[The potential effect mechanism and research progress of extreme temperature exposure on asthma attacks].

Asthma is one of the common chronic respiratory diseases, and its incidence has been increasing worldwide in recent years. In the context of climate change, the frequency and intensity of extreme weather events are increasing. A large body of evidence suggests that exposure to extreme temperatures can increase the risk of asthma attacks, but the underlying mechanisms that trigger asthma attacks are still unclear. This study aims to systematically review the research progress on the association between extreme temperature and asthma attacks, and to elucidate the synergistic effects of extreme temperatures, indoor/outdoor environments, and individual vulnerabilities on asthma attacks. Additionally, this review discusses the potential mechanisms of asthma attacks triggered by extreme temperature, and highlights the important role of immune regulation and neuroregulation in the inflammatory response of asthma induced by extreme temperature. Moreover, we propose a potential mechanism framework to explain the disease pathogenesis of asthma which is induced by the interactions between extreme temperature and environmental factors, in order to provide a scientific basis for addressing the adverse impacts of extreme weather events and climate change.

Development of the first PCR for detection of Psoroptes ovis var. cuniculi infection and its comparison to microscopic examination and serological assay in rabbits.

Psoroptes mites are the common ecto-parasites of wild and domestic animals worldwide, which causes considerable economic losses in livestock industry. Microscopy is deemed to be the 'gold standard' for the diagnosis of Psoroptes mite infection but it has poor sensitivity for low mite infections and/or sub-clinical infections. To overcome these shortcomings, we screened four genes to develop a sensitive and specific PCR for the detection of Psoroptes mite infection in rabbits, and confirmed its practicability in detecting early infection and monitoring treatment outcome with traditional microscopy and serological tests. Results showed that PCR assay targeting ITS2 (ITS2-PCR) had a high specificity and sensitivity (detection limit: 40.3 pg/µL DNA) for detecting P. ovis DNA. In rabbits artificially infected with P. ovis, all three diagnostic tests showed the same detection rate from 14 days post infection (dpi) to 42 days dpi. However, these diagnostic tests behave differently at 7 dpi and after treatment: at 7 dpi, the detection rate of ITS2-PCR was higher than rPsoSP3-based iELISA and traditional microscopy (ITS2-PCR: 88.9%, rPsoSP3-iELISA: 77.7%, microscopy: 33.3%); at 7 days post treatment (dpt), positivity rates of ITS2-PCR and microscopy rapidly decreased to 0.00% and 11.1%, whereas rPsoSP3-iELISA remained 100% positive rate. Furthermore, the comprehensive comparisons of diagnostic performance and features of three diagnostic tests at 7 dpi were performed. Compared to ITS2-PCR or rPsoSP3-iELISA, microscopy had the lowest sensitivity, and the agreement between these assays was low (κ < 0.3). Field study showed that ITS2-PCR showed a higher detection rate than microscopy (19.4% and 11.1%, respectively). Our results suggested that the ITS2-PCR developed in this study provided a new laboratory tool for diagnosis of P. ovis var. cuniculi infection, and it had advantages over microscopic examination in detection low-level mite infections and serological assay in monitoring treatment outcome.

[The association between apparent temperature and hand, foot, and mouth disease and its spatial heterogeneity in Guangdong, Anhui and Jilin provinces].

Objective: To study the association between apparent temperature (AT) and the incidence of hand,foot, and mouth disease (HFMD) and its spatial heterogeneity in 46 cities in Guangdong, Anhui and Jilin provinces, and provide scientific evidence for the early warning of HFMD. Methods: The data of HFMD incidence and meteorological factors from 2009 to 2018 in Guangdong province, 2009 to 2015 in Anhui province, and 2013 to 2018 in Jilin province were collected. Distributed lag non-linear models were constructed to investigate the association between AT and the incidence of HFMD in 46 cities from three provinces in China. Meta-analysis was used to pool the city-specific estimates, and Meta-regression was applied to analyze the factors that may cause spatial heterogeneity. Results: The relationship between daily AT and the incidence of HFMD in 46 cities appeared nonlinear. The association in Guangdong was similar to that in Jilin, and the risk of HFMD increased with the increase of AT. While the risk of HFMD in Anhui first increased with the increase of AT, and peaked at 18.1 ℃ and then went down. AT on different levels showed different lag impacts and the higher AT showed greater and longer lag impact. The spatial heterogeneity of associations may have been caused by latitude, longitude, average temperature, and average sunshine hours. Conclusions: AT is a comprehensive index to evaluate the association between temperature, relative humidity and wind speed and the incidence of HFMD. Higher AT may increase the risk of HFMD. The AT and HFMD relationship across spatial heterogeneity varies depending on geographic location and meteorological conditions.

