bluuebunny/crossref_metadata_2025_split huggingface dataset:
Can shear stress direct stem cell fate?
Authors: Stolberg Sarah , McCloskey Kara E. 
Published: February 2009

AbstractMechanical forces are important signals in the development and function of the heart and lung, growth of skin and muscle, and maintenance of cartilage and bone. The specific mechanical force “shear stress” has been implicated as playing a critical role in the physiological responses of blood vessels through endothelial cell signaling. More recently, studies have shown that shear stress can induce differentiation of stem cells toward both endothelial and bone‐producing cell phenotypes. This review will highlight current data supporting the role of shear stress in stem cell fate and will propose potential mechanisms and signaling cascades for transducing shear stress into a biological signal. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009
Observing Proteins as Single Molecules Encapsulated in Surface‐Tethered Polymeric Nanocontainers
Authors: Rosenkranz Tobias , Katranidis Alexandros , Atta Diaa , Gregor Ingo , Enderlein Jörg , Grzelakowski Mariusz , Rigler Per , Meier Wolfgang , Fitter Jörg 
Published: February 2009

AbstractProtein unfolding inside immobilized polymerosomes: One of the most interesting properties of polymeric vesicles is their remarkable stability against extreme temperatures and osmotic stress, and their longevity even under harsh environmental conditions. We have demonstrated, in an application on protein folding, that surface‐tethered polymerosomes are suitable for performing time‐resolved single molecule studies with encapsulated proteins, as illustrated here.magnified imageImmobilizing biomolecules provides the advantage of observing them individually for extended time periods, which is impossible to accomplish for freely diffusing molecules in solution. In order to immobilize individual protein molecules, we encapsulated them in polymeric vesicles made of amphiphilic triblock copolymers and tethered the vesicles to a cover slide surface. A major goal of this study is to investigate polymeric vesicles with respect to their suitability for protein‐folding studies. The fact that polymeric vesicles possess an extreme stability under various chemical conditions is supported by our observation that harsh unfolding conditions do not perturb the structural integrity of the vesicles. Moreover, polymerosomes prove to be permeable to GdnHCl and, thereby, ideally suited for unfolding and refolding studies with encapsulated proteins. We demonstrate this with encapsulated phosphoglycerate kinase, which was fluorescently labeled with Atto655, a dye that exhibits pronounced photoinduced electron transfer (PET) to a nearby tryptophan residue in the native state. Under unfolding conditions, PET was reduced, and we monitored alternating unfolding and refolding conditions for individual encapsulated proteins.
Beyond Molecular Beacons: Optical Sensors Based on the Binding‐Induced Folding of Proteins and Polypeptides
Authors: Oh Kenneth J. , Cash Kevin J. , Plaxco Kevin W. 
Published: February 2009

AbstractA beacon in the night! The binding‐induced folding of otherwise unfolded biopolymers may prove a generic signal‐transduction mechanism for protein‐ and polypeptide‐based biosensors. An example of such a biosensor is illustrated here.magnified imageMany polypeptides and small proteins can be readily engineered such that they only fold upon binding a specific target ligand. This approach couples target recognition with a considerable change in polymer structure and dynamics. Recent years have seen the development of a number of biosensors that couple these large changes to readily measurable optical (fluorescent) outputs. These sensors afford the detection of a wide variety of macromolecular targets including proteins, polypeptides, and nucleic acids. Here we describe the design of such biosensors, from the first iterations as protein engineering experiments, to the development of biosensors targeting a range of protein and nucleic acid targets.
Insight Into the Defects of Cage‐Type Silica Mesoporous Crystals with Fd$\bar 3$m Symmetry: TEM Observations and a New Proposal of “Polyhedron Packing” for the Crystals
Authors: Han Lu , Sakamoto Yasuhiro , Che Shunai , Terasaki Osamu 
Published: February 2009

