Thermal Decomposition Studies of Organoplatinum Films

 This study examines the thermal decomposition of 1,5-cyclooctadiene platinum (II) chloride organometallic films, deposited by thermal evaporation. The thin film samples were annealed both in air and hydrogen with well-controlled temperature regimes. After annealing, the decomposed thin films were examined by AFM and STM scanning probe, XPS and TEM microbeam analytical techniques. The experimental results confirm that the thermal decomposition products on silicon substrates are composed predominantly of metallic platinum. Annealing in hydrogen can reduce substantially the decomposition temperature of the material from around 250 to 160 °C but the surface morphology of the decomposed films is significantly different to those annealed in air. The metallic nature of the thermally decomposed films was confirmed by bonding configuration recognition, electronic property probing and microstructure analysis.     

Characteristic negative ion fragmentations of deprotonated peptides containing post-translational modifications: mono-phosphorylated Ser, Thr and Tyr. A joint experimental and theoretical study

Peptides and proteins may contain post-translationally modified phosphorylated amino acid residues, in particular phosphorylated serine (pSer), threonine (pThr) and tyrosine (pTyr). Following earlier work by Lehmann et al., the [M-H]- anions of peptides containing pSer and pThr functionality show loss of the elements of H3PO4. This process, illustrated for Ser (and using a model system), is CH3CONH-C(CH2OPO3H2)CONHCH(3) --> [CH3CONHC(==CH2)CONHCH3 (-OPO3H2)] (a) --> [CH3CONHC(==CH2)CONHCH3-H]- + H3PO4, a process endothermic by 83 kJ mol(-1) at the MP2/6-31++G(d,p)//HF/6-31++G(d,p) level of theory. In addition, intermediate (a) may decompose to yield CH3CONHC(==CH2)CONHCH3 + H2PO4 - in a process exothermic by 3 kJ mol(-1). The barrier to the transition state for these two processes is 49 kJ mol(-1). Characteristic cleavages of pSer and pThr are more energetically favourable than the negative ion backbone cleavages of peptides described previously. In contrast, loss of HPO3 from [M-H]- is characteristic of pTyr. The cleavage [NH2CH(CH2-C6H4-OPO3H-)CO2H] --> [NH2C(CH2-C6H4-O-)CO2H (HPO3)] (b) --> NH2CH(CH2-C6H4-O-)CO2H + HPO3 is endothermic by 318 kJ mol(-1) at the HF/6-31+G(d)//AM1 level of theory. In addition, intermediate (b) also yields NH2CH(CH2-C6H4-OH)CO2H + PO3 - (reaction endothermic by 137 kJ mol(-1)). The two negative ion cleavages of pTyr have a barrier to the transition state of 198 kJ mol(-1) (at the HF/6-31+G(d)//AM1 level of theory) comparable with those already reported for negative ion backbone cleavages.     

SEM and ECIS Investigation of Cells Cultured on Nanopillar Modified Interdigitated Impedance Electrodes for Analysis of Cell Growth and Cytotoxicity of Potential Anticancer Drugs

Cell‐based biosensors treat living cells as sensing elements and are able to detect the functional information of biologically active analytes. Monitoring cytotoxicity with high sensitivity, rapidity and at low cost is of great interest in the fields of clinical diagnostics, environmental monitoring, food safety and security. This research investigates the behaviour of different cell types on nanostructured architectures. The development of cell‐based assays using bioimpedance devices has the potential of screening anti‐cancer drugs; these have a potential impact for developing new techniques and tools for the analysis of cells in the bio‐pharma industry. Gold impedance electrodes have been successfully fabricated for impedance measurement on cells cultured on the electrode surface which was modified with gold nanopillars with a height of 60 nm and 150 nm diameter in a highly ordered layout thanks to the e‐beam lithography technique. This article investigates the effects on the sensitivity achieved with the ECIS (Electric Cell‐substrate Impedance Spectroscopy) measurements while monitoring the cytotoxicity of two different drugs (Antrodia Camphorata extract and Nicotine) on different cell lines (HeLa, A549 and BALBc 3T3) cultured on the nanostructured devices. The change of morphology of cells growing on the nanostructured electrodes was also investigated through SEM imaging.     

