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N Kröger

Publications and source records attributed to N Kröger.

At least 19 recordsLinked to original sources
PubMed2006

Allogeneic stem-cell transplantation in patients with refractory acute leukemia: a long-term follow-up.

We examined retrospectively 44 patients with refractory acute leukemia (acute myeloid leukemia (AML)/acute lymphoblastic leukemia=25/19) who underwent allogeneic transplantation at our center between 11/1990 and 04/2004. The median leukemic blasts was 25% and age 28 years (range, 3-56). Twenty-one patients had untreated relapse, 13 failed reinduction, eight in partial remission and two aplastic. Conditioning was myeloablative using cyclophosphamide, busulfan, total-body irradiation and etoposide (Bu/Cy/VP, n=22; TBI/Cy/VP, n=17; others, n=5) followed by marrow or peripheral blood transplant (n=23/21) from unrelated or related donors (n=28/16). All patients had graft-versus-host disease (GVHD) prophylaxis with cyclosporin and methotrexate. One patient experienced late graft failure. Severe acute-GVHD and chronic-GVHD appeared in eight and 14 patients, respectively. Thirteen patients (30%) remain alive after a median of 25.3 months (range, 2.4-134.1); with 31 deaths, mostly from relapse (n=15) and infections (n=12). Overall survival (OS) and progression-free survival (PFS) at 5 years was 28 and 26%, respectively. OS and PFS were significantly better with blasts < or =20% and time to transplant < or =1 year while transplant-related mortality was less with the use of TBI. We conclude that patients with refractory leukemia can benefit from allogeneic BMT, especially with < or =20% marrow blast.

Adolescent↗
PubMed2006

Comparable results in patients with acute lymphoblastic leukemia after related and unrelated stem cell transplantation.

We report the results of 84 patients with ALL after related (n = 46) or unrelated (n = 38) allogeneic SCT. Mean recipient age was 23 years (range: 1-60) and median follow-up was 18 months (range: 1-133). Forty-three patients were transplanted in CR1; 25 in CR2 or CR3; four were primary refractory; four in PR; eight in relapse. The conditioning regimen consisted of TBI/VP16/CY (n = 76), TBI/VP16 (n = 2), TBI/CY (n = 2), Bu/VP16/CY (n = 4). The OS at 3 years was 45% (44% unrelated, 46% related). Univariate analysis showed a significantly better OS for patients <18 years (P=0.03), mismatched sex-combination (P = 0.03), both with a stronger effect on increasing OS after unrelated SCT. Factors decreasing TRM were patient age <18 years (P = 0.004), patient CMV-seronegativity (P = 0.014), female recipient (P = 0.04). There was no significant difference in TRM and the relapse rate was similar in both donor type groups. Multivariate analysis showed that factors for increased OS which remained significant were mismatched sex-combination (RR: 0.70,95% CI: 0.51-0.93, P = 0.015), patient age < 18 years (RR: 0.66, 95% CI: 0.47-0.93, P = 0.016). A decreased TRM was found for female patients (RR: 0.56, 95% CI: 0.33-0.98, P=0.042), negative CMV status of the patient (RR: 0.57, 95% CI: 0.36-0.90, P = 0.015). Unrelated stem cell transplantation for high-risk ALL patients with no HLA-compatible family donor is justifiable.

Adolescent↗
PubMed2006

Autologous stem cell transplantation for therapy-related acute myeloid leukemia and myelodysplastic syndrome.

We report the results of 65 patients with treatment-related myelodysplastic syndrome (MDS)/acute myelogenous leukemia (AML) who were transplanted from an autograft and reported to the EBMT. The median age was 39 years (range, 3-69), and stem cell source was bone marrow (n = 31), or peripheral blood progenitor cells (n = 30), or the combination of both (n = 4). The primary disease was solid tumors (n = 37), Hodgkin's disease (n = 13), non-Hodgkin's lymphoma (n = 10), acute lymphoblastic leukemia (n = 2) or myeloproliferative syndromes (n = 3). The types of MDS were as follows: RAEB (n = 1; 2%), RAEB-t (n = 3; 5%), or AML (n = 56; 87%). The median time between diagnosis and transplantation was 5 months (range, 3-86). The Kaplan-Meier estimates of the probability of 3-year overall and disease-free survival were 35% (95% CI: 21-49%) and 32% (95% CI: 18-45%), respectively. The median leukocyte engraftment was faster after transplantation with peripheral blood stem cells than with bone marrow: 12 (range, 9-26) vs 29 (range, 11-67) days (P<0.001). The cumulative incidence of relapse was 58% (95% CI: 44-72%) and of treatment-related mortality 12% (95% CI: 6-38%). Lower relapse rate was seen in patients transplanted in first complete remission (CR1 vs non-CR1: 3 years: 48 vs 89%; P = 0.05). Furthermore, age beyond 40 years resulted in a higher treatment-related mortality (47 vs 7%; P = 0.01). In a multivariate analysis, transplantation in CR1 age as well as their interaction influenced overall survival significantly. Autologous transplantation may cure a substantial number of patients with treatment-related MDS/AML, especially if they are in CR1 and of younger age.

