Structure—activity relationships for chloro‐ and nitrophenol toxicity in the pollen tube growth test

—Acute toxicity of 10 chlorophenols and 10 nitrophenols with identical substitution patterns is analyzed with the pollen tubegrowth (PTG) test. Concentration values of 50% growth inhibition (IC50) between 0.1 and 300 mg/L indicate that the absolutesensitivity of this alternative biotest is comparable to conventional aquatic test systems. Analysis of quantitative structure–activityrelationships using lipophilicity (log Kow), acidity (pKa), and quantum chemical parameters to model intrinsic acidity, solvation interactions,and nucleophilicity reveals substantial differences between the intraseries trends of log IC50. With chlorophenols, a narcotictyperelationship is derived, which, however, shows marked differences in slope and intercept when compared to reference regressionequations for polar narcosis. Regression analysis of nitrophenol toxicity suggests interpretation in terms of two modes of action:oxidative uncoupling activity is associated with a pKa window from 3.8 to 8.5, and more acidic congeners with diortho- substitutionshow a transition from uncoupling to a narcotic mode of action with decreasing pKa and log Kow. Model calculations for phenolnucleophilicity suggest that differences in the phenol readiness for glucuronic acid conjugation as a major phase-II detoxication pathway have no direct influence on acute PTG toxicity of the compounds

Nonlinear principal component analysis

We study the extraction of nonlinear data models in high-dimensional spaces with modified self-organizing maps. We present a general algorithm which maps low-dimensional lattices into high-dimensional data manifolds without violation of topology. The approach is based on a new principle exploiting the specific dynamical properties of the first order phase transition induced by the noise of the data. Moreover we present a second algorithm for the extraction of generalized principal curves comprising disconnected and branching manifolds. The performance of the algorithm is demonstrated for both one- and two-dimensional principal manifolds and also for the case of sparse data sets. As an application we reveal cluster structures in a set of real world data from the domain of ecotoxicology

1-Methyl-4-(4-nitro­benzo­yl)pyridinium perchlorate

In the main mol­ecule of the title compound, C13H11N2O3 +·ClO4 −, the two aromatic rings are twisted by 56.19 (3)° relative to each other and the nitro group is not coplanar with the benzene ring [36.43 (4)°]. The crystal packing is dominated by infinite aromatic stacks in the a-axis direction. These are formed by the benzene units of the mol­ecule featuring an alternating arrangement, which explains the two different distances of 3.3860 (4) and 3.4907 (4) Å for the aromatic units (these are the perpendicular distances of the centroid of one aromatic ring on the mean plane of the other other aromatic ring). Adjacent stacks are connected by π–π stacking between two pyridinium units [3.5949 (4) Å] and weak C—H⋯O inter­actions. The perchlorate anions are accomodated in the lattice voids connected to the cation via weak C—H⋯O contacts between the O atoms of the anion and various aromatic as well as methyl H atoms