Carbohydrate Hydroxyl Research Articles

Equilibrium of sorption of Tribulus Terrestris steroid saponins on a natural polymer sorbent – chitosan

Steroidal saponins have a wide spectrum of pharmacological action and therefore are widely used in pharmacological practice. Chitosan is a unique material. Its biocompatibility, biodegradability, non-toxicity, as well as its cationic nature reveal the potential of this biopolymer as a carrier of drugs for their targeted delivery. The immobilization of biologically active substances can be carried out in a variety of ways - nanomicelles with an encapsulated drug or their polyelectrolyte complexes with oligochitosans, depending on the nature of the active substance. The study of the sorption of saponins by chitosan under equilibrium conditions was studied. An analysis of the equilibrium curves of sorption of Tribulus Terrestris saponin on chitosan was carried out. The presence of a local minimum on the isotherm in the region of solution concentrations corresponding to micellization was revealed. It has been established that the course of the saponin sorption isotherm is determined by competing association processes in a solution and on the surface of chitosan. The pH of the solution did not change, which indicated the absence of ionic interactions involving the protonated amino group of chitosan. The moisture content of chitosan during the sorption of saponin was studied. The antibatic nature of the absorption curves and moisture content curves of chitosan was revealed. An analysis of the saponin sorption isotherm was carried out using the adsorption theories of Langmuir, Freundlich, and BET. High values of the correlation coefficients allowed us to use the Freundlich equation for a quantitative description of the isotherm in the initial section, and to analyse the entire isotherm using the BET theory, which takes into account the polymolecular nature of sorption. The results obtained for the description of the sorption isotherm of saponin were consistent with the proposed mechanism of its absorption by chitosan. Using IR spectroscopy, it was established that the interaction in the sorbent-sorbate system was due to the emerging hydrogen bonds between the amino and hydroxyl groups of chitosan and the hydroxyl groups of saponin carbohydrates. The results obtained, as well as literature data, confirm the formation of cavities in polysaccharides into which saponin is “incorporated”. In our case, the presence of cavities formed by seven monomer fragments of chitosan, the stability of which is fixed by hydrogen bonds was discussed.

Production and structural characterization of eco-friendly bioemulsifier SC04 from Saccharomyces cerevisiae strain MYN04 with potential applications

BackgroundBioemulsifiers are natural or microbial-based products with the ability to emulsify hydrophobic compounds in water. These compounds are biodegradable, eco-friendly, and find applications in various industries.ResultsThirteen yeasts were isolated from different sources in Alexandria, Egypt, and evaluated for their potential to produce intracellular bioemulsifiers. One yeast, isolated from a local market in Egypt, showed the highest emulsification index (EI24) value. Through 26S rRNA sequencing, this yeast was identified as Saccharomyces cerevisiae strain MYN04. The growth kinetics of the isolate were studied, and after 36 h of incubation, the highest yield of cell dry weight (CDW) was obtained at 3.17 g/L, with an EI24 of 55.6%. Experimental designs were used to investigate the effects of culture parameters on maximizing bioemulsifier SC04 production and CDW. The study achieved a maximum EI24 of 79.0 ± 2.0%. Furthermore, the crude bioemulsifier was precipitated with 50% ethanol and purified using Sephadex G-75 gel filtration chromatography. Bioemulsifier SC04 was found to consist of 27.1% carbohydrates and 72.9% proteins. Structural determination of purified bioemulsifier SC04 was carried out using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), high-performance liquid chromatography (HPLC), and nuclear magnetic resonance spectroscopy (NMR). FTIR spectroscopy revealed characteristic bands associated with carboxyl and hydroxyl groups of carbohydrates, as well as amine groups of proteins. HPLC analysis of monosaccharide composition detected the presence of mannose, galactose, and glucose. Physicochemical characterization of the fraction after gel filtration indicated that bioemulsifier SC04 is a high molecular weight protein-oligosaccharide complex. This bioemulsifier demonstrated stability at different pH values, temperatures, and salinities. At a concentration of 0.5 mg/mL, it exhibited 51.8% scavenging of DPPH radicals. Furthermore, in vitro cytotoxicity evaluation using the MTT assay revealed a noncytotoxic effect of SC04 against normal epithelial kidney cell lines.ConclusionsThis study presents a new eco-friendly bioemulsifier, named SC04, which exhibits significant emulsifying ability, antioxidant and anticancer properties, and stabilizing properties. These findings suggest that SC04 is a promising candidate for applications in the food, pharmaceutical, and industrial sectors.

