TY - JOUR
A1 - Krüger, Tobias
A1 - Linker, Torsten
T1 - Synthesis of gamma-spirolactams by Birch reduction of arenes
JF - European journal of organic chemistry
N2 - A convenient method for the synthesis of gamma-spirolactams in only three steps is described. Birch reduction of inexpensive and commercially available aromatic carboxylic acids in the presence of chloroacetonitrile affords nitriles in moderate to good yields. Suitable precursors are methyl-substituted benzoic acids, naphthoic, and anthroic acid. Subsequent catalytic hydrogenation proceeds smoothly with PtO2 or Raney Ni as catalysts and lactams are isolated in excellent yields and stereoselectivities. Thus, up to 3 new stereogenic centers can be constructed as sole diastereomers from achiral benzoic acids. Furthermore, it is possible to control the degree of saturation at different pressures, affording products with 0, 1, or 2 double bonds. Overall, more than 15 new gamma-spirolactams have been synthesized in analytically pure form.
KW - Arenes
KW - Birch reduction
KW - Hydrogenation
KW - Lactams
KW - Synthetic methods
Y1 - 2021
U6 - https://doi.org/10.1002/ejoc.202100056
SN - 1099-0690
VL - 2021
IS - 10
SP - 1585
EP - 1591
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Fudickar, Werner
A1 - Metz, Melanie
A1 - Mai-Linde, Yasemin
A1 - Krüger, Tobias
A1 - Kelling, Alexandra
A1 - Sperlich, Eric
A1 - Linker, Torsten
T1 - Influence of functional groups on the ene reaction of singlet oxygen with 1,4-cyclohexadienes
JF - Photochemistry and photobiology : the official journal of the American Society for Photobiology
N2 - The photooxygenation of 1,4-cyclohexadienes has been studied with a special focus on regio- and stereoselectivities. In all examples, only the methyl-substituted double bond undergoes an ene reaction with singlet oxygen, to afford hydroperoxides in moderate to good yields. We explain the high regioselectivities by a "large-group effect" of the adjacent quaternary stereocenter. Nitriles decrease the reactivity of singlet oxygen, presumably by quenching, but can stabilize proposed per-epoxide intermediates by polar interactions resulting in different stereoselectivities. Spiro lactams and lactones show an interesting effect on regio- and stereoselectivities of the ene reactions. Thus, singlet oxygen attacks the double bond preferentially anti to the carbonyl group, affording only one regioisomeric hydroperoxide. If the reaction occurs from the opposite face, the other regioisomer is exclusively formed by severe electrostatic repulsion in a perepoxide intermediate. We explain this unusual behavior by the fixed geometry of spiro compounds and call it a "spiro effect" in singlet oxygen ene reactions.
Y1 - 2021
U6 - https://doi.org/10.1111/php.13422
SN - 0031-8655
SN - 1751-1097
VL - 97
IS - 6
SP - 1289
EP - 1297
PB - Wiley
CY - Malden, Mass.
ER -
TY - JOUR
A1 - Schwarze, Thomas
T1 - Determination of Pd2+ by fluorescence enhancement caused by an off-switching of an energy- and an electron transfer
JF - ChemistrySelect
N2 - In this paper, we introduce a fluorescent dye 1, which is able to detect selectively Pd2+ by a clear fluorescence enhancement (FE) in THF. In the presence of eight Pd2+ equivalents, we observed a fluorescence enhancement factor (FEF) of 28.3. The high Pd2+ induced FEF can be explained by an off switching of multiple quenching processes within 1 by Pd2+. In the free dye 1 a photoinduced electron transfer (PET) and energy transfer (ET) takes place and quenches the anthracenic fluorescence. The coordination of eight Pd2+ units by the alkylthio-substituted porphyrazine receptor suppresses the PET and ET quenching process and the anthracenic fluorescence is switched on.
