Predicting Organometallic Intermediates in the Surface-Assisted Ullmann Coupling of Chrysene Isomers.

On-surface polymerization of functional organic molecules has been recently recognized as a promising route to persistent low-dimensional structures with tailorable properties. In this contribution, using the coarse-grained Monte Carlo simulation method, we study the initial stage of the Ullmann coupling of doubly halogenated chrysene isomers adsorbed on a catalytically active (111) crystalline surface. To that end, we focus on the formation of labile metal-organic precursor structures preceding the covalent bonding of chrysene monomers. Four monomeric chrysene units with differently distributed halogen substituents were probed in the simulations, and the resulting precursor structures were compared and quantified. Moreover, the effect of (pro)chirality of chrysene tectons on the structure formation was elucidated by running separate simulations in enantiopure and racemic systems. The calculations showed that suitable manipulation of the halogen substitution pattern allows for the creation of diverse precursor architectures, ranging from straight and winded chains to cyclic oligomers with enantiopure, racemic, and nonracemic composition. The obtained findings can be helpful in developing synthetic strategies for covalent polymers with predefined architecture and functionality.

Structural Quantification of the Surface-Confined Metal-Organic Precursors Simulated with the Lattice Monte Carlo Method.

The diversity of surface-confined metal-organic precursor structures, which recently have been observed experimentally, poses a question of how the individual properties of a molecular building block determine those of the resulting superstructure. To answer this question, we use the Monte Carlo simulation technique to model the self-assembly of metal-organic precursors that precede the covalent polymerization of halogenated PAH isomers. For this purpose, a few representative examples of low-dimensional constructs were studied, and their basic structural features were quantified using such descriptors as the orientational order parameter, radial distribution function, and one- and two-dimensional structure factors. The obtained results demonstrated that the morphology of the precursor (and thus the subsequent polymer) could be effectively tuned by a suitable choice of molecular parameters, including size, shape, and intramolecular distribution of halogen substituents. Moreover, our theoretical investigations showed the effect of the main structural features of the precursors on the related indirect characteristics of these constructs. The results reported herein can be helpful in the custom designing and characterization of low-dimensional polymers with adjustable properties.

Theoretical Modeling of the Metal-Organic Precursors of Anthracene-Based Covalent Networks on Surfaces.

Surface-assisted fabrication of molecular network architectures has been a promising route to low-dimensional materials with unique physicochemical properties and functionalities. One versatile way in this field is the Ullmann coupling reaction of halogenated organic monomers on catalytically active metallic surfaces. In this work, using the coarse-grained Monte Carlo simulations, we studied the on-surface self-assembly of metal-organic precursors preceding the covalent Ullman-type linkage of tetrahalogenated anthracene building blocks. To that end, a series of positional isomers was examined and classified with respect to their ability of creation of extended network structures. Our simulations focused on the identification of basic types of self-assembly scenarios distinguishing enantiopure and racemic systems and producing periodic and aperiodic networks. The calculations carried out for selected tectons demonstrated wide possibilities of controlling porosity (e. g. pore size, shape, periodicity, chirality, heterogeneity) of the networks by suitable functionalization of the monomeric unit. The findings reported herein can be helpful in rational designing of 2D polymeric networks with predefined structures and properties.

Designing 2D covalent networks with lattice Monte Carlo simulations: precursor self-assembly.

Organic synthesis reactions in the adsorbed phase have been recently an intensively studied topic in heterogeneous catalysis and material engineering. One of such processes is the Ullmann coupling in which halogenated organic monomers are transformed into covalently bonded polymeric structures. In this work, we use the lattice Monte Carlo simulation method to study the on-surface self-assembly of organometallic precursor architectures comprising tetrasubstituted naphthalene building blocks with differently distributed halogen atoms. In the coarse grained approach adopted herein the molecules and metal atoms were modeled by discrete segments, two connected and one, respectively, placed on a triangular lattice representing a (111) metallic surface. Our simulations focused on the influence of the intramolecular distribution of the substituents on the morphology of the resulting superstructures. Special attention was paid to the molecules that create porous networks characterized by long-range order. Moreover, the structural analysis of the assemblies comprising prochiral building blocks was made by running simulations for the corresponding enantiopure and racemic adsorbed systems. The obtained results demonstrated the possibility of directing the on-surface self-assembly towards networks with controllable pore shape and size. These findings can be helpful in designing covalently bonded 2D superstructures with predefined architecture and functions.

