Md. Badruz Zaman

Unusual sculpting of dipeptide particles by ultrasound induces gelation.

A readily synthesized dipeptide shows unprecedented gelation behavior when dispersed and submitted to ultrasound in nonsolvents. SEM and FFEM revealed spectacular shape changes from a sheet-like material into a highly interconnected fiber network and ribbons while the dipeptide maintains an anti conformation inside β-sheets at the molecular scale.

Low-temperature approach to highly emissive copper indium sulfide colloidal nanocrystals and their bioimaging applications.

We report our newly developed low-temperature synthesis of colloidal photoluminescent (PL) CuInS2 nanocrystals (NCs) and their in vitro and in vivo imaging applications. With diphenylphosphine sulphide (SDPP) as a S precursor made from elemental S and diphenylphosphine, this is a noninjection based approach in 1-dodecanethiol (DDT) with excellent synthetic reproducibility and large-scale capability. For a typical synthesis with copper iodide (CuI) as a Cu source and indium acetate (In(OAc)3) as an In source, the growth temperature was as low as 160 °C and the feed molar ratios were 1Cu-to-1In-to-4S. Amazingly, the resulting CuInS2 NCs in toluene exhibit quantum yield (QY) of ~23% with photoemission peaking at ~760 nm and full width at half maximum (FWHM) of ~140 nm. With a mean size of ~3.4 nm (measured from the vertices to the bases of the pyramids), they are pyramidal in shape with a crystal structure of tetragonal chalcopyrite. In situ (31)P NMR (monitored from 30 °C to 100 °C) and in situ absorption at 80 °C suggested that the Cu precursor should be less reactive toward SDPP than the In precursor. For our in vitro and in vivo imaging applications, CuInS2/ZnS core-shell QDs were synthesized; afterwards, dihydrolipoic acid (DHLA) or 11-mercaptoundecanoic acid (MUA) were used for ligand exchange and then bio-conjugation was performed. Two single-domain antibodies (sdAbs) were used. One was 2A3 for in vitro imaging of BxPC3 pancreatic cancer cells. The other was EG2 for in vivo imaging of a Glioblastoma U87MG brain tumour model. The bioimaging data illustrate that the CuInS2 NCs from our SDPP-based low-temperature noninjection approach are good quality.

Solid state NMR studies of photoluminescent cadmium chalcogenide nanoparticles

Solid state (113)Cd, (77)Se, (13)C and (31)P NMR have been used to study a number of Cd chalcogenide nanoparticles synthesized in tri-n-octyl-phosphine (TOP) with different compositions and architectures. The pure CdSe and CdTe nanoparticles show a dramatic, size-sensitive broadening of the (113)Cd NMR line, which can be explained in terms of a chemical shift distribution arising from multiple Cd environments. From (13)C NMR, it has been discovered that TOP, or its derivatives such as TOPO (trioctylphosphine oxide), is rapidly moving about the surface of the nanoparticles, indicating that it is relatively weakly bound as compared to other materials used as surface ligands, such as hexadecylamine. (31)P NMR of the nanoparticles shows at least five species arising from coordination of the ligands to different surface sites. (113)Cd NMR of CdSeTe alloy and layered nanoparticles has provided crucial information which, in conjunction with results from other techniques (especially optical characterization), has made it possible to develop a detailed picture of the composition and structure of these materials: (i) a true CdSeTe homogeneous alloy nanoparticle, (ii) a nanoparticle segregated into an alloy core region rich in Te, with a CdSeTe (close to 1 : 1 Se : Te) alloy shell and (iii) a CdSe/CdTe/CdSe layered nanoparticle in which the CdTe layer contains a small amount of Se and which forms a Quantum Dot Quantum Well (QDQW) system. The results demonstrate that solid state NMR is a vital tool in the arsenal of characterisation techniques available for nanomaterials.

Two different one-dimensional structural motifs in the same coordination polymer: a novel interpenetration of infinite ladders by bundles of infinite chains

A coordination polymer with a novel structural motif consisting of stacks of infinite ladders interpenetrated by bundles of infinite chains is described; geometrical arguments are made for the requirements that can lead to such interpenetration as a function of ligand dimensions.

