Computational insights into the photocyclization of diclofenac in solution: Effects of halogen and hydrogen bonding

The effects of noncovalent interactions, namely halogen and hydrogen bonding, on the photochemical conversion of the photosensitizing drug diclofenac (DCF) in solution were investigated computationally. Both explicit and implicit solvent effects were qualitatively and quantitatively assessed employing the DFT/6-31+G(d) and SQM(PM7) levels of theory. Full geometry optimizations were performed in solution for the reactant DCF, hypothesized radical-based intermediates, and the main product at both levels of theories. Notably, in good agreement with previous experimental results concerning the intermolecular halogen bonding of DCF, the SQM(PM7) method revealed different values for d(Cl⋯O, Å) and ∠(C–Cl⋯O, °) for the two chlorine-substituents of DCF, with values of 2.63 Å/162° and 3.13 Å/142° for the trans and cis orientations, respectively. Employing the DFT/6-31+G(d) method with implicit solvent effects was not conclusive; however, explicit solvent effects confirmed the key contribution of hydrogen and halogen bonding in stabilizing/destabilizing the reactant and hypothesized intermediates. Interestingly, the obtained results revealed that a protic solvent such as water can increase the rate of photocyclization of DCF not only through hydrogen bonding effects, but also through halogen bonding. Furthermore, the atomic charges of atoms majorly involved in the photocyclization of DCF were calculated using different methods, namely Mulliken, Hirshfeld, and natural bond orbital (NBO). The obtained results revealed that in all cases there is a notable nonequivalency in the noncovalent intermolecular interactions of the two chlorine substituents of DCF and the radical intermediates with the solvent, which in turn may account for the discrepancy of their reactivity in different media. These computational results provide insight into the importance of halogen and hydrogen bonding throughout the progression of the photochemical conversion of DCF in solution.The partial financial support by Qatar University is thankfully acknowledgedScopu

Spectrofluorometric investigations on the solvent effects on the photocyclization reaction of diclofenac

The solvent effects on the photochemical conversion rate of the photosensitizing drug diclofenac (DCF) were investigated using steady-state fluorescence spectroscopy. The spectral information obtained for the photochemical reaction of DCF in a set of neat solvents demonstrates that the photoconversion reaction rate of DCF is not only medium polarity dependent but also hydrogen-bonding dependent. The solvent effects were qualitatively and quantitatively assessed employing various solvatochromic models, including multi-parameter linear regression analysis (MLRA). Interestingly, the MLRA results (R = 0.99) revealed that the photoconversion rate increases with increasing solvent polarizability (π*) and H-bond donor capability (α), whereas the rate decreases with increasing hydrogen-bond acceptor capability (β). However, predominant effect of the solvent acidity compared to basicity and polarizability was observed. A hypothesis rationalizing the effects of H-bonding and medium polarity on DCF photoconversion reaction is presented and discussed.Partial support from Qatar University is acknowledged. Open Access funding provided by the Qatar National Library

Experimental and DFT/TD-DFT computational investigations of the solvent effect on the spectral properties of nitro substituted pyridino[3,4-c]coumarins

The UV/Vis absorption characteristics of newly synthesized pyridino[3,4-c] coumarins in different neat solvents were investigated experimentally and computationally. It is noted that the nitro-substituted pyridocoumarins can exhibit spectral features with characteristic band in the visible region, which in turn is solvent's polarity dependent with negative solvatochromic behavior. Using the Kamet-Taft approach, the obtained results (R = 0.991) revealed that this negative solvatochromic behavior is dominantly influenced by the solvents' polarizability and hydrogen bonding capability. The experimental results of the spectral properties in solution were interpreted at the molecular level with aid of the DFT and TD-DFT/CAM-B3LYP/6-31+G(d) computational methods with IEFPCM implicit solvation approach. Per benchmarking the TD-DFT simulated spectra with the experimental one, it is demonstrated that the nitro group can induce an intramolecular charge transfer to afford two resonance structures of distinctive spectral features. Such difference in spectral features is interpreted in terms of molecular orbitals, where the two potential resonance structures exhibit different natures for the frontier molecular orbitals, namely the HOMO and LUMO with a significant difference in the corresponding energy gaps. Moreover, the electrostatic potential surfaces of both structures indicate relatively different accessibility toward intermolecular hydrogen bonding with the solvent molecules. The achieved results would provide valuable insights concerning the noteworthy influence of the substituents of pyridocoumarins on their spectral properties and correspondingly their solvatochromic behaviors at the molecular level in different media

