Dramatic influence of the orientation of linker between hydrophilic and hydrophobic lipid moiety in liposomal gene delivery

A number of prior studies have demonstrated that the DNA-binding and gene transfection efficacies of cationic amphiphiles crucially depend on their various structural parameters including hydrophobic chain lengths, headgroup functionalities, and the nature of the linker-functionality used in tethering the polar headgroup and hydrophobic tails. However, to date addressing the issue of linker orientation remains unexplored in liposomal gene delivery. Toward probing the influence of linker orientation in cationic lipid mediated gene delivery, we have designed and synthesized two structurally isomeric remarkably similar cationic amphiphiles 1 and 2 bearing the same hydrophobic tails and the same polar headgroups connected by the same ester linker group. The only structural difference between the cationic amphiphiles 1 and 2 is the orientation of their linker ester functionality. While lipid 1 showed high gene transfer efficacies in multiple cultured animal cells, lipid 2 was essentially transfection incompetent. Findings in both transmission electron microscopic and dynamic laser light scattering studies revealed no significant size difference between the lipoplexes of lipids 1 and 2. Findings in confocal microscopic and fluorescence resonance energy transfer (FRET) experiments, taken together, support the notion that the remarkably higher gene transfer efficacies of lipid 1 compared to those of lipid 2 presumably originate from higher biomembrane fusogenicity of lipid 1 liposomes. Differential scanning calorimetry (DSC) and fluorescence anisotropy studies revealed a significantly higher gel-to-liquid crystalline temperature for the lipid 2 liposomes than that for lipid 1 liposomes. Findings in the dye entrapment experiment were also consistent with the higher rigidity of lipid 2/cholesterol (1:1 mole ratio) liposomes. Thus, the higher biomembrane fusibility of lipid 1 liposomes than that of lipid 2 liposomes presumably originates from the more rigid nature of lipid 2 cationic liposomes. Taken together, the present findings demonstrate for the first time that even as minor a structural variation as linker orientation reversal in cationic amphiphiles can profoundly influence DNA-binding characteristics, membrane rigidity, membrane fusibility, cellular uptake, and consequently gene delivery efficacies of cationic liposomes.     

Penicillamine and captopril: mechanistic exploration of defensive actions of thiol drugs against a metal bound-superoxo complex

In acid-media ([H⁺] = 0.01–0.06 M), each of the thiol compounds, D-penicillamine (PEN, L_PH₂) and captopril (CAP, L_CH₂) exist in several proton-dependent forms which can reduce the superoxo complex [(en)(dien)Co^III(O₂)Co^III(en)(dien)]⁵⁺ (1) to the corresponding peroxo [(en)(dien)Co^III(O₂)Co^III(en)(dien)]⁴⁺ (2) or the hydroperoxo complex [(en)(dien)Co^III(OOH)Co^III(en)(dien)]⁵⁺ (3). The observed first-order rate constants, k_o,P and k_o,C for PEN and CAP increase with the increase in [T_PEN] and [T_CAP] (which are the analytical concentrations of the respective thiols) but decrease with the increase in the media-acidity ([H⁺]) and the media ionic strength (I). The protolytic equilibria in aqueous solution allow several potentially reducing forms to coexist for both PEN (L_PH₃⁺, L_PH₂, L_PH^?, and L_P^2?) and CAP (L_CH₂, L_CH^?, L_C^2?) but the kinetic analyses reveal that the order of reactivity for the species are L_PH₃⁺ ~ L_PH₂ <<< L_PH^? and L_CH₂ < L_CH^? <<< L_C^2?, respectively. The predominance and higher reactivities of the anionic species, L_PH^? and L_C^2? are supported by the negative slopes of the plots of k_o,P or k_o,C versus I. Moreover, a large value of k_H/k_D for PEN suggests an inner-sphere electroprotic reaction pathway while the absence of such effect for CAP strongly supports an outer-sphere electron transfer reaction. These propositions are supported by the structural features of L_PH^? and L_C^2?.     

