Optimization of silver nanoparticles for surface enhanced Raman spectroscopy of structurally diverse analytes using visible and near-infrared excitation

Several experimental parameters affecting surface enhanced Raman (SER) signals using 488, 785 and 1064 nm excitation for eight diverse analytes are reported. Citrate reduced silver colloids having average diameters ranging from 40 ± 10 to 100 ± 20 nm were synthesized. The nanoparticles were characterized by transmission electron microscopy, dynamic light scattering and absorbance spectrophotometry before and after inducing nanoparticle aggregation with 0.99% v/v 0.5 M magnesium chloride. The nanoparticle aggregates and SERS signal were stable between 30 and 90 minutes after inducing aggregation. For the analytes 4-mercaptopyridine, 4-methylthiobenzoic acid and the dipeptide phenylalanine-cysteine using all three excitation wavelengths, the highest surface area adjusted SER signal was obtained using 70 ± 20 nm nanoparticles, which generated 290 ± 40 nm aggregates with the addition of magnesium chloride. The decrease in the SER signal using non-optimum colloids was 12 to 42% using 488 nm excitation and larger decreases in signal, up to 92%, were observed using near infrared excitation wavelengths. In contrast, pyridine, benzoic acid, and phenylalanine required 220 ± 30 nm aggregates for the highest SER signal with 785 or 1064 nm excitation, but larger aggregates (290 ± 40 nm) were required with 488 nm excitation. The optimum experimental conditions measured with the small molecule analytes held for a 10 amino acid peptide and hemoglobin. Reproducible SERS measurements with 2 to 9% RSD have been obtained by considering nanoparticle size, aggregation conditions, excitation wavelength and the nature of the analyte-silver interaction.     

Polymorphisms in genes involved in innate immunity and susceptibility to benzene-induced hematotoxicity

Benzene, a recognized hematotoxicant and carcinogen, can damage the human immune system. We studied the association between single nucleotide polymorphisms (SNPs) in genes involved in innate immunity and benzene hematotoxicity in a cross-sectional study of workers exposed to benzene (250 workers and 140 controls). A total of 1,236 tag SNPs in 149 gene regions of six pathways were included in the analysis. Six gene regions were significant for their association with white blood cell (WBC) counts (MBP, VCAM1, ALOX5, MPO, RAC2, and CRP) based on gene-region (P<0.05) and SNP analyses (FDR<0.05). VCAM1 rs3176867, ALOX5 rs7099684, and MPO rs2071409 were the three most significant SNPs. They showed similar effects on WBC subtypes, especially granulocytes, lymphocytes, and monocytes. A 3-SNP block in ALOXE3 (rs7215658, rs9892383, and rs3027208) showed a global association (omnibus P = 0.0008) with WBCs even though the three SNPs were not significant individually. Our study suggests that polymorphisms in innate immunity genes may play a role in benzene-induced hematotoxicity; however, independent replication is necessary.     

Interactions of halichondrin B and eribulin with tubulin

Compounds that modulate microtubule dynamics include highly effective anticancer drugs, leading to continuing efforts to identify new agents and improve the activity of established ones. Here, we demonstrate that [(3)H]-labeled halichondrin B (HB), a complex, sponge-derived natural product, is bound to and dissociated from tubulin rapidly at one binding site per αβ-heterodimer, with an apparent K(d) of 0.31 μM. We found no HB-induced aggregation of tubulin by high-performance liquid chromatography, even following column equilibration with HB. Binding of [(3)H]HB was competitively inhibited by a newly approved clinical agent, the truncated HB analogue eribulin (apparent K(i), 0.80 μM) and noncompetitively by dolastatin 10 and vincristine (apparent K(i)'s, 0.35 and 5.4 μM, respectively). Our earlier studies demonstrated that HB inhibits nucleotide exchange on β-tubulin, and this, together with the results presented here, indicated the HB site is located on β-tubulin. Using molecular dynamics simulations, we determined complementary conformations of HB and β-tubulin that delineated in atomic detail binding interactions of HB with only β-tubulin, with no involvement of the α-subunit in the binding interaction. Moreover, the HB model served as a template for an eribulin binding model that furthered our understanding of the properties of eribulin as a drug. Overall, these results established a mechanistic basis for the antimitotic activity of the halichondrin class of compounds.     

Diagnostic di‐ and triphosphate cyclisation in the negative ion electrospray mass spectra of phosphoSer peptides

It has been shown previously that [M–H]^– anions of small peptides containing two phosphate residues undergo cyclisation of the phosphate groups, following collision‐induced dissociation (CID), to form a characteristic singly charged anion A (H₃P₂O₇^–, m/z 177). In the present study it is shown that the precursor anions derived from the diphosphopeptides of caerin 1.1 [GLLSVLGSVAKHVLPHVVPVIAEHL(NH₂)] and frenatin 3 [GLMSVLGHAVGNVLGGLFKPKS(OH)] also form the characteristic product anion A (m/z 177). Both of the precursor peptides show random structures in water, but partial helices in membrane‐mimicking solvents [e.g. in d₃‐trifluoroethanol/water (1:1)]. In both cases the diphosphopeptide precursor anions must have flexible conformations in order to allow approach of the phosphate groups with consequent formation of A: for example, the two pSer groups of 4,22‐diphosphofrenatin 3 are seventeen residues apart. Finally, CID tandem mass spectrometric (MS/MS) data from the [M–H]^– anion of the model triphosphoSer‐containing peptide GpSGLGpSGLGpSGL(OH) show the presence of both product anions A (m/z 177) and D (m/z 257, H₄P₃O₁₀^–). Ab initio calculations at the HF/6‐31+G(d)//AM1 level of theory suggest that cyclisation of the three phosphate groups occurs by a stepwise cascade mechanism in an energetically favourable reaction (ΔG = ?245 kJ mol^–1) with a maximum barrier of +123 kJ mol^–1. Copyright © 2011 John Wiley & Sons, Ltd.     

