Interaction between gastric enzyme pepsin and tetradecyltrimethylammonium bromide in presence of sodium electrolytes: Exploration of micellization behavior

Pepsin is a proteolytic enzyme used in the treatment of digestive disorders. In this study, we investigated the physicochemical properties of the tetradecyltrimethylammonium bromide (TTAB) and pepsin protein mixture in various sodium salt media within a temperature range of 300.55-320.55 K with 5 K intervals. The conductometric study of the TTAB+pepsin mixture revealed a reduction in the critical micelle concentration (CMC) in electrolyte media. The micellization of TTAB was delayed in the presence of pepsin. The CMC of the TTAB + pepsin mixture was found to depend on the concentrations of electrolytes and protein, as well as the temperature variations. The aggregation of the TTAB+pepsin mixture was hindered as a function of [pepsin] and increasing temperatures, while micellization was promoted in aqueous electrolyte solutions. The negative free energy changes (∆Gm0) indicated the spontaneous aggregation of the TTAB+pepsin mixture. Changes in enthalpy, entropy, molar heat capacities, transfer properties, and enthalpy-entropy compensation variables were calculated and illustrated rationally. The interaction forces between TTAB and pepsin protein in the experimental solvents were primarily hydrophobic and electrostatic (ion-dipole) in nature. An analysis of molecular docking revealed hydrophobic interactions as the main stabilizing forces in the TTAB-pepsin complex.

Aggregation phenomena and physico-chemical properties of tetradecyltrimethylammonium bromide and protein (bovine serum albumin) mixture: Influence of electrolytes and temperature

It is important for biological, pharmaceutical, and cosmetic industries to understand how proteins and surfactants interact. Herein, the interaction of bovine serum albumin (BSA) with tetradecyltrimethylammonium bromide (TTAB) in different inorganic salts (KCl, K2SO4, K3PO4.H2O) has been explored through the conductivity measurement method at different temperatures (300.55 to 325.55 K) with a specific salt concentration and at a fixed temperature (310.55 K) using different salts concentrations. The extent of micelle ionization (α) and different thermodynamic parameters associated with BSA and TTAB mixtures in salt solutions were calculated. Evaluation of the magnitudes of ∆Hm0 and ∆Sm0 showed that the association was exothermic and primarily an enthalpy-operated process in all cases at lower contents of BSA, but the system became endothermic, and entropy driven in the presence of K3PO4.H2O at a relatively higher concentration of BSA. The enthalpy-entropy compensation variables were determined, which explained the types and nature of interactions between TTAB and BSA in salt media. Molecular docking analysis revealed that the main stabilizing factors in the BSA-TTAB complex are electrostatic and hydrophobic interactions. These findings aligned with the significant results obtained from the conductometry method regarding the nature and characteristics of binding forces observed between BSA and TTAB.

Physicochemical parameters and modes of interaction associated with the micelle formation of a mixture of tetradecyltrimethylammonium bromide and cefixime trihydrate: effects of hydrotropes and temperature

The interaction between an antibiotic drug (cefixime trihydrate (CMT)) and a cationic surfactant (tetradecyltrimethylammonium bromide (TTAB)) was examined in the presence of both ionic and non-ionic hydrotropes (HTs) over the temperature range of 300.55 to 320.55 K. The values of the critical micelle concentration (CMC) of the TTAB + CMT mixture were experienced to have dwindled with an enhancement of the concentrations of resorcinol (ReSC), sodium benzoate (NaBz), sodium salicylate (NaS), while for the same system, a monotonically augmentation of CMC was observed in aq. 4-aminobenzoic acid (PABA) solution. A gradual increase in CMC, as a function of temperature, was also observed. The values of the degree of counterion binding (β) for the TTAB + CMT mixture were experienced to be influenced by the concentrations of ReSC/NaBz/NaS/PABA and a change in temperature. The micellization process of TTAB + CMT was observed to be spontaneous (negative standard Gibbs free energy change (ΔG0m)) at all conditions studied. Also, the values of standard enthalpy change (ΔH0m) and entropy change (ΔS0m) were found negative and positive, respectively (with a few exceptions), for the test cases indicating an exothermic and enthalpy-entropy directed micellization process. The recommended interaction forces between the components in the micellar system are electrostatic and hydrophobic interactions. In this study, the values of ΔC0m were negative in aqueous NaBz, ReSC, and PABA media, and positive in case of NaS. An excellent compensation scenario between the enthalpy and entropy for the CMT + TTAB mixed system in the investigated HTs solutions is well defined in the current work.

