Unveiling the binding interaction of zinc (II) complexes of homologous Schiff-base ligands on the surface of BSA protein: A combined experimental and theoretical approach

Four new zinc (II) complexes [Zn (HL¹H)Br₂] (1), [Zn (HL¹H)Cl₂] (2), [Zn₂(HL²)Br₃] (3), and [Zn (HL²)Cl] (4) have been synthesized by adopting template synthetic strategy and utilizing two homologous Schiff base ligands (H₂L¹ = 4-bromo-2-{[2-(2-hydroxyethylamino)-ethylimino]-methyl}-6-methoxyphenol, H₂L² = 4-bromo-2-{[3-(2-hydroxyethylamino)propylimino]methyl}-6-methoxyphenol), differing in one -CH₂- unit in the ligating backbone, by adopting template synthetic strategy. All the complexes have been characterized by single crystal X-ray diffraction analysis as well as by other routine physicochemical techniques. Ligand mediated structural variations have been observed and rationalized by density functional theoretical (DFT) calculations. Interaction of the complexes 1–4 with Bovine Serum Albumin protein (BSA) has been studied by different spectroscopic techniques. A complete thermodynamic profile (ΔH^o, ΔS^o and ΔG^o) was evaluated initially from the change in absorption and fluorescence spectra upon addition of BSA to the complexes. Appreciable binding constant values in the range ~ 0.94–4.51 × 10⁴ M⁻¹ indicate efficient binding tendency of the complexes to BSA with the sequence 1 ≅ 2 > 3 ≅ 4. Circular dichroism (CD), isothermal calorimetric titration experiments, molecular docking and molecular dynamics have been performed to gain deep insight into the binding regions of complex 1 to BSA. Experimental evidences suggest an interaction of zinc complexes at the surface of BSA protein and this particular binding has been exploited to determine unknown concentration of BSA protein. For this purpose complex 1 was explored as a BSA protein quantification tool.     

Deciphering Internal and External π-Conjugation in C3-Symmetric Multiple Azobenzene Connected Systems in Self-Assembly

Two tripodal C₃-symmetric photoswitchable molecular systems T1 and T2 are reported that have extended conjugation at external and internal positions using an acryl group. The influence of the extended π-bonds in their absorption properties, thermal relaxation of the photoisomers and their propensities in forming supramolecular self-assemblies have been explored through spectroscopy, and microscopic studies. In particular, the investigations on the self-assembly have been carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), polarized optical microscopy (POM), X-ray diffraction studies (XRD) and atomic force microscopy (AFM). Remarkably, the position of the acryl group influences the behaviour of the two target molecules in supramolecular assembly, and also in the formation of photoresponsive organic hydrogels or microcrystals.     

Brønsted Acid Catalyzed [3+2]‐Cycloaddition of 2‐Vinylindoles with In Situ Generated 2‐Methide‐2H‐indoles: Highly Enantioselective Synthesis of Pyrrolo[1,2‐a]indoles

Pyrrolo[1,2‐a]indoles are privileged structural elements of many natural products and pharmaceuticals. An efficient one‐step process for their highly diastereo‐ and enantioselective synthesis, comprising a direct [3+2]‐cycloaddition, has been developed. A chiral BINOL‐derived phosphoric acid catalyzes the reaction of in situ‐generated 2‐methide‐2H‐indoles with 2‐vinylindoles, furnishing the target products incorporating three contiguous stereogenic centers as single diastereoisomers and with excellent yields and enantioselectivities.     

Hydrogen bonding cooperativity of water to nucleotide recognition: structure of octadecahydrated inosine 5′-monophosphate, 2(C10H12N4O8P)·18H2O at atomic resolution

The crystal structure of an octadecahydrated complex between two inosine 5-monophosphate (IMP) has been determined at atomic resolution, which reveals the hydrogen bonding and the coordination cooperativity of water molecules to nucleotide recognition. The crystal belongs to monoclinic space group P2₁ with cell dimensions a = 8.65(1), b = 21.90(1), c = 12.37(1)Å, and = 110.38(9)°. The ribose hydroxyls, purine N7, keto(O6) bonded water molecules W1, W2, W5, W6, W8 and the phosphate bridge forming water oxygens of W4, W7, W11 appear to play an invariant role in their hydrogen bonding interactions with the IMPs. The synergistic role of the water molecules W5, W6, W8 in the purine staking domain N27W5=2.583,O16W8=2.759,O2627W6=2.723 Åhave been clearly observed for the first time. The complexation of the water molecules through variable hydrogen bonding coordination indicate their functional involvement through extensive cooperative donor-acceptor network mechanism. The occurrence of hydrogen-bonded water spines, water bridges and their interplay in the structural association of IMPs could indicate the possible viability of those aquatic centers in the biological situation.     

