High Plaque Levels after Thorough Toothbrushing: What Impedes Efficacy?

OBJECTIVES: Previous studies have shown high levels of dental plaque after toothbrushing and poor toothbrushing performance. There is a lack of evidence about what oral hygiene behavior predicts persistent plaque. The present cross-sectional study thus relates toothbrushing behavior to oral cleanliness after brushing and to gingivitis. METHODS: All young adults from a central town in Germany who turned 18 y old in the year prior to the examination were invited to participate in the study. They were asked to clean their teeth to their best abilities while being filmed. Videos were analyzed regarding brushing movements (vertical, circular, horizontal, modified Bass technique) and evenness of distribution of brushing time across vestibular (labial/buccal) and palatinal (lingual/palatinal) surfaces. Dental status, gingival bleeding, and oral cleanliness after oral hygiene were assessed. RESULTS: Ninety-eight young adults participated in the study. Gingival margins showed persistent plaque at 69.48% ± 12.31% sites (mean ± SD) after participants brushed to their best abilities. Regression analyses with the brushing movements and evenness of distribution of brushing time as predictors explained 15.2% (adjusted R2 = 0.152, P = 0.001) of the variance in marginal plaque and 19.4% (adjusted R2 = 0.194, P < 0.001) of the variance in bleeding. Evenness of distribution of brushing time was the most important behavioral predictor. CONCLUSION: Even when asked to perform optimal oral hygiene, young German adults distributed their brushing time across surfaces unevenly. Compared with brushing movements, this factor turned out to be of more significance when explaining the variance of plaque and bleeding. KNOWLEDGE TRANSFER STATEMENT: Results of this study can help clinicians and patients understand the meaning of specific behavioral aspects of toothbrushing for oral cleanliness and oral health.

Eficacia de leuprolide 11, 25 mg para supresión de testosterona en pacientes con cáncer prostático / Leuprolide s efficacy 11, 25 mg for suppression of testosterone in patients with prostatic cancer

Introducción: Los agonistas LHRH son de elección en bloqueo androgénico por cáncer prostático. En base a pacientes castrados se considera un bloqueo adecuado una testosterona total plasmática < 50 ng/dl. Se ha sugerido controlar la testosterona total por la posibilidad de no lograr una supresión adecuada. Material y método: Entre junio de 2008 a marzo de 2009 se midió el nivel de testosterona total al tercer mes de administrada una dosis de leuprolide 11,25 mg IM. Los exámenes se realizaron en la mañana y en el mismo laboratorio. En un grupo de pacientes se estimó peso, talla e índice de masa corporal (IMC) y se evaluó su asociación con los niveles de testosterona alcanzados. Resultados: Se evaluaron 81 pacientes, la edad promedio fue 76,4 años. La testosterona total plasmática promedio fue 33,9 ng/dl. En 12/81 pacientes (14,8 por ciento) el nivel de testosterona fue menos 50 ng/dl. No se observó asociación entre la duración de hormonoterapia y los niveles de testosterona. En 40 pacientes se estimó peso, talla e IMC sin encontrarse asociación de estas variables con el nivel de testosterona. En los pacientes en que se aumentó la dosis a leuprolide 22,5 mg se obtuvo una adecuada supresión de testosterona. Conclusión: En los pacientes en tratamiento con agonistas LHRH se debe medir el nivel de testosterona plasmática dada la posibilidad de un bloqueo inadecuado. En pacientes en tratamiento con leuprolide 11,25 mg y testosterona menos 50 ng/dl el aumento de la dosis a 22,5 mg lograría un nivel de testosterona en rangos de castración quirúrgica.

Introduction: The agonistas are LHRH of election in blockage androgenic for prostatic cancer. On the basis of castrated patients considers an adequate blockage a total plasmatic testosterone < 50 ng/dl. The total testosterone for the possibility to not to achieve an adequate suppression has been suggested to control. Material and method: Between June 2008 to March 2009 leuprolide’s dose measured the level of total testosterone itself to person under administration’s third month 11.25 mg IM. The exams had done in the morning and at the same laboratory. Weight, size and index of muscle mass (IMC) were estimated in patients’ group and his association with the levels of testosterone caught up with was evaluated. Results: We evaluated 81 patients, the mean age was 76.4 years. The total testosterone the average plasmatic was 33.9 ng/dl. In 12/81 patient (14.8 percent) the level of testosterone was > 50 ng/dl. we did not observe association between hormonoterapia’s duration and the levels of testosterone. Weight, size and IMC without finding association of these variables with the level of testosterone were estimated in 40 patients. We got an adequate suppression from testosterone in the patients that 22.5 mg increased itself the dose in to leuprolide. Conclusion: LHRH must try on in the patients in treatment with agonistic the level of plasmatic testosterone once the possibility of an inadequate blockage was given. In patients in treatment with leuprolide 11.25 mg and testosterone > 50 ng/dl the increase of the dose to 22.5 mg would achieve a level of testosterone in ranges of surgical castration.

