Biomedical subjects

Xiaohong Chen

Publications and source records attributed to Xiaohong Chen.

At least 19 recordsLinked to original sources

PubMed2026

Puerarin Attenuates Binge Ethanol-Induced Cortical Neurotoxicity in Association with AKT/mTOR Signaling and Autophagy-Related Responses.

Puerarin (Pue), a major isoflavone derived from Pueraria lobata, has demonstrated neuroprotective potential in multiple neurological disorders; however, its effects on ethanol (EtOH)-induced cortical injury and the associated molecular responses remain incompletely understood. In the present study, network pharmacology was combined with in vivo and in vitro experiments to investigate molecular responses associated with the effects of Pue on EtOH-induced neurotoxicity. Public databases were used to predict targets of Pue and alcohol-related brain injury, followed by protein-protein interaction analysis, Gene Ontology annotation, and Kyoto Encyclopedia of Genes and Genomes pathway enrichment. A total of 101 overlapping targets were identified, among which TNF, AKT1, EGFR, TP53, and PPARG emerged as major hub targets, and PI3K-Akt signaling pathway was among the pathways that remained significantly enriched after FDR correction. In a 4-day binge EtOH rat model, Pue attenuated EtOH-associated increases in oxidative stress, neuronal degeneration, and apoptotic markers in cortical tissue. This was accompanied by attenuation of the EtOH-associated reductions in the p-AKT/AKT and p-mTOR/mTOR ratios, as well as an attenuation of EtOH-associated changes in LC3, ATG5, and Beclin-1 expression. In primary cortical neurons, Pue partially attenuated the EtOH-associated loss of neuronal viability and preserved neurite morphology. Bafilomycin A1 (BafA1)-based analysis of LC3-II and p62/SQSTM1 showed an overall BafA1-sensitive increase in LC3-II without a significant treatment-dependent difference in the BafA1 response. Collectively, these findings suggest that Pue attenuates binge EtOH-induced cortical neurotoxicity in association with changes in AKT/mTOR phosphorylation and autophagy-related responses.

AKT/mTOR signaling↗

PubMed2026

Multi-omics unveils seasonal remodeling and metabolic crosstalk between testis and abdominal fat body in a non-amplexus stream frog Nanorana taihangnica (Anura: Dicroglossidae).

BACKGROUND: Energy allocation between reproduction and survival represents a fundamental life-history challenge for animals in seasonal environments. Using integrated transcriptomics and metabolomics, we investigated Nanorana taihangnica (Anura: Dicroglossidae), a non-amplexus stream frog endemic to China, to elucidate the seasonal morphological and molecular coordination between the testis and abdominal fat body. RESULTS: Morphological analysis showed that fat body adipocyte cross-sectional area minimized at the end of the breeding season but rapidly recovered thereafter, while testicular volume continued declining post-breeding and only recovered during the non-breeding period. During breeding season, multi-omics analyses revealed that the fat body enhanced fatty acid oxidation, upregulated histidine-carnosine metabolism, activated NAD+ metabolism and FOXO3-mediated antioxidative responses to mitigate metabolic stress, and regulated adipocyte survival and apoptosis via sphingolipid signaling. Seasonal testicular development was centrally regulated by the mTOR signaling pathway, whose activity integrated autophagy levels, NAD+ availability, and aspartate metabolism to coordinate spermatogonial proliferation and spermatogenesis. CONCLUSIONS: This study demonstrates that N. taihangnica optimizes seasonal energy storage, allocation, and reproductive investment through molecular and metabolic crosstalk between the fat body and testis, providing empirical insights into the physiological integration of life-history strategies in animals inhabiting fluctuating environments.

Animals↗

PubMed2025

Strain-Promoted mRNA Transdermal Delivery by Lipoic Lipid Nanoparticles for Therapeutic Skin Genome Editing.

