Imaging of single uncoated DNA molecules by scanning tunneling microscopy.

Scanning tunneling microscope images of DNA molecules absorbed onto highly oriented pyrolytic graphite have been obtained. Three methods of deposition and sample preparation have been utilized. In the first method, a highly concentrated solution of DNA is sonicated, and a drop is deposited on freshly cleaved graphite. Under these conditions, the molecules tend to align in a parallel fashion, forming liquid-crystalline phases. In the second method, a solution of DNA is deposited directly on the graphite surface without sonication. In this case, ammonium acetate, a volatile salt, is used to decrease the amount of the residual salt crystals left after drying. In the third method, a solution containing lysed phage particles and DNA is adsorbed onto a graphite surface. The molecules are seen either isolated or in small bundles. The values of height, periodicity, and thickness observed and the handedness of the molecules are consistent with those expected for DNA. In all cases, the molecules were identified by their characteristic periodic structure and because, at higher magnification, no graphite-like structure was detectable on the surface of the molecules. Often the DNA molecules appear to adsorb in areas of the graphite that have many steps and defects. A mechanism that explains the magnitude of the tunneling currents measured in DNA is proposed. This mechanism, in turn, suggests a general method by which large insulating molecules can be rendered conductive.     

Photochemistry and spectroscopy of a five-chlorophyll reaction center of photosystem II isolated by using a Cu affinity column

A reaction center of photosystem II was isolated from Pisum sativum by using immobilized metal affinity chromatography. This reaction center is photochemically active and has a room temperature Qgamma chlorophyll (Chl) absorption band peaking at 677.5 nm. From HPLC analysis, the pigment stoichiometry was suggested to be 5 Chls per 1 beta-carotene per 2 pheophytins. Low-temperature absorption measurements at 77 K were consistent with the removal of one of the Chls associated with the usual form of the reaction center isolated by using ion-exchange chromatography. Transient absorption spectroscopy on the picosecond time scale indicated that the Chl removed belongs to a pool of Chl absorbing at approximately 670 nm (C670II) that transfers energy relatively slowly to the primary donor P680 in support of our recently proposed model. The results also support the previous conclusion that radical pair formation is largely associated with a 21-ps time constant when P680 is directly excited and that the identity of C670II is likely to be peripherally bound Chls possibly ligated to conserved His residues at positions 118 on the D1 and D2 proteins.     

Ultra-high vacuum scanning tunneling microscopy and theoretical studies of 1-halohexane monolayers on graphite

A simple model system for the 2D self-assembly of functionalized organic molecules on surfaces was examined in a concerted experimental and theoretical effort. Monolayers of 1-halohexanes were formed through vapor deposition onto graphite surfaces in ultrahigh vacuum. Low-temperature scanning tunneling microscopy allowed the molecular conformation, orientation, and monolayer crystallographic parameters to be determined. Essentially identical noncommensurate monolayer structures were found for all 1-halohexanes, with differences in image contrast ascribed mainly to electronic factors. Energy minimizations and molecular dynamics simulations reproduced structural parameters of 1-bromohexane monolayers quantitatively. An analysis of interactions driving the self-assembly process revealed the crucial role played by small but anisotropic electrostatic forces associated with the halogen substituent. While alkyl chain dispersion interactions drive the formation of a close-packed adsorbate monolayer, electrostatic headgroup forces are found to compete successfully in the control of both the angle between lamella and backbone axes and the angle between surface and backbone planes. This competition is consistent with energetic tradeoffs apparent in adsorption energies measured in earlier temperature-programmed desorption studies. In accordance with the higher degree of disorder observed in scanning tunneling microscopy images of 1-fluorohexane, theoretical simulations show that electrostatic forces associated with the fluorine substituent are sufficiently strong to upset the delicate balance of interactions required for the formation of an ordered monolayer. The detailed dissection of the driving forces for self-assembly of these simple model systems is expected to aid in the understanding of the more complex self-assembly processes taking place in the presence of solvent.     

