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1.
Flávia Gomes de Góes Rocha Karen Cristina Barbosa Chaves Cinthia Zanini Gomes Camila Barricheli Campanharo Lilia Coronato Courrol Nestor Schor Maria Helena Bellini 《Journal of fluorescence》2010,20(6):1225-1231
Renal cell carcinoma (RCC) remains one of the greatest challenges of urological oncology and is the third leading cause of
death in genitourinary cancers. RCCs are highly vascularized and are amenable to antiangiogenic therapy. Endostatin (ES) is
a fragment of collagen XVIII that possesses antiangiogenic activity. In this study, we examined the potential of erythrocyte
PpIX fluorescence spectroscopy for monitoring the efficacy of antiangiogenic therapy in metastatic renal cell carcinoma (mRCC),
using an orthotopic metastatic mouse model. Balb/C-bearing Renca cells were treated with NIH/3T3-LendSN cells. Lung weight,
nodule area, microvascular area (MVA), and erythrocyte PpIX fluorescence were evaluated. Emission spectra were obtained by
exciting the samples at 405 nm. There was a significant decrease in lung wet weight, lung nodule area and MVA in the treated
group compared to the control group (P < 0.001). Significant differences in autofluorescence shape were observed in the 620–650 nm spectral region. The most intense
fluorescence peak was observed at ∼632 nm. The autofluorescence of the control samples was about 53% higher than that of normal
blood (P < 0.05). In the group treated with ES, the autofluorescence was about 54% lower than in the control group (P < 0.05). Fluorescence intensity was positively correlated with the nodule area (R
2 = 0.8859; P < 0.001) and MVA (R
2 = 0.9431; P < 0.001) in the ES-treated group. These results demonstrate that the spectroscopic analysis method allows a selective detection
of tumor masses. This preliminary study suggests that PpIX fluorescence may be useful as a biomarker for antiangiogenic cancer
therapy. 相似文献
2.
Correlation Between Autofluorescence Intensity and Tumor Area in Mice Bearing Renal Cell Carcinoma 总被引:3,自引:2,他引:1
Bellini MH Coutinho EL Courrol LC Rodrigues de Oliveira Silva F Vieira Júnior ND Schor N 《Journal of fluorescence》2008,18(6):1163-1168
Protoporphyrin IX (PpIX) is a porphyrin derivative that is accumulated in cancerous tissue in consequence of the tumor-specific
metabolic alterations. The aim of this study was to evaluate the accumulation of PpIX in mice bearing renal cell carcinoma
by spectroscopy analysis. A total of 24 male Balb/c mice, 6 weeks old, were divided into six groups: Normal (without inoculation
of tumor cells) and 4, 8, 13, 16, and 20 days after inoculation of tumor cells. The orthotopic tumor model of renal cancer
was used. Murine renal cell carcinoma (Renca cells) were inoculated into the subcapsular space of the kidney. Normal and tumor-bearing
kidneys in different progression stages were removed and analyzed by ex-vivo spectroscopy and by microscopy, for tumor histometric
analysis. Emission spectra were obtained by exciting the samples at 405 nm. Significant differences between normal and tumor-bearing
kidneys in autofluorescence shape occurred in the 600–700 nm spectral region. A good correlation was found between emission
band intensity at 635 nm and the tumor area. 相似文献
3.
Flávia?Rodrigues?de Oliveira Silva Maria?Helena?Bellini Vivian?Regina?Trist?o Nestor?Schor Nilson?Dias?VieiraJr. Lilia?Coronato?Courrol 《Journal of fluorescence》2010,20(6):1159-1165
Prostate cancer is one of the most common types of cancer in men, and unfortunately many prostate tumours remain asymptomatic
until they reach advanced stages. Diagnosis is typically performed through Prostate-Specific Antigen (PSA) quantification,
Digital Rectal Examination (DRE) and Transrectal Ultrasonography (TU). The antigen (PSA) is secreted by all prostatic epithelial
cells and not exclusively by cancerous ones, so its concentration also increases in the presence of other prostatic diseases.
DRE and TU are not reliable for early detection, when histological analysis of prostate tissue obtained from a biopsy is necessary.
