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Biomedical subjects

A Mar

Publications and source records attributed to A Mar.

At least 19 recordsLinked to original sources
PubMed2001

Nb(9)PdAs(7): a unique arrangement in the M(n2+3n+2)X(n2+n)Y family of hexagonal structures.

The ternary transition-metal arsenide Nb(9)PdAs(7) has been prepared through reaction of the elements, and its structure has been determined by single-crystal X-ray diffraction methods. It adopts a new structure type (Pearson symbol hP51, hexagonal, space group P6, Z = 3), with unit cell parameters a = 16.6955(6) and c = 3.5582(1) A. The structure contains assemblies of As-centered trigonal prisms that extend as triangular columns through sharing of the triangular faces. Not only does Nb(9)PdAs(7) extend a family of hexagonal structures with general formula M(n2+3n+2)X(n2+n)Y to n = 4, the highest member known thus far, but it also displays the unique feature in which there are two distinct types of triangular columns, one having corner atoms (Pd) different from the other atoms (Nb). Structural relationships between members of the M(n2+3n+2)X(n2+n)Y family are presented. The chemical bonding in Nb(9)PdAs(7) was analyzed through an extended Hückel band structure calculation.

Journal Article↗
PubMed2001

Nb4Pd0.5ZSb2 (Z = Cr, Fe, Co, Ni, Si): the first ordered quaternary variants of the W5Si3-type structure.

A family of quaternary (or pseudoquaternary) antimonides Nb4Pd0.5ZSb2 (Z = Cr, Fe, Co, Ni, Si) containing up to three transition metals in an ordered arrangement has been prepared by reactions of the elements. These antimonides are isostructural, crystallizing as substitutional variants of the W5Si3-type structure (tetragonal, space group -I4/mcm, Z = 4) with unit cell parameters a = 10.4407(3) A and c = 5.0020(2) A for Nb4Pd0.5Cr0.28(3)Si0.72Sb2, a = 10.4825(6) A and c = 4.9543(3) A for Nb4Pd0.5FeSb2, a = 10.4603(5) A and c = 4.9457(3) A for Nb4Pd0.5CoSb2, a = 10.4332(7) A and c = 4.9649(3) A for Nb4Pd0.5Ni0.78(1)Sb2, and a = 10.3895(10) A and c = 4.9634(4) A for Nb4Pd0.5SiSb2. They are distinguished by the filling of interstitial Z atoms into the centers of Nb8 square antiprismatic clusters that are linked by PdSb4 tetrahedra. The Nb8 square antiprisms share opposite square faces to form one-dimensional chains along the c axis so that Z-Z bonding distances of approximately 2.5 A result. Extended Hückel band structure calculations were carried out to interpret the homo- and heteroatomic metal-metal interactions in the structure. The resistivity of one member, Nb4Pd0.5SiSb2, was measured, indicating metallic behavior.

Journal Article↗
PubMed2001

Biflavonoids as novel antituberculosis agents.

A series of naturally occurring and synthetic biflavonoids was evaluated for inhibitory activity against Mycobacterium tuberculosis H37Rv (Mtb). Compounds 6, 24, and 25 demonstrated 96, 95, and 87% inhibition, respectively, at a screening concentration of 12.5 microg/mL. The type of linkage and the presence of methoxy- and nitro-substituents in biflavonoids may contribute to the observed inhibitory activity. The results of this study represent the discovery of biflavonoids as a potential new class of antituberculosis agent.

Antitubercular Agents↗
PubMed2001

Layered rare-earth gallium antimonides REGaSb(2) (RE = La--Nd, Sm).

