Electron-beam-promoted fullerene dimerization in nanotubes: insights from DFT computations.

Fullerene dimerization inside a peapod is analyzed at DFT level by characterizing the stationary points and deriving the energy profile of the initial and reversible process named phase 1. We find that the barriers for the radical cation mechanism are significantly lower than those found for the neutral pathway. The peapod is mainly providing one-dimensional confinement for the reaction to take place in a more efficient way. Car-Parrinello metadynamics simulations provide hints on structures for the initial steps of the irreversible phase 2 where bond formation and breaking lead to important structural reorganizations within the coalescence process.

Cerebral and systemic near infrared spectroscopy patterns in preterm infants treated by caffeine.

AIM: To investigate the effects of caffeine loading/maintenance administration on near-infrared spectroscopy cerebral, kidney and splanchnic patterns in preterm infants. METHODS: We conducted a multicentre case-control prospective study in 40 preterm infants (gestational age 29 ± 2 weeks) where each case acted as its own control. A caffeine loading dose of 20 mg/kg and a maintenance dose of 5 mg/kg after 24 h were administered intravenously. Near infrared spectroscopy monitoring parameters were monitored 30 min before, 30 min during and 180 min after caffeine therapy administration. RESULTS: A significant increase (p < 0.05) in splanchnic regional oxygenation and tissue function and a decrease (p < 0.05) in cerebral tissue function after loading dose was shown. A preferential hemodynamic redistribution from cerebral to splanchnic bloodstream was also observed. After caffeine maintenance dose regional oxygenation did not change in the monitored districts, while tissue function increased in kidney and splanchnic bloodstream. CONCLUSION: Different caffeine administration modalities affect cerebral/systemic oxygenation status, tissue function and hemodynamic pattern in preterm infants. Future studies correlating near infrared spectroscopy parameters and caffeine therapy are needed to determine the short/long-term effect of caffeine in preterm infants.

Actinide-lanthanide single electron metal-metal bond formed in mixed-valence di-metallofullerenes.

Understanding metal-metal bonding involving f-block elements has been a challenging goal in chemistry. Here we report a series of mixed-valence di-metallofullerenes, ThDy@C2n (2n = 72, 76, 78, and 80) and ThY@C2n (2n = 72 and 78), which feature single electron actinide-lanthanide metal-metal bonds, characterized by structural, spectroscopic and computational methods. Crystallographic characterization unambiguously confirmed that Th and Y or Dy are encapsulated inside variably sized fullerene carbon cages. The ESR study of ThY@D3h(5)-C78 shows a doublet as expected for an unpaired electron interacting with Y, and a SQUID magnetometric study of ThDy@D3h(5)-C78 reveals a high-spin ground state for the whole molecule. Theoretical studies further confirm the presence of a single-electron bonding interaction between Y or Dy and Th, due to a significant overlap between hybrid spd orbitals of the two metals.

U@Cs(4)-C82: A Different Cage Isomer with Reactivity Controlled by U-Sumanene Interaction.

Actinide endohedral metallofullerenes (EMFs) are a fullerene family that possess unique actinide-carbon cage host-guest molecular and electronic structures. In this work, a novel actinide EMF, U@Cs(4)-C82, was successfully synthesized and characterized, and its chemical reactivity was investigated. Crystallographic analysis shows that U@Cs(4)-C82, a new isomer of U@C82, has a Cs(4)-C82 cage, which has never been discovered in the form of empty or endohedral fullerenes. Its unique chemical reactivities were further revealed through the Bingel-Hirsch reaction and carbene addition reaction studies. The Bingel-Hirsch reaction of U@Cs(4)-C82 shows exceptionally high selectivity and product yield, yielding only one major addition adduct. Moreover, the addition sites for both reactions are unexpectedly located on adjacent carbon atoms far away from the actinide metal, despite the nucleophilic (Bingel-Hirsch) and electrophilic (carbene addition) nature of either reactant. Density functional theory (DFT) calculations suggest that this chemical behavior, unprecedented for EMFs, is directed by the unusually strong interaction between U and the sumanene motif of the carbon cage in U@Cs(4)-C82, which makes the energy increase when it is disrupted. This work reveals remarkable chemical properties of actinide EMFs originating from their unique electronic structures and highlights the key role of actinide-cage interactions in the determination of their chemical behaviors.

