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PubMed2005

Effects of salt concentration on the yield stress of sodium montmorillonite suspension.

The yield stress of Na-montmorillonite suspension in an electrostatically dispersed state was studied to confirm the validity of previously proposed equation for the dependency of the yield stress on the volume fraction of clay and ionic strength. In the derivation of the equation, it is assumed that (1) clay layers array in parallel, and (2) the yield stress is equivalent to the strength of electrostatic repulsion when it reaches the yield stress. Measurements of the yield stress were performed with the vane method, varying the volume fraction of clay, phi, under controlled ionic strength for the region of 0.008<phi<0.023 and 10(-2)<NaCl<10(-5) M. Experimental data qualitatively agreed with theoretical predictions; however, quantitative differences were found to range from 0.1 to 1000 times. This discrepancy can be eliminated if we introduce a correction factor. Reasonable agreement was obtained when the factor was proportional to n(0)(-0.256).

Journal Article↗
PubMed2006

Nanopore-protein interactions dramatically alter stability and yield of the native state in restricted spaces.

We have studied the stability and the yield of the folded WW domains in a spherical nanopore to provide insights into the changes in the folding characteristics due to interactions of the polypeptide (SP) with the walls of the pore. Using different models for the interactions between the nanopore and the polypeptide chain we have obtained results that are relevant to a broad range of experiments. (a) In the temperature and the strength of the SP-pore interaction plane (lambda), there are four "phases," namely, the unfolded state, the native state, the molten globule phase (MG), and the surface interaction-stabilized (SIS) state. The MG and SIS states are populated at moderate and large values of lambda, respectively. For a fixed pore size, the folding rates vary non-monotonically as lambda is varied with a maximum at lambda approximately 1 at which the SP-nanopore interaction is comparable to the stability of the native state. At large lambda values, the WW domain is kinetically trapped in the SIS states. Using multiple sequence alignment, we conclude that similar folding mechanism should be observed in other WW domains as well. (b) To mimic the changes in the nature of the allosterically driven SP-GroEL interactions we consider two models for the dynamic Anfinsen cage (DAC). In DAC1, the SP-cavity interaction cycles between hydrophobic (lambda>0) and hydrophilic (lambda=0) with a period tau. The yield of the native state is a maximum for an optimum value of tau=tau(OPT). At tau=tau(OPT), the largest yield of the native state is obtained when tau(H) approximately tau(P) where tau(H)(tau(P)) is the duration for which the cavity is hydrophobic (hydrophilic). Thus, in order to enhance the native state yield, the cycling rate, for a given loading rate of the GroEL nanomachine, should be maximized. In DAC2, the volume of the cavity is doubled (as happens when ATP and GroES bind to GroEL) and the SP-pore interaction simultaneously changes from hydrophobic to hydrophilic. In this case, we find greater increase in yield of the native state compared to DAC1 at all values of tau.

Mathematics↗
PubMed2006

Blood storage at 4 degrees C-factors involved in DNA yield and quality.

BACKGROUND: Whole blood provides one of the most common sources of both high-quality DNA and high-quantity DNA for molecular biological purposes. Typically, blood storage at 4 degrees C is short term, which ranges from a few days to a few weeks. However, long-term storage usually involves blood being frozen, with a resultant loss in DNA yield. The authors examined the effects of long-term storage at 4 degrees C. METHODS: Duplicate blood samples were collected from 301 participants (aged 20-98 years) enrolled as part of ongoing studies. Samples were stored at 4 degrees C for between 11 days and 922 days, and DNA was subsequently extracted using a phenol/chloroform procedure. RESULTS: A negative correlation of the number of storage days existed at 4 degrees C with DNA yield. The main determinant on DNA yield was the age of the participant in the study, with older persons having a lower DNA yield. CONCLUSIONS: Long-term storage of blood at 4 degrees C does have a detrimental effect on DNA yield, but this effect seemed less significant than the age of a person. The impact of age of a person or storage time has a minimal impact on DNA quality. Therefore, storage of blood at 4 degrees C offers an acceptable alternative to frozen storage.

Adult↗
PubMed2006

Stereotactic computed tomography-guided brain biopsy: diagnostic yield based on a series of 170 patients.

