On the Stability of Clathrate Hydrates Encaging Polar Guest Molecules: Contrast in the Hydrogen Bonds of Methylamine and Methanol Hydrates

Abstract

The stability of clathrate hydrates encaging highly polar guests has been investigated in order to explain the experimental observation that some amines form clathrate hydrates but alcohols act as inhibitor to hydrate formation. We choose methylamine and methanol as guest species and examine the stable structure, at which the total potential energy has a minimum value. At the local minima of those two hydrates, the potential energies of water-water and guest-water, and their hydrogen bonded networks are compared. It is found that methanol does not retain the host lattice structure, while the host-network structure is kept in the presence of methylamine. It is shown that the difference in the magnitude of the partial charge on the hydrogen atom between the hydroxyl and amino groups plays a much more significant role on the stability of both clathrate hydrates than the difference in molecular geometry. This is supported from the result of a methylamine-like model that has the same partial charges on the atoms in the hydrophilic site as methanol.     

SV40 T-antigen is required for maintenance of immortal growth in SV40-transformed human fibroblasts.

Two lines of immortal human fibroblasts were isolated following transfection of TIG-3 cells with plasmid DNA, pMT-1ODtsA, that contained SV40 early gene with a deletion in replication origin and ts mutation in coding sequence for T-antigen. These cells continued proliferation at 34 degrees C, over 565 population doubling level (PDL) which is far over the limited division potential of untransformed normal TIG-3 of 70-80 PDL. When the culture temperature was shifted to 40 degrees C after 70 PDL, they ceased proliferation immediately. One of these immortal clones, SVts8, lost its ts phenotype after retransformation with wtT-antigen gene. These results indicated that the function of intact T-antigen is required for maintenance of immortal proliferation, at least in one of the SV40 transformed immortal clones.     

Calcium/phospholipid-dependent kinase recognizes sites in microtubule-associated protein 2 which are phosphorylated in living brain and are not accessible to other kinases

Microtubule-associated protein 2 (MAP-2) purified after microtubule assembly cycles from bovine brain had been shown to contain about 10 esterified phosphates (mol/mol), which were relatively phosphatase resistant and essentially confined to the projection domain which contributes to the visible arms on microtubules. The kinase responsible for phosphorylating these sites had not been identified. We have approached this question by using a phosphatase that releases the bulk of these residues and then determining which kinase can now add additional residues corresponding to those released. Three kinases were chosen because of their abundance in brain and/or proximity to microtubules. Of these only Ca/phospholipid-dependent kinase was able to recognize the previously occupied sites. We also found that MAP-2 isolated from rat brain without assembly cycles contained more phosphate than previously recognized, greater than 30 mol/mol, suggesting that 20 of these had been inadvertently released by phosphatase during assembly cycles. All 3 kinases (Ca/phospholipid-dependent, cAMP-dependent, and Ca/calmodulin-dependent kinase II) recognized more sites in the bovine than in the rat MAP-2.     

Peroxyoxalate chemiluminescent assay for oxidase activities based on detecting enzymatically formed hydrogen peroxide

A sensitive peroxyoxalate chemiluminescent (PO-CL) assay for activities of oxidases (uricase, choline oxidase, cholesterol oxidase and xanthine oxidase) which catalyse a formation of hydrogen peroxide was developed using 4,4′-oxalyl-bis[(trifluoromethylsulphonyl)imino]trimethylene-bis(4-methylmorpholinium)trifluoromethanesulphonate as a chemiluminogenic reagent and 2,4,6,8-tetramorpholinopyrimido[5,4-d]pyrimidine as a fluorophore. The standard curve for hydrogen peroxide was linear over the range 1 × 10^?7-1 × 10^?4 mol/L. Relative standard deviations for oxidase assays were 5.1–12.7% (n = 10). Detection limits were 1 × 10^?3 U/mL for uricase, 5 × 10^?4 U/mL for choline oxidase, 5 × 10^?3 U/mL for cholesterol oxidase and 5 × 10^?4 U/mL xanthine oxidase (sample to blank ratio, 3).     

Induction of histidine decarboxylase activity in mouse skin after application of indole alkaloids,a new class of tumor promoter

The effects of various promoters in two-step carcinogenesis on the induction of histidine decarboxylase in the skin of mice was investigated. The potencies of various phorbol esters in inducing histidine decarboxylase activity were parallel with their tumor-promoting activities. Indole alkaloids such as dihydroteleocidin B and lyngbyatoxin A, which induced ornithine decarboxylase and promoted tumor development in the skin of mice with the same potency as 12-O-tetradecanoylphorbol-13-acetate (TPA), also induced histidine decarboxylase activity. These results suggest that histamine produced by this inducible histidine decarboxylase may play some role in tumor promotion.     

Preparation of a fluorescent derivative of benzoylecgonine, and preliminary studies of its application to the analysis of urine

A sensitive high-performance liquid chromatographic method using 3-bromomethyl-6,7-dimethoxy-1-methyl-2(1H)-quinoxalinone (Br-DMEQ) as a fluorescent labeling reagent is described for the determination of benzoylecgonine (BE) and ecgonine (EC). The Br-DMEQ derivatives of BE and EC were separated on a C₁₈ column and detected at 455 nm with excitation at 370 nm. The detection limits of the proposed method were 18.7 fmol for BE and 12.5 pmol for EC at a signal-to-noise ratio of 3. Relative standard deviations of five replicate measurements were 1.94% (10 pmol) and 2.98% (50 pmol) for BE and 6.3% (250 pmol) and 5.62% (1.25 pmol) for EC. This method was applied to the determination of BE in human urine. BE was extracted from urine by solvent extraction with chloroform—isopropyl alcohol (9:1, v/v) solution. Levels of 2.5 · 10⁻⁸ M BE in urine (25 pmol/ml) could be determined.     

Macaque monkeys show reversed ocular following responses to two-frame-motion stimulus presented with inter-stimulus intervals

Journal of Computational Neuroscience - When two-frame apparent motion stimuli are presented with an appropriate inter-stimulus interval (ISI), motion is perceived in the direction opposite to the...