VCH Publishers Research Articles

Development of Electrochemical Nanosensor for the Detection of Malaria Parasite in Clinical Samples

Malaria is an intricate, infectious, hematologic disease instigated by a protozoan parasite named Plasmodium falciparum (Priyamvada et al., 2014). The parasite lives part of its life in human and part in Anopheles mosquitoes. Malaria is the fifth most common cause of death in the world due to its infectious characteristics and the second in Africa, after HIV/AIDS (WHO, 2000). Development of sensitive, selective, accurate, rapid as well as cheap techniques for clinical diagnosis has been the major focus of researchers recently. Electrochemical sensors using nanoparticles have emerged as one of the suitable technologies for the detection of analytes of interest in clinical chemistry due to their high sensitivity and selectivity, rapid response time and low-cost (Wang, 1994). Beta-hematin have been extensively explored for the synthesis of antimalaria drugs and can also serve as a biomarker for the diagnosis of malaria. It is a microcrystalline cyclic dimer of ferriprotoporphyrin IX (Fe(III)PPIX) in which the propionate side chain of one protoporphyrin coordinates to the iron(III) center of the other. In this study, Electrochemical nanosensors were developed from the synthesised metal oxide (MO) nanoparticles by supporting it on a gold electrode (Au). The activity of the developed nanosensor towards the detection of malaria biomarker (β-hematin) was determined and the optimum conditions at which the maximum detection and quantification occurred was established. β-Hematin current response at the sensors was higher compared with the bare Au electrode and followed the order Au-CuO (C) > Au-CuO (M) > Au-Fe₂O₃ (M) > Au-Fe₂O₃ (C) > Au-Al₂O₃ (M) > Au-Al₂O₃ (C) > bare Au. The developed sensors were stable with a relatively low current drop (10.61 - 17.35 %) in the analyte. Au-CuO sensor has the best performance towards the biomarker and quantitatively detected P. berghei in infected mice’s serum samples at 3.60 – 4.8 mM and P. falciparum in human blood serum samples at 0.65 – 1.35 mM concentration. The developed sensor detected malaria biomarker successfully without interference from typhoid signal solving the problem of clinical diagnosis confusion of malaria and typhoid diseases. Keywords: β-hematin, Metal Oxide Nanoparticles, Sensor, Cyclic Voltammetry, Square Wave Voltammetry References Priyamvada, J., Babina, C., Sanjukta, P., and Pranab, G. (2014). Potential Biomarkers and Their Applications for Rapid and Reliable Detection of Malaria. Hindawi Publishing Corporation BioMed Research International, Volume 2014, Article ID 852645, 20 pages. WHO (2000). Malaria diagnosis new perspectives: report of a joint WHO/ USAID informal consultation. Geneva: World Health Organization 2000, 1–57.Wang, J. (1994). Analytical Electrochemistry, VCH Publishers Inc. New York

Polymer Electrolytes for Electrochromic Devices

Polymer electrolytes are currently the focus of much attention as potential electrolytes in electrochemical devices such as batteries, display devices and sensors [1,2]. Generically, solid polymer electrolytes (SPEs) are mixtures of salts with soft polar polymers. SPEs have many advantages including high energy density, no risk of leakage, no issues related to the presence of solvent, wide electrochemical stability windows, simplified processability and light weight. With the goal of developing a new family of environmentally friendly multifunctional biohybrid materials displaying high ionic conductivity we have produced in the present work, flexible films based on different polymers or hybrids incorporating different salts. The polymer electrolytes studied here have been characterized by means of Differential Scanning Calorimetry, Thermogravimetric Analysis, X-ray diffraction, Polarized Optical Microscopy, complex impedance spectroscopy and cyclic voltammetry. An evaluation of the performance of the sample with the highest conductivity as electrolyte in all solid-state ECDs was performed [3]. Acknowledgments:This work is funded by FCT- Fundação para a Ciência e a Tecnologia, project references Project Pest-C/QUI/UIO686/2013, PEst-OE/QUI/UI0616/2014, POPH/FSE for a grant (SFRH/BPD/87759/2012) (R.F.P.P.), POPH/FSE for a grant SRFH/BD/90366/2012 (R.L), grant POPH/FSE for a grant SFRH/BD/97232/2013 (R. A) and COST Action MP1202 ‘‘Rational design of hybrid organic–inorganic interfaces.” M. M. Silva acknowledges CNPq, for the mobility grant provided by this institution. REFERENCES [1] F.M. Gray, in Solid Polymer Electrolytes: Fundamentals and Technological Applications, VCH Publishers, Inc. (1991). [2] J.R. MacCallum, C.A. Vincent, Polymer Electrolyte Reviews, vol. 1, Elsevier, London, 1987. [3] S. C. Nunes, V. de Zea Bermudez, M. M. Silva, M. J. Smith, D. Ostrovskii, R. A. Sá Ferreira L.D. Carlos and J. Rocha, A. Gonçalves, E. Fortunato “Sol-gel derived potassium-based di-ureasils for smart windows”, Journal of Materials Chemistry 17 (2007) 4239-4248.

