Shining light on fluoride detection: a comprehensive study exploring the potential of coumarin precursors as selective turn-on fluorescent chemosensors

In this study, we report a fluoride chemosensor based on the use of a non-fluorescent pre-coumarin, compound 1. This compound undergoes selective fluoride-triggered formation of coumarin 2, with a concomitant turn-on fluorescence signal. Although compound 1 exists as a mixture of alkene isomers (2 : 1 in favor of the E isomer), only the minor Z-isomer undergoes cyclization. Nonetheless, comprehensive computational and experimental studies provide evidence that in situ isomerization of E-1 to Z-1, followed by fluoride-triggered phenolate evolution and intramolecular cyclization, facilitates the generation of coumarin 2 in high yield. Moreover, this system is an effective turn-on fluorescence sensor for fluoride anions, which displays outstanding selectivity (limited response to other commonly occurring analytes), sensitivity (lowest reported limits of detection for this sensor class), and practicality (works in solution and on paper to generate both fluorometric and colorimetric responses). Ongoing efforts are focused on expanding this paradigm to other pre-coumarin scaffolds, which also undergo analyte-specific coumarin formation accompanied by turn-on fluorescence.

Thioxobimanes

Dioxobimanes, colloquially known as bimanes, are a well-established family of N-heterobicyclic compounds that share a characteristic core structure, 1,5-diazabicyclo[3.3.0]octadienedione, bearing two endocyclic carbonyl groups. By sequentially thionating these carbonyls in the syn and anti isomers of the known (Me,Me)dioxobimane, we were able to synthesize a series of thioxobimanes, representing the first heavy-chalcogenide bimane variants. These new compounds were extensively characterized spectroscopically and crystallographically, and their aromaticity was probed computationally. Their potential role as ligands for transition metals was demonstrated by synthesizing a representative gold(I)-thioxobimane complex.

Reaction of FeaqII with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of FeaqIV and Carbonate Radical Anions

Many advanced oxidation processes (AOPs) use Fenton-like reactions to degrade organic pollutants by activating peroxymonosulfate (HSO₅^-, PMS) or peroxydisulfate (S₂O₈^2-, PDS) with Fe(H₂O)₆²⁺ (Fe_aq^II). This paper presents results on the kinetics and mechanisms of reactions between Fe_aq^II and PMS or PDS in the absence and presence of bicarbonate (HCO₃^-) at different pH. In the absence of HCO₃^-, Fe_aq^IV, rather than the commonly assumed SO₄^•-, is the dominant oxidizing species. Multianalytical methods verified the selective conversion of dimethyl sulfoxide (DMSO) and phenyl methyl sulfoxide (PMSO) to dimethyl sulfone (DMSO₂) and phenyl methyl sulfone (PMSO₂), respectively, confirming the generation of Fe_aq^IV by the Fe_aq^II-PMS/PDS systems without HCO₃^-. Significantly, in the presence of environmentally relevant concentrations of HCO₃^-, a carbonate radical anion (CO₃^•-) becomes the dominant reactive species as confirmed by the electron paramagnetic resonance (EPR) analysis. The new findings suggest that the mechanisms of the persulfate-based Fenton-like reactions in natural environments might differ remarkably from those obtained in ideal conditions. Using sulfonamide antibiotics (sulfamethoxazole (SMX) and sulfadimethoxine (SDM)) as model contaminants, our study further demonstrated the different reactivities of Fe_aq^IV and CO₃^•- in the Fe_aq^II-PMS/PDS systems. The results shed significant light on advancing the persulfate-based AOPs to oxidize pollutants in natural water.

A dipodal bimane-ditriazole-diCu(II) complex serves as an ultrasensitive water sensor

An ultrasensitive fluorescent water sensor based on a dipodal bimane-Cu(II) complex is reported here. This complex, which is non-fluorescent in the absence of water, demonstrates a remarkable turn-on fluorescence in the presence of extremely low (0.000786% v/v) concentrations of water, via highly selective water-induced displacement of copper and restoration of the innate bimane fluorescence.

