Reaction Patterns Research Articles

Functional and structural analysis of a cyclization domain in a cyclic β-1,2-glucan synthase

Cyclic β-1,2-glucan synthase (CGS) is a key enzyme in production of cyclic β-1,2-glucans (CβGs) which are involved in bacterial infection or symbiosis to host organisms. Nevertheless, a mechanism of cyclization, the final step in the CGS reaction, has not been fully understood. Here we performed functional and structural analyses of the cyclization domain of CGS alone from Thermoanaerobacter italicus (TiCGSCy). We first found that β-glucosidase-resistant compounds are produced by TiCGSCy with linear β-1,2-glucans as substrates. The 1H-NMR analysis revealed that these products are CβGs. Next, action pattern analyses using β-1,2-glucooligosaccharides revealed a unique reaction pattern: exclusive transglycosylation without hydrolysis and a hexasaccharide being the minimum length of the substrate. These analyses also showed that longer substrate β-1,2-glucooligosaccharides are preferred, being consistent with the fact that CGSs generally produce CβGs with degrees of polymerization of around 20. Finally, the overall structure of the cyclization domain of TiCGSCy was found to be similar to those of β-1,2-glucanases in phylogenetically different groups. Meanwhile, the identified catalytic residues indicated clear differences in the reaction pathways between these enzymes. Overall, we propose a novel reaction mechanism of TiCGSCy. Thus, the present group of CGSs defines a new glycoside hydrolase family, GH189.Key points• It was clearly evidenced that cyclization domain alone produces cyclic β-1,2-glucans.• The domain exclusively catalyzes transglycosylation without hydrolysis.• The present catalytic domain defines as a new glycoside hydrolase family 189.Graphical

Zipper-Confined DNA Nanoframe for High-Efficient and High-Contrast Imaging of Heterogeneous Tumor Cell.

Current study in the heterogeneity and physiological behavior of tumor cells is limited by the fluorescence in situ hybridization technology in terms of probe assembly efficiency, background suppression capability, and target compatibility. In a typically well-designed assay, hybridization probes are constructed in a confined nanostructure to achieve a rapid assembly for efficient signal response, while the excessively high local concentration between different probes inevitably leads to nonspecific background leakage. Inspired by the fabric zipper, we propose a novel confinement reaction pattern in a zipper-confined DNA nanoframe (ZCDN), where two kinds of hairpin probes are independently anchored respective tracks. The metastable states of the dual tracks can well avoid signal leakage caused by the nonspecific probe configuration change. Biomarker-mediated proximity ligation reduces the local distance of dual tracks, kinetically triggering an efficient allosteric chain reaction between the hairpin probes. This method circumvents nonspecific background leakage while maintaining a high efficiency in responding to targets. ZCDN is employed to track different cancer biomarkers located in both the cytoplasm and cytomembrane, of which the expression level and oligomerization behavior can provide crucial information regarding intratumoral heterogeneity. ZCDN exhibits high target response efficiency and strong background suppression capabilities and is compatible with various types of biological targets, thus providing a desirable tool for advanced molecular diagnostics.

Following the Writer’s Path to the Dynamically Coalescing Reactive Chains Design Pattern

Two recent studies addressed the problem of reducing transitional turbulence in applications developed in C# on .NET. The first study investigated this problem in desktop and Web GUI applications and the second in virtual and augmented reality applications using the Unity3D game engine. The studies used similar solution approaches, but both were somewhat embedded in the details of their applications and implementation platforms. This paper examines these two families of applications and seeks to extract the common aspects of their problem definitions and solution approaches and codify the problem-solution pair as a new software design pattern. To do so, the paper adopts Wellhausen and Fiesser’s writer’s path methodology and follows it systematically to discover and write the pattern, recording the reasoning at each step. To evaluate the pattern, the paper applies it to an arbitrary C#/.NET GUI application. The resulting design pattern is named Dynamically Coalescing Reactive Chains (DCRC). It enables the approach to transitional turbulence reduction to be reused across a range of related applications, languages, and user interface technologies. The detailed example of the writer’s path can assist future pattern writers in navigating through the complications and subtleties of the pattern-writing process.

