Energy Difference Research Articles

Minimum Energy Conical Intersection Optimization Using DFT/MRCI(2).

The combined density functional theory and multireference configuration interaction (DFT/MRCI) method is a semiempirical electronic structure approach that is both computationally efficient and has predictive accuracy for the calculation of electronic excited states and for the simulation of electronic spectroscopies. However, given that the reference space is generated via a selected-CI procedure, a challenge arises in the construction of smooth potential energy surfaces. To address this issue, we treat the local discontinuities that arise as noise within the Gaussian progress regression framework and learn the surfaces by explicitly incorporating and optimizing a white-noise kernel. The characteristic polynomial coefficient surfaces of the potential matrix, which are smooth functions of nuclear coordinates even at conical intersections, are learned in place of the adiabatic energies and are used to optimize the DFT/MRCI(2) minimum energy conical intersection geometries for representative intersection motifs in the molecules ethylene, butadiene, and fulvene. One consequence of explicitly treating the noise in the surfaces is that the energy difference cannot be made arbitrarily small at points of nominal intersection. Despite the limitations, however, we find the structures as well as the branching spaces to compare well with ab initio MRCI and conclude that this approach is a viable method to learn a smooth representation of DFT/MRCI(2) surfaces.

Exploring low barrier quantum tunneling and structural planarity in 3-methylstyrene conformers: Insights from microwave spectroscopy.

The first ground-state rotational spectrum of 3-methylstyrene (3MS) was measured by Fourier transform microwave spectroscopy under supersonic jet-cooled conditions. Transitions were assigned for two conformers: cis-3MS and trans-3MS. In the cis conformer, the vinyl group is oriented toward the methyl group, while in the trans conformer, it is positioned away from the methyl. The energy difference between the two conformers was calculated to be only 2.1cm-1, with the cis conformer having lower energy. Significant tunneling splitting, caused by the low-barrier internal rotation of the methyl group, was observed and analyzed using the XIAM and BELGI-Cs codes. The BELGI results show that the V3 barrier is 30.6688(87) cm-1 for the cis conformer and 11.0388(88) cm-1 for the trans conformer. The experimental rotational and torsional parameters are compared to their density functional theory counterparts. The planarity of the molecular geometry of cis- and trans-3MS is discussed, contributing to the long-standing topic of discussion about the planarity of styrene derivatives.

Confined active area and aggregation kinetic-based AuNPs@PVP nanosensors for simultaneous colorimetric detection of cysteine and homocysteine as homologues in human urine and serum.

The detection of cysteine (Cys) and homocysteine (Hcy) in biological fluids has great significance for early diagnosis, including Alzheimer's and Parkinson's disease. Thesimultaneous determination of Cys and Hcywith a single probe is still a huge challenge. Toenlarge the differences in space structure (line and ring) and energy (-721.78 and -761.08 Hartree) between Cys and Hcy, and to causeadifference of aggregation kinetics, gold nanoparticles (AuNPs) are capped with hydrophilic and low-toxic polyvinylpyrrolidone (PVP) (namedAuNPs@PVP) andsome surface-active sites of AuNPs are masked, the active area for the binding between AuNPs and the detection object is confined, meanwhile, the stability of AuNPs is improved. A novel nanosensorbased on confined active area and aggregation kinetics of AuNPs@PVP, is designed for the identification and determination of Cys and Hcy in 1 and 3min, respectively, with sufficiently lowdetection limit (4.12 and 4.35μM) and linear range (4.12-100μM) for health evaluation. This single colorimetric sensor wasapplied successfully tothe determination of urine and serum, evidencing highanti-interference ability.

Solvent influence on the optical absorption, frontier molecular orbitals, and electronic structure of 1-bromo adamantane.

