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PubMed2005

Sodium dialkyl-amidozincates: alkyl or amido bases? An experimental and theoretical case study.

Alkali metal zincate reagents are attracting considerable attention at present in respect to their often special reactivity/selectivity in hydrogen-metal and halogen-metal interconversion reactions. Heteroleptic diorgano-amidozincates, typified by lithium di-tert-butyltetramethylpiperidinozincate, have proved to be especially useful reagents in such applications. In this paper the related sodium TMP-zincate, prepared as its TMEDA (N,N,N',N'-tetramethylethylenediamine) adduct, [TMEDA.Na(mu-tBu)(mu-TMP)Zn(tBu)], 1, is introduced. This new zincate was synthesized from a 1:1:1 mixture of tBu2Zn, NaTMP, and TMEDA in hexane solution, as a colorless crystalline solid in an isolated yield of 58%. It has been characterized in solution by 1H and 13C NMR spectroscopic studies. An X-ray crystallographic study reveals that 1 adopts a five-membered (NaNZnCC) ring system featuring a TMP bridge and an unusual, asymmetrical tBu bridge involving a Na...Me agostic contact. Probing the basicity of 1, reaction with benzene affords the new hetero(tri)leptic zincate [TMEDA.Na(mu-Ph)(mu-TMP)Zn(tBu)], 2, which has also been crystallographically characterized. Thus, in this hydrogen-metal exchange reaction 1 functions as an alkyl base, with the elimination of butane, as opposed to an amido base. Also reported are DFT calculations using B3LYP functionals and the 6-311G** basis set on model zincate systems, which intimate that the preference of 1 for tBu ligand transfer over TMP ligand transfer in the reaction toward benzene is due to favorable thermodynamic factors.

Journal Article↗
PubMed1984

Bis(m-nitrophenyl) and bis(p-nitrophenyl) esters and the phosphorodiamidate of thymidine 5'-phosphate as potential sources of intracellular thymidine 5'-phosphate in mouse cells in culture.

Thymidine 5'-phosphate (TMP) derivatives with masked phosphate groups were synthesized in tritiated form from [methyl-3H]thymidine. They were of interest as models for 5' nucleotide derivatives that might be able to permeate mammalian cells and then liberate intracellular antimetabolite 5' nucleotides by loss of the masking groups. Mouse L fibroblasts were grown in vitro in the presence of 1 mM 5'-amino-5'-deoxythymidine, which was found to suppress greater than 99% of cellular thymidine kinase activity while inhibiting the rate of cell division by only 30%. The TMP derivatives were less effective than thymidine in labeling the deoxyribonucleic acid (DNA) of the L cells. The labeling was inhibited 95-99% by 5'-amino-5'-deoxythymidine, indicating that it represented incorporation into DNA of [3H]thymidine formed from degradation of the test compounds. No evidence was obtained that the compounds acted as sources of intracellular TMP by cell permeation followed by loss of phosphate blocking groups. Similar studies yielded no evidence that the bis(m-nitrophenyl) ester of TMP produced intracellular TMP by that route in the LM(TK-) strain of L cells that are genetically deficient in thymidine kinase.

Amides↗
PubMed2003

Further studies on 2,4-diamino-5-(2',5'-disubstituted benzyl)pyrimidines as potent and selective inhibitors of dihydrofolate reductases from three major opportunistic pathogens of AIDS.