Synthesis of Phthalocyanines Using Triorganoindium Reagents

Phthalocyanines (Pcs) have attracted much attention due to their singular electronic properties, exceptional chemical and photochemical stabilities, and strong absorption of visible light [1]. Although there is a great variety of methods for the preparation of substituted phthalocyanines, introducing the substituents either on the phthalonitrile precursor or on the already formed phthalocyanine core, we have decided to explore the palladium-catalysed coupling reaction between haloaromatics and triorganoindium reagents [2]. The latter benefits from high reactivity, efficiency, versatility and chemoselectivity, together with the low toxicity associated with indium derivatives. We have indeed already experimented with this process, first exploring some basics about the scope [3] and new procedures for the synthesis of the triorganoindium reagents [4], and later using it in the preparation of hole transporting materials [5]. In this occasion we will discuss our more recent results in the preparation of substituted phthalocyanines using triorganoindium reagents. Taking advantage of the previously commented properties of Pcs, the synthesized compounds are excellent candidates for the preparation of photovoltaic devices, either Dye-Sensitized Solar Cells (DSSCs) or Bulk Heterojunction (BHJs) [6,7]. Acknowledgements. This work has been supported by the Spanish Ministerio de Economía y Competitividad, Generalitat Valenciana and the European FEDER funds (grants CTQ 2010-20349, CTQ2011-26455, CTQ2013-47922-R, PROMETEO 2012/010 and ISIC/2012/008). References Phthalocyanines: Properties and Applications, Leznoff, C. C.; Lever, A, B. P. Eds.; VCH Publishers, Weinheim, 1990-1996, Vols. 1-4.Pérez, I.; Pérez-Sestelo, J.; Sarandeses, L. A. Org. Lett. 1999, 1, 1267-1269.Font-Sanchis, E.; Céspedes-Guirao, F. J.; Sastre-Santos, A.; Fernández-Lázaro, F. J. Org. Chem. 2007, 72, 3589-3591.Font-Sanchis, E.; Sastre-Santos, A.; Fernández-Lázaro, F. Dalton Trans. 2009, 2470-2473. Lana-Villareal, T.; Font-Sanchis, E.; Sastre-Santos, A.; Fernández-Lázaro, F.; Gómez, R. ChemPhysChem 2011, 12, 1155-1164.Martín-Gomis, L.; Fernández-Lázaro, F.; Sastre-Santos, A. J. Mater. Chem. A 2014, 2, 15672-15682.Molina, D.; Guerrero, A.; García-Belmonte, G.; Fernández-Lázaro, F.; Sastre-Santos, A. Eur. J. Org. Chem. 2014, 4585-4591. Figure 1

Synthesis, Characterization and Electrochemical Investigation of Phthalocyanine Compounds Bearing Fluorine Functionality

Peripherally substituted symmetrical phthalocyanine derivatives have the potential to use in a wide range of high technology applications, such as in catalysis, in photodynamic therapy, in electrochromic display devices, and as a molecular electronics, or magnetic devices. Phthalocyanines possess an extended π-conjugated electron system which permits π stacking between planar macrocycles. Adding substituents to the periphery of the macrocycles increases their solubility since these substituents increase the distance between the stacked phthalocyanines and enable their solvation. The phthalocyanine complexes are also electrochemically precious complexes due to their excellent electrochemical behaviors. It is well known that the different functionalities changes the features of the MPc complexes, thus electrochemical properties of these complexes should be investigated for possible applications. [1-3]We present here the syntheses of tetra-substituted fluorine containing biphenyl-malonic ester groups bearing phthalocyanine derivatives with different central metal atoms and investigation of their electrochemical behaviors. All synthesized novel phthalocyanine compounds have been characterized by using their elemental analyses, FT-IR, UV-Vis, 1H NMR, 13C NMR and mass spectroscopic methods. The electrochemical activity of phthalocyanine derivatives were also evaluated from the current–voltage curves obtained by cyclic and differential pulse voltammetric methods. REFERENCES 1- A. Koca, Y. Arslanoğlu, E. J Electroanal Chem, 616 (2008), pp. 107–116 2- N.B. Mckeown, B. Dunn, J.W. Goodby, A.R. West (Eds.), Phthalocyanine materials: synthesis, structure and function, Cambridge University Press, Cambridge (1998) 3- H.S. Nalwa, J.S. Shirk, C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocyanines: properties and applications, VCH Publishers Inc, New York (1996), pp. 79–181.