Monomeric and trimeric forms of photosystem I reaction center of Mastigocladus laminosus: crystallization and preliminary characterization.

Photosystem I (PSI) reaction centers (RCs) of the thermophilic cyanobacterium Mastigocladus laminosus were purified and characterized. The PSI RC was obtained in two forms, monomeric and trimeric. The two forms contained the same number of pigments per P700 and displayed similar photochemical activities. The two forms had nearly identical polypeptide subunit compositions; the only observed difference was an additional subunit of about 12 kDa observed in the trimeric form. The purified preparations of both the monomeric and the trimeric forms were used for crystallization and preliminary crystallographic analysis. The trimeric PSI RC preparations produced several three-dimensional crystal forms, one of which, the "hexagonal needle" form (THN), had a hexagonal unit cell with dimensions of 300 x 300 x 160 A, containing four PSI RC trimers. The monomeric preparations also produced single crystals of several forms under various crystallization conditions. One of these crystal forms, the "hexagonal plate" (MHP), diffracted to a resolution of about 5.5 A. It had a hexagonal unit cell with dimensions of 192 x 192 x 163 A, containing six PSI RC monomers. Comparison of the PSI RCs in the crystals with those in the precrystallization preparations demonstrated that neither the monomeric nor the trimeric form of PSI RC was altered by the crystallization process. Both forms retained their original polypeptide subunit composition and their pigment content.     

Molecular characterization of PsbW, a nuclear-encoded component of the photosystem II reaction center complex in spinach.

We describe the isolation and characterization of cDNAs encoding the precursor polypeptide of the 6.1-kDa polypeptide associated with the reaction center core of the photosystem II complex from spinach. PsbW, the gene encoding this polypeptide, is present in a single copy per haploid genome. The mature polypeptide with 54 amino acid residues is characterized by a hydrophobic transmembrane segment, and, although an intrinsic membrane protein, it carries a bipartite transit peptide of 83 amino acid residues which directs the N terminus of the mature protein into the chloroplast lumen. Thylakoid integration of this polypeptide does not require a delta pH across the membrane, nor is it azide-sensitive, suggesting that the polypeptide chain inserts spontaneously in an as yet unknown way. The PsbW mRNA levels are light regulated. Similar to cytochrome b559 and PsbS, but different from the chlorophyll-complexing polypeptides D1, D2, CP43, and CP47 of photosystem II, PsbW is present in etiolated spinach seedlings.     

Images of a lipid bilayer at molecular resolution by scanning tunneling microscopy.

The molecular structure of a fatty acid bilayer has been recorded with a scanning tunneling microscope operating in air. The molecular film, a bilayer of cadmium icosanoate (arachidate), was deposited onto a graphite substrate by the Langmuir-Blodgett technique. The packing of the lipid film was found to be partially ordered. Along one axis of the triclinic unit cell the intermolecular distance varied randomly around a mean of 5.84 A with a SD of 0.24 A. Along the other axis the mean distance was 4.1 A and appeared to vary monotonically over several intermolecular distances, indicating that a superstructure of longer range may exist. The molecular density was one molecular per 19.4 A2. The surprising ability of the scanning tunneling microscope to image the individual molecular chains demonstrates that electrons from the graphite can be transferred along the molecular chains for a distance of 50 A.     

Independent initiation of primary electron transfer in the two branches of the photosystem I reaction center