BACKGROUND: Stereotactic CT-guided biopsy is a valuable and safe procedure for diagnosing intracranial lesions. The objectives of this article are to analyze the diagnostic yield in a series of stereotactic CT-guided brain biopsies and to evaluate whether predictive factors may influence diagnostic yield. METHODS: The medical records of a series of patients who underwent stereotactic CT-guided brain biopsy from 1993 to 2005 in a neurosurgical center were reviewed. Clinical data were stored and analyzed with Microsoft Access (Microsoft Corp, Seattle, WA) and SPSS V11.0 software (SPSS, Inc, Chicago, IL). The following variables were analyzed: age, sex, anatomopathologic diagnosis, lesion topography and volume, postsurgical complications, and predictive factors that may affect diagnostic yield. RESULTS: One hundred seventy patients (102 males, 68 females; average age, 48.5 years) were analyzed. Stereotactic CT-guided biopsies allowed diagnosis in 157 cases (92%). The most frequent anatomopathologic diagnoses were high-grade glioma (n = 45), low-grade glioma (n = 31), nonspecific inflammatory lesions (n = 19), metastasis (n = 10), and lymphoma (n = 10). The most frequent topographies were frontal (n = 42), basal ganglia (n = 40), and parietal (n = 27) and front-parietal lobes (n = 9). Complications occurred in 5 patients (2.9%). Mortality rate was 1.2% (2 patients). Age had a positive impact, whereas female sex negatively affected diagnostic yield. All other predictive factors analyzed were not significant. CONCLUSION: Stereotactic CT-guided brain biopsies performed presented acceptable anatomopathologic diagnostic rate. Age had a positive impact, whereas female sex negatively affected diagnostic yield in this series.

Adult↗
PubMed1998

The yield of bone marrow biopsy and culture compared with blood culture in the evaluation of HIV-infected patients for mycobacterial and fungal infections.

PURPOSE: To compare the clinical utility of bone marrow biopsy and culture specimens with blood cultures for mycobacterial and fungal infections among human immunodeficiency virus (HIV)-infected patients. PATIENTS AND METHODS: All bone marrow biopsies obtained from HIV-infected patients at the University of Alabama at Birmingham (UAB) Medical Center during 1993 to 1995 were blindly reviewed in a standardized format. Bone marrow culture results and blood culture results obtained within 6 weeks of each bone marrow study were compiled. Medical records were reviewed to determine indications for performing bone marrow biopsies, empiric or prophylactic antimicrobial therapies preceding the biopsy, and CD4 counts. RESULTS: Eighty-two bone marrow studies were obtained from 76 patients. Most were performed during the evaluation of fever, cytopenia, or weight loss. Of 55 bone marrow mycobacterial cultures, 13 yielded Mycobacterium avium complex (MAC) and 2 yielded M tuberculosis (MTB). Of 51 bone marrow fungal cultures performed, 2 yielded Cryptococcus neoformans and 1 Histoplasma capsulatum. All patients with a bone marrow culture positive for MAC had a CD4 count of 20 cells/mm3 or less. The mean CD4 count in this group (+/-95% confidence interval) (8+/-3 cells/mm3) was lower than that of culture-negative cases (41+/-25 cells/mm3); P <0.015). When bone marrow cultures and mycobacterial blood cultures were concurrently obtained, results were usually in agreement between the two sites. The mean time until the report of positive mycobacterial bone marrow cultures (22+/-5 days) was similar to that for blood cultures (24+/-3 days). Most (84%) patients with multiple mycobacterial cultures had completely concordant results (all positive or all negative). When blood or bone marrow culture yielded mycobacteria, only 29% of the corresponding bone marrow examinations revealed stainable acid-fast bacilli (AFB). In contrast, all 3 cases with positive fungal bone marrow cultures also had stainable organisms on histologic examination. CONCLUSIONS: The combined use of bone marrow biopsy and culture as well as blood cultures provide the maximum diagnostic yield when evaluating patients with AIDS for mycobacterial or fungal infections. However, when mycobacterial infections were diagnosed, bone marrow results seldom provided more immediate or specific information than lysis centrifugation blood cultures. A single lysis centrifugation blood culture should be the first step in the routine evaluation of HIV-infected patients when disseminated MAC infection is suspected.

AIDS-Related Opportunistic Infections↗
PubMed1982

Temperature dependence of the yield shear resultant and the plastic viscosity coefficient of erythrocyte membrane. Implications about molecular events during membrane failure.

