Solvent response to fluorine-atom reaction dynamics in liquid acetonitrile.

Time-resolved infra-red (IR) absorption spectroscopy is used to follow the production of HF from the reaction of fluorine atoms in liquid acetonitrile (CH3CN). Photolysis of dissolved XeF2 using ∼50 fs duration, 267 nm laser pulses generates F atoms and XeF on prompt (sub-ps) timescales, as verified by broadband transient electronic absorption spectroscopy. The fundamental vibrational band of HF in solution spans more than 400 cm(-1) around the band centre at 3300 cm(-1), and analysis of portions of the time-resolved spectra reveals time constants for the rise in HF absorption that become longer to lower wavenumber. The time constants for growth of 40 cm(-1) wide portions of the IR spectra centred at 3420, 3320 and 3240 cm(-1) are, respectively, 3.04 ± 0.26, 5.48 ± 0.24 and 7.47 ± 0.74 ps (1 SD uncertainties). The shift to lower wavenumber with time that causes these changes to the time constants is attributed to evolution of the micro-solvation environment of HF following the chemical reaction. The initial growth of the high-wavenumber portion of the band may contain a contribution from relaxation of initially vibrationally excited HF, for which a time constant of 2.4 ± 0.2 ps is deduced from IR pump and probe spectroscopy of a dilute HF solution in acetonitrile.

A Multipronged Comparative Study of the Ultraviolet Photochemistry of 2-, 3-, and 4-Chlorophenol in the Gas Phase.

The S1((1)ππ*) state of the (dominant) syn-conformer of 2-chlorophenol (2-ClPhOH) in the gas phase has a subpicosecond lifetime, whereas the corresponding S1 states of 3- and 4-ClPhOH have lifetimes that are, respectively, ∼2 and ∼3-orders of magnitude longer. A range of experimental techniques-electronic spectroscopy, ultrafast time-resolved photoion and photoelectron spectroscopies, H Rydberg atom photofragment translational spectroscopy, velocity map imaging, and time-resolved Fourier transform infrared emission spectroscopy-as well as electronic structure calculations (of key regions of the multidimensional ground (S0) state potential energy surface (PES) and selected cuts through the first few excited singlet PESs) have been used in the quest to explain these striking differences in excited state lifetime. The intramolecular O-H···Cl hydrogen bond specific to syn-2-ClPhOH is key. It encourages partial charge transfer and preferential stabilization of the diabatic (1)πσ* potential (relative to that of the (1)ππ* state) upon stretching the C-Cl bond, with the result that initial C-Cl bond extension on the adiabatic S1 PES offers an essentially barrierless internal conversion pathway via regions of conical intersection with the S0 PES. Intramolecular hydrogen bonding is thus seen to facilitate the type of heterolytic dissociation more typically encountered in solution studies.

Assessing the Efficacy of Active Learning to Support Student Performance Across Undergraduate Programmes in Biomedical Science.

Introduction: Active learning is a useful tool to enhance student engagement and support learning in diverse educational situations. We aimed to assess the efficacy of an active learning approach within a large interprofessional first year Medical Cell Biology module taken by six healthcare programmes across the School of Biomedical Sciences at Ulster University, United Kingdom. Materials and methods: An active learning approach was developed for weekly formative assessment using Smartwork to design a weekly interactive multiple-choice quiz to reinforce key concepts specifically for each lecture. We tracked and assessed student performance in the module overall and in each element of course work and exam for 2 years prior to and following the introduction of an active learning strategy to engage and support learning for students from all academic backgrounds and abilities. Results: Full engagement with active learning was significantly associated with an increased overall module performance as well as a significantly increased performance in each element of class test (No engagement vs. Full engagement, p < 0.001), exam (No Engagement vs. Full engagement, p < 0.05) and coursework (No engagement vs. Full engagement, p < 0.001) within this overall total (No Engagement vs. Full engagement, p < 0.01). Partial engagement with active learning was associated significantly improved class test (No engagement vs. partially engaged, p < 0.001) and coursework (No engagement vs. partially engaged, p < 0.05) performance. While a trend toward increased performance in exam and overall module mark was observed, these were not significant. Discussion: Active learning is a useful tool to support student learning across a range of healthcare programmes taken by students with differing backgrounds and academic abilities in an interprofessional and widening participation setting. Student engagement in active learning was highlighted as a key contributory factor to enhanced student performance in all aspects of assessment.

