« Lecture 9 Notes |
| Problem Set 2 - Due 10/17/2012 »
Please post this week's minute papers as "comments" to this post. Minute papers should be posted by 5 pm on Friday. Feel free to read your classmate's posts.
Posted by Christy Haynes on October 10, 2012 10:38 AM | Permalink
Minute Paper #6 (10/11/2012) – Sarah Anciaux
Title: Improving the Comprehensiveness and Sensitivity of Sheathless Capillary Electrophoresis–Tandem Mass Spectrometry for Proteomic Analysis
Author: Yates et al.
Journal: Analytical Chemistry
In this paper the authors attempt to develop a new interface for proteomic analysis by capillary electrophoresis (CE) coupled to electrospray ionization (ESI). These authors propose solid-phase micro-extraction (SPME) and transient isotachophoresis (tITP) coupled to a porous CE tip for electrospray generation.
The authors developed this method by employing an SPME column to trap and concentrate samples and then allow for sequential elution. This step allows for the comprehensiveness to be improved prior to the tITP separation, electrospray and mass analysis. By combining these methods into one in-line platform, the injections are no longer mass-limited due to the SPME trapping column and results in better sensitivity and comprehensiveness. This new method (SPME-tITP-CE-MS/MS) was compared to plain CE-MS/MS and nano liquid chromatography (nLC)-MS/MS. SPME-tITP-CE-MS/MS was found to be comparable to the other platforms when analyzing larger sample quantities of 100 ng but three times more effective at mass-limited injections of 5 ng. This would allow for much easier proteomic analysis of low concentration samples.
The authors claim to have successfully developed and implemented a new platform for coupling a CE technique to MS analysis but there are a few areas that could be addressed further. For instance, with the addition of a trapping column it’s possible that the percent recovery decreases as some analytes might be very hard to elute. Some may not even release from the column during the separation period. I think this could be explored and optimized further by monitoring the re-equilibration of the column and perhaps even extracting the column and analyzing the stationary phase for remnant sample. If this part of the platform could be achieved by a different means it might be possible to increase the efficiency of the platform, and total protein identifications, even more. Another area of concern stems from the porous CE tip coupled to the ESI source. In the introduction the authors state that these porous tips are very difficult to make and only labs that are experienced in HF etching are capable of making them. Meanwhile, in the methods and materials section, they state that the capillary with the porous tips are simply purchased. This was just a little confusing and it would be nice to know how the porous tips were actually made or if they can be purchased. Finally, the authors explore many variables and do a very good job of evaluating each of them, but they neglected to test different capillary coatings. The authors also didn’t state why they used the coating they did. I think it would be interesting to investigate different coatings and the effect of electroosmotic flow on the efficiency of the separation.
Sarah Anciaux |
October 11, 2012 9:37 AM
Title: Visible Light and Sunlight Photoinduced ATRP with ppm of Cu Catalyst
Authors: Konkolewicz, D., et al.
Journal: ACS Macro Letters
Konkolewicz et al. studied photochemically induced atom transfer radical polymerization (PI-ATRP) in the presence of copper catalysts. Unlike older ATRP methods which need high concentrations of catalyst, PI-ATRP is interesting because it only requires low concentrations (ppm) of the copper catalyst, which is desirable for the development of solar fuels and novel photo-driven organic reactions. The authors studied the PI-ATRP of ethyl acrylate (EA), methyl acrylate (MA), and methyl methacrylate (MMA) in the presence of a catalyst of CuBr2 complexed with an amine ligand. Ethyl alpha-bromoisobutyrate and ethyl alpha-bromophenylacetate were used as the initiators for the acrylates and methacrylates, respectively. In this publication, the authors investigated the kinetics of PI-ATRP and the UV absorbance of the various components of the reaction.