Reporte de un caso de tumor desmoplásico de células pequeñas redondas / Case report: patient with round cell desmoplastic tumor

Introducción: El tumor de células pequeñas redondas desmoplásico (TCPRD), es una neoplasia agresiva maligna poco frecuente que afecta a adolescentes y adultos jóvenes. Usualmente son intraabdominales asociados con un mal pronóstico. Existen algunas publicaciones donde incluyen manifestaciones paratesticulares. Caso: Reportamos un caso de un joven de 29 años que consulta por aumento de volumen del hemiescroto izquierdo de 3 meses de evolución. Al examen destacaba 2 nódulos duros uno en relación al polo inferior y el otro al epidídimo de aproximadamente 2 cm. Alfafetoproteína y beta HCG eran normales. Se decide exploración quirúrgica donde biopsia rápida confirma tumor que se origina en las envolturas y que infiltra hacia el testículo. La biopsia definitiva informó tumor desmoplásico de células pequeñas redondas. El estudio de extensión con tomografía axial computarizada y radiografía de tórax no mostró metástasis. El paciente recibió 2 ciclos de QMT con ciclofosfamida, etoposido, adriamicina y cisplatino, con buena tolerancia, evolucionando con depresión medular moderada que se recupera. Actualmente 6 años después del diagnóstico el paciente se encuentra en remisión completa. Discusión: Al parecer y según los últimos reportes de la literatura, la ubicación paratesticular ha mostrado mejor pronóstico en comparación con los tumores abdominales. Se debe incluir este diagnóstico diferencial al enfrentarse con tumores paratesticulares.

Introduction: Small round cell desmoplastic tumor (SRCDT) is an infrequent malignant tumor that affects adolescents and young adults. Usually they occur in the abdomen. Paratesticular manifestations have been reported. Case report: A 29 year old male presented with a 3 month history of a mass in the left scrotum. Physical exam showed 2 hard nodules in the scrotum. Serum levels of alpha-fetoprotein and beta-HCG were normal. The patient was submitted to surgery. Frozen section confirmed a tumor arising in the paratesticular area with involvement of the testis. Permanent sections showed a SRCDT. CT scans and chest x-rays showed no metastases. The patient received two courses of ciclophosphamide, etoposide, adryamicin and cisplatinum. Treatment was well tolerated. The patient is in complete remission at 6 years following the diagnosis. Discussion: Paratesticular location seems to have a better prognosis compared to intraabdominal tumors. SRCDT should be included in the differential diagnosis of paratesticular tumors.

Expresión de marcadores tumorales P16, ciclina D1, BCL2 y Ki67 en cáncer de pene / Expression of tumor markers P16, ciclin D1, BCL2 and Ki67 in penile cancer

El cáncer de pene es una enfermedad de baja incidencia. Su tratamiento se basa en la cirugía y no está establecido si el control tumoral local debe o no ser complementado con linfadenectomía inguinal y pélvica. La linfadenectomía en el cáncer de pene se asocia a elevadas tasas de complicaciones y no está establecido a qué pacientes se les debe realizar. Éste trabajo retrospectivo analiza la expresión de marcadores tumorales en cáncer de pene y su correlación con otros factores pronósticos. La expresión del marcador Ciclina D1 fue alta en todas las muestras, la de Ki-67 y P16 fue alta en los tumores de alto grado y la de BCL-2 fue negativa en todos los casos.

Penile carcinoma is a low incidence disease. Treatment is based in surgery and controversy persists regarding the need of inguinal and pelvic lymphadenectomy. To date, no specific inclusion criteria have been established to indicate surgery. This retrospective work analyses the expression of tumoral markers in penile cancer and correlation with other prognostic factors. The expression of the Cicline D1 marker was high in all the samples, Ki-67, P16 was high in high grade tumors and BCL-2 was negative in all cases.

