Conceptual Representations within the Social and Material Contexts of an Engineering Workplace and Academic Environments

Situated cognition theory emphasizes the role that social and material contexts have on learning and knowledge application. Several studies of engineering workplace environments have noted differences between the social and material contexts of the workplace and those of undergraduate engineering education. No existing research has studied the social and material contexts of both workplace and academic environments, specifically focusing on how these contexts influence conceptual representations within a single engineering discipline. Conceptual representations are the social and material contexts that mediate how concepts are represented, such as language, text, symbols, diagrams, equations, and other tools. Differences in the social and material contexts mediating conceptual representations across workplace and academic environments may be partially responsible for the engineering education-practice gap and is an underexplored topic. The purpose of this research is to explore a structural engineering workplace environment and undergraduate structural engineering courses to document conceptual representations and the social and material contexts that mediate them within both these workplace and academic environments. Ethnographic methods were used to access and explore these environments in-depth through participating in and observation of their respective social and material contexts. Findings from this exploration noted that conceptual representations in the academic environments exhibited a lesser degree of tangibility to real-world conditions, project/stakeholder constraints, and engineering tools than conceptual representations in the workplace. Furthermore, engineering tools such as codes and standards were applied in more evaluative ways in the workplace environment compared to more prescriptive applications of these tools in the academic environments. Lastly, engineering heuristics in the workplace environments were more likely to be practice-based than the heuristics used in the academic environment, which were more profession-based. These findings offer unique frameworks for characterizing conceptual representations such as: degrees of tangibility, prescriptive versus evaluative code use, and practice-based versus profession-based heuristics, which may be applicable for describing the sociomaterial nature of conceptual representations across other engineering workplace and academic environments

Ugi multicomponent reaction to prepare peptide–peptoid hybrid structures with diverse chemical functionalities

Monodisperse sequenced peptides and peptoids present unique nano-structures based on their self-assembled secondary and tertiary structures. However, the generation of peptide and peptoid hybrid oligomers in a sequence-defined manner via Ugi multicomponent reaction has not yet been studied. Herein, we report a synthetic strategy that enables both the modification of peptides as well as the generation of sequence-defined peptide–peptoid hybrid structures. Our synthetic methodology rests on the fusion of solid phase peptide synthesis with Ugi multicomponent reactions. We evidence that a diversity of chemical functionalities can be inserted into peptides or used in the design of peptide–peptoid hybrids exploiting a wide functional array including amines, carboxylic acids, hydrocarbons, carbohydrates as well as polymers, introducing a sequence-defined synthetic platform technology for precision peptoid hybrids

Stability of star-shaped RAFT polystyrenes under mechanical and thermal stress

Well-defined three-arm and four-arm star polymers designed via a Z-group approach carrying trithiocarbonate functionalities at the core are prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization featuring molecular weights of Mn{,}SEC = 156 kDa{,} D = 1.16 (3-arm) and Mn{,}SEC = 162 kDa{,} D = 1.15 (4-arm) based on multi-angle laser light scattering (MALLS) detection{,} respectively. The star-shaped polystyrenes are subjected (in bulk) to thermal stress in the temperature range between 140 and 200 [degree]C from 10 minutes up to 96 h. The thermally treated 3-arm and 4-arm star polymers are analyzed via size exclusion chromatography (SEC) to quantify the degradation process at variable temperatures as a function of time under an argon atmosphere. Cleavage rate coefficients of the star polymers are deduced as a function of temperature{,} resulting in activation parameters for the cleavage process{,} i.e. Ea = 131 kJ mol-1; A = 3.93 [times] 1011 s-1 (Mn{,}SEC = 156 kDa{,} D = 1.16{,} 3-arm star) and Ea{,} = 134 kJ mol-1; A = 9.13 [times] 1011 s-1 (Mn{,}SEC = 162 kDa{,} D = 1.15{,} 4-arm star){,} respectively. Processing of the star-shaped polymers is mimicked via a small scale counter rotating twin screw extrusion to achieve nonlinear shear and elongation flow under pressure. Furthermore{,} a rheological assessment via the linear shear deformation region (small amplitude oscillatory shear{,} SAOS) allows for a correlation of the processing conditions with the thermal degradation properties of the star polymers in the melt. Zero shear viscosity ([small eta]0) as a criterion of the degradation process is measured in the rheometer and correlated to the weight-average molecular weight{,} Mw