Early changes in S100B maternal blood levels can predict fetal intrauterine growth restriction.

OBJECTIVES: Intrauterine growth restriction (IUGR) represents one of the main causes of perinatal mortality and morbidity. Nowadays, IUGR early diagnosis is mandatory in order to limit the occurrence of multiorgan failure, especially the brain. Therefore, we investigated whether longitudinal S100B assessment in maternal blood could be a trustable predictor of IUGR. METHODS: We conducted a prospective study in 480 pregnancies (IUGR: n=40; small for gestational age, SGA: n=40; controls: n=400) in whom S100B was measured at three predetermined monitoring time-points (T1: 8-18 GA; T2: 19-23 GA; T3: 24-28 GA). RESULTS: Lower S100B in IUGR fetuses than SGA and controls (p<0.05, for all) at T1-T3. Receiver operating characteristic curve showed that S100B at T1 was the best predictor of IUGR (sensitivity: 100 %; specificity: 81.4 %) than T2, T3. CONCLUSIONS: The early lower S100B concentration in pregnant women lately complicated by IUGR support the notion that non-invasive early IUGR diagnosis and monitoring is becoming feasible. Results open the way to further studies aimed at diagnosing and monitoring fetal/maternal diseases at earliest time.

Effects of Solvents on Reaction Products: Synthesis of Endohedral Metallofullerene Oxazoline and Epoxide.

Herein, we performed the reactions of M3N@Ih-C80 (M = Sc and Lu) with the methanol (CH3OH) solution of TBAOH (note that both CH3O- and OH- are nucleophiles) in benzonitrile (PhCN) and dimethylformamide, respectively. It is found that OH- ions rather than CH3O- ions selectively attacked the fullerene cage to form the M3N@C80--O- intermediate. Although the fullerene cage is initially attacked by OH- in both PhCN and DMF solvents, the products are quite different. In PhCN, two isomeric Sc3N@Ih-C80 fullerooxazoline heterocyclic products (1 and 2) were synthesized. Whereas, in DMF, an epoxide of Lu3N@Ih-C80 (3) was obtained. The preference for fullerooxazoline formation over that of fullerene epoxy in PhCN is well explained by density functional theory calculations. Plausible reaction mechanisms for the formation of metallofullerene oxazoline and epoxide were proposed based on the experimental and theoretical results.

Modulation of Chiroptical and Photophysical Properties in Helicenic Rhenium(I) Systems: The Use of an N-(Aza[6]helicenyl)-NHC Ligand.

The photophysical and chiroptical properties of a novel, chiral helicene-NHC-Re(I) complex bearing an N-(aza[6]helicenyl)-benzimidazolylidene ligand are described, showing its ability to emit yellow circularly polarized luminescence. A comparative analysis of this new system with other helicene-Re(I) complexes reported to date illustrates the impact of structural modifications on the emissive and absorptive properties.

Structurally Defined Water-Soluble Metallofullerene Derivatives towards Biomedical Applications.

Endohedral metallofullerenes (EMFs) are excellent carriers of rare-earth element (REE) ions in biomedical applications because they preclude the release of toxic metal ions. However, existing approaches to synthesize water-soluble EMF derivatives yield mixtures that inhibit precise drug design. Here we report the synthesis of metallobuckytrio (MBT), a three-buckyball system, as a modular platform to develop structurally defined water-soluble EMF derivatives with ligands by choice. Demonstrated with PEG ligands, the resulting water-soluble MBTs show superb biocompatibility. The Gd MBTs exhibit superior T1 relaxivity than typical Gd complexes, potentially superseding current clinical MRI contrast agents in both safety and efficiency. The Lu MBTs generated reactive oxygen species upon light irradiation, showing promise as photosensitizers. With their modular nature to incorporate other ligands, we anticipate the MBT platform to open new paths towards bio-specific REE drugs.