Association behavior and physico-chemical parameters of a cetylpyridinium bromide and levofloxacin hemihydrate mixture in aqueous and additive media

The investigation of the micellization of a mixture of cetylpyridinium bromide (CPB) and levofloxacin hemihydrate (LFH) was carried out by a conductivity technique in aqueous and aq. additive mixtures, including NaCl, NaOAc, NaBenz, 4-ABA, and urea. The aggregation behavior of the CPB + LFH mixture was studied considering the variation in additive contents and the change in experimental temperature. The micelle formation of the CPB + LFH mixture was examined from the breakpoint observed in the specific conductivity versus surfactant concentration plots. Different micellar characteristics, such as the critical micelle concentration (CMC) and the extent of counter ion bound (β), were evaluated for the CPB + LFH mixture. The CMC and β were found to undergo a change with the types of solvents, composition of solvents, and working temperatures. The ΔG⁰_m values of the CPB + LFH system in aqueous and aq. additive solutions were found to be negative, which denotes a spontaneous aggregation phenomenon of the CPB + LFH system. The changes in ΔH⁰_m and ΔS⁰_m for the CPB + LFH mixture were also detected with the alteration in the solvent nature and solution temperature. The ΔH⁰_m and ΔS⁰_m values obtained for the association of the CPB + LFH mixture reveal that the characteristic interaction forces may possibly be ion-dipole, dipole-dipole, and hydrophobic between CPB and LFH. The thermodynamics of transfer and ΔH⁰_m-ΔS⁰_m compensation variables were also determined. All the parameters computed in the present investigation are illustrated with proper logic.

Investigation of the impacts of simple electrolytes and hydrotrope on the interaction of ceftriaxone sodium with cetylpyridinium chloride at numerous study temperatures

Herein, interactions between cetylpyridinium chloride (CPC) and ceftriaxone sodium (CTS) were investigated applying conductivity technique. Impacts of the nature of additives (e.g. electrolytes or hydrotrope (HDT)), change of temperatures (from 298.15 to 323.15 K), and concentration variation of CTS/additives were assessed on the micellization of CPC + CTS mixture. The conductometric analysis of critical micelle concentration (CMC) with respect to the concentration reveals that the CMC values were increased with the increase in CTS concentration. In terms of using different mediums, CMC did not differ much with the increase in electrolyte salt (NaCl, Na2SO4) concentration, but increased significantly with the rise of HDT (NaBenz) amount. In the presence of electrolyte, CMC showed a gentle increment with temperature, while the HDT showed the opposite trend. Obtained result was further correlated with conventional thermodynamic relationship, where standard Gibb's free energy change ( Δ G m o ) , change of enthalpy ( Δ H m o ) , and change of entropy ( Δ S m o ) were utilized to investigate. The Δ G m o values were negative for all the mixed systems studied indicating that the micellization process was spontaneous. Finally, the stability of micellization was studied by estimating the intrinsic enthalpy gain (Δ H m o , ∗ ) and compensation temperature (Tc). Here, CPC + CTS mixed system showed more stability in Na2SO4 medium than the NaCl, while in NaBenz exhibited the lowest stability.