Insights into the binding mechanism of 2,5‐substituted 4‐pyrone derivatives as therapeutic agents for fused dimeric interactions: A computational study using QTAIM, dynamics and docking simulations of protein–ligand complexes

AbstractThe study is focused on examining 2,5‐Substituted 4‐Pyrone based compounds through quantum chemical and topological analysis techniques, evaluating the properties of these compounds, including their geometrical structure, intermolecular interactions and assess their possible applications. Additionally, the molecular stability, charge delocalization and UV‐Visible data was investigated and compared with the calculated energy and oscillator strength using the TD‐DFT approach. The researchers observed that charge transfer occurred within the molecule, indicated by the HOMO and LUMO energies. It was also found that the compound exhibited planarity and higher chemical reactivity. The calculated Mulliken charges and molecular electrostatic potential were used to interpret the Fukui index data that help predict reactive sites and understand the reactivity patterns of specific atoms in a compound. The study is aimed to understand the role of NCI in the molecule under investigation using electron localization functions and localized orbit locator methods. Molecular docking and ADMET studies were conducting involving a detailed MD simulation of a protein‐ligand complex using the OPLS3e force field and the SPC water model. These findings could prove to be beneficial in developing new therapeutic agents with various pharmacological effects and potential toxicities.

Synthesis of 1,7-Fused Indolines Tethered with Spiroindolinone Based on C-H Activation Strategy with Air as a Sustainable Oxidant.

Herein, we present an efficient synthesis of 1,7-fused indolines tethered with a spiroindolinonyl moiety through the cascade reaction of indolin-1-yl(aryl)methanimines with diazo oxindoles. To the best of our knowledge, this is the first example in which 1,7-fused indoline skeleton was constructed along with the simultaneous introduction of a spiro element initiated by the C-H bond activation of indoline. In forming the title product, the indoline substrate and the diazo coupling partner demonstrated an unprecedented reaction pattern in which the latter acts as a C1 synthon to participate in the construction of the spirocyclic scaffold through the reductive elimination of a key seven-membered Ru(II) species by using air as an effective and sustainable oxidant to regenerate the active catalyst. Moreover, studies on the cytotoxicity of selected products against several human cancer cell lines demonstrated their potential as lead compounds for the development of anticancer drugs. With notable features such as simple and economical substrates, pharmaceutically valuable products with sophisticated spirocyclic skeleton, mild reaction conditions, cost-free and sustainable oxidants, high efficiency, excellent compatibility with diverse functional groups, and scalability, this method is expected to find wide applications in related areas.

Examining Reactivity and Recovery Patterns of Pain-Evoked Cortisol and Alpha-Amylase Trajectories: Relations Between Psychological Markers of Risk and Resilience

Chronic low back pain (cLBP) is one of the leading causes of disability globally and represents an enormous burden to aging adults. While numerous factors contribute to cLBP, dysregulation in the hypothalamic-pituitary-adrenal axis and autonomic nervous system functioning have been implicated in its pathogenesis. It is well documented that negative psychological states can modulate biological stress responsivity in chronic pain; however, little is known regarding the influence of positive psychological factors in this relationship. The aim of this study was to examine the association between psychological risk and resilience factors with patterns of physiological stress reactivity and recovery in 60 older adults with cLBP. Participants completed measures of hope, optimism, pain catastrophizing, and perceived stress, and underwent psychophysical pain testing assessing responses to painful pressure, heat, and cold stimuli. Salivary samples were obtained prior to pain induction and at 7 time points spanning 90 minutes after pain testing terminated. To examine reactivity and recovery profiles in hypothalamic-pituitary-adrenal axis and autonomic nervous system function, samples were assayed for cortisol and alpha-amylase, respectively. Results revealed higher levels of hope and optimism were associated with increased cortisol reactivity (p’s < .003) and more rapid recovery (p’s = .001). Further, pain catastrophizing and perceived stress were associated with cortisol reactivity, with lower levels of these factors predicting larger increases in cortisol from baseline to peak levels (p’s < .04). No significant differences in reactivity or recovery patterns emerged for alpha-amylase. Overall, findings highlight the role of psychological risk and resilience factors in modulating physiological stress reactivity. PerspectiveThis article investigated whether psychosocial risk and resilience factors were associated with stress reactivity and recovery in response to laboratory-based pain testing in older adults with chronic low back pain. Results indicate that high resilience factors may be protective by modulating adrenocortical reactivity and recovery profiles.

