Programmable Peptide-Cross-Linked Nucleic Acid Nanocapsules as a Modular Platform for Enzyme Specific Cargo Release.

Herein we describe a modular assembly strategy for photo-cross-linking peptides into nucleic acid functionalized nanocapsules. The peptides embedded within the nanocapsules form discrete nanoscale populations capable of gating the release of molecular and nanoscale cargo using enzyme-substrate recognition as a triggered release mechanism. Using photocatalyzed thiol-yne chemistry, different peptide cross-linkers were effectively incorporated into the nanocapsules and screened against different proteases to test for degradation specificity both in vitro and in cell culture. By using a combination of fluorescence assays, confocal and TEM microscopy, the particles were shown to be highly specific for their enzyme targets, even between enzymes of similar protease classes. The rapid and modular nature of the assembly strategy has the potential to be applied to both intracellular and extracellular biosensing and drug delivery applications.

Salient features of enantioselective gas chromatography: the enantiomeric differentiation of chiral inhalation anesthetics as a representative methodological case in point.

The enantiomeric differentiation of the volatile chiral inhalation anesthetics enflurane, isoflurane, and desflurane by analytical and preparative gas chromatography on various modified cyclodextrins is described. Very large enantioseparation factors α are obtained on the chiral selector octakis(3-O-butanoyl-2,6-di-O-pentyl)-γ-cyclodextrin (Lipodex E). The gas-chromatographically observed enantioselectivities are corroborated by NMR-spectroscopy using Lipodex E as chiral solvating agent and by various sensor devices using Lipodex E as sensitive chiral coating layer. The assignment of the absolute configuration of desflurane is clarified. Methods are described for the determination of the enantiomeric distribution of chiral inhalation anesthetics during narcosis in clinical trials. The quantitation of enantiomers in a sample by the method of enantiomeric labeling is outlined. Reliable thermodynamic parameters of enantioselectivity are determined by using the retention-increment R' approach for the enantiomeric differentiation of various chiral halocarbon selectands on diluted cyclodextrin selectors.

Halogen bonded complexes between volatile anaesthetics (chloroform, halothane, enflurane, isoflurane) and formaldehyde: a theoretical study.

The structures and intermolecular interactions in the halogen bonded complexes of anaesthetics (chloroform, halothane, enflurane and isoflurane) with formaldehyde were studied by ab initio MP2 and CCSD(T) methods. The CCSD(T)/CBS calculated binding energies of these complexes are between -2.83 and -4.21 kcal mol(-1). The largest stabilization energy has been found for the C-Br···O bonded halothane···OCH(2) complex. In all complexes the C-X bond length (where X = Cl, Br) is slightly shortened, in comparison to a free compound, and an increase of the C-X stretching frequency is observed. The electrostatic interaction was excluded as being responsible for the C-X bond contraction. It is suggested that contraction of the C-X bond length can be explained in terms of the Pauli repulsion (the exchange overlap) between the electron pairs of oxygen and halogen atoms in the investigated complexes. This is supported by the DFT-SAPT results, which indicate that the repulsive exchange energy overcompensates the electrostatic one. Moreover, the dispersion and electrostatic contributions cover about 95% of the total attraction forces, in these complexes.

An isothermal titration calorimetry study on the binding of four volatile general anesthetics to the hydrophobic core of a four-alpha-helix bundle protein.

A molecular understanding of volatile anesthetic mechanisms of action will require structural descriptions of anesthetic-protein complexes. Previous work has demonstrated that the halogenated alkane volatile anesthetics halothane and chloroform bind to the hydrophobic core of the four-alpha-helix bundle (Aalpha(2)-L38M)(2) (Johansson et al., 2000, 2003). This study shows that the halogenated ether anesthetics isoflurane, sevoflurane, and enflurane are also bound to the hydrophobic core of the four-alpha-helix bundle, using isothermal titration calorimetry. Isoflurane and sevoflurane both bound to the four-alpha-helix bundle with K(d) values of 140 +/- 10 micro M, whereas enflurane bound with a K(d) value of 240 +/- 10 micro M. The DeltaH degrees values associated with isoflurane, sevoflurane, and enflurane binding were -7.7 +/- 0.1 kcal/mol, -8.2 +/- 0.2 kcal/mol, and -7.2 +/- 0.1 kcal/mol, respectively. The DeltaS degrees values accompanying isoflurane, sevoflurane, and enflurane binding were -8.5 cal/mol K, -10.4 cal/mol K, and -8.0 cal/mol K, respectively. The results indicate that the hydrophobic core of (Aalpha(2)-L38M)(2) is able to accommodate three modern ether anesthetics with K(d) values that approximate their clinical EC(50) values. The DeltaH degrees values point to the importance of polar interactions for volatile general anesthetic binding, and suggest that hydrogen bonding to the ether oxygens may be operative.

