Conformations of Steroid Hormones: Infrared and Vibrational Circular Dichroism Spectroscopy.

Steroid hormone molecules may exhibit very different functionalities based on the associated functional groups and their 3D arrangements in space, i.e., absolute configurations and conformations. Infrared (IR) and vibrational circular dichroism (VCD) spectra of four different steroid hormones, namely dehydroepiandrosterone (DHEA), 17α-methyltestosterone (MTTT), (16α,17)-epoxyprogesterone (Epoxy-P4), and dehydroepiandrosterone acetate (AcO-DHEA), were measured in deuterated dimethyl sulfoxide and some also in carbon tetrachloride. Extensive conformational searches were carried out using the recent developed conformer-rotamer ensemble sampling tool (CREST) which also accounts for solvent effects using an implicit solvation model. All the CREST conformational candidates were then reoptimized at the B3LYP-D3BJ/def2-TZVPD with the PCM of solvent. The good agreements between the experimental IR and VCD spectra and the theoretical simulations provide a conclusive information about their conformational distribution and absolute configurations. The experimental and theoretical IR and VCD spectra of AcO-DHEA in the carbonyl and alkene stretching region showed some discrepancies, and the possible causes related to solvent effects, large amplitude motions and levels of theory used in the modelling were explored in detail. As part of the investigation, additional calculations at the B3LYP-D3BJ/6-31++G (2d,p) and B3LYP-D3BJ/cc-pVTZ levels, as well as some 'mixed' calculations with the double-hybrid functional B2PLYP-D3 were also carried out. The results indicate that the double-hybrid functional is important for predicting the correct IR band pattern in the carbonyl and alkene stretching region.

Basis Set Dependence of Optical Rotation Calculations with Different Choices of Gauge.

In this work, the basis set dependence of optical rotation (OR) calculations is examined for various choices of gauge/level of theory. The OR is calculated for a set of 50 molecules using B3LYP and CAM-B3LYP and 17 molecules using coupled cluster with single and double excitations (CCSD). The calculations employ the correlation-consistent basis sets, aug-cc-pVζZ with ζ = D, T, Q. An inverse-power extrapolation formula is then utilized to obtain OR values at the complete basis set (CBS) limit. We investigate the basis set convergence for these methods and three choices of gauge: length gauge (with gauge-including atomic orbitals, LG(GIAOs), for DFT), the origin-invariant length gauge [LG(OI)], and the modified velocity gauge (MVG). The results show that all methods converge smoothly to the CBS limit and that the LG(OI) approach has a slightly faster convergence rate than the other choices of gauge. While the DFT methods reach gauge invariance at the CBS limit, CCSD does not. The significant difference between the MVG and LG(OI) results at the CBS limit, 26%, indicates that CCSD is not quite at convergence in the description of electron correlation for this property. On the other hand, gauge invariance at the CBS limit for DFT does not lead to the same OR values for the two density functionals, which is also due to electron correlation incompleteness. A limited comparison to gas-phase experimental OR values for the DFT methods shows that CAM-B3LYP seems more accurate than B3LYP. Overall, this study shows that the LG(OI) approach with the aug-cc-pVTZ basis set for DFT, and with the CBS(DT) extrapolation for CCSD, provides a good cost/accuracy balance.

Unusual binary aggregates of perylene bisimide revealed by their electronic transitions in helium nanodroplets and DFT calculations.

The S1 ← S0 electronic transition of perylene bisimide (PBI) and its binary aggregates were investigated using a combination of helium nanodroplet isolation spectroscopy and computational methods. First, well-resolved vibronic bands of the PBI monomer obtained under the superfluid helium nanodroplet environment were compared to simulated vibronic spectra with anharmonic corrections of the band positions. Second, about ten sets of weaker vibronic bands were observed, which show similar vibronic patterns as that of the PBI monomer and have their band origins red-shifted by about 8 to 218 cm-1. Experimental Poisson curve analyses, performed at the origins of these new sets of bands and the PBI monomer, indicate that the carriers of these weaker red-shifted vibronic bands are binary adducts of PBI. Three types of PBI dimer structures where the electronic transition dipole moments of the two subunits are perpendicular to each other were proposed as possible carriers of these red-shifted vibronic patterns. Extensive vibronic simulations were carried out in a multi-step procedure with TD-DFT, vertical Hessian, and finally adiabatic Hessian approaches. Small red-shifted band origins and very similar vibronic patterns to that of the monomer were predicted for unusual, T-shaped, type I dimer structures and are in close agreement with the experimental data. The combined experimental and theoretical results indicate that the helium nanodroplet environment enables the formation of these unusual T-shaped dimers and stabilizes them.