AbstractThe many faces of crystals: Silica mesoporous crystals were synthesized by using a co‐structure directing method. Structural defects in the crystals with Fd$\bar 3$m symmetry—described as tetrahedrally close‐packed and consisting of 512 and 51264 polyhedra—were found (see figure). These defects were explained through the use of simulated TEM images. The defect formation is also discussed.magnified imageSilica mesoporous crystals were synthesized by using a gemini cationic surfactant (C18‐3‐1) as the directing agent, carboxyethylsilanetriol sodium salt as the co‐structure directing agent (CSDA), and varying amounts of HCl. By using transmission electron microscopy (TEM) we observed 1) a structural change from the close‐packed structures of spherical micelles—face‐centered cubic (Fm$\bar 3$m) and hexagonal close‐packed (P63/mmc)—to Fd$\bar 3$m structures with an increase of HCl and 2) a few structural defects in the crystals with Fd$\bar 3$m symmetry. The structure of a crystal with Fd$\bar 3$m symmetry is described as one of the tetrahedrally close‐packed (tcp) structures consisting of 512 and 51264 polyhedra. The observed TEM images of the structural defects were explained well through use of simulated TEM images by introducing new 13–15 polyhedra comprising 51262, 51263, 4151062, 425865, and 4151064, which have been observed in bubbles by Matzke. The mesostructural changes and defect formation are discussed in terms of the hardness of micelles composed of surfactant/CSDA/silica species that have formed through a change of the interaction between the surfactant and CSDA, which causes the micelles to change from a regime of close‐packing to one of minimum‐area packing.
TiO2‐Modified Macroporous Silica Foams for Advanced Enrichment of Multi‐Phosphorylated Peptides
Authors: Wan Jingjing , Qian Kun , Qiao Liang , Wang Yunhua , Kong Jilie , Yang Pengyuan , Liu Baohong , Yu Chengzhong 
Published: February 2009

AbstractEnriching peptides: Novel TiO2‐modified macroporous materials (Ti‐MOSF, see figure) have been synthesized with high surface area, large pore volume, and functional surfaces that are rich in coordinatively unsaturated TiIV species, which can be applied in the specific extraction of phosphopeptides and which show a preferential capture of multi‐phosphorylated peptides with low detection limits and high selectivity.magnified image
Stoichiometric Valence and Structural Valence—Two Different Sides of the Same Coin: “Bonding Power”
Authors: Liebau Friedrich , Wang Xiqu , Liebau Waltrude 
Published: February 2009

AbstractTwo valencies instead of one!Stoichiometric valence and structural valence are two distinct properties of atoms. The former,stoichV, is derived from the composition of a compound and has integer values; the latter,structV, depends on the structure of a compound and has non‐integer values. The scheme shows a representation of valence states of antimony and oxidation of SbIIIto SbV, as a function of the eccentricity parameterΦi.magnified imageRecent studies use the term valence to describe two distinct aspects of the phenomenon bonding power of an atom. Measured in valence units, one valence term, the classical chemical valence, has integer values and is derived solely from the composition of a compound. The second one, used mainly by solid‐state physicists and crystallographers, has non‐integer values. It is determined from structure data, which are derived from diffraction experiments, spectroscopy, or quantum‐chemical calculations. To distinguish clearly between these two types of valencies, the descriptive termsstoichiometric valenceandstructural valenceand the respective symbolsstoichVandstructVshould be used. For the majority of crystalline structures, values ofstoichVandstructV, both measured in valence units, differ by less than 5 %. However, for p‐block atoms with one lone electron pair, differences betweenstoichVandstructVof up to 30 % have been reported.
Topology of Electron Charge Density for Chemical Bonds from Valence Bond Theory: A Probe of Bonding Types
Authors: Zhang Lixian , Ying Fuming , Wu Wei , Hiberty Philippe C. , Shaik Sason 
Published: February 2009

