pinecone/core-2020-05-10-deduplication huggingface dataset:
Synthesis of Alkaline Earth Diazenides MAEN2 (MAE = Ca, Sr, Ba) by Controlled Thermal Decomposition of Azides under High Pressure

The alkaline earth diazenides MAEN2 with MAE = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at highpressure/ high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group I4/mmm (no. 139), a = 3.5747(6) Å, c = 5.9844(9) Å, Z = 2, wRp = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN2 and BaN2. Accordingly, CaN2 is isotypic with SrN2 (space group I4/mmm (no. 139), a = 3.8054(2) Å, c = 6.8961(4) Å, Z = 2, wRp = 0.057) and the corresponding alkaline earth acetylenides (MAEC2) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN2 adopts a more distorted structure in space group C2/c (no. 15) with a = 7.1608(4) Å, b = 4.3776(3) Å, c = 7.2188(4) Å, β = 104.9679(33)°, Z = 4 and wRp = 0.049). The N−N bond lengths of 1.202(4) Å in CaN2 (SrN2 1.239(4) Å, BaN2 1.23(2) Å) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N2]2−. Temperature-dependent in situ powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides MAE2N (MAE = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm−1 assigned to the N−N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides.
Dynamic Combinatorial Libraries: From Exploring Molecular Recognition to Systems Chemistry

Dynamic combinatorial chemistry (DCC) is a subset of combinatorial chemistry where the library members interconvert continuously by exchanging building blocks with each other. Dynamic combinatorial libraries (DCLs) are powerful tools for discovering the unexpected and have given rise to many fascinating molecules, ranging from interlocked structures to self-replicators. Furthermore, dynamic combinatorial molecular networks can produce emergent properties at systems level, which provide exciting new opportunities in systems chemistry. In this perspective we will highlight some new methodologies in this field and analyze selected examples of DCLs that are under thermodynamic control, leading to synthetic receptors, catalytic systems, and complex self-assembled supramolecular architectures. Also reviewed are extensions of the principles of DCC to systems that are not at equilibrium and may therefore harbor richer functional behavior. Examples include self-replication and molecular machines.
Modification of chiral dimethyl tartrate through transesterification: Immobilisation on POSS and enantioselectivity reversion in Sharpless asymmetric epoxidation

Modification of dimethyl tartrate has been investigated through transesterification with aminoalcohols to provide reactive functionalities for the covalent bonding of chiral tartrate to polyhedral oligomeric silsesquioxanes. The transesterification of dimethyl tartrate has been widely studied by means of using different catalytic systems and reaction conditions. Through the proper selection of both, the catalytic system and the reaction conditions, it is possible to achieve the mono- or the bis-substituted tartrate derivative as sole products. All the intermediate chiral tartrate-derived ligands were successfully used in the homogeneous enantioselective epoxidation of allylic alcohols providing moderate enantiomeric excess over the products. Attached amine groups have been used to support the modified tartrate ligands onto a haloaryl-functionalized silsesquioxane moiety. This final chiral tartrate ligand displays enantioselectivity reversion in the asymmetric epoxidation of allylic alcohols with regards to the starting dimethyl tartrate ligand, having both molecules them the same chiral sign. However, the POSS-containing ligand can be easily recovered in almost quantitative yield and reused in asymmetric epoxidation reactions. In addition, recovered silsesquioxane-pendant ligand, though displaying decreasing catalytic activity in recycling epoxidation tests, showed very stable enantioselective behavior
A VCD robust mode analysis of induced chirality: the case of pulegone in chloroform

Vibrational modes in an achiral molecule may acquire rotational strength by complexation to a chiral molecule, as happens for achiral solvent molecules complexed to a chiral solute. We investigate this transfer of chirality in vibrational circular dichroism for the pulegone molecule in CDCl3 solvent from the point of view of the robustness concept introduced recently. It turns out that the transfer of chirality yields non-robust modes, which means that, although they are observed in VCD experiments, the sign of these modes cannot be predicted reliably with standard (DFT) VCD calculations. This limits the usefulness of the induced chirality phenomenon for obtaining information on the intermolecular interactions that give rise to it
Polarization control of ultrashort mid-IR laser pulses for transient vibrational circular dichroism measurements