The ternary rare-earth gallium antimonides, REGaSb(2) (RE = La--Nd, Sm), have been synthesized through reaction of the elements. The structures of SmGaSb(2) (orthorhombic, space group D(5)(2)-C222(1), Z = 4, a = 4.3087(5) A, b = 22.093(4) A, c = 4.3319(4) A) and NdGaSb(2) (tetragonal, space group D(19)(4h)-I4(1)/amd, Z = 8, a = 4.3486(3) A, c = 44.579(8) A) have been determined by single-crystal X-ray diffraction. The SmGaSb(2)-type structure is adopted for RE = La and Sm, whereas the NdGaSb(2)-type structure is adopted for RE = Ce--Nd. The layered SmGaSb(2) and NdGaSb(2) structures are stacking variants of each other. In both structures, two-dimensional layers of composition (2)(infinity)[GaSb] are separated from square nets of Sb atoms [Sb] by RE atoms. Alternatively, the structures may be considered as resulting from the insertion of zigzag Ga chains between (2)(infinity)[RE Sb(2)] slabs. In SmGaSb(2), all of the Ga chains are parallel and the (2)(infinity)[SmSb(2)] layers are stacked in a ZrSi(2)-type arrangement. In NdGaSb(2), the Ga chains alternate in direction, resulting in a doubling of the long axis relative to SmGaSb(2), and the (2)(infinity)[NdSb(2)] layers are stacked in a Zr(3)Al(4)Si(5)-type arrangement. Extended Hückel band structure calculations are used to explain the bonding in the [GaSb(2)](3-) substructure.

Journal Article↗
PubMed2001

Evaluation of the Skin and Cancer Foundation standard series in the diagnosis of allergic contact dermatitis.

The use of a standard series of 37 allergens was evaluated in a retrospective study of 817 consecutive patients seen between April 1988 and January 1993 at the Skin and Cancer Foundation, Melbourne, Australia. Of the 316 patients with clinically relevant patch test results, 134 (42%) reacted to an allergen in the standard series alone, while an additional 122 (39%) had reactions to allergens in both the standard and supplementary series. The remaining 60 (19%) patients reacted only to allergens in the supplementary series. These data suggest that the use of our standard series alone will detect about 80% of allergic contact dermatitis cases, but that many of these may be insufficiently evaluated. Use of supplementary allergen testing in a specialised clinic is recommended for patients who may have allergic contact dermatitis.

Allergens↗
PubMed2000

Ternary early-transition-metal palladium pnictides Zr3Pd4P3, Hf3Pd4P3, HfPdSb, and Nb5Pd4P4.

Several ternary palladium pnictides of the early transition metals have been prepared by arc-melting of the elemental metals and the binary pnictides ZrP, HfP, HfSb2, or NbP, and their structures have been determined by X-ray diffraction methods. The phosphides M3Pd4P3 (M = Zr, Hf) adopt a new structure type (Pearson symbol oP40), crystallizing in the orthorhombic space group Pnma with Z = 4 and unit cell parameters of a = 16.387(2), b = 3.8258(5), and c = 9.979(1) A for Zr3Pd4P3 and a = 16.340(2), b = 3.7867(3), and c = 9.954(1) A for Hf3Pd4P3. The antimonide HfPdSb was identified by powder X-ray diffraction (orthorhombic, Pnma, Z = 4, a = 6.754(1) A, b = 4.204(1) A, and c = 7.701(2) A) and confirmed to be isostructural to ZrPdSb, which adopts the TiNiSi-type structure. The phosphide Nb5Pd4P4 adopts the Nb5Cu4Si4-type structure, crystallizing in the tetragonal space group I4/m with Z = 2, a = 10.306(1) A, and c = 3.6372(5) A. Coordination geometries of pentacapped pentagonal prisms for the early transition metal, tetracapped distorted tetragonal prisms for Pd, and tricapped trigonal prisms for the pnicogen are found in the three structures; tetracapped tetragonal prisms for Nb are also found in Nb5-Pd4P4. In common with many metal-rich compounds whose metal-to-nonmetal ratio is equal or close to 2:1, the variety of structures formed by these ternary palladium pnictides arises from the differing connectivity of pnicogen-filled trigonal prisms. Pnicogen-pnicogen bonds are absent in these structures, but metal-metal bonds (in addition to metal-pnicogen bonds) are important interactions, as verified by extended Hückel band structure calculations on Zr3Pd4P3.

Journal Article↗
PubMed2000

Antidepressants preferentially enhance habituation to novelty in the olfactory bulbectomized rat.

