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At least 1,387 records · Page 77Linked to original sources
PubMed2005

Enzymatic clipping of DNA wires coated with magnetic nanoparticles.

The study describes how DNA coated with magnetic nanoparticles remains biologically active and accessible to the BamH1 restriction enzyme. Long DNA molecules are coated with magnetic nanoparticles using electrostatic interactions. The coated, stretched, and surface-bound DNA is incubated in the restriction enzyme that specifically recognizes any strand containing the GGATCC base sequence and clips the DNA. We show that, despite the presence of the nanoparticles on the DNA, the enzyme is still able to recognize the cleavage site and effectively digest the assembly.

Bacteriophage lambda↗
PubMed2004

Metal clips induce folding of a short unstructured peptide into an alpha-helix via turn conformations in water. Kinetic versus thermodynamic products.

Short peptides corresponding to two to four alpha-helical turns of proteins are not thermodynamically stable helices in water. Unstructured octapeptide Ac-His1-Ala2-Ala3-His4-His5-Glu6-Leu7-His8-NH(2) (1) reacts with two [Pd((15)NH(2)(CH(2))(2)(15)NH(2))(NO(3))(2)] in water to form a kinetically stable intermediate, [[Pden](2)[(1,4)(5,8)-peptide]](2), in which two 19-membered metallocyclic rings stabilize two peptide turns. Slow subsequent folding to a thermodynamically more stable two-turn alpha-helix drives the equilibrium to [[Pden](2)[(1,5)(4,8)-peptide]] (3), featuring two 22-membered rings. This transformation from unstructured peptide via turns to an alpha-helix suggests that metal clips might be useful probes for investigating peptide folding.

Circular Dichroism↗
PubMed2006

Molecular tweezer and clip in aqueous solution: unexpected self-assembly, powerful host-guest complex formation, quantum chemical 1H NMR shift calculation.

The newly prepared water-soluble naphthalene tweezer 2a and anthracene clip 4a (substituted both with lithium methanephosphonate groups in the central spacer unit) undergo an unexpected self-assembly in aqueous solution. The highly ordered intertwined structures of the self-assembled dimers [2a]2 and [4a]2 were elucidated by quantum chemical 1H NMR shift calculations. 2a and 4a form extremely stable host-guest complexes with N-methylnicotinamide 8 in methanol and water as well. According to the thermodynamic parameters determined by 1H NMR titration experiments at various temperatures the self-assembly of 2a and 4a and their strong binding to NMNA 8 observed in aqueous solution are enthalpy driven (DeltaH << 0); the enthalpic driving force is partially compensated by an unfavorable entropy (TDeltaS < 0). Self-assembly and the host-guest binding are therefore beautiful examples of the nonclassical hydrophobic effect.

Journal Article↗
PubMed2006

Mimicking [2,2]paracyclophane topology: molecular clips for the coordination-driven cofacial assembly of pi-conjugated systems.

Self-assembly of CuI dimers, featuring a bridging phosphole ligand, and ditopic cyano-substituted chromophores affords nanosize supramolecular cationic rectangles. Due to the short Cu-Cu distance in the bimetallic clips, the coordinated chromophores are forced to participate in cofacial pi-pi interactions as evidenced by X-ray data. In addition, intermolecular pi-pi interactions in the solid state are observed leading to infinite columns of pi-stacked (para-phenylenevinylene)-based chromophores.

Journal Article↗
PubMed1999

Synthesis and Photophysical Properties of Porphyrin-Functionalized Molecular Clips.

Different clip-shaped receptor molecules functionalized at one side-wall with a porphyrin unit have been synthesized by a condensation involving a diamino glucoluril derivative and a porphyrin dione. A similar condensation reaction with a porphyrin tetraone resulted in porphyrin molecule with two receptor sites. The binding and photophysical properties of some of these porphyrin-receptor molecules are described.

Journal Article↗
PubMed2002

Self-assembly of molecular prisms via an organometallic "clip".

[reaction: see text] Under the appropriate conditions, the combination of two tritopic pyridyl ligands with three metal-containing molecular "clips" spontaneously generates supramolecular coordination cages with trigonal prismatic frameworks.

Magnetic Resonance Spectroscopy↗
PubMed2004

Strained aromatic oligoamide macrocycles as new molecular clips.

Can one join both ends of a helix? A helical aromatic oligoamide was macrocyclized into a saddle-shaped bifunctional clip molecule that self-assembles into discrete circular dodecamers in the solid state and shows great potential for binding aromatic acid guests in solution. The cyclization step requires that the helix is only partly denatured in the reaction medium.

Journal Article↗
PubMed2006

Subjective, behavioral, and physiological reactivity to ethnically matched and ethnically mismatched film clips.