Chitosan and Ionic Liquid Based Solid Polymer Electrolytes: The Anion Alkyl Chain Length Effect

It has been long recognized that polymer electrolytes (PEs) are potentially interesting as electrolytes for solid-state electrochemical devices 1-3 . It is also recognized that the most important properties of electrolyte solutions are non-volatility and high ionic conductivity. If the former property is easily fulfilled because polymers do not vaporize, only decompose at higher temperatures, the latter one is the major drawback that is delaying their application in commercial devices. To overcome this, the solvent-free polymer electrolytes (SPEs) community has been paying great attention to ionic liquids (ILs). Since ILs are composed only of ions, and show very high ionic conductivity, non-volatility and non-flammability 4 .Nowadays, safety, environmental issues also pose a significant concern. Because of that, some research groups have been turning their attention to natural polymers, due to their biodegradability, low toxicity and extraction from renewable sources, as fast growing plants and animals 5 . Among the extensive range of the existing natural polymers is chitosan. Chitosan is obtained by deacetylation of its parent polymer chitin, a polysaccharide widely distributed in nature (e.g. crustaceans, insects and certain fungi) 6 .This work describes the results of the characterization of polymer electrolytes using chitosan matrix doped with ionic liquids series 1-ethyl-3-methylimidazolium dialkylphosphate [C2mim][CnPO4], 1-ethyl-3-methylimidazolium alkylsulfonate [C2mim][CnSO3] and 1-ethyl-3-methylimidazolium alkylsulfate [C2mim][CnSO4]. This work studies the effect of increasing the alkyl chain length of the anion on the thermal, morphological and electrochemical properties of these SPEs.The samples have been characterized by thermal analysis (TGA and DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), polarized optical microscopy (POM), complex impedance spectroscopy and cyclic voltammetry. Acknowledgements This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/QUI/UI0686/2011 and PEST-OE/EQB/LA0004/2011, projects PTDC/CTM-NAN/121274/2010 and PTDC/QUI-QUI/117340/2010, grant SRFH/BD/90366/2012 (R.L.) and Investigador FCT grant (J.M.S.S.E.). References 1P.V. Wright, Br. Poly. J. 7 (1975) 319–327. 2 M. Armand, M. T. Duclot, J.M. Chabagno, In Proceedings of the Second International Meeting on Solid State Electrolytes; St. Andrews, Scotland, Sept 20_22, 1978; 1978; Extended 6.5. 3F.M. Gray, in Solid Polymer Electrolytes: Fundamentals and Technological Applications, VCH Publishers, Inc., New York, 1991. 4 H. Ohno, Electrochemical Aspects of Ionic Liquids, 2nd ed. John Wiley & Sons, Inc., New Jersey, 2011. 5R. Leones, F. Sentanin, L.C. Rodrigues, I.M. Marrucho, J.M.S.S. Esperança, A. Pawlicka, M.M. Silva, eXPRESS Polymer Letters 6 (12) (2012) 1007. 6 R.A.A. Muzzarelli, Natural chelating polymers: alginic acid, chitin and chitosan, Pergamon Press Oxford, New York, 1973.