Structural failure of the erythrocyte membrane in shear deformation occurs when the maximum shear resultant (force/length) exceeds a critical value, the yield shear resultant. When the yield shear resultant is exceeded, the membrane flows with a rate of deformation characterized by the plastic viscosity coefficient. The temperature dependence of the yield shear resultant and the plastic viscosity coefficient have been measured over the temperature range 10-40 degrees C. Over this range the yield shear resultant does not change significantly (+/- 15%), but the plastic viscosity coefficient changes exponentially from a value of 1.3 X 10(-2) surface poise (dyn s/cm) at 10 degrees C to a value of 6.2 X 10(-4) surface poise (SP) at 40 degrees C. The different temperature dependence of these two parameters is not surprising, inasmuch as they characterize different molecular events. The yield shear resultant depends on the number and strength of intermolecular connections within the membrane skeleton, whereas the plastic viscosity depends on the frictional interactions between molecular segments as they move past one another in the flowing surface. From the temperature dependence of the plastic viscosity, a temperature-viscosity coefficient, E, can be calculated: eta p = constant X exp(--E/RT). This quantity (E) is related to the probability that a molecular segment can "jump" to its next location in the flowing network. The temperature-viscosity coefficient for erythrocyte membrane above the elastic limit is calculated to be 18 kcal/mol, which is similar to coefficients for other polymeric materials.

Erythrocyte Membrane↗
PubMed1997

When do sphenoidal electrodes yield additional data to that obtained with antero-temporal electrodes?

The advantage of using sphenoidal (SE) over antero-temporal electrodes (ATE) remains controversial among epileptologists. Yet, in a recently published study of 17 patients with seizures of antero-temporal origin (Kanner et al., 1995), we demonstrated that SE placed under fluoroscopic guidance (FPSE), in order to insure that their recording tips are positioned immediately below the foramen ovale (FO), yielded a significant advantage over SE placed with the standard blind method of insertion (BPSE), in both interictal and ictal recordings. This study was done to test the following hypothesis: FPSE advantage over BPSE and ATE resides in the recording of epileptiform activity with a restricted electric field. We compared spike voltages at FPSE, BPSE and ATE in sets of 5 randomly selected spikes per interictal focus, recorded in the course of separate monitoring studies with BPSE and FPSE. We represented the voltage differences as ratios, VATE/FPSE and VATE/BPSE and calculated a mean ratio for each spike set. The spikes' voltage was almost identical at BPSE and at ATE (mean VATE/BPSE = 0.94), while it was significantly higher at FPSE than at ATE (mean VATE/FPSE = 0.66; P < 0.001, t test). A significantly narrower electric field contour was found among interictal foci in which FPSE yielded additional data during interictal (P < 0.001) and ictal (P = 0.016) recordings. Conversely, VATE/FPSE did not differ from VATE/BPSE among interictal foci where FPSE failed to yield any advantage over BPSE in either interictal (P = 0.240), or ictal (P = 0.311) recordings. These findings prove that SE yield additional localizing data when recording epileptiform activity with a restricted field, provided that its recording tip is positioned below the FO. When distant from FO, SE can be expected to yield comparable data to that obtained with ATE.

Action Potentials↗
PubMedDate not supplied

A laser-induced scar at the cardia increases the yield pressure of the lower esophageal sphincter.

Low yield pressure of the lower esophageal sphincter is associated with esophageal reflux, and fundoplication must increase yield pressure if it is to prevent reflux. We attempted to increase yield pressure endoscopically in the dog by using the Nd:YAG laser to produce a fibrous scar at the cardia in the approximate line of the gastric sling fibers. Ten beagle dogs were studied. In a pilot study with two dogs, 15 watts for 4.2 sec were found to produce a scar deep into the muscle coat of the stomach. Three configurations of scar were used. One produced significant rises in yield pressure in all four of the dogs treated, the second produced a significant rise in one of the two dogs treated, and the third caused a significant drop in yield pressure in the one dog treated. One dog died of gastric perforation 10 days after lasering, but no other animal experienced any ill effects. These findings may have therapeutic implications for the management of esophageal reflux.

Animals↗
PubMed1997

Evaluation of the pattern of liver tests and yield of cholangiography in symptomatic choledocholithiasis: a prospective study.

