Impact Of Substitution Pattern Research Articles

Impact of Substitution Pattern and Chain Length on the Thermotropic Properties of Alkoxy-Substituted Triphenyl-Tristriazolotriazines.

Tristriazolotriazines (TTTs) with a threefold alkoxyphenyl substitution were prepared and studied by DSC, polarized optical microscopy (POM) and X-ray scattering. Six pentyloxy chains are sufficient to induce liquid-crystalline behavior in these star-shaped compounds. Thermotropic properties of TTTs with varying substitution patterns and a periphery of linear chains of different lengths, branching in the chain and swallow-tails, are compared. Generally, these disks display broad and stable thermotropic mesophases, with the tangential TTT being superior to the radial isomer. The structure–property relationships of the number of alkyl chains, their position, length and structure were studied.

Comparative enantioseparation of chiral 4,4’-bipyridine derivatives on coated and immobilized amylose-based chiral stationary phases

The chromatographic performances of four coated and immobilized amylose phenylcarbamate-based chiral columns were evaluated and compared under normal phase (NP) elution conditions by using chiral 4,4’-bipyridine derivatives as analytes. n-Hexane/2-propanol 90:10 and n-hexane/2-propanol/methanol 90:5:5 mixtures were employed as mobile phases (MPs), and the effect of adding methanol in the MP on retention and selectivity was considered. The effect of temperature on retention and selectivity was also evaluated, and overall thermodynamic parameters associated with the analyte adsorption onto the CSP surface were derived from van't Hoff plots. Interesting cases of enantiomer elution order (EEO) reversal, which are dependent on the nature of polar modifier, analyte structure, column-type, and temperature, were observed. The impact of substitution pattern and electronic properties of analytes and selectors on the separation behaviour was investigated by correlating chromatographic parameters and molecular properties determined by using density functional theory (DFT) calculations. Both coated and immobilized amylose tris(3,5-dimethylphenylcarbamate) columns allowed for the baseline enantioseparation (2.0 ≤ RS ≤ 4.9) of all 4,4’-bipyridines considered in this study. These results appear particularly useful because both enantiomers of these 4,4’-bipyridine derivatives are currently under investigation as new inhibitors of transthyretin fibrillogenesis, a biochemical phenomenon which is implicated to cause amyloid diseases.

Insights into the impact of shape and electronic properties on the enantioseparation of polyhalogenated 4,4′-bipyridines on polysaccharide-type selectors. Evidence of stereoselective halogen bonding interactions

Starting from the high-performance liquid chromatography (HPLC) enantioseparation data collected by using twelve polyhalogenated 2,2′-dichloro-3-substituted-5,5′-dihalo-4,4′-bipyridines as test probes on seven polysaccharide-based chiral stationary phases (CSPs) under multimodal elution, the impact of substitution pattern, shape and electronic properties of the molecules on the separation behaviour was investigated through the evaluation of the chromatographic parameters (k, α, Rs) and molecular properties determined by means of quantum chemistry calculations. The computational/chromatographic screening furnished relevant structure-chromatographic behaviour relationships and some molecular interactions involved in the chiral discrimination process could be identified. In particular, a halogen bonding interaction (I.O) could reasonably explain the high enantioseparation (α=1.80, Rs=8.2) observed for the 2,2′-dichloro-3,5′-diiodo-5-bromo-4,4′-bipyridine on Lux Cellulose-1. To the best of our knowledge, this is the first report supporting the involvement of a stereoselective halogen bonding interaction in polysaccharide-based CSPs. Moreover, having at disposal a sufficient set of data, the unknown absolute configurations of the eluted enantiomers of 3-methyl-, 3-thiomethyl- and 3-diphenylphosphinoyl-2,2′-dichloro-5,5′-dibromo-4,4′-bipyridines could be deduced by chromatographic correlation with the enantiomer elution order (EEO) of the related compounds of known absolute configuration.