[Impact of additional time spent for vaccination services on overall satisfaction rate in parents].

Objective: To understand the overall satisfaction rate with vaccination services in parents of children, and the impact of additional time consumed for vaccination service on overall satisfaction rate. Methods: From December 2019 to January 2020, a total of 3 178 parents of 0-3 years old children were investigated to collect the information about their basic characteristics, additional time spent for vaccination service and overall satisfaction through questionnaires. Binary logistic regression model and restricted cubic spline model were used to evaluate the impact of additional time spend on the overall satisfaction rate. Results: The overall satisfaction rate of parents with vaccination services was 92.32%. The median time for parents to move from home to vaccination clinic was 10.00 (10.00, 20.00) minutes, the median waiting time to make an appointment was 10.00 (5.00, 15.00) minutes, the median waiting time for vaccination was 5.00 (3.00, 10.00) minutes, and the median total additional time spent was 30.00 (20.00, 45.00) minutes. The binary logistic regression analysis showed that after adjusting the relevant factors, the main factors affecting the overall satisfaction rate were the waiting time for making an appointment (the 4- minutes group vs. 8- minutes group: OR=1.863, 95%CI: 1.307-2.657), waiting time for vaccination (the <4 minutes group vs. 8- minutes group: OR=1.529, 95%CI: 1.102-2.120; the 4- minutes group vs. 8- minutes group: OR=1.534, 95%CI: 1.104-2.130), total additional time spent (the 15- minutes group vs. 30- minutes group: OR=1.470, 95%CI: 1.094-1.976). Restricted cubic spline analysis showed that the waiting time for making an appointment (non-linear: χ2=13.18, P=0.001), the waiting time for vaccination (non-linear: χ2=13.50, P=0.001), and the total additional time consumed (non-linear: χ2=9.38, P=0.009) showed a non-linear inverted "V" dose response relationship to the overall satisfaction of vaccination services. Conclusions: The waiting time for parents to make an appointment, the waiting time for vaccination and the total additional time spent for receiving vaccination services affected the overall satisfaction rate of the vaccination services. And the waiting time for making an appointment was the most important factor, and it is necessary to shorten the waiting time for appointment. It is suggested that the vaccination clinic should make use of information technology (such as WeChat public account, APP) to make accurate appointments, make appointments to the time period to control the number of people within time period.

Cerebrospinal fluid 14-3-3-gamma protein level in eight HIV-negative cryptococcal meningitis adults.

The clinical data and cerebrospinal fluid (CSF) 14-3-3-gamma protein detection of eight adult HIV-negative cryptococcal meningitis (CM) cases were examined. The eight cases included six males and two females aged 35-70 years (mean = 49.8 years). The duration between the onset of CM symptoms and the first CSF study ranged from 1 to 60 days. Initial neuroimaging study was abnormal in 87.5% (7/8) of the cases. All the eight had positive initial and subsequent follow-up CSF 14-3-3-gamma protein detection. The densitometric values of CSF 14-3-3-gamma protein were not correlated with either the CSF white blood cell counts or the therapeutic results. The therapeutic results showed that three cases died and five survived. Significant neurologic deficits were shown in 60% (3/5) of the survivors. This study revealed that HIV-negative CM patients have elevated CSF 14-3-3-gamma protein levels, and that this level is not changed with a short-term treatment.