BACKGROUND: The role of ERCP in the management of choledocholithiasis in an era of minimally invasive therapy continues to be defined. METHODS: We evaluated prospectively the pattern of liver test abnormalities and yield of cholangiography after presentation with illnesses suggesting choledocholithiasis. Ninety-four consecutive patients, all with liver test abnormalities (total bilirubin, alkaline phosphatase, AST, and ALT) at presentation, had serial determinations to within 24 hours of cholangiography and were divided into four groups based on their patterns of rise or fall of liver test results as well as presenting clinical syndrome. Group I: normalized liver tests; Group II: falling liver tests, and alkaline phosphatase falling greater than 50% of the difference between presentation value and upper limit of normal; Group III: alkaline phosphatase falling less than 50%; and Group IV: any liver test with increasing levels. Clinical syndromes included cholangitis, pancreatitis, combined cholangitis and pancreatitis, and biliary pain with abnormal liver tests. RESULTS: Yields of choledocholithiasis were 13% (Group I), 50% (Group II), 67% (Group III), and 94% (Group IV). Yield by syndromes were 36% (biliary pancreatitis), 72% (biliary pain and abnormal liver tests), 87% (cholangitis), and 100% (cholangitis and pancreatitis). CONCLUSION: The degree of decline in liver test levels is inversely related to the yield of cholangiography in symptomatic choledocholithiasis; the yield of ERCP in these patients (with normalized liver tests) is low and they do not require ERCP. Pre-ERCP estimates of the likelihood of choledocholithiasis can be made on the basis of the pattern of liver tests, and biliary pancreatitis patients with normalized liver tests do not require ERCP.

Adult↗
PubMed1998

Diagnostic yield and cost-effectiveness of endoscopy in chronic human immunodeficiency virus-related diarrhea.

BACKGROUND: Endoscopy is commonly performed in patients with chronic human immunodeficiency virus (HIV)-related diarrhea after negative stool studies. The aim of this study was to determine the diagnostic yield and cost-effectiveness of endoscopy in this setting. METHODS: Consecutive HIV-infected patients with chronic unexplained diarrhea who were referred for diagnostic endoscopy were identified. Patient charts, pathology reports, and endoscopy records were reviewed. RESULTS: A total of 479 endoscopic procedures were performed in 307 patients. A pathogen was identified in 147 patients (47.9%); cytomegalovirus was the most frequent organism found (21.5%). The average cost of identifying a pathogen by endoscopy was $3822.94. Colonoscopy had a greater diagnostic yield than flexible sigmoidoscopy (38.7% vs. 22.4%, p = 0.009) and was more cost-effective. The yield of upper endoscopy was 29.6%. In patients with a CD4 count of less than 100/mm3, endoscopy had a higher diagnostic yield (62.8% vs. 8.3%, p < 0.0001) and a lower cost of identifying a pathogen ($2943.92 vs. $21,583.51) than in those with higher CD4 counts. CONCLUSIONS: Endoscopy frequently identifies a pathogen in HIV-related chronic diarrhea. Colonoscopy is the most cost-effective procedure. Endoscopic evaluation has a significantly higher diagnostic yield and is considerably more cost-effective in patients with a CD4 count of less than 100/mm3 than in those with higher CD4 counts.

AIDS-Related Opportunistic Infections↗
PubMed2003

The effect of occlusal rest size and shape on yield strength.

STATEMENT OF PROBLEM: Occlusal rests, essential for conventional removable partial dentures, may fracture and cause failure of the prosthesis. It is unknown whether alterations in the size or shape of occlusal rests might improve their performance. PURPOSE: In this in vitro study, 3-dimensional finite element analysis was used to evaluate the effects of occlusal rest size and shape on yield strength. MATERIAL AND METHODS: An occlusal rest and a minor connector as part of a clasp assembly were modeled for 3-dimensional finite element analysis with 3 variations of width (2.0, 3.0, and 4.0 mm), thickness (0.7, 1.0, and 1.5 mm) and length (2.0, 3.0, and 4.0 mm). A concentrated vertical load of 100 N was applied at the most protruded point of the occlusal rest base. Maximal principal stress and yield strength were calculated. In addition, the following parameters were altered: radius of curvature at the inner connection (r), thickness of the minor connector (m), inclination of horizontal axis of occlusal rest (i), and thickness at the most protruded point (t). RESULTS: Yield strength increased with increased width (183% to 242% from 2.0 to 4.0 mm) and thickness (141% to 230% from 0.7 to 1.5 mm). Alterations in length had a lesser effect on yield strength (120% to 178% from 4.0 to 2.0 mm). All other parameters except thickness at the most protruded point (t) affected yield strength. CONCLUSION: The results of this in vitro study suggest basic principles for optimizing the size and shape of occlusal rests. In general, increased width and thickness are desirable, whereas overrounded or sharp line angles and excessive rest inclination should be avoided. These principles may be useful in removable partial denture design.