Lipid nanoparticle (LNP)-mRNA formulations have revolutionized the field of nucleic acid therapeutics, yet their broader clinical application is constrained by inflammatory side effects and oxidative stress, particularly in the context of inflammatory diseases. Herein, we report the rational design and synthesis of a lipoic acid-based ionizable lipid library to address these limitations. By leveraging the antioxidant properties and thiol-mediated uptake potential of lipoic acid, we identified LA-A2B2CD3 as an optimal candidate through a structure-activity relationship study and design of experiment (DOE) optimization. LA-A2B2CD3 LNPs exhibited superior reactive oxygen species scavenging, enhanced mRNA translation, and reduced inflammatory cytokine production in vitro and in vivo. Mechanistic studies revealed that the efficient cellular uptake and the transdermal delivery capacity of LA-A2B2CD3 heavily rely on the reducible disulfide ring of lipoic acid. Application of LA-A2B2CD3 LNPs for the localized transdermal delivery of Cas9 mRNA and CD93 sgRNA in a murine model of psoriasis resulted in effective CD93 genome editing and the inhibition of the CD93-p38 MAPK-AKT-SMAD2/3 pathway, leading to significant therapeutic improvement. This work presents a robust, biocompatible LNP platform with minimized immunogenicity and strong potential for genome-editing therapies in inflammatory conditions, offering a transformative approach for the mRNA-based treatment of skin and other inflammation-related disorders.

Animals↗

PubMed2007

Urinary bladder epithelium antigen induces CD8+ T cell tolerance, activation, and autoimmune response.

The effort to explore the specific autoimmune mechanisms of urinary bladder has long been hindered due to a lack of proper animal models. To better elucidate this issue, we developed a novel line of transgenic (Tg) mice, designated as URO-OVA mice, that express the model Ag OVA as a "self"-Ag on the bladder epithelium. URO-OVA mice are naturally tolerant to OVA and show no response to OVA stimulation. Adoptive transfer of naive OVA-specific T cells showed cell proliferation, activation, and infiltration but no bladder histopathology. In contrast, adoptive transfer of activated OVA-specific T cells induced OVA-mediated histological bladder inflammation. Increased mast cells and up-regulated mRNA expressions of TNF-alpha, nerve growth factor, and substance P precursor were also observed in the inflamed bladder. To further facilitate bladder autoimmunity study, we crossbred URO-OVA mice with OVA-specific CD8(+) TCR Tg mice (OT-I mice) to generate a dual Tg line URO-OVA/OT-I mice. The latter mice naturally acquire clonal deletion for autoreactive OT-I CD8(+) T cells (partial deletion in the thymus and severe deletion in the periphery). Despite this clonal deletion, URO-OVA/OT-I mice spontaneously develop autoimmune cystitis at 10 wk of age. Further studies demonstrated that the inflamed bladder contained infiltrating OT-I CD8(+) T cells that had escaped clonal deletion and gained effector functions before developing histological bladder inflammation. Taken together, we demonstrate for the first time that the bladder epithelium actively presents self-Ag to the immune system and induces CD8(+) T cell tolerance, activation, and autoimmune response.

Adenoviridae↗

PubMed2006

Nociceptin/orphanin FQ blocks the antinociception induced by mu, kappa and delta opioid agonists on the cold water tail-flick test.

Nociceptin/orphanin FQ (N/OFQ), a 17-amino-acid peptide, is an endogenous agonist whose receptor is similar in sequence to mu, delta and kappa opioid receptors. It has been reported that N/OFQ can block antinociceptive effects induced by opioid receptor agonists in the radiant heat tail-flick test and warm water tail-withdrawal test. The present study was designed to see the effect of N/OFQ on antinociception induced by opioid receptor agonists in the cold water tail-flick (CWT) test, which measures a different type of pain. In adult male Sprague-Dawley (S-D) rats given subcutaneous (s.c.) injections of saline or morphine (8 mg/kg), intracerebroventricular (i.c.v.) injection of N/OFQ (18 microg) 15 min later produced a significant reversal of morphine antinociception (P<0.01, ANOVA followed by Duncan's test), compared to the corresponding saline control group. Saline (t=+15 min, i.c.v.) had no effect on s.c. morphine antinociception (P>0.01), compared to the corresponding saline control group. When the kappa opioid receptor agonist spiradoline (80 mg/kg, s.c.) was used instead of morphine, similar results were observed. In another series of experiments, it was found that i.c.v. injection of N/OFQ (18 microg) reversed the antinociception induced by i.c.v. injection of the selective mu opioid agonist PL017 (2 microg), delta opioid agonist DPDPE (50 ng) and kappa opioid agonist dynorphin (21.5 microg), respectively. These results indicate that N/OFQ may be an endogenous anti-opioid peptide in the brain of rats in the CWT test.

Analgesics, Opioid↗

PubMed2006

Rapid heterologous desensitization of antinociceptive activity between mu or delta opioid receptors and chemokine receptors in rats.

