RESUMO
A small chemical modification of the nucleobase structure can significantly enhance the photoactivity of DNA, which may incur DNA damage, thus holding promising applications in photochemotherapy treatment of cancers or pathogens. However, single substitution confers only limited phototoxicity to DNA. Herein, we combine femtosecond and nanosecond time-resolved spectroscopy with high-level ab initio calculations to disentangle the excited-state dynamics of 6-methylthioguanine (me6-TG) under variable wavelength UVA excitation (310-330 nm). We find that double substitution of nucleobases (thionation and methylation) boosts the photoactivity by introducing more reactive channels. Intriguingly, 1nNπ*, rather than 1nSπ*, acts as the doorway state engendering the formation of the long-lived reactive triplet state in me6-TG. The 1nNπ* induces a low spin-orbit coupling of 8.3 cm-1, which increases the intersystem crossing (ISC) time (2.91 ± 0.14 ns). Despite the slowed ISC, the triplet quantum yield (ΦT) still accounts for a large fraction (0.6 ± 0.1), consistent with the potential energy surface that favors excited-state bifurcation to 1nNπ*min (3.36 ± 0.15 ps) rather than 1ππ*min (5.05 ± 0.26 ps), such that the subsequent ISC to triplet via 1nNπ*min constitutes the main relaxation pathway in me6-TG. Although this ΦT is inferior to its single-substituted predecessor 6-thioguanine (6-TG, 0.8 ± 0.2), the effect of thionation in synergy with methylation opens a unique C-S bond cleavage pathway through crossing to a repulsive 1πσ* state, generating thiyl radicals as highly reactive intermediates that may invoke biological damage. This photodissociation channel is extremely difficult for conventional nucleobases. These findings demonstrate the synergistic effects of double functionality substitution in modulating excited-state dynamics and enhancing the photolabile character of DNA nucleobases, providing inspirations for the rational design of advanced photodynamic and photochemotherapy approaches.
RESUMO
Dramatic fluorescence quenching of small heterocyclic ligands trapped in the abasic site (AP) of DNA has been implemented as an unprecedented strategy recognizing single-base mutations in sequence analysis of cancer genes. However, the key mechanisms governing selective nucleobase recognition remain to be disentangled. Herein, we perform fluorescence quenching dynamics studies for 2-amino-7-methyl-1,8-naphthyridine (AMND) in well-designed AP-containing DNA single/double strands. The primary mechanism is discovered, showing that AMND only targets cytosine to form a pseudo-base pair, and therefore, fluorescence quenching of AMND arises through the DNA-mediated electron transfer (ET) between excited state AMND* and flanking nucleobases, most favorably with flanking guanines. Subtle dynamic conformational variations induced by different flanking nucleobases are revealed and found to modulate efficiencies of electron transfer and fluorescence quenching. These findings provide critical mechanistic insights for guiding the design of photoinduced electron transfer (PET)-based fluorescent ligands as sensitive single-base recognition reporters.
Assuntos
DNA , Naftiridinas , DNA de Cadeia Simples , Corantes Fluorescentes , Ligantes , Espectrometria de FluorescênciaRESUMO
Triplex DNA structure has potential therapeutic application in inhibiting the expression of genes involved in cancer and other diseases. As a DNA-targeting antitumor and antibiotic drug, coralyne shows a remarkable binding propensity to triplex over canonical duplex and thus can modulate the stability of triplex structure, providing a prospective gene targeting strategy. Much less is known, however, about coralyne-binding interactions with triplex. By combining multiple steady-state spectroscopy with ultrafast fluorescence spectroscopy, we have investigated the binding behaviors of coralyne with typical triplexes. Upon binding with a G-containing triplex, the fluorescence of coralyne is markedly quenched owing to the photoinduced electron transfer (PET) of coralyne with the G base. Systematic studies show that the PET rates are sensitive to the binding configuration and local microenvironment, from which the coexisting binding modes of monomeric (full and partial) intercalation and aggregate stacking along the sugar-phosphate backbone are distinguished and their respective contributions are determined. It shows that coralyne has preferences for monomeric intercalation within CGG triplex and pure TAT triplex, whereas CGC+ triplex adopts mainly backbone binding of coralyne aggregates due to charge repulsion, revealing the sequence-specific binding selectivity. The triplex-DNA-induced aggregation of coralyne could be used as a probe for recognizing the water content in local DNA structures. The strong π-π stacking of intercalated coralyne monomer with base-triplets plays an important role in stabilizing the triplex structure. These results provide mechanistic insights for understanding the remarkable propensity of coralyne in selective binding to triplex DNA and shed light on the prospective applications of coralyne-triplex targeted anti-gene therapeutics.
