Ni-Fe bimetallic catalysts with high dispersion supported by SBA-15 evaluated for the selective oxidation of benzyl alcohol to benzaldehyde.

A wetness impregnation method was used to impregnate the substrate with a substantial quantity of oleic acid together with a metal precursor, leading to significantly dispersed Ni-Fe bimetallic catalysts based on mesoporous SBA-15. Using a wide variety of characterization methods, such as XRD, BET, and TEM Analysis, the physiochemical properties of the catalyst were determined. The addition of the metal does not have any effect on the structural characteristics of the SBA-15 catalyst, as validated by transmission electron microscopy (TEM), which shows that the prepared SBA-15 supported catalyst has a hexagonal mesoporous structure. The catalytic capabilities of the Ni-Fe-SBA-15 catalysts were evaluated in the conversion of BzOH using tert-butyl hydroperoxide (TBHP) as an oxidant and acetonitrile as a solvent. The Ni/Fe-SBA-15 (NFS-15) catalytic composition is the best of the developed catalysts, with a maximum conversion of 98% and a selectivity of 99%. In-depth investigations were conducted into the molar ratio of TBHP to BzOH, the dosage of the catalyst, the reaction rate, temperature, and solvent. The recycling investigations indicate that the synthesized Ni/Fe-SBA-15 (NFS-15) catalyst seems to be more durable up to seven successive cycles.

Isomerization of C7 and C8 through Ionic Liquids Supported by a Fe/SBA-15 Catalyst.

Isomerization is extensively utilized in the petroleum industry, and this study demonstrates an energy-efficient process utilizing an ionic liquid catalyst. 1-Ethyl-3-methylimidazolium triflate [Emim][TFO] as an ionic liquid was immobilized on solid support Fe/SBA-15. Variants of the catalyst were developed with the Fe constant at 5% and different ratios of ionic liquid. In the catalyst Fe/[Emim][TFO]/SBA-15, the metal Fe was loaded via the impregnation method, and subsequently, the ionic liquid variants Fe/[Emim][TFO](10)/SBA-15, Fe/[Emim][TFO](20)/SBA-15, and Fe/[Emim][TFO](30)/SBA-15 were synthesized. The physical properties of the synthesized catalyst were studied using standard characteristic techniques. The process performance was studied for variants of each parameter, which include temperature, hydrogen flow rate, pressure, and weight hourly space velocity. The iso-products of n-heptane and n-octane were obtained with an appreciable conversion of >90% and a selectivity of >95% with the catalyst Fe/[Emim][TFO](20)/SBA-15 among the other synthesized catalysts. The process yielded a high quantum of iso-products with negligible cracked products at a low temperature of 140 °C. The catalyst Fe/[Emim][TFO](20)/SBA-15 at 140 °C delivered the highest yield of iso-alkanes among the three catalysts. Iso-alkanes are instrumental tools for increasing the octane number of a fuel. This study delivers high iso-alkane content fuel, which can provide the best anti knock capability and enhance fuel efficiency for the life of modern high-powered engines. The results demonstrate a process that is energy-efficient, economic, and environmentally friendly.

Complexity of the Role of Various Site-Specific and Selective Sudlow Binding Site Drugs in the Energetics and Stability of the Acridinedione Dye-Bovine Serum Albumin Complex: A Molecular Docking Approach.

Molecular docking (Mol.Doc) techniques were employed to ascertain the binding affinity of two resorcinol-based acridinedione dyes (ADR1 and ADR2) with the widely studied globular protein Bovine Serum Albumin (BSA) in the presence of site-selective binding drugs by Autodock Vina 4.2 software. Docking of various feasible conformers of ADR1 dye with BSA was found to be energetically more favored than ADR2 dye, even though both these dyes differ in the 9th position of the basic dye structure. Analysis of dyes with BSA establishes the location of dye in all of the binding sites of BSA, predominantly through conventional and nonconventional hydrogen-bonding (HB) interactions. The coexistence of hydrophobic interactions resulted in the stability of various conformers generated. The introduction of site I and site II (Sudlow site binding drugs) into ADR1-BSA and ADR2-BSA complexes effectively destabilizes the dye-protein complex; however, the drugs do not displace ADR dyes completely from their selective binding domains. Site II binding drugs effectively destabilize the binding ability of the dye-protein complex rather than site I drugs. However, docking of site I drug 3-carboxyl-4-methyl-5-propyl-2-furanpropanic acid (CMPF) largely destabilizes the ADR1-protein complex, whereas indomethacin (INDO) enhances the binding affinity of the ADR2-protein complex. Interestingly, simultaneous docking of ADR dyes to the BSA-drug complex results in larger stability of the protein-drug complex through HB interactions rather than hydrophobic interactions. Both ADR1 and ADR2 dyes predominantly occupy the Sudlow binding sites of BSA, and the introduction of either site I or site II binding drugs does not displace the dye efficiently from the corresponding binding sites, rather the drugs are effectively displaced toward other binding domains apart from their specific site-binding domains of BSA. Through Mol.Doc techniques, we authenticate that the interactions in host-guest complex systems involving competing ligands are established in depth, wherein the dye as well as the amino acid (AA) moieties in BSA act as both HB donor and acceptor sites apart from several hydrophobic interactions coexisting toward the stability.