As part of an ongoing effort to discover novel small-molecule antifolates combining the enzyme-binding species selectivity of trimethoprim (TMP) with the potency of piritrexim (PTX), 10 previously unreported 2,4-diamino-5-(2'-methoxy-5'-substituted)benzylpyrimidines (2-11) containing a carboxyl group at the distal end of the 5'-substituent were synthesized and tested as inhibitors of dihydrofolate reductase (DHFR) from Pneumocystis carinii (Pc), Toxoplasma gondii (Tg), and Mycobacterium avium (Ma), three of the opportunistic pathogens frequently responsible for life-threatening illness in people with impaired immune systems as a result of HIV infection or immunosuppressive chemotherapy. The selectivity index of DHFR inhibition was evaluated by comparing the potency of each compound against the parasite enzymes with its potency against rat liver DHFR. 2,4-Diamino-5-[5'-(5-carboxy-1-pentynyl)-2'-methoxybenzyl]pyrimidine (3) inhibited Pc DHFR with a selectivity index of 79 and was 430 times more potent than TMP. 2,4-Diamino-5-[5'-(4-carboxy-1-butynyl)-2'-methoxybenzyl]pyrimidine (2), with one less carbon than 3 in the side chain, had a selectivity index of 910 against Ma DHFR and was 43 times more potent than TMP. 2,4-Diamino-5-[5'-(5-carboxypentyl)-2'-methoxybenzyl]pyrimidine (6) had a selectivity index of 490 against Tg DHFR and was 320 times more potent than TMP. 2,4-Diamino-5-[5'-(6-carboxy-1-hexynyl)-2'-methoxybenzyl]pyrimidine (4), with one more carbon than 3, was less potent against all three of the parasite enzymes than either 3 or 6 and also had a lower selectivity index than 3 against the Pc enzyme. However, 4 was the only member of the series with a selectivity index of >300 against both Tg and Ma DHFR. Given that PTX is at least 10 times more potent against rat DHFR than against P. carinii or T. gondii DHFR and that the selectivity index of several of the compounds matches or exceeds that of TMP as well as PTX, our results suggest that it may be possible to develop clinically useful nonclassical antifolates that are both potent and selective against the major opportunistic pathogens of AIDS.

AIDS-Related Opportunistic Infections↗
PubMed2004

New 2,4-diamino-5-(2',5'-substituted benzyl)pyrimidines as potential drugs against opportunistic infections of AIDS and other immune disorders. Synthesis and species-dependent antifolate activity.

In a continuing effort to design small-molecule inhibitors of dihydrofolate reductase (DHFR) that combine the enzyme-binding selectivity of 2,4-diamino-5-(3',4',5'-trimethoxybenzyl)pyrimidine (trimethoprim, TMP) with the potency of 2,4-diamino-5-methyl-6-(2',5'-dimethoxybenzyl)pyrido[2,3-d]pyrimidine (piritrexim, PTX), seven previously undescribed 2,4-diamino-5-[2'-methoxy-5'-(substituted benzyl)]pyrimidines were synthesized in which the substituent at the 5'-position was a carboxyphenyl group linked to the benzyl moiety by a bridge of two or four atoms in length. The new analogues were all obtained from 2,4-diamino-5-(5'-iodo-2'-methoxybenzyl)pyrimidine via a Sonogashira reaction, followed, where appropriate, by catalytic hydrogenation. The new analogues were tested as inhibitors of DHFR from Pneumocystis carinii (Pc), Toxoplasma gondii (Tg), and Mycobacterium avium (Ma), three life-threatening pathogens often found in AIDS patients and individuals whose immune system is impaired as a result of treatment with immunosuppressive chemotherapy or radiation. The selectivity index (SI) of each compound was obtained by dividing its 50% inhibitory concentration (IC(50)) against Pc, Tg, or Ma DHFR by its IC(50) against rat DHFR. 2,4-Diamino-[2'-methoxy-5'-(3-carboxyphenyl)ethynylbenzyl]pyrimidine (28), with an IC(50) of 23 nM and an SI of 28 in the Pc DHFR assay, had about the same potency as PTX and was 520 times more potent than TMP. As an inhibitor of Tg DHFR, 28 had an IC(50) of 5.5 nM (510-fold lower than that of TMP and similar to that of PTX) and an SI value of 120 (2-fold better than TMP and vastly superior to PTX). Against Ma DHFR, 28 had IC(50) and SI values of 1.5 nM and 430, respectively, compared with 300 nM and 610 for TMP. Although it had 2.5-fold lower potency than 28 against Ma DHFR (IC(50) = 3.7 nM) and was substantially weaker against Pc and Tg DHFR, 2,4-diamino-[2'-methoxy-5'-(4-carboxyphenyl)ethynylbenzyl]pyrimidine (29), with the carboxy group at the para rather than the meta position, displayed 2200-fold selectivity against the Ma enzyme and was the most selective 2,4-diamino-5-(5'-substituted benzyl)pyrimidine inhibitor of this enzyme we have encountered to date. Additional bioassay data for these compounds are also reported.