A combined solid-state NMR and quantum chemical calculation study of hydrogen bonding in two forms of α-d-glucose

Hydrogen bonding plays an important role in the structure and function of a wide range of materials. Solid-state 1H nuclear magnetic resonance (NMR) spectroscopy provides a very sensitive tool to investigate the local structure of hydrogen atoms involved in hydrogen bonding. While there is extensive 1H solid-state NMR data on O–H - - O hydrogen bonding in solid carboxylic acids, there has been no systematic 1H solid-state NMR studies of hydroxyl groups in carbohydrates (and hydroxyl groups in general). With a view to studying the hydrogen bonding in more complex materials such as cellulose polymorphs, we carried out a detailed solid-state 1H NMR investigation of the model compounds α-d-glucose and α-d-glucose monohydrate. Through a combination of fast magic-angle spinning (MAS), combined rotation and multiple pulse spectroscopy (CRAMPS), and two-dimensional (2D) correlation experiments carried out at ultrahigh magnetic fields, it was possible to assign all of the aliphatic (CH), hydroxyl (OH), and water (H2O) 1H chemical shifts in both forms of α-d-glucose. Plane-wave DFT calculations were employed to improve the hydrogen atom positions for α-d-glucose monohydrate and to calculate 1H chemical shifts, providing additional support for the experimentally determined peak assignments. Finally, the relationship between the hydroxyl 1H chemical shifts and their hydrogen bonding geometry was investigated and compared to the well-established relationship for carboxylic acid protons.

SELECTION AND CHARACTERIZATION OF PEAT AND PLANT MATERIALS FOR BIOCIDAL PREPARATIONS

Sphagnum moss and peat formed on its basis is estimated by experts as ecologically pure raw material resource for development of new effective medicines as their structure contains a wide set of biologically active compounds of different classes: polysaccharides, uronic acids, flavonoids, phenocarboxylic acids, aldehydes, coumarins, triterpene
 compounds, organic acids, mineral salts, and in peat also humic substances. The objects of the study were sphagnum
 magellanicum and sphagnum fuscum peat and 4 samples of sphagnum moss: Sph. magellanicum, Sph. fuscum, Sph. angustifolium and Sph. apiculatum which in the future is supposed to be used as a raw material for preparation of biocidal
 agents. The geobotanical and physico-chemical characteristics of the selected samples was carried out. All of them are characterized by low ash content (1.32–3.59 %), high content of organic substances and their active acidity is within the range 3.8–4.4 units, which is typical for sphagnum-type raised peat and sphagnum moss. In the infrared spectra of all samples observed absorption bands due to valence and strain vibrations of hydroxyl, carboxyl, carbonyl, amide and other functional groups of carbohydrates, phenols, alcohols, organic acids, esters of aliphatic and aromatic nature, typical for
 plants-peat formers and upper peats of low degree of decomposition. It has been established that samples of sphagnum
 mosses and sphagnum peat are labile hemicellulose-containing raw materials; the amount of easily hydrolyzable polysaccharides in mosses reaches 55 %, in peats – 45 % of organic matter. The content of reducing substances in hydrolysates of hemicelluloses of mosses is 55–59 %, that of peat is 53–54 %. The mass fraction of cellulose in the organic matter of sphagnum mosses is 23–26 %, in peat 22–24, in humic substances 17.7–20.9 %. All samples contain small amounts
 (0.8–2.3 %) of extractive substances extracted by organic solvents and 7.1–13.0 % of lignin. Literature data, as well as the
 performed spectral and chemical characteristics of the selected samples showed that among the biologically active substances found in their composition, the most interesting are polysaccharide and phenolic complexes, since the pharmacological properties of sphagnum mosses and low-degradation peat can be attributed to the presence of these compounds.