AbstractCovalent, ionic, or something new?A new interpretation of the topology of the electron density at the bond critical point is proposed to characterize covalent, ionic, and charge‐shift bonding from the density point of view (see figure). The topological properties of the density representation confirm the reality of charge‐shift bonds, in which the covalent contribution is weak or repulsive, and most of the bonding is due to the covalent–ionic resonance energy.magnified imageTo characterize the nature of bonding we derive the topological properties of the electron charge density of a variety of bonds based on ab initio valence bond methods. The electron density and its associated Laplacian are partitioned into covalent, ionic, and resonance components in the valence bond spirit. The analysis provides a density‐based signature of bonding types and reveals, along with the classical covalent and ionic bonds, the existence of two‐electron bonds in which most of the bonding arises from the covalent–ionic resonance energy, so‐called charge‐shift bonds. As expected, the covalent component of the Laplacian at the bond critical point is found to be largely negative for classical covalent bonds. In contrast, for charge‐shift bonds, the covalent part of the Laplacian is small or positive, in agreement with the weakly attractive or repulsive character of the covalent interaction in these bonds. On the other hand, the resonance component of the Laplacian is always negative or nearly zero, and it increases in absolute value with the charge‐shift character of the bond, in agreement with the decrease of kinetic energy associated with covalent–ionic mixing. A new interpretation of the topology of the total density at the bond critical point is proposed to characterize covalent, ionic, and charge‐shift bonding from the density point of view.
Mechanism of Pd(OAc)2/Pyridine Catalyst Reoxidation by O2: Influence of Labile Monodentate Ligands and Identification of a Biomimetic Mechanism for O2 Activation
Authors: Popp Brian V. , Stahl Shannon S. 
Published: February 2009

AbstractAerobic oxidation: Mechanisms of aerobic oxidation of the PdII(OAc)2/pyridine catalyst system were evaluated by using density functional theory methods. The results reveal that labile monodentate ligands, such as pyridine, favor a catalyst reoxidation pathway that proceeds via Pd0, rather than direct reaction of O2 with a PdII–hydride intermediate (see scheme).magnified imageThe mechanism of catalyst oxidation by O2 in Pd‐catalyzed aerobic oxidation reactions has been the subject of considerable debate, particularly with respect to the reactivity of PdII–hydride species. Here, we describe the use of unrestricted DFT computational methods to investigate the mechanism of catalyst reoxidation with the Pd(OAc)2/pyridine catalyst system, one of the most widely used catalysts. These studies probe four different pathways for the formation of a PdII–hydroperoxide species from the reaction of O2 from the corresponding PdII–hydride [(py)nPdII(H)OAc]: 1) a homolytic pathway involving hydrogen‐atom abstraction by O2; 2) AcOH reductive elimination to yield a Pd0 species that subsequently reacts with O2; 3) migratory insertion of O2 into a PdH bond; and 4) oxidative addition of O2 to PdII to yield a PdIV(η2‐peroxo) species. In contrast to previous studies of reactions between O2 and Pd–hydride species, the reductive‐elimination pathway (mechanism 2) is significantly more favorable than any of the other pathways. This outcome is traced to the presence of labile ligands (pyridine) that can readily dissociate from Pd to enable the hydride and acetate ligands to occupy cis‐coordination sites. These results strongly support the involvement of Pd0 as an intermediate in the catalytic cycle. Investigations of the mechanism of the reaction of O2 with the Pd0 intermediate revealed a novel, previously unrecognized mechanism that yields a Pd–OOH product without proceeding through the intermediacy of a PdII(η2‐peroxo) species. This mechanism resembles pathways commonly observed in biological O2 activation and suggests that noble‐metal and biological oxidation mechanisms may be more similar than previously appreciated.
Mesoporous Nanofibers from Dual Structure‐Directing Agents in AAO: Mesostructural Control and their Catalytic Applications
Authors: Lee Kyung Jin , Min Sa Hoon , Jang Jyongsik 
Published: February 2009

AbstractControl yourself! The mesoporous silica nanofibers (MSNFs) from dual structure‐directing agents were fabricated inside the pores of porous alumina (AAO, see figure) by using vapor phase synthesis. The pore structures could be controlled to form a range of structures from mesocellular foams to cylindrical mesopores with long‐range order by adding cationic cosurfactants.magnified image
Transportprozesse von Schüttungen aus Biomasse und Pyrolysaten im Drehrohr
Authors: Gómez A. , Klose W. 
Published: February 2009

AbstractDie Transportprozesse und die Verweilzeit von Schüttungen aus Biomasse und Pyrolysaten werden im einbautenlosen Drehrohr durch die Bestimmung der charakteristischen Winkel der Schüttungen untersucht. Zusätzlich werden die Einflüsse der Anwendung eines Wehres am Austritt des Reaktors auf die Transportprozesse und Verweilzeit ausgewertet. Die Nutzung von Wehren ermöglicht für die gleichen Prozessbedingungen die Zunahme des Füllungsgrades im Reaktor. Alle Versuche erfolgen bei Raumtemperatur.
Use of graded exercise testing in assessing the hypertensive patient
Authors: Millar‐Craig M. W. , Balasubramanian V. , Mann S. , Raftery E. B. 
Published: February 2009