Interaction of an Aldose Sugar with Photoinduced Electron Transfer (PET) and Non-PET Based Acridinedione Dyes in Water: Hydrogen-bonding Evidences from Fluorescence Spectral Techniques Assisted by Molecular Docking Approach.

Fluorescence spectral techniques aided by molecular docking (Mol.Doc) approach were employed in probing the molecular interactions existing between D-glucose and resorcinol based acridinedione (ADR) dyes. ADR dyes has been classified into PET and non-PET dyes based on the substitution in the 9th position of acridinedione ring structure. Addition of glucose to PET dye (ADR1) resulted in a decrease in the absorbance whereas to that of ADR2 dye (non-PET character in aqueous medium) resulted in a significant increase in the absorbance. The formation of an isosbestic point reveals the existence of a ground state interaction existing between the dye and sugar molecule. Addition of glucose to PET dye resulted in a drastic increase in the fluorescent enhancement (FE) and subsequent addition resulted in a marked decrease in the fluorescent intensity with no apparent shift of emission maximum. Interestingly, neither characteristic shift nor variation in emission intensity was observed in the case of ADR2 dye. Fluorescence lifetime studies of ADR1 dye in the presence of glucose illustrate the existence of multiple distinguishable micro environments of dye. Mol.Doc studies authenticate the co-existence of hydrogen bonding (HB) and hydrophobic interaction wherein the dye and sugar molecule acts as HB donor and acceptor resulting in a stable conformer. These conformers are governed predominantly by HB interactions. The nature of interaction of a simple sugar with ADR dyes are explored in depth by fluorescent techniques in coordination with docking studies is imparted in the present study.

Electrochemical Investigation and Molecular Docking Techniques on the Interaction of Acridinedione Dyes with Water-Soluble Nonfluorophoric Simple Amino Acids.

Electrochemical studies of resorcinol-based acridinedione (AD) dyes with nonfluorophoric simple amino acids, glycine, alanine, and valine, were carried out in water. AD probes are classified into photoinduced electron transfer (PET) and non-PET-based dyes, wherein the electrochemical properties and photophysical and photochemical behavior vary significantly based on the nature of substituent groups and the nature of the solute. The oxidation potential of PET dye (ADR1) to that of non-PET-based dye (ADR2) differs significantly such that the addition of amino acids results in a shift of the oxidation peak to a less positive potential and the reduction peak to a lesser negative potential. The extent of shift of oxidation and reduction potential in PET dye is more pronounced than that of non-PET dye on the addition of valine rather than glycine. The variation in the shift is attributed to the presence of an electron-donating moiety (OCH3) group in the ninth position of ADR1 dye. Consequently, the quenching of fluorescence is observed in ADR2 with non fluorophoric amino acids that are authenticated by the shift of the anodic and cathodic peaks toward a lesser positive potential. Molecular docking (MD) studies of PET and non-PET dye with amino acids portray that neither hydrophobic interactions nor electrostatic or weak interactions such as van der Waals and pi-pi interactions govern the electrochemical nature of dye on the addition of amino acids. Furthermore, the formation of a conventional hydrogen bond between dye and amino acid is established from MD studies. The existence of dye-water-amino acid competitive hydrogen-bonding interactions is presumably well-oriented throughout the aqueous phase as observed through photophysical studies which support our electrochemical investigation.

A fluorescence approach on the investigation of urea derivatives interaction with a non-PET based acridinedione dye-beta Cyclodextrin (ß-CD) complex in water: Hydrogen-bonding interaction or hydrophobic influences or combined effect?

Photophysical studies of resorcinol based acridinedione dyes with beta Cyclodextrin (ß-CD) in the presence of urea (U) and tetramethylurea (TMU) were carried out in water. A marked variation in the absorption spectra of dye-ß-CD complex was found to be more significant in the case of U rather in TMU. Interestingly, the role of urea on the excited state behavior of dye-ß-CD complex is found to be entirely different from that of TMU. The formation of urea-water hydrogen-bonding self assemblies and creation of microspheres of varying environment results in an effective displacement of dye from the hydrophobic nanocavity of ß-CD. On the contrary, the dye prefers a more confined hydrophobic micro environment in the presence of TMU. The nature of urea derivative, hydrogen-bonding of urea-water assemblies and hydrophobic influences of methyl moieties in urea molecular framework governs the stability and also the dissociation of dye-ß-CD complex. The displacement of dye from the environment of the sugar molecule by urea derivatives is established from fluorescence studies wherein the variation in the spectral behavior of non-PET based dye-ß-CD complex is found to be entirely different from that of PET dye. Both hydrogen-bonding along with hydrophobic interactions influences the excited state properties of the both PET and non-PET based acridinedione dyes are elucidated through fluorescence spectral studies. The extent of binding and the microenvironment of the dye in the presence of ß-CD and urea are established through molecular docking and fluorescence anisotropy studies.

