Effects of structural differences on the NMR chemical shifts in cinnamic acid derivatives: Comparison of GIAO and GIPAW calculations

A Comprehensive Survey of Phenolic Constituents Reported in Monofloral Honeys around the Globe

The aim of this review is to provide a comprehensive overview of the large variety of phenolic compounds that have to date been identified in a wide range of monofloral honeys found globally. The collated information is structured along several themes, including the botanical family and genus of the monofloral honeys for which phenolic constituents have been reported, the chemical classes the phenolic compounds can be attributed to, and the analytical method employed in compound determination as well as countries with a particular research focus on phenolic honey constituents. This review covers 130 research papers that detail the phenolic constituents of a total of 556 monofloral honeys. Based on the findings of this review, it can be concluded that most of these honeys belong to the Myrtaceae and Fabaceae families and that Robinia (Robinia pseudoacacia, Fabaceae), Manuka (Leptospermum scoparium, Myrtaceae), and Chestnut (Castanea sp., Fagaceae) honeys are to date the most studied honeys for phenolic compound determination. China, Italy, and Turkey are the major honey phenolic research hubs. To date, 161 individual phenolic compounds belonging to five major compound groups have been reported, with caffeic acid, gallic acid, ferulic acid and quercetin being the most widely reported among them. HPLC with photodiode array detection appears to be the most popular method for chemical structure identification.

Phytochemical, Antiplasmodial, Cytotoxic and Antimicrobial Evaluation of a Southeast Brazilian Brown Propolis Produced by Apis mellifera Bees

Seven phenolic compounds (ferulic acid, caffeic acid, 4-methoxycinnamic acid, 3,4-dimethoxycinnamic acid, 3-hydroxy-4-methoxybenzaldehyde, 3-methoxy-4-hydroxypropiophenone and 1-O,2-O-digalloyl-6-O-trans-p-coumaroyl-β-D-glucopyranoside), a flavanonol (7-O-methylaromadendrin), two lignans (pinoresinol and matairesinol) and six diterpenic acids/alcohol (19-acetoxy-13-hydroxyabda-8(17),14-diene, totarol, 7-oxodehydroabietic acid, dehydroabietic acid, communic acid and isopimaric acid) were isolated from the hydroalcoholic extract of a Brazilian Brown Propolis and characterized by NMR spectral data analysis. The volatile fraction of brown propolis was characterized by CG-MS, composed mainly of monoterpenes and sesquiterpenes, being the major α-pinene (18.4 %) and β-pinene (10.3 %). This propolis chemical profile indicates that Pinus spp., Eucalyptus spp. and Araucaria angustifolia might be its primary plants source. The brown propolis displayed significant activity against Plasmodium falciparum D6 and W2 strains with IC₅₀ of 5.3 and 9.7 μg/mL, respectively. The volatile fraction was also active with IC₅₀ of 22.5 and 41.8 μg/mL, respectively. Among the compounds, 1-O,2-O-digalloyl-6-O-trans-p-coumaroyl-β-D-glucopyranoside showed IC₅₀ of 3.1 and 1.0 μg/mL against D6 and W2 strains, respectively, while communic acid showed an IC₅₀ of 4.0 μg/mL against W2 strain. Cytotoxicity was determined on four tumor cell lines (SK-MEL, KB, BT-549, and SK-OV-3) and two normal renal cell lines (LLC-PK1 and VERO). Matairesinol, 7-O-methylaromadendrin, and isopimaric acid showed an IC₅₀ range of 1.8-0.78 μg/mL, 7.3-100 μg/mL, and 17-18 μg/mL, respectively, against the tumor cell lines but they were not cytotoxic against normal cell lines. The crude extract of brown propolis displayed antimicrobial activity against C. neoformans, methicillin-resistant Staphylococcus aureus, and P. aeruginosa at 29.9 μg/mL, 178.9 μg/mL, and 160.7 μg/mL, respectively. The volatile fraction inhibited the growth of C. neoformans at 53.0 μg/mL. The compounds 3-hydroxy-4-methoxybenzaldehyde, 3-methoxy-4-hydroxypropiophenone and 7-oxodehydroabietic acid were active against C. neoformans, and caffeic and communic acids were active against methicillin-resistant Staphylococcus aureus.