Clonality analysis of lymphoproliferative disorders in patients with Sjögren's syndrome.

The aim of this study was to clarify the nature of the clonal lymphocyte infiltration in Sjögren's syndrome (SS) patients associated with lymphoproliferative disorders. We examined B cell clonality in lymphoproliferative tissues from six primary SS patients associated with lymphoproliferative disorders or lymphoma by cloning and sequencing of the gene rearrangement of the immunoglobulin heavy chain complementarity determining region 3 (IgVH-CDR3). Three patients with sequential observation showed progressional clonal expansion with the presence of the same subclone in different tissues during the course of disease. Among them, one patient developed mucosa-associated lymphoid tissue (MALT) lymphoma in glandular parotid. The other three SS patients concomitant with malignant B cells lymphomas showed different clonal expansion of B cells between nodal sites and salivary glands. The cloanality analysis indicated that monoclonal B cell population could spread from one glandular site to another site during the course of SS, suggesting that the malignant clone may arise from the general abnormal microenvironment, not restricted to the glandular tissue, in some SS patients.

Hepatocellular carcinoma presenting as nervous system involvement.

To analyze the clinical features of hepatocellular carcinoma (HCC) in patients with signs and symptoms of nervous system involvement as the initial presentation. Over a period of 11 years (January 1993 to December 2003), 15,008 HCC patients were identified at the Chang Gung Memorial Hospital in Kaohsiung, Taiwan. Amongst them, 42 cases had nervous system involvement, of which six had nervous system involvement as their initial presentation. These six cases were enrolled in this study and their clinical and laboratory data were analyzed. The clinical features of the other 36 HCC cases with nervous system involvement were also analyzed for comparison. The six cases were all males, aged 36-68 years old. The involved parts of the nervous system were the cerebellar hemisphere (one), the frontal lobe (one), the sphenoid sinus, sellar turcica, and cavernous sinus (one), the cervical spine (one), and the thoracic spine (two). Their corresponding neurologic presentations were back pain, headache, consciousness disturbance, visual disturbance, and limb weakness. Whilst three out of six patients presenting with nervous system manifestations were found to have concurrent systemic metastases in other expected sites (lung, bone), three had isolated nervous system involvement even after extensive work up. The associated medical conditions of the six cases included hepatitis B (three), hepatitis C (one), liver cirrhosis (two), portal vein thrombosis (three), and diabetes mellitus (two). All the six died within 9 months after the detection of nervous system involvement. The prevalence of nervous system involvement in HCC patients is 0.28% (42/15,088), with 0.04% (6/15,088) having this as their initial presentation. The prognosis of HCC with nervous system involvement is grave. Their clinical and laboratory data are not unique but the diagnosis could only be confirmed by hepatic and nervous system imaging studies, histopathologic examination, and serum alpha-fetoprotein detection. This consideration should be emphasized especially in areas that are hyperendemic for HCC and if the original focus of metastatic lesion is obscure.

Time course of cerebral hemodynamics in cryptococcal meningitis in HIV-negative adults.

To evaluate the cerebral hemodynamics in cryptococcal meningitis (CM) patients using non-invasive studies. Serial trans-cranial color-coded sonography (TCCS) and magnetic resonance angiography (MRA) studies were performed to measure the cerebral vasculopathy of 12 HIV-negative CM patients. With TCCS, 8 of the 22 middle cerebral arteries (MCAs) showed stenotic velocities, whereas the time-mean velocity (V(mean)) of the 20 anterior cerebral arteries (ACAs), 22 posterior cerebral arteries (PCAs), and 12 basilar arteries (BAs) did not. In total, five patients had stenotic velocities, three of whom had bilateral M1 stenosis (<50%), whilst two had unilateral M1 stenosis (<50%). The V(mean) of MCA increased from day 1 to day 35 and substantially decreased thereafter. The mean Pulsatility Index (PI) in the studied vessels was higher during the study period. A mismatch of the findings between TCCS and MRA studies were also demonstrated. There was a high incidence and a longer time-period of disturbed cerebral hemodynamics during the clinical course of CM. However, because of the limited case numbers for this study, further large-scale studies are needed to delineate the clinical characteristics and therapeutic influence of cerebrovascular insults in HIV-negative CM patients.