The study of the influence of solvent on 1-bromo adamantane (BAD) exposes prominent solvatochromatic shifts in the optical absorbance and substantial solvent effects on the electronic structure. This facilitates the molecular probe abilities for the BAD with respect to the surrounding environments such as dielectric constant and polarity. BAD exhibits positive solvatochromism for nonpolar solvents and negative solvatochromatic shifts for polar and aromatic solvents. In accordance with this, significant energy changes are obtained on the orbital occupancies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), resulting in a large difference in energy among the various solvation environments. According to this, the HOMO-LUMO gap decreases in nonpolar solvents, and it increases with respect to polarity in the case of polar and aromatic solvents. Computed thermodynamic parameters and noncovalent interaction analysis also demonstrate the noticeable changes for different solvent dielectric continuums with more changes for solvent continuums with large dielectric constants. Experimentally recorded UV-Vis absorption spectra of the solvents exhibit positive and negative solvatochromism for the n to σ* electronic transition. Computational investigations carried out with equation-of-motion coupled-cluster with single and double excitations and configuration interaction singles calculations by means of the solvent model density implicit solvation model clearly demonstrate the strong influence of solvents on the electronic structure of the BAD molecule.

The Effect of Sulphur Atoms on the Structure of Biomolecule 2-Thiocytosine in the Gas-Phase, Solid-State, and Hydrated Forms and in DNA–DNA Microhelices as Compared to Canonical Ones

This study is focused on the effects of the sulphur atom in position 2 of the cytosine molecule, 2-thiocytosine (2TC), on the molecular structural parameters in the isolated state, as well as in the hydration, solid state arrangement, Watson–Crick pairs, and DNA–DNA microhelices, as compared to the canonical form. The main six tautomers were optimised at the MP2 and CCSD levels, and the sulphur atom does not show any effect on the stability trend of cytosine. The energy difference between T2b and T2a tautomers is twice as low in 2TC (1.15 kJ/mol) than in cytosine (2.69 kJ/mol). The IR and laser Raman spectra of 2TC were accurately assigned using DFT computations and solid-state simulations of the crystal unit cell through several tetramer forms. The results notably improve those previously published by other authors. The effect of explicit water molecules surrounding 2TC up to 30, corresponding to the first and second hydration shells, on geometries and tautomerism was analysed. The Watson–Crick base pairs’ stability (ΔECP = −97.458 kJ/mol) was found to be less than with cytosine (−105.930 kJ/mol). The calculated dipole moment was also lower (4.205 D) than with cytosine (5.793 D). The effect of 2TC on the 5′-dG-dC-dG-3′ and 5′-dA-dC-dA-3′ DNA–DNA optimised microhelices was evaluated through their calculated helical parameters, which indicates a clear deformation of the helix formation. The radius (R) with 2TC appears considerably shorter (6.200 Å) in the 5′-dA-dC-dA-3′ microhelix than that with cytosine (7.050 Å). Because of the special characteristics of the 2TC molecule, it can be used as an anticancer drug.

Structural Control of Photoconductivity in a Flexible Titanium-Organic Framework.

The soft nature of Metal-Organic Frameworks (MOFs) sets them apart from other non-synthetic porous materials. Their flexibility allows the framework components to rearrange in response to environmental changes, leading to different states and properties. The work extends this concept to titanium frameworks, demonstrating control over charge transport in porous molecular crystals. MUV-35 is a two-fold catenated framework composed of heterometallic TiMn2 trimers and electron donor 4,4',4″-(benzo[1,2-b:3,4-b':5,6-b″]trithiophene-2,5,8-triyl)tribenzoic acid (H3BTTTB) linkers, forming a rare sit-c net topology that can fold to reduce its volume by ≈40% through a single-crystal transformation controlled by linker conformation in open, intermediate, and closed states. This process, driven by a free energy difference of ≈300kJmol-1, originates from the formation of a continuous network of non-covalent interactions that force the spontaneous loss of the solvent in the pores of the framework to establish charge transport pathways that afford photocurrents of 2.5 × 10-3Sm-1 under visible light for an ON/OFF ratio (∆R) of four orders of magnitude. This photoconductivity rivals the best conductivity values described for though-transport conductive MOFs while maintaining a porosity of ≈1.000m2g-1.

