Chemphyschem最新文献

The application of RF power for CEST measurements requires heating effects, sensitivity, and spectral resolution to be balanced. The Front Cover shows how the chemical shifts for Xe, with fast exchange in cucurbit[6]uril and slow exchange in cryptophane-A, respond differently to temperature changes. The CEST response for fast exchange is much more sensitive to changes in saturation power. More information can be found in the Research Article by R. Schoof, L. Schröder and co-workers (DOI: 10.1002/cphc.202401037). Artwork by Barth van Rossum.

A combination of DFT and classical molecular dynamics simulations were performed to unveil the guiding force in the self-assembly process of the Pyrazine-based biopolymers to helical nanostructures.  The highlight of the study shows the decisive role of the solvent-ligand H-bonding and the inter-molecular pi-pi stacking not only ensures the uni-directional packing of the helical structure but also the rotation of left-handed to the right-handed helical structure of the molecule. This transition is supported by the bulk release of the "ordered" water molecules. The extent of this bonding can be tuned by the temperature, concentration, and the type of the metal ions. Smaller ions like Na+ and Al3+ destroyed the structure, whereas bigger ions like Zn2+, Ni2+, and Au3+ preserved and rotated the structure according to their concentration. The interaction energy between the Pyrazine derivatives was found to be high (-9000 kJ/mol) for right-handed rotation of the helix, which increases further with the addition of D-histidine, forming a superhelical structure (-10300 kJ/mol). The insights gained from this work can be used to generate nanostructures of desired morphology .

All-atom quantum mechanics (AQM) methodologies are assessed to evaluate one- and two-photon absorption (1PA and 2PA) of realistic systems. All-atom single structure QM (ASQM) and dynamic structure QM (ADQM) methodologies are discussed. These workflows are possible thanks to developments in simplified quantum chemistry methods and in particular with both sTD-DFT-xTB and dt-sTD-DFT-xTB schemes. The ASQM scheme is tested to compute the 1- and 2PA of two proteins: bacteriorhodopsin and iLOV. Results show that the ASQM methodology is able to describe higher-energy transitions involving π-conjugated amino acids such as tryptophan or tyrosine. Then, two variants of the ADQM workflow are evaluated to reproduce the 1- and 2PA of the flavin mononucleotide (FMN) in aqueous solution, involving either Boltzmann ensemble of conformers in implicit solvent (ADQM-Boltz.) or snapshots of molecular dynamics of explicitly solvated systems (ADQM-MD). Spectra computed with the ADQM-MD approach provide striking comparisons with respect to experiment while the ADQM-Boltz. approach provides little change with respect to the ASQM workflow.

Sulfuric acid-ammonia clusters play important roles in atmospheric nucleation processes. However, experimental structural analysis of relative medium-sized or large-sized clusters at the molecular level has always been lacking. Herein, tandem mass spectrometry and IR photondissociation (IRPD) spectroscopy were applied to mass-selected medium-sized cluster ions that have diameters of 1.0-1.2 nm. The differences in their dissociation behaviors and IRPD spectra of the cluster cations and anions are attributed to their structural characteristics, which are further revealed by the combination of theoretical calculations. The protonated clusters can be treated as structures composed of ammonium cations and hydrogen sulfate anions with an alternate acid-base arrangement, which makes their dissociation characterized by the loss of the acid-base pair. For deprotonated clusters, the mobility of intra-cluster protons lowers energy barriers of isomerization, making their dissociation pathways more complicated. The differences and commonalities in the formation of organic acid- and inorganic acid- ammonia clusters are also discussed, as well as their impacts on nucleated orders and sizes. The method can be further extended to other clusters for obtaining the lacking information of relative key species in the formation of new particles in the atmosphere.

The influence of La promoter on the catalytic performance of Rh nanoparticles supported on TiO2 nanotubes (TNTs) in the hydroformylation of vinyl acetate was investigated. The catalysts were characterized using ICP-MS, BET, XRD, SEM, TEM, XPS, FT-IR, and H2/CO TPD. The results indicated that an effect attributed to the formation of LaOx-Rh active sites during the catalytic reaction. The optimized Rh0.25-La/TNTs catalyst (0.14 wt.% Rh, 0.29 wt.% La) achieved a high vinyl acetate conversion of 89%, an aldehyde selectivity of 66%, and a remarkable TOF of 5796 h-1.