Unraveling the spontaneous zwitterionic copolymerization mechanism of cyclic imino ethers and acrylic acid

We report a high-resolution electrospray ionization mass spectrometric (HR ESI MS) access route leading to in-depths insight into the spontaneous zwitterionic copolymerization mechanism between cyclic imino ethers (i.e. 2-methyl-2-oxazoline (MeOx), 2-ethyl-2-oxazoline (EtOx) or 2-ethyl-2-oxazine (EtOz)) with acrylic acid (AA), exploiting the characteristic species accumulating during the copolymerization as well as tandem mass spectrometry (MS/MS). We demonstrate preferences in α,ω-end group formation by screening various feed ratios of cyclic imino ethers and acrylic acid (e.g. MeOx:AA = 1:1; MeOx:AA = 2:1; MeOx:AA = 1:2). Critically, a calibration curve – based on AA-MeOx-AA dimer – was established allowing for semi-quantitative determination of the end group ratios with different feed ratios of acrylic acid. The formation of, previously suggested, alternating copolymers was confirmed by MS/MS experiments. Deviations from an ideal alternating composition were found to decrease from MeOx to EtOx to EtOz. The results of (semi-quantitative) HR ESI MS and MS/MS measurements suggest, for the first time presented in such precision, a polymerization mechanism for the spontaneous zwitterionic (alternating) copolymerization indicating optimal monomer ratios and pairings

Ferrocene-driven single-chain polymer compaction

We introduce single-chain nanoparticles (SCNPs) exclusively folded by covalently bonded ferrocene units. Specifially, we demonstrate the ability of 2-ferrocenyl-1,10-phenanthroline to fuse single-chain collapse with the concomitant introduction of a donor functionality allowing the installation of a Pd-catalytic site, affording the first heterobimetallic ferrocene-functionalized SCNP

Hetero-Diels–Alder Cycloaddition with RAFT Polymers as Bioconjugation Platform

We introduce the bioconjugation of polymers synthesized by RAFT polymerization, bearing no specific functional end group, by means of hetero‐Diels–Alder cycloaddition through their inherent terminal thiocarbonylthio moiety with a diene‐modified model protein. Quantitative conjugation occurs over the course of a few hours, at ambient temperature and neutral pH, and in the absence of any catalyst. Our technology platform affords thermoresponsive bioconjugates, whose aggregation is solely controlled by the polymer chains

Hetero-Diels-Alder-Cycloaddition mit RAFT-Polymeren als Biokonjugationsplattform

Wir stellen die Biokonjugation von Polymeren vor, die durch RAFT‐Polymerisation mittels Hetero‐Diels‐Alder‐Cycloaddition durch ihren inhärenten terminalen Thiocarbonylthiorest mit einem dienmodifizierten Modellprotein synthetisiert wurden und keine spezifische funktionelle Endgruppe tragen. Die quantitative Konjugation erfolgt im Verlauf einiger Stunden bei Raumtemperatur und nahezu neutralem pH‐Wert und in Abwesenheit jeglichen Katalysators. Unsere Technologieplattform liefert thermoresponsive Biokonjugate, deren Aggregation allein durch die Polymerketten gesteuert wird

Self-reporting and refoldable profluorescent single-chain nanoparticles

We pioneer the formation of self-reporting and refoldable profluorescent single-chain nanoparticles (SCNPs) via the light-induced reaction (λmax = 320 nm) of nitroxide radicals with a photo-active crosslinker. Whereas the tethered nitroxide moiety in these polymers fully quenches the luminescence (i.e. fluorescence) of the aromatic backbone, nitroxide trapping of a transient C-radical leads to the corresponding closed shell alkoxyamine thereby restoring luminescence of the folded SCNP. Hence, the polymer in the folded state is capable of emitting light, while in the non-folded state the luminescence is silenced. Under oxidative conditions the initially folded SCNPs unfold, resulting in luminescence switch-off and the reestablishment of the initial precursor polymer. Critically, we show that the luminescence can be repeatedly silenced and reactivated. Importantly, the self-reporting character of the SCNPs was followed by size-exclusion chromatography (SEC), dynamic light scattering (DLS), fluorescence, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR) and diffusion ordered NMR spectroscopy (DOSY)