A self-assembled binuclear coordination cage of the PdL formulation has been constructed by complexation of Pd(NO) with N, N'-bis(3-pyridylmethyl)naphthalenediimide (L). The cage, i.e., [Pd(L)](NO) (1), displayed a further self-assembly phenomenon to afford a gel phase, upon dissolution in either dimethyl sulfoxide or acetonitrile-water (1:1) followed by standing at room temperature. It was observed that a synergy among the metal ion, ligand, counteranion, solvent, and concentration played a vital role for metallogel formation. The morphology of the metallogel as observed from microscopy studies revealed the formation of a rare variety of nanoscale metal-organic particles. Salient features of the gel include the thixotropic (mechanoresponsive) nature, in addition to the reversible chemical-stimuli-responsive behavior. The presence of naphthalenediimide moieties at the backbone of the cage and the cationic nature of the cavity of the cage could be exploited to study the functional aspects of the gel. The porous gel exhibited the abilities to uptake pyrene as a guest and to selectively remove anionic dyes from aqueous solutions. The gel could bind representative anionic dyes like "acid blue 93" and "methyl orange" in the absence or presence of certain cationic dyes, making the material suitable for selective dye removal applications.

A rare variety of coordination rings having the M3L6 composition are prepared by the combination of Pd(NO3)2 with an imidazolyl or benzimidazolyl appended bidentate non-chelating ligand (i.e.L1 or L2). The variable concentration 1H NMR spectra of the trinuclear complexes [Pd3(L1)6](NO3)6, 1a and [Pd3(L2)6](NO3)6, 2a in DMSO-d6 provided valuable information on the self-assembly phenomenon of the already self-assembled complexes. Interestingly, the signals of 2a are broadened upon increasing the concentration. The solution of 2a in DMSO formed a supramolecular metallogel above a certain concentration (i.e. 2% w/v), however, complex 1a could not form any gel. This phenomenon is attributed to the presence of an auxiliary π-surface in the benzimidazole moiety in L2, in contrast to the imidazole moiety of L1. The influence of anions in gel formation was studied by preparing several samples using a variety of palladium(II) salts and L2 in DMSO. It was found that oxoanions like nitrate, perchlorate, triflate and tosylate are amicable for gel formation, probably due to their capabilities of forming H-bonds. The counter anions like tetrafluoroborate, hexafluorophosphate, or hexafluoroantimonate could not assist in the formation of gel. The stimuli-responsive nature of the gel and the reversible gel–sol conversion were demonstrated by dis-assembly and re-assembly processes of 2a as controlled by a pair of stimuli such as halide-nitrate, DMAP-HNO3, and ethylenediamine-Pd(NO3)2. No gel could be prepared by the combination of Ni(NO3)2 or Pt(NO3)2 with ligand L2. Thus, a subtle change in the ligand design, metal ion and counter anion is demonstrated as the responsible parameter for the construction of the three component multi-stimuli-responsive supramolecular gel.

A series of cephalosporin-derived reverse hydroxamates and oximes were prepared and evaluated as inhibitors of representative metallo- and serine-β-lactamases. The reverse hydroxamates showed submicromolar inhibition of the GIM-1 metallo-β-lactamase. With respect to interactions with the classes A, C, and D serine β-lactamases, as judged by their correspondingly low Km values, the reverse hydroxamates were recognized in a manner similar to the non-hydroxylated N-H amide side chains of the natural substrates of these enzymes. This indicates that, with respect to recognition in the active site of the serine β-lactamases, the O=C-NR-OH functionality can function as a structural isostere of the O=C-NR-H group, with the NO-H group presumably replacing the amide N-H group as a hydrogen bond donor to the appropriate backbone carbonyl oxygen of the protein. The reverse hydroxamates, however, displayed kcat values up to three orders of magnitude lower than the natural substrates, thus indicating substantial slowing of the hydrolytic action of these serine β-lactamases. Although the degree of inactivation is not yet enough to be clinically useful, these initial results are promising. The substitution of the amide N-H bond by N-OH may represent a useful strategy for the inhibition of other serine hydrolases.

A series of self-assembled binuclear complexes (1-4) of PdL'L composition are prepared by combination of selected cis-protected palladium(II) component cis-PdL' with equimolar amount of the nonchelating bidentate ligand 1,3-bis((pyridine-4-yl)methyl)urea, L. The cis-protecting unit L' crafted in the complexes [Pd(L')(L)](NO), 1-4, are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2'-bipyridine (bpy), and 1,10-phenanthroline (phen), respectively. Complexation of palladium(II) with the ligand L, however, resulted in the self-assembled trinuclear complex [Pd(L)](NO), 5, of PdL composition. A few other mononuclear complexes relevant to this work are the homoleptic (6-9) and the heteroleptic (10-12) of PdL' composition, where the term L' in the formula stands for en, tmeda, bpy, and phen. The two units of L' in the complexes 6-12 are en-en, tmeda-tmeda, bpy-bpy, phen-phen, en-tmeda, en-bpy, and en-phen, respectively. Keeping in mind the recombination of fragments in biomolecular systems, it was considered to study the recombination of fragments among assorted self-assembled coordination complexes. In this context, the complexes 1-12 are employed. The recombination was planned on the basis of information already coded in the complexes that we realized from our experience. Designated complexes from this list are subjected to deliberate circumstances, whereupon remarkable "molecular recombination" processes ensued. For instance, combination of [Pd(en)(L)](NO), 1 with [Pd(tmeda)](NO), 7 at 1:2 molar ratio produced [Pd(tmeda)(L)](NO), 2 and concomitant [Pd(en)(tmeda)](NO), 10 at 1:2 molar ratio. A number of reorganization reactions are studied through selective combinations of two types of complexes from the pool of 1-12. The detailed finding is described in the article so as to conceptualize molecular recombination and other related dynamic processes in self-assembled coordination complexes of a chosen family. Crystal structures of a few complexes (2, 4, and 5) and intermolecular interactions in the crystal packing with particular reference to π-π interactions in 4 are also discussed.

Metallo-supramolecular self-assembly has yielded a plethora of discrete nanosystems, many of which show competence in capturing guests and catalyzing chemical reactions. However, the potential of low-molecular bottom-up self-assemblies in the development of structured inorganic materials has rarely been methodically explored so far. Herein, we present a new type of metallo-supramolecular surfactant with the ability to stabilize non-aqueous emulsions for a significant period. The molecular design of the surfactant is based on a heteroleptic coordination cage (CGA-3; CGA = Cage-based Gemini Amphiphile), assembled from two pairs of organic building blocks, grouped around two Pd(II) cations. Shape-complementarity between the differently functional-ized components generates discrete amphiphiles with a tailor-made polarity profile, able to stabilize non-aqueous emulsions, such as hexadecane-in-DMSO. These emulsions were used as a medium for the synthesis of spherical metal oxide microcapsules (titanium oxide, zirconium oxide, and niobium oxide) from soluble, water-sensitive alkoxide precursors by allowing a controlled dosage of water to the liquidliquid phase boundary. Synthesized materials were analyzed by a combination of electron microscopic techniques. In situ liquid cell transmission electron microscopy (LC-TEM) was utilized for the first time to visualize the dynamics of the emulsion-templated formation of hollow inorganic titanium oxide and zirconium oxide microspheres.