Conformer specific dissociation dynamics of iodocyclohexane studied by velocity map imaging.

The photodissociation dynamics of iodocyclohexane has been studied using velocity map imaging following excitation at many wavelengths within its A-band (230 ≤ λ ≤ 305 nm). This molecule exists in two conformations (axial and equatorial), and one aim of the present experiment was to explore the extent to which conformer-specific fragmentation dynamics could be distinguished. Ground (I) and spin-orbit excited (I∗) state iodine atom products were monitored by 2 + 1 resonance enhanced multiphoton ionization, and total kinetic energy release (TKER) spectra and angular distributions derived from analysis of images recorded at all wavelengths studied. TKER spectra obtained at the longer excitation wavelengths show two distinct components, which can be attributed to the two conformers and the different ways in which these partition the excess energy upon C-I bond fission. Companion calculations based on a simple impulsive model suggest that dissociation of the equatorial (axial) conformer preferentially yields vibrationally (rotationally) excited cyclohexyl co-fragments. Both I and I∗ products are detected at the longest parent absorption wavelength (λ ∼ 305 nm), and both sets of products show recoil anisotropy parameters, ß > 1, implying prompt dissociation following excitation via a transition whose dipole moment is aligned parallel to the C-I bond. The quantum yield for forming I∗ products, Φ(I∗), has been determined by time resolved infrared diode laser absorption methods to be 0.14 ± 0.02 (at λ = 248 nm) and 0.22 ± 0.05 (at λ = 266 nm). Electronic structure calculations indicate that the bulk of the A-band absorption is associated with transition to the 4A(') state, and that the (majority) I atom products arise via non-adiabatic transfer from the 4A(') potential energy surface (PES) via conical intersection(s) with one or more PESs correlating with ground state products.

Studies of the putative transforming protein of the type I human T-cell leukemia virus.

The putative transforming protein of the type I human T-cell leukemia virus (HTLV-1) is a 40-kilodalton protein encoded by the X region and is termed p40XI. On the basis of both subcellular fractionation techniques and immunocytochemical analysis, it is now shown that p40XI is a nuclear protein with a relatively short half-life (120 minutes). It is synthesized de novo in considerable quantities in a human T-cell line infected with and transformed by the virus in vitro, and it is not packaged in detectable amounts in the extracellular virus.

Studies of the human c-myb gene and its product in human acute leukemias.

The myb gene is the transforming oncogene of the avian myeloblastosis virus (AMV); its normal cellular homolog, c-myb, is conserved across a broad span of evolution. In humans, c-myb is expressed in malignant hematopoietic cell lines and in primary hematopoietic tumors. Partial complementary DNA clones were generated from blast cells of patients with acute myelogenous leukemia. The sequences of the clones were compared to the c-myb of other species, as well as the v-myb of AMV. In addition, the carboxyl terminal region of human c-myb was placed in an expression vector to obtain protein for the generation of antiserum, which was used to identify the human c-myb gene product. Like v-myb, this protein was found within the nucleus of leukemic cells where it was associated with the nuclear matrix. These studies provide further evidence that c-myb might be involved in human leukemia.

Recombinant human granulocyte colony-stimulating factor: effects on normal and leukemic myeloid cells.

Experiments were conducted to isolate and characterize the gene and gene product of a human hematopoietic colony-stimulating factor with pluripotent biological activities. This factor has the ability to induce differentiation of a murine myelomonocytic leukemia cell line WEHI-3B(D+) and cells from patients with newly diagnosed acute nonlymphocytic leukemia (ANLL). A complementary DNA copy of the gene encoding a pluripotent human granulocyte colony-stimulating factor (hG-CSF) was cloned and expressed in Escherichia coli. The recombinant form of hG-CSF is capable of supporting neutrophil proliferation in a CFU-GM assay. In addition, recombinant hG-CSF can support early erythroid colonies and mixed colony formation. Competitive binding studies done with 125I-labeled hG-CSF and cell samples from two patients with newly diagnosed human leukemias as well as WEHI-3B(D+) cells showed that one of the human leukemias (ANLL, classified as M4) and the WEHI-3B(D+) cells have receptors for hG-CSF. Furthermore, the murine WEHI-3B(D+) cells and human leukemic cells classified as M2, M3, and M4 were induced by recombinant hG-CSF to undergo terminal differentiation to macrophages and granulocytes. The secreted form of the protein produced by the bladder carcinoma cell line 5637 was found to be O-glycosylated and to have a molecular weight of 19,600.