An Analysis of the Kinetic Energy in the Basket to Handstand on Parallel Bars: A Case Study of an Elite Gymnast

(1) Background: This study aimed to examine the differences in the kinetic energy of the body’s center of mass between successful and unsuccessful attempts at transitioning from a basket to a handstand on the parallel bars. Special attention was given to the analysis of kinetic energy as a key factor in the efficient execution of this complex element. (2) Methods: The sample consisted of 10 successful and 10 unsuccessful attempts performed by an elite gymnast (a multiple-medalist in World and European Championships). All attempts and kinematic data were recorded and analyzed using high-frequency cameras (300 Hz) and the Ariel Performance 3D video system, respectively. Successful and unsuccessful performances were compared using a paired-sample t-test. (3) Results: Significant differences in kinetic energy were observed in the first part of the anti-gravitational phase of movement between successful and unsuccessful attempts. Successful attempts demonstrated a more favorable position at the beginning of this phase, allowing better utilization of accumulated kinetic energy—a higher position of the feet and hips, and a smaller shoulder joint angle at the moment the shoulder passed through the lower vertical. (4) Conclusions: Successful attempts in gymnastics are characterized by better biomechanical optimization and efficient kinetic energy use, achieved through an earlier entry into the second phase of movement with optimal body positioning, leading to greater peripheral and angular velocities crucial for performance.

Does physical activity level and total energy expenditure relate to food intake, appetite, and body composition in healthy older adults? A cross-sectional study

PurposeWith ageing, older adults (≥ 65 years) may experience decreased appetite, contributing to declines in body weight and muscle mass, potentially affecting physical capabilities. Physical activity (PA) has been suggested as a potential strategy to enhance appetite in older adults, but evidence supporting this is insufficient. This study aimed to investigate the relationship between PA levels, total energy expenditure (TEE), body composition, energy intake (EI) and appetite in older adults.MethodsOne hundred and eight healthy older adults (age 70 ± 4 years; BMI 24.3 ± 2.6 kg/m2) were categorised into three groups (low, medium, high) based on accelerometer-measured PA level (AMPA) and TEE from 7-day PA diaries. Body composition was measured using bioelectrical impedance. Energy and nutrient intakes were assessed using 3-day weighed food diaries. Appetite was assessed using the visual analogue scales at 30-min intervals throughout 1 day.ResultsTEE was positively correlated with EI and % muscle mass (p < 0.05), with higher % muscle mass and TEE associated with higher EI. Energy and protein intake were significantly higher in the high TEE group than the low group (p = 0.03, p = 0.01; respectively). No significant differences in energy and macronutrient intake were observed across AMPA groups, and appetite components (hunger, fullness, desire to eat, prospective consumption) did not differ significantly in either the AMPA or TEE groups.ConclusionsHigher TEE is associated with higher energy and protein intake, with body composition playing a crucial role. These findings highlight the importance of considering PA, TEE, and body composition in interventions aimed at improving EI in older adults.Clinical Trail registration: clinicaltrials.gov as NCT05067036. Registered 2 October 2021, https://classic.clinicaltrials.gov/ct2/show/NCT05067036

Carbamate-Functionalized NLOphores via a Formal [2+2] Cycloaddition-Retroelectrocyclization Strategy.

This study introduces a new donor group capable of activating click-type [2+2] cycloaddition-retroelectrocyclizations, generally known for their limited scope. Target chromophores were synthesized using isocyanate-free urethane synthesis. The developed synthetic method allows for the tuning of the optical properties of the chromophores by modifying the donor groups, the acceptor units, and the side chains. The charge transfer (CT) bands of the chromophores exhibit λmax values ranging from 363 to 692 nm. The CT bands observed have been supported by solvatochromism and protonation experiments. The synthesized compounds exhibit positive solvatochromism. Due to their potential as NLOphore candidates, the stability of the synthesized compounds have been investigated both experimentally through TGA and theoretically by calculating parameters such as frontier orbital energy differences, electronegativity, and global hardness/softness. TD-DFT calculations were used to elucidate the nature of the electronic transitions, revealing that the bands correspond to CT arising from HOMO-to-LUMO excitations. The NLO properties of the chromophores were investigated theoretically by DFT methods and experimentally by the EFISHG technique. Both results are shown to be in agreement with HOMO-LUMO energy differences. The experimental μβ values of the selected molecules range from 470 × 10-48 to 5400 × 10-48 esu.