This study examined whether individuals from 4 major ethnic groups within the United States (African American, Chinese American, European American, and Mexican American) showed greater subjective, behavioral, and physiological responses to emotional film clips (amusement, sadness, and disgust) with actors from their own ethnic group (ethnically matched) compared with actors from the other 3 ethnic groups (ethnically mismatched). Evidence showed greater responsivity to ethnically matched films for African Americans and European Americans, with the largest effect for African Americans. These findings were consistent across both sex and level of cultural identification. Findings of ethnic difference notwithstanding, there were many areas in which ethnic differences were not found (e.g., little or no evidence was found of greater response to ethnically matched films in Chinese-American or Mexican- American participants). These findings indicate that the emotional response system clearly reacts to stimuli of diverse ethnic content; however, the system is also amenable to subtle "tuning" that allows for incrementally enhanced responding to members of one's own ethnic or cultural group.

Adolescent↗
PubMedDate not supplied

Signal clipping by the rod output synapse.

The properties of synapses between retinal neurons make an essential contribution to early visual processing. Light produces a graded hyperpolarization in photoreceptors, up to 25 mV in amplitude, and it is conventionally assumed that all of this response range is available for coding visual information. We report here, however, that the rod output synapse rectifies strongly, so that only potential changes within 5 mV of the rod dark potential are transmitted effectively to postsynaptic horizontal cells. This finding is consistent with the voltage-dependence of the calcium current presumed to control neurotransmitter release from rods. It suggests functional roles for the strong electrical coupling of adjacent rods and the weak electrical coupling of adjacent rods and cones. The existence of photoreceptor coupling resolves the apparent paradox that rods have a 25 mV response range, while signals greater than 5 mV in amplitude are clipped during synaptic transmission. We predict that the strengths of rod-rod and rod-cone coupling are quantitatively linked to the relationship between the rod response range and the synapse operating range.

Animals↗
PubMed1985

Nephron responses to converting enzyme inhibition in non-clipped kidney of Goldblatt hypertensive rat at normotensive pressures.

To evaluate the effects of angiotensin converting enzyme inhibition (SQ 20881, CEI) on superficial nephron function of the non-clipped kidney in Goldblatt hypertensive rats in the absence of alterations in renal arterial pressure, control renal arterial pressure (RAP) was reduced first to the range generally obtained during CEI (124 +/- 4 mm Hg). RAP was maintained during the CEI period by adjustment of a suprarenal aortic clamp. At the reduced RAP, whole kidney and single nephron glomerular filtration rates (GFR) were reduced from the hypertensive levels and were lower than the measurements in normotensive control rats. During CEI, whole kidney GFR and single nephron GFR increased by 55 and 42%, respectively. There were decreases in absolute as well as fractional proximal reabsorption rates. In the intermediate nephron segment, fractional reabsorption was decreased, but absolute fluid reabsorption increased in proportion to the increased delivery rate. Proximal tubule and peritubular capillary hydrostatic pressures increased significantly during CEI also. These results indicate that an increased activity of the renin-angiotensin system occurring in Goldblatt hypertensive rats subjected to aortic constriction exerts effects to lower GFR and increase proximal reabsorption rate. The concomitant superficial nephron and whole kidney GFR responses to CEI when arterial pressure was maintained suggests that the pre-existing levels of angiotensin exerted similar influences on the total nephron population.

Angiotensin II↗
PubMed2005

A switchable macrocycle-clip complex that functions as a NOR logic gate.

We have synthesized a new molecular switch-based on a macrocycle-clip complex-whose switching behavior not only can be controlled through the use of either K+-[2,2,2]cryptand or NH4+-Et3N systems but also provides color changes that are visible to the naked eye; consequently, this system operates as a two-input NOR functioning molecular logic gate.

Journal Article↗
PubMed1983

A new mass-spectrometric C-terminal sequencing technique finds a similarity between gamma-interferon and alpha 2-interferon and identifies a proteolytically clipped gamma-interferon that retains full antiviral activity.

A novel mass-spectrometric technique is described that permits the identification of the C-terminal peptide of a protein. The technique involves the incorporation of 18O into all alpha-carboxy groups liberated during enzyme-catalysed partial hydrolysis of the protein, followed by mass spectrometry to identify as the C-terminal peptide the only peptide that did not incorporate any 18O. The technique has been used to identify the true C-terminal tryptic peptide of a bacterially produced gamma-interferon and to distinguish it from a peptide produced by anomalous tryptic cleavage. It was found that a closely similar sequence segment of bacterially produced alpha 2-interferon undergoes an analogous cleavage. The technique was also used to identify the C-terminus of a clipped gamma-interferon that retains full antiviral activity.