Reactions of diphosphine-stabilized Os3 clusters with triphenylantimony: syntheses and structures of new antimony-containing Os3 clusters via Sb-Ph bond cleavage

The reactivity of the trimetallic clusters [Os₃(CO)₁₀(μ-dppm)] [dppm = bis(diphenylphosphino)methane] and [HOs₃(CO)₈{μ₃-Ph₂PCH₂PPh(C₆H₄-μ₂,σ¹)}] with triphenylantimony (SbPh₃) has been examined. [Os₃(CO)₁₀(μ-dppm)] reacts with SbPh₃ in refluxing toluene to yield three new triosmium clusters [Os₃(CO)₉(SbPh₃)(μ-dppm)] (1), [HOs₃(CO)₇(SbPh₃){μ₃-Ph₂PCH₂PPh(C₆H₄-μ₂,σ¹)}] (2), and [HOs₃(CO)₇(SbPh₃)(μ-C₆H₄)(μ-SbPh₂)(μ-dppm)] (3). [HOs₃(CO)₈{μ₃-Ph₂PCH₂PPh(C₆H₄-μ₂,σ¹)}] reacts with SbPh₃ (excess) at room temperature to afford [Os₃(CO)₈(SbPh₃)(η¹-Ph)(μ-SbPh₂)(μ-dppm)] (4) as the sole product. A series of control experiments have also been conducted to establish the relationship between the different products. The molecular structure of each product has been determined by single-crystal X-ray diffraction analysis, and the bonding in these new clusters has been investigated by electronic structure calculations.

A new synthetic route for the preparation of [Os3(CO)10(μ-OH)(μ-H)] and its reaction with bis(diphenylphosphino)methane (dppm): syntheses and X-ray structures of two isomers of [Os3(CO)8(μ-OH)(μ-H)(μ-dppm)] and [Os3(CO)7(μ3-CO)(μ3-O)(μ-dppm)]

The triosmium cluster [Os₃(CO)₁₀(μ-OH)(μ-H)] containing bridging hydride and hydroxyl groups at a common Os–Os edge was obtained in good yield (ca. 75%) from the hydrolysis of the labile triosmium cluster [Os₃(CO)₁₀(NCMe)₂] in THF at 67 °C. [Os₃(CO)₁₀(μ-OH)(μ-H)] reacts with dppm at 68 °C to afford the isomeric clusters 1 and 2 with the general formula [Os₃(CO)₈(μ-OH)(μ-H)(μ-dppm)] that differ by the disposition of bridging dppm ligand. Cluster 1 is produced exclusively from the reaction of [Os₃(CO)₁₀(μ-OH)(μ-H)] with dppm in CH₂Cl₂ at room temperature in the presence of added Me₃NO. Heating cluster 1 at 81 °C furnishes 2 in a process that likely proceeds by the release of one arm of the dppm ligand, followed by ligand reorganization about the cluster polyhedron and ring closure of the pendent dppm ligand. The oxo-capped [Os₃(CO)₇(μ₃-CO)(μ₃-O)(μ-dppm)] (3) has been isolated starting from the thermolysis of either 1 or 2 at 139 °C. Reactions of [Os₃(CO)₁₀(μ-dppm)] with ROH (R = Me, Et) in the presence of Me₃NO at 80 °C furnish [Os₃(CO)₈(μ-OH)(μ,η¹,κ¹-OCOR)(μ-dppm)] (4, R = Me; 5, R = Et). Clusters 1–5 have been characterized by a combination of analytical and spectroscopic studies, and the molecular structure of each product has been established by X-ray crystallography. The bonding in these products has been examined by electronic structure calculations, and cluster 1 is confirmed as the kinetic product of substitution, while cluster 2 represents the thermodynamically favored isomer.

The cluster [Os₃(CO)₁₀(μ-OH)(μ-H)] was obtained in 75% from the hydrolysis of [Os₃(CO)₁₀(NCMe)₂].

