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Single Molecule (single + molecule)
Selected AbstractsAmbiphilicity of Dichlorosilylene in a Single MoleculeCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2010Rajendra SiCl2as a simultaneous ,-donor and -acceptor: The reaction of the Lewis base stabilized dichlorosilylene L,SiCl2 with B(C6F5)3 (L=imidazol-2-ylidene derivative) afforded the first silylene donor acceptor L,SiCl2,B(C6F5)3 complex (shown here). Charge density analysis revealed that the two C,Si and Si,B donor bonds are of considerably different quality. However, plain bond length consideration might suggest simple CSi and SiB single bonds. [source] Molecular Self-Assembly of Jointed Molecules on a Metallic Substrate: From Single Molecule to MonolayerCHEMPHYSCHEM, Issue 9 2006Tomaso Zambelli Dr. Organic hinges: The "flexure hinges" in V -Landers (VL) molecules (C108H104) play an essential role in the adaptability of the molecule to the substrate (see figure). The molecules cannot simply be considered as rigid objects and it is mandatory to take into account their internal molecular degrees of freedom in order to understand the observed structures. [source] Engineering of a monomeric and low-glycosylated form of human butyrylcholinesteraseFEBS JOURNAL, Issue 2 2002Expression, characterization, crystallization, purification Human butyrylcholinesterase (BChE; EC 3.1.1.8) is of particular interest because it hydrolyzes or scavenges a wide range of toxic compounds including cocaine, organophosphorus pesticides and nerve agents. The relative contribution of each N-linked glycan for the solubility, the stability and the secretion of the enzyme was investigated. A recombinant monomeric BChE lacking four out of nine N-glycosylation sites and the C-terminal oligomerization domain was stably expressed as a monomer in CHO cells. The purified recombinant BChE showed catalytic properties similar to those of the native enzyme. Tetragonal crystals suitable for X-ray crystallography studies were obtained; they were improved by recrystallization and found to diffract to 2.0 Å resolution using synchrotron radiation. The crystals belong to the tetragonal space group I422 with unit cell dimensions a = b = 154.7 Å, c = 124.9 Å, giving a Vm of 2.73 Å3 per Da (estimated 60% solvent) for a single molecule of recombinant BChE in the asymmetric unit. The crystal structure of butyrylcholinesterase will help elucidate unsolved issues concerning cholinesterase mechanisms in general. [source] Crystal Structures and Magnetic Properties of Nitronyl Nitroxide RadicalsHELVETICA CHIMICA ACTA, Issue 4 2003Alexander Zakrassov The crystal structures and magnetic properties of the nitronyl nitroxide radicals 4,5-dihydro-4,4,5,5-tetramethyl-3-oxido(1H -imidazol-1-yloxyl) (1), 4,5-dihydro-2,4,4,5,5-pentamethyl-3-oxido(1H -imidazol-1-yloxyl) (2), 2-(4-chlorophenyl)-4,5-dihydro-4,4,5,5-tetramethyl-3-oxido(1H -imidazol-1-yloxyl) (3), and 4,5-dihydro-2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-3-oxido(1H -imidazol-1-yloxyl) (4) are reported. Compound 1 has two polymorphic forms: the , phase is monoclinic (P21/n space group), with a single molecule in the asymmetric unit, and the , phase is monoclinic (P21/c space group), with four molecules in the asymmetric unit. In the two polymorphs, the molecules are arranged in dimers formed by hydrogen bonds of the type CH,,,ON. The crystal structure of 3 contains layers of antiparallel ribbons of molecules. Compound 4 crystallizes with solvent molecules, and an intramolecular hydrogen bond is formed between the 2-OH group of the phenyl ring and the nitroxide O-atom. Compound 4 also loses the two O-atoms of the nitroxide moiety upon heating to 90°. Magnetic measurements showed that both , and , polymorphs of 1 exhibit antiferromagnetic coupling. The best fit to the experimental data was obtained using BleanyBower's singlet-triplet model (H=,2JSaSb): J=,11.2,K for the , phase and J=,15.0,K for the , phase. Compounds 3 and 4 show no evidence for spin coupling. [source] Evolution of cannibalism and female's response to oviposition-deterring pheromone in aphidophagous predatorsJOURNAL OF ANIMAL ECOLOGY, Issue 5 2009Xavier Martini Summary 1. ,Egg cannibalism by larvae is common in Coccinellidae and is known to be advantageous for the cannibals. Furthermore, larvae of aphidophagous ladybirds usually produce an oviposition-deterring pheromone (ODP), which inhibits oviposition by adult females. It has been proposed that the response to ODP has evolved because of the high costs of cannibalism. However, this has never been formally proved. 