Excimer emission of caffeine with α- and β-cyclodextrins: spectral and molecular modelling studies

Excimer emission of caffeine with α-CD and β-CD were studied by UV-visible, fluorescence, time-resolved fluorescence, FTIR, ¹H NMR and molecular modelling techniques. Changes in the absorbance and fluorescence and lifetime of the caffeine with cyclodextrin (CD) solutions indicate (i) caffeine shows dual emission in the CD solutions, (ii) normal emission originates from a monomer and the longer wavelength emission is due to excimer and (iii) in both CDs caffeine forms 1:2 inclusion complex. Carbonyl stretching frequency moved to higher wave numbers and broadening of the N–H stretching band indicated the formation of inclusion complex. The resonance of the methyl protons of caffeine show remarkable upfield or downfield shift in the ¹H NMR, which indicates imidazole ring of the caffeine entrapped in the CD cavities. Investigations of energetic, thermodynamic and electronic properties of PM3 computational calculations confirmed the stability of the inclusion complex.     

Marine Bioluminescence: Measurement by a Classical Light Sensor and Related Foraging Behavior of a Deep Diving Predator

Bioluminescence is produced by a broad range of organisms for defense, predation or communication purposes. Southern elephant seal (SES) vision is adapted to low‐intensity light with a peak sensitivity, matching the wavelength emitted by myctophid species, one of the main preys of female SES. A total of 11 satellite‐tracked female SESs were equipped with a time‐depth‐light 3D accelerometer (TDR10‐X) to assess whether bioluminescence could be used by SESs to locate their prey. Firstly, we demonstrated experimentally that the TDR10‐X light sensor was sensitive enough to detect natural bioluminescence; however, we highlighted a low‐distance detection of the sensor. Then, we linked the number of prey capture attempts (PCAs), assessed from accelerometer data, with the number of detected bioluminescence events. PCA was positively related to bioluminescence, which provides strong support that bioluminescence is involved in predator–prey interactions for these species. However, the limitations of the sensor did not allow us to discern whether bioluminescence (i) provided remote indication of the biological richness of the area to SES, (ii) was emitted as a mechanic reaction or (iii) was emitted as a defense mechanism in response to SES behavior.     

An Ethenoadenine FAD Analog Accelerates UV Dimer Repair by DNA Photolyase

Reduced anionic flavin adenine dinucleotide (FADH^?) is the critical cofactor in DNA photolyase (PL) for the repair of cyclobutane pyrimidine dimers (CPD) in UV‐damaged DNA. The initial step involves photoinduced electron transfer from *FADH^? to the CPD. The adenine (Ade) moiety is nearly stacked with the flavin ring, an unusual conformation compared to other FAD‐dependent proteins. The role of this proximity has not been unequivocally elucidated. Some studies suggest that Ade is a radical intermediate, but others conclude that Ade modulates the electron transfer rate constant (k_ET) through superexchange. No study has succeeded in removing or modifying this Ade to test these hypotheses. Here, FAD analogs containing either an ethano‐ or etheno‐bridged Ade between the AN1 and AN6 atoms (e‐FAD and ε‐FAD, respectively) were used to reconstitute apo‐PL, giving e‐PL and ε‐PL respectively. The reconstitution yield of e‐PL was very poor, suggesting that the hydrophobicity of the ethano group prevented its uptake, while ε‐PL showed 50% reconstitution yield. The substrate binding constants for ε‐PL and rPL were identical. ε‐PL showed a 15% higher steady‐state repair yield compared to FAD‐reconstituted photolyase (rPL). The acceleration of repair in ε‐PL is discussed in terms of an ε‐Ade radical intermediate vs superexchange mechanism.     

Damaging Effects of Ultraviolet Radiation on the Cornea

The cornea sits at the anterior aspect of the eye and, like the skin, is highly exposed to ultraviolet radiation (UVR). The cornea blocks a significant proportion of UVB from reaching the posterior structures of the eye. However, UVA can penetrate the full thickness of the cornea, even reaching the anterior portion of the lens. Epidemiological data indicate that UVR is a contributing factor for a multitude of diseases of the cornea including pterygium, photokeratitis, climatic droplet keratopathy and ocular surface squamous neoplasia (OSSN), although the pathogenic mechanisms of each require further elucidation. UVR is a well‐known genotoxic agent, and its effects have been well characterized in organs such as the skin. However, we are only beginning to identify its effects on the cornea, such as the UVR signature C → T and CC → TT transversions identified by sequencing and increased proliferative and shedding rates in response to UVR exposure. Alarmingly, a single low‐dose exposure of UVR to the cornea is sufficient to elicit genetic, molecular and cellular changes, supporting the consideration of using protective measures, such as wearing sunglasses when outdoors. The aim of this review was to describe the adverse effects of UVR on the cornea.     