Photosystem I (PSI) is a large pigment-protein complex that unites a reaction center (RC) at the core with ∼100 core antenna chlorophylls surrounding it. The RC is composed of two cofactor branches related by a pseudo-C2 symmetry axis. The ultimate electron donor, P₇₀₀ (a pair of chlorophylls), and the tertiary acceptor, F_X (a Fe₄S₄ cluster), are both located on this axis, while each of the two branches is made up of a pair of chlorophylls (ec2 and ec3) and a phylloquinone (PhQ). Based on the observed biphasic reduction of F_X, it has been suggested that both branches in PSI are competent for electron transfer (ET), but the nature and rate of the initial electron transfer steps have not been established. We report an ultrafast transient absorption study of Chlamydomonas reinhardtii mutants in which specific amino acids donating H-bonds to the 13¹-keto oxygen of either ec3_A (PsaA-Tyr696) or ec3_B (PsaB-Tyr676) are converted to Phe, thus breaking the H-bond to a specific ec3 cofactor. We find that the rate of primary charge separation (CS) is lowered in both mutants, providing direct evidence that the primary ET event can be initiated independently in each branch. Furthermore, the data provide further support for the previously published model in which the initial CS event occurs within an ec2/ec3 pair, generating a primary ec2⁺ec3^- radical pair, followed by rapid reduction by P₇₀₀ in the second ET step. A unique kinetic modeling approach allows estimation of the individual ET rates within the two cofactor branches.     

The nature of the excited state of the reaction center of photosystem II of green plants: A high-resolution fluorescence spectroscopy study

We studied the electronically excited state of the isolated reaction center of photosystem II with high-resolution fluorescence spectroscopy at 5 K and compared the obtained spectral features with those obtained earlier for the primary electron donor. The results show that there is a striking resemblance between the emitting and charge-separating states in the photosystem II reaction center, such as a very similar shape of the phonon wing with characteristic features at 19 and 80 cm⁻¹, almost identical frequencies of a number of vibrational modes, a very similar double-Gaussian shape of the inhomogeneous distribution function, and relatively strong electron-phonon coupling for both states. We suggest that the emission at 5 K originates either from an exciton state delocalized over the inactive branch of the photosystem or from a fraction of the primary electron donor that is long-lived at 5 K. The latter possibility can be explained by a distribution of the free energy difference of the primary charge separation reaction around zero. Both possibilities are in line with the idea that the state that drives primary charge separation in the reaction center of photosystem II is a collective state, with contributions from all chlorophyll molecules in the central part of the complex.     

From antenna to reaction center: Pathways of ultrafast energy and charge transfer in photosystem II

The photosystem II core complex (PSII-CC) is the smallest subunit of the oxygenic photosynthetic apparatus that contains core antennas and a reaction center, which together allow for rapid energy transfer and charge separation, ultimately leading to efficient solar energy conversion. However, there is a lack of consensus on the interplay between the energy transfer and charge separation dynamics of the core complex. Here, we report the application of two-dimensional electronic-vibrational (2DEV) spectroscopy to the spinach PSII-CC at 77 K. The simultaneous temporal and spectral resolution afforded by 2DEV spectroscopy facilitates the separation and direct assignment of coexisting dynamical processes. Our results show that the dominant dynamics of the PSII-CC are distinct in different excitation energy regions. By separating the excitation regions, we are able to distinguish the intraprotein dynamics and interprotein energy transfer. Additionally, with the improved resolution, we are able to identify the key pigments involved in the pathways, allowing for a direct connection between dynamical and structural information. Specifically, we show that C505 in CP43 and the peripheral chlorophyll Chlz_D1 in the reaction center are most likely responsible for energy transfer from CP43 to the reaction center.