Ciclo único de quimioterapia adyuvante en cáncer testicular no seminoma Etapa I / Single cycle adyuvant chemotherapy in stage I nonseminomatous testis cancer

El cáncer de testículo es la neoplasia sólida más frecuente en el hombre entre los 15-35 años de edad y su incidencia a nivel mundial ha aumentado en los últimos 40 años. Ello puede ser el resultado de efectos exógenos, como influencia prenatal, o predisposición genética. A pesar del aumento de la incidencia, su mortalidad ha disminuido a cifras menores del 5 por ciento gracias a la combinación de métodos diagnósticos adecuados, marcadores tumorales sensibles y tratamientos efectivos. El tratamiento de esta enfermedad es un ejemplo de manejo multimodal del cáncer, ya que luego de orquiectomía el paciente puede requerir cirugía de estadiaje, radioterapia o quimioterapia complementaria o entrará a un régimen de observación vigilada, dependiendo de la histología y etapa tumoral. En el caso del tumor testicular de células germinales no seminomatoso (NSCGT) etapa I (pT1-4NxMoSo), la recomendación es determinar la presencia de factores pronósticos que pueden predecir la presencia de ganglios retroperitoneales metastásicos luego del tratamiento o recaída luego de orquiectomía con linfadenectomía retroperitoneal. Los principales factores de riesgo analizados son la etapa del tumor primario >pT1, invasión vascular y/o linfática, presencia de carcinoma embrionario, ausencia de elementos de tumor de saco vitelino y marcadores tumorales elevados preorquiectomía.

The cancer of testicle is the most frequent solid neoplasia in the man between 15-35 years of age and his(her,your) incident worldwide has increased in the last ones 40 años. It can be the result of exogenous effects, as prenatal influence, or genetic predisposition. In spite of the increase of the incident, his(her,your) mortality has diminished minor numbers(figures) of 5 percent thanks to the combination of diagnostic methods tumour sensitive scoreboards and treatments efectivos. The treatment of this disease is an example of multimodal managing of the cancer, since after orquiectomía the patient can need surgery of estadiaje, radiotherapy or complementary chemotherapy or it(he,she) will enter to a regime(diet) of monitored observation, depending on the histology and tumour stage. In case of the tumor testicular of cells they germinate Not seminomatoso (NSCGT) stage I (pT1-4NxMoSo), the recommendation is the presence of factors determines forecasts(predictions) that can predict the presence of ganglions retroperitoneales metastásicos after the treatment or relapse after orquiectomía with linfadenectomía retroperitoneal. The principal factors of risk analyzed are the stage of the primary tumor> pT1, vascular and / or lymphatic invasion, presence of carcinoma Embryonic, absence of elements of tumor of sack vitelino and tumour high scoreboards preorquiectomía.

Analysis of atropine, its degradation products and related substances of natural origin by means of reversed-phase high-performance liquid chromatography.

Chromatographic separation and quantification methods of tropa alkaloids were often described. In order to separate atropine from its degradation products ion-pair chromatography (IPC) has been frequently applied. Beside long equilibration times IPC often suffers from poor robustness. The aim of this study was to develop robust and simple HPLC methods for both stability testing of atropine solutions and limitation of related substances in atropine from plant material. Using a hydrophilic embedded RP18 column and a gradient elution gave baseline separation of all components.

Two-year follow-up study of elderly residents in S. Paulo, Brazil: methodology and preliminary results.

INTRODUCTION: Previous cross-sectional studies have shown a high prevalence of chronic disease and disability among the elderly. Given Brazil's rapid aging process and the obvious consequences of the growing number of old people with chronic diseases and associated disabilities for the provision of health services, a need was felt for a study that would overcome the limitations of cross-sectional data and shed some light on the main factors determining whether a person will live longer and free of disabling diseases, the so-called successful aging. The methodology of the first follow-up study of elderly residents in Brazil is presented. METHOD: The profile of the initial cohort is compared with previous cross-sectional data and an in-depth analysis of nonresponse is carried out in order to assess the validity of future longitudinal analysis. The EPIDOSO ('Epidemiologia do Idoso') Study conducted a two-year follow-up of 1,667 elderly people (65+), living in S. Paulo. The study consisted of two waves, each consisting of household, clinical, and biochemical surveys. RESULTS AND CONCLUSIONS: In general, the initial cohort showed a similar profile to previous cross-sectional samples in S. Paulo. There was a majority of women, mostly widows, living in multigenerational households, and a high prevalence of chronic illnesses, psychiatric disturbances, and physical disabilities. Despite all the difficulties inherent in follow-up studies, there was a fairly low rate of nonresponse to the household survey after two years, which did not actually affect the representation of the cohort at the final household assessment, making unbiased longitudinal analysis possible. Concerning the clinical and blood sampling surveys, the respondents tended to be younger and less disabled than the nonrespondents, limiting the use of the clinical and laboratory data to longitudinal analysis aimed at a healthier cohort. It is worth mentioning that gender, education, family support, and socioeconomic status were not important determinants of nonresponse, as is often the case.