Adolescent↗
PubMed2006

Reduced-toxicity conditioning with treosulfan, fludarabine and ATG as preparative regimen for allogeneic stem cell transplantation (alloSCT) in elderly patients with secondary acute myeloid leukemia (sAML) or myelodysplastic syndrome (MDS).

We investigated a dose-reduced conditioning regimen consisting of treosulfan and fludarabine followed by allogeneic stem cell transplantation (SCT) in 26 patients with secondary AML or MDS. Twenty patients were transplanted from matched or mismatched unrelated donors and six from HLA-identical sibling donors. The median age of the patients was 60 years (range, 44-70). None of the patients was eligible for a standard myeloablative preparative regimen. No graft-failure was observed, and leukocyte and platelet engraftment were observed after a median of 16 and 17 days, respectively. Acute graft-versus-host disease (GvHD) grade II-IV was seen in 23% and severe grade III GvHD in 12% of the patients. No patients experienced grade IV acute GvHD. Chronic GvHD was noted in 36% of the patients, which was extensive disease in 18%. The 2-year cumulative incidence of relapse was 21%. The relapse rate was higher in patients beyond CR1 or with intermediate two or high risk MDS (P = 0.02). The treatment-related mortality at day 100 was 28%. The 2-year estimated overall and disease-free survival was 36-34%, respectively. No difference in survival was seen between unrelated and related SCT.

Acute Disease↗
PubMed2006

Prognostic factors for donor lymphocyte infusions following non-myeloablative allogeneic stem cell transplantation in multiple myeloma.

In this retrospective study, we evaluated donor lymphocyte infusions given for relapsed (n=48) or persistent (n=15) myeloma following non-myeloablative allogeneic stem cell transplantation (Allo-SCT). Twenty-four of 63 patients (38.1%) responded: 12 patients (19.0%) with a partial response (PR) and 12 patients (19.0%) with a complete response (CR). Overall survival after donor lymphocyte infusions (DLI) was 23.6 months (1.0-50.7+). Median overall survival for non-responding patients was 23.6 months and has not been reached for the patients responding to DLI. In responders, progression-free survival after DLI was 27.8 months (1.2-46.2+). Patients with a PR had a median progression-free survival of 7.0 months, whereas patients with a CR to DLI had a median progression-free survival of 27.8 months. Major toxicities were acute graft-versus-host disease (GVHD) (38.1%) and chronic GVHD (42.9%). Seven patients (11.1%) died from treatment-related mortality. The only significant prognostic factors for response to DLI were the occurrence of acute and chronic GVHD. There was a trend towards significance for time between transplantation and DLI, and response. Donor lymphocyte infusion following non-myeloablative Allo-SCT is a valuable strategy for relapsed or persistent disease.

Acute Disease↗
PubMed2006

CD34(+)-selected stem cell boost for delayed or insufficient engraftment after allogeneic stem cell transplantation.

BACKGROUND: Poor graft function without rejection may occur after stem cell transplantation (SCT). CD34(+) stem cell boost (SCB) can restore marrow function but may induce or exacerbate GvHD. We therefore investigated the feasibility and efficacy of CD34(+)-selected SCB in some patients with poor graft function. We present the results for eight patients (median age 46 years) transplanted initially for myelofibrosis, acute leukemia, myeloma and NHL. Six patients had received HLA-matched and two mismatched grafts (PB, BM; n=5, 3). After a median of 128 days post-transplant, the median leukocyte and platelet counts were, respectively, 2.05/nL and 18/nL. None had achieved platelet counts >50/nL even though donor chimerism was >95% in seven recipients. METHODS: Positive selection of CD34(+) stem cells was performed on a CliniMACS device, observing GMP and achieving a median of 98.5% purity. The patients received a median of 1.7 x 10(6)/kg CD34(+) cells and 2.5 x 10(3)/kg CD3(+) T lymphocytes. RESULTS: Hemograms at days +30, +60 and +90, respectively, showed steadily increasing median leukocyte (2.55, 3.15 and 4.20/nL) and platelet (29, 39 and 95/nL) counts. After a median follow-up of 144 days, five patients remained alive. No patient had developed acute or chronic GvHD. One patient died of leukemic relapse and two others of systemic mycosis. DISCUSSION: These preliminary results point to the possibility of safely improving graft function using CD34(+) positively selected stem cells without necessarily increasing the incidence of GvHD in patients with poor graft function post-SCT. Experience with more patients and longer follow-up should clarify the optimal role for this procedure.

