Stimulated Raman scattering in natural crystals of fluorapatite,Ca5(PO4)3F

Hexagonal Ca₅(PO₄)₃F, known as natural crystal fluorapatite and oldest host‐crystal for Ln³⁺‐lasant ions, is presented as a Raman‐active material. High‐order Raman‐induced χ⁽³⁾‐nonlinear processes are discovered in natural crystals of fluorapatite under picosecond pumping at 1.064 μm and 0.532 μm wavelength. A multitude of Stokes and anti‐Stokes components is generated in the ultraviolet, visible and near‐infrared spectral region by stimulated Raman scattering (SRS) and Raman four‐wave mixing (FWHM), resulting in a frequency comb with a width of 520 THz. The spectral lines are identified and attributed to the ν₁(A_g) vibration mode of the tetrahedral [PO₄] units which is related to a Raman shift of ω_SRS ≈ 965 cm⁻¹. The first Stokes steady‐state Raman gain coefficient in the near‐infrared spectral range is estimated to be >0.38 cm·GW⁻¹. Finally, a short review of SRS‐promoting vibration modes and observed χ⁽³⁾‐ nonlinear interactions in all known SRS‐active natural crystals (minerals) is given.

     

Two CdII/CoII‐Imidazolate Coordination Polymers: Syntheses,Crystal Structures,Stabilities, and Luminescent/Magnetic Properties

Cadmium(II) based 2D coordination polymer [Cd(L1)₂(DMF)₂] ( 1 ) (L1 = 4,5‐dicyano‐2‐methylimidazolate, DMF = N,N′‐dimethylformamide) and 2D cobalt(II)‐imidazolate framework [Co(L3)₄] ( 2 ) (L3 = 4,5‐diamide‐2‐ethoxyimidazolate) were synthesized under solvothermal reaction conditions. The materials were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction measurement (PXRD) and single‐crystal X‐ray diffraction. Compound 1 has hexacoordinate Cd^II ions and forms a zigzag chain‐like coordination polymer structure, whereas compound 2 exhibits a 2D square grid type structure. The thermal stability analysis reveals that 2 showed an exceptional thermal stability up to 360 °C. Also, 2 maintained its fully crystalline integrity in boiling water as confirmed by PXRD. The solid state luminescent property of 1 was not observed at room temperature. Compound 2 showed an independent high spin central Co^II atom.     

Capillary isoelectric focusing immunoassay as a new nanoscale approach for the detection of oligoclonal bands

The detection of oligoclonal bands (OCBs) in cerebrospinal fluid is an indicator of intrathecal synthesis of immunoglobulins which is a neurochemical sign of chronic inflammatory brain diseases. Intrathecally synthesized IgGs are typically observed in patients with multiple sclerosis. The current standard protocol for the detection of OCBs is IEF on agarose or polyacrylamide gels followed by immunoblotting or silver staining. These methods are time consuming, show substantial interlaboratory variation and cannot be used in a high throughput‐approach. We have developed a new nanoscale method for the detection of OCBs based on automated capillary IEF followed by immunological detection. Evidence for intrathecal IgG synthesis was found in all tested patients (n = 27) with multiple sclerosis, even in two subjects who did not have oligoclonal bands according to standard methods. The test specificity was at 97.5% (n = 19). Our findings indicate that the novel OCB‐CIEF‐immunoassay is suitable for the rapid and highly sensitive detection of OCBs in clinical samples. Furthermore, the method allows for a higher sample throughput than the current standard methods.     

Dividing a complex reaction involving a hypervalent iodine reagent into three limiting mechanisms by ab initio molecular dynamics

The electrophilic N‐trifluoromethylation of MeCN with a hypervalent iodine reagent to form a nitrilium ion, that is rapidly trapped by an azole nucleophile, is thought to occur via reductive elimination (RE). A recent study showed that, depending on the solvent representation, the S_N2 is favoured to a different extent over the RE. However, there is a discriminative solvent effect present, which calls for a statistical mechanics approach to fully account for the entropic contributions. In this study, we perform metadynamic simulations for two trifluoromethylation reactions (with N‐ and S‐nucleophiles), showing that the RE mechanism is always favoured in MeCN solution. These computations also indicate that a radical mechanism (single electron transfer) may play an important role. The computational protocol based on accelerated molecular dynamics for the exploration of the free energy surface is transferable and will be applied to similar reactions to investigate other electrophiles on the reagent. Based on the activation parameters determined, this approach also gives insight into the mechanistic details of the trifluoromethylation and shows that these commonly known mechanisms mark the limits within which the reaction proceeds. © 2015 Wiley Periodicals, Inc.     