Editorial: Twenty‐Five Years Later…

Editorial: Twenty‐Five Years Later…

The Small G Protein Rac1 Activates Phospholipase Cδ1 through Phospholipase Cβ2

Rac1, which is associated with cytoskeletal pathways, can activate phospholipase Cbeta2 (PLCbeta2) to increase intracellular Ca(2+) levels. This increased Ca(2+) can in turn activate the very robust PLCdelta1 to synergize Ca(2+) signals. We have previously found that PLCbeta2 will bind to and inhibit PLCdelta1 in solution by an unknown mechanism and that PLCbeta2.PLCdelta1 complexes can be disrupted by Gbetagamma subunits. However, because the major populations of PLCbeta2 and PLCdelta1 are cytosolic, their regulation by Gbetagamma subunits is not clear. Here, we have found that the pleckstrin homology (PH) domains of PLCbeta2 and PLCbeta3 are the regions that result in PLCdelta1 binding and inhibition. In cells, PLCbeta2.PLCdelta1 form complexes as seen by Förster resonance energy transfer and co-immunoprecipitation, and microinjection of PHbeta2 dissociates the complex. Using PHbeta2 as a tool to assess the contribution of PLCbeta inhibition of PLCdelta1 to Ca(2+) release, we found that, although PHbeta2 only results in a 25% inhibition of PLCdelta1 in solution, in cells the presence of PHbeta2 appears to eliminates Ca(2+) release suggesting a large threshold effect. We found that the small plasma membrane population of PLCbeta2.PLCdelta1 is disrupted by activation of heterotrimeric G proteins, and that the major cytosolic population of the complexes are disrupted by Rac1 activation. Thus, the activity of PLCdelta1 is controlled by the amount of bound PLCbeta2 that changes with displacement of the enzyme by heterotrimeric or small G proteins. Through PLCbeta2, PLCdelta1 activation is linked to surface receptors as well as signals that mediate cytoskeletal pathways.

Symmetry – An International and Interdisciplinary Scientific Open Access Journal

As the publisher of MDPI journals, I am pleased to launch Symmetry (ISSN 2073-8994), an international and interdisciplinary open access scientific journal. Twenty years ago, a journal entitled Symmetry – An Interdisciplinary and International Journal was launched by VCH Publishers, Inc. in New York, with Professor Istvan Hargittai as Editor-in-Chief. I submitted a paper which was processed by Professor Sven J. Cyvin from The University of Trondheim – The Norwegian Institute of Technology. The paper was accepted and scheduled for publication in the printed issue 4 of volume 1, 1990. I still keep a copy of the galley proofs. However, the publication of this journal was terminated after just the release of the first issue of volume 1, and this paper was finally published elsewhere [1]. [...]

Evidence for a Second, High Affinity Gβγ Binding Site on Gαi1(GDP) Subunits

It is well known that Galpha(i1)(GDP) binds strongly to Gbetagamma subunits to form the Galpha(i1)(GDP)-Gbetagamma heterotrimer, and that activation to Galpha(i1)(GTP) results in conformational changes that reduces its affinity for Gbetagamma subunits. Previous studies of G protein subunit interactions have used stoichiometric amounts of the proteins. Here, we have found that Galpha(i1)(GDP) can bind a second Gbetagamma subunit with an affinity only 10-fold weaker than the primary site and close to the affinity between activated Galpha(i1) and Gbetagamma subunits. Also, we find that phospholipase Cbeta2, an effector of Gbetagamma, does not compete with the second binding site implying that effectors can be bound to the Galpha(i1)(GDP)-(Gbetagamma)(2) complex. Biophysical measurements and molecular docking studies suggest that this second site is distant from the primary one. A synthetic peptide having a sequence identical to the putative second binding site on Galpha(i1) competes with binding of the second Gbetagamma subunit. Injection of this peptide into cultured cells expressing eYFP-Galpha(i1)(GDP) and eCFP-Gbetagamma reduces the overall association of the subunits suggesting this site is operative in cells. We propose that this second binding site serves to promote and stabilize G protein subunit interactions in the presence of competing cellular proteins.

Ferritin Contains Less Iron (59Fe) in Cells When the Protein Pores Are Unfolded by Mutation

Ferric minerals in ferritins are protected from cytoplasmic reductants and Fe2+ release by the protein nanocage until iron need is signaled. Deletion of ferritin genes is lethal; two critical ferritin functions are concentrating iron and oxidant protection (consuming cytoplasmic iron and oxygen in the mineral). In solution, opening/closing (gating) of eight ferritin protein pores controls reactions between external reductant and the ferritin mineral; pore gating is altered by mutation, low heat, and physiological urea (1 mm) and monitored by CD spectroscopy, protein crystallography, and Fe2+ release rates. To study the effects of a ferritin pore gating mutation in living cells, we cloned/expressed human ferritin H and H L138P, homologous to the frog open pore model that was unexpressable in human cells. Human ferritin H L138P behaved like the open pore ferritin model in vitro as follows: (i) normal protein cage assembly and mineralization, (ii) increased iron release (t1/2) decreased 17-fold), and (iii) decreased alpha-helix (8%). Overexpression (> 4-fold), in HeLa cells, showed for ferritin H L138P equal protein expression and total cell 59Fe but increased chelatable iron, 16%, p < 0.01 (59Fe in the deferoxamine-containing medium), and decreased 59Fe in ferritin, 28%, p < 0.01, compared with wild type. The coincidence of decreased 59Fe in open pore ferritin with increased chelatable 59Fe in cells expressing the ferritin open pore mutation suggests that ferritin pore gating influences to the amount of iron (59Fe) in ferritin in vivo.