Linear dichroism and birefringence artifacts are a major source of concern in transient circular dichroism measurements. They mainly arise from interaction of an imperfectly circular polarized probe beam with a nonisotropic sample. We present in this article a procedure to generate mid-IR pulses of highly symmetric left and right handed circular or elliptical polarization states for transient VCD measurements. An infrared femtosecond laser source is synchronized to the natural frequency of a photo elastic modulator. Residual static birefringence of the modulator and the sample cell can be largely compensated by carefully controlling the arrival time of the ultrashort probe pulses at the modulator
Evaluation of Instrumental Errors Built in Circular Dichroism Spectrometers

Because of the increased use of circular dichroism (CD) spectroscopy
as a routine technique by nonspecialists to determine the conformational/configurational
properties of biomolecules, we have decided to present here some criteria to accurately
check the ordinate scale calibration of a CD spectrometer particularly in the critical lowwavelength
UV region, to understand, and correct, where possible, the potential limitations
coming from the hardware. We also analyze some wavelength calibration methods,
and some standards for the CD-scale calibration, and we discuss the critical characteristics
of current instrumentation affecting measurements. The example of the bovine catalase
CD spectrum is considered
Practical access to the proline analogs (S,S,S)- and (R,R,R)-2- methyloctahydroindole-2-carboxylic acids by HPLC enantioseparation

An efficient methodology for the preparation of the α- tetrasubstituted proline analog (S,S,S)-2-methyloctahydroindole-2-carboxylic acid, (S,S,S)-(αMe)Oic, and its enantiomer, (R,R,R)-(αMe)Oic, has been developed. Starting from easily available substrates and through simple transformations, a racemic precursor has been synthesized in excellent yield and further subjected to HPLC resolution using a cellulose-derived chiral stationary phase. Specifically, a semipreparative (250 mm × 20 mm ID) Chiralpak® IC column has allowed the efficient resolution of more than 4 g of racemate using a mixture of n-hexane/tert-butyl methyl ether/2-propanol as the eluent. Multigram quantities of the target amino acids have been isolated in enantiomerically pure form and suitably protected for incorporation into peptides. © 2011 Wiley-Liss, Inc.Contract grant sponsors: Ministerio de Ciencia e Innovación–FEDER, Gobierno de Aragón; Contract grant numbers: CTQ2007-62245, CTQ2010- 17436, PIP206/2005 and research group E40.Peer Reviewe
Stereoselective pharmacokinetics of stable isotope (+/-)-[13C]-pantoprazole: Implications for a rapid screening phenotype test of CYP2C19 activity

AIMS:

We have previously shown that the (±)-[(13) C]-pantoprazole breath test is a promising noninvasive probe of CYP2C19 activity. As part of that trial, plasma, breath test indices and CYP2C19 (*2, *3, and *17) genotype were collected. Here, we examined whether [(13) C]-pantoprazole exhibits enantioselective pharmacokinetics and whether this enantioselectivity is correlated with indices of breath test.

METHODS:

Plasma (-)- and (+)-[(13) C]-pantoprazole that were measured using a chiral HPLC were compared between CYP2C19 genotypes and correlated with breath test indices.

RESULTS:

The AUC( 0-∞) of (+)-[(13) C]-pantoprazole in PM (*2/*2, n = 4) was 10.1- and 5.6-fold higher that EM (*1/*1or *17, n = 10) and IM (*1/*2or *3, n = 10) of CYP2C19, respectively (P < 0.001). The AUC( 0-∞) of (-)-[(13) C]-pantoprazole only significantly differed between PMs and EMs (1.98-fold; P = 0.05). The AUC( 0-∞) ratio of (+)-/(-)-[(13) C]-pantoprazole was 3.45, 0.77, and 0.67 in PM, IM, and EM genotypes, respectively. Breath test index, delta over baseline show significant correlation with AUC( 0-∞) of (+)-[(13) C]-pantoprazole (Pearson's r = 0.62; P < 0.001).

CONCLUSIONS:

[(13) C]-pantoprazole exhibits enantioselective elimination. (+)-[(13) C]-pantoprazole is more dependent on CYP2C19 metabolic status and may serve as a more attractive probe of CYP2C19 activity than (-)-[(13) C]-pantoprazole or the racemic mixture
Ultraviolet, Circular Dichroism, Fluorescence, and Circularly Polarized Luminescence Spectra of Regioregular Poly-[3-((S)-2-Methylbutyl)-Thiophene] in Solution.