Reactions of triosmium and triruthenium clusters with 2-ethynylpyridine: new modes for alkyne C-C bond coupling and C-H bond activation

The reaction of the trimetallic clusters [H₂Os₃(CO)₁₀] and [Ru₃(CO)₁₀L₂] (L = CO, MeCN) with 2-ethynylpyridine has been investigated. Treatment of [H₂Os₃(CO)₁₀] with excess 2-ethynylpyridine affords [HOs₃(CO)₁₀(μ-C₅H₄NCH=CH)] (1), [HOs₃(CO)₉(μ₃-C₅H₄NC Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH₂)] (2), [HOs₃(CO)₉(μ₃-C₅H₄NCCCO₂)] (3), and [HOs₃(CO)₁₀(μ-CHCHC₅H₄N)] (4) formed through either the direct addition of the Os–H bond across the C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bond or acetylenic C–H bond activation of the 2-ethynylpyridine substrate. In contrast, the dominant pathway for the reaction between [Ru₃(CO)₁₂] and 2-ethynylpyridine is C–C bond coupling of the alkyne moiety to furnish the triruthenium clusters [Ru₃(CO)₇(μ-CO){μ₃-C₅H₄NCCHC(C₅H₄N)CH}] (5) and [Ru₃(CO)₇(μ-CO){μ₃-C₅H₄NCCHC(C₅H₄N)CHCHC(C₅H₄N)}] (6). Cluster 5 contains a metalated 2-pyridyl-substituted diene while 6 exhibits a metalated 2-pyridyl-substituted triene moiety. The functionalized pyridyl ligands in 5 and 6 derive via the formal C–C bond coupling of two and three 2-ethynylpyridine molecules, respectively, and 5 and 6 provide evidence for facile alkyne insertion at ruthenium clusters. The solid-state structures of 1–3, 5, and 6 have been determined by single-crystal X-ray diffraction analyses, and the bonding in the product clusters has been investigated by DFT. In the case of 1, the computational results reveal a rare thermodynamic preference for a terminal hydride ligand as opposed to a hydride-bridged Os–Os bond (3c,2e Os–Os–H bond).

The reactivity of 2-ethynylpyridine at low-valent triosmium and triruthenium centers has been investigated.

New molecular architectures containing low-valent cluster centres with di- and trimetalated 2-vinylpyrazine ligands: synthesis and molecular structures of Ru5(CO)15(μ5-C4H2N2CH[double bond, length as m-dash]CH)(μ-H)2 and Ru8(CO)24(μ7-C4H2N2CH[double bond, length as m-dash]C)(μ-H)3

Reaction of 2-vinylpyrazine with Ru₃(CO)₁₂ results in multiple C-H bond activations to afford penta- and octa-ruthenium clusters, Ru₅(CO)₁₅(μ₅-C₄H₂N₂CH[double bond, length as m-dash]CH)(μ-H)₂ (2) and Ru₈(CO)₂₄(μ₇-C₄H₂N₂CH[double bond, length as m-dash]C)(μ-H)₃ (3), in which a Ru₃ sub-unit is linked to Ru₂ and Ru₅ centres via di- and tri-metalated 2-vinylpyrazine ligands, exhibiting novel coordination modes including the loss of ring aromaticity in 2. The bonding of 2 and the mechanism for the fluxional behaviour of the hydrides have been examined by electronic structure calculations.

Experimental and computational preference for phosphine regioselectivity and stereoselective tripodal rotation in HOs3(CO)8(PPh3)2(μ-1,2-N,C-η1,κ1-C7H4NS)