Assuntos
DNA , Espectrometria de Fluorescência , Desnaturação de Ácido Nucleico , Conformação de Ácido Nucleico , DNA/químicaRESUMO
This study aimed to extract orthophosphate (ortho-P) from lipid-rich waste AF liquor (AFL) by Mg/Al layered double hydroxides (Mg/Al LDHs) adsorption, evaluate the influence of carbonate and investigate adsorption mechanisms. The carbonate influence experiment using synthetic P-rich wastewater indicated that low carbonate level was favorable for P extraction by LDHs. And then, real AFL rich in volatile fatty acids (VFAs), carbonate and ortho-P was applied as adsorbate to explore the Mg/Al LDHs adsorption performance. Experimental results indicated that 4 g/L Mg/Al LDHs could extract 88.3% of ortho-P from the AFL with low carbonate level (4829.83 mg CaCO3/L), and the adsorption quantity was 62.99 mg P/g LDHs, however, negligible VFAs were extracted. Kinetics and mechanisms analysis indicated that adsorption of P onto Mg/Al LDHs was a rapid physiochemical process, including ion exchange and surface adsorption. Finally, the nutrients release test confirmed the slow-release property of intercalated P.
Assuntos
Hidróxidos , Fósforo , Fermentação , Anaerobiose , Magnésio , L-Lactato Desidrogenase , LipídeosRESUMO
The nucleobase analog 6-thioguanine (6-TG) has emerged as important immunosuppressant, anti-inflammatory, and anticancer drug in the past few decades, but its unique photosensitivity of absorbing strongly ultraviolet UVA light elicits photochemical hazards in many ways. The particularly intriguing yet unresolved question is whether the direct photoreaction of 6-TG can promote DNA-protein cross-links (DPCs) formation, which are large DNA adducts blocking DNA replication and physically impede DNA-related processes. Herein, by real-time observation of radical intermediates using time-resolved UV-vis absorption spectroscopy in conjunction with product analysis by HPLC-MS, we discover that UVA excitation of 6-TG triggers direct covalent cross-linking with tryptophan (TrpH) via an exquisite radical mechanism of electron transfer. The photoexcitation prepares the redox-active triplet 36-TG*, which initiates electron transfer with TrpH, creating TrpHâ¢+ and 6-TGâ¢- in the first step. The deprotonated Trp⢠undergoes radical-recombination with its geminate partner 6-TGâ¢- and eliminates a H2S, leading to the cross-linking product 6-TG-Trp. The photoadduct structures (two chiral isomers and one constitutional isomer) are identified unambiguously, validating further the mechanism. These findings pinpoint the exact amino acid that is vulnerable to photo-cross-linking with 6-TG and establish a mechanistic framework for understanding mutagenic DPCs formation and developing photoprobes based on this new type of photo-cross-linking.