KW - Palladium ion
KW - electron transfer
KW - energy transfer
KW - fluorescence
KW - porphyrazine
Y1 - 2021
U6 - https://doi.org/10.1002/slct.202003975
SN - 2365-6549
VL - 6
IS - 3
SP - 318
EP - 322
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Sand, Patrick
A1 - Schmidt, Bernd
T1 - Pd-catalyzed oxidative sulfoalkenylation of acetanilides and traceless removal of the catalyst directing group
JF - ChemistrySelect
N2 - The palladium-catalyzed oxidative Heck-reaction, also referred to as Fujiwara-Moritani-reaction, has been investigated for the synthesis of styrenylsulfonyl compounds. Acetanilides and vinylsulfonyl compounds undergo dehydrogenative coupling reactions in moderate to quantitative yields, using benzoquinone as the oxidant of choice. Potassium peroxodisulfate, which had previously been identified as a superior oxidant for the coupling with acrylates, did not provide any coupling products with these olefins. Traceless removal of the catalyst directing group through a deacetylation-diazotation-coupling (DDC) sequence was demonstrated for 2-arylethene sulfones.
KW - arenes
KW - C− H activation
KW - Heck reactions
KW - Palladium
KW - sulfones
Y1 - 2021
U6 - https://doi.org/10.1002/slct.202101009
SN - 2365-6549
VL - 6
IS - 14
SP - 3563
EP - 3567
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Raju, Rajarshi Roy
A1 - Koetz, Joachim
T1 - Inner rotation of Pickering Janus emulsions
JF - Nanomaterials : open access journal
N2 - Janus droplets were prepared by vortex mixing of three non-mixable liquids, i.e., olive oil, silicone oil and water, in the presence of gold nanoparticles (AuNPs) in the aqueous phase and magnetite nanoparticles (MNPs) in the olive oil. The resulting Pickering emulsions were stabilized by a red-colored AuNP layer at the olive oil/water interface and MNPs at the oil/oil interface. The core–shell droplets can be stimulated by an external magnetic field. Surprisingly, an inner rotation of the silicon droplet is observed when MNPs are fixed at the inner silicon droplet interface. This is the first example of a controlled movement of the inner parts of complex double emulsions by magnetic manipulation via interfacially confined magnetic nanoparticles.
KW - Janus droplets
KW - Pickering emulsions
KW - magnetic manipulation
KW - gold nanoparticles
KW - magnetite nanoparticles
Y1 - 2021
U6 - https://doi.org/10.3390/nano11123312
SN - 2079-4991
VL - 11
IS - 12
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Hermanns, Jolanda
A1 - Keller, David
T1 - School-related content knowledge in organic chemistry
BT - How does the Bachelor and Master studies?
JF - Journal of chemical education / Division of Chemical Education, Inc., American Chemical Society
N2 - In this paper the development, use, and evaluation of tasks based on the construct of school-related content knowledge are described. The tasks were used in seminars on organic chemistry for bachelor and master preservice chemistry teachers at a German university. For the evaluation a questionnaire with open and closed items was used. The tasks were rated by the preservice chemistry teachers as relevant for their future profession as a chemistry teacher if the content of the tasks is part of the school curriculum. If the content does not belong to the school curriculum, they rated the nature of the tasks still as relevant; they seem to recognize the importance of conceptual knowledge for their future profession. However, the master's preservice teachers argued with this conceptual knowledge more often than the bachelor's preservice teachers. Although the study is cross-sectional, a certain shift from the focus on the content to conceptual knowledge from bachelor's to master's preservice teachers can be observed.
KW - Organic Chemistry
KW - Second-Year Undergraduate
KW - Analogies/Transfer
Y1 - 2021
U6 - https://doi.org/10.1021/acs.jchemed.0c01415
SN - 0021-9584
SN - 1938-1328
VL - 98
IS - 3
SP - 763
EP - 773
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Picconi, David
T1 - Nonadiabatic quantum dynamics of the coherent excited state intramolecular proton transfer of 10-hydroxybenzo[h]quinoline
JF - Photochemical & photobiological sciences
N2 - The photoinduced nonadiabatic dynamics of the enol-keto isomerization of 10-hydroxybenzo[h]quinoline (HBQ) are studied computationally using high-dimensional quantum dynamics. The simulations are based on a diabatic vibronic coupling Hamiltonian, which includes the two lowest pi pi* excited states and a n pi* state, which has high energy in the Franck-Condon zone, but significantly stabilizes upon excited state intramolecular proton transfer. A procedure, applicable to large classes of excited state proton transfer reactions, is presented to parametrize this model using potential energies, forces and force constants, which, in this case, are obtained by time-dependent density functional theory. The wave packet calculations predict a time scale of 10-15 fs for the photoreaction, and reproduce the time constants and the coherent oscillations observed in time- resolved spectroscopic studies performed on HBQ. In contrast to the interpretation given to the most recent experiments, it is found that the reaction initiated by 1 pi pi* <- S-0 photoexcitation proceeds essentially on a single potential energy surface, and the observed coherences bear signatures of Duschinsky mode-mixing along the reaction path. The dynamics after the 2 pi pi* <- S-0 excitation are instead nonadiabatic, and the n pi* state plays a major role in the relaxation process. The simulations suggest a mainly active role of the proton in the isomerization, rather than a passive migration assisted by the vibrations of the benzoquinoline backbone.