Characterization of thioether compounds formed from alkaline degradation products of enflurane.

BACKGROUND: Renal toxicity has occasionally been observed after enflurane anesthesia. Although originally attributed to its oxidative metabolism to inorganic fluoride, serum levels of inorganic fluoride appear to be small to explain these renal effects. Formation of potentially nephrotoxic halogenated alkenes during alkaline degradation in carbon dioxide absorbers and subsequent bioactivation via the glutathione conjugation pathway may be considered as an alternative mechanism for renal toxicity. The aim of this study was to characterize the thioethers formed chemically and biosynthetically. METHODS: Alkaline degradation of enflurane was achieved by stirring with pulverized potassium hydroxide. Volatile degradation products were analyzed by 19F nuclear magnetic resonance (NMR) analysis of head space gasses trapped in dimethyl sulfoxide (DMSO). Thioethers were generated chemically by trapping head space gasses in DMSO containing N-acetyl-L-cysteine or 2-mercaptoacetic acid as model thiol compounds. Glutathione conjugates were generated biosynthetically by passing head space through rat liver fractions in presence of glutathione. Products formed were analyzed by gas chromatography-mass spectroscopy and 19F-NMR. RESULTS: Direct analysis of head space gasses showed formation of 1-chloro-1,2-difluorovinyl difluoromethyl ether and two unidentified fluorine-containing products as alkaline degradation products of enflurane. When trapped in DMSO-N-acetyl-L-cysteine-triethylamine, N-acetyl-S-(2-chloro-1,2-difluoro-1-(difluoromethoxy)ethyl)-L-cysteine was identified as the major product. Another N-acetyl-L-cysteine S-conjugate formed was N-acetyl-S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine, a potent nephrotoxin in rats. 19F-NMR analysis of glutathione conjugates formed after incubation with rat liver fractions resulted in formation of corresponding S-conjugates. CONCLUSIONS: The current study demonstrates that alkaline degradation products of enflurane can be conjugated to thiol compounds, forming S-conjugates that could theoretically contribute to adverse renal effects observed occasionally with enflurane anesthesia. The N-acetyl-L-cysteine S-conjugates identified may be biomarkers to assess exposure of humans to alkaline degradation products of enflurane.

Amsorb: a new carbon dioxide absorbent for use in anesthetic breathing systems.

BACKGROUND: This article describes a carbon dioxide absorbent for use in anesthesia. The absorbent consists of calcium hydroxide with a compatible humectant, namely, calcium chloride. The absorbent mixture does not contain sodium or potassium hydroxide but includes two setting agents (calcium sulphate and polyvinylpyrrolidine) to improve hardness and porosity. METHODS: The resultant mixture was formulated and subjected to standardized tests for hardness, porosity, and carbon dioxide absorption. Additionally, the new absorbent was exposed in vitro to sevoflurane, desflurane, isoflurane, and enflurane to determine whether these anesthetics were degraded to either compound A or carbon monoxide. The performance data and inertness of the absorbent were compared with two currently available brands of soda lime: Intersorb (Intersurgical Ltd., Berkshire, United Kingdom) and Dragersorb (Drager, Lubeck, Germany). RESULTS: The new carbon dioxide absorbent conformed to United States Pharmacopeia specifications in terms of carbon dioxide absorption, granule hardness, and porosity. When the new material was exposed to sevoflurane (2%) in oxygen at a flow rate of 1 l/min, concentrations of compound A did not increase above those found in the parent drug (1.3-3.3 ppm). In the same experiment, mean +/-SD concentrations of compound A (32.5 +/- 4.5 ppm) were observed when both traditional brands of soda lime were used. After dehydration of the traditional soda limes, immediate exposure to desflurane (60%), enflurane (2%), and isoflurane (2%) produced concentrations of carbon monoxide of 600.0 +/- 10.0 ppm, 580.0 +/- 9.8 ppm, and 620.0 +/-10.1 ppm, respectively. In contrast, concentrations of carbon monoxide were negligible (1-3 ppm) when the anhydrous new absorbent was exposed to the same anesthetics. CONCLUSIONS: The new material is an effective carbon dioxide absorbent and is chemically unreactive with sevoflurane, enflurane, isoflurane, and desflurane.