Utilization of Stable and Efficient High-Entropy (Ni0.2Zn0.2Mg0.2Cu0.2Co0.2)Al2O4 Catalyst with Polyvalent Transition Metals to Boost Peroxymonosulfate Activation toward Pollutant Degradation.

A polyacrylamide gel method has been used to synthesize a variety of polyvalent-transition-metal-doped Ni position of high entropy spinel oxides (Ni0.2Zn0.2Mg0.2Cu0.2Co0.2)Al2O4-800°C (A2) on the basis of NiAl2O4, and the catalytic activity of A2 is studied under the synergistic action of peroxymonosulfate (PMS) activation and simulated sunlight. The A2 containing polyvalent transition metals (Ni2+, Cu2+, and Co2+) can effectively activate PMS and efficiently degrade levofloxacin (LEV) and tetracycline hydrochloride (TCH) under simulated sunlight irradiation. After 90 min of light exposure, the degradation percentages of LEV (50 mg L-1) and TCH (100 mg L-1) degrade by the A2/PMS/vis system reach 87.0% and 90.2%, respectively. The superoxide radicals, photoinduced holes, and singlet oxides dominate the catalytic process, while hydroxyl radicals and sulfate radicals play only a small role. The adsorption energy and charge density difference between different systems and PMS are calculated by density functional theory, and the activation efficiency of PMS is studied by combining with the change of the length of the O─O bond of the PMS after adsorption. The catalytic mechanism of A2/PMS/vis system is proposed, which provides a new idea and method for the study of high entropy oxides in the field of catalysis.

Electronic-decay-process spectra including nuclear degrees of freedom

In the field of chemistry, where nuclear motion has traditionally been a focal point, we now explore the ultrarapid electronic motion spanning attoseconds to femtoseconds, demonstrating that it is equally integral and relevant to the discipline. The advent of ultrashort attosecond pulse technology has revolutionized our ability to directly observe electronic rearrangements in atoms and molecules, offering a time-resolved insight into these swift processes. Prominent examples include Auger-Meitner decay and interparticle Coulombic decay. However, the real challenge lies in interpreting these observations, where theoretical models are indispensable. Building upon the analytical framework introduced by Fasshauer and Madsen [], which analyzed the spectra of electrons emitted during electronic decay processes from a purely electronic perspective, we extend this theoretical base to include nuclear dynamics, utilizing the Born-Oppenheimer approximation to deepen our understanding of the intricate interaction between electronic and nuclear motion in these processes. We illustrate the impact of incorporating nuclear degrees of freedom in several theoretical cases characterized by different numbers of vibrational bound states in both the electronic resonance and the electronic final state. This approach not only clarifies complex spectral features and unusual peak shapes but also demonstrates a method for extracting the energy differences between multiple vibrational resonance states through their distinctive interference patterns. Published by the American Physical Society 2025

Understanding the CO2 Reduction Selectivity toward Ethanol on Single Atom Doped Cu/Cu2O Catalysts: Insights from Bader Charge as a Descriptor.