The age-related accumulation of a mitochondrial DNA control region mutation in muscle, but not brain, detected by a sensitive PNA-directed PCR clamping based method.

The peptide nucleic acid (PNA)-directed PCR clamping technique was modified and applied to the detection of mitochondrial DNA mutations with low heteroplasmy. This method is extremely specific, eliminating false positives in the absence of mutant molecules, and highly sensitive, being capable of detecting mutations at the level of 0.1% of total molecules. Moreover, the reaction can be multiplexed to identify more than one mutation per reaction. Using this technique, the levels of three point mutations, the tRNA(Leu(UUA)) 3243 mutation causing mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS); the tRNA(Lys) 8344 mutation causing myoclonic epilepsy and ragged red fibers (MERRF); and the nucleotide position 414 mutation adjacent to the control region promoters, were evaluated in human brain and muscle from individuals of various ages. While none of the mutations were detected in brain samples from individuals ranging in age from 23 to 93, the 414 mutation could be detected in muscle from individuals 30 years and older. These data demonstrate that the 3243 and 8344 mutations do not accumulate with age to levels greater than 0.1% in brain and muscle. By contrast, the 414 mutation accumulates with age in normal human muscle, though not in brain. The reason for the striking absence of the 414 mutation in aging brain is unknown.

Two versus six hours of bed rest following left-sided cardiac catheterization and a meta-analysis of early ambulation trials.

The present study and associated meta-analysis shows that 6 hours of bed rest after outpatient cardiac catheterization offers no advantage over 2 hours of bed rest with respect to groin bleeding complications. The occasional bleeding observed occurred shortly after ambulation rather than after discharge.

Clinical and cost comparison of ibutilide and direct-current cardioversion for atrial fibrillation and flutter.

The clinical effectiveness and cost to convert recent-onset atrial fibrillation or flutter to sinus after 3 to 4 weeks of anticoagulation with intravenous ibutilide was compared with direct-current cardioversion. The low success rate with ibutilide made direct-current cardioversion the more clinical and cost-effective method to restore sinus rhythm.

Ventricular fibrillation during coronary angiography in dogs: the role of calcium-binding additives.

Coronary angiography with Renografin 76 (RG76) occasionally results in ventricular fibrillation (VF). Angiovist 370 (AV370) is a contrast medium similar to RG76 except the calcium-sequestering agents, sodium citrate and EDTA in RG76 have been replaced by calcium EDTA. To determine whether these sequestering agents contribute to contrast medium-induced VF, a comparison was made of the effects of intracoronary injections of RG76, AV370, and saline solutions containing sodium citrate and EDTA (CIT/EDTA) and calcium EDTA (CA EDTA) on myocardial conduction, local QT intervals, and incidence of spontaneous and induced VF in 32 dogs. Four milliliters of RG76 produced a 111 +/- 12-ms increase in local QT intervals, compared with a 73 +/- 8-ms increase with AV370 (p less than 0.001). Spontaneous VF occurred in 12 of 16 six-milliliter injections of RG76, compared with 4 of 16 injections of AV370 (p less than 0.02) An early-cycle premature impulse applied after every fourth beat induced VF in 15 of 16 four-milliliter injections of RG76 compared with 5 of 16 injections of AV370 (p less than 0.01). As the premature beat conducted through the left anterior descending region, conduction slowing and fractionation occurred, which was less with AV370 than with RG76. The CIT/EDTA solution produced a greater increase in QT intervals (77 +/- 5 ms) than the CA EDTA solution (29 +/- 3 ms) or 0.9% saline solution alone (28 +/- 2 ms) (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant human granulocyte colony stimulating factor: molecular and biological characterization.

Human or rodent bone marrow treated with recombinant human granulocyte colony-stimulating factor (rhG-CSF) in a CFU-GM assay yield predominantly granulocytic colonies. The specificity for granulocyte progenitors in vitro is also demonstrated in vivo by a five- to six-fold elevation in hamster peripheral blood neutrophils. Other cell types (monocytes, lymphocytes and eosinophils) remain stable. Analysis of mRNA from the bladder carcinoma cell line 5637 (1A6) shows the predominant species of mRNA codes for a mature protein of 174 amino acids. A small fraction of the mRNA can code for an alternative form of hG-CSF containing additional three amino acids between positions 35 and 36.