Surfactants produced from carbohydrate derivatives: A review of the biobased building blocks used in their synthesis

AbstractThis work reviews the use of carbohydrates and their derivatives as renewable raw materials in the production of surfactants. Methods to attain state‐of‐the‐art carbohydrate‐derived surfactants are described. This includes surfactants widely used nowadays and others that have not yet transcended beyond the academic field. Given the abundance of hydroxyl groups in carbohydrates and the considerable quantity of different surfactant structures that can be generated during their synthesis, selectively obtaining a target product represents a challenge. Therefore, this work focuses on the platform chemicals available to synthesize biobased surfactants. The first part of the review comprises a brief introduction of simple and complex carbohydrates to better understand their chemistry. Then, a description of the processes to obtain biobased building blocks derived from carbohydrates according to the National Renewable Energy Laboratory (NREL, USA), and their usefulness in synthesizing surfactants is presented. This provides an organized inventory of the knowledge around the synthesis–production of surfactants from carbohydrate derivatives, emphasizing raw materials that could be inserted into the circular bioeconomy concept. Finally, the current industry trends and the potential role of biobased surfactants around new dioxane regulations are discussed.

Activation and Conjugation of Soluble Polysaccharides using 1-Cyano-4-Dimethylaminopyridine Tetrafluoroborate (CDAP)

Conjugate vaccines are remarkable advances in vaccinology. For the preparation of polysaccharide conjugate vaccines, the polysaccharides can be conveniently functionalized and linked to vaccine carrier proteins using 1-cyano-4-dimethylaminopyridine tetrafluoroborate (CDAP), an easy-to-handle cyanylating reagent. CDAP activates polysaccharides by reacting with carbohydrate hydroxyl groups at pH 7-9. The stability and reactivity of CDAP are highly pH-dependent. The pH of the reaction also decreases during activation due to the hydrolysis of CDAP, which makes good pH control the key to reproducible activation. The original CDAP activation protocol was performed at room temperature in unbuffered pH 9 solutions. Due to the rapid reaction under this condition (<3 min) and the accompanying fast pH drop from the rapid CDAP hydrolysis, it was challenging to quickly adjust and maintain the target reaction pH in the short time frame. The improved protocol described here is performed at 0 °C, which slows CDAP hydrolysis and extends the activation time from 3 min to ~15 min. Dimethylaminopyridine (DMAP) was also used as a buffer to pre-adjust the polysaccharide solution to the target activation pH before adding the CDAP reagent. The longer reaction time, coupled with the slower CDAP hydrolysis and the use of DMAP buffer, makes it easier to maintain the activation pH for the entire duration of the activation process. The improved protocol makes the activation process less frenetic, more reproducible, and more amenable to scaling up.

Activation and Conjugation of Soluble Polysaccharides using 1-Cyano-4-Dimethylaminopyridine Tetrafluoroborate (CDAP).

Conjugate vaccines are remarkable advances in vaccinology. For the preparation of polysaccharide conjugate vaccines, the polysaccharides can be conveniently functionalized and linked to vaccine carrier proteins using 1-cyano-4-dimethylaminopyridine tetrafluoroborate (CDAP), an easy-to-handle cyanylating reagent. CDAP activates polysaccharides by reacting with carbohydrate hydroxyl groups at pH 7-9. The stability and reactivity of CDAP are highly pH-dependent. The pH of the reaction also decreases during activation due to the hydrolysis of CDAP, which makes good pH control the key to reproducible activation. The original CDAP activation protocol was performed at room temperature in unbuffered pH 9 solutions. Due to the rapid reaction under this condition (<3 min) and the accompanying fast pH drop from the rapid CDAP hydrolysis, it was challenging to quickly adjust and maintain the target reaction pH in the short time frame. The improved protocol described here is performed at 0 °C, which slows CDAP hydrolysis and extends the activation time from 3 min to ~15 min. Dimethylaminopyridine (DMAP) was also used as a buffer to pre-adjust the polysaccharide solution to the target activation pH before adding the CDAP reagent. The longer reaction time, coupled with the slower CDAP hydrolysis and the use of DMAP buffer, makes it easier to maintain the activation pH for the entire duration of the activation process. The improved protocol makes the activation process less frenetic, more reproducible, and more amenable to scaling up.