Ultraviolet (UV), Circular Dichroism(CD), Fluorescence, and Circularly Polarized\ud
Luminescence (CPL) spectra were recorded for mixed chloroform/methanol and chloroform/\ud
butanol solutions of regioregular poly[3-((S)-2-methylbutyl)-thiophene]. An evaluation of the chiral\ud
and nonchiral components in solution is proposed on the basis of the UV and CD spectra. The\ud
fluorescence and CPL spectra are observed in a wavelength range where some UV and CD activity\ud
still appears. For this reason, the observed CPL features are strongly influenced by CD. A general\ud
procedure for evaluating true CPL spectra is proposed, when absorption and emission coexist
Diastereoselective Osmium-catalyzed Vicinal Oxyamination of Acyclic Allylic Alcohol Derivatives

The osmium-catalyzed oxyamination of chiral acyclic allylic alcohol derivatives bearing mono- and 1,1-di-substituted double bonds with benzyl N-(4-tosyloxy)carbamate proceeds with high regioselectivity and moderate levels of diastereoselectivity favoring the anti product. The observed stereoselectivity shows a clear and systematic trend with anti:syn ratios increasing in line with the size of substituent at both the allylic stereocenter and double bond alpha-carbon. The stereoinduction is in accord with the sense of diastereoselectivity predicted by Kishi’s empirical rule and a previously reported transition state model for the osmium-catalyzed dihydroxylation of allylic alcohol derivatives. In contrast, allylic alcohol derivatives bearing trisubstituted double bonds show low or no reactivity in the oxyamination reaction affording the syn product in low yield in the cases examined.Directorate General of Higher Education Indonesia (DIKTI
Resolution of 1-n-Butyl-3-Methyl-3-Phospholene 1-Oxide with TADDOL Derivatives and Calcium Salts of O,O’-Dibenzoyl-(2R,3R)- or O,O’-di-p-Toluoyl-(2R,3R)-tartaric Acid

The resolution methods applying (−)-(4R,5R)-4,5-bis(diphenylhydroxymethyl)-2,2-dimethyldioxolane (“TADDOL”), (−)-(2R,3R)-α,α,α',α'-tetraphenyl-1,4-dioxaspiro[4.5]decan-2,3-dimethanol (“spiro-TADDOL”), as well as the acidic and neutral Ca2+ salts of (−)-O,O’-dibenzoyl- and (−)-O,O’-di-p-toluoyl-(2R,3R)-tartaric acid were extended for the preparation of 1-n-butyl-3-methyl-3-phospholene 1-oxide in optically active form. In one case, the intermediate diastereomeric complex could be identified by single crystal X-ray analysis. The absolute P-configuration of the enantiomers of the phospholene oxide was also determined by comparing the experimentally obtained and calculated CD spectra
Enantiopure O-Ethyl Phenylphosphonothioic Acid : A Solvating Agent for the Determination of Enantiomeric Excesses

An improved method, which is highly reproducible, was developed for the enantioseparation of racemic O-ethyl phenylphosphonothioic acid (1a) with brucine by introducing seeding to a supersaturated solution of the diastereomeric salt mixture. The present method gave both diastereomeric salts in high yields with a diastereomeric ratio of >99.5:0.5 upon choosing the crystallization solvent (MeOH for the (R)-1a salt and MeOH/H_2O for the (S)-1a salt). The enantiopure acid 1a showed a good chirality recognition ability for not only strong bases, such as amines and amino alcohols, but also weakly basic alcohols and was applicable as a solvating agent to the ^1H NMR determination of the enantiomeric excess of chiral amines, amino alcohols, and alcohols, including aliphatic substrates
A Langevin canonical approach to the dynamics of chiral two level
  systems. Thermal averages and heat capacity

A Langevin canonical framework for a chiral two--level system coupled to a
bath of harmonic oscillators is developed within a coupling scheme different to
the well known spin-boson model. Thermal equilibrium values are reached at
asymptotic times by solving the corresponding set of non--linear coupled
equations in a Markovian regime. In particular, phase difference thermal values
(or, equivalently, the so--called coherence factor) and heat capacity through
energy fluctuations are obtained and discussed in terms of tunneling rates and
asymmetries.Comment: 9 pages, 7 figures. arXiv admin note: text overlap with
  arXiv:1207.334
Enzymatic Resolution of α-Methyleneparaconic Acids and Evaluation\ud
of their Biological Activity