Reaction of H2 with polyoxometalate supported Rhodium(0) and Iridium(0) nanoparticles in aqueous suspensions: a kinetic study

The mechanism of the reaction between Rh0 and Ir0 NPs with H2 was measured in the absence of an electrical bias via monitoring the catalytic reduction of PW12O403− and it was compared to the previous results of Pt0 NPs.

Discovery of Dolastatinol: A Synthetic Analog of Dolastatin 10 and Low Nanomolar Inhibitor of Tubulin Polymerization

We developed a highly potent anticancer agent, dolastatinol, which is a methylene hydroxyl derivative of dolastatin 10. Dolastatinol is a synthetic analog of dolastatin 10, synthesized by a solid-phase peptide Fmoc chemistry protocol on 2-chlorotrityl chloride resin utilizing a pH-triggering self-immolative monosuccinate linker. The introduction of the C-terminus hydroxyl methylene functionality preserves the anticancer properties of the parent dolastatin 10, including strong suppression of the cell proliferation, migration, high cytotoxicity. Our research establishes a new facile route toward the further development of C-terminus-modified dolastatin-10-based microtubule inhibitors for anticancer treatment.

The Role of Common Alcoholic Sacrificial Agents in Photocatalysis: Is It Always Trivial?

Photocatalytic hydrogen production is proposed as a sustainable energy source. Simultaneous reduction and oxidation of water is a complex multistep reaction with high overpotential. Photocatalytic processes involving semiconductors transfer electrons from the valence band to the conduction band. Sacrificial substrates that react with the photochemically formed holes in the valence band are often used to study the mechanism of H₂ production, as they scavenge the holes and hinder charge carrier recombination (electron-hole pairs). Here, we show that the desired sacrificial agent is one forming a radical that is a fairly strong reducing agent, and whose oxidized form is not a good electron acceptor that might suppress the hydrogen evolution reaction (HER). In an acidic medium, methanol was found to fulfill both these requirements better than ethanol and propan-2-ol in the TiO₂ -(M⁰ -NPs) (M=Au or Pt) system, whereas in an alkaline medium, the alcohols exhibit a reverse order of activity. Moreover, we report that CH₂ (OH)₂ is by far the most efficient sacrificial agent in a nontrivial mechanism in acidic media. Our study provides general guidelines for choosing an appropriate sacrificial substrate and helps to explain the variance in the performance of alcohol scavenger-based photocatalytic systems.

Surface modifications of carbon nanodots reveal the chemical source of their bright fluorescence

Fluorescent carbon nanodots (CNDs) have drawn increasing attention in recent years. These cost-effective and eco-friendly nanomaterials with bright fluorescence have been investigated as promising materials for electrooptic and bioimaging applications. However, the chemical source stimulating their strong fluorescence has not been completely identified to date. Depending on the chemical composition, two absorption peaks are observed in the visible range. In this study, we applied selected chemical modifications to CNDs in order to elucidate the correlation between the chemical structure and optical behavior of CNDs. Varying the amount of acetic acid in the synthesis process resulted in different effects on the absorbance and fluorescence photo-spectra. Specifically, at a low concentration (10%), the fluorescence is dramatically red shifted from 340 to 405 nm. Comprehensive characterization of the chemical modification by FTIR and XPS allows identification of the role of acetic acid in the reaction mechanism leading to the modified photoactivity. The functional group responsible for the 405 nm peak was identified as HPPT. We describe a chemical mechanism involving acetic acid that leads to an increased concentration of HPPT groups on the surface of the CNDs. Applying two additional independent chemical and consequently optical modifications namely solution pH and annealing on the nanodots further supports our proposed explanation. Understanding the molecular origin of CND fluorescence may promote the design and control of effective CND fluorescence in optical applications.

Kinetics of the reaction of H2 with Pt0-nanoparticles in aqueous suspensions monitored by the catalytic reduction of PW12O403−

The mechanism of the reaction between Pt⁰ nanoparticles and Hydrogen was measured in the absence of an electric field via following the formation of PW₁₂O₄₀^4−/5−.