In this context, fluorescence techniques are very important for the diagnosis of cancer. In this paper we explore the potential
of using endogenous phorphyrin blood fluorescence as tumour marker for prostate cancer. Substances such as porphyrin derivatives
accumulate substantially more in tumours than in normal tissues; thus, measuring blood porphyrin concentration by autofluorescence
intensity may provide a good parameter for determining tumour stage. In this study, the autofluorescence of blood porphyrin
was analyzed using fluorescence and excitation spectroscopy on healthy male NUDE mice and in those with prostate cancer induced
by inoculation of DU145 cells. A significant contrast between the blood of normal and cancer subjects could be established.
Blood porphyrin fluorophore showed an enhancement on the fluorescence band around 632 nm following tumour growth. Fluorescence
detection has advantages over other light-based investigation methods: high sensitivity, high speed and safety. However it
does carry the drawback of low specificity of detection. The extraction of blood porphyrin using acetone can solve this problem,
since optical excitation of further molecular species can be excluded, and light scattering from blood samples is negligible. 相似文献
4.
Al-Salhi M Masilamani V Vijmasi T Al-Nachawati H VijayaRaghavan AP 《Journal of fluorescence》2011,21(2):637-645
Lung cancer takes a heavy toll every year, since the survival rate is not more than 15%. In this paper, we present results
of a novel technique based on the autofluorescence of body fluids like blood plasma, acetone extract of cellular components,
sputa and urine of lung cancer patients (N = 27). A set of ratio parameters based on the fluorescence peaks of tryptophan and elastin, in plasma and sputum; flavin,
NADH (reduced nicotinamide adenine dinucleotide) and porphyrin in urine; porphyrin alone in acetone extract of formed elements,
were all evaluated. Similar sets of ratios were obtained for age adjusted normal controls (N = 27) and all these ratios were given as inputs to multivariate (principle component and discriminant) analyses, which showed
that the two groups could be classified with an accuracy of about 90%. Since the instrumentation involved was an ordinary
steady state Xe lamp based spectrofluorometer, the technique is of significant advantage in screening and early detection
of lung cancer in high risk population such as heavy smokers. 相似文献
5.
Laser-induced autofluorescence for medical diagnosis 总被引:1,自引:0,他引:1
The naturally occurring autofluorescence of cells and tissues is based on biomolecules containing intrinsic fluorophores, such as porphyrins, the amino acids tryptophan and tyrosine, and the coenzymes NADH, NADPH, and flavins. Coenzymes fluoresce in the blue/green spectral region (fluorecence lifetimes: 0.5–6 ns) and are highly sensitive indicators of metabolic function. Steadystate and time-resolved blue-green autofluorescence is, therefore, an appropriate measure of the function of the respiratory chain as well as of cellular and tissue damage. Autofluorescence in the yellow/red spectral region is based mainly on endogenous porphyrins and metalloporphyrins, such as coproporphyrin, protoporphyrin (fluorescence lifetime of porphyrin monomers: >10 ns), and Zn-protoporphyrin (2 ns). Various pathological microorganisms such asPropionibacterium acnes, Pseudomonas aeruginosa, Actinomyces odontolyticus, Bacteroides intermedius, andSaccharomyces cerevisiae are able to synthesize large amounts of these fluorophores and can therefore be located. This permits fluorescence-based detection of a variety of diseases, including early-stage dental caries, dental plaque, acne vulgaris, otitis externa, and squamous cell carcinoma. The sensitivity of noninvasive autofluorescence diagnostics can be enhanced by time-gated fluorescence measurements using an appropriate time delay between ultrashort laser excitation and detection. For example, videocameras with ultrafast shutters, in the nanosecond region, can be used to create caries images of the teeth. Alternatively, autofluorescence can be enhanced by stimulating protoporphyrin biosynthesis with the exogenously administered porphyrin precursor 5-aminolevulinic acid (ALA). The fluorophore protoporphyrin IX (PP IX) is photolabile and photodynamically active. Irradiation of PP IX-containing tissue results in cytotoxic reactions which correlate with modifications in fluorescence due to photobleaching and singlet oxygen-dependent photoproduct formation. Therefore, on-line autofluorescence measurements during the phototreatment can yield information on the efficiency of ALA-based photodynamic therapy. 相似文献
6.