Purification of a NifEN Protein Complex That Contains Bound Molybdenum and a FeMo-Co Precursor from an Azotobacter vinelandii ΔnifHDK Strain

The NifEN protein complex serves as a molecular scaffold where some of the steps for the assembly of the iron-molybdenum cofactor (FeMo-co) of nitrogenase take place. A His-tagged version of the NifEN complex has been previously purified and shown to carry two identical [4Fe-4S] clusters of unknown function and a [Fe-S]-containing FeMo-co precursor. We have improved the purification of the his-NifEN protein from a DeltanifHDK strain of Azotobacter vinelandii and have found that the amounts of iron and molybdenum within NifEN were significantly higher than those reported previously. In an in vitro FeMo-co synthesis system with purified components, the NifEN protein served as a source of both molybdenum and a [Fe-S]-containing FeMo-co precursor, showing significant FeMo-co synthesis activity in the absence of externally added molybdate. Thus, the NifEN scaffold protein, purified from DeltanifHDK background, contained the Nif-Bco-derived Fe-S cluster and molybdenum, although these FeMo-co constituents were present at different levels within the protein complex.

Organization and Assembly of Metal-Thiolate Clusters in Epithelium-specific Metallothionein-4

Mammalian metallothionein-4 (MT-4) was found to be specifically expressed in stratified squamous epithelia where it plays an essential but poorly defined role in regulating zinc or copper metabolism. Here we report on the organization, stability, and the pathway of metal-thiolate cluster assembly in MT-4 reconstituted with Cd(2+) and Co(2+) ions. Both the (113)Cd NMR studies of (113)Cd(7)MT-4 and the spectroscopic characterization of Co(7)MT-4 showed that, similar to the classical MT-1 and MT-2 proteins, metal ions are organized in two independent Cd(4)Cys(11) and Cd(3)Cys(9) clusters with each metal ion tetrahedrally coordinated by terminal and bridging cysteine ligands. Moreover, we have demonstrated that the cluster formation in Cd(7)MT-4 is cooperative and sequential, with the Cd(4)Cys(11) cluster being formed first, and that a distinct single-metal nucleation intermediate Cd(1)MT-4 is required in the cluster formation process. Conversely, the absorption and circular dichroism features of metal-thiolate clusters in Cd(7)MT-4 indicate that marked differences in the cluster geometry exist when compared with those in Cd(7)MT-1/2. The biological implication of our studies as to the role of MT-4 in zinc metabolism of stratified epithelia is discussed.

Converting a β-Glycosidase into a β-Transglycosidase by Directed Evolution

Directed evolution was applied to the beta-glycosidase of Thermus thermophilus in order to increase its ability to synthesize oligosaccharide by transglycosylation. Wild-type enzyme was able to transfer the glycosyl residue with a yield of 50% by self-condensation and of about 8% by transglycosylation on disaccharides without nitrophenyl at their reducing end. By using a simple screening procedure, we could produce mutant enzymes possessing a high transferase activity. In one step of random mutagenesis and in vitro recombination, the hydrolysis of substrates and of transglycosylation products was considerably reduced. For certain mutants, synthesis by self-condensation of nitrophenyl glycosides became nearly quantitative, whereas synthesis by transglycosylation on maltose and on cellobiose could reach 60 and 75%, respectively. Because the most efficient mutations, F401S and N282T, were located just in front of the subsite (-1), molecular modeling techniques were used to explain their effects on the synthesis reaction; we can suggest that repositioning of the glycone in the (-1) subsite together with a better fit of the acceptor in the (+1) subsite might favor the attack of a glycosyl acceptor in the mutant at the expense of water. Thus these new transglycosidases constitute an interesting alternative for the synthesis of oligosaccharides by using stable and accessible donor substrates.

Molecular, Biochemical, and Functional Characterization of a Nudix Hydrolase Protein That Stimulates the Activity of a Nicotinoprotein Alcohol Dehydrogenase

