Enhanced Genotoxicity of Silver Nanoparticles in DNA Repair Deficient Mammalian Cells

Silver nanoparticles (Ag-np) have been used in medicine and commercially due to their anti-microbial properties. Therapeutic potentials of these nanoparticles are being explored extensively despite the lack of information on their mechanism of action at molecular and cellular level. Here, we have investigated the DNA damage response and repair following Ag-np treatment in mammalian cells. Studies have shown that Ag-np exerts genotoxicity through double-strand breaks (DSBs). DNA-PKcs, the catalytic subunit of DNA dependent protein kinase, is an important caretaker of the genome which is known to be the main player mediating Non-homologous End-Joining (NHEJ) repair pathway. We hypothesize that DNA-PKcs is responsible for the repair of Ag-np induced DNA damage. In vitro studies have been carried out to investigate both cytotoxicity and genotoxicity induced by Ag-np in normal human cells, DNA-PKcs proficient, and deficient mammalian cells. Chemical inhibition of DNA-PKcs activity with NU7026, an ATP-competitive inhibitor of DNA-PKcs, has been performed to further validate the role of DNA-PKcs in this model. Our results suggest that Ag-np induced more prominent dose-dependent decrease in cell viability in DNA-PKcs deficient or inhibited cells. The deficiency or inhibition of DNA-PKcs renders the cells with higher susceptibility to DNA damage and genome instability which in turn contributed to greater cell cycle arrest/cell death. These findings support the fact that DNA-PKcs is involved in the repair of Ag-np induced genotoxicity and NHEJ repair pathway and DNA-PKcs particularly is activated to safeguard the genome upon Ag-np exposure

8-Methyl-2-[4-(trifluoro­meth­yl)phen­yl]-8H-pyrazolo­[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine methanol disolvate

In the title compound, C14H10F3N7·2CH4O, the heterocyclic ring system is essentially planar (r.m.s. deviation = 0.009 Å) and makes a dihedral angle of 6.91 (8)° with the attached benzene ring. In the crystal, the main mol­ecules form centrosymmetric R 2 2(8) dimers via pairs of N—H⋯N hydrogen bonds between the amino groups and pyrimidine N atoms. One of the independent methanol mol­ecules and its inversion equivalent are linked to the dimers via O—H⋯N and N—H⋯O hydrogen bonds, forming R 4 4(16) graph-set motifs. The dimers along with the hydrogen-bonded methanol mol­ecules are stacked along the a axis, with π–π inter­actions between the pyrazole and triazole rings [centroid–centroid distance = 3.4953 (10) Å]

N-Carbethoxy-N′-(3-phenyl-1H-1,2,4-triazol-5-yl)thiourea

The title compound {systematic name: ethyl N-[N-(3-phenyl-1H-1,2,4-triazol-5-yl)carbamothio­yl]carbamate}, C12H13N5O2S, exists in the 3-phenyl-5-thio­ureido-1H-1,2,4-triazole tautomeric form stabilized by intra­molecular hydrogen bonding between the endocyclic NH H atom and the thio­ureido S atom. The mol­ecular structure is also stabilized by intra­molecular N—H⋯O=C hydrogen bonds arranged in an S(6) graph-set motif within the carbethoxy­thio­urea moiety. The mean planes of the phenyl and 1,2,4-triazole rings make a dihedral angle of 7.61 (11)°. In the crystal, the mol­ecules form two types of inversion dimers. Inter­molecular hydrogen bonds are arranged in R 2 2(6) and R 2 2(8) graph-set motifs, together forming a network parallel to (111)

6-Chloro-2-methyl-4-phenyl-3-[1-phenyl-5-(2-thien­yl)-4,5-dihydro-1H-pyrazol-3-yl]quinoline

In the title mol­ecule, C29H22ClN3S, the quinoline ring system, thio­phene ring and phenyl ring substituents are inclined at angles of 71.70 (7), 59.26 (9) and 81.61 (9)°, respectively, to the 4,5-dihydro­pyrazole ring. In the 4-phenyl­quinoline ring system, the phenyl ring makes a dihedral angle of 62.49 (7)° with mean plane of quinoline ring system. In the crystal structure, mol­ecules are linked via weak inter­molecular C—H⋯N hydrogen bonds, forming an extended one-dimensional chain along the b axis and are further consolidated by C—H⋯π and π–π stacking inter­actions [centroid–centroid distances = 3.7022 (10) Å]

The value of double balloon enteroscopy in diagnosing blue rubber bleb naevus syndrome: a case report

Blue rubber bleb naevus syndrome is a rare vascular disorder associated with multiple gastrointestinal haemangiomas that have the potential for life-threatening haemorrhage. These may be difficult to diagnose, and have classically been described using computed tomographic studies and/or mesenteric angiography. Resected surgical specimens of these lesions, especially in the small bowel, have often been extensive and poorly localized. The recent advent and progressive development of double balloon enteroscopy has allowed the direct visualization and marking of these enteric lesions and serves as a valuable adjunct not only in diagnosis but also planning prior to surgery to allow accurate estimate of the extent of resection

