and a consecutive 1,4-addition of hydrogen chloride generating 3-chloropropionyl chloride, as presented in this paper. Up to 94 % conversion was reached in 25 minutes at mild temperatures and pressures. This continuous flow method offers a safer alternative and is highly efficient in terms of consumption of starting product and shorter residence time. Valorization of this building block is exemplified by the synthesis of beclamide, a compound with sedative and anticonvulsant properties. Over 80 % conversion towards this drug was achieved in 1 minute in a continuous flow setup. Further research is needed to telescope the synthesis of 3-chloropropionyl chloride and subsequent beclamide formation without intermediate purification.
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http://dx.doi.org/10.1002/chem.201802208DOI Listing
August 2018

Medicinal Chemistry and Use of Myosin II Inhibitor ( S)-Blebbistatin and Its Derivatives.

J Med Chem 2018 11 21;61(21):9410-9428. Epub 2018 Jun 21.

Research Group SynBioC, Department of Green Chemistry and Technology, Faculty of Bioscience Engineering , Ghent University, Campus Coupure , Coupure Links 653 bl. B , 9000 Gent , Belgium.

( S)-Blebbistatin, a chiral tetrahydropyrroloquinolinone, is a widely used and well-characterized ATPase inhibitor selective for myosin II. The central role of myosin II in many normal and pathological biological processes has been revealed with the aid of this small molecule. The first part of this manuscript provides a summary of myosin II and ( S)-blebbistatin literature from a medicinal chemist's perspective. The second part of this perspective deals with the physicochemical deficiencies that trouble the use of ( S)-blebbistatin in advanced biological settings: low potency and solubility, fluorescence interference, (photo)toxicity, and stability issues. A large toolbox of analogues has been developed in which particular shortcomings have been addressed. This perspective provides a necessary overview of these developments and presents guidelines for selecting the best available analogue for a given application. As the unmet need for high-potency analogues remains, we also propose starting points for medicinal chemists in search of nanomolar myosin II inhibitors.
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http://dx.doi.org/10.1021/acs.jmedchem.8b00503DOI Listing
November 2018

Synthesis of C-ring-modified blebbistatin derivatives and evaluation of their myosin II ATPase inhibitory potency.

Bioorg Med Chem Lett 2018 07 22;28(13):2261-2264. Epub 2018 May 22.

Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653 bl. B, 9000 Gent, Belgium. Electronic address:

(S)-Blebbistatin is a micromolar myosin II ATPase inhibitor that is extensively used in research. In search of analogs with improved potency, we have synthesized for the first time C-ring modified analogs. We introduced hydroxymethyl or allyloxymethyl functionalities in search of additional favorable interactions and a more optimal filling of the binding pocket. Unfortunately, the resulting compounds did not significantly inhibit the ATPase activity of rabbit skeletal-muscle myosin II. This and earlier reports suggest that rational design of potent myosin II inhibitors based on the architecture of the blebbistatin binding pocket is an ineffective strategy.
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http://dx.doi.org/10.1016/j.bmcl.2018.05.041DOI Listing
July 2018

Design of a Mesoscale Continuous-Flow Route toward Lithiated Methoxyallene.

ChemSusChem 2018 Jul 1;11(13):2248-2254. Epub 2018 Jun 1.

Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium.

The unique nucleophilic properties of lithiated methoxyallene allow for C-C bond formation with a wide variety of electrophiles, thus introducing an allenic group for further functionalization. This approach has yielded a tremendously broad range of (hetero)cyclic scaffolds, including precursors to active pharmaceutical ingredients. To date, however, its valorization at scale is hampered by the batch synthesis procedure, which suffers from serious safety issues. Hence, the attractive heat- and mass-transfer properties of flow technology were exploited to establish a mesoscale continuous-flow route toward lithiated methoxyallene. An excellent conversion of 94 % was obtained, corresponding to a methoxyallene throughput of 8.2 g h . The process is characterized by short reaction times, mild reaction conditions and a stoichiometric use of reagents.
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http://dx.doi.org/10.1002/cssc.201800760DOI Listing
July 2018

Enhancing Zeolite Performance by Catalyst Shaping in a Mesoscale Continuous-Flow Diels-Alder Process.

ChemSusChem 2018 May 26;11(10):1686-1693. Epub 2018 Apr 26.

Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium.

In contrast to most lab-scale batch procedures, a continuous-flow implementation requires a thorough consideration of the solid catalyst design. In a previous study, irregular zeolite pellets were applied in a miniaturized continuous-flow reactor for the Diels-Alder reaction in the construction of norbornene scaffolds. After having faced the challenges of continuous operation, the aim of this study is to exploit catalyst structuring. To this end, microspheres with high uniformity and various sphere diameters were synthesized according to the vibrational droplet coagulation method. The influence of the use of these novel zeolite shapes in a mesoscale continuous-flow Diels-Alder process of cyclopentadiene and methyl acrylate is discussed. An impressive enhancement of catalyst lifetime is demonstrated, as even after a doubled process time of 14 h, the microspheres still exceeded the conversion after 7 h when using zeolite pellets by 30 %. A dual reason is found for this beneficial impact of catalyst shaping. The significant improvement in catalyst longevity can be attributed to the interplay of the chemical composition and the porosity structure of the microspheres.
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http://dx.doi.org/10.1002/cssc.201800362DOI Listing
May 2018

Automated reaction database and reaction network analysis: extraction of reaction templates using cheminformatics.

J Cheminform 2018 Mar 9;10(1):11. Epub 2018 Mar 9.

Laboratory for Chemical Technology, Department of Materials, Textiles and Chemical Engineering, Ghent University, Technologiepark 914, 9052, Ghent, Belgium.

Both the automated generation of reaction networks and the automated prediction of synthetic trees require, in one way or another, the definition of possible transformations a molecule can undergo. One way of doing this is by using reaction templates. In view of the expanding amount of known reactions, it has become more and more difficult to envision all possible transformations that could occur in a studied system. Nonetheless, most reaction network generation tools rely on user-defined reaction templates. Not only does this limit the amount of chemistry that can be accounted for in the reaction networks, it also confines the wide-spread use of the tools by a broad public. In retrosynthetic analysis, the quality of the analysis depends on what percentage of the known chemistry is accounted for. Using databases to identify templates is therefore crucial in this respect. For this purpose, an algorithm has been developed to extract reaction templates from various types of chemical databases. Some databases such as the Kyoto Encyclopedia for Genes and Genomes and RMG do not report an atom-atom mapping (AAM) for the reactions. This makes the extraction of a template non-straightforward. If no mapping is available, it is calculated by the Reaction Decoder Tool (RDT). With a correct AAM-either calculated by RDT or specified-the algorithm consistently extracts a correct template for a wide variety of reactions, both elementary and non-elementary. The developed algorithm is a first step towards data-driven generation of synthetic trees or reaction networks, and a greater accessibility for non-expert users.
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http://dx.doi.org/10.1186/s13321-018-0269-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5845084PMC
March 2018
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