Adolescent↗
PubMed2006

Comparison of flow cytometry vs. a haematology cell analyser-based method to guide the optimal time-point for peripheral blood stem cell apheresis.

BACKGROUND AND OBJECTIVES: For timing the onset of apheresis, parameters obtained by flow cytometry and by a haematological cell analyser were compared. MATERIALS AND METHODS: Haematopoietic cell counts (n = 159) were performed by two different methods; CD34 analyses by flow cytometry, immature myeloid information (IMI) and human progenitor cell counts (HPC) by a haematological cell analyser. RESULTS: Comparing the IMI total results with CD34+ analyses (n = 159) revealed a correlation of r = 0.46 (P < 0.05). Similar results were obtained for HPC (r = 0.44; P < 0.05). CONCLUSION: The haematology analyser-based method does not allow the precise determination of absolute haematopoietic stem cell numbers and is thus not able to replace flow cytometry for the monitoring of peripheral blood stem cell counts.

Blood Component Removal↗
PubMed2005

Stem cell transplantation from identical twins in patients with myelodysplastic syndromes.

In a multicentre retrospective EBMT database study, we analysed factors influencing outcome in 38 patients with MDS/sAML who were transplanted with stem cells from their syngeneic twin and compared those to 1444 patients who were transplanted from an HLA-identical sibling. The median time to leukocyte and platelet engraftment was faster in the twin group: 14 vs 17 (P=0.02) and 16 vs 26 days (P=0.09), respectively. The 5 years cumulative incidence of treatment-related mortality (TRM) was higher in the sibling than in the twin group (38 vs 27%; P=0.05). The 5 year cumulative incidence of relapse was 32% (95% CI: 29-35%) for the siblings and 39% (95% CI: 26-60%; P=0.6) for the twins. A trend for better 5-years disease-free and overall survival was observed in the twin group: 34% (95% CI: 14-54%) vs 28% (95% CI: 25-31%; P=0.2) and 36% (95% CI: 15-57%) vs 32% (95% CI: 29-35%; P=0.09), respectively. In a multivariate analysis, stem cell transplantation from identical twins had a lower TRM: HR: 0.4 (95% CI: 0.2-0.9; P=0.03). The relapse rate was similar for both groups with a HR of 1.2 (95% CI: 0.07-2.1; P=0.5), with a better survival for the twins: HR 0.6 (95% CI: 0.4-1.0; P=0.07). We conclude that twin transplantation in MDS/sAML is associated with a similar relapse risk, a lower TRM and a trend for better overall survival in comparison to transplantation from HLA-identical siblings.

Adolescent↗
PubMed2005

The impact of donor gender on outcome of allogeneic hematopoietic stem cell transplantation for multiple myeloma: reduced relapse risk in female to male transplants.

The impact of the donor gender on outcome in HLA-identical sibling donor hematopoietic stem cell transplantation for multiple myeloma was studied in a retrospective registry study of 1312 patients (476 male to male (M --> M); 334 female to male (F --> M); 258 male to female (M --> F); 244 female to female (F --> F) reported to the European Group for Blood and Marrow Transplantation (EBMT). The best overall survival (OS) from the time of transplantation was found in F --> F (median 41 months) with no significant difference between other groups (median 25 months in M --> M, 18 months in F --> M, 19 months in M --> F) despite a significantly higher nonrelapse mortality in F --> M. This was due to a significantly lower relapse rate (REL) in F --> M compared to all other groups. Before 1994, OS was poorer in F --> M than in M --> M, which improved to similarity from 1994 onwards (median 29 months in M --> M and 25 months in F --> M). The reduced REL contributed to this improvement in F --> M indicting a gender-specific graft vs myeloma effect. Therefore, a female donor is as good as a male one for male patients, while for female patients gender disparity is a negative factor for outcome.