HLA class I peptide polymorphisms contribute to class II DQβ0603:DQα0103 antibody specificity

Antibodies reactive to human leukocyte antigens (HLA) represent a barrier for patients awaiting transplantation. Based on reactivity patterns in single-antigen bead (SAB) assays, various epitope matching algorithms have been proposed to improve transplant outcomes. However, some antibody reactivities cannot be explained by amino acid motifs, leading to uncertainty about their clinical relevance. Antibodies against the HLA class II molecule, DQβ0603:DQα0103, present in some candidates, represent one such example. Here, we show that peptides derived from amino acids 119-148 of the HLA class I heavy chain are bound to DQβ0603:DQα0103 proteins and contribute to antibody reactivity through an HLA-DM-dependent process. Moreover, antibody reactivity is impacted by the specific amino acid sequence presented. In summary, we demonstrate that polymorphic HLA class I peptides, bound to HLA class II proteins, can directly or indirectly be part of the antibody binding epitope. Our findings have potential important implications for the field of transplant immunology and for our understanding of adaptive immunity.

To Observe the patterns of Cutaneous Adverse Drug Reactions in a Tertiary health care teaching hospital in Hyderabad

Cutaneous adverse drug reactions are very common and seen quite often during clinical practice. It is difficult to get a comprehensive list of the various types of drug reactions and their corresponding drug due to many cases going unreported. There is a possibility of a cutaneous drug reaction every time a new drug is introduced into the market. While most types of drug reactions are trivial and benign, there is always a possibility of the reaction attaining a more malignant nature. The diagnosis of a CADR is more often based on a clinical examination. However, in order to understand the full scope of the reaction it must be reported and studied. The pharmacovigilance programme takes into account the spontaneous nature of the cases and employs alogical approach based on clinical characteristics, chronologic factors, and generation of a focused differential diagnosis. Using study tools like Naranjo scale and Modified Hartwig and Siegel scale, a physician can easily determine the severity and causality of the drug reaction. After compiling the data, one can determine the trend of the morphology of these CADRs, and determine the most likely drug responsible for the reaction. The data obtained in this study is useful for helping the clinician in the proper identification, approach and treatment of a patient suffering from a cutaneous adverse rug reaction.

Evaluation of screening methods for anthracnose fruit rot resistance in chilli (Capsicum spp.)

Anthracnose fruit rot caused by Colletotrichum spp. is a serious production constraint causing severe marketable yield loss in chilli. Field evaluation of chilli accessions for resistance to Colletotrichum spp. depends on various factors affecting disease expression such as edaphic conditions, temperature, rainfall, humidity and other variables that are difficult to control, therefore considered less accurate. Also, high chances of cross contamination with different Colletotrichum species leads to inconclusive assays for specific pathogen species and isolate. To identify a stable and reliable screening method, various chilli accessions were subjected to in vitro pin-prick and non-wounding spray methods using a specific pathogen isolates. When chilli accessions were screened against C. gloeosporioides isolate ‘IHRCg-1’, the in vitro pin- prick method showed positive correlation with the non- wounding spray method, except in the accession PBC80. The change in bioassay influenced the disease reaction pattern in the accession PBC 80, probably the pin pricks break the basal cuticle defense mechanism that was retained in spray inoculation method indicating varied resistance pattern. However, in the accession PBC 81 stable resistance pattern was observed against isolates of both species viz., C. truncatum ‘IIHR Ct-1’ and C. gloeosporioides ‘IIHR Cg-1’ and in the accession PBC 80 against C. truncatum ‘IIHR Ct-1’ in both the inoculation methods that depicted the expression of resistance genes during both methods of inoculation. Based on disease development pattern, the red ripe chilli expressed a variant reaction to infection by C. truncatum and C. gloeosporioides. The peak anthracnose infection at 10 DAI and 14 DAI is an accurate duration to record ‘IIHR Cg-1’ and ‘IIHR Ct-1’ infection, respectively on chilli ripe fruit for assaying the resistance.