Adult Pseudomonas aeruginosa meningitis: high incidence of underlying medical and/or postneurosurgical conditions and high mortality rate.

We analyzed the clinical and laboratory characteristics, therapeutic outcome and prognostic factors of 25 cases of cerebrospinal fluid (CSF) culture-proven Pseudomonas aeruginosa adult bacterial meningitis (ABM). Twelve P. aeruginosa strains, isolated from clinical CSF specimens, were tested for antibiotic susceptibility. The 25 cases included 17 men and 8 women, aged 17 to 86 years (median=51). Of the 25 cases of P. aeruginosa ABM, 18 were the result of postneurosurgical infection and the other 7 were spontaneous infections. The latter 7 cases had serious underlying medical conditions. The antibiotic susceptibility rates of the 12 strains were as follows: ceftriaxone 16.7% (2/12), ceftazidime 91.7% (11/12), cefepime 83.3% (10/12), imipenem 83.3% (10/12), meropenem 83.3% (10/12) and ciprofloxacin 66.7% (8/12). The therapeutic results showed an overall mortality rate of 40% (10/25). The emergence of third-generation cephalosporin-resistant P. aeruginosa strains cultured from clinical CSF specimens in recent years has resulted in a therapeutic challenge in the treatment of ABM.

Epidermal growth factor-induced ANGPTL4 enhances anoikis resistance and tumour metastasis in head and neck squamous cell carcinoma.

Epidermal growth factor (EGF) is important for cancer cell proliferation, angiogenesis and metastasis in many types of cancer. However, the mechanisms involved in EGF-induced head and neck squamous cell carcinoma (HNSCC) metastasis remain largely unknown. In this study, we reveal that angiopoietin-like 4 (ANGPTL4) plays an important role in the regulation of EGF-induced cancer metastasis. We showed that EGF-induced ANGPTL4 expression promoted anoikis resistance and cancer cell migration and invasion in HNSCC. In addition, depletion of ANGPTL4 inhibited EGF-induced cancer cell invasion. Autocrine production of EGF-induced ANGPTL4 regulated the expression of matrix metalloproteinases (MMPs). The induction of MMP-1 gene expression by ANGPTL4-activated integrin ß1 signalling occurred through the AP-1 binding site in the MMP-1 gene promoter. Furthermore, down-regulation of MMP-1 impeded EGF- and recombinant ANGPTL4-enhanced HNSCC cell migration and invasion. Depletion of ANGPTL4 significantly blocked EGF-primed extravasation and metastatic seeding of tumour cells and MMP-1 expression in lungs. However, no effect of ANGPTL4 on tumour growth was observed. These results suggest that EGF-induced expression and autocrine production of ANGPTL4 enhances HNSCC metastasis via the up-regulation of MMP-1 expression. Inhibition of ANGPTL4 expression may be a potential strategy for the treatment of EGFR-mediated HNSCC metastasis.

Cerebral haemodynamics in acute bacterial meningitis in adults.

BACKGROUND: Vascular complications are an important cause of neurological sequelae among adult survivors of acute bacterial meningitis (ABM). AIM: To examine the haemodynamic changes associated with ABM. METHODS: Serial transcranial colour-coded sonography (TCCS) and magnetic resonance angiography (MRA) were used to examine cerebrovascular changes in adult ABM patients. Outcome at 3 months was categorized using a modified Barthel index. RESULTS: We recruited 24 patients, 12 men and 12 women, aged 21-68 years. Mean cerebral blood flow velocity (V(mean)) increased from day 1 to day 4 in the middle cerebral artery (MCA), anterior cerebral artery (ACA) and posterior cerebral artery (PCA). On day 4, V(mean) values in the MCA, ACA and PCA were all significantly higher than reference values in healthy volunteers. At 3 months follow-up, 16 cases had good outcomes, while the other eight had poor outcomes. Under multiple logistic regression analysis, only Glasgow coma score (GCS) at admission was independently associated with the three-month outcome. DISCUSSION: In these patient, stenosis as demonstrated by TCCS did not wholly coincide with stenosis as demonstrated by MRA, and the presence of intracranial stenosis was not predictive of a poor outcome at 3 months. Further studies are needed to delineate the characteristics and significance of cerebrovascular changes in adult ABM.