JUSTIFICATION OF THE POSSIBILITY OF USING THERMOMODIFIED VENEER IN AN ENVIRONMENT WITH HIGH HUMIDITY

Thermally modified wood is widely used in the woodworking industry, as it has increased resistance to environmental factors (humidity, temperature). The effect of high temperature on wood causes a decrease in water adsorption by reducing the available free hydroxyl groups of carbohydrates. The reduction in hygroscopicity contributes to the treated material size stability, as swelling and shrinkage are mainly associated with the phenomena of absorption and water desorption. The study of natural weathering always takes many years. Therefore, to study the resistance of thermodified wood to environmental influences, artificial weathering is used - modeling of external factors (cyclic change of UV light and moisture). The effectiveness of the thermodified veneer use as a material for lining the furniture facades which working in different temperature and humidity conditions was established. The values of moisture and water absorption on the samples of oak veneer, which have previously undergone the heat treatment process, have been determined. It was found that the samples of oak veneer gained the most moisture from the environment in the first two days. The weight of unmodified veneer increased by 0.06 g, similar results showed veneer modified at temperatures of 160 and 190 °C. Thermodified veneer at a temperature of 250 °C for the first two days gained twice less. By the end of the experiment (next 11 days), the samples of ordinary and modified veneer at all temperatures absorbed the same amount of moisture. Untreated veneer and thermodified at temperatures of 160 and 220 °C absorbed 50-66 % of its initial weight, and modified at 250 °C – 20-36 %. Control samples of veneer during the determination of water absorption gained 98 % of the initial weight. Samples modified at 160 °C – 10, 20, 30 min showed the best result – reducing the value to 94 %, 93 % and 91 %. There is a slight improvement in water absorption after exposure to temperature 220 °C for 10, 20, 30 min – 91 %, 91 % and 90 %. Values water absorption at the level of 90 %, 89 % and 86 % were recorded in veneer samples modified at 250 °C.

Linkage Analysis of Oligosaccharides and Polysaccharides: A Tutorial.

Polysaccharides and oligosaccharides are a diverse group of natural polymers with important biological functions. The diversity of carbohydrate polymers is vast, ranging from small oligosaccharides of defined composition decorating proteins, to large, complex heteropolymers comprising integral cell wall components of plants, fungi and bacteria. An important step in the elucidation of unknown carbohydrate structures in a sample is the assessment of the various linkages present. This is accomplished by performing linkage analysis of the sample. The analysis proceeds as a successive series of chemical steps in which unlinked carbohydrate hydroxyls are marked with methyl groups, the sample is hydrolyzed into monosaccharides and reduced to alditols, and finally free hydroxyls are acetylated. Gas chromatography-mass spectrometry (GC-MS) analysis is employed to analyze the resultant partially methylated alditol acetates (PMAAs). The following paper reviews the major literature pertaining to the specific protocol for linkage analysis of carbohydrates outlined herein. The review details additional steps necessary for the completion of uronic acid linkage analysis, as well as analysis of chitin containing polymers. It also gives chromatographic examples of common erroneous results which the first time practitioner will want to be aware of. Our hope is that this protocol will serve as a definitive guide, allowing novice researchers to perform linkage analysis of carbohydrates in their own lab.

In Ukrainian

Nowadays, it is relevant to study the processes that occur at the boundary of biomolecule (cell)-nanoparticle phase distribution. There is a growing interest in studying the interaction of ultrafine silica (UFC) with saccharides, in particular glucose and fructose, as well as with N-acetylneuraminic acid (NANA) (which is а part of the body’s cell membrane), for further creation of nanocomposites with biomolecules to use in biological systems. Using the density functional theory method (DFT) within the polarization continuum model (PCM), the interaction peculiarities of monosaccharides with silica surface were examined and the influence of the NANA molecule on this process was determined. The results of the analysis of quantum chemical calculations indicate that glucose and fructose can be used as modifiers for NANA adsorption. The molecules of these carbohydrates are related to silica surface and form a complex with N-acetylneuraminic acid. It is found that hydrogen bonds between hydroxyl groups of carbohydrates and silanol groups of the UFC surface play a major part in the formation of intermolecular complexes. The calculations show that the adsorption of monosaccharides on silica surface is possible considering their location, and it also depends on how to carry out the adsorption. That is, whether the adsorption of saccharides and then of NANA, or the adsorption from monosaccharides-NANA solution on silica surface is sequential.

