Ahmad Husain

Single Crystals Popping Under UV Light: A Photosalient Effect Triggered by a [2+2] Cycloaddition Reaction†

The extremely rare examples of dynamic single crystals where excitation by light or heat induces macroscopic motility present not only a visually appealing demonstration of the utility of molecular materials for conversion of energy to work, but they also provide a unique opportunity to explore the mechanistic link between collective molecular processes and their consequences at a macroscopic level. Here, we report the first example of a photosalient effect (photoinduced leaping) observed with crystals of three coordination complexes which is induced by a [2+2] photocycloaddition reaction. Unlike a plethora of other dimerization reactions, when exposed to even weak UV light, single crystals of these materials burst violently, whereby they are propelled to travel several millimeters. The results point to a multistep mechanism where the strain energy that has been accumulated during the dimerization triggers a rapid structure transformation which ultimately results in crystal disintegration.

Perpetually self-propelling chiral single crystals.

When heated, single crystals of enantiomerically pure D- and L-pyroglutamic acid (PGA) are capable of recurring self-actuation due to rapid release of latent strain during a structural phase transition, while the racemate is mechanically inactive. Contrary to other thermosalient materials, where the effect is accompanied by crystal explosion due to ejection of debris or splintering, the chiral PGA crystals respond to internal strain with unprecedented robustness and can be actuated repeatedly without deterioration. It is demonstrated that this superelasticity is attained due to the low-dimensional hydrogen-bonding network which effectively accrues internal strain to elicit propulsion solely by elastic deformation without disintegration. One of the two polymorphs (β) associated with the thermosalient phase transition undergoes biaxial negative thermal expansion (αa = -54.8(8) × 10(-6) K(-1), αc = -3.62(8) × 10(-6) K(-1)) and exceptionally large uniaxial thermal expansion (αb = 303(1) × 10(-6) K(-1)). This second example of a thermosalient solid with anomalous expansion indicates that the thermosalient effect can be expected for first-order phase transitions in soft crystals devoid of an extended 3D hydrogen-bonding network that undergo strongly anisotropic thermal expansion around the phase transition.

Synthesis and Characterization of Novel n-9 Fatty Acid Conjugates Possessing Antineoplastic Properties

The present study enumerates the synthesis, spectroscopic characterization, and evaluation of anticancer potential of esters of two n-9 fatty acids viz., oleic acid (OLA) and ricinoleic acid (RCA) with 2,4- or 2,6-diisopropylphenol. The synthesis strategy involved esterification of the hydroxyl group of diisopropylphenol (propofol) to the terminal carboxyl group of n-9 fatty acid. The synthesized propofol-n-9 conjugates having greater lipophilic character were tested initially for cytotoxicity in-vitro. The conjugates showed specific growth inhibition of cancer cell lines whereas no effect was observed in normal cells. In general, pronounced growth inhibition was found against the human skin malignant melanoma cell line (SK-MEL-1). The anticancer potential was also determined by testing the effect of these conjugates on cell migration, cell adhesion and induction of apoptosis in SK-MEL-1 cancer cells. Propofol-OLA conjugates significantly induced apoptosis in contrast to propofol-RCA conjugates which showed only weak signals for cytochrome c. Conclusively, the synthesized novel ester conjugates showed considerable moderation of anti-tumor activity. This preliminary study places in-house synthesized conjugates into the new class of anticancer agents that possess selectivity toward cancer cells over normal cells.

Synthesis, characterization, thermal and antioxidant studies of potassium dihydrobisphenothiazinyl borate and its transition metal complexes

The bidentate borate anion H(2)B(ptz)(2)(-) and its transition metal complexes have been synthesized and characterized by elemental analyses, magnetic susceptibility, electronic, IR, (1)H and (13)C NMR data. The molar conductance of 10(-3) M solution for all the complexes supports their non-ionic nature. The TGA profile of borate anion shows a single stage unlike that of two stage decomposition plot of the metal complexes. On the basis of spectroscopic studies the geometry of all the complexes have been proposed to be distorted-tetrahedral. The in vitro antioxidant and lipid oxidation inhibition of the ligand and its complexes have also been studied. The Cu[B(ptz)(2)](2) complex was found to be most effective in all the studies.

A C-shaped p -sulfonatocalix[4]arene-based supermolecule exhibiting mutual-inclusion and bilayer insertion of dipicolinate

A p-sulfonatocalix[4]arene-based supermolecule, [Ce3(PDA)4(C4AS)2·13H2O](NO3)·25H2O 1 was prepared by slow evaporation of a solution of Ce(NO3)3·6H2O, 2,6-pyridinedicarboxylic acid (PDA) and pentasodium p-sulfonatocalix[4]arene salt. The molecular and crystal structure of 1 was determined by single crystal X-ray structural analysis and characterized by thermal methods (TG, DSC and hot-stage microscopy) and Hirshfeld analysis. The supermolecule is C-shaped with alternating calixarene and PDA ligands linked to three Ce(III) cations. The supermolecules exhibit mutual-inclusion via its PDA ligands with the remaining PDA ligands inserted into the calixarene bilayer. The bilayer consists of an “up–down” arrangement of calixarenes, with the inserted PDA ligands effecting a zig-zag propagation of the calixarenes within the bilayer.