Unusual nucleotide stability through C–H ⋅ ⋅ ⋅ water interaction in crystal: Recognition of nucleotide-water duplex-helix

The direct and indirect roles of the C2- and C8-bonded water molecules (C–H    O_W) in the stabilization of unusual inosine monophosphate containing nucleotides have been observed in their highly hydrated and amino acid cocrystals, which have been discussed in this work for the first time. The intermolecular H-bonding of W_R (the oxygen of ribose 2- and 3-hydroxyls bonded water molecule, O2    W_R    O3) with the C2–H bonded O_W's (O_W    W_R 2.43–2.78 Å) can influence the ribose and thus the nucleotide stability, whereas the water molecule (O_W) of C8–H    O_W can participate in the base stability by sandwiching the stacked purines through N7    O_W    N7 intermolecular interactions, with N7    O_W 2.63–2.75 Å. However, in some cases the water oxygen (O_W) of C8–H can get intermolecularly H-bonded to water molecular oxygen W_N (with O_W    W_N 2.57–2.85 Å), which has previously stabilized the nucleotide single-strand through intermolecular stacking N7    W_N    N7 interaction (N7    W_N 2.56–2.63 Å). The conjugal survival of the H-bonded nucleotide single-strand with the water-helix thus forming the duplex and its stabilization through the C–H    O_W mediated water molecular (O_W) cooperative H-bonding network, specially with the ribose and the base units, in the crystals could favor the support of single-stranding potentiality and thus the stability of the purine-rich RNAs or the small unusual nucleotides in the aquated environment besides the other interactive factors.     

Synthesis of a bimetallic platinum-tungsten complex with a bridging micro-diboranyl-oxycarbyne moiety

The novel bimetallic micro-diboranyl-oxycarbyne bridged platinum-tungsten complex [W{eta(1),micro-CO-B(NMe(2))-B(NMe(2))-(eta(5)-C(5)H(4))}(CO)(2){Pt(PPh(3))(2)}] (W-Pt) () has been synthesised by a two-step reaction, starting from the dilithiated half-sandwich compound Li[W(eta(5)-C(5)H(4)Li)(CO)(3)] () via the ansa-diboranyl-oxycarbyne tungsten complex [W{eta(1)-CO-B(NMe(2))B(NMe(2))(eta(5)-C(5)H(4))}(OC)(2)] () by use of stoichiometric amounts of B(2)(NMe(2))(2)Br(2) and [Pt(eta(2)-C(2)H(4))(PPh(3))(2)], respectively.     

Synthesis and characterization of mono- and micro6-sulfato hexanuclear zinc complexes of a new symmetric dinucleating ligand

Zinc complexes of a new symmetric dinucleating ligand, N,N'-Bis[2-carboxybenzomethyl]-N,N'-Bis[carboxymethyl]-1,3-diaminopropan-2-ol (H5ccdp) with mixed donating groups, have been studied in the solid state as well as in solution. In methanol, the reaction of stoichiometric and substoichiometric amounts of Zn(ClO4)2 x 6H2O and the ligand H5ccdp, in the presence of K2CO3 or Et3N, afforded a mononuclear zinc complex, [Zn(H2O)6][Zn(H2ccdp)(H2O)2]2 x 12H2O (1). The solid state structure of 1 contains two units of the zinc-ligand anion, [Zn(H2ccdp)(H2O)2]-, and one [Zn(H2O)6]2+ counter cation. The Zn(II) center of the anion is in a distorted octahedral geometry. However, in methanol, the reaction of ZnSO4 x 7H2O and the ligand Hsccdp in the presence of NaOH afforded a unique micro6-sulfato hexanuclear zinc complex, Na6[Zn6(ccdp)3(micro6-SO4)](OH) x 10.5H2O (2). The structure of 2 contains a [ZnII6(micro6-SO4)] core unit which is held together by three heptadentate bridging ligands, ccdp5-. Three of the Zn(II) centers are in highly distorted square pyramidal geometry, the other three Zn(II) centers are in a distorted octahedral geometry.     

A stereodefined approach towards the bicyclo[3.3.1]nonan-9-one core of the phloroglucin natural products guttiferone A and hypersampsone F

An approach towards the highly functionalized bicyclo[3.3.1]nonan-9-one core present in the phloroglucin natural products guttiferone A and hypersampsone F is disclosed in which the key C7 and C8 stereogenic centres have been successfully installed.     

Controlled Annealing in Adaptive Multicomponent Gels

We use a pH-driven annealing process to convert between co-assembled and self-sorted networks in multicomponent gels. The initially formed gels at low pH are co-assembled, with the two components coexisting within the same self-assembled structures. We use an enzymatic approach to increase the pH, resulting in a gel-to-sol transition, followed by a hydrolysis to lower the pH once again. As the pH decreases, a self-sorted network is formed by a two-stage gelation process determined by the pK_a of each component. This approach can be expanded to layered systems to generate many varied systems by changing composition and rates of pH change, adapting their microstructure and so allowing access to a far greater range of morphologies and complexity than can be achieved in single component systems.