Photodynamics of a PV Trimer in High‐Viscosity Solvents and in PMMA Films: A New Insight into Energy Transfer versus Conformational Relaxation in Conjugated Polymers

Non‐Stokes–Einstein relaxation : The rate constant of conformational relaxation of a phenylenevinylene trimer (see picture) in different solvents is proportional to η^?α, with α values decreasing from close to unity (low viscosity) to zero at sufficiently high solvent viscosity. This behaviour is attributed to the flexible methylbutyl side chains of the trimer, which partially screen the solvent friction.

     

Evaluation of the potential of Raman microspectroscopy for prediction of chemotherapeutic response to cisplatin in lung adenocarcinoma

The study of the interaction of anticancer drugs with mammalian cells in vitro is important to elucidate the mechanisms of action of the drug on its biological targets. In this context, Raman spectroscopy is a potential candidate for high throughput, non-invasive analysis. To explore this potential, the interaction of cis-diamminedichloroplatinum(II) (cisplatin) with a human lung adenocarcinoma cell line (A549) was investigated using Raman microspectroscopy. The results were correlated with parallel measurements from the MTT cytotoxicity assay, which yielded an IC(50) value of 1.2 ± 0.2 μM. To further confirm the spectral results, Raman spectra were also acquired from DNA extracted from A549 cells exposed to cisplatin and from unexposed controls. Partial least squares (PLS) multivariate regression and PLS Jackknifing were employed to highlight spectral regions which varied in a statistically significant manner with exposure to cisplatin and with the resultant changes in cellular physiology measured by the MTT assay. The results demonstrate the potential of the cellular Raman spectrum to non-invasively elucidate spectral changes that have their origin either in the biochemical interaction of external agents with the cell or its physiological response, allowing the prediction of the cellular response and the identification of the origin of the chemotherapeutic response at a molecular level in the cell.     

Characterization of an immobilized antibody-enzyme complex

Antiserum specific for propanediol dehydrogenase, an enzyme found inNeisseria gonorrhoeae cells, has been immobilized to glass. When mixed withN gonorrhoeae cell lysates, the immobilized antibody (IMA) binds the enzyme. Over 70% of the calculated adsorbed activity can be recovered from the immobilized antibody-enzyme (IMA-E) complex. When mixed with bacterial lysates prepared from different organisms having propanediol dehydrogenase-like activity, the IMA specifically adsorbed the enzyme from theN gonorrhoeae lysate. IMA-E complexes have been prepared and their kinetic, temperature and chemical stability, and antigenic properties investigated. These studies demonstrated the feasibility of using an immobilized antibody in the detection of the propanediol dehydrogenase enzyme.     

Metal Cyanide Ions Mx(CN)y]+,- in the gas phase: M = Fe,Co, Ni,Zn, Cd,Hg, Fe + Ag,Co + Ag

The generation of metal cyanide ions in the gas phase by laser ablation of M(CN)(2) (M = Co, Ni, Zn, Cd, Hg), Fe(III)[Fe(III)(CN)(6)] x xH(2)O, Ag(3)[M(CN)(6)] (M = Fe, Co), and Ag(2)[Fe(CN)(5)(NO)] has been investigated using Fourier transform ion cyclotron resonance mass spectrometry. Irradiation of Zn(CN)(2) and Cd(CN)(2) produced extensive series of anions, [Zn(n)(CN)(2n+1)](-) (1 < or = n < or = 27) and [Cd(n)(CN)(2n+1)](-) (n = 1, 2, 8-27, and possibly 29, 30). Cations Hg(CN)(+) and [Hg(2)(CN)(x)](+) (x = 1-3), and anions [Hg(CN)(x)](-) (x = 2, 3), are produced from Hg(CN)(2). Irradiation of Fe(III)[Fe(III)(CN)(6)] x xH(2)O gives the anions [Fe(CN)(2)](-), [Fe(CN)(3)](-), [Fe(2)(CN)(3)](-), [Fe(2)(CN)(4)](-), and [Fe(2)(CN)(5)](-). When Ag(3)[Fe(CN)(6)] is ablated, [AgFe(CN)(4)](-) and [Ag(2)Fe(CN)(5)](-) are observed together with homoleptic anions of Fe and Ag. The additional heterometallic complexes [AgFe(2)(CN)(6)](-), [AgFe(3)(CN)(8)](-), [Ag(2)Fe(2)(CN)(7)](-), and [Ag(3)Fe(CN)(6)](-) are observed on ablation of Ag(2)[Fe(CN)(5)(NO)]. Homoleptic anions [Co(n)(CN)(n+1)](-) (n = 1-3), [Co(n)(CN)(n+2)](-) (n = 1-3), [Co(2)(CN)(4)](-), and [Co(3)(CN)(5)](-) are formed when anhydrous Co(CN)(2) is the target. Ablation of Ag(3)[Co(CN)(6)] yields cations [Ag(n)(CN)(n-1)](+) (n = 1-4) and [Ag(n)Co(CN)(n)](+) (n = 1, 2) and anions [Ag(n)(CN)(n+1)](-) (n = 1-3), [Co(n)(CN)(n-1)](-) (n = 1, 2), [Ag(n)Co(CN)(n+2)](-) (n = 1, 2), and [Ag(n)Co(CN)(n+3)](-) (n = 0-2). The Ni(I) species [Ni(n)(CN)(n-1)](+) (n = 1-4) and [Ni(n)(CN)(n+1)](-) (n = 1-3) are produced when anhydrous Ni(CN)(2) is irradiated. In all cases, CN(-) and polyatomic carbon nitride ions C(x)N(y)(-) are formed concurrently. On the basis of density functional calculations, probable structures are proposed for most of the newly observed species. General structural features are low coordination numbers, regular trigonal coordination stereochemistry for d(10) metals but distorted trigonal stereochemistry for transition metals, the occurrence of M-CN-M and M(-CN-)(2)M bridges, addition of AgCN to terminal CN ligands, and the occurrence of high spin ground states for linear [M(n)(CN)(n+1)](-) complexes of Co and Ni.     