Previous studies have shown pretreatment with chemokines CCL5/RANTES (100 ng) or CXCL12/SDF-1alpha (100 ng) injected into the periaqueductal grey (PAG) region of the brain, 30 min before the mu opioid agonist DAMGO (400 ng), blocked the antinociception induced by DAMGO in the in vivo cold water tail-flick (CWT) antinociceptive test in rats. In the present experiments, we tested whether the action of other agonists at mu and delta opioid receptors is blocked when CCL5/RANTES or CXCL12/SDF-1alpha is administered into the PAG 30 min before, or co-administered with, opioid agonists in the CWT assay. The results showed that: (1) CXCL12/SDF-1alpha (100 ng, PAG) or CCL5/RANTES (100 ng, PAG), given 30 min before the opioid agonist morphine, or selective delta opioid receptor agonist DPDPE, blocked the antinociceptive effect of these drugs; (2) CXCL12/SDF-1alpha (100 ng, PAG) or CCL5/RANTES (100 ng, PAG), injected at the same time as DAMGO or DPDPE, significantly reduced the antinociceptive effect induced by these drugs. These results demonstrate that the heterologous desensitization is rapid between the mu or delta opioid receptors and either CCL5/RANTES receptor CCR5 or CXCL12/SDF-1alpha receptor CXCR4 in vivo, but the effect is greater if the chemokine is administered before the opioid.

Analgesics, Opioid↗

PubMed2006

The arginine anomaly: arginine radicals are poor hydrogen atom donors in electron transfer induced dissociations.

Arginine amide radicals are generated by femtosecond electron transfer to protonated arginine amide cations in the gas phase. A fraction of the arginine radicals formed (2-amino-5-dihydroguanid-1'-yl-pentanamide, 1H) is stable on the 6.7 micros time scale and is detected after collisional reionization. The main dissociation of 1H is loss of a guanidine molecule from the side chain followed by consecutive dissociations of the 2-aminopentanamid-5-yl radical intermediate. Intramolecular hydrogen atom transfer from the guanidinium group onto the amide group is not observed. These results are explained by ab initio and density functional theory calculations of dissociation and transition state energies. Loss of guanidine from 1H is calculated to require a transition state energy of 68 kJ mol(-)(1), which is substantially lower than that for hydrogen atom migration from the guanidine group. The loss of guanidine competes with the reverse migration of the arginine alpha-hydrogen atom onto the guanidyl radical. RRKM calculations of dissociation kinetics predict the loss of guanidine to account for >95% of 1H dissociations. The anomalous behavior of protonated arginine amide upon electron transfer provides an insight into electron capture and transfer dissociations of peptide cations containing arginine residues as charge carriers. The absence of efficient hydrogen atom transfer from charge-reduced arginine onto sterically proximate amide group blocks one of the current mechanisms for electron capture dissociation. Conversely, charge-reduced guanidine groups in arginine residues may function as radical traps and induce side-chain dissociations. In light of the current findings, backbone dissociations in arginine-containing peptides are predicted to involve excited electronic states and proceed by the amide superbase mechanism that involves electron capture in an amide pi* orbital, which is stabilized by through-space coulomb interaction with the remote charge carriers.

Arginine↗

PubMed2006

Highly enantioselective cyanation of aldehydes catalyzed by a multicomponent titanium complex.

A new multicomponent bifunctional catalytic system based on a titanium complex was used for the efficient enantioselective cyanation of aldehydes. The catalyst was readily prepared from tetraisopropyl titanate (Ti(Oi-Pr)4), (S)-6,6'-dibromo-1,1'-bi-2-naphthol (1e), cinchonine (2a), and (1R,2S)-(-)-N-methylephedrine (3b). It was revealed that the combination of 1e, 2a, 3b, and Ti(IV) was essential in this cyanation. The reaction proceeded smoothly in the presence of a catalytic amount of the multicomponent catalyst to afford the desired cyanohydrins ethyl carbonates in moderate to excellent isolated yields (up to 95%) with high enantioselectivities (up to 94% ee). A catalytic cycle based on experimental phenomena was proposed to explain the origin of the asymmetric induction.

Aldehydes↗

PubMed2006

Surface imprinting strategies for the detection of trypsin.

