Monitoring ALA-induced PpIX photodynamic therapy in the rat esophagus using fluorescence and reflectance spectroscopy

The presence of phased protoporphyrin IX (PpIX) bleach kinetics has been shown to correlate with esophageal response to 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT) in animal models. Here we confirm the existence of phased PpIX photobleaching by increasing the temporal resolution of the fluorescence measurements using the therapeutic illumination and long wavelength fluorescence detection. Furthermore fluorescence differential pathlength spectroscopy (FDPS) was incorporated to provide information on the effects of PpIX and tissue oxygenation distribution on the PpIX bleach kinetics during illumination. ALA at a dose of 200 mg kg(-1) was orally administered to 15 rats, five rats served as control animals. PDT was performed at an in situ measured fluence rate of 75 mW cm(-2) using a total fluence of 54 J cm(-2). Forty-eight hours after PDT the esophagus was excised and histologically examined for PDT-induced damage. Fluence rate and PpIX photobleaching at 705 nm were monitored during therapeutic illumination with the same isotropic probe. A new method, FDPS, was used for superficial measurement on saturation, blood volume, scattering characteristics and PpIX fluorescence. Results showed two-phased PpIX photobleaching that was not related to a (systematic) change in esophageal oxygenation but was associated with an increase in average blood volume. PpIX fluorescence photobleaching measured using FDPS, in which fluorescence signals are only acquired from the superficial layers of the esophagus, showed lower rates of photobleaching and no distinct phases. No clear correlation between two-phased photobleaching and histologic tissue response was found. This study demonstrates the feasibility of measuring fluence rate, PpIX fluorescence and FDPS during PDT in the esophagus. We conclude that the spatial distribution of PpIX significantly influences the kinetics of photobleaching and that there is a complex interrelationship between the distribution of PpIX and the supply of oxygen to the illuminated tissue volume.     

Heterobimetallic Complexes: Substitution Effects in the [Tetracarbonylrhodiumbis{μ‐(diphenylphosphino)}{μ‐(η:η2‐(4‐diphenylphosphino‐κP)‐2‐methyl‐oxobutyl)}molybdenum](Mo‐Rh) System

Syntheses of the array of heterobimetallic complexes [(OC)₃M(μ‐PPh₂)₂(μ‐O‐C(CHMe(CH₂)₂PPh₂)RhL], M = Cr, Mo, W, L = ^tBuNC, are described, extending the previous study of the counterpart array for L = CO. A single crystal X‐ray structure determination is reported for the M = Mo adduct, enabling comparison with its previously reported L = CO counterpart, for which an improved redetermination is also reported. In the present complex the ^tBuNC ligand is found to be much more weakly bound (Rh‐C 2.026(5) Å) than the carbonyl group it displaces (Rh‐C 1.945(2) Å) with concomitant minor impact on the remainder of the rhodium ambience.     

On the benefits of acquiring peptide fragment ions at high measured mass accuracy

The advantages and disadvantages of acquiring tandem mass spectra by collision-induced dissociation (CID) of peptides in linear ion trap Fourier-transform hybrid instruments are described. These instruments offer the possibility to transfer fragment ions from the linear ion trap to the FT-based analyzer for analysis with both high resolution and high mass accuracy. In addition, performing CID during the transfer of ions from the linear ion trap (LTQ) to the FT analyzer is also possible in instruments containing an additional collision cell (i.e., the "C-trap" in the LTQ-Orbitrap), resulting in tandem mass spectra over the full m/z range and not limited by the ejection q value of the LTQ. Our results show that these scan modes have lower duty cycles than tandem mass spectra acquired in the LTQ with nominal mass resolution, and typically result in fewer peptide identifications during data-dependent analysis of complex samples. However, the higher measured mass accuracy and resolution provides more specificity and hence provides a lower false positive ratio for the same number of true positives during database search of peptide tandem mass spectra. In addition, the search for modified and unexpected peptides is greatly facilitated with this data acquisition mode. It is therefore concluded that acquisition of tandem mass spectral data with high measured mass accuracy and resolution is a competitive alternative to "classical" data acquisition strategies, especially in situations of complex searches from large databases, searches for modified peptides, or for peptides resulting from unspecific cleavages.     

Sign changes in sums of the Liouville function

The Liouville function is the completely multiplicative function whose value is at each prime. We develop some algorithms for computing the sum , and use these methods to determine the smallest positive integer where . This answers a question originating in some work of Turán, who linked the behavior of to questions about the Riemann zeta function. We also study the problem of evaluating Pólya's sum , and we determine some new local extrema for this function, including some new positive values.

     

Anthracene-Porphyrin Nanoribbons

π-Conjugated nanoribbons attract interest because of their unusual electronic structures and charge-transport behavior. Here, we report the synthesis of a series of fully edge-fused porphyrin-anthracene oligomeric ribbons (dimer and trimer), together with a computational study of the corresponding infinite polymer. The porphyrin dimer and trimer were synthesized in high yield, via oxidative cyclodehydrogenation of singly linked precursors, using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and trifluoromethanesulfonic acid (TfOH). The crystal structure of the dimer shows that the central π-system is flat, with a slight S-shaped wave distortion at each porphyrin terminal. The extended π-conjugation causes a dramatic red-shift in the absorption spectra: the absorption maxima of the fused dimer and trimer appear at 1188 nm and 1642 nm, respectively (for the nickel complexes dissolved in toluene). The coordinated metal in the dimer was changed from Ni to Mg, using p-tolylmagnesium bromide, providing access to free-base and Zn complexes. These results open a versatile avenue to longer π-conjugated nanoribbons with integrated metalloporphyrin units.     