Can One Measure Resonance Raman Optical Activity?

Resonance Raman optical activity (RROA) is commonly measured as the difference in intensity of Raman scattered right and left circularly polarized light, IR -IL , when a randomly polarized light is in resonance with a chiral molecule. Strong and sometimes mono-signate experimental RROA spectra of several chiral solutes were reported previously, although their signs and relative intensities could not be reproduced theoretically. By examining multiple light-matter interaction events which can occur simultaneously under resonance, we show that a new form of chiral Raman spectroscopy, eCP-Raman, a combination of electronic circular dichroism and circularly polarized Raman, prevails. By incorporating the finite-lifetime approach for resonance, the experimental patterns of the model chiral solutes are captured theoretically by eCP-Raman, without any RROA contribution. The results open opportunity for applications of eCP-Raman spectroscopy and for extracting true RROA experimentally.

Way-finding in displaced clock-shifted bees proves bees use a cognitive map.

Mammals navigate by means of a metric cognitive map. Insects, most notably bees and ants, are also impressive navigators. The question whether they, too, have a metric cognitive map is important to cognitive science and neuroscience. Experimentally captured and displaced bees often depart from the release site in the compass direction they were bent on before their capture, even though this no longer heads them toward their goal. When they discover their error, however, the bees set off more or less directly toward their goal. This ability to orient toward a goal from an arbitrary point in the familiar environment is evidence that they have an integrated metric map of the experienced environment. We report a test of an alternative hypothesis, which is that all the bees have in memory is a collection of snapshots that enable them to recognize different landmarks and, associated with each such snapshot, a sun-compass-referenced home vector derived from dead reckoning done before and after previous visits to the landmark. We show that a large shift in the sun-compass rapidly induced by general anesthesia does not alter the accuracy or speed of the homeward-oriented flight made after the bees discover the error in their initial postrelease flight. This result rules out the sun-referenced home-vector hypothesis, further strengthening the now extensive evidence for a metric cognitive map in bees.

Absolute configuration of remisporines A & B.

The absolute configuration of remisporine B was determined based on a comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Density functional theory (DFT) was used to calculate the ECD spectra varying the parameter controlling the number of calculated electronic transitions. Mapping the reaction surface provided support for the proposed Diels-Alder dimerization of remisporine A to form remisporine B.

Conformational dynamics of carbohydrates: Raman optical activity of D-glucuronic acid and N-acetyl-D-glucosamine using a combined molecular dynamics and quantum chemical approach.

As two biologically and medically relevant monosaccharides, the constituents of hyaluronic acid, d-glucuronic acid and N-acetyl-d-glucosamine, constitute perfect test cases for the development of carbohydrate-specific structural methods. These two molecules have been analysed by Raman optical activity (ROA), a spectroscopic technique exhibiting exquisite sensitivity to stereochemistry. We show that it is possible to support the experiment with a simulation approach combining density functional theory (DFT) and molecular dynamics (MD), both using explicit solvation. Thus, we have gained new insight into the crucial hydration effects that contribute to the conformational dynamics of carbohydrates and managed to characterize in detail the poorly understood vibrational nature of this class of biomolecules. Experimental and calculated ROA spectra of these two molecules are reported and excellent agreement has been found. More specifically, comparison has been made with the more commonly used gas phase and implicitly solvated calculation approaches, which offer poor or zero modelling of solvent interactions. The calculated spectra have been used to resolve the structural origins of the observed bands, a current challenge in the study of carbohydrates due to a lack of definitive vibrational assignments. We report and analyse major features in the fingerprint region of the ROA spectra, with recurrent structural and spectral features between the two monosaccharides observed.

