Protein-templated gold nanoclusters as specific bio-imaging probes for the detection of Hg(ii) ions in in vivo and in vitro systems: discriminating between MDA-MB-231 and MCF10A cells.

Gold nanoclusters (AuNCs) synthesized within a protein (Human Serum Albumin, HSA) template exhibited intense red luminescence accompanied by a quantum yield >10% and remarkable photo and cluster-core stability for a prolonged period (more than a year). These photoluminescent nanoclusters (NCs) were resistant to chemical and thermal perturbations but break down selectively and highly sensitively in the presence of mercury, Hg(ii), ions. The AuNCs were efficient in quantifying Hg(ii) ions in solution as well as bound to the hormone insulin. By exploiting the auto-fluorescence of these AuNCs, we demonstrated that our AuNCs were able to sense Hg(ii) ions at single-molecule sensitivity using Fluorescence Correlation Spectroscopy (FCS), highlighting a detection limit in the sub-nanomolar regime. The translational diffusion time of the AuNCs decreased significantly upon the interaction with Hg(ii) ions and resulted in the formation of smaller sized clusters. A cell viability study reveals the non-toxic nature of these nano-probes, which thus can be used for cell imaging. Interestingly, a cell line-based study reveals that the fluorescence intensity of AuNCs could be detected in cancerous MDA-MB-231 cells but not in non-cancerous breast-derived MCF10A cells. Further, time lapse fixed cell imaging by confocal microscopy revealed that the fluorescence of AuNCs could be quenched by Hg(ii) ions inside the MDA-MB-231 cells. Thus the objective of our study is to appraise the sensitive in vivo as well as in vitro detection of Hg(ii) ions using AuNCs as a probe.

N-(6-Bromo-meth-yl-2-pyrid-yl)acetamide.

The title acetamide compound, C(8)H(9)BrN(2)O, crystallizes with three crystallographically independent mol-ecules (A, B and C) in the asymmetric unit. In mol-ecule A, the mean plane through the acetamide unit is inclined at a dihedral angle of 4.40 (11)° with respect to the pyridine ring [10.31 (12) and 2.27 (11)°, respectively, for mol-ecules B and C]. In the crystal structure, mol-ecules are inter-connected into sheets parallel to the ac plane by N-H⋯O, C-H⋯Br, C-H⋯O and C-H⋯N hydrogen bonds. The structure is further stabilized by weak inter-molecular C-H⋯π inter-actions.

N-(6-{2-[6-(2,2-Dimethyl-propanamido)-2-pyrid-yl]eth-yl}-2-pyrid-yl)-2,2-dimethyl-propanamide.

The title compound, C(22)H(30)N(4)O(2), lies about a crystallographic inversion center. The whole mol-ecule is disordered over two positions with a refined occupancy ratio of 0.636 (10):0.364 (10). The pyridine rings are approximately planar, with maximum deviations of 0.033 (10) and 0.063 (17) Šfor the major and minor components, respectively. The mean planes of the pyridine rings form dihedral angles of 17 (2)° in the major component and 18 (2)° in the minor component with the respective formamide groups attached to them. In the crystal packing, inter-molecular N-H⋯O and C-H⋯O hydrogen bonds link the mol-ecules into two-dimensional networks parallel to the ab plane.

Quinoxaline-2-carbonitrile.

In the title compound, C(9)H(5)N(3), the quinoxaline ring is essentially planar, with a maximum deviation of 0.012 (1) Å. Short inter-molecular distances between the centroids of the 2,3-dihydro-pyrazine and benzene rings [3.6490 (5) Å] indicate the existence of π⋯π inter-actions. In the crystal packing, the mol-ecules are linked via two pairs of inter-molecular C-H⋯N inter-actions, forming R(2) (2) (8) and R(2) (2) (10) ring motifs; these mol-ecules are further linked into a two-dimensional network parallel to (1 0 2) via another C-H⋯N inter-action.

7-(2,2-Dimethylpropanamido)-2-methyl-1,8-naphthyridin-1-ium chloride monohydrate.