Selective enzymatic labeling to detect packing-induced denaturation of double-stranded DNA at interfaces

The adsorption of DNA on surfaces is a widespread procedure and is a common way for fabrication of biosensors, DNA chips, and nanoelectronic devices. Although the biologically relevant and prevailing in vivo structure of DNA is its double-stranded (dsDNA) conformation, the characterization of DNA on surfaces has mainly focused on single-stranded DNA (ssDNA). Studying the structure of dsDNA on surfaces is of invaluable importance to microarray performance since their effectiveness relies on the ability of two DNA molecules to hybridize and remain stable. In addition, many of the enzymatic transactions performed on DNA require dsDNA, rather than ssDNA, as a substrate. However, it is not established that adsorbed dsDNA remains in its structure and does not denature. Here, two methodologies have been developed for distinguishing between surface-adsorbed single- and double-stranded DNA. We demonstrate that, upon formation of a dense monolayer, the nonthiolated strand comprising the dsDNA is released and the monolayer consists of mostly ssDNA. The fraction of dsDNA within the ssDNA monolayer depends on the length of the oligomers. A likely mechanism leading to this rearrangement is discussed.     

Selective surface patterning for the coadsorption of self-assembled gold and semiconductor nanoparticles

The predetermined patterned adsorption of two types of nanoparticles on the same substrate may be of considerable importance in various applications, among others, to enhance the absorption of semiconductor nanoparticles by the plasmonic effect of metal NPs. We describe here a simple method for self-assembling 2D lateral patterns in which both gold and semiconductor nanoparticles are adsorbed, each in a predesigned area. Our method is based on a one-step lithographic process and the adsorption of two distinct self-assembled monolayers that can selectively bind only one type of nanoparticle.     

Upgrading of paper grade pulps to dissolving pulps by nitren extraction: yields,molecular and supramolecular structures of nitren extracted pulps

Different paper grade pulps were extracted with nitren in order to produce dissolving pulps and polymeric xylan. The yield and molecular structure of the extracted pulps were investigated by carbohydrate analysis and HPSEC combined with fluorescence labelling in order to additionally monitor the carbonyl and carboxyl group profiles of the pulps. The supramolecular structure of selected pulps were further studied by solid state ¹³C-CP/MAS-NMR and wide-angle X-ray scattering (WAXS). These supramolecular data of nitren extracted pulps were compared to samples extracted with NaOH and a conventional dissolving pulp in order to classify the properties of nitren extracted pulps. Nitren extraction results in selective xylan removal without noticeable degradation or oxidation of the cellulose fraction. The resulting dissolving pulps have high molar masses, a narrow molar mass distribution and the typical contents of carbonyl and carboxyl groups. The supramolecular structure of cellulose is less affected by nitren compared to strong NaOH, and the resultant dissolving pulps still have the cellulose I structure. All laboratories are members of the European polysaccharide network of excellence EPNOE.     

Probing kinase activities by electrochemistry, contact-angle measurements, and molecular-force interactions

Three different methods to investigate the activity of a protein kinase (casein kinase, CK2) are described. The phosphorylation of the sequence-specific peptide (1) by CK2 was monitored by electrochemical impedance spectroscopy (EIS). Phosphorylation of the peptide monolayer assembled on a Au electrode yields a negatively charged surface that electrostatically repels the negatively charged redox label [Fe(CN)6]3-/4-, thus increasing the interfacial electron-transfer resistance. The phosphorylation process by CK2 is further amplified by the association of the anti-phosphorylated peptide antibody to the monolayer. Binding of the antibody insulates the electrode surface, thus increasing the interfacial electron-transfer resistance in the presence of the redox label. This method enabled the quantitative analysis of the concentration of CK2 with a detection limit of ten units. The second method employed involved contact-angle measurements. Although the peptide 1-functionalized electrode revealed a contact angle of 67.5 degrees , phosphorylation of the peptide yielded a surface with enhanced hydrophilicity, 36.8 degrees. The biocatalyzed cleavage of the phosphate units with alkaline phosphatase regenerates the hydrophobic peptide monolayer, contact angle 55.3 degrees . The third method to characterize the CK2 system involved chemical force measurements between the phosphorylated peptide monolayer associated with the Au surface and a Au tip functionalized with the anti-phosphorylated peptide antibody. Although no significant rupture forces existed between the modified tip and the 1-functionalized surface (6+/-2 pN), significant rupture forces (multiples of 120+/-20 pN) were observed between the phosphorylated monolayer-modified surface and the antibody-functionalized tip. This rupture force is attributed to the dissociation of a simple binding event between the phosphorylated peptide and the fluorescent antibody (Fab) binding region.