Synthesis and Optical Properties of Thiol Functionalized CdSe/ZnS (Core/Shell) Quantum Dots by Ligand Exchange

The colloidal photoluminescent quantum dots (QDs) of CdSe (core) and CdSe/ZnS (core/shell) were synthesized at different temperatures with different growth periods. Optical properties (i.e., UV/Vis spectra and photoluminescent emission spectra) of the resulting QDs were investigated. The shell-protected CdSe/ZnS QDs exhibited higher photoluminescent (PL) efficiency and stability than their corresponding CdSe core QDs. Ligand exchange with various thiol molecules was performed to replace the initial surface passivation ligands, that is, trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP), and the optical properties of the surface-modified QDs were studied. The thiol ligand molecules in this study included 1,4-benzenedimethanethiol, 1,16-hexadecanedithiol, 1,11-undecanedithiol, biphenyl-4,4′-dithiol, 11-mercapto-1-undecanol, and 1,8-octanedithiol. After the thiol functionalization, the CdSe/ZnS QDs exhibited significantly enhanced PL efficiency and storage stability. Besides surface passivation effect, such enhanced performance of thiol-functionalized QDs could be due to cross-linked assembly formation of dimer/trimer clusters, in which QDs are linked by dithiol molecules. Furthermore, effects of ligand concentration, type of ligand, and heating on the thiol stabilization of QDs were also discussed.

Perturbation induced formation of a 3D-network of microcrystals producing soft materials

Toluene and 1-chloronaphthalene immobilization was observed when perturbing stimuli such as agitation or ultrasound are applied during the cooling of a hot supersaturated solution of the rigid dinitroxide bTbk. X-Ray diffraction and cryo-SEM on gels and solid samples (crystal, powder) confirmed the pivotal role of clathrate type microcrystals in the solvent immobilization process.

Size reduction of CdSe/ZnS quantum dots by a peptidic amyloid supergelator.

Anchoring of a self-assembling dipeptide on the surface of core/shell CdSe/ZnS quantum dots resulted in a competition between coordination of the surface atoms of the QDs and the strong tendency for the dipeptide to self-assemble in toluene. This resulted in a mild QD etching and in a corresponding increase in the band gap of the nanocrystals whose photoluminescent emission gradually turns blue with time. The FmocLeuLeuOH dipeptide supergelator self-assembles in fibrils in which the Fmoc groups are surrounded by the pendant isobutyl side chains of the leucine residues with vibrational circular dichroism (VCD) and liquid- and solid-state NMR attributes of twist anti-parallel β-sheets.

Synthesis and crystal structures of decamethylferrocenium salts of anilate anions derived from bromanilic acid, chloranilic acid and cyananilic acid

Abstract Four complexes were synthesized using bis(pentamethylcyclopentadienyl)iron Fe(C5Me5)2 as an organometallic donor and three anilic acids (2,5-dibromo-3,6-dihydroxy-1,4-benzoquinone; BA, 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone; CA and 2,5-dicyano-3,6-dihydroxy-1,4-benzoquinone; CNA) as an organic acceptor. The molecular-based structures with different stoichiometric ratios [1:1, 1:1:1(H2O) and 2:1] of these complexes have been determined by X-ray crystallographic analysis and elemental analysis. These complexes have a one-dimensional alternated stacking arrangement as ⋯D+A−D+A−⋯ type. Close contacts between the bromine atoms and oxygen atoms of the BA units are observed in the structure [Fe(C5Me5)2](BA) (1) of 1:1 composition. Interestingly, the structures [Fe(C5Me5)2](CA)(H2O) (2) and [Fe(C5Me5)2](CNA)(H2O) (3) of 1:1:1(H2O) ratio contain one-dimensional molecular tape structures with the combination of the CA or the CNA units and water molecules via O–H⋯O hydrogen bonds. Different stoichiometric ratios and structures are found from the CNA complexes [Fe(C5Me5)2](CNA)(H2O) (3) and [Fe(C5Me5)2]2(CNA) (4).

Novel supramolecular synthon in crystal engineering: ionic complexes of 4,4′-bipyridine and 1,2-bis(2-pyridyl)ethylene with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone

4,4′-Bipyridine (BPY) and 1,2-bis(2-pyridyl)ethylene (2-PDE) form bifurcated hydrogen bonds with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid, 2H-CLA) to afford [BPY-2H]2+[CLA]2– 1 and [2-PDE-2H]2+[CLA]2– 2; their crystal structures exhibit a new type supramolecular synthon and links as molecular chains and zigzag tapes, respectively.

Centrosymmetric cyananilic acid: a molecule for functional solids

This article investigates the recent research on a series of anilic acid molecules. The crystallisation of molecules in high symmetry space groups is discussed and rationalised by the arrangement of charge-transfer complexes, which leads to the occurrence of repeated embrace motifs. Since 1997, cyananilic acid (2,5-dicyano-3,6-dihydroxy-1,4-benzoquinone) has been explored due to its valuable physico-chemical features. It is an organic acid that has Mott-insulator properties and organic ferroelectricity. Understanding these properties is an active area of supramolecular chemistry.