The cytoplasmic coenzyme NAD(+)-dependent alcohol (methanol) dehydrogenase (MDH) employed by Bacillus methanolicus during growth on C(1)-C(4) primary alcohols is a decameric protein with 1 Zn(2+)-ion and 1-2 Mg(2+)-ions plus a tightly bound NAD(H) cofactor per subunit (a nicotinoprotein). Mg(2+)-ions are essential for binding of NAD(H) cofactor in MDH protein expressed in Escherichia coli. The low coenzyme NAD(+)-dependent activity of MDH with C(1)-C(4) primary alcohols is strongly stimulated by a second B. methanolicus protein (ACT), provided that MDH contains NAD(H) cofactor and Mg(2+)-ions are present in the assay mixture. Characterization of the act gene revealed the presence of the highly conserved amino acid sequence motif typical of Nudix hydrolase proteins in the deduced ACT amino acid sequence. The act gene was successfully expressed in E. coli allowing purification and characterization of active ACT protein. MDH activation by ACT involved hydrolytic removal of the nicotinamide mononucleotide NMN(H) moiety of the NAD(H) cofactor of MDH, changing its Ping-Pong type of reaction mechanism into a ternary complex reaction mechanism. Increased cellular NADH/NAD(+) ratios may reduce the ACT-mediated activation of MDH, thus preventing accumulation of toxic aldehydes. This represents a novel mechanism for alcohol dehydrogenase activity regulation.

Molecular Cloning and Characterization of the Gene Coding for Azoreductase from Bacillus sp. OY1-2 Isolated from Soil

Azo dyes are regarded as pollutants because they are not readily reduced under aerobic conditions. Bacillus sp. OY1-2 transforms azo dyes into colorless compounds, and this reduction is mediated by a reductase activity for the azo group in the presence of NADPH. A 1.2-kbp EcoRI fragment containing the gene that encodes azoreductase was cloned by screening the genomic library of Bacillus sp. OY1-2 with digoxigenin-labeled probe designed from the N-terminal amino acid sequence of the purified enzyme. An open reading frame encoding the azoreductase, consisting of 178 amino acids, was predicted from the nucleotide sequence. In addition, because only a Bacillus subtillis hypothetical protein was discovered in the public databases (with an amino acid identity of 52.8%), the gene encoding the azoreductase cloned in this study was predicted to be a member of a novel family of reductases. Southern blot analysis revealed that the azoreductase gene exists as a single copy gene on a chromosome. Escherichia coli-expressing recombinant azoreductase gave a ten times greater reducing activity toward azo dyes than the original Bacillus sp. OY1-2. In addition, the expressed azoreductase purified from the recombinant E. coli lysate by Red-Sepharose affinity chromatography showed a similar activity and specificity as the native enzyme. This is the first report describing the sequencing and characterization of a gene encoding the azo dye-reducing enzyme, azoreductase, from aerobic bacteria and its expression in E. coli.

The High Mobility Group I/Y Protein Is Hypophosphorylated in Endoreduplicating Maize Endosperm Cells and Is Involved in Alleviating Histone H1-mediated Transcriptional Repression

The High Mobility Group I/Y Protein Is Hypophosphorylated in Endoreduplicating Maize Endosperm Cells and Is Involved in Alleviating Histone H1-mediated Transcriptional Repression

Medical physicists should position themselves as institutional resources in expanding areas such as healthcare informatics and information networking.

Medical PhysicsVolume 27, Issue 4 p. 631-633 Point/CounterpointFree Access Medical physicists should position themselves as institutional resources in expanding areas such as healthcare informatics and information networking Jon H. Trueblood, Jon H. Trueblood Medical College of Georgia, Department of Radiology, Augusta, Georgia 30912-3950Search for more papers by this authorKenneth R. Hogstrom, Kenneth R. Hogstrom The University of Texas M. D. Anderson Cancer Center, Department of Radiation Physics, Houston, Texas 77030Search for more papers by this authorWilliam R. Hendee, William R. Hendee ModeratorSearch for more papers by this author Jon H. Trueblood, Jon H. Trueblood Medical College of Georgia, Department of Radiology, Augusta, Georgia 30912-3950Search for more papers by this authorKenneth R. Hogstrom, Kenneth R. Hogstrom The University of Texas M. D. Anderson Cancer Center, Department of Radiation Physics, Houston, Texas 77030Search for more papers by this authorWilliam R. Hendee, William R. Hendee ModeratorSearch for more papers by this author First published: 05 April 2000 https://doi.org/10.1118/1.598946Citations: 4AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL REFERENCES 1E. Coiera, Guide to Medical Informatics, the Internet, and Telemedicine (Chapman & Hall, London, 1997). 2H. K. Huang, PACS, Picture Archiving and Communication Systems in Biomedical Imaging (VCH Publishers, Inc., New York, 1996). 3G. Starkschall, S. Bujnowski, X-J. Li, N. Wong, A. Garden, and K. Hogstrom, “A picture archival and communications system for radiotherapy,” Proceedings of the International Symposium on 3-D Radiation Treatment Planning and Conformal Therapy (Medical Physics Publishing, Wisconsin, 1993), pp. 411–420. Citing Literature Volume27, Issue4April 2000Pages 631-633 ReferencesRelatedInformation