The site preference for ligand substitution in the benzothiazolate-bridged cluster HOs₃(CO)₁₀(μ-1,2-N,C-η¹,κ¹-C₇H₄NS) (1) has been investigated using PPh₃. 1 reacts with PPh₃ in the presence of Me₃NO to afford the mono- and bisphosphine substituted clusters HOs₃(CO)₉(PPh₃)(μ-1,2-N,C-η¹,κ¹-C₇H₄NS) (2) and HOs₃(CO)₈(PPh₃)₂(μ-1,2-N,C-η¹,κ¹-C₇H₄NS) (3), respectively. 2 exists as a pair of non-interconverting isomers where the PPh₃ ligand is situated at one of the equatorial sites syn to the edge-bridging hydride that shares a common Os–Os bond with the metalated heterocycle. The solid-state structure of the major isomer establishes the PPh₃ regiochemistry at the N-substituted osmium center. DFT calculations confirm the thermodynamic preference for this particular isomer relative to the minor isomer whose phosphine ligand is located at the adjacent C-metalated osmium center. 2 also reacts with PPh₃ to give 3. The locus of the second substitution occurs at one of the two equatorial sites at the Os(CO)₄ moiety in 2 and gives rise to a pair of fluxional stereoisomers where the new phosphine ligand is scrambled between the two equatorial sites at the Os(CO)₃P moiety. The molecular structure of the major isomer has been determined by X-ray diffraction analysis and found to represent the lowest energy structure of the different stereoisomers computed for HOs₃(CO)₈(PPh₃)₂(μ-1,2-N,C-η¹,κ¹-C₇H₄NS). The fluxional behavior displayed by 3 has been examined by VT NMR spectroscopy, and DFT calculations provide evidence for stereoselective tripodal rotation at the Os(CO)₃P moiety that serves to equilibrate the second phosphine between the two available equatorial sites.

The site preference for PPh₃ substitution in HOs₃(CO)₁₀(PPh₃)₂(μ-1,2-N,C-η¹,κ¹-C₇H₄NS) (1) has been investigated.

Mixed-valence dimolybdenum complexes containing hard oxo and soft carbonyl ligands: synthesis, structure, and electrochemistry of Mo2(O)(CO)2(μ-κ2-S(CH2)nS)2(κ2-diphosphine)

Mixed-valence dimolybdenum complexes Mo2(O)(CO)2{μ-κ2-S(CH2)nS}2(κ2-Ph2P(CH2)mPPh2) (n = 2, 3; m = 1, 2) (1-4) have been synthesized from one-pot reactions of fac-Mo(CO)3(NCMe)3 and dithiols, HS(CH2)nSH, in the presence of diphosphines. The dimolybdenum framework is supported by two thiolate bridges, with one molybdenum carrying a terminal oxo ligand and the second two carbonyls. The dppm (m = 1) products exist as a pair of diastereomers differing in the relative orientation of the two carbonyls (cis and trans) at the Mo(CO)2(dppm) center, while dppe (m = 2) complexes are found solely as the trans isomers. Small amounts of Mo(CO){κ3-S(CH2CH2S)2}(κ2-dppe) (5) also result from the reaction using HS(CH2)2SH and dppe. The bonding in isomers of 1-4 has been computationally explored by DFT calculations, trans diastereomers being computed to be more stable than the corresponding pair of cis diastereomers for all. The calculations confirm the existence of Mo[triple bond, length as m-dash]O and Mo-Mo bond orders and suggest that the new dimeric compounds are best viewed as Mo(v)-Mo(i) mixed-valence systems. The electrochemical properties of 1 have been investigated by CV and show a reversible one-electron reduction associated with the Mo(v) centre, while two closely spaced irreversible oxidation waves are tentatively assigned to oxidation of the Mo(i) centre of the two isomers as supported by DFT calculations.

Alkyne activation and polyhedral reorganization in benzothiazolate-capped osmium clusters on reaction with diethyl acetylenedicarboxylate (DEAD) and ethyl propiolate