AIDS-Related Opportunistic Infections↗
PubMed1996

Lipophilicity determination of psoralens used in therapy through solubility and partitioning: comparison of theoretical and experimental approaches.

The aim of this study was to determine and to compare experimental and theoretical solubilities (S) as well as partition coefficients (PC) in an octanol/water system of psoralen (P), 8-methoxypsoralen (8-MOP), 5-methoxypsoralen (5-MOP) and 4,5',8-trimethylpsoralen (TMP). For each psoralen, experimental results were performed in triplicate with a spectrofluorimetric technique. The measurements were achieved 10 times for each solution. The obtained order of the solubilities in pure octanol was 5-MOP approximately TMP > P > 8-MOP, while in water-saturated octanol it was expressed as follows: TMP approximately 5-MOP > P > 8-MOP. However, the following order was found for hydrophobicity: TMP > 5-MOP > 8-MOP > P. The solubility ratios (SR) in pure octanol and water were assessed (mean +/- SD): 3.13 +/- 0.01 (P), 2.60 +/- 0.01 (8-MOP), 3.75 +/- 0.01 (5-MOP), and 5.11 +/- 0.01 (TMP). In saturated phases, they were 3.27 +/- 0.01, 2.63 +/- 0.01, 3.85 +/- 0.01, and 5.32 +/- 0.01, respectively. The PCs were determined with low concentrations according to the Dearden and Bresnen32 method and they were 1.67 +/- 0.01, 1.93 +/- 0.01, 2.00 +/- 0.01, and 3.14 +/- 0.01, respectively. Solubility parameters (delta), in Hildebrand unit (H) or in (cal/cm3)1/2, were evaluated. They confirmed the polarity of psoralens, previously expressed through the PC, although the positional isomers (5-MOP and 8-MOP) revealed no difference. Hildebrand's approach to the solubility of regular solutions and Yalkowsky's concept of the solubility of nonelectrolytes and weak electrolytes in an octanol/water system permitted a comparison of the theoretical and experimental results. The perspective of this work is to use the physicochemical properties of the psoralens in practice for insuring convenient experimental assays and the prediction, in vitro, of the percutaneous absorption of these compounds.

5-Methoxypsoralen↗
PubMed2003

Successful orthotopic liver transplantation after trimethoprim-sulfamethoxazole associated fulminant liver failure.

Trimethoprim-sulfamethoxazole (TMP-SMZ) is one of the most commonly used antibiotics. Although many of its adverse effects are well recognized, TMP-SMZ related hepatotoxicity is considered rare and is usually characterized by cholestasis or mixed hepatocellular-holestatic reactions. In this study, we describe the case of a previously healthy young man with acute fulminant liver failure caused by TMP-SMZ. The patient presented with complaints of 'flu-like' symptoms with myalgia and fever after taking TMP-SMZ for 7 d for otitis externa. The patient subsequently developed fever, worsening jaundice, and a rash on his neck and chest. Liver enzymes peaked on day 3 with alanine aminotransferase (ALT) 11,549, aspartate aminotransferase (AST) 23,289, alkaline phosphatase 245, and total bilirubin 10.3 mg/dL, with a conjugated bilirubin of 8.3 mg/dL, prothrombin time (PT) 60.5 s, partial normalized ratio (PTT) 49 s, and international normalized ratio (INR) 7.5. Of note, acetaminophen level on admission was undetectable. Serology for hepatitis A, B, C, cytomegalovirus, HIV, toxoplasmosis, and blood cultures were all negative. The patient developed hepatic encephalopathy with hallucination on day 4. Laboratory tests revealed a serum ammonia level of 190 U, serum creatinine kinase (CK) 10,466 (42 on admission), serum creatinine 8.2 mg/dL (1.2 on admission), and significant metabolic acidosis. Renal ultrasound was unremarkable. The patient was started on hemodialysis for acute renal failure. Meanwhile, liver transplantation assessment was also initiated. On day 8 post-admission (15 d after taking TMP-SMZ), the patient received a successful orthotopic liver transplant.