Combination of solid-state NMR, molecular mechanics and DFT calculations for the molecular structure determination of methyl glycoside benzoates

A reliable method for molecular structure determination, excluding single-crystal X-ray diffraction (SCXRD), has been applied to six methyl glycoside tetrabenzoates. The proposed method is based on a global conformational search using molecular mechanics and subsequent DFT calculations guided by a solid-state NMR experiment. The accuracy of the applied method has been verified on three methyl glycoside benzoates for which the SCXRD analysis has been completed. It appeared that the calculated conformations of unprivileged energy could be found in the solid state. Bulky substituents (benzoates) exerted less energetically favored interactions in crystals in contrast to isolated molecules. Therefore, solid-state NMR was revealed to be an indispensable approach for choosing credible conformations from the calculated conformations.

Encapsulation of essential oils using cinnamic acid grafted chitosan nanogel: Preparation, characterization and antifungal activity

Chemical modifications in the chitosan structure may result in obtaining a new material with improved chemical properties, such as an ability to encapsulate lipophilic compounds. This study aimed to synthesize cinnamic acid grafted chitosan nanogel to encapsulate the essential oils of Syzygium aromaticum and Cinnamomum ssp., in order to develop a material to be applied in the control of dermatophytosis caused by the fungus Microsporum canis. The cinnamic acid graft in chitosan was verified by the Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Solid State Nuclear Magnetic Resonance of the ¹³C Nucleus (¹³C SSNMR) and Thermal analysis coupled to mass spectrometry (TG-MS) techniques. The nanogel obtained showed affinity for the essential oils of S. aromaticum and Cinnamomum, with encapsulation efficiencies equal to 74% and 89%, respectively. When in an aqueous medium the nanogel with the encapsulated essential oils was able to form stable nanoparticles with average sizes of 176.0 ± 54.3 nm and 263.0 ± 81.4 nm. The cinnamic acid grafted chitosan nanogel showed antifungal activity in vitro against M. canis, inhibiting up to 53.96% of its mycelial growth. Complete inhibition of mycelial growth was achieved by the nanogel with encapsulated essential oils. The results found in this work demonstrated the development of a material with potential application in the control of dermatophytosis caused by the fungus M. canis.

Pharmaceutical Hydrates Analysis-Overview of Methods and Recent Advances

This review discusses a set of instrumental and computational methods that are used to characterize hydrated forms of APIs (active pharmaceutical ingredients). The focus has been put on highlighting advantages as well as on presenting some limitations of the selected analytical approaches. This has been performed in order to facilitate the choice of an appropriate method depending on the type of the structural feature that is to be analyzed, that is, degree of hydration, crystal structure and dynamics, and (de)hydration kinetics. The presented techniques include X-ray diffraction (single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD)), spectroscopic (solid state nuclear magnetic resonance spectroscopy (ssNMR), Fourier-transformed infrared spectroscopy (FT-IR), Raman spectroscopy), thermal (differential scanning calorimetry (DSC), thermogravimetric analysis (TGA)), gravimetric (dynamic vapour sorption (DVS)), and computational (molecular mechanics (MM), Quantum Mechanics (QM), molecular dynamics (MD)) methods. Further, the successful applications of the presented methods in the studies of hydrated APIs as well as studies on the excipients' influence on these processes have been described in many examples.

Application of Various Molecular Modelling Methods in the Study of Estrogens and Xenoestrogens

In this review, applications of various molecular modelling methods in the study of estrogens and xenoestrogens are summarized. Selected biomolecules that are the most commonly chosen as molecular modelling objects in this field are presented. In most of the reviewed works, ligand docking using solely force field methods was performed, employing various molecular targets involved in metabolism and action of estrogens. Other molecular modelling methods such as molecular dynamics and combined quantum mechanics with molecular mechanics have also been successfully used to predict the properties of estrogens and xenoestrogens. Among published works, a great number also focused on the application of different types of quantitative structure-activity relationship (QSAR) analyses to examine estrogen's structures and activities. Although the interactions between estrogens and xenoestrogens with various proteins are the most commonly studied, other aspects such as penetration of estrogens through lipid bilayers or their ability to adsorb on different materials are also explored using theoretical calculations. Apart from molecular mechanics and statistical methods, quantum mechanics calculations are also employed in the studies of estrogens and xenoestrogens. Their applications include computation of spectroscopic properties, both vibrational and Nuclear Magnetic Resonance (NMR), and also in quantum molecular dynamics simulations and crystal structure prediction. The main aim of this review is to present the great potential and versatility of various molecular modelling methods in the studies on estrogens and xenoestrogens.

