Computational prediction of formulation strategies for beyond-rule-of-5 compounds ☆

Tetraphenylporphyrin (H2TPP) and zinc tetraphenylporphyrin (ZnTPP) are widely used benchmark molecules in diverse photochemical studies given facile synthetic access, rich visible-region spectra, and broad structural analogy to chlorophylls. Yet the literature values for each key photophysical parameter – the molar absorption coefficient (e), fluorescence quantum yield (Φf), and also singlet excited-state lifetime (τS) – vary over an astonishing range. Here, a comprehensive literature review (∼1940–September 2020) encompassing 871 publications is reported for these essential parameters. Each parameter is determined by measurement with distinct instrumentation and suffers idiosyncratic sources of error. The best values for H2TPP are e = 460,000 cm−1·M−1, Φf = 0.090, and τS = 12.8 ns in Ar- purged toluene (Φf = 0.070, τS = 9.9 ns in toluene in air); the best values for ZnTPP are e = 560,000 cm−1·M−1, Φf = 0.030, and τS = 2.1 ns in Ar-purged toluene (Φf = 0.029, τS = 2.0 ns in toluene in air). The choice of values for such parameters has far-reaching consequences in photochemistry ranging from fluorescence (or Forster) resonance energy transfer (FRET) processes to assessments of molecular brightness.

Comprehensive review of photophysical parameters (ε, Φf, τs) of tetraphenylporphyrin (H2TPP) and zinc tetraphenylporphyrin (ZnTPP) – Critical benchmark molecules in photochemistry and photosynthesis

This highlight critically compares various techniques to grow single crystals when only a few milligrams are available of the compound of interest. The authors describe vapour diffusion, evaporation, cooling, and layering techniques, as well as crystallisation in gels. A table of successfully applied solvent/antisolvent combinations for initial screening is given. Additionally, a comprehensive table of 107 solvents with their boiling points, densities and dielectric constants helps to optimise the crystal growth.

/pdf/some-thoughts-about-the-single-crystal-growth-of-small-10b2w3ah66.pdf

Some thoughts about the single crystal growth of small molecules

We present a novel computational tool which predicts the glass-forming ability of drug compounds solely from their molecular structure Compounds which show solid-state limited aqueous solubility were selected, and their glass-forming ability was determined upon spray-drying, melt-quenching and mechanical activation The solids produced were analyzed by differential scanning calorimetry (DSC) and powder X-ray diffraction Compounds becoming at least partially amorphous on processing were classified as glass-formers, whereas those remaining crystalline regardless of the process method were classified as non-glass-forming compounds A predictive model of the glass-forming ability, designed to separate between these two classes, was developed through the use of partial least-squares projection to latent structure discriminant analysis (PLS-DA) and calculated molecular descriptors In total, ten of the 16 compounds were determined experimentally to be good glass-formers and the PLS-DA model correctly sorted 15 of the compounds using four molecular descriptors only An external test set was predicted with an accuracy of 75%, and, hence, the PLS-DA model developed was shown to be applicable for the identification of compounds that have the potential to be designed as amorphous formulations The model suggests that larger molecules with a low number of benzene rings, low level of molecular symmetry, branched carbon skeletons and electronegative atoms have the ability to form a glass To conclude, we have developed a predictive, transparent and interpretable computational model for the identification of drug molecules capable of being glass-formers The model allows an assessment of amorphization as a formulation strategy in the early drug development process, and can be applied before compound synthesis

Toward in silico prediction of glass-forming ability from molecular structure alone: a screening tool in early drug development.

Materials containing azobenzene chromophores exhibit photomechanical behaviors, including the formation of surface relief gratings (SRG) caused by irradiation with two interfering laser beams. While azo-functionalized polymers were extensively studied, small molecules offer the advantage of being monodisperse species, which translates into easier synthesis and purification, as well as more uniform behavior. A drawback is that they tend to crystallize and do not always form high-quality thin films. Glass-forming compounds incorporating azobenzene were previously synthesized in several synthetic steps and in low yield. Herein, a Disperse Red 1 (DR1) functionalized with a mexylaminotriazine group is synthesized in 94% yield using a simple and straightforward procedure. It shows both the ability to form extremely stable glassy phases, and the ability to form SRG in the solid state with growth rates and grating heights closely similar to DR1-functionalized polymers.

Disperse and disordered: a mexylaminotriazine-substituted azobenzene derivative with superior glass and surface relief grating formation

A glass forming module for organic molecules: making tetraphenylporphyrin lose its crystallinity.

One ring to rule them all: effect of aryl substitution on glass-forming ability in mexylaminotriazine molecular glasses

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A glass forming module for organic molecules: making tetraphenylporphyrin lose its crystallinity.

One ring to rule them all: effect of aryl substitution on glass-forming ability in mexylaminotriazine molecular glasses