Templating and selection in the formation of macrocycles containing [[P(micro-NtBu)(2)](micro-NH)](n) frameworks: observation of halide ion coordination

Amination of [ClP(micro-NtBu)](2) (1) using NH(3) in THF gives the cyclophospha(III)zane dimer [H(2)NP(micro-NtBu)](2) (2), in good yield. (31)P NMR spectroscopic studies of the reaction of 1 with 2 in THF/Et(3)N show that almost quantitative formation of the cyclic tetramer [[P(micro-NtBu)](2)(micro-NH)](4) (3) occurs. The remarkable selectivity of this reaction can (in part) be attributed to pre-organisation of 1 and 2, which prefer cis arrangements in the solid state and solution. The macrocycle 3 can be isolated in yields of 58-67 % using various reaction scales. The isolation of the major by-product of the reaction (ca. 0.5-1 % of samples of 3), the pentameric, host-guest complex [[P(micro-NtBu)(2)](2)(micro-NH)](5)(HCl).2 THF] (4.2 THF), gives a strong indication of the mechanism involved. In situ (31)P NMR spectroscopic studies support a stepwise condensation mechanism in which Cl(-) ions play an important role in templating and selection of 3 and 4. Amplification of the pentameric arrangement occurs in the presence of excess LiX (X=Cl, Br, I). In addition, the cyclisation reaction is solvent- and anion-dependent. The X-ray structures of 2 and 4.2 THF are reported.     

Built to order: molecular tinkertoys from the [Re(6)(mu(3)-Se)(8)](2+) clusters

Ligand substitution of [Re(6)(mu(3)-Se)(8)(PEt(3))(5)(CH(3)CN)](SbF(6))(2) (1) with pyridyl-based ligands, 2,4,6-tri-4-pyridyl-1,3,5-triazine (L1) and 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (L2), produced respectively the star-shaped tricluster (T1) and tetracluster (T2) arrays, wherein three (T1) and four (T2) units of the [Re(6)(mu(3)-Se)(8)](2+) core-containing clusters are interconnected by the corresponding bridging ligands. These novel supramolecular assemblies were characterized by a combination of NMR ((1)H and (31)P) spectroscopy, ESI-MS, and microanalysis. The molecular and solid-state structures of T1 have also been established by single-crystal X-ray diffraction.     

Validation of TPEN as a Zinc Chelator in Fluorescence Probing of Calcium in Cells with the Indicator Fura-2

Fura-2 is widely used as a fluorescent probe to monitor dynamic changes in cytosolic free calcium in cells, where Ca²⁺ can enter through several types of voltage-operated or ligand-gated channels. However, Fura-2 is also sensitive to other metal ions, such as zinc, which may be involved in ionic channels and receptors. There is interest, in particular, in studying the synapses between mossy fibers and CA3 pyramidal cells which contain both calcium and high quantities of free or loosely bound zinc. We have found, through fluorescence probing, that endogenous zinc inhibits mossy fiber calcium transients. However, since these results might be explained by an effect of the zinc chelator N,N,N’,N’-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) on the spectral properties of Fura-2, we have carried out a validation of the method through fluorescence excitation spectra of the complex Fura-2/calcium, and show that TPEN does not affect these spectra. This supports the idea that the observed calcium enhancement is related to a zinc inhibition of presynaptic calcium mechanisms, and confirms the use of the chelator TPEN as a general procedure for the biophysical study of Ca(II) in the presence of Zn(II) using Fura-2.     

Specific and nonspecific collapse in protein folding funnels

Experiments with fast folding proteins are beginning to address the relationship between collapse and folding. We investigate how different scenarios for folding can arise depending on whether the folding and collapse transitions are concurrent or whether a nonspecific collapse precedes folding. Many earlier studies have focused on the limit in which collapse is fast compared to the folding time; in this work we focus on the opposite limit where, at the folding temperature, collapse and folding occur simultaneously. Real proteins exist in both of these limits. The folding mechanism varies substantially in these two regimes. In the regime of concurrent folding and collapse, nonspecific collapse now occurs at a temperature below the folding temperature (but slightly above the glass transition temperature).