RATIONALE: The mechanisms whereby antidepressant drugs exert their therapeutic effects remain unknown. Responses to stressful stimuli are currently thought to contribute to the onset and course of affective disorders. It has been postulated that antidepressants might act by ameliorating response patterns to challenging life events, such as processes of reactivity and/or habituation. OBJECTIVE: Using the olfactory bulbectomy (OBX) rat model, this study examined the effects of various antidepressants on measures of reactivity and habituation in behavioral tests assessing responses to novel stimuli. METHODS: Sham-operated and OBX rats received 21 daily injections of fluoxetine (10 mg/kg), amitriptyline (10 mg/kg), desipramine (10 mg/kg), buspirone (3 mg/kg), or vehicle. Forty-eight hours after the last injection, animals were tested in the open field, elevated plus maze, and startle apparatus. For each test, time series data were collected and fit with exponential random effects models, in which estimated parameters assessed behavioral reactivity and habituation. RESULTS: Relative to sham controls, OBX rats displayed increased total locomotor activity in the open field and exhibited increased open arm behavior in the elevated plus maze. Through comparison with zinc sulfate-treated anosmic controls, these OBX-induced increases were attributed to both an augmentation of initial reactivity due to anosmia and an attenuation of the average rate of habituation. Chronic antidepressant treatment did not reduce the anosmia-related initial reactivity levels of OBX rats to that of sham controls. Rather, the antidepressants evoked their restorative effects by increasing the rate of habituation. CONCLUSIONS: These findings suggest that antidepressants restore normal responding by permitting more effective adaptation to novel stimuli.

Animals↗
PubMed1999

The cumulative incidence of atopic dermatitis in the first 12 months among Chinese, Vietnamese, and Caucasian infants born in Melbourne, Australia.

BACKGROUND: Atopic dermatitis (AD), a disease with both inherited and environmental components determining its clinical expression, has been reported to be more frequent in people of Asian origin. OBJECTIVE: Our purpose was to compare the 12-month cumulative incidence of AD in Caucasian, Chinese, and Vietnamese babies born in Australia. METHODS: Sixty-two Caucasian, 61 Chinese, and 59 Vietnamese babies born in Melbourne, Australia were examined soon after birth and then followed up for 12 months to assess the frequency of AD. Parental education, employment history, and housing conditions were also recorded. RESULTS: AD developed in 21% of Caucasians, 44% of Chinese, and 17% of Vietnamese infants. Parents of the Chinese and Caucasian infants had similar socioeconomic and housing conditions compared with the parents of the Vietnamese infants, who tended to be of lower socioeconomic status with communal housing and lack of plush-pile carpeting. CONCLUSION: The high incidence of AD in Chinese compared with Caucasian infants tends to reflect genetic differences between the two populations, whereas the difference in incidence between the Chinese and Vietnamese infants possibly reflects more the environmental contribution to disease expression.

China↗
PubMed1999

The descriptive epidemiology of atopic dermatitis in the community.

Atopic dermatitis (AD) is a common condition in the community, particularly amongst children. Although comparison of prevalence data between surveys is made difficult by differences in methodology, the available data suggest that there has been a substantial rise in the prevalence of AD, and that social, geographical and racial variation in disease frequency exists. There is a lack of quality data relating to the prognosis of AD. Recently a reliable set of diagnostic criteria has been developed and a number of severity scoring systems have been proposed for use in epidemiological studies.

Dermatitis, Atopic↗
PubMed1999

Unilateral pigmented purpuric eruption.

Three cases of unilateral pigmented purpuric eruption (UPPE) occurring in children aged between 7 and 12 years are reported. The lesions were asymptomatic and occurred on the lower limb and torso; one case demonstrated a quadrantic configuration with a sharp midline cutoff. The purpuric component resolved spontaneously within 3 months in all cases, while pigmentation showed partial resolution in the two cases followed up for 12 months. Our cases support previous reports of UPPE being a benign self-limiting condition mainly affecting young patients. The cause is unknown.

Child↗
PubMed1996

Modulation of conduction block in leech mechanosensory neurons.