A charged diatomic triple-bonded U≡N species trapped in C82 fullerene cages.

Actinide diatomic molecules are ideal models to study elusive actinide multiple bonds, but most of these diatomic molecules have so far only been studied in solid inert gas matrices. Herein, we report a charged U≡N diatomic species captured in fullerene cages and stabilized by the U-fullerene coordination interaction. Two diatomic clusterfullerenes, viz. UN@Cs(6)-C82 and UN@C2(5)-C82, were successfully synthesized and characterized. Crystallographic analysis reveals U-N bond lengths of 1.760(7) and 1.760(20) Å in UN@Cs(6)-C82 and UN@C2(5)-C82. Moreover, U≡N was found to be immobilized and coordinated to the fullerene cages at 100 K but it rotates inside the cage at 273 K. Quantum-chemical calculations show a (UN)2+@(C82)2- electronic structure with formal +5 oxidation state (f1) of U and unambiguously demonstrate the presence of a U≡N bond in the clusterfullerenes. This study constitutes an approach to stabilize fundamentally important actinide multiply bonded species.

Organic radicals with inversion of SOMO and HOMO energies and potential applications in optoelectronics.

Organic radicals possessing an electronic configuration in which the energy of the singly occupied molecular orbital (SOMO) is below the highest doubly occupied molecular orbital (HOMO) level have recently attracted significant interest, both theoretically and experimentally. The peculiar orbital energetics of these SOMO-HOMO inversion (SHI) organic radicals set their electronic properties apart from the more common situation where the SOMO is the highest occupied orbital of the system. This review gives a general perspective on SHI, with key fundamental aspects regarding the electronic and structural factors that govern this particular electronic configuration in organic radicals. Selected examples of reported compounds with SHI are highlighted to establish molecular guidelines for designing this type of radical, and to showcase the potential of SHI radicals in organic spintronics as well as for the development of more stable luminescent radicals for OLED applications.

Density Functional Response Calculations of Dispersion Coefficients C6 and C9 of Closed- and Open-Shell Systems.

Dipole polarizabilities and C6 and C9 dispersion coefficients are computed for closed- and open-shell atoms and molecules, using dynamic (time-dependent) density functional (TD-DFT) linear response theory as implemented in the response module of the NWChem quantum chemistry package. The response module is capable of accurate calculations of these properties, based on spin-restricted and spin-unrestricted formalisms. The calculated static polarizabilities and dispersion coefficients are compared to available experimental and other theoretical data. The behavior of the dynamic polarizability at imaginary frequencies is analyzed for differently sized closed- and open-shell systems. An interpolation method enforcing the monotonic decrease of the polarizability with increasing imaginary frequency is beneficial for the integration used to obtain C6 and C9. Scaling of the TD-DFT data by ratios of the static polarizability, which can be calculated with a variety of methods, including highly accurate theories, may be used as a leading-order correction.

Measuring the elastic modulus of soft biomaterials using nanoindentation.

The measurement of the elastic modulus of soft biomaterials via nanoindentation relies on the accurate determination of the zero-point of the tip-sample interaction on which the depth of penetration into the sample is based. Non-cantilever based nanoindentation systems were originally designed for hard materials, and therefore monitoring the zero-point contact presents a significant challenge for the characterisation of very soft biomaterials. This study investigates the ability of non-cantilever based nanoindentation to differentiate between hydrogels with elastic moduli on the order of single kiloPascals (kPa) using a bespoke soft contact protocol and low flexural stiffness of instrument. Polyethylene glycol (PEG) hydrogels were fabricated as a model system with a range of elastic moduli by varying the polymer concentration and degree of crosslinking. Elastic modulus values were calculated using the Oliver-Pharr method, Hertzian contact model, as well as a viscoelastic model to account for the time-dependent behaviour of the gels. The stiffness measurements were validated by measuring cantilever beams with the equivalent flexural stiffness to that of the PEG hydrogels being tested. The results demonstrated a high repeatability of the measurements, enabling differentiation between hydrogels with elastic moduli in the single kPa to hundreds of kPa range.