Self-organized receptor layers are synthesized by molecular imprinting methods directly on pre-coated 10 MHz quartz-crystal microbalances (QCMs). The surface-imprinting is performed by three methods using amorphous, crystalline and solubilized trypsin, respectively, as templates. These attempts allowed us to compare imprinting results obtained with templating proteins in the dry state as well as in aqueous solution. All methods are generally applicable for surface imprinting of thin films. The biomimetic sensor layers allow selective enzyme enrichment on the imprinted electrode with detection limits as low as 100 ng ml(-1) and response times of a few minutes. Solution-based polymer imprinting with native trypsin as template resulted in the highest specific enzyme recognition, which even allowed us to distinguish denatured trypsin from the native form.

Animals↗

PubMed2006

Pharmacokinetic and pharmacodynamic profiles of the novel serotonin and norepinephrine reuptake inhibitor desvenlafaxine succinate in ovariectomized Sprague-Dawley rats.

Desvenlafaxine succinate (DVS) is a novel serotonin (5-HT) and norepinephrine (NE) reuptake inhibitor (SNRI) that is currently in clinical development for the treatment of major depressive disorder and vasomotor symptoms associated with menopause. Previous studies have documented the pharmacokinetic and pharmacodynamic profiles of DVS in male rats. Similar studies, however, have not been performed in ovariectomized (OVX) rats, a model that mimics the loss of ovarian hormones that occurs at menopause. The goal of the present study, therefore, was to characterize the pharmacokinetic and pharmacodynamic properties of DVS in OVX rats. Desvenlafaxine levels peaked in plasma, brain (total brain minus hypothalamus) and hypothalamus at concentrations of 7.0, 10.8 and 9.5 microM (assuming 1 g = 1 ml), respectively, 30 min post-dosing DVS (30 mg/kg, oral). The apparent terminal half-lives of desvenlafaxine in plasma, brain and hypothalamus were 3.0, 2.1 and 2.5 h, respectively. Based on AUC(0-last), brain to plasma and hypothalamus to plasma ratios were 1.7 and 1.3, respectively. Microdialysis experiments in the medial preoptic area of the hypothalamus showed that DVS (30 mg/kg, s.c.), in the presence of WAY-100635 (5-HT(1A) antagonist), increased 5-HT levels 225% at 1 h post-dosing. Norepinephrine levels increased 44% at 3 h post-dosing while dopamine levels were unchanged. Thus, in OVX rats, DVS has good pharmacokinetic properties, rapid brain penetration, excellent brain penetrability and selectively increases 5-HT and NE levels in the hypothalamus. This work supports the notion that DVS could have utility for treating disorders in menopausal women in which changes in 5-HT and/or NE have been implicated.

Adrenergic Uptake Inhibitors↗

PubMed2006

Viewing chemokines as a third major system of communication in the brain.

There is irrefutable proof that opioids and other classes of centrally acting drugs have profound effects on the immune system. Evidence is mounting that products of the immune system, such as chemokines, can reciprocally alter the actions of these drugs and the endogenous ligands for their receptors. Chemokines are a family of small (8 to 12 kDa) proteins involved in cellular migration and intercellular communication. With a few exceptions, they act on more than one receptor. Although the chemokines and their G protein-coupled receptors are located in both glia and neurons throughout the brain, they are not uniformly distributed. They are found in such brain areas as the hypothalamus, nucleus accumbens, limbic system, hippocampus, thalamus, cortex, and cerebellum. Among the chemokines differentially localized in brain neurons and glia are CCL2/MCP-1, CXCL12/SDF-1alpha, CX3CL1/fractalkine, CXCL10/IP 10, CCL3/MIP-1alpha, and CCL5/RANTES. Functional roles for the chemokine system, composed of the chemokine ligands and their receptors, have been suggested in brain development and heterologous desensitization. The system can alter the actions of neuronally active pharmacological agents such as opioids and cannabinoids and interact with neurotransmitter systems. In this review, we propose that the endogenous chemokine system in the brain acts in concert with the neurotransmitter and neuropeptide systems to govern brain function. It can thus be thought of as the third major system in the brain.

Animals↗

PubMed2006

Poly(methyl methacrylate) CE microchips replicated from poly(dimethylsiloxane) templates for the determination of cations.