Assuntos
Tioguanina , Triptofano , DNA , Transporte de Elétrons , ElétronsRESUMO
The triplet metal to ligand charge transfer (3MLCT) luminescence of ruthenium (II) polypyridyl complexes offers attractive imaging properties, specifically towards the development of sensitive and structure-specific DNA probes. However, rapidly-deactivating dark state formation may compete with 3MLCT luminescence depending on different DNA structures. In this work, by combining femtosecond and nanosecond pump-probe spectroscopy, the 3MLCT relaxation dynamics of [Ru(phen)2(dppz)]2+ (phen = 1,10-phenanthroline, dppz = dipyridophenazine) in two iconic G-quadruplexes has been scrutinized. The binding modes of stacking of dppz ligand on the terminal G-quartet fully and partially are clearly identified based on the biexponential decay dynamics of the 3MLCT luminescence at 620 nm. Interestingly, the inhibited dark state channel in ds-DNA is open in G-quadruplex, featuring an ultrafast picosecond depopulation process from 3MLCT to a dark state. The dark state formation rates are found to be sensitive to the content of water molecules in local G-quadruplex structures, indicating different patterns of bound water. The unique excited state dynamics of [Ru(phen)2(dppz)]2+ in G-quadruplex is deciphered, providing mechanistic basis for the rational design of photoactive ruthenium metal complexes in biological applications.
RESUMO
One-electron oxidation of adenine (A) leads initially to the formation of adenine radical cation (Aâ¢+). Subsequent deprotonation of Aâ¢+ can provoke deoxyribonucleic acid (DNA) damage, which further causes senescence, cancer formation, and even cell death. However, compared with considerable reports on Aâ¢+ reactions in free deoxyadenosine (dA) and duplex DNA, studies in non-B-form DNA that play critical biological roles are rare at present. It is thus of vital importance to explore non-B-form DNA, among which the triplex is an emerging topic. Herein, we investigate the deprotonation behavior of Aâ¢+ in the TAT triplex with continuous A bases by time-resolved laser flash photolysis. The rate constants for the one-oxidation of triplex 8.4 × 108 M-1 s-1 and Aâ¢+ deprotonation 1.3 × 107 s-1 are obtained. The kinetic isotope effect of Aâ¢+ deprotonation in the TAT triplex is 1.8, which is characteristic of a direct release of the proton into the solvent similar to free base dA. It is thus elucidated that the Aâ¢+ proton bound with the third strand is most likely to be released into the solvent because of the weaker Hoogsteen H-bonding interaction and the presence of the highly mobile hydration waters within the third strand. Additionally, it is confirmed through Fourier transform infrared spectroscopy that the deprotonation of Aâ¢+ results in the dissociation of the third strand and disruption of the secondary structure of the triplex. These results provide valuable kinetic data and in-depth mechanistic insights for understanding the adenine oxidative DNA damage in the triplex.
Assuntos
Adenina/química , DNA/química , Elétrons , Timina/química , Ligação de Hidrogênio , OxirreduçãoRESUMO
Phosphorothioate (PS) modifications naturally appear in bacteria and archaea genome and are widely used as antisense strategy in gene therapy. But the chemical effects of PS introduction as a redox active site into DNA (S-DNA) is still poorly understood. Herein, we perform time-resolved spectroscopy to examine the underlying mechanisms and dynamics of the PS oxidation by potent radicals in free model, in dinucleotide, and in S-oligomer. The crucial sulphur-centered hemi-bonded intermediates -P-Sâ´S-P- were observed and found to play critical roles leading to the stable adducts of -P-S-S-P-, which are backbone DNA lesion products. Moreover, the oxidation of the PS moiety in dinucleotides d[GPSG], d[APSA], d[GPSA], d[APSG] and in S-oligomers was monitored in real-time, showing that PS oxidation can compete with adenine but not with guanine. Significantly, hole transfer process from A+⢠to PS and concomitant -P-Sâ´S-P- formation was observed, demonstrating the base-to-backbone hole transfer unique to S-DNA, which is different from the normally adopted backbone-to-base hole transfer in native DNA. These findings reveal the distinct backbone lesion pathway brought by the PS modification and also imply an alternative -P-Sâ´S-P-/-P-S-S-P- pathway accounting for the interesting protective role of PS as an oxidation sacrifice in bacterial genome.