Lithium/carbon monofluoride (Li/CFx): a new pacemaker battery.

The reduction in pacemaker size coupled with the addition of more current demanding functions has motivated the development of batteries that can supply higher current densities at useful voltages than the lithium/iodine batteries in use today while retaining the volumetric energy density of that system. The lithium/CFx system offers an attractive alternative for advanced pacemaker systems. The battery can deliver currents in the milliampere range without significant voltage drop. The system is compatible with titanium casing, allowing a 50% reduction in weight over the same size lithium/iodine battery. Cells have been designed and tested in these laboratories and have been shown to be suitable for advanced pacemaker applications.

Uretrocervicopexia de Burch en el tratamiento de la incontinencia urinaria de esfuerzo / Burch's urethro-cervicopexy in the treatment of stress urinary incontinence

La incontinencia de orina de esfuerzo (IOE) se define como la pérdida involuntaria de orina asociada a maniobras que significan un aumento de la presión intraabdominal. Su mecanismo de producción no está claramente establecido, siendo la teoría más aceptada el descenso del cuello vesical, el cual se ubicaría bajo el diafragma urogenital, perdiendo su posición intraabdominal y la consiguiente transmisión de presión a la uretra proximal. Esta patología constituye un motivo importante de consulta en nuestra región, siendo aún subdiagnosticado debido a razones culturales. Se han descrito diferentes tipos de tratamientos y técnicas quirúrgicas. Comunicamos nuestra experiencia con la técnica de Burch en 36 pacientes operadas en el período abril 1994-junio 1996. En el 30 por ciento de los casos se realizó otro tipo de cirugía simultánea, especialmente ginecológica. La edad promedio fue de 47,6 años (28-68). El tiempo quirúrgico fue de 53,4 min (40-70) cuando se realizó como procedimiento único y de 96,3 min (50-120) cuando se asoció a otra cirugía. El tiempo de sonda postoperatorio fue de 72 horas en las primeras 25 pacientes y de 24 horas en la últimas 11 operadas. Esta reducción en el tiempo de sonda no ha significado ninguna variación en los resultados de la técnica, pudiendo las pacientes ser dads de altaa a las 48 horas. Las complicaciones postoperatorias fueron la retención urinaria o residuos postmiccionales elevados en 4 pacientes y la infección de herida operatoria en 1 caso. El seguimiento promedio fue de 13 meses (26-2) no observándose recidivas. La uretrocervicopexia de Burch constituye una técnica efectiva, de baja morbilidad, que permite asociar otros tipos de cirugía, especialmente ginecológica, y con estadía postoperatoria breve

Using linkers to investigate the spatial separation of the conserved nucleotides A9 and G12 in the hammerhead ribozyme.

Two series of hammerhead-derived ribozymes, or 'minizymes', in which helix II has been replaced by linkers of non-nucleotidic moieties, have been synthesised by solid-phase methods. In the first series, the minizymes had linkers containing one, two, three, four or five repeated units of phosphopropanediol, so that the number of atoms in the chain connecting the 3'O of the conserved A9 to the 5'O of the conserved G12 varied from 7 to 31. In the second, more-limited series, the minizymes contained linkers of either tetra- or hexa-ethyleneglycol. The rates at which these minizymes cleaved their cognate 13-nucleotide substrate were determined at 30 degrees C, and compared with the rates of cleavage by an analogous series of minizymes containing from two to six repeated units of thymine deoxyribonucleotide in place of helix II. In all three series, the cleavage rates increased with increasing linker length, with a plateau being reached at the longer lengths tested. Relative cleavage rates within the phosphopropanediol and the thymidine series depended strongly on linker length, but maximal activity was achieved in both series with 25 atoms in the chain joining A9 and G12. The lengths of linkers required to achieve maximal activity of the minizymes are considerably greater than the linkers of 13 atoms which are sufficient to stabilise the ends of double-helices of DNA or RNA.