Order-Disorder Transition of Two-Dimensional Molecular Networks through a Stoichiometric Design.

Materials with disordered structures may exhibit interesting properties. Metal-organic frameworks (MOFs) are a class of hybrid materials composed of metal nodes and coordinating organic linkers. Recently, there has been growing interest in MOFs with structural disorder and the investigations of amorphous structures on surfaces. Herein, we demonstrate a bottom-up method to construct disordered molecular networks on metal surfaces by selecting two organic molecule linkers with the same symmetry but different sizes for preparing two-component samples with different stoichiometric ratios. The amorphous networks are directly imaged by scanning tunneling microscopy under ultrahigh vacuum with a submolecular resolution, allowing us to quantify its degree of disorder and other structural properties. Furthermore, we resort to molecular dynamics simulations to understand the formation of the amorphous metal-organic networks. The results may advance our understanding of the mechanism of formation of monolayer molecular networks with structural disorders, facilitating the design and exploration of amorphous MOF materials with intriguing properties.

Morphometric study of the triangle of Petit in human fetuses.

BACKGROUND: The inferior lumbar triangle of Petit is bounded by the iliac crest, lateral border of the latissimus dorsi and the medial border of the external oblique. OBJECTIVES: In the present study, we aimed to quantitatively examine the base, sides, area, and interior angles of the inferior lumbar triangle in the human fetus so as to provide their growth dynamics. MATERIAL AND METHODS: Using anatomical dissection, digital image analysis (NIS-Elements AR 3.0), and statistics (Student's t-test, regression analysis), we measured the base, 2 sides, area and interior angles of Petit's triangle in 35 fetuses of both sexes (16 male, 19 female) aged 14-24 weeks. RESULTS: Neither sex nor laterality differences were found. All the parameters studied increased commensurately with age. The linear functions were computed as follows: y = -0.427 + 0.302 × age for base, y = 1.386 + 0.278 × age for medial side, y = 0.871 + 0.323 × age for lateral side, and y = -13.230 + 1.590 × age for area of the Petit triangle. CONCLUSIONS: In terms of geometry, Petit triangle reveals neither male-female nor right-left differences. An increase in both lengths and area of the inferior lumbar triangle follows proportionately. The Petit triangle is an acute one in the human fetus.

Growth dynamics of the triceps brachii muscle in the human fetus.

BACKGROUND: The triceps brachii muscle, the strongest extensor of the elbow joint, is characterized by the three heads: long, lateral and medial. OBJECTIVES: In the present study we aimed to examine the linear parameters (length, width) of the fetal triceps brachii muscle and to provide their growth dynamics. MATERIAL AND METHODS: Using anatomical dissection, digital image analysis (Multiscan v.14.02), and statistics (Student's t-test, regression analysis) we measured in mm the length and width of the triceps brachii in 30 fetuses of both sexes (12♂,18♀) aged 12-29 weeks. RESULTS: Neither sex nor laterality differences were found. All the parameters studied increased proportionately with age. The linear functions were computed as follows: y = 6.797 + 2.079 x Age (r = 0.886) for length of the long head's belly, y = - 0.041 + 0.215 × Age (r = 0.786) for width of the long head's belly, y = 1.889 + 0.174 × Age (r = 0.796) for length of the long head's proximal tendon, y = 0.158 + 0.052 × Age (r = 0.864) for width of the long head's proximal tendon, y = 5.270 + 1.809 × Age (r = 0.855) for length of the lateral head's belly, y = 0.348 + 0.284 × A ge (r = 0.829) for width of the lateral head's belly, y = 0.942 + 1.837 × Age (r = 0.839) for length of the medial head's belly, y = 0.314 + 0.234 × Age (r = 0.852) for width of the medial head's belly, y = - 3.191 + 0.984 × Age (r = 0.929) for lenght of the common tendon, and y = - 0.478 + 0.133 × Age (r = 0.933) for width of the common tendon. CONCLUSIONS: Neither male-female nor right-left differences are observed in morphometric parameters of the triceps brachii muscle. The long head's belly is the thinnest, while the lateral head's belly is the widest one. The long head is the longest and the medial head is the shortest one. The developmental dynamics of the triceps brachii muscle follow proportionately.