Dimethyl 4-(4-ethoxy­phen­yl)-2,6-dimethyl-1,4-dihydro­pyridine-3,5-dicarboxyl­ate

In the title mol­ecule, C19H23NO5, the dihedral angle formed by the benzene ring and the planar part of the dihydro­pyridine ring is 83.52 (5)°. The dihydro­pyridine ring adopts a flattened boat conformation. In the crystal, mol­ecules are linked by N—H⋯O hydrogen bonds, generating chains running parallel to [100]. The crystal structure is consolidated by C—H⋯O contacts

7-Dimethyl­amino-2-phenyl-1,2,4-triazolo[1,5-a][1,3,5]triazin-5-amine methanol solvate1

7-Dimethyl­amino-2-phenyl-1,2,4-triazolo[1,5-a][1,3,5]triazin-5-amine crystallized with one mol­ecule of methanol to give the title compound, C12H13N7·CH3OH. The triazolo[1,5-a][1,3,5]triazine heterocyclic core is essentially planar as are both amino groups that are involved in π-electron delocalization with the triazolo[1,5-a][1,3,5]triazine nucleus. The methyl groups of the dimethyl­amino fragment are involved in the formation of weak intra­molecular C—H⋯N hydrogen bonds with the N atoms of the heterocyclic system. The crystal packing is stabilized by inter­molecular N—H⋯N hydrogen bonds between the triazolo[1,5-a][1,3,5]triazine mol­ecules. The methanol solvent mol­ecule also participates in the formation of the crystal structure via inter­molecular O—H⋯N, N—H⋯O and weak C—H⋯O hydrogen bonds, linking the layers of triazolo[1,5-a][1,3,5]triazine mol­ecules

Stability of trions in strongly spin-polarized two-dimensional electron gases

Low-temperature magneto-photoluminescence studies of negatively charged excitons (X- trions) are reported for n-type modulation-doped ZnSe/Zn(Cd,Mn)Se quantum wells over a wide range of Fermi energy and spin-splitting. The magnetic composition is chosen such that these magnetic two-dimensional electron gases (2DEGs) are highly spin-polarized even at low magnetic fields, throughout the entire range of electron densities studied (5e10 to 6.5e11 cm^-2). This spin polarization has a pronounced effect on the formation and energy of X-, with the striking result that the trion ionization energy (the energy separating X- from the neutral exciton) follows the temperature- and magnetic field-tunable Fermi energy. The large Zeeman energy destabilizes X- at the nu=1 quantum limit, beyond which a new PL peak appears and persists to 60 Tesla, suggesting the formation of spin-triplet charged excitons.Comment: 5 pages (RevTex), 4 embedded EPS figs. Submitted to PRB-R

(4Z,6Z,12Z,14Z)-2,10-Dimethyl-2,8,10,16-tetra­hydro­dipyrazolo[3,4-e:3′,4′-l][1,2,4,8,9,11]hexa­azacyclo­tetra­decine-4,12-diamine

The title compound, C12H16N12, is a centrosymmetric mol­ecule which comprises of a hexa­aza[14]annulene macrocyclic ring fused with two pyrazole rings. The macrocyclic ring is essentially planar, with an r.m.s. deviation of 0.0381 Å. The electron pairs of the amino groups are delocalized with the conjugated system of the macrocycle. Strong intra­molecular N—H⋯N hydrogen bonds arranged in an S 2 2(10) graph-set motif are present in the macrocyclic ring. In the crystal, the amino groups act as donors for inter­molecular N—H⋯N inter­actions with the N atoms of the heterocyclic system, forming a network of two types of extended chains oriented parallel to the [101] and [011] directions. The crystal packing is also stabilized by weak inter­molecular C—H⋯N hydrogen bonds formed between pyrazole C—H groups and N atoms of the macrocyclic ring, running in the [10] direction

3-Phenyl-1H-1,2,4-triazol-5-amine–5-phenyl-1H-1,2,4-triazol-3-amine (1/1)

In the title compound, C8H8N4·C8H8N4, two tautomers, viz. 3-phenyl-1,2,4-triazol-5-amine and 5-phenyl-1,2,4-triazol-3-amine, are crystallized together in equal amounts. The 3-phenyl-1,2,4-triazol-5-amine mol­ecule is essentially planar; the phenyl ring makes a dihedral angle of 2.3 (2)° with the mean plane of the 1,2,4-triazole ring. In the 5-phenyl-1,2,4-triazol-3-amine tautomer, the mean planes of the phenyl and 1,2,4-triazole rings form a dihedral angle of 30.8 (2)°. The π-electron delocalization of the amino group with the 1,2,4-triazole nucleus in the 3-phenyl-1,2,4-triazol-5-amine mol­ecule is more extensive than that in the 5-phenyl-1,2,4-triazol-3-amine tautomer. The mol­ecules are linked into a two-dimensional network parallel to (100) by N—H⋯N hydrogen bonds