A novel method for the rapid fabrication of poly(methyl methacrylate) (PMMA) microfluidic chips using poly(dimethylsiloxane) (PDMS) templates has been demonstrated. The PDMS molds were fabricated by soft lithography. The dense prepolymerized solution of methyl methacrylate containing thermal and UV initiators was allowed to polymerized between a PDMS template and a piece of a 1 mm thick commercial PMMA plate under a UV lamp. The images of microchannels on the PDMS template were precisely replicated into the synthesized PMMA substrates during the UV-initiated polymerization of the prepolymerized solution on the surface of the PMMA plate at room temperature. The polymerization could be completed within 10 min under ambient temperature. The chips were subsequently assembled by thermal bonding of the channel plate and the cover sheet. The new fabrication method obviates the need for specialized replication equipment and reduces the complexity of prototyping and manufacturing. Nearly 20 PMMA chips were replicated using a single PDMS mold. The attractive performance of the new microfluidic chips has been demonstrated by separating and detecting cations in connection with contactless conductivity detection. The fabricated PMMA microchip has also been successfully employed for the determination of potassium and sodium in environmental and biological samples.

Cations, Monovalent↗

PubMed2006

Optimal allocation of water resources in Guangzhou City, South China.

Based on the theory of decompose-coordination for large-scale systems, a systematic optimal operation model with multi-objective programming is developed for optimal allocation of water resources in Guangzhou City, South China. The methods of hierarchical analysis and step by step toleration obligation are used in the process of coordination through the sub-systems. Through the integrated regulation of 13 reservoirs and 6 main rivers and the regional watersheds, estimated water amount for dry year (P=97%) is distributed optimally to 14 water resource units to meet water demand in the year 2020. Water shortage due to lack of runoff and insufficient water supply projects is analyzed. The scheme of water allocation within seven water resource districts is put forward to match the sustainable balance of water supply to water demand in Guangzhou City.

China↗

PubMed2006

Phosphorylation of Jak2 on Ser(523) inhibits Jak2-dependent leptin receptor signaling.

The leptin receptor, LRb, and other cytokine receptors are devoid of intrinsic enzymatic activity and rely upon the activity of constitutively associated Jak family tyrosine kinases to mediate intracellular signaling. In order to clarify mechanisms by which Jak2, the cognate LRb-associated Jak kinase, is regulated and mediates downstream signaling, we employed tandem mass spectroscopic analysis to identify phosphorylation sites on Jak2. We identified Ser523 as the first-described site of Jak2 serine phosphorylation and demonstrated that this site is phosphorylated on Jak2 from intact cells and mouse spleen. Ser523 was highly phosphorylated in HEK293 cells independently of LRb-Jak2 activation, suggesting a potential role for the phosphorylation of Ser523 in the regulation of LRb by other pathways. Indeed, mutation of Ser523 sensitized and prolonged signaling by Jak2 following activation by the intracellular domain of LRb. The effect of Ser523 on Jak2 function was independent of Tyr570-mediated inhibition. Thus, the phosphorylation of Jak2 on Ser523 inhibits Jak2 activity and represents a novel mechanism for the regulation of Jak2-dependent cytokine signaling.

Animals↗

PubMed2005

Simple b ions have cyclic oxazolone structures. A neutralization-reionization mass spectrometric and computational study of oxazolone radicals.

The 2-methyloxazol-5-on-2-yl radical (3) and its deuterium labeled analogs were generated in the gas-phase by femtosecond electron-transfer and studied by neutralization-reionization mass spectrometry and quantum chemical calculations. Radical 3 undergoes fast dissociation by ring opening and elimination of CO and CH(3)CO. Loss of hydrogen is less abundant and involves hydrogen atoms from both the ring and side-chain positions. The experimental results are corroborated by the analysis of the potential energy surface of the ground electronic state in 3 using density functional, perturbational, and coupled-cluster theories up to CCSD(T) and extrapolated to the 6-311 ++ G(3df,2p) basis set. RRKM calculations of radical dissociations gave branching ratios for loss of CO and H that were k(CO)/k(H) > 10 over an 80-300 kJ mol(-1) range of internal energies. The driving force for the dissociations of 3 is provided by large Franck-Condon effects on vertical neutralization and possibly from involvement of excited electronic states. Calculations also provided the adiabatic ionization energy of 3, IE(adiab) = 5.48 eV and vertical recombination energy of cation 3(+), RE(vert) = 4.70 eV. The present results strongly indicate that oxazolone structures can explain fragmentations of b-type peptide ions upon electron capture, contrary to previous speculations.