Neutral and anionic cyclodextrins in capillary zone electrophoresis: enantiomeric separation of ephedrine and related compounds.

Two methods for the enantiomeric separation of chiral ephedrine alkaloids (ephedrine, methylephedrine, methylpseudoephedrine and norephedrine) by capillary zone electrophoresis in uncoated capillaries were developed. Both methods were optimized to more than 100,000 theoretical plate numbers. The first method used a neutral cyclodextrin (CD) derivative: heptakis (2,6-di-O-methyl)-beta-cyclodextrin at an acidic pH of 2.5 (20 mM phosphate buffer) at an 18 mM concentration. The second used a newly developed acidic CD derivative, the tetrakis[6-O-(4-sulfobutyl)]-beta-cyclodextrin sodium salt. The benefits of this new reagent for the chiral separation are a wide range of basic pH available for the enantiomeric resolution. It is also useful for other cases, e.g. preventing adsorption without additives.

Crystal and molecular structure of r(CGCGAAUUAGCG): an RNA duplex containing two G(anti).A(anti) base pairs.

BACKGROUND: Non-Watson-Crick base pair associations contribute significantly to the stabilization of RNA tertiary structure. The conformation adopted by such pairs appears to be a function of both the sequence and the secondary structure of the RNA molecule. G.A mispairs adopt G(anti).A(anti) configurations in some circumstances, such as the ends of helical regions of rRNAs, but in other circumstances probably adopt an unusual configuration in which the inter-base hydrogen bonds involve functional groups from other bases. We investigated the structure of G.A pairs in a synthetic RNA dodecamer, r(CGCGAAUUAGCG), which forms a duplex containing two such mismatches. RESULTS: The structure of the RNA duplex was determined by single crystal X-ray diffraction techniques to a resolution in the range 7.0-1.8A, and found to be an A-type helical structure with 10 Watson-Crick pairs and two G.A mispairs. The mispairs adopt the G(anti).A(anti) conformation, held together by two obvious hydrogen bonds. Unlike analogous base pairs seen in a DNA duplex, they do not exhibit a high propeller twist and may therefore be further stabilized by weak, reverse, three-center hydrogen bonds. CONCLUSIONS: G(anti).A(anti) mispairs are held together by two hydrogen of guanine and the N6 and N1 of adenine. If the mispairs do not exhibit high propeller twist they may be further stabilized by inter-base reverse three-centre hydrogen bonds. These interactions, and other hydrogen bonds seen in our study, may be important in modelling the structure of RNA molecules and their interactions with other molecules.

Thermodynamic stability and solution conformation of tandem G.A mismatches in RNA and RNA.DNA hybrid duplexes.

G.A mismatches form a variety of hydrogen-bonded structures in DNA, most of which destabilise the duplex. Tandem G.A mismatches in the context YGAR (Y = pyrimidine, R = purine), however, form base pairs using the amino group of the guanine residue [Li, Y., Zon. G. & Wilson, W.D. (1991) Proc. Natl Acad. Sci. USA 88, 26-30], which permits extensive base-base stacking, leading to a slight stabilisation of the helix [Ebel, S., Lane, A. N. & Brown, T. (1992) Biochemistry 31, 12083-12086]. We have measured the thermodynamic stability of several RNA and RNA.DNA hybrid duplexes containing tandem G.A mismatches. The RNA duplexes are intrinsically much more stable than the corresponding DNA duplexes and the mutations are destabilising in all cases. NOE and coupling-constant data show that all of the sugars are in the C3'-endo range of conformations, and glycosidic torsion angles are in the range -160 degrees to -180 degrees in [sequence: see text]. Both sequential NOE intensities and circular-dichroism measurements indicate that the global conformation of the mismatched RNA is A-like. The N1H group of the mismatched guanine residue is not involved in hydrogen bonding with the adenine residue, indicating the presence of the amino-pairing scheme. Determination of the structure using 'loose' NMR-derived constraints shows that the potential energies of the imino-paired and amino-paired forms are similar, but substantially higher than energy-minimised RNA. Using tighter constraints derived from more extensive analysis of one-dimensional and two-dimensional NOE data showed that the amino-paired structure agrees with the constraint data better than the imino-paired structure, and also accounts for unusual chemical shifts and the lack of hydrogen bonding of the guanine N1H group. Resulting molecular models show that the amino-paired mismatches are not as extensively stacked on the neighbouring part of the duplex as in the B-DNA analogues, largely accounting for the lower thermodynamic stability in the RNA duplexes.