The authors ran the polymerizations of each monomer under sunlight and three light-emitting diodes (LED) that emitted violet (392 nm), blue (450 nm), or red light (631 nm). For each monomer the polymerization was fastest under sunlight, while the kinetics slowed as the wavelength of light increased. In fact, none of the monomers polymerized under red light. Based on this result, the authors hypothesized that the Cu(II) complex strongly absorbs UV wavelength and weakly absorbs the violet and blue lights. Additionally, they suspected that the failure of the red light to induce polymerization is because an efficient ligand to metal charge transfer in the excited state is not achieved at that wavelength. They also claimed that this sort of behavior of copper complexes is well discussed in the literature.
To test their hypothesis, the authors examined the UV/vis/NIR spectra of blank experiments of monomer only, monomer and initiator only, and monomer and catalyst only. The blank solutions were then exposed to sunlight. In the case of the monomer only and monomer and initiator only, there was not a significant amount of UV absorbance and only a small amount of polymerization occurred under sunlight. For the monomer and catalyst only case, a large amount of UV absorbance was observed and the polymerization proceeded to completion, corroborating the authors’ hypothesis.
Though this publication does generate a lot of excitement, there are still several questions that remain unanswered. The authors claim the polymerization proceeds fastest when exposed to UV light, but they did not run any polymerization under only UV light. This can simply be performed by either using a UV source or running regular light through a band pass filter that only allows light in the UV range to be transmitted. Additionally, the authors only used acrylate or methacrylate monomers. It would be interesting to run this polymerization with a wider variety of monomers, such as styrene or acrylamides. Finally, the authors never discuss if the molecular weights of the polymers synthesized by PI-ATRP to those synthesized by other forms of ATRP. This information is critical for applications in which high molecular weight polymers are necessary.
Ralm Ricarte |
October 11, 2012 5:04 PM
Minute Paper #5 (10/12/12) – Matt Irwin
Title: Preparation and Morphology of Hybrids Composed of a Block Copolymer and Semiconductor Nanoparticles via Hydrogen Bonding
Authors: A. Noro et al.
The development of well-ordered organic-inorganic nanocomposites is important for the advancement of next-generation electronic and photonic devices. In this paper, the authors describe a unique method for incorporating hydroxyl-capped cadmium selenide (h-CdSe) nanoparticles into the poly(4-vinylpyridine) (P4VP) phase of a poly(styrene-¬b-4-vinylpyridine) (PS-P4VP) block copolymer melt via hydrogen bonding. Techniques used include reversible addition-fragmentation chain transfer polymerization, size exclusion chromatography, Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and small-angle x-ray scattering (SAXS).
Initially, FT-IR was performed on both neat PS-P4VP and hybrids to elucidate the CdSe incorporation mechanism. The authors found that the absorbance for free pyridine at 993 cm-1 decreased and hydrogen-bonded pyridine at 1003 cm-1 increased with increased h-CdSe loading, indicating that the h-CdSe preferentially hydrogen bonds with the pyridine phase. DSC results indicated that the glass transition temperature (Tg) of P4VP was increased by the addition of h-CdSe while the Tg of the PS phase was unaffected, suggesting that h-CdSe does not interact with the PS block. Three block copolymers were then synthesized with the same length PS block but different length P4VP blocks to determine how the ratio of pyridine to CdSe hydroxyls affected the morphology. For long P4VP and roughly symmetric PS-P4VP, the hybrids exhibited a lamellar morphology up to 30 wt% h-CdSe loading. For intermediate P4VP length and 1:2 P4VP to PS weight fraction, the system transitioned from a cylindrical to lamellar morphology at 10 wt% h-CdSe. Finally, for short P4VP and 1:10 P4VP to PS by weight, the system transitioned from a spherical morphology to macrophase separated and spherical coexistence. In cases where the blend did not phase separate, SAXS demonstrated that the domain spacing generally increased with increased h-CdSe loading, suggesting that the PS-b-P4VP/h-CdSe hybrid behaves like a block copolymer/homopolymer blend in which the homopolymer swells the block copolymer morphology. This swelling is likely the reason for the observed phase transition from cylindrical to lamellar for medium length P4VP chains. On the other hand, for short P4VP chains, the authors suggest that the reason for the macrophase separated regions of h-CdSe is an insufficient number of available pyridines which could hydrogen bond with and solvate the CdSe.