Computer Simulation↗

PubMed2005

The dynamic relationship between mu and kappa opioid receptors in body temperature regulation.

Previous studies demonstrated that intracerebroventricular (icv) injection of a kappa opioid receptor agonist decreased, and a mu agonist increased, body temperature (Tb) in rats. A dose-response study with the selective kappa antagonist nor-binaltorphimine (nor-BNI) showed that a low dose (1.25 nmol, icv) alone had no effect, although a high dose (25 nmol, icv) increased Tb. It was hypothesized that the hyperthermia induced by nor-BNI was the result of the antagonist blocking the kappa opioid receptor and releasing its inhibition of mu opioid receptor activity. To determine whether the Tb increase caused by nor-BNI was a mu receptor-mediated effect, we administered the selective mu antagonist CTAP (1.25 nmol, icv) 15 min after nor-BNI (25 nmol, icv) and measured rectal Tb in unrestrained rats. CTAP significantly antagonized the Tb increase induced by icv injection of nor-BNI. Injection of 5 or 10 nmol of CTAP alone significantly decreased the Tb, and 1.25 nmol of nor-BNI blocked that effect, indicating that the CTAP-induced hypothermia was kappa-mediated. The findings strongly suggest that mu antagonists, in blocking the basal hyperthermia mediated by mu receptors, can unmask the endogenous kappa receptor-mediated hypothermia, and that there is a tonic balance between mu and kappa opioid receptors that serves as a homeostatic mechanism for maintaining Tb.

Animals↗

PubMed2005

A novel anticancer approach: SEA-anchored tumor cells expressing heat shock protein 70 onto the surface elicit strong anticancer efficacy.

Heat shock proteins (HSP) are attractive for their initiation of anticancer specific immunity via a distinct mechanism. To facilitate the induction process, we targeted HSP onto vaccine cell surface genetically. Then, SEA (a typical superantigen) was anchored on the cells by its fusion protein with transmembrane sequence, in order to produce immune-activated microsurrounding for further improvement of specific immunity. Thereby, the dual-modified vaccine, the surface-targeting-HSP70 and SEA-anchored vaccine, was developed successfully. Both in a therapeutic setting and in a pre-immune model, the mice vaccinated with the dual-modified vaccine displayed significant lymphocyte proliferation, higher NK and CTL activity, marked tumor suppression and prolonged survival when compared with those vaccinated with the vaccine modified alone with surface-targeting HSP70 or the SEA-anchored vaccine. Of all the vaccines, the dual-modified vaccine generated the best therapeutic efficacy on melanoma-bearing mice, the strongest protection against melanoma challenge. These results suggested that the dual-modified vaccine could induce more potent anticancer specific immunity while non-specific immunity was augmented.

Animals↗

PubMed2005

Adenine radicals in the gas phase: an experimental and computational study of hydrogen atom adducts to adenine.

The elusive hydrogen atom adduct to the N-1 position in adenine, which is thought to be the initial intermediate of chemical damage, was specifically generated in the gas phase and characterized by neutralization-reionization mass spectrometry. The N-1 adduct, 1,2-dihydroaden-2-yl radical (1), was generated by femtosecond electron transfer to N-1-protonated adenine that was selectively produced by electrospray ionization of adenine in aqueous-methanol solution. Radical 1 is an intrinsically stable species in the gas phase that undergoes specific loss of the N-1-hydrogen atom to form adenine, but does not isomerize to the more stable C-2 adduct, 1,2-dihydroaden-1-yl radical (5). Radicals 1 that are formed in the fifth and higher electronically excited states of DeltaE > or = 2.5 eV can also undergo ring-cleavage dissociations resulting in expulsion of HCN. The relative stabilities, dissociation, and transition state energies for several hydrogen atom adducts to adenine have been established computationally at highly correlated levels of theory. Transition state theory calculations of 298 K rate constants in the gas phase, including quantum tunnel corrections, indicate the branching ratios for H-atom additions to C-8, C-2, N-3, N-1, and N-7 positions in adenine as 0.68, 0.20, 0.08, 0.03, and 0.01, respectively. The relative free energies of adenine radicals in aqueous solution point to the C-8 adduct as the most stable tautomer, which is predicted to be the predominating (>99.9%) product at thermal equilibrium in solution at 298 K.

Adenine↗