Adult↗
PubMed2005

Aldehyde dehydrogenase activity as a marker for the quality of hematopoietic stem cell transplants.

Taking advantage of fluorescent substrates for their metabolic marker aldehyde dehydrogenase (ALDH), hematopoietic stem cells (HSC) were defined as SSC(lo)ALDH(br) - reflecting their low orthogonal light scattering and bright fluorescence intensity in flow cytometry. Based thereon, we investigated the usefulness of ALDH activity for characterizing HSC graft quality, particularly under stress conditions. We first compared the expression of ALDH vs CD34 in bone marrow and peripheral blood stem cell (PBSC) samples over 7 days. We noted that (i) only ALDH activity but not CD34 expression strongly reflected colony-forming ability over time, and that (ii) PBSC grafts stored at room temperature lost most of their progenitor cells within just 48 h. We then retrospectively related ALDH and CD34 expression as well as granulocyte-macrophage colony-forming units (CFU-GM) potential for 19 cryopreserved allogeneic PBSC grafts to engraftment data. Strikingly, in all six patients who received markedly decreased numbers of SSC(lo)ALDH(br) cells, this was associated not only with almost complete loss of CFU-GM potential but also with delayed establishment/permanent absence of full hematopoietic donor cell chimerism, whereas all other patients showed early complete donor chimerism. In conclusion, we suggest to measure ALDH activity as a surrogate marker for HSC activity, and to transport and store PBSC under controlled cooling conditions.

Aldehyde Dehydrogenase↗
PubMed2005

Hematopoietic stem-cell transplantation from unrelated donors in elderly patients (age >55 years) with hematologic malignancies: older age is no longer a contraindication when using reduced intensity conditioning.

Allogeneic stem cell transplantation (SCT) is a potentially curative approach for patients with hematological malignancies. Reduced-intensity conditioning regimens allow SCT in elderly patients; however, there are only limited data on the feasibility and outcomes of unrelated donor SCT in these patients. In this study, we analyzed, retrospectively, data of 36 patients with various hematological malignancies and median age 58 years (range, 55-66), who were given unrelated donor SCT after reduced-intensity conditioning. The preparative regimen consisted of fludarabine combined with oral busulfan (8 mg/kg, n=8), intravenous busulfan (6.4 mg/kg, n=11), treosulfan (30 g/m(2), n=5) or melphalan (100-150 mg/m(2), n=12). Patients were also given serotherapy, ATG (n=32), or alemtuzumab (n=4). The probabilities of overall survival, disease-free survival, and nonrelapse mortality at 1 year after SCT were 52, 43, and 39%, respectively. Acute graft-versus-host disease (GVHD) grade II-IV and chronic GVHD occurred in 31 and 45%, respectively. Multivariable analysis determined that survival rates were higher in patients with chemosensitive disease (HR 4.5), and patients conditioned with intravenous busulfan or treosulfan (HR 3.9). Unrelated donor SCT is feasible in elderly patients, with outcomes that are similar to younger patients. Favorable outcome was observed in patients with myeloid malignancies, and those transplanted in remission and early in the course of disease. Age alone should not be considered a contraindication to unrelated donor SCT.

Aged↗
PubMed2004

High-dose chemotherapy with autologous hematopoietic stem-cell support compared with standard-dose chemotherapy in breast cancer patients with 10 or more positive lymph nodes: first results of a randomized trial.

PURPOSE: Investigation of high-dose chemotherapy (HD-CT) followed by autologous hematopoietic stem-cell support compared with standard-dose chemotherapy (SD-CT) as adjuvant treatment in patients with primary breast cancer and 10 or more positive axillary lymph nodes. PATIENTS AND METHODS: Between November 1993 and September 2000, 307 patients were randomized to receive (following four cycles of epirubicin 90 mg/m(2) and cyclophosphamide 600 mg/m(2), intravenously every 21 days) either HD-CT of cyclophosphamide 1500 mg/m(2), thiotepa 150 mg/m(2), and mitoxantrone 10 mg/m(2), intravenously for 4 consecutive days followed by stem-cell support; or SD-CT in three cycles of cyclophosphamide 500 mg/m(2), methotrexate 40 mg/m(2), and fluorouracil 600 mg/m(2) intravenously on days 1 and 8, every 28 days. The primary end point was event-free survival. RESULTS: After a median follow-up of 3.8 years, 144 events with respect to event-free survival have been observed (HD-CT: 63 events; SD-CT: 81 events). The first event of failure (HD-CT v SD-CT) was an isolated locoregional recurrence (nine v 11), a distant failure (52 v 68), and death without recurrence (two v two). The estimated relative risk of HD-CT versus SD-CT was 0.75 (95% CI, 0.54 to 1.06; P =.095). Overall survival showed no difference (HD-CT: 40 deaths; SD-CT: 49 deaths). CONCLUSION: There was a trend in favor of HD-CT with respect to event-free survival, but without statistical significance. Further follow-up and a meta-analysis of all randomized studies will reveal the effect of HD-CT as compared with SD-CT as adjuvant treatment in high-risk primary breast cancer.