Combined experimental and computational investigations of the fluorosolvatochromism of chromeno[4,3-b]pyridine derivatives: Effect of the methoxy substitution

Extensive research has been conducted on the spectral properties of chromeno[4,3-b]pyridine derivatives, owing to their potential applications in sensing, optoelectronic devices, and drug discovery. This study presents a comprehensive investigation into the fluorosolvatochromism of selected chromeno[4,3-b]pyridine derivatives, with a particular emphasis on the impact of methoxy substitution. Three derivatives were synthesized and subjected to spectral analysis: chromeno[4,3-b]pyridine-3-carboxylate (I) as the parent compound, and its 7-methoxy (II) and 8-methoxy (III) substituted derivatives. The UV–Vis absorption spectra of all derivatives exhibited a broad band with a maximum absorption wavelength that remained unaffected by the surrounding medium. However, distinct fluorescence properties were observed among them. Specifically, derivative II displayed notable fluorescence, while derivatives I and III exhibited no fluorescence properties. Furthermore, derivative II exhibited a fluorescence spectrum that is significantly influenced by the polarity of the medium. To investigate the fluorosolvatochromic behavior in depth, we conducted a comprehensive analysis using various neat solvents with different polarities and hydrogen bonding capabilities. The results obtained revealed a significant positive fluorosolvatochromism, with a bathochromic shift in the fluorescence spectrum as the solvent polarity increased. To understand how specific and non-specific interactions between the solute and the solvent affected the fluorosolvatochromism of II, we employed the four empirical scales model of Catalán. The obtained results demonstrated that intramolecular charge transfer played a crucial role in the fluorescence behavior of II. To provide a molecular-level explanation for the experimental spectral properties, we utilized the DFT and TD-DFT/B3LYP/6-31 + G(d) computational methods with the IEFPCM implicit solvation approach. The spectral differences between II and III were rationalized in terms of the frontier molecular orbitals (FMOs: the HOMO and LUMO), where distinct natures were observed among the examined derivatives. This study offers valuable insights into the impact of methoxy substitution on the physical and chemical properties of chromeno[4,3-b]pyridine derivatives, specifically concerning their spectral properties as elucidated by their fluorosolvatochromic behavior.The support from Qatar University is thankfully acknowledged. We thank the Central Laboratories Unit at Qatar University for their support in compounds analysis. Major aspects of the calculations were performed using the supercomputing facility at Texas A&M University in Qatar. Open Access funding provided by the Qatar National Library.Scopu

Experimental and theoretical investigations of the effect of bis-phenylurea-based aliphatic amine derivative as an efficient green corrosion inhibitor for carbon steel in HCl solution