Carbazole Isomerism in Helical Radical Cations: Spin Delocalization and SOMO-HOMO Level Inversion in the Diradical State.

We report a new molecular design to afford persistent chiral organic open-shell systems with configurational stability and an inversion in energy of the singly occupied molecular orbital (SOMO) and the highest doubly occupied molecular orbital (HOMO) for both mono- and diradical states. The unpaired electron delocalization within the designed extended helical π-conjugated systems is a crucial factor to reach chemical stabilities, which is not obtained using the classical steric protection approach. The unique features of the obtained helical monoradicals allow an exploration of the chiral intramolecular electron transfer (IET) process in solvents of different polarity by means of optical and chiroptical spectroscopies, resulting in an unprecedented electronic circular dichroism (ECD) sign inversion for the radical transitions. We also characterized the corresponding helical diradicals, which show near-infrared electronic circular dichroism at wavelengths up to 1100 nm and an antiferromagnetic coupling between the spins, with an estimated singlet-triplet gap (ΔEST) of about -1.2 kcal mol-1. The study also revealed an intriguing double SOMO-HOMO inversion (SHI) electronic configuration for these diradicals, providing new insight regarding the peculiar energetic ordering of radical orbitals and the impact on the corresponding (chiral) optoelectronic properties.

Helical Chiral N-Heterocyclic Carbene Ligands in Enantioselective Gold Catalysis.

The first chiral helicene-NHC gold(I) complexes efficient in enantioselective catalysis were prepared. The L-shaped chiral ligand is composed of an imidazo[1,5-a]pyridin-3-ylidene (IPy) scaffold laterally substituted by a configurationally stable [5]-helicenoid unit. The chiral information was introduced in a key post-functionalization step of a NHC-gold(I) complex bearing a symmetrical anionic fluoreno[5]helicene substituent, leading to a racemic mixture of complexes featuring three correlated elements of chirality, namely central, axial and helical chirality. After HPLC enantiomeric resolution, X-ray crystallography and theoretical calculations enabled structural and stereochemical characterization of these configurationally stable NHC-gold(I) complexes. The high potential in asymmetric catalysis is demonstrated in the benchmark cycloisomerization of N-tethered 1,6-enynes with up to 95 : 5 er.

S100B Maternal Blood Levels in Gestational Diabetes Mellitus Are Birthweight, Gender and Delivery Mode Dependent.

Gestational Diabetes Mellitus (GDM) is one of the main causes of perinatal mortality/morbidity. Today, a parameter offering useful information on fetal central nervous system (CNS) development/damage is eagerly awaited. We investigated the role of brain-protein S100B in the maternal blood of GDM pregnancies by means of a prospective case-control study in 646 pregnancies (GDM: n = 106; controls: n = 530). Maternal blood samples for S100B measurement were collected at four monitoring time-points from 24 weeks of gestation to term. Data was corrected for gender and delivery mode and correlated with gestational age and weight at birth. Results showed higher (p < 0.05) S100B from 24 to 32 weeks and at term in GDM fetuses than controls. Higher (p < 0.05) S100B was observed in GDM male new-borns than in females from 24 to 32 weeks and at term, in GDM cases delivering vaginally than by caesarean section. Finally, S100B positively correlated with gestational age and weight at birth (R = 0.27; R = 0.37, respectively; p < 0.01). The present findings show the usefulness of S100B in CNS to monitor high-risk pregnancies during perinatal standard-of-care procedures. The results suggest that further investigations into its potential role as an early marker of CNS growth/damage in GDM population are needed.

Artificial Cornea: Past, Current, and Future Directions.

