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Experimental Approaches to the Corey-Bakshi-Shibata and Dakin-West Reactions as Model Systems for Machine Learning Applications in the Small-Data Regime
(2026) Pereira, Oliver Simão
Predicting enantioselectivity remains a fundamental challenge in asymmetric organocatalysis. While Machine Learning (ML) offers data-driven pathways for catalyst optimization, its application is hindered by data scarcity and publication bias. This work investigates the integration of experimental data into predictive ML models within the small-data regime, using the Corey-Bakshi-Shibata (CBS) reduction and the asymmetric variant of the Dakin-West reaction as model reactions. The primary objective was the development of robust predictive models from limited, unbiased datasets, and to delineate the operational limits of current molecular representations as well as ML algorithms. Initial investigations of the CBS reduction of ketones yielded a graph-based ML model that predicts stereochemical outcomes and identifies promising catalyst precursors. However, the synthesis and investigation of additional precursors, enabled by a newly developed synthetic route, revealed deviations from previous predictions. This demonstrates that the reliability of small-data ML models depends on high-quality datasets and robust analytics to avoid the compensation for empirical artifacts. Further investigations of CBS catalysts into ketimine substrates revealed that an unselective background reaction consistently outpaces the catalyzed pathway. This inherent lack of stereocontrol renders ketimines unsuitable for modeling, making the suppression of the background pathway an essential prerequisite for future work. For the asymmetric Dakin-West reaction, the research strategy prioritized empirical data generation over premature modeling. Through systematic parameter optimization, a comprehensive data set was established, which maps complex structure-activity relationships and provides a solid, high-quality foundation for future ML applications. Ultimately, this work demonstrates that advancing ML-powered catalyst design within the small-data regime depends on the synergy of high-precision experimental data and rigorous analytical validation. By focusing on data quality in addition to increasing data quantity, the operational boundaries of predictive modeling can be pushed to address complex synthetic challenges.
An empirical three-dimensional metric field for color space
(2026) Koenderink, Jan J.; van Doorn, Andrea J.; Braun, Doris I.; Gegenfurtner, Karl R.
A complete empirical characterization of color discrimination in three dimensions has long remained out of reach. Classical studies, beginning with MacAdam's ellipses, provided local measurements in restricted chromatic planes, but a spatially dense and internally consistent mapping of discrimination structure across full color space has not yet been achieved. Here, we present such a systematic three-dimensional measurement of color discrimination in the standardized sRGB stimulus space. Eight observers measured discrimination regions at 35 reference colors distributed on a body-centered cubic lattice within the RGB cube. At each location, color differences were probed along seven orientations, yielding 14 directional extents. These measurements defined centrally symmetric convex regions that were fitted with minimum-volume ellipsoids, providing a compact description of local discrimination structure. Ellipsoids were represented as symmetric positive-definite matrices and analyzed using a Frobenius geometry, enabling normalization across observers and smooth interpolation to arbitrary locations. The resulting metric field is spatially smooth, highly structured, and remarkably consistent across observers up to an individual global scale factor. Grain size increases along the achromatic axis and exhibits systematic chromatic asymmetries. Comparison with CIEDE2000 reveals substantial agreement in overall scale variation but systematic differences in local anisotropy. Because the metric field is defined geometrically, it can be transformed into linear RGB or any other color representation through the corresponding coordinate transformations. Together, these data provide a coherent three-dimensional empirical mapping of color discrimination across a large ecologically relevant volume of color space and establish an empirical framework for perceptual color metrics.
Methodological factors affecting canine vaginal cytology : the influence of sampling site, swab condition, and fixation method
(2026) Plato, Katrin von; Sendag, Sait; Yildiz, Mehmet; Wehrend, Axel
Background: Vaginal cytology is widely used for cycle staging in bitches because of its practicality and low cost; however, its diagnostic reliability is strongly infuenced by methodological variability. The present study aimed to evaluate the impact of sampling site, swab type, and fxation method on the interpretation of exfoliative vaginal cytology. Materials and Methods: Exfoliative vaginal cytology samples were obtained from 332 clinically healthy bitches representing all stages of the estrous cycle. Samples were collected from diferent locations (vestibulum vs. vagina) using either dry or saline- moistened swabs and prepared as air-dried or spray-fxed smears, followed by eosin–thiazine staining. Clinical examination and serum progesterone concentrations served as the reference method for cycle staging. Results: The proportions of diferent cell types were signifcantly infuenced by the sampling location. Vestibular smears contained higher proportions of keratinized and intermediate cells (p < 0.0001), whereas basal cells (p = 0.0078) and anuclear superfcial cells (p < 0.0001) were more frequently observed in vaginal smears. Overall, sampling location signifcantly afected the distinction between proestrus and estrus. Swab condition signifcantly infuenced smear quality and cellular presentation but had minimal impact on cycle stage classifcation. Smears obtained using saline-moistened swabs showed signifcantly higher cellular yield per microscopic feld (p < 0.0001). Bacteria, cellular debris, and secretory material were less frequently observed in moistened smears (p < 0.0001), whereas free nuclei were detected more frequently (p < 0.0001). Cotton fbers were more common in dry swab preparations (p < 0.0001). Cellular arrangement also difered between sampling methods (p = 0.003). The fxation method infuenced certain morphological features but did not afect cytological stage classifcation. No signifcant diferences in total cellular yield were observed between air-dried and spray-fxed smears. Conclusion: Among the factors evaluated, only the sampling location exerted a clinically relevant efect on cycle stage determination, particularly for distinguishing proestrus from estrus.
Preparation of cleared whole-mount urethra and urinary bladder from transcardially perfused mice for immunolabeling and analysis by CLSM
(2026) Pfeil, Uwe; Dettler, Felix; Perniss, Alexander; Anekal, Praju Vikas; Bankova, Lora; Montero LIopis, Paula; Deckmann, Klaus
The distribution of cells within organs, their involvement in tissue structure, and their organization in three-dimensional networks are important aspects in the analysis and understanding of biological processes. Here, we present a protocol for preparing whole-mount urethra and urinary bladder from transcardially perfused mice for immunolabeling and analysis by confocal laser scanning microscopy. We describe steps for perfusion, preparation, tissue clearing, and analysis using confocal laser scanning microscopy. We then detail procedures for three-dimensional processing of the murine urethra and urinary bladder.
Renal recovery patterns and long-term kidney function decline in pulmonary hypertension
(2026) Hintz, Lukas; Stampouloglou, Anastasios; Rangaswami, Janani; Lo, Kevin Brian; Seeger, Werner; Ghofrani, Hossein-Ardeschir; Gall, Henning; Tello, Khodr; Husain-Syed, Faeq
Pulmonary hypertension (PH) is frequently accompanied by a decline in kidney function. In this retrospective cohort, worsening PH was associated with long-term eGFR decline only when accompanied by transition from acute kidney injury (AKI) to acute kidney disease (AKD), defined as persistent kidney dysfunction beyond 7 days after AKI onset, whereas early AKI reversal was not. These findings suggest that renal recovery patterns, rather than transient changes in kidney function, may determine longitudinal kidney outcomes in PH and warrant further prospective investigation.