Assuntos
Bactérias/genética , DNA Bacteriano/química , Oligonucleotídeos Fosforotioatos/química , Enxofre/química , Genoma Bacteriano/genética , Conformação de Ácido Nucleico , Oxirredução , Análise EspectralRESUMO
Human telomeric RNA (TERRA) containing thousands of G-rich repeats has the propensity to form parallel-stranded G-quadruplexes. The emerging crucial roles of TERRA G-quadruplexes in RNA biology fuel increasing attention for studying anticancer ligand binding with such structures, which, however, remains scarce. Here we utilized multiple steady-state and time-resolved spectroscopy analyses in conjunction with NMR methods and investigated thoroughly the binding behavior of TMPyP4 to a TERRA G-quadruplex dimer formed by the 10-nucleotide sequence r(GGGUUAGGGU). It is clearly identified that TMPyP4 intercalates into the 5'-5' stacking interface of two G-quadruplex blocks with a binding stoichiometry of 1:1 and binding constant of 1.92 × 106 M-1. This is consistent with the unique TERRA structural features of the enlarged π-π stacking plane of the A·(G·G·G·G)·A hexad at 5'-ends of each G-quadruplex block. The preferential binding of π-ligand porphyrin to the 5'-5' stacking interface of the native TERRA G-quadruplex dimer is first ascertained by the combination of dynamics and structural characterization.
Assuntos
Quadruplex G , Substâncias Intercalantes/química , Porfirinas/química , RNA/química , Telômero/química , Sequência de Bases , Dimerização , Humanos , Cinética , Ligantes , Modelos Moleculares , Estrutura Molecular , Relação Estrutura-AtividadeRESUMO
Radical cations of nucleobases are key intermediates causing genome mutation, among which cytosine Câ¢+ is of growing importance because the ensuing cytosine oxidation causes GC â AT transversions in DNA replication. Although the chemistry and biology of steady-state C oxidation products have been characterized, time-resolved study of initial degradation pathways of Câ¢+ is still at the preliminary stage. Herein, we choose i-motif, a unique C-quadruplex structure composed of hemiprotonated base pairs C(H)+:C, to examine Câ¢+ degradation in a DNA surrounding without interference of G bases. Comprehensive time-resolved spectroscopy were performed to track Câ¢+ dynamics in i-motif and in free base dC. The competing pathways of deprotonation (1.4 × 107 s-1), tautomerization (8.8 × 104 s-1), and hydration (5.3 × 103 s-1) are differentiated, and their rate constants are determined for the first time, underlining the strong reactivity of Câ¢+. Distinct pathway is observed in i-motif compared with dC, showing the prominent features of Câ¢+ hydration forming C(5OH)⢠and C(6OH)â¢. By further experiments of pH-dependence, comparison with single strand, and with Ag+ mediated i-motif, the mechanisms of Câ¢+ degradation in i-motif are disclosed. The hydrogen-bonding within C(H)+:C plays a significant role in guiding the reaction flux, by blocking the tautomerization of C(-H)⢠and reversing the equilibrium from C(-H)⢠to Câ¢+. The C radicals in i-motif thus retain more cation character, and are mainly subject to hydration leading to lesion products that can induce disruption of i-motif structure and affect its critical roles in gene-regulation.
Assuntos
Citosina/química , DNA/química , Desoxicitidina/química , Cátions/química , Radicais Livres/química , Ligação de Hidrogênio , Conformação de Ácido NucleicoRESUMO
Recognition of unusual left-handed Z-DNA by specific binding of small molecules is crucial for understanding biological functions in which this particular structure participates. Recent investigations indicate that zinc cationic porphyrin (ZnTMPyP4) is promising as a probe for recognizing Z-DNA due to its characteristic chiroptical properties upon binding with Z-DNA. However, binding mechanisms of the ZnTMPyP4/Z-DNA complex remain unclear. By employing time-resolved UV-visible absorption spectroscopy in conjunction with induced circular dichroism (ICD), UV-vis, and fluorescence measurements, we examined the binding interactions of ZnTMPyP4 towards B-DNA and Z-DNA. For the ZnTMPyP4/Z-DNA complex, two coexisting binding modes were identified as the electrostatic interaction between pyridyl groups and phosphate backbones, and the major groove binding by zinc(II) coordinating with the exposed guanine N7. The respective contribution of each mode is assessed, allowing a complete scenario of binding modes revealed for the ZnTMPyP4/Z-DNA. These interaction modes are quite different from those (intercalation and partial intercalation modes) for the ZnTMPyP4/B-DNA complex, thereby resulting in explicit differentiation between B-DNA and Z-DNA. Additionally, the binding interactions of planar TMPyP4 to DNA were also investigated as a comparison. It is shown that without available virtual orbitals to coordinate, TMPyP4 binds with Z-DNA solely in the intercalation mode, as with B-DNA, and the intercalation results in a structural transition from Z-DNA to B-ZNA. These results provide mechanistic insights for understanding ZnTMPyP4 as a probe of recognizing Z-DNA and afford a possible strategy for designing new porphyrin derivatives with available virtual orbitals for the discrimination of B-DNA and Z-DNA.