On the robustness of discontinuous patterns in degenerate reaction–diffusion systems with perturbed hysteresis

In this paper, we study the dynamics of a morphogenesis model which reproduces the formation of discontinuous patterns observed in numerous biological or ecological systems. This model is determined by a degenerate reaction–diffusion system with hysteresis in the non-diffusive equation. We focus on the robustness of discontinuous patterns under the action of a perturbation of the hysteresis process. We analyze the bifurcations of homogeneous stationary solutions to this nonlinear model and prove that the trivial solution is the only one to resist to a perturbation of strong intensity. We then prove an original result on the structural transformation of discontinuous patterns, which are seen to react by acquiring a supplementary discontinuity jump under the effect of a perturbation of small intensity. We interpret the supplementary jump for ecological systems as the possible emergence of an invasive ecosystem. Numerical simulations and animations are finally provided to guide intuition on the complex morphogenesis process of this dynamical system.

Organization of Somatosensory Cortex in the South American Rodent Paca (Cuniculus paca)

Introduction: The study of non-laboratory species has been part of a broader effort to establish the basic organization of the mammalian neocortex, as these species may provide unique insights relevant to cortical organization, function, and evolution. Methods: In the present study, the organization of three somatosensory cortical areas of the medium-sized (5–11 kg body mass) Amazonian rodent, the paca (Cuniculus paca), was determined using a combination of electrophysiological microelectrode mapping and histochemical techniques (cytochrome oxidase and NADPH diaphorase) in tangential sections. Results: Electrophysiological mapping revealed a somatotopically organized primary somatosensory cortical area (S1) located in the rostral parietal cortex with a characteristic foot-medial/head-lateral contralateral body surface representation similar to that found in other species. S1 was bordered laterally by two regions housing neurons responsive to tactile stimuli, presumably the secondary somatosensory (S2) and parietal ventral (PV) cortical areas that evinced a mirror-reversal representation (relative to S1) of the contralateral body surface. The limits of the putative primary visual (V1) and primary auditory (A1) cortical areas, as well as the complete representation of the contralateral body surface in S1, were determined indirectly by the histochemical stains. Like the barrel field described in small rodents, we identified a modular arrangement located in the face representation of S1. Conclusions: The relative location, somatotopic organization, and pattern of neuropil histochemical reactivity in the three paca somatosensory cortical areas investigated are similar to those described in other mammalian species, providing additional evidence of a common plan of organization for the somatosensory cortex in the rostral parietal cortex of mammals.

A RETROSPECTIVE ANALYSIS OF REPORTED CUTANEOUS ADVERSE DRUG REACTIONS IN A TERTIARY CARE TEACHING HOSPITAL

Objectives: Analysis of adverse drug reactions (ADR) reports enriches and updates physician’s awareness about the pattern of cutaneous adverse reactions in the population studied and may play an important role to envision the frequency of appearance of reactions to specific drugs and morphological designs. This study intends to portray the clinical profile and causative agents of dermal ADRs in our population. Methods: All the ADR reporting forms received from February 2021 to February 2023 were scrutinized, and forms with cutaneous ADRs (CADRs) were analyzed. The data about the history of drug intake, names of the drug taken, time lag of appearance of reaction, and clinical examination details were collected from the reports. Demography, prevalence, reaction time morphological pattern, and causative agents of CADRs were evaluated. Results: Among the CADRs, acute urticaria 53.4 was the most common followed by acute exanthematous reaction 35.8% and lichenoid drug eruption 3.8%. Among the drugs causing CADRs, antibiotics top the list with 47% followed by ATT at 29.7% and iron sucrose 12.9%. Among the antimicrobials, fluoroquinolones 48% top the list followed by cephalosporins 21.6% and penicillins and vancomycin each 8.3%. Conclusion: Physician’s knowledge about pattern and causative agents of CADR in the specific population can aid in prevention and early management of ADRs and thereby reducing hospitalization.