2. ,In this paper, we study the theoretical evolution of this system. We first look at the conditions under which cannibalism and the response to ODP can evolve. Subsequently, we examine the occurrence of polymorphism both in the production of larval tracks and in the sensitivity of females to specific pheromones. 3. ,The models predict that the amount of cannibalism should not depend on prey density and that evolution should lead to a continuous increase in cannibalism, and consequently larvae should always cannibalize eggs when possible. In response to the cost of cannibalism, ODP recognition can evolve, so that females avoid laying eggs in patches of prey already occupied by conspecific larvae. The result is an arms race between larvae and adult females, which favours a diversification of ODP pheromones. Our models show that: (i) females should be able to recognize mixtures of hydrocarbons rather than a single molecule; and (ii) females should be more sensitive to the tracks of their own offspring than those of non-related larvae. [source] Synthesis of new heterocyclic compounds having 1,2,3-triazole and isoxazole rings in a single moleculeJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2008Qiu Chen Five series of new heterocyclic compounds of 1,2,4-triazole Mannich bases, 1,3,4-oxadiazole Mannich bases, 1,3,4-oxadiazolines, 1,2,4-triazolo[3,4- b]1,3,4-thiadiazines and 1,2,4-triazolo[3,4- b]1,3,4-thiadiazoles, in which 1,2,3-triazolyl and isoxazolyl have been united, were synthesized from the intermediate of 5-methyl-3-(2-phenyl-2H -1,2,3-triazol-4-yl)isoxazole-4-carbohydrazide, Their structures were established by spectroscopy. [source] Nanometre localization of single ReAsH moleculesJOURNAL OF MICROSCOPY, Issue 3 2004H. PARK Summary ReAsH is a red-emitting dye that binds to the unique sequence Cys-Cys-Xaa-Xaa-Cys-Cys (where Xaa is a noncysteine amino acid) in the protein. We attached a single ReAsH to a calmodulin with an inserted tetracysteine motif and immobilized individual calmodulins to a glass surface at low density. Total internal reflection fluorescence microscopy was used to image individual ReAsH molecules. We determined the centre of the distribution of photons in the image of a single molecule in order to determine the position of the dye within 5 nm precision and with an image integration time of 0.5 s. The photostability of ReAsH was also characterized and observation times ranging from several seconds to over a minute were observed. We found that 2-mercaptoethanesulphonic acid increased the number of collected photons from ReAsH molecules by a factor of two. Individual ReAsH molecules were then moved via a nanometric stage in 25 or 40 nm steps, either at a constant rate or at a Poisson-distributed rate. Individual steps were clearly seen, indicating that the observation of translational motion on this scale, which is relevant for many biomolecular motors, is possible with ReAsH. [source] A di(bisphosphonic acid) for protein coupling and targeting to boneJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2004Geeti Bansal Abstract Proteins intended for treatment of bone diseases should ideally exhibit a high bone affinity, so that they are preferentially deposited to bones after systemic administration. This can be achieved by combining molecules having a high affinity to bone with the proteins. Bisphosphonates (BPs) are chemical analogs of pyrophosphate that possess exceptional bone mineral affinity. To this end, we synthesized a novel BP, 3,5-di(ethylamino-2,2-bisphosphono)benzoic acid (6), which contains two BP moieties on a single molecule, unlike conventional BPs that contain one BP moiety per molecule. 6 was then conjugated to two model proteins, bovine serum albumin and nonspecific bovine immunoglobulin G by the carbodiimide chemistry. By varying the reagent concentrations, the conjugation efficiency (i.e., number of 6 per protein) was readily controlled under the experimental conditions. The protein- 6 conjugates exhibited an in vitro mineral affinity that was proportional to the number of conjugated 6. The 6 -conjugates of both bovine serum albumin and immunoglobulin G were found to be bone seeking in rats, based on the increased concentration of 6 -conjugated proteins in bone tissue after intravenous administration. We conclude that the novel BP synthesized (6) can serve as a carrier for bone delivery while reducing the extent of protein modification necessary for bone targeting. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2788,2799, 2004 [source] Observation of SERS effect in Raman optical activity, a new tool for chiral vibrational spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2006Salim Abdali Abstract A new tool for chiral vibrational spectroscopy is reported here. A surface enhanced effect was observed using Raman optical activity (ROA). This observation opens new possibilities for ROA as a tool for vibrational spectroscopy. The combination of surface enhanced effect (SE) and ROA into surface enhanced Raman optical activity (SEROA) takes this tool to another level, where a single molecule may be studied with respect to chirality, secondary structure and fold determination. ROA has been able to provide information about important dynamics in molecular understanding. Until recently, however, ROA measurements required a longer exposure and higher concentration of the sample. With SEROA these obstacles can be overcome because both studies on single molecule, i.e. very low concentration, and faster acquisition of the signal can be carried out. In the present, work silver colloids were mixed with solution, in which a pentapeptide, Met-Enkephalin, was dissolved. SEROA signals were recorded and the results are reported here. Copyright © 2006 John Wiley & Sons, Ltd. [source] Kondo effect in oscillating moleculesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2009Jernej Mravlje Abstract We consider electronic transport through break-junctions bridged by a single molecule in the Kondo regime. We describe the system by a two-channel Anderson model. We take the tunneling matrix elements to depend on the position of the molecule. It is shown, that if the modulation of the tunneling by displacement is large, the potential confining the molecule to the central position between the leads is softened and the position of the molecule is increasingly susceptible to external perturbations that break the inversion symmetry. In this regime, the molecule is attracted to one of the leads and as a consequence the conductance is small. We argue on semi-classical grounds why the softening occurs and corroborate our findings by numerical examples obtained by Wilson's numerical renormalization group and Schönhammer,Gunnarsson's variational method (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Large-scale preparation of the homogeneous LolA,lipoprotein complex and efficient in vitro transfer of lipoproteins to the outer membrane in a LolB-dependent mannerPROTEIN SCIENCE, Issue 12 2007Shoji Watanabe Abstract An ATP-binding cassette transporter LolCDE complex of Escherichia coli releases lipoproteins destined to the outer membrane from the inner membrane as a complex with a periplasmic chaperone, LolA. Interaction of the LolA,lipoprotein complex with an outer membrane receptor, LolB, then causes localization of lipoproteins to the outer membrane. As far as examined, formation of the LolA,lipoprotein complex strictly depends on ATP hydrolysis by the LolCDE complex in the presence of LolA. It has been speculated, based on crystallographic and biochemical observations, that LolA undergoes an ATP-dependent conformational change upon lipoprotein binding. Thus, preparation of a large amount of the LolA,lipoprotein complex is difficult. Moreover, lipoproteins bound to LolA are heterogeneous. We report here that the coexpression of LolA and outer membrane-specific lipoprotein Pal from a very efficient plasmid causes the unusual accumulation of the LolA,Pal complex in the periplasm. The complex was purified to homogeneity and shown to be a functional intermediate of the lipoprotein localization pathway. In vitro incorporation of Pal into outer membranes revealed that a single molecule of LolB catalyzes the incorporation of more than 100 molecules of Pal into outer membranes. Moreover, the LolB-dependent incorporation of Pal was not affected by excess-free LolA, indicating that LolB specifically interacts with liganded LolA. Finally, the LolB depletion caused the accumulation of a significant amount of Pal in the periplasm, thereby establishing the conditions for preparation of the homogeneous LolA,lipoprotein complex. [source] An X-ray diffraction study of partially ordered electron density in clathrates of Dianin's compound that include simple carboxylic acidsACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2003Ronald W. H. Small The nature of the inclusions in ten clathrate complexes of Dianin's compound have been investigated by the use of electron-density difference maps. The guest species are the first eight straight-chain carboxylic acids, formic to octanoic, a branched-chain acid (dimethylacetic acid) and trifluoroacetic acid. The point-group symmetry of the clathrate cavity, , is satisfied by partial occupation of symmetry-related sites by two included molecules in the case of formic, acetic and trifluoroacetic acids and by a single molecule in the remainder. Hydrogen-bonding requirements in the case of formic and acetic acids are satisfied by dimer formation; in the trifluoroacetic acid complex the two acid molecules form hydrogen bonds to framework O atoms at either end of the cavity. The adoption of gauche conformations in heptanoic and octanoic acid chains shortens them sufficiently that they fit the cavity with only slight distortion. [source] 2-(Pyrrolidin-1-yl)-1,4-naphthoquinone and 2-phenylsulfanyl-3-(pyrrolidin-1-yl)-1,4-naphthoquinoneACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2002Daniel E. Lynch The structure of 2-(pyrrolidin-1-yl)-1,4-naphthoquinone, C14H12.95Cl0.05NO2, (I), is actually a 0.95:0.05 mixture including 2-chloro-3-(pyrrolidin-1-yl)-1,4-naphthoquinone as a minor impurity, but (I) was resolved as a single molecule containing a Cl atom with 5% occupancy at the 3-position. Compound (I) was prepared from the fully chloro-substituted analogue in an attempt to produce the disubstituted pyrrolidinyl derivative. 2-Phenylsulfanyl-3-(pyrrolidin-1-yl)-1,4-naphthoquinone, C20H17NO2S, (II), was also prepared from 2-chloro-3-(pyrrolidin-1-yl)-1,4-naphthoquinone, using a strong exocyclic nucleophile. The structure of (II) differs from previous structures of 2,3-dichloro-1,4-naphthoquinone and its derivatives in that the naphthoquinone ring is non-planar. [source] Preliminary X-ray crystallographic analysis of a soluble form of MntC, a periplasmic manganese-binding component of an ABC-type Mn transporter from Synechocystis sp.ACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2002PCC 680 Manganese is recruited in microorganisms by way of ABC-type transporter systems. Here, the expression, purification and preliminary crystallographic analysis of a soluble form of the MntC solute-binding protein component of the MntABC manganese-import system from the cyanobacterium Synechococystis sp. PCC 6803 is reported. The protein (321 amino-acid residues) was expressed exclusively in inclusion bodies, which required unfolding and refolding in the presence of manganese prior to purification. The purified protein was crystallized in the presence of PEG and zinc. The crystals belong to space group P6222, with unit-cell parameters a = b = 128.1, c = 90.0,Å and a single molecule in the asymmetric unit. The crystals diffract to 2.6,Å under cryoconditions using synchrotron radiation. [source] Crystallization and preliminary X-ray crystallographic analysis of highly thermostable L2 lipase from the newly isolated Bacillus sp.ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2010Purified thermostable recombinant L2 lipase from Bacillus sp. L2 was crystallized by the counter-diffusion method using 20% PEG 6000, 50,mM MES pH 6.5 and 50,mM NaCl as precipitant. X-ray diffraction data were collected to 2.7,Å resolution using an in-house Bruker X8 PROTEUM single-crystal diffractometer system. The crystal belonged to the primitive orthorhombic space group P212121, with unit-cell parameters a = 87.44, b = 94.90, c = 126.46,Å. The asymmetric unit contained one single molecule of protein, with a Matthews coefficient (VM) of 2.85,Å3,Da,1 and a solvent content of 57%. [source] Production, crystallization and preliminary X-ray diffraction analysis of the allergen Can,f,2 from Canis familiarisACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2009Chaithanya Madhurantakam The allergen Can f 2 from dog (Canis familiaris) present in saliva, dander and fur is an important cause of allergic sensitization worldwide. Here, the production, isolation, crystallization and preliminary X-ray diffraction analysis of two crystal forms of recombinant Can f 2 are reported. The first crystal form belonged to space group C222, with unit-cell parameters a = 68.7, b = 77.3, c = 65.1,Å, and diffracted to 1.55,Å resolution, while the second crystal form belonged to space group C2, with unit-cell