The authors do a great job of analyzing a system that parallels homopolymer/block copolymer blends, but more work still could be done. First, the authors note that the h-CdSe behaves much like a homopolymer that swells the morphology. The authors should therefore compare their results to blends made with P4VP homopolymer of volume roughly equal to that of h-CdSe to see if the same phase transitions occur. If similar phase transitions occur, the authors could then perform a study in which they form blends of PS/h-CdSe/PS-b-P4VP to deduce a blend composition which yields a bicontinuous microemulsion morphology in which PS and h-CdSe/P4VP phases are cocontniuous. Because no alignment of the sample morphology would be necessary, such a morphology would easily permit testing of electronic and photonic properties.
Matt Irwin |
October 11, 2012 5:06 PM
Title: Chemical Characterization of Latent Fingerprints by Matrix-Assisted Laser Desorption Ionization, Time-of-Flight Secondary Ion Mass Spectrometry, Mega Electron Volt Secondary Mass Spectrometry, Gas Chromatography/Mass Spectrometry, X‑ray Photoelectron Spectroscopy, and Attenuated Total Reﬂection Fourier Transform
Infrared Spectroscopic Imaging: An Intercomparison
By: Bleay et.al.
Journal: Analytical Chemistry
In this paper, the authors compare different analytical techniques for analysis of fingerprint residues. They tested fingerprints for compounds that could identify who the fingerprints came from using techniques such as, XPS, ATR-FT-IR (for imaging of compounds on the fingerprint), GC-MS, MeV-SIMS, MALDI MS (for imaging), and ToF SIMS. It is important to keep in mind, as the authors note, that for a technique to be viable in forensics it must be universally sensitive to many compounds as well as able to detect reproducible differences between samples.
The authors found unsurprisingly that each technique had different strengths in sensitivity. MALDI was sensitive to fatty acids and peptides that did not appear in the other techniques. GC-MS was sensitive to many analytes, but required eight fingerprint samples to get a measurable reading. This is not useful for forensic applications. MeV-SIMS was sensitive to inorganics, which is also true of XPS. The authors do note that since MeV-SIMS is a newer technique, mass resolution is poor.
While these techniques did show promise for forensic science, they are expensive instruments. It would be uneconomical to have all of these instruments in a forensics lab for use. It is interesting to see that fingerprints have unique endogenous compounds to individuals based on where they have been in contact with things and how old the fingerprint is. This could be a feasible way to “recreate” fingerprints with imaging techniques. I would start a study of re-imaging partial fingerprints based on an endogenous compound such as some fatty acid. I would try it with MALDI imaging to see if it would work. The authors showed that it could deduce fingerprint ridge detail based on the MALDI imaging, so I think it should work. I would also work on a method for using MALDI or GC/MS for fingerprint analysis as they are cheaper than the others, and do not require as much special instrumentation. Using the information provided on what compounds are present in fingerprints, I would work on creating a better fingerprint development reagent that would enhance the detail of the fingerprint and make it easier to spot when analyzing a crime scene.
Alex Johnson |
October 11, 2012 7:38 PM
Minute Paper #6, Marzieh Ramezani
Subject: Enabling Chemical Synthesis with Visible Light
By: Corey Stephenson, Boston University (Departmental Seminar)
One of the most important factors in organic reactions is using the right catalyst which can activate the reaction and lead you to a desirable chemoselective product. Many years ago, visible light have been used as an initiator for many organic synthesis areas like natural product total synthesis, catalytic bond functionalization, and catalytic free radical chemistry. However, the application of visible light has been limited due to the lack of absorbance by many organic compounds. In this seminar Stephenson provides a historical overview of visible light photoredox catalysis in organic synthesis and highlighted the application of visible light (blue LED) in synthesizing Ru(II)polypyridine complexes.