A New Compound for Sequential Sensing of Picric Acid and Aliphatic Amines: Physicochemical Details and Construction of Molecular Logic Gates

Picric acid (PA) at low concentration is a serious water pollutant. Alongside, aliphatic amines (AAs) add to the queue to pollute surface water. Plenty of reports are available to sense PA with an ultralow limit of detection (LOD). However, only a handful of works are testified to detect AAs. A new fluorescent donor-acceptor compound has been synthesized with inherent intramolecular charge transfer (ICT) character that enables selective and sensitive colorimetric quantitative detection of PA and AAs with low LODs in non-aqueous as well as aqueous solutions. The synthesized compound is based on a hemicyanine skeleton containing two pyridenylmethylamino groups at the donor and a benzothiazole moiety at the acceptor ends. The detailed mechanisms and reaction dynamics are explained spectroscopically along with computational support. The fluorescence property of the detecting compound changes due to protonation of its pyridinyl centers by PA leading to quenching of fluorescence and subsequently de-protonation by AAs to revive the signal. We have further designed logic circuits from the acquired optical responses by sequential interactions.     

Platinum(II)-Catalyzed Novel Synthesis of 3,4-Fused Furans

A novel synthesis of 3,4-fused furans (both tricyclic and bicyclic) through platinum-catalyzed cyclization of 3-(2-formylcycloalkenyl)-acrylic amides 2 in methanol is described (up to 90% yield). Tricyclic 3,4-fused dihydrofuran derivatives were also obtained via reductive cyclization of 2. The substrates 2 were obtained from β- bromovinyl aldehydes by a Pd-catalyzed Heck reaction.     

Potential Therapeutic Target Protein Tyrosine Phosphatase-1B for Modulation of Insulin Resistance with Polyphenols and Its Quantitative Structure–Activity Relationship

The increase in the number of cases of type 2 diabetes mellitus (T2DM) and the complications associated with the side effects of chemical/synthetic drugs have raised concerns about the safety of the drugs. Hence, there is an urgent need to explore and identify natural bioactive compounds as alternative drugs. Protein tyrosine phosphatase 1B (PTP1B) functions as a negative regulator and is therefore considered as one of the key protein targets modulating insulin signaling and insulin resistance. This article deals with the screening of a database of polyphenols against PTP1B activity for the identification of a potential inhibitor. The research plan had two clear objectives. Under first objective, we conducted a quantitative structure–activity relationship analysis of flavonoids with PTP1B that revealed the strongest correlation (R² = 93.25%) between the number of aromatic bonds (naro) and inhibitory concentrations (IC₅₀) of PTP1B. The second objective emphasized the binding potential of the selected polyphenols against the activity of PTP1B using molecular docking, molecular dynamic (MD) simulation and free energy estimation. Among all the polyphenols, silydianin, a flavonolignan, was identified as a lead compound that possesses drug-likeness properties, has a higher negative binding energy of −7.235 kcal/mol and a pKd value of 5.2. The free energy-based binding affinity (ΔG) was estimated to be −7.02 kcal/mol. MD simulation revealed the stability of interacting residues (Gly183, Arg221, Thr263 and Asp265). The results demonstrated that the identified polyphenol, silydianin, could act as a promising natural PTP1B inhibitor that can modulate the insulin resistance.     

Thermodynamic properties of a hindered rotator

It is demonstrated that a finite dimensional representation of the hamiltonian of a hindered rotator can be used to get reasonably accurate values of thermodynamic properties, e.g., the specific heat of an assembly of such rotators. It is known that there is a large difference between the classical values and quantum statistical values when the height of the hindering potential is small.     

Effect of spatial dispersion on van der Waals interactions between molecules

It is found that in many practical applications, e.g. physical adsorption problems, the spatial dispersion effect on van der Waals interactions between molecules can be neglected. It is established when it is permissible to do this.     

Encapsulation of norharmane in cyclodextrin: formation of 1:1 and 1:2 inclusion complexes

Steady state absorption and fluorometric techniques have been used to investigate the photophysics of norharmane (NHM), a bioactive fluorophore, in aqueous as well as aqueous cyclodextrin (CD) environments. The absorption and steady state fluorescence spectral studies reveal the formation of two types of inclusion complexes between the fluorophore and beta-cyclodextrin (beta-CD) depending on the relative population of the two. The stoichiometries and association constants of these complexes have been determined monitoring the fluorescence data. alpha-and gamma-cyclodextrin (alpha-CD, gamma-CD) do not have appreciable effect on the spectral pattern of the fluorophore. The differential fluorimetric behavior of NHM in different CD environments has been rationalized from the variation of the relative dimensions of the probe and the CD cavities.