Flávia R. O. Silva Camila T. Nabeshima Maria H. Bellini Nestor Schor Nilson D. Vieira Jr Lilia C. Courrol 《Journal of fluorescence》2013,23(1):131-135
This paper describes the elimination of porphyrins by feces. It was demonstrated that porphyrin accumulates substantially more in tumors than in normal tissues, and consequently more PPIX reaches the blood of patients and animals with tumors, and then, it needs to be eliminated. The fluorescence of feces revealed that there are large amounts of PPIX in the excreta of animals with cancer comparing with healthy animals. The autofluorescence of feces porphyrin extracted with acetone was analyzed using fluorescence spectroscopy of animals inoculated with DU145 cells into the prostate and healthy animals to monitor the PPIX concentration. Emission spectra were obtained by exciting the samples at 405 nm. Significant differences were observed in autofluorescence intensities measured in the 575–725 nm spectral regions for the studied groups. The results showed a noninvasive, simple, rapid and sensitive method to detect cancer by feces analysis. 相似文献
7.
Vivian?Regina?Trist?o Fernando?Felippe?de?Carvalho Cinthia?Zanini?Gomes Adriana?Regina?Miranda Cíntia?C.?Vequi-Suplicy Maria?Teresa?Lamy Nestor?Schor Maria?Helena?Bellini 《Journal of fluorescence》2010,20(3):665-669
The progression to end-stage renal failure is independent of the initial pathogenic mechanism. Metabolic acidosis is a common
consequence of chronic renal failure that results from inadequate ammonium excretion and decreased tubular bicarbonate reabsorption.
Protoporphyrin IX (PpIX) is the immediate metabolic precursor of the heme molecule. The purpose of this study was to evaluate
the levels of erythrocytes protoporphyrin IX at an animal model during progressive renal disease. A total of 36 eight-week-old
male Wistar rats were divided into six groups: Normal, 4 and 8 weeks after 5/6 nephrectomy (NX). Renal function was evaluated
by creatinine clearance and plasma creatinine levels. The autofluorescence of erythrocytes porphyrin of healthy and NX rats
was analyzed using fluorescence spectroscopy. Emission spectra were obtained by exciting the samples at 405 nm. Significant
differences between normal and NX rats autofluorescence shape occurred in the 600–700 nm spectral region. A correlation was
observed between emission band intensity at 635 nm and progression of renal disease. 相似文献
8.
Prerequisites for successful flow cytometry investigations are specific antibodies labeled with appropriate fluorochromes
and negligible autofluorescence of the untreated cells at the wavelength of interest. The aim of this study was (a) to characterize
frequently used urological carcinoma cell lines with regard to their autofluorescence properties, (b) to demonstrate the autofluorescence
as a serious interfering factor on FACS analysis of urological carcinoma cell lines and (c) to suggest an alternative to avoid
interfering autofluorescence. Twenty-one cell lines originating from prostate carcinoma, renal cell carcinoma and bladder
cancer were included in this study. The various cell lines were read on a flow cytometer in comparison to human erythrocytes
as cells with low fluorescence intensity. Urological cell lines show a high autofluorescence when flow cytometry analyses
are performed at the frequently used excitation wavelengths at 405 and 488 nm. At excitation wavelength of 633 nm, this problem
was reduced and most of the cell lines (14/21) were without autofluorescence at the emission wavelength of 785 nm. In addition,
with a spectrofluorometer three exemplary cell lysates were investigated. The above observations were confirmed. The dye APC-Cy7
is one suitable fluorochrome for successful investigation under these measurement conditions. 相似文献
9.
无创人皮肤浅表组织血液中卟啉的荧光光谱分析 总被引:2,自引:0,他引:2
人体中含有的卟啉化合物主要有血红蛋白、血红素、原卟啉、粪卟啉、尿卟啉等。健康状况影响卟啉代谢,恶性肿瘤影响原卟啉(PPⅨ)与类胡萝卜素的相对含量。采用钛宝石激光器、光导纤维、荧光探头、多色仪、CCD、微机,组建起实施人体皮肤浅表组织内血液中的卟啉进行无创荧光检测系统。对人耳垂皮肤浅表组织内血液进行了荧光分析,结果同P_pⅨ水溶液的荧光谱一致。 相似文献
10.