Photosynthesis is the process through which solar energy is converted into chemical energy (1–3). Photosystem II (PSII), a pigment–protein complex found in cyanobacteria, algae, and land plants, is the site of water splitting and is therefore crucial for photosynthetic function (4–6). It is connected with a large light-harvesting antenna system that collects solar energy and transfers the energy to the reaction center (RC), where charge separation (CS) occurs. Unlike the antenna system of purple bacteria that has a clear energy funnel, the PSII antenna system has a more complicated composition and a very complex energy landscape (4–7). These features allow for regulation that responds to rapid environmental fluctuations and protect the organisms in, for example, excess light, while maintaining highly efficient electronic energy transfer (EET) under optimal conditions (8). To understand the intricate interactions between the subunits that allow for the robustness of this photosynthetic system, the first step is to understand how the antenna system is connected to the RC. The PSII core complex (PSII-CC) is the smallest unit in which the RC is connected to the antenna proteins. It is a dimeric pigment–protein complex in which each monomer contains an RC and two core antenna proteins, namely, CP43 and CP47 (1, 7). These core antennas not only harvest solar energy but also act as the crucial bridge between the peripheral light-harvesting antenna system and the RC. Fig. 1A shows the pigment arrangement of the PSII-CC. The RC, consisting of the D1 and D2 branches, binds the following pigments: 1) two special pair chlorophyll a (P_D1 and P_D2), 2) two accessory chlorophyll a (Chl_D1 and Chl_D2), 3) two pheophytin a (Pheo_D1 and Pheo_D2), and 4) two peripheral chlorophyll a (Chlz_D1 and Chlz_D2) (9, 10). Despite the similarity between the D1 and D2 branches, CS occurs only along the D1 branch (11, 12). CP43, one of the two core antenna proteins, contains 13 chlorophyll a (Chls) and is located closer to the D1 active branch. CP47 contains 16 Chls and is located closer to the D2 branch (10). Together, these proteins provide highly effective EET and CS, which are key to the high quantum yield of CS in the RC.Open in a separate windowFig. 1.(A) Pigment arrangement of monomeric PSII-CC (whereas it is typically found as a dimer) depicted based on the cryoelectron microscopy structure (3JCU) reported by Wei et al. (10). The pigments of CP43, RC, and CP47 are shown in green, blue, and red, respectively. (B) Corresponding excitonic energy levels of monomeric PSII-CC color coded to match pigments in A (55–57). The gray shaded regions in the background represent the three groups based on similar characteristic dynamics. Note that the boundaries between the groups provide only a rough separation region as the dynamical behaviors change gradually along ω_exc. The asterisk (for the RC state) indicates an optically dark state.Despite the importance of the PSII-CC, its early time dynamics is not fully understood—specifically the competition between EET and CS (5, 7). This is largely due to the highly congested excitonic manifold (Fig. 1B) and ultrafast EET timescales, which challenge ultrafast spectroscopic techniques. Two distinct models have been put forth to try to describe the function of the PSII-CC. These two models are the “exciton/radical pair equilibrium” (ERPE) model (13–17) and the “transfer-to-trap limited” (TTTL) model (18–22). An early fluorescence decay experiment (13, 14) suggested that rapid EET allows the excitonic states to reach an equilibrium between the core antennas and the RC before CS occurs (k_EET ≫ k_CS), which is the basis for the ERPE model. This model was later supported by improved time-resolved fluorescence (15) and transient absorption experiments (16). However, a major discrepancy in this model arose with the measurement of the X-ray crystal structure of the PSII-CC (18). It was suggested that the large distances (center-to-center distance, >20 Å) between antenna and RC pigments resolved in the crystal structure would mean that ultrafast EET between the antenna proteins and the RC is unlikely. A model was then put forth that instead suggested that the EET from the core antenna to the RC is slow compared to CS (k_EET ≪ k_CS), and therefore, the EET to the trap becomes a kinetic bottleneck (18). This TTTL model was later supported by transient infrared (IR) (19) and time-resolved fluorescence experiments (20, 21) as well as structure-based simulations (22). Additionally, Kaucikas et al. (23) performed a polarized transient IR experiment on an oriented single PSII-CC crystal. The decay of the polarization-dependent signature (50–100 ps) observed in their experiment suggests that equilibration between different subunits is slow, consistent with the TTTL model. However, it has been pointed out that satisfactory fitting of the spectral evolution to this model does not necessarily imply that it is correct (24, 25), especially as others have shown that the EET dynamics cannot be adequately described by a single hopping scheme (26, 27). A recent two-dimensional electronic spectroscopy (2DES) experiment (28) with improved time resolution has also revealed the existence of ultrafast EET (<100 fs) that was not predicted by theoretical calculations. In their work, Pan et al. (28) attributed the origin of this unexpectedly fast EET pathway to polaron formation. Vibronic effects on the ultrafast EET and CS dynamics of other photosynthetic proteins have also been discussed (29–38).The lack of detailed understanding of the PSII-CC early time dynamics, in particular the EET between the core antennas and the RC, highlights the need for further experimental input with the ability to make specific assignments of the dynamical pathways. This, however, requires simultaneous high temporal and spectral resolution, which remains a challenge for ultrafast spectroscopic techniques. Here, we describe the application of two-dimensional electronic-vibrational (2DEV) spectroscopy (39–41) to the PSII-CC. The combination of both spectral dimensions provides an improved resolution that allows us to obtain much more detailed dynamical information in complex systems. The excitonic energy landscapes generated by electronic coupling in photosynthetic complexes, combined with site-dependent and charge state–dependent vibrational spectra, allow the resolution along both axes of 2DEV spectra to provide a direct connection between energetic space (via visible excitation) and physical space (via IR detection). This advantage has proven to be useful for the studies of dynamics in photosynthetic pigment–protein complexes (33, 40–45). Specifically, the resolution along the electronic excitation axis allows for the separation of the contributions from different pathways, while the resolution along the vibrational detection axis provides a way to identify the protein subunits or even specific states involved in the dynamics. As we will show, this unique feature of 2DEV spectroscopy provides insight into the complex dynamics of the PSII-CC.In the following text, we will show that the sub-100-ps dynamics of the PSII-CC extracted from spinach are highly dependent on the excitation frequency range. The resolution along the detection axis allows different dominant dynamics to be identified. In addition, we will demonstrate how 2DEV spectroscopy allows us to connect the observed dynamics to specific excitonic states. This connection allows us to obtain a more specific pigment assignment for the EET pathways and therefore provides a more detailed understanding of the finely tuned interactions between the RC and the core antennas (specifically CP43, which is closer to the active D1 branch). We will conclude with a comparison between our results and the existing models in order to provide a path forward in the understanding of this critical photosynthetic component.     