In the CO2 reduction reactions (CO2RR), the product selectivity is strongly dependent on the binding energy differences of the key intermediates. Herein, we systematically evaluated the CO2RR reaction pathways on single transition metal atom doped catalysts TM1Cu/Cu2O by density functional theory (DFT) methods and found that *CO is more likely to undergo C-O bond cleavage rather than be hydrogenated on TM1Cu/Cu2O (TM = Sc, Ti, V, Cr, Mn, Fe, Co), which facilitates C2+ production with a low-energy pathway of OC-C coupling, while it prefers to be hydrogenated to form CHO on TM1Cu/Cu2O (TM = Ni, Cu). The defects of Cu in TM1Cu/Cu2O were confirmed to enhance the production of ethanol. Furthermore, we established a scaling relationship between binding free energies of the key intermediates with the Bader charges of the active sites TM on TM1Cu/Cu2O and defective TM1Cu/Cu2O surfaces. This relationship facilitates a rational and efficient design of Cu/Cu2O-based catalysts.

Detection and distinction of amino acids and post-translational modifications with gold nanojunctions.

Amino acids are fundamental building blocks of proteins, playing critical roles in medical diagnostics, environmental monitoring, and biomarker identification. The development of nanoscale electronic sensors capable of single-amino-acid recognition has gained significant attention due to their potential for label-free, real-time detection. In this study, we investigate the electronic transport properties of amino acids in two gold-based nanodevices with distinct architectures: a gold nanojunction and a gold-capacitor system. Using density functional theory (DFT) in combination with nonequilibrium Green's function (NEGF) calculations, we explore the sensing mechanism and conductance variations induced by different amino acids, including select phosphorylated variants. Each device was assigned a reference amino acid, F (M), for a capacitor (nanojunction) to differentiate its conductance from other molecules. Our results reveal distinct conductance that enables amino acid classification based on their electronic signatures, demonstrating that molecular discrimination is primarily governed by conductance variations as a function of the binding energy differences. The nanojunction exhibited remarkable differentiation for the amino acids S, pS, Y, and pY, rendering it especially proficient in distinguishing between structurally analogous molecules. These findings highlight the strong potential of gold-based nanodevices for precise amino acid detection, paving the way for advancements in biosensing technologies, molecular diagnostics, and biomedical applications.

Computational Study of the 1,3-Dipolar Cycloaddition between Criegee Intermediates and Linalool: Atmospheric Implications.

In this research, we investigated the essential role of biogenic volatile organic compound emissions in regulating tropospheric ozone levels, atmospheric chemistry, and climate dynamics. We explored linalool ozonolysis and secondary organic aerosol formation mechanisms, providing key insights into atmospheric processes. Computational techniques, such as density functional theory calculations and molecular dynamics simulations, were employed for the analysis. Our study delves into the energetic and mechanistic aspects of the 1,3-dipolar cycloadditions involving linalool and its ozonolysis byproducts, known as Criegee intermediates. A total of 24 reactions were analyzed from the three possible Criegee intermediates formed, resulting from different reactant orientations and their endo/exo isomers. We found that only four of these reactions exhibit large rate constants that can compete with tropospheric reactions. This reactivity pattern was characterized by analyzing reactivity indices from conceptual density functional theory and determining that electron flux originates from linalool to the Criegee intermediates. Greater electrophilicity in the Criegee intermediates results in a lower reaction activation energy, confirmed by the global electrophilicity index. Furthermore, using the activation strain model and energy decomposition analysis, we found that differences in activation energies were primarily driven by nonorbital energy factors. Finally, molecular dynamics simulations showed that the final cycloaddition adducts of the most favorable 1,3-dipolar cycloaddition interact favorably with water molecules in an exergonic process, adsorbing up to 92% of the water molecules after 20 ns. Our findings provide insights that enhance our understanding of the interactions between natural emissions and atmospheric constituents.

Computational Insights into "Lone Pair-Lone Pair Interaction-Controlled" Isomerization in the Asymmetric Total Syntheses of (+)-3-(Z)-Laureatin and (+)-3-(Z)-Isolaureatin.