Mutation of Tyrosine Residues Involved in the Alkylation Half Reaction of Epoxide Hydrolase from Agrobacterium radiobacter AD1 Results in Improved Enantioselectivity

Mutation of Tyrosine Residues Involved in the Alkylation Half Reaction of Epoxide Hydrolase from <i>Agrobacterium radiobacter</i> AD1 Results in Improved Enantioselectivity

Tandem Oxidative Cyclization with Rhenium Oxide. Total Synthesis of 17,18-bisepi-Goniocin

Many of the acetogenins isolated from the Annonaceae plants1 have shown remarkable cytotoxic, antitumor, antimalarial, immunosuppressive, pesticidal, and antifeedant activities.2 Classification of these fatty acid derivatives into three subgroups is based on the number and relative positioning of the tetrahydrofuran moieties within the molecule: the mono-THF, the adjacent bis-THF, and the nonadjacent bis-THF acetogenins.1 We have recently shown that many acetogenins of the first and second subgroups, including solamin, reticulatacin, asimicin, bullatacin, trilobacin, and trilobin, can be efficiently synthesized3 either by a convergent approach or via the “naked” carbon skeleton strategy,4,5 combining the Sharpless asymmetric dihydroxylation (AD) reaction6 with the Kennedy oxidative cyclization reaction.7 Goniocin, which has been recently isolated from Goniothalamus giganteus,8 possesses three adjacent THF rings and, therefore, represents the first example of a new subclass of Annonaceous acetogenins. Structure 1 was proposed for goniocin on the basis of its MS and 1H and 13C NMR data.8 Clearly, construction of the tris-trans-THF fragment I with the appropriate configuration of the seven stereogenic carbinol centers represents the main challenge in the synthesis of 1. Our retrosynthetic analysis (Scheme 1) was based on previous findings that two consecutive oxidative cyclizations with 4,8dienols can be carried out in a single step to produce bis-THF derivatives.9 We reasoned that I could be synthesized from a 4,8,12-trienol substrate using the tandem oxidative cyclization methodology. Coupling of I with the butenolide fragment II could lead to an efficient total synthesis of 1. Here, we report that all trans-4,8,12-trienol substrates indeed undergo a highly stereospecific triple oxidative cyclization reaction in the presence of a rhenium(VII) reagent to produce a single stereoisomer of a tris-THF product. Surprisingly, however, the product’s stereochemistry is not trans-threo-transthreo-trans-threo as expected, but trans-threo-cis-threo-cisthreo. Consequently, we have synthesized 17,18-bisepigoniocin (2) rather than 1. The key intermediate in our synthesis (Scheme 2) is the “naked” carbon skeleton (6) which is easily prepared from (E,E)ethyl heneicosa-4,8-dienoate3a (see the Supporting Information). Asymmetric epoxidation10 of 3 using Ti(OPr)4 and (-)-DIPT produces epoxy alcohol 4 in more than 95% ee. Reductive cleavage of the epoxide ring using Red-Al affords the 1,3-diol 5,11 which is then monoprotected at the primary position to give the silyl ether 6. We planned to use the single stereogenic center in 6 as the only source of chirality at the tris-THF fragment and achieve the other six stereogenic carbinol centers by a tandem oxidative cyclization reaction using a Re(VII) reagent. We found that both reagents originally used by Kennedy, i.e. Re2O7/lutidine and Re2O7/H5IO6 in dichloromethane, are useful for monocyclization with simple substrates possessing one double bond. However, for double cyclization with substrates containing two double bonds, the more reactive mixture, Re2O7/H5IO6, was † The Scripps Research Institute. ‡ Technion. (1) Zeng, L.; Ye, Q.; Oberlies, N. H.; Shi, G.; Gu, Z.-M.; He, K.; McLaughlin, J. L. Nat. Prod. Rep. 1996, 275. (2) Gu, Z.-M.; Zhao, G.-X.; Oberlies, N. H.; Zeng, L.; McLaughlin, J. L. In Recent AdVances in Phytochemistry; Arnason, J. T., Mata, R., Romeo, J. T., Eds.; Plenum Press: New York, 1995; Vol. 29, pp 249-310. (3) (a) Sinha, S. C; Keinan, E. J. Am. Chem. Soc. 1993, 115, 4891. (b) Sinha, S. C.; Sinha-Bagchi, A.; Yazbak, A.; Keinan, E. Tetrahedron Lett. 1995, 36, 9257. (c) Sinha, S. C.; Sinha, A.; Yazbak, A.; Keinan, E. J. Org. Chem. 1996, 61, 7640. (d) Sinha, A.; Sinha, S. C.; Keinan, E. Submitted. (4) Keinan, E.; Sinha, A.; Yazbak, A.; Sinha, S. C.; Sinha, S. C. Pure Appl. Chem. 1997, 69, 423. (5) (a) Sinha, S. C; Keinan, E. J. Org. Chem. 1994, 59, 949. (b) Sinha, S. C; Keinan, E. J. Org. Chem. 1997, 62, 377. (c) Sinha, S. C; SinhaBagchi, A.; Keinan, E. J. Org. Chem. 1993, 58, 7789. (6) Kolb, H. C.; VanNieuwenhze, M. S.; Sharpless, K. B. Chem. ReV. 1994, 94, 2483. (7) (a) Tang, S.; Kennedy, R. M. Tetrahedron Lett. 1992, 33, 3729. (b) Tang, S.; Kennedy, R. M. Tetrahedron Lett. 1992, 33, 5299. (c) Tang, S.; Kennedy, R. M. Tetrahedron Lett. 1992, 33, 5303. (d) Boyce, R. S.; Kennedy, R. M. Tetrahedron Lett. 1994, 35, 5133. (8) Gu, Z.-M.; Fang, X.-P.; Zeng, L.; McLaughlin, J. L. Tetrahedron Lett. 1994, 35, 5367. (9) Sinha, S. C; Sinha-Bagchi, A.; Keinan, E. J. Am. Chem. Soc. 1995, 117, 1447. (10) (a) Johnson, R. A.; Sharpless, K. B. In Catalytic Asymmetric Synthesis; Ojima, I., Ed.; VCH Publishers Inc.: New York, 1993; p 103. (b) Gao, Y.; Hanson, R. M.; Klunder, J. M.; Ko, S. Y.; Masamune, H.; Sharpless, K. B. J. Am. Chem. Soc. 1987, 109, 5765. (11) (a) Finan, J. M.; Kishi, Y. Tetrahedron Lett. 1982, 23, 2719. (b) Viti, S. M. Tetrahedron Lett. 1982, 23, 4541. Scheme 1

