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ABSTRACT Having a sense of belonging can promote persistence in the STEM fields, but less is known about what it means to develop that sense of belonging. To investigate this phenomenon, we conducted semi‐structured interviews with a cohort of STEM students (n = 10) nearing graduation at an urban university regarding their sense of belonging and qualitatively coded the interviews using thematic analysis. Results revealed that all interviewed students clearly articulated feelings of belonging, making them an ideal population from which to learn more. We applied two frameworks to guide our understanding of what factors promoted the development of a sense of belonging for these students: the Network Theory of Social Capital and the Counterspaces Framework. The students described their experiences in relation to elements of social capital and counterspace processes as they reflected on the development of feelings of belonging. One element of social capital, “reinforcement,” or assurance and recognition of one's worthiness as a member of a group, was the most prevalent element of social capital influencing the participants' development of a sense of belonging. “Direct relational transactions,” or the exchange of resources within a community, was the most prevalent counterspace process discussed by the participants. Our findings expand the utility and add to the theoretical underpinnings of the two frameworks, indicating that gaining social capital and experiencing counterspaces can contribute to undergraduate STEM student development of a sense of belonging. 

The importance of electron deficient Tp ligands motivates the introduction of electron-withdrawing substituents into the scorpionate framework. Since perfluorophenyltris(pyrazol-1-yl)borate affects significant anodic shifts in half-cell potentials in their metal complexes relative those of phenyltris(pyrazol-1-yl)borate analogues, the tuning opportunities achieved using 3,4,5-trifluorophenyl- and 3,5-bis(trifluoromethyl)phenyl(pyrazol-1-yl)borates were explored. Bis(amino)boranes ((3,4,5-F)C 6 H 2 )B(NMe 2 ) 2 and ((3,5-CF 3 )C 6 H 3 )B(NMe 2 ) 2 are precursors to fluorinated tris(pyrazol-1-yl)phenylborates. Thallium salts of these scorpionates exhibit bridging asymmetric κ 3 - N , N , N coordination modes consistent with the reduced π-basicity of the fluorinated phenyl substituents relative those of other structurally characterized tris(pyrazol-1-yl)phenylborates. While a comparative analysis of the spectral and X-ray crystallographic data for classical Mo(0), Mo( ii ), Mn( i ), Fe( ii ) and Cu( ii ) complexes of [((3,4,5-F)C 6 H 2 )Bpz 3 ] − and [((3,5-CF 3 )C 6 H 3 )Bpz 3 ] − could not differentiate these ligands with respect to their metal-based electronic impacts, cyclic voltammetry suggests that 3,4,5-trifluorophenyl- and 3,5-bis(trifluoromethyl)phenyl(pyrazol-1-yl)borates affect similar anodic shifts within their metal complexes, with coordination of [((3,5-CF 3 )C 6 H 3 )Bpz 3 ] − rendering metal centers more difficult to oxidize, and sometimes even more difficult to oxidize than their [C 6 F 5 Bpz 3 ] − analogues. These data suggest that the extent of phenyl substituent fluorination necessary to minimize metal center electron-richness in phenyltris(pyrazol-1-yl)borate complexes cannot be confidently predicted. 

Natural and laboratory-guided evolution has created a rich diversity of fluorescent protein (FP)-based sensors for chloride (Cl − ). To date, such sensors have been limited to the Aequorea victoria green fluorescent protein (avGFP) family, and fusions with other FPs have unlocked ratiometric imaging applications. Recently, we identified the yellow fluorescent protein from jellyfish Phialidium sp. (phiYFP) as a fluorescent turn-on, self-ratiometric Cl − sensor. To elucidate its working mechanism as a rare example of a single FP with this capability, we tracked the excited-state dynamics of phiYFP using femtosecond transient absorption (fs-TA) spectroscopy and target analysis. The photoexcited neutral chromophore undergoes bifurcated pathways with the twisting-motion-induced nonradiative decay and barrierless excited-state proton transfer. The latter pathway yields a weakly fluorescent anionic intermediate , followed by the formation of a red-shifted fluorescent state that enables the ratiometric response on the tens of picoseconds timescale. The redshift results from the optimized π–π stacking between chromophore Y66 and nearby Y203, an ultrafast molecular event. The anion binding leads to an increase of the chromophore p K a and ESPT population, and the hindrance of conversion. The interplay between these two effects determines the turn-on fluorescence response to halides such as Cl − but turn-off response to other anions such as nitrate as governed by different binding affinities. These deep mechanistic insights lay the foundation for guiding the targeted engineering of phiYFP and its derivatives for ratiometric imaging of cellular chloride with high selectivity. 

The visualization of chloride in living cells with fluorescent sensors is linked to our ability to design hosts that can overcome the energetic penalty of desolvation to bind chloride in water. Fluorescent proteins can be used as biological supramolecular hosts to address this fundamental challenge. Here, we showcase the power of protein engineering to convert the fluorescent proton-pumping rhodopsin GR from Gloeobacter violaceus into GR1, a red-shifted, turn-on fluorescent sensor for chloride in detergent micelles and in live Escherichia coli . This non-natural function was unlocked by mutating D121, which serves as the counterion to the protonated retinylidene Schiff base chromophore. Substitution from aspartate to valine at this position (D121V) creates a binding site for chloride. The binding of chloride tunes the p K a of the chromophore towards the protonated, fluorescent state to generate a pH-dependent response. Moreover, ion pumping assays combined with bulk fluorescence and single-cell fluorescence microscopy experiments with E. coli , expressing a GR1 fusion with a cyan fluorescent protein, show that GR1 does not pump ions nor sense membrane potential but instead provides a reversible, ratiometric readout of changes in extracellular chloride at the membrane. This discovery sets the stage to use natural and laboratory-guided evolution to build a family of rhodopsin-based fluorescent chloride sensors with improved properties for cellular applications and learn how proteins can evolve and adapt to bind anions in water.