parameters a = 75.7, b = 48.3, c = 68.7,Å, , = 126.5°, and diffracted to 2.1,Å resolution. Preliminary data analysis indicated the presence of a single molecule in the asymmetric unit for both crystal forms. [source] Multicolor in vivo targeted imaging to guide real-time surgery of HER2-positive micrometastases in a two-tumor coincident model of ovarian cancerCANCER SCIENCE, Issue 6 2009Michelle Longmire One of the primary goals of oncological molecular imaging is to accurately identify and characterize malignant tissues in vivo. Currently, molecular imaging relies on targeting a single molecule that while overexpressed in malignancy, is often also expressed at lower levels in normal tissue, resulting in reduced tumor to background ratios. One approach to increasing the specificity of molecular imaging in cancer is to use multiple probes each with distinct fluorescence to target several surface antigens simultaneously, in order to identify tissue expression profiles, rather than relying on the expression of a single target. This next step forward in molecular imaging will rely on characterization of tissue based on fluorescence and therefore will require the ability to simultaneously identify several optical probes each attached to different targeting ligands. We created a novel ,coincident' ovarian cancer mouse model by coinjecting each animal with two distinct cell lines, HER2+/red fluorescent protein (RFP), SKOV3 and HER2,/RFP+ SHIN3-RFP, in order to establish a model of disease in which animals simultaneously bore tumors with two distinct phenotypes (HER2+/RFP,, HER2,/RFP+), which could be utilized for multicolor imaging. The HER2 receptor of the SKOV3 cell line was targeted with a trastuzumab,rhodamine green conjugate to create green tumor implants, whereas the RFP plasmid of the SHIN3 cells created red tumor implants. We demonstrate that real-time in vivo multicolor imaging is feasible and that fluorescence characteristics can then serve to guide the surgical removal of disease. (Cancer Sci 2009; 100: 1099,1104) [source] Current,Voltage Characteristics of a Homologous Series of Polycyclic Aromatic HydrocarbonsCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2007Thilo Böhme Dr. Abstract A novel alkyl-substituted polycyclic aromatic hydrocarbon (PAH) with D2h symmetry and 78 carbon atoms in the aromatic core (C78) was synthesized, thereby completing a homologous series of soluble PAH compounds with increasing size of the aromatic , system (42, 60, and 78 carbon atoms). The optical band gaps were determined by UV/Vis and fluorescence spectroscopy in solution. Scanning tunneling microscopy (STM) and spectroscopy (STS) revealed diode-like current versus voltage (I,V) characteristics through individual aromatic cores in monolayers at the interface between the solution and the basal plane of graphite. The asymmetry of the current,voltage (I,V) characteristics increases with the increasing size of the aromatic core, and the concomitantly decreasing HOMO,LUMO gap. This is attributed to resonant tunneling through the HOMO of the adsorbed molecule, and an asymmetric position of the molecular species in the tunnel junction. Consistently, submolecularly resolved STM images at negative substrate bias are in good agreement with the calculated pattern for the electron densities of the HOMOs. The analysis provides the basis for tailoring rectification with a single molecule in an STM junction. [source] Progress in the Understanding of Drug,Receptor Interactions, Part,2: Experimental and Theoretical Electrostatic Moments and Interaction Energies of an Angiotensin II Receptor Antagonist (C30H30N6O3S)CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2007Raffaella Soave Dr. Abstract A combined experimental and theoretical charge density study of an angiotensin II receptor antagonist (1) is presented focusing on electrostatic properties such as atomic charges, molecular electric moments up to the fourth rank and energies of the intermolecular interactions, to gain an insight into the physical nature of the drug,receptor interaction. Electrostatic properties were derived from both the experimental electron density (multipole refinement of X-ray data collected at T=17,K) and the ab initio wavefunction (single molecule and fully periodic calculations at the DFT level). The relevance of S,,,O and S,,,N intramolecular interactions on the activity of 1 is highlighted by using both the crystal and gas-phase geometries and their electrostatic