Carbonate-radical-anions, and not hydroxyl radicals, are the products of the Fenton reaction in neutral solutions containing bicarbonate

The Fenton reaction, Fe(H₂O)₆²⁺ + H₂O₂ → Oxidizing product, is of major importance in biology as the major cause of oxidative stress, and in advanced oxidation processes. It is commonly assumed that ·OH is the product of the Fenton reaction. The results presented herein point out that ·OH is indeed the oxidizing product in acidic solutions for [Fe(H₂O)₆²⁺] > [H₂O₂]; Fe^IV_aq is the active oxidizing product in neutral solutions; in slightly acidic solutions for [H₂O₂] > [Fe(H₂O)₆²⁺] a mixture of ·OH and Fe^IV_aq is formed. However CO₃·^- is the active oxidizing product in neutral solutions containing HCO₃^- even at low concentrations, i.e. under physiological conditions. The implications to our understanding of the origins of oxidative stress and of catalytic oxidations in advanced oxidation processes are discussed.

Visual Function during Acute Hypoglycaemia

Hypoglycaemia symptoms are of particular interest in view of the importance of hypoglycaemia unawareness. Visual symptoms arising during acute hypoglycaemia may be the result of metabolic disturbances in the visual pathways within the central nervous system or impairment of the refractive apparatus of the eye and binocular function. This study investigated the effect of hypoglycaemia upon visual acuity, binocular interaction and contrast sensitivity. Various aspects of visual function were examined in ten normal subjects before, during and after acute insulin-induced hypoglycaemia. A simultaneous study of hypoglycaemic symptoms enabled us to relate the objective findings to the symptoms as reported by the subjects. Snellen visual acuity, fusion and stereopsis were not affected by hypoglycaemia. Five subjects noted visual disturbance. Eight developed significant impairment of contrast sensitivity, which closely matched the lowered blood glucose concentration.

These observations suggest that hypoglycaemic visual symptoms are due to neuroglycopenia of central visual pathways rather than changes within the refractive apparatus or abnormality of binocular function. Although these symptoms are not a constant feature of the hypoglycaemic state, subtle impairment of visual function occurs in most cases. Contrast sensitivity testing can be useful for assessment of fine changes in visual function.

Contamination from Syringes and Blood Container Pots in Trace Element Analysis

Syringes, blood container pots and test tubes have been investigated to determine whether they act as sources of contaminants during trace element analyses. Urine containers were investigated to decide which materials do not absorb mercury from dilute solutions.

No copper and little magnesium contamination was found. Zinc contamination was unpredictable. Very large amounts of zinc leached from the rubber end cap of the piston of disposable, plastic sterile syringes.

The B.S.I. Standards for disposable syringes were shown to be unacceptable for heavy metals.

Notes on the Radioimmunoassay of Human Thyrotrophin

This paper describes the use of screened transfusion plasma as a source of human thyroid stimulating hormone (h-TSH) free protein for standardization of a conventional “double antibody” h-TSH radioimmunoassay. Serum and plasma immunoreactive h-TSH levels have been shown to be stable for up to four days at 4°C and 25°C. A 37°C incubation procedure has been developed which gives an acceptable standard curve, but with some loss of “between batch” precision.

(1)H NMR studies distinguish the water soluble metabolomic profiles of untransformed and RAS-transformed cells

Metabolomic profiling is an increasingly important method for identifying potential biomarkers in cancer cells with a view towards improved diagnosis and treatment. Nuclear magnetic resonance (NMR) provides a potentially noninvasive means to accurately characterize differences in the metabolomic profiles of cells. In this work, we use (1)H NMR to measure the metabolomic profiles of water soluble metabolites extracted from isogenic control and oncogenic HRAS-, KRAS-, and NRAS-transduced BEAS2B lung epithelial cells to determine the robustness of NMR metabolomic profiling in detecting differences between the transformed cells and their untransformed counterparts as well as differences among the RAS-transformed cells. Unique metabolomic signatures between control and RAS-transformed cell lines as well as among the three RAS isoform-transformed lines were found by applying principal component analysis to the NMR data. This study provides a proof of principle demonstration that NMR-based metabolomic profiling can robustly distinguish untransformed and RAS-transformed cells as well as cells transformed with different RAS oncogenic isoforms. Thus, our data may potentially provide new diagnostic signatures for RAS-transformed cells.