Preparative enantiomer separation of the inhalation anesthetics enflurane, isoflurane and desflurane by gas chromatography on a derivatized gamma-cyclodextrin stationary phase.

The preparative enantiomeric separation of the inhalation anesthetics enflurane (1) and isoflurane (2) in very high chemical (> 99.5%) and enantiomeric excess (ee > 99%) by gas chromatography (GC) on octakis(3-O-butanoyl-2,6-di-O-n-pentyl)-gamma-cyclodextrin (4), dissolved in the apolar polysiloxane SE-54 and coated on Chromosorb P AW DMCS, is described. Up to 1 g of each enantiomer of 1-2 can been obtained per diem. The enantiomers of the highly volatile desflurane (3) can also be separated, albeit with diminished ee. The enantiomeric excess of 1-3 was checked by analytical GC on 4 and the absolute configuration of 2 and 3 has been determined via anomalous X-ray diffraction.

Approach to the thermodynamics of enantiomer separation by gas chromatography. Enantioselectivity between the chiral inhalation anesthetics enflurane, isoflurane and desflurane and a diluted gamma-cyclodextrin derivative.

The thermodynamics of enantioselectivity, -delta D,L(delta G), -delta D,L(delta H), delta D,L(delta S) and Tiso, have been determined by gas chromatography employing the concept of the retention increment R' for the inhalation anesthetics enflurane (1), isoflurane (2) and desflurane (3) and the selector octakis(3-O-butanoyl-2,6-di-O-n-pentyl)-gamma-cyclodextrin (4) in the polysiloxane SE-54. It is shown that the separation factor alpha is concentration-dependent. Therefore, the separation factor alpha should not be employed as a criterion for enantioselectivity in diluted systems. The -delta DL(delta G) data for 1 and 4 are corroborated by 1H NMR spectroscopic measurements.

[Interactions of dry soda lime with enflurane and sevoflurane. Clinical report on two unusual anesthesias]. / Interaktion von trockenem Atemkalk mit Enfluran und Sevofluran. Klinischer Bericht über zwei ungewöhnliche Anästhesieverläufe.

UNLABELLED: We report two cases of unexpected courses of inhalation anaesthesia with sevoflurane and enflurane which were caused by the presence dry soda lime. Case 1: During mask induction of a healthy 46-year-old female patient for elective hysterectomy it was noted that the vaporizer setting of 5% sevoflurane (in 50% O2, 50% N2O) did not result in the expected increase of inspiratory sevoflurane concentration. At the same time, the anaesthesiologist observed that the patient did not lose consciousness while the temperature of the soda lime canister increased sharply and the colour of the soda lime turned to blue with condensing water visible in the tubing. It was later determined that this anaesthesia machine had not been used for more than 2 weeks. Analysis of the soda lime showed a water content of <1%. Case 2: Following intravenous induction of a non-smoking 64-year-old male patient for elective gastrectomy, it was noted that the concomitant inhalation of enflurane was associated with a sharp rise in the temperature of the soda lime canister, a colour change of the soda lime to blue and a decrease in the measured inspiratory enflurane concentration despite an unchanged or even increased vaporizer setting. Arterial blood gas analysis revealed a CO-Hb concentration of 8.8% with otherwise normal acidity and partial gas pressures. Immediate change of the absorbant resulted in a decline in the CO-Hb concentration to 6.9% within 3 h. It was later determined that the anaesthesia machine had not been used for 34 h. Analysis of the soda lime showed a water content of 5.4%. DISCUSSION: Both case reports were associated with a rise in temperature and a colour change to blue of the soda lime. Reactions of desflurane, enflurane or isoflurane with dry soda lime resulting in significant CO-Hb formation have been previously reported. Reactions of sevoflurane with dry soda lime have been observed but have so far not been published. Until further analysis of these phenomena is completed, it is mandatory for the patient's safety to guarantee that only soda lime with a sufficient water content be used for clinical anaesthesia.

Breathing systems: effect of fresh gas flow rate on enflurane consumption.

The vaporization rates of enflurane were measured in 412 anaesthetics using appropriate fresh gas flow rates in Bain (12 litre min-1), Magill (6 litre min-1) and circle systems (3 litre min-1, 1 litre min-1 and "closed"). In all patients reducing the fresh gas flow rate resulted in lower enflurane consumption. The percent savings were 18-86% depending on the initial fresh gas flow rate and the size of the change in fresh gas flow. The reduction in enflurane use was more marked in inpatients (long cases) than in day-case patients (short cases).