Adult↗
PubMed2000

Cumulative UV radiation dose and outcome in clinical practice: effectiveness of trioxsalen bath PUVA with minimal UVA exposure.

BACKGROUND: The cumulative artificial ultraviolet (UV) exposure dose of dermatological patients was prospectively monitored in clinical conditions for a total of 2 years (August 1997 - July 1999). We focused on whole body UV treatments, i.e. the trioxsalen (TMP) bath PUVA, the broad-band UVB, and the UVA plus UVB phototherapy. METHODS: Irradiance of the UV devices was calibrated with a spectroradiometer. The cumulative UV doses received by the patients were recorded. A visual analog scale scoring system (VAS) was employed to assess the improvement of various skin conditions at the end of the treatment course. RESULTS: The analysis included 265 patients (141 females and 124 males) and a total of 311 UV treatment courses. Treatments consisted of 86 courses of TMP bath PUVA for psoriasis with a mean cumulative UVA dose of 3.54 J/cm2 and an improvement rate of 89%. For other conditions, 30 courses were needed, with a cumulative UVA dose of 1.47 J/cm2 and an improvement rate of 76%. Altogether, 47 UVB courses were undertaken for psoriasis, and the mean cumulative unweighted UV dose was 2.20 J/cm2, equivalent to 85 standard erythema doses (SED), and an improvement rate of 85%. A total of 25 UVB courses was used for other skin conditions with a mean UV dose of 1.05 J/ cm2, equivalent to 40 SED, and an improvement rate of 71%. A total of 123 courses of UVA plus UVB phototherapy were completed, resulting in a mean cumulative dose of 73.01 J/cm2 for UVA and 0.75 J/cm2 for the unweighted UVB, equivalent to 29 SED. The VAS improvement rate was 85%. CONCLUSION: The exceptionally low mean cumulative UVA dose in the TMP bath PUVA, taken together with the previous report showing no increase in the risk of squamous cell carcinoma or cutaneous malignant melanoma after TMP bath PUVA, suggests that TMP bath PUVA is an effective and safe therapeutic option.

Adolescent↗
PubMed1985

Pharmacodynamic evaluation of the benzodiazepine-oral contraceptive interaction.

The sedative, psychomotor, and memory effects of single oral doses of alprazolam (ALP), lorazepam (LOR), temazepam (TMP), and triazolam (TRZ) were evaluated in women taking oral contraceptives (OCs) and a comparable group of control women. Nine women taking OCs and 11 control women took doses of 1 mg ALP and 2 mg LOR and 10 OC users and 10 control women took 30 mg TMP and 0.5 mg TRZ on two occasions separated by 28 days. Minimal psychomotor impairment was noted after TMP. ALP, LOR, and TRZ produced greater performance impairment in the OC users. Correcting the maximum observed performance decrement for plasma concentration did not account for the differences between OC users and controls. After TMP, there was less sedation during the first 2 hours in OC users, who also had higher plasma TMP clearance. There were no differences in sedation between OC users and controls after ALP, LOR, and TRZ; however, there was less than 50% power to detect a 30% difference. Amnestic effects in OC users and controls did not differ after any of the four drugs. The observed patterns of anterograde amnesia were different, with the earliest and most pronounced recognition failure after TRZ (50% at 1.5 hours), while the LOR effect increased to a maximum (30%) 4 hours after dosing. Our data suggest that differences in benzodiazepine pharmacokinetics between OC users and control women do not account for observed differences in psychomotor impairment. Women taking OCs are more sensitive to the psychomotor effects of single oral doses of benzodiazepines.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Trimethoprim-sulfamethoxazole prophylaxis against urinary tract infection in the chronic spinal cord injury patient.