Nucleophilicities NHnA of hydrides of atoms A acting as hydrogen-bond acceptors in complexes HnALHX are reported. The HnA initially chosen were HB, H2C, H3N, H2O and HF, that is from Groups 13, 14, 15, 16 and 17, respectively, of Row 1 of the Periodic Table.  The Lewis acids HX involved in the complexes were HF, HCl, HBr, HI, HCCH, and HCP.  Nucleophilicities were determined from dissociation energies De for the process HnALHX = HnA + HX by  using De = cNHnA.EHX, where EHX are electrophilicities of the Lewis acids HX.  This procedure was also followed for hydrides HnA  where the atoms A were from the same Groups, but from Rows 2, 3, and 4 of the Periodic Table. The order of NHnA values found was Row 1 > Row2 ~ Row3 ~ Row 4 in each of the Groups 13, 15, 15, 16 and 17, with a large decrease from Row 1 to Row 2 but with small decreases from Rows 2 to 3 to 4. The series RgLHX, was similarly investigated to give the order of nucleophilicities Rg = Xe > Kr > Ar. > Ne, which is reversed from that in the hydrides of Groups 13 to 17.

With growing interest in carbon-based materials for energy storage and active research in the field of advanced optoelectronic devices, we theoretically designed ten complexes by cyclo[18]carbon (C18) inside and outside complexing alkali-metal ion (M+ = Li+, Na+, K+, Rb+, and Cs+), respectively referred to as M+@C18in and M+@C18out, and performed careful analyses of their structure, binding interaction between M+ and C18, as well as optical properties of stable endohedral complexes M+@C18in. The effects of atomic number of alkali-metals on structure, binding interaction, electronic absorption spectrum, and molecular (hyper)polarizability of the M+@C18in were studied using accurate (time-dependent) density functional theory [(TD-)DFT)] calculations. The research suggests that the binding modes and strengths of different M+ with C18 are different, but there is no evident difference in electronic absorption spectra of the complexes; the polarizability and second hyperpolarizability of M+@C18in containing different alkali-metal ions are close due to the similarity of ionic properties, but their first hyperpolarizability differ greatly by reason of discrepancy in molecular symmetry. The similarities and differences in structure, fragment interaction, electronic absorption spectrum, and (hyper)polarizability of M+@C18in were explored using advanced wavefunction analysis methods.

Understanding protein folding pathways is crucial to deciphering the principles of protein structure and function. Here, we investigate the unfolding dynamics of the 35-residue villin headpiece (HP35) and a norleucine-substituted variant (2F4K) using a combination of experimental and computational techniques. Time-resolved X-ray solution scattering (TRXSS) coupled with equilibrium Molecular Dynamics (MD) simulations and Markov State modeling reveals distinct unfolding mechanisms between the two variants: HP35 and 2F4K. Specifically, HP35 exhibits a two-state unfolding process, whereas an intermediate state was identified for the 2F4K mutant. A Markov state model constructed from simulations was used to map atomic-level transitions to experimental observations, providing insights into the role of sequence variations in modulating folding pathways. Our findings underscore the importance of integrating experimental and computational approaches to unravel protein unfolding mechanisms between heterogenous structural ensembles.

The spin-crossover (SCO) properties of the dinuclear complex [{Fe(H2B(pz)2)2}2μ-(ac(bipy)2)] were studied as (sub)-monolayer and thin film deposited by an ultrahigh vacuum liquid-jet deposition technique on highly oriented pyrolytic graphite (HOPG) by X-ray absorption spectroscopy. A comparison of the SCO properties of thin films and a dropcast sample indicates that the spinswitching probability of the thin films is limited due to substrate-molecule interactions. The maximum percentage of molecules in the low-spin (LS) state observed for 0.7 and 1.8 monolayers (ML) is approximately 43% at a temperature of 80K in comparison to the dropcast sample where ≈ 66% of the complex is in the LS state. The similar switching properties of the dropcast sample as of a bulk powder sample confirm that the SCO properties are not affected by the presence of solvent necessary for deposition. The soft- X-ray-induced excited spin-state trapping (SOXIESST) effect is pronounced in all samples, although the light-induced high-spin (HS) fraction of the dropcast and the thin-film samples on HOPG is higher as compared to the HS fraction attained by SOXIESST, which confirms the sensitivity of the complex to light.

The reaction of CO2 with seven molecules featuring a 1,4-diborinine central ring has been studied by means of Density Functional Theory calculations. The selected systems present five- and six-membered aza rings surrounding the 1,4-diborinine with neutral, anion and dianion charges. In all cases, the reaction is exothermic and exergonic. The computed reactivity trends and origin of regioselectivity have been quantitatively analyzed in detail with the activation strain model in combination with the energy decomposition analysis method, which indicates the crucial role of electrostatic and orbital interactions in the transformations.