Competitive hydrogen bonding influences of fluorophore- urea-adenine system in water: Photophysical and photochemical approaches.

Photophysical and photochemical investigation of photoinduced electron transfer (PET)-based acridinedione dye (ADR1) with urea in the presence of a nitrogenous base (adenine) were carried out in water. Urea suppresses the PET resulting in a fluorescence enhancement and the extent of binding is correlated and governed by the number of urea molecules surrounding the close vicinity of dye. On the contrary, adenine forms a true 1:2 complex with dye. Presence of adenine in dye-urea microenvironment results in the displacement of dye from the vicinity of urea molecules. The stability of dye-urea network in the presence of adenine reveals that the microenvironment of dye is governed and influenced by both urea and adenine. Introduction of adenine to dye-urea results in the formation of several hydrogen bonding assemblies that are competitive and influences the excited state characteristics of ADR1 dye. The micro assemblies comprise dye-urea (DU), dye-adenine (DA), urea-adenine (UA), urea-water (UW), urea-urea (UU), and adenine-water (AW) framework and the existence of several competitive hydrogen bonding results in a large variation in fluorescence properties of ADR1 dye. The presence of several assemblies also signifies that no confined phase selectively of DU or DA assemblies exist in any stoichiometric proportion in the aqueous phase. The binding constant, the variation in the fluorescence lifetime and its relative amplitude of DA in the presence of urea authenticate that the binding nature of dye-urea-adenine (DUA) is dependent on the several hydrogen bonding assemblies that coexist at any concentration. The extent of hydrogen bonding of DA is found to be entirely different from that of urea. Further, urea resulted in changes in the transient absorption peak of dye with a large variation in lifetime and shift of the transient absorption peaks. Fluorescence spectral techniques are used as an efficient tool in elucidating the binding nature of DU framework in the presence of non-fluorescent hydrogen-bonding solute like adenine.

Electrostatic Investigation of 4-Dicyanomethylene-2,6-dimethyl-4H-pyran (DDP) Dye with Amide Derivatives in Water.

Cyclic voltammetry (CV) studies of 4-dicyanomethylene-2,6-4H-pyran (DDP) dye with alkyl-substituted amides were carried out in an aqueous solution. Formamide and substituted amide interaction with DDP dye were characterized by fluorescence spectral techniques in an aqueous solution, but the electrochemical nature and the interaction at the interface region between dye-amide remains largely unexplored. The introduction of formamide to DDP dye exhibits an increase in the peak current accompanied with potential values gradually shifting more toward a less positive region. A large variation in the current-potential characteristics is observed in alkyl-substituted amides. The cyclic voltammograms of alkyl amides are found to be entirely different from each other. The role of alkyl substitution in the amide molecular framework influences the reduction potential of the dye in an aqueous medium. The mode of interaction of the dye with alkyl-substituted amides is predominantly due to the electrostatic behavior, even though hydrogen-bonding interactions coexist throughout the aqueous phase. The binding constant parameter (K), free-energy changes (ΔG), and the variation in the potential behavior of the dye in the presence of formamide and alkyl amides authenticate that the nature of interaction operates by both hydrogen-bonding mode and electrostatic interactions. Electrochemical techniques when coupled with fluorescence methods provide an efficient method of determining the interaction at the bulk and the interface regions of a water-soluble dye with nonfluorophoric solutes.

Fluorescence coupled with electrochemical approach at the bulk and the interface region of hydrogen-bonding self assemblies of urea derivatives with DDP dye in aqueous solution.

Photophysical and electrochemical techniques were employed to hydrogen-bonding self assemblies forming solutes (Urea, Dimethylurea and Tetramethylurea) in the presence of 4-dicyanomethylene 2, 6-dimethyl-4H-pyran (DDP) dye. Addition of urea derivatives to DDP dye (Intramolecular Charge Transfer (ICT)) results in a fluorescence enhancement accompanied with a significant shift. Fluorescence lifetime behavior exhibits a tri-exponential decay with a large variation in the fluorescence lifetime and relative amplitude distribution. The coexistence of three different fluorescence lifetime components of DDP with urea derivatives signifies the existence of heterogeneous micro environment. The dye is surrounded by varying proportion of solute and water molecules are established from fluorescence lifetime studies. Urea derivatives govern the excited state characteristics of DDP dye resulting in the formation and promotion of different microenvironment which are clearly distinguishable. The existence of multi environment attributed to urea-water structural behaviour is authenticated by electrochemical impedance spectral studies (EIS). A large variation in the contour pattern, shape and intensity in 3D fluorescence contour spectra of dye with urea validate the existence of dye in a heterogeneous micro environment. The hydrophobicity of urea derivatives along with the hydrogen-bonding properties of urea-water and urea-urea influence the photophysical and electrochemical nature of dye is emphasized.