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KW - Excited state proton transfer
KW - Quantum dynamics
KW - Nonadiabatic effects
KW - Spectroscopy
KW - Coherences
Y1 - 2021
U6 - https://doi.org/10.1007/s43630-021-00112-z
SN - 1474-905X
SN - 1474-9092
VL - 20
IS - 11
SP - 1455
EP - 1473
PB - Springer
CY - Heidelberg
ER -
TY - JOUR
A1 - Hermanns, Jolanda
A1 - Keller, David
T1 - How do preservice chemistry teachers rate tasks following the construct of school-related content knowledge in a concept-orientated course on organic chemistry?
JF - Journal of chemical education / Division of Chemical Education, Inc., American Chemical Society
N2 - In this paper, we describe a study on tasks following the construct of school-related content knowledge. We know from previous studies that such tasks were rated by the preservice chemistry teachers as important for their future profession. Those studies were conducted in a traditional course on organic chemistry which was organized around chemical families. Therefore, we used and evaluated the tasks again in a new course on organic chemistry which is organized around basic concepts in organic chemistry. The results of this evaluation show that the students rate the tasks equally well but use other arguments for their rating. They do not focus only on the content of the tasks and whether this content belongs to the school curriculum or not. The students of the conceptual course rated the content more often (95%) as important for their future profession compared with the students in the traditional course (57%). Both groups of students rated the importance of the nature of the task the same way.
KW - Organic chemistry
KW - Second-Year undergraduate
KW - Alcohols
KW - Curriculum
KW - Molecular structure
KW - Organic structure
KW - Students
Y1 - 2021
U6 - https://doi.org/10.1021/acs.jchemed.1c00593
SN - 0021-9584
SN - 1938-1328
VL - 98
IS - 11
SP - 3442
EP - 3449
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Hermanns, Jolanda
T1 - The task navigator following the STRAKNAP concept
BT - Development, application, and evaluation of a new scaffold to support nonmajor chemistry students while solving tasks in organic chemistry
JF - Journal of chemical education / Division of Chemical Education, Inc., American Chemical Society
N2 - Educational Scaffolding was first mentioned in 1976 by Wood et al. Several examples for scaffolding in chemistry are also known from the literature. As written scaffolds, stepped supporting tools to support students while solving problems in organic chemistry were developed, applied, and evaluated. Although the students rated the tool as very helpful, a think-aloud study showed that the support given by this scaffold was not sufficient. As a further development of stepped supporting tools, task navigators were therefore developed, applied, and evaluated. This new scaffold gives tips on strategy, knowledge, and application of knowledge after the STRAKNAP concept. The evaluation of this tool shows that the students rated the tool as being very helpful. A think-aloud study showed that the scaffold supports the students while they solve a problem. Because of the stepwise construction of the task navigators and the providing of the knowledge needed for the application, the students can solve parts of the task successfully even if they do not solve all parts correctly; the students can always start from scratch. When students use the tool regularly, their knowledge of organic chemistry increases compared to students who did not use the tool at all. The task navigator is not only a scaffold for the content of the task but also for the development of methodological competences on the field of strategies and applying knowledge.