Assuntos
DNA/química , Metaloporfirinas/química , Conformação de Ácido Nucleico , DNA/metabolismo , DNA de Forma B/química , DNA de Forma B/metabolismo , DNA Forma Z/química , DNA Forma Z/metabolismo , Metaloporfirinas/metabolismo , Porfirinas/química , Porfirinas/metabolismo , Ligação Proteica , Análise EspectralRESUMO
The interaction of ligands with G-quadruplexes has attracted considerable attention due to its importance in molecular recognition and anticancer drugs design. Here, we utilize triplet excited state as a sensitive reporter to study the binding interaction of zinc cationic porphyrin (ZnTMPyP4) with three G-quadruplexes, AG3(T2AG3)3, (G4T4G4)2, and (TG4T)4. By monitoring the triplet decay dynamics of ZnTMPyP4 with transient absorption spectroscopy, the coexisted binding modes via π-π stacking of porphyrin macrocycle and the G-quartets are allowed to be identified quantitatively, which involve intercalation (25% and 36%) versus end-stacking (75% and 64%) for AG3(T2AG3)3 and (G4T4G4)2, and end-stacking (23%) versus partial intercalation (77%) for (TG4T)4. It is shown that the steric hindrance of the axial water decreases greatly the percentage of intercalation. Further, a rapid assessment of binding stoichiometry is fulfilled by measuring the triplet decay dynamics under various [G-quadruplex]/[ZnTMPyP4] ratios. The binding stoichiometric ratios of G-quadruplex/ZnTMPyP4 are 1:2 for AG3(T2AG3)3, 1:1 for (G4T4G4)2, and 1:2 for (TG4T)4, which agree well with results obtained by the conventional method of continuous variation analysis. These results reveal a clear scenario of G-quadruplex/ZnTMPyP4 interaction and provide mechanistic insights for the application of anticancer drug designs using G-quadruplex as target.
RESUMO
G-rich and C-rich DNA can fold into the tetrastranded helical structures G quadruplex or C quadruplex (i-motif), which are considered to be specific drug targets for cancer therapy. A large number of small molecules (so-called ligands), which can bind and modulate the stability of G quadruplex structures, have been widely examined. Much less is known, however, about the ligand binding interactions with the C quadruplex (i-motif). By combining steady-state measurements (UV/Vis, fluorescence, and induced circular dichroism (ICD)) with time-resolved laser flash photolysis spectroscopy, we have studied the binding interactions of cationic porphyrin (5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21 H,23 H-porphyrin, abbreviated as TMPyP4) with i-motifs (C3 TA2 )3 C3 T and (C4 A4 C4 )2. The intercalation binding mode through π-π stacking of the porphyrin macrocycle and the C:C+ hemiprotonated base pair has been identified for the first time. The coexistent binding modes of intercalation (≈80 %) versus external major-groove binding (≈20 %) have been determined quantitatively, thereby allowing a fuller understanding of the porphyrin-i-motif interactions. The ionic strength was found to play an important role in affecting affects the binding modes, with the progressive increase in the ionic strength resulting in the gradual decrease in the intercalation percentage and an increase in the groove-binding percentage. Furthermore, an extended study of the porphyrin derivative with four bulky side-arm substituents (T4) suggests a complete prohibition of the intercalation mode owing to large steric hindrance, thereby providing a novel groove-binding ligand with site selectivity. These results provide in-depth mechanistic insights to better understand the ligand interactions with i-motifs and guidance for related applications in anticancer drug design.