Systematic search in conformational analysis

The coupling of conformation to activity and reactivity is a widely accepted concept, and as such has driven the development of tools which execute conformational searches in rapid and robust fashion [T.F. Havel, Prog. Biophys. Molec. Biol., 56 (1991) 43–78; A.R. Leach, In Rev. Comput. Chem.; K.B. Lipkowitz and D.B. Boyd, Ed.; VCH Publishers, Inc.: New York, N.Y., 1991, Vol. II, pp. 1–55]. Among the aims of these methods are the determination of a complete set of local minima from which the global energy minimum can be identified, or the generation of conformations consistent with constraints derived from SAR or structural studies. Most methods fall into two broad categories: those which are random or stochastic, and those which are systematic. Yet another group consists of those which are based on heuristics and artificial intelligence [A.R. Leach, K. Prout, D.P. Dolata, J. Comput. Chem. 11 (1990) 680–693]. The first category is typified by molecular dynamics [W.F. van Gunsteren and H.J.C. Berendsen, Angew. Chem. Int. Ed. Eng., 29 (1990) 992–1023], Monte Carlo [M.P. Alien and D.J. Tildesley, Computer Simulation of Liquids, Oxford Science Publications, 1989], distance geometry [J.M. Blaney and J.S. Dixon, in K.B. Lipkowitz and D.B. Boyd (Eds.), Reviews in Computational Chemistry, VCH, New York, Vol. 5, pp. 299–335, 1994], and other approaches [M. Saunders, J. Comput. Chem., 10 (1989) 203–208] in which the path by which conformational space is examined is ideally completely random, but bounded by the geometries of covalent bond lengths and angles. In traditional systematic searches, the variable to be examined, e.g. torsion angles, is divided into a regular grid. Each and every grid point is evaluated in a systematic fashion to determine its validity. The path through the grid points is regular and defined. In principle, systematic search can, within the resolution of the grid, identify all sterically allowed conformations of a molecule. Consequently, systematic search is an ideal tool for conformational analysis because it is not path dependent and cannot become entrapped in local minima. In this article we review some of the basics of systematic search, algorithmic improvements that have enhanced its speed, and new developments that have increased its accuracy by moving away from the limitations of a fixed torsional grid.