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J Heck

Publications and source records attributed to J Heck.

At least 19 recordsLinked to original sources
PubMed2001

Organometallic supramolecular chemistry with monosaccharides: triethylammonium mu-chloro-bis[chloro(eta5-cyclopentadienyl)-(methyl 4,6-o-benzylidene-beta-D-glucopyranosidato-1kappaO2,1:2kappaO3) zirconate].

The reaction of [CpZrCl3(thf)2] with methyl 4,6-O-benzylidene-beta-D-glucopyranoside (beta-MeBGH2, 1) in the presence of Et3N results in the formation of the zirconate complex [Et3NH] [(CpZrCl)2(mu-Cl) (mu-(beta-MeBG)]2] (2). X-ray structure analyses were performed from the ligand precursor beta-MeBGH2 1 as well as from 2. Compound 1 crystallizes in the monoclinic chiral space group P2(1). The molecules show a flat arrangement including the benzylidene protecting group, and are packed in columns. The columns are held together in pairs by the formation of hydrogen bonds between the hydroxy functions in positions 2 and 3. Compound 2 crystallizes in the orthorhombic space group P2(1)2(1)2(1). The beta-MeBG ligands are chelating the Zr atoms through the oxygen atoms in positions 2 and 3 of the glucopyranosidato ligand revealing a 1-zircona-2,5-dioxolane moiety each; the oxygen atom in position 3 is linked to both of the Zr atoms. Additionally one chloro ligand is bridging the two Zr centers. Two terminally bound chloro ligands stick out from the two Zr atoms into a chiral U-shaped cavity constructed by the two beta-MeBG ligands. The cavity incorporates the tertiary ammonium cation [Et3NH]+ which is bound to one of the terminal chloro ligands through a hydrogen bond. The inclusion of the [Et3NH]+ cation in the U-shaped cavity, even in solution, is demonstrated by NMR spectroscopic data.

Crystallography, X-Ray↗
PubMed2000

Electronic structure of [(CpCr)[(CO)3M]]mu-Cot (M = Cr, Fe): a theoretical study.

The electronic structure of two cyclooctatetraene-bridged dinuclear first-row transition metal complexes of the type [(CpM)[(CO)3M']]mu-Cot (M = Cr; M' = Fe (1), Cr (2)) was investigated by complete active space self-consistent field (CASSCF) calculations. In this context the differences in the binding capabilities of the complex fragments CpM and (CO)3M are discussed on the basis of extended Huckel molecular orbital (MO) calculations. The geometries used for the CASSCF calculations for complex 1 were obtained from the crystal structure. For 2 a model structure was established by geometry optimization using density functional methods. The CASSCF results agree well with the experimental findings and provide insight into the binding situation of the two compounds. Complex 1 can be regarded as being composed of a chromocene-like subunit CpCr(eta5-C5H5) and the fragment (CO)3Fe(eta3-C3H3). A direct metal-metal bond is found, involving one initially singly occupied orbital of each fragment, leading to a doublet ground state for 1 with the remaining unpaired electron localized at the chromium center. For 2 no such direct metal-metal bond can be recognized. A very weak direct metal-metal interaction is induced by electron donation from the Cot2- ligand into a formally unoccupied metal-metal binding orbital combination. In the quartet ground state all three unpaired electrons are localized at the chromium center of the formally doubly positive charged CpCr unit, on which complex fragment [(CO)3Cr(eta5-Cot)]2- acts like a cyclopentadienyl ligand. The coordination sphere of the chromium center of the CpCr unit resembles that of a metallocene metal center and its metal 3d occupation scheme corresponds to that of vanadocene.

Journal Article↗
PubMed1997

Intracellular structures of normal and aberrant Plasmodium falciparum malaria parasites imaged by soft x-ray microscopy.

Soft x-ray microscopy is a novel approach for investigation of intracellular organisms and subcellular structures with high spatial resolution. We used x-ray microscopy to investigate structural development of Plasmodium falciparum malaria parasites in normal and genetically abnormal erythrocytes and in infected erythrocytes treated with cysteine protease inhibitors. Investigations in normal red blood cells enabled us to recognize anomalies in parasite structures resulting from growth under unfavorable conditions. X-ray microscopy facilitated detection of newly elaborated structures in the cytosol of fixed, unstained, intact erythrocytes, redistribution of mass (carbon) in infected erythrocytes, and aberrant parasite morphology. In cysteine protease inhibitor-treated, infected erythrocytes, high concentrations of material were detected in abnormal digestive vacuoles and aggregated at the parasite plasma membrane. We have demonstrated that an abnormal host erythrocyte skeleton affects structural development of parasites and that this aberrant development can be detected in the following generation when parasites from protein 4.1-deficient red blood cells infect normal erythrocytes. This work extends our current understanding of the relationship between the host erythrocyte membrane and the intraerythrocytic malaria parasite by demonstrating for the first time that constituents of the erythrocyte membrane play a role in normal parasite structural development.