Synthesis of glycoconjugates utilizing the regioselectivity of a lytic polysaccharide monooxygenase

Polysaccharides from plant biomass are the most abundant renewable chemicals on Earth and can potentially be converted to a wide variety of useful glycoconjugates. Potential applications of glycoconjugates include therapeutics and drug delivery, vaccine development and as fine chemicals. While anomeric hydroxyl groups of carbohydrates are amenable to a variety of useful chemical modifications, selective cross-coupling to non-reducing ends has remained challenging. Several lytic polysaccharide monooxygenases (LPMOs), powerful enzymes known for their application in cellulose degradation, specifically oxidize non-reducing ends, introducing carbonyl groups that can be utilized for chemical coupling. This study provides a simple and highly specific approach to produce oxime-based glycoconjugates from LPMO-functionalized oligosaccharides. The products are evaluated by HPLC, mass spectrometry and NMR. Furthermore, we demonstrate potential biodegradability of these glycoconjugates using selective enzymes.

Peptidyl ω-Asp Selenoesters Enable Efficient Synthesis of N-Linked Glycopeptides.

Chemical synthesis is an attractive approach allows for the assembly of homogeneous complex N-linked glycopeptides and glycoproteins, but the limited coupling efficiency between glycans and peptides hampered the synthesis and research in the related field. Herein we developed an alternative glycosylation to construct N-linked glycopeptide via efficient selenoester-assisted aminolysis, which employs the peptidyl ω-asparagine selenoester and unprotected glycosylamine to perform rapid amide-bond ligation. This glycosylation strategy is highly compatible with the free carboxylic acids and hydroxyl groups of peptides and carbohydrates, and readily available for the assembly of structure-defined homogeneous N-linked glycopeptides, such as segments derived from glycoprotein EPO and IL-5.

Solid-state 17O NMR analysis of synthetically 17O-enriched d-glucosamine

The hydroxyl groups of carbohydrates are critical determinants of their conformational dynamics and intermolecular interactions but are difficult to characterize by conventional 1H nuclear magnetic resonance (NMR) approaches in solution. Here, we report a solid-state 17O NMR analysis of synthetic glucosamine with 17O enrichment at position 6. Based on magic-angle spinning and stationary spectral data obtained at varying magnetic fields in conjunction with quantum chemical calculations, we successfully estimated 17O chemical shift and electric field gradient tensors, providing benchmark for 17O NMR analyses of oligosaccharide structures.

Achieving multiple hydrogen/deuterium exchange timepoints of carbohydrate hydroxyls using theta-electrospray emitters.

Hydrogen/deuterium exchange coupled to mass spectrometry (HDX-MS) is a well-established technique for structural analysis of proteins. In HDX experiments it is common to label for multiple, different lengths of time to characterize protein structures and dynamics. However, applications of HDX to carbohydrates have been limited due to the rapid exchange rates of hydroxyls, which have also prevented the development and application of methods that sample HDX at multiple timepoints. Theta capillaries pulled to electrospray tips have been used to achieve microsecond reaction times. Here, we report the utilization of theta-ESI emitters to achieve multiple timepoints for deuteration of carbohydrates. We increased the labeling time for HDX by increasing the initial ESI droplet sizes using theta-ESI emitters with increasing tip opening sizes. The reaction times achieved by varying the tip sizes ranged from sub-microsecond to ∼20 μs, with the average number of deuterium exchanges varying from 0.5 ± 0.2 D to 5 ± 3 D for sodium-adducted melezitose, which contains 11 labile hydrogens. Our findings are significant because this is the first report of carbohydrates analyzed by solution-phase HDX to achieve multiple H/D exchange timepoints.

Site-Selective and Stereoselective O-Alkylation of Glycosides by Rh(II)-Catalyzed Carbenoid Insertion.

Carbohydrates are synthetically challenging molecules with vital biological roles in all living systems. Selective synthesis and functionalization of carbohydrates provide tremendous opportunities to improve our understanding on the biological functions of this fundamentally important class of molecules. However, selective functionalization of seemingly identical hydroxyl groups in carbohydrates remains a long-standing challenge in chemical synthesis. We herein describe a practical and predictable method for the site-selective and stereoselective alkylation of carbohydrate hydroxyl groups via Rh(II)-catalyzed insertion of metal carbenoid intermediates. This represents one of the mildest alkylation methods for the systematic modification of carbohydrates. Density functional theory (DFT) calculations suggest that the site selectivity is determined in the Rh(II)-carbenoid insertion step, which prefers insertion into hydroxyl groups with an adjacent axial substituent. The subsequent intramolecular enolate protonation determines the unexpected high stereoselectivity. The most prevalent trans-1,2-diols in various pyranoses can be systematically and predictably differentiated based on the model derived from DFT calculations. We also demonstrated that the selective O-alkylation method could significantly improve the efficiency and stereoselectivity of glycosylation reactions. The alkyl groups introduced to carbohydrates by OH insertion reaction can serve as functional groups, protecting groups, and directing groups.