Assuntos
Antineoplásicos/farmacologia , Motivos de Nucleotídeos/efeitos dos fármacos , Porfirinas/química , Antineoplásicos/síntese química , Antineoplásicos/química , Sítios de Ligação/efeitos dos fármacos , Ligantes , Estrutura MolecularRESUMO
The effect of Cu impurities on the absorption cross section, the rate of hot exction thermalization, and on exciton recombination processes in InAs quantum dots was studied by femtosecond transient absorption. Our findings reveal dynamic spectral effects of an emergent impurity sub-band near the bottom of the conduction band. Previously hypothesized to explain static photophysical properties of this system, its presence is shown to shorten hot carrier relaxation. Partial redistribution of interband oscillator strength to sub-band levels reduces the band edge bleach per exciton progressively with the degree of doping, even though the total linear absorption cross section at the band edge remains unchanged. In contrast, no doping effects were detected on absorption cross sections high in the conduction band, as expected due to the relatively high density of sates of the undoped QDs.
RESUMO
Above band-edge photoexcitation of PbSe nanocrystals induces strong below band gap absorption as well as a multiphased buildup of bleaching in the 1Se1Sh transition. The amplitudes and kinetics of these features deviate from expectations based on biexciton shifts and state filling, which are the mechanisms usually evoked to explain them. To clarify these discrepancies, the same transitions are investigated here by double-pump-probe spectroscopy. Re-exciting in the below band gap induced absorption characteristic of hot excitons is shown to produce additional excitons with high probability. In addition, pump-probe experiments on a sample saturated with single relaxed excitons prove that the resulting 1Se1Sh bleach is not linear with the number of excitons per nanocrystal. This finding holds for two samples differing significantly in size, demonstrating its generality. Analysis of the results suggests that below band edge induced absorption in hot exciton states is due to excited-state absorption and not to shifted absorption of cold carriers and that 1Se1Sh bleach signals are not an accurate counter of sample excitons when their distribution includes multiexciton states.
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Esophageal reconstruction can be performed with skin or bowel flaps. The choice of flap remains controversial, as the long-term outcomes of skin flaps cannot always be assessed in patients with limited life expectancies due to advanced malignancy, unlike the pediatric and benign cases which have had esophageal reconstruction using bowel flaps. We report the long-term clinical and histopathological outcomes in a series of 45 cases repaired with combined skin and bowel flaps.Four patients developed symptomatic strictures after corrosive esophageal injuries were repaired with a combination of a tubed free radial forearm fasciocutaneous flap and a pedicled bowel flap. On average, 24 years had passed since uneventful initial esophageal reconstructions. Barium esophagograms were obtained in all cases and pathological examination was performed upon all surgical specimens.The cutaneous portions of the reconstructed esophagus exhibited a variety of findings on barium examination. Each of the 4 cases developed an esophagocutaneous fistula after revision; an average of 4 surgeries was required to close these fistulae. The inner surfaces of the portion of esophagus repaired with skin flaps showed extensive ulceration, polypoid lesions, and fibrosis. Pathology specimens from skin flaps showed extensive acute and chronic inflammation, microabscesses, fibrosis, and acanthosis, with depletion and degeneration of the pilosebaceous units. By contrast, adjacent parts of the esophagus repaired with bowel were widely patent with normal appearing mucosa.Our findings indicate that a bowel flap is durable with good tolerance to gastrointestinal content over long periods, whereas skin flaps often developed morphological changes and could not maintain long-term esophageal function without eventual stricture and dysphagia. We therefore recommend use of bowel flaps for esophageal reconstruction in patients with long life expectancy.