An approach to long-range electron transfer mechanisms in metalloproteins: In situ scanning tunneling microscopy with submolecular resolution

In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode can be controlled, reflected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2- to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins.     

Realization of a four-step molecular switch in scanning tunneling microscope manipulation of single chlorophyll-a molecules

Single chlorophyll-a molecules, a vital resource for the sustenance of life on Earth, have been investigated by using scanning tunneling microscope manipulation and spectroscopy on a gold substrate at 4.6 K. Chlorophyll-a binds on Au(111) via its porphyrin unit while the phytyl-chain is elevated from the surface by the support of four CH(3) groups. By injecting tunneling electrons from the scanning tunneling microscope tip, we are able to bend the phytyl-chain, which enables the switching of four molecular conformations in a controlled manner. Statistical analyses and structural calculations reveal that all reversible switching mechanisms are initiated by a single tunneling-electron energy-transfer process, which induces bond rotation within the phytyl-chain.     

Mutational analysis of the structure and biogenesis of the photosystem I reaction center in the cyanobacterium Synechocystis sp. PCC 6803

We have utilized the unicellular cyanobacterium Synechocystis sp. PCC 6803 to incorporate site-directed amino acid substitutions into the photosystem I (PSI) reactioncenter protein PsaB. A cysteine residue (position 565 of PsaB) proposed to serve as a ligand to the [4Fe-4S] center Fx was changed to serine, histidine, and aspartate. These three mutants--C565S, C565H, and C565D--all exhibited greatly reduced accumulation of PSI reaction-center proteins and failed to grow autotrophically, indicating that this cysteine most likely does coordinate Fx, which is crucial for PSI biogenesis. Interestingly, the strain C565S accumulated significantly more PSI than the other two cysteine mutants and displayed photoreduction of the [4Fe-4S] terminal electron acceptors FA and FB. Mutations were also introduced into a leucine zipper motif of PsaB, proposed to participate in reaction-center dimerization. The mutants L522V, L536M, and L522V/L536M all exhibited wild-type characteristics and grew autotrophically, whereas the L522P mutation prevented PSI accumulation. These data do not provide support for a major structural role of the leucine zipper in reaction-center dimerization or in assembly of Fx. However, the amino acid substitutions incorporated were conservative and might not have perturbed the leucine zipper.     