Suppressive therapy with antibiotics has long been thought to decrease the number of complications from the neuropathic bladder in spinal cord injury patients, but it may also induce resistance to antibiotics which subsequently causes difficulties in treating symptomatic urinary tract infections. Forty-three chronic spinal cord injury patients were randomized to continue to receive daily trimethoprim-sulfamethoxazole (TMP-SMX) urinary tract prophylaxis versus discontinuing antibiotic prophylaxis. Patients were all at least 6 months after spinal cord injury. Patients were followed for a minimum of 3 months, with weekly catheter urine cultures. The difference in the colonization rate at onset and after 3 months (percent of cultures with asymptomatic bacteriuria) between the control and prophylaxis group was not statistically significant (P > 0.1). There was a significant decrease in the percentage of TMP-SMX resistant asymptomatic bacteriuria in the control group, 78.8%, compared to 94.1% in the suppressive group (P < 0.05). There was no significant difference in the number of symptomatic urinary tract infections following the withdrawal of suppressive therapy between the control group, 0.035/week, and the prophylaxis group, 0.043/week (P > 0.5). There was a larger percentage of TMP-SMX resistant symptomatic urinary tract infections in the treated group, 42.5% versus 37.5% in the control group, but the difference was not significant (P > 0.5). Irrespective of the method of bladder management, suppressive therapy with TMP-SMX did not reduce the incidence of symptomatic bacteriuria and did increase the percentage of cultures resistant to TMP-SMX in asymptomatic patients.

Adult↗
PubMed2002

Distribution of orally administered trimethoprim and sulfadiazine into noninfected subcutaneous tissue chambers in adult ponies.

The distribution of trimethoprim (TMP) and sulfadiazine (SDZ) into subcutaneously implanted noninfected tissue chambers was studied in healthy adult ponies. Six ponies were given an oral TMP/SDZ paste formulation at a dose of 5 mg/kg TMP and 25 mg/kg SDZ at 12 h intervals for 2 days in order to reach steady-state concentrations. Plasma concentrations and tissue chamber fluid (TCF) concentrations of both drugs were measured at regular intervals during a period commencing 24 h after the last oral administration. The peak concentration of TMP (mean +/- SD) was 2.92 +/- 0.86 microg/mL for plasma and 1.09 +/- 0.25 microg/mL for TCF. For SDZ, the mean peak concentration was 40.20 +/- 14.74 microg/mL for plasma and 23.48 +/- 5.84 microg/mL for TCF. TMP peak concentrations in plasma were reached at 3.17 +/- 03.48 h and those in TCF at 7.33 +/- 03.72 h. SDZ peak concentrations in plasma were reached at 1.83 +/- 02.04 h and those in TCF at 8.00 +/- 03.10 h. Concentrations of TMP and SDZ in TCF remained above the generally accepted breakpoint for susceptibility (0.5/9.5 for the TMP/SDZ combination) for 12 h. Therefore, in ponies oral administration of TMP/SDZ at a dose rate of 30 mg/kg given twice daily in the form of a paste should be appropriate for effective treatment of infections caused by susceptible bacteria.

Administration, Oral↗
PubMed2000

Regulation of secretory protein gene expression in paramecium role of the cortical exocytotic sites.

In cells that possess a regulated secretory pathway, exocytosis can lead to transcriptional activation of genes encoding products stored in secretory granules as well as genes required for granule biogenesis. With the objective of understanding this response, we have examined the expression of Paramecium secretory protein genes in different physiological and genetic contexts. The genes belong to the trichocyst matrix protein (TMP) multigene family, encoding polypeptides that form the crystalline matrix of the secretory granules, known as trichocysts. Approximately 1000 trichocysts per cell are docked at pre-formed cortical exocytotic sites. Their rapid and synchronous exocytosis can be triggered by vital secretagogues such as aminoethyldextran without harming the cells. Using this exocytotic trigger, we found that the transcription of TMP genes undergoes rapid, transient and co-ordinate 10-fold activation in response to massive exocytosis, leading to a 2.5-fold increase in the pool of TMP mRNA. Experiments with exocytosis-deficient mutants show that the secretagogue-induced increase in intracellular free calcium implicated in stimulus/secretion coupling is not sufficient to activate TMP gene expression. We present evidence that the state of occupation of the cortical exocytotic sites can affect TMP gene expression and suggest that these sites play a role in gene activation in response to exocytosis.

Animals↗
PubMed1999

Acute hemodynamic effects of tetramethylpyrazine and tetrandrine on cirrhotic rats.