Animals↗
PubMed1997

Estrogen induction of plasma vitellogenin in the Kemp's ridley sea turtle (Lepidochelys kempi).

Estrogen stimulation of the production of teh yolk protein precursor vitellogenin was demonstrated in immature Kemp's ridley sea turtles. 17beta-Estradiol injection elicited an increase in serum estrogen, protein, protein phosphorus, and total calcium within 7 days. Associated with these changes was the appearance of a single, dimethylformamide-precipitable, 205-kDa estradiol-induced serum protein, which became the predominant serum protein identified by polyacrylamide gel electrophoresis. The effects of estradiol injection were maintained for 3 months following termination of estradiol administration, despite a decline in serum estrogen levels. Although studies in other species have indicated that changes in circulating vitellogenin levels can influence thyroid hormone transport, no changes were observed throughout the study in total blood levels of thyroxine or triiodothyronine or protein binding of these hormones. We conclude that in the immature Kemp's ridley estrogen induces the synthesis and secretion of a vitellogenin which resembles that of other reptiles, but which does not influence thyroid hormone transport. The prolonged presence of vitellogenin in the blood may be due to a lack of an active ovarian uptake mechanism in these immature animals.

Animals↗
PubMed1996

Local cerebral glucose utilization in fetal guinea pigs at 0.75 gestation.

OBJECTIVE: Using the 2-deoxyglucose method, measurements of local cerebral glucose utilization in large fetal animals are very difficult and expensive. To circumvent these problems we recently modified the 2-deoxyglucose method for use in the fetal guinea pig in utero (Berger et al., J Neurochem 1994; 63: 271-279). The present study was designed to measure the rates of local cerebral glucose utilization in fetal guinea pigs at 0.75 of gestation. STUDY DESIGN: After intravenous injection of 14C 2-deoxyglucose into the dams, local cerebral glucose utilization of the fetuses was measured from the time integral of the tracer in the maternal plasma and the autoradiographically determined concentration of the tracer in various parts of the fetal brain. RESULTS: Fetal cerebral glucose utilization was low as compared to adult animals and varied in different brain structures from 19 +/- 4 to 29 +/- 7 mumol/100 g/min. CONCLUSION: This study demonstrates the feasibility to measure local cerebral glucose utilization in undisturbed fetal guinea pigs in utero. We conclude that the low rate of cerebral glucose utilization and its small overall variability may reflect the neurological immaturity of the fetal brain.

Animals↗
PubMed1994

Extension of the 2-deoxyglucose method to the fetus in utero: theory and normal values for the cerebral glucose consumption in fetal guinea pigs.

Fetal cerebral metabolism changes during development. The normal fetal metabolic rate must be known to evaluate pathophysiological changes. Therefore, we determined the regional cerebral glucose consumption in the fetal guinea pig. This required the application of the 2-deoxyglucose method to this species. We measured both the transfer coefficients of deoxyglucose and glucose between the maternal arterial plasma and the fetal brain and the lumped constant in chronically prepared undisturbed guinea pig dams using a three-compartment model. Furthermore, the ratio between the initial clearances of deoxyglucose and glucose between the maternal arterial plasma and the fetal brain and the ratio between the phosphorylation coefficients of these substrates in the fetal brain were determined. The total cerebral glucose consumption measured by the deoxyglucose method (10 +/- 1.2 mumol/100 g/min) was similar to that calculated from the glucose concentration and the phosphorylation coefficient of glucose in the cerebrum (10 +/- 0.4 mumol/100 g/min). We conclude that the 2-deoxyglucose method is applicable to the guinea pig, and we further conclude that in the fetal guinea pig cerebral glucose consumption is 10 times lower than that in the adult.

Animals↗
PubMed1993

Drug testing.

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Journal Article↗
PubMed1991

[Cardiac involvement in non-Hodgkin's lymphoma].

In a 47-year-old man with non-Hodgkin's lymphoma which had been treated by polychemotherapy and radiation, cardiac involvement was suspected on computed tomography (CT) two years after diagnosis. The ECG demonstrated atrial flutter and a slow ventricular rate. After a further cycle of chemotherapy the patients declined further treatment. Two years later he was admitted urgently because of cardiac failure, atrial fibrillation with a slow ventricular rate, and clear signs of abnormal repolarization. CT of the thorax again provided signs of cardiac involvement with lymphoma. In addition there were extensive tumour infiltrates in the liver and paraaortic lymph-node. Despite intensive medical treatment he died shortly after admission from cardiac failure. At necropsy all four cardiac chambers and the coronary arteries were surrounded completely by tumour tissue. The membranous interventricular septum, the area of the Hiss bundle and the tricuspid and mitral valves had also been infiltrated. Histologically the infiltrates consisted of lymphoid cells of centrocytic type. Increasing tumour cell involvement went together with complete disintegration of myocardial fibres.