Isolation of a photosystem II reaction center consisting of D-1 and D-2 polypeptides and cytochrome b-559

A photosystem II reaction center complex consisting of D-1 and D-2 polypeptides and cytochrome b-559 was isolated from spinach grana thylakoids, treated with 4% (wt/vol) Triton X-100, by ion-exchange chromatography using DEAE-Toyopearl 650S. The isolated complex appears to contain five chlorophyll a, two pheophytin a, one β-carotene, and one or two cytochrome b-559 heme(s) (molar ratio) and exhibits a reversible absorbance change attributable to the photochemical accumulation of reduced pheophytin typical for the intermediary electron acceptor of photosystem II reaction center. These results strongly suggest that the site of primary charge separation in photosystem II is located on the heterodimer composed of D-1 and D-2 subunits.     

Thylakoid membrane polypeptides of Chlamydomonas reinhardtii: wild-type and mutant strains deficient in photosystem II reaction center.

Unstacked thylakoid membrane vesicles were obtained from a homogenate of Chlamydomonas reinhardtii by flotation in a 1.8 M sucrose layer containing 5 mM HEPES (N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid)-10 mM EDTA (pH 7.5). Sodium dodecyl sulfate-gradient gel electrophoresis showed that the wildtype membranes have a total of at least 33 polypeptides ranging in molecular weights from 68,000 to less than 10,000. The wild-type and three non-photosynthetic mutant strains were studied with respect to their photosynthetic electron transport properties, their fluorescence rise kinetics, and their membrane polypeptide compositions. The results showed a strong correlation between the presence of a membrane polypeptide (molecular weight = 47,000) and the activity of the photosystem II reaction center. This polypeptide is missing from F34 (a mendelian mutant lacking Q, the primary electron acceptor of photosystem II), but is partially restored in a suppressed strain of F34 in which there is an incomplete recovery of photosystem II activity. In a thermosensitive mutant, T4, the same polypeptide is present in reduced amount only in cells grown at 35 degrees but not in those grown at 25 degrees. Evidence from fluorescence rise kinetics and partial photochemical reactions show that the cells grown at 25 degree are similar to wild-type cells but the cells grown at 35 degrees are greatly deficient in Q.     

Thickness determination of biological samples with a zeta-calibrated scanning tunneling microscope.

A single-tube scanning tunneling microscope has been zeta-calibrated by using atomic steps of crystalline gold and was used for measuring the thickness of two biological samples, metal-coated as well as uncoated. The hexagonal surface layer of the bacterium Deinococcus radiodurans with an open network-type structure shows thickness values that are strongly influenced by the substrate and the preparation method. In contrast, the thickness of the purple membrane of Halobacterium halobium with its densely packed less-corrugated structure exhibits very little variation in thickness in coated preparations and the values obtained are in good agreement with x-ray data.     