High-performance liquid chromatography enantioseparation of atropisomeric 4,4′-bipyridines on polysaccharide-type chiral stationary phases: Impact of substituents and electronic properties

The high performance liquid chromatography (HPLC) enantioseparation of eleven atropisomeric 4,4′-bipyridines was performed in the normal and polar organic phase mode using three cellulose-based chiral stationary phases (CSPs), namely Lux® Cellulose-1, Lux® Cellulose-2, Lux® Cellulose-4, and two amylose-based CSPs, Chiralpak® AD-H and Lux® Amylose-2. n-Hexane/2-propanol mixtures and pure ethanol were employed as mobile phases. The combined use of Chiralpak® AD-H and Lux® Cellulose-2 allowed to enantioseparate all the considered bipyridines. Ten bipyridines were enantioseparated at the multimilligram level allowing the elution sequence determination of the enantiomers as well as their future use for the preparation of homochiral metal organic frameworks (MOFs). Moreover, the performance of the CSPs regarding the same bipyridine was different and dependent on the backbone as well as on the side chain of the polymer. The impact of substitution pattern, shape and electronic properties of the molecules on the separation behavior was investigated through the evaluation of retention factors (k), separation factors (α), resolution (Rs) and molecular properties determined using density functional theory (DFT) calculations. In this regard, the substituents at the 3,3′,5,5′ positions of the 4,4′-bipyridyl rings exhibited a pivotal role on the enantioseparation.

Synthesis, characterization, and spectroscopy of 4,7,12,15-[2.2]paracyclophane containing donor and acceptor groups: impact of substitution patterns on through-space charge transfer.

This paper reports the synthesis of 4,7,12,15-tetra(4'-dihexylaminostyryl)[2.2]paracyclophane (1), 4-(4'-dihexylaminostyryl)-7,12,15-tri(4' '-nitrostyryl)[2.2]paracyclophane (2), 4,7-bis(4'-dihexylaminostyryl)-12,15-bis(4' '-nitrostyryl)-[2.2]paracyclophane (3), 4,7,12-tris(4'-dihexylaminostyryl)-15-(4' '-nitrostyryl)[2.2]paracyclophane (4), 4,15-bis(4'-dihexylaminostyryl)-7,12-bis(4' '-nitrostyryl)[2.2]paracyclophane (5), and 4,12-bis(4'-dihexylaminostyryl)-7,15-bis(4' '-nitrostyryl)[2.2]paracyclophane (6). These molecules represent different combinations of bringing together distyrylbenzene chromophores containing donor and acceptor groups across a [2.2]paracyclophane (pCp) bridge. X-ray diffraction studies show that the lattice arrangements of 1 and 3 are considerably different from those of the parent chromophores 1,4-bis(4'dihexylaminostyryl)benzene (DD) and 1,4-di(4'-nitrostyryl)benzene (AA). Differences are brought about by the constraint by the pCp bridge and by virtue of chirality in the "paired" species. The absorption and emission spectra of 1-6 are also presented. Clear evidence of delocalization across the pCp structure is observed. Further, in the case of 2, 3, and 4, emission from the second excited state takes place.

Impact of substitution patterns on phonological learning by misarticulating children

Impact of substitution patterns on phonological learning by misarticulating children

Impact of substitution patterns on phonological learning by misarticulating children

Learning and generalization of treated sounds to different word positions is a desired outcome of intervention in the phonologically disordered child's system. Unfortunately, children do not always learn the sound that is treated; nor do they always demonstrate across-word generalization. One possible explanation for differences in treatment outcome may relate to the pretreatment substitution patterns used by different disordered children. This post-hoc analysis of treatment data examines the effects on sound learning and generalization of consistent versus inconsistent substitutes. With a consistent substitute across-word position (CS), the same phone was used in initial, medial and final position for a phoneme that was not in the child's inventory. An inconsistent substitute was evidenced by a different phone for a target sound in each position of a word (InAP), or even within word position (InWP) for an error sound. Fourteen children with severe phonological disorders were treated on an obstruent in initial or final word position. Seven of these children had a consistent substitute for the treated obstruent, two children had variable substitutes across word position, and five children had variable substitutes within and across word position. The analysis revealed a tight relationship between pretreatment substitution patterns and learning. The seven children with a consistent substitute for an error sound learned the sound targeted in treatment and generalized this knowledge to other word positions. Children who had variable substitutes across word position learned the treated sound, but only in the treated word position. Four of the five children in the InWP group did not learn to produce the sound targeted in treatment in any word position. These results suggest that pretreatment substitution patterns may be a predictor of learning and generalization in phonologically disordered children.