The hemodynamic effects of tetramethylpyrazine (TMP) and tetrandrine (TET), both alkaloids isolated from Chinese herbs Ligusticum wallichii Franch and Stephania tetrandra S. Moore, respectively, were assessed in anesthetized cirrhotic rats. TMP induced dose-dependent decreases of portal venous pressure (P.V.P.) and mean arterial pressure (M.A.P.) after intravenous infusion. The maximum percentage reduction of P.V.P. after TMP was 3.6 +/- 0.8%, 6.8 +/- 0.5%, and 17.8 +/- 0.6% of baseline, respectively, for the dosages given (3.0, 9.9 and 30.0 mg/kg). Similarly, TET induced dose-dependent decreases of P.V.P. and M.A.P. The maximum percentage reduction of P.V.P. after TET was 5.4 +/- 1.0%, 9.2 +/- 0.8%, and 23.7 +/- 1.2% of baseline, respectively, for the dosages given (2.0, 6.6 and 20.0 mg/kg). Total peripheral resistance was also reduced by TMP as well as TET. Our results showed that TMP and TET induced P.V.P. reduction in cirrhotic rats, together with reduction in M.A.P. and total peripheral resistance.

Alkaloids↗
PubMed2003

Tetramethylpyrazine as potassium channel opener to lower calcium influx into cultured aortic smooth muscle cells.

In the present study, the effect of tetramethylpyrazine (TMP) on calcium (Ca 2+) influx was investigated in cultured vascular smooth muscle (A7r5) cells using Fura-2 as an indicator. The increase of Ca 2+ concentration in A7r5 cells produced by vasopressin or phenylephrine was attenuated by TMP from 0.01 micromol/L to 1 mmol/L. The decrease in the intracellular potassium concentration in A7r5 cells by TMP from 0.01 micromol/L to 10 micromol/L was characterized using PBFI/AM. Inhibitors specific to the small conductance calcium-activated potassium (SKCa ) channel or the ATP-sensitive potassium (K ATP ) channel abolished the actions of TMP. The obtained results indicate that the decrease of Ca 2+ influx into A7r5 cells by TMP is mainly mediated by the opening of potassium channels.

Animals↗
PubMed1989

Alteration of intracranial pressure, cerebral blood flow, autoregulation and carbondioxide-reactivity by hypotensive agents in baboons with intracranial hypertension.

Intracranial pressure (ICP) was recorded by epidural transducer and cisterna magna catheter, and regional cerebral blood flow (rCBF) using the intraarterial Xenon 133-technique were measured in baboons with normal and during increased ICP provoked by an inflatable balloon positioned subdurally. Arterial blood pressure was altered by controlled infusion of Sodium-nitroprusside (SNP), Nitroglycerine (NG) or Trimetaphan (TMP) with the aim of reducing blood pressure by about 20%. During exflated balloon SNP provoked an increase of ICP which was more prominent than with NG and TMP. During increased ICP (due to inflation of the balloon) again SNP led to a higher further increase of ICP than both NG and TMP. rCBF rose during the state of normal ICP when SNP was infused. This was not observed with infusion of NG or TMP. When ICP was increased again by inflation of the balloon all 3 substances reduced rCBF, indicating damage to the autoregulation. CO2-reactivity as measured by induced hyperventilation with reduction of arterial CO2-tension was affected by all 3 substances thus indicating impairment of vasoconstriction during increase of ICP and simultaneous decrease of blood pressure. However, this impairment of physiological vasoconstriction was more prominent with SNP than with NG and TMP. The results indicate that all 3 substances should be used with care to reduce blood pressure during surgery or under intensive care condition, particularly in patients with increased ICP.

Animals↗
PubMed1982

Treatment of travelers' diarrhea with trimethoprim/sulfamethoxazole and with trimethoprim alone.