Despite of iridium complexes that usually are being investigated by UV spectroscopy, ruthenium complexes are being examined by visible light because of having nice overlap of absorption and emission spectra in the blue region. Irradiation of Ru(bpy)3Cl2 with visible light at λ = 448 nm populates the triple excited state Ru(bpy)32+* via metal to ligand charge transfer(MLCT). This excited state can go to an oxidation/reduction cycle and Ru(bpy)32+* can be used as an electron oxidant or reductant.
Stephenson’s goal was to convert the benzylic alcohol to the corresponding alkyl/aryl halide in DMF , then reduce the inactivated halides using photoredox oxidation/reduction cycle in CH3CN in both small and large scales. He noticed that it usually takes ~12 hours to synthesize the desired product in small scale like 3mmols, and near 72 hours for synthesizing 20mmols without using the catalyst. In accordance with their observations, by exploring the percentage of blue light absorbed by the Ru(bpy)32+* as a function of path length , he realized that the reaction time depends on the intensity of LED light. Thus, for increasing the yield of the reaction and decreasing the time they used direct light coupled with two silver mirrors which reflect the light and help it to go back and forth in the reaction vessel. Consequently, by incorporating mirrors, the reaction was accelerated and took just four minutes to be completed with 95% yield and very high enantiomeric excess.
Above all, the interesting part of his research was forming free radicals from activated halogen bonds by employing optical methods, using visible light (blue LED). Employing this simple optical method, makes photoredox catalysis attractive and ‘green’ substitute for chemical synthesis compared to previous methods using Bu3SnH-based which was toxic.
Marzieh Ramezani |
October 11, 2012 11:05 PM
Minute Paper 6
Intracavity dna melting analysis with optofluidic lasers
Authors: Lee, W. and Fan, X.
Journal: Analytical Chemistry
In the 90s with the help of supercomputers, sequencing the genome became faster and more efficient. The next step was to look at what each part coded for and the genetic modifications caused by those differences in coding. Currently, the method to distinguish between two DNA strands that have one mismatched base is high resolution melting where they look at when the tagged DNA stops fluorescing to determine where the melting point is. Due to the fact that one base change only changes the melting temp slightly, the fluorescence levels only vary by a small percent. In order to optimize the difference in the signals, the authors built an optofluidic laser cavity in which they could put the DNA and saturation dyes in. They then use an optofluidic laser to detect the stimulated emission signal whose laser gain varies drastically as the DNA denatures.
In the cavity of the device they put several of the cloned DNA strands and slowly changed the temperature to see how the signal changed at each temperature point. This procedure was repeated for the one base modified DNA strand, in order to compare the signals. The results showed that they could clearly distinguish the data sets from each other in both their 40 and 100 long base DNA strands.
Since they were able to distinguish the two strands more clearly, they accomplished their goal of amplifying the signal found in high resolution melting. However, it would have been interesting to see what they actually changed their one base pair with, and where they changed the base pair. This is important for two reasons. The first is that if they changed a G with a C, the melting point would still have been the same or a lot closer to the template DNA since they are base pairs and they increase the melting point by ~4cegrees Celsius instead of ~2degrees Celsius which A and T do. Since modifications to the DNA do not always go to one of the other base pairs, the temperature difference might not be there. The second reason is the amount the temperature changes depend on where the base is put. On the outer edges, the temp changes are less than in the middle.
If they did the smallest modification in temperature possible with the one base pair change, then this method would work well at distinguishing two separate strands. However if there is more than one base pair change, then it might be better to go back to old methods such as using molecular beacons because a couple of different modifications might end up reversing the effects of the other modifications and leave the melting point the same. I think the next step for this project is to combine their device with a PCR microfluidic device in order to streamline the process and do both steps in one device.
Sarah Gruba |
October 12, 2012 6:09 AM
Title: Three-color fluorescence cross-correlation spectroscopy for analyzing complex nanoparticle mixtures
Author: Blades et. al.
In this paper, the authors use 3-color fluorescence cross-correlation spectroscopy (3C-FCCS) to distinguish between free quantum dots from beads that have been 'barcoded' with quantum dots. They propose that the validity of this technique will be useful for monitoring or tracking the assembly of macromolecules and nanomaterials.