General anesthesia alters time perception by phase shifting the circadian clock.

Following general anesthesia, people are often confused about the time of day and experience sleep disruption and fatigue. It has been hypothesized that these symptoms may be caused by general anesthesia affecting the circadian clock. The circadian clock is fundamental to our well-being because it regulates almost all aspects of our daily biochemistry, physiology, and behavior. Here, we investigated the effects of the most common general anesthetic, isoflurane, on time perception and the circadian clock using the honeybee (Apis mellifera) as a model. A 6-h daytime anesthetic systematically altered the time-compensated sun compass orientation of the bees, with a mean anticlockwise shift in vanishing bearing of 87° in the Southern Hemisphere and a clockwise shift in flight direction of 58° in the Northern Hemisphere. Using the same 6-h anesthetic treatment, time-trained bees showed a delay in the start of foraging of 3.3 h, and whole-hive locomotor-activity rhythms were delayed by an average of 4.3 h. We show that these effects are all attributable to a phase delay in the core molecular clockwork. mRNA oscillations of the central clock genes cryptochrome-m and period were delayed by 4.9 and 4.3 h, respectively. However, this effect is dependent on the time of day of administration, as is common for clock effects, and nighttime anesthesia did not shift the clock. Taken together, our results suggest that general anesthesia during the day causes a persistent and marked shift of the clock effectively inducing "jet lag" and causing impaired time perception. Managing this effect in humans is likely to help expedite postoperative recovery.

Increased accuracy of vibrational circular dichroism calculations for isotopically labeled helical peptides.

Vibrational circular dichroism (VCD) spectra have been computed with qualitatively correct sign patterns for α-helical peptides using various methods, ranging from empirical models to ab initio quantum mechanical computations. However, some details, such as deuteration effects and isotope substitution shifts and sign patterns for the resultant amide I' band shape, have remained a predictive challenge. Fully optimized computations for a 25-residue Ala-rich peptide, including implicit solvent corrections and explicit side chains that experimentally stabilize these model helical peptides in water, have been carried out using density functional theory (DFT). These fully minimized structures show minor changes in the (ϕ,ψ) torsions at the termini and yield an extra negative band to the low energy side of the characteristic amide I' couplet VCD, in agreement with experiments. Additionally, these calculations give the right sign and relative intensity patterns, as compared to experimental results, for several 13C=O substituted variants. The differences from previously reported computations that used ideal helical structures and vacuum conditions imply that inclusion of distorted termini and solvent effects can have an impact on the final detailed spectral patterns. Inclusion of side chains in these calculations had very little effect on the computed amide I' IR and VCD. Tests of constrained geometries, varying dielectric, and different functionals indicate that each can affect the band shapes, particularly for the 12C=O components, but these aspects do not fully explain the difference from previous spectral simulations. Inclusion of long-range amide coupling, as obtained from DFT computation of the full structure, or transfer of parameters from a somewhat longer peptide model, rather than shorter model, seems to be more important for the final detailed band shape under isotopic substitution. However, these corrections can also induce other changes, suggesting that previously reported, limited calculations may have been qualitatively useful due to a balance of errors. This may also explain the success of simple empirical IR models.

Brachial arterial temperature as an indicator of core temperature: proof of concept and potential applications.