Abstract 1840: Metabolomic profiling of gastrointestinal stromal tumor (GIST) T1 cell lines in response to imatinib therapy

Background: There is a growing need for novel drugs to treat drug resistant GIST. The aim of this study was to evaluate chronological metabolic changes in GIST cells treated with imatinib mesylate.

Methods: Human GIST T1 cells were incubated with imatinib 0.5 mM. Metabolomic profiling was performed in extracted cell pellets at 12, 24 and 48 hours, after viability and cell counting was done, and compared with controls via acquisition of 1H-NMR spectra using a 500MHz spectrometer equipped with a 5mm TCI 500S2 H-C/N-D-05 Z cryoprobe head at 298 K. Standard, one-dimensional NOESYpr1D pre-saturation pulse program was used. Spectra were further processed in an NMR suite processor; Partial Least Squares Discriminant Analysis (PLS-DA) model was used for characterization of chronological biochemical differences.

Results:

By 48 hours of exposure of cells to imatinib, glucose initially increased then significantly decreased with gradual decrease of lactate production and minimal changes in pyruvate and succinate denoting shifting from cytosolic to mitochondrial glycolysis, this was echoed with consumption of glutamine and glutamate. Glutathione and cell membrane phospholipids as phosphocholine gradually decreased by a factor of 1.6 for each, suggesting inhibited growth and invasiveness. Aspartate, myo-inositol, glycerophosphocholine and taurine gradually increased by a factor of 1.6, 1.7, 2.6 and 1.3, respectively. Tyrosine, valine and leucine showed minimal changes. Cell viability was directly correlated to changes in choline, creatine phosphate, myo-inositol and taurine (Pearson's R >0.65). PLS-DA model suggested that changes in myoinositol, glycerophosphocholine, glutamate, aspartate, phosphcholine and glutathione were the metabolites mostly influencing the differential chronological global metabolic profiles of the cells with continued exposure to imatinib (R2X = 0.76, R2Y = 0.60, Q2(cum) = 0.20).

Conclusion:

Metabolomic profiling of GIST cells exposed to signal transduction modulators supplements molecular findings and provides further mechanistic insights into longitudinal changes of the mitochondrial and glycolytic pathways of oncogenesis, it can potentially provide novel as well as complementary therapeutic targets.

Citation Format: Vered Marks, Gregory Tiesi, Ana Paz Mejia, Jonathan Trent, Jamie Walls, Alan Livingstone, Danny Yakoub. Metabolomic profiling of gastrointestinal stromal tumor (GIST) T1 cell lines in response to imatinib therapy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1840. doi:10.1158/1538-7445.AM2015-1840

1,1-diamino-2,2-dinitroethylenes are always zwitterions

The nitration of tetraiodoethylene (7) yields 1,1-diiodo-2,2-dinitroethylene (8). The latter reacts with alkylamines 9 or alkyldiamines 11 to give the corresponding acyclic 1,1-diamino-2,2-dinitroethylenes 10 or their cyclic analogs 12, respectively. On the basis of liquid and solid-state (13)C and (15)N NMR data, x-ray analysis and ab initio calculations, we suggest that the title compounds are always zwitterionic and that the C(A)-C(N) bond is not a true double bond.

The radioimmunoassay of tricyclic antidepressants

An antiserum to nortriptyline has been produced in a sheep against a nortriptyline-bovine serum albumin conjugate. The conjugate was prepared using the reagent N-(4-bromobutyl) phthalimide followed by a carbodiimide reaction to link the hapten to the carrier protein. The antibodies produced were shown to be specific for the tricyclic group of drugs. The sensitivity of the radioimmunoassay developed is currently limited by the lack of a high specific activity label. The possibilities of developing a radioimmunoassay for nortriptyline in plasma are discussed.