KW - First-Year Undergraduate/General
KW - Organic Chemistry
KW - Distance
KW - Learning/Chemistry Education Research
Y1 - 2021
U6 - https://doi.org/10.1021/acs.jchemed.0c01162
SN - 0021-9584
SN - 1938-1328
VL - 98
IS - 4
SP - 1077
EP - 1087
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Krüger, Tobias
A1 - Bramborg, Andrea
A1 - Kelling, Alexandra
A1 - Sperlich, Eric
A1 - Linker, Torsten
T1 - Birch Reduction of Arenes as an Easy Entry to γ-Spirolactones
JF - European journal of organic chemistry
N2 - A convenient method for the synthesis of γ-spirolactones in only 2–3 steps is described. Birch reduction of inexpensive and commercially available aromatic carboxylic acids in the presence of ethylene oxide affords hydroxy acids, which undergo direct lactonization during work-up. Suitable precursors are methyl-substituted benzoic acids, naphthoic, and dicarboxylic acids. Subsequent hydrogenation proceeds smoothly with Pd/C as catalyst and saturated γ-spirolactones are isolated in excellent yields and stereoselectivities. Thus, up to 3 new stereogenic centers can be constructed as sole diastereomers from achiral benzoic acids. Furthermore, it is possible to control the degree of saturation with Raney nickel or Wilkinson's catalyst to obtain products with 1 double bond. Overall, more than 30 new γ-spirolactones have been synthesized in analytically pure form.
KW - Arenes
KW - Birch reduction
KW - Hydrogenation
KW - Lactones
KW - Synthetic methods
Y1 - 2021
U6 - https://doi.org/10.1002/ejoc.202101018
SN - 1434-193X
SN - 1099-0690
VL - 2021
IS - 46
SP - 6383
EP - 6391
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Neffe, Axel T.
A1 - Zhang, Quanchao
A1 - Hommes-Schattmann, Paul J.
A1 - Lendlein, Andreas
T1 - Ethylene oxide sterilization of electrospun poly(L-lactide)/poly(D-lactide) core/shell nanofibers
JF - MRS advances
N2 - The application of polymers in medicine requires sterilization while retaining material structure and properties. This demands detailed analysis, which we show exemplarily for the sterilization of PLLA/PDLA core-shell nanofibers with ethylene oxide (EtO). The electrospun patch was exposed to EtO gas (6 vol% in CO2, 1.7 bar) for 3 h at 45 degrees C and 75% rel. humidity, followed by degassing under pressure/vacuum cycles for 12 h. GC-MS analysis showed that no residual EtO was retained. Fiber diameters (similar to 520 +/- 130 nm) of the patches remained constant as observed by electron microscopy. Young's modulus slightly increased and the elongation at break slightly decreased, determined at 37 degrees C. No changes were detected in H-1-NMR spectra, in molar mass distribution (GPC) or in crystallinity measured for annealed samples with comparable thermal history (Wide Angle X-Ray Scattering). Altogether, EtO emerged as suitable sterilization method for polylactide nanofibers with core-shell morphology.
Y1 - 2021
U6 - https://doi.org/10.1557/s43580-021-00058-5
SN - 2059-8521
VL - 6
IS - 33
SP - 786
EP - 789
PB - Springer
CY - Cham
ER -
TY - JOUR
A1 - Rethfeldt, Nina
A1 - Brinkmann, Pia
A1 - Riebe, Daniel
A1 - Beitz, Toralf
A1 - Köllner, Nicole
A1 - Altenberger, Uwe
A1 - Löhmannsröben, Hans-Gerd
T1 - Detection of Rare Earth Elements in Minerals and Soils by Laser-Induced Breakdown Spectroscopy (LIBS) Using Interval PLS
JF - Minerals
N2 - The numerous applications of rare earth elements (REE) has lead to a growing global demand and to the search for new REE deposits. One promising technique for exploration of these deposits is laser-induced breakdown spectroscopy (LIBS). Among a number of advantages of the technique is the possibility to perform on-site measurements without sample preparation. Since the exploration of a deposit is based on the analysis of various geological compartments of the surrounding area, REE-bearing rock and soil samples were analyzed in this work. The field samples are from three European REE deposits in Sweden and Norway. The focus is on the REE cerium, lanthanum, neodymium and yttrium. Two different approaches of data analysis were used for the evaluation. The first approach is univariate regression (UVR). While this approach was successful for the analysis of synthetic REE samples, the quantitative analysis of field samples from different sites was influenced by matrix effects. Principal component analysis (PCA) can be used to determine the origin of the samples from the three deposits. The second approach is based on multivariate regression methods, in particular interval PLS (iPLS) regression. In comparison to UVR, this method is better suited for the determination of REE contents in heterogeneous field samples. View Full-Text
