Small-molecule ligands strongly affect the Förster resonance energy transfer between a quantum dot and a fluorescent protein

We report herein the study of F?rster resonance energy transfer (FRET) between a CdSe/ZnS core/shell quantum dot (QD) capped with three different small-molecule ligands, 3-mercaptopropionic acid (MPA), glutathione (GSH), and dihydrolipoic acid (DHLA), and a hexa-histidine (His(6))-tagged fluorescent protein, mCherry (FP). The F?rster radius (R(0)) and the corresponding donor-acceptor distances (r) for each of the QD-FP FRET systems were evaluated by using the F?rster dipole-dipole interaction formula. Interestingly, both the FRET efficiency (E) and r were found to be strongly dependent on the capping small-molecule ligands on the QD surface, where E ≈ 85% was obtained at a FP:QD copy number of 2:1 for the MPA capped QD, while that for the DHLA capped QD was <25% under the same conditions. A molecular model was proposed to explain the possible reasons behind these observations. The dissociation constants (K(d)s) and kinetics of the self-assembled QD-FP systems were also evaluated. Results show that the QD-FP self-assembly process is fast (completes in minutes at low nM concentrations), strong (with K(d) ≈ 1 nM) and positively cooperative (with the Hill coefficient n > 1), suggesting that the QD-His(6)-tagged biomolecule self-assembly is a facile, effective approach for making compact QD-bioconjugates which may have a wide range of sensing and biomedical applications.     

Effect of acidification on elemental and isotopic compositions of sediment organic matter and macro‐invertebrate muscle tissues in food web research

Stable isotope techniques in food web studies often focus on organic carbon in food sources which are subsequently assimilated in the tissue of consumer organisms through diet. The presence of non‐dietary carbonates in bulk samples can affect their δ¹³C values, altering how their results are interpreted. Acidification of samples is a common practice to eliminate any inorganic carbon present prior to analysis. We examined the effects of pre‐analysis acidification on two size fractions of sediment organic matter (SOM) from marine and freshwater wetlands and pure muscle tissue of a common freshwater invertebrate (Cherax destructor). The elemental content and isotopic ratios of carbon and nitrogen were compared between paired samples of acidified and control treatments. Our results showed that acidification does not affect the elemental or isotopic values of freshwater SOM. In the marine environment acidification depleted the δ¹³C and δ¹⁵N values of the fine fraction of saltmarsh and δ¹⁵N values of mangrove fine SOM. Whilst acidification did not change the elemental content of invertebrate muscle tissue, the δ¹³C and δ¹⁵N values were affected. We recommend to researchers considering using acidification techniques on material prepared for stable isotope analysis that a formal assessment of the effect of acidification on their particular sample type should be undertaken. Further detailed investigation to understand the impact of acidification on elemental and isotopic values of organic matter and muscular tissues is required. Copyright © 2010 John Wiley & Sons, Ltd.     

Interactions of CO molecules adsorbed on oxidised Cu(111) and Cu(110)

Reflection absorption infrared spectroscopy has been used in conjunction with LEED and surface potential measurements to study low temperature CO adsorption on the oxidised Cu surfaces Cu(111)O|$\text{3}\text{2}\text{?}\text{2}$|, Cu(110)O(2 × 1) and Cu(110)Oc(6 × 2). On all three surfaces adsorption at 80 K yields surface potential changes in excess of 0.6 V and does not lead to the formation of an ordered overlayer. At high coverages the adsorption enthalpy is lower than on the clean surfaces. Infrared spectra show the growth of a doublet band with components initially at 2100 and 2117 cm^?1 on the oxidised Cu(111) surface. Similar features seen on the oxidised Cu(110) surfaces are accompanied by a band at 2140 cm^?1: a very weak band at the same frequency on oxidised Cu(111) is attributed to defect sites. Studies of the temperature dependence of the spectrum from oxidised Cu(111) lead to the conclusion that two different binding sites are occupied. Spectra of ${}^{12}\text{CO}{}^{13}\text{CO}$ mixtures show that the molecules occupying these sites are in close proximity to each other, and that the spectrum is subject to large but opposing coverage-dependent frequency shifts.     