There is potential for heat loss and hypothermia during anesthesia and also for hyperthermia if heat conservation and active warming measures are not accurately titrated. Accurate temperature monitoring is particularly important in procedures in which the patient is actively cooled and then rewarmed such as during cardiopulmonary bypass surgery (CPB). We simultaneously measured core, nasopharyngeal, and brachial artery temperatures to investigate the last named as a potential peripheral temperature monitoring site. Ten patients undergoing hypothermic CPB were instrumented for simultaneous monitoring of temperatures in the pulmonary artery (PA), aortic arterial inflow (AI), nasopharynx (NP), and brachial artery (BA). Core temperature was defined as PA temperature before and after CPB and the AI temperature during CPB. Mean deviations of BA and NP temperatures from core temperature were calculated for three steady-state periods (before, during, and after CPB). Mean deviation of BA and NP temperatures from AI temperature was also calculated during active rewarming. A total of 1862 measurements were obtained and logged from eight patients. Mean BA and NP deviations from core temperature across the steady-state periods (before, during, and after CBP) were, respectively: .23 +/- .25, -.26 +/- .3, and -.09 +/- .05 degrees C (BA), and .11 +/- .19, -.1 +/- .47, and -.04 +/- .3 degrees C (NP). During steady-state periods, there was no evidence of a difference between the mean BA and NP deviation. During active rewarming, the mean difference between the BA and AI temperatures was .14 +/- .36 degrees C. During this period, NP temperature lagged behind AI and BA temperatures by up to 41 minutes and was up to 5.3 degres C lower than BA (mean difference between BA and NP temperatures was 1.22 +/- .58 degrees C). The BA temperature is an adequate surrogate for core temperature. It also accurately tracks the changing AI temperature during rewarming and is therefore potentially useful in detecting a hyperthermic perfusate, which might cause cerebral hyperthermia.

Experimental and theoretical polarized Raman linear difference spectroscopy of small molecules with a new alignment method using stretched polyethylene film.

This paper reports the development of the new technique of Raman linear difference (RLD) spectroscopy and its application to small molecules: anthracene and nucleotides adenosine-5'-monophosphate, thymidine-5'-monophosphate, guanosine-5'-monophosphate, and cytidine-5'-monophosphate. In this work we also present a new alignment method for Raman spectroscopy where stretched polyethylene films are used as the matrix. Raman spectra using light polarized along the orientation direction and perpendicular to it are reported. The polyethylene (PE) film spectra are consistent with powder samples and films deposited on quartz. RLD spectra determined from the difference of the parallel and perpendicular polarized light Raman spectra are also reported. The equations describing RLD are derived, and RLD spectra of anthracene and thymidine are calculated from these equations using Density Functional Theory and assuming perfect orientation of the samples. Because of the wealth of spectroscopic information in the vibrational spectra of biomolecules together with our ability to calculate spectra as a function of orientation, we conclude that RLD has the potential to provide structural information for biological samples that currently cannot be extracted from any other method.

Breakdown of the pseudopotential approximation for magnetizabilities and electric multipole moments. II. The importance of gauge invariance for large-core semi-local pseudopotentials.

In a previous paper we pointed out that core contributions to the static magnetizability are non-negligible, and can therefore lead to erroneous results within the pseudopotential approximation [P. Schwerdtfeger, B. Assadollahzadeh, U. Rohrmann, R. Schäfer, and J. R. Cheeseman, J. Chem. Phys. 134, 204102 (2011)]. In a recent paper van Wüllen showed that additional terms arising from the gauge-invariant condition for the semi-local part of a pseudopotential operator can lead to non-negligible contributions to the magnetizability tensor, which are sensitive to the gauge origin and basis set chosen [C. van Wüllen, J. Chem. Phys. 136, 114110 (2012)]. These terms were neglected in previous calculations as they were assumed to be small. In this paper we analyze the importance of the gauge-dependent semi-local pseudopotential correction term in detail for AuF and clusters of Sn showing that it leads indeed to very large corrections to the paramagnetic term for large-core pseudopotentials. Without this correction the results become very sensitive to the basis set applied. This now resolves some of the unusual large paramagnetic contributions reported before for both AuF and Sn(2).

Calculation of Raman optical activity spectra of methyl-ß-D-glucose incorporating a full molecular dynamics simulation of hydration effects.

We report calculations of the Raman and Raman optical activity (ROA) spectra of methyl-ß-D-glucose utilizing density functional theory combined with molecular dynamics (MD) simulations to provide an explicit hydration environment. This is the first report of such combination of MD simulations with ROA ab initio calculations. We achieve a significant improvement in accuracy over the more commonly used gas phase and polarizable continuum model (PCM) approaches, resulting in an excellent level of agreement with the experimental spectrum. Modeling the ROA spectra of carbohydrates has until now proven a notoriously difficult challenge due to their sensitivity to the effects of hydration on the molecular vibrations involving each of the chiral centers. The details of the ROA spectrum of methyl-ß-D-glucose are found to be highly sensitive to solvation effects, and these are correctly predicted for the first time including those originating from the highly sensitive low frequency vibrational modes. This work shows that a thorough consideration of the role of water is pivotal for understanding the vibrational structure of carbohydrates and presents a new and powerful tool for characterizing carbohydrate structure and conformational dynamics in solution.