nature is documented by means of QTAIM atomic charges. The derived electrostatic properties are consistent with a nearly spherical electron density distribution, characterised by an intermingling of electropositive and -negative zones rather than by a unique electrophilic region opposed to a nucleophilic area. This makes the first molecular moment scarcely significant and ill-determined, whereas the second moment is large, significant and highly reliable. A comparison between experimental and theoretical components of the third electric moment shows a few discrepancies, whereas the agreement for the fourth electric moment is excellent. The most favourable intermolecular bond is show to be an NH,,,N hydrogen bond with an energy of about 50,kJ,mol,1. Key pharmacophoric features responsible for attractive electrostatic interactions include CH,,,X hydrogen bonds. It is shown that methyl and methylene groups, known to be essential for the biological activity of the drug, provide a significant energetic contribution to the total binding energy. Dispersive interactions are important at the thiophene and at both the phenyl fragments. The experimental estimates of the electrostatic contribution to the intermolecular interaction energies of six molecular pairs, obtained by a new model proposed by Spackman, predict the correct relative electrostatic energies with no exceptions. [source] An Experimental and Computational Study on Intramolecular Charge Transfer: A Tetrathiafulvalene-Fused Dipyridophenazine MoleculeCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2007Chunyang Jia Prof. Abstract To study the electronic interactions in donor,acceptor (D,A) ensembles, D and A fragments are coupled in a single molecule. Specifically, a tetrathiafulvalene (TTF)-fused dipyrido[3,2- a:2,,3,- c]phenazine (dppz) compound having inherent redox centers has been synthesized and structurally characterized. Its electronic absorption, fluorescence emission, photoinduced intramolecular charge transfer, and electrochemical behavior have been investigated. The observed electronic properties are explained on the basis of density functional theory. [source] Complexes of Diquat with Dibenzo-24-Crown-8CHINESE JOURNAL OF CHEMISTRY, Issue 9 2009Shijun Li Abstract The complexation between dibenzo-24-crown-8 (1) and diquat (2) was investigated in detail by NMR, MS and X-ray analysis. It was found that dibenzo-24-crown-8 and diquat formed a 1:1 complex 1·2 in acetone with Ka=2.0×102 L·mol,1, but, as shown by X-ray analysis, a crystalline 2:1 host:guest inclusion complex 12·2 was isolated, in which a single molecule of diquat is enclosed in the concave cavity provided by two dibenzo-24-crown-8 host molecules. Both results are different from the previously assumed stoichiometry of the complexation between dibenzo-24-crown-8 and diquat. This result enriches the range of host-guest complexes based on dibenzo-24- crown-8 and provides new opportunities for developing more complicated structures and chemosensors for diquat. [source] Visualization of the interaction between archaeal DNA polymerase and uracil-containing DNA by atomic force microscopyGENES TO CELLS, Issue 1 2006Yasuo Asami Deamination of cytosine to uracil is a hydrolytic reaction that is greatly accelerated at high temperatures. The resulting uracil pairs with adenine during DNA replication, thereby inducing G:C to A:T transitions in the progeny. Interestingly, B-family DNA polymerases from hyperthermophilic Archaea recognize the presence of uracil in DNA and stall DNA synthesis. To better understand the recognition mechanism, the binding modes of DNA polymerase B1 of Sulfolobus solfataricus (Pol B1) to uracil-containing DNA were examined by gel mobility shift assays and atomic force microscopy. Although PolB1 per se specifically binds to uracil-containing single-stranded DNA, the binding efficiency was substantially enhanced by the initiation of DNA synthesis. Analysis by the atomic force microscopy showed a number of double-stranded DNA (dsDNA) in the products of DNA synthesis. The generation of ds DNA was significantly inhibited, however, by the presence of template uracil, and intermediates where monomeric forms of Pol B1 appeared to bind to uracil-containing DNA were observed. These results suggest that Pol B1 more efficiently recognizes uracil in DNA during DNA synthesis rather than during random diffusion in solution, and that single molecules of Pol B1 bind to template uracil and stall