Speckle phenomena at 10 micron wavelength

Naturally occurring solid surfaces display structure over wide ranges of spatial wavelength, and this has important influences upon their radiation scattering characteristics. Fluctuations in scattered intensity are less severe than for smoothly-profiled surfaces, but the fine structure of the surface enhances scattering through large angles. Laboratory measurements of scattering of 10.6 micron CO₂ laser radiation by roughened surfaces are used to illustrate these effects and show the extent to which they may be modelled using physical optics.     

The photodimerisation of trans-cinnamic acid and its derivatives: a study by vibrational microspectroscopy

Infrared and Raman spectroscopies have been used to monitor the [2 + 2] photodimerisation reactions of alpha-trans-cinnamic acid and of a number of its derivatives. The principal changes observed in the spectra upon dimerisation are decay of a band around 1637 cm(-1), which is assigned to v(C=C) of the ethene bond of the monomer, and growth of bands just above 3000 cm(-1), which result from v(C-H) of saturated carbon atoms of the dimer. The use of microscope attachments has allowed us to follow the reactions of single crystals and we conclude that the reactions are topotactic in nature. We have carried out preliminary kinetic experiments in which spectra of one single crystal are recorded after sequential periods of photolysis. We find that the rates of dimerisation of differently substituted cinnamic acids are similar, with physical effects, such as the thickness of an individual crystal, outweighing any observed electronic effects (inductive or mesomeric).     

FLUORESCENCE ENERGY TRANSFER BETWEEN DIMETHYLDIAZAPEROPYRENIUM DICATION AND ETHIDIUM INTERCALATED IN POLY d(A-T)

Dimethyldiazaperopyrenium is one of the largest known DNA intercalators. Fluorescence energy transfer occurred between dimethyldiazaperopyrenium (donor) and ethidium (acceptor) when these dyes were bound to a double-stranded polynucleotide such as poly d(A-T). The addition of increasing amounts of ethidium bromide led to a marked shortening of the fluorescence lifetime of the donor, whereas the excited state of the acceptor was progressively populated via energy transfer from the donor. Critical Förster distance between these two chromophores was calculated to be 3.8 nm. The observed transfer efficiency was lower than that calculated on the basis of this critical distance and a statistical distribution of bound drugs. These results are discussed taking into account the conformational change induced by intercalation of dimethyldiazaperopyrenium in the double-stranded polynucleotide.     

The synthesis of heterocyclic derivatives of dibenzo[a,d]cycloheptene

The synthesis of 2-amino-7,8-dihydrobenzo[1,2]cyclohepta[3,4,5-de]quinazoline ( 10 ) and 6,7-dihydrobenzo[1,2]cyclohepta[3,4,5-cd]indazole ( 5 ) is described.     

Novel mixed ligand coordination compounds of some rare earth metal cations containing acesulfamato/N,N-diethylnicotinamide

The mixed ligand coordination compounds containing acesulfamato and N,N -diethylnicotinamide biomolecules of some rare earth metal cations (Eu³⁺, Tb³⁺, Ho³⁺, Er³⁺ and Yb³⁺) were synthesized, and their structural properties were investigated. Possible structural formulas have been proposed by determining the chemical composition of molecules (elemental analysis), binding properties (infrared spectroscopy, mass analysis, solid-state UV-vis spectroscopy), thermal degradation properties (TGA / DTA curves). Based on the data collected, it is suggested that rare earth metal cations with a 3+ oxidation state have sextet coordination. The geometries of the structures were thought to be distorted octahedral. The charge balance of the coordination sphere is balanced by a monoanionic acesulfamato located outside the coordination sphere. When the thermal behaviours of the complexes were examined, it was determined that the compounds with Eu³⁺, Tb³⁺, and Yb³⁺ metal cations contained one hydrate water outside the coordination sphere. Hydrate waters do not exist in the Ho³⁺ and Er³⁺ metal cation-centred complexes. At the end of the thermal decomposition analysis of all complex structures, it was determined that they leave the relevant metal oxides in the reaction vessels as final decomposition products.