肿瘤组织自体荧光光谱测量与分析 总被引:4,自引:2,他引:2
首先介绍了对人工培养鼠肿瘤组织的激光诱导荧光光谱的实验测量结果,并与同一机体正常组织的自体荧光光谱进行了比较,然后对肿瘤组织自体荧光的来源,与正常组织光谱特征差异的本质进行了详细分析,从而得出结论,生物组织自体荧光光谱能够反映肿瘤组织的特异性,可以作为组织诊断的依据。 相似文献
11.
Excited light and corresponding intrinsic fluorescence diffusion inside teeth tissue are an essential problem for light-based
carious lesion detection. Based on finite element numerical analysis of diffusion equation, the photon density distribution
of both excited light and autofluorescence of 2D premolar teeth model is obtained. The dependence of excited light and autofluorescence
density distribution inside the teeth model on the scattering coefficient of enamel (5–25 mm−1) and dentine (100–140 mm−1) is numerically simulated and analyzed. The fitted results reveal that fluorescence intensity decreases exponentially. Optical
penetration depth and fluorescence relative depth declined with the increment of scattering coefficient of enamel. And the
dentine had the opposite effect. Finally, the experiment of measurement of fluorescence intensity on the teeth surface is
conducted and the result is compared with the numerical computation. 相似文献
12.
Elena M. Kirilova Inta Kalnina Tija Zvagule Natalija Gabruseva Natalja Kurjane Irina I. Solomenikova 《Journal of fluorescence》2011,21(3):923-927
The use of hydrophobic fluorescent probe ABM (benzanthrone derivative) and albumin autofluorescence allowed show conformational
alterations in Chernobyl clean-up workers blood plasma. Results obtained in 1996–1997 suggest that acidic expansion of plasma
albumin takes place. Latest data (2006–2008) result in splitting of albumin alterations onto two stages - acidic expansion
and N-F transition. The N-F transition is accompanied by the blue shift of fluorescence spectra and dehydration of tryptophanyl
region of albumin molecule. In 2007 obtained.patterns of ABM spectra had never been previously seen in examined healthy individuals
or patients with tuberculosis, multiple sclerosis, rheumatoid arthritis, etc. Patterns of ABM fluorescence spectra are associated
with conformational changes of blood plasma albumin. The use of probe ABM and albumin auto-fluorescence allowed show conformational
alterations in albumin of Chernobyl clean-up workers blood plasma. It is necessary to note that all investigated parameters
significantly differ in observed groups of patients. These findings reinforce our understanding that the blood plasma albumin
is a significant biological target of radiation. It may be concluded that fluorescence characteristics are representative
of radiation induced albumin alterations and its carrier function. 相似文献
13.
Steady state and time-resolved autofluorescence spectroscopies are employed to study the autofluorescence characteristics of human colonic tissues in vitro. The excitation wavelength varies from 260 to 540 nm, and the corresponding fluorescence emission spectra are acquired from 280 to 800 nm. Significant difference in fluorescence intensity of excitation-emission matrices (EEMs) is observed between normal and tumor colonic tissues. Compared with normal colonic tissue, low nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and flavin adenine dinucleotide (FAD), and high amino acids and protoporphyrin Ⅸ (PpⅨ) fluorescences characterize high-grade malignant tissue. Moreover, the autofluorescence lifetimes of normal and carcinomatous colonic tissues at 635 nm under 397-nm excitation are about 4.32±0.12 and 18.45±0.05 ns, respectively. The high accumulation of endogenous PpⅨ in colonic cancers is demonstrated in both steady state and time-resolved autofluorescence spectroscopies. 相似文献
14.
Synthesis and spectral-luminescence properties of the conjugate of 24-epibrassinolide with porphyrin
T.?F.?Raichyonok V.?A.?Khripach V.?N.?Zhabinskii O.?V.?Konstantinova P.?B.?Dra?ar D.?Monti 《Journal of Applied Spectroscopy》2009,76(4):542-546
The synthesis of a previously unknown conjugate of 24-epibrassinolide with porphyrin is described. Four molecules of 24-epibrassinolide
are bonded to a molecule of porphyrin by selective formation of cyclical boric ethers in diol groups of the side chain. Electronic
spectra of the synthesized conjugate of 24-epibrassinolide with porphyrin are measured and analyzed. The spectral and luminescence
characteristics of the initial porphyrin and the conjugate are found to be similar. The quantum yield and fluorescence lifetime
of the conjugate in tetrahydrofuran are 0.06 and 10.6 ns, respectively. The extinction coefficient of the conjugate in tetrahydrofuran
is 385,000 (M∙cm)–1 at a wavelength of 418 nm. 相似文献
15.