In multi-color FCCS, complex assembly processes can be tracked in real time by measuring the fluorescence intensity fluctuations of fluorescently-tagged molecules passing through a small 'interrogation' volume. In the past, the authors have tracked DNA assembly using three differently colored quantum dots (QDs) as the fluorescent 'nanobarcode' tags. In this case, there were very few free QDs in the background, leading the authors to test whether their 3C-FCCS technique could reliably measure the concentration of QD-tagged nanobarcode components in a solution where free components are much higher in concentration.
The authors tested the ability of 3C-FCCS to detect species labelled with three QDs in a background of single color species. The amplitude of the 3C-FCCS decay of the three-color particles decreased with increasing single-color free QD concentration, as expected. Even at the highest concentration of free QDs tested, the three-color nanobarcode particle decay was easily measured.
As a final test, the authors added free QDs of all three colors to the three-color particle solution. Even in a solution with an 800:1 ratio of free dots to nanobarcode particles, the authors were able to measure the three-color nanobarcode particle decay with an excellent signal to noise ratio.
The 3C-FCCS data can be collected over a short time period, suggesting that this technique can be used to measure the kinetics of association and dissociation even in a background with a high concentration of free particles.
The authors note that QDs used are particularly bright but suggest that the use of organic fluorophores instead of QDs would only decrease the sensitivity by one order of magnitude. Because the QD 3C-FCCS method was able to study three-color particles at concentrations of 10 pM, this loss of sensitivity is not likely to be significant.
The authors conclude that 3C-FCCS can be used to simultaneously determine the concentration of all species in complex nanoparticle solution, including singly and triply labelled species. They also show that they can determine the size of the triply-labelled species. Finally, the authors state that their method can now measure the kinetics of complex assembly and disassembly of higher-order nanoparticles and the repair mechanism of DNA, in real time.
Alex Schnepper |
October 12, 2012 11:23 AM
Title: Aspartic Acid-Promoted Highly Selective and Sensitive Colorimetric Sensing of Cysteine in Rat Brain
Author: Qin Qian, et al.
Journal: Analytical Chemistry
In this paper, the authors presented a selective and sensitive method to detect Cysteine in the rat brain by using gold nanoparticles (Au-NPs). After cysteine was added into the aspartic acid containing Au-NPs solution, it bound to the Au-NPs surface by Au-S bond, which caused Au-NPs aggregation through the ion pair interaction between cysteine and aspartic acid. As a result, a significant color change was observed and UV-vis spectroscopy was utilized to quantitatively determine the aggregation of Au-NPs.
For the detection, Au-NPs was synthesized and characterized by TEM and UV-vis spectroscopy. Cysteine solutions of different concentration were then introduced to the mixed solution of aspartic acid and Au-NPs and incubated for 10 min at 37 ℃. Signals were recorded by UV-vis spectroscopy, which indicated a detection limit of 100 nM, with a linear correlation between absorbance and cysteine concentration ranging from 0.166 to 1.67 μM. As to the selectivity of this method, several control experiments were conducted, including Thiol-containing small molecules, such as cystine, homocysteine and glutathione, other natural amino acid with similar structures to cysteine and some important species existing in the brain system, like glucose, lactate and uric acid. However, none of them produced remarkable signal change. Therefore, all these results confirmed that this method was highly specific for cysteine detection. The detection was then extended to the rat brain system. Microdialysate collected from the rat striatum was tested and the cysteine in the rat brain microdialysate was determined to be approximately 9.6 μM, according to the calibration curve obtained from the above experiments.