KW - LIBS
KW - rare earth elements
KW - minerals
KW - PCA
KW - iPLS regression
Y1 - 2021
U6 - https://doi.org/10.3390/min11121379
SN - 2075-163X
VL - 11
SP - 1
EP - 17
PB - MDPI
CY - Basel, Schweiz
ER -
TY - JOUR
A1 - Balderas-Valadez, Ruth Fabiola
A1 - Pacholski, Claudia
T1 - Plasmonic Nanohole Arrays on Top of Porous Silicon Sensors
BT - A Win-Win Situation
JF - ACS applied materials & interfaces
N2 - Label-free optical sensors are attractive candidates, for example, for detecting toxic substances and monitoring biomolecular interactions. Their performance can be pushed by the design of the sensor through clever material choices and integration of components. In this work, two porous materials, namely, porous silicon and plasmonic nanohole arrays, are combined in order to obtain increased sensitivity and dual-mode sensing capabilities. For this purpose, porous silicon monolayers are prepared by electrochemical etching and plasmonic nanohole arrays are obtained using a bottom-up strategy. Hybrid sensors of these two materials are realized by transferring the plasmonic nanohole array on top of the porous silicon. Reflectance spectra of the hybrid sensors are characterized by a fringe pattern resulting from the Fabry–Pérot interference at the porous silicon borders, which is overlaid with a broad dip based on surface plasmon resonance in the plasmonic nanohole array. In addition, the hybrid sensor shows a significant higher reflectance in comparison to the porous silicon monolayer. The sensitivities of the hybrid sensor to refractive index changes are separately determined for both components. A significant increase in sensitivity from 213 ± 12 to 386 ± 5 nm/RIU is determined for the transfer of the plasmonic nanohole array sensors from solid glass substrates to porous silicon monolayers. In contrast, the spectral position of the interference pattern of porous silicon monolayers in different media is not affected by the presence of the plasmonic nanohole array. However, the changes in fringe pattern reflectance of the hybrid sensor are increased 3.7-fold after being covered with plasmonic nanohole arrays and could be used for high-sensitivity sensing. Finally, the capability of the hybrid sensor for simultaneous and independent dual-mode sensing is demonstrated.
KW - optical sensors
KW - porous silicon
KW - surface plasmon resonance
KW - plasmonic
KW - nanohole arrays
KW - bottom-up fabrication
Y1 - 2021
U6 - https://doi.org/10.1021/acsami.1c07034
SN - 1944-8244
SN - 1944-8252
VL - 13
IS - 30
SP - 36436
EP - 36444
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Hermanns, Jolanda
T1 - Training OC
BT - A new course concept for training the application of basic concepts in organic chemistry
JF - Journal of chemical education
N2 - The course design "Training OC" for training the application of basic concepts consists of four topics: formula language, structure-property relations, reaction mechanisms, and complex tasks that the students should solve with the conceptual knowledge they acquired in the first three topics. A main goal of the course was to enable the students to solve reaction mechanisms. To achieve the goals of the course, several games were specially designed and used. The course was conducted at a German university with ca. 30 students who participated voluntarily. The course was evaluated by several tools: students' products were collected in the course, there were two pre/post-tests, and additionally, interviews on the strategy of designing reaction mechanisms were conducted. The performance of the teacher and the self-assessment of the students were also part of the evaluation. The results of the written exam were compared with the results of the bachelor chemistry major students. The course "Training OC" was rated very well by the students. They were of the opinion that they learned the application of basic concepts taught in this course. This is supported by the results of the evaluation and the written exams. The course concept of Training OC will therefore become a permanent part of the course "Organic Chemistry I" which will be redesigned for the next round in 2020-21.