The effect of sodium on the fibrillatory propensity of nonionic contrast media.

Removing sodium from standard ionic contrast media markedly increases the incidence of ventricular fibrillation in patients undergoing coronary angiography. Newer nonionic contrast media, iopamidol, iohexol, and ioversol contain only trace amounts of sodium. To determine whether sodium attenuates or potentiates ventricular fibrillation from nonionic contrast media, we measured the prolongation in QT interval and performed programmed electrical stimulation with one, two and three extra ventricular stimuli in 40 dogs during 4-mL intracoronary injections of iopamidol, iohexol, and ioversol. Solutions of each contrast medium with added NaCl at concentrations of 0.225%, 0.45%, and 0.9% were compared with standard contrast media. The addition of NaCl markedly increased the amount of QT interval prolongation produced by each contrast medium. With iopamidol, the amount of QT interval prolongation was 40 +/- 11 msec with standard iopamidol, but was 58 +/- 11 msec with 0.225% NaCl/iopamidol, 84 +/- 17 msec with 0.45% NaCl/iopamidol, and 132 +/- 42 msec with 0.9% NaCl/iopamidol (P less than .001). Similar results were seen with iohexol and ioversol. Ventricular fibrillation was difficult to induce with standard solutions of these agents (even with three extra stimuli), but became progressively easier to induce when NaCl was added. Three extra stimuli produced ventricular fibrillation in zero of 11 dogs with standard iopamidol, zero of 11 with 0.225% NaCl/iopamidol, three of 11 with 0.45% NaCl/iopamidol, and eight of 11 with 0.9% NaCl/iopamidol (P less than .001). Similar results were observed with iohexol and ioversol. The addition of choline chloride or dextrose did not increase ventricular fibrillation and QT interval prolongation. It is concluded that standard preparations of nonionic contrast media have a very low fibrillatory propensity.(ABSTRACT TRUNCATED AT 250 WORDS)

Contrast media-induced ventricular fibrillation. A comparison of Hypaque-76, Hexabrix, and Omnipaque.

Contrast media occasionally produce ventricular fibrillation during coronary angiography. We compared the fibrillatory propensity of the conventional ionic contrast medium, Hypaque-76 (H76) to the low osmolar ionic dimer Hexabrix (HB) and to the nonionic agent Omnipaque (OM) in 20 open chest anesthetized dogs. Intracoronary injection of 6 mL of contrast medium produced spontaneous ventricular fibrillation in four of ten dogs with H76, compared with two of ten with HB, and zero of ten with OM (P = .07). The induction of two premature beats by programmed stimulation of the myocardium during injection of 4 mL of contrast medium produced ventricular fibrillation in ten of ten dogs with H76, compared with three of ten with HB, and zero of ten with OM (P less than .001). Both H76 and HB produced ventricular fibrillation in ten of ten dogs when three premature beats were induced, compared with two of ten dogs with OM (P less than .001). Four mL H76 produced a 109 +/- 18 msec increase in the QT interval, compared with an 82 +/- 17 msec increase with HB, and a 45 +/- 12 msec increase with OM. We conclude that both low osmolar HB and OM are less fibrillatory than the conventional ionic medium H76, and that the nonionic medium OM is less fibrillatory than the ionic dimer contrast medium HB.

Effects of contrast media on the conducting system of the heart during coronary angiography. A comparison of Renografin-76 to Hypaque-76.

Electrocardiographic changes induced by ionic contrast media can cause complications during coronary angiography. A conduction delay through various parts of the heart is one factor in the genesis of asystole or ventricular fibrillation. Hypaque-76 (H76) and Renografin-76 (R76) are nearly identical ionic contrast media except that R76 binds more calcium than H76 because of the presence of sodium citrate and EDTA in R76. To determine whether the calcium binding additives in ionic contrast media contribute to the cardiac conduction abnormalities, we examined conduction time through the atrioventricular (AV) nodal tissue (via bipolar His bundle electrograms) and through the distal part of the conduction system (recording the QRS complex from the ECG) during coronary angiography. We injected 10 mL of H76 and R76 in 19 closed chest dogs in a blinded, randomized fashion during coronary angiography. The effects of H76 and R76 on heart rate, AH interval, HV interval, V interval and PR interval, and QRS complex duration were recorded. In 14 nonatrial pacing dogs, compared with H76, R76 produced a greater increase in the AV interval (32.9 +/- 6 milliseconds vs 12.4 +/- 2 milliseconds, P less than .01) and the PR interval (29.6 +/- 6 milliseconds vs 11.9 +/- 4 milliseconds, P less than .02). Additionally, the heart rate decreased 13.9 +/- 3.5 beats/minute from control with R76 compared with a decrease of 4.2 +/- 2.6 beats/minute from control with H76 (P less than .05). There was no significant difference between the prolongation of the HV interval and V interval, or QRS complex duration generated by R76 and H76.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of programmed electrical stimulation to assess the fibrillatory propensity of ionic and nonionic contrast media.