AbstractTwenty‐five patients with suspected hypertension were studied using the “Oxford” continuous intra‐arterial blood pressure recording technique. Each patient carried out graded exercise on a bicycle ergometer, using a standard protocol, and then underwent a fully ambulatory 24‐h outpatient blood pressure recording. Using computer analysis, ambulatory blood pressure in each patient was characterised by measuring the mean daytime systolic and diastolic pressures. Exercise was found to be associated with a characteristic increase in systolic and diastolic blood pressure. Submaximal and maximal exercise blood pressures were shown to correlate strongly with ambulatory blood pressure. A much weaker correlation was found between clinic and ambulatory blood pressure. These findings suggest that the blood pressure response to exercise may be a better indicator of elevated blood pressure than a casual clinic blood pressure in individual borderline subjects.
Severe mitral stenosis secondary to massive calcification of the mitral annulus with unusual echocardiographic manifestations
Authors: Ramirez J. , Flowers N. C. 
Published: February 2009

AbstractIn mitral annular calcifications, hemodynamic documentation of a significant diastolic gradient across the mitral valve has been rarely demonstrated, and then only with the associated finding of a small left ventricular cavity with hypertrophic left ventricular wall. We present a patient with severe mitral annular calcification, with a significant diastolic gradient and unusual echocardiographic manifestations which include a densely calcified mitral valve annulus with anterior mitral valve leaflets consistent with what is seen in patients with mitral stenosis. When recordings were made immediately below the mitral valve annulus at the free edge of the mitral valve, its leaflets were seen departing in opposite directions, certainly not suggestive of outflow obstruction of the left atrium. Although in previous studies it has been suggested that mitral stenosis does not exist in the presence of mitral annulus calcification, our present report indicates that significant diastolic gradients can be found in patients with mitral annular calcifications. Because of the predominance of this condition in the elderly population, it is suggested that a more aggressive approach be taken in those patients in whom it is warranted by clinical circumstance.
Long‐term results of coronary artery bypass surgery for unstable angina: incidence of mortality, myocardial infarction, and angina resumption
Authors: Davidson D. M. , Lamb I. , Schroeder J. S. 
Published: February 2009

AbstractTo determine if routine treadmill testing would be helpful in identifying patients at high risk for subsequent events, the first 81 patients to undergo coronary artery bypass0 surgery for unstable angina pectoris at Stanford University Medical Center were reevaluated at four intervals after surgery. Evaluations, including assessment of angina pectoris and a treadmill test, were done at mean times of 18,40, and 72 months after surgery. At a mean time of 90 months postoperatively, angina status was determined in survivors. The prevalence of angina rose from 19% during the first year to 53% during the fourth and fifth postoperative years. Cardiac deaths and myocardial infarctions were frequent during the first postoperative year, and were more frequent in patients with three‐vessel disease and those with one or more severely narrowed coronary arteries which were not bypassed. Cardiac events were rare between 12 and 36 months after operation; clinical and treadmill variables did not predict these events. During the fourth and subsequent postoperative years, the incidence of cardiac events increased. While the presence of stable angina pectoris was the clinical variable most useful prognostically, treadmill testing added additional independent prognostic information (p<0.0001). During the intervals between visits 1 and 2, and visits 2 and 3, cardiac events were ten times more frequent in persons with a maximal heart rate of 130 beats/min or less on the treadmill at 18 and 40 months.We conclude that the prevalence of angina increased steadily during the first 5 postoperative years. Myocardial infarction and cardiac death rates were high during the first postoperative year, low during the second and third postoperative years, and then began to rise thereafter. The early events were more frequent in persons with three‐vessel disease and one or more severely narrowed coronary arteries which were unbypassed. The late events were more frequent in persons with a maximal heart rate of 130 beats/min or less on treadmill exercise testing. No other clinical or treadmill variables added additional independent prognostic information.
QTc intervals in acute myocardial infarction: First‐year prognostic implications
Authors: Helmers C. , Ahnve S. , Lundman T. , Rehnqvist N. , Sjögren A. 
Published: February 2009