Directing the persulfate activation reaction pathway by control of Fe-Nx/C single-atom catalyst coordination

In the reaction systems involving peroxymonosulfate (PMS) activation, the degradation of organic pollutants is influenced by the distinct roles played by the oxidation of free radicals and non-free radicals. The synergistic effect resulting from both oxidation pathways is often more efficient compared to a single oxidation pathway, as it allows for the optimal utilization of oxidation capacity and adaptation to complex reaction environments. Nitrogen-doped carbon substrates hosting single-atom catalysts (SACs) are anticipated to serve as an optimal platform for managing the dual oxidation pathways in the PMS activation reaction. This is attributed to the availability of numerous reaction sites that meet the activation requirements. However, there's a lack of substantial reports on this subject. Herein, we synthesized a series of single-atoms Fe nitrogen-doped carbon catalysts with different coordination structures by adjusting the coordination numbers between Fe and N atoms. It is used to investigate the reaction pattern of PMS over SACs, so as to enhance the catalytic efficacy of SACs through distinct coordination structures. The experimental and theoretical results indicate that PMS functions as both an electron receiver and provider on FeNx/C catalysts. Moreover, the specific arrangement of the Fe-N-C structure influences the exchange of electrons between the catalysts and PMS. Hence, the co-oxidation pathway of free radicals (OH, SO4− and O2−) and non-free radicals (1O2) can be modulated by altering the coordination number of Fe and N atoms during PMS activation. The elimination efficiency of tetracycline hydrochloride was significantly enhanced due to the abundance of both free radical and non-free radical species generated in the FeN3/C/PMS reaction system, exhibiting a degradation kinetic constant of 0.564 min−1. In addition, it showed promising potential for application in practical wastewater degradation, exhibiting high anti-interference to general environmental disturbances (such as humic acid, chloride ions, bicarbonate ions and nitrate ions).

Pattern of central nervous system related adverse drug reactions (ADRs) due to anti-retroviral therapy in HIV infected patients in tertiary care hospitals in North India

Background: Anti-retroviral therapy is associated with myriads of side-effects. Central nervous system related side effects are troublesome and mostly self limiting. Working knowledge of these side effects can improve the prescription habits of physicians. The study aimed pattern of central system related adverse drug reactions (ADRs) due to anti-retroviral therapy in HIV infected patients in tertiary care hospitals in North India. Materials and methods: A prospective observational study was conducted and all HIV positive patients, previously registered and new; attending OPD who encountered ADRs were enrolled in our study irrespective of their age and sex. Data was collected using ADR reporting form issued by Indian Pharmacopoeia Commission. Causality assessment was done by using Naranjo’s Probability Scale. Modified Hartwig severity scale was used to evaluate severity, WHO criteria for seriousness and guidelines of council for international organizations of medical sciences to decide the predictability of ADRs. Results: A total of 250 patients encountered various types of ADRs during the study period. Total number of ADRs recorded was 452. Out of total ADRs (n=452) recorded, 20.35% (n=92) were central system related ADRs. Most common central nervous system related ADR was dizziness. Most central nervous system related ADRs were of moderate type and possible in nature on causality assessment. Conclusion: Relatively overweight, older age and baseline CD4 absolute count below 250 cells/mm3, were predictors for central nervous system related side effects due to anti-retroviral therapy in HIV patients. We suggest that more stringent evaluation and monitoring should be carefully done in all HIV/AIDS patients who will receive and on efavirenz based anti-retroviral therapy, especially if they have the above predictors.

Rare-earth metal complexes bearing electrophilic and nucleophilic carbon centres and their unique reactivity patterns towards pyridine derivatives.