Is Gum Arabic a Good Emulsifier Due to CH...π Interactions? How Urea Effectively Destabilizes the Hydrophobic CH...π Interactions in the Proteins of Gum Arabic than Amides and GuHCl?

The photophysical studies of gum arabic (GA) in the presence of urea, 1,3-dimethylurea (DMU), tetramethylurea (TMU), guanidine hydrochloride (GuHCl), formamide (FA), acetamide (AA), and dimethyl formamide (DMF) were carried out by monitoring the emission, three-dimensional emission contour, and time-correlated fluorescence lifetime techniques. On addition of only 1 × 10-3 M urea, 75.0% of the fluorescence of GA is quenched, while the same occurs in GuHCl at 3.0 M. FA quenched 50% of the fluorescence of GA at 5.0 M. However, DMU, TMU, AA, and DMF resulted in a fluorescence enhancement. The unusual fluorescence trends reveal the existence of CH...π interactions in the proteins of GA. The experimental results and the structural aspects of proteins in GA led us to propose that the aggregation of polyproline helices in GA, through several CH...π interactions, would have a major role to play in the emulsification mechanism of GA.

Fluorescence Spectral Studies on the Interaction of Alanine and Valine with Resorcinol-Based Acridinedione Dyes in Aqueous Solution: A Comparative Study with Glycine.

Photophysical studies were carried out for simple amino acids like alanine and valine with resorcinol-based aqueous acridinedione (ADDR) dyes. ADDR dyes exhibit interesting excited-state characteristics on altering the substituents at the 9th and 10th sites (Scheme 1). The longest-wavelength absorption maxima remain the same on adding the amino acids to the fluorophore, whereas the excited-state behavior varies significantly mostly based on the nature of the substituent at the 9th position. The absence of fluorescence enhancement was observed with addition of ß-alanine, l-alanine, and l-valine to ADDR1 dye (photoinduced electron transfer, PET), whereas addition of glycine exhibits enhancement accompanied with a shift toward a longer-wavelength region. Interestingly, the addition of amino acids to non-PET dyes results in a fluorescence quenching accompanied with a larger shift toward the shorter-wavelength region. The properties of fluorophore and nonfluorophore dyes in the presence of alanine or valine are found to be entirely different from those of glycine. The interaction of alanine with ADDR dyes is predominantly through H-bonding, but the structural aspects of H-bonding interactions of alanine and water are completely different from those of glycine and water. The time-correlated single-photon counting method portrays the existence of fluorophore in two distinguishable microenvironments in the presence of amino acids. The fluorescence spectral technique used as a tool in elucidating the mode of interaction of dye with neutral amino acids in aqueous solution is illustrated in the present study.

Multicharacteristic Behavior of Tyrosine Present in the Microdomains of the Macromolecule Gum Arabic at Various pH Conditions.

Gum arabic (GA), the dried exudates of Acacia seyal and Acacia senegal trees, being a biopolymer, has found many applications in the food, pharmaceutical, cosmetic, and lithography industries. GA, a water-soluble food hydrocolloid, is a complex and variable mixture of arabinogalactan oligosaccharides, polysaccharides, and glycoproteins. It has been a subject of great interest and a wide range of research has been done on the polysaccharide structural aspects and the emulsifying properties only. In the present study, fluorescence spectral technique is employed as an analytical tool to understand the photophysics of GA. The tyrosine microenvironment of GA was explored by studying the steady-state absorption, emission, fluorescence lifetime, and three-dimensional (3D) emission contour spectra of GA at various pH conditions in aqueous solution. The multiple emissive states are attributed to the presence of intrinsic fluorophore tyrosine in a heterogeneous microenvironment. The study portrays the multicharacteristic behavior of tyrosine in various pH conditions and in different microdomains. The exposure of the buried tyrosine to the heterogeneous aqueous phase was authenticated by 3D emission contour spectral studies. An interesting visualization of tyrosine involving in hydrogen-bonding network with another tyrosine moiety at neutral pH was ascertained. The coexistence of hydrophilic carbohydrate and hydrophobic protein in GA enables its emulsification and stabilization properties. Hence, any advancement toward understanding the protein microenvironment of GA is of great significance for chemists, as the molecular modeling and biosynthesis of the gum with desired end product are underway in many research institutes.