AbstractCorrected QT (QTc) intervals were measured retrospectively in 160 consecutive survivors of acute myocardial infarction under 66 years of age. Calculations were made the first 2 d in the coronary care unit (CCU), the first post‐CCU day, at discharge, and at 1–3, 6, and 12 months after discharge. All patients were in sinus rhythm and without bundle branch block at discharge from the hospital. Sixteen patients died during the first follow‐up year. Twenty patients suffered a reinfarction, five of whom died.The highest QTc values were registered in the CCU and the lowest at the 1‐year control. Patients with subendocardial infarcts had longer QTc intervals than those with transmural infarcts, especially during the acute phase. Patients with inferior infarcts had shorter QTc intervals during the CCU period.Those who reinfarcted or died a cardiac death (particularly when sudden) during the follow‐up year had longer QTc intervals during the post‐CCU phase. A multivariate analysis of risk factors revealed that the QTc interval at discharge was of significant independent value for predicting major cardiac events after discharge from the hospital. It is concluded that repeated measurements of QTc may be of value when assessing prognosis after acute myocardial infarction.
The effect of intravenous nitroglycerin on coronary blood flow and infarct size during myocardial infarction in conscious dogs
Authors: Fukuyama T. , Roberts R. 
Published: February 2009

AbstractNitroglycerin (TNG), based on electrocardiographic evidence, has been shown to reduce myocardial ischemia, but its effect on morphometrically and enzymatically estimated infarct size has not been defined. Accordingly, coronary occlusion was produced in 50 conscious dogs without LV failure. Twenty‐five received TNG (200–300 m̈g/min i.v. for 8 h) and the results compared with those in 25 untreated dogs. Coronary blood flow was measured with 141Ce, 85Sr, and 95Nb (9 m̈m) after occlusion before TNG, 30 min after TNG, and again at 8 h. Mean blood pressure decreased from 103 to 84 mmHg with TNG vs. 99 to 94 mmHg in controls (p<0.02). Average heart rates were similar [135±26 vs. 120±33 beats/min (SD)]. TNG Did not increase total transmural coronary flow in any region but increased subendocardial flow in the central ischemic areas by 45% (0.09 ml/min/g vs. 0.13 ml/min/g). Animals were sacrificed after 24 h. Infarct size estimated morphometrically (25± 1.5 vs. 26± 1.5 of LV weight) and from myocardial CK depletion (23±2 vs. 23±2) was similar for the two groups. Thus, despite increased subendocardial flow, prolonged i.v. TNG did not decrease infarct size even though a difference of 15% would have been detected with this sample size. TNG May relieve coronary spasm but does not appear to be beneficial with sustained coronary occlusion.
Myoglobin and creatine kinase rates of release during acute myocardial infarction
Authors: Sylvén J. C. H. 
Published: February 2009

AbstractThe release of cardiac enzymes as an index of infarct size (IS) development was studied in patients with acute myocardial infarction (AMI) treated at a coronary care unit. Serial determinations of serum myoglobin (MG) and creatine kinase (CK) were made on 34 consecutive patients with duration of symptoms less than 6 h at admission and with initial CK values below the upper reference limit. Computer‐calculated CK‐IS was determined on the basis of the log‐normal algorithm. This was compared to discretely calculated CK and MG release.The correlation between computer‐ and discretely calculated cumulated CK release was 0.995 with a regression close to the line of equivalence.Computer‐calculated CK rates of release showed a one‐peak development, while, when discretely calculated, mostly three or four peaks were observed, as found also for MG rates of release. The occurrence of MG and CK peaks was related as indicated by a correlation coefficient of 0.75. The initial CK rate of release was slower when computer‐calculated.In the group studied, CK release began about 3 h post onset of symptoms, at which time 56% had an MG value above the upper reference limit. The CK and MG releases were finished about 31 and 36 h post onset of symptoms, respectively, with MG peaks at 6, 11, 19, and 22 h with corresponding CK peaks delayed 2, 3, 3, and 9 h. The first MG and CK peaks represented between 30 and 40% of the total release while the following three peaks represented between 20 and 30% each. Cumulative MG release was correlated to the time of AMI development. No such correlation was found for CK.The results indicate that the development of AMI is a wavelike process not sufficiently described by the log‐normal algorithm, on the basis of which, however, an index of total release might be obtained.