Described herein is our computational study to rationalize the stereoselective epimerization of α,α'-cis-disubstituted oxolane and oxetane ketones 6 and 7 to the corresponding α,α'-trans ketones 8 and 9 reported in our previous total syntheses of (+)-3-(Z)-isolaureatin (1) and (+)-3-(Z)-laureatin (2). Density functional theory (DFT) calculations using appropriately truncated models revealed that the α,α'-trans ketones are more stable than the α,α'-cis ketones, in very good agreement with experimental results. The computational results showed that the isomer with a longer interatomic distance between the two ring oxygen atoms was lower in energy, which suggested the presence of repulsive interactions between those oxygen atoms. Support for these distance-dependent repulsive interactions came from the observation that the energy differences between the two isomers correlated with the solvent polarity. Most importantly, a larger interoxygen distance difference could be responsible for the enhanced stereoselectivity for epimerization of oxetane ketone 7 compared to oxolane ketone 6 [0.25 Å (trans only) vs 0.13 Å (trans/cis = 4:1)].

Intermittent standing does not acutely improve postprandial metabolism in university students

ABSTRACT Height-adjustable workstations offer a practical strategy to reduce sedentary behaviour in student populations, but the effect of standing intervals on young adults’ metabolic health remains uncertain. This study investigated the acute impact of breaking up sitting time with intermittent standing on postprandial metabolic responses in university students. Using a randomised, cross-over design, 23 participants (13 females, 10 males; age, 24 ± 5 years; BMI, 23.2 ± 3.1 kg/m2) completed two trials: 2 hours of uninterrupted sitting (SIT); and 2 hours alternating between sitting and standing every 30 minutes (STAND). During this period, participants underwent an oral glucose tolerance test, with [glucose] and [insulin] measured. Ad libitum food intake post intervention was also measured. No significant effects between trials nor trial × time interaction was found for [glucose] or [insulin] (all p > 0.05). The postprandial iAUC did not differ for [glucose] (p = 0.824; SIT: 222 ± 83 mmol/L; STAND: 225 ± 90 mmol/L) or [insulin] (p = 0.269; SIT: 17507 ± 9738 pmol/L; STAND: 15649 ± 10181 pmol/L). There were no differences in energy or macronutrient intake between trials. These findings indicate that interrupting sitting with 30-minute standing intervals does not improve postprandial metabolic responses in young, normal-weight adults.

Effect of Nitrogen Composition on Band Gap Energy and Photocatalytic Activity of TiO2-N/Zeolite Composite

In this study, the application and performance of TiO2-N/Zeolite composites for MB photodegradation under UV irradiation have been reviewed. To improve the removal performance, the TiO2-N/Zeolite composite was varied based on the concentration ratio of urea to TiO2, where urea is a precursor of nitrogen. UV-Vis DRS tests were also carried out to compare and evaluate differences in band gap energy for each variant, analysis of degradation results and MB removal mechanisms by TiO2-N/Zeolite composites are described in this study. The aim of this research is to determine the effect of the urea to TiO2 concentration ratio (urea:TiO2), on the photocatalytic activity of the TiO2-N/Zeolite composite and also its physical characteristics, namely band gap energy. Thus, as a comparison, TiO2 and TiO2-N were also tested for photocatalytic activity and band gap energy physical characteristics. The conclusion obtained from this research is that the smaller the nitrogen composition in the TiO2-N/Zeolite composite, the greater the photocatalytic activity capability in degrading MB, in this case the TiO2-N/Zeolite (1.5) sample has the best photocatalytic activity. The next conclusion is that the higher the nitrogen composition in the TiO2-N/Zeolite composite, the smaller the band gap energy.

Unveiling the Reaction Mechanism of Diels-Alder Cycloadditions between 2,5-Dimethylfuran and Ethylene Derivatives Using Topological Tools.