Self assembled homodinuclear dithiocarbamates: One pot synthesis and spectral characterization

Several self assembled homodinuclear complexes of the type [M2(Ldtc)2·4H2O] derived from quadridentate ligand (Ldtc), where Ldtc = 2-aminobenzoylhydrazidebis(dithiocarbamate) and M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) have been reported. The in situ procedure gives high yield with the formation of single product as evident by TLC and various other physicochemical techniques. Elemental analysis, TGA, (1)H NMR, (13)C NMR, ESI mass spectrometry, EPR, UV-vis. and IR spectroscopy were used to characterize the homodinuclear complexes. The spectroscopic evidences and room temperature magnetic moment values suggest that all the complexes have octahedral geometry around the transition metal atom. A symmetrical bidentate coordination of the dithiocarbamato moiety has been observed in all the complexes. The energy-minimized structure of the molecule also showed that each metal atom acquires a distorted octahedral geometry. The complexes exhibit a three-step thermolytic pattern and are non-electrolyte in nature.

A Functional Zn(II) Metallacycle Formed from an N-Heterocyclic Carbene Precursor: A Molecular Sensor for Selective Recognition of Fe3+ and IO4– Ions

We have reported the synthesis and structural characterization of a unique Zn(II) metallacycle (1) and its utilization as a fluorescent probe for the shape-specific selective recognition (turn-off) of Fe3+ and IO4- ions. The relevant Stern-Volmer graphs indicate that the recognitions of Fe3+ and IO4- ions are examples of diphasic and monophasic quenchings, respectively. The title metallacycle has been prepared by the reaction of a novel N-heterocyclic carbene precursor, 1,3-bis(2,6-diisopropyl-4-(pyridin-4-yl)phenyl)-1H-imidazol-3-ium chloride/bromide (L), and zinc(II) chloride salt. Notably, the ligand itself did not show any type of recognition for any ions. DFT calculations were performed on L and metallacycle 1 using the geometric parameters, obtained from their single-crystal X-ray diffraction data, to understand the electronic structures of the ligand and macrocycle. The detection limit for the recognition of the Fe3+ ion was determined to be 2.5 × 10-6 mol/L, and that for IO4- ion was found to be 6.3 × 10-5 mol/L.

Synthesis, crystal structure, and magnetic properties of single end-to-end azido-bridged 1-D chain coordination polymers of Cu(II)

The synthesis and spectroscopic characterization of azido derivatives of Cu(II) complexes with macrocyclic building blocks of the type [CuLN3] n  · [ClO4 · 3/2H2O] n (1), [CuL(N3)2] (2) and [CuL1N3]n · [ClO4]n (3) (where L = 3,10-bisbenzyl-1,3,5,8,10,12-hexaazacyclotetradecane and L1 = 3,10-bisbenzyl-6,13-dimethyl-1,3,5,8,10,12-hexaazacyclotetradecane) are reported. On the basis of single-crystal X-ray diffraction, 1 and 3 have a 1-D polymeric chain where Cu(II) ions are bridged by single azide in the μ-1,3 (end-to-end) bridging mode in a trans-position with respect to the azide. When [CuLN3] n  · [ClO4 · 3/2H2O] n was recrystallized from acetone, the non-polymeric 2 was obtained, where Cu(II) is in a tetragonally distorted octahedral environment. The chains of [CuLN3] n  · [ClO4 · 3/2H2O] n and [CuL1N3] n  · [ClO4] n propagate parallel to the crystallographic b-axis and are stacked one over the other along the c-axis by hydrogen bonding. The azides exhibit symmetric coordination. The ions fill channels formed between the strings of octahedra and are held in place by hydrogen bonds leading to the formation of a 3-D network. Compound 1 exhibits only very weak antiferromagnetic interactions, while 2 and 3 show no signs of magnetic exchange.

Novel mixed 1D–2D lanthanide coordination polymers based on p -sulfonatocalix[4]arene and 4,4′-bipyridine- N , N ′-dioxide where p -sulfonatocalix[4]arene acts as a guest

Two novel mixed 1D–2D coordination polymers based on 2D [Ln(4,4′-bpdo)2(NO3)2(H2O)2]n+ sheets and 1D [Ln2(4,4′-bpdo)2(C4AS)(NO3)(H2O)9]n chains (Ln = Sm for 1 and Ln = Nd for 2) sustained by π⋯π interactions and lattice water facilitated hydrogen bonds have been established. The chains are arranged such that the p-sulfonatocalix[4]arene anions occupy the cavities of the 2D coordination polymer, and so act as guests rather than as hosts, which is their more usual role.

Synthesis, spectroscopic, magnetic and thermal properties of bimetallic salts, [Ni(L)][MCl4] [where M=Co(II), Zn(II), Hg(II) and L=3,7-bis(2-aminoethyl)-1,3,5,7-tetraazabicyclo(3.3.1)nonane]. X-ray structure of [Ni(L)][CoCl4].

New bimetallic complex salts corresponding to the formulation [Ni(L)][MCl(4)] have been synthesized by the facile reaction between [Ni(L)](ClO(4))(2) and [MCl(2)(PPh(3))(2)] in high yields [where M=Co(II), Zn(II), Hg(II) and L=3,7-bis(2-aminoethyl)-1,3,5,7-tetraazabicyclo(3.3.1)nonane]. The complexes were characterized by IR, electronic spectra, TGA/DSC, magnetic moment and conductivity measurements. The X-ray crystal structure for [Ni(L)][CoCl(4)] clearly establishes the cationic-anionic interaction. It crystallizes in the space group P1 with unit cell dimensions a=7.1740(15)A, b=8.1583(16)A and c=8.3102(16)A. A square-planar geometry is evident for the [Ni(L)](2+) cation while the anion is found to be tetrahedral. A two-step thermolytic pattern is observed in the pyrolysis of the bimetallic complex salts.