Poly (ethylene glycol)-co-(
L
-Lactic acid) diacrylate (PEG-PLLA-DA) copolymers have been extensively investigated for a number of applications in medicine.
PEG-PLLA-DA is biodegradable and the human body can process its degradation products. In this study, we describe the autofluorescence
of PEG-PLLA-DA copolymers and compared it to the fluorescence of poly(ethylene glycol) diacrylate (PEG-DA) and the precursor
molecules used for their synthesis. In addition, we examined the influence of pH on the fluorescence spectra. We found that
PEG-PLLA-DA exhibits higher fluorescence than PEG-DA and all reagents involved in the synthesis of PEG-PLLA-DA. The fluorescence
of PEG-PLLA-DA was affected by pH with fluorescence decreasing at high pH values. At high pH, PEG-PLLA-DA could not polymerize
into hydrogels and exhibited a dramatic decrease in autofluorescence, suggesting that hydrolysis of the ester bond affected
its autofluorescence. At low pH, PEG-PLLA-DA exhibited higher fluorescence and it was able to form crosslinked hydrogels.
The autofluorescence of PEG-PLLA-DA could be exploited to monitor polymer degradation and material structure without the need
to introduce exogenous fluorescent probes. The origin of fluorescence is not clear at this point in time but it appears to
result from a synergetic effect of both lactate units and diacrylate groups in the PEG-PLLA-DA backbone. The observed autofluorescence
of PEG-PLLA-DA persists after reaction of the acrylate groups in the polymerization reaction. This autofluorescence is advantageous
because it could assist in the study of polymers used for drug delivery and tissue engineering applications. 相似文献
16.
L. A. Grubina 《Journal of Applied Spectroscopy》1997,64(6):759-763
The aim of the present work was to use the fluorescence method for elucidating the laws governing porphyrin exchange in children
with thyroid pathology to estimate the possibility of creating in future nontradiational approaches to the diagnosis of oncologic
diseases. A systematic investigation of the level of photo- and coproporphyrins in the erythrocytes of children and adolescents
of from 8 to 17 years old with thyroid pathology (cancer, ganglia, autoimmune thyroiditis) is carried out. A control group
of the same ages was examined for comparison. It is shown than in all of the pathologies considered one observes an individual
character of porphyrin variation, which affects the content of protoporphyrin and corproporphyrin in erythrocytes. A decrease
in the level of endogenic porphyrins in the blood of children with malignant tumors is discovered.
Institute of Molecular and Atomic Physics of the Academy of Sciences of Belarus, 70, Skorina Ave., Minsk, 220072, Belarus.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 748–752, November–December, 1997. 相似文献
17.
Victor N. Zozulya Olga A. Ryazanova Igor M. Voloshin Alexandr Yu. Glamazda Victor A. Karachevtsev 《Journal of fluorescence》2010,20(3):695-702
Self-assembly of tetracationic porphyrin TMPyP4+ onto polyanionic matrix of inorganic polyphosphate (PPS) in aqueous solutions has been studied in a wide range of molar phosphate-to-dye
ratios using techniques of polarized fluorescence, absorption, resonance Raman spectroscopy and static light scattering. The
binding of TMPyP4+ to PPS is characterized by the binding constant of 3 × 105 M−1 and the cooperativity parameter of about 150. The fluorescence quenching of the bound TMPyP4+ evidences the stacking of the porphyrine chromophores. Under the stoichiometric binding ratio TMPyP4+ forms extended continuous face-to-face aggregates (so-called H-aggregates) which manifest themselves by a blue shift (12 nm)
and a large hypochromisity (51%) of the Soret absorption band. Each face-to-face TMPyP4+ stack is formed with participation of four PPS chains. Formation of such columnar aggregates is promoted by the ability of
PPS chains to take a helix conformation where negative charges are arranged along two oppositely situated rows with intercharge
distance of 0.36 nm which corresponds to the thickness of the porphyrin π-electronic system. The ability of each PPS strand
to be template for formation of two porphyrin stacks results in the integration of the adjacent stacks into higher-order aggregates
which dimension was estimated from the fluorescence polarization data. 相似文献
18.