Although this method shows high selectivity and sensitivity, it can still be improved. First, when explaining the mechanism, the authors claimed that cysteine could bind with Au-NPs through Au-S bond, but providing no experimental evidence. To verify that, TEM analysis could be conducted to visualize the Au-NPs-Cysteine complex. Zeta potential values can also be tested to determine the binding by comparing the difference between the value of Au-NPs and that of Au-NPs-Cysteine complex. As to the control experiment, it is rather confusing why homocysteine, which shares almost the same structure to cysteine, would not cause the aggregation of Au-NPs. According to the authors, the slightly longer carbon chain leads to an increase of structural flexibility and consequently the decrease of ion pair formation. The reason is not convincing enough, but I am not sure what can be done to validate it.
Furthermore, the size of the Au-NPs would affect the reaction surface of Au-NPs. Thus Au-NPs with different size, which are easily prepared by adjusting the citrate concentration added to the reaction mixture, can also be tested to compare their sensitivity and achieve a best detection condition. Finally, the concentration of cysteine in the microdialysate exceeds the linear range obtained from the titration experiment. It is possible that the correlation between the absorbance and cysteine concentration is no longer linear in such high concentration area. So it is necessary to redo the titration experiment with higher cysteine concentration.
Yi Zhang |
October 12, 2012 12:49 PM
Minute Paper #6 October 12, 2012
A Rapid Microfluidic Mixer for High Viscosity Fluids to Track Ultrafast Early Folding Kinetics of G-Quadruplex Under Molecular Crowding Conditions
By: Ying Li, Youzhi Xu, Xiaojun Feng and Bi-Feng Liu
The study of folding kinetics is an important field when attempting to understand the conformational shapes and changes of various bio-macromolecules. Since bio-macromolecules are typically found under crowding conditions during in-vivo studies, in-vitro studies seek to replicate those crowded conditions and thus attempt to analyze folding kinetics using these parameters. However, due to the high viscosity of solutions when in molecular crowding conditions, analyzing bio-macromolecule folding kinetics is a very complicated process.
Rapid mixing has traditionally been the approach to study fast reaction kinetics, and to some degree, overcome issues of high viscosity solutions. There is a point however, when the high viscosity of solution over-powers the rapid mixing, no longer allowing folding kinetics to be analyzed. In order to compensate for high viscosity solutions, the authors of this paper designed a unique T-type of microfluidic device that operated as a mixer. Seven ω-shaped baffles, or restricting devices to prevent the flow of liquid to an undesirable location, were constructed in a line to create this fast mixing of high viscosity solutions. The microfluidic mixer was prepared using poly(dimethylsiloxane), or PDMS, and fabricated using a negative photoresist known as SU8. The PDMS was then peeled off the molding wafer and permanently bound to a glass chip.
The human telomere G-quadruplex is formed from a glycine-rich portion of a specific DNA sequence known to play an important role in the human aging process and in cancer therapy. Under molecular crowding conditions, this species was kinetically monitored during the early phases of folding, and it was discovered that the G-quadruplex initially folds in an exponential process. A more compact structure was achieved when the crowding conditions were increased around this particular analyte. Basic experimental studies also showed that the newly fabricated micromixer could mix solutions of 33.6 times the viscosity of water at speeds around 579.4 μs. This development is approximately a 1000 times improvement on previously recorded studies.
The conclusion of the study was the ω micromixer was a simple and easy design that led to shortened mixing times of extremely high viscosity solutions. This new technology has applications in the fields of bio-macromolecule folding kinetics, chemical synthesis and polymer studies. Although the ease of fabrication was most likely the reason behind the decision to use PDMS, glass is known to be the better selection when designing a microfluidic device – although the cost and difficulty fabricating glass are often used as reasons to convert to PDMS. Since glass is sometimes more efficient of a substance on microfluidic devices, I am curious to see if the ω design would still work, and be manageable, in a glass structure.
Megan Weisenberger |
October 12, 2012 2:23 PM
Title: Oligonucleotide analysis by nanoparticle-assisted laser desorption/ionization mass spectrometry (Nano-PALDI)
Author: Shu Taira et al.
