PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Silicon Compounds”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources
PubMed1984

Benzamidomethaneboronic acid: synthesis and inhibition of chymotrypsin.

Benzamidomethaneboronic acid (2) has been synthesized unambiguously from the reaction of dibutyl iodomethaneboronate and N-lithiohexamethyldisilazane to form dibutyl [bis(trimethylsilyl)amino]methaneboronate (4), which was desilylated, benzoylated, and hydrolyzed to 2. It has been shown that 2 is a strong competitive inhibitor of alpha-chymotrypsin (Ki = 8.1 X 10(-6) M, pH 7.5). The reaction product from dibutyl iodomethaneboronate and sodiobenzamide, previously shown to be a potent inhibitor of chymotrypsin, was shown by this work to be O-linked isomer, benzimidoxy-methaneboronic acid (3). The pH-Ki profile over the pH range 6.5-9.5 was consistent with the formation of an enzyme-inhibitor complex which resembled the metastable tetrahedral reaction intermediates occurring during acylation and deacylation of chymotrypsin-catalyzed hydrolysis.

Acylation↗
PubMed1976

Phosphorylation in isolated chloroplasts coupled to dichlorophenyldimethylurea-insensitive silicomolybdate reduction.

1. The electron transport in isolated chloroplasts with silicomolybdate as electron acceptor has been reinvestigated. The silicomolybdate reduction has been directly measured as deltaA750 or indirectly as O2 evolution (in the presence or absence of ferricyanide). 2. Silicomolybdate-dependent O2 evolution is inhibited to a similar extent by 3-(3,4-dichlorophenyl) 1, 1-dimethylurea (DCMU) or dibromothymoquinone (DBMIB), indicating the existence of two different sites of silicomolybdate reduction: one before the DCMU block (i.e. at Photosystem II) and one after the DBMIB block (i.e. at Photosystem I). 3. Silicomolybdate-dependent O2 evolution is coupled to ATP synthesis with an ATP/2e- ratio of 1.0 to 1.1. The presence of ferricyanide inhibits this ATP synthesis (ATP/2e- ratio then is about 0.3). 4. Silicomolybdate-dependent O2 evolution is also coupled to ATP-synthesis in the presence of DCMU with an ATP/2e- ratio of 0.6-0.8 characteristic of Site II; in this case the electron transport itself is not affected by uncouplers or energy-transfer inhibitors. 5. The data are interpreted as a further demonstration that the water-splitting reaction is responsible for the conservation of energy at Photosystem II.

Adenosine Triphosphate↗
PubMed1977

Pathways of silicomolybdate photoreduction and associated photophosphorylation in tobacco chloroplasts.

Three sites of silicomolybdate reduction in the electron transport chain of isolated tobacco chloroplasts are described. The relative participation of these sites is greatly influenced by the particular reaction conditions. One site (the only site when the reaction medium contains high concentrations of bovine serum albumin (greater than 5 mg/ml) is associated with Photosystem I, since it supports phosphorylation with a P/e2 value close to 1 and the reaction is totally sensitive to both plastocyanin inhibitors and 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Two other sites of silicomolybdate reduction are associated with Photosystem II. One site is 3-(3,4-dichlorophenyl)-1,1-dimethylurea insensitive and supports phosphorylation when the reaction mixture contains dimethyl sulfoxide and glycerol (protective agents). The P/e2 value routinely observed is about 0.2. Bovine serum albumin (1-2 mg/ml) can also act as a protective agent, but the efficiency of Photosystem II phosphorylation observed is lower. Silicomolybdate reduction supports virtually no phosphorylation, regardless of the reduction pathway, when the reaction mixture contains no protective agents. This is due to irreversible uncoupling by silicomolybdate itself. The silicomolybdate uncoupling is potentiated by high salt concentrations even if the presence of protective agents. Exposure of chloroplasts to silicomolybdate in the absence of protective agents rapidly inactivates both photosystems.

Binding Sites↗
PubMed1980

Two possible 3-(3,4-dichlorophenyl)-1,1-dimethylurea-insensitive sites in photosystem II of spinach chloroplasts.

Two possible 3-(3,4-dichlorophenyl)-1,1-dimethylurea-insensitive sites were found in PS II of spinach chloroplasts, depending on the pH of the assay medium used. The low site (pH 6) can be inhibited by certain quinolines, such as 8-hydroxyquinoline at concentrations less than 50 microM. The high pH site (pH 8) can be inhibited by disodium cyanamide, folic acid, or 5,6-benzoquinoline at concentrations from 50 microM to 5 mM. With the exception of orthophenanthroline, which stimulates the high pH site but does not show much inhibition at low pH, all other inhibitors gave opposite effects at the pH values used, i.e., they stimulated at low pH or inhibited at high pH, or vice versa. Several mechanisms for the observed effects are discussed.

Ammonium Chloride↗
PubMed1985

The cutaneous blood supply of the neck: relevance to incision planning and surgical reconstruction.