Periodic DFT Calculations-Review of Applications in the Pharmaceutical Sciences

In the introduction to this review the complex chemistry of solid-state pharmaceutical compounds is summarized. It is also explained why the density functional theory (DFT) periodic calculations became recently so popular in studying the solid APIs (active pharmaceutical ingredients). Further, the most popular programs enabling DFT periodic calculations are presented and compared. Subsequently, on the large number of examples, the applications of such calculations in pharmaceutical sciences are discussed. The mentioned topics include, among others, validation of the experimentally obtained crystal structures and crystal structure prediction, insight into crystallization and solvation processes, development of new polymorph synthesis ways, and formulation techniques as well as application of the periodic DFT calculations in the drug analysis.

A theoretical NMR study of polymorphism in crystal structures of azoles and benzazoles

The NMR chemical shifts of two azoles and one benzazole whose crystal structures present polymorphism have been computed using the GIPAW approach. ¹⁵ N and ¹³ C nuclei have been studied. Statistical analysis of the computed ¹³ C and ¹⁵ N chemical shifts indicates that the GIPAW chemical shifts reproduce with a high degree of accuracy those experimentally reported. This methodology can be used to identify other polymorphic crystal structures.

Application of combined solid-state NMR and DFT calculations for the study of piracetam polymorphism

Piracetam, a popular nootropic drug, widely used in the treatment of age-associated mental decline and disorders of the nervous system such as Alzheimer's disease and dementia exists under normal pressure in three polymorphic forms (P1, P2 and P3) of different stability. In this work the relative stability of piracetam polymorphs depending on the temperature was studied using the ssNMR spectroscopy combined with ab initio DFT calculations. The ssNMR spectroscopy enabled the analysis of polymorphic phase transition in the case of pure active substance as well as polymorphic form identification in the analysis of the commercial solid dosage formulations. Quantum chemical calculations of phonon density of states were performed to obtain the temperature dependence of the enthalpy, entropy and free energy of the piracetam polymorphs in a quasi-harmonic approximation. GIPAW NMR calculations combined with molecular dynamics were performed to support the chemical shift assignment. The obtained results showed that DFT calculations can be used not only to obtain the NMR parameters but also to predict the influence of the temperature on the stability order of the polymorphic forms of molecular crystals.

A theoretical NMR study of selected benzazoles: Comparison of GIPAW and GIAO-PCM (DMSO) calculations

This paper compares the absolute shieldings obtained by gauge-including-projected-augmented-wave (GIPAW) to those obtained by gauge-invariant atomic orbital/Becke, 3-parameter, Lee-Yang-Parr (GIAO/B3LYP)/6-311++G(d,p)-polarizable continuum model (PCM, dimethyl sulfoxide) for nine benzazoles (benzimidazoles, indazoles, and benzotriazoles) recorded in the solid-state. Three nuclei were explored, ¹³ C, ¹⁵ N, and ¹⁹ F, and the gauge-including-projected-augmented-wave approach only proved better for ¹⁵ N MAS NMR.

Pharmaceutical aspects of salt and cocrystal forms of APIs and characterization challenges

In recent years many efforts have been devoted to the screening and the study of new solid-state forms of old active pharmaceutical ingredients (APIs) with salification or co-crystallization processes, thus modulating final properties without changing the pharmacological nature. Salts, hydrates/solvates, and cocrystals are the common solid-state forms employed. They offer the intriguing possibility of exploring different pharmaceutical properties for a single API in the quest of enhancing the final drug product. New synthetic strategies and advanced characterization techniques have been recently proposed in this hot topic for pharmaceutical companies. This paper reviews the recent progresses in the field particularly focusing on the characterization challenges encountered when the nature of the solid-state form must be determined. The aim of this article is to offer the state-of-the-art on this subject in order to develop new insights and to promote cooperative efforts in the fascinating field of API salt and cocrystal forms.