We conducted a double-blind treatment study of 110 adults from the United States who were attending summer classes in Guadalajara, Mexico, and had diarrhea (four or more unformed stools in 24 hours, or three or more unformed stools per eight-hour period plus one or more additional clinical indicators of enteric infection). Thirty-seven patients received trimethoprim/sulfamethoxazole (TMP/SMX) (160 mg of TMP and 800 mg of SMX), 38 were given TMP alone (200 mg), and 35 took a placebo twice daily for five days. By the end of the first 24 hours of treatment, patients taking either TMP/SMX or TMP alone passed fewer unformed stools than did patients given placebo (P = 0.0002 and P = 0.01, respectively). Abdominal pain and nausea were reduced in both treatment groups. The beneficial effect was seen in treatment of Escherichia coli-induced diarrhea, shigellosis, and diarrhea not associated with an enteropathogen. Five per cent of patients given TMP/SMX, 8 per cent of those given TMP, and 49 per cent of those given placebo were considered treatment failures (P less than 0.001 for both active drugs as compared with placebo). Early treatment with TMP/SMX or TMP is an alternative to prophylactic use of drugs for travelers' diarrhea.

Adult↗
PubMed1997

A spatial gradient of acceleration and temporal extension underlies three illusions of motion.

If an object (or cue), is presented and shortly afterwards a line is drawn with one end near to the object, motion away from the object location is induced within the line. This line-motion illusion has best been explained by postulating a facilitative spatial gradient that accelerates signal transmission most strongly near to the object, and less so with increasing distance away from the object. This simple accelerative-gradient model was tested in four experiments by either briefly presenting the line, or replacing the line rendering with a dot moving at high velocity towards (or away from) the initial object location. Observers first perceived motion away from the cue followed by motion towards the cue (hence this new illusion is referred to as the "two motion percepts", or TMP illusion). The generality of the TMP illusion was investigated through the reports of forty-five inexperienced undergraduates who were presented with TMP displays. Observers who were asked to pictorially reproduce their motion experience, drew a line expanding away from the cue then contracting back towards it 85% of the time. Over 90% of individuals reported experiencing the illusion with a quickly moving dot. The effects of several presentation parameters were investigated by the moving-dot method, and it was concluded that the accelerative-gradient model by itself was inadequate to explain TMP phenomena. Two extended versions of the gradient model are proposed that place the locus of the TMP effects in properties of motion detection mechanisms or in temporal aspects of visual-signal transmission.

Computer Graphics↗
PubMed1988

Relevance of the reaction of a manganese(III) chelate with hydroxide ion to photosynthesis: Reaction of hydroxide ion with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphinatomanganese(III) in ligating and nonligating solvents.

The reaction of HO(-) with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphinatomanganese(III) chloride [(TMP)Mn(III)(Cl)] in ligating solvents (CH(3)CN, dimethyl sulfoxide, pyridine) results in formation of (TMP)Mn(II) ( approximately 10(6) M(-1).s(-r)), which in a slower reaction is converted to a product whose structure is suggested to be that of a porphyrin manganese(III) peroxo dimer. Admittance of O(2) at any time during these reactions leads to formation of the manganese(III) peroxide (TMP)Mn(III)(O(2))(-). In nonligating solvents [CH(2)Cl(2), (CH(3))(2)CO], the reaction of HO(-) with (TMP)Mn(III)(Cl) yields (TMP)Mn(IV)(OH)(2).

Journal Article↗
PubMed1983

Toxicological properties of trialkyl phosphorothioate and dialkyl alkyl- and arylphosphonothioate esters.

Impurities such as O,S,S-trimethyl phosphorodithioate (TMPD) and the S-methyl isomer of malathion (isomalathion) strongly potentiated the mammalian toxicity of malathion. In contrast, impurities present in the phosphoramidothioate insecticide acephate had an antagonizing effect on its mammalian toxicity. The potentiation of the toxicity of malathion was attributed to inhibition of mammalian liver and serum carboxylesterase. O,O,S-Trimethyl phosphorothioate (TMP), another impurity present in technical malathion and in other organophosphorus insecticides, proved to be highly toxic. Rats given a single oral dose of TMP at a level as low as 20 mg/kg died over a period of three weeks, with death occurring with non-cholinergic signs of poisoning. TMPD also caused similar delayed death in rats. O,O,O-Trimethyl phosphorothioate (TMP=S), also another impurity in technical malathion and a structural isomer of TMP, was a potent antagonist to the delayed toxicity of TMP. Examination of a number of related trialkyl phosphorothioate and dialkyl alkylphosphonothioate esters revealed several of these compounds to be highly toxic to rats.

Animals↗