KW - Second-Year Undergraduate
KW - Organic Chemistry
KW - Humor/Puzzles/Games
KW - Collaborative/Cooperative Learning
Y1 - 2020
U6 - https://doi.org/10.1021/acs.jchemed.0c00567
SN - 0021-9584
SN - 1938-1328
VL - 98
IS - 2
SP - 374
EP - 384
PB - American Chemical Society. Division of Chemical Education
CY - Washington
ER -
TY - JOUR
A1 - Kwesiga, George
A1 - Sperlich, Eric
A1 - Schmidt, Bernd
T1 - Scope and applications of 2,3-oxidative aryl rearrangements for the synthesis of isoflavone natural products
JF - The journal of organic chemistry
N2 - The reaction of flavanones with hypervalent iodine reagents was investigated with a view to the synthesis of naturally occurring isoflavones. In contrast to several previous reports in the literature, we did not observe the formation of any benzofurans via a ring contraction pathway, but could isolate only isoflavones, resulting from an oxidative 2,3-aryl rearrangement, and flavones, resulting from an oxidation of the flavanones. Although the 2,3-oxidative rearrangement allows a synthetically useful approach toward some isoflavone natural products due to the convenient accessibility of the required starting materials, the overall synthetic utility and generality of the reaction appear to be more limited than previous literature reports suggest.
Y1 - 2021
U6 - https://doi.org/10.1021/acs.joc.1c01375
SN - 0022-3263
SN - 1520-6904
VL - 86
IS - 15
SP - 10699
EP - 10712
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Fudickar, Werner
A1 - Linker, Torsten
T1 - Photooxygenation of naphthalene
JF - ChemPhotoChem
N2 - The photooxygenation of naphthalene to the corresponding endoperoxide (EPO) under various conditions is described. Substantial conversion is only observed at -10 degrees C and after more than two days, indicating that the [4+2] cycloaddition of singlet oxygen to this acene proceeds much more slowly than corresponding reactions of substituted naphthalenes, a rate constant of k = 5.4 +/- 0.3 M(-1)s(-1) was determined by competition kinetics. Another problem is the thermal lability and photochemical cleavage of the naphthalene EPO. We investigated the mechanism of this radical process depending on the light source and sensitizer in comparison to known cyclohexadiene EPO. Thus, bisepoxides and keto epoxides are formed after homolysis of the O-O bond by irradiation with sodium lamps or blue LEDs and subsequent cyclization. This process is accelerated by the sensitizers methylene blue and 9,10-dicyanoanthracene, indicating an electron transfer mechanism. Finally, the cleavage of the peroxidic bond is inhibited with red LEDs, and photooxygenation under such conditions affords 20 % EPO. Thus, we could demonstrate that contrary to literature statements singlet oxygen does indeed react with naphthalene.
KW - naphthalene
KW - photooxygenation
KW - reaction mechanisms
KW - reactive
KW - intermediates
KW - singlet oxygen
Y1 - 2021
U6 - https://doi.org/10.1002/cptc.202100097
VL - 5
IS - 11
SP - 1004
EP - 1008
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Bauch, Marcel
A1 - Fudickar, Werner
A1 - Linker, Torsten
T1 - Stereoselective [4+2] Cycloaddition of Singlet Oxygen to Naphthalenes Controlled by Carbohydrates
JF - Molecules : a journal of synthetic chemistry and natural product chemistry
N2 - Stereoselective reactions of singlet oxygen are of current interest. Since enantioselective photooxygenations have not been realized efficiently, auxiliary control is an attractive alternative. However, the obtained peroxides are often too labile for isolation or further transformations into enantiomerically pure products. Herein, we describe the oxidation of naphthalenes by singlet oxygen, where the face selectivity is controlled by carbohydrates for the first time. The synthesis of the precursors is easily achieved starting from naphthoquinone and a protected glucose derivative in only two steps. Photooxygenations proceed smoothly at low temperature, and we detected the corresponding endoperoxides as sole products by NMR. They are labile and can thermally react back to the parent naphthalenes and singlet oxygen. However, we could isolate and characterize two enantiomerically pure peroxides, which are sufficiently stable at room temperature. An interesting influence of substituents on the stereoselectivities of the photooxygenations has been found, ranging from 51:49 to up to 91:9 dr (diastereomeric ratio). We explain this by a hindered rotation of the carbohydrate substituents, substantiated by a combination of NOESY measurements and theoretical calculations. Finally, we could transfer the chiral information from a pure endoperoxide to an epoxide, which was isolated after cleavage of the sugar chiral auxiliary in enantiomerically pure form.