Breakdown of the pseudopotential approximation for magnetizabilities and electric multipole moments: test calculations for Au, AuF, and Sn(n) cluster (n ≤ 20).

The response of the electronic wavefunction to an external electric or magnetic field is widely considered to be a typical valence property and should, therefore, be adequately described by accurately adjusted pseudopotentials, especially if a small-core definition is used within this approximation. In this paper we show for atomic Au and Au(+), as well as for the molecule AuF and tin clusters, that in contrast to the case of the static electric dipole polarizability or the electric dipole moment, core contributions to the static magnetizability are non-negligible, and can therefore lead to erroneous results within the pseudopotential approximation. This error increases with increasing size of the core chosen. For tin clusters, which are of interest in ongoing molecular beam experiments currently carried out by the Darmstadt group, the diamagnetic and paramagnetic isotropic components of the magnetizability tensor almost cancel out and large-core pseudopotentials do not even predict the correct sign for this property due to erroneous results in both the diamagnetic and (more importantly) the paramagnetic terms. Hence, all-electron calculations or pseudopotentials with very small cores are required to adequately predict magnetizabilities for atoms, molecules and the solid state, making it computationally more difficult to obtain this quantity for future investigations in heavy atom containing molecules or clusters. We also demonstrate for this property that all-electron density functional calculations are quite robust and give results close to wavefunction based methods for the atoms and molecules studied here.

Use of a new task-relevant test to assess the effects of shift work and drug labelling formats on anesthesia trainees' drug recognition and confirmation.

BACKGROUND: Drug administration errors occur in every aspect of clinical practice. Using a novel task-relevant Medication Recognition and Confirmation Test (MRCT), we investigated the effects on performance of working night and day shifts and labelling different drug formats. METHODS: Anesthesia trainees (n = 18) participated in one of two experiments during an 8-12 hr day shift and an 8-12 hr night shift. In Experiment-1 (n = 10), we compared standardized colour-coded labels with pictures of ampoules. In Experiment-2 (n = 8), we compared colour-coded labels with black and white labels. Sleep was measured with wrist actigraphy during both day and night shift runs over seven to eight days. The MRCT outcome measures were reaction times and drug errors. RESULTS: In the two experiments, colour-coded labels were recognized (and therefore selected) more quickly than pictures of conventional ampoules (mean difference 332 msec, 95% confidence interval (CI) 242-422 msec; P < 0.0001) and faster than black and white labels (mean difference 96 msec, 95% CI 46-146 msec; P < 0.0001). Participants obtained less sleep while working night shifts than while working day shifts (mean difference 57 min, 95% CI 0:15-1:39 hr; P = 0.013). Mean confirmation reaction times were slower during night shifts than during day shifts (mean difference 60 msec, 95% CI 1-120 msec; P = 0.048). No differences in error rates were observed between shifts or among drug label types. CONCLUSIONS: Label format influenced recognition and confirmation reaction times to representations of drugs in this study, and we found some evidence to suggest that performance is better during day shifts than during night shifts. The task-relevant test evaluated here may have further application in measuring performance in the wider clinical setting.

Circadian rhythms and their development in children: implications for pharmacokinetics and pharmacodynamics in anesthesia.

The influence of time-of-day on the action and toxicity of drugs may be an important factor in the design of pharmacokinetic (PK) and pharmacodynamic (PD) studies, and the interpretation of data resulting from these studies. Time-of-day can have a profound influence on the action of drugs. In some settings (e.g. cancer chemotherapy), the timing of drug administration has been utilized to maximize therapeutic effect and minimize toxicity. Time-of-day variation in the action of anesthetic drugs has been clearly demonstrated in adults. For example, local anesthetic action is longest during the afternoon, and neuromuscular blockade by rocuronium lasts one-third longer in the morning than the afternoon. Circadian rhythms develop over the first months and years of life. Robust rhythms in hormone production (e.g. melatonin and cortisol) are seen at approximately 3 months of age, but it remains unclear as to when daily rhythms in drug PK and PD first appear. Here, we review the evidence for time-of-day effects in anesthetic drugs in adults and children and outline the potential influence this has on pediatric anesthesia.