Samhan-Arias AK García-Bereguiaín MA Martín-Romero FJ Gutiérrez-Merino C 《Journal of fluorescence》2006,16(3):393-401
Flavoproteins are components of plasma membrane redox chains, which have been suggested to play major roles in neuronal activity and survival. We found that the red/orange autofluorescence of mature primary cultures of cerebellar granule neurons (8–9 days in vitro) was largely quenched by millimolar concentrations of dithionite added to the extracellular medium, and pointed out that nearly 50% of this autofluorescence was due to plasma membrane-bound flavoproteins. We report in this work that the lipophilic neuronal plasma membrane markers N-(3-triethylammoniumpropyl)-4-(4-(4-(diethylamino)phenyl)butadienyl)-pyridinium dibromide (RH-414) and N-(3-triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridinium dibromide (FM4-64) can form fluorescence energy transfer donor–acceptor pairs with flavoproteins with calculated R
0 values between 3.7 and 4.2 nm. The quantification of the efficiency of fluorescence energy transfer with different concentrations of acceptor dyes has been worked out with re-suspended neurons. Using quantitative images of the neurons in culture, acquired with a CCD camera attached to an epifluorescence microscope, regionalization of the plasma membrane-bound flavoproteins of cerebellar granule neurons has been achieved from the quenching by dithionite of the fluorescence of the acceptor dye. The results unraveled that plasma membrane-bound flavoproteins are largely enriched in interneuronal contact sites forming clusters of 0.5–1 μm diameter size, which appears largely regionalized in the neuron's cell body. 相似文献
19.
We describe an optical processing method for characterizing tissue pathology that is based on principal-component analysis of light-induced autofluorescence. A set of optical spectral filters, which are related to the principal-component loading vectors, is designed to process the autofluorescence signal optically and to generate principal-component scores from the autofluorescence spectra. The scores are then correlated with the tissue pathology. An optical processing system is designed that uses the in vivo fluorescence spectra recorded from nasopharyngeal tissues. We demonstrate that the system can differentiate nasopharyngeal carcinoma from normal tissue with a high degree of sensitivity and specificity and that the optical filters used in the system can be manufactured. 相似文献
20.
Suthari Prashanthi P. Hemant Kumar Li Wang Arun Kumar Perepogu Prakriti Ranjan Bangal 《Journal of fluorescence》2010,20(2):571-580
Steady state and time resolved fluorescence quenching behaviors of meso-Tetrakis (pentafluorophenyl) porphyrin (H2F20TPP) in presence of different aliphatic and aromatic amines have been executed in homogeneous dichloromethane (DCM) solution.
At room temperature in DCM, free base (H2F20TPP) shows fluorescence with two distinct peaks at 640 and 711 nm and natural lifetime τ
f = 9.8 ns which are very similar to that of meso-tetraphenyl porphyrin (TPP). Unlike TPP, addition of both aliphatic and aromatic
amines to a solution containing H2F20TPP results in an efficient decrease in fluorescence intensity without altering the shape and peak position of fluorescence
emission. Upon addition of amines there was no change in optical absorption spectra of H2F20TPP. The fluorescence quenching rate constants ranged from 1 × 109 to 4 × 109 s−1, which are one order below to the diffusion control limit, and temperature dependent quenching rate constants yield the activation
energies which are found to be order of 0.1 eV. Femto second transient absorption studies reveal the existence of amine cation
radical and porphyrin anion radicals with very short decay time (15 ps). The fluorescence quenching reaction follows Stern–Volmer
kinetics. Steady state and time-resolved data are interpreted within general kinetic scheme of Marcus semi-classical model
which attributes bimolecular electron transfer process between amines and the lowest excited singlet state of H2F20TPP. Calculated internal reorganization energies are found to be in between 0.04 and 0.22 ev. Variation of electron transfer
rate as function of free energy change (∆G0) points the ET reactions in the present systems are in Marcus normal region. This is the first example of reductive fluorescence
quenching of free base neutral porphyrins in homogeneous organic solvent ever known. 相似文献