Absorption enhancement study of astragaloside IV based on its transport mechanism in caco-2 cells.

The purpose of this study was to investigate the transport characteristics and mechanisms for discovering the possible causes of the low bioavailability of astragaloside IV and to develop an absorption enhancement strategy. Caco-2 cells used as the in vitro model. Results showed a low permeability coefficient (3.7 x 10(-8)cm/s for transport from the AP to BL direction), which remained unchanged throughout the concentration range studied, indicating that the transport of astragaloside IV was predominantly via a passive route. The AP to BL transport of astragaloside IV was found to be highly sensitive to the extracellular Ca2+ concentration, which suggested that its transport may be via a paracellular route. Both chitosan and sodium deoxycholate can increase the permeation efficiency of astragaloside IV. This study indicated that astragaloside IV having a low fraction dose absorbed in humans mainly due to its poor intestinal permeability, high molecular weight, low lipophilicity as well as its paracelluar transport may directly result in the low permeability through its passive transport. Meanwhile, chitosan and sodium deoxycholate can be used as absorption enhancers based on its transport mechanism.

Cloning and characterization of the latent membrane protein (LMP) of a specific Epstein-Barr virus variant derived from the nasopharyngeal carcinoma in the Taiwanese population.

A DNA fragment containing Epstein-Barr virus (EBV) terminal fragment sequence was obtained from a genomic library of nasopharyngeal carcinoma (NPC). One of the clones (clone 1510) contained the gene encoding latent membrane protein (LMP). Sequence analysis revealed that this gene had 95% homology with the LMP sequence of the B95-8 strain. Among the sequence variations, there was a change from G to T at nucleotide position 169,426, resulting in the loss of an XhoI site in exon 1 of the LMP gene. A pair of primers bracketing the XhoI site were designed to synthesize the EBV DNA fragment from nucleotides 169,081-169,577 by using the polymerase chain reaction (PCR) method. The PCR products were then subject to XhoI digestion and to DNA sequencing analysis. This restriction enzyme site polymorphism along with the sequence variations were also observed in 50 biopsy tissues as well as in the throat washings of 6 out of 20 healthy individuals that we examined, indicating that the EBV strain predominantly existing in these biopsy tissues was different from strains of B95-8, Jijoye or nude mouse passaged cells (C15) with an African origin, but closely resembled other nude mouse passaged CAO cells which were originally derived from China. Balb/c 3T3 cells carrying this NPC-LMP gene showed a transformed cell morphology and were tumorigenic in nude mice. The relationship between this unique type of EBV and NPC has yet to be established.

Demonstration of different modes of cell death upon herpes simplex virus 1 infection in different types of oral cells.

The effects of Herpes simplex virus 1 (HSV-1) infection on five different types of oral cancerous cells (neck metastasis of gingival carcinoma (GNM) cells and tongue squamous cells of carcinoma (TSCCa) and non-cancerous cells (buccal mucosal fibroblasts (BF), gingival fibroblasts (GF), oral submucosal fibrosis cells (OSF)) and one type of non-oral cancerous cells (KB cells) were investigated. In HSV-1-infected cells the cell viability, CPE, viral antigens accumulation, caspase-3 activity, annexin V binding and DNA fragmentation were estimated. Three different forms or pathways of cell death were considered: apoptosis (the presence or rise of caspase-3 activity, DNA fragmentation and annexin V binding), slow cell death (the presence or rise of DNA fragmentation, the absence or decline of caspase-3 activity and annexin V binding), and necrosis (the absence of decline of caspase-3 activity, DNA fragmentation and annexin V binding). The viability of all cell types, except for KB cells, was reduced by the infection. CPE and viral antigens data demonstrated that all six types of cells could be infected with HSV-1. Upon HSV-1 infection there occurred (i) a classical apoptosis in GF cells, (ii) apoptosis in the early phase of infection and necrosis in the late phase of infection in GNM and TSCCa cells, (iii) slow cell death followed by necrosis in BF and OSF cells (however, these cells showed a different type of CPE), (iv) a classical slow cell death in KB cells. It is hypothesized that HSV-1 infection has a potential to induce several distinct pathways leading to cell death or several forms of cell death. Moreover, more than one pathway may be involved in the death of particular cell type. As HSV-1 was demonstrated to infect different oral and non-oral cells and cause different pathways or forms of cell death, the safety of using HSV-1 as a vector for gene therapy should be re-considered.