Properties of multiple G.A mismatches in stable oligonucleotide duplexes.

The solution structure of the deoxydecanucleotide [sequence: see text] has been determined by NMR methods. This duplex, which contains six G.A mismatches and four Watson-Crick base pairs, is thermodynamically more stable than a decamer where T.A base pairs are substituted for the G.A mismatches, and is less stable than the duplex that contains G.C base pairs. Circular-dichroism spectroscopy indicates an overall B-like conformation for the decamer, but stronger than usual base stacking. 1H-NMR spectroscopy revealed that the N1H groups of the mismatched guanine residues are not hydrogen bonded, and 31P-NMR showed the presence of BII phosphate conformations for the GpA steps. Detailed analysis of the NMR data showed that all nucleotides have anti glycosidic torsion angles and S type sugar puckers. The G.A mismatches pair in the amino form as originally proposed by Li et al. [Li, Y., Zon, G. & Wilson, W. D. (1991) Proc. Natl Acad. Sci. USA 88, 26-30], which results in extensive base-base stacking between the tandem G.A base pairs and their nearest neighbours. The terminal G.A base pairs are less stable than the central base pairs and show evidence of an equilibrium between two conformations, one involving BII phosphate.

The role of the physical therapist in hospice care.

The role of the physical therapist in hospice care is different from the role the therapist plays when a member of a rehabilitation team. This article will address the need for a fundamental role change and offer suggestions for ways physical therapists can contribute to the care of the hospice patient. In working with hospice patients, therapists must, for the most part, change from a controlling role to one of listener and problem-solver. In this manner, therapists can: Assist the patient to maintain functional abilities for as long as possible; Reduce the burden of care for the caregivers; Assist in pain control. Physical therapists can provide hospice nurses with valuable assistance in caring for hospice patients.

NMR assignments and solution conformation of the DNA.RNA hybrid duplex d(GTGAACTT).r(AAGUUCAC).

Nearly complete assignments of the 1H-NMR spectrum of the DNA.RNA hybrid d(GTGAACTT).r(AAGUUCAC) have been obtained by two-dimensional methods. Three-bond coupling constants measured from cross-sections of two-dimensional NOE spectra and double quantum-filtered correlation spectra showed that the sugars in the DNA strand are predominantly in the S domain of puckers, whereas the ribofuranoses are mainly C3'-endo. Analysis of time-dependent NOE intensities from one- and two-dimensional experiments showed that the glycosidic torsion angles in the DNA strand are near -120 degrees, whereas those in the RNA strand are in the range- 140 degrees to -160 degrees. These nucleotide conformations correspond to those typically found in B-DNA and A-RNA, respectively. The circular dichroism of the duplex is similar to that of A-form RNA, consistent with a global A-like conformation. A large number of duplex structures was generated in which the nucleotides were fixed in the experimentally determined conformations. A subset of these structures was found that satisfied the internucleotide NOE intensities, backbone constraints and had acceptable Lennard-Jones energies. The base pairs in the duplex were found to have positive inclinations, a translation (Dx) of about 0.4 nm from the helix axis, and more than 10 bp/turn on average. This implies a helical structure in the A family of conformations.

Thermodynamic stability and drug-binding properties of oligodeoxyribonucleotide duplexes containing 3-deazaadenine:thymine base pairs.

We have used ultraviolet melting techniques to study the effect on stability of incorporating the nucleoside analogue 2'-deoxy-3-deazaadenosine (d3cA) into the duplex 5'-d(CGCAATCG)-3'-d(GCGTTAGC). Our results demonstrate that the successive replacement of dA by d3CA increasingly destabilises the duplex. The destabilising effect of this analogue is considerably enhanced as the pH is lowered and the results are consistent with protonation of 3-deazaadenine (probably at N-1) contributing to duplex destablisation. Surprisingly, the incorporation of d3CA does not significantly affect the binding of distamycin-A.