Conduction block is a mechanism of activity-dependent neuronal plasticity, but little is known about its possible neuromodulation. Extensive activity in leech touch (T), pressure (P), and nociceptive (N) mechanosensory neurons results in conduction block of their minor receptive fields. We have examined whether the duration of conduction block could be modulated by the serotonergic Retzius neurons or by application of serotonin (5-HT). Activation of one Retzius cell reduced the duration of conduction block in T and P cell posterior fields, but their anterior fields and N cell fields were unaffected. Perfusion with 5-HT had stronger effects, reducing the duration of conduction block in T, P, and lateral N cells in the posterior fields and either reducing or more often enhancing the expression of conduction block in anterior fields. The effects of 5-HT on posterior fields were blocked by the nonspecific 5-HT antagonist methysergide and were partly suppressed by the 5-HT2 antagonist ketanserin. To determine the site of 5-HT action, the central ganglion or peripheral skin was perfused independently. T and to a greater extent P cells showed a preferential sensitivity to application of 5-HT onto the central ganglion. Interestingly, medial N cells exhibited a progressive decrease in the duration of conduction block during repeated trials ("wind-up") that was unaffected by 5-HT. We conclude that secretion of 5-HT by the Retzius cells has a central modulatory effect on the duration of conduction block in T, P, and lateral N cells.

Animals↗
PubMed1996

Recurrent nonmelanoma skin cancer in southern Australia.

BACKGROUND AND OBJECTIVE: In retrospective studies of non-melanoma skin cancers, the recurrence rates were relatively high. This study had as its aim to determine the recurrence rate of nonmelanoma skin cancer (NMSC) and prospectively, risk factors for recurrence in southern Australia. STUDY DESIGN: This is a prospective study of outpatients with histologically confirmed NMSC. All patients seen by a dermatologist between November 1988 and November 1989 were entered into the study and followed for at least 3 years. Any recurrent NMSCS were removed and recorded. RESULTS: Four hundred and eighty-one patients were entered and 420 followed for at least 3 years. A recurrent NMSC developed in 8% (adjusted for losses). A multivariate analysis determined that the main risk factor for recurrence within the first 3 years of follow-up was the number of NMSC a patient had when entering into the study. Those with 3 to nine NMSC were five times more likely to develop a recurrence than those with less than three NMSC. Those with 10 or more NMSC were 25 times more likely to develop a recurrence. Age, sex, and types of skin cancers removed were not risk factors within the first 3 years of follow-up. CONCLUSION: Patients who have had multiple skin cancers require careful follow-up because of the risk of developing recurrences.

Aged↗
PubMed1996

Cell-mediated immunity of patients who have had basal cell carcinomas.

The cell-mediated immunity of patients who had basal cell carcinomas (BCCs) removed was studied by measuring cuntaneous delayed hypersensitivity reactions to recall antigens (Multitest CMI, Pasteur-Merieux), and by measuring lymphocyte counts and subsets. One group of patients had multiple BCCs (3 or more) removed and were considered to have a high risk of new BCC formation. The other group consisted of patients who had one BCC and had not developed another within 5 years; these were considered to have a low risk of new BCC formation. The low-risk patients had significantly larger cutaneous reactions to recall antigens (p < 0.05) and significantly fewer were anergic (p < 0.01). There was a correlation between smaller cutaneous reactions and increasing numbers of BCCs (p < 0.05). There was no significant difference between the groups in lymphocyte counts or subsets, but the low-risk patients had a significantly higher CD4:CD8 ratio (p < 0.05) than the high-risk group. The Multitest CMI test can be used to determine which patients are at risk of developing many BCCs.

Adult↗
PubMed1994

Metastases from squamous cell carcinoma of the skin in southern Australia.

BACKGROUND: The frequency with which squamous cell carcinoma (SCC) of the skin metastasizes is a matter of dispute. Studies from private practices have reported much lower rates than hospital-based surveys, and one school of thought is that SCCs which arise in sun-damaged skin have a low risk of metastasis. METHODS: A prospective study of out-patients with histologically confirmed SCC was undertaken in southern Australia, a region with a very high incidence of skin cancer. RESULTS: Between November 1988 and November 1989, 481 patients were entered into the study and 420 followed for at least 3 years. An SCC was the initial diagnosis for 73 patients, 3 were immunosuppressed and 2 had an SCC of the lip, leaving 68 immunocompetent patients with SCC of the skin. Metastatic SCC developed in 2 patients (5.8% adjusted for losses) within 3 years. The SCCs were small and arose in sun-damaged skin. CONCLUSION: Patients with SCC of the skin need a careful follow-up because of the risk of metastasis.