Thermodynamic Analysis of the Geldanamycin–Hsp90 Interaction in a Whole Cell Lysate Using a Mass Spectrometry-Based Proteomics Approach

Geldanamycin is a natural product with well-established and potent anti-cancer activities. Heat shock protein 90 (Hsp90) is the known target of geldanamycin, which directly binds to Hsp90’s N-terminal ATP binding domain and inhibits Hsp90’s ATPase activity. The affinity of geldanamycin for Hsp90 has been measured in multiple studies. However, there have been large discrepancies between the reported dissociation constants (i.e., K_d values), which have ranged from low nanomolar to micromolar. Here the stability of proteins from rates of oxidation (SPROX) technique was used in combination with an isobaric mass tagging strategy to measure the binding affinity of geldanamycin to unpurified Hsp90 in an MCF-7 cell lysate. The K_d values determined here were dependent on how long geldanamycin was equilibrated with the lysate prior to SPROX analysis. The K_d values determined using equilibration times of 0.5 and 24 h were 1 and 0.03 μM, respectively. These K_d values, which are similar to those previously reported in a geldanamycin–Hsp90 binding study that involved the use of a fluorescently labeled geldanamycin analogue, establish that the slow-tight binding behavior previously observed for the fluorescently labeled geldanamycin analogue is not an artifact of the fluorescent label, but rather an inherent property of the geldanamycin–Hsp90 binding interaction. The slow-tight binding property of this complex may be related to time-dependent conformational changes in Hsp90 and/or to time-dependent chemical changes in geldanamycin, both of which have been previously proposed to explain the slow-tight binding behavior of the geldanamycin–Hsp90 complex.

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Ab initio computational study of 1-methyl-4-silatranone and attempts at its conventional synthesis

1-Methyl-4-silatranone could exhibit the structural aspects of a typical silatrane including a short N–Si bond distance reflecting a dative bond. But given the significant amide resonance in a [3.3.3] bridgehead bicyclic lactam, the lone pair could be shared with the carbonyl group leading to a very long N–Si bond, essentially a “non-silatrane.” Ab initio calculations (MP2/6-311 + G*) predict that ground state conformations of this molecule are best regarded as lactams rather than silatranes, the most stable having a calculated N–Si bond length of 2.902 Å and an N–CO bond length of 1.387 Å. The calculated transition state for inversion of the amide ring retains very little amide resonance (N–CO, 1.440 Å). Some of this loss is compensated through tightening of the N–Si bond (2.422 Å), leading to a net energy of activation of ca 8 kcal/mol. Attempts to synthesize 1-methyl-4-silatranone using conventional pathways successful for 1-methylsilatrane [condensations employing N,N-bis(2-hydroxyethyl)glycolamide in place of tris(2-hydroxyethyl)amine] were unsuccessful. This is due to the net loss in resonance energy of the amide reactant relative to that in the [3.3.3] system, the essential absence of the N–Si dative bond, and the rigidity introduced by the planar amide linkage in the starting material. A more likely pathway to successful synthesis should be formation of the amide linkage in the final step.     

Survey of the diversity space coverage of reported combinatorial libraries

Courtesy of the annual collections reported by Roland E. Dolle in the Journal of Combinatorial Chemistry, all three-point diverse libraries reported in the literature since 1992 have been evaluated according to their similarity at the library level (the Diversity Space approach).1 This comparison enabled the identification of several particularly promising scaffold hopping opportunities and highlighted a number of optimal libraries (surrogates) expected to reveal binding information characteristic of an entire area of chemical space. As highlighted herein, future library design pursuits would benefit from a methodology such as the Diversity Space approach to ensure access to novel areas within the chemical landscape, thereby avoiding the expenditure of additional resources to cover a previously explored region.