DNA synthesis. [source] From Molecules to TissuesIMAGING & MICROSCOPY (ELECTRONIC), Issue 1 2008Optical Tools for Cancer Research Modern optical microscopy has always represented an indispensable tool for biomedical research. One of the most relevant and successful transformations of the modern microscope is the ability to parallel an instrumental modification with the development of new assays for the determination of functional parameters. Instrument performances have been consequently optimized for the analysis of extremely heterogeneous targets, ranging from single molecules up to living organisms. [source] Physicochemical Properties, Firmness, and Nanostructures of Sodium Carbonate-Soluble Pectin of 2 Chinese Cherry Cultivars at 2 Ripening StagesJOURNAL OF FOOD SCIENCE, Issue 6 2008Lifen Zhang ABSTRACT:, Firmness and physicochemical properties of 2 Chinese cherry (Prunus pseudocerasus L.) cultivars (soft cultivar "Caode" and crisp cultivar "Bende") at unripe and ripe stages were investigated, and the qualitative and quantitative information about sodium carbonate-soluble pectin (SSP) nanostructures was determined by atomic force microscopy (AFM). The lengths and widths of the cherry SSPs are very regular: almost all of the widths and lengths of SSP single molecules are composed of several basic units. The widths of the SSP chains are 37, 47, 55, and 61 nm, and the lengths are 123, 202, and 380 nm in both cultivars. The results show that the firmer cherry groups (crisp fruit) contain more percentages of wide and short SSP chains than soft fruit, and the unripe groups contain more percentages of wide and long SSP chains than corresponding ripe groups. They indicate that those nanostructural characteristics of SSP are closely related with firmness of the Chinese cherries in each cultivar. [source] Single-molecule near-field optical energy transfer microscopy with dielectric tipsJOURNAL OF MICROSCOPY, Issue 3 2003W. Trabesinger Summary The fluorescence lifetime and the fluorescence rate of single molecules are recorded as a function of the position of a Si3N4 atomic force microscopy tip with respect to the molecule. We observe a decrease of the excited state lifetime and the fluorescence rate when the tip apex is in close proximity to the molecule. These effects are attributed to the fact that the dielectric tip converts non-propagating near-fields to propagating fields within the dielectric tip effectively quenching the fluorescence. The spatial extension of the quenching area is of subwavelength dimensions. The results are discussed in terms of molecular fluorescence in a system of stratified media. The experiment provides surprising new insights into the interactions between a fluorescent molecule and a dielectric tip. The methodology holds promise for applications in ultra high-resolution near-field optical imaging at the level of single fluorophores. [source] Past, present and future of atomic force microscopy in life sciences and medicineJOURNAL OF MOLECULAR RECOGNITION, Issue 6 2007Pierre Parot Abstract To introduce this special issue of the Journal of Molecular Recognition dedicated to the applications of atomic force microscopy (AFM) in life sciences, this paper presents a short summary of the history of AFM in biology. Based on contributions from the first international conference of AFM in biological sciences and medicine (AFM BioMed Barcelona, 19,21 April 2007), we present and discuss recent progress made using AFM for studying cells and cellular interactions, probing single molecules, imaging biosurfaces at high resolution and investigating model membranes and their interactions. Future prospects in these different fields are also highlighted. Copyright © 2007 John Wiley & Sons, Ltd. [source] Cyclodextrin polyrotaxanes assembled from a molecular construction kit in aqueous solutionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2009Gerhard Wenz Abstract We describe a molecular construction kit in which amphiphilic polymers and functionalized cyclodextrins are arranged into sophisticated molecular architectures in aqueous solution without the need to perform chemical reactions. Therefore, these systems are highly biocompatible and show programmable lifetimes. The kinetic stabilities of our polyrotaxane structures are tunable using sterically demanding groups that hinder dissociation. These cyclodextrin-based polymer systems are applicable in principle for the detection of analytes at the level of single molecules. These systems may also serve well in targeted drug delivery and gene transfection. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6333,6341, 2009 [source] Surface-enhanced Raman spectroscopy: advancements and applicationsJOURNAL OF RAMAN SPECTROSCOPY, Issue 6-7 2005Z. Q. Tian Abstract Since the mid-1990s, surface-enhanced Raman scattering (SERS) has advanced greatly and gained wider application and a renewal of interest. There have been several new and creative developments, e.g. SERS of single molecules, nanostructures and transition metals, tip-enhanced Raman scattering (TERS), surface-enhanced hyper-Raman scattering (SEHRS), ultraviolet-excited SERS (UV-SERS) and surface-enhanced resonance Raman scattering (SERRS), and their wide applications in biology, medicine, materials science and electrochemistry. It is timely to publish a special issue reporting these initiatives and the progress made in the past 7 years. This issue consists of 30 invited articles that are roughly divided into three SERS research themes: theories, methods and applications. These up-to-date representatives of the research results clearly show that SERS is important not only for Raman spectroscopy and surface science but also for nanoscience. Copyright © 2005 John Wiley & Sons, Ltd. [source] Role of Star-Like Hydroxylpropyl Lignin in Soy-Protein PlasticsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 5 2006Ming Wei Abstract Summary: Star-like hydroxypropyl lignin (HL) was compounded into soy protein isolated (SPI) to develop a potential biodegradable plastic with better mechanical performance than pure sheet-SPI. The structure and properties of the composite materials were characterized by WAXD, DSC, SEM, TEM and tensile tests. The addition of just 2 wt.-% HL resulted in tensile strength (,b) of 16.8 MPa, 2.3 times that of pure sheet-SPI, with no accompanying decrease in elongation at break as a result of strong interaction and with good miscibility among components. As the HL content increased, the HL molecules could self-aggregate as oblate supramolecular domains, while the stronger interactions between HL and glycerol resulted in the detaching of glycerol from the SPI matrix. It can be concluded that the insertion of HL as single molecules into the SPI matrix would provide materials with optimum mechanical properties. Compared with other lignin/SPI composites, the stretching chains on HL play a key role in the improvement of mechanical properties because of a stronger adhesion of HL onto the SPI matrix as well as the interpenetration of SPI into supramolecular HL domains. Schematic illustration of the supramolecular domain created by the aggregation of hydroxypropyl lignin, which can interpenetrate with soy protein isolate. [source] The Molecular Phenotype of Kidney TransplantsAMERICAN JOURNAL OF TRANSPLANTATION, Issue 10 2010P. F. Halloran Microarray studies of kidney transplant biopsies provide an opportunity to define the molecular phenotype. To facilitate this process, we used experimental systems to annotate transcripts as members of pathogenesis-based transcript sets (PBTs) representing biological processes in injured or diseased tissue. Applying this annotation to microarray results revealed that changes in single molecules and PBTs reflected a large-scale coordinate disturbance, stereotyped across various diseases and injuries, without absolute specificity of individual molecules or PBTs for rejection. Nevertheless, expression of molecules and PBTs was quantitatively specific: IFNG effects for rejection; T cell and macrophage transcripts for T cell-mediated rejection; endothelial and NK transcripts for antibody-mediated rejection. Various diseases and injuries induced the same injury,repair response, undetectable by histopathology, involving epithelium, stroma and endothelium, with increased expression of developmental, cell cycle and apoptosis genes and decreased expression of differentiated epithelial features. Transcripts reflecting this injury,repair response were the best correlates of functional disturbance and risk of future graft loss. Late biopsies with atrophy-fibrosis, reflecting their cumulative burden of injury, displayed more transcripts for B cells, plasma cells and mast cells. Thus the molecular phenotype is best described in terms of three elements: specific diseases, including rejection; the injury,repair response and the cumulative burden of injury. [source] | |||||||||||||||||||||||||||||||