In this publication, Shu Taira et al. optimized the nano-PALDI MS method to analyze oligonucleotides. The author demonstrates that Iron oxide nanoparticles with diammonium hydrogen citrate serve as an effective ionization-assisting reagent in MS for chemical drugs, peptides, and oligonucleotides without the aid of a specific chemical matrix used in conventional MS methods. They also show that the number of metal-adducted ion signals depends on the length of the oligonucleotide.
Several metal oxide NPs (Cr-, Fe-, Mn-, Co-based) were prepared by mixing aqueous solutions and then dried and pulverized. XRD was used to confirm the particle structure/diameter. Random sequences of oligonucleotides were synthesized (6-mer to 12-mer assortment of DNA and RNA), along with 3 control molecules. 3-HPA and AHC were used as matrix sources.
The valency of the NPs from the core structure were estimated (Fe- and Cr-based =trivalent, Co- and Mn-based =bivalent), and infrared spectra showed that amino and hydroxyl groups existed on the surface of the NPs surrounded by SiO2.
MS results showed that the Fe- and Co-based NPs could ionize DNA but Cr- and Mn-based NPs could not. A mass spectra figure showed that four signals were detected by Co- and Fe-based NPs, while only three signals were detected by conventional MALDI. From the resulting spectra they justified signals of sodium or potassium adducts were not present because the NPs were inhibiting them compared to conventional MALDI.
Spectra pointed iron–oligonucleotide as being bivalent in contrast with NPs valency, and speculated that the iron valency was converted from Fe(III) to Fe(II) and Fe2+ was produced during the desorption process (accelerated by AHC).
Results showed that the number of iron ions increased with increasing phosphate group pairs. Thus, the oligonucleotide length could partially be estimated from the maximum number of metal ion-adducted signals. Results from the control experiment showed a sodium and a potassium adduct were detected without iron adducted signals.
The author states that the iron-oxide ionization-assisting phenomenon was only observed using bivalent metal core NPs, and not with any other valency metal core NPs. They should check if there is an influence on the ionization based upon the size of the particles because the surface-area to volume ratio will influence ionization energy. In these tests relatively short oligonucleotides were used, but It would also be interesting to setup some tests with longer oligonucleotides to see if there is an upper limit at which ionization is no longer efficient, and separation between spectra is difficult because of localized facile fragmentation. Also test for particle agglomeration in medium, and whether this affects localized ionization.
Forrest Johnson |
October 12, 2012 2:54 PM
Title: Hierarchically Assembled Theranostic Nanostructures for siRNA
Delivery and Imaging Applications
By: Shrestha et al.
Recent advances in nanostructure technology have the potential for multiple functionalities in medicine. Herein, shell cross-linked knedel-like nanostructures (SCKs) were assembled with two different modules for purposes of therapy and diagnostics (theranostics). The techniques featured in this work include nanoparticle synthesis and characterization, as well as gel electrophoresis, laser scanning confocal microscopy (LSCM) and radio instant thin-layer chromatography.
SCK synthesis, which included a host of block copolymers, ultimately templated cationic SCKs (cSCKs) to negatively charged cyanine-labeled siRNA (Cy3-siRNA) on anionic shell cross-linked rods (SCRs) and incorporation of 76Br radiolabeling agents into core sites. This novel cSCK and SCR integration procedure produced hierarchically assembled theranostic (HAT) nanostructures. siRNA binding efficiency to cSCKs was confirmed by agarose gel-electrophoresis at different amine-to-phosphodiester (N/P) ratios. cSCKs and siRNA binding at N/P 2 suggested electrostatic cross-linking interactions were not compromised, which is likely due to the high surface area of cSCKs. Although SCRs had the highest 76Br radiolabeling yield (94%), the final HAT cross-linked structures had reasonable radiolabeling yields (72%). This suggested HAT structures could effectively serve as positron emission tomography (PET) agents. Uptake and siRNA transfection studies via LSCM on human ovarian adenocarcinoma cells revealed HAT structures induced higher cell death rates than cSCKs alone. This may be explained by lengthier, multivalent binding of HAT structures to cell surfaces, which may then provide more opportunity for successful siRNA transfection.