Assuntos
Queimaduras Químicas/cirurgia , Colo/transplante , Estenose Esofágica/cirurgia , Esofagoplastia/métodos , Jejuno/transplante , Transplante de Pele/métodos , Retalhos Cirúrgicos/transplante , Adulto , Idoso , Anastomose Cirúrgica , Queimaduras Químicas/complicações , Estenose Esofágica/induzido quimicamente , Esôfago/lesões , Esôfago/cirurgia , Feminino , Seguimentos , Humanos , Masculino , Pessoa de Meia-Idade , Complicações Pós-Operatórias/cirurgia , Reoperação , Resultado do TratamentoAssuntos
Carcinoma de Células Escamosas/patologia , Neoplasias Esofágicas/patologia , Neoplasias Hepáticas/secundário , Neoplasias Pulmonares/secundário , Adulto , Carcinoma de Células Escamosas/diagnóstico , Neoplasias Esofágicas/diagnóstico , Humanos , Neoplasias Hepáticas/diagnóstico , Neoplasias Pulmonares/diagnóstico , Masculino , Tomografia Computadorizada por Raios X , Carga TumoralRESUMO
A 25-year-old woman had carcinosarcoma of uterine cervix after definitive treatment. One year later, local recurrent disease was found in the right posterior pelvis on FDG PET/CT. FDG PET/CT also disclosed an incidental intramural hypermetabolic lesion in the rectum, which seemed separate from the right pelvic lesion on contrast-enhanced CT. The rectal lesion was confirmed as metastatic carcinosarcoma from uterine cervix after endoscopic biopsy.
Assuntos
Tumor Mulleriano Misto/patologia , Neoplasias Retais/patologia , Neoplasias Retais/secundário , Neoplasias do Colo do Útero/patologia , Adulto , Feminino , Humanos , Imagem Multimodal , Tomografia por Emissão de Pósitrons , Neoplasias Retais/diagnóstico por imagem , Neoplasias Retais/fisiopatologia , Tomografia Computadorizada por Raios XRESUMO
A 55-year-old man was diagnosed with squamous cell carcinoma in the middle thoracic esophagus. The FDG PET/CT revealed an incidental strong FDG-avid finding (SUVmax, 11) in the right parotid gland, which was subsequently confirmed as metastasis from the squamous cell carcinoma of esophagus via surgery. The current case adds another differential diagnosis of parotid FDG-avid lesion to the existing literature.
Assuntos
Carcinoma de Células Escamosas/patologia , Neoplasias Esofágicas/patologia , Fluordesoxiglucose F18 , Imagem Multimodal , Neoplasias Parotídeas/diagnóstico por imagem , Neoplasias Parotídeas/secundário , Tomografia por Emissão de Pósitrons , Tomografia Computadorizada por Raios X , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
Time-resolved infrared (TR-IR) absorption spectroscopy in both the femtosecond and nanosecond time domain has been applied to examine the photolysis of benzoic acid in acetonitrile solution following either 267 nm or 193 nm excitation. By combining the ultrafast and nanosecond TR-IR measurements, both the excited states and the photofragments have been detected and key mechanistic insights were obtained. We show that the solvent interaction modifies the excited state relaxation pathways and thus the population dynamics, leading to different photolysis behavior in solution from that observed in the gas phase. Vibrational energy transfer to solvents dissipates excitation energy efficiently, suppressing the photodissociation and depopulating the excited S(2) or S(3) state molecules to the lowest T(1) state with a rate of â¼2.5 ps after a delayed onset of â¼3.7 ps. Photolysis of benzoic acid using 267 nm excitation is dominated by the formation of the T(1) excited state and no photofragments could be detected. The results from TR-IR experiments using higher energy of 193 nm indicate that photodissociation proceeds more rapidly than the vibrational energy transfer to solvents and C-C bond fission becomes the dominant relaxation pathway in these experiments as featured by the prominent observation of the COOH photofragments and negligible yield of the T(1) excited state. The measured ultrafast formation of T(1) excited state supports the existence of the surface intersections of S(2)/S(1), S(2)/T(2), and S(1)/T(1)/T(2), and the large T(1) quantum yield of â¼0.65 indicates the importance of the excited state depopulation to triplet manifold as the key factor affecting the photophysical and photochemical behavior of the monomeric benzoic acid.