Kinetics of carbon dioxide absorption from air in a flow reactor with a fixed bed of K<Subscript>2</Subscript>CO<Subscript>3</Subscript>-based sorbent

Sorption of carbon dioxide from air in a flow reactor with a bulky fixed bed of the K₂CO₃/Al₂O₃ composite sorbent was studied. The dynamic sorption capacity of the material was shown to depend on the relative humidity of the inlet air. A numerical model was constructed for evaluating the profile of СО₂ concentration in the layer and kinetic curves of CO₂ breakthrough at the outlet of the reactor. The results of simulation allowed us to adequately describe the experimental kinetic curves at 20–40% humidity.     

Two crystalline polymorphic forms of α-(<Emphasis Type="Italic">N</Emphasis>-benzoxazolin-2-one)acetic acid

Two crystalline polymorphic forms of α-(N-benzoxazolin-2-one)acetic acid (BAA) are prepared by changing the temperature of its crystallization from solution in ethanol. Crystallographic data of the α-form are determined: a = 12.7769(17) Å, b = 8.2574(9) Å, c = 16.7390(19) Å, β = 105.087(13)°, space group C2/c, V = 1705.2(4) ų, and Z = 8, while those of β form are a = 5.2854(4) Å, b = 5.9880(4) Å, c = 13.4509(5) Å, β = 94.666(4)°, space group P2₁, V = 424.30(4) ų, and Z = 2. It is found that BAA molecules of the α form combine into infinite one-dimensional chains arranged along axis b by means of O?H···O and C?H···O hydrogen bonds, and these chains are crosslinked via C?H···O hydrogen bonds to form a threedimensional structure. The β form has another system of hydrogen bonds, one of which is bifurcated (O4···O2, O4···O3), and the π–π-interactions between the benzoxazolinone fragments of BAA molecules combined into a chain also arranged along axis b are observed. Calorimetric analysis shows that the polymorphic transition from the α form to the β form occurs at 129°C.     

Visible and near-IR spectroscopy of endohedral Gd@C82(C 2v ) and Ho@C82(C 2v ) metallofullerenes and their monoanions

Solutions of endohedral Gd@C₈₂(C _2v ) and Ho@C₈₂(C _2v ) metallofullerenes are studied by means of visible and near-IR spectroscopy upon their conversion from neutral to the anionic form via a redox reaction with the electron donor potassium perchlorotriphenylmethide K(18-crown-6)[C(C₆Cl₅)₃]. The concentrations of the studied solutions of endohedral Gd@C₈₂(C _2v ) and Ho@C₈₂(C _2v ) metallofullerenes in o-dichlorobenzene were determined from the spectroscopic data, and their molar extinction coefficients are calculated.

     

An efficient microwave assisted synthesis of N′-aryl/(alkyl)-substituted N-(4-hydroxy-6-phenylpyrimidin-2-yl)guanidines: Scope and limitations

Treatment of N-[(4-hydroxy-6-phenyl)pyrimidin-2-yl]cyanamide with 1° alkyl or arylamines in isopropyl alcohol for only 10 min at 110–120 °C under microwave conditions gave the corresponding N′-alkyl(aryl)guanidine derivatives in excellent yields (65–84%). Isolated yields were greatest when >1.0 equiv. of amines were employed, but excellent results were also obtained when aryl and alkylamines were reacted with a more atom-economical loading (1.0 equiv.; 70% and 72% ave. yields, respectively). Arylamines with either highly electron withdrawing substituents (e.g. CO₂H) or pi-deficient heterocycles (e.g. variously substituted aminopyridines) did not work well under these conditions, and reaction with ureas and/or amino acids did not give detectable products. Work-up was exceedingly simple, and involved simple collection and washing of product on a sintered glass funnel. Products were obtained in analytically pure form and required approximately 1 h to prepare, start to finish.     

Epoxy lactones by photooxidative rearrangement of 6β-acetoxyvouacapane

The first study of photooxidation reaction of 6β-acetoxyvouacapane isolated from Caesalpinia platyloba is reported. The reaction yielded four new epoxy lactones, 6β-acetoxy-15,16α-epoxy-13-spirocassa-12,16-olide, 6β-acetoxy-15,16β-epoxy-13-spirocassa-12,16-olide, 6β-acetoxy-12,13β-epoxycassa-16,12-olide and 6β-acetoxy-12,13α-epoxycassa-16,12-olide. All the structures were supported by 1D and 2D NMR spectroscopy as well as mass spectrometry. The stereochemistry was established on the base of single crystal X-ray diffraction.     

Synthesis of highly functionalized indeno[1,2-b]furans

Some novel functionalized indeno[1,2-b]furans were synthesized from the reaction of indandione/indanone and aldehydes at room temperature followed by the reaction of the Knoevenagel condendensed intermediate with 4-hydroxycoumarins in the presence of iodine as catalyst in dimethyl sulfoxide (DMSO) under thermal conditions. The reaction involved in a condensation and Michael addition followed by lactone ring opening and intramolecular cyclization process to afford the product in high yield in easy work-up procedure.