Arrhythmias, Cardiac↗
PubMed1988

Results of a stimulatory therapy of low bone metabolism in osteoporosis with (1-38)hPTH and diphosphonate EHDP. Protocol of study I, osteoporosis trial Hannover.

In contrast to prevention, the therapy of manifest osteoporosis remains a clinically significant problem. So far all therapeutic attempts have yielded unsatisfying results. For this reason we have tried to achieve a positive bone balance by sequential stimulation and inhibition of the osseous metabolism. The therapy consisted of six 14-day courses with 400 units (1-38)hPTH per day and, in addition, starting with the 2nd week of PTH therapy, EHDP 5 mg per kg body weight per day for a total of 2 weeks. Already the initial therapeutic course resulted in a stimulation of decreased bone metabolism which could be documented by an increase in the calcium-47 accretion rate (six patients). An increase of the alkaline phosphatase could be noted (four patients); this, however, did not correlate with the calcium accretion. A positive calcium balance could, nonetheless, only be attained in four of eight patients within this period, while neither the alkaline phosphatase nor the kinetics would allow a prediction of this effect. Changes of the balance coincided with equal changes in the net calcium absorption. The urinary calcium excretion increased temporarily during the therapeutic phase. We were not able to detect an influence on the vitamin D metabolites. Histomorphometric studies did not demonstrate an increase in bone mass in the iliac creast after six therapeutic courses. Nevertheless, progressive deformations of vertebral bodies did not occur. We conclude that already after 2 weeks this therapeutic concept can lead to a stimulation of bone metabolism.

Adult↗
PubMed1982

Substrate and product specificity of Arthrobacter sialophilus neuraminidase.

Arthrobacter sialophilus neuraminidase catalyzes the hydrolysis of N-acetylneuraminyl-alpha-oxygen, nitrogen, and azido glycosides. The most effective of those substrates examined was N-acetylneuraminyl-alpha-4-methylumbelliferylglycoside (AcNeu-alpha-4-MU; Km app, 0.0193 mM; kcat, 136.4 sec-1). The products resulting from the enzymic hydrolysis of N-acetylneuraminyl-alpha-azido-glycoside were N-acetylneuraminic acid and azide ion. N-acetylneuraminyl-alpha-2,3-thiogalactylglycoside and N-acetylneuraminyl-alpha-2,6-thiogalactylglycoside were competitive inhibitors of the enzyme having KI values of 1.52 mM and 1.70 mM, respectively. Dissociation constants for these thioglycosides were also determined by fluorescence enzyme titrations which gave values similar to those determined kinetically. N-Acetylneuraminic acid, but not its methyl ester, was a competitive inhibitor of neuraminidase. Its KI value, 0.18 mM, was also determined by both methods. 5-Acetamido-2,6-anhydro-3,5-dideoxy-D-glycero-D-talo-nonulosonic acid (2-deoxy-4-epi-AcNeu) was found to be a weak competitive inhibitor (KI, 12.1 mM). A. sialophilus neuraminidase further catalyzes transglycosidation reactions with methanol as acceptor. Methanol had no effect on the release of 4-MU by enzymatic hydrolysis of AcNeu-alpha-4-MU, suggesting that the formation of the enzyme-glycone intermediate is the rate-determining step. The anomeric configuration of the product of this reaction, as shown by 13C-nmr spectroscopy, is N-acetylneuraminyl-alpha-methylglycoside. Neuraminidase, therefore, catalyzes its reactions with overall retention of configuration.

Arthrobacter↗
PubMed1976

[Frequency and pathogenis of thrombocytopenia in cardiac failure].

In 395 consecutively investigated patients with cardiac failure of varying aetiologythe platelet ocurt in venous blood was less than 100 000/mm(3) in 5.3% and below the 2s devaition (less than 136 000/mm (3)) in 19.2. The average platelet count of the whole group was 197 500 +/- 70 800/mm (3) which was significantly lower (P less than 0.001) than in normal controls (n = 128). In 6 patients a (51)Cr study of platelet kinetics was performed; the results support the conclusion that the faculatative thrombocytopenia in cardiac failure is mainly,but not exclusively, due to an increased uptake of platelets in the congested spleen.

Blood Cell Count↗