Computer Simulation↗
PubMed1976

Effect of phosphate fertilization and seed inoculation with ""Okadin'' at high rate on yield of broadbean and lentil.

The effect of phosphate fertilization and seed inoculation with ""Okadin'' preperation of rhizobia strains on the yield of broadbean and lentil was tested in field experiments during the seasons 1969 to 1972 in the farm of Faculty of Agriculture, Assiut University. Superphosphate was added at the rate of 0, 50, 100, or 200 kg/fa., and ""Okadin'' preparation, specific for the kind of legume planted, was applied to the seeds at 10 times the recommended rate. Application of superphosphate at any of the tested rates did not significantly affect total yield obtained, seeds yield, or the nitrogen content of seeds of lentil or braodbean. Seed inoculation with Okadin showed no significant effect on the yield of broadbean, but resulted in significant reduction in the yield of lentil seeds in the two seasons of the experiment.

Agriculture↗
PubMed2001

Quantitative structure-property relationships (QSPRs) on direct photolysis quantum yields of PCDDs.

By the use of partial least squares (PLS) method and 16 fundamental quantum chemical descriptors computed by PM3 Hamiltonian, quantitative structure-property relationships (QSPRs) were obtained for direct photolysis quantum yields of selected polychlorinated dibenzo-p-dioxins (PCDDs). Direct photolysis quantum yields for PCDDs without experimental quantum yield values were predicted. The QSPR results showed that it was mainly the number of chlorine atoms bonded to the parent structure, the largest positive atomic charge on a chlorine atom, the dipole moment, and the frontier molecular orbital energies (Ehomo and Elumo) that determine the direct photolysis quantum yields of the PCDDs. Increasing the number of chlorine atoms, dipole moment, and the largest positive atomic charge on a chlorine atom, leads to decrease of photolysis quantum yields. Increasing Elumo, Ehomo and Elumo - Ehomo values lead to increase of log Y values.

Chlorine↗
PubMed1998

The yielding, plastic flow, and fracture behavior of ultra-high molecular weight polyethylene used in total joint replacements.

The yielding, plastic flow, and fracture behavior of UHMWPE plays an important role in wear and failure mechanisms of total joint replacement components. The primary objective of this study was to compare the yielding, plastic flow, and fracture behavior of two implantable grades of UHMWPE (GUR 1120 vs 4150 HP). The first part of this work explored the hypothesis that up to the polymer yield point, the monotonic loading behavior of UHMWPE displays similar true stress strain behavior in tension and compression. Uniaxial tension and compression tests were conducted to compare the equivalent true stress vs strain response of UHMWPE up to 0.12 true strain. During monotonic loading, the equivalent true stress strain behavior was similar in tension and compression up to the yield point. However, investigation of the unloading behavior and permanent plastic deformations showed that classical deviatoric rate independent plasticity theory may dramatically overpredict the permanent strains in UHMWPE. A secondary goal of this study was to determine the ultimate true stress and strain for UHMWPE and to characterize the fracture surfaces after failure. Using a fracture mechanics approach, the critical flaw sizes were used in combination with the true ultimate stresses to predict the fracture toughness of the two resins. A custom video-based strain measurement system was developed and validated to characterize the true stress-strain behavior up to failure and to verify the accuracy of the incompressibility assumption in calculating the true stress-strains up to failure. In a detailed uncertainty analysis, theoretical expressions were derived for the relative uncertainty in digital video-based estimates of nominal strain, true strain, homogeneous stress, and true stress. Although the yielding behavior of the two UHMWPE resins was similar, the hardening and plastic flow behavior clearly discriminated between the GUR 1120 and 4150 HP. A statistically significant difference between the fracture toughness of the two resins was also evident. The long-term goal of this research is to provide detailed true stress strain data for UHMWPE under uniaxial tension and compression for future numerical simulations and comparison with more complex multiaxial loading conditions.

Biocompatible Materials↗
PubMed2002

The influence of metabolic network structures and energy requirements on xanthan gum yields.