The asymmetric unit of the title compound, C(14)H(18)N(3)O(+)·Cl(-)·H(2)O, comprises a substituted amido-naphthyridine cation, a chloride anion and a water mol-ecule of crystallization. Intra-molecular C-H⋯O hydrogen bonds generate six-membered rings, producing an S(6) ring motif. The amido group is twisted from the naphthyridine ring, making a dihedral angle of 17.65 (7)°. The crystal structure is stabilized by inter-molecular N-H⋯O, N-H⋯Cl, O-H⋯Cl (× 2), and C-H⋯O (× 2) hydrogen bonds. These inter-actions linked neighbouring mol-ecules into chains along the a and b axes of the crystal, thus forming mol-ecular sheets parallel to the (001) plane.

2,7-Dimethyl-1,8-naphthyridine.

The asymmetric unit of the title compound, C(10)H(10)N(2), contains one half-mol-ecule with the two shared C atoms lying on a twofold rotation axis. The 1,8-naphthyridine is almost planar with a dihedral angle of 0.42 (3)° between the fused pyridine rings. In the crystal, mol-ecules are linked into infinite chains along the c axis by inter-molecular C-H⋯N hydrogen bonds, generating R(2) (2)(8) ring motifs. In addition, the crystal structure is further stabilized by C-H⋯π inter-actions.

Photostable Copper Nanoclusters: Compatible Förster Resonance Energy-Transfer Assays and a Nanothermometer.

To address the concern of material chemists over the issue of stability and photoluminescent (PL) characteristics of Cu nanoclusters (NCs), herein we present an efficient protocol discussing PL Cu NCs (Cu/HSA) having blue emission and high photostability. These PL NCs were illustrated as efficient probes for Förster resonance energy transfer (FRET) with a compatible fluorophore (Coumarin 153). Our spectroscopic results were well complemented by our molecular docking calculations, which also favored our proposed mechanism for Cu NC formation. The beneficial aspect and uniqueness of these nontoxic Cu/HSA NCs highlights their temperature-dependent PL reversibility as well as the reversible FRET with Coumarin 153, which enables them to be used as a nanothermometer and a PL marker for sensitive biological samples.

Temperature induced morphological transitions from native to unfolded aggregated States of human serum albumin.

The circulatory protein, human serum albumin (HSA), is known to have two melting point temperatures, 56 and 62 °C. In this present manuscript, we investigate the interaction of HSA with a synthesized bioactive molecule 3-pyrazolyl 2-pyrazoline (PZ). The sole tryptophan amino acid residue (Trp214) of HSA and PZ forms an excellent FRET pair and has been used to monitor the conformational dynamics in HSA as a function of temperature. Molecular docking studies reveal that the PZ binds to a site which is in the immediate vicinity of Trp214, and such data are also supported by time-resolved FRET studies. Steady-state and time-resolved anisotropy of PZ conclusively proved that the structural and morphological changes in HSA mainly occur beyond its first melting temperature. Although the protein undergoes thermal denaturation at elevated temperatures, the Trp214 gets buried inside the protein scaffolds; this fact has been substantiated by acrylamide quenching studies. Finally, we have used atomic force microscopy to establish that at around 70 °C, HSA undergoes self-assembly to form fibrillar structures. Such an observation may be attributed to the loss of α-helical content of the protein and a subsequent rise in ß-sheet structure.

A new rhodamine based colorimetric 'off-on' fluorescence sensor selective for Pd2+ along with the first bound X-ray crystal structure.

A new fluorescence rhodamine derivative bearing an 8-aminoquinoline moiety has been designed and synthesized for selective sensing of Pd(2+) in the presence of other competing metal ions in aqueous media. Pd(2+) induced spirolactam ring opening of rhodamine is confirmed for the first time by the X-ray crystal structure of the bound Pd(2+)-complex.

A new highly selective, ratiometric and colorimetric fluorescence sensor for Cu(2+) with a remarkable red shift in absorption and emission spectra based on internal charge transfer.

A new 1,8-diaminonaphthalene based ratiometric and highly selective colorimetric "off-on" type of fluorescent probe, receptor 2 has been designed and synthesized that senses only Cu(2+) among the other heavy and transition metal ions examined on the basis of internal charge transfer (ICT). The visual sensitivity of the receptor 2 is remarkable, showing dual color changes from colorless (receptor) to purple followed by blue and a large red shift in emission upon Cu(2+) complexation.