Previous descriptions of the blood supply of the neck have been contradictory. Neck dissections were performed on 17 adult cadavers after perfusion with radio-opaque microfil silicone rubber compound. In four cadavers cervical incisions were created and flaps elevated prior to perfusion to help demonstrate vascular pathways. In all cadavers myocutaneous perforators were seen passing from the sternocleidomastoid, strap muscles, and trapezius to supply the dermal-subdermal plexus. Also, there were consistently identifiable branches of the superior thyroid, posterior auricular, occipital, facial and transverse cervical arteries, which supply both the platysmal vascular plexus and the overlying dermal-subdermal plexus. The dermal-subdermal plexus is continuous across the midline and this contralateral pathway is supplied chiefly from branches of the superior thyroid artery, facial artery, and myocutaneous perforators of the strap muscles. This information may be useful in the planning of cervical incisions and the design of platysma myocutaneous flaps.

Adult↗
PubMed1993

Interaction of carbonyl cyanide m-chlorophenylhydrazone with the photosystem II acceptor side.

We show that CCCP, known as an uncoupler of photophosphorylation and an ADRY agent, inhibits FeCy photoreduction and coupled O2 evolution by isolated chloroplasts equally (I50 approximately 2 microM), but is practically without effect on the O2 evolution coupled with SiMo reduction within the 0.2-10 microM concentration range. CCCP has no effect on the nanosecond chlorophyll fluorescence in chloroplasts incubated at low light intensity, but decreases it at high light intensity. The electron transfer from reduced TMPD or duroquinol to methylviologen is resistant to CCCP. The efficiency of the CCCP inhibitory action on the FeCy photoreduction depends on the rate of electron flow, which is controlled by the light intensity. The data obtained show that CCCP is oxidized by the photosystem II donor side and is reduced by QP, competing for electrons with FeCy and the cytochrome blf complex.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1995

Molecular interactions of the redox-active accessory chlorophyll on the electron-donor side of photosystem II as studied by Fourier transform infrared spectroscopy.

A Fourier transform infrared (FTIR) difference spectrum upon photooxidation of the accessory chlorophyll (Chlz) of photosystem II (PS II) was obtained at 210 K with Mn-depleted PS II membranes in the presence of fericyanide and silicomolybdate. The observed Chlz+/Chlz spectrum showed two differential bands at 1747/1736 and 1714/1684 cm-1. The former was assigned to the free carbomethoxy C = 0 and the latter to the keto C = 0 that is hydrogen-bonded or in a highly polar environment. Also, the negative 1614 cm-1 band assignable to the macrocycle mode indicated 5-coordination of the central Mg. The negative 1660 cm-1 band, possibly due to the strongly hydrogen-bonded keto C = 0, may suggest oxidation of one more Chlz, although an alternative assignment, the amide I mode of proteins perturbed by Chlz oxidation, is also possible.

Cell Membrane↗
PubMed1986

Utility of specimen angiography in angiodysplasia of the colon.

This study reviews the utility of specimen angiography in identifying colonic lesions clinically thought to represent angiodysplasia. Four elderly patients presented with acute rectal bleeding. The diagnosis of angiodysplasia was made preoperatively in 3 patients by colonoscopy or angiography, or both. These specimens were injected with silicon rubber compound, xerographed, cleared with methyl salicylate, and examined with transillumination before histologic sampling. Although this technique was not used in the fourth case, fortuitous random sampling of the ascending colon revealed vascular changes indicative of angiodysplasia that correlated with a preoperative bleeding scan. Associated lesions in 1 patient were carcinoma of the colon and primary amyloidosis, the concurrence of which has not been described previously. With the injection technique the lesions of angiodysplasia appear grossly as spiderlike, dilated blood vessels. Microscopically, dilated veins, venules, and capillaries are found in the submucosa only or in the mucosa and submucosa. The importance of the postoperative injection is that it prevents the collapse of the blood vessels and enables the pathologist to identify the lesions grossly. As these lesions are usually small, this is important for proper sampling and histologic documentation.

Adenocarcinoma↗
PubMed1976

Thin-layer chromatography of homopyrimidazole derivatives.

The chromatographic behaviour of 14 homopyrimidazole derivatives has been studied on thin layers of silica gel, aluminium oxide and ammonia-saturated silica gel. The relationships between structure and chromatographic behaviour, as well as the most suitable systems for separating the individual derivatives, are discussed on the basis of RF values. The delta RMg values, showing the effect on the polarity, are given for certain functional groups.

Aluminum↗
PubMed1992

Cation-exchange liquid chromatography of choline and acetylcholine on free shielded silanols of silica-based reversed-phase stationary phases.

Free anionic functions present on the surface of reversed-phase packing materials were used for the selective cation-exchange preconcentration and separation of the neurotransmitters choline and acetylcholine from a biological matrix. The cation-exchange behaviour of different reversed-phase packing materials in the neat aqueous mobile phase, the properties of an end-capped column, the dependence of capacity factors and peak shape on the concentration of counter ions, ionic strength, pH and the addition of acetonitrile and optimum conditions for enzymatic conversion of solutes to hydrogen peroxide were studied. The studied reversed-phase columns exhibit better pH stability and longer lifetimes than normal silica-based cation exchangers. Acetylcholine is an effective and sensitive test sample for the measurement of adsorption on silica support. A large sample volume was injected onto a precolumn inserted instead of an injection valve and after injection the solutes were focused and separated on an analytical column with a mobile phase containing tetramethylammonium perchlorate as the counter ion.

Acetonitriles↗