The rare-earth metal dialkyl complexes (κ2-L1)RE(CH2SiMe3)2·(THF)2 [RE = Lu(1a), Yb(1b), Er(1c), Y(1d), Dy(1e)] (L1 = 1-(2-N-C5H10NCH2CH2)-3-(2,6-iPr2C6H3N[double bond, length as m-dash]CH)-C8H4N) and the rare-earth metal monoalkyl complexes (κ2-L1)2RE(CH2SiMe3)·(THF) n [n = 0, RE = Lu(2a), Yb(2b); n = 1, Er(2c), Y(2d), Dy(2e)], (κ2-L2)2RE(CH2SiMe3)·THF [RE = Yb(3a), Er(3b), Y(3c), Dy(3d), Gd(3e)] (L2 = 1-(2-N-C5H10NCH2CH2)-3-(AdN[double bond, length as m-dash]CH)-C8H4N) (Ad = adamantyl, C10H15) have been synthesized and fully characterized. These complexes feature chelate ligands having a conjugated system (-C[double bond, length as m-dash]C-C[double bond, length as m-dash]N) with an sp2 carbon, which enables both electrophilic and nucleophilic carbon centres to be directly connected to the highly electrophilic rare-earth metal ions. The reactions of these complexes with different pyridine derivatives have been systematically investigated with the discovery of reactivity patterns distinct from those of previously reported transition metal complexes. These unusual reactivity patterns include consecutive C-H activation/1,1-migratory insertion/C-N and C-H activation, C-H activation/1,1-migratory insertion/C-N bond activation, C-H activation/1,1-migratory insertion, and homolytic redox reactions. DFT calculation results together with experimental evidences support the key mechanistic proposal that the indol-2-yl carbon of the ligands exhibits electrophilic carbene character accounting for the subsequent 1,1-migratory insertion reaction after C-H activation.

Pattern and Incidence of Covid-19 Vaccine Reactions among Adult Clients in a Tertiary Health Facility in a North-Central State of Nigeria

Introduction: As a result of the rapid development and approval of the COVID-19 vaccine during the pandemic, there was serious misinformation about the safety of the COVID-19 vaccine. Providing evidence-based proof of the safety of the COVID-19 vaccine could dispel this scepticism. The study aimed to assess the pattern and incidence of COVID-19 vaccine reactions among adult clients in a tertiary health facility following immunization. Methods: The cross-sectional study was conducted in a tertiary care institute among recipients of the first dose of the of the COVID-19 vaccine between April and July 2021. Study populations were adults above 18 years. Participants were assessed for any reactions four times. Immediately after vaccination and later, same day one, day 2, day 3, and on/after day 7. A telephone interview was conducted, and the recipients were assessed according to the time and type of reactions, actions taken following reactions, and severe forms of reactions. Results: A total of 1535 participants were assessed post-COVID-19 vaccination reactions, and 805 (52.4%) reported at least one of the COVID-19 vaccine reactions following vaccination, and less than a percent reported perceived severe adverse reactions. Pain at the injection site (5.0%), myalgia (2.8%), and headache (1.6%) were the common adverse events reported immediately after vaccination. The majority of the respondents (93.4%) were willing to take the second dose of the of the COVID-19 vaccine. The major factor associated with COVID-19 vaccine reactions following vaccination was the age group. Conclusion: Many people still experience a certain type of discomfort after vaccinations; this discomfort is often mild to moderate and is more prevalent in young adults. Most of the reactions resolve after a few days without intervention.

Reactions of alkynes with C-S bond formation: recent developments.

Alkynes are important in organic synthesis. This review mainly focuses on recent advances (2013-2023) on alkynes with C-S bond formation, based on more than 30 types of sulfur reagents. The reactions of alkynes with various sulfur-containing compounds including RSSR (disulfides), RSH (thiols), S8 (elemental sulphur), alkynyl thioethers, RSCN, AgSCF3, K2S, Na2S, dithiane, RSCl, NFSI, RNCS, EtOCS2K, thiocarbamate, RSONH2, thiourea, sulfoxide, RSO2N3, CS2, RSO2NH2, RSO2NHNH2, RSO2Cl, RSO2Oar, RSO2SR', DABCO·(SO2)2, Na2S2O5, K2S2O5, RSO2H, RSO2Na and related compounds are discussed. Diverse mechanisms such as radical, electrophilic/nucleophilic addition, rearrangement, C-C bond cleavage, and CuAAC are discussed. The content is organized by substrates and reactivity patterns. We hope it will help in future research in this area.

Heavy-atom tunnelling in benzene isomers: how many tricyclic species are truly stable?

