Chemistry. Snapshots of water at work.
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Comment↗
Biomedical subjects
Mark A Johnson
Publications and source records attributed to Mark A Johnson.
Spectroscopic determination of the OH- solvation shell in the OH-.(H2O)n clusters.
There has been long-standing uncertainty about the number of water molecules in the primary coordination environment of the OH- and F- ions in aqueous chemistry. We report the vibrational spectra of the OH-.(H2O)n and F-.(H2O)n clusters and interpret the pattern of OH stretching fundamentals with ab initio calculations. The spectra of the cold complexes are obtained by first attaching weakly bound argon atoms to the clusters and then monitoring the photoinduced evaporation of these atoms when an infrared laser is tuned to a vibrational resonance. The small clusters (n </= 3) display an isolated, sharp feature near the free OH stretching vibration, the signature of open solvation morphologies where each water molecule binds independently to the ion. Pronounced changes in the spectra are observed at n = 4 in the hydroxide ion and at n = 5 in the fluoride ion. In both cases, new features appear in the region typically associated with interwater hydrogen bonding. This behavior establishes that the primary hydration shells occur at n = 3 and 4 in hydroxide and fluoride, respectively.
Journal Article↗
On your mark, get set, GROW! LePRK2-LAT52 interactions regulate pollen tube growth.
Recent discoveries show that LAT52 and LePRK2, two pollen-specific proteins, interact in what might be an autocrine signaling system. This exciting finding indicates that successful fertilization requires ligand-receptor kinase signals that regulate pollen-tube growth. The stage is now set to identify other components of this pathway and to explore their connections with the many signals exchanged between pollen and pistil.
Fertility↗
Chemistry. Caught in the act of dissolution.
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Molecular aspects of halide ion hydration: the cluster approach.
This review provides a historical context for our understanding of the hydration shell surrounding halide ions and illustrates how the cluster systems can be used, in combination with theory, to elucidate the behavior of water molecules in direct contact with the anion. We discuss how vibrational predissociation spectroscopy, carried out with weakly bound argon atoms, has been employed to deduce the morphology of the small water networks attached to anions in the primary steps of hydration. We emphasize the importance of charge-transfer in the binary interaction, and discuss how this process affects the structures of the larger networks. Finally, we survey how the negatively charged water clusters (H2O)n(-) are providing a molecular-level perspective on how diffuse excess electrons interact with the water networks.
Journal Article↗
Plotting a course: multiple signals guide pollen tubes to their targets.
Pollen plays a critical role in the life cycle of all flowering plants, generating a polarized pollen tube that delivers sperm to the eggs in the interior of the flower. Pollen tubes perceive multiple extracellular signals during their extended growth through different floral environments; these environments discriminate among pollen grains, allowing only those that are appropriately recognized to invade. The phases of pollen tube growth include interactions that establish pollen polarity, entry of pollen tubes into female cell walls, and adhesion-based pollen tube motility through a carbohydrate-rich matrix. Recent studies have identified cells within the female germ unit as important sources of pollen guidance cues. Other signals undoubtedly exist, and their discovery will require genetic screens that target diploid tissues as well as haploid male and female cells.
Gene Expression Regulation, Plant↗
Massive life-threatening lower gastrointestinal hemorrhage following hemorrhoidal rubber band ligation.
Hemorrhoids are common, and a significant proportion of patients who have hemorrhoids experience symptoms such as bleeding, pain and itching. Endoscopic hemorrhoidal ligation is a safe and effective technique indicated for the treatment of grade 1 to 3 hemorrhoids, with a high success and low complication rate. Complications, when they occur, are minor and may include painful thrombosed prolapsed hemorrhoids, slippage of bands, minor rectal bleeding and chronic longitudinal ulcer. Rare, potentially life-threatening complications are massive hemorrhage and pelvic sepsis. A case of massive, life-threatening lower gastrointestinal hemorrhage following endoscopic hemorrhoidal rubber-band ligation is presented. Our patient ingested aspirin intermittently following the procedure. In a study documenting complications after hemorrhoidal band ligation, two of three individuals requiring transfusion for massive hemorrhage were taking aspirin on a regular basis. The risk of massive hemorrhage after hemorrhoidal rubber band ligation is probably increased by ingestion of nonsteroidal anti-inflammatory drugs. It may be wise to withhold such drugs soon after the procedure, if feasible.
Digestive System Surgical Procedures↗