Both enantiomers of three biologically relevant paraconic acids—MB-3, methylenolactocin, and C75—were obtained with enantioselectivities up to 99% by kinetic enzymatic resolutions. Good enantiomeric excesses were obtained for MB-3 and methylenolactocin, using α-chymotrypsin and aminoacylase as enantiocomplementary enzymes, while C75 was resolved with aminoacylase. They all were evaluated for their antiproliferative, antibacterial, and antifungal activities, showing weak effects and practically no difference between enantiomers in each case. At high concentrations (16–64 μg/mL), (–)- C75 acted as an antimicrobial agent against Gram-positive bacteria
Enantioseparation on Riboflavin Derivatives Chemically Bonded to Silica Gel as Chiral Stationary Phases for HPLC

International audienceAcetylated and/or 3,5-dimethylphenylcarbamated riboflavins were prepared and the resulting riboflavin derivatives as well as natural riboflavin were regioselectively immobilized on silica gel through chemical bonding at the 5’-O- or 3-N-position of the riboflavin to develop novel chiral stationary phases (CSPs) for enantioseparation by high-performance liquid chromatography (HPLC). The chiral recognition abilities of the obtained CSPs were significantly dependent on the structures of the riboflavin derivatives, the position of the chemical bonding on the silica gel, and the structures of the racemic compounds. The CSPs bonded at the 5’-O-position on the silica gel tended to well separate helicene derivatives, while the CSPs bonded at the 3-N-position composed of acetylated and 3,5-dimethylphenylcarbamated riboflavins showed a better resolving ability toward helicene derivatives and bulky aromatic racemic alcohols, respectively, and some of them were completely separated into the enantiomers. The observed difference in the chiral recognition abilities of these riboflavin-based CSPs is discussed based on the difference in their structures, including the substituents of riboflavin and the positions immobilized on the silica gel
Glycosaminoglycan and DNA binding induced intra- and intermolecular exciton coupling of the bis-4-aminoquinoline surfen

Despite the diverse biological activities of the glycosaminoglycan (GAG) antagonist surfen, the molecular details of its interaction with biomacromolecules remain poorly understood. Therefore, heparin and DNA binding properties of surfen were studied by circular dichroism (CD) and UV absorption spectroscopy methods. High-affinity (Ka ~ 107 M-1) association of surfen to the chiral heparin chain gives rise to a characteristic biphasic CD pattern due to the conformational twist of the aminoquinoline moieties around the central urea bridge. At higher drug loading, intermolecular stacking of surfen molecules alters the induced CD profile and also provokes strong UV hypochromism. In contrast to the right-handed heparin template, binding of surfen to the left-helicity chondroitin sulfate chains produces inverted CD pattern. Large UV hypochromism as well as polyphasic induced ellipticity bands indicate that surfen intercalates between the base pairs of calf-thymus DNA. Extensive CD spectroscopic changes observed at higher drug binding ratios refer to cooperative binding interactions between the intercalated drug molecules. The inherent conformational flexibility of surfen demonstrated here for the first time is important in its binding to distinct macromolecular targets and should be considered for rational drug design of novel GAG antagonists
Cooperative effects between arginine and glutamic acid in the amino acid catalyzed aldol reaction

Catalysis of the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde by mixtures of L-Arg and of L-Glu in wet DMSO takes place with higher enantioselectivity (up to a seven-fold enhancement in the anti- aldol for the 1:1 mixture) than that observed when either L-Glu or L-Arg alone are used as the catalysts. These results can be explained by the formation of a catalytically active hydrogen-bonded complex between both amino acids, and demonstrate the possibility of positive cooperative effects in catalysis by two different α-amino acids. Chiralit
Hemin and bile pigments are the secondary structure regulators of intrinsically disordered antimicrobial peptides