Adult↗
PubMed2004

[Allogenic stem cell transplantation following dose-reduced conditioning in patients with hematologic systemic diseases or solid tumors].

Allogeneic stem cell transplantation is an established treatment modality for a variety of hematologic malignancies. However this allogeneic stem cell transplantation carries the risk of severe complications which are partly due to the intensity of the conditioning regimen. Therefore, allogeneic stem cell transplantation has been so far only performed in younger patients with good performance status. Dose-reduced or non-myeloablative conditioning regimen has been proposed as an alternative that would allow exploiting the graft versus leukemia effect of allogeneic stem cell transplantation without severe toxicity. Clinical studies have shown that dose-reduced conditioning followed by allogeneic stem cell transplantation allows stable engraftment with lower toxicities which can be associated with long-term disease control. Therefore, dose-reduced conditioning followed by allogeneic stem cell transplantation can be offered to older and more debilitated patients who were no candidates for standard allogeneic stem cell transplantation.

Antineoplastic Agents↗
PubMed2004

Reduced-intensity conditioning with busulfan and fludarabine with or without antithymocyte globulin in HLA-identical sibling transplantation--a retrospective analysis.

It is unknown whether the addition of antithymocyte globulin (ATG) to reduced-intensity conditioning with busulfan (BU) and fludarabine (FLU) is beneficial in HLA-identical sibling transplantation. Therefore, we analyzed retrospectively data on 83 patients, who received peripheral blood stem cells from HLA-identical siblings after conditioning with either 8 mg/kg BU and 150 mg/m2 FLU (n=45) or 8 mg/kg BU, 180 mg/m2 FLU and 40 mg/kg ATG (n=38). Graft-versus-host disease (GVHD) prophylaxis consisted of CSA alone (n=32) or a combination with either MTX or MMF (n=51). The median age was 52 years. Graft failure occurred in two patients after BU/FLU and in three after BU/FLU/ATG (P=0.66). After conditioning with BU/FLU, platelet recovery was significantly faster (P=0.017), and less platelet (P<0.001) and red blood cell (P=0.002) support was needed. Incidences of acute GVHD grades II and IV were 46 and 49%, respectively. Limited chronic GVHD occurred more often after BU/FLU compared to BU/FLU/ATG (54 vs 23%, P=0.02). The overall survival, non-relapse and relapse mortality did not differ significantly. We conclude that in peripheral blood stem cell transplantation from HLA-identical siblings after reduced-intensity conditioning with BU and FLU, ATG has no major impact on the rate of graft rejection and acute GVHD, but it reduces the incidence of limited chronic GVHD.

Acute Disease↗
PubMed2004

Isolated HLA-C mismatches in unrelated donor transplantation for CML.

HLA-incompatibility is a major factor associated with outcome of allogeneic stem cell transplantation, but little is known on the impact of isolated HLA-C mismatches. We analyzed the outcome of 114 CML patients transplanted with marrow from unrelated donors of whom 24 were mismatched for HLA-C only (9/10 match). Univariate estimates of 5-year survival (SRV) (median follow-up: 47 months) in the HLA-matched group were 68+/-12 vs 42+/-20% (P=0.03) for the patients mismatched for HLA-C only and 33+/-33% in the mismatched group (non-HLA-C single mismatches and multiple mismatches) (P=0.0004). Disease stage, GVHD-prophylaxis (T-cell depletion), CMV-status and HLA-incompatibility were the risk factors associated (all P< or =0.005) with poor outcome. In the multivariate analysis, patients mismatched for loci other than HLA-C were at high risk of an adverse outcome (death: RR, 2.9; CI, 1.6-5.4, P=0.008, transplant-related mortality (TRM): RR, 3; CI, 1.5-5.9, P=0.0015). For patients mismatched for HLA-C only, the increased risk was of borderline significance (death: RR, 1.9; CI, 1-3.9, P=0.06, TRM: RR, 2.1; CI, 1-4.5, P=0.07). In spite of their lower expression, HLA-C antigens still represent relevant transplantation barriers that should be considered when searching for an unrelated donor.