Screening solution-phase combinatorial libraries using pulsed ultrafiltration/electrospray mass spectrometry.

A method is described whereby a family of homologues is synthesized in a one-pot reaction, without isolation or purification, and the reaction mixture is screened using a competitive binding assay based on pulsed ultrafiltration/electrospray mass spectrometry (PUF/ESMS) to tentatively identify those derivatives having the highest affinity for a target receptor. As a model system to test this approach, a synthetic scheme designed to prepare a series of analogues of the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), as diastereomeric mixtures, was carried out. Pulsed ultrafiltration screening of the crude reaction mixture against controls without protein detected protonated molecules corresponding to EHNA-type derivatives and three of its linear, alkyl homologues but did not show protonated molecules for an isobutyl or benzylic EHNA derivative, suggesting the latter was inactive. To verify this conclusion, we prepared E/THNA, the linear homologues, and the benzylic derivative (each as a diastereomeric mixture) and bioassayed them for them adenosine deaminase inhibition index ([I]/[S]0.5). The bioassay results for the individually synthesized analogues were in good agreement with that predicted by the observed relative ion enhancement in the PUF experiments. Thus, the PUF protocol might be used as a general method to quickly provide direction to the chemist in search of drug candidates.

HPLC preparation of highly purified single-stranded M13 DNA.

Closed-circular, single-stranded viral DNAs are widely employed in DNA cloning and sequencing experiments. Because of their well-defined structure and sequence, closed-circular, single-stranded DNAs have also been used for ligand binding experiments and light scattering measurements. However, there is a high molecular weight impurity observed in light scattering experiments, which sometimes contaminates single-stranded DNA purified from phage that has been precipitated in polyethylene glycol, average molecular weight 8000, and purified by standard phenol-chloroform extraction. Three methods have been examined that remove this impurity from closed-circular, single-stranded M13mp19 DNA (SS M13 DNA). One employs a commercial peparation. This procedure yields pure but degraded SS M13 DNA, as shown by light scattering measurements and HPLC. Another employs a Whatman DE52 (diethylamino cellulose) column. This procedure yields intact DNA, but in poor yield (less than 20% of that obtained by phenol-chloroform extraction). The last was the most successful. This employs HPLC with a Waters AP-1 column with DEAE 8HR bedding. This procedure, which provides DNA in high yield (80%-90% column recovery) with an intact structure, is an efficient method for the isolation of high-purity, closed-circular, single-stranded viral DNA suitable for physical investigations and ligand binding measurements.

Hepatic resection of hepatocellular carcinoma in cirrhotic livers: is it unjustified in impaired liver function?