The metabolic network of Xanthomonas campestris is complex since a number of cyclic pathways are present making simple stoichiometric yield predictions difficult. The influence of certain pathway configurations and the resulting variations in flux have been examined as regards the maximum yield potential of this bacteria for xanthan gum production. These predictions have been compared with experimental results showing that the strain employed is functioning close to its theoretical maximum as regards yield criteria. The major constraint imposed on the network concerns energy availability which has a more pronounced effect on yield than carbon precursor supply. This can be attributed to the relatively high maintenance requirements determined experimentally and incorporated into the model. While some of this overall energy burden will undoubtedly be associated with incompressible metabolic requirements such as sugar uptake and xanthan efflux mechanisms, future strain improvement strategies will need to attack other non-essential energy-consuming reactions, if yields are to be further increased.

Bioreactors↗
PubMed1997

Effects of ozone on yield, growth, and root starch concentrations of two alfalfa (Medicago sativ A L.) cultivars.

Ozone (O3) is considered to be a major air pollutant that affects the yield of several sensitive crop species. Its concentration may reach phytotoxic levels several times during the growing season in Eastern Canada. This study was initiated to evaluate the O3 effects on alfalfa, a major crop species. The objective was to compare the yield and growth parameters of the main alfalfa cultivar used in Québec, Apica, to a cultivar more tolerant to O3, Team. Effects on root starch concentrations were also examined as this parameter is an important indicator of alfalfa perennity. The results obtained have shown that the forage yield of Apica was more reduced by O3 during two growing seasons than the yield of Team. For O3 concentrations of 20 to 40 nl liter(-1), yield reductions were 14-26% for Apica and 0-20% for Team. Whereas Apica could be considered more susceptible to O3 than Team, the latter has shown contrasting responses from year to year. This fact suggests that the mechanisms involved in O3-tolerance could be modulated by environmental conditions. At low O3 levels, Apica has shown reduced root growth in terms of dry matter and length. However, contrary to the current hypothesis that O3 would affect more root than shoot growth, we were unable to show a consistent alteration of the biomass allocation between the two. Ozone seems to reduce globally the growth of the whole plants. The greater O3-tolerance of Team could partly be associated to its capacity to maintain more leaves, to delay their senescence, or to keep a larger leaf:stem ratio under increasing levels of O3. At the end of the two growing seasons, the amount of starch reserves stored below ground was shown to be reduced by the current O3 levels. This reduction was mainly associated with a decrease in root biomass under O3 stress. This result support the hypothesis that O3 may accelerate alfalfa decline under field conditions.

Journal Article↗
PubMed1990

Consumer perception of cigarette yields: is the message relevant?

Over 1200 randomly selected subjects from the U.S. and key European countries were interviewed by telephone, to establish how consumers perceive the meaning and relative value scale of tar yields of commercial cigarettes. Some 50% of respondents interpreted numerical tar yields as being precise quantitative predictors of intake related to health effects. A less precise quantitative intuition is shown by 20-30% of respondents. The remaining respondents had little or no interest in, or understanding of, tar yield meaning. Despite local differences, the aggregate responses from the U.S. were analogous to European responses and were not significantly affected by age, sex, or socioeconomic status. The results show that consumers expect a cigarette grading message predictive of actual intake from different brands. The current message based on standard analytical yields does not meet this requirement and needs modification. Cigarette ratings based on the tar-to-nicotine ratio of standard yields could offer the basis for an acceptable message.

Advertising↗
PubMed2001

Quantum yield of singlet oxygen production by monomeric and aggregated forms of hematoporphyrin derivative.

Hematoporphyrin derivative (HpD) is a complex mixture of monoporphyrinic compounds, including hematoporphyrin, and oligomers containing up to eight porphyrin units. In methanol a sensitizer concentration-independent quantum yield of 0.64 is measured for the HpD-induced production of singlet molecular oxygen O2 (1Delta(g)). This finding is consistent with the dye components remaining unassociated in this solvent. In water pH 7.4 HpD consists of a complex mixture of non-aggregated and self- and cross-aggregated monoporphyrinic and oligomeric species, and the quantum yield of O2 (1Delta(g)) formation decreases significantly with increasing HpD concentration due to the lower quantum yield of aggregates. These variations can be quantitatively described in terms of a monomer-dimer equilibrium, with quantum yields of 0.64 and 0.11, respectively, for monomers and dimers. The yields of unassociated species are identical in methanol and water.

Dimerization↗