A comprehensive review of oral glucosamine use and effects on glucose metabolism in normal and diabetic individuals

Glucosamine (GlcN) is a widely utilized dietary supplement that is used to promote joint health. Reports that oral GlcN supplementation at usual doses adversely affects glucose metabolism in subjects with impaired glucose tolerance have raised concerns that GlcN should be contraindicated in individuals with diabetes and those at risk for developing it. This review addresses its potential, when used at typical doses, to affect glucose metabolism and insulin sensitivity in healthy individuals and those with diabetes or 'pre-diabetes'. Publicly available scientific information and data on GlcN were systematically compiled using the electronic search tool, Dialog , and reviewed with special emphasis on human studies. In long-term clinical trials, including those containing subjects with type 2 diabetes or 'pre-diabetes', GlcN produced a non-significant lowering of fasting blood glucose concentrations in all groups of subjects treated for periods of up to 3 years. Owing to limitations in study design, conclusions based on studies that report adverse affects of GlcN on insulin sensitivity and glucose tolerance in pre-diabetic subjects are suspect. However, no definitive long-term studies of GlcN use for individuals with pre-diabetes are available. Nevertheless, based on available evidence, we conclude that GlcN has no effect on fasting blood glucose levels, glucose metabolism, or insulin sensitivity at any oral dose level in healthy subjects, individuals with diabetes, or those with impaired glucose tolerance.

Some effects of melatonin and the control of its secretion in humans

Whether or not the pineal gland has a significant physiological role in humans is not known. There has nevertheless been speculation about the potential therapeutic use of melatonin (in view of its hypnotic and possible zeitgeber properties) in conditions such as insomnia and jet lag, and in shift-workers. Our work concerns the effects of melatonin administration in humans and the interactions between melatonin and other circadian variables. Chronic (one month), timed (1700 h), low-dose (2 mg daily) melatonin administration to normal subjects without environmental control consistently increased evening fatigue and slightly modified the 24 h prolactin rhythm without effect on cortisol, growth hormone, luteinizing hormone, thyroxine, testosterone or self-rated mood. In five out of 11 subjects the endogenous melatonin rhythm was advanced by one to three hours. During fractional desynchronization of circadian rhythms by increasing imposed 'day' length (26-29 h, 24 days, 500 lux), 5 mg melatonin per os at lights-out in two subjects resulted in better entrainment of the fatigue rhythm to the zeitgeber than in five out of six control subjects, without major consistent effects on other measured circadian variables. Using a new radioimmunoassay for 6-hydroxymelatonin sulphate (aMT6s), the major melatonin metabolite, we have shown that the urinary aMT6s rhythm is closely correlated to that of melatonin in plasma and is completely suppressed by an acute dose of atenolol (100 mg per os), a peripheral beta-adrenergic antagonist. During fractional desynchronization by increasing imposed 'day' length in one subject and decreasing imposed 'day' length in two subjects, the urinary aMT6s rhythm behaved similarly to that of core temperature. The results suggest that fatigue (or alertness) may be entrained by melatonin, but whether critical performance rhythms can be suitably manipulated remains to be clarified. It is likely that melatonin production is linked to the so-called 'strong' circadian oscillator.

Structures of pahayokolides A and B, cyclic peptides from a Lyngbya sp

The isolation and structure elucidation of two cyclic peptides, pahayokolides A (1) and B (2), is described. Structural features determined for these compounds include a pendent N-acetyl-N-methyl leucine, both E- and Z-dehydrobutyrines, a homophenylalanine, and an unusual polyhydroxy amino acid that is most likely of mixed polyketide synthase/nonribosomal peptide synthase origin. These peptides were purified from a new species of cyanobacteria of the genus Lyngbya, which was isolated from a periphyton mat from the Florida Everglades.

1,3-dipolar cycloadditions of trimethylsilyldiazomethane revisited: steric demand of the dipolarophile and the influence on product distribution

The 1,3-dipolar cycloaddition of trimethylsilyldiazomethane with alpha,beta-unsaturated esters was examined. The resulting 1-pyrazolines isomerize to regioisomeric 2-pyrazolines (a or b) or undergo desilylation (c). Acrylates yield only b or c. beta-Substituted dipolarophiles may yield all three types of products. This work demonstrates that the distribution of 2-pyrazoline products is highly dependent on the relative configuration of the substituents on the 1-pyrazoline intermediate.