The Effects of General Anaesthesia and Light on Behavioural Rhythms and GABAA Receptor Subunit Expression in the Mouse SCN.

General anaesthesia (GA) is known to affect the circadian clock. However, the mechanisms that underlie GA-induced shifting of the clock are less well understood. Activation of γ-aminobutyric acid (GABA)-type A receptors (GABAAR) in the suprachiasmatic nucleus (SCN) can phase shift the clock and thus GABA and its receptors represent a putative pathway via which GA exerts its effect on the clock. Here, we investigated the concurrent effects of the inhalational anaesthetic, isoflurane, and light, on mouse behavioural locomotor rhythms and on α1, ß3, and γ2 GABAAR subunit expression in the SCN of the mouse brain. Behavioural phase shifts elicited by exposure of mice to four hours of GA (2% isoflurane) and light (400 lux) (n = 60) were determined by recording running wheel activity rhythms in constant conditions (DD). Full phase response curves for the effects of GA + light on behavioural rhythms show that phase shifts persist in anaesthetized mice exposed to light. Daily variation was detected in all three GABAAR subunits in LD 12:12. The γ2 subunit expression was significantly increased following GA in DD (compared to light alone) at times of large behavioural phase delays. We conclude that the phase shifting effect of light on the mouse clock is not blocked by GA administration, and that γ2 may potentially be involved in the phase shifting effect of GA on the clock. Further analysis of GABAAR subunit expression in the SCN will be necessary to confirm its role.

General Anaesthesia Shifts the Murine Circadian Clock in a Time-Dependant Fashion.

Following general anaesthesia (GA), patients frequently experience sleep disruption and fatigue, which has been hypothesized to result at least in part by GA affecting the circadian clock. Here, we provide the first comprehensive time-dependent analysis of the effects of the commonly administered inhalational anaesthetic, isoflurane, on the murine circadian clock, by analysing its effects on (a) behavioural locomotor rhythms and (b) PER2::LUC expression in the suprachiasmatic nuclei (SCN) of the mouse brain. Behavioural phase shifts elicited by exposure of mice (n = 80) to six hours of GA (2% isoflurane) were determined by recording wheel-running rhythms in constant conditions (DD). Phase shifts in PER2::LUC expression were determined by recording bioluminescence in organotypic SCN slices (n = 38) prior to and following GA exposure (2% isoflurane). Full phase response curves for the effects of GA on behaviour and PER2::LUC rhythms were constructed, which show that the effects of GA are highly time-dependent. Shifts in SCN PER2 expression were much larger than those of behaviour (c. 0.7 h behaviour vs. 7.5 h PER2::LUC). We discuss the implications of this work for understanding how GA affects the clock, and how it may inform the development of chronotherapeutic strategies to reduce GA-induced phase-shifting in patients.

The Effect of General Anaesthesia on Circadian Rhythms in Behaviour and Clock Gene Expression of Drosophila melanogaster.

General anaesthesia (GA) is implicated as a cause of postoperative sleep disruption and fatigue with part of the disturbance being attributed to a shift of the circadian clock. In this study, Drosophila melanogaster was used as a model to determine how Isoflurane affects the circadian clock at the behavioural and molecular levels. We measured the response of the clock at both of these levels caused by different durations and different concentrations of Isoflurane at circadian time 4 (CT4). Once characterized, we held the duration and concentration constants (at 2% in air for 6 h) and calculated the phase responses over the entire circadian cycle in both activity and period expression. Phase advances in behaviour were observed during the subjective day, whereas phase delays were associated with subjective night time GA interventions. The corresponding pattern of gene expression preceded the behavioural pattern by approximately four hours. We discuss the implications of this effect for clinical and research practice.