KW - singlet oxygen
KW - photooxygenation
KW - naphthalenes
KW - carbohydrates
KW - stereoselectivity
KW - auxiliary control
KW - [4+2] cycloaddition
Y1 - 2021
U6 - https://doi.org/10.3390/molecules26040804
SN - 1420-3049
VL - 16
IS - 4
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Bäckemo, Johan Dag Valentin
A1 - Liu, Yue
A1 - Lendlein, Andreas
T1 - Bio-inspired and computer-supported design of modulated shape changes in polymer materials
JF - MRS communications / a publication of the Materials Research Society
N2 - The Venus flytrap is a fascinating plant with a finely tuned mechanical bi-stable system, which can switch between mono- and bi-stability. Here, we combine geometrical design of compliant mechanics and the function of shape-memory polymers to enable switching between bi- and mono-stable states. Digital design and modelling using the Chained Beam Constraint Model forecasted two geometries, which were experimentally realized as structured films of cross-linked poly[ethylene-co-(vinyl acetate)] supported by digital manufacturing. Mechanical evaluation confirmed our predicted features. We demonstrated that a shape-memory effect could switch between bi- and mono-stability for the same construct, effectively imitating the Venus flytrap.
KW - Additive manufacturing
KW - Biomimetic
KW - Shape memory
KW - Modelling
KW - Polymer
Y1 - 2021
U6 - https://doi.org/10.1557/s43579-021-00056-6
SN - 2159-6867
VL - 11
IS - 4
SP - 462
EP - 469
PB - Springer
CY - Berlin
ER -
TY - JOUR
A1 - López-Salas, Nieves
A1 - Albero, Josep
T1 - CxNy
BT - new carbon nitride organic photocatalysts
JF - Frontiers in Materials
N2 - The search for metal-free and visible light-responsive materials for photocatalytic applications has attracted the interest of not only academics but also the industry in the last decades. Since graphitic carbon nitride (g-C3N4) was first reported as a metal-free photocatalyst, this has been widely investigated in different light-driven reactions. However, the high recombination rate, low electrical conductivity, and lack of photoresponse in most of the visible range have elicited the search for alternatives. In this regard, a broad family of carbon nitride (CxNy) materials was anticipated several decades ago. However, the attention of the researchers in these materials has just been awakened in the last years due to the recent success in the syntheses of some of these materials (i.e., C3N3, C2N, C3N, and C3N5, among others), together with theoretical simulations pointing at the excellent physico-chemical properties (i.e., crystalline structure and chemical morphology, electronic configuration and semiconducting nature, or high refractive index and hardness, among others) and optoelectronic applications of these materials. The performance of CxNy, beyond C3N4, has been barely evaluated in real applications, including energy conversion, storage, and adsorption technologies, and further work must be carried out, especially experimentally, in order to confirm the high expectations raised by simulations and theoretical calculations. Herein, we have summarized the scarce literature related to recent results reporting the synthetic routes, structures, and performance of these materials as photocatalysts. Moreover, the challenges and perspectives at the forefront of this field using CxNy materials are disclosed. We aim to stimulate the research of this new generation of CxNy-based photocatalysts, beyond C3N4, with improved photocatalytic efficiencies by harnessing the striking structural, electronic, and optical properties of this new family of materials.
KW - CXNY
KW - carbon nitrides
KW - C2N
KW - C3N
KW - C1N1
KW - C3N5
KW - photocatalysis
Y1 - 2021
U6 - https://doi.org/10.3389/fmats.2021.772200
SN - 2296-8016
VL - 8
PB - Frontiers Media
CY - Lausanne
ER -
TY - JOUR
A1 - Lendlein, Andreas
A1 - Heuchel, Matthias
T1 - Shape-memory polymers designed in view of thermomechanical energy storage and conversion systems
BT - Effective temporary shape fixation by strain-induced formation of supramolecular nanostructures enables high energy density one-way shape-memory polymers
JF - ACS central science
KW - Actuators
KW - Deformation
KW - Energy
KW - Energy storage
KW - Polymers
Y1 - 2021
U6 - https://doi.org/10.1021/acscentsci.1c01032
SN - 2374-7951
VL - 7
IS - 10
SP - 1599
EP - 1601
PB - American Chemical Society
CY - Washington
ER -