A novel bis-phenylurea-based aliphatic amine (BPUA) was prepared via a facile synthetic route, and evaluated as a potential green organic corrosion inhibitor for carbon steel in 1.0 M HCl solutions. NMR spectroscopy experiments confirmed the preparation of the targeted structure. The corrosion inhibitory behavior of the prospective green compound was explored experimentally by electrochemical methods and theoretically by DFT-based quantum chemical calculations. Obtained results revealed an outstanding performance of BPUA, with efficiency of 95.1% at the inhibitor concentration of 50 mg L−1 at 25 °C. The novel compound has improved the steel resistivity and noticeably reduced the corrosion rate from 33 to 1.7 mils per year. Furthermore, the adsorption study elucidates that the mechanism of the corrosion inhibition activity obeys Langmuir isotherm with mixed physisorption/chemisorption modes for BPUA derivatives on the steel surface. Calculated Gibb's free energy of the adsorption process ranges from −35 to −37 kJ mol−1.The SEM morphology analysis validates the electrochemical measurements and substantiates the corrosion-inhibiting properties of BPUA. Additionally, the eco-toxicity assessment on human epithelial MCF-10A cells proved the environmental friendliness of the BPUA derivatives. Density functional theory (DFT) calculations correlated the inhibitor's chemical structure with the corresponding inhibitory behavior. Quantum descriptors disclosed the potentiality of BPUA adsorption onto the surface through the heteroatom-based functional groups and aromatic rings.The support from Qatar University is gratefully acknowledged especially the Department of Chemistry and Earth Sciences and the Gas Processing Center. We also thank the Central Laboratories Unit, Qatar University for their support in material characterization. The primary computations were conducted using the advanced computational resources available at the supercomputing center located at Texas A&M University in Qatar. Open Access funding provided by the Qatar National Library

Computational study on the mechanism of the photouncaging reaction of vemurafenib: Toward an enhanced photoprotection approach for photosensitive drugs

The photochemical behavior of the photosensitive first-line anticancer drug vemurafenib (VFB) is of great interest due to the impact of such behavior on its pharmacological activity. In this work, we computationally elucidated the mechanism of the photoinduced release of VFB from the 4,5-dimethoxy-2-nitrobenzene (DMNB) photoprotecting group by employing various density functional theory (DFT)/time-dependent DFT (TD-DFT) approaches. The computational investigations included a comparative assessment of the influence of the position of the photoprotecting group as a substituent on the thermodynamics and kinetics of the photouncaging reactions of two VFB-DMNB prodrugs, namely pyrrole (NP) and sulfonamide (NS). With the aid of the DFT calculations concerning the activation energy barrier (∆G‡), the obtained results suggest that the step of the photoinduced intramolecular proton transfer of the DMNB moiety is not detrimental concerning the overall reaction profile of the photouncaging reaction of both prodrugs. However, the obtained results suggested that the position of the substitution position of the DMNB photoprotecting group within the prodrug structure has a substantial impact on the photouncaging reaction. In particular, the DMNB-Ns-VFB prodrug exhibited a notable increase in ∆G‡ for the key step of ring opining within the DMNB moiety indicative of potentially hindered kinetics of the photouncaging process compared with DMNB-Np-VFB. Such an increase in ∆G‡ may be attributed to the electronic influence of the NP fragment of the prodrug. The results reported herein elaborate on the mechanism of the photoinduced release of an important anticancer drug from photoprotecting groups with the aim of enhancing our understanding of the photochemical behavior of such photosensitive pharmaceutical materials at the molecular level.This work was supported by Qatar University [QUCD-CAS-2020-1]

On the molecular properties of graphene-pyrazines conjugated Ru and Fe complexes: Computational insights

Graphene and related materials can exhibit substantial molecular properties of significant importance in various landscapes of interests including catalysis. On the other hand, transition-metal-based molecular heterogeneous electrocatalysts can demonstrate enhanced catalytic usability compared to homogeneous analogues concerning recoverability and durability. We present in this study computational investigations on selected molecular properties graphene-based heterogenized molecular complexes of the (2,2′-bipyridyl)-metal complexes, [M(bpy)3]2+ (M = Fe, Ru). The computational study was conducted using the density functional theory (DFT) approach with an implicit solvation model (IEFPCM). Interestingly, the DFT results revealed that the key structural properties of the complexes are not disrupted by heterogenization. Also, the DFT-based calculated reduction potential of all examined species revealed a good agreement between the graphene-based heterogeneous electrocatalysts and their corresponding homogeneous analogues in terms of the redox potentials and the corresponding molecular properties in implicit acetonitrile. The finding reported herein demonstrates the applicability of graphene in covalent heterogenization of a molecular catalyst. As such, these computational insights can be useful in future efforts toward developing efficient heterogeneous molecular catalysts for a wide range of important chemical transformations.This work was funded by Qatar University. Open Access funding provided by the Qatar National Library