Corneal diseases are a leading cause of blindness with an estimated 10 million patients diagnosed with bilateral corneal blindness worldwide. Corneal transplantation is highly successful in low-risk patients with corneal blindness but often fails those with high-risk indications such as recurrent or chronic inflammatory disorders, history of glaucoma and herpetic infections, and those with neovascularisation of the host bed. Moreover, the need for donor corneas greatly exceeds the supply, especially in disadvantaged countries. Therefore, artificial and bio-mimetic corneas have been investigated for patients with indications that result in keratoplasty failure. Two long-lasting keratoprostheses with different indications, the Boston type-1 keratoprostheses and osteo-odonto-keratoprostheses have been adapted to minimise complications that have arisen over time. However, both utilise either autologous tissue or an allograft cornea to increase biointegration. To step away from the need for donor material, synthetic keratoprostheses with soft skirts have been introduced to increase biointegration between the device and native tissue. The AlphaCor™, a synthetic polymer (PHEMA) hydrogel, addressed certain complications of the previous versions of keratoprostheses but resulted in stromal melting and optic deposition. Efforts are being made towards creating synthetic keratoprostheses that emulate native corneas by the inclusion of biomolecules that support enhanced biointegration of the implant while reducing stromal melting and optic deposition. The field continues to shift towards more advanced bioengineering approaches to form replacement corneas. Certain biomolecules such as collagen are being investigated to create corneal substitutes, which can be used as the basis for bio-inks in 3D corneal bioprinting. Alternatively, decellularised corneas from mammalian sources have shown potential in replicating both the corneal composition and fibril architecture. This review will discuss the limitations of keratoplasty, milestones in the history of artificial corneal development, advancements in current artificial corneas, and future possibilities in this field.

Luminescent Chiral Exciplexes with Sky-Blue and Green Circularly Polarized-Thermally Activated Delayed Fluorescence.

Luminescent exciplexes based on a chiral electron donor and achiral acceptors are reported as a new approach to design circularly polarized (CP) and thermally activated delayed fluorescence (TADF) emitters. This strategy results in rather high CP luminescence (CPL) values with glum up to 7×10-3 , one order of magnitude higher in comparison to the CPL signal recorded for the chiral donor alone (glum ∼7×10-4 ). This increase occurs concomitantly with a CPL sign inversion, as a result of the strong charge-transfer emission character, as experimentally and theoretically rationalized by using a covalent chiral donor-acceptor model. Interestingly, blue, green-yellow and red chiral luminescent exciplexes can be obtained by modifying with the electron accepting character of the achiral unit while keeping the same chiral donor unit. These results bring new (inter)molecular guidelines to obtain simply and efficiently multi-color CP-TADF emitters.

Exciton coupling chirality in helicene-porphyrin conjugates.

Enantiopure helicene-porphyrin conjugates were prepared. They show strong changes in their circular dichroic response as compared to classical helicene derivatives, with highly intense bisignate Exciton Coupling (EC) signal and Δε values up to 680 M-1 cm-1 for the Soret band. They also display circularly polarized fluorescence in the (far-)red region, with dissymmetry factors up to 7 × 10-4.

UCN@Cs(6)-C82: An Encapsulated Triangular UCN Cluster with Ambiguous U Oxidation State [U(III) versus U(I)].

Understanding the chemical behavior of actinide elements is essential for the effective management and use of actinide materials. In this study, we report an unprecedented η2 (side-on) coordination of U by a cyanide in a UCN cluster, which was stabilized inside a C82 fullerene cage. UCN@Cs(6)-C82 was successfully synthesized and fully characterized by mass spectrometry, single crystal X-ray crystallography, cyclic voltammetry, spectroscopy, and theoretical calculations. The bonding analysis demonstrates significant donation bonding between CN- and uranium, and covalent interactions between uranium and the carbon cage. These effects correlate with an observed elongated cyanide C-N bond, resulting in a rare case where the oxidation state of uranium shows ambiguity between U(III) and U(I). The discovery of this unprecedented triangular configuration of the uranium cyanide cluster provides a new insight in coordination chemistry and highlights the large variety of bonding situations that uranium can have.

Correction: Unexpected formation of 1,2- and 1,4-bismethoxyl Sc3N@I h-C80 derivatives via regioselective anion addition: an unambiguous structural identification and mechanism study.

[This corrects the article DOI: 10.1039/D1SC01178B.].