Amino Acid Sequence↗
PubMed1980

Baroreflex sensitivity changes during the development of Goldblatt two-kidney one-clip hypertension in rats.

1. The time course of changes in baroreceptor reflex sensitivity during the development of renovascular hypertension was studied in male Wistar rats in which the left renal arteries were constricted by silver wire clips of 0.18 mm internal diameter. 2. Groups of animals were studied at 3, 7, 14 and 25 days after induction of renovascular hypertension. Rats of comparable ages were included as controls. There was a significant decrease in mean baroreflex sensitivity from 0.950 +/- 0.157 ms/mmHg (n = 8) in the normal control group to 0.537 +/- 0.105 ms/mmHg (n = 8) in the 3 day hypertensive group (P < 0.05). Baroreflex sensitivity in the 3 day hypertensive rats was independent of the level of arterial pressure achieved in individual animals. 3. These changes in baroreflex sensitivity at 3 days precede the development of left ventricular hypertrophy and, as previously shown in this model, also precede structural vascular adaptation and resetting of the carotid sinus baroreceptor threshold. 4. A further loss of baroreflex sensitivity, which may be structurally based, occurred later. Baroreflex sensitivity in the 14 day hypertensive rats fell to 0.182 +/- 0.039 ms/mmHg (n = 8) compared with the 3 day hypertensive rats (P < 0.01).

Animals↗
PubMed1980

Impaired autoregulatory responses in contralateral kidneys of two-kidney, one-clip hypertensive rats.

1. Micropuncture and clearance experiments in two-kidney, one-clip renal vascular hypertensive rats examined the ability of the kidney contralateral to renal vascular stenosis to maintain renal function during conditions of reduced renal arterial blood pressure. 2. At their respective spontaneous blood pressures, renal vascular resistance was higher and glomerular filtration rate (GFR) and renal blood flow were not different in the contralateral kidneys of the hypertensive rats (170 +/- 5 mmHg) compared with normal animals (129 +/- 1 mmHg). Urine flow and absolute and fractional excretion of electrolyte were greater from the kidneys of the hypertensive animals. However, pressures in cortical structures were similar in the two groups. 3. As blood pressure was reduced acutely, the kidney contralateral to the renal artery stenosis achieved only small decreases in renal vascular resistance that failed to allow GFR, renal blood flow or pressures in cortical structures to be maintained. In contrast, normal rats efficiently autoregulated renal vascular resistance to allow GFR, renal blood flow and cortical pressures to be unchanged as blood pressure was altered between 130 and 115 mmHg. Urine flow and electrolyte excretion decreased to a greater extent in the hypertensive kidneys; at comparable blood pressure these indices of excretory function were not different in the two groups. 4. These observations indicate that the contralateral kidney can maintain normal haemodynamic and glomerular function only at elevated blood pressure and suggest the possibility that the impaired capacity to autoregulate renal resistances may contribute to the maintenance of hypertension observed in this model.

Animals↗
PubMed1981

Chemical renal medullectomy; effect upon reversal of two-kidney, one-clip hypertension in the rat.

1. Chemical renal medullectomy was produced in rats by injection of 2-bromoethylamine hydrobromide. Plasma creatinine and blood pressure were unchanged although urine volume was increased fourfold. 2. Left renal artery constriction resulted in similar degrees of hypertension in both intact and medullectomized rats. This was associated with a significantly smaller rise in plasma renin concentration in the latter. 3. Blood pressure in conscious intact hypertensive rats became normal within 24 h of unclipping whereas blood pressure of medullectomized rats remained significantly elevated. 4. The presence of an intact renal medulla is essential to the complete reversal of two-kidney, one-clip hypertension in the rat. This may reflect the loss of a medullary vasodepressor system.

Animals↗
PubMed1983

Kinetics of proliferation of rat aortic smooth muscle cells in Goldblatt one-kidney, one-clip hypertension.

Wistar female rats were made hypertensive by applying a silver clip to the left renal artery and removing the right kidney. In aortas, the proliferation fraction of smooth muscle cells, DNA synthesis and wet weight have been correlated with the blood pressure increase subsequent to the operation. A wave of proliferation of smooth muscle cells in the aortic media is triggered immediately after the highest increased rate of blood pressure. When blood pressure stabilizes at high values, the metabolism of nucleic acid within the aortic media resumes its normal level but the arterial changes previously established persist. The sequence of pathological events responsible for these changes could be: increment of blood pressure; increase in wall stress; proliferation of smooth muscle cells; thickening of arterial wall; correction of the wall stress; end of proliferation. The consequence of this early proliferation of aortic smooth muscle cells is not clear but it is probably one of the mechanisms through which high blood pressure is sustained. It can also participate in atherogenesis, being in this way one of the bases of the well-known relationship between hypertension and atherosclerosis.

Animals↗