The [4+2] Diels-Alder cycloaddition reaction between 2,5-DMF (1) and ethylene derivatives (2a-h) activated by electron-withdrawing groups has been studied at the density functional theory levels using a panoply of tools to unravel the reaction mechanisms. From the analysis of the reactivity indices, 2a-h behave as electrophiles while 1 as nucleophile, and the activation of the double bond of ethylene increases its electrophilicity, which is accompanied by an enhancement of the polarity of the reaction. The activation Gibbs free energy decreases linearly as a function of this increase of polarity, as estimated by the electrophilicity difference between the reactants. The difference of electrophilicity drives also the global electron density transfer at the transition state and the asynchronicity of the reaction, as evaluated by the difference of carbon-carbon bond lengths in the transition state. Then, Bonding Evolution Theory shows that the activation of the double bond of ethylene by an electron-withdrawing group changes the reaction mechanism from a one-step synchronous process to a one-step asynchronous process. Generally, the endo pathway is kinetically favored but, thermodynamically, it is the exo pathway. Finally, using the Distortion/Interaction-Activation Strain, it is shown that the endo/exo selectivity is mostly driven by the differences of interaction energies.

A computational study on the effect of structural isomerism on the excited state lifetime and redox energetics of archetype iridium photoredox catalyst platforms [Ir(ppy)2(bpy)]+ and Ir(ppy)3.

This study investigates the impact of structural isomerism on the excited state lifetime and redox energetics of heteroleptic [Ir(ppy)2(bpy)]+ and homoleptic Ir(ppy)3 photoredox catalysts using ground-state and time-dependent density functional theory methods. While the ground- and excited-state reduction potentials differ only slightly among the isomers of these complexes, our findings reveal significant variations in the radiative and non-radiative decay rates of the reactivity-controlling triplet 3MLCT states of these closely related species. The observed differences in radiative decay rates could be traced back to variations in the transition dipole moment, vertical energy gaps, and spin-orbit coupling of the isomers. In [Ir(ppy)2(bpy)]+, transition dipole moment differences play a significant role in controlling the relative lifetime of the triplet states, which we rationalized by a vectorial analysis of permanent dipole moments of the ground and excited states. Regarding the two isomers of Ir(ppy)3, changes in radiative decay rates were primarily attributed to variations in vertical energy gaps and intensity borrowing from other singlet-singlet transitions driven by spin-orbit coupling. Non-radiative decay variations were assessed in terms of differences in reorganization energies, adiabatic energy gap, and spin-orbit coupling. For both complexes, reorganization energies associated with low-energy molecular vibrations and metal-ligand bond length changes following the de-excitation process were major contributors. These insights provide a deeper understanding of how molecular design can be leveraged to optimize the performance of iridium-based photoredox catalysts, potentially guiding the development of more efficient catalytic systems for future applications.

The Enzyme Effect: Broadening the Horizon of MS Optimization to Nontryptic Digestion in Proteomics.

In recent years, alternative enzymes with varied specificities have gained importance in MS-based bottom-up proteomics, offering orthogonal information about biological samples and advantages in certain applications. However, most mass spectrometric workflows are optimized for tryptic digests. This raises the questions of whether enzyme specificity impacts mass spectrometry and if current methods for nontryptic digests are suboptimal. The success of peptide and protein identifications relies on the information content of MS/MS spectra, influenced by collision energy in collision-induced dissociation. We investigated this by conducting LC-MS/MS measurements with different enzymes, including trypsin, Arg-C, Glu-C, Asp-N, and chymotrypsin, at varying collision energies. We analyzed peptide scores for thousands of peptides and determined optimal collision energy (CE) values. Our results showed a linear m/z dependence for all enzymes, with Glu-C, Asp-N, and chymotrypsin requiring significantly lower energies than trypsin and Arg-C. We proposed a tailored CE selection method for these alternative enzymes, applying ca. 20% lower energy compared to tryptic peptides. This would result in a 10-15 eV decrease on a Bruker QTof instrument and a 5-6 NCE% (normalized collision energy) difference on an Orbitrap. The optimized method improved bottom-up proteomics performance by 8-32%, as measured by peptide identification and sequence coverage. The different trends in fragmentation behavior were linked to the effects of C-terminal basic amino acids for Arg-C and trypsin, stabilizing y fragment ions. This optimized method boosts the performance and provides insight into the impact of enzyme specificity. Data sets are available in the MassIVE repository (MSV000095066).