Systematic evaluation of acetone and acetonitrile for use in hydrophilic interaction liquid chromatography coupled with electrospray ionization mass spectrometry of basic small molecules

Sub‐2‐µm particle size hydrophilic interaction liquid chromatography [HILIC] combined with mass spectrometry has been increasing in popularity as a complementary technique to reversed‐phase LC for the analysis of polar analytes. The organic‐rich mobile phase associated with HILIC techniques provides increases in compound ionization, due to increased desolvation efficiency during electrospray ionisation mass spectrometric (ESI‐MS) analysis. Although recent publications illustrated selectivity and response comparisons between reversed‐phase LC/MS and HILIC LC/MS, there are limited discussions evaluating the optimisation of the mass spectrometry parameters regarding analytes and alternative mobile phases. The use of acetone as an alternative organic modifier in HILIC has been investigated with respect to signal‐to‐noise in ESI‐MS for a variety of polar analytes. Analyte reponses were measured based on a variety of cone and capillary voltages at low and high pH in both acetone and acetonitrile. In order to visualise compound behaviour in the ESI source, surface plots were constructed to assist in interpreting the observed results. The use of acetone in ESI is complicated at low m/z due to the formation of condensation products. Favourable responses were observed for certain analytes and we envisage offering an insight into the use of acetone as an alternative to acetonitrile under certain analytical conditions for particular compound classifications for small molecule analysis. We also highlight the importance of optimising source voltages in order to obtain the maximum signal stability and sensitivity, which are invariably, highly solvent composition dependent parameters. Copyright © 2011 John Wiley & Sons, Ltd.     

Characterization of polyether‐poly(methyl methacrylate)‐lithium perchlorate blend electrolytes

Solid polymer electrolyte (SPE) systems based on interpenetrating blends of poly(ethylene oxide‐co‐propylene oxide) and poly(methyl methacrylate) host matrices, with lithium perchlorate as guest salt, were prepared. These electrolytes were presented as free‐standing films, and their thermal and electrochemical properties were characterized by conductivity and electrochemical stability measurements. The properties of the interpenetrating blends of poly(ethylene oxide‐co‐propylene oxide) and poly(methyl methacrylate) host matrices as the electrolyte component of a solid‐state electrochromic device are reported and the results obtained suggest that this electrolyte provides an encouraging performance in this application. The most conducting electrolyte composition of this SPE system is the formulation designated as SPE2‐0PC (5.01 × 10^?4 S cm^?1 at about 57°C). The lowest decomposition temperature was registered with the SPE6‐15PC composition (233°C). The average transmittance in the visible region of the spectrum was above 41% for all the samples analyzed. After coloration the device assembled with 71 wt% PC presented an average transmittance of 15.71% and an optical density at 550 nm of 0.61. Copyright © 2010 John Wiley & Sons, Ltd.     

Tandem multi-step synthesis of C-carboxyazlactones promoted by N-heterocyclic carbenes

Cascade reaction sequences incorporating N-heterocyclic carbene-based organocatalysis have been developed that allow the direct preparation of a range of (+/-)-4-phenoxycarbonylazlactones in good isolated yields (66-84%) from the corresponding N-p-anisoyl amino acids.     

A Kirkwood-Buff Derived Force Field for Aqueous Alkali Halides

A classical nonpolarizable force field is presented for the simulation of aqueous alkali halide solutions (MX), where M = Li(+), Na(+), K(+), Rb(+), Cs(+) and X = F(-), Cl(-), Br(-), I(-), and their interactions with biomolecules. The models are specifically designed to reproduce the experimental Kirkwood-Buff integrals, and thereby the solution salt activities, as a function of salt concentration. Additionally, we demonstrate that these models reasonably reproduce other experimental properties including ion diffusion constants, dielectric decrements, and the excess heats of mixing. The parameters are developed by considering the properties of aqueous NaX and MCl solutions using a previously established model for NaCl. Transferability of the parameters to other salts is then established by the successful simulation of additional aqueous salt solutions, KI and CsBr, not originally included in the parameterization procedure.     

Design, synthesis, and biological evaluation of diminutive forms of (+)-spongistatin 1: lessons learned

The design, synthesis, and biological evaluation of two diminutive forms of (+)-spongistatin 1, in conjunction with the development of a potentially general design strategy to simplify highly flexible macrocyclic molecules while maintaining biological activity, have been achieved. Examination of the solution conformations of (+)-spongistatin 1 revealed a common conformational preference along the western perimeter comprising the ABEF rings. Exploiting the hypothesis that the small-molecule recognition/binding domains are likely to comprise the conformationally less mobile portions of a ligand led to the design of analogues, incorporating tethers (blue) in place of the CD and the ABCD components of the (+)-spongistatin 1 macrolide, such that the conformation of the retained (+)-spongistatin 1 skeleton would mimic the assigned solution conformations of the natural product. The observed nanomolar cytotoxicity and microtubule destabilizing activity of the ABEF analogue provide support for both the assigned solution conformation of (+)-spongistatin 1 and the validity of the design strategy.