Adult↗
PubMed1994

The development of non-melanocytic skin cancers in people with a history of skin cancer.

OBJECTIVE: To determine the incidence of new skin cancer formation in people who have had skin cancer removed. STUDY DESIGN: A prospective study of Melbourne out-patients with histologically confirmed non-melanoma skin cancer (NMSC). All patients with NMSC seen by one author (D.C.) between November 1988 and November 1989 were entered into the study and reviewed regularly. New skin cancers were removed and recorded. RESULTS: Four hundred and eighty-one patients were entered and 420 followed for at least 3 years. New NMSC developed in 60% (adjusted for losses) by the end of 3 years. A multivariate analysis determined that the main risk factor for new NMSC formation was the number of previous skin cancers that a patient had. Those who had had multiple skin cancers (3 or more) were at significantly greater risk than those with less than 3. Age, sex and type of NMSC were not risk factors for new skin cancer formation. CONCLUSION: Patients with NMSC require long-term follow-up because of the risk of new skin cancer formation. Those with multiple NMSC need more careful follow-up, and possibly more frequent examinations, because they are at greater risk.

Adult↗
PubMed1991

Synthesis of the coenzymes adenosine diphosphate glucose, guanosine diphosphate glucose, and cytidine diphosphoethanolamine under primitive Earth conditions.

The nonenzymatic synthesis of the coenzymes adenosine diphosphate glucose (ADPG), guanosine diphosphate glucose (GDPG), and cytidine diphosphoethanolamine (CDP-ethanolamine) has been carried out under conditions considered to have been prevalent on the early Earth. The production of these compounds was performed by allowing simple precursor molecules to react under aqueous solutions, at moderate temperatures and short periods of time, with mediation by cyanamide or urea. These two condensing agents are considered to have been present in significant amounts on the primitive Earth and have been previously used in the nonenzymatic synthesis of several other important biochemical compounds. In our experiments, ADPG was obtained by heating glucose-1-phosphate (G1P) and ATP in the presence of cyanamide for 24 h at 70 degrees C. The reaction of G1P and GTP under the same conditions yielded GDPG. The cyanamide-mediated production of CDP-ethanolamine was carried out by reacting a mixture of ethanolamine phosphate and CTP for 24 h at 70 degrees C. The separation and identification of the reaction products was carried out by paper chromatography, thin-layer chromatography, high performance thin-layer chromatography, high performance liquid chromatography, both normal and reverse-phase, UV spectroscopy, enzymatic assays, and acid hydrolysis. Due to the mild conditions employed, and to the relative ease of these reactions, these studies offer a simple attractive system for the nonenzymatic synthesis of phosphorylated high-energy metabolic intermediates under conditions considered to have been prevalent on the ancient Earth.

Adenosine Diphosphate Glucose↗
PubMed1987

Non-enzymatic synthesis of the coenzymes, uridine diphosphate glucose and cytidine diphosphate choline, and other phosphorylated metabolic intermediates.

The synthesis of uridine diphosphate glucose (UDPG), cytidine diphosphate choline (CDP-choline), glucose-1-phosphate (G1P) and glucose-6-phosphate (G6P) has been accomplished under simulated prebiotic conditions using urea and cyanamide, two condensing agents considered to have been present on the primitive Earth. The synthesis of UDPG was carried out by reacting G1P and UTP at 70 degrees C for 24 hours in the presence of the condensing agents in an aqueous medium. CDP-choline was obtained under the same conditions by reacting choline phosphate and CTP X G1P and G6P were synthesized from glucose and inorganic phosphate at 70 degrees C for 16 hours. Separation and identification of the reaction products have been performed by paper chromatography, thin layer chromatography, enzymatic analysis and ion pair reverse phase high performance liquid chromatography. These results suggest that metabolic intermediates could have been synthesized on the primitive Earth from simple precursors by means of prebiotic condensing agents.

Choline↗