Adult↗
PubMed2003

Allogeneic stem cell transplantation after a fludarabine/busulfan-based reduced-intensity conditioning in patients with myelodysplastic syndrome or secondary acute myeloid leukemia.

We report the feasibility and efficacy of a fludarabine/busulfan-based dose-reduced conditioning regimen followed by stem cell transplantation from related ( n=19) or unrelated HLA-matched donors ( n=18) in 37 patients with myelodysplastic syndrome (MDS) or secondary acute myeloid leukemia (sAML) who were not eligible for a standard myeloablative conditioning regimen. The conditioning regimen consisted of fludarabine (120-180 mg/m(2)), busulfan (8 mg/kg p.o. or 6.4 mg/kg i.v.), and antithymocyte globulin ( n=25). Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine ( n=36) and a short course of methotrexate ( n=29) or mycophenolate mofetil ( n=3). The median age of the patients was 55 years (range: 23-72). The reasons to perform a dose-reduced conditioning were reduced performance status ( n=14), age ( n=12), prior autologous ( n=5) or allogeneic ( n=1) transplantation, or prior/active fungal infection ( n=5). Diagnoses at transplantation were refractory anemia (RA) ( n=8), refractory anemia with excess of blasts (RAEB) ( n=6), RAEB in transformation (RAEB-T) ( n=13), chronic myelomonocytic leukemia (CMML) ( n=3), and sAML ( n=7). Stem cell sources were peripheral blood stem cells (PBSC) ( n=29) or bone marrow ( n=8). One patient received a T-cell-depleted peripheral stem cell graft. Two primary graft failures were observed (6%). Engraftment of leukocytes (>1.0x10(9)/l) and platelets (>20x10(9)/l) was seen after a median of 14 days. Acute GVHD grade II-IV was seen in 37%, while severe grade III/IV GVHD was observed in six patients (17%). Chronic GVHD was seen in 13 patients (48%). There were ten deaths (27%) due to treatment (TRM). The probability of TRM was higher in patients with unrelated donors (45 vs 12%, p=0.03) and in patients with poor cytogenetics in comparison to those with a low or intermediate karyotype (75 vs 20%, p=0.009). During follow-up 12 patients relapsed (32%). Patients without chronic GVHD had a significantly higher probability of relapse compared to those with chronic GVHD (70 vs 15%, p=0.02). After a median follow-up of 20 months, the 3-year estimated disease-free survival (DFS) is 38% [95% confidence interval (CI): 21-55%] and the overall survival (OS) is 39% (95% CI: 22-56%). The OS and DFS after related and unrelated transplantations was 45% (95% CI: 19-71%) vs 31% (95% CI: 9-53%) (n.s.) and 51% (95% CI: 29-73%) vs 25% (95% CI: 4-47%) (n.s.), respectively. We conclude that dose-reduced conditioning followed by allogeneic stem cell transplantation from related or unrelated donors is an effective treatment approach in patients with MDS/sAML and might cure a substantial number of patients who are not eligible for a standard allogeneic transplantation.

Adolescent↗
PubMed2003

Solid-state 29Si MAS NMR studies of diatoms: structural characterization of biosilica deposits.

Four different diatom species (Chaetoceros debilis, Chaetoceros didymum, Cylindrotheca fusiformis, Nitzschia angularis) were studied by solid-state (29)Si MAS NMR spectroscopy. To determine the Q(2):Q(3):Q(4) ratios in the biosilica deposits of the diatoms, quantitative (29)Si MAS NMR experiments were performed. This analysis did not reveal any differences regarding the molecular architecture of the silica (i.e. the degree of condensation of the SiOH units (2 identical with SiOH --> identical with Si-O-Si identical with + H(2)O)) from the different diatom species. However, complete cells showed significantly smaller Q(4):Q(3) ratios (1.8-1.9) than extracted cell walls (2.5-2.8), indicating the existence of intracellular pools of less condensed silica.

Diatoms↗