Evidence for a biological role in photosynthesis for cytochrome b-559--a component of photosystem II reaction center

Absorbance changes in untreated intact leaf discs, produced upon excitation with high-intensity red light, were shown to be due to the photooxidation of cytochrome b-559. At low intensities (<100 W/m2), photooxidation was almost undetectable. Photooxidation occurred with a half-time of 4.3 sec and an extent of 0.64 mol of cytochrome per 320 mol of chlorophyll. Upon transition to darkness, an additional oxidation occurred that exhibited faster kinetics (t/12 < 100 msec) and 0.32 mol of cytochrome was oxidized per 320 mol of chlorophyll. Photooxidation was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and was specifically induced by red light since far-red light did not cause any absorbance decrease. These results suggest that the redox changes of cytochrome b-559 are driven by photosystem II. Photooxidation was increased by 67% and its initial rate was doubled upon incubation of the leaf in carbonylcyanide p-trifluoromethoxy-phenylhydrazone. Exposure of the leaf to mild water stress or mild heat stress resulted in an increase in the extent of photooxidation and in a 6-fold decrease in the rate constant. Mild heat stress also induced a large increase of the rate constant for the dark reduction of the cytochrome. The dependence of photooxidation on high-intensity red light, its inhibition criteria, the fast transient dark oxidation, and enhancement of both photooxidation and dark transient oxidation by treatments that affect Z, the primary donor to P680, indicate that cytochrome b-559 in vivo is involved in cyclic electron flow around photosystem II. Its primary role in photosynthesis is to divert excess photons from a linear to a cyclic electron flow at high light intensities for protection of the D1 and D2 proteins against photodamage. Dark oxidation of the cytochrome is suggested to reflect a second role, that of deactivation of the powerful oxidant Z+ in the dark.     

Inflammatory bowel disease with thrombosis: a single center retrospective study

<正>Objective To analyze the clinical features and clinical significance of patients with inflammatory bowel disease (IBD) complicated by thrombosis. Methods From March 14th,2001 to February sixth 2017,at Nanjing General Hospital of Nanjing Military Command,27 IBD patients with thrombosis diagnosed by clinical symptoms,     

Treatment of renal diseases with plasma exchange: a single center experience

Over the last decades, plasma exchange (PE) has been applied in the treatment of over 150 different diseases including nephrological, hematological, neurological, and rheumatological. Clinical benefit has been demonstrated in only about 40 of them and the best results were achieved in diseases with pathogenic autoimmune mechanisms. We used PE most frequently in patients with immune and autoimmune nephropathies aiming to decrease pathologically elevated antibody levels, autoantibodies and immune complexes. PE was applied in 40 patients with chronic glomerulonephritis, 29 patients with lupus nephritis, and 9 patients with Schoenlein‐Henoch nephritis. After 3 to 4 PE sessions, continuous immunosuppressive drug therapy was initiated. Significant reduction of antibody titers and immune complexes was achieved. PE was also applied in 45 plasmacytoma patients with nephropathy to reduce plasma viscosity and slow down the progression of myeloma nephropathy. The result was a significant reduction of pathologically elevated plasma viscosity and a detoxification effect. In our clinic plasma exchange procedures were performed by either centrifugal method with Haemonetics M‐30 device or by plasma filtration. An average of 1316 mL plasma was removed during a PE session. For substitution purposes donor plasma and saline solutions were used. Clinical remission was achieved in 61.3% of all patients without slowing the progression of renal failure, however.     

Structure and structural transition of chiral domains in oligo(p-phenylenevinylene) assembly investigated by scanning tunneling microscopy

OPV3-CHO molecules are employed to prepare assembly on highly oriented pyrolytic graphite, and the so-prepared assembly is investigated by scanning tunneling microscopy. In the assembly chiral domains are observed with various structures such as linear and windmill. The chiral structural formation, stability, transition, and possible unification are intensively studied. After thermal annealing, linear structure was the only structure. To achieve a unified assembly with a single structure, an efficient method is proposed by coadsorption of OPV3-CHO with selected molecules. For example, an assembly with side-by-side helix structure is formed by a simple coadsorption of OPV3-CHO with alkyl bromide (C_nH_2n+1Br, n = 15–18). The experiments by cocrystallization of OPV3-CHO/C_nH_2n+1X (X = Cl, Br, and I) show the important role of halogen bonding in formation of the uniform structure. The results are significant in understanding the intermolecular noncovalent interactions that dominate the surface structure and chirality.