BACKGROUND: Resection for hepatocellular carcinoma in patients with cirrhosis and impaired liver function is usually unjustified because of higher surgical risks and poorer long-term prognosis. METHODS: A retrospective comparison of the background and resectional results of patients with cirrhosis and hepatocellular carcinoma was carried out between those with preoperative indocyanine green 15-minute retention rate of 20% or greater (group A, impaired function group, n = 36) and those with indocyanine green 15-minute retention rate of 10% or less (group B, normal function group, n = 34). RESULTS: The group A patients had significantly lower serum albumin level and higher serum bilirubin level, longer prothrombin time, higher incidence of associated esophageal varices, and poorer Child's classifications for cirrhosis. Although the tumor diameter in both groups was similar (A, 6.9 versus B, 7.1 cm; p = 0.94), the resected liver amount in group B was greater (227.4 versus 473.2 gm; p = 0.038) because of a greater extent of liver resection (p < 0.001) and a wider surgical margin (0.34 versus 1.85 cm; p < 0.0001). The amount of operative blood loss and blood transfusion, operative morbidity, and operative mortality were not different between the two groups. The pathologic characteristics and staging were also comparable. The 5-year disease-free and actuarial survival rates of groups A and B were 30.9% and 29.6% (p = 0.16) and 45.2% and 33.4% (p = 0.11), respectively. CONCLUSIONS: If the amount of resected nontumorous liver parenchyma could be reduced, resection of hepatocellular carcinoma in selected patients with cirrhosis and impaired liver function is still justified in spite of a narrow surgical margin.

Room-temperature steady-state fluorescence properties of poly(dG-dC).poly(dG-dC).

We report the steady-state fluorescence properties of the alternating polynucleotide poly(dG-dC).poly(dG-dC) in low-salt solution at room temperature for excitation at the Hg lines 265, 280 and 297 nm. Its fluorescence spectrum peaks at about 325 nm and, within the experimental error, its shape does not change significantly with the excitation wavelength. The fluorescence anisotropy is found to decrease strongly for short-wavelength excitation, a behavior which is very similar to that exhibited by free guanine. In view of the fact that the anisotropy for free cytosine is virtually constant at the aforementioned three excitation wavelengths, the results suggest that in this polynucleotide the emission stems from guanine. The values of the fluorescence quantum yield for the three excitation wavelengths are found to be very low, 0.8 x 10(-5), 0.8 x 10(-5), and 2.8 x 10(-5), respectively; these are compatible with transfer of energy from the lower-energy electronic state of guanine, before vibronic relaxation is established, to cytosine. Upon denaturation, the fluorescence spectrum becomes very broad and the fluorescence quantum yield increases; these observations support the authenticity of the emission from the nondenatured polynucleotide.

Singlet-singlet energy transfer along the helix of a double-stranded nucleic acid at room temperature.

An irreversible electronic energy trap has been formed in calf thymus DNA by methylating about 75% of its G bases at position N-7. This has allowed us to measure for the first time the efficiency of transfer of energy along the helix of a double-stranded nucleic acid at room temperature. It is found that about one out of every three photons absorbed by the other bases is trapped. We have also simulated the data with a stochastic model that uses the dipole-dipole interaction to calculate the efficiency of transfer. In order to approximate the experimental results, the model requires that: (i) the fluorescence quantum yield of T, C, and G in DNA be about 2 x 10(-3), which is about two orders of magnitude larger than the value of the fluorescence quantum yield reported for DNA; and (ii) the fluorescence quantum yield of A in DNA be negligibly small. Requirement (i) is consistent with energy transfer taking place before a very efficient fluorescence quenching process sets in, which could be formation of excited-state complexes (excimers) that do not fluoresce appreciably. Requirement (ii) implies a very short fluorescence lifetime for A, which is consistent with the reported absence of a significant number of photoproducts formed by A in DNA. The simulations find that, on the average, the excitation energy takes about 1.2 steps to reach the trap; that is to say, bases that are nearest and next nearest neighbors of the trap are, in effect, the only energy donors. Both intra- as well as interstrand energy transfer (the latter only for the C-trap base pair) make significant contributions. The value of the efficiency for pairwise base-base intrastrand transfer is about 60%, whereas those for base-trap intra- and interstand transfer are 90% and 80%, respectively. The corresponding values for the rate constant of transfer are 2 x 10(11), 1 x 10(12), and 4 x 10(11) s-1. Transfer is inefficient when A is the donor or the acceptor. In addition to the dipole-dipole term, the only other significant term in the expansion of the interaction potential is the dipole-quadrupole term which, however, makes only a small contribution to the overall transfer efficiency. The electron exchange interaction appears to be much less efficient than the coulombic interaction.