The variety of possible benzene isomers may provide a fundamental basis for understanding structural and reactivity patterns in organic chemistry. However, the vast majority of these isomers remain unsynthesized, while most of the experimentally known species are only moderately stable. Consequently, there is a high probability that the theoretically proposed isomers would also be barely metastable, a factor that must be taken into account if their creation in the laboratory is sought. In this work, we studied the kinetic stability of all 73 hypothetical tricyclic benzene isomers, especially focusing on their nuclear quantum effects. With this in mind, we evaluated which species are theoretically possible to synthesize, detect, and isolate. Our computations predict that 26% of the previously deemed stable molecules are completely unsynthesizable due to their intrinsic quantum tunnelling instability pushing for their unimolecular decomposition even close to the absolute zero. Five more systems would be detectable, but they will slowly and inevitably degrade, while seven more supposedly stable systems will break apart in barrierless mechanisms.

A density functional theory analysis of the C-H activation reactivity of iron(IV)-oxo complexes with an 'O' substituted tetramethylcyclam macrocycle.

In this article, we present a meticulous computational study to foresee the effect of an oxygen-rich macrocycle on the reactivity for C-H activation. For this study, a widely studied nonheme Fe(IV)O molecule with a TMC (1,4,8,11-tetramethyl 1,4,8,11-tetraazacyclotetradecane) macrocycle that is equatorially attached to four nitrogen atoms (designated as N4) and acetonitrile as an axial ligand has been taken into account. For the goal of hetero-substitution, step-by-step replacement of the N4 framework with O atoms, i.e., N4, N3O1, N2O2, N1O3, and O4 systems, has been considered, and dihydroanthracene (DHA) has been used as the substrate. In order to neutralise the system and prevent the self-interaction error in DFT, triflate counterions have also been included in the calculations. The study of the energetics of these C-H bond activation reactions and the potential energy surfaces mapped therefore reveal that the initial hydrogen abstraction, which is the rate-determining step, follows the two-state reactivity (TSR) pattern, which means that the originally excited quintet state falls lower in the transition state and the product. The reaction follows the hydrogen atom transfer (HAT) mechanism, as indicated by the spin density studies. The results revealed a fascinating reactivity order, in which the reactivity increases with the enrichment of the oxygen atom in the equatorial position, namely the order follows N4 < N3O1 < N2O2 < N1O3 < O4. The impacts of oxygen substitution on quantum mechanical tunneling and the H/D kinetic isotope effect have also been investigated. When analysing the causes of this reactivity pattern, a number of variables have been identified, including the reactant-like transition structure, spin density distribution, distortion energy, and energies of the electron acceptor orbital, i.e., the energy of the LUMO (σ*z2), which validate the obtained outcome. Our results also show very good agreement with earlier combined experimental and theoretical studies considering TMC and TMCO-type complexes. The DFT predictions reported here will undoubtedly encourage experimental research in this biomimetic field, as they provide an alternative with higher reactivity in which heteroatoms can be substituted for the traditional nitrogen atom.

Biomaterials based on advanced oxidation processes in tooth whitening: fundamentals, progress, and models.

The increasing desire for aesthetically pleasing teeth has resulted in the widespread use of tooth whitening treatments. Clinical tooth whitening products currently rely on hydrogen peroxide formulations to degrade dental pigments through oxidative processes. However, they usually cause side effects such as tooth sensitivity and gingival irritation due to the use of high concentrations of hydrogen peroxide or long-time contact. In recent years, various novel materials and reaction patterns have been developed to tackle the issues related to H2O2-based tooth whitening. These can be broadly classified as advanced oxidation processes (AOPs). AOPs generate free radicals that have potent oxidizing properties, which can thereby increase the oxidation power and/or reduce the exposure time and can probably minimize the side effects of tooth bleaching. While there have been several reviews on clinical tooth whitening and the application of novel nanomaterials, a review based on the concept of AOPs in tooth bleaching application has not yet been conducted. This review describes the common types and mechanisms of AOPs, summarizes the latest research progress of new tooth bleaching materials based on AOPs, and proposes a model for tooth bleaching and a rate control step at the molecular level. The paper also reviews the shortcomings and suggests future development directions.