Efficient synthesis of N- and O-linked glycopeptides using acid-labile Boc groups for the protection of carbohydrate moieties

Development of a synthetic method for the preparation of homogeneous glycopeptides and glycoproteins is important for the elucidation of their structures and functions. Here, we report on the concise and facile synthesis of glycopeptides using Boc groups for the protection of carbohydrate hydroxyl groups. This method enables us to remove the protecting groups from peptide and carbohydrate moieties in a single-step process without undesirable any side reaction.

Progress on Selective Acylation of Carbohydrate Hydroxyl Groups

AbstractSugars have always been an important component of drugs, and their design, discovery, synthesis and preparation play an important role in the diagnosis, prevention and treatment of diseases. To synthesize functional oligosaccharides, we need to perform a variety of selective hydroxyl protections of monosaccharides to synthesize functional sugar building blocks. Among these protection reactions, acylation is the most commonly used method to protect the hydroxyl groups in sugars. Regioselective acylation of saccharide hydroxyl groups needs to be achieved by catalysts. How to efficiently synthesize the target products and how to develop more selective, wider ranging, and more environmentally friendly chemical methods are a consistent goal pursued by chemistry researchers. This paper mainly introduces the research progress on six kinds of approaches for the regioselective acylation of sugar hydroxyl groups: those based on organotin, organoboron, organosilicon, metal salts, hydrogen‐bonding small organic molecules and enzyme reagents. Finally, the Minireview also summarizes the advantages and disadvantages of these catalysts and prospects for the selective acylation of sugar hydroxyl groups.

Regioselective Ring Opening of 1,3‐Dioxane‐Type Acetals in Carbohydrates

The (regio)selective manipulation of hydroxyl groups in carbohydrates has been a long‐standing challenge in (bio)organic chemistry and continues to trigger the creative minds of many chemists. Among the various strategies that have been developed to address these issues, mostly relying on multistep procedures involving the use of protecting groups, the regioselective ring opening of 1,3‐dioxane‐type acetals has emerged as a powerful tool. Since the first papers on this subject appeared in the 1960s, a large variety in both acetal types and reagents for their partial cleavage has come to the fore. This review aims to give an overview of the different carbohydrate‐derived ring systems, ranging from four‐ to seven‐membered rings, on which regioselective ring‐openings have been performed, along with the appropriate reagents and combinations thereof. The transformations on 1,3‐dioxane acetals fit in a larger group of ring opening reactions of structurally related cyclic functional groups, including 1,3‐dioxolanes, 1,3‐oxathianes, orthoesters, cyclic carbonates and silylene acetals, which will not be discussed in this review.

Direct Observation of Carbohydrate Hydroxyl Protons in Hydrogen Bonds with a Protein.

Hydroxyl proton resonances of uniformly 13C-labeled Manα(1-2)Manα(1-2)ManαOMe (Man3) bound to cyanovirin-N (CV-N) were detected at ambient temperature in aqueous solution by NMR spectroscopy. The directions of the hydroxyl groups were determined on the basis of NOEs, and a previously unknown hydrogen-bonding network between Man3 and CV-N was discovered. This is the first report on detecting hydroxyl protons of a protein-bound carbohydrate in aqueous solution by NMR. Approaches such as those presented here may open the door for accurately determining intermolecular hydrogen bonds in carbohydrate-protein complexes.

Catalytic Site-Selective Acylation of Carbohydrates Directed by Cation-n Interaction.

Site-selective functionalization of hydroxyl groups in carbohydrates is one of the long-standing challenges in chemistry. Using a pair of chiral catalysts, we now can differentiate the most prevalent trans-1,2-diols in pyranoses systematically and predictably. Density functional theory (DFT) calculations indicate that the key determining factor for the selectivity is the presence or absence of a cation-n interaction between the cation in the acylated catalyst and an appropriate lone pair in the substrate. DFT calculations also provided a predictive model for site-selectivity and this model is validated by various substrates.