Although this work provided useful insight into developing novel theranostic devices, much work remains. No stability studies of cSCKs, SCR or HAT nanostructures were conducted. Work concerning particle, integrated siRNA and 76Br stability in biological media, such as simulated body fluid, would be vital for understanding the viability of this class of devices for in vivo use; I imagine biological media with dissolved salts could significantly deteriorate siRNA integration within HAT structures. Despite ample evidence for successful 76Br radiolabeling of HAT structures, no in vivo imaging work was included in the study. This thereby leaves the purported diagnostic quality of these new materials in question. TEM images of HAT structures revealed cylindrical devices of approximately 0.5 μm in length. This significantly limits HAT structures for in vivo theranostic use, as large particle sizes significantly reduce circulation time. Another striking feature of this work is the authors’ claim that HAT structure surfaces can easily be modified with poly(ethylene) glycol (PEG) for improved cellular viability, yet they make no effort to do so. PEG modification of HAT structures would likely improve the viability for its in vivo use.
Although the materials presented in this paper are novel, I struggle to see how these HAT structures improve upon current theranostic devices. Mesoporous silica nanoparticles (MSNs) have proven to be stable in biological media, promising for in vivo work, acceptable for siRNA delivery and suitable for 11C radiolabeling. Furthermore, MSNs are more commercially viable theranostic devices than HAT structures, as they can be easily and cheaply synthesized.
Sam Egger |
October 12, 2012 4:21 PM
Title: Application of Operando XAS, XRD, and Raman Spectroscopy for Phase Speciation in Water Gas Shift Reaction Catalysts
By: E. Stavitski and A. I. Frenkel et al.
Journal: ACS catalysis
In this paper, the group studied the phase change of catalysts for water gas shift(WGS) reaction using operando X-ray absorption fine structure(XAS), X-ray diffraction(XRD), and Raman spectroscopy. They said that WGS reaction is important for the hydrogen production, a prospective for renewable energy. In addition, they said only operando spectroscopies can reveal the structure changes which occur during reaction. Also, if you use a combination of several spectroscopies, you can investigate several properties at once. Thus, specifically, they compared pure ɣ-Fe2O3 and 3% Cr2O3/Fe2O3 during pretreatment and WGS reaction. For this study, they used XAS, XRD, Raman, and mass spectroscopy.
They found that bulk Fe2O3 (⍺-Fe2O3) was formed after pretreatment. For pure ɣ-Fe2O3, they could not detect it using XRD but Raman spectroscopy. For mixed catalyst, 3% Cr2O3/Fe2O3, they could observe it using simple XRD. During reaction ɣ- Fe2O3 was reduced to Fe3O4 for oxidation of CO. They detected it using XAS. In addition, while reaction occurred, Cr2O3 particle stabilized the active Fe3O4 by embedding into Fe3O4 lattice. It was confirmed from Raman spectroscopy. The peak at 830cm-1, the peak for CrO42- and representing Cr2O3, disappeared after reaction. It means Cr2O3 ¬particles were incorporated into Fe2O3 structures. So, each spectroscopy techniques compensated each other. XAS were good at studying interatomic distances, XRD was good at revealing normal structures, and Raman was good at investigating low portion of catalysts, such as small part of bulk Fe2O3 and Cr2O3.
However, for Raman spectroscopy, they did not operate this technique in operando. If they could detect Raman at higher reaction temperature in real-time, they could exactly confirm the embedding of Cr2O3 to Fe3O4 lattice. The peak for Cr2O3 will become smaller as reaction proceeds. They did not use reaction rate data to study structure of catalyst. I think they can use reaction rate data to count active sites on the surface and how much Cr2O3 will be embedded to Fe2O3. They can change mass of catalyst or pressure of reactant and measure the number of active sites. They can see change in intensity of peaks in XRD or Raman. They can analyze quantitatively using reaction rate data. They might be able to find ideal ratio between Cr2O3 and Fe2O3.
Minje Kang |
October 12, 2012 4:57 PM
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June 21, 2013 4:01 AM
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