Coronary angiography occasionally results in ventricular fibrillation. To compare the fibrillatory propensity of conventional ionic and nonionic contrast media, we measured QT intervals and performed programmed electrical stimulation during intracoronary injection of Renografin 76 (R76), Hypaque 76 (H76), and iopamidol (IOP) in 16 open chest dogs. In ten dogs the incidence of ventricular fibrillation following induction of a single premature ventricular beat after every fourth atrial paced beat was 19/20 with R76, 8/20 with H76, and 0/20 with IOP (P less than .001). When two premature beats were induced, the incidence of ventricular fibrillation was 20/20 with R76, 19/20 with H76, and 1/20 with IOP (P less than .001). In six additional dogs, the mean prolongation of the QT interval was 170 +/- 20 msec with R76, 105 +/- 14 msec with H76, and 63 +/- 9 msec with IOP (P less than .001). Thus, programmed electrical stimulation readily induces ventricular fibrillation during intracoronary injection of conventional ionic contrast media. The incidence of ventricular fibrillation parallels the amount of QT interval prolongation produced. H76, which lacks EDTA and sodium citrate, is less fibrillatory than R76. However, the nonionic medium IOP appears far less fibrillatory than either R76 or H76.

Pacemaker malfunction: fact or artifact?

In summary, the present examples illustrate how pacemaker malfunction can be simulated by the sources of artifact produced or detected by the monitoring equipment. This form of pseudopacemaker malfunction remains a common cause of mistaken diagnosis of pacemaker malfunction. A thorough understanding of the examples outlined above should help distinguish true pacemaker malfunction from pseudopacemaker malfunction produced by artifact.

Simultaneous presence of a large coronary aneurysm and ectasia in a young patient with myocardial infarction--a case report.

Idiopathic or congenital coronary artery ectasias and aneurysms are uncommon forms of coronary artery disease. The prognosis and optimal management of such patients remains unknown. The authors describe the case of an otherwise healthy 30-year-old man with concomitant severe right coronary artery ectasia and left main coronary artery aneurysm who sustained a mild anterior myocardial infarction. There was no obstructive coronary artery disease, and no cause for the lesions could be identified. Chronic anticoagulation and antiplatelet therapy were initiated with resolution of symptoms.

Effects of treatment with thiamin antagonists, oxythiamin and pyrithiamin and of thiamin excess of the levels and distribution of thiamin in rat tissues.

Levels of thiamin and its derivatives in brain, heart and liver were determined in control, thiamin-deficient, pyrithiamin-treated and oxythiamin-treated rats at various times after the start of treatment. With 10 micrograms of thiamin/100 g/day subcutaneously, rats rapidly lost thiamin from the tissues until growth maintenance levels were reached. Oxythiamin had a minimal further effect on tissue thiamin while pyrithiamin caused further marked reduction. With higher levels of thiamin intake, tissue thiamin levels increased with intakes of up to 150-200 micrograms/100 g/day after which they did not show any further significant increase. Levels of pyrithiamin above 50 microgram/100 g/day for 20 days had only minimal further effect upon tissue thiamin levels over that with 50 micrograms.

Coronary stenting for coronary artery disease in a cardiac transplant recipient.

Accelerated coronary artery disease in the transplanted heart remains the leading cause of death in heart transplant recipients. Traditional treatment modalities have generally yielded sub-optimal results. Coronary artery stents are used frequently in the non-transplanted heart to treat coronary artery disease. Only a few cases using this approach in the cardiac transplant recipient have been reported. This report details the use of this modality in a transplant recipient with significant two-vessel coronary artery disease 11 years after orthotopic cardiac transplantation.