The reactivity of the face-capped benzothiazolate clusters HOs₃(CO)₉[μ₃-C₇H₃(R)NS] (1a, R = H; 1b, R = 2-CH₃) with alkynes has been investigated. 1a reacts with DEAD at 67 °C to furnish the isomeric alkenyl clusters Os₃(CO)₉(μ-C₇H₄NS)(μ₃-EtO₂CCCHCO₂Et) (2a and 3a). X-ray crystallographic analyses of 2a and 3a have confirmed the stereoisomeric relationship of these products and the regiospecific polyhedral expansion that follows the formal transfer of the hydride to the coordinated alkyne ligand in HOs₃(CO)₉(μ-C₇H₄NS)(η²-DEAD). The significant structural differences between the two isomers, as revealed by the solid-state structures, derives from the regiospecific cleavage of one of the three Os-Os bonds in the intermediate alkenyl cluster Os₃(CO)₉(μ-C₇H₄NS)(η¹-EtO₂CCCHCO₂Et), which follows hydride transfer to the coordinated alkyne ligand in the pi compound HOs₃(CO)₉(μ-C₇H₄NS)(η²-DEAD). Control experiments confirm the reversibility of the reaction leading to the formation of 2a and 3a. Whereas heating either isomer in refluxing THF or benzene affords a binary mixture containing 2a and 3a, thermolysis in refluxing toluene leads to the activation of the alkenyl ligand and formation of the new cluster Os₃(CO)₉(μ-C₇H₄NS)(μ₃-EtO₂CCCH₂) (4). 4 was independently synthesized from 1a and ethyl propiolate at room temperature. The computed mechanisms that account for the formation of 2a and 3a are presented, along with the mechanism for the reaction of 1a with ethyl propiolate to give 4.

Gamma Radiation Treated Chitosan Solution for Strawberry Preservation: Physico-Chemical Properties and Sensory Evaluation

The research was designed to extend shelf life of stored strawberry by bioactive chitosan coating. Strawberry fruits were dipped for 2 min in different concentration of irradiated chitosan (300, 500, 1000 and 1500 ppm) solution which were subjected to different gamma radiation doses (30, 40, 50 and 60 kGy) while uncoated fruits were served as control. Samples were packed in zip bags and stored in 4°C and kept for observation. Fruits treated with 50 kGy irradiated chitosan at 1500 ppm concentration showed significant delays in the change of weight loss, decay percentage, pH, and ascorbic acid content as compared with the uncoated control fruits. Samples stored in 4°C and packed in zip bags showed an increased shelf life up to 21 days whereas control samples with same condition could maintain edible quality only up to 3 days. Compared to the controls, all coating formulations had positive effect on the inhibition of cell wall degrading enzymes. These findings suggest that the use of irradiated chitosan coatings can be very useful for extending the shelf-life and maintaining quality of strawberry fruit.

Gamma Radiation Treated Chitosan Solution for Strawberry Preservation: Physico-Chemical Properties and Sensory Evaluation

The research was designed to extend shelf life of stored strawberry by bioactive chitosan coating. Strawberry fruits were dipped for 2 min in different concentration of irradiated chitosan (300, 500, 1000 and 1500 ppm) solution which were subjected to different gamma radiation doses (30, 40, 50 and 60 kGy) while uncoated fruits were served as control. Samples were packed in zip bags and stored in 4°C and kept for observation. Fruits treated with 50 kGy irradiated chitosan at 1500 ppm concentration showed significant delays in the change of weight loss, decay percentage, pH, and ascorbic acid content as compared with the uncoated control fruits. Samples stored in 4°C and packed in zip bags showed an increased shelf life up to 21 days whereas control samples with same condition could maintain edible quality only up to 3 days. Compared to the controls, all coating formulations had positive effect on the inhibition of cell wall degrading enzymes. These findings suggest that the use of irradiated chitosan coatings can be very useful for extending the shelf-life and maintaining quality of strawberry fruit.

Electrocatalytic proton reduction catalysed by the low-valent tetrairon-oxo cluster [Fe4(CO)10(κ2-dppn)(μ4-O)]2− [dppn = 1,1′-bis(diphenylphosphino)naphthalene]

[Fe₄(CO)₁₀(κ²-dppn)(μ₄-O)]²⁻ reduces protons and DFT calculations support the sequential formation of hydride and dihydrogen ligands at the unique iron centre.