The interaction of protoporphyrin compounds of human origin with the major bee venom component melittin (26 a.a., Z +6) and its hybrid derivative (CM15, 15 a.a., Z +6) were studied by a combination of various spectroscopic methods. Throughout a two-state, concentration-dependent process, hemin and its metabolites (biliverdin, bilirubin, bilirubin ditaurate) increase the parallel β-sheet content of the natively unfolded melittin, suggesting the oligomerization of the peptide chains. In contrast, α-helix promoting effect was observed with the also disordered but more cationic CM15. According to fluorescence quenching experiments, the sole Trp residue of melittin is the key player during the binding, in the vicinity of which the first pigment molecule is accommodated presumably making indole-porphyrin π-π stacking interaction. As circular dichroism titration data suggest, cooperative association of additional ligands subsequently occurs, resulting in multimeric complexes with an apparent dissociation constant ranged from 20 to 65 μM. Spectroscopic measurements conducted with the bilirubin catabolite urobilin and stercobilin refer to the requirement of intact dipyrrinone moieties for inducing secondary structure transformations. The binding topography of porphyrin rings on a model parallel β-sheet motif was evaluated by absorption spectroscopy and computational modeling showing a slipped-cofacial binding mode responsible for the red shift and hypochromism of the Soret band. Our results may aid to recognize porphyrin-responsive binding motifs of biologically relevant, intrinsically disordered peptides and proteins, where transient conformations play a vital role in their functions
Tetrathiafulvalene‐[2.2]paracyclophanes: Synthesis, crystal structures, and chiroptical properties

Two racemic tetrathiafulvalene‐[2.2]paracyclophane electron donors EDT‐TTF‐[2.2]paracyclophane 1 and (COOMe)2‐TTF‐[2.2]paracyclophane 2 have been synthesized via the phosphite mediated cross coupling strategy. Chiral HPLC allowed the optical resolution of the (Rp) and (Sp) enantiomers for both compounds. Solid‐state structures of (Rp)‐1 and (rac)‐2 have been determined by single crystal X‐ray analysis. Intermolecular π‐π and S•••S interactions are disclosed in the packing. Single crystal X‐ray analysis of (Rp)‐1 combined with experimental and theoretical circular dichroism spectra allowed the assignment of the absolute configuration of the enantiomers of 1 and 2
Neural adaptation and the ECAP response threshold: a pilot study

The electrically evoked compound action potential (ECAP) amplitude resulting from a train of pulses of finite duration (100 ms or 200 ms) was found to vary inversely to the stimulation rate (pulse rate), corroborating well with neural adaptation results from a previous study (Dillier et al., 2005). Amplitude growth functions based on these adapted responses yield thresholds (TNRT) that increase with increasing pulse rate, contrary to behavioural thresholds, which are known to vary inversely with the stimulation rate. Adaptation effects are therefore a confounding factor that must be accounted for when attempting to compare behavioural and objective measures
hMSC production in disposable bioreactors with regards to GMP and PAT

Reactor concepts for human mesenchymal stem cell (hMSC) production are introduced. Thereby, special interest is laid on the realization of these concepts as disposables fulfilling the GMP and PAT requirements. The specialty of the hMSC production process is the cell itself being the product. This results in completely different process requirements compared to e.g. protein production in mammalian cells. Thus, great attention has to be given to the shear sensitivity of the cells. The cultivation and the harvest of the cells have to be very gentle to neither influence cell viability nor cell differentiability. Further, the production process should not cause any undesirable cell changes. For hMSC production, cell harvest is the main challenging process step. The reactor concepts should be suitable for hMSC production for clinical trials as ATMPs. Therefore, disposable systems are especially applicable. The review describes more detailed bone marrow-derived hMSC production in a disposable stirred tank reactor as promising reactor concept
Numerical Modelling of Braiding and Meandering Instabilities in Gravity-Driven Liquid Rivulets

Rivulet instabilities appear in many engineering applications. In absorption equipment, they affect the interface area available for mass transfer, and thus, reducing the efficiency. Here, computational fluid dynamics are used to reproduce the meanders and braids in rivulets flowing down an inclined channel. Fast oscillations of the meander (f = 5.6 Hz) are observed at low flow rates. At greater flow rates, an analysis of the transversal velocity in the retraction waves shows the effect of the surface tension, which causes the braiding phenomenon, and thus, the reduction in gas-liquid interface area
Do Nonprofit Organizations Manage Earnings towards Zero Profit and does Governmental Financing Play a Role?

Prior research documented earnings management in for-profit settings. Nonprofit organizations are thought to pay less attention to the bottom line of the income statement. Earnings management research in nonprofit settings has therefore focused on the manipulation of expenses in order to improve efficiency ratios or taxable income, not reported earnings per se. Considering a different institutional setting characterized by the absence of such ratios and the presence of important subsidies, management of the actual bottom line is analyzed in the light of the importance of these subsidies. The results of our analyses suggest that organizations drive their results towards zero profit and that this is intensified by increased governmental funding when unmanaged results are positive. The relation between downward earnings management and the presence of subsidies is particularly evident for organizations whose accumulated reserves are high.status: publishe