Excursion to the World of Heptacyclic Compounds Made of Azulenes and Acetylenedicarboxylates

Azulenes and acetylenedicarboxylates react under acid catalysis (Brønsted or Lewis) and form (2aRS,8aSR)‐2a,8a‐dihydrocyclopenta[cd]azulene‐1,2‐dicarboxylates as intermediate products, which then dimerize by central bond‐formation between C(2a¹) and C(2′a¹) and various peripheral C,C′‐atoms of the dihydroazulene fragments, depending on the substituents present. The reactions are often accompanied by the formation of side‐products, such as 2‐(azulen‐1‐yl)fumarates and ‐maleates and others caused by H‐shifts of the primary intermediates. H‐Shifts between the two tetrahydrocyclopenta[cd]azulene parts of the heptacyclic structures were also found.     

Two 2,6‐Dioxabicyclo[3.3.1]nonan‐3‐ones from Phragmanthera capitata (Spreng.) Balle (Loranthaceae)

Phytochemical investigation of the leaves of Phragmanthera capitata collected on Cassia spectabilis tree led to the isolation of two natural lactones, rel‐(1R,5S,7S)‐7‐[2‐(4‐hydroxyphenyl)ethyl]‐2,6‐dioxabicyclo[3.3.1]nonan‐3‐one ( 1 ) and 4‐{2‐[rel‐(1R,3R,5S)‐7‐oxo‐2,6‐dioxabicyclo[3.3.1]non‐3‐yl]ethyl}phenyl 3,4,5‐trihydroxybenzoate ( 2 ) together with the known compounds betulinic acid ( 3 ), dodoneine ( 4 ), quercetin 3‐O‐α‐L ‐rhamnopyranoside ( 5 ), quercetin 3‐O‐α‐L ‐arabinofuranoside ( 6 ), quercetin ( 7 ), betulin ( 8 ), lupeol ( 9 ), and sitosterol ( 10 ). Their structures were established by means of modern spectroscopic techniques, and the relative configuration of compound 1 was confirmed by X‐ray analysis. Compounds 1 and 2 were tested in vitro for their antiplasmodial activity against the Plasmodium falciparum chloroquine sensitive‐strains NF54 and 3D7. Compound 2 exhibited good antiplasmodial activity against both strains with IC₅₀ of 2.4 and 4.9 μM , respectively, while compound 1 was inactive.     

Dual‐Modal Magnetic Resonance/Fluorescent Zinc Probes for Pancreatic β‐Cell Mass Imaging

Despite the contribution of changes in pancreatic β‐cell mass to the development of all forms of diabetes mellitus, few robust approaches currently exist to monitor these changes prospectively in vivo. Although magnetic‐resonance imaging (MRI) provides a potentially useful technique, targeting MRI‐active probes to the β cell has proved challenging. Zinc ions are highly concentrated in the secretory granule, but they are relatively less abundant in the exocrine pancreas and in other tissues. We have therefore developed functional dual‐modal probes based on transition‐metal chelates capable of binding zinc. The first of these, Gd ?1 , binds Zn^II directly by means of an amidoquinoline moiety (AQA), thus causing a large ratiometric Stokes shift in the fluorescence from λ_em=410 to 500 nm with an increase in relaxivity from r₁=4.2 up to 4.9 mM ^?1 s^?1. The probe is efficiently accumulated into secretory granules in β‐cell‐derived lines and isolated islets, but more poorly by non‐endocrine cells, and leads to a reduction in T₁ in human islets. In vivo murine studies of Gd ?1 have shown accumulation of the probe in the pancreas with increased signal intensity over 140 minutes.     

Probing the Diastereoselectivity of Staudinger Reactions Catalyzed by N‐Heterocyclic Carbenes

The reaction of ethylphenylketene with 1,3‐dimesitylimidazol‐2‐ylidene (IMes) or 1,3‐dimesitylimidazolin‐2‐ylidene (SIMes) afforded the corresponding azolium enolates in high yields. The two zwitterions were fully characterized by various analytical techniques. Their thermal stabilities were monitored by thermogravimetric analysis and the molecular structure of SIMes ? EtPhC?C?O was determined by means of X‐ray crystallography. A mechanism was proposed to account for the trans‐diastereoselectivity observed in the [2+2] cycloaddition of ketenes and N‐protected imines catalyzed by N‐heterocyclic carbenes and an extensive catalytic screening was performed to test its validity. The steric bulk of the NHC catalyst markedly affected the cis/trans ratio of the model β‐lactam product. The nature of the solvent used to carry out the Staudinger reaction also significantly influenced its diastereoselectivity. Conversely, the nature of the substituent on the N‐sulfonated imine reagent and the reaction temperature were less critical parameters.