Synchronous spectrofluorimetric study of the supramolecular host–guest interaction of β-cyclodextrin with propranolol: A comparative study

The objective of this work is to assess the use of constant-wavelength synchronous fluorescence spectroscopy (SFS) in comparison to conventional fluorescence spectroscopy (CFS) for the investigation of the supramolecular host–guest interaction of β-CD with propranolol (PPL) in aqueous solutions. Scanning for the optimal Δλ at which the SFS can be performed in the presence of β-CD was examined. The results obtained revealed three distinguishable shapes for PPL using SFS that can be represented by three different Δλ values, namely 10, 40, and 100nm. However, the effect of the β-CD concentration on the fluorescence intensity of PPL was examined using CFS and SFS of PPL at a Δλ of 10 and 100nm. The change in the fluorescence intensity was used to calculate the equilibrium constant (Keq) for the formation of the β-CD:PPL inclusion complex by applying the Benesi–Hildebrand method. Keq values of 108, 112, and 117M−1 were obtained using SFS with a Δλ of 10 and 100nm, and CFS, respectively. Further, the SFS method was successfully employed to examine the iodide quenching effect on the fluorescence intensity of PPL, where the results obtained revealed a Stern–Volmer quenching constant of 42.8M−1, which is in good agreement with results obtained using CFS. All results obtained using the SFS method were compared with the results obtained using the CFS method

Computational exploration of the effect of molecular medium on the tautomerization of azo prodrug of 5-aminosalicylic acid

The characterization of potential tautomerization of pharmaceutical materials has significant importance. Sulfasalazine (SSZ) is a prodrug that bears 5-aminosalicylic acid and pyridylamino-sulfonyl-phenyl moieties bridged by the azo group. SSZ may be present in various tautomeric forms, where dual tautomerization may occur; namely, amide imide and azo hydrazone tautomerization through the pyridylamino-sulfonyl-phenyl and salicylic acid moieties, respectively. In this report, we describe the prospects of the effect of molecular medium on the tautomerization of SSZ using selected computational methods. Two approaches were deliberated; namely, the explicit intermolecular hydrogen bonding (HB) through complexation with dimethylformamide (DMF) and implicit solvent effects. Using the DFT/B97XD/6-31G+(d) calculations, we conducted geometry optimization calculations of all possible tautomers of SSZ and their corresponding HB complexes with DMF with stoichiometric ratios (SSZ:DMF) of 1:1 and 1:2. The stability of the SSZ tautomeric forms and their corresponding H-Bonded DMF complexes were examined employing the ADMP molecular dynamics approach. Obtained results demonstrate that the amide and azo tautomers are favored over imide and hydrazone in the gas phase with Etaut of 8.3 and 12.8 kcal/mol, respectively. However, these preferences were significantly affected by the implicit solvation effect of water with E of 0.5 and 3.1 kcal mol, respectively. Obtained results demonstrate as well that DMF can bind to various sites of SSZ tautomers through intermolecular HBs with length in the range of 1.76 2.39. This in turn demonstrates that intramolecular and intermolecular HB could not only play a significant role in directing the favored tautomeric forms of SSZ, but also distorting the planarity of the molecular comprising the azo and phenyl groups of the SSZ molecule. The ADMP-MD results verified that these complexes and the corresponding intra- and intermolecular HBs are stable over a timeframe of 100 femtosecond. The NBO analysis of the optimized geometries revealed that SSZ:DMF complexes can be stabilized by strong intermolecular HB, as indicated by the second perturbation energy of interaction (E(2)intr). Moreover, these results showed that the intermolecular HB of SSZ:DMF complexes has a notable effect on reducing the strength of intramolecular HB of certain tautomeric forms of SSZ and hence promotes the preference of SSZ toward a specific tautomeric form.Scopu