Novel Carboxylated Pyrrole- and Carbazole-Based Monomers. Synthesis and Electro-Oxidation Features

Carboxylated pyrrole (Pyr, a index)- and carbazole (Cbz, b index)-containing monomers 6-7a/b and 9a/b have been readily synthesized from the monobenzyl ester of L-glutamic acid and triamine 2 using Clauson-Kaas and amide coupling reactions. In contrast to Pyr-containing compounds 6-7a, and 9a, the three Cbz-containing monomers 6-7b, and 9b have been found electroactive and were successfully electropolymerized on a Pt electrode resulting in the deposition of corresponding insoluble electroconducting polyCOOH polyCbz-films poly(6-7b) and poly(9b).

Dynamic and static conformational analysis of acylated tetrahydrobenzazepines

A detailed high-field NMR analysis of several acylated tetrahydrobenzazepines, supported by molecular mechanics calculations, indicates that the heterocyclic ring in these compounds exists in a chair conformation, with the carbonyl oriented anti to the aryl moiety in the dominant rotamer. Surprisingly, ring methylenes are typically diastereotopic at room temperature, as the barriers for the process of enantiomerization of the seven-membered ring are much higher than expected. It is shown that ring inversion is correlated (but not concerted) with rotation of the amide moiety, as the carbonyl is forced out of conjugation with the nitrogen in the transition state.

Best practice No 173: clinical and laboratory investigation of adult spontaneous hypoglycaemia

Adult spontaneous hypoglycaemia is not a diagnosis per se but a manifestation of a disease. Although rare, it is important to identify spontaneous hypoglycaemia and its causes because treatment may be preventative or curative. Hypoglycaemia can occur as an epiphenomenon in many serious diseases. It is sufficient to recognise the disease's association with hypoglycaemia and then take appropriate action to prevent the recurrence of hypoglycaemia. In investigating apparently healthy individuals, common pitfalls to avoid are: failure to recognise subacute neuroglycopenia clinically; failure to document hypoglycaemia adequately during symptoms; failure to measure pancreatic hormones, counter-regulatory hormones, and ketones in hypoglycaemic samples; failure to recognise pre-analytical and analytical limitations of laboratory assays; and failure to abandon obsolete and inappropriate investigations. Providing these caveats are met, appropriate laboratory and radiological investigations will almost always uncover the cause of spontaneous hypoglycaemia.

Crystal structure and rotational barrier of octakis(bromomethyl)naphthalene

Octakis(bromomethyl)naphthalene (4) adopts in the crystal a chiral conformation with a helical central naphthalene core and the bromomethyl groups disposed in an alternate up-down "in" arrangement. According to MM3 calculations, this conformation is less stable than the corresponding all alternated "out" form, while B3LYP/LANL2DZ calculations suggest the opposite stability order. The topomerization barrier (16.0 kcal mol(-1)) is ascribed to an enantiomerization process requiring 180 degrees rotation of all the bromomethyl groups and reversal of the helical sense of the naphthalene core.

Polyethylated triptycene derivatives

The octaethyl triptycenes 7 and 8 were synthesized by Diels-Alder reaction of the octaethylanthracene 4with the corresponding benzynes. Low-temperature NMR spectra of 7 and 8 are consistent with the presence of the fully alternated conformation "a" of C(2) symmetry. However, in the determined crystal structures, the compounds adopt a higher energy conformation with a pair of vicinal ethyls oriented in the same direction.

The biochemical investigation of cases of hypoglycaemia: an assessment of the clinical effectiveness of analytical services

AIM

To assess the extent to which biochemical analytical services contribute to the diagnosis and management of clinical cases of hypoglycaemia.

METHODS

All cases of confirmed hypoglycaemia, referred during a six month period, were included in the survey. Questionnaires were sent to each referring laboratory requesting information on the clinical progress and current status of the patient.

RESULTS

The level of influence exerted by analytical data was assigned in each case and those with similar outcomes combined. Identifiable case groups were: (1) Results not recorded in the patients' notes (15.7%). (2) Inappropriate requesting of insulin and C peptide measurements in cases of diabetes (11.4%). (3) Patient died soon after investigation (20.0%). (4) Patient recovered spontaneously (17.1%). (5) Patient received effective medical or surgical treatment (12.9%). (6) Patient awaiting or not requiring pathology based treatment (31.4%). (7) Inconclusive outcome prompting further investigation (5.7%).

CONCLUSIONS

Within the timescale of the survey (approximately 12 months), positive progress had been made towards diagnosis and subsequent treatment in only 10% of cases. Another 30% were either awaiting some form of treatment or further diagnostic tests. The remaining 60% did not appear to benefit in any way from the biochemical investigations.

Polyethylated aromatic rings: conformation and rotational barriers of 1,2,3,4,5,6,7,8-octaethylanthracene, 1,2,3,4,6,7,8-heptaethylfluorene, and 1,2,3,4,5,6,7,8-octaethylfluorene

1,2,3,4,5,6,7,8-Octaethylanthracene (5), 1,2,3,4,6,7,8-heptaethylfluorene (7), and 1,2,3,4,5,6,7,8-octaethylfluorene (8) were synthesized by Friedel-Crafts ethylations of 9,10-dihydroanthracene and fluorene. MM3 calculations indicate that the two ethylated six-membered rings of 5 and 7 are conformationally independent. According to the calculations, two low-energy conformers of each compound are possible with the ethyl groups attached to the external aryl rings arranged in an alternated "up-down" orientation. MM3 calculations indicate that in the lowest energy conformation the central fluorene core of 8 adopts a twisted conformation to avoid repulsive steric interactions between the ethyls at the bay region. Two fully alternated up-down conformations are possible for 8, differing in the orientation ("in" or "out") of the ethyls in the bay region. MM3 calculations predict that the lowest energy conformer is the fully alternated "out" form of C(2)() symmetry. The rotational barriers of 5, 7, and 8 are in the 8.7-11.3 kcal mol(-1) range, the largest barrier corresponding to the more crowded octaethylfluorene 8. Anthracene 5 adopts in the crystal a conformation of approximate C(2)(h) symmetry with pairs of peri groups on the same edge of the molecule oriented syn. The conformations adopted in the crystal by 7 and 8 do not correspond to the calculated lowest energy form. In the conformation of 7 in the crystal the ethyl groups on the trisubstituted ring adopt the unusual all syn arrangement. Octaethylfluorene 8 adopts a conformation with a twisted central fluorene core but with a syn arrangement of a pair of vicinal ethyl groups.

Hypoglycemic disorders

Hypoglycemia occurs as an epiphenomenon in many serious diseases and further investigation may be unnecessary. In other, often seemingly healthy individuals, it is responsible for their presenting symptoms. In them preliminary diagnosis depends on demonstrating a low blood glucose concentration during spontaneous symptoms by ambulatory self-collection of capillary blood and its analysis for glucose in the laboratory. Subsequent investigation requires appropriate plasma hormone analysis on blood collected while the patient is hypoglycemic.

Preparation and conformation of octaethylbiphenylene

Dimerization of tetraethylbenzyne (generated by reaction of 1, 2-dibromo-3,4,5,6-tetraethylbenzene (8) with 1 equiv of BuLi) afforded in low yield octaethylbiphenylene (3), together with a major product which was characterized as 2,3,4,5,3',4', 5'-heptaethyl-2'-vinylbiphenyl (9). X-ray diffraction indicates that biphenylene 3 adopts in the crystal a conformation of approximate C(2)(h )()symmetry with the ethyl groups within each phenylene ring arranged in an alternated up-down fashion. Notably, pairs of vicinal ethyl groups located at peri positions are oriented in a syn arrangement in the crystal. Low temperature NMR spectroscopy is consistent with the presence in solution of either the crystal conformation or a fully alternated conformation lacking any syn interaction. Molecular mechanics (MM3), semiempirical (AM1, PM3), and ab initio calculations indicate that the crystal conformation is a high energy form, and that the lowest energy conformation is the fully alternated form. The topomerization barrier of the methylene protons of the ethyl groups of 3 is 9.4 +/- 0.1 kcal mol(-)(1), which is between the rotational barriers of 8 and 1,2,3, 4-tetraethylbenzene 7 (9.9 +/- 0.1 and 8.2 +/- 0.1 kcal mol(-)(1), respectively). The similarity in